The effect of a finite focal spot size on location dependent detectability in a fan beam CT system

Byeongjoon Kim; Jongduk Baek

doi:10.1117/12.2253981

9 March 2017 The effect of a finite focal spot size on location dependent detectability in a fan beam CT system

Byeongjoon Kim, Jongduk Baek

Proceedings Volume 10132, Medical Imaging 2017: Physics of Medical Imaging; 1013254 (2017) https://doi.org/10.1117/12.2253981
Event: SPIE Medical Imaging, 2017, Orlando, Florida, United States

Abstract

A finite focal spot size is one of the sources to degrade the resolution performance in a fan beam CT system. In this work, we investigated the effect of the finite focal spot size on signal detectability. For the evaluation, five spherical objects with diameters of 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm were used. The optical focal spot size viewed at the iso-center was a 1 mm (height) × 1 mm (width) with a target angle of 7 degrees, corresponding to an 8.21 mm (i.e., 1 mm / sin (7°)) focal spot length. Simulated projection data were acquired using 8 × 8 source lets, and reconstructed by Hanning weighted filtered backprojection. For each spherical object, the detectability was calculated at (0 mm, 0 mm) and (0 mm, 200 mm) using two image quality metrics: pixel signal to noise ratio (SNR) and detection SNR. For all signal sizes, the pixel SNR is higher at the iso-center since the noise variance at the off-center is much higher than that at the iso-center due to the backprojection weightings used in direct fan beam reconstruction. In contrast, detection SNR shows similar values for different spherical objects except 1 mm and 2 mm diameter spherical objects. Overall, the results indicate the resolution loss caused by the finite focal spot size degrades the detection performance, especially for small objects with less than 2 mm diameter.

Citation Download Citation

Byeongjoon Kim and Jongduk Baek "The effect of a finite focal spot size on location dependent detectability in a fan beam CT system", Proc. SPIE 10132, Medical Imaging 2017: Physics of Medical Imaging, 1013254 (9 March 2017); https://doi.org/10.1117/12.2253981

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