Application Of Multi-modal Magnetic Resonance Imaging In Rectal Carcinoma

Objectives:1.To study the value of 3.0 T MRI in the preoperative assessment of rectal carcinoma.2.To compare different diffusion models of diffusion weighted imaging(DWI)including traditional monoexpontial model,biexponential model namely intravoxel incoherent motion(IVIM)and stretched-exponential model(SEM)at 3.0 T MRI in patients with rectal carcinoma,and to determine the optimal model for detecting the water diffusion properties and characterization of rectal cancer.Methods:1.The study recruited 41 patients who were confirmed by biopsy of rectal carcinoma and underwent conventional MRI,high-resolution MRI(HR-MRI)and diffusion weighted imaging(DWI),then measuring the distance from the inferior part of tumor to transitional skin and the percentage of circumferential invasion,observing the morphology of tumor,assessing the tumor's T staging,N staging,and the status of circumferential resection margin(CRM)and extramural vascular invasion(EMVI).MRI findings were compared with endoscope and postoperative pathological results.2.45 patients who were pathologically confirmed as rectal adenocarcinoma underwent DWI with 13 b-values at a 3.0 T MRI system.DWI signals were fitted to the monoexponential,IVIM and SEM on tumor and adjacent normal rectal tissue.Parameters of standard apparent diffusion coefficient(ADCStand),slow apparent diffusion coefficient(ADCSlow),fast apparent diffusion coefficient(ADCFast),perfusion fraction(f),distributed diffusion coefficient(DDC)and ? value were generated and t test was used to compare these MRI parameters between the tumor and normal rectal tissues,ROC was used to evaluate the diagnostic efficiency.Results:1.MRI can accurately show the distance from the inferior part of tumor to transitional skin(P>0.05);The mean percentage of circumferential invasion for the tumor with T1-2 or T3 were 61%,83% separately(P>0.05);The total accuracy of T/N staging diagnose were 80.5%/75.6% separately,having better consistent with pathological T/N staging(Kappa=0.564,0.634);The total accuracy of CRM and EMVI diagnose were90.2%,73.2% separately,having better or moderate consistent with pathological diagnose(Kappa=0.765,0.461).2.The SEM exhibited the best fitting results of actual DWI signal in rectal cancer and the normal rectal wall(R2 = 0.9983,0.9988 respectively).In comparison to normal tissue,a significant reduction of these parameters(ADCStand,ADCSlow,f,DDC,?)were found in rectal adenocarcinoma [normal rectal tissue:(1.400±0.128)×10-3mm2/s,(1.070±0.089)×10-3mm2/s,0.410±0.091,(1.754±0.414)×10-3mm2/s,0.775±0.078;rectal cancer:(0.810±0.064)×10-3mm2/s,(0.602±0.402)×10-3mm2/s,0.277±0.044,(0.833±0.139)×10-3mm2/s,0.722±0.045](P<0.05).No significant difference was observed in the ADCFast between the two groups [(12.578±7.071)×10-3mm2/s and(10.818±4.207)×10-3mm2/s ](P>0.05).In the ROC-analyse,the DDC achieved relatively high area under the curve(AUC = 0.997)in differentiating tumor from the normal rectal wall,when the cut-off value was 1.230×10-3mm2/s,the specificity and sensitivity were respectively 96%,100%.Conclusions:1.The 3.0 T MRI had the unique application in the preoperative assessment of rectal carcinoma,which can provide more comprehensive information for doctors.2.Biexponential model and stretched-exponential diffusion models could assess tissue properties more accurately than the ADC derived from monoexponential diffusion model.SEM may be used as a potential optimal model for characterization of rectal cancer,DDC had a relatively high diagnosis efficiency.