Comparison: PET, PET-MRI, SPECT and Dual-Energy CT

Feature	PET	PET-MRI	SPECT	Dual-Energy CT
Type	Nuclear (functional)	Hybrid functional plus soft-tissue anatomy	Nuclear (functional)	Anatomical plus material information
Source	Positron emitter (F-18 FDG), annihilation gives two 511 keV gamma rays	Same as PET plus magnetic field and RF	Gamma emitters (Tc-99m, I-123)	X-ray tube at two energies (e.g. 80 and 140 kVp)
Detection	Ring of detectors, coincidence detection	PET detectors (SiPM) inside MRI	Gamma camera rotating, collimator	Dual-source, fast kVp switching or dual-layer detector
Resolution	About 4 to 6 mm	PET about 4 mm, MRI sub-mm	About 8 to 12 mm	Sub-mm
Sensitivity	High	High	Lower	High
Radiation dose	Moderate	Lower than PET-CT (no CT dose)	Moderate	Similar to CT, can be reduced
Time	About 20 to 30 min	Long (60 min)	30 to 60 min	Seconds
Main use	Cancer staging, brain, heart metabolism	Brain, prostate, paediatric oncology, soft tissue	Bone scan, myocardial perfusion, thyroid	Material separation: kidney stones, gout, iodine maps, metal artefact reduction
Cost	High	Very high	Moderate	Moderate to high

Exam tip

Tabulate source, detection, resolution and uses; mention PET-MRI avoids CT radiation.