Objective: To evaluate the value of T2WI, DWI and 3D-VBIE at 3.0 T MR in the differentiation of recurrent rectal cancer and benign pelvic lesions after curative rectal operation.
Methods: A total of 28 patients with abnormal pelvic lesions confirmed by CT or MR from April 2007 to October 2010 were evaluated with MR imaging. All the patients received examinations of both T2WI and DWI, and 24 of them received additional examination of 3D-VIBE. Thirteen patients with MR imaging in the same period who were confirmed to have no diseases of the rectum were used as control group. The mean apparent diffusion coefficient(ADC) value and the ratio of the signal intensity(SI) of the lesions to the gluteus maximus in T2WI(SI(L)/SI(M)) and the ratio of the net added signal intensity of the lesions to the net added signal intensity of the iliac artery(SI(L)/SI(A)) at the time of 35 seconds after the iliac artery achieved its highest intensity were measured and calculated. The type of the time-intensity curve(TIC) was over viewed and classified as the benign type when the TIC was rising slowly or constantly and lasted for more than 90 s; however the malignant type when the TIC was rising significantly but lasted less than 90 s kept as a horizontal line for a period or was descending slowly or rising slowly.
Results: There were 29 lesions of different final diagnosis, including 17 recurrence rectal cancers, 4 fibrous masses, 6 stoma inflammations, 1 sinus and 1 abscess. Fourteen of them were confirmed by pathological examination. The ratio of SI(L)/SI(M) was 2.84±1.52 in the benign group, 2.58±0.80 in the malignant group, and 2.13±0.58 in the control group, the differences between the 3 groups were not statistically significant(F=1.620, P=0.211). When the ADC value of 1.21×10(-3) mm(2)/s was set as a diagnostic threshold, the sensitivity, specificity, accuracy and coherence for the diagnosis of the malignant lesions were 100%(17/17), 91.7%(11/12), 96.6%(28/29) and 0.928, respectively. When the SI(L)/SI(A) value of 0.28 was set as a diagnostic threshold, the sensitivity, specificity, accuracy and coherence for the diagnosis of the malignant lesions were 100%(13/13), 66.7%(8/12), 84.0%(21/25) and 0.675. When considering the TIC as the diagnostic standard, the sensitivity, specificity and accuracy for the diagnosis of the malignant lesions were 100%(13/13), 83.3%(10/12) and 92.0%(23/25), respectively.
Conclusion: The signal intensity of T2WI has no specificity in the differentiation of malignant lesions and benign lesions while the DWI and the 3D-VIBE have high values in it.