Quality Assurance, Quality Control, and Equipment Calibration
What the exam tests
QA/QC items test the schedule, acceptance limits, and corrective action for gamma cameras, dose calibrators, survey meters, well counters, and ancillary equipment. You must know what is daily, weekly, quarterly, and annual.
Core rules
- Gamma camera daily QC: energy peak check and flood uniformity (intrinsic or extrinsic), plus background. Uniformity drift affects SPECT reconstruction; document and service if outside limits.
- SPECT QC includes center-of-rotation correction and resolution checks; PET QC includes detector normalization, daily blanks, and calibration.
- Dose calibrator QC: daily constancy, accuracy with a traceable source (commonly ±5%), linearity by decay (commonly ±5–10%), geometry, and annual calibration. Record isotope setting and geometry.
- Survey meters: daily battery/function check with a check source and annual calibration. Well counters: daily background and periodic efficiency.
- Ancillary equipment (thermometers, pipettes, balances) needs scheduled calibration; QA records must be contemporaneous and retrievable.
Worked example
A dose calibrator is set to Tc-99m and a traceable 10.0 mCi standard reads 9.4 mCi. Error = |9.4 − 10.0|/10.0 × 100 = 6%, which exceeds a ±5% limit. The correct response is to investigate geometry, background, source decay, and isotope setting, then recalibrate or service before patient use. The calculation is simple; the exam tests whether you know the acceptance limit and the required action.
Traps that cost marks
- Performing QC after the first patient instead of before use.
- Using the wrong isotope button or source geometry.
- Confusing precision (reproducibility) with accuracy (closeness to true activity).
- Filing an out-of-limit result without corrective action or documentation.