MR-based attenuation correction for torso-PET/MR imaging: pitfalls in mapping MR to CT data

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MR-based attenuation correction (AC) will become an integral part of combined PET/MR systems. Here, we propose a toolbox to validate MR-AC of clinical PET/MRI data sets.


Torso scans of ten patients were acquired on a combined PET/CT and on a 1.5-T MRI system. MR-based attenuation data were derived from the CT following MR-CT image co-registration and subsequent histogram matching. PET images were reconstructed after CT- (PETCT) and MR-based AC (PETMRI). Lesion-to-background (L/B) ratios were estimated on PETCT and PETMRI.


MR-CT histogram matching leads to a mean voxel intensity difference in the CT- and MR-based attenuation images of 12% (max). Mean differences between PETMRI and PETCT were 19% (max). L/B ratios were similar except for the lung where local misregistration and intensity transformation leads to a biased PETMRI.


Our toolbox can be used to study pitfalls in MR-AC. We found that co-registration accuracy and pixel value transformation determine the accuracy of PETMRI.

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