Medical Physicist's Notes · Co-57 Flood Source
A daily flood, a weekly NEMA measurement —and the action path when a test fails.
The daily flood catches the obvious problems before the morning list begins; the weekly quantitative measurement catches the slow drift before it becomes a daily failure. The action path turns a uniformity failure into a documented response, not a guessed one. Three columns below — each sourced to AAPM TG-22 / TG-150 and NEMA NU-1-2007.
Three lanes of the uniformity QA workflow
Daily routine on the left, weekly quantitative in the middle, failure-response action path on the right.
Before the morning list — daily flood
- Source removed from lead carry case after the camera has warmed up
- Source placed centred on the detector (intrinsic — collimator removed; or extrinsic — collimator on)
- Acquire flood with the daily-QA recipe (typically 5–10 M counts, Tc-99m window with ±10 %)
- Visual review of the flood for obvious cold/hot spots, dead PMTs or detector damage
- Action: pass / fail logged in the daily QA log; threshold-failure routes per the SOP
- Source returned to the lead carry case; activity-decay note updated
Source: AAPM TG-22 / TG-150 SPECT QA guidance; site SOP.
Weekly — NEMA NU-1 quantitative flood
- Higher-count acquisition (typically 30 M+ counts) for quantitative analysis
- Software calculates integral and differential uniformity per NEMA NU-1-2007
- IU (integral) and DU (differential) values logged; trending plotted against last 12 weeks
- Compare to vendor specification + AAPM action thresholds (typically IU ≤ 3 %, DU ≤ 2 %)
- Drift toward threshold triggers root-cause analysis before failure event
- Result archived in the QA dossier for the annual physics report
Source: NEMA NU-1-2007 § Uniformity; AAPM TG-150 SPECT QA.
When a uniformity test fails
- Confirm the failure: re-acquire with the same recipe to rule out a single-event glitch
- Inspect for source-side causes: source positioning, source decay (compare activity to certificate)
- Inspect for camera-side causes: PMT gain map, energy-peak drift, crystal damage
- If the camera fails the action threshold, suspend patient imaging on that detector head
- Notify service; document the failure, the immediate action and the restoration verification
- Re-baseline uniformity after any PMT or crystal-related service work
Source: AAPM TG-22 / TG-150; AERB Safety Code for Nuclear Medicine Facility.
Scope of this page
The cadence, count thresholds and action levels above are typical for clinical SPECT cameras and align with AAPM TG-22 / TG-150 and NEMA NU-1-2007. The exact daily count target, the IU / DU action threshold and the trending plot format vary by vendor and by department SOP — confirm against the site's QA programme document and the camera vendor's recommended specification before adopting verbatim.
Sources cited on this page
- National Electrical Manufacturers Association.NEMA NU-1-2007 — Performance Measurements of Gamma Cameras. NEMA, 2007.
- American Association of Physicists in Medicine.AAPM TG-22 / TG-150 — SPECT QA guidance.
- Atomic Energy Regulatory Board (India).Safety Code for Nuclear Medicine Facility.AERB PDF ↗