Rotating quadrant slant-hole SPECT scintimammography: an initial investigation

Abstract

The authors investigate the use of rotating quadrant slant-hole (RQSH) collimation in SPECT scintimammography (SM). A RQSH collimator is able to acquire a complete set of projection data for fully 3-D reconstruction of the breast with 90 degrees of collimator rotation at each of 2-3 collimator detector positions on a 90-120 degree arc around the breast. The use of a 90-120 degree arc allows the collimator to remain close to the breast throughout the data acquisition, providing better resolution in the reconstructed image as compared to the conventional parallel-hole collimation SPECT acquisition. In addition, a RQSH collimator for SPECT SM has 2.8-3.5 times the efficiency of a conventional parallel-hole collimator with equivalent spatial resolution. While the field-of-view of each quadrant of the RQSH collimator can encompass a medium sized breast, significant truncation of the body occurs. It is essential that the collimator design parameters and the data acquisition orbit be chosen in such a way as to minimize the effect of truncation on the reconstruction of the breast. Here, the authors investigate the choice of collimator design parameters and data acquisition orbits for RQSH SPECT SM. These initial experiments are performed using the 3-D mathematical cardiac torso (MCAT) phantom with a realistic medium sized breast model. The reconstructions are performed using an iterative ML-EM algorithm and transformation based projector/back-projector pair. The results indicate that while the projection images are severely truncated when using the RQSH collimator, appropriate collimator design parameters and data acquisition orbits can be chosen to limit the effects of truncation on the reconstruction of the breast region.