背景 新辅助化疗和放疗 (NCRT) 后局部晚期直肠癌的观察等待方案依赖于确定肿瘤的完全缓解。然而，T2加权和扩散加权MRI（T2DWI）组合的完全缓解与肿瘤的病理完全缓解（pCR；即ypT0N0）之间的一致性并不令人满意。目的 评估动脉期对比增强 (CE) T1 加权 MRI 上粘膜线性增强 (MLE) 的识别是否与 NCRT 后局部晚期直肠癌患者的 ypT0 状态相关，并评估是否将 CE T1 加权 MRI 上的 MLE 与 ypT0 状态相关。加权 MRI 和 T2DWI 阴性淋巴结转移 (LNM) 可以提高 pCR 的识别。材料和方法 这项回顾性研究纳入了 2020 年 7 月至 2023 年 7 月期间在三级转诊学术中心接受 NCRT 后接受全直肠系膜切除术的局部晚期直肠癌患者。 MRI 再分期包括用于原发肿瘤评估的 T2DWI 和动脉期 CE T1 加权 MRI，以及用于评估 LNM 状态的 T2DWI。通过多变量回归分析确定了与 ypT0 状态相关的影像学特征。结果 总共对 239 名患者（平均年龄，58 岁 ± 12 [SD]；180 名男性患者）进行了评估。 NCRT 后，ypT0 组的 MLE 比 ypT1-4 组更常见（分别为 73% 和 4%；P < .001）。在调整分析中，MLE 与 ypT0 状态的较高几率相关（优势比，137；95% CI：25, 767；P < .001）。 MLE 和阴性 LNM 状态相结合，pCR 的受试者工作特征曲线下面积达到 0.84（95% CI：0.79，0.88）。结论 CE MRI 的 MLE 与较高的肿瘤完全缓解几率相关。结合 MLE 和阴性 LNM 状态在识别肿瘤完全缓解方面表现出良好的性能，并且可以排除局部晚期直肠癌患者 NCRT 后的残留肿瘤。 © RSNA，2024 本文提供补充材料。另请参阅本期 Schoellnast 的社论。

Background A watch-and-wait regimen for locally advanced rectal cancer after neoadjuvant chemotherapy and radiation therapy (NCRT) relies on identifying complete tumor response. However, the concordance between a complete response at combined T2-weighted and diffusion-weighted MRI (T2DWI) and pathologic complete response (pCR; ie, ypT0N0) in the tumor is unsatisfactory. Purpose To assess whether identification of mucosal linear enhancement (MLE) at arterial-phase contrast-enhanced (CE) T1-weighted MRI is associated with ypT0 status in patients with locally advanced rectal cancer after NCRT and to evaluate whether combining MLE at CE T1-weighted MRI and negative lymph node metastasis (LNM) at T2DWI can improve identification of pCR. Materials and Methods This retrospective study included patients with locally advanced rectal cancer who underwent total mesorectal excision after NCRT between July 2020 and July 2023 at a tertiary referral academic center. Restaging MRI included T2DWI and arterial-phase CE T1-weighted MRI for primary tumor assessment and T2DWI for evaluation of LNM status. Imaging features associated with ypT0 status were identified at multivariable regression analysis. Results In total, 239 patients (mean age, 58 years ± 12 [SD]; 180 male patients) were assessed. MLE was more common in the ypT0 group than in the ypT1-4 group after NCRT (73% vs 4%, respectively; P < .001). MLE was associated with higher odds of ypT0 status in an adjusted analysis (odds ratio, 137; 95% CI: 25, 767; P < .001). The combination of MLE and negative LNM status achieved an area under the receiver operating characteristic curve of 0.84 (95% CI: 0.79, 0.88) for pCR. Conclusion MLE at CE MRI was associated with higher odds of complete tumor response. Combining MLE and negative LNM status showed good performance for identifying complete tumor response and may exclude residual tumors after NCRT in patients with locally advanced rectal cancer. © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Schoellnast in this issue.