Investigation of angular smoothing of PET data

Radial filtering of emission and transmission data is routinely performed in PET during reconstruction in order to reduce image noise. Angular smoothing is not typically done, due to the introduction of a non-uniform resolution loss. The goal of this paper was to assess the effects of angular smoothing on noise and resolution. Angular smoothing was incorporated into the reconstruction process on the Scanditronix PC2048-15B brain PET scanner. In-plane spatial resolution and noise reduction were measured for different amounts of radial and angular smoothing. For radial positions away from the center of the scanner, noise reduction and degraded tangential resolution with negligible loss of radial resolution were seen. Near the center, no resolution loss was observed, but there was also no reduction in noise even for large amounts of angular filtering. These results can be understood by recognizing that angular filtering is equivalent to a weighted sum of rotated images. We conclude that angular smoothing is not optimal due to its anisotropic noise reduction and resolution degradation properties.