Implementation of a piecewise-linear dynamic attenuator

Bennett, N. Robert; Hsieh, Scott S.; Pelc, Norbert J.

doi:10.1117/1.jmi.6.2.023502

Cited by 3 publications

(4 citation statements)

References 21 publications

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“…Assuming a photon-counting detector, the optimization methods for different attenuators as described in Section 2.3.A were applied. For the piecewise-linear attenuator, 11 stainless steel wedges with width similar to reference [20] were assumed, and the wedge maximum thickness was chosen to achieve four orders of magnitude in attenuation.…”

Section: Methodsmentioning

confidence: 99%

“…For dynamic bowtie designs with adaptive components, the piecewise‐linear attenuator and the digital beam attenuator offer flexibility by having multiple wedges, each covering different fan angles. Moving a wedge in the axial direction changes the thickness presented to the x‐ray beam in the axial slice.…”

Section: Introductionmentioning

confidence: 99%

“…Fluids containing high atomic number elements are potential choices for this purpose. Like many of the other dynamic attenuator approaches, our approach aims to control the intensity as a function of position in the fan‐beam and view angle but transmission does not vary with the axial dimension in multi‐detector row systems. Other filter designs using fluid in channels were also proposed, but the long axis of the channels are aligned with the direction of x‐ray travel (source‐to‐detector direction) and the local attenuation of the x‐ray beam is controlled by the thickness of liquid in one channel (analog).…”

Section: Introductionmentioning

confidence: 99%

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Fluid‐filled dynamic bowtie filter: Description and comparison with other modulators

Hsieh

Pelc

2018

Medical Physics

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Purpose: A dynamic bowtie filter can modulate flux along both fan and view angles for reduced patient dose, scatter, and required photon flux, which is especially important for photon counting detectors (PCDs). Among the proposed dynamic bowtie designs, the piecewise-linear attenuator (Hsieh and Pelc, Med Phys 2013) offers more flexibility than conventional filters, but relies on analog positioning of a limited number of wedges. In this work, we study our previously proposed dynamic attenuator design, the fluid-filled dynamic bowtie filter (FDBF) that has digital control. Specifically, we use computer simulations to study fluence modulation, reconstructed image noise, and radiation dose and to compare it to other attenuators. FDBF is an array of small channels each of which, if it can be filled with dense fluid or emptied quickly, has a binary effect on the flux. The cumulative attenuation from each channel along the x-ray path contributes to the FDBF total attenuation. Methods: An algorithm is proposed for selecting which FDBF channels should be filled. Two optimization metrics are considered: minimizing the maximum-count-rate for PCDs and minimizing peak-variance for energy-integrating detectors (EIDs) at fixed radiation dose (for optimizing dose efficiency). Using simulated chest, abdomen, and shoulder data, the performance is compared with a conventional bowtie and a piecewise-linear attenuator. For minimizing peak-variance, a perfect-attenuator (hypothetical filter capable of adjusting the fluence of each ray individually) and flat-variance attenuator are also included in the comparison. Two possible fluids, solutions of zinc bromide and gadolinium chloride, were tested. Results: To obtain the same SNR as routine clinical protocols, the proposed FDBF reduces the maximum-count-rate (across projection data, averaged over the test objects) of PCDs to 1.2 Mcps/mm2, which is 55.8 and 3.3 times lower than the max-count-rate of the conventional bowtie and the piecewise-linear bowtie, respectively. (Averaged across objects for FDBF, the max-count-rate without object and FDBF is 2063.5 Mcps/mm2, and the max-count-rate with object without FDBF is 749.8 Mcps/mm2.) Moreover, for the peak-variance analysis, the FDBF can reduce entrance-energy-fluence (sum of energy incident on objects, used as a surrogate for dose) to 34% of the entrance-energy-fluence from the conventional filter on average while achieving the same peak noise level. Its entrance-energy-fluence reduction performance is only 7% worse than the perfect-attenuator on average and is 13% better than the piecewise-linear filter for chest and shoulder. Furthermore, the noise-map in reconstructed image domain from the FDBF is more uniform than the piecewise-linear filter, with 3 times less variation across the object. For the dose reduction task, the zinc bromide solution performed slightly poorer than stainless steel but was better than the gadolinium chloride solution. Conclusions: The FDBF allows finer control over flux distribution compared to piecewis...

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fluid‐filled dynamic bowtie filter: Description and comparison with other modulators

Hsieh

Pelc

2018

Medical Physics

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“…In addition, the bowtie filter partially reduces the scattered signal and mitigates the variation in the non-uniform noise distribution throughout the field of view (Bartolac et al 2011, McKenney et al 2011. However, due to the elliptical shape characteristic of the human anatomical structure on the transverse section, the bowtie filter gradually thickens from the position of the principal x-ray projection to the outside (Shunhavanich et al 2019). Therefore, the thickness of the bowtie filter is generally different for each x-ray and each viewing angle.…”

Section: Introductionmentioning

confidence: 99%

Pixel-by-pixel correction of beam hardening artifacts by bowtie filter in fan-beam CT

Ye,

Zhao,

Shimomura

et al. 2024

Phys. Med. Biol.

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Objective: Beam hardening (BH) artifacts in computed tomography (CT) images originate from the polychromatic nature of X-ray photons. In a CT system with a bowtie filter, residual BH artifacts remain when polynomial fits are used. These artifacts lead to worse visuals, reduced contrast, and inaccurate CT numbers. This work proposes a pixel-by-pixel correction (PPC) method to reduce the residual BH artifacts caused by a bowtie filter.Approach: The energy spectrum for each pixel at the detector after the photons pass through the bowtie filter was calculated. Then, the spectrum was filtered through a series of water slabs with different thicknesses. The polychromatic projection corresponding to the thickness of the water slab for each detector pixel could be obtained. Next, we carried out a water slab experiment with a mono energy E = 69 keV to get the monochromatic projection. The polychromatic and monochromatic projections were then fitted with a 2nd-order polynomial. The proposed method was evaluated on digital phantoms in a virtual CT system and phantoms in a real CT machine. Main results: In the case of a virtual CT system, the standard deviation of the line profile was reduced by 23.8%, 37.3%, and 14.3%, respectively, in the water phantom with different shapes. The difference of the linear attenuation coefficients (LAC) in the central and peripheral areas of an image was reduced from 0.010cm-1 to 0.003cm-1 and 0.007cm-1 to 0 in the biological tissue phantom and human phantom, respectively. The method was also validated using CT projection data obtained from Activion16. The difference in the LAC in the central and peripheral areas can be reduced by a factor of two.Significance: The proposed PPC method can successfully remove the cupping artifacts in both virtual and authentic CT images. The scanned object's shapes and materials do not affect the technique.

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Design of a digital, motion-free mechanism for fluence field modulation

Hsieh

Leng

et al. 2022

Medical Imaging 2022: Physics of Medical Imaging

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Implementation of a piecewise-linear dynamic attenuator

Cited by 3 publications

References 21 publications

Fluid‐filled dynamic bowtie filter: Description and comparison with other modulators

Fluid‐filled dynamic bowtie filter: Description and comparison with other modulators

Pixel-by-pixel correction of beam hardening artifacts by bowtie filter in fan-beam CT

Design of a digital, motion-free mechanism for fluence field modulation

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