Dynamic fluence field modulation for miscentered patients in computed tomography

Andrew Mao; Grace J. Gang; William Shyr; Reuven Levinson; Jeffrey H. Siewerdsen; Satomi Kawamoto; J. Webster Stayman

doi:10.1117/1.JMI.5.4.043501

24 October 2018 Dynamic fluence field modulation for miscentered patients in computed tomography

Andrew Mao, Grace J. Gang, William Shyr, Reuven Levinson, Jeffrey H. Siewerdsen, Satomi Kawamoto, J. Webster Stayman

Author Affiliations +

Journal of Medical Imaging, Vol. 5, Issue 4, 043501 (October 2018). https://doi.org/10.1117/1.JMI.5.4.043501

Abstract

Traditional CT image acquisition uses bowtie filters to reduce dose, x-ray scatter, and detector dynamic range requirements. However, accurate patient centering within the bore of the CT scanner takes time and is often difficult to achieve precisely. Patient miscentering combined with a static bowtie filter can result in significant increases in dose, reconstruction noise, and CT number variations, and consequently raise overall exposure requirements. Approaches to estimate the patient position from scout scans and perform dynamic spatial beam filtration during acquisition are developed and applied in physical experiments on a CT test bench using different beam filtration strategies. While various dynamic beam modulation strategies have been developed, we focus on two approaches: (1) a simple approach using attenuation-based beam modulation using a translating bowtie filter and (2) dynamic beam modulation using multiple aperture devices (MADs)—an emerging beam filtration strategy based on binary filtration of the x-ray beam using variable width slits in a high-density beam blocker. Improved dose utilization and more consistent image performance with respect to an unmodulated baseline (static filter) are demonstrated for miscentered objects and dynamic beam filtration in physical experiments. For a homogeneous object miscentered by 4 cm, the dynamic filter reduced the maximum regional noise and dose penalties (compared with a centered object) from 173% to 16% and 42% to 14%, respectively, for a traditional bowtie, 29% to 8% and 24% to 15%, respectively, for a single MAD, and 275% to 11% and 56% to 18%, respectively, for a dual-MAD filter. The proposed methodology has the potential to relax patient centering requirements within the scanner, reduce setup time, and facilitate additional CT dose reduction.

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Andrew Mao, Grace J. Gang, William Shyr, Reuven Levinson, Jeffrey H. Siewerdsen, Satomi Kawamoto, and J. Webster Stayman "Dynamic fluence field modulation for miscentered patients in computed tomography," Journal of Medical Imaging 5(4), 043501 (24 October 2018). https://doi.org/10.1117/1.JMI.5.4.043501

Received: 9 April 2018; Accepted: 17 September 2018; Published: 24 October 2018

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