Practical gamma camera quality control with a four-point phantom

A gamma camera QC phantom for practical assessment of resolution (average FWHM), spatial calibration (pixels/mm), nonhomogeneity of spatial calibration, and average point-source sensitivity (cpm/μCi) was developed and evaluated. The phantom consists of four ⁵⁷Co-point sources mounted on a Plexiglas base at corners of a square 10 cm on each side. Computer acquisition and processing are fully automated annd require less than 1 min for point sources totaling 100 μCi (3.7 MBq) activity. The normal range of variability of measured QC parameters from a 12 wk evaluation period with four different gamma cameras (assumed to be operating normally) yielded coefficients of variation ranging from 0.3% for spatial calibration (pixels/mm) to 2.3% for sensitivity (cpm/μCi) assessments. From the normal range of variability a minimum detectable difference (MDD) was determined for each measured parameter and each gamma camera. The range of acceptable operation of a gamma camera system was set as the measured value +/-MDD for each QC parameter. The ability to detect and track small changes in the measured QC parameters was evaluated.