9 March 2018 Accurate centroid determination for evaluating the modulation transfer function with a circular edge in CT images
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The in-plane modulation transfer function (MTF) for multi-slice computed tomography (CT) can be found by scanning a phantom with cylindrical contrast inserts and making use of the circular edges presented in reconstructed axial images. Pixel data across the edge are used to establish an edge spread function, which is then used to obtain the line spread function and finally the MTF. A crucial step in this approach is to accurately locate the centroid of the circular region. Since the ESF is usually established in subpixel scale, slight deviation of the centroid may result in large errors. It has been a common practice to apply a preset threshold and calculate the center of mass in the binary output on each individual slice. It has also been suggested to locate the centroid on each slice by maximizing the sum of pixel values lying under a predefined template. In this paper, we propose a new algorithm based on registering the entire cylindrical object in 3D space. In a test on a high-noise low-contrast edge, both the threshold and the maximization algorithm showed scattered distribution of centroids across consecutive slices, resulting in underestimation of the MTF up to 10% at intermediate frequencies. In comparison, the method based on 3D registration has been found more robust to noise and the centroid locations are more consistent in the longitudinal direction. It is therefore recommended to use the proposed algorithm for centroid determination in evaluating the MTF with a circular edge in CT images.
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Guozhi Zhang, Andreas Stratis, Nicholas Marshall, and Hilde Bosmans "Accurate centroid determination for evaluating the modulation transfer function with a circular edge in CT images", Proc. SPIE 10573, Medical Imaging 2018: Physics of Medical Imaging, 1057344 (9 March 2018); doi: 10.1117/12.2292908; https://doi.org/10.1117/12.2292908

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