- This retrospective study compared positron emission tomography/magnetic resonance imaging (PET/MRI) with stand-alone MRI for staging rectal cancer in 62 patients
- Average tumor length was 43 mm by sigmoidoscopy, 54 mm by MRI and 44 mm by PET/MRI (P=0.004)
- Extent of sphincter infiltration was correct by MRI in 6/10 patients and by PET/MRI in 9/10 (P=0.003)
- For assessing T stage and extramural vascular invasion (EMVI), PET/MRI showed a non-significant trend toward better performance than MRI
- PET/MRI correctly assigned N stage in 79% of cases vs. 58% for standalone MRI (P=0.02)
Both MRI and PET/CT have limitations for locoregional staging of rectal cancer. Onofrio A. Catalano, MD, PhD, medical director of PET/MR at the Martinos Center for Biomedical Imaging at Massachusetts General Hospital, and Bruce Rosen, MD, PhD, director of the Martinos Center, and colleagues have observed that hybrid PET/MRI is more precise than MRI for assessing the extent of rectal cancer, N status and sphincter involvement.
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Their report appears in the European Journal of Nuclear Medicine and Molecular Imaging.
The researchers reviewed images from 62 patients with untreated locally advanced rectal cancer who underwent PET/MRI between January 2016 and August 2019. Follow-up ended in March 2020.
MR and PET/MRI images were evaluated separately at least four weeks apart. When evaluating MR images, readers did not have access to co-acquired PET data.
- The average tumor length was 43 mm by sigmoidoscopy, 54 mm by MRI and 44 mm by PET/MRI (P=0.004)
- The extent of sphincter infiltration was correct by MRI in 6/10 patients and by PET/MRI in 9/10 (P=0.003), with the reference being surgical pathology or the combination of follow-up imaging, digital rectal examination and post-chemotherapy surgical pathology
- The modalities performed similarly in assessing mesorectal fascia involvement and extramural vascular invasion, though there was a non-significant trend toward higher performance with PET/MRI: 11/12 detected as opposed to 8/12 in the case of MRI alone
- For T stage and EMVI, PET/MRI showed a non-significant trend toward better performance.
In three low rectal cancer cases, external sphincter infiltration was missed by MRI and therefore erroneously classified as T3.
MRI correctly assigned N stage in 58% of cases vs. 79% for PET/MRI (P=0.02).
PET/MRI can help improve clinical decision-making, especially when low rectal tumors have possible external sphincter involvement.
Learn more about the Martinos Center for Biomedical Imaging
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