Effect of Mo-99 breakthrough on gamma camera images

Mo-99 breakthrough from Mo-99/Tc-99m generation is rare, but may reach levels --1,000 times the regulatory limit of 0.15 μCi Mo-99/mCi Tc-99m. The effect of various levels of Mo-99 contamination on Tc-99m image quality due to partially absorbed Mo-99 photons was observed. With a Schramm head phantom, at and above 150 μCi/mCi, count rate saturation occurs, the phantom is not seen, and camera-dependent streak artifacts occur. Above 15 μCi/mCi, the image is degraded by the loss of 5 mm features at the collimator face, or by the loss of 8 mm features and 20% contrast steps at 10 cm from the face. At 1.5 μCi/mCi a 20% deadtime loss was still observed. In linespread functions at 15 μCi/mCi, septal penetration tails double the full width hundredth maximum. Thus, in addition to a high radiation dose (--50 rad/mCi Mo-99 to the liver), the diagnostic usefulness of the clinical image would be compromised