Application Of Mri In Diagonsis And Preoperative Evaluation Of Rectal Cancer

Background and Objective Rectal cancer is one of the main cause of death in the western countries.With the improvement of the living conditions and the changes in the food ingredient in our country, the incidence of rectal cancer has an increasing trendency year by year. The clinical treatment planning is quite different with the different staging and the survival rate of the patient is also obviously different. Operation is still the preferred treatment of rectal cancer. Due to the special anatomic structure of the rectum, diverse operation approachs are chosen for rectal cancer with different positions and stages and prognosis is different also. The assistant radiotherapy and chemotherapy before the operation can reduce the postoperative recurrence and metastasis of rectal cancer to those patients who staged as T3 and T4, or have signs of lymph node metastasis. Therefore, early diagnosis can effectively improve the postoperative survival rate and the living quality. The accurate preoperative evaluation can provide important information to the choice of the indudivlized treatement solution and the operation approach. MRI is a unique modality in the imaging diagnosis of rectal cancer due to its excellent image resolution to the soft tissue and special multiplanar imaging ability. Furthermore, DWI, the only imaging method to reflect the diffusion ability and the moving direction of the water molecule in the living organism up to now, become the hotspot in the research of this field. In this research,we analyze the diagnostic value of a combination of routine MRI with DWI in rectal cancer, and the clinical value of HR-MRI in the staging and preoperative evaluation of rectal cancer.Materials and Methods DWI and conventional sequences were performed in 57 patients with endoscopically diagnosed rectal cancer and 23 patients without rectal cancer. Two doctors, who were blind to the history of the patients, interpreted the imaging findings. The sensitivity and specificity of convertional sequences with and without DWI were analyzed using receiver operating characteristic curve(ROC). Fifty seven patients with rectal cancer were staged preoperatively using magnetic resonance imaging.All of the patients underwent operation within 1 week after MRI examination.The diagnosis of specimens were reported according to the 2002 TNM staging system for primary colorectal cancer of the American Joint Committee on Cancer(AJCC).The agreement between the radiologic staging of the tumor and local lymph nodes,and pathologic reporting was assessed by means of the Kappa analysis. The curve distance between the lesions and the anal margin is compared with the distance measured from the operative specimen and paired T test is used.Results The Kappa value was 0.819 for conventional sequences alone and 0.761 for DWI with conventional sequences. The areas under ROC were 0.923 and 0.925 for conventionaI sequences alone, and 0.991 and 0.989 for conventional sequences with DWI, respectively. It indicates that although both of them were optimal methods for the diagnosis of rectal cancer, the accuracy of conventional sequences combined with DWl is significantly higher than that of conventional sequences alone. Of all the 57 patients, 48 cases were staged correctly by MRI before operation ,4 cases were understaged,and 5 overstaged. Statistically, there was good agreement between the pathologic and radiologic tumor staging (Kappa=0.731, P=0.000). The preoperative MRI correctly staged lymph node status in 40 patients,understaged in 8 and overstaged in 9. Statistically, common agreement was achieved between the pathologic and radiologic lymph node staging (Kappa=0.410, P=0.009). No statistically significant difference was found at the curve distance between the lesion and the anal margin measured by MRI and by operational specimen (t=1.686,P=0.106).Conclusion MRI has great value in the diagnosis and preoperative staging of rectal cancer. DWI is better to clearly demonstrate the tumor. Conventional T2WI combined with DWI can provides better detection for rectal cancer than T2WI alone. HR-MRI has good accuracy in the preoperative tumor staging, common accuracy in the lymph node staging. It also provide accurate evaluation to the curve distance between the lesions and the anal margin.