Patients
The study was approved by the ethical committee of our institution, and informed consent was obtained. Our retrospective study was conducted all eligible CHC patients on the basis of following inclusion criteria between 2004 and 2016. HCC patients , who met following inclusion criteria during this period, were randomly included in our study with a ratio of HCC : CHC = 2 : 1. The inclusion criteria were as follows: (1) primary HCC or CHC diagnosed histopathologically after biopsy or surgery, (2) patients with high risk for HCC (cirrhosis or chronic hepatitis viral infection), (3) Available CEUS examination performed 2 weeks before operation.
The exclusion criteria were as follows: (1) unavailability of histological evaluation by surgery or biopsy, (2) incomplete clinic-pathological data or CE US data.
The flow chart of the study population was presented in Figure 1.
US imaging acquisition
US studies were performed first for scanning entire liver by experienced radiologist with the following equipment: (1) Aplio SSA-770 or Aplio 500 (Toshiba Medical Systems, Tokyo, Japan) with a 375BT convex transducer with frequency range, of 1.9 to 6.0 MHz. (2) Acuson Sequoia 512 (Siemens Medical Solutions, Mountain View, CA, United States) with a 4V1 vector transducer with frequency range of 1.0 to 4.0 MHz. (3) Aixplorer Ultrasound system (SuperSonic Imagine, Aix-en-Provence, France) equipped with the SC6-1 convex probe with frequency range of 1.0 to 6.0 MHz. If patients had multiple liver lesions, the largest one was regarded as target lesion. After identifying the target lesion and storing images recorded size, location, echo, shape, boundary, and margin, CE US examination with the same probe was performed after administration of 1.2 - 2.4 mL of SonoVue (Bracco Imaging, Milan, Italy) within 1-2 seconds into the antecubital vein followed by a 5 mL normal saline flush. The target lesion were observed continuously for at least 5 minutes for recording CE US features. Arterial phase hyperenhancement is described as entirely or partially (not rimlike and peripheral discontinuous globular) hyperechoic compared with the surrounding parenchyma. Washout is described as occurring of hypoechoic relative to liver after hyperechoic or isoechoic during the arterial phase. Early washout is defined as that occurs within 60s after injection of the contrast agent, and marked washout is defined when punched-out appearance (markedly hypoechoic emerging black) appears within 2 minutes.
CE US LI-RADS categories
The records of the whole process of CE US examination were independently analyzed by two experienced radiologists (reader 1 and reader 2, not involved in US examinations) with more than 8 years of experience in CE US. The discussion will focus on the cases where two readers have different opinions until the final consensus is reached. All of them were blind to the pathological and other imaging information. They were asked to classify into CE US LR-1 to LR-5 or LR-M according to CE US LI-RADS v2017. CE US LR-5 (not rim and peripheral discontinuous globular APHE with late and mild washout, meanwhile nodules size ≥ 10mm) is defined as HCC. Then the evaluation of diagnostic performance of v2017 LI-RADS would be conducted for HCC and CHC.
Ultrasomics features extraction and ultrasomics models
Images of each lesion confirmed by two radiologists in consensus (including 4 images from baseline US, arterial, portal venous and late phases of CE US, respectively) were used to delineate a region of interest (ROI) around the outline of the tumor using ITK-SNAP software (version 3.6.0; www.itksnap.org). ROI of each image included 1 cm around the lesion margin, but not the portion beyond the liver parenchyma. Then 5936 features were extracted from one single ROI (A total of 23744 features from each patient) using the Ultrasomics-Platform (Version 2.1, Ultrasomics Artificial Intelligence X-lab, Guangzhou), which mainly contains two major functions of ultrasomics feature mining and machine learning for model building. It is a kind of software for medical research including essential four modules of segmentation, calculation, feature selection and machine learning, and based on automatic analysis of the heterogeneity of the ROI, the clinical prediction is finally achieved through the above key processes. Finally, A ultrasomics model was developed based on features selected by spearman rank correlation analysis and machine-learning algorithms of support vector machine using software, and a ultrasomics score (U-score) was calculated by the ultrasomics model (U model) for each patient. The optimal cut-off value for U model were determined using receiver operating curve (ROC) analysis. HCC was defined as a U-score of each lesion greater than optimal cut-off value.
CHC and HCC patients finally included in this study were respectively grouped into training cohort and validation cohort at a ratio of 7 : 3 randomly. U model was developed in training cohort, confirmed in validation cohort.
Statistical analysis
Continuous variables were expressed as means ± standard deviations. Categorical variables were reported as numbers and percentage, compared by the chi-square test. The optimal cut-off values for U model were determined using ROC analysis. The diagnostic performance of LI-RADS or U model was assessed by ROC and the area under the curve (AUC), accuracy, sensitivity, specificity with 95% confident interval (CI). Delong’s test was used to compare the statistical differences between any two AUCs.
Statistical analysis was performed with SPSS 22.0 for Windows (Chicago, IL) and Ultrasomics-Platform (Version 2.1, Ultrasomics Artificial Intelligence X-lab, Guangzhou). P < 0.05 was considered statistically significant.