A Threshold Structure Metric for Medical Image Interrogation: The 2D Extension of Approximate Entropy

摘要

Reconstructive imaging permeates medical practice because of its apparently clear grey-scale depiction of anatomy. However, the tell tale signs of abnormality and its delineation for treatment demand experts work at the threshold of visibility for hints of structure. Hitherto, a suitable assistive metric that chimes with clinical experience has been absent. This paper develops the complexity measure approximate entropy (ApEn) from its one-dimensional physiological origin into a two-dimensional algorithm to fill this gap. The first detailed algorithm is presented and then applied to X-ray computed tomography used in image guided radiotherapy for cancer. Results clearly reveal the fine structural detail missed by grey-scale metrics, the strength of which is calibrated by the ApEn process itself. Machine assisted manual interaction and automated image interrogation for radiomics is envisaged.