Which imaging modality uses gamma-emitting isotopes to create three-dimensional images showing tissue perfusion?

• A. Angiography
• B. Single Photon Emission Computed Tomography
• C. MRI
• D. EEG

Answer: (B)

This item is about imaging that visualizes how blood is reaching tissues in three dimensions using radioactive tracers. Gamma-emitting radiotracers are given to the patient, and detectors pick up the gamma photons they emit. By rotating the detectors around the body and reconstructing the data with computer algorithms, a three-dimensional map of tracer distribution is produced, which reflects tissue perfusion—the blood flow to tissues. This approach is characteristic of Single Photon Emission Computed Tomography, which uses tracers such as technetium-99m compounds or thallium-201 for perfusion imaging in the brain or heart.

In contrast, angiography relies on X-ray imaging with contrast to visualize vessels; MRI uses magnetic fields and radiofrequency signals to create detailed structural and sometimes functional images; EEG records electrical activity from the brain. So the modality described by three-dimensional perfusion imaging with gamma-emitting isotopes is SPECT.