Physical attributes, limitations, and future potential for PET and SPECT

Advances in SPECT and PET imaging hardware, software, and radiotracers are vastly improving the non-invasive evaluation of myocardial perfusion and function. In contrast to traditional dual-headed, sodium iodide crystal and photomultiplier cameras with mechanical collimators, new SPECT camera designs utilize novel, collimators, and solid-state detectors that convert photons directly to electrical signals. These cameras simultaneously collect data from as many as 76 small detectors narrowly focused on the heart. New noise regularization and resolution recovery/noise reduction reconstruction software interprets emitted counts more efficiently and thus more effectively discriminates between useful signals and noise. As a result, shorter acquisition times and/or lower tracer doses produce higher quality SPECT images than were possible before. PET perfusion imaging has benefitted from the introduction of novel detectors that now allow true 3D imaging, new radiopharmaceuticals, and precise attenuation correction (AC). These developments have resulted in perfusion images with higher spatial and contrast resolution that may be acquired in shorter protocols and/or with less patient radiation exposure than traditional SPECT. Hybrid SPECT/CT and PET/CT cameras utilize transmission computed tomographic (CT) scans for AC, and offer the additional clinical advantages of evaluating coronary calcium, myocardial anatomy (including non-invasive CT angiography), myocardial function, and myocardial perfusion in a single imaging procedure.