Coronary CT angiogram
Computed tomographic (CT) imaging of the blood vessels supplying oxygenated blood to the heart (coronary arteries) is known as coronary CT angiogram. It is being used more often as an executive screening test for detection of blocks in coronary arteries. It has good value in excluding significant coronary artery disease, though the test does involve ionization radiation and is as expensive as conventional coronary angiogram. The attraction of CT angiogram is that it is less invasive than conventional coronary angiogram. Only a single injection of iodinated contrast material (‘dye’) is required and further imaging is done by a multi-detector computerized scanner which rapidly scans the heart in an automated fashion. The signals received are timed according to the electrocardiogram (ECG) and three dimensional reconstructions of coronary arteries are made by the computer program. Major blocks in the coronary arteries can be detected by the technique, though it still lacks the precision needed to make major decisions on treatment like coronary angioplasty (removal of blocks by balloons) or coronary artery bypass surgery. Still it has good negative predictive value in that if CT angiogram is normal, significant blocks in the coronary arteries are unlikely. It is useful mostly in those with a low or moderate probability of coronary artery disease. In those with a high probability of disease as assessed from symptoms or non-invasive tests like ECG, echocardiogram or treadmill exercise testing, it is better to go directly for conventional invasive coronary angiography.