Reconstruction-Incorporated Respiratory Motion Correction in Clinical Simultaneous PET/MR Imaging for Oncology Applications

Abstract

Simultaneous PET and MR imaging is a promising new technique allowing the fusion of functional (PET) and anatomic/functional (MR) information. In the thoracic-abdominal regions, respiratory motion is a major challenge leading to reduced quantitative and qualitative image accuracy. Correction methodologies include the use of gated frames that lead to low signal-to-noise ratio considering the associated low statistics. More advanced correction approaches, previously developed for PET/CT imaging, consist of either registering all the reconstructed gated frames to the reference frame or incorporating motion parameters into the iterative reconstruction process to produce a single motioncompensated PET image. The goal of this work was to compare these two-previously implemented in PET/CT-correction approaches within the context of PET/MR motion correction for oncology applications using clinical 4-dimensional PET/MR acquisitions. Two different correction approaches were evaluated comparing the incorporation of elastic transformations extracted from 4-dimensional MR imaging datasets during PET list-mode image reconstruction to a postreconstruction imagebased approach. Methods: Eleven patient datasets acquired on a PET/MR system were used. T1-weighted 4D MR images were registered to the end-expiration image using a nonrigid B-spline registration algorithm to derive deformation matrices accounting for respiratory motion. The derived matrices were subsequently incorporated within a PET image reconstruction of the original emission list-mode data (reconstruction space [RS] method). The corrected images were compared with those produced by applying the deformation matrices in the image space (IS method) followed by summing the realigned gated frames, as well as with uncorrected motion-averaged images. Results: Both correction techniques led to significant improvement in accounting for respiratory motion artifacts when compared with uncorrected motionaveraged images. These improvements included signal-to-noise ratio (mean increase of 28.0% and 24.2% for the RS and IS methods, respectively), lesion size (reduction of 60.4% and 47.9%, respectively), lesion contrast (increase of 70.1% and 57.2%, respectively), and lesion position (changes of 60.9% and 46.7%, respectively). Conclusion: Our results demonstrate significant respiratory motion compensation using both methods, with superior results from a 4D PET RS approach.

Magnetic Resonance–based Motion Correction for Quantitative PET in Simultaneous PET-MR Imaging

“…Figure 1 illustrates the diagram for the RTA and the MCIR methods for PET motion correction. Several phantom and patient studies 35–38 compared both approaches based on the OSEM image reconstruction and regularized reconstruction, and reported that the MCIR approach yielded better motion-corrected images as compared with the RTA approach.…”

Cardiac and Respiratory Motion Correction for Simultaneous Cardiac PET/MR

“…Several studies have shown that respiratory motion information obtained with MR can strongly improve the quality of PET images (16,17). Furthermore, tagged MR images have been used for cardiac motion correction in phantom experiments (18).…”

The Promise of Hybrid PET\/MRI: Technical advances and clinical applications

“…Preliminary results using computer simulations and a deformable phantom appear promising. Further investigation reported in more recent studies demonstrated the full potential of MRI-guided motion correction and its feasibility in clinical and research settings [73]- [75].…”