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

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 ↗

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Co-57 in plain English

Why Co-57 at 122 keV is the daily QA stand-in for the Tc-99m window; NEMA NU-1 thresholds.

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Specs and AERB documentation

Sizing options, NEMA / ANSI compliance, lead-shielded carry case, AERB sealed-source path.