Purpose: Radiological longitudinal follow-up of liver tumors in CT scans is the standard of care for disease progression assessment and for liver tumor therapy. Finding new tumors in the follow-up scan is essential to determine malignancy, to evaluate the total tumor burden, and to determine treatment efficacy. Since new tumors are typically small, they may be missed by examining radiologists.
Methods: We describe a new method for the automatic detection and segmentation of new tumors in longitudinal liver CT studies and for liver tumors burden quantification. Its inputs are the baseline and follow-up CT scans, the baseline tumors delineation, and a tumor appearance prior model. Its outputs are the new tumors segmentations in the follow-up scan, the tumor burden quantification in both scans, and the tumor burden change. Our method is the first comprehensive method that is explicitly designed to find new liver tumors. It integrates information from the scans, the baseline known tumors delineations, and a tumor appearance prior model in the form of a global convolutional neural network (CNN) classifier. The method is hybrid so to benefit from the advantages of both human-engineered and machine learning methods. It includes deformable liver and known tumors registration and candidate new tumors detection and segmentation. Unlike other deep learning based methods, it does not require large tagged training sets.
Results: Our experimental results on 37 longitudinal liver CT studies with 246 tumors, of which 97 were new tumors, with radiologist approved ground-truth segmentations yields a true positive new tumors detection rate of 86% vs. 72% with stand-alone detection, and a tumor burden volume overlap error of 16%.
Conclusions: New tumors detection and tumor burden volumetry are important for diagnosis and treatment. Our new method enables a simplified radiologist-friendly workflow that is potentially more accurate and reliable than the existing one by automatically and accurately following known tumors and detecting new tumors in the follow-up scan.
