Spectral imaging using clinical megavoltage beams and a novel multi-layer imager

Myronakis, Marios; Fueglistaller, Rony; Rottmann, Joerg; Hu, Yue‐Houng; Wang, Adam; Baturin, Paul; Huber, Pascal; Morf, Daniel; Star‐Lack, Josh; Berbeco, R.

doi:10.1088/1361-6560/aa94f9

Cited by 12 publications

(14 citation statements)

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“…[2][3][4] Previously published work with the MLI included quantitative image metric evaluation on planar images, 1,5 theoretical design optimization studies for MVCBCT, [2][3][4] and feasibility and optimization of MV spectral imaging. 6,7 Low-dose MVCBCT has been a goal for image-guided radiotherapy. [8][9][10][11][12][13][14][15] However, MVCBCT with conventional electronic portal imagers (EPIDs) suffers from low image contrast as a result of the higher beam energy used to form the image and the limited detection efficiency of the EPID.…”

Section: Introductionmentioning

confidence: 99%

“…This novel design can benefit task‐specific imaging in radiotherapy such as portal imaging, motion‐tracking, and MV cone‐beam computed tomography (CBCT) by improving image contrast and noise characteristics . Previously published work with the MLI included quantitative image metric evaluation on planar images, theoretical design optimization studies for MVCBCT, and feasibility and optimization of MV spectral imaging …”

Section: Introductionmentioning

confidence: 99%

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Low‐dose megavoltage cone‐beam computed tomography using a novel multi‐layer imager (MLI)

et al. 2020

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Purpose: The feasibility of low-dose megavoltage cone-beam acquisition (MVCBCT) using a novel, high detective quantum efficiency (DQE) multi-layer imager (MLI) was investigated. The aim of this work was to reconstruct MVCBCT images using the MLI at different total dose levels, and assess Hounsfield Unit (HU) accuracy, noise and contrast-to-noise ratio (CNR) for low-dose megavoltage cone-beam acquisition. Methods: The MLI has four stacked layers; each layer contains a combination of copper filter/converter, gadolinium oxysulfide (GOS) scintillator and a-Si detector array. In total, 720 projections of a CATPHAN â phantom were acquired over 360°at 2.5, 6, and 6 MV flattening filter free (FFF) beam energies on a Varian TrueBeam LINAC. The dose per projection was 0.01, 0.0167, and 0.05 MU for 2.5, 6, and 6 MV FFF, respectively. MVCBCT images were reconstructed with varying numbers of projections to provide a range of doses for evaluation. Hounsfield Unit uniformity, accuracy, noise and CNR were estimated. Improvements were quantified relative to the standard AS1200 single-layer imager. Results: Average HU uniformity for the MLI reconstructions was within a range of 95%-99% for all of the energies studied. Relative electron density estimation from HU values was within 0.4% AE 1.8% from nominal values. The CNR for MVCBCT based on MLI projections was 2-49 greater than from AS1200 projections. The 2.5 MV beam acquisition with the MLI exhibited the lowest noise and the best balance between CNR and dose for low-dose reconstructions. Conclusions: Megavoltage cone-beam acquisition imaging with a novel MLI prototype mounted on a clinical linear accelerator demonstrated substantial improvement over the standard AS1200 EPID. Further optimization of MVCBCT reconstruction, particularly for 2.5 MV acquisitions, will improve image metrics. Overall, the MLI improves CNR at substantially lower doses than currently required by conventional detectors. This new high DQE detector could provide high-quality MVCBCT at

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Low‐dose megavoltage cone‐beam computed tomography using a novel multi‐layer imager (MLI)

et al. 2020

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“…Recently, a great deal of research effort has been devoted to the development of high detective quantum efficiency (DQE) EPIDs with the goal of improving image quality at MV energies. Adoption of multilayer architecture, structured and pixilated scintillators, novel scintillation materials, and novel direct conversion detector design have all been investigated and found to improve detector DQE. Presently, we introduce a new, inexpensive scintillating glass called LKH‐5 (Collimated Holes Inc., Campbell, CA, USA) and characterize the fundamental, planar imaging performance.…”

Section: Introductionmentioning

confidence: 99%

Characterizing a novel scintillating glass for application to megavoltage cone‐beam computed tomography

Shedlock

Wang

et al. 2019

Medical Physics

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Purpose The purpose of this study was to evaluate the performance of a prototype electric portal imaging device (EPID) with a high detective quantum efficiency (DQE) scintillator, LKH‐5. Specifically, image quality in context of both planar and megavoltage (MV) cone‐beam computed tomography (CBCT) is analyzed. Methods Planar image quality in terms of modulation transfer function (MTF), noise power spectrum (NPS), and DQE are measured and compared to an existing EPID (AS‐1200) using the 6 MV beamline for a Varian TrueBeam linac. Imager performance is contextualized for three‐dimensional (3D), MV‐CBCT performance by measuring imager lag and analyzing the expected degradation of the DQE as a function of dose. Finally, comparisons between reconstructed images of the Catphan phantom in terms of qualitative quality and signal‐difference‐to‐noise ratio (SDNR) are made for 6 MV images using both conventional and LKH‐5 EPIDs as well as for the kilovoltage (kV) on‐board imager (OBI). Results Analysis of the NPS reveals linearity at all measured doses using the prototype LKH‐5 detector. While the first zero of the MTF is much lower for the LKH‐5 detector than the conventional EPID (0.6 cycles/mm vs 1.6 cycles/mm), the normalized NPS (NNPS) multiplied by total quanta (qNNPS) of the LKH‐5 detector is roughly a factor of seven to eight times lower, yielding a DQE(0) of approximately 8%. First, second, and third frame lag were measured at approximately 23%, 5%, and 1%, respectively, although no noticeable image artifacts were apparent in reconstructed volumes. Analysis of low‐dose performance reveals that DQE(0) remains at 80% of its maximum value at a dose as low as 7.5 × 10−6 MU. For a 400 projection technique, this represents a total scan dose of 0.0030 MU, suggesting that if imaging doses are increased to a value typical of kV‐CBCT scans (~2.7 cGy), the LKH‐5 detector will retain quantum noise limited performance. Finally, comparing Catphan scans, the prototype detector exhibits much lower image noise than the conventional EPID, resulting in improved small object representation. Furthermore, SDNR of H2O and polystyrene cylinders improved from −1.95 and 2.94 to −15 and 18.7, respectively. Conclusions Imaging performance of the prototype LKH‐5 detector was measured and analyzed for both planar and 3D contexts. Improving noise transfer of the detector results in concurrent improvement of DQE(0). For 3D imaging, temporal characteristics were adequate for artifact‐free performance and at relevant doses, the detector retained quantum noise limited performance. Although quantitative MTF measurements suggest poorer resolution, small object representation of the prototype imager is qualitatively improved over the conventional detector due to the measured reduction in noise.

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“…Megavoltage spectral imaging (MVSPI) of clinical radiotherapy x-ray beams was recently proposed with a novel multi-layered imager (MLI) (Myronakis et al, 2017). The MLI design was composed of four layers of conventional electronic portal imaging devices (EPID) made of copper (Cu), gadolinium oxysulfide (GOS) and amorphous silicon (aSi) components (Rottmann et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

“…More recent studies used a weighted subtraction approach that does not require such calibration and can be readily implemented computationally (Shkumat et al, 2008; Hoggarth et al, 2013; Patel et al, 2014). Our previous work used this to take advantage of beam hardening between the MLI components at clinical photon beam energies (Myronakis et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Multi-layer imager design for mega-voltage spectral imaging

Myronakis¹,

Hu²,

Fueglistaller³

et al. 2018

Phys. Med. Biol.

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The architecture of multi-layer imagers (MLIs) can be exploited to provide megavoltage spectral imaging (MVSPI) for specific imaging tasks. In the current work, we investigated bone suppression and gold fiducial contrast enhancement as two clinical tasks which could be improved with spectral imaging. A method based on analytical calculations that enables rapid investigation of MLI component materials and thicknesses was developed and validated against Monte Carlo computations. The figure of merit for task-specific imaging performance was the contrast-to-noise ratio (CNR) of the gold fiducial when the CNR of bone was equal to zero after a weighted subtraction of the signals obtained from each MLI layer. Results demonstrated a sharp increase in the CNR of gold when the build-up component or scintillation materials and thicknesses were modified. The potential for low-cost, prompt implementation of specific modifications (e.g. composition of the build-up component) could accelerate clinical translation of MVSPI.

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Spectral imaging using clinical megavoltage beams and a novel multi-layer imager

Cited by 12 publications

References 14 publications

Low‐dose megavoltage cone‐beam computed tomography using a novel multi‐layer imager (MLI)

Low‐dose megavoltage cone‐beam computed tomography using a novel multi‐layer imager (MLI)

Characterizing a novel scintillating glass for application to megavoltage cone‐beam computed tomography

Multi-layer imager design for mega-voltage spectral imaging

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