This study demonstrates that radiomics model can be trained to distinguish S-HCC and pre-HCC based on precontrast MRI. We also found the FS-T2WI shows better performance on single sequence.
The radiomics features categorized into first-order features, shape features, second-order texture features and higher-order features. First-order features describe the intensity characteristics of tumors, and are general and basic indicators to describe the distribution of voxel intensity within the image region. Shape features described the three-dimensional dimensions, size, and shape of the lesion area, and were used to describe the characteristics of tumors with spherical or aspirated shapes. Second-order features, namely texture features, could quantify the heterogeneity within the tumor and represent the three-dimensional spatial characteristics of the lesion. Higher-order statistics features were robust features transformed from the first- and second-order features by filers. Five types of filters were applied: exponential, square, square root, logarithm and wavelet (which was applied as either a high- (H) or a low-pass(L)filter in each of the three dimensions: wavelet-LHL, wavelet-LHH, wavelet-HLL, wavelet-LLH, wavelet-HLH, wavelet-HHH, wavelet-HHL, wavelet-LLL) [15]. In present study, we obtained meaningful radiomincs feature sets from precontrast MRI, in which higher-order statistics features provided significant role. We also found the shape features were the most in efficient. It might because the lesion is too small and the image layer is too thick, the shape of the lesion could not be used to distinguish S-HCC from pre-HCC.
We found that the radiomics model based on FS-T2WI shows the better performance on single sequence. We would like to elaborate them combining the definitions of the radiomics features. The optimal radiomics features extracted from FS-T2WI mainly including the higher-order features which transformed from some first-order and second-order features. Next, we would introduce the meaning of the related radiomics features. Firstorder-Mean means the average gray level intensity within the ROI. Firstorder-10th percentile means the 10th percentile of the set of voxels included in the ROI. They were first-order features related to the intensity of the nodule [17]. GLSZM_size zone non-uniformity measures the variability of size zone volumes throughout the image, with a lower value indicating more homogeneity among zone size volumes in the image. And GLSZM_zone percentage measures the coarseness of the texture by taking the ratio of number of zones and number of voxels in the ROI. GLDM_dependence non-uniformity normalized measures the similarity of dependence throughout the image, with a lower value indicating more homogeneity among dependengcies in the image. NGTDM_contrast is a measure of the spatial intensity change, and it also dependent on the overall gray level dynamic range, for example, an image with a large range of gray level, with large changes between voxels and their neighbourhood [17]. These second-order features describe heterogeneity of lesions.
The effective features may be associated with different pathological characteristics during hepatocarcinogenesis. First, growing evidences suggest that chronic inflammation causes repeated cycles of cell injury, death and regeneration, which promoting aberrant cell signaling, epigenetic changes, mutational events, and accumulation of genetic damage [18–21]. During this phase, phenotypic and alteration occurred. Second, angiogenesis progresses is one of the key structural alteration during hepatocarcinogenesis, which is characterized by the presence of unpaired arteries and sinusoidal capillarization. Meanwhile, the portal tracts progressively diminish [19, 20, 22, 23]. Third, in cirrhotic livers, fat and iron content may change in hepatocytes. Because in the transition phase from portal to arterial supply, there is a period in which the development of unpaired arteries is not sufficient to compensate for the reduced portal venous and nontumoral arterial flow [24]. The change of fat and iron content is though to be associated with ischemic environment. In a word, these pathological characteristic may affect the signal of the lesion and cause heterogeneity within the lesion.
And why FS-T2WI features showed better performance? We speculate that there may be several reasons. First of all, as is well-known, most tumors have higher intracellular and/or extracellular water content than normal tissues. This may be related to the heterogeneity of tumor cells. Heterogeneity can be manifested in abnormal cell size, cell pleomorphism, nucleus-cytoplasm ratio, etc. During hepatocarcinogenesis, with the mutation of the gene, affected cells composed of pre-HCC and S-HCC acquire progressively atypical phenotypic features [25], and the corresponding water content of the cells is also different, which maybe reflected in T2 signal intensity. In addition, Shinmura et al. found that there was a significant association between the intranodular portal venous and arterial blood supplies and the T2-weighted MR imaging signal intensity in various types of hepatocellular nodules associated with liver cirrhosis [21]. Namely, the signal intensity on T2-weighted MR images increased as the intranodular portal venous blood supply decreased and arterial supply increased [21]. This conclusions may also be applicable to distinguish S-HCC and pre-HCC. Moreover, in terms of the step of delineating lesions in the radiomics study, a more complete radiomics feature of lesions can be obtained from T2WI because the edges of lesions can be more clearly and accurately identified by naked eye. This random errors may also cause differences between the performance of radiomics models based on T1WI or T2WI [26].
This study confirmed that radiomics can be used to distinguish S-HCC from pre-HCC based on precontrast MRI. And the radiomics model based on FS-T2WI showed the better performance on single sequence. Mokrane et al validated Delta V-A_DWT_LL_Variance-2D, a single radiomics feature of CT, which quantifying changes between arterial and portal venous phases can diagnose HCC in cirrhotic patients with indeterminate liver nodules [27]. In our study, radiomic models were based on precontrast MRI, which were more convenience and ignoring the contraindication of enhanced scanning. Cause of the repeatability and non-fatigue characteristics of the radiomics, it might has potential clinical application value. In this study, we delineated around each lesion outline for 3D volume area to obtain whole radiomics features as far as possible. To make precise classification, we certified all lesions by postoperative pathology. Thus, it was a reliable and noninvasive method for differential diagnosis between S-HCC and pre-HCC.
There are several limitations. Firstly, the sample size was small. A large number date from multi-center should validate and improve the generalisability of our finding. Secondly, other MRI sequences, such as in-, out-phase and DWI, should be enrolled in further studies. Thirdly, clinical characteristic might be helpful in distinguishing S-HCCs from pre-HCCs and should be further studied.