Fast atlas-based MRI-guided PET attenuation map generation in whole-body PET/MR imaging

摘要

We propose a one registration multi atlas (ORMA) pseudo-CT generation algorithm for attenuation correction in whole-body PET/MRI based on an optimized atlas-guided bone segmentation procedure. The proposed approach requires only one online registration between the target and reference images regardless of the number of atlas images N, while for the remaining subjects belonging to the atlas dataset, the pre-computed transformation matrices obtained from registration to the reference image is used to align them to the target image. The performance characteristics of the proposed method were evaluated and compared to conventional atlas-based attenuation map generation consisting of direct registration of the entire atlas images to the target. Four different PET attenuation maps were produced using direct registration and ORMA, voxelwise weighted (VWW-Direct and VWW-ORMA) and arithmetic average (AA-Direct and AA-ORMA) atlas fusion strategies. The comparison of validation measures characterizing the accuracy of extracted whole-body bone demonstrated the superiority of VWW-Direct atlas fusion technique resulting in a Dice similarity measure of 0.82±0.04 compared to 0.60±0.02 for AA-Direct. Conversely, the ORMA approach yielded a Dice similarity measure of 0.76±0.05 for VWW-ORMA and 0.55±0.03 for AA-ORMA. Quantitative analysis of PET data revealed good correlation (y=1.01x+0.1, R2=0.99) between PET images corrected for attenuation using the proposed pseudo-CT method and the corresponding reference CT images. The proposed method generates decent attenuation maps and enables to reduce the processing time for atlas-based pseudo-CT generation reduced by a factor N.