Evaluation of spatial resolution and linearity QC tests for modern gamma cameras imaging systems

Objectives The purpose of the study was to evaluate alternative methods and frequencies for assessment of spatial resolution and spatial linearity.

Methods Manufacturer’s service reports from 8 Siemens ECAM and one Siemens Symbia SPECT/CT imaging systems were reviewed from June 2003 through December 2009. Specific issues that would cause spatial non-linearities such as system electronic functions were cataloged. The weekly four-quadrant bar phantom (4-QBP) tests were qualitatively evaluated and deviations were cataloged. Spatial resolution was quantified using data acquired from monthly center of rotation acquisitions. For each detector, a line profile was drawn on the image of the center point source located 20 cm from the low energy high resolution collimator. Spatial resolution for each system was evaluated for consistency.

Results From June 2003 through December 2009, 44 events that may have caused spatial non-linearity were found. Of these events, 72.7% involved changes in the image quality and 27.3% were found by the manufacturer’s computer system checks. None of the potential non-linearity changes were found using the weekly 4-QBP test. Qualitative resolution of all systems was 2.5 mm resolved bars. Assuming the point sources was 20 cm from the collimator, the average resolution of all systems for the year 2009, was 15.8 +/- 1.9 mm. As expected, the measured system resolution of the oldest camera compared to the newest camera system were different, but only borderline statistically significant (p= 0.06). Similarly, imaging systems with the same manufacturing dates had similar spatial resolution measurements (p= 0.94).

Conclusions This study has shown that spatial resolution and spatial non-linearity issues can more accurately be monitored through manufacturer system controls, daily imaging uniformity evaluations, and monthly resolution evaluations