Whole-body motion correction in 13N-ammonia myocardial perfusion imaging using positron emission tracking

Patient motion during positron emission tomography (PET) studies leads to degradation of image quality. Not only does patient motion lead to blurring of regions of tracer uptake but it can also lead to mis-alignment artifacts associated with spatial mis-registration between the emission and transmission data used for attenuation correction. In this study we examine the benefits of a three-dimensional whole-body motion correction algorithm based on the use of tracking external radioactive markers placed on the patient. We used the positron emission tracking (PeTrack) algorithm to estimate translational patient motion for three patients who underwent
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N-ammonia myocardial perfusion imaging studies at rest and stress. PeTrack was used to identify instances of whole-body patient motion and its extent with respect to a reference position. This information was used to bin the raw list-mode data based on patient-motion amplitudes. The resulting set of gated emission data were reconstructed after using the PeTrack data to rigidly align the attenuation image to each gate. The final set of images were then re-aligned to the reference position. The weighted average of the individual gated images produces the final motion-corrected static image. This approach was evaluated by comparing the relative perfusion in the three arterial regions of the left-ventricular (LV) polar maps. Additionally, regional LV wall thickness and blood pool volume were measured. Whole-body motion in this small sample was limited and largely returned to the reference position. When considering rest and stress acquisitions, no statistically significant differences were observed for any of the metrics. LV wall thicknesses were significantly reduced after motion correction for the stress cases which exhibited the greatest motion. The benefits of motion correction may not be realized unless the extent of whole-body patient motion is large and/or non-returning. Our study demonstrated successful motion tracking using PeTrack, but this work must be extended to include more cases with more severe motion is indicated.