Transcript Computed Tomography Angiography (CTA) and Magnetic

Computed Tomography
Angiography (CTA)
and
Magnetic Resonance
Angiography (MRA)
What Are They?

Computed Tomography Angiography
(CTA)
Imaging of the vasculature using CT techniques
 Can be 3-D
 Requires contrast
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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 plaque
 Areas
that are scan for plaque include:
Carotid Bulb
 Iliac arteries
 Coronary arteries
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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

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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
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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
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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
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 Faster
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
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Accuracy of CTA

16-slice multidetector machine
 Sensitive
and specific for 2mm diameter or
greater 92-93%
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Ultra fast 16-slice multidetector machine
 Sensitive
and specific for 2mm diameter or
greater 95-98%
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64-slice multidetector machine
 Sensitive
and specific for 2mm diameter or
greater 92-93%
Accuracy of MRA
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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?
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Improved spatial resolution
 Resolutions
due to software advancements are
improving
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Decreasing costs
Screening
 CTA screening
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Joint Modalities
 Combining
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for CAD
of the two for better images
Better accuracy
 New
contrast medias for MR and faster CT machines
Bibliography
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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
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Sheth, T. et. al., (2005), Coronary Computed Tomography
Angiography: Emerging Technique for Coronary Artery Imaging,
JACR 2005:56(1):15-24
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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
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www.medscape.com/viewarticle/521872?rss
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www.radiologyinfo.org/content/ct-angiography.htm
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www.radiologyinfo.org/content/mr-angiography.htm