1. Computed Tomography Angiography (CTA) and Magnetic Resonance Angiography (MRA)

2. 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
No contrast required

3. 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

4. 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

5. What is CTA used for? Imaging of calcified atherosclerotic plaque
Areas that are scan for plaque include:
Carotid Bulb
Iliac arteries
Coronary arteries
Used to detect legs clots before they break and cause pulmonary emboli

6. Calcified plaque seen on CTA
Angiogram of the same vessel

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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 organs
Faster gantry times will solve this problem

13. 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

14. Accuracy of CTA 16-slice multidetector machine
Sensitive 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 machine
Sensitive and specific for 2mm diameter or greater 92-93%

15. 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

16. What’s to come? Improved spatial resolution Decreasing costs Screening
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

17. Bibliography
Dargan, R., Volkin, L., New Application Enhances Capabilities of Angiographic CT, retrieved February 5, from: Briefs/CT/NewApplica 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:
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