There have been tremendous advances in technology in the field of nuclear medicine, over the past decade.1 In particular, there has been significant growth in hybrid single photon emission computed tomography and computed tomography (SPECT–CT) and positron emission tomography computed tomography (PET–CT) systems driven in large part by oncologic imaging. A fortuitous byproduct of this has been the development, application, and validation of myocardial perfusion imaging (MPI) using these hybrid systems. Cardiac hybrid SPECT–CT and PET–CT systems offer certain advantages compared with traditional SPECT or PET imaging. The use of CT-based attenuation correction improves the sensitivity and specificity of MPI over non-attenuation-corrected imaging. The addition of a coronary calcium score also adds incremental diagnostic and prognostic information. Hybrid PET–CT scanners offer the ability to combine a physiologic assessment of perfusion, function, or metabolism with an anatomic assessment of atherosclerosis and structural heart disease. By doing so, hybrid PET–CT imaging offers tremendous opportunities for molecular cardiology research. On-going and future research will help define the role of SPECT–CT and PET–CT in the diagnosis and management of patients with cardiovascular disease. The primary focus of this chapter is to discuss the clinical applications of hybrid SPECT–CT and PET–CT imaging of the heart.
All SPECT–CT and PET–CT scanners offer CT-based attenuation correction. The hardware of SPECT–CT and PET–CT scanners comprises of a conventional SPECT scanner or a PET scanner coupled with a CT scanner of various configurations. Based on the configuration of the CT scanner, calcium scoring and CT coronary angiography may be performed on hybrid SPECT–CT and PET–CT scanners (≥4 or ≥16-slice MDCT, respectively). Sample hybrid SPECT–CT and PET–CT protocols are shown in Fig. 13-1A and B. The CT coronary angiogram study can be performed sequentially right after the SPECT or PET scan or at a separate setting.
(A and B) Sample protocols for PET/CT and SPECT/CT myocardial perfusion imaging. CTAC: CT for AC (10 mA, 120 keV, non-gated free breathing); CAC: calcium score CT scan (300 mA, 140 keV, ECG-gated CT scan with breath hold).
ATTENUATION CORRECTON WITH CT FOR BOTH SPECT AND PET
After myocardial uptake of a radiotracer, the emitted photons must traverse various soft tissue structures (adipose tissue, muscle mass, bone, diaphragm, and breast tissue) before reaching the photodetectors of the gamma camera. In transit, the photons can get attenuated (absorbed or deflected by soft tissues), resulting in lower sensitivity and specificity for the detection of coronary artery disease (CAD).1 Various strategies have been devised to address attenuation including measurement and correction of soft tissue densities using transmission scanning employing external radioactive sources or cardiac CT. Attenuation correction improves the count uniformity of the image and helps distinguish attenuation artifacts from real defects. It also offers the possibility of stress-only imaging (if ...