Cardiac motion compensation and resolution modeling in simultaneous PET-MR: a cardiac lesion detection study

Abstract

Cardiac motion and Partial Volume Effects (PVE) are two of the main causes of image degradation in cardiac PET. Motion generates artifacts and blurring while PVE lead to erroneous myocardial activity measurements. Newly available simultaneous PET-MR scanners offer new possibilities in cardiac imaging as MRI can assess wall contractility while collecting PET perfusion data. In this perspective, we develop a list-mode iterative reconstruction framework incorporating both tagged-MR derived non-rigid myocardial wall motion and position dependent detector Point Spread Function (PSF) directly into the PET system matrix. In this manner, our algorithm performs both motion “deblurring” and PSF deconvolution while reconstructing images with all available PET counts. The proposed methods are evaluated in a beating non-rigid cardiac phantom whose hot myocardial compartment contains small transmural and non-transmural cold defects. In order to accelerate imaging time, we investigate collecting full and half k-space tagged MR data to obtain tagged volumes that are registered using non-rigid B-spline registration to yield wall motion information. Our experimental results show that tagged-MR based motion correction yielded an improvement in defect/myocardium contrast recovery of 34-206% as compared to motion uncorrected studies. Likewise, lesion detectability improved by respectively 115-136% and 62-235% with MR-based motion compensation as compared to gating and no motion correction and made it possible to distinguish non-transmural from transmural defects, which has clinical significance given inherent limitations of current single modality imaging in identifying the amount of residual ischemia. The incorporation of PSF modeling within the framework of MR-based motion compensation significantly improved defect/myocardium contrast recovery (5.1-8.5%, p<0.01) and defect detectability (39-56%, p<0.01). No statistical difference was found in PET contrast and lesion detectability based on motion fields obtained with half and full k-space tagged data.

Feasibility of using respiration‐averaged MR images for attenuation correction of cardiac PET/MR imaging

“…Several authors have proposed MR‐based respiratory motion correction for thorax PET/MR, 34 , 35 , 36 , 37 and at least one phantom‐based study tested a tagged MR imaging‐based technique for cardiac motion correction (38) . Although such approaches aim to eliminate the impact of motion in the reconstructed PET image, they usually require nonstandard MR sequences that are not clinically available.…”

Quantitative PET image reconstruction employing nested expectation-maximization deconvolution for motion compensation

“…Recently, we proposed a clinically feasible 18 F-FDG PET parametric imaging framework [8], capable of delivering highly quantitative WB parametric images by supporting i) multiple PET acquisition passes over multiple beds and ii) graphical analysis of the acquired 4D WB data using robust standard linear Patlak (sPatlak) [9] or non-linear generalized Patlak (gPatlak) methods [40]. Although the associated total scan duration of ~30-40min may be considered clinically feasible, such protocols are naturally expected to increase the likelihood of bulk motion during the acquisition [41].…”

Imaging moving heart structures with PET

“…PET/MR results show that tagged MR-based motion correction yielded significant improvements in defect/ myocardium contrast recovery and lesion detectability. 29,30 Furthermore, respiratory motion can be detected using 1D navigator MRI data acquired perpendicular to the diaphragm, eliminating the need for external respiratory gating. 31 This would allow for the detection of the diaphragm position for respiratory gating.…”