방사선의학 웹진

바로가기  >

Abstract

Inaccuracy in magnetic resonance image (MRI)-based attenuation correction (MR-AC) leads to errors in quantification and the misinterpretation of lesions in brain PET/MRI studies. To resolve this problem, we propose an improved ultrashort echo time (UTE) MR-AC method that is based on a multiphase level-set algorithm with B0 inhomogeneity correction. We also assessed the feasibility of this level-set-based MR-AC method (MR-AClevel), compared with CT-AC and MR-AC provided by the manufacturer of the PET/MRI scanner (MR-ACmMR).

METHODS:

Ten healthy volunteers and 20 Parkinson's disease patients underwent [18F]FDG and [18F]FP-CIT PET scans, respectively, using both PET/MRI and PET/CT scanners. The level-set-based segmentation algorithm automatically delimited air, bone, and soft tissue from the UTE MR images. For the comparison, MR-AC maps were coregistered to reference CT. PET sinogram data obtained from PET/CT studies were then reconstructed using the CT-AC, MR-ACmMR and MR-AClevel maps. The accuracies of SUV, SUVr and specific to nonspecific binding ratios (BR) obtained using MR-AClevel and MR-ACmMR were compared with CT-AC using ROI- and voxel-based analyses.

RESULTS:

There was remarkable improvement in the segmentation of air cavities and bones and the quantitative accuracy of PET measurement using the level set. While the striatal and cerebellar activities in [18F]FP-CIT PET and frontal activity in [18F]FDG PET were significantly underestimated by the MR-ACmMR, the MR-AClevel provided almost equivalent PET images to the CT-AC. PET quantification error was reduced by a factor of three using MR-AClevel (SUV error < 10% in MR-AClevel and < 30% in MR-ACmMR [version VB18P], and < 5% in MR-AClevel and < 15% in MR-ACmMR [VB20P]).

CONCLUSION:

The results of this study indicate that our new multiphase level-set-based MR-AC method improves the quantitative accuracy of brain PET in PET/MRI studies.

Author information

An HJ1, Seo S1, Kang H1, Choi H1, Cheon GJ1, Kim HJ1, Lee DS1, Song IC1, Kim YK2, Lee JS1.​

1 Seoul National University College of Medicine, Korea, Republic of;

2 Seoul National University Bundang Hospital, Korea, Republic of.