By varying its thickness to compensate for the different path length through the patient as a function of fan angle, a pre-patient bowtie filter modulates flux distribution to reduce patient dose, scatter, and detector dynamic range, and to improve image quality. A dynamic bowtie filter is superior to its traditional, static counterpart in its ability to adjust its thickness along different fan and view angles to suit a specific patient and task. Among the proposed dynamic bowtie designs, the piecewise-linear and the digital beam attenuators offer more flexibility than conventional filters, but rely on analog positioning of a limited number of wedges. In this work, we introduce a new approach with digital control, called the fluid-filled dynamic bowtie filter. It is a two-dimensional array of small binary elements (channels filled or unfilled with attenuating liquid) in which the cumulative thickness along the x-ray path contributes to the bowtie’s total attenuation. Using simulated data from a pelvic scan, the performance is compared with the piecewise-linear attenuator. The fluid-filled design better matches the desired target attenuation profile and delivers a 4.2x reduction in dynamic range. The variance of the reconstruction (or noise map) can also be more homogeneous. In minimizing peak variance, the fluid-filled attenuator shows a 3% improvement. From the initial simulation results, the proposed design has more control over the flux distribution as a function of both fan and view angles.
[1]
S J Riederer,et al.
Noise Due to Photon Counting Statistics in Computed X‐Ray Tomography
,
1977,
Journal of computer assisted tomography.
[2]
C. Mistretta,et al.
Design of a digital beam attenuation system for computed tomography. Part II. Performance study and initial results.
,
2013,
Medical physics.
[3]
Norbert J Pelc,et al.
The feasibility of a piecewise-linear dynamic bowtie filter.
,
2013,
Medical physics.
[4]
N. Pelc,et al.
Control algorithms for dynamic attenuators.
,
2014,
Medical physics.
[5]
Jiang Hsieh,et al.
Computed Tomography: Principles, Design, Artifacts, and Recent Advances, Fourth Edition
,
2022
.
[6]
N. Pelc,et al.
Dose reduction using a dynamic, piecewise-linear attenuator.
,
2014,
Medical physics.
[7]
N. Pelc,et al.
The piecewise-linear dynamic attenuator reduces the impact of count rate loss with photon-counting detectors
,
2014,
Physics in medicine and biology.
[8]
Timothy P. Szczykutowicz,et al.
Design of a digital beam attenuation system for computed tomography: part I. System design and simulation framework.
,
2013,
Medical physics.