Design of a digital beam attenuation system for computed tomography: Part I. System design and simulation framework

Szczykutowicz, Timothy P.; Mistretta, Charles A.

doi:10.1118/1.4773879

Cited by 53 publications

(73 citation statements)

References 25 publications

(45 reference statements)

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“…The work presented in this study explains the first experimental realization of a device capable of modulating the x-ray dose within the fan beam for non-inverse geometry CT (Szczykutowicz & Mistretta 2013 a , Szczykutowicz & Mistretta 2013 b , Szczykutowicz & Mistretta 2012, Szczykutowicz & Mistretta 2013 c , Szczykutowicz & Mistretta 2013 d ). The device used to obtain such a modulation is referred to as digital beam attenuator (DBA).…”

Section: Introduction: a Short History Of Ffm In Ct Imagingmentioning

confidence: 99%

Experimental realization of fluence field modulated CT using digital beam attenuation

Szczykutowicz¹,

Mistretta²

2014

Phys. Med. Biol.

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Purpose Tailoring CT scan acquisition parameters to individual patients is a topic of much research in the CT imaging community. It is now common place to find automatically adjusted tube current options for modern CT scanners. In addition, the use of beam shaping filters, commonly called bowtie filters, is available on most CT systems and allows for different body regions to receive different incident x-ray fluence distributions. However, no method currently exists which allows for the form of the incident x-ray fluence distribution to change as a function of view angle. This study represents the first experimental realization of fluence field modulated CT (FFMCT) for a c-arm geometry CT scan. Methods: X-ray fluence modulation is accomplished using a digital beam attenuator (DBA). The device is composed of 10 iron wedge pairs that modulate the thickness of iron x-rays must traverse before reaching a patient. Using this device, experimental data was taken using a Siemens Zeego c-arm scanner. Scans were performed on a cylindrical polyethylene phantom and on two different sections of an anthropomorphic phantom. The DBA was used to equalize the x-ray fluence striking the detector for each scan. Non DBA, or “flat field” scans were also acquired of the same phantom objects for comparison. In addition, a scan was performed in which the DBA was used to enable volume of interest (VOI) imaging. In VOI, only a small sub-volume within a patient receives full dose and the rest of the patient receives a much lower dose. Data corrections unique to using a piece-wise constant modulator were also developed. Results The feasibility of FFMCT implemented using a DBA device has been demonstrated. Initial results suggest dose reductions of up to 3.6 times relative to “flat field” CT. In addition to dose reduction, the DBA enables a large improvement in image noise uniformity and the ability to provide regionally enhanced signal to noise using VOI imaging techniques. Conclusions The results presented in this paper take the field of FFMCT from the theoretical stage to that of possible clinical implementation. FFMCT, as shown in this paper, can reduce patient dose while maintaining or improving image quality. In addition, the DBA has been experimentally shown to be well suited to implement entirely new imaging methods like photon counting and VOI imaging.

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Section: Introduction: a Short History Of Ffm In Ct Imagingmentioning

confidence: 99%

Experimental realization of fluence field modulated CT using digital beam attenuation

Szczykutowicz¹,

Mistretta²

2014

Phys. Med. Biol.

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“…For diagnostic CT, cycle times less than a quarter of a second would be required, and for cone beam CT, cycle times of 1 to 5 s are required. 2,16 A more detailed analysis of some of the factors influencing cycle time for liquids is given in Sec. 2.5.…”

Section: Selection Of Attenuatorsmentioning

confidence: 99%

“…Previous work has simulated dynamic bowtie filters for both types of FFMCT. [1][2][3][4][5][6] As current solid-metal attenuator solutions may be difficult to extend to 2-D modulation, we propose to use liquid-and gas-based attenuators which can be arrayed in a 2-D pattern to implement FFMCT. This idea is not entirely new to x-ray imaging; it was actually proposed in the early 1980s for chest radiography.…”

Section: Description Of Purposementioning

confidence: 99%

“…This minimum pressure would contribute to tube loading if it could not be incorporated into the standard beam prefiltration as described in our earlier work. 2,3 Potentially high pressures would be required to modulate the gas density to limits corresponding to meaningful tissue compensation amounts. Therefore, the wall thickness of the 2-D array must be made thick enough to support these high pressures without warping or bursting.…”

Section: Gas Attenuatorsmentioning

confidence: 99%

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Two-dimensional dynamic fluid bowtie attenuators

Hermus

Szczykutowicz

2016

J. Med. Imag

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“…Also, a piecewise constant dynamic bowtie has been described, in spirit quite similar to our own proposed design. 12,25,26 One advantage of the piecewise-linear design is that it avoids discontinuities in the attenuation profile that can cause imaging artifacts.…”

Section: Introductionmentioning

confidence: 99%

The feasibility of a piecewise‐linear dynamic bowtie filter

Hsieh

Pelc

2013

Medical Physics

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Purpose: The prepatient attenuator (or "bowtie filter") in CT is used to modulate the flux as a function of fan angle of the x-ray beam incident on the patient. Traditional, static bowtie filters are tailored only for very generic scans and for the average patient. The authors propose a design for a dynamic bowtie that can produce a time-dependent piecewise-linear attenuation profile. This dynamic bowtie may reduce dynamic range, dose or scatter, but in this work they focus on its ability to reduce dynamic range, which may be particularly important for systems employing photon-counting detectors. Methods: The dynamic bowtie is composed of a set of triangular wedges. Each wedge is independently moved in order to produce a time-dependent piecewise-linear attenuation profile. Simulations of the bowtie are conducted to estimate the dynamic range reduction in six clinical datasets. The control of the dynamic bowtie is determined by solving a convex optimization problem, and the dose is estimated using Monte Carlo techniques. Beam hardening artifacts are also simulated. Results:The dynamic range is reduced by factors ranging from 2.4 to 27 depending on the part of the body studied. With a dynamic range minimization objective, the dose to the patient can be reduced from 6% to 33% while maintaining peak image noise. Further reduction in dose may be possible with a specific dose reduction objective. Beam hardening artifacts are suppressed with a two-pass algorithm. Conclusions: A dynamic bowtie producing a time-dependent, piecewise-linear attenuation profile is possible and can be used to modulate the flux of the scanner to the imaging task. Initial simulations show a large reduction in dynamic range. Several other applications are possible.

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Design of a digital beam attenuation system for computed tomography: Part I. System design and simulation framework

Cited by 53 publications

References 25 publications

Experimental realization of fluence field modulated CT using digital beam attenuation

Experimental realization of fluence field modulated CT using digital beam attenuation

Two-dimensional dynamic fluid bowtie attenuators

The feasibility of a piecewise‐linear dynamic bowtie filter

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