Computed Tomography Angiography (CTA)andMagnetic Resonance Angiography (MRA)

What Are They? Computed Tomography Angiography

(CTA) Imaging of the vasculature using CT techniques Can be 3-D Requires contrast

Magnetic Resonance Angiography (MRA) Imaging of the vasculature system using MRI

techniques Can be 3-D No contrast required

How Does CTA Work?

Uses X-rays Tube rotates around patient at high speed Detector picks up attenuated beam Computer generates the image Collects image in axial plane but can be

converted into sagittal, or coronal views Computer can generate 3-d images

How Does MRA work? Uses a large magnet align hydrogen atom in the

body Pulsed radio-waves cause hydrogen atoms to flip

out of alignment When the radio-waves are turned off the

hydrogen atom flip back and give off their own signal

Signal is detected by the computer and used to generate an image

Different body tissues have different amounts of Hydrogen

What is CTA used for?

Imaging of calcified atherosclerotic plaqueAreas that are scan for plaque include:

Carotid Bulb Iliac arteries Coronary arteries

Used to detect legs clots before they break and cause pulmonary emboli

Calcified plaque seen on CTA Angiogram of the same vessel

What is MRA used for?

MRA is used to image many peripheral vessels Areas that are imaged include:

Circle of Willis Cerebral Arteries Renal Arteries

If there is a contrast allergy then MRA is used

Benefits of CTA Detecting narrowing vessels in time for

intervention Better anatomical detail than with MRA or

ultrasound Can be used for screening for arterial disease Less costly and safer than conventional angiography Contrast reactions are less severe

Risks of CTA

Allergic reactions to contrast media Avoided in patients with kidney disease

due to contrast Ionizing radiation is used Pregnant women should not have a CT

due to radiation

Benefits of MRA Detailed images without damaging the artery with a

catheter Shorter procedure and recovery times than with

conventional angiography Less costly than catheter angiography No exposure to ionizing radiation Use of contrast is

not necessary to

obtain good images

Risks of MRA

Metal implants may be affected by the magnetic field

Claustrophobic patients may need ot be sedated

It is unknown how the magnetic field affects the fetus so first trimester patients should not have an MRI

Limitations of CTA

Fuzzy images if there is patient movement Heart beat can blur images Blocked vessels are harder to interpret Not reliable for imaging small twisted

vessels in rapidly moving organsFaster gantry times will solve this problem

Limitations of MRA

Any metal object in the patient is contraindicative

Image clarity is not as good as conventional angiography

Cannot image calcified plaque Hard to image very small vessels

Accuracy of CTA

16-slice multidetector machineSensitive and specific for 2mm diameter or

greater 92-93% Ultra fast 16-slice multidetector machine

Sensitive and specific for 2mm diameter or greater 95-98%

64-slice multidetector machineSensitive and specific for 2mm diameter or

greater 92-93%

Accuracy of MRA Detecting Cerebral aneurysms with an average

accuracy of about 70% without contrast False positives averaged approx. 27 With contrast 100% sensitive for aneurysmal

and stenotic lesions Specificity of completely occluded lesions also

100% Drops to 83.3% when only partially occluded

What’s to come?

Improved spatial resolution Resolutions due to software advancements are

improving Decreasing costs Screening

CTA screening for CAD Joint Modalities

Combining of the two for better images Better accuracy

New contrast medias for MR and faster CT machines

Bibliography Dargan, R., Volkin, L., New Application Enhances Capabilities of

Angiographic CT, retrieved February 5, from: www.asrt.org/content/News/IndustryNews Briefs/CT/NewApplica050318.aspx

Sheth, T. et. al., (2005), Coronary Computed Tomography Angiography: Emerging Technique for Coronary Artery Imaging, JACR 2005:56(1):15-24

Tripathi, RP, et. al., (2002), Three-Dimensional Contrast-Enhanced Magnetic Resonance Angiography- Our Preliminary Experience, Ind. J. Raiol. Imag. 2002, 12:2:179-188

www.cir.uc.edu/ research.html www.medscape.com/viewarticle/521872?rss

www.radiologyinfo.org/content/ct-angiography.htm

www.radiologyinfo.org/content/mr-angiography.htm