1. A method of determining the histological grade of Hepatocellular Carcinoma (HCC), comprising: acquiring a Computed Tomography (CT) image of a person including an HCC tumor; delineating the HCC tumor; and assigning a histological grade to the HCC tumor, wherein assigning the histological grade to the HCC tumor comprises: applying a plurality of filters to the HCC tumor, wherein each of the filters produces a corresponding response image and, for each of the filters, a convolution operation is performed on the filter and the CT image to produce the response image corresponding to that filter; computing an average response of the HCC tumor in each of the response images and recording each of the average responses as an Independent Subspace Analysis (ISA) feature; and determining the histological grade of the HCC tumor based on the ISA features by using a classifier.