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

Abstract

Cardiac imaging is a promising application for combined PET/MR imaging. However, current MR imaging protocols for whole‐body attenuation correction can produce spatial mismatch between PET and MR‐derived attenuation data owing to a disparity between the two modalities' imaging speeds. We assessed the feasibility of using a respiration‐averaged MR (AMR) method for attenuation correction of cardiac PET data in PET/MR images. First, to demonstrate the feasibility of motion imaging with MR, we used a 3T MR system and a two‐dimensional fast spoiled gradient‐recalled echo (SPGR) sequence to obtain AMR images of a moving phantom. Then, we used the same sequence to obtain AMR images of a patient's thorax under free‐breathing conditions. MR images were converted into PET attenuation maps using a three‐class tissue segmentation method with two sets of predetermined CT numbers, one calculated from the patient‐specific (PS) CT images and the other from a reference group (RG) containing 54 patient CT datasets. The MR‐derived attenuation images were then used for attenuation correction of the cardiac PET data, which were compared to the PET data corrected with average CT (ACT) images. In the myocardium, the voxel‐by‐voxel differences and the differences in mean slice activity between the AMR‐corrected PET data and the ACT‐corrected PET data were found to be small (less than 7%). The use of AMR‐derived attenuation images in place of ACT images for attenuation correction did not affect the summed stress score. These results demonstrate the feasibility of using the proposed SPGR‐based MR imaging protocol to obtain patient AMR images and using those images for cardiac PET attenuation correction. Additional studies with more clinical data are warranted to further evaluate the method.PACS number: 87.57.uk

Coronary Artery PET/MR Imaging

“…The appearance of the artifacts was reminiscent of artifacts at the diaphragm arising from mismatch of the PET emission and attenuation data because of respiratory motion, which has been previously noted on both PET/CT and PET/MR imaging (23,24). The need for matching attenuation and PET data has also been previously described for cardiac PET/MR imaging (25). In addition, we observed that the bronchi were not segmented from the surrounding structures in the attenuation maps produced by the standard MR imaging protocol ( Figure 1 ).…”

Effect of Time-of-Flight Information on PET/MR Reconstruction Artifacts: Comparison of Free-breathing versus Breath-hold MR-based Attenuation Correction

“…Notice that PET/CT data would still not constitute a standard of reference. Barring sophisticated approaches not used in clinical practice (eg, attenuation correction on the basis of dynamic CT) (17)(18)(19)(20), there is no practical way to estimate patient attenuation in the presence of respiratory motion.Voxel-wise maps offer the most intuitive representation of the bias that respiratory mismatch can introduce in PET ). Notice how normalized error values larger than 610% can be found over the entire lung contour.…”

PET/MRI attenuation estimation in the lung: A review of past, present, and potential techniques

“…Ai and Pan demonstrated the feasibility of using respiration‐averaged MRI on one patient. Using a two‐dimensional (2D) multi‐slice, multi‐phase spoiled gradient‐recalled echo sequence they acquired 12 consecutive time frames at each slice location to have good coverage over the full respiratory cycle at each slice location.…”