Discovery NM — Engineer Field Guide

Top failure modes

1. Crystal hygroscopic damage — NaI(Tl) is hygroscopic. Any seal breach → crystal clouding → ruined image quality. Replacement = factory event.
2. PMT gain drift — uniformity calibration shifts. Monthly flood QC catches it; tuning resolves most drift.
3. Center-of-rotation drift — SPECT reconstruction quality depends on it. Calibration phantom every 6 months.
4. Collimator damage — drops deform the lead foil. Inspect after every collimator swap.
5. CZT pixel drop-out (530c) — cumulative, not reversible. Track pixel count over time.

Accepting a refurbished Discovery NM

• Extrinsic flood uniformity report (all collimators)
• Intrinsic flood uniformity
• Center-of-rotation calibration
• Energy resolution at 140 keV
• Collimator set inventory
• Crystal integrity (no visible clouding)
• NRC license transferability