Molecular Imaging of Experimental Abdominal Aortic Aneurysms

Hindawi Publishing CorporationThe Scientific World JournalVolume 2013 Article ID 973150 18 pageshttpdxdoiorg1011552013973150

Review ArticleMolecular Imaging of Experimental AbdominalAortic Aneurysms

Aneesh K Ramaswamy Mark Hamilton II Rucha V Joshi Benjamin P Kline Rui LiPu Wang and Craig J Goergen

Weldon School of Biomedical Engineering Purdue University West Lafayette IN 47907 USA

Correspondence should be addressed to Craig J Goergen cgoergenpurdueedu

Received 1 February 2013 Accepted 19 March 2013

Academic Editors A Ciarmiello B A Kaufmann and A Takano

Copyright copy 2013 Aneesh K Ramaswamy et alThis is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Current laboratory research in the field of abdominal aortic aneurysm (AAA) disease often utilizes small animal experimentalmodels induced by genetic manipulation or chemical application This has led to the use and development of multiple high-resolution molecular imaging modalities capable of tracking disease progression quantifying the role of inflammation andevaluating the effects of potential therapeutics In vivo imaging reduces the number of research animals used provides molecularand cellular information and allows for longitudinal studies a necessity when tracking vessel expansion in a single animal Thisreview outlines developments of both established and emerging molecular imaging techniques used to study AAA disease Beyondthe typical modalities used for anatomical imaging which include ultrasound (US) and computed tomography (CT) previousmolecular imaging efforts have usedmagnetic resonance (MR) near-infrared fluorescence (NIRF) bioluminescence single-photonemission computed tomography (SPECT) and positron emission tomography (PET) Mouse and rat AAA models will hopefullyprovide insight into potential disease mechanisms and the development of advanced molecular imaging techniques if clinicallyuseful may have translational potential These efforts could help improve the management of aneurysms and better evaluate thetherapeutic potential of new treatments for human AAA disease

1 Introduction

Abdominal aortic aneurysm (AAA) is an expansion andweakening of the abdominal aortic wall [1] typically definedas a pathological dilation of at least 50 [2] It is estimatedthat AAAs affect somewhere between 05 and 32 of theUS population [3] but incidence rates rise to between 4and 7 in men over the age of 65 [4] Aortic aneurysms thatare typically detected through screening are small requiringonly periodic observations [5] However once the vesseldiameter grows beyond 55 cm the risk of vessel ruptureincreases drastically Rupture of an AAA is often a lethalevent and in many cases the first and only clinical symptomof pathological aortic expansion [6] Death caused by AAArupture is estimated at about 14000 per year though thisfigure may be an underestimation [7] While open surgicalintervention is currently the standard treatment for high-riskAAA less invasive endovascular aneurysm repair (EVAR)

is developing into a second common treatment procedure[8]

Small animal models of AAA have been established tocharacterize mechanistic properties of human AAA progres-sion [9] These small animal models closely mimic patho-physiology of human AAA including increased matrix met-alloproteinase (MMP) activity inflammation extracellularmatrix (ECM) degradation smooth muscle cell apoptosisand neovascularization [10] Currently murine models aremost frequently used because of cost considerations well-documented genetic backgrounds and relative ease in theability to produce genetically modified animals [11 12] Inorder to study the molecular pathways and the progressionof small animal AAA a wide variety of imaging modalitieshave been employed These include ultrasound computedtomography (CT) magnetic resonance (MR) near-infraredfluorescence (NIRF) bioluminescence single-photon emis-sion computed tomography (SPECT) and positron emission

2 The Scientific World Journal

tomography (PET) Each modality has strengths and weak-nesses making recently developed combined imaging sys-tems (such as SPECTCT PETCT and PETMR) attractivealternatives as they become readily available

Significant challenges exist in adapting clinical imagingsystems for small animal use Considerations can includeradioactive dose requirements body mass anesthesia pro-cedures and contrast infusion techniques all of which candiffer greatly from a clinical setting [13] New challengesarise while engineering dedicated small animal systems Forexample PET image resolution must be significantly higherwith a small animal scanner than with a clinical system[14] With small animal ultrasound the signal-to-noise ratioand tissue contrast are often insufficient when imaging miceand rats [13] In spite of these challenges some imagingsystems scale favorably for small animals For example thestatic MR field strength can be higher and the receivingcoil can be closer with small bore scanners both of whichlead to an increased signal-to-noise ratio In addition invivo optical imaging is easier in small animals due to thedecreased path-length photons are required to travel Smallanimal imaging has become an important tool in preclinicalaneurysm research

In this review we highlight the recent evolutions in smallanimal AAA models induced via exogenous chemicals andgenetic disruptions We also describe established anatomicalandmolecular imaging methods address clinical translationand identify possible future approaches to small animalAAA imaging The work highlighted in this review is mostlyintended to characterize aneurysm progression through theuse of small animal imaging with the hope of one day leadingto improved clinical AAA treatment

2 Small Animal Models

Exogenous Chemical Induction The three most commonmouse models for exogenous chemical induction of AAAuse pancreatic porcine elastase calcium chloride (CaCl

2) or

angiotensin II (AngII)

21 Elastase Elastase-induced AAA in animal models wasdeveloped from early clinical data suggesting that elastindegradation played a significant role in AAA formation [1516] Clinical pathology showed elastin structure deficienciesand high elastase activity in aneurysmal tissue This ledto early use of luminal perfusion with porcine pancreaticelastase within rats to induce aneurysms [17] Higher concen-trations of elastase led to more severe elastic tissue damageand arterial dilation AAAs have been produced within themurine infrarenal aorta by utilizing porcine pancreatic elas-tase administered via an inserted catheter at the iliac bifurca-tion [18] Elastase leads to elastin fiber degradation andhigherlevels of MMP-2 and MMP-9 expression Though this is atransluminal perfusion the outer adventitia is thought to playa role in the inflammatory signalingmacrophage cascade thatfollows [9] Other work with mice deficient for MMP-12 [18]or IL-17 [19] showed reduced aortic dilation Interestinglygender research revealed that male rats formed larger AAAs

at a higher rate of incidence while females were partiallyprotected through estrogen-mediated reductions of MMP-9production [20] Successful elastase variations have led tofurther characterization of this murine AAA model Forexample porcine pancreatic elastase applied periadventitiallyalso produces an AAA and is an easier surgical procedure[21]

22 Calcium Chloride To induce a murine CaCl2aneurysm

a small gauze saturated in a CaCl2solution is placed centrally

onto the exposed abdominal aorta resulting in intimaland medial macrophage infiltration and significant diameterincrease 14 days after surgery [22] Researchers hypothesizedthat calcium chloride treatments disrupted the targeted elast-in network from calcium precipitates thus activating inflam-matory pathways also observed in the human AAAs

Further genetic characterization focused on the effectsof MMP activity within transgenically modified mice Micedeficient in MMP-9 (macrophage cell derived) or MMP-2(mesenchymal cell derived) were treated with CaCl

2in order

to induce AAAs [23] After 10 weeks no aneurysm forma-tion was seen in either knockout model Interestingly thecompetent macrophages from wild-type controls were theninfused into the corresponding knockout resulting in AAAreconstitution in MMP-9minusminus animals but not MMP-2minusminusmice [23]

23 Angiotensin II The AngII model creates suprarenalAAAs by continuously infusing AngII subcutaneously in lowdensity lipoprotein receptor (ldlrminusminus) or apolipoprotein E(apoEminusminus) knockout mice [24] This vessel expansion wasunexpected and the mechanisms that lead to the dilationare still not fully understood AngII doses did not alterarterial blood pressure murine body weight serum choles-terol concentrations or lipoprotein-cholesterol distribution[25] The addition of doxycycline a broad-system MMPinhibitor reduced AAA incidence by 51 within AngII-induced murine aneurysms [26 27] even though no effectswere observed on blood pressure or serum cholesterolconcentrations Other studies have tried to define the rolethat AngII-induced hypertension plays within this AAAmodel For example ldlrminusminus and apoEminusminus mice were infusedwith AngII or norepinephrine producing similarly increasedblood pressures for both groups Aneurysm formationand atherosclerotic lesion incidence in AngII-infused miceincreased while norepinephrine-infused mice did not showan increase in vessel diameter or atherosclerotic lesions[28] Administration of hydralazine (a vasodialator) reducedsystolic blood pressure without slowing AAA formation orreducing atherosclerotic lesion incidence

Much is already known about the pathophysiology un-derlying the AngIIapoEminusminus AAA model Infrarenal medialmacrophage accumulation and medial dissection are the firststage of AngII-induced murine AAA progression acting asa stimulus for elastin degradation [29] Vascular hematomamacrophage infiltration [25] and thrombus formation all ofwhich are common in human AAAs typically occur after 3ndash10 days in the murine model Remodeling and aneurysmal

The Scientific World Journal 3

tissue generation follow associated with elastic fiber regener-ation luminal surface reendothelialization and aneurysmalneovascularization Recently transforming growth factorbeta (TGF-120573) was shown to limit the innate immune responseand preserve murine vessel integrity as inhibition of thisgrowth factor enhanced monocyte invasiveness andMMP-12activity [30] This work has identified TGF-120573 as a potentialtherapeutic for the treatment of aneurysms and should befurther investigated

24 Gene Disruption AAAs within small animal modelshave also been induced through the use of engineered geneticmanipulations Extracellular matrix maturation defects dis-abling collagen and elastin crosslinking have been shownto increase AAA susceptibility [31] Genetic inactivation oflysyl oxidase (Lox) an extracellular copper enzyme initiatingcollagen and elastin crosslinking resulted in aortic aneurysmdevelopment through fragmented elastic fibers and high rup-ture rates [32] However these animal models often developthoracic aortic aneurysms (rather than AAAs) limiting theirusefulness for abdominal investigations [9]

Genetic inhibition of MMPs is a common mechanismto study AAA progression within all three aforementionedchemically induced murine models TIMP-1 deficient miceproduced pseudomicroaneurysms andmedial rupture stem-ming frommacrophage infiltration of medial elastic lamellae[33 34] Some recent genetic MMP characterization hasfocused on the overriding effect of membrane type-1 MMP(MT1-MMP) with the CaCl

2model Investigators utilized

MT1-MMPminusminus MMP-2minusminus and MMP-9minusminus knockout miceto investigate extracellular matrix breakdown [35] Theyfound lymphocyte infiltration was greatly reduced in theMT1-MMPminusminus model indicating that MT1-MMP plays anunexpected but dominant role in macrophage-mediatedelastolysis Other work has shown that MMP-2 and MMP-9expression can be attenuated due to tumor necrosis factor-alpha (TNF-120572) deficiency indicating that TNF-120572 plays acentral role in regulating matrix remodeling during AAAformation [36]

Evidence that inflammation plays an important role inaneurysm progression has been confirmed time and againMast cells a key component of the inflammatory processare thought to contribute to AAA pathogeneses in miceprimarily through release of the proinflammatory cytokinesinterleukin-6 (IL-6) and interferon-120574 (IFN-120574) Investigationsdone using IL-6 and IFN-120574 knockout mice showed that theinflammatory cascade produced lesions in the smoothmusclecell layer leading to aortic smooth muscle cell apoptosismatrix-degrading protease expression and vascular wallremodeling [37] Disruption of IL-1120573 signaling via a geneticdeletion significantly protects against disease progression inthe elastase-perfusion model [2] Elastin preservation andreduced macrophage and neutrophil infiltration suggest thatIL-1120573 disruption could be used as a novel AAA therapeuticstrategy Similarly platelet receptor inhibition within theAngII murine model limited AAA progression macro-phage infiltration and MMP production [38] Thus there is

a growing amount of evidence in a variety of animal modelsthat supports the key role inflammation plays inAAAdisease

3 Anatomical Imaging

Monitoring the progression or regression of aneurysms hasbecome easier due to recent developments in vascular imag-ing methods The most frequent clinically utilized techniqueis ultrasound imaging Other conventional imaging modal-ities that produce high-resolution images are computedtomography (CT) and magnetic resonance (MR) imagingResearchers should choose the imaging technique that is bestfor their work based on the modalityrsquos strengths and weak-nesses For small animal AAA research the use of multipleimaging modalities can often provide more information thatcan be used to characterize mechanistic and physiologicalprogression

31 Ultrasound Ultrasound is the standard technique fordiagnosing and monitoring nonruptured AAAs in the clinic[39] It is noninvasive accurate reproducible fast usesno ionizing radiation and is widely available to cliniciansmaking it possible to continuouslymonitor AAA progressionand development over time [10] It involves a transducerplaced against skin that emits high-frequency sound waveswhich are then reflected back by internal organs to produceultrasound images The effective contrast depends on anumber of factors such as sound speed sound attenuationback scatter and imaging algorithms [40] Ultrasound is closeto 100 sensitive for detecting aneurysms with a diametergreater than 30mm [41 42] and also provides informationon size and shape of intraluminal thrombi [43]

Wang et al (2001) were the first to use ultrasound technol-ogy to measure aneurysms noninvasively in mice [44] Sincethen ultrasound has witnessed tremendous progress Morerecently developed commercially available high-frequencyultrasound imaging systems (VisualSonics Inc TorontoCanada) can provide increased spatial resolution and makeit possible to apply ultrasound for the accurate quantificationof aortic diameter and wall thickness inmice [45ndash49] Othershave measured aortic diameter in vivo using transabdominal40MHz B-mode imaging of AngII-induced AAAs [48]High-frequency ultrasound was also successfully used toshow that suprarenal aortic expansion occurs rapidly afterinitiation of AngII infusion [50] Examples of transverse andlongitudinal ultrasound images showing a murine AngII-induced AAA are shown in Figures 1(a) and 1(b) Thesemeasurements made with ultrasound were confirmed by apostmortem examination and histological sectioning of theabdominal aorta as reported by Martin-Mcnulty et al [45]Another example of longitudinal and transverse ultrasoundimaging using the elastase model is shown in Figures 1(e)ndash1(g) as reported by Azuma et al They assessed the utilityof high-frequency ultrasound measurements of aortic lumendiameter eliminating the need for sacrifice required for in situmicroscopy [46]

The ability of ultrasound to diagnose and characterizeAAAs has been improved recently through the development


Suprarenal aorta

Infrarenal aorta

(a) (b) (c) (d)

Before surgery

Sham

Elastase

(e) (f) (g)

Figure 1 Example of high-frequency anatomical ultrasound images of abdominal aortas obtained noninvasively ((a)ndash(d)) Images of asuprarenal angiotensin II-induced abdominal aortic aneurysm (AAA) (a) Transverse ultrasound images of suprarenal and correspondinginfrarenal aorta (b) Longitudinal view of a suprarenal AAA (c) Dissected abdominal aorta for anatomical comparison and (d) histologicalcross-section of the suprarenal aorta from the same animal in the dilated region ((e)ndash(g)) Images of elastase-induced AAAs (e) Longitudinalimages of the vessel before surgery after sham surgery and after intraluminal elastase perfusion (f) Corresponding transverse images and(g) histological cross-sections stained with H amp E Figure adapted from [45] for ((a)ndash(d)) and [46] for ((e)ndash(g))

of several advanced imaging techniques speckle trackingthree-dimensional ultrasound imaging Doppler imagingand pulse wave velocity measurements Speckle trackinghas been used to quantify asymmetry and circumferentialstrain in AngII-inducedAAAs [51]Three-dimensional ultra-sound imaging systems are useful whenmeasuring aneurysmlength diameter and volume [52 53] Dynamic properties ofvessels can also be measured by ultrasound using M-modeor other tracking features [54] thus obtaining additionalinformation about the distensibility of aneurysms [55] TissueDoppler imaging is an ultrasound technique that canmeasure

in vivo wall motion along an arterial segment [45 56ndash59]Since traditional ultrasound sensitivity is limited improve-ments have been reported through the use of color duplexultrasound scanning and contrast-enhanced ultrasound [6061] Finally amore recent technique using pulse wave velocity(PWV) can accurately indicate changes in AAA wall prop-erties (and possibly AAA rupture potential) by measuringthe velocity of pressure waves generated by the left ventricleas it travels down the aorta [62 63] Although useful aorticPWV does not provide localized data something that MRand computed tomography (CT) imaging can acquire [64]


While ultrasound still remains the most common tech-nique for imaging AAAs it does have its limitations Compli-cated and tortuous geometries are more difficult to evaluatewith ultrasound than with cross-sectional imaging tech-niques due to limited resolution and limited signal-to-noiseratio Furthermore artifacts from bowel gas and obesitycan limit the use of ultrasound [10] Thus CT and MR(as described in the following sections) can provide certainadvantages [65]

32 Computed Tomography Computed tomography (CT)can produce high-resolution three-dimensional images ofinternal objects and can measure aortic diameter with moreprecision than ultrasound [66] Multiple X-ray images aretaken around a single axis of rotation and then reconstructedto produce an anatomical image [67] Apart from use inpreoperative diagnosis [68] CT is also the preferred clin-ical method for small aneurysm followup largely due togreat spatial resolution speed and reproducibility Radiationdosages can be a concern but risks are minimized if imagingis managed appropriately [10 69] Contrast-enhanced spiralCT angiography is often used for preoperative planning andevaluation prior to treating AAA patients with stent grafts[65 67] It can be used to measure the maximal transversediameter of the aneurysm identify major branching arteriesdetect the presence of intraluminal thrombus and determinethe extent and calcification of tortuous vessels [43] Incurrent clinical practice both ultrasound and CT are used assurveillance imaging tools especially in the early followupGenerally when the aneurysm sac begins to shrink it is saidto be reasonable to move from CT to ultrasound due toradiation dosage concerns thus reserving CT for high-riskpatients [69]

Reliable and accurate 3D geometrical models of themurine aorta have been reconstructed using in vivo micro-CT with a vascular contrast agent (Fenestra VC-131) [70]Trachet et al went further and developed an experimental-computational framework combining information from bothcontrast-enhanced micro-CT (arterial geometry) and high-frequency ultrasound (for flow boundary conditions) to setup mouse-specific computational fluid dynamic simulationsin apoEminusminus mice [71 72] This work provides insight into thedifferences in flow characteristics between mice and humansthat may help elucidate the suprarenal location of AngII-induced aneurysms

33 Magnetic Resonance Imaging Anatomical Magnetic res-onance (MR) imaging allows accurate detection of AAAwithout requiring contrast agents intravascular catheter orionizing radiation Similar to CT angiography MR provideshigh-resolution 3D anatomical imaging of aneurysms inboth humans and small animals [73] MR takes advantageof the fact that atoms with angular momentum such asthe hydrogen atoms in water can be thought of as chargedspheres with a small magnetic moment The combination ofa static magnetic field with overlaid magnetic field gradientscan produce an image by identifying the signalrsquos originIn biological tissue proton-proton and proton-tissue inter-actions can produce useful contrast [74] Differing tissue

relaxation times gives rise to endogenousMR contrast whereT1- and T2-weighted spin echo sequences can be used toclearly identify the various constitutive AAA layers

MR has emerged as a leading noninvasive in vivo imag-ing modality to assess AAA morphometry in mice in vivo[64 75ndash77] For example MR was used to assess vesseldilation for both AngII and elastase-induced aneurysms inmice over a four-week period as highlighted in Figure 2Temporally and spatially resolved data quantifying murineaortic motion and curvature in vivo was obtained by Goer-gen et al in apoEminusminus mice by acquiring time-of-flight MRangiography [64] Choke et al successfully used MR alongwithmicroscopy to determinemaximumdiameter and cross-sectional area of AAA in apoEminusminusmousemodels [78] Klink etal also demonstrated use of high-resolution multisequenceMR to characterize the temporal progression of an AAA inAngII infused mice [79] In addition in vivo phase-contrastmagnetic resonance (PCMR) velocity measurements wereused by Amirbekian et al to characterize the hemodynamicenvironment of the suprarenal and infrarenal abdominalaorta of normal and apoEminusminus mice [80] Longitudinal high-resolution MR scans have recently been used to charac-terize aneurysm development in murine elastase-inducedAAAs without significant mortality measuring inner lumendiameter outer vessel diameter and vessel wall thickness[73]

Modified MR techniques can be applied to provide moreinformation than just vessel expansion In patients dynamicgadolinium-enhancement techniques have been shown tohelp characterize AAA [81]Magnetic resonance angiographyhas also been used in the clinic to characterize aortic stiffnessand elastic modulus as indices of arterial wall complianceduring the cardiac cycle [82] Furthermore the assessment ofaortic flow patterns has been made possible by the develop-ment of 3D time-resolved phase-contrast velocity-mappingmagnetic resonance sequenceswhich allows for acquisition ofshear-stress measurements of the arterial wall [83] Howeverthe clinical relevance of these techniques continues to beexplored [43]

It is now evident that a variety of anatomical imagingmodalities are capable of tracking AAA progression in bothhumans and small animals Yet other less developed molec-ular imaging techniques may provide more informationthat could be used to better predict AAA progression anarea of certain clinical interest Indeed the development ofradiotracers that target specific molecules involved in AAAgrowth or the use of molecular optical imaging could providenew insights into aneurysmal disease

4 Molecular and Functional Imaging

41 Magnetic Resonance Imaging Molecular Molecular MRcan explore events that occur at cellular and subcellular levelswith nanomolar sensitivity [84] Anatomical MR even whenusing contrast agents has only micromolar sensitivity [85]Thus the development of new molecular contrast agents isan area of current research aiming to increase the capabilitiesof magnetic resonance [86]


Days 0 3 7 14 21 28

AngII

Day 28119899 = 10

(a)

0 3 7 14 21 28Days

Elastase

Day 28119899 = 12

(b)

Figure 2 Coronal magnetic resonance maximum intensity projections showing lumen expansion in (a) angiotensin II-induced (AngII) and(b) elastase-induced abdominal aortic aneurysms (AAA) Angiotensin II-induced AAAs appear suddenly (arrowhead) and expand leftwarddirectly above the right renal artery (arrow) Ten additional angiotensin II AAAs are shown at day 28 Elastase-induced AAAs expand slowlySmall region of signal hypointensity is seen at day 3 (triangle) due to a suture in the vessel Twelve additional elastase AAAs are shown at day28 The testicular artery is highlighted (arrow) Figure adapted from [77]

One of the more established uses for molecular MRin AAA research is monitoring macrophage accumulationUltrasmall superparamagnetic iron oxide (USPIO) particlesare a useful label for macrophages with phagocytic activityalthough surrounding tissue uptake of USPIOs can alsocause some imaging difficulty [87] In general iron oxideparticles reduce the T2 relaxation time of nearby absorbingtissues [88 89] To increase in vivo macrophage imagingsensitivity iron oxides (specifically heavy chain ferritin orHFn) were attached to Arg-Gly-Asp (RGD) a short integrinbinding sequence that has been used to image atheroscle-rosis [90] HFn molecular imaging is enhanced with RGDtargeting extending imaging capabilities to atherosclerotic

macrophages and angiogenic endothelial cells [90] Similarstudies have been done clinically with similar results ashuman AAAs also show uptake of USPIOs which is sugges-tive of inflammation [91]

Contrast agents specific to MMPs have been developedand used to further explore the molecular processes asso-ciated with AAAs P947 a recently developed MR contrastagent was created to target atherosclerotic plaque by couplingan MMP inhibitor to a gadolinium chelate (Gd-DOTA) [92]Gd-DOTA and other gadolinium chelates enhanceMR imag-ing by shortening the T1 relaxation time of nearby protons[93] P947 was shown to have higher affinity for MMPs thanGd-DOTA alone particularly within more stable plaques


(a) (b) (c)

(d)

Figure 3 Transverse T2lowast-weightedmagnetic resonance images the spin-spin relaxation timemeasured in gradient echo sequences of a singlemurine abdominal aortic aneurysm prior to iron oxide nanoparticle-labeled vascular smooth muscle cell delivery (a) and on postdeliverydays 0 (b) 21 (c) and 28 (d) Arrows represent areas of hypointense signal in the aortic wall The vessel lumen is highlighted with (995333) Scalebar represents 1mm Figure adapted from [96]

[92] P947 greatly enhanced the MR signal in atheroscleroticvessel walls of the apoEminusminus mice significantly more thaneither its untargeted counterpart (a scrambled form of P947)or a Gd-DOTA control [94] In an elastase-induced AAAmodel P947 has shown enhanced MMP targeting in AAAMR imaging when compared to either control [95] In allof the P947 studies areas with P947 enhanced MR imagecontrast also had a variety of active MMPs

Another contrast agent the collagen-specific proteinCNA-35 has been used in the AngII-induced AAA modelMicelles of CNA-35 were created as the contrast agent whilea mutant version was used for comparison [79] Addition ofCNA-35 micelles enhanced MR signal in the aneurysm wallassociating with the breakdown of collagen during aneurysmprogression This property can also be used to differentiatebetween collagen rich and collagen poor AAAs [79]

MR can also be used to track cellular implantation andmigration One such example is the uptake of iron oxidenanoparticles into vascular smooth muscle cells (VSMCs)[96] One recent study examines how iron oxide nanoparti-cles (IONPs) change the therapeutic effects of VSMCs [96]Not only do IONP-VSMCs show the same efficiency of celldelivery as VSMCs alone but they can also be detected

with MR imaging This allows for unhindered monitoring ofVSMCs that have migrated in or near the AAA As shownin Figure 3 the use of IONP-labeled VSMC is effective inrevealing the labeled smooth muscle cells collecting aroundan aneurysm [96] All parts of Figure 3 are taken from thesame animal verifying that IONPs can be used as an effectivein vivo contrast agent

While every imaging modality has its own advantagescombining various approaches allows for more imagingcapabilities For example characterizing macrophage accu-mulation in AAAs can be done using molecular MR com-plemented with bioluminescence Super paramagnetic ironoxide (SPIO) nanoparticles and transgenically modifiedluciferase expressing macrophages can be used to quantifyinflammation with MR and bioluminescence [97] Bothmodalities confirmed macrophage accumulation at the AAAand also showed that a majority of macrophages ended up inthe adventitia

One of the main advantages of MR is its noninvasivenature The ability to acquire images at multiple timepointswithin the same animal reduces the overall number of ani-mals needed and provides evidence for disease progressionover timeMolecularMR is currently limited inmeasurement


Control Elastase AAA Angiotensin II AAA

L R

I

S

(a) (b) (c) (e)

(d)

Ventral

Dorsal

Figure 4 Near-infrared fluorescence (NIRF) image of both angiotensin II-induced and elastase-induced aneurysms (a) Controlapolipoprotein-E deficient mouse aorta after injection of MMPSense 680 (b) Infrarenal aortic aneurysm induced via elastase infusion (c)Suprarenal aortic aneurysm induced via angiotensin II infusion (d) Dorsal and (e) ventral NIRF images of angiotensin II-induced abdominalaortic aneurysms showing asymmetric probe accumulation suggestive of regional differences in protease activation and inflammation Figureadapted from [77]

capabilities Contrast agents are available to target a handfulof molecules and cells but there are many applications yet tobe explored Developing new and innovative contrast agentsanddualmodality imaging strategies are both areas that couldlead to further imaging advancements

42 Near-Infrared Fluorescence There are three generalparameters that describe the interaction of photons withbiological tissues absorption of light scattering of lightand fluorescence emission The light absorption by endoge-nous chromophores in living tissues (including hemoglobinmelanin and lipid [98ndash101]) is typically within the visiblespectral region (400ndash700 nm) limiting penetration to only afew millimeters Additionally light absorption due to wateris notably increased above 900 nm [98] Photons in thenear-infrared (NIR) range (700ndash900 nm) however penetratedeeper than visible light [99] Hence the NIR window is oftenutilized in biomedical imaging as photons have a penetrationdepth of several centimeters in tissue [98ndash101] For exam-ple near-infrared fluorescence (NIRF) and bioluminescenceimaging are both highly sensitive techniques that can providemolecular information [102ndash106]

Indocyanine green the only currently FDA-approvedNIR cyanine fluorescent dye has been used to assess mi-crovasculature in tumors [107 108] lymph nodes [109 110]and atherosclerotic plaques [111] but has not yet been appliedto AAAs More recent work has used indocyanine green toimage cerebral aneurysms during surgery [112 113] providinghope that fluorescent imaging of abdominal aneurysms mayalso be useful The location of the aorta certainly provides

challenges but access through catheters or during opensurgical procedures could certainly help overcome some ofthe technical challenges associated with optical imaging inthe clinic

In preclinical research some of the most common ac-tivatable optical probes are those sensitive to protease acti-vation By using the MMP-activatable probe MMPSense(PerkinElmer Waltham MA USA) a direct linear relation-ship between proteolytic activity and aneurysmal growth wasshown through in vivo imaging with the CaCl

2model [114]

Moreover Kaijzel et al showed increased MMP activity infibulin-4 mice well before the aneurysm had actually formed[115] Figure 4 highlights the spatial distribution of relativeMMP activity showing a correlation between inflammationand fluorescent signal a result that was also seen with acathepsin sensitive probe [77] These data suggest that pro-tease accumulation and activation are increased in regions ofvessel remodeling

Transmural inflammation and adventitial neovascular-ization are pathological characteristics of AAAs Previouswork using in situNIRF imaging revealed significant vascularendothelial growth factor receptor (VEGFR) expression inthe AngII model [48] These results showed that muralVEGFR expression as measured with fluorescence imagingand immunohistochemistry increased in a diameter-de-pendent fashion with AAA progressionThis study then wentfurther and showed that an angiogenesis inhibitor decreasedthe inflammatory response and attenuated AAA formation[48] results that suggest that angiogenesis inhibition shouldbe further explored as it may expand therapeutic alternativesfor the treatment of AAA disease


(a)

4000

8000

(b)

(c)

400

800

(d)

Figure 5 ((a) (b)) In situ and ((c) (d)) ex vivo bioluminescent images of an infrarenal abdominal aortic aneurysm ((a) (c)) and controlvessel ((b) (d)) with arbitrary units Aneurysms were induced via elastase perfusion Figure adapted from [97]

Inflammation is seen in the vast majority of AAAsmaking vascular inflammation-targeted imaging an activearea of research As mentioned previously Kitagawa et alevaluated the inflammation process in the AngII model usingRGD-conjugated HFn that were also labeled with fluorescentCy55 [90] AAAs showed higher fluorescent signal intensitywhen compared to surrounding tissue and these resultswere confirmed with immunohistochemistry [90] Thesedata suggest that targeted human ferritin might be a usefulplatform for vascular inflammation imaging in humans

43 Bioluminescence Bioluminescence imaging uses cellsthat have been transgenically engineered to express luciferaseThese cells are implanted in animals allowed to proliferateand produce light when they come in contact with luciferin[106] Figure 5 shows the application of bioluminescenceto study macrophage accumulation in the elastase-inducedaneurysm model [97] Macrophages from transgenic miceexpressing luciferase were injected in mice from both dis-eased and control groups Both the in situ and ex vivo bio-luminescence images show high macrophage accumulationin AAAs when compared to control mice (Figure 5) Whilebioluminescence excels at providing information about the

location of transgenically modified cells image resolutionand sensitivity degrade as tissue depth increases [116] Com-plications associated with implantation of genetically alteredcells into humans also limit the use of bioluminescence fornoninvasive characterization of AAAs in the clinic

44 Radionuclide Imaging For the purposes of molecularand functional imaging of AAA single-photon emissioncomputed tomography (SPECT) provides many advantagesand has become a powerful tool Unlike contrast agents thatalter image contrast radionuclide imaging uses radioactivetracers as imaging agents The objective of SPECT is tocollect 120574 and X-ray signals from radiopharmaceuticals withinthe body and use these signals to create 3D tomographicimages [117] These images represent the biodistribution ofthe radionuclides and are obtained noninvasively In SPECTimaging gamma photons are emitted and lead collima-tors designed to reject photons measure the signal that isproduced within a small range of angular incidence Thismeasurement method results in low geometric efficiencies(sim001) compared to positron emission tomography (PET)which uses a coincidence-detection method and eliminatesthe need for collimators Due to the nature of positron


annihilation PET systems measure two photons emitted inopposite directions For PET the geometric efficiency is onthe order of sim1 [118] However SPECT systems use lessexpensive and more stable radionuclides and can completescans faster than PET systems [119] Similar to SPECT PETuses radionuclides to construct 3D images The main advan-tage of PET over SPECT systems includes improved resolu-tion though rapidly decaying radionuclides create logisticaldifficulties [119]

45 Single-Photon Emission Computed Tomography A vari-ety of radionuclide tracers have been used to obtain molec-ular images of AAA using SPECT In the late 1970s redblood cells labeled with technetium-99m (99mTc) were usedto image AAA in human patients [120] Also 99mTc-fucoidanwas used to detect aneurysmal intraluminal mural thrombiThis is due to the high affinity that fucoidan has for P-selectin an adhesion molecule whose expression is involvedin aneurysmal pathophysiology [121] Luminal thrombi inmurine AAAs were also imaged using 99mTc-annexin 99mTc-annexin works by binding to phosphatidylserine on apop-totic cells and activated platelets [122] 99mTc-labeled anti-smooth muscle myosin antibodies have shown promise forthe imaging of dissecting aneurysms as previous researchshowed that this tracer localizes to aortic dissections in arat model [123] Platelets labeled with indium 111 (111In)have shown small animal aortic imaging possibilities as well[124] However in human patients 111In has exhibited apropensity to sequester in the spleen liver and bonemarrowcausing reduced aneurysm accumulation [125] Thallium 201(201Tl) is commonly used as a myocardial perfusion agent[126] Myocardial perfusion in patients with AAA has beenquantitatively evaluated using 201Tl suggesting that thistracer may be useful in predicting AAA rupture SPECT canbe used to detect multiple radionuclides at once making itpossible to analyze multiple molecular processes and givingit a distinct advantage over other modalities [127]

In order to give anatomical context and to improve quan-titative SPECT data SPECT systems are often coupled withCT [128]This coupling has proven very useful due to the factthat functional images of the thorax and abdomen providefew landmarks to correlate with the surrounding anatomySPECT imaging has been used for molecular functionaland anatomical imaging in a wide variety of areas includingmyocardial perfusion cancer diagnosis functional brainimaging bone imaging Alzheimerrsquos diagnosis and quan-tifying thrombus formation in AAAs [122 129ndash134] Overthe past ten to fifteen years dedicated small animal SPECTsystems have been developed to aid in preclinical research[135] This advancement has made it possible for researchersto observe molecular processes in a single animal overtime Traditionally snapshotmolecular data was collected viatissue sectioning microscopy or 120574 counting after euthanasiaAs small animal models for AAA continue to develop andimprove SPECT systems have become increasingly valuablein research

Despite the promise that SPECT presents for AAAmolecular and functional imaging it has several limitations

including low geometric efficiency of collimators subparattenuation compared to PET low temporal resolution ina-bility to eliminate crosstalk between radionuclide tracers andinefficient reconstruction software [118] While some solu-tions to these issues have been addressed the complexity andcost of SPECT and SPECTCT systems slow improvementsRecent SPECTadvances include improved scintillators solid-state photon transducers attenuation correction improvedimage reconstruction and dynamic SPECT [117] As theseimprovements are implemented SPECT will continue to bean attractive modality for molecular and functional imagingof AAA

46 Positron Emission Tomography Aswith SPECT the addi-tion of CT to stand-alone PET systems helps provide anatom-ical context to the generated images Most PETCT systemsconsist of both systems working in tandem and scanningsequentially although some are able to scan simultaneously[136] Figure 6 shows a series of images obtained from aPETCT system [137] In that study fluorine-18 (18F) labelednanoparticles were used to target macrophages that are amarker of inflammation in themurine AngIIapoEminusminusmodelThese results demonstrate the ability of CT to give anatomicalcontext to otherwise ambiguous PET images

In a similar study 18F-labeled fluorodeoxyglucose (FDG)18F-fluoromethylcholine (FCH) and 18F-DPA714 (a periph-eral benzodiazepine receptor antagonist) were used to targetinflammation and imageAAAs in rats [134] Results indicatedthat sensitivity was higher for FDG-PET than FCH andDPA714 PET increasing interest in the FDG tracer foraneurysm imaging High uptake of FDG is attributed toinflammation in the aneurysm wall and is thus a commontracer for molecular imaging of AAA [138 139] Researchershave also tried to correlate FDG uptake with aneurysmrupture risk in humans however quantifying this relation-ship has proven to be nontrivial [140] In another studyFDG was used with PETCT to investigate aneurysm wallpathology and coincidentally identified concomitant tumorsin several patients [141]This discovery illustrates the diversityof applications for PETCT

The future of PET imaging is largely in the developmentof new molecular probes and in improved multimodalitysystems (PETCT andPETMR)Development of new tracersis a very complex process in which the desired target mustbe matched with the proper targeting ligand and optimizedfor high efficiency binding Due to the short lifespan ofradioisotopes proficient labeling of new tracers to pep-tides and antibodies requires specialized personnel oftenunavailable in small medical research facilities In additiona suitable radionuclide must be selected based on availabilityhalf-life binding capability and specific activity [142] Thisprocess can be lengthy arduous and expensive Small animalPET can act as a means to test new tracers for efficacy ina preclinical setting Multimodality PET systems such asPETCT (and more recently PETMR) seem to be the futureof PET molecular imaging Researchers and clinicians alikeimmediately embraced PETCT but limitations remain andimprovements continue to be developed in the areas of device


Figure 6 PETCT imaging in mice with aortic aneurysms induced via angiotensin II infusion Apolipoprotein E-deficient (apoEminusminus) micewere compared to wild-type controls (apoE++) Dotted lines and yellow arrows outline the aneurysmal aorta Liver signal highlighted with(lowast) PETCT images illustrate the ability of CT to add anatomical context for PET images Figure adapted from [137]

hardware reconstruction software and detector sensitivity[143] Progress in the area of radiopharmaceuticals is slowas regulations for clinical trials are stringent for radioactivematerials Radiotracers that have already been developedmust endure extensive approval processes before humantesting can occur As these advancements are implementedmolecular and functional imaging for AAA will significantlyimprove

5 Conclusions and Future Possibilities

Several imagingmodalities applied to small animalAAAhavebeen reviewed in this paper (see Table 1) Well-establishedimaging methods such as ultrasound CT and MR canprovide anatomical images of mouse and rat AAAs Theyhave been extensively applied in both preclinical research andin the clinic for diagnosis and monitoring aneurysms Theuse of molecular imaging to investigate AAA progression hasrecently become more popular although clinical translationof these technologies remains difficult Molecular aneurysmimaging is likely to grow as more potential AAA biomarkersare identifiedThe future ofAAA imaging lies in severalmajordirections understanding underlying progression mecha-nisms multimodality imaging application or developmentof novel AAA imaging technology and clinical translation ofmolecular imaging methods These future directions includeseveral aspects which should be addressed

First development of clinically relevant animal models islikely required to elucidate mechanisms of AAA progression

Though mice and rats are the most frequently used speciesfor aneurysm models many studies only observe vesseldilation through the first four weeks after AAA onset Thecurrent technique of aneurysm screening in humans rarelyidentifies vascular dilation this early in AAA developmentand treatment is usually started well outside of this four-weekrange Additionally there is currently no singlemurinemodelable to accurately mimic all physiological features observedin the human condition [12] Murine AAAs rarely continueto expand until rupture the major clinical concern inpatients with aneurysmsThus development of more realisticanimal models may provide a better understanding of theunderlying disease Future small animal model refinementswill also likely help guide the design and evaluation of newmonoclonal antibodies or small molecules that could preventAAA growth

Second novel imaging methods and contrast agentscould be used to provide new insights into vascular diseasePhotoacoustic (PA) imaging which detects the acoustic waverising from photon absorption is one promising technologyfor AAA imaging Biomedical PA imaging has superiortissue penetration due to acoustic detection and molecularspecificity because it utilizes optical excitation [144 145]Recent studies of atherosclerosis usingmicroscopic [146 147]and intravascular [148 149] PA imaging raise the intrigu-ing possibility of using PA methods to study aneurysmsAnother potential method for AAA visualization is Ramanspectroscopy and imaging The contrast from Raman spec-troscopy originates from molecular vibrations which is a


Table 1 Summary of imaging modalities used to image small animal abdominal aortic aneurysms

Modality Capabilities Application Contrast AgentsRadionuclide Tracers

Anatomical MolecularFunctional Benefits Limitations

Ultrasound XRapid accurate low costreproducibility widelyavailable

Limited resolution imageinterpretation difficultartifacts common

Microbubbles

CT XRapid high resolutionuseful for early clinicalfollowup

Ionizing radiation requirescontrast agent Iodine or Barium

MRI X Soft tissue contrast highresolution

High cost large equipmentrequired Gadolinium chelates

X Customizable moleculartargeting cell tracking

Limited sensitivity requirescontrast agent

USPIOs or gadoliniumchelates

NIRF X Low cost widely availablePhotobleaching lowquantum yield shallowtissue penetration

MMPSense scVEGFCyRGD-HFn-Cy55

Bioluminescence X High sensitivity highspecificity

Shallow tissue penetrationrequires transgenicmodification

Exotic transgenic cellscombined with luciferin

SPECT X

3D imaging widelyavailable highly sensitivesimultaneous imaging ofmultiple processes

Limited temporalresolution fewradionuclide tracers

99TC 111In 201Tl 123I 131I

PET X

Quantification ofmetabolism and blood flowhigh sensitivity manyradionuclide tracersavailable

High cost limitedavailability largeequipment required shorttracer half-life singleprocess evaluation

18F 11C 13N 15O 82RB

direct measurement of molecular properties Intravascu-lar Raman spectroscopic catheters have been applied tohuman coronary atherosclerosis [150] This work suggeststhat Raman spectroscopy could also be used to investigate theconstituents of the aneurysmal wall in vivo

Third development of new contrast agents particularlynanostructures is also advancing the field of vascular molec-ular imaging While NIRF imaging has been used to assessMMP activation VEGF expression and inflammation thisprevious work has used fluorescent dyes that are limitedby photobleaching and low quantum yields Semiconductorquantum dots a newly developed nanoparticle fluorescentprobe are remarkably resistant to photobleaching with muchhigher quantum yields when compared to standard fluores-cent molecules Although quantum dots have toxicity issuesthey have presently been applied for targeted in vivo imagingof tumors in animal models [151 152] Other works utilizedsingle-walled carbon nanotubes (SWNTs) as a murine in vivocontrast agent for real-time fluorescence imaging throughthe second near-infrared region (1000ndash1400 nm) [153 154]Due to reduced optical scattering in this window significantresolution improvements were achieved when comparedto traditional near-infrared imaging [154] This concept isattractive to molecular imaging of AAAs since the SWNTscan be functionalized to target specific molecules Thusdual molecular fluorescence imaging with quantum dots

or SWNTS may provide new information when used withexperimental AAA models

Finally intravascular imaging using catheter technologyhas helped many imaging techniques translate into the clinicIntravascular imaging can define arterial wall compositionwith high temporal and spatial resolution and is often usedto guide stent implantation in coronary arteries Opticalimaging methods are often feasible during intravascularprocedures since near-infrared light can penetrate throughthe thickness of most arterial walls Such optical methodsincluding intravascular-basedNIRF [114 155ndash158] NIR spec-troscopy [159 160] Raman spectroscopy [150] PA imag-ing [148 149] and optical coherent tomography [157 161]have all been shown to successfully characterize coronaryatherosclerosis through selective chemical contrast Howevercoronary artery and aorta sizes are quite different makingimplementation of intravascular optical methods for abdom-inal imaging challenging For example blood in coronaryarteries is often flushed and replaced with saline to minimizelight scattering a procedure that is likely not possible in theabdominal aorta Engineering modifications are thus neededto optimize techniques for imaging both experimental andclinical AAAs

In summary this review has described ongoing effortsto characterize AAA initiation and progression throughimaging a variety of small animal models Anatomical and


molecular imaging modalities continue to develop givingresearchers a better picture of AAA pathogenesis throughlongitudinal imaging studiesWhile the long-termgoal of thisfield is to help humanAAApatients a detailed understandingof small animal aneurysm models through in vivo imagingshould help to bring novel therapies closer to clinical appli-cation

Acknowledgment

The authors gratefully acknowledge funding support fromthe Weldon School of Biomedical Engineering at PurdueUniversity

References

[1] S J Belsley and M D Tilson ldquoTwo decades of research onetiology and genetic factors in the abdominal aortic aneurysm(AAA)mdashwith a glimpse into the 21st centuryrdquo Acta ChirurgicaBelgica vol 103 no 2 pp 187ndash196 2003

[2] W F JohnstonM Salmon G Su et al ldquoGenetic and pharmaco-logic disruption of interleukin-1120573 signaling inhibits experimen-tal aortic aneurysm formationrdquo Arteriosclerosis Thrombosisand Vascular Biology vol 33 no 2 pp 294ndash304 2013

[3] F A Lederle G R Johnson S E Wilson et al ldquoPrevalence andassociations of abdominal aortic aneurysm detected throughscreeningrdquo Annals of Internal Medicine vol 126 no 6 pp 441ndash449 1997

[4] R S von Allmen and J T Powell ldquoThe management ofruptured abdominal aortic aneurysms screening for abdominalaortic aneurysm and incidence of rupturerdquo The Journal ofCardiovascular Surgery vol 53 no 1 pp 69ndash76 2012

[5] S Nanda S G Sharma and S Longo ldquoMolecular targets andabdominal aortic aneurysmsrdquo Recent Patents on CardiovascularDrug Discovery vol 4 no 2 pp 150ndash159 2009

[6] J T Powell and R M Greenhalgh ldquoSmall abdominal aorticaneurysmsrdquoThe New England Journal of Medicine vol 348 no19 pp 1895ndash1901 2003

[7] K C Kent R M Zwolak N N Egorova et al ldquoAnalysis of riskfactors for abdominal aortic aneurysm in a cohort of more than3 million individualsrdquo Journal of Vascular Surgery vol 52 no 3pp 539ndash548 2010

[8] M Prinssen E L G Verhoeven J Buth et al ldquoA random-ized trial comparing conventional and endovascular repair ofabdominal aortic aneurysmsrdquo The New England Journal ofMedicine vol 351 no 16 pp 1607ndash1618 2004

[9] A Daugherty and L A Cassis ldquoMouse models of abdominalaortic aneurysmsrdquo Arteriosclerosis Thrombosis and VascularBiology vol 24 no 3 pp 429ndash434 2004

[10] H Hong Y Yang B Liu and W Cai ldquoImaging of abdominalaortic aneurysm the present and the futurerdquo Current VascularPharmacology vol 8 no 6 pp 808ndash819 2010

[11] A Trollope J V Moxon C S Moran and J GolledgeldquoAnimal models of abdominal aortic aneurysm and their rolein furthering management of human diseaserdquo CardiovascularPathology vol 20 no 2 pp 114ndash123 2011

[12] H Lu D L Rateri D Bruemmer L A Cassis and A Daugh-erty ldquoNovel mechanisms of abdominal aortic aneurysmsrdquoCurrent Atherosclerosis Reports vol 14 no 5 pp 402ndash412 2012

[13] R S Balaban and V A Hampshire ldquoChallenges in small animalnoninvasive imagingrdquo ILAR Journal vol 42 no 3 pp 248ndash2622001

[14] R Lecomte J Cadorette P Richard S Rodrigue and DRouleau ldquoDesign and engineering aspects of a high resolutionpositron tomograph for small animal imagingrdquo IEEE Transac-tions on Nuclear Science vol 41 no 4 pp 1446ndash1452 1994

[15] R W Busuttil H Rinderbriecht A Flesher and C CarmackldquoElastase activity the role of elastase in aortic aneurysmformationrdquo Journal of Surgical Research vol 32 no 3 pp 214ndash217 1982

[16] E J Andrews W J White and L P Bullock ldquoSpontaneous aor-tic aneurysms in Blotchy micerdquo American Journal of Pathologyvol 78 no 2 pp 199ndash210 1975

[17] S Anidjar J L Salzmann D Gentric P Lagneau J P Camilleriand J B Michel ldquoElastase-induced experimental aneurysms inratsrdquo Circulation vol 82 no 3 pp 973ndash981 1990

[18] R Pyo J K Lee J M Shipley et al ldquoTargeted gene disruptionof matrix metalloproteinase-9 (gelatinase B) suppresses devel-opment of experimental abdominal aortic aneurysmsrdquo Journalof Clinical Investigation vol 105 no 11 pp 1641ndash1649 2000

[19] A K Sharma G Lu A Jester et al ldquoExperimental abdominalaortic aneurysm formation is mediated by IL-17 and attenuatedby mesenchymal stem cell treatmentrdquo Circulation vol 126 no11 supplement 1 pp S38ndashS45 2012 Erratum in Circulation vol126 no 17 p e278 2012

[20] G Ailawadi J L Eliason K J Roelofs et al ldquoGender differencesin experimental aortic aneurysm formationrdquo ArteriosclerosisThrombosis and Vascular Biology vol 24 no 11 pp 2116ndash21222004

[21] C M Bhamidipati G S Mehta G Lu et al ldquoDevelopment of anovel murine model of aortic aneurysms using peri-adventitialelastaserdquo Surgery vol 152 no 2 2012

[22] A C Chiou B Chiu and W H Pearce ldquoMurine aorticaneurysm produced by periarterial application of calciumchloriderdquo Journal of Surgical Research vol 99 no 2 pp 371ndash3762001

[23] G M Longo W Xiong T C Greiner Y Zhao N Fiotti and BT Baxter ldquoMatrix metalloproteinases 2 and 9 work in concertto produce aortic aneurysmsrdquo Journal of Clinical Investigationvol 110 no 5 pp 625ndash632 2002

[24] A Daugherty MWManning and L A Cassis ldquoAngiotensin IIpromotes atherosclerotic lesions and aneurysms in apolipopro-tein E-deficient micerdquo Journal of Clinical Investigation vol 105no 11 pp 1605ndash1612 2000

[25] P Ravisankar L A Cassis S Szilvassy and A DaughertyldquoAbsence of CCR2 receptors in bone marrow-derived cellsdecreases angiotensin II induced atherosclerosis and abdomi-nal aortic aneurysms in ApoE deficient micerdquo ArteriosclerosisThrombosis and Vascular Biology vol 22 no 5 2002

[26] M W Manning L A Cassis and A Daugherty ldquoDifferentialeffects of doxycycline a broad-spectrum matrix metallopro-teinase inhibitor on angiotensin II-induced atherosclerosis andabdominal aortic aneurysmsrdquo Arteriosclerosis Thrombosis andVascular Biology vol 23 no 3 pp 483ndash488 2003

[27] X Xie H Lu J J Moorleghen et al ldquoDoxycycline doesnot influence established abdominal aortic aneurysms inangiotensin II-infused micerdquo PLoS One vol 7 no 9 Article IDe46411 2012

[28] L A Cassis M Gupte S Thayer et al ldquoANG II infusion pro-motes abdominal aortic aneurysms independent of increased


blood pressure in hypercholesterolemic micerdquo American Jour-nal of Physiology vol 296 no 5 pp H1660ndashH1665 2009

[29] K Saraff F Babamusta L A Cassis and A Daugherty ldquoAorticdissection precedes formation of aneurysms and atherosclerosisin angiotensin II-infused apolipoprotein E-deficient micerdquoArteriosclerosis Thrombosis and Vascular Biology vol 23 no9 pp 1621ndash1626 2003

[30] Y Wang H Ait-Oufella O Herbin et al ldquoTGF-120573 activityprotects against inflammatory aortic aneurysm progressionand complications in angiotensin II-infused micerdquo Journal ofClinical Investigation vol 120 no 2 pp 422ndash432 2010

[31] J M Reilly E B Savage C M Brophy and M D TilsonldquoHydrocortisone rapidly induces aortic rupture in a geneticallysusceptible mouserdquo Archives of Surgery vol 125 no 6 pp 707ndash709 1990

[32] J M Maki J Rasanen H Tikkanen et al ldquoInactivation of thelysyl oxidase gene Lox leads to aortic aneurysms cardiovasculardysfunction and perinatal death in micerdquo Circulation vol 106no 19 pp 2503ndash2509 2002

[33] V Lemaıtre P D Soloway and J DrsquoArmiento ldquoIncreasedmedial degradation with pseudo-aneurysm formation in apol-ipoprotein E-knockout mice deficient in tissue inhibitor ofmetalloproteinases-1rdquo Circulation vol 107 no 2 pp 333ndash3382003

[34] B T BaxterWH Pearce E AWaltke et al ldquoProlonged admin-istration of doxycycline in patients with small asymptomaticabdominal aortic aneurysms report of a prospective (Phase II)multicenter studyrdquo Journal of Vascular Surgery vol 36 no 1 pp1ndash12 2002

[35] W Xiong R Knispel J MacTaggart T C Greiner S JWeiss and B T Baxter ldquoMembrane-type 1 matrix metallopro-teinase regulatesmacrophage-dependent elastolytic activity andaneurysm formation in vivordquo Journal of Biological Chemistryvol 284 no 3 pp 1765ndash1771 2009

[36] W Xiong J MacTaggart R Knispel J Worth Y Persidsky andB T Baxter ldquoBlocking TNF-120572 attenuates aneurysm formationin a murine modelrdquo Journal of Immunology vol 183 no 4 pp2741ndash2746 2009

[37] J Sun G K Sukhova M Yang et al ldquoMast cells modulate thepathogenesis of elastase-induced abdominal aortic aneurysmsin micerdquo Journal of Clinical Investigation vol 117 no 11 pp3359ndash3368 2007

[38] O Liu L Jia X Liu et al ldquoClopidogrel a platelet P2Y12 receptorinhibitor reduces vascular inflammation and angiotensin IIinduced-abdominal aortic aneurysm progressionrdquo PloS Onevol 7 no 12 Article ID e51707 2012

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[40] M H Wink H Wijkstra J J M C H de La Rosette andC A Grimbergen ldquoUltrasound imaging and contrast agents asafe alternative to MRIrdquoMinimally InvasiveTherapy and AlliedTechnologies vol 15 no 2 pp 93ndash100 2006

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[42] J S Lindholt S Vammen S Juul E W Henneberg and HFasting ldquoThe validity of ultrasonographic scanning as screeningmethod for abdominal aortic aneurysmrdquo European Journal of

Vascular and Endovascular Surgery vol 17 no 6 pp 472ndash4751999

[43] A Klink F Hyafil J Rudd et al ldquoDiagnostic and therapeu-tic strategies for small abdominal aortic aneurysmsrdquo NatureReviews Cardiology vol 8 no 6 pp 338ndash347 2011

[44] Y X Wang B Martin-McNulty A D Freay et al ldquoAngiotensinII increases urokinase-type plasminogen activator expressionand induces aneurysm in the abdominal aorta of apolipoproteinE-deficient micerdquoAmerican Journal of Pathology vol 159 no 4pp 1455ndash1464 2001

[45] B Martin-Mcnulty J Vincelette R Vergona M E Sullivanand Y X Wang ldquoNoninvasive measurement of abdominalaortic aneurysms in intactmice by a high-frequency ultrasoundimaging systemrdquoUltrasound inMedicine andBiology vol 31 no6 pp 745ndash749 2005

[46] J Azuma L Maegdefessel T Kitagawa R L Dalman M VMcConnell and P S Tsao ldquoAssessment of elastase-inducedmurine abdominal aortic aneurysms comparison of ultrasoundimaging with in situ video microscopyrdquo Journal of Biomedicineand Biotechnology vol 2011 Article ID 252141 2011

[47] F S Foster M Y Zhang Y Q Zhou et al ldquoA new ultrasoundinstrument for in vivo microimaging of micerdquo Ultrasound inMedicine and Biology vol 28 no 9 pp 1165ndash1172 2002

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[49] J M Spin M Hsu J Azuma et al ldquoTranscriptional profilingand network analysis of the murine angiotensin II-inducedabdominal aortic aneurysmrdquo Physiological Genomics vol 43no 17 pp 993ndash1003 2011

[50] C Barisione R Charnigo D A Howatt J J Moorleghen DL Rateri and A Daugherty ldquoRapid dilation of the abdominalaorta during infusion of angiotensin II detected by noninvasivehigh-frequency ultrasonographyrdquo Journal of Vascular Surgeryvol 44 no 2 pp 372ndash376 2006

[51] J T Favreau B T Nguyen I Gao et al ldquoMurine ultrasoundimaging for circumferential strain analyses in the angiotensin IIabdominal aortic aneurysmmodelrdquo Journal of Vascular Surgeryvol 56 no 2 pp 462ndash469 2012

[52] D F Leotta M Paun K W Beach T R Kohler R EZierler and D E Strandness Jr ldquoMeasurement of abdominalaortic aneurysms with three-dimensional ultrasound imagingpreliminary reportrdquo Journal of Vascular Surgery vol 33 no 4pp 700ndash707 2001

[53] A Goldberg P Pakkiri E Dai A Lucas and A FensterldquoMeasurements of aneurysm morphology determined by 3-Dmicro-ultrasound imaging as potential quantitative biomarkersin a mouse aneurysm modelrdquo Ultrasound in Medicine andBiology vol 33 no 10 pp 1552ndash1560 2007

[54] C J Goergen B L Johnson J M Greve C A Taylorand C K Zarins ldquoIncreased anterior abdominal aortic wallmotion possible role in aneurysm pathogenesis and design ofendovascular devicesrdquo Journal of Endovascular Therapy vol 14no 4 pp 574ndash584 2007

[55] R Brekken S Muller S U Gjerald and T A Hernes ldquoSimula-tion model for assessing quality of ultrasound strain estimationin abdominal aortic aneurysmrdquo Ultrasound in Medicine ampBiology vol 38 no 5 pp 889ndash896 2012

[56] A L Goertzen A K Meadors R W Silverman and S RCherry ldquoSimultaneous molecular and anatomical imaging of


the mouse in vivordquo Physics in Medicine and Biology vol 47 no24 pp 4315ndash4328 2002

[57] A Long L Rouet A Bissery P Rossignol D Mouradianand M Sapoval ldquoCompliance of abdominal aortic aneurysmsevaluation of tissue doppler imagingrdquo Ultrasound in Medicineand Biology vol 30 no 9 pp 1099ndash1108 2004

[58] A Long L Rouet A Bissery P Rossignol D Mouradianand M Sapoval ldquoCompliance of abdominal aortic aneurysmsevaluated by tissue doppler imaging correlation with aneurysmsizerdquo Journal of Vascular Surgery vol 42 no 1 pp 18ndash26 2005

[59] J Fromageau S Lerouge R L Maurice G Soulez andG Cloutier ldquoNoninvasive vascular ultrasound elastographyapplied to the characterization of experimental aneurysms andfollow-up after endovascular repairrdquo Physics in Medicine andBiology vol 53 no 22 pp 6475ndash6490 2008

[60] R Iezzi R Basilico D Giancristofaro D Pascali A R Cotro-neo and M L Storto ldquoContrast-enhanced ultrasound versuscolor duplex ultrasound imaging in the follow-up of patientsafter endovascular abdominal aortic aneurysm repairrdquo Journalof Vascular Surgery vol 49 no 3 pp 552ndash560 2009

[61] V Napoli I Bargellini S G Sardella et al ldquoAbdominal aorticaneurysm contrast-enhanced US for missed endoleaks afterendoluminal repairrdquo Radiology vol 233 no 1 pp 217ndash2252004

[62] K Fujikura J Luo V Gamarnik et al ldquoA novel noninvasivetechnique for pulse-wave imaging and characterization ofclinically-significant vascular mechanical properties in vivordquoUltrasonic Imaging vol 29 no 3 pp 137ndash154 2007

[63] J Luo K Fujikura L S Tyrie M D Tilson and E EKonofagou ldquoPulse wave imaging of normal and aneurysmalabdominal aortas in vivordquo IEEE Transactions on Medical Imag-ing vol 28 no 4 pp 477ndash486 2009

[64] C J Goergen K N Barr D T Huynh et al ldquoIn vivo quan-tification of murine aortic cyclic strain motion and curvatureimplications for abdominal aortic aneurysm growthrdquo Journal ofMagnetic Resonance Imaging vol 32 no 4 pp 847ndash858 2010

[65] R Nyman and M O Eriksson ldquoThe future of imaging inthe management of abdominal aortic aneurysmrdquo ScandinavianJournal of Surgery vol 97 no 2 pp 110ndash115 2008

[66] A drsquoAudiffret P Desgranges D H Kobeiter and J PBecquemin ldquoFollow-up evaluation of endoluminally treatedabdominal aortic aneurysms with duplex ultrasonographyvalidation with computed tomographyrdquo Journal of VascularSurgery vol 33 no 1 pp 42ndash50 2001

[67] K J Mortele J McTavish and P R Ros ldquoCurrent techniquesof computed tomography helical CT multidetector CT and 3Dreconstructionrdquo Clinics in Liver Disease vol 6 no 1 pp 29ndash522002

[68] L R Sprouse G H Meier F N Parent et al ldquoIs three-dimensional computed tomography reconstruction justifiedbefore endovascular aortic aneurysm repairrdquo Journal of Vas-cular Surgery vol 40 no 3 pp 443ndash447 2004

[69] M M Lawrence-Brown Z Sun J B Semmens K LiffmanI D Sutalo and D B Hartley ldquoType II endoleaks whenis intervention indicated and what is the index of suspicionfor types I or IIIrdquo Journal of Endovascular Therapy vol 16supplement 1 pp I106ndashI118 2009

[70] B Vandeghinste B Trachet M Renard et al ldquoReplacingvascular corrosion casting by in vivo micro-ct imaging forbuilding 3D cardiovascular models in micerdquoMolecular Imagingand Biology vol 13 no 1 pp 78ndash86 2011

[71] B Trachet M Renard G de Santis et al ldquoAn integrated frame-work to quantitatively link mouse-specific hemodynamics toaneurysm formation in angiotensin II-infused ApoE -- micerdquoAnnals of Biomedical Engineering vol 39 no 9 pp 2430ndash24442011

[72] B Trachet J Bols G de Santis S Vandenberghe B Loeys andP Segers ldquoThe impact of simplified boundary conditions andaortic arch inclusion on CFD simulations in the mouse aortaa comparison with mouse-specific reference datardquo Journal ofBiomechanical Engineering vol 133 no 12 Article ID 1210062011

[73] M A Bartoli F Kober R Cozzone R W Thompson M CAlessi andM Bernard ldquoIn vivo assessment of murine elastase-induced abdominal aortic aneurysm with high resolution mag-netic resonance imagingrdquo European Journal of Vascular andEndovascular Surgery vol 44 no 5 pp 475ndash481 2012

[74] Z Li andC Kleinstreuer ldquoBlood flow and structure interactionsin a stented abdominal aortic aneurysm modelrdquo Medical Engi-neering and Physics vol 27 no 5 pp 369ndash382 2005

[75] G H Turner A R Olzinski R E Bernard et al ldquoIn vivo serialassessment of aortic aneurysm formation in apolipoprotein E-deficient mice via MRIrdquo Circulation Cardiovascular Imagingvol 1 no 3 pp 220ndash226 2008

[76] Y Yao Y Wang Y Zhang et al ldquoIn vivo imaging of macro-phages during the early-stages of abdominal aortic aneurysmusing high resolution MRI in ApoE micerdquo PloS One vol 7 no3 Article ID e33523 2012

[77] C J Goergen J Azuma K N Barr et al ldquoInfluences of aorticmotion and curvature on vessel expansion in murine experi-mental aneurysmsrdquo Arteriosclerosis Thrombosis and VascularBiology vol 31 no 2 pp 270ndash279 2011

[78] E Choke G W Cockerill J Dawson et al ldquoVascular endothe-lial growth factor enhances angiotensin II-induced aneurysmformation in apolipoprotein E-deficient micerdquo Journal of Vas-cular Surgery vol 52 no 1 pp 159ndash166 2010

[79] A Klink J Heynens B Herranz et al ldquoIn vivo characterizationof a new abdominal aortic aneurysm mouse model with con-ventional and molecular magnetic resonance imagingrdquo Journalof the American College of Cardiology vol 58 no 24 pp 2522ndash2530 2011

[80] S Amirbekian R C Long M A Consolini et al ldquoIn vivoassessment of blood flow patterns in abdominal aorta of micewithMRI implications forAAA localizationrdquoAmerican Journalof Physiology vol 297 no 4 pp H1290ndashH1295 2009

[81] C N Ludman S W Yusuf S C Whitaker R H GregsonS Walker and B R Hopkinson ldquoFeasibility of using dynamiccontrast-enhanced magnetic resonance angiography as the soleimaging modality prior to endovascular repair of abdominalaortic aneurysmsrdquo European Journal of Vascular and Endovas-cular Surgery vol 19 no 5 pp 524ndash530 2000

[82] J A van Herwaarden B E Muhs K L Vincken et al ldquoAorticcompliance following EVAR and the influence of differentendografts determination using dynamic MRArdquo Journal ofEndovascular Therapy vol 13 no 3 pp 406ndash414 2006

[83] A Frydrychowicz R Arnold D Hirtler et al ldquoMultidirec-tional flow analysis by cardiovascular magnetic resonance inaneurysm development following repair of aortic coarctationrdquoJournal of Cardiovascular Magnetic Resonance vol 10 no 1article 30 2008

[84] R Weissleder ldquoMolecular imaging in cancerrdquo Science vol 312no 5777 pp 1168ndash1171 2006


[85] C M Kramer L A Cerilli K Hagspiel J M DiMaria F HEpstein and J A Kern ldquoMagnetic resonance imaging identifiesthe fibrous cap in atherosclerotic abdominal aortic aneurysmrdquoCirculation vol 109 no 8 pp 1016ndash1021 2004

[86] D E Sosnovik and R Weissleder ldquoEmerging concepts inmolecular MRIrdquo Current Opinion in Biotechnology vol 18 no1 pp 4ndash10 2007

[87] G H Turner A R Olzinski R E Bernard et al ldquoAssessment ofmacrophage infiltration in a murine model of abdominal aorticaneurysmrdquo Journal of Magnetic Resonance Imaging vol 30 no2 pp 455ndash460 2009

[88] RWeissleder K Kelly E Y Sun T Shtatland and L JosephsonldquoCell-specific targeting of nanoparticles by multivalent attach-ment of small moleculesrdquo Nature Biotechnology vol 23 no 11pp 1418ndash1423 2005

[89] L Josephson J Lewis P Jacobs P FHahn andDD Stark ldquoTheeffects of iron oxides on proton relaxivityrdquoMagnetic ResonanceImaging vol 6 no 6 pp 647ndash653 1988

[90] T Kitagawa H Kosuge M Uchida et al ldquoRGD-conjugatedhuman ferritin nanoparticles for imaging vascular inflam-mation and angiogenesis in experimental carotid and aorticdiseaserdquo Molecular Imaging and Biology vol 14 no 3 pp 315ndash324 2012

[91] J M J Richards S I Semple T J MacGillivray et alldquoAbdominal aortic aneurysm growth predicted by uptake ofultrasmall superparamagnetic particles of iron oxide a pilotstudyrdquo Circulation Cardiovascular Imaging vol 4 no 3 pp274ndash281 2011

[92] E Lancelot V Amirbekian I Brigger et al ldquoEvaluation ofmatrix metalloproteinases in atherosclerosis using a novelnoninvasive imaging approachrdquo Arteriosclerosis Thrombosisand Vascular Biology vol 28 no 3 pp 425ndash432 2008

[93] H J Weinmann R C Brasch W R Press and G E WesbeyldquoCharacteristics of gadolinium-DTPA complex a potentialNMR contrast agentrdquo American Journal of Roentgenology vol142 no 3 pp 619ndash624 1984

[94] V Amirbekian J G S Aguinaldo S Amirbekian et alldquoAtherosclerosis and matrix metalloproteinases experimentalmolecular MR imaging in vivordquo Radiology vol 251 no 2 pp429ndash438 2009

[95] R Bazeli M Coutard B D Duport et al ldquoIn vivo evaluationof a new magnetic resonance imaging contrast agent (P947)to target matrix metalloproteinases in expanding experimentalabdominal aortic aneurysmsrdquo Investigative Radiology vol 45no 10 pp 662ndash668 2010

[96] J F Deux J Dai C Riviere et al ldquoAortic aneurysms in arat model in vivo MR imaging of endovascular cell therapyrdquoRadiology vol 246 no 1 pp 185ndash192 2008

[97] N Miyama M M Dua G M Schultz et al ldquoBioluminescenceand magnetic resonance imaging of macrophage homing toexperimental abdominal aortic aneurysmsrdquoMolecular Imagingvol 11 no 2 pp 126ndash134 2012

[98] K Licha B Riefke B Ebert and C Grotzinger ldquoCyanine dyesas contrast agents in biomedical optical imagingrdquo AcademicRadiology vol 9 supplement 2 pp S320ndashS322 2002

[99] B J Tromberg N Shah R Lanning et al ldquoNon-invasive invivo characterization of breast tumors using photon migrationspectroscopyrdquo Neoplasia vol 2 no 1-2 pp 26ndash40 2000

[100] D J Hawrysz and EM Sevick-Muraca ldquoDevelopments towarddiagnostic breast cancer imaging using neer-infrared opticalmeasurements and fluorescent contrast agentsrdquo Neoplasia vol2 no 5 pp 388ndash417 2000

[101] J V Frangioni ldquoIn vivo near-infrared fluorescence imagingrdquoCurrent Opinion in Chemical Biology vol 7 no 5 pp 626ndash6342003

[102] J CWu I Y Chen G Sundaresan et al ldquoMolecular imaging ofcardiac cell transplantation in living animals using optical bio-luminescence and positron emission tomographyrdquo Circulationvol 108 no 11 pp 1302ndash1305 2003

[103] C H Contag and M H Bachmann ldquoAdvances in in vivobioluminescence imaging of gene expressionrdquo Annual Reviewof Biomedical Engineering vol 4 no 1 pp 235ndash260 2002

[104] L Uhrbom E Nerio and E C Holland ldquoDissecting tumormaintenance requirements using bioluminescence imaging ofcell proliferation in a mouse glioma modelrdquo Nature Medicinevol 10 no 11 pp 1257ndash1260 2004

[105] R Weissleder ldquoScaling down imaging molecular mapping ofcancer in micerdquo Nature Reviews Cancer vol 2 no 1 pp 11ndash182002

[106] A Sato B Klaunberg andR Tolwani ldquoIn vivo bioluminescenceimagingrdquo Comparative Medicine vol 54 no 6 pp 631ndash6342004

[107] A J Mueller D U Bartsch R Folberg et al ldquoImagingthe microvasculature of choroidal melanomas with confocalindocyanine green scanning laser ophthalmoscopyrdquo Archives ofOphthalmology vol 116 no 1 pp 31ndash39 1998

[108] A Poellinger S Burock D Grosenick et al ldquoBreast cancerearly- and late-fluorescence near-infrared imaging with indo-cyanine greenmdasha preliminary studyrdquo Radiology vol 258 no 2pp 409ndash416 2011

[109] Y Tajima K Yamazaki Y Masuda et al ldquoSentinel nodemapping guided by indocyanine green fluorescence imaging ingastric cancerrdquoAnnals of Surgery vol 249 no 1 pp 58ndash62 2009

[110] T Kitai T InomotoMMiwa and T Shikayama ldquoFluorescencenavigation with indocyanine green for detecting sentinel lymphnodes in breast cancerrdquo Breast Cancer vol 12 no 3 pp 211ndash2152005

[111] C Vinegoni I Botnaru E Aikawa et al ldquoIndocyaninegreen enables near-infrared fluorescence imaging of lipid-rich inflamed atherosclerotic plaquesrdquo Science TranslationalMedicine vol 3 no 84 Article ID 84ra45 2011

[112] J Oda Y Kato S F Chen et al ldquoIntraoperative near-infraredindocyanine green-videoangiography (ICG-VA) and graphicanalysis of fluorescence intensity in cerebral aneurysm surgeryrdquoJournal of Clinical Neuroscience vol 18 no 8 pp 1097ndash11002011

[113] G Esposito A Durand T van Doormaal and L ReglildquoSelective-targeted extra-intracranial bypass surgery in com-plexmiddle cerebral artery aneurysms correctly identifying therecipient artery using indocyanine green videoangiographyrdquoNeurosurgery vol 71 no 2 supplement pp 274ndash284 2012

[114] R A Sheth M Maricevich and U Mahmood ldquoIn vivo opticalmolecular imaging of matrix metalloproteinase activity inabdominal aortic aneurysms correlates with treatment effectson growth raterdquo Atherosclerosis vol 212 no 1 pp 181ndash187 2010

[115] E L Kaijzel P M van Heijningen P A Wielopolski et alldquoMultimodality imaging reveals a gradual increase in matrixmetalloproteinase activity at aneurysmal lesions in live fibulin-4 micerdquo Circulation Cardiovascular Imaging vol 3 no 5 pp567ndash577 2010

[116] B W Rice M D Cable and M B Nelson ldquoIn vivo imaging oflight-emitting probesrdquo Journal of Biomedical Optics vol 6 no4 pp 432ndash440 2001


[117] M T Madsen ldquoRecent advances in SPECT imagingrdquo Journal ofNuclear Medicine vol 48 no 4 pp 661ndash673 2007

[118] A Rahmim and H Zaidi ldquoPET versus SPECT strengthslimitations and challengesrdquo Nuclear Medicine Communicationsvol 29 no 3 pp 193ndash207 2008

[119] S B Cherry ldquoFundamentals of positron emission tomographyand applications in preclinical drug developmentrdquo Journal ofClinical Pharmacology vol 41 no 5 pp 482ndash491 2001

[120] U Y Ryo and S M Pinsky ldquoRadionuclide angiography with99m technetium-RBCsrdquo CRC Critical Reviews in Clinical Radi-ology and Nuclear Medicine vol 8 no 1 pp 107ndash128 1976

[121] F Rouzet L Bachelet-Violette J M Alsac et al ldquoRadiolabeledfucoidan as a P-selectin targeting agent for in vivo imaging ofplatelet-rich thrombus and endothelial activationrdquo Journal ofNuclear Medicine vol 52 no 9 pp 1433ndash1440 2011

[122] L Sarda-Mantel M Coutard F Rouzet et al ldquo99mTc-annexin-V functional imaging of luminal thrombus activity in abdomi-nal aortic aneurysmsrdquo Arteriosclerosis Thrombosis and Vascu-lar Biology vol 26 no 9 pp 2153ndash2159 2006

[123] T Iwasaki T Iwasaki Y Aihara et al ldquoImmunoscintigraphyof aortic dissection with 99mTc-labeled murine anti-smoothmuscle myosin monoclonal antiboby in ratsrdquo Journal of NuclearMedicine vol 42 no 1 pp 130ndash137 2001

[124] S Vemulapalli S D Metzler G Akabani et al ldquoCell therapyin murine atherosclerosis in vivo imaging with high-resolutionhelical SPECTrdquo Radiology vol 242 no 1 pp 198ndash207 2007

[125] A D Heyns M G Lotter P N Badenhorst O van Reenen HPieters and P C Minnaar ldquoKinetics and fate of (111)Indium-oxine labelled blood platelets in asplenic subjectsrdquo Thrombosisand Haemostasis vol 44 no 2 pp 100ndash104 1980

[126] Y Murata I Yamada I Umehara and H Shibuya ldquoTl-201myocardial SPECT in patients with systemic arterial diseasesrdquoClinical Nuclear Medicine vol 23 no 12 pp 832ndash835 1998

[127] D S Berman H Kiat K van Train J D Friedman F P Wangand G Germano ldquoDual-isotope myocardial perfusion spectwith rest thallium-201 and stress Tc-99m sestamibirdquo CardiologyClinics vol 12 no 2 pp 261ndash270 1994

[128] A K Buck S Nekolla S Ziegler et al ldquoSPECTCTrdquo Journal ofNuclear Medicine vol 49 no 8 pp 1305ndash1319 2008

[129] H Iida and S Eberl ldquoQuantitative assessment of regionalmyocardial blood flow with thallium-201 and SPECTrdquo Journalof Nuclear Cardiology vol 5 no 3 pp 313ndash331 1998

[130] M Kobayashi T Mogami M Uchiyama et al ldquoUsefulness of99mTc-MIBI SPECT in themetastatic lesions of thyroid cancerrdquoNihon Igaku Hoshasen Gakkai Zasshi vol 57 no 3 pp 127ndash1321997

[131] I Shibata ldquoDevelopment of three-dimensional brain SPECTimaging the future of functional imagingrdquo Journal of theMedical Society of Toho University vol 50 no 2 pp 124ndash1272003

[132] L E Holder J L Machin P L Asdourian J M Links and CC Sexton ldquoPlanar and high-resolution SPECT bone imaging inthe diagnosis of facet syndromerdquo Journal of Nuclear Medicinevol 36 no 1 pp 37ndash44 1995

[133] I A Illan J M Gorriz J Ramırez et al ldquoProjecting inde-pendent components of SPECT images for computer aideddiagnosis of Alzheimerrsquos diseaserdquo Pattern Recognition Lettersvol 31 no 11 pp 1342ndash1347 2010

[134] L Sarda-Mantel J M Alsac R Boisgard et al ldquoComparison of18F-fluoro-deoxy-glucose 18F-fluoro-methyl-choline and 18F-DPA714 for positron-emission tomography imaging of leuko-cyte accumulation in the aortic wall of experimental abdominal

aneurysmsrdquo Journal of Vascular Surgery vol 56 no 3 pp 765ndash773 2012

[135] B L Franc P D Acton C Mari and B H Hasegaway ldquoSmall-animal SPECT and SPECTCT important tools for preclinicalinvestigationrdquo Journal of Nuclear Medicine vol 49 no 10 pp1651ndash1663 2008

[136] T C Kwee S Basu and A Alavi ldquoPET and PETCT forunknown primary tumorsrdquo in Positron Emission TomographyM E Juweid and O S Hoekstra Eds pp 317ndash333 HumanaPress Inc Totowa NJ USA 2011

[137] M Nahrendorf E Keliher B Marinelli et al ldquoDetection ofmacrophages in aortic aneurysms by nanoparticle positronemission tomography-computed tomographyrdquo ArteriosclerosisThrombosis and Vascular Biology vol 31 no 4 pp 750ndash7572011

[138] D Palombo S Morbelli G Spinella et al ldquoA positron emissiontomographycomputed tomography (PETCT) evaluation ofasymptomatic abdominal aortic aneurysms another point ofviewrdquo Annals of Vascular Surgery vol 26 no 4 pp 491ndash4992012

[139] M D Wilkinson E Szeto M J Fulham C J Constableand B C McCaughan ldquoFDG positron emission tomographicimaging of a large abdominal aortic aneurysmrdquoClinical NuclearMedicine vol 28 no 2 pp 130ndash131 2003

[140] N Sakalihasan H van Damme P Gomez et al ldquoPositronemission tomography (PET) evaluation of abdominal aorticaneurysm (AAA)rdquo European Journal of Vascular and Endovas-cular Surgery vol 23 no 5 pp 431ndash436 2002

[141] M Truijers J A Pol H Kurvers S Bredie W J Oyen and JD Blankensteijn ldquoIncidental finding of malignancy in patientspreoperatively evaluated for aneurysm wall pathology usingPETCTrdquo Journal of Vascular Surgery vol 49 no 5 pp 1313ndash1315 2009

[142] K Serdons A Verbruggen and G M Bormans ldquoDevelopingnewmolecular imaging probes for PETrdquoMethods vol 48 no 2pp 104ndash111 2009

[143] O Mawlawi and D W Townsend ldquoMultimodality imaging anupdate on PETCT technologyrdquo European Journal of NuclearMedicine and Molecular Imaging vol 36 supplement 1 pp 15ndash29 2009

[144] L V Wang and S Hu ldquoPhotoacoustic tomography in vivoimaging from organelles to organsrdquo Science vol 335 no 6075pp 1458ndash1462 2012

[145] L VWang Photoacoustic Imaging and Spectroscopy CRC PressNew York NY USA 2009

[146] H W Wang N Chai P Wang et al ldquoLabel-free bond-selectiveimaging by listening to vibrationally excited moleculesrdquo Physi-cal Review Letters vol 106 no 23 Article ID 238106 2011

[147] P Wang H W Wang M Sturek and J X Cheng ldquoBond-selective imaging of deep tissue through the optical windowbetween 1600 and 1850 nmrdquo Journal of Biophotonics vol 5 no1 pp 25ndash32 2012

[148] K Jansen A F W van der Steen H M M van Beusekom JW Oosterhuis and G van Soest ldquoIntravascular photoacousticimaging of human coronary atherosclerosisrdquoOptics Letters vol36 no 5 pp 597ndash599 2011

[149] B Wang A Karpiouk D Yeager et al ldquoIntravascular pho-toacoustic imaging of lipid in atherosclerotic plaques in thepresence of luminal bloodrdquo Optics Letters vol 37 no 7 pp1244ndash1246 2012


[150] Y Komachi H Sato and H Tashiro ldquoIntravascular Ramanspectroscopic catheter for molecular diagnosis of atheroscle-rotic coronary diseaserdquoApplied Optics vol 45 no 30 pp 7938ndash7943 2006

[151] X Gao Y Cui R M Levenson L W K Chung and S NieldquoIn vivo cancer targeting and imaging with semiconductorquantum dotsrdquo Nature Biotechnology vol 22 no 8 pp 969ndash976 2004

[152] A M Smith S Dave S Nie L True and X Gao ldquoMulticolorquantum dots for molecular diagnostics of cancerrdquo ExpertReview ofMolecular Diagnostics vol 6 no 2 pp 231ndash244 2006

[153] K Welsher S P Sherlock and H Dai ldquoDeep-tissue anatomicalimaging of mice using carbon nanotube fluorophores in thesecond near-infrared windowrdquo Proceedings of the NationalAcademy of Sciences of the United States of America vol 108 no22 pp 8943ndash8948 2011

[154] G Hong J C Lee J T Robinson et al ldquoMultifunctional in vivovascular imaging using near-infrared II fluorescencerdquo NatureMedicine vol 18 no 12 pp 1841ndash1846 2012

[155] M A Calfon C Vinegoni V Ntziachristos and F A JafferldquoIntravascular near-infrared fluorescence molecular imagingof atherosclerosis toward coronary arterial visualization ofbiologically high-risk plaquesrdquo Journal of Biomedical Optics vol15 no 1 Article ID 011107 2010

[156] F A Jaffer M A Calfon A Rosenthal et al ldquoTwo-dimensionalintravascular near-infrared fluorescence molecular imaging ofinflammation in atherosclerosis and stent-induced vascularinjuryrdquo Journal of the American College of Cardiology vol 57no 25 pp 2516ndash2526 2011

[157] H Yoo J W KimM Shishkov et al ldquoIntra-arterial catheter forsimultaneous microstructural and molecular imaging in vivordquoNature Medicine vol 17 no 12 pp 1680ndash1684 2011

[158] F A Jaffer C Vinegoni M C John et al ldquoReal-time cathetermolecular sensing of inflammation in proteolytically activeatherosclerosisrdquoCirculation vol 118 no 18 pp 1802ndash1809 2008

[159] C M Gardner H Tan E L Hull et al ldquoDetection of lipid corecoronary plaques in autopsy specimens with a novel catheter-based near-infrared spectroscopy systemrdquo JACC Cardiovascu-lar Imaging vol 1 no 5 pp 638ndash648 2008

[160] S Brugaletta H M Garcia-Garcia P W Serruys et alldquoNIRS and IVUS for characterization of atherosclerosis inpatients undergoing coronary angiographyrdquo JACC Cardiovas-cular Imaging vol 4 no 6 pp 647ndash655 2011

[161] G J Tearney M E Brezinski B E Bouma et al ldquoIn vivoendoscopic optical biopsy with optical coherence tomographyrdquoScience vol 276 no 5321 pp 2037ndash2039 1997

Submit your manuscripts athttpwwwhindawicom

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


MEDIATORSINFLAMMATION

of


Behavioural Neurology

EndocrinologyInternational Journal of



Disease Markers


BioMed Research International

OncologyJournal of



Oxidative Medicine and Cellular Longevity


PPAR Research

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Immunology ResearchHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

ObesityJournal of



Computational and Mathematical Methods in Medicine

OphthalmologyJournal of


Diabetes ResearchJournal of



Research and TreatmentAIDS


Gastroenterology Research and Practice


Parkinsonrsquos Disease

Evidence-Based Complementary and Alternative Medicine

Volume 2014Hindawi Publishing Corporationhttpwwwhindawicom


tomography (PET) Each modality has strengths and weak-nesses making recently developed combined imaging sys-tems (such as SPECTCT PETCT and PETMR) attractivealternatives as they become readily available

Significant challenges exist in adapting clinical imagingsystems for small animal use Considerations can includeradioactive dose requirements body mass anesthesia pro-cedures and contrast infusion techniques all of which candiffer greatly from a clinical setting [13] New challengesarise while engineering dedicated small animal systems Forexample PET image resolution must be significantly higherwith a small animal scanner than with a clinical system[14] With small animal ultrasound the signal-to-noise ratioand tissue contrast are often insufficient when imaging miceand rats [13] In spite of these challenges some imagingsystems scale favorably for small animals For example thestatic MR field strength can be higher and the receivingcoil can be closer with small bore scanners both of whichlead to an increased signal-to-noise ratio In addition invivo optical imaging is easier in small animals due to thedecreased path-length photons are required to travel Smallanimal imaging has become an important tool in preclinicalaneurysm research

In this review we highlight the recent evolutions in smallanimal AAA models induced via exogenous chemicals andgenetic disruptions We also describe established anatomicalandmolecular imaging methods address clinical translationand identify possible future approaches to small animalAAA imaging The work highlighted in this review is mostlyintended to characterize aneurysm progression through theuse of small animal imaging with the hope of one day leadingto improved clinical AAA treatment

2 Small Animal Models

Exogenous Chemical Induction The three most commonmouse models for exogenous chemical induction of AAAuse pancreatic porcine elastase calcium chloride (CaCl

2) or

angiotensin II (AngII)

21 Elastase Elastase-induced AAA in animal models wasdeveloped from early clinical data suggesting that elastindegradation played a significant role in AAA formation [1516] Clinical pathology showed elastin structure deficienciesand high elastase activity in aneurysmal tissue This ledto early use of luminal perfusion with porcine pancreaticelastase within rats to induce aneurysms [17] Higher concen-trations of elastase led to more severe elastic tissue damageand arterial dilation AAAs have been produced within themurine infrarenal aorta by utilizing porcine pancreatic elas-tase administered via an inserted catheter at the iliac bifurca-tion [18] Elastase leads to elastin fiber degradation andhigherlevels of MMP-2 and MMP-9 expression Though this is atransluminal perfusion the outer adventitia is thought to playa role in the inflammatory signalingmacrophage cascade thatfollows [9] Other work with mice deficient for MMP-12 [18]or IL-17 [19] showed reduced aortic dilation Interestinglygender research revealed that male rats formed larger AAAs

at a higher rate of incidence while females were partiallyprotected through estrogen-mediated reductions of MMP-9production [20] Successful elastase variations have led tofurther characterization of this murine AAA model Forexample porcine pancreatic elastase applied periadventitiallyalso produces an AAA and is an easier surgical procedure[21]

22 Calcium Chloride To induce a murine CaCl2aneurysm

a small gauze saturated in a CaCl2solution is placed centrally

onto the exposed abdominal aorta resulting in intimaland medial macrophage infiltration and significant diameterincrease 14 days after surgery [22] Researchers hypothesizedthat calcium chloride treatments disrupted the targeted elast-in network from calcium precipitates thus activating inflam-matory pathways also observed in the human AAAs

Further genetic characterization focused on the effectsof MMP activity within transgenically modified mice Micedeficient in MMP-9 (macrophage cell derived) or MMP-2(mesenchymal cell derived) were treated with CaCl

2in order

to induce AAAs [23] After 10 weeks no aneurysm forma-tion was seen in either knockout model Interestingly thecompetent macrophages from wild-type controls were theninfused into the corresponding knockout resulting in AAAreconstitution in MMP-9minusminus animals but not MMP-2minusminusmice [23]

23 Angiotensin II The AngII model creates suprarenalAAAs by continuously infusing AngII subcutaneously in lowdensity lipoprotein receptor (ldlrminusminus) or apolipoprotein E(apoEminusminus) knockout mice [24] This vessel expansion wasunexpected and the mechanisms that lead to the dilationare still not fully understood AngII doses did not alterarterial blood pressure murine body weight serum choles-terol concentrations or lipoprotein-cholesterol distribution[25] The addition of doxycycline a broad-system MMPinhibitor reduced AAA incidence by 51 within AngII-induced murine aneurysms [26 27] even though no effectswere observed on blood pressure or serum cholesterolconcentrations Other studies have tried to define the rolethat AngII-induced hypertension plays within this AAAmodel For example ldlrminusminus and apoEminusminus mice were infusedwith AngII or norepinephrine producing similarly increasedblood pressures for both groups Aneurysm formationand atherosclerotic lesion incidence in AngII-infused miceincreased while norepinephrine-infused mice did not showan increase in vessel diameter or atherosclerotic lesions[28] Administration of hydralazine (a vasodialator) reducedsystolic blood pressure without slowing AAA formation orreducing atherosclerotic lesion incidence

Much is already known about the pathophysiology un-derlying the AngIIapoEminusminus AAA model Infrarenal medialmacrophage accumulation and medial dissection are the firststage of AngII-induced murine AAA progression acting asa stimulus for elastin degradation [29] Vascular hematomamacrophage infiltration [25] and thrombus formation all ofwhich are common in human AAAs typically occur after 3ndash10 days in the murine model Remodeling and aneurysmal















Suprarenal aorta

Infrarenal aorta

(a) (b) (c) (d)

Before surgery

Sham

Elastase

(e) (f) (g)
















Days 0 3 7 14 21 28

AngII

Day 28119899 = 10

(a)

0 3 7 14 21 28Days

Elastase

Day 28119899 = 12

(b)






(a) (b) (c)

(d)










L R

I

S

(a) (b) (c) (e)

(d)

Ventral

Dorsal







2model [114]




(a)

4000

8000

(b)

(c)

400

800

(d)





























Microbubbles













SPECT X



99TC 111In 201Tl 123I 131I

PET X



18F 11C 13N 15O 82RB








Acknowledgment


References
















































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of






























Suprarenal aorta

Infrarenal aorta

(a) (b) (c) (d)

Before surgery

Sham

Elastase

(e) (f) (g)
















Days 0 3 7 14 21 28

AngII

Day 28119899 = 10

(a)

0 3 7 14 21 28Days

Elastase

Day 28119899 = 12

(b)






(a) (b) (c)

(d)










L R

I

S

(a) (b) (c) (e)

(d)

Ventral

Dorsal







2model [114]




(a)

4000

8000

(b)

(c)

400

800

(d)





























Microbubbles













SPECT X



99TC 111In 201Tl 123I 131I

PET X



18F 11C 13N 15O 82RB








Acknowledgment


References
















































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

















Suprarenal aorta

Infrarenal aorta

(a) (b) (c) (d)

Before surgery

Sham

Elastase

(e) (f) (g)
















Days 0 3 7 14 21 28

AngII

Day 28119899 = 10

(a)

0 3 7 14 21 28Days

Elastase

Day 28119899 = 12

(b)






(a) (b) (c)

(d)










L R

I

S

(a) (b) (c) (e)

(d)

Ventral

Dorsal







2model [114]




(a)

4000

8000

(b)

(c)

400

800

(d)





























Microbubbles













SPECT X



99TC 111In 201Tl 123I 131I

PET X



18F 11C 13N 15O 82RB








Acknowledgment


References
















































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of




























Days 0 3 7 14 21 28

AngII

Day 28119899 = 10

(a)

0 3 7 14 21 28Days

Elastase

Day 28119899 = 12

(b)






(a) (b) (c)

(d)










L R

I

S

(a) (b) (c) (e)

(d)

Ventral

Dorsal







2model [114]




(a)

4000

8000

(b)

(c)

400

800

(d)





























Microbubbles













SPECT X



99TC 111In 201Tl 123I 131I

PET X



18F 11C 13N 15O 82RB








Acknowledgment


References
















































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

















Days 0 3 7 14 21 28

AngII

Day 28119899 = 10

(a)

0 3 7 14 21 28Days

Elastase

Day 28119899 = 12

(b)






(a) (b) (c)

(d)










L R

I

S

(a) (b) (c) (e)

(d)

Ventral

Dorsal







2model [114]




(a)

4000

8000

(b)

(c)

400

800

(d)





























Microbubbles













SPECT X



99TC 111In 201Tl 123I 131I

PET X



18F 11C 13N 15O 82RB








Acknowledgment


References
















































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

















(a) (b) (c)

(d)










L R

I

S

(a) (b) (c) (e)

(d)

Ventral

Dorsal







2model [114]




(a)

4000

8000

(b)

(c)

400

800

(d)





























Microbubbles













SPECT X



99TC 111In 201Tl 123I 131I

PET X



18F 11C 13N 15O 82RB








Acknowledgment


References
















































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of


















L R

I

S

(a) (b) (c) (e)

(d)

Ventral

Dorsal







2model [114]




(a)

4000

8000

(b)

(c)

400

800

(d)





























Microbubbles













SPECT X



99TC 111In 201Tl 123I 131I

PET X



18F 11C 13N 15O 82RB








Acknowledgment


References
















































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

















(a)

4000

8000

(b)

(c)

400

800

(d)





























Microbubbles













SPECT X



99TC 111In 201Tl 123I 131I

PET X



18F 11C 13N 15O 82RB








Acknowledgment


References
















































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of







































Microbubbles













SPECT X



99TC 111In 201Tl 123I 131I

PET X



18F 11C 13N 15O 82RB








Acknowledgment


References
















































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of






























Microbubbles













SPECT X



99TC 111In 201Tl 123I 131I

PET X



18F 11C 13N 15O 82RB








Acknowledgment


References
















































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of






















Microbubbles













SPECT X



99TC 111In 201Tl 123I 131I

PET X



18F 11C 13N 15O 82RB








Acknowledgment


References
















































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of


















Acknowledgment


References
















































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of



































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of




































































































































of






Disease Markers



OncologyJournal of





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Documents

Molecular Imaging of Experimental Abdominal Aortic Aneurysms