Which detector is used by SPECT imaging?

• A. Gamma camera
• B. PET detector
• C. MRI coil
• D. Ultrasound transducer

Answer: (A)

In SPECT imaging, the detector needs to register individual gamma photons emitted by the radiotracer inside the body. A gamma camera is designed for exactly this task. It uses a sodium iodide crystal that scintillates when struck by a gamma photon, producing light, which is then picked up by an array of photomultiplier tubes to locate where the interaction occurred. A collimator sits in front to ensure photons are detected from specific directions, providing spatial information. By rotating the camera around the patient and collecting projections from multiple angles, you can reconstruct a three-dimensional distribution of radiotracer uptake.

This is why the gamma camera is the detector used in SPECT. PET detectors, in contrast, are built to detect pairs of photons from positron annihilation and use coincidence timing, which is a different imaging approach. MRI coils and ultrasound transducers are used for MRI and ultrasound imaging, respectively, not for gamma-ray detection in SPECT.