Methods for quantification of coronary artery calcifications with electron beam and conventional CT and pushing the spiral CT envelope: new cardiac applications.

Abstract

Detection of coronary artery calcifications with slice by slice prospective ECG triggering is feasible with electron beam CT as well as with single and multi-row-detector CT (MDCT). The radiation exposure to the patient to obtain comparable image quality is similar for all three modalities utilizing this prospective acquisition technique. Alternatively, coronary screening can be performed by MDCT with retrospective EKG spiral gating. Radiation exposure to the patient with this technique is significantly higher than with prospective triggering. Nevertheless, acquisition of the entire volume of the heart with retrospective gating holds promise to improve reproducibility of coronary calcium measurements, especially in patients with a low amount of coronary calcium and in patients with atrial fibrillation. If retrospective gating is used for CT angiography (CTA) with MDCT this allows to use thin slices (1.25 mm) and to perform the acquisition within one breath hold period (app. 35 s). This technique is currently limited by the temporal resolution per slice (250 ms). In order to achieve diagnostic image quality the heart rate of the patient thus needs to be sufficiently low. Therefore, in cases with heart rates significantly higher than 70 beats/min betablocker have to be administered for patient preparation as long as there are no contraindications for such a regimen. Because of low image noise and high spatial resolution CTA with MDCT is able to display the entire extent of atherosclerosis allowing to visualize calcified as well as non-calcified plaques of the coronary arteries. Under clinical conditions CTA has the potential to accurately rule out or diagnose significant coronary stenoses of the proximal and mid-segments of the coronary artery tree when compared to conventional selective coronary angiography.