Misalignment in abdominal organ images cut with simultaneous MR/PET

Simultaneous MR/PET acquisition provides more accurate alignment of hybrid datasets than retrospective fusion of MR images and PET data, according to a study published online May 8 in Radiology.

Specifically, misalignment in abdominal organs is reduced with simultaneous MR/PET compared with fused images, and misalignment in urinary bladder images is also reduced with MR/PET compared with PET/CT.

The study, authored by Cornelia B. Brendle, MD, and colleagues from Eberhard-Karls University Tuebingen, Tuebingen, Germany, analyzed misalignment in 28 abdominal patient data sets acquired with MR/PET, PET/CT and retrospective MR/PET fusion. The authors also examined the effects of different breathing, registration and gating protocols.

Results showed alignment improved an average of 51 percent across all abdominal organs using simultaneous MR/PET. Mean misalignment was 5.8 mm with MR/PET compared with 11.9 mm using retrospectively fused MR and PET images.

Compared with PET/CT images, MR/PET also improved alignment between morphological images and PET in the urinary bladder by nearly 50 percent, according to the authors.

“Thoracic MR/PET with inspiratory breath-hold MR showed the largest misalignment (mean, 24.5 mm),” wrote Brendle and colleagues. “None of the other thoracic protocols that were composed of different acquisition, registration, or gating procedures differed significantly from one another.” They added that MR-based gated PET with an end-expiratory attenuation correction map added a higher noise level.

Further analysis of the intrarater and interrater variability showed alignment differences within the modalities were at least twice as high as the reader bias, according to the authors.

“The possible benefit of MR-based motion correction of PET data combined with motion-corrected attenuation correction maps needs to be further evaluated,” they concluded.