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

Xiang Li; William P. Segars; Ehsan Samei

doi:10.1117/12.2008505

21 March 2013 Organ dose in chest CT: effect of modulation scheme on estimation accuracy

Xiang Li, William P. Segars, Ehsan Samei

Proceedings Volume 8668, Medical Imaging 2013: Physics of Medical Imaging; 86682A (2013) https://doi.org/10.1117/12.2008505
Event: SPIE Medical Imaging, 2013, Lake Buena Vista (Orlando Area), Florida, United States

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 (CTDI_vol) 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 CTDI_vol computed from the average mA of the entire scan. For organs inside the scan coverage, the best accuracy is achieved when using CTDI_vol computed from the volume-averaged mA values of all the axial slices containing the organ.

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Xiang Li, William P. Segars, and Ehsan Samei "Organ dose in chest CT: effect of modulation scheme on estimation accuracy", Proc. SPIE 8668, Medical Imaging 2013: Physics of Medical Imaging, 86682A (21 March 2013); https://doi.org/10.1117/12.2008505

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KEYWORDS

Modulation

Chest

Computed tomography

Monte Carlo methods

X-ray computed tomography

Signal attenuation

Lung

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