Automated localization of mini-screw fiducials in spine CT scans

Abstract

Miniature Screws, often used for fiducials, are currently localized on DICOM images manually. This time-consuming process can add tens of minutes to the computational process for registration, or error analysis. Through a series of morphological operations, this localization task can be completed in a time much less than a second when performed on a standard laptop. Two image sets were analyzed. The first data set consisted of six intraoperative CT (iCT) scans of the lumbar spine of both cadaver and live porcine samples. This dataset includes not only implanted mini-screws, but other metal instrumentation. The second dataset consists of 6 semi-rigidly deformed CT (uCT) scans of the lumbar spine of the same animals. This dataset has been intensity down sampled from 16 bits to eight bits as a pre-processing step. Also, due to other deformation steps, other artifacts are apparent. Both datasets show at least 18 mini-screws which were rigidly implanted in the lumbar vertebrae. Each vertebra has at least three mini-screws implanted. These images were processed as follows: projection image forming via maximum row values, thresholding, opening, non-circular regions were removed, and circular regions were eroded. Leaving voxel locations of the center of each mini-screw. The aforementioned steps can be completed with a mean computational efficiency of .0365 seconds. Which is an unobtainable time for manual localization. Even by the most skilled. The true positive rates of the iCT and uCT datasets were 96.