矢田 典久, 工藤 正俊

Norihisa YADA, Masatoshi KUDO

近畿大学医学部消化器内科

Department of Gastroenterology and Hepatology, Kinki University Faculty of Medicine, Japan

キーワード :

Elastography can be classified into two principles, one is strain imaging and the other method is measuring a shear wave velocity, so called shear wave imaging. Real-time Tissue Elastography （RTE） is one of the most commonly used strain imaging methods. Applied with a constant stress, a strain is greater in soft tissue than hard tissue. In the other word, soft tissue is deformed greater than hard tissue. Relative strain is calculated by measuring the displacement of the before and after deformation.
In mammary gland, thyroid and prostate, the degree of relative strain can distinguish malignant spaceoccupying lesion from non-malignant lesion. Manual compression from the body surface is possible to apply pressure up to the diagnostic depth in the body surface organs such as mammary gland and thyroid. But manual compression is not easily transmitted to the deep organs such as liver. Therefore, displacement induced by cardiac motion is used for evaluation of liver RTE.
In chronic liver disease, as liver fibrosis progresses, an area of the blue （relatively hard） portion tends to increase in RTE. To perform an objective and quantitative evaluation, the image features from RTE image were extracted. Liver Fibrosis Index （LFI） was calculated by multiple regression analysis, with the image features （independent variable） and fibrosis stage （dependent variable） among 310 patients with chronic hepatitis C and 15 healthy volunteers. Among another 241 patients with chronic hepatitis C, validation study of LFI was performed. The mean of LFI in stage F0F1, F2, F3, and F4 was 1.64, 2.11, 2.52, and 2.72, respectively, demonstrating a stepwise increase with increasing severity of liver fibrosis （p ＜ 0.001）. The area under the receiver operating characteristic curve of the LFI, platelet count, aspartate/alanine aminotransferase ratio, aspartate aminotransferase-to-platelet ratio, and FibroIndex for predicting cirrhosis （F4 vs. F0F3） was 0.842, 0.833, 0.688, 0.797 and 0.841; for predicting F3 stage or higher （F3F4 vs. F0F2） was 0.875, 0.831, 0.723, 0.784 and 0.826, respectively. In patients with high activity or jaundice, the shear wave velocity was changed over the short-term treatment, but LFI was not changed.
RTE is a non-invasive tool to diagnose liver fibrosis without affected activity and jaundice.