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Proceedings Paper

Organ dose in chest CT: effect of modulation scheme on estimation accuracy
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Paper Abstract

The purpose of this study was to evaluate how different implementations of the tube current modulation (TCM) technology affect organ dose conversion factors in chest CT and how organ dose can be accurately estimated for various modulation schemes. Computational phantom of a normal-weight female patient was used. A method was developed to generate tube current (mA) modulation profiles based on the attenuation of the phantom, taking into account the geometry of the CT system as well as the x-ray energy spectrum and bowtie filtration in a CT scan. The mA for a given projection angle was calculated as a power-law function of the attenuation along this projection. The exponent of this function, termed modulation control strength, was varied from 0 to 1 to emulate the effects of different TCM schemes. Organ dose was estimated for a chest scan for each modulation scheme and was subsequently normalized by volume-weighted CT dose index (CTDIvol) to obtain conversion factors. The results showed that the conversion factors are second-order polynomial functions of the modulation control strength. The conversion factors established for a fixed-mA scan may be used to estimate organ dose in a TCM scan. For organs on the periphery of the scan coverage, the best accuracy is achieved when using CTDIvol computed from the average mA of the entire scan. For organs inside the scan coverage, the best accuracy is achieved when using CTDIvol computed from the volume-averaged mA values of all the axial slices containing the organ.

Paper Details

Date Published: 21 March 2013
PDF: 10 pages
Proc. SPIE 8668, Medical Imaging 2013: Physics of Medical Imaging, 86682A (21 March 2013); doi: 10.1117/12.2008505
Show Author Affiliations
Xiang Li, Carl E. Ravin Advanced Imaging Labs. (United States)
Duke Univ. (United States)
William P. Segars, Carl E. Ravin Advanced Imaging Labs. (United States)
Duke Univ. (United States)
Duke Univ. Medical Physics Graduate Program (United States)
Ehsan Samei, Carl E. Ravin Advanced Imaging Labs. (United States)
Duke Univ. (United States)
Duke Univ. Medical Physics Graduate Program (United States)


Published in SPIE Proceedings Vol. 8668:
Medical Imaging 2013: Physics of Medical Imaging
Robert M. Nishikawa; Bruce R. Whiting; Christoph Hoeschen, Editor(s)

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