Patient motion correction for multicamera SPECT using 360° acquisition/detector

Conventional partial orbit SPECT acquisition (90°, 120° or 180° depending on number of camera heads) on multihead cameras enhance the problems caused by patient motion or change in organ position ("cardiac creep"), since the misplaced data are present at several intervals in the projection set. The authors investigated the effects of source motion and developed new image motion correction methods based on 360° acquisition of each detector on a three camera SPECT system. Experimental measurements with point sources and cardiac phantom were used to evaluate the influence of source motion on SPECT images. A point source phantom was rotated 5-30° CCW and moved axially 0.5-4.0 cm. A cardiac phantom was moved in laterally (0.5-4.0 cm) and in the axial direction (0.5-4.0 cm). Cross-correlation of images from different heads at the same angular position is used to detect and correct for motion. Two correction methods were investigated: (1) summation of complete 360° projection sets without correction, (2) time normalization of projection frames without motion to replace frames affected by motion. The first method corrects for small displacement of the source (<0.5 cm translation and <5° rotation). The second method significantly decreases degradation in image quality and can reduce or eliminate losses in accuracy of quantitative indices calculated from image data since uncorrupted data sets at each angular position are available and used for correction. The proposed method with 360° rotation successfully corrects for arbitrary motion (translations and/or rotations).