Catheter-directed gadolinium-enhanced MR angiography

Catheter-directed gadolinium-enhanced MR angiography

Reed A. Omary, MD, MSa,*, Jordin Green, BSb, J. Paul Finn, MDb,Debiao Li, PhDb

aDepartment of Radiology, Northwestern University Medical School, 676 North Saint Clair, Suite 800, Chicago, IL 60611, USAbDepartment of Radiology, Northwestern University, Suite 700, 448 East Ontario Street, Chicago, IL 60611, USA

Magnetic resonance imaging (MRI) guidance for

endovascular procedures offers several important

advantages over conventional x-ray guidance. These

advantages include (1) lack of ionizing radiation

exposure, which benefits not only the patient, but

the operator and team who perform a lifetime of

procedures; (2) lack of iodinated contrast agents, with

their attendant risks of nephrotoxicity and allergic

reactions; (3) the ability to detect blood vessels and

three-dimensional (3D) anatomy at the same time, an

important feature for performing procedures such as

transjugular intrahepatic portosystemic shunt (TIPS)

placement; and (4) the ability to detect changes in end-

organ (eg, kidney, heart, or brain) function at the time

of an endovascular intervention, a capacity that is not

readily available with x-ray–guided techniques.

MRI-guided procedures are still early in their

development. Most studies have occurred in animals,

with little published about these procedures in humans.

In animal models, published applications of MRI-

guided endovascular interventions include inferior

vena cava filter placement [1,2], percutaneous trans-

luminal angioplasty (PTA) of the aorta [3–5] and renal

artery [6,7], stent placement within the iliac artery

[8,9] and aorta [9,10], coronary angiography [11,12],

TIPS [13], and carotid artery aneurysm embolization

[14]. In humans, MRI-guided hemodialysis, Brescia-

Cimino arteriovenous and loop graft fistulagraphy

[15], and iliac artery stent placement [16] also have

been performed.

Whether performed under x-ray or MRI guidance,

these endovascular procedures require multiple con-

trast-agent injections to define baseline vascular

anatomy, to confirm intraluminal position of endo-

vascular devices, and to document changes in vascular

anatomy following an intervention. Direct catheter-

based injections of gadolinium (Gd) chelates under

MRI guidance can be used in the same manner as

injections of iodinated contrast material under x-ray

guidance. The primary rationale for using catheter-

directed rather than conventional intravenous (IV)

injections under MRI is to conserve contrast agent.

Because multiple injections are required during an

MRI-guided endovascular intervention, the Food and

Drug Administration (FDA)-mandated daily dose

limit of Gd, 0.3 mmol/kg, is easily exceeded using

IV injections. Catheter -directed injections use smaller

volumes of dilute contrast agent. These smaller Gd

doses not only should help the operator remain below

the FDA dose limits, but also should reduce back-

ground tissue enhancement. A secondary benefit of

these catheter-based injections is that only the artery

of interest is enhanced. Other adjacent vascular beds

remain suppressed, which facilitates artery visualiza-

tion and disease detection.

This article reviews catheter-directed Gd-enhanced

MR angiography (MRA), with special focus on intra-

arterial (IA) injections. Catheter-directed IA Gd-

enhanced MRA has been used in animals in the aorta

[12,17–19], carotid arteries [12,14,18,20], renal arter-

ies [6,12,19,21], iliac arteries [18,19,21], and coronary

arteries [12,22]. The authors present background

theory; discuss IA injection protocols, MRA se-

quences, and methods to limit contrast agent dose;

0033-8389/02/$ – see front matter D 2002, Elsevier Science (USA). All rights reserved.

PII: S0033 -8389 (02 )00014 -3

R.A. Omary was supported in part by NIH K08

DK60020.

* Corresponding author.

E-mail address: [email protected]

(R.A. Omary).

Radiol Clin N Am 40 (2002) 953–963

and describe how to perform IA injections. Finally, the

authors discuss the accuracy, advantages, and limita-

tions of IA injections.

Theory of local Gd injections

Gd-enhanced MRA is based on the T1 shortening

effect of Gd in blood. T1 shortening increases MR

signal. Gd, however, also shortens blood T2*, which

results in MR signal loss with a gradient-echo

sequence. Consequently, there is an optimal Gd

concentration ([Gd]), where the T1 shortening signal

gain is balanced with the competing T2 signal loss,

and the blood signal is maximal. Fig. 1 compares T1

and T2* shortening effects during selective renal-

artery injections.

If dilute Gd is required, then what is the optimal

concentration? This question has been addressed

using (1) theoretic expressions [18,19], (2) static

[12,17] and dynamic [21] phantoms, and (3) in vivo

[12,18,19,21] experiments. Using complex theoretic

expressions, Frayne et al [18] derive 2% Gd as the

optimal concentration for MR vascular signal for

typical MRA acquisition parameters. Bos et al [19]

find that 3% to 6% is optimal. In initial static

phantom experiments, Omary et al [17] show that

optimal arterial [Gd] range between 1% and 6%,

depending on the selected imaging parameters. In

subsequent static phantom experiments, Serfaty et al

[12] find 6% [Gd] to be optimal. In vivo optimal

arterial Gd concentrations range from 1% to 5%

[18,21].

This spectrum of optimal values reinforces a key

point: satisfactory vascular depiction occurs over a

relatively broad range of arterial [Gd] [12,18,19].

There is little practical difference in vessel enhance-

ment or signal-to-noise ratio (SNR) between Gd sol-

utions ranging in concentrations between 1% and 6%.

Regarding nomenclature, dilute Gd solutions are

generally presented in one of three ways: (1) dilution

ratios (eg, 1:20, which is equivalent to 1 part Gd and

20 parts saline); (2) millimolar concentration (eg, 50

mM); and (3) percentage concentration (eg, 4% Gd).

While all these methods are equivalent, they have

varying degrees of scientific validity and practicality.

The dilution ratio and percentage concentration meth-

ods are clearly the most intuitive; one need not be

familiar with the standard molar concentration of Gd

(500 mM) to recognize how to produce these dilu-

tions. The mM method is scientifically most correct

because full-strength contrast agent within the dis-

pensing bottle is itself a solution of Gd chelate. The

mM method is limited in practice because it requires

a priori knowledge of this concentration and is not

readily intuitive to most radiologists.

Fig. 1. Coronal 2D MRA using selective Gd injection in swine right renal artery. (A) Injected [Gd] = 1.8%, injection rate = 1 mL/

second, arterial [Gd] = 1%, total injected Gd dose = 0.13 mL. (B) Injected [Gd] = 14%, injection rate = 2 mL/second, arterial

[Gd] = 10%, total injected Gd dose = 2.0 mL. The injection in (A) shows optimal signal-to-noise ratio, with T1 shortening effects

predominating over T2* effects. The injection in (B) shows signal loss due to T2* effects. (From Omary RA, Henseler KP, Unal

O, Smith RJ, Ryu RK, Resnick SA, et al. Validation of injection parameters for catheter-directed intraarterial gadolinium-

enhanced MR angiography. Acad Radiol 2002;9:172–85; with permission.)

R.A. Omary et al / Radiol Clin N Am 40 (2002) 953–963954

Intra-arterial injection protocol

Knowledge of the optimal arterial Gd concentra-

tion is only the first step in performing an IA

injection. It is paramount to recognize that the desired

arterial [Gd] differs in most instances from the

injected [Gd]. The difference between injected and

arterial Gd concentrations results from further dilu-

tion of injected Gd by inflowing blood. Arterial [Gd]

is based on three factors: injected [Gd], injection rate,

and arterial blood flow rate. Frayne et al [18] and Bos

et al [19] postulate relationships between these injec-

tion parameters by assuming that all injected Gd is

diluted by inflowing blood. Their injection relation-

ships are similar, except that Frayne et al [18] account

for the influence of injection rate on overall arterial

blood flow rates.

The IA injection protocol proposed by Frayne et al

[18] is:

½Gd�inj ¼ ð1þ Qartery

Qinj

Þ � ½Gd�artery

where [Gd]inj = injected [Gd] (%), Qartery = blood

flow rate in vessel of interest (mL/s), Qinj = injection

rate of Gd agent (mL/s), and [Gd]artery = desired

arterial concentration of Gd (%). By substituting

injection parameters into Equation 1, interventional

radiologists can devise injection protocols for IA

Gd-enhanced MRA.

This injection protocol has been validated in

dynamic flow phantoms and in swine [21]. Accord-

ing to the injection protocol, there is an inverse

relationship between injected [Gd] and injection rate.

To obtain a desired arterial [Gd], either (1) increase

the injection rate and reduce the injected [Gd] or (2)

increase the injected [Gd] and reduce the injection

rate. This trade-off occurs because both techniques

deliver the same local Gd mass flux [18] to the

blood vessel.

MRA sequences

The selection of MRA sequences should be

based on the intended purpose of an IA injection.

If a rapid vascular roadmap is desired and the blood

vessels are located within a defined thin-imaging slab,

then a standard two-dimensional (2D) time-resolved

sequence should be used. With tortuous vessels, it is

better to use a thicker 2D-imaging slab, arbitrarily

called ‘‘projection MRA.’’ The term ‘‘projection’’

refers to 2D imaging over a thick-imaging slab, gen-

erally 5 to 20 cm, similar to 2D x-ray fluoroscopy.

Projection MRA emphasizes a larger imaging slab at

the expense of vessel signal. If greater accuracy and the

ability to perform multiplanar volumetric reconstruc-

tions are desired, then three-dimensional (3D) se-

quences should be used. Potential problems with 3D

imaging are that the temporal resolution will be com-

promised and more contrast agent will be required. In

general, short repetition time (TR)/short echo time

(TE) T1-weighted sequences, similar to conventional

IV-Gd–enhanced MRA, can be used for 2D and 3D

MRA. Electrocardiographic (ECG) gating may be

used for some vascular distributions, such as the heart

(Fig. 2). Typical imaging parameters for each sequence

are shown in Table 1.

According to Equation 1, knowledge of the local

blood flow rate adjacent to the catheter is necessary to

use the injection protocol relationship. This blood

flow rate is empirically estimated based on experience

or estimates from the literature. To be more accurate,

however, a 2D cine-phase contrast sequence [18,21,

23,24] is used to measure the local blood flow rate.

There are several methods to suppress background

for IA-Gd–enhanced MRA. One involves subtraction

of source-imaging data obtained prior to the admin-

Fig. 2. Coronal 3D coronary MRA in canine using selective

left circumflex artery Gd injection. Electrocardiographic-

triggering was used. Injection parameters included injected

[Gd] = 6%, injection rate = 0.3 mL/second, injection vol-

ume = 10 mL, slice thickness = 16 mm (interpolated to

32 mm), and temporal resolution = 0.5 frames/second.

(Equation 1)

R.A. Omary et al / Radiol Clin N Am 40 (2002) 953–963 955

istration of contrast agent [25]. This method is limited

because it requires additional image processing.

Motion between data acquisitions also causes image

artifacts after subtraction. A gradient dephaser has

been used in the slice direction to suppress signals

from the thick, homogeneous background [26,27].

The effectiveness of this scheme, however, depends

on the anatomical structure of the imaging slice.

Recently, magnetization preparation has been used

to suppress background in contrast-enhanced MRA

[20,22,28,29]. This method may be a useful approach

for 2D projection MRA.

Limiting contrast-agent dose

Because MRI-guided endovascular interventions

require at least as many separate injections as x-ray

guided procedures, it is essential to limit contrast-

agent dose during each injection. Limiting injected-

Gd dose not only reduces the likelihood of exceeding

FDA Gd-dose limitations during an intervention, but

it also has the added imaging advantage of minimiz-

ing background tissue enhancement.

There are several techniques available to limit

contrast-agent dose. These can be categorized as

Table 1

Typical imaging parameters used for Gd-enhanced MRA

Technique Parameters

2D cine-phase contrast TR (repetition time)/TE (echo time)/flip = 10.1 ms/4.7 ms/45�;field of view (FOV) = 24 � 11 cm; acquisition matrix = 256 � 128;

reconstruction matrix = 256 � 256; slice thickness = 5 mm;

velocity-encoding value = 300 cm/s; duration = 18 s

Time-resolved 2D TR/TE/flip = 5.8 ms/1.4 ms/ 30�; FOV = 24 � 18 cm;

acquisition matrix = 256 � 160; reconstruction matrix = 256 � 256;

slice thickness = 20 mm; scan duration = 7 s

Single-phase 3D TR/TE/flip = 8.3 ms/ 1.6 ms/ 45�; FOV = 24 � 18 cm;

acquisition matrix = 512 � 192; reconstruction matrix = 512 � 512;

slice thickness = 2.6 mm with 16 partitions (acquired) and 1.3 mm

with 32 partitions (reconstructed); scan duration = 26 s

Fig. 3. Coronal 2D MRA using selective Gd injection in swine right-iliac artery. (A) Injected [Gd] = 10%, injection rate = 1 mL/

second, arterial [Gd] = 4%. (B) Injected [Gd] = 2.5%, injection rate = 1 mL/second, arterial [Gd] = 1%. There is no significant

difference in arterial depiction between images. The selective injection, however, depicted in (A) required a total of 0.70 mL of

undiluted Gd, while the injection depicted in (B) required only 0.18 mL. (From Omary RA, Henseler KP, Unal O, Smith RJ, Ryu

RK, Resnick SA, et al. Validation of injection parameters for catheter-directed intraarterial gadolinium-enhancedMR angiography.

Acad Radiol 2002;9:172–85; with permission.)


injection parameters, imaging techniques, and cath-

eter location.

Injection parameters

These techniques use arterial [Gd] equal to 1%.

Whereas optimal SNR is obtained with arterial [Gd]

ranging from 1% to 6%, aiming for 1% reduces

contrast agent dose six-fold over 6%. This reduction

is a result of the direct relationship between arterial

[Gd] and injected dose (Equation 1). Fig. 3 depicts

selective iliac artery injections in a pig. Images show

how aiming for arterial [Gd] of 1% rather than 4%

reduces injected-Gd dose without appreciably affect-

ing vascular depiction.

Imaging techniques

1. Tailor injections toward imaging goal. Early

experience with IA injections [17] suggests that

injection duration should cover at least a

substantial portion of the image acquisition

period. Because image acquisition time is much

faster for 2D rather than 3D techniques, 2D IA-

MRA uses considerably less contrast agent than

3D IA-MRA. Roadmaps using 2D projection

methods thus save considerable contrast agent

over 3D IA-MRA. Reserve 3D methods for

occasions when high diagnostic accuracy or

multiplanar volumetric reconstructions are re-

quired. Fig. 4 shows how image quality differs

between 2D projection and 3D techniques for

catheter-directed MR aortography.

2. Reduce imaging times. This can be accom-

plished by: (1) shortening the TR, (2) using

partial Fourier acquisitions, or (3) reducing the

number of phase encoding steps.

3. Reduce injection duration. For 3D IA-MRA,

Hwang et al [30] show that injection duration

can be reduced to 50% of the image acquisition

Fig. 4. Catheter-based Gd injections in aorta of same pig. (A) 2D coronal projection MRA using injected [Gd] = 4%, injection

rate = 5 mL/second, injection duration = 1 second, total undiluted Gd dose = 0.2 mL, slice thickness = 50 mm, and temporal

resolution approximately 2 frames/second. (B) 3D coronal MRA (maximum intensity projection) using injected [Gd] = 4%,

injection rate = 5 mL/second, injection duration = 8 seconds, total undiluted Gd dose = 1.6 mL, slice thickness = 48 mm (after

interpolation), and temporal resolution = one image every 6 second. The 3D acquisition has better image quality than the 2D

projection acquisition but uses more contrast agent and requires a longer acquisition time.


time without significant loss of SNR in the

aorta and iliac arteries. For smaller vessels,

such as the renal arteries, injection duration can

be reduced to 75% of the image acquisition

time without significant loss of SNR. Hwang

et al [30] found no difference in SNR between

elliptical centric and conventional sequential

linear encoding schemes for IA-MRA. Fig. 5

depicts sample 3D IA-Gd–enhanced images

from a dynamic arterial flow phantom using

both encoding schemes at the different in-

jection durations.

Catheter location

Place catheters as selectively as possible. Major

reductions in contrast-agent dose occur when cathe-

ters are positioned within smaller vessels. This effect

on dose reduction can be seen from Equation 1:

smaller vessels have reduced blood flow rates com-

pared to larger vessels. Consequently, performing a

selective renal artery injection uses substantially less

contrast agent than an abdominal aortic injection.

For example, the selective 2D renal MRA shown in

Fig. 1a uses only 0.13 mL of undiluted Gd. In a 25-kg

pig, 115 separate similar injections can be per-

formed without exceeding the FDA Gd-dose limit of

0.3 mmol/kg/day.

How to perform an IA injection

Equation 1 describes the relationship between

three pertinent injection parameters: injection rate,

injected [Gd], and blood flow rate. Although Equa-

tion 1 can be used to establish an injection protocol

for IA-Gd–enhanced MRA, it still leaves many

injection parameter choices available to the operator.

The authors present the following method of

approaching an IA injection:

1. Place catheter selectively into vessel of interest.

2. Measure or estimate blood flow rate (Q) in

mL/second in the catheterized vessel. To meas-

Fig. 5. Coronal 3D MRA using aortic catheter-based injections in a dynamic aortorenal-iliac flow phantom. Two series of images

acquired with aortic blood flow rate of 29 mL/second and an injection rate of 4 mL/second, using elliptical (a–d) and sequential

(e–h) encoding. Both series are shown with decreasing injection coverage: 100% (a,e), 75% (b,f ), 50% (c,g), and 30% (d,h). No

statistical difference ( P > 0.05) in signal-to-noise ratio (SNR) is present between the two encoding schemes. When injection

coverage is dropped to 30%, there is a statistically significant drop in SNR for all vessel segments ( P < 0.05). (From Hwang KP,

Green JD, Li D, Simonetti OP, Resnick SA, Finn JP, et al. Minimizing contrast-agent dose during intraarterial gadolinium-

enhanced MR angiography: in vitro assessment. J Magn Reson Imaging 2002;15:55–61; with permission.)


ure blood flow rates directly, use 2D cine-

phase contrast MRA [18,21,23,24]. Estimates

of blood flow rate can be obtained from the

literature or from operator experience. Esti-

mates are often sufficient, given the wide

variation in acceptable arterial [Gd]. This is not

unlike the case with x-ray digital subtraction

angiography (DSA). Significant vascular pa-

thology, however, might introduce more varia-

tion into estimates and potentially limit the

effectiveness of IA injections.

3. Select an injection rate. Injection rates might

range from 1 to 10 mL/second, given the

availability/preference of automated injectors

versus hand injections. A smaller injection rate

is beneficial because it uses smaller volumes of

dilute contrast agent. Smaller injection rates

might result in suboptimal mixing of contrast

Fig. 6. Pig following surgical induction of bilateral renal artery stenosis. (A) X-ray digital substration angiography shows 70%

right renal artery stenosis and 53% left renal artery stenosis; (B) IV-Gd–enhanced 3D MRA shows 68% right renal artery

stenosis and 65% left renal artery stenosis. (C) IA-Gd–enhanced 3D MRA shows 65% right renal artery stenosis and 75% left

renal artery stenosis. Both MR images are coronal-maximum intensity projections obtained with same 3D-fast spoiled gradient

echo acquisition. (From Omary RA, Henseler KP, Unal O, Maciolek LJ, Finn JP, Li D, et al. Comparison of intraarterial and

intravenous gadolinium-enhanced MR angiography with x-ray digital subtraction angiography for the detection of renal artery

stenosis in pigs. AJR Am J Roentgenol 2002;178:119–27; with permission.)


agent and blood. Faster injection rates should

improve mixing in large vessels. Use of

injection rate of 1 mL/second, however, will

simplify the math underlying Equation 1. This

injection rate works in most vessels, especially

if they are smaller.

4. Select desired arterial-Gd concentration

([Gd]artery). The authors suggest using

[Gd]artery = 1%, which should minimize

injected contrast dose and still provide ade-

quate images.

5. Determine injected-Gd concentration ([Gd]inj).

Assuming use of [Gd]artery = 1%, [Gd]inj = 1 +

(blood flow rate/injection rate)%. As an

example, for blood flow rate = 12 mL/second

and injection rate = 4 mL/second, substitution

yields [Gd]inj = 4%. Injecting at 1 ml/second,

requires [Gd]inj = 13%. To produce this injected

[Gd], dilute full-strength Gd (500 mM) with

normal saline.

6. Determine purpose of injection. Use 2DMRA to

verify catheter positioning, to confirm intra-

luminal catheter location, or to perform rapid

vascular roadmaps. These images can be pro-

jectional (5–20 cm slab) for tortuous vessels.

Use 3D MRA for its improved diagnostic ac-

curacy at the beginning and end of MRI-guided

endovascular procedures.

7. Determine injection duration. For fast time-

resolved 2D MRA, injection can coincide with

image acquisition and continue for the desired

number of arterial-phase imaging frames. For

3D MRA, injection should begin two seconds

prior to image acquisition, which will facilitate

adequate mixing of injected contrast agent with

inflowing blood. To minimize injected contrast

agent, injection duration can be reduced to the

first 50% of the image acquisition time in

medium or large vessels without loss of SNR.

For instance, injection duration should be

10 seconds for a 3D selective iliac artery

acquisition that lasts 16 seconds (2 second lead

time plus 8 seconds). In smaller vessels, such

as renal or coronary arteries, injection duration

should cover the first 75% of image acquisition

time. A similar 3D injection in a renal artery

might require injection duration of 14 seconds

(2 second lead time plus 12 seconds).

Fig. 7. Scatter plot shows swine renal artery stenosis measurements obtained for IV- and intraarterial (IA)-3D MRA using x-ray

digital substration angiography as reference standard. Stenoses were induced using reverse cable ties. IA MRA has slightly

greater scatter than IV MRA. (From Omary RA, Henseler KP, Unal O, Maciolek LJ, Finn JP, Li D, et al. Comparison of

intraarterial and intravenous gadolinium-enhanced MR angiography with x-ray digital subtraction angiography for the detection

of renal artery stenosis in pigs. AJR Am J Roentgenol 2002;178:119–27; with permission.)


To simplify Equation 1, substitute [Gd]artery = 1%

and injection rate = 1 ml/second [21]. This substi-

tution leads to:

½Gd�inj ¼ ð1þ QÞ � 1%;

where [Gd]inj = injected [Gd] (%) and Q = blood

flow rate in vessel of interest (mL/second).

Using Equation 2, the injected [Gd] in percent

equals one plus the estimated blood flow rate in

mL/second.

Accuracy of IA injections

The accuracy of IA injections are theoretically at

least as effective as, if not better than, conventional

IV-Gd–enhanced MRA because both rely on T1

shortening by contrast agent to produce bright vas-

cular signal. There are limited data available to

confirm this accuracy. In a reverse-cable tie-swine

model of renal artery stenosis; however, Omary et al

[24] compare the accuracy of IV and IA MRA

methods using x-ray DSA as a reference standard.

In this study, the same 3D MRA sequence is used to

compare an IA injection protocol, using Equation 1,

with conventional IV double-dose (0.2 mmol/kg) Gd -

enhanced MRA. Fig. 6 shows sample images from

their experiments. Their results indicate that there is

no significant difference ( P >0.05) in accuracy

between IA- and IV-Gd–enhanced MRA. Both injec-

tion methods also have similar accuracy to x-ray DSA.

IA stenosis measurements have slightly greater varia-

tion than IV measurements (Fig. 7). The IA injections,

however, use approximately 38% less Gd dose than

IV injections.

Advantages to IA injections

During MRI-guided endovascular procedures, IA

injections offer several advantages over conventional

IV administration of contrast agent. The most impor-

tant advantage is reduced contrast-agent dosage. Sec-

ond, the local delivery of contrast agent is much more

efficient than IVadministration. Instead of waiting for

first-pass arterial passage of Gd, there is immediate

contrast-agent delivery into the vessel of interest,

analogous to x-ray DSA. IA injections thereby avoid

the need for a dose-timing test bolus [31] or other

complex schemes [25,32,33] to synchronize the arrival

of contrast agent with image acquisition. Third, per-

fusion assessment, although not yet proven, should be

superior with IA injections because the local delivery

provides a more compact immediate input bolus.

Fourth, IA injections are required for projection

imaging when there are other overlapping vascular

beds near the artery of interest, such as with the

coronary circulation (Fig. 8). Finally, IA injections

have reduced contrast-agent dispersion compared with

IV injections.

Limitations to IA injections

There are several important limitations to IA

injections of Gd. First, the FDA has not approved

catheter-directed injections for MRA. These injec-

tions represent an off-label use and unapproved route

of administration of contrast agent. Second, the

safety of IA-Gd injections is not proven. Because

the major use of IA injections will be during MRI-

guided endovascular interventions, there is little

Fig. 8. Coronal electrocardiographic-triggered 2D MRA in

canine using selective left circumflex artery Gd injection.

Injection parameters were: injected [Gd] = 6%, injection

rate = 1.5 mL/second, injection duration = 4 seconds, slice

thickness = 20 mm, and temporal resolution = 0.5 frames/

second. Direct contrast-agent injection into the left circumflex

artery prevents overlap with the left anterior descending

artery distribution during 2D projection imaging.

(Equation 2)


incremental risk for each injection. Gd as an alterna-

tive contrast agent for x-ray DSA has achieved

widespread use by interventional radiologists. Sev-

eral publications document its safety for DSA [34,35]

and endovascular interventions [36,37] performed

under x-ray guidance, particularly in patients with

underlying renal insufficiency. Third, there is limited

experience in humans. The expanded use of IA injec-

tions in humans is tied directly to increased use ofMRI

guidance for endovascular interventions. There may

be, however, a role for IA injections as a problem-

solving tool in selected diagnostic applications [38].

Finally, more research needs to be performed to

confirm its diagnostic accuracy for detecting stenoses

in multiple vascular distributions.

Summary

In the setting of MRI-guided endovascular inter-

ventions, catheter-directed Gd-enhanced MRA offers

many of the same capabilities as conventional x-ray

DSA. Local injections permit rapid depiction of

blood vessels and help guide interventions. The

primary benefit of IA injections is significant reduc-

tion of administered contrast-agent dose compared

with conventional IV injections. Another major bene-

fit is facilitated background suppression, including

that of adjacent vascular beds. As MRI guidance

methods improve, catheter-based Gd injections

should gain expanded use in clinical practice.

Acknowledgments

The authors thank Toye Spencer and David Botos

for assistancewithmanuscript preparation andRichard

Tang for expert help with the animal experiments.

References

[1] Bartels LW, Bos C, van der Weide R, Smits HFM,

Bakker CJG, Viergever MA. Placement of an inferior

vena cava filter in a pig guided by high resolution MR

fluoroscopy at 1.5T. J Magn Reson Imaging 2000;12:

599–605.

[2] Bucker A, Neurburg JM, Adam GB, Glowinski A,

Schaeffter T, Rasche V, et al. Real-time guidance for

inferior vena cava filter placement in an animal model.

J Vasc Interv Radiol 2001;12:753–6.

[3] Yang X, Bolster B, Kraitchman D, Atalar E. Intravas-

cular MR-monitored balloon angioplasty: an in vivo

feasibility study. J Vasc Interv Radiol 1998;9:953–9.

[4] Yang X, Atalar E. Intravascular MR imaging-guided

balloon angioplasty with an MR imaging guide wire:

feasibility study in rabbits. Radiology 2000;217:501–6.

[5] Godart F, Beregi JP, Nicol L, Occelli B, Vincentelli A,

Daanen V, et al. MR-guided balloon angioplasty of

stenosed aorta: in vivo evaluation using near-standard

instruments and a passive tracking technique. J Magn

Reson Imaging 2000;12:639–44.

[6] Omary RA, Frayne R, Unal O, et al. Magnetic reso-

nance-guided angioplasty of renal artery stenosis in a

pigmodel: a feasibility study. J Vasc Interv Radiol 2000;

11:373–81.

[7] Le Blanche AF, Rossert J, Wassef M, Levy B, Bigot

M, Boudghene F. MR-guided PTA in experimental bi-

lateral rabbit renal artery stenosis and MR angiography

follow-up versus histomorphometry. Cardiovasc Inter-

vent Radiol 2000;23:368–74.

[8] Buecker A, Neuerburg JM, Adam GB, Glowinski A,

Schaeffter T, Rasche V, et al. Real-time MR fluoros-

copy for MR-guided iliac artery stent placement. J

Magn Reson Imaging 2000;12:616–22.

[9] Dion YM, Ben El Kadi H, Boudoux C, Gourdon J,

Chakfe N, Traore A, et al. Endovascular procedures

under near-real-time magnetic resonance imaging guid-

ance: an experimental feasibility study. J Vasc Surg

2000;32:1006–14.

[10] Quick HH, Ladd ME, Nanz D, Mikolajczyk KP, De-

batin JF. Vascular stents as RF antennas for intravas-

cular MR guidance and imaging. Magn Reson Med

1999;42:738–45.

[11] Serfaty JM, Yang X, Aksit P, Quick HH, Solaiyappan

M, Atalar E. Toward MRI-guided coronary catheteri-

zation: visualization of guiding catheters, guidewires,

and anatomy in real time. J Magn Reson Imaging

2000;12:590–4.

[12] Serfaty JM, Atalar E, Declerck J, et al. Real-time pro-

jection MR angiography: feasibility study. Radiology

2000;217:290–5.

[13] Kee ST, Rhee JS, Butts K, Daniel B, Pauly J, Kerr A,

et al. MR-guided transjugular portosytemic shunt place-

ment in a swine model. J Vasc Interv Radiol 1999;

10:529–35.

[14] Strother CM, Unal O, Frayne R, Turk A, Omary RA,

Korosec FR, et al. Endovascular treatment of experi-

mental canine aneurysms: feasibility with MR imaging

guidance. Radiology 2000;215:516–9.

[15] Bos C, Smits HM, Zijlstra JJ, van der Mark WAMA,

Blankestijn PJ, Bakker CJG, et al. MRA of hemodialy-

sis access grafts and fistulae using selective contrast

injection and flow interruption. Magn Reson Med

2001;45:557–61.

[16] Manke C, Nitz WR, Djavidani B, Strotzer M, Lenhart

M, Volk M, et al. MR imaging-guided stent placement

in iliac arterial stenoses: a feasibility study. Radiology

2001;219:527–34.

[17] Omary RA, Frayne R, Unal O, Grist TM, Strother CM.

Intra-arterial gadolinium-enhanced 2D and 3D mag-

netic resonance angiography: a preliminary study. J

Vasc Interv Radiol 1999;10:1315–21.


[18] Frayne R, Omary RA, Unal O, Strother CM. Determi-

nation of optimal injection parameters for intra-arterial

gadolinium-enhanced MR angiography. J Vasc Interv

Radiol 2000;11:1277–84.

[19] Bos C, Smits HFM, Bakker CJG, Viergever MA. Se-

lective contrast-enhanced MR angiography. Magn Re-

son Med 2000;44:575–82.

[20] Bos C, Bakker CJG, Viergever MA. Background sup-

pression using magnetization preparation for contrast-

enhanced MR projection angiography. Magn Reson

Med 2001;46:78–87.

[21] Omary RA, Henseler KP, Unal O, Smith RJ, Ryu RK,

Resnick SA, et al. Validation of injection parameters

for catheter-directed intraarterial gadolinium-enhanced

MR angiography. Acad Radiol 2002;9:172–85.

[22] Green JD, Omary RA, Vasireddy S, Tang R, Li Y, Finn

JP, et al. MR coronary angiography with intraarterial

gadolinium injection using an inversion recovery-

prepared sequence. Presented at the 29th Annual

Meeting and Scientific Session of the North American

Society for Cardiac Imaging. Chicago, October 2001.

[23] Schoenberg SO, Knopp MV, Bock M, et al. Renal

artery stenosis: grading of hemodynamic changes with

cine phase-contrast MR blood flow measurements. Ra-

diology 1997;203:45–53.

[24] Omary RA, Henseler KP, Unal O, Maciolek LJ, Finn JP,

Li D, et al. Comparison of intraarterial and intravenous

gadolinium-enhanced MR angiography with x-ray dig-

ital subtraction angiography for the detection of renal

artery stenosis in pigs. AJR Am J Roentgenol 2002;

178:119–27.

[25] Korosec FR, Frayne R, Grist TM, Mistretta CA. Time-

resolved contrast-enhanced 3D MR angiography.

Magn Reson Med 1996;36:345–51.

[26] Unal O, Korosec FR, Frayne R, Strother CM, Mistretta

CA. A rapid 2D time-resolved variable-rate k-space

sampling MR technique for passive catheter tracking

during endovascular procedures. Magn Reson Med

1998;40:356–62.

[27] Omary RA, Unal O, Koscielski DS, et al. Real-time

MR imaging-guided passive catheter tracking with use

of gadolinium-filled catheters. J Vasc Interv Radiol

2000;11:1079–85.

[28] Li D, Carr JC, Shea SM, Zheng J, Deshpande VS,

Wielopolski PA, et al. Coronary arteries: magnetiza-

tion-prepared contrast-enhanced three-dimensional vol-

ume-targeted breath-hold MR angiography. Radiology

2001;219:270–7.

[29] Omary RA, Green J, Tang R, Vasireddy S, Finn JP, Li

D. Catheter-directed Gd-enhanced renal MRA. Pres-

ented at the 13th International Workshop on MRA.

Madison (WI), September, 2001.

[30] Hwang KP, Green JD, Li D, Simonetti OP, Resnick SA,

Finn JP, et al. Minimizing contrast agent dose during

intraarterial gadolinium-enhanced MR angiography:

in vitro assessment. J Magn Reson Imaging 2002;15:

55–61.

[31] Earls JP, Rofsky NM, DeCorato DR, Krinsky GA,

Weinreb JC. Hepatic arterial-phase dynamic gadoli-

nium-enhanced MR imaging: optimization with a test

examination and a power injector. Radiology 1997;203:

268–73.

[32] Foo TKF, Saranathan M, Prince MR, Chenevert TL.

Automated detection of bolus arrival and initiation of

data acquisition in fast, three-dimensional, gadolinium-

enhanced MR angiography. Radiology 1997;203:275–

80.

[33] Wilman AH, Riederer SJ, King BF, Debbins JP, Ross-

man PJ, Ehman RL. Fluoroscopically triggered con-

trast-enhanced three-dimensional MR angiography

with elliptical centric view order: application to the

renal arteries. Radiology 1997;205:137–46.

[34] Kinno Y, Odagiri K, Andob K, Itoh Y, Tarao K. Ga-

dopentetate dimeglumine as an alternative contrast ma-

terial for use in angiography. AJR Am J Roentgenol

1993;160:1293–4.

[35] Matchett WJ, McFarland DR, Russell DK, Sailors DM,

Moursi MM. Azotemia: gadopentetate dimeglumine as

contrast agent at digital subtraction angiography. Radi-

ology 1996;201:569–71.

[36] Spinosa DJ, Matsumoto AH, Angle JF, Hagspiel KD.

Use of gadopentetate dimeglumine as a contrast agent

for percutaneous transluminal renal angioplasty and

stent placement. Kidney Int 1998;53:503–7.

[37] Spinosa DJ, Matsumoto AH, Angle JF, Hagspiel KD,

McGraw JK, Ayers C. Renal insufficiency: usefulness

of gadodiamide-enhanced renal angiography to supple-

ment CO2-enhanced renal angiography for diagnosis

and percutaneous treatment. Radiology 1999;210:

663–72.

[38] Taylor DJ, Brown G. Intra-arterial contrast enhanced

MR angiography (IA-CEMRA) In: Proceedings of the

International Society of Magnetic Resonance in Med-

icine. 8th edition. Berkeley (CA): International Society

of Magnetic Resonance in Medicine; 2000. p. 466

[abstract].


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Catheter-directed gadolinium-enhanced MR angiography