- Single-Photon Emission Computed Tomography (SPECT) is a nuclear medicine imaging technique that provides three-dimensional (3D) functional information about organs and tissues in the body. It works by detecting gamma rays emitted from radiopharmaceuticals—radioactive compounds administered to the patient—which accumulate in specific organs depending on their biological characteristics. By rotating gamma cameras around the body and capturing radiation from multiple angles, SPECT reconstructs cross-sectional images that reflect physiological activity rather than just anatomical structure.
- SPECT imaging is especially useful for evaluating blood flow, metabolism, and receptor binding in tissues, making it widely applicable in cardiology, neurology, and oncology. In cardiology, SPECT is commonly used for myocardial perfusion imaging, which assesses blood flow to the heart muscle during stress and rest, helping to diagnose coronary artery disease and determine the extent of tissue damage after a heart attack. In neurology, SPECT aids in the evaluation of epilepsy, dementia, Parkinson’s disease, and cerebral blood flow abnormalities, providing insight into brain function that may not be evident through CT or MRI. In oncology, SPECT is used to detect bone metastases, thyroid cancer, and certain types of neuroendocrine tumors.
- The radiopharmaceuticals used in SPECT typically emit single gamma photons and include isotopes such as technetium-99m (⁹⁹ᵐTc), iodine-123, and thallium-201, among others. Once administered, the gamma camera rotates 360 degrees around the patient to collect emission data. This data is processed using computer algorithms to create detailed images in axial, sagittal, and coronal planes. These images allow physicians to observe physiological processes in vivo, detect functional abnormalities, and monitor treatment effectiveness.
- One of the advantages of SPECT is its relatively low cost and broad availability compared to PET imaging. It also has a longer history of clinical use and a wide range of available radiotracers tailored to specific diagnostic needs. However, SPECT typically has lower spatial resolution and sensitivity than PET, which may limit its ability to detect very small or low-activity lesions. Nonetheless, the development of SPECT/CT hybrid scanners, which combine functional imaging with precise anatomical localization, has significantly enhanced diagnostic accuracy and interpretation.
- SPECT is generally safe, with minimal side effects. The amount of radiation exposure is low and considered acceptable in clinical settings, though appropriate precautions are taken, especially in children and pregnant patients. The choice of radiopharmaceutical and imaging protocol depends on the specific clinical question and the organ system being evaluated.
