Imaging interpretation

Compared with the adjacent non-tumorous regions, the liver parenchyma and vascularity patterns of lesions in SCEUS were classified as having hyper, iso, or hypovascularity when more than 50% of the lesion area corresponded to the above patterns. In EOB-MRI, all images were estimated in the transverse plane. The lesion’s signal intensity and surrounding non-tumorous liver parenchyma were measured using an operator-defined region of interest on unenhanced T1-weighted and HBP images. The lesions were measured at the level of the largest diameter when they were displayed most clearly. The area without respiratory motion artifacts was chosen to be the surrounding area. Quantitative analysis of the pre-contrast ratio, post-contrast ratio, and EOB enhancement ratio was carried out with the following formulas taken from the literature (16):

Pre-contrast ratio = signal intensity of lesion/signal intensity of the non-tumorous regions in unenhanced T1-weighted images.

Post-contrast ratio = signal intensity of lesion/signal intensity of the non-tumorous regions in HBP images.

To assess the actual degree of tumor enhancement by EOB in comparison with the surrounding liver parenchyma, we also calculated the relative enhancement ratio of the lesions as follows (16):

EOB enhancement ratio = post-contrast ratio/pre-contrast ratio.

The schematic diagram of measurement is shown in Figure 2. Tumor vascularity was evaluated in the AP EOB-MRI images. The signal intensity of the tumorous area relative to the non-tumorous liver parenchyma was observed. A lesion’s hypervascularity was defined as a hyperenhanced appearance compared with the surrounding liver parenchyma; otherwise, lesions were classified as non-hypervascular (21,22).

Schematic diagram of the quantitative measurement methods for the pre-contrast ratio, post-contrast ratio, and gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (EOB) enhancement ratios. (A,B,C,D) and (E,F) are 2 different cases with characteristics of small size and unclear margin, respectively. Images (A,C,E,G) show the unenhanced T1-weighted images, while (B,D,F,H) show hepatobiliary phase (HBP) images. In (C,D,G,H), the regions of interest of our target lesions are marked in red, and the surrounding non-tumorous regions which were used as a reference are marked in green. In principle, the priority of reference should be given to uniform liver parenchyma without blood vessels with a similar size to the target lesions. (C,G) show unenhanced T1-weighted images, pre-contrast ratio = signal intensity of lesion (red area)/signal intensity of non-tumorous regions (green area). (D,H) show HBP images, post-contrast ratio = signal intensity of lesion (red area)/signal intensity of non-tumorous regions in the HBP image (green area). The EOB enhancement ratio = post-contrast ratio/pre-contrast ratio. The arrows indicate the target lesion.

Images obtained from EOB-MRI and SCEUS examinations were evaluated independently by 2 hepatologists (SCEUS: HN and KO; EOB-MRI: MC and SM), who has worked in the field of HCC for 8 years and have more than 5 years of experience in liver imaging. For quantitative data (enhancement ratio in EOB-MRI), the average value was used for analysis. For qualitative data (echogenicity in SCEUS), any interpretation discrepancies were resolved by consensus with a third expert hepatologist (KN) with 20 years of HCC diagnosis and treatment experience. The operators were unaware of the final diagnosis, the patients’ clinical conditions, and other radiological information.