SPECT

 

SPECT (Single Photon Emission Computed Tomography) is used in myocardial perfusion imaging (MPI) and is currently the most common imaging modality used in nuclear cardiology.  During the past three decades, cardiac SPECT imaging has made advances in several areas, including diagnostic accuracy, optimising image quality and reducing radiation exposure.  According to the American Society of Nuclear Cardiology (ASNC) regarding SPECT imaging guidelines which address instrumentation, acquisition, processing and interpretation, this is in addition to stress, protocols, and tracers. The configuration of most SPECT systems use dual-detectors which possess parallel-hole collimation.  The scintillation cameras contain sodium iodide and are fixed at right angles to each other. This configuration produces acquisition greater than 180° with an associated gantry rotation of 90°. To carry out nuclear cardiology, the detectors are fixed at 90°. However, for cardiac imaging, the large field-of-view detectors are set at  90° and  180° for a broad range of nuclear medicine procedures.  However, this set has not changed very much although advances in reconstruction algorithms and processing techniques have significantly improved performance.  The more modern SPECT scanners have increased photon sensitivity through the use of high-sensitivity collimation and multiple detectors to perform a cardio centric or heart-centred acquisitions.  However, for high-sensitivity SPECT imaging cadmium zinc telluride (CZT) solid-state detectors are used with a different collimation set-up. The main advantage of the CZT  detector is that it provides improvement to the energy resolution than NaI scintillation and can be used to construct compact pixelated detector modules, where each pixel (a single CZT crystal 2.46 mm on each side) is smaller than the intrinsic resolution of a NaI scintillation camera.  Clinical CZT systems achieve energy resolution greater than 7%, compared to about 11% for a conventional scintillation camera. Both systems use detectors based on modular units of 16 x 16 CZT pixels but in different arrangements.