Scattered radiation effects on the extrinsic sensitivity and counting efficiency of a gamma camera

Abstract

An evaluation of the effect of scattered radiation on the performance of a gamma camera is carried out using a specially designed home-made homogeneous circular planar flood source filled with 0.2±0.01GBq of 99mTc solution as a scattering medium. The scatter effects are assessed by analyzing the energy spectrum of 99mTc for the scatter fraction and calculating the camera's extrinsic counting efficiency and sensitivity, for five flood source thicknesses (12, 50, 100, 150 and 200mm ) and three source-to-detector distances (0.7, 0.9 and 1.1m). Results showed an increase in the scatter fraction from 0.29 to 22.96 as the source thickness increased. This increase was associated with a decrease in the extrinsic sensitivity from 121.36 to 49.58counts/sGBq, and a decrease in counting efficiency as from 3.78 to 1.55%. With the increase in source-to-detector distance, the extrinsic sensitivity decreases from 121.36 to 118.77counts/sGBq, while the counting efficiency increases from 3.78 to 11.66%. It was found that a source-to-detector distance of 0.96±9×10−3m is a good compromise for an acceptable extrinsic sensitivity and a reasonable counting efficiency.