Objective To investigate imaging characteristics of human skin in different sites by using 20-MHz and 50-MHz high-frequency ultrasonography,and to compare the reliability of skin thickness measurement by the above two approaches of ultrasonography.Methods A total of 39 healthy volunteers aged 18-39 years were enrolled into this study.Then,20-MHz and 50-MHz ultrasonography were separately performed to image 20 different sites on the body,and the thickness of the epidermis and dermis were measured and evaluated by 3 dermatologists independently.The ultrasonic images were analyzed,and the intraclass correlation coefficient (ICC) was used to assess and compare the reliability of skin thickness measurement by 20-MHz and 50-MHz ultrasound.Results The ICC values were less than or close to 0.7 in epidermal thickness measurement at almost all the tested sites between 20-MHz and 50-MHz ultrasonography,suggesting poor reliability.However,20-MHz and 50-MHz ultrasonography showed excellent reliability in dermal thickness measurement with the ICC greater than 0.75 at almost all the tested smooth and flat body sites.The 20-MHz ultrasound could provide clear images of the dermis and subcutaneous tissue,while 50-MHz ultrasound could only provide clearer images of the dermis in details.In some uneven sites with complex anatomical structures,20-MHz and 50-MHz ultrasound probes had their own advantages and disadvantages in imaging depth and detail resolution.Conclusions The 20-MHz and 50-MHz ultrasono-graphy both can serve as non-invasive imaging techniques to show structures of the epidermis and dermis better.In different parts of human body,ultrasound frequencies should be selected according to their imaging characteristics.

Objective To explore the correlations between intravoxel incoherent motion (IVIM) parameters measured at different time points and histopathological markers in an orthotopic xenograft hepatocellular carcinoma (HCC) nude mice model. Methods A total of 40 HCC orthotopic bearing mouse models were established. When they grew to 21 days, 10 HCC-bearing mice were randomly selected as the baseline group (Group A) by a numeric table method. Then the rest mice were randomly selected on the 28th day, 35th day, and 42nd day of the growth by using the same method, 10 each for B, C, and D groups, respectively. All mice underwent MR IVIM study and apparent diffusion coefficient (ADC), true diffusion coefficient (D), pseudo-diffusion coefficient (D*) and perfusion fraction (f) were measured. After the MRI scanning, the tumors were removed for pathological examination. The necrosis score (NF), tumor size and microvessel density (MVD) were calculated. The IVIM parameters were compared among these 4 groups by Kruskal-Wallis H test and the correlations between these IVIM parameters and histological features were studied with Spearman rank correlation test. Results One tumor in each of C and D groups was excluded because f values of IVIM were close to zero. There were significant differences found in ADC and D among all the 4 groups (P＜0.05). However, no difference was found in D*and f (P＞0.05). Compared with the baseline (group A), ADC decreased significantly at 7 and 14 days, whilst D decreased significantly at 7 days. The differences in tumor size, MVD and NF between the 4 groups were statistically significant. Compared with the baseline, the tumor size and NF significantly increased at 7, 14 and 21 days, and MVD increased at 14 and 21 days. Significantly positive correlations were demonstrated between ADC and MVD, NF (r=0.461 and 0.442, P＜0.05), between D and MVD, NF (r=0.568 and 0.519, P＜0.05) after exclusion of the data from the baseline. The parameter f from all the time points including the baseline was positively correlated with histological MVD and NF (r=0.590 and 0.458, P＜0.05). Conclusion IVIM parameters may reflect the intratumoral vascularity, tumor cell proliferation and necrosis of HCC, and they are correlated with the pathological indicators.