Abstract
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Objectives Resolution compensation (RC) through modeling spatial resolution in iterative reconstruction has been shown to enable a reduction of imaging time/administered activity. However, differences in wall localization and shape have been noted clinically with RC that conflicted with the appearance when RC was not included. It has been shown that convergence occurs significantly slower with RC. We investigated the impact of the number of iterations and respiratory motion (RM) to determine if these observed differences could be understood.
Methods Acquisitions of the Data Spectrum torso phantom with heart insert were performed with the BrightView SPECT system. Studies were performed with and without simulated RM using the Quasar motion platform. Acquisitions were made for variations in RM, heart insert orientation, and with and without added breast attenuation. The projections were reconstructed with and without RC using clinical software for a range of iterations.
Results Without RC, the walls were uniform in the absence of motion, and anterior/inferior cooling was seen with RM. With RC, lateral and septal wall cooling were observed without motion for a low iterations. These artifacts decreased with increasing iteration number. With simulated RM, at low iterations the motion induced cooling in the anterior/inferior walls balanced with the cooling in the lateral and septal walls, resulting in relatively uniform slices. As the iteration number increases lateral/inferior cooling returns.
Conclusions SPECT reconstruction employing RC requires a higher number of iterations than without. This enhances noise, but can be compensated by post-smoothing. Clinically the effect of low iteration number can be balanced somewhat by RM, depending on heart angulation and extent of motion. In combination, these effects can mislead readers to prefer low iteration number defaults, which potentially can result in erroneous interpretations.
Research Support This work was supported by the National Institute of Biomedical Imaging and Bioengineering Grant No. R01 EB001457. The contents are solely the responsibility of the authors and do not necessarily represent the official views of the National Institutes of Health