Electron beam CT vs Multi slice CT
Electron beam computerised tomography (EBCT) and multi detector computerised tomography (MDCT) are the two modalities of CT scans used for evaluating the coronary arteries. EBCT has higher temporal resolution, since there is no gantry movement; electron beam is rotated using magnetic fields. MDCT has higher spatial resolution, but the temporal resolution is lower as more time is required for gantry movement. Multiple detectors, even upto 320 slice MDCT have been developed for clinical use. But the major studies have been conducted only with upto 64 slice MDCT.
Glagov phenomenon is the positive remodeling of arteries described by Seymour Glagov in 1987. By meticulous serial sectioning of left main coronary arteries in necropsy specimens, Glagov observed that the arterial size is proportional to the plaque burden. The process of enlargement of the artery to accomodate the plaque and maintain the lumen has been called as the Glagov phenomenon. It also known as compensatory enlargement or positive remodeling of the artery.
Calcium scoring of coronary arteries
The scoring can be done with EBCT, while the vessel assessment can be done only with MDCT. The calcium scoring scale is known as Agatston score. A score of 0 means that there is no identifiable calcium.
If there is no calcium there is no obstuctive coronary artery disease (CAD); if calcium score is more than 100 , it predicts obstructive CAD.
Calcium scoring is useful to differentiate ischemic dilated cardiomyopathy from the idiopathic variety. If the calcium score is negative, it is unlikely to be ischemic in origin.
Radiation exposure in cardiac CT angiography
CT angiography has higher radiation dose than conventional coronary angiography, almost 5 times. Radiation exposure is low for EBCT.
Contrast load is also higher with CT angiography.