Three-region MRI-based whole-body attenuation correction for automated PET reconstruction

In this study we proposed and developed a simple attenuation mapping approach based on magnetic resonance imaging (MRI) for the purpose of reconstructing positron emission tomography (PET) images in PET/MRI imaging devices.

After experimental development, an in vivo calibration was performed by whole-body scanning of five beagles on both a PET/CT and an MRI. The attenuation was determined by using an automated segmentation algorithm to segment regions of background, lung, soft tissue and bone, and assigning them values of 0.002, 0.030, 0.098 and 0.130 cm(-1), respectively.

The CT-attenuated and MRI-attenuated PET images had average standardized uptake values (SUVs) that differed by 1-6% for most regions of interest (ROIs). Also, mean relative differences (MRDs) between the images were between 5% and 9% for most regions. The only exception is bone, where the three-region MRI-attenuated PET images had an SUV 10% less on average than the CT-attenuation images, and the MRD averaged 14%. Also, additional segmentation of the bone in the four-region MRI-attenuated PET images reduced the SUV difference to 3% and the MRD to 6%.

Therefore, despite the improvements in the four-region segmentation, the three-region segmentation, without delineation of osseous tissues, produces high-quality images that are sufficient for most expected clinical and research purposes.