Infographics / Nuclear Medicine

NaI(Tl) crystal: thickness vs resolution/sensitivity

Cross-section of a gamma camera head. A 140 keV photon is absorbed by the photoelectric effect in a single monolithic sodium iodide (thallium) crystal, producing a burst of about 5000 scintillation light photons that spread through a flat transparent light guide onto several photomultiplier tubes. The crystal is hygroscopic and brittle, so it is hermetically sealed in an aluminium housing. A trade-off panel shows that a thinner crystal gives better intrinsic spatial resolution (narrow light spread) while a thicker crystal gives higher detection efficiency but wider light spread and more depth-of-interaction blur.