cardiovascular disorders
Cardiac Imaging Tests
Computed Tomography (CT) in Cardiac Diagnosis
 may be used to evaluate Pericarditis , This image shows dense coronary calcifications in the left main (red arrow) and left anterior descending artery (green arrow). © 2017 Elliot K. Fishman, MD. This is an oblique view of the left side, looking toward the front of the chest (left). The prosthetic heart valve (white) is visible at center, where the aorta (upper center) meets the heart (lower center). The stitches used to close the chest are visible at upper left. ZEPHYR/SCIENCE PHOTO LIBRARY This contrast CT shows normal coronary arteries. The left main is indicated by the red arrow. The left anterior descending and left circumflex arteries are indicated by the green and blue arrows respectively and the right coronary artery is indicated by the purple arrow. © 2017 Elliot K. Fishman, MD. This contrast CT shows normal coronary arteries. The left main is indicated by the red arrow. The left anterior descending and left circumflex arteries are indicated by the green and blue arrows, respectively, and the right coronary artery is indicated by the purple arrow. © 2017 Elliot K. Fishman, MD. This contrast CT shows normal coronary arteries. The left main is indicated by the red arrow. The left anterior descending and left circumflex arteries are indicated by the green and blue arrows respectively and the right coronary artery is indicated by the purple arrow. © 2017 Elliot K. Fishman, MD. This contrast CT shows normal coronary arteries. The left main is indicated by the red arrow. The left anterior descending and left circumflex arteries are indicated by the green and blue arrows respectively and the right coronary artery is indicated by the purple arrow. © 2017 Elliot K. Fishman, MD. This contrast CT shows normal coronary arteries. The left main is indicated by the red arrow. The left anterior descending and left circumflex arteries are indicated by the green and blue arrows respectively and the right coronary artery is indicated by the purple arrow. © 2017 Elliot K. Fishman, MD. This contrast CT shows normal coronary arteries. The left main is indicated by the red arrow. The left anterior descending and left circumflex arteries are indicated by the green and blue arrows respectively and the right coronary artery is indicated by the purple arrow. © 2017 Elliot K. Fishman, MD. Electron beam CT,formerly called ultrafast CT or cine CT, unlike conventional CT, does not use a moving x-ray source and target. Instead, the direction of the x-ray beam is guided by a magnetic field and detected by an array of stationary detectors. Because mechanical motion is not required, images can be acquired in a fraction of a second (and recorded at a specific point in the cardiac cycle). Electron beam CT is used primarily to detect and quantify coronary artery calcification, an early sign of atherosclerosis. However, spatial resolution is poor and the equipment cannot be used for noncardiac disorders, so newer standard CT techniques are becoming preferred for cardiac use. Multidetector CT(MDCT), with≥64 detectors, has a very rapid scan time; some advanced machines may generate an image from a single heartbeat, although typical acquisition time is 30 seconds. Dual-source CT uses 2 x-ray sources and 2 multidetector arrays on a single gantry, which cuts scan time in half. Both of these modalities appear able to identify coronary calcifications and flow-limiting (ie,>50% stenosis) coronary artery obstruction. Typically, an IV contrast agent is used, although nonenhanced scans can detect coronary artery calcification. MDCT, a noninvasive alternative to Angiography , is used mainly for patients with stable angina to identify obstructive coronary artery disease or patients with chest pain and a low to intermediate probability of acute coronary syndrome. Although the radiation dose can be significant, about 15 mSv (vs 0.1 mSv for a chest x-ray and 7 mSv for coronary angiography), newer imaging protocols can reduce the exposure to 5 to 10 mSv. The presence of high-density calcified plaques creates imaging artifacts that interfere with interpretation. Nonenhanced scans to evaluate for coronary artery calcification can be done with even lower radiation exposure. The amount of coronary artery calcium present can be used to determine the 10-year risk of coronary artery disease (see 