Experimental validation of a method characterizing bow tie filters in CT scanners using a real‐time dose probe

McKenney, Sarah E.; Nosratieh, Anita; Gelskey, Dale E.; Yang, Kai; Huang, Shin Ying; Chen, Lin; Boone, John M.

doi:10.1118/1.3551990

Cited by 54 publications

(58 citation statements)

References 22 publications

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“…The rotational isotropy of the RTSS chamber was previously reported (McKenney et al , 2011) to have a relative angular measurement uncertainty of 0.80%. For the RTAI chamber, measurements were also made with a stationary source.…”

Section: Methodsmentioning

confidence: 96%

“…Multiple gantry rotations allow for a greater number of samples for each beam filter. A previously-described correction algorithm (McKenney et al , 2011) was used to reduce the effects of the inverse square law, which analyzed the unattenuated portions of the signal train and applied a sinusoidal scaling correction to the entire dataset (Fig 7.b). …”

Section: Methodsmentioning

confidence: 99%

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Real-time dosimeter employed to evaluate the half-value layer in CT

et al. 2013

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Half-value layer (HVL) measurements on commercial whole body CT scanners require serial measurements and, in many institutions, the presence of a service engineer. An assembly of aluminum filters (AAF), designed to be used in conjunction with a real-time dosimeter, was developed to provide estimates of the HVL using clinical protocols. Two real-time dose probes, a solid-state and air ionization chamber, were examined. The AAF consisted of eight rectangular filters of high purity aluminum (Type 1100), symmetrically positioned to form a cylindrical “cage” around the probe’s detective volume. The incident x-ray beam was attenuated by varying thicknesses of aluminum filters as the gantry completed a minimum of one rotation. Measurements employing real-time chambers were conducted both in service mode and with a routine abdomen/pelvis protocol for several combinations of x-ray tube potentials and bow tie filters. These measurements were validated against conventional serial HVL measurements. The average relative difference between the HVL measurements using the two methods was less than 5% when using a 122 mm diameter AAF; relative differences were reduced to 1.1% when the diameter was increased to 505 mm, possibly due to a reduced scatter contamination. Use of a real-time dose probe and the AAF allowed for time-efficient measurements of beam quality on a clinical CT scanner using clinical protocols.

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Section: Methodsmentioning

confidence: 96%

Section: Methodsmentioning

confidence: 99%

Real-time dosimeter employed to evaluate the half-value layer in CT

et al. 2013

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“…22 In previous studies, 23 we found such amplification to be on the order of a factor of 2, which would make the uncertainties of this film method larger than the 10% reported when using the dynamic dosimeter. 12 Determining how the uncertainty of the fan beam profile propagates in patient dose calculation by Monte Carlo methods 11,[24][25][26] is an active area of research, as is the influence of bow tie profile uncertainty in statistical iterative reconstruction algorithms. 19 If more accurate bow tie profiles are required, improving radiochromic precision by repeated measurements could be required, as well as energy-response calibration.…”

Section: Discussionmentioning

confidence: 99%

“…11,12 His experiments used a custom-designed prototype dosimeter that was not publically available. In a related paper, 13 we reported using Boone's technique with a newly available commercial dosimeter.…”

Section: Introductionmentioning

confidence: 99%

Technical Note: Measurement of bow tie profiles in CT scanners using radiochromic film

et al. 2015

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Purpose: To provide a noninvasive technique to measure the intensity profile of the fan beam in a computed tomography (CT) scanner that is cost effective and easily implemented without the need to access proprietary scanner information or service modes. Methods: The fabrication of an inexpensive aperture is described, which is used to expose radiochromic film in a rotating CT gantry. A series of exposures is made, each of which is digitized on a personal computer document scanner, and the resulting data set is analyzed to produce a self-consistent calibration of relative radiation exposure. The bow tie profiles were analyzed to determine the precision of the process and were compared to two other measurement techniques, direct measurements from CT gantry detectors and a dynamic dosimeter. Results: The radiochromic film method presented here can measure radiation exposures with a precision of ∼6% root-mean-square relative error. The intensity profiles have a maximum 25% root-mean-square relative error compared with existing techniques. Conclusions: The proposed radiochromic film method for measuring bow tie profiles is an inexpensive (∼$100 USD + film costs), noninvasive method to measure the fan beam intensity profile in CT scanners. C 2015 American Association of Physicists in Medicine. [http://dx

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“…Systems seem to have different filtration for static scout modes compared to rotating acquisitions, so static measurements in service mode would be required. Two other methods have been proposed: 1) measuring the variance in an empty gantry (air) scan sinogram (Whiting 2006); 2) measuring the waveform from a high-frequency dosimeter position away from the isocenter (Boone 2011, McKenney 2013. The former requires access to raw sinogram files, which are considered proprietary, and the latter involves expensive equipment (e.g., Radcal AccuGold dosimeters, >$10K).…”

Section: Introductionmentioning

confidence: 99%

Method for measuring the intensity profile of a CT fan-beam filter

Whiting

Dohatcu

2014

SPIE Proceedings

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Research on CT systems often requires knowledge of intensity as a function of angle in the fan-beam, due to the presence of bowtie filters, for studies such as dose reduction simulation, Monte Carlo dose calculations, or statistical reconstruction algorithms. Since manufacturers consider the x-ray bowtie filter design to be proprietary information, several methods have been proposed to measure the beam intensity profile independently: 1) calculate statistical properties of noise in acquired sinograms (requires access to raw data files, which is also vendor proprietary); 2) measure the waveform of a dosimeter located away from the isocenter (requires dosimeter equipment costing > $10K). We present a novel method that is inexpensive (parts costing ~$100 from any hardware store, using Gafchromic film at ~$3 per measurement), requires no proprietary information, and can be performed in a few minutes. A fixture is built from perforated steel tubing, which forms an aperture that selectively samples the intensity at a particular fan-beam angle in a rotating gantry. Two exposures (1x & 2x) are made and self-developing radiochromic film (Gafchromic XR-Ashland Inc.) is then scanned on an inexpensive PC document scanner. An analysis method is described that linearizes the measurements for relative exposure. The resultant profile is corrected for geometric effects (1/L^2 fall-off, gantry dwell time) and background exposure, providing a noninvasive estimate of the CT fan-beam intensity present in an operational CT system. This method will allow researchers to conveniently measure parameters required for modeling the effects of bowtie filters in clinical scanners.

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Experimental validation of a method characterizing bow tie filters in CT scanners using a real‐time dose probe

Abstract: The COBRA method is a fast and accurate method for BT filter characterization, which requires a simple experimental setup in a clinical environment. Because of the ease of data acquisition, multienergy scans can be acquired which allow characterization of the BT filter thickness.

Cited by 54 publications

References 22 publications

Real-time dosimeter employed to evaluate the half-value layer in CT

Real-time dosimeter employed to evaluate the half-value layer in CT

Technical Note: Measurement of bow tie profiles in CT scanners using radiochromic film

Method for measuring the intensity profile of a CT fan-beam filter

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