Bowtie filters for dedicated breast CT: Theory and computational implementation

Kontson, Kimberly; Jennings, Robert J.

doi:10.1118/1.4908002

Cited by 12 publications

(14 citation statements)

References 35 publications

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“…The usage of bowtie filters for bCT has been proposed. [12][13][14] Their usage, however, results in a fixed attenuation profile during a scan. The designs of bowtie filters in whole-body systems, where their usage is prolific, are mostly proprietary information.…”

Section: Introductionmentioning

confidence: 99%

“…The usage of bowtie filters for bCT has been proposed . Their usage, however, results in a fixed attenuation profile during a scan.…”

Section: Introductionmentioning

confidence: 99%

“…This assumption, however, is an oversimplification in many cases, including in bCT. Multiple research groups have designed fixed bowtie filters specific to bCT, with different shapes and materials, demonstrating potential benefits in dose savings, and reduction in scatter and detector dynamic range . However, limitations of bowtie filters designed for whole‐body CT systems, specifically their exclusion of variations in axial direction, also impact their potential for application in bCT.…”

Section: Introductionmentioning

confidence: 99%

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A fluence modulation and scatter shielding apparatus for dedicated breast CT: Theory of operation

Ghazi¹

2020

Medical Physics

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Purpose: To introduce an auxiliary apparatus of fluence modulation and scatter shielding for dedicated breast computed tomography (bCT) and the corresponding patient-specific method of image acquisition. Methods: The apparatus is composed of two assemblies, referred to herein as the "Dynamic Fluence Gate" (FG) and "Scatter Shield" (SS), that work in synchrony to form a narrow beam sweeping the entire fan angle coverage of the imaging system during a projection. The apparatus, as a whole, is referred to as FG-SS. FG and SS are pre-patient and post-patient units, respectively. Each is composed of a rotating drum, on top of which are installed two sheets of high x-ray attenuating material, a sensory system, and the constituent robotics. The sheets of each unit are positioned such that an openinga window Fluence Modulation and Scatter Shielding is formed between them. The rotations of the drums and positioning of the sheets are synchronized and adjusted such that a line of sight is created between the source, FG window, the breast, and the SS window. With line of sight achieved, the narrow beam transitions from the source to the detector. The fluence of the narrow beam during a projection depends on the size, shape, and positioning of the breast. The FG-SS method of imaging is discussed mathematically and demonstrated using computer simulations. A series of Monte Carlo simulations are conducted to evaluate the performance of the system as relates to its impact on the imager's dynamic range, dose distribution to the breast, noise inhomogeneity in reconstructed images, and scatter buildup in projections within small, medium, and large breasts composed of homogeneous medium breast tissue. Results: Implementation of FG-SS results in near scatter-free projections, reduction in both dose and the required dynamic range of the imager, and equalization of the quantum noise distribution in the reconstructed image. Using the disclosed design, the dynamic range was reduced by factors ranging from 1.6 to 5.5 across the range of breast sizes studied. A reduction in the acquisition of the scattered rays, varying between the factors of 6.1 (in the small breast) and 9.8 (in that large breast) was achieved and consequently, shading artifacts were suppressed. Noise in the CT image was equalized by reducing the overall spatial variation from 29% to <5% in small breast and from 45% to 14% in the large breast. An overall reduction in deposited dose to the breast was achievedbetween 26% and 39% depending on the breast size. Conclusions: Utilization of the FG-SS apparatus and technique was demonstrated via simulations to result in: significant reductions in dose to the breast, reductions in scatter uptake in projections, reduced required dynamic range of the imager, and homogenizing of quantum noise throughout the reconstructed image.

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Section: Introductionmentioning

confidence: 99%

“…The usage of bowtie filters for bCT has been proposed . Their usage, however, results in a fixed attenuation profile during a scan.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A fluence modulation and scatter shielding apparatus for dedicated breast CT: Theory of operation

Ghazi¹

2020

Medical Physics

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“…Additionally, clinical CBCT systems utilize bowtie filters to reduce imaging dose, the dynamic range requirement of the imaging panel, scatter and beam hardening artefacts [14]. The bowtie filters have been optimised for specific geometries and positions of the imaging object [15,16]. It is unclear how the presence of a bowtie filter interacts with artefact modelling and correction strategies.…”

Section: Introductionmentioning

confidence: 99%

Decoupling of bowtie and object effects for beam hardening and scatter artefact reduction in iterative cone-beam CT

Cai

Byrne²,

Archibald-Heeren³

et al. 2020

Phys Eng Sci Med

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Cone-beam computed tomography (CBCT) is an important imaging modality for image-guided radiotherapy and adaptive radiotherapy. Feldkamp-Davis-Kress (FDK) method is widely adopted in clinical CBCT reconstructions due to its fast and robust application. While iterative algorithms have been shown to outperform FDK techniques in reducing noise and imaging dose, they are unable to correct projection-domain artefacts such as beam hardening and scatter. Empirical correction techniques require a holistic approach as beam hardening and scatter coexist in the measurement data. This multi-part proof of concept study conducted in MATLAB presents a novel approach to artefact reduction for CBCT image reconstruction. Firstly, we decoupled the beam hardening and scatter contributions originating from the imaging object and the bowtie filter. Next, a model was constructed to apply pixel-wise corrections to separately account for artefacts induced by the imaging object and the bowtie filter, in order to produce mono-energetic equivalent and scatter-compensated projections. Finally, the effectiveness of the correction model was tested on an offset phantom scan as well as a clinical brain scan. A conjugategradient least-squares algorithm was implemented over five iterations using FDK result as the initial input. Our proposed correction model was shown to effectively reduce cupping and shading artefacts in both phantom and clinical studies. This simple yet effective correction model could be readily implemented by physicists seeking to explore the benefits of iterative reconstruction.

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“…[9][10][11] Our group has designed three different types of bowtie filters that can mimic certain x-ray (XR) characteristics of breast tissue or produce a constant effective attenuation coefficient at the detector. 12 Two of these designs use the ideas of spectral matching and basis-material decomposition to match either the transmitted spectral shape of breast tissue using a single material design (bowtie design #1) or to match both the transmitted spectral shape and intensity of transmitted radiation through the breast using a two-material design (bowtie design #2). Bowtie design #3 produces the same effective attenuation coefficient at the detector.…”

Section: Introductionmentioning

confidence: 99%

Bowtie filters for dedicated breast CT: Analysis of bowtie filter material selection

Kontson

Jennings

2015

Medical Physics

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Bowtie filters for dedicated breast CT: Theory and computational implementation

Cited by 12 publications

References 35 publications

A fluence modulation and scatter shielding apparatus for dedicated breast CT: Theory of operation

A fluence modulation and scatter shielding apparatus for dedicated breast CT: Theory of operation

Decoupling of bowtie and object effects for beam hardening and scatter artefact reduction in iterative cone-beam CT

Bowtie filters for dedicated breast CT: Analysis of bowtie filter material selection

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