Understanding Single Photon Emission Computed Tomography Imaging and its Medical Applications
Single Photon Emission Computed Tomography, commonly referred to as SPECT imaging, is a type of nuclear imaging technology that uses radioisotopes to produce three-dimensional images of internal organs and structures within the body. In SPECT imaging, a small amount of radioactive tracer is injected into the body and then detected by a SPECT camera, providing information about organ function and blood flow.
How does SPECT Imaging Work?
SPECT imaging relies on radioactive tracers that are selectively absorbed by specific tissues, organs or cells. Common radioactive tracers used in SPECT include technetium-99m (Tc-99m), gallium-67 (Ga-67) and thallium-201 (Tl-201). Once injected into the body, the tracer accumulates in organs or areas of interest and releases gamma ray photons. A circular gantry, containing one or more detector heads that rotate around the patient, detects these gamma rays and processes the information. Computer software then analyzes this data and reconstructs three-dimensional images of the tracer concentration within the body’s internal structures. Areas where the radioactive tracer accumulates appear bright in the images, while areas with less radioactivity appear dim.
What Can Single Photon Emission Computed Tomography Imaging Diagnose?
Some of the most common clinical applications of SPECT imaging include:
Cardiac imaging – Single Photon Emission Computed Tomography can detect reduced blood flow to the heart muscle and is often used to help diagnose coronary artery disease. It is also used to help predict heart disease risks and guide treatment decisions. Myocardial perfusion SPECT provides information on both the location and severity of any reduced blood flow to the heart muscle.
Brain imaging – Functional brain SPECT imaging is useful for evaluating cerebrovascular disorders, dementia, seizures and brain tumors. It can show areas of abnormal blood flow or chemical activity in the brain.
Bone imaging – Nuclear bone scanning with tracers like Tc-99m are commonly used to identify and evaluate bone fractures, bone infections or tumors. It is very sensitive for identifying abnormal areas of increased or decreased bone activity throughout the entire skeletal system.
Lung imaging – Ventilation/perfusion lung scanning with agents like Tc-99m evaluates for conditions like pulmonary embolism, which appears as a defect on the scan where a blood clot has blocked a pulmonary blood vessel.
Thyroid imaging – SPECT imaging with radioactive iodine can detect abnormalities in the thyroid gland like nodules, inflammation or cancer. It evaluates both thyroid function and anatomy.
Liver and spleen imaging – Functional liver and spleen SPECT scans are useful for conditions like hepatitis, cirrhosis or tumors. Tracers accumulate differently in normal versus abnormal liver and spleen tissue.
Sentinel lymph node biopsy – Radioactive tracers can be injected near a tumor to map the sentinel (first) lymph node it drains to. This helps surgeons locate and biopsy sentinel nodes to stage cancers like breast and melanoma.
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