computed tomography angiography (cta) and magnetic resonance angiography (mra)
TRANSCRIPT
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