Ring artefact reduction via multi-point piecewise linear flat field correction for X-ray computed tomography.

X-ray computed tomography (XCT) is a well-established method for measuring and inspecting an object's internal structure in a non-destructive manner. Ring artefacts are unwanted high- or low-intensity rings that appear in CT images that influence CT-based measurements. The cause of the subtle ring artefacts found in high-resolution XCT data is found to be due to inadequate flat field detector correction. Therefore, in this work, the usual two-point flat field correction is replaced by a multi-point, piecewise linear flat field correction. The proposed method is shown to increase the signal-to-noise ratio of exemplary CT data by up to 12.1%. Based on the results presented, it is recommended that a minimum of seven open field images should be used for flat field correction.