Mr. Andrew Mao Profile

Andrew Mao

Student at Johns Hopkins Univ

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SPIE Journal Paper | 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

JMI, Vol. 5, Issue 04, 043501, (October 2018) https://doi.org/10.1117/12.10.1117/1.JMI.5.4.043501

KEYWORDS: Modulation, Image filtering, Sensors, X-ray computed tomography, Computed tomography, X-rays, Calibration, Image quality, Aluminum, Scanners

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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.

Proceedings Article | 9 March 2018 Presentation + Paper

Dynamic beam filtering for miscentered patients

Andrew Mao, William Shyr, Grace Gang, J. Webster Stayman

Proceedings Volume 10573, 105730U (2018) https://doi.org/10.1117/12.2293696

KEYWORDS: Image filtering, Sensors, Modulation, X-ray computed tomography, X-rays, Calibration, Scanners, Image quality

Read Abstract +

Traditional CT image acquisitions use bowtie filters to enable dose reduction. However, accurate patient centering within the bore of the CT scanner takes time and is often difficult to achieve precisely. Patient miscentering can result in significant dose, reconstruction noise, and CT number variations–raising overall exposure requirements. Approaches to estimate 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 proposed, we focus on two different approaches: 1) simple attenuation-based beam modulation using a translating bowtie filter, and 2) dynamic beam modulation using multiple aperture devices, an emerging beam filtration strategy base 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 is demonstrated for miscentered objects and dynamic beam filtration as compared to static filtration. The new methodology has the potential to relax patient centering requirements within the scanner, reduce set-up time, and facilitate additional CT dose reductions.

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