A medical physicist is compiling a safety and training manual comparing different diagnostic imaging modalities. Which of the following statements correctly identifies the imaging technique, its primary physical detection mechanism, and its radiation hazard classification?
PET scan: Detects coincident 0.511 MeV0.511\text{ MeV}0.511 MeV gamma-ray photon pairs emitted during positron-electron annihilation; classified as ionising radiation.
MRI scan: Detects the relaxation of precessing hydrogen nuclei stimulated by pulsed microwave radiation; classified as non-ionising radiation.
CT scan: Detects the spatial attenuation of rotating, highly coherent optical laser beams; classified as ionising radiation.
A-scan Ultrasound: Detects the Doppler frequency shift of reflected shear waves to determine tissue boundaries; classified as non-ionising radiation.
