isointensity on arterial phase and hyperintensity on DWI. The combination of DWI and Gd-DTPA-enhanced MR imaging may help to accurately diagnose HCCs.

Objective To investigate the value ofin vivo proton MR spectroscopy(1H-MRS)in the assessment of large focal hepatic tumors.Methods Fifty-three consecutive patients with 54 large(no less than 4 cm in dimneter)hepatic tumors and 19 normal volunteers were:included in this study.MRS of the 25 HCC confirmed by pathological examination,the choline-to-lipid mtios(Cho/Lip)were measured by dividing the peak area of choline at 3.2 ppm and lipid at 1.3 ppm.Differences in the ratios of normal liver,benign tumors and HCC were analyzed by Dunnett-t test.The sensitivity and specificity prof'des of 1H-MRS in the diagnosis of HCC were determined by plotting receiver operating characteristic(ROC)curves.Results The mean Cho/Lip ratios for normal liver(n=17),benign tumor(n=8),and HCC(n=25)were 0.07±0.04,0.11 ±0.06 and 0.55±0.17,respectively(F=6.58,P＜0.05).A significant statistical difference was found in the mean Cho/Lip ratios between HCC and benign liver tumors or normal liver(t=2.99,2.32;P＜0.05).But there wag no difference between benign hepatic tumors and norlnal liver(t=1.53,P＞0.05).The ROC curve showed proton MRS had moderate discriminating ability in diagnosing HCC.The area under the curve was 0.77. If 0.1 was chosen ns the cut-off value for diagnosing HCC with MRS,the sensitivity and specificity for HCC were 80.0%and 62.59b,respectively.Conclusion In vivo proton MRS is technically feasible for the evaluation of focal hepatic lesions,and may be useful in the diagnosis and differential diagnosis of HCC by providing metabolic ifformafion.

Objective To evaluate the differential diagnostic value of 18F-FDG PET/CT between pancreatic lymphoma (PL) and pancreatic carcinoma (PC).Methods The 18 F-FDG PET-CT data of 16 patients who were pathological diagnosed with PL were retrospectively reviewed and compared with those of 32 consecutive pancreatic cancer patients who were pathologically diagnosed and randomly enrolled.The age,location,diameter and the maximum standard uptake values (SUVmax) of pancreatic lesions,pancreatic ductal dilatation,distal pancreatic atrophy,serum CA19-9 level and extrapancreatic organs involvement were analyzed.Results The 16 patients with PL included 8 men and 8 women,the mean age was (46 ± 17)year,and 11.1％ (1/9) patients had elevated CA19-9.The 32 patients with PC included 15 men and 17 women,the mean age was (61 ± 12)year,and 81.3％ patients had elevated CA19-9.There were no significant differences on gender between the two groups,while the mean age of PL patients was younger than that of PC,elevated CA19-9 was less common than that in PC,and the differences were statistically significant (all P＜0.05).There were 12 cases of diffusive large B cell lymphoma,2 cases of B lymphoblastic lymphoma/leukaemia,1 case of follicular lymphoma and 1 case of dysplastic large T cell lymphoma in 16 PL patients.There was no significant difference on the site of pancreatic lesions between the two groups,but long diameter of PL lesions was larger than that of PC [(6.6 ± 3.3) vs (4.3 ± 1.8) cm,P =0.038].Dilated pancreatic duct and distal parenchyma atrophy in PL were less than those in PC (3/16 vs 17/32,1/16 vs 13/32),and SUVmax of PL lesions was significantly higher than that of PC (12.0 ± 5.5 vs 8.6 ± 3.8),indicating that the differences were statistically significant (all P ＜ 0.05).The cut-off value of SUVmax was 9.95,and Youden's index was 0.406 with the sensitivity and specificity of 68.8％ and 71.9％ for differentiating PL from PC.The incidence of extrapancreatic lesions including bone marrow and kidney and spleen infiltration was significantly more frequent in patients with PL than that in patients with PC(56.3％ vs 6.25％,43.8％ vs 3.1％,50.0％ vs 6.3％),while the incidence of liver metastases was significantly lower than that in PC (12.5％ vs 5.0％),indicating that the differences were statistically significant (all P ＜0.01).There were no significant differences on the incidence of other extrapancreatic lesions.Conclusions PL should be considered in relatively younger patients and manifested as a bulky mass with significant FDG uptake and extrapancreatic involvement of bone,kidney and spleen but without distinct pancreatic ductal dilation or distal parenchymal atrophy or liver metastasis.

Objective To study the features and clinical value of 18F-fluorodeoxyglucose (FDG) PET/CT in prosthetic vascular graft infections (PVGIs) after endovascular aortic repair (EVAR).Methods Data of 27 patients (22 males and 5 females,age range:21-77 years,average age:42 years) who underwent PET/CT imaging after EVAR from October 2011 to January 2017 were studied retrospectively.A total of 11 cases were finally diagnosed as PVGIs (PVGIs group),and the remaining 16 cases were defined as the negative group.PET/CT imaging features were compared between two groups.The detection rates of PET/CT and aortic CT angiography (CTA) for PVGIs were calculated and compared.Two-sample t test and Fisher exact test were used for data analysis.Results Significant uptake of FDG around the stents was detected by PET/CT in all patients in PVGIs group.The maximum standardized uptake value (SUVmax) of 11 patients in early imaging was 14.9±3.3 (10.8-21.8) and that of 9 patients in delayed imaging was 13.8±3.4 (10.6-19.1).Six patients of the negative group underwent the delayed imaging.No uptake or mild uptake of FDG around the stents was observed in negative group,with the SUVmax of 1.7±0.8(1.0--2.9) in early imaging and 1.6±0.7(1.1-2.5) in delayed imaging.SUVmax in negative group was significantly lower than that in PVGIs group (t values:12.6 and 11.8,both P＜0.001).Five patients in PVGIs group were diagnosed as graft infections by the aortic CTA,while the remaining 6 cases showed no definitive infection signs on aortic CTA.The detection rate of aortic CTA was 5/11,which was significantly lower than that of PET/CT (P＜0.05).In negative group,6 patients had abnormal FDG uptakes in other areas and were finally confirmed as infectious lesions (n=3) or malignant tumors (n=3).Conclusion Compared with aortic CTA,18F-FDG PET/CT is more sensitive and accurate in detection and diagnosis of PVGIs after EVAR.