Analysis of the Geometrical and Physical Fluctuations While Performing Intrinsic Uniformity Test for Philips Forte Gamma Camera

Intrinsic flood field uniformity is a fundamental quality control test that is considered as prerequisite for performing clinical routine exams using the gamma camera. Every gamma camera vendor provides recommended geometrical and physical parameters that should be followed while performing this test. Conventional methods using NEMA recommended parameters also can be used as well. The aim of the current study was to analyze the geometrical and physical fluctuations during performing intrinsic uniformity test for the gamma camera. Materials and Methods: The intrinsic uniformity was tested for one detector of Philips Forte dual head gamma camera while changing the following geometrical factors the source distance from the detector face, the point source volume and the off-center in the X axis for the source position. Other physical factors were tested; the numbers of acquired counts and the matrix size used in the acquisition protocol, all tests have been done for both integral and differential intrinsic uniformity. The Tc 99m radioactive source was used for performing the tests and it measured using a calibrated dose calibrator. Results showed that the best intrinsic uniformity was found at 200 cm point source to detector face distance, the source position from the center of the detector face in the xaxis should be at the center ( zero shift), the total number of acquired counts during the test should be from 30-60 M count and gives the best results at 30 M counts, the point source volume should be from 0.1 to 0.5 ml and the matrix size used in the acquisition protocol should be adjusted with 512X512 matrix. Conclusion: There were statistically significant differences between the results for each studied factor which indicates that there is an optimum value that should be used in each test at which the best integral and differential uniformity results were measured, deviation from this value lead to deterioration of the integral and differential uniformity as well, which in turn will affect the clinical image. Also there are acceptable limits by which the results of the test could be accepted for each factor studied according to the NEMA specifications of the studied (Philips, Forte) gamma camera.