SPECT-CT in the diagnosis of coronary artery disease

Two-dimensional invasive coronary angiography (ICA), although showing high temporal and spatial resolution, is neither able to predict the physiologic relevance of a stenosis nor able to determine the prognosis of both symptomatic and asymptomatic patients. Therefore, the ICA can hardly represent the sole gold standard in clinical decision making. Additionally, the small but distinct morbidity and mortality rate of this method and the inconvenience of patients undergoing ICA have strengthened the search for a non-invasive alternative. Recent publications have shown high accuracy for spiral computed tomography (MDCT) angiography acquired with a 64-slice CT scanner compared to ICA in detecting 'obstructive' coronary artery disease, defined as stenosis of more than 50%. Otherwise, although well known limitations of MDCT like motion artifacts or severe vessel calcifications could be clearly reduced with the newest scanner generation, this technique lacks of delivering exact lumen quantification compared to ICA in a clinical setting. Furthermore, there is evidence that exact quantification of coronary artery stenoses is of minor impact on clinical decision making, if lesion location and functional status are known. A first publication showed that combined imaging of MDCT angiography and PET myocardinal perfusion scanning with [13N]ammonia was feasible with an integrated PET/CT scanner and reported high sensitivity and specificity to detect hemodynamically relevant coronary artery stenoses compared to the combination of PET plus ICA. However, PET perfusion tracers are not widely available at present and the well accepted reference for detecting myocardial ischemia, based on numerous publications, is myocardial perfusion SPECT (MPI). MPI is an established method for the non-invasive assessment of functional significance of coronary stenoses and delivers valuable information for risk stratification. Patients with stable angina and normal stress sestamibi SPECT have a very low risk of death or fatal myocardial infarction (MI), therefore no intervention is required for these patients. According to the current guidelines for management of patients with chronic stable angina, both morphological and functional information about the coronary artery tree should be present before revascularization therapy is performed. The combination of 64-slice CT angiography plus gated myocardial SPECT could provide both non-invasive three-dimensional anatomical and functional information of the coronary artery tree. (orig.)