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CCTA (without dose modulation) = 15 mSv
Diagnostic invasive coronary angiography = 3-10 mSv
SPECT sestamibi = 12 mSv
SPECT thallium = 25mSv
CXR = .04 mSv
Standard chest CT = 7 mSv
Average background radiation in the U.S. = 3.6 mSv
Coronary artery disease (CAD) remains the leading cause of death in the United States. The medical work-up for CAD has traditionally involved careful history and physical, appropriate laboratory analysis and nuclear medicine stress testing, followed by traditional invasive coronary angiography. Computed tomography angiography (CCTA) of the heart and the coronary arteries is an emerging technique that has the potential to become a valuable complement to the work-up and management of known or suspected coronary artery disease.
CCTA Technique The coronary arteries have remained a challenge to image with CT because of the small size of the anatomy and the constant cardiac motion. Over the past decade, there have been significant improvements in CT technology with the advent of spiral CT and the increasing number of detectors. This rapid technologic development has led to increasing spatial and temporal resolution of CT. The entire heart can now be imaged in 5 heartbeats with the 64 detector CT at Martha Jefferson Hospital. A slow, steady heart rate is necessary for a diagnostic CCTA examination. A heart rate greater than 60 beats per minute can result in motion artifact of the coronary arteries and make some coronary artery segments "noninterpretable". A slow, steady heart rate is achieved by the pre-procedure administration of oral beta blockers. Sublingual nitrates are also administered to maximize vasodilation of the coronary arteries. Each CCTA examination is tailored to each individual patient. A test injection of intravenous iodinated contrast is administered to determine cardiac circulation time and to optimize the contrast opacification of the coronary arteries. The exam is gated to an EKG to monitor the heart rate and to trigger the CT scanner at the appropriate time in the R-R interval. This EKG gating allows the physician to retrospectively EKG edit the CT data to select the time in the cardiac cycle where there is the least amount of motion. This timing will vary with each individual patient and with each coronary artery segment. For example, the right coronary artery is typically better imaged in late systole, whereas the left coronary arteries are typically better imaged at late diastole.