Evaluation of a pinhole collimator for I-131 SPECT head imaging

The performance of a pinhole collimator for I-131 SPECT of the head was evaluated. The evaluation included planar and SPECT spatial resolution, sensitivity in air and in water, septal penetration, reconstructed image quality, and activity quantitation within a simple phantom that models tumor uptake in the head. The pinhole collimator was compared to medium and high energy parallel hole collimators. The pinhole collimator demonstrated improved resolution/sensitivity tradeoff compared with the parallel hole collimators over the range of distances relevant to head imaging. In planar point source images the pinhole collimator showed reduced penetration effects although in reconstructed images penetration effects were not apparent for either pinhole or high energy parallel hole collimators. Comparable activity quantitation accuracy was observed with all collimators. The accuracy was dependent on the segmentation threshold and calibration procedure. These results indicate that the pinhole collimator can provide improved performance conventional parallel hole collimators for I-131 imaging in the head.