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 advanced in several areas, including diagnostic accuracy, optimising image quality and reducing radiation exposure.
According to the American Society of Nuclear Cardiology (ASNC), SPECT imaging guidelines address instrumentation, acquisition, processing, interpretation, stress, protocols, and tracers. The configuration of most SPECT systems uses 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 much, although advances in reconstruction algorithms and processing techniques have significantly improved performance. Modern SPECT scanners have increased photon sensitivity by using high-sensitivity collimation and multiple detectors to perform a cardio-centric or heart-centred acquisition. However, cadmium zinc telluride (CZT) solid-state detectors are used with a different collimation setup for high-sensitivity SPECT imaging.
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.
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