Fundamental limitations imposed by x-ray interactions on the modulation transfer function of existing x-ray detectors

George Hajdok; Jerry J. Battista; Ian A. Cunningham

doi:10.1117/12.480359

5 June 2003 Fundamental limitations imposed by x-ray interactions on the modulation transfer function of existing x-ray detectors

George Hajdok, Jerry J. Battista, Ian A. Cunningham

Author Affiliations +

Proceedings Volume 5030, Medical Imaging 2003: Physics of Medical Imaging; (2003) https://doi.org/10.1117/12.480359
Event: Medical Imaging 2003, 2003, San Diego, California, United States

Abstract

The development of new detectors for diagnostic x-ray imaging is a complex and expensive endeavour. An understanding of fundamental performance potential and limitations is therefore critical to the wise allocation of research resources. We present a Monte Carlo study in which the fundamental spatial resolution limitations imposed by x-ray interactions were determined for both direct conversion amorphous selenium (a-Se) and indirect conversion cesium iodide (CsI) detectors. Using a simulated infinitesimal x-ray beam, the absorbed energy point spread function (PSF) in each detector material was scored within rectilinear bin sizes of 5 mm for incident x-ray energies between 10 and 100 keV. The modulation transfer function (MTF) was determined from each simulated PSF and characterized in terms of the 50% MTF frequency, f₅₀, and the equivalent passband, N_e. Both materials demonstrated: (i) a drop in f₅₀ (a-Se: 25%, CsI: 85%) and N_e (a-Se: 45%, CsI: 75%) immediately above the K-edge energy due to re-absorption of characteristic radiation, and (ii) a moderate recovery of f₅₀ and N_e levels with further increase in energy. In addition, within the diagnostic energy range and spatial frequency range of 0 -- 20 cycles/mm, the values of the fundamental MTF due to x-ray interactions remain above 50%. In general, we conclude that existing amorphous selenium and cesium iodide detectors operate far from fundamental spatial resolution limits in both mammography and radiography applications. Further reduction in detector element size will potentially improve spatial resolution in these detectors.

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George Hajdok, Jerry J. Battista, and Ian A. Cunningham "Fundamental limitations imposed by x-ray interactions on the modulation transfer function of existing x-ray detectors", Proc. SPIE 5030, Medical Imaging 2003: Physics of Medical Imaging, (5 June 2003); https://doi.org/10.1117/12.480359

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