15-minute PET acquisition time for rectal cancer improves care—without extending scan time

Extending PET acquisition time during PET/MRI for rectal cancer staging increases identified lymph nodes and has no impact on scan time, reported authors of a recent American Journal of Roentgenology study.

Lead author Jason J. Bailey with the University of California, San Francisco, and colleagues performed 29 total studies across 22 patients with biopsy-proven rectal cancer. Each exam involved whole-body PET/MRI and a pelvic-specific PET/MRI. Three- and 15-minute PET acquisition times were tested in pelvic scans.

After radiological review, authors found the 15-minute PET acquisition detected 40 percent more FDG-avid lymph nodes than the standard three minutes.

There was no evidence 15-minute acquisition extended patient scan times.

“These findings indicate that PET/MRI of the pelvis in rectal cancer staging should include a dedicated 15-minute PET acquisition of the pelvis, particularly given that this extended PET acquisition time does not increase overall scan time,” authors wrote.

Bailey and colleagues suggested the improved count for each voxel during the extended acquisition is probably why more lymph nodes were detected. Those findings were likely present on the three minute tests, but indistinguishable due to noise, they wrote.

Further studies using postoperative pathology as a baseline and more patients should be done in the future, authors said, to determine if increasing PET acquisition time can also detect a higher number of normal lymph nodes.