MDCT emerges as alternative to EBCT in noninvasive coronary imaging

Steady but significant changes are occurring in how coronary calcification is imaged. Consensus is growing among researchers that the results of multidetector CT compare well with those of the gold standard, electron-beam CT, although they emphasise that further studies are needed.

MDCT has higher spatial resolution than EBCT, but there are fewer than 50 articles in the peer-reviewed literature, no industry standards, and no prognostic, autopsy, and intravascular ultrasound (IVUS) data, according to Dr. Rozemarijn Vliegenthart, a radiologist at Groningen University Hospital in the Netherlands.

"The situation is changing monthly," she said at Sunday's refresher course on coronary radiology.

In comparison, EBCT has higher temporal resolution, lower radiation dose, and has been approved by the FDA. More than 1000 articles about the technique have been published, and the data are reproducible.

Coronary heart disease is usually caused by the rupture of atherosclerotic plaque, which results in complete occlusion of the coronary artery. In the developed world, half of all men and a third of all women will suffer from it after age 40. The main cardiovascular risk factors are smoking, high blood pressure, high serum total cholesterol, low serum HDL cholesterol, diabetes mellitus, and advancing age.

MDCT for assessment of coronary calcification is usually performed in the axial mode, with prospective ECG triggering and a temporal resolution of 320 to 500 msec. The spiral mode is not used because of the high radiation dose, Vliegenthart said.

Coronary calcium is of high prognostic value for identifying asymptomatic patients at increased risk of coronary events. Using both MDCT and EBCT, the calcium scores obtained are similar when the burden of atherosclerosis is very high, but caution is recommended with low MDCT scores.

"MDCT will need its own scoring algorithms prior to widespread application," she said.

For MDCT, the entire body circumference is exposed to radiation. With EBCT, the x-ray beam enters only from the back, while anterior radiosensitive organs are subjected to a much lower dose of radiation.

"In the detection of coronary calcification, plaque burden is more predictive than stenosis," Vliegenthart concluded. "Future studies will help to define the role of coronary calcium detection in risk stratification."

At the same session, Prof. Matthijs Oudkerk, also from the radiology department at Groningen University Hospital, said that the clinical information on stenoses provided by 16-slice MDCT and EBCT scanners is far more reliable than coronary angiography (CAG).

The main limitations of CAG are the contraindications, projection dependency, left main stenoses, myocardial bridging, intraluminal summation effects, and lack of visualization of the coronary vessel wall, he said.

"MDCT and EBT visualize the coronary vessel wall and detect soft and calcified plaque, as well as intraluminal thrombus development. Contrary to IVUS and CAG, they can establish a total plaque burden, differentiating soft, calcified, obstructing, nonobstructing, and thrombotic lesions," Oudkerk said.

MDCT and EBCT are indicated in coronary pathology in which 3D anatomy is required. Other primary indications are coronary aneurysms, Kawasaki's disease, anomalies, and coronary bypasses.

"If coronary flow evaluation is crucial, invasive coronary catheterization is indicated," Oudkerk said.

He added that this may be true in cases of in-stent restenosis, anomalous anastomosis, vasoconstriction, vasodilatation, functional collateral flow, hypoplasia, and fistula.