List-mode-based reconstruction for respiratory motion correction in PET using non-rigid body transformations

Abstract

Respiratory motion in emission tomography leads to reduced image quality. Developed correction methodology has been concentrating on the use of respiratory synchronized acquisitions leading to gated frames. Such frames, however, are of low signal-to-noise ratio as a result of containing reduced statistics. In this work, we describe the implementation of an elastic transformation within a list-mode-based reconstruction for the correction of respiratory motion over the thorax, allowing the use of all data available throughout a respiratory motion average acquisition. The developed algorithm was evaluated using datasets of the NCAT phantom generated at different points throughout the respiratory cycle. List-mode-data-based PET-simulated frames were subsequently produced by combining the NCAT datasets with Monte Carlo simulation. A non-rigid registration algorithm based on B-spline basis functions was employed to derive transformation parameters accounting for the respiratory motion using the NCAT dynamic CT images. The displacement matrices derived were subsequently applied during the image reconstruction of the original emission list mode data. Two different implementations for the incorporation of the elastic transformations within the one-pass list mode EM (OPL-EM) algorithm were developed and evaluated. The corrected images were compared with those produced using an affine transformation of list mode data prior to reconstruction, as well as with uncorrected respiratory motion average images. Results demonstrate that although both correction techniques considered lead to significant improvements in accounting for respiratory motion artefacts in the lung fields, the elastic-transformation-based correction leads to a more uniform improvement across the lungs for different lesion sizes and locations.

The Use of Anatomical Information for Molecular Image Reconstruction Algorithms: Attenuation/Scatter Correction, Motion Compensation, and Noise Reduction

“…The third method is to incorporate motion information into the measurement model [35,36,[95][96][97], called parametric motion model (PMM) [92,93]. The gated measurement model (10) can be combined with Eq.…”

“…However, joint estimation methods require high computation complexity. Motion estimation from gated 4D CT was considered in [35,36], but radiation dose and motion mismatch due to sequential acquisition of CT and PET (or SPECT) were major concerns. Recent advances in simultaneous PET-MR showed potentials to estimate accurate motion from highresolution MR images without additional radiation dose and achieved substantial quantitative improvements in PET imaging [37][38][39][40].…”

“…More recently, using the fact that molecular and anatomical images are affected by the same motion, motion correction for emission tomography has been investigated. Motion information from high-resolution anatomical information such as CT [35,36] or MR [37][38][39][40] was incorporated into reconstruction for motion-corrected PET or SPECT. Ideas of using structural couplings between molecular and anatomical images for reconstruction have been studied a couple of decades ago [41][42][43].…”

Self-gated Radial MRI for Respiratory Motion Compensation on Hybrid PET/MR Systems

“…The non-linear reconstruction may recover such small structures in the former case, but fail to do so in the latter. Here, applying the motion compensation already during rather than after PET reconstruction [12] promises improved sensitivity.…”

“…The PET gates are reconstructed using conventional algorithms, then warped to a common respiratory phase, and finally averaged [4,6]. We followed this approach rather than incorporating the motion model directly into the PET reconstruction, as recently suggested in literature [7,[12][13][14], because we focused on the formation of the motion model in this work. The utilized post-reconstruction registration approach is well-studied, reproducible, and provides comparable results given that the respiratory bins have similar and sufficient count statistics [13][14][15].…”