Ultra-Fast List-Mode Reconstruction of Short PET Frames and Example Applications.

Standard clinical reconstructions usually require several minutes to complete, which is mostly independent of the duration of the data being reconstructed. Applications such as data-driven motion estimation which require many short frames over the duration of the scan become unfeasible with such long reconstruction times. In this work we present an infrastructure whereby ultra-fast list-mode reconstructions of very short frames (≤ 1 sec) are performed. With this infrastructure it is possible to have a dynamic series of frames which can be used for various applications, such as data-driven motion estimation, whole-body surveys, quick reconstructions of gated data to select the optimal gate for a given attenuation map, and, if the infrastructure runs simultaneously with the scan, real-time display of the reconstructed data during the scan and automated alerts for patient motion. Methods: A fast ray-tracing TOF projector was implemented and parallelized. The reconstruction parameters were optimized to allow for fast performance: only a few iterations are performed, without point spread function modelling, and scatter correction is not used. The resulting reconstructions are thus not quantitative, but this is acceptable for motion estimation and visualization purposes. Data-driven motion estimation can be performed using image registration, with the resultant motion data being used in a full motion corrected list-mode reconstruction. Results: The infrastructure is shown to provide images which can be used for visualization and gating purposes, and for motion estimation using image registration. A number of case studies are presented including data-driven motion estimation and correction for brain studies, abdominal studies where respiratory and cardiac motion is visible, and a whole-body survey. Video material is provided in the Supplementary Material. Conclusion: The presented infrastructure provides the capability to quickly create a series of very short frames for PET data which can be used in a variety of applications.