To evaluate the efficacy of diffusion-weighted imaging with background suppression (DWIBS) at 3.0T magnetic resonance (MR) for diagnosing rectal cancer, and analyze the relationship between apparent diffusion coefficient (ADC) values and pathological results of tumor.

The study included 42 patients with rectal cancer who underwent preoperative routine MRI + DWI examination and were treated by rectal cancer dissection, and then obtained pathological results. ADC values of tumors and normal rectal walls were measured respectively, and statistical analysis was made.

(1) The ADC values of total 42 patients of rectal primary tumors and normal rectal wall were (0.76 ± 0.11) × 10^-3 mm²/s and (1.22 ± 0.16) × 10^-3 mm²/s respectively. The ADC value of rectal cancer was statistically significant different from that of the normal rectal wall tissue (t = 15.439, P <0.001). The optimal cutoff ADC value in differentiating rectal cancer from normal rectal wall was (0.96 × 10^-3) mm²/s, representing 95.2% sensitivity and 97.6% specificity. (2) The ADC values of one case of well differentiated, 33 cases of moderately differentiated and 5 cases of poorly differentiated rectal adenocarcinoma were 0.78 × 10^-3 mm²/s, (0.75 ± 0.12) × 10^-3 mm²/s and (0.77 ± 0.11) × 10^-3 mm²/s respectively. There was no statistically difference between moderately differentiated and poorly differentiated rectal adenocarcinoma in ADC value (P > 0.05).

3.0T MR diffusion-weighted imaging can improve the tumor detection rate of rectal cancer. The ADC value of primary tumor is significantly lower than the normal rectal wall, and there is no statistically difference between different degrees of differentiation of rectal adenocarcinoma in ADC value.