Application Of Diffusion-weighted Imaging In Focal Hepatic Lesions

Background Echo-planar imaging (EPI) with fast imaging times minimize the effect of bulk motions from pulsation, involuntary motion, bowel peristalsis, respiration and cardiac movement. With the advent of EPI technique, diffusion-weighted imaging (DWI) has been used in the central nervous system, but also successfully in abdomen, especially in liver disease. Focal hepatic lesions include metastases, hepatocellular carcinomas (HCCs), cholangiocarcinomas, hemangiomas, cysts and inflammatory lesions. In this study, DWI sequences were performed with respiration-triggered single-shot echo-planar imaging technique to (a) compare the efficacy of DWI for detection of focal hepatic lesions, (b) evaluate manifestations of focal hepatic lesions, (c) determine the threshold apparent diffusion coefficient (ADC) value to differentiate benign lesions from malignant lesions. Materials and Methods 10 healthy volunteers and 81 patients with focal hepatic lesions were examined with traditional MRI and diffusion-weighted MRI with four values (0, 50, 100, 400s/mm~2). Five patient were excluded forpoor image quality. Among the 76 patients, 24 had metastases, 17 had HCCs, 7 had cholangiocarcinomas, 14 had hemangjomas, 11 had cysts, and 3 had inflammatory lesions. ADC values of the lesions were measured. Results On diffusion weighted image of healthy volunteers, the signal of liver parenchyma attenuated homogeneously according to the gradient factor (b value). ADC value of liver parenchyma was moderate on ADC map. b value had a closely relationship to the quality of diffusion weighted image, and the value of ADC.The lesions detected on DWI were much more than those on TiWI, especially for hepatocellular carcinomas and metastases, but not for hemangiomas and cysts, whereas no significant differences between those on DWI and those on T2WI or on CE-TiWI. ADC values with two different b values (0, 400s/mm2) in metastasis, hepatocellular carcinoma, cholangiocarcinoma, haemangioma, cyst and inflammatory lesion were 1.518±0.399xl0'3mm2/s, 1.227±0.261><10'3m m2/s, 1.476±0.225xl(r3m m2/s, 1.982±0.658xl0'3m m2/s, 3.302±0.212xl0"3m m2/s, 2.118±0.780xl0"3m m2/s, respectively. ADC values of malignant tumors were lower than that of benign lesions. With ADC value of 1.70xl0"3m m2/s as the threshold for malignant tumors and benign lesion, the sensitivity, specificity, accuracy, positive predictive value, negative predictive value, positive likelihood ratio, and negative likelihood ratio were 81.1%, 79.1%, 80.3%, 91.2%, 57.5%, 4.20, 0.30, respectively.Conclusion DWI sequences were performed with respiration-triggered single-shot echo-planar imaging technique successfully, the signal of liver parenchyma attenuated homogeneously according to the gradient factor (bvalue). ADC value of liver parenchyma was moderate on ADC map. The lesions detected on DWI were much more than those on TiWI, especially for hepatocellular carcinomas and metastases, but not for hemangiomas and cysts, whereas no significant differences between those on DWI and those on T2WI or on CE-TiWI. ADC values of malignant tumors were lower than that of benign lesions. Proper threshold ADC value was helpful to differentiating malignant tumor from benign lesion.