Spect

Single Photon Emission Computed Tomography (SPECT) is a nuclear medicine imaging technique that provides functional information about physiological processes. After administration of a gamma-emitting radiopharmaceutical, a gamma camera rotates around the patient to acquire multiple projections, which are reconstructed into three-dimensional images of tracer distribution.

SPECT relies on single-photon detection and tomographic reconstruction, using methods such as filtered back projection or iterative algorithms to produce volumetric images that can be fused with anatomy for localization of abnormalities.

Common radiopharmaceuticals include technetium-99m–labeled compounds for myocardial perfusion (sestamibi, tetrofosmin), 99mTc-HMPAO or 99mTc-ECD for brain perfusion, and 99mTc-labeled phosphonates for bone imaging. Additional tracers enable thyroid, infection, and organ-specific studies.

Hybrid systems combining SPECT with CT (SPECT/CT) provide attenuation correction and anatomical localization, improving diagnostic accuracy.

Compared with PET, SPECT generally offers lower spatial resolution and quantitative accuracy but benefits from broader availability, lower cost, and a wide range of radiopharmaceuticals. Advances in detectors and reconstruction have narrowed the gap in image quality.

Clinical applications include cardiology, neurology, oncology, and inflammatory or infectious disease imaging. Radiation exposure from radiopharmaceuticals is a consideration, with dose depending on tracer, activity, and protocol.

History: SPECT emerged from rotating gamma cameras and tomographic reconstruction in the late 20th century, building on Anger camera technology to enable functional 3D imaging.