Computed Tomography for Nuclear Medicine (NMTCB(CT))
Core concepts
This post-primary domain covers CT physics and operation as it applies to hybrid SPECT/CT and PET/CT. You need CT numbers (Hounsfield units), window width and level, reconstruction kernels, pitch, collimation, and dose metrics (CTDIvol, DLP).
Hounsfield units anchor interpretation: water is 0, air about −1000, dense bone up to +1000 and beyond, fat negative. Window level sets the center (brightness) and window width sets the contrast range; a narrow window exaggerates soft-tissue differences but clips extremes.
Technique and dose
Pitch equals table travel per gantry rotation divided by beam width. Higher pitch lowers dose and scan time but can affect image noise and slice coverage. Understand mA modulation, kV selection, and how iterative reconstruction reduces noise at lower dose. Know that CTDIvol reflects dose per volume scanned while DLP integrates over length; effective dose follows DLP times a region-specific conversion factor.
Hybrid workflow
CT provides attenuation correction and anatomic localization. Be able to explain misregistration artifacts from patient motion or breathing, metal and contrast artifacts, and why oral or IV contrast can alter attenuation maps. Truncation and beam-hardening artifacts are common question targets.
Rule of thumb
If a structure measures near 0 HU it is fluid or water density; near −100 HU it is fat; above +300 HU it is bone, metal, or dense contrast. Use HU ranges to answer tissue-identification items quickly.