SPECT-CT in myocardial perfusion scintigraphy

The main application of SPECT-CT in Nuclear Cardiology is for attenuation correction AC. The nonuniform attenuation, scatter and distance-dependant resolution are confounding factors inherent in SPECT imaging. The specific effects on myocardial images, due to subdiaphragmatic, or to the breast tissue attenuation present as irreversible or reversible false positive defects - artifacts. They can decrease the specificity of the examinations and increase the inconclusive interpretations. SPECT-CT permits fast creation of attenuation maps (within seconds). The AC improves the diagnostic accuracy, the normalcy rate in patients with low probability of coronary artery disease (CAD), the viability detection and the detection of stenoses in multiple vascular distributions. In order to avoid AC generated artifacts an adequate quality control is mandatory: of body truncation, of patient’s motion, of accurate registration of attenuation maps and emission data. Incorrect fusion of SPECT and CT images can cause serious mistakes. The reduction of equivocal interpretations offers additional benefit in the use of stress-only imaging for patients with low pretest likelihood of CAD, or rest-only imaging in patients with acute chest pain. The review of low-dose CT scan adds important unexpected findings of concomitant extracardiac pathology (e.g. pleural and pericardial effusions, mediastinal masses and pulmonary lesions). Recent equipment development made it possible to introduce, in clinical practice, hybrid SPECT/CT cameras that perform not only CT AC but which also acquire high quality CT-images for the purpose of coronary calcium scoring and CT coronary angiograms. The integration of nuclear cardiac imaging and cardiac CT combines in one setting the assessment of coronary anatomy and perfusion and provides determination of the physiologic significance of lesions.