Abstract
Imperfections such as septal tears, improper alignment of channels, and improper seating can be built into collimators at the time of manufacture. The purpose of this study was to compare the collimator uniformity of a high-resolution low-energy foil collimator to that of a similar cast collimator. A 5 mCi point source of technetium-99m (99mTc) placed 5 m from the collimator face was imaged with both collimators. Line sources were imaged at 5 to 30 cm from the collimator face, both above and below the imaging table. A SPECT phantom filled with 10 mCi of 99mTc was imaged with both collimators. Transaxial images were reconstructed, and uniformity corrections were obtained, based on data from each collimator. In the distant point-source images, using the foil collimator, linear streaks and a sizeable cold defect were seen. These almost disappeared in the sheet-source images. Linear streaks were also present in the line-source images. The SPECT images showed small ring artifacts in three areas. None of these defects were seen with the cast collimator. These findings illustrate the importance of properly evaluating the uniformity of each collimator purchased with a new system.
