To investigate the effect of radiotherapy on sacral nerve morphology in patients with rectal cancer using the three-dimensional T₂-weighted fast field echo (3D-T₂WI-FFE) sequence combined with curved planar reformation, and to explore its clinical significance.

From November 2019 to May 2022, 19 patients with rectal cancer were enrolled at the Department of Gastrointestinal Surgery of Peking University Shougang Hospital. The average number of radiotherapy sessions was 23.26±4.27, and the radiation dose was 16~54 Gy. At the same time, 26 healthy volunteers were collected. Pelvic scans were performed with a Philips Ingenia 1.5TX magnetic resonance machine, including T₁WI axial scan and T₂W-3D-FFE coronal scan. The original data obtained from the two sets of scans were used in the workstation to reconstruct the sacral nerve using curved planar reformation (CPR), and the score was graded according to the imaging quality of the sacral nerve. The scores of sacral nerve rating, sacral nerve signal intensity, piriform muscle signal intensity, and the contrast noise ratio (CNR) of the two groups were compared by the t-test.

After the original data of 3D-T₂-FFE sequence were reconstructed by curved planar reformation, the sacral nerve exhibited a high signal strip structure, the surrounding musculoskeletal tissues had a low signal, and the sacral nerve and surrounding tissues were clearly contrasted. There were statistical differences between the two groups in the scores of the first, second, and third sacral nerves. There was no significant difference in nerve signal intensity between the two groups (χ²=1.978, P=0.051). There was a statistical difference in the signal intensity of the piriformis muscle between the two groups (χ²=6.77, P＜0.05). The CNR of the sacral nerve and adjacent piriformis muscle also differed significantly between the two groups (χ²=-3.78, P＜0.05).

3D-T₂-FFE sequence combined with curved planar reformation technology can directly and accurately display the sacral nerve, and can display the changes of sacral nerve morphology after radiotherapy, which provides a basis for further clinical planning and evaluation of therapeutic effects.