Cardiac: Coronary CT angiography
With their small dimensions and fast motion, the coronary vessels are not easy to interpret by CT and impeccable image quality is a prerequisite to reliably detect or rule out stenoses. Owing to its high temporal and spatial resolution Dual Source CT should allow for reliable assessment of the coronary arteries.
Although invasive coronary angiography still constitutes the clinical gold standard, computed tomography has progressed to a stage that allows relatively reliable visualization of the coronary artery lumen and analysis concerning the presence of atherosclerotic lesions. There are however still some limiting factors.
Dual Source CT provides heart-rate independent temporal resolution
Regular and low heart rates (optimally less than 60 bpm) are a prerequisite for reliable imaging of the coronary arteries by 16 and 64 slice MDCT, requiring the administration of short-acting beta-blockers prior to the MDCT scan. With Dual Source CT and its temporal resolution of 82 ms, it is not necessary to lower the heart rate, though administration of sublingual nitroglycerine is always recommended to achieve coronary vasodilation.
CT angiography (CTA) has high negative predictive value
In studies performed using recent generations of 16 to 64-slice CT, per-patient sensitivity for the detection of coronary stenosis in comparison with invasive coronary angiography ranged from 93% to 100%. Thus, MDCT in tends to slightly overestimate disease severity in some situations. A high negative predictive value of 92% to 100% in both per-segment and per-patient evaluation methods does indicate the method’s ability to reliably rule out the presence of coronary artery stenosis, if the MDCT scan is expertly acquired and evaluated.
Grading of lesion severity more accurate with Dual Source CT
Clinically, coronary CT angiography would currently not be considered a routine replacement for the catheter-based coronary angiogram. Due to limited spatial resolution, accurate grading of the severity of stenosis is currently not possible on a routine basis with conventional MDCT. Pronounced coronary calcifications as well as motion or trigger artefacts and high image noise can prevent reliable evaluation. However, preliminary experience indicates that Dual Source CTs are better able to handle these factors than previous scanner generations.
CTA rule-out beneficial in terms of complications and cost
Coronary CT angiography is especially likely to be of benefit in those clinical situations where coronary stenoses need to be ruled out but the pretest likelihood of stenoses is not very high. It may also be very useful in patients with acute chest pain to rapidly assess the presence of stenoses and determine the necessity of further treatment.
The potential clinical utility of coronary CTA in these situations has been reported in a recent scientific statement by the American Heart Association and is also supported by a multi-society consensus paper on the appropriate use criteria for cardiac imaging. While not specifically mentioned in these documents, Dual Source CT has substantially improved image quality and should allow for more widespread clinical application of coronary CT angiography.
Authors: Stephan Achenbach, Axel Kuettner, Dieter Ropers
See corresponding cases: Ruling out coronary stenosis in acute chest pain, Diagnosis of a coronary occlusion in a patient with atypical chest pain
See corresponding protocol: Coronary CT Angiography
