الفهرس 
Gross Anatomy of the Coronary ArteriesOnly 14 pages are availabe for public view
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Abstract
Ischemic heart disease (IHD) is the generic designation
for a group of closely related clinical presentations, resulting
from myocardial ischemia; an imbalance between the blood
supply (perfusion) and demands of the myocardium for
oxygenated blood. In most cases, the cause of myocardial
ischemia is reduction blood supply because of atherosclerotic
coronary artery disease.
Multislice CT is a recent development in the spiral CT.
The MSCT scanners are equipped with multiple and thinner
detector rows, and has a faster tube rotation speed creating two
major advantages; high spatial resolution and short acquisition
time that enable high-quality examinations. It is only with this
immense increase it the data acquisition volume per unit time,
that CT assessment of the coronary arteries has become
possible.
High and consistent vascular enhancement within the
vessel lumen is a prerequisite for successful CT angiography.
Adequate enhancement is needed to visualize the vessel wall
and the small side branches of the coronary tree. In addition,
high and homogeneous enhancement serves as the basis for
threshold-dependent three-dimensional (3D) visualizationtechniquesFor CTCA, the chest is scanned from above the left main
coronary artery to below the diaphragmatic surface of the heart.
The appropriate beginning and ending positions are determinedfrom a scout view. The acquired CT and ECG data are to be
sent to a separate advanced workstation with dedicated cardiac
reconstruction software used to reconstruct the images.
The initial and most important step in the interpretation
of CT coronary angiography is the careful review of the axial
images that necessitate thorough knowledge of the coronary
anatomy including the origin, course, caliber and branches of
each coronary artery and experience in CT analysis. This also
allows recognition of coronary calcifications and possibly
significant, stenoticlesions and image artifacts related to
cardiac motion.
The evaluation of MDCT coronary angiograms, has been
performed interactively on off-line workstations, by using a
combination of transverse, MPR, MIP, and 3D VRT images.
Challenges in evaluating the coronary arteries at CT are
the small size and tortuous courses of the vessels and their
continuous movements being intimately related to the cardiac
chambers. Controlled heart rate and good breath-holding help to
reduce cardiac and respiratory motion artifacts respectively.
Retrospective ECG gating and proper choice of the
reconstruction window would significantly improve the
examination quality.
Since introduction of the MSCT as a non-invasive tool
for prediction of CAD, the clinical value CT coronary
angiography has been subject for research work..
Summary
- 135 -
Four-detector CT scanner were limited by motion
artifacts, the presence of significant coronary calcium, the need
for long breath holds, and less-than optimal spatial resolution.
lmprovements of the recently developed 64-channel CT
scanners, including the improved spatial and temporal
resolutions and considerably reduced acquisition times were
reflected on the image quality leading to better results .The
current results show that the MSCT angiography is a good
noninvasive coronary imaging modality that is able to evaluate
the coronary anatomy and early detect and grade coronary
lesions competing with other noninvasive examinations used to
detect CAD, such as exercise stress testing. Because of its high
negative predictive value, CT angiography might be employed
to exclude significant CAD and thus avoid unnecessary
coronary angiograms in certain groups of patients.
Various artifacts associated with data creation and
reformation, post-processing methods, and image interpretation
can hamper accurate diagnosis. These artifacts can be related to
cardiac respiratory or respiratory motions, partial volume
averaging, high attenuation entities (e.g. stents and surgical
clips), inappropriate scan pitch and patient body state. Some
artifacts have already been resolved with technical advances,
whereas others represent partially inherent limitations for
coronary CT angiography.
Problems and limitations remain, as always, and will
trigger scientific and technical innovation. Conceivablestrategies to improve scanner performance include evaluation of
the EBCT detectors to allow simultaneous acquisition of
multiple sections and trial of the dual-source computed
tomography (DSCT) equipped with two X-ray tubes and two
corresponding groups of detectors mounted on the rotating
gantry with an angular offset of 90° aiming at improvement of
the temporal resolution
The potential role for CT angiography as a non-invasivemodality in evaluating the coronary arteries:
An appropriateness review was conducted at 2006 under
by the American College of Cardiology Foundation (ACCF).
According to the appropriateness review, the following
conditions were considered inappropriate to cardiac CT:
• Detection of CAD in asymptomatic patient with low or
moderate risk factors.
• Detection of CAD in asymptomatic patient with high risk
factors when there is previous negative CT coronary
angiography or conventional angiography at the last 2 years.
• Detection of CAD in asymptomatic patient with high risk
factors for CAD when the calcium score is equal to or more
than 400.
• Evaluation of acute chest pain when there is high pre-test
probability for CAD or elevated ST-segment at ECG or
positive cardiac enzymes or when there is evidence of
moderate or severe ischemia at stress test.• Preoperative evaluation for non-cardiac low risk surgery in
patients with low or intermediate risk for CAD.
• Evaluation of the in-stent re-stenosis.
• Evaluation of the coronary arterial bypass grafts in
asymptomatic patients.
• Coronary calcium score for asymptomatic patients with low
risk for CAD or when there is negative test within the
previous 5 years.
• Evaluation of LV function following myocardial infarction
or in heart failure patients.
According to the appropriateness review; the
following conditions were considered appropriate tocardiac CT:
• Evaluation of suspected coronary anomalies.
• Assessment of complex congenital heart disease including
anomalies of coronary circulation, great vessels, and cardiac
chambers and valves.
• Symptomatic cases with ischemic chest pain in case of:
- Intermediate pre-test probability for CAD when the
ECG is un-interpretable or when the patient is unable- Intermediate pre-test probability for CAC and
interpretable or equivocal stress tests.Acute chest pain in case of:
- Intermediate pre-test probability for CAD when the
ECG is negative or with serial negative cardiac
enzymes.
- Evaluation of suspected aortic dissection or thoracic
aortic aneurysm.
- Evaluation of suspected pulmonary embolism.
• Evaluation of coronary arteries in patients with new onset
heart failure to assess etiology.
• Noninvasive coronary arterial mapping, including internal
mammary artery prior to repeat cardiac surgical
revascularization.
• Evaluation of cardiac mass (suspected tumor or thrombus) in
patients with technically limited images from
echocardiogram, MRI, or TEE.
• Evaluation of pericardial conditions (pericardial mass,constrictive pericarditis, or complications of cardiac surgery)
in patients with technically limited images from
echocardiogram, MRI, or TEE.
• Evaluation of pulmonary vein anatomy prior to invasive
radiofrequency ablation for atrial fibrillation.
• Noninvasive coronary vein mapping prior to placement of
biventrlcular pacemaker.
According to the appropriateness review; the followingCoronary calcium Score for asymptomatic patents with
intermediate or high risk for CAD.
• CT coronary angiography for asymptomatic patients with
high risk for CAD.
• Acute chest pain in case of:
a. Low pre-test probability of CAD when there is no ECG
changes and serial enzymes negative.
b. ”Triple rule out” to exclude obstructive dissection, and
pulmonary embolism in intermediate pre-test probability
for one of when there is no ECG changes and serial
negative.
• Post-revascularization (PC or CABG), in cases with chest
pain for:
a. Evaluation of bypass grafts and native coronary arteries.
b. History of PCI with stents to evaluate the coronary• Preoperative evaluation for non-cardiac intermediate or high
risk surgery in patients with intermediate risk for CAD.
• Evaluation of LV function following myocardial infarction
OR in heart failure patients in cases with technically limited
images from echocardiogram .
• Characterization of native and prosthetic cardiac valves in
patients with technically limited images from echacardiagram,
MRI, or TEE.