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Title: Modeling and measurement of the detector presampling MTF of a variable resolution x-ray CT scanner

Abstract

The detector presampling modulation transfer function (MTF) of a 576-channel variable resolution x-ray (VRX) computed tomography (CT) scanner was evaluated in this study. The scanner employs a VRX detector, which provides increased spatial resolution by matching the scanner's field of view (FOV) to the size of an object being imaged. Because spatial resolution is the parameter the scanner promises to improve, the evaluation of this resolution is important. The scanner's pre-reconstruction spatial resolution, represented by the detector presampling MTF, was evaluated using both modeling (Monte Carlo simulation) and measurement (the moving slit method). The theoretical results show the increase in the cutoff frequency of the detector presampling MTF from 1.39 to 43.38 cycles/mm as the FOV of the VRX CT scanner decreases from 32 to 1 cm. The experimental results are in reasonable agreement with the theoretical data. Some discrepancies between the measured and the modeled detector presampling MTFs can be explained by the limitations of the model. At small FOVs (1-8 cm), the MTF measurements were limited by the size of the focal spot. The obtained results are important for further development of the VRX CT scanner.

Authors:
;  [1]
  1. Department of Biomedical Engineering and Imaging, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee 38163 (United States)
Publication Date:
OSTI Identifier:
20951093
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 3; Other Information: DOI: 10.1118/1.2436977; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; COMPUTERIZED SIMULATION; COMPUTERIZED TOMOGRAPHY; EVALUATION; IMAGES; MODULATION; MONTE CARLO METHOD; SPATIAL RESOLUTION

Citation Formats

Melnyk, Roman, and DiBianca, Frank A. Modeling and measurement of the detector presampling MTF of a variable resolution x-ray CT scanner. United States: N. p., 2007. Web. doi:10.1118/1.2436977.
Melnyk, Roman, & DiBianca, Frank A. Modeling and measurement of the detector presampling MTF of a variable resolution x-ray CT scanner. United States. doi:10.1118/1.2436977.
Melnyk, Roman, and DiBianca, Frank A. Thu . "Modeling and measurement of the detector presampling MTF of a variable resolution x-ray CT scanner". United States. doi:10.1118/1.2436977.
@article{osti_20951093,
title = {Modeling and measurement of the detector presampling MTF of a variable resolution x-ray CT scanner},
author = {Melnyk, Roman and DiBianca, Frank A.},
abstractNote = {The detector presampling modulation transfer function (MTF) of a 576-channel variable resolution x-ray (VRX) computed tomography (CT) scanner was evaluated in this study. The scanner employs a VRX detector, which provides increased spatial resolution by matching the scanner's field of view (FOV) to the size of an object being imaged. Because spatial resolution is the parameter the scanner promises to improve, the evaluation of this resolution is important. The scanner's pre-reconstruction spatial resolution, represented by the detector presampling MTF, was evaluated using both modeling (Monte Carlo simulation) and measurement (the moving slit method). The theoretical results show the increase in the cutoff frequency of the detector presampling MTF from 1.39 to 43.38 cycles/mm as the FOV of the VRX CT scanner decreases from 32 to 1 cm. The experimental results are in reasonable agreement with the theoretical data. Some discrepancies between the measured and the modeled detector presampling MTFs can be explained by the limitations of the model. At small FOVs (1-8 cm), the MTF measurements were limited by the size of the focal spot. The obtained results are important for further development of the VRX CT scanner.},
doi = {10.1118/1.2436977},
journal = {Medical Physics},
number = 3,
volume = 34,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
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  • Empirical determination of the modulation transfer function (MTF) for analog and digital megavoltage x-ray imagers is a challenging task. The most common method used to determine MTF at megavoltage x-ray energies employs a long, narrow slit formed by two parallel, metal blocks in order to form a 'slit beam'. In this work, a detailed overview of some of the important considerations of slit design is presented. Based on these considerations, a novel, compact slit, using 19 cm thick tungsten blocks, was designed. The prototype slit was configured to attach to the accessory slot of the gantry of a linear accelerator,more » which greatly simplified the measurement process. Measurements were performed to determine the presampling MTF at 6 MV for an indirect detection active matrix flat panel imager prototype previously developed for megavoltage imaging applications. In addition, the effects of two important slit design parameters, material type and thickness, on the accuracy of MTF determination were investigated via a Monte Carlo-based theoretical study. Empirically determined MTFs obtained from the prototype slit closely match those from an earlier, less compact slit design based on 40 cm thick steel blocks. The results of the Monte Carlo-based theoretical studies indicate that the prototype slit achieves close-to-ideal performance in terms of accurately determining the MTF by virtue of practically 100% beam attenuation in regions other than the slit gap. Furthermore, the theoretical results suggest that it may be possible to achieve even further reductions in slit thickness without compromising measurement accuracy.« less
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