What are the main categories of nuclear imaging?

• A. Static/planar and dynamic
• B. PET and MRI
• C. CT and MRI
• D. Ultrasound and X-ray

Answer: (B)

Nuclear imaging centers on functional information gathered from radiotracers, rather than just anatomy. The two main modalities are PET and SPECT. PET uses tracers that emit positrons; when these positrons collide with electrons, they produce pairs of gamma photons that the scanner detects, giving highly sensitive, quantitative images of metabolic and molecular processes. SPECT uses tracers that emit single gamma photons, captured by rotating gamma cameras to reconstruct three-dimensional distributions, often showing perfusion or functional status of tissues. MRI, CT, ultrasound, and X-ray are not nuclear imaging—they do not rely on radioactive decay or radiotracers. Therefore, the combination that truly represents the main categories of nuclear imaging is PET and SPECT.