Cross-talk and spatial resolution in a CT scanner with a flat panel detector

Seemeen Karimi; Joseph Tringe

doi:10.1117/12.2632198

14 October 2022 Cross-talk and spatial resolution in a CT scanner with a flat panel detector

Seemeen Karimi, Joseph Tringe

Proceedings Volume 12242, Developments in X-Ray Tomography XIV; 122421A (2022) https://doi.org/10.1117/12.2632198
Event: SPIE Optical Engineering + Applications, 2022, San Diego, California, United States

Abstract

The spatial resolution of an x-ray computed tomography (CT) system is determined by its components, including the x-ray source, detector, and image reconstruction process. It is necessary to analyze the contributions of each component to understand the total spatial resolution of the system. Detector blur in flat panels is usually estimated with an edge function and data fitting, but the contribution of cross-talk (inter-pixel signal leakage) to detector blur is difficult to measure directly. Here, we report a simple method to isolate the cross-talk. We analytically modeled the spatial resolution of a CT scanner that uses a Varex flat-panel detector with 0.2 mm pixels and a 450 kVp, dual-focus x-ray tube. Our model examines the contributions of the x-ray focal spot size, detector pixel size, cross-talk, filtering, and backprojection. For the cross-talk model, we measured covariance in air, and from the covariance, we generated a digital filter that approximates the blur due to cross-talk. We validated the model by experimentally measuring spatial resolution with a 0.05 mm-diameter tungsten wire. The wire serves as an impulse function. The image is therefore an impulse response, and its Fourier transform yields the modulation transfer function (MTF). The model and measurement show correspondence within 5% at the 50% point. Our main finding was that detector cross-talk dominates the blurring, dropping the total MTF by over 30 % at the 50% point. Our methods are easily reproducible and do not require sophisticated test-objects, difficult alignment procedures, or image-processing as is common with other measurement methods.

Conference Presentation

Citation Download Citation

Seemeen Karimi and Joseph Tringe "Cross-talk and spatial resolution in a CT scanner with a flat panel detector", Proc. SPIE 12242, Developments in X-Ray Tomography XIV, 122421A (14 October 2022); https://doi.org/10.1117/12.2632198

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