Use of beam shapers for cone-beam CT with off-centered flat detector

Menser, Bernd; Wiegert, Jens; Wiesner, Steffen; Bertram, Matthias

doi:10.1117/12.844437

Cited by 4 publications

(8 citation statements)

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“…These ASGs consists of a one-dimensional array of radiopaque septa separated by aluminum or fiber spacers that support septa (such ASGs are referred as 1DASG in the rest of the text).1DASGs typically provide a factor of 2 to 5 reduction in SPR values, and subsequently improve CT number accuracy and reduce image artifacts. Moreover, bow tie (BT) filters were also employed in CBCT, and they were shown to reduce scatter fraction in sections of the object close to the CBCT isocenter 5, 10–13 . While such scatter suppression devices help to reduce relative scatter intensity, residual scatter reaching the FPD is still high enough to deteriorate CBCT image quality.…”

Section: Introductionmentioning

confidence: 99%

Transmission characteristics of a two dimensional antiscatter grid prototype for CBCT

et al. 2017

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Aim High fraction of scattered radiation in cone-beam CT (CBCT) imaging degrades CT number accuracy and visualization of low contrast objects. To suppress scatter in CBCT projections, we developed a focused, two-dimensional antiscatter grid (2DASG) prototype. In this work, we report on the primary and scatter transmission characteristics of the 2DASG prototype aimed for linac mounted, offset detector geometry CBCT systems in radiation therapy, and compared its performance to a conventional one-dimensional ASG (1DASG). Methods The 2DASG is an array through-holes separated by 0.1 mm septa that was fabricated from tungsten using additive manufacturing techniques. Through-holes’ focusing geometry was designed for offset detector CBCT in Varian TrueBeam system. Two types of ASGs were evaluated: a) a conventional 1DASG with a grid ratio of 10, b) the 2DASG prototype with a grid ratio of 8.2. To assess the scatter suppression performance of both ASGs, Scatter-to-primary ratio (SPR) and scatter transmission fraction (Ts) were measured using the beam stop method. Scatter and primary intensities were modulated by varying the phantom thickness between 10 and 40 cm. Additionally, the effect of air gap and bow tie (BT) filter on SPR and Ts were evaluated. Average primary transmission fraction (TP) and pixel specific primary transmission were also measured for both ASGs. To assess the effect of transmission characteristics on projection image signal-to-noise ratio (SNR) improvement factor was calculated. Improvement in contrast to noise ratio (CNR) was demonstrated using a low contrast object. Results In comparison to 1DASG, 2DASG reduced SPRs by a factor of 3 to 6 across the range of phantom setups investigated. Ts values for 1D and 2DASGs were in the range of 21 to 29%, and 5 to 14%, respectively. 2DASG continued to provide lower SPR and Ts at increased air gap and with BT filter. Tp of 1D and 2DASGs were 70.6% and 84.7%, respectively. Due to the septal shadow of the 2DASG, its pixel specific primary transmission values varied between 32.5% and 99.1%. With respect to 1DASG, 2DASG provided up to factor of 1.7 more improvement in SNR across the SPR range investigated. Moreover, 2DASG provided improved visualization of low contrast objects with respect to 1DASG and NOASG setups. Conclusions When compared to a conventional 1DASG, 2DASG prototype provided noticeably lower SPR and Ts values, indicating its superior scatter suppression performance. 2DASG also provided 19% higher average primary transmission that was attributed to the absence of interseptal spacers and optimized grid geometry. Our results indicate that the combined effect of lower scatter and higher primary transmission provided by 2DASG may potentially translate into more accurate CT numbers and improved contrast resolution in CBCT images.

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Section: Introductionmentioning

confidence: 99%

Transmission characteristics of a two dimensional antiscatter grid prototype for CBCT

et al. 2017

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“…The Scanora 3D applies an offset scanning technique, which is implemented nowadays as a solution to the growing demand of large FOVs on the one hand and the cost-prohibitive flat panel detectors on the other hand [4,11]. It allows the CBCT system to reconstruct an FOV of some nominal volume using a detector of roughly half the size compared with that in a symmetrical setup.…”

Section: Scanora 3d Cone Beam Ct Systemmentioning

confidence: 99%

“…The use of bowtie filters is known to give a reduction in the radiation dose at the periphery of the imaging field of view (FOV) [1,3]. They have also been found effective in reducing scatter, a major cause of image artefacts [1,3,4]. Furthermore, they have the potential to flatten the scatter distribution, which is beneficial for post-processing scatter correction strategies [7].…”

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confidence: 99%

“…Computer simulation methods offer a more convenient approach, allowing exploration of parameters for a given imaging system beyond its nominal design [4,7,9]. In a previous paper, we reported a hybrid technique to simulate the complete imaging chain of CBCT [10].…”

mentioning

confidence: 99%

“…Bowtie filters are widely applied in current mutislice CT and cone beam CT (CBCT) to modulate the output of the radiation source [1][2][3][4][5]. The term "bowtie" applies to a class of filter shapes featuring bilateral symmetry with a thickness that increases with the distance from the centre.…”

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confidence: 99%

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Bowtie filtration for dedicated cone beam CT of the head and neck: a simulation study

Zhang

Marshall²,

Jacobs³

et al. 2013

BJR

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Objective: To investigate the influence of bowtie filtration on dedicated cone beam CT (CBCT) of the head and neck. Methods: A validated hybrid simulation technique was used to model a commercial CBCT system with offset scanning geometry, 90 kV tube potential and 145375 mm imaging field of view. Three bowtie filters were formulated to produce uniform flux intensity in the projection image of cylindrical objects of diameter 14, 16 and 18 cm. The influence of these simulated filters was compared with the original flat filtration in terms of the output radiation field, the dose delivered to the object, the scatter distribution in projections and the quality of the reconstructed image. Results: Compared against flat filtration, dose reduction for the bowtie case, examined as a function of radial distance within a 16-cm-diameter water cylinder, varied from 8.7% at the centre to 53.8% at the periphery. Scatter reduction, quantified using scatter-to-primary ratio in projection images, was up to 37.6% for a 14-cm-diameter cylindrical contrast phantom. Using the supplied routine image reconstruction, bowtie filtration resulted in comparable noise appearance, contrast resolution and artefact pattern for computational anatomical phantoms, with ,5% difference in contrast-to-noise ratio. Conclusion: Bowtie filtration can effectively reduce the dose and scatter in CBCT of the head and neck. For better image quality, corresponding modification to the image pre-processing and reconstruction is needed. Advances in knowledge: The hybrid simulation approach can usefully explore the impact of proposed system component and design changes.

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Scatter kernel parameters optimization for digital radiography

Liao

2019

Eleventh International Conference on Digital Image Processing (ICDIP 2019)

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Use of beam shapers for cone-beam CT with off-centered flat detector

Cited by 4 publications

References 0 publications

Transmission characteristics of a two dimensional antiscatter grid prototype for CBCT

Transmission characteristics of a two dimensional antiscatter grid prototype for CBCT

Bowtie filtration for dedicated cone beam CT of the head and neck: a simulation study

Scatter kernel parameters optimization for digital radiography

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