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Huck SM, Fung GSK, Parodi K, Stierstorfer K. On the potential of ROI imaging in x-ray CT - A comparison of novel dynamic beam attenuators with current technology. Med Phys 2021; 48:3479-3499. [PMID: 33838055 DOI: 10.1002/mp.14879] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Revised: 03/24/2021] [Accepted: 03/29/2021] [Indexed: 12/30/2022] Open
Abstract
PURPOSE In this work, we explore the potential of region-of-interest (ROI) imaging in x-ray computed tomography (CT). Using two dynamic beam attenuator (DBA) concepts for fluence field modulation (FFM) previously developed, we investigate and evaluate the potential dose savings in comparison with current FFM technology. METHODS ROI imaging is a special application of FFM where the bulk of x-ray radiation is propagated toward a certain anatomical target (ROI), specified by the imaging task, while the surrounding tissue is spared from radiation. We introduce a criterion suitable to quantitatively describe the balance between image quality inside an ROI and total radiation dose with respect to a given ROI imaging task. It accounts for the mean image variance at the ROI and the effective patient dose calculated from Monte Carlo simulations. The criterion is further used to compile task-specific DBA trajectories determining the primary x-ray fluence, and eventually used for comparing different FFM techniques, namely the sheet-based dynamic beam attenuator (sbDBA), the z-aligned sbDBA (z-sbDBA), and an adjustable static operation mode of the z-sbDBA. Furthermore, two static bowtie filters and the influence of tube current modulation (TCM) are included in the comparison. RESULTS Our findings demonstrate by simulations that the presented trajectory optimization method determines reasonable DBA trajectories. The influence of TCM is strongly depending on the imaging task. The narrow bowtie filter allows for dose reductions of about 10% compared to the regular bowtie filter in the considered ROI imaging tasks. The DBAs are shown to realize substantially larger dose reductions. In our cardiac imaging scenario, the DBAs can reduce the effective dose by about 30% (z-sbDBA) or 60% (sbDBA). We can further verify that the noise characteristics are not adversely affected by the DBAs. CONCLUSION Our research demonstrates that ROI imaging using the presented DBA concepts is a promising technique toward a more patient- and task-specific CT imaging requiring lower radiation dose. Both the sbDBA and the z-sbDBA are potential technical solutions for realizing ROI imaging in x-ray CT.
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Affiliation(s)
- Sascha Manuel Huck
- Siemens Healthcare GmbH, Forchheim, Germany.,Department of Medical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München, Garching, Germany
| | | | - Katia Parodi
- Department of Medical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München, Garching, Germany
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Huck SM, Fung GSK, Parodi K, Stierstorfer K. The z-sbDBA, a new concept for a dynamic sheet-based fluence field modulator in x-ray CT. Med Phys 2020; 47:4827-4837. [PMID: 32754971 DOI: 10.1002/mp.14430] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2020] [Revised: 07/20/2020] [Accepted: 07/24/2020] [Indexed: 01/28/2023] Open
Abstract
PURPOSE We present a new concept for dynamic fluence field modulation (FFM) in x-ray computed tomography (CT). The so-called z-aligned sheet-based dynamic beam attenuator (z-sbDBA) is developed to dynamically compensate variations in patient attenuation across the fan beam and the projection angle. The goal is to enhance image quality and to reduce patient radiation dose. METHODS The z-sbDBA consists of an array of attenuation sheets aligned along the z direction. In neutral position, the array is focused toward the focal spot. Tilting the z-sbDBA defocuses the sheets, thus reducing the transmission for larger fan beam angles. The structure of the z-sbDBA significantly differs from the previous sheet-based dynamic beam attenuator (sbDBA) in two features: (a) The sheets of the z-sbDBA are aligned parallel to the detector rows, and (b) the height of the sheets increases from the center toward larger fan beam angles. We built a motor actuated prototype of the z-sbDBA integrated into a clinical CT scanner. In experiments, we investigated its feasibility for FFM. We compared the z-sbDBA to common CT bowtie filters in terms of the spectral dependency of the transmission and possible image variance distribution in reconstructed phantom images. Additionally, the potential radiation dose saving using z-sbDBA for region-of-interest (ROI) imaging was studied. RESULTS Our experimental results confirm that the z-sbDBA can realize variable transmission profiles of the radiation fluence by only small tilts. Compared to the sbDBA, the z-sbDBA can mitigate some practical and mechanical issues. In comparison to bowtie filters, the spectral dependency is considerably reduced when using the z-sbDBA. Likewise, more homogeneous image variance distributions can be attained in reconstructed phantom images. The z-sbDBA allows controlling the spatial image variance distribution which makes it suitable for ROI imaging. Our comparison on ROI imaging reveals skin dose reductions of up to 35% at equal ROI image quality by using the z-sbDBA. CONCLUSION Our new concept for FFM in x-ray CT, the z-sbDBA, was experimentally validated on a clinical CT scanner. It facilitates dynamic FFM by realizing variable transmission profiles across the fan beam angle on a projection-wise basis. This key feature allows for substantial improvements in image quality, a reduction in patient radiation dose, and additionally provides a technical solution for ROI imaging.
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Affiliation(s)
- Sascha Manuel Huck
- Siemens Healthcare GmbH, Siemensstr. 3, Forchheim, 91301, Germany.,Department of Medical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München, Am Coulombwall 1, Garching, 85748, Germany
| | - George S K Fung
- Siemens Medical Solutions USA, Inc., 40 Liberty Bouldevard, Malvern, PA, 19355, USA.,Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, 601 N Caroline St, JHOC 4253, Baltimore, MD, 21287, USA
| | - Katia Parodi
- Department of Medical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München, Am Coulombwall 1, Garching, 85748, Germany
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Jacobsen MC, Thrower SL. Multi-energy computed tomography and material quantification: Current barriers and opportunities for advancement. Med Phys 2020; 47:3752-3771. [PMID: 32453879 PMCID: PMC8495770 DOI: 10.1002/mp.14241] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Revised: 04/20/2020] [Accepted: 05/07/2020] [Indexed: 12/21/2022] Open
Abstract
Computed tomography (CT) technology has rapidly evolved since its introduction in the 1970s. It is a highly important diagnostic tool for clinicians as demonstrated by the significant increase in utilization over several decades. However, much of the effort to develop and advance CT applications has been focused on improving visual sensitivity and reducing radiation dose. In comparison to these areas, improvements in quantitative CT have lagged behind. While this could be a consequence of the technological limitations of conventional CT, advanced dual-energy CT (DECT) and photon-counting detector CT (PCD-CT) offer new opportunities for quantitation. Routine use of DECT is becoming more widely available and PCD-CT is rapidly developing. This review covers efforts to address an unmet need for improved quantitative imaging to better characterize disease, identify biomarkers, and evaluate therapeutic response, with an emphasis on multi-energy CT applications. The review will primarily discuss applications that have utilized quantitative metrics using both conventional and DECT, such as bone mineral density measurement, evaluation of renal lesions, and diagnosis of fatty liver disease. Other topics that will be discussed include efforts to improve quantitative CT volumetry and radiomics. Finally, we will address the use of quantitative CT to enhance image-guided techniques for surgery, radiotherapy and interventions and provide unique opportunities for development of new contrast agents.
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Affiliation(s)
- Megan C. Jacobsen
- Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Sara L. Thrower
- Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
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Dickmann J, Rit S, Pankuch M, Johnson RP, Schulte RW, Parodi K, Dedes G, Landry G. An optimization algorithm for dose reduction with fluence‐modulated proton CT. Med Phys 2020; 47:1895-1906. [DOI: 10.1002/mp.14084] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2019] [Revised: 01/30/2020] [Accepted: 02/05/2020] [Indexed: 01/12/2023] Open
Affiliation(s)
- J. Dickmann
- Department of Medical Physics Faculty of Physics Ludwig‐Maximilians‐Universität München Am Coulombwall 1 85748 Garching b. München Germany
| | - S. Rit
- Univ Lyon INSA‐Lyon Université Claude Bernard Lyon 1 UJM‐Saint Étienne CNRS, Inserm CREATIS UMR 5220 U1206 F‐69373 Lyon France
| | - M. Pankuch
- Northwestern Medicine Chicago Proton Center Warrenville IL 60555 USA
| | - R. P. Johnson
- Department of Physics University of California Santa Cruz Santa Cruz CA 95064 USA
| | - R. W. Schulte
- Division of Biomedical Engineering Sciences Loma Linda University Loma Linda CA 92354 USA
| | - K. Parodi
- Department of Medical Physics Faculty of Physics Ludwig‐Maximilians‐Universität München Am Coulombwall 1 85748 Garching b. München Germany
| | - G. Dedes
- Department of Medical Physics Faculty of Physics Ludwig‐Maximilians‐Universität München Am Coulombwall 1 85748 Garching b. München Germany
| | - G. Landry
- Department of Medical Physics Faculty of Physics Ludwig‐Maximilians‐Universität München Am Coulombwall 1 85748 Garching b. München Germany
- Department of Radiation Oncology University Hospital, LMU Munich 81377 Munich Germany
- German Cancer Consortium (DKTK) 81377 Munich Germany
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Huck SM, Fung GSK, Parodi K, Stierstorfer K. Technical Note: Sheet‐based dynamic beam attenuator – A novel concept for dynamic fluence field modulation in x‐ray CT. Med Phys 2019; 46:5528-5537. [DOI: 10.1002/mp.13690] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2018] [Revised: 05/22/2019] [Accepted: 06/17/2019] [Indexed: 11/11/2022] Open
Affiliation(s)
- Sascha Manuel Huck
- Siemens Healthcare GmbH Siemensstr. 3 91301Forchheim Germany
- Department of Medical Physics, Faculty of Physics Ludwig‐Maximilians‐Universität München Am Coulombwall 1 85748Garching Germany
| | - George S. K. Fung
- Siemens Medical Solutions USA, Inc 40 Liberty Boulevard Malvern PA 19355USA
- Russell H. Morgan Department of Radiology and Radiological Science Johns Hopkins University 601 N Caroline St Baltimore MD 21287USA
| | - Katia Parodi
- Department of Medical Physics, Faculty of Physics Ludwig‐Maximilians‐Universität München Am Coulombwall 1 85748Garching Germany
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Shunhavanich P, Bennett NR, Hsieh SS, Pelc NJ. Implementation of a piecewise-linear dynamic attenuator. J Med Imaging (Bellingham) 2019. [DOI: 10.1117/1.jmi.6.2.023502] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
| | | | - Scott S. Hsieh
- University of California, Los Angeles, Department of Radiological Sciences, Los Angeles, California
| | - Norbert J. Pelc
- Stanford University, Department of Bioengineering, Stanford, California
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Gang GJ, Mao A, Wang W, Siewerdsen JH, Mathews A, Kawamoto S, Levinson R, Stayman JW. Dynamic fluence field modulation in computed tomography using multiple aperture devices. Phys Med Biol 2019; 64:105024. [PMID: 30939459 PMCID: PMC6897305 DOI: 10.1088/1361-6560/ab155e] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
A novel beam filter consisting of multiple aperture devices (MADs) has been developed for dynamic fluence field modulation (FFM) in CT. Each MAD achieves spatial modulation of x-ray through fine-scale, highly attenuating tungsten bars of varying widths and spacings. Moiré patterns produced by relative motions between two MADs provide versatile classes of modulation profiles. The dual-MAD filter can be designed to achieve specific classes of target profiles. The designed filter was manufactured through a laser-sintering process and integrated to an experimental imaging system that enables linear actuation of the MADs. Dynamic FFM was achieved through a combination of beam shape modulation (by relative MAD motion) and amplitude modulation (by view-dependent mAs). To correct for gains associated with the MADs, we developed an algorithm to account for possible focal spot changes during/between scans and spectral effects introduced by the MADs. We performed FFM designs for phantoms following two imaging objectives: (1) to achieve minimum mean variance in filtered backprojection (FBP) reconstruction, and (2) to flatten the fluence behind the phantom. Comparisons with conventional FFM strategies involving a static bowtie and pulse width modulation were performed. The dual-MAD filter produced modulation profiles closely matched with the design target, providing varying beam widths not achievable by the static bowtie. The entire range of modulation profiles was achieved by 0.373 mm of MAD displacement. The correction algorithm effectively alleviated ring artifacts as a result of MADs while preserving phantom details such as wires and tissue boundaries. Dynamic FFM enabled by the MADs were effective in achieving the imaging objectives and demonstrated superior FFM capabilities compared to the static bowtie. In an ellipse phantom, the FFM of objective 1 achieved the lowest mean variance in all cases investigated. The FFM of objective 2 produce nearly isotropic local noise power spectrum and homogeneous noise magnitude. The dual-MAD filter provides an effective tool for fluence control in CT to overcome limitations of conventional static bowties and to further enable patient-specific FFM studies for a wide range of dose and image quality objectives.
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Affiliation(s)
- Grace J Gang
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States of America
| | - Andrew Mao
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States of America
| | - Wenying Wang
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States of America
| | - Jeffrey H Siewerdsen
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States of America
| | - Aswin Mathews
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States of America
| | - Satomi Kawamoto
- Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States of America
| | | | - J Webster Stayman
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States of America
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Wu P, Stayman JW, Sisniega A, Zbijewski W, Foos D, Wang X, Aygun N, Stevens R, Siewerdsen JH. Statistical weights for model-based reconstruction in cone-beam CT with electronic noise and dual-gain detector readout. ACTA ACUST UNITED AC 2018; 63:245018. [DOI: 10.1088/1361-6560/aaf0b4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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Rädler M, Landry G, Rit S, Schulte RW, Parodi K, Dedes G. Two-dimensional noise reconstruction in proton computed tomography using distance-driven filtered back-projection of simulated projections. Phys Med Biol 2018; 63:215009. [PMID: 30277469 DOI: 10.1088/1361-6560/aae5c9] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We present a formalism for two-dimensional (2D) noise reconstruction in proton computed tomography (pCT). This is necessary for the application of fluence modulated pCT (FMpCT) since it permits image noise prescription and the corresponding proton fuence optimization. We aimed at extending previously published formalisms to account for the impact of multiple Coulomb scattering (MCS) on projection noise, and the use of filtered back projection (FBP) reconstruction along curved paths with distance driven binning (DDB). 2D noise reconstruction for a beam of protons with parallel initial momentum vectors, and for projections binned both at the rear tracker and with DDB, was established. Monte Carlo (MC) simulations of pCT scans of a water cylinder were employed to generate pCT projections and to calculate their noise for use in 2D noise reconstruction. These were compared to results from an analytical model accounting for MCS for rear tracker binning as well as against the previously published central pixel model which ignores MCS. Image noise reconstructed with the formalism for rear tracker binning and DDB were compared to MC results using annular regions of interest (ROIs). Agreement better than 8% was obtained between the noise of projections calculated with MC simulation and our model. Noise from annular ROIs agreed with our noise reconstructions for rear tracker binning and DDB. The central pixel model ignoring MCS underestimated projection and thus image noise by up to 40% towards the object's edge. The use of DDB decreased the image noise towards the object's edge when compared to rear tracker binning and yielded more uniform noise throughout the image. MCS should not be neglected when predicting image noise for pixels away from the center of an object in a pCT scan due to the increasing influence of the gradient of the object's hull closer to the edges.
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Affiliation(s)
- Martin Rädler
- Department of Medical Physics, Ludwig-Maximilians-Universität München, 85748 Garching b. München, Germany. Authors contributed equally
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Mao A, Gang GJ, Shyr W, Levinson R, Siewerdsen JH, Kawamoto S, Webster Stayman J. Dynamic fluence field modulation for miscentered patients in computed tomography. J Med Imaging (Bellingham) 2018; 5:043501. [PMID: 30397631 PMCID: PMC6199669 DOI: 10.1117/1.jmi.5.4.043501] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Accepted: 09/17/2018] [Indexed: 11/14/2022] Open
Abstract
Traditional CT image acquisition uses bowtie filters to reduce dose, x-ray scatter, and detector dynamic range requirements. However, accurate patient centering within the bore of the CT scanner takes time and is often difficult to achieve precisely. Patient miscentering combined with a static bowtie filter can result in significant increases in dose, reconstruction noise, and CT number variations, and consequently raise overall exposure requirements. Approaches to estimate the patient position from scout scans and perform dynamic spatial beam filtration during acquisition are developed and applied in physical experiments on a CT test bench using different beam filtration strategies. While various dynamic beam modulation strategies have been developed, we focus on two approaches: (1) a simple approach using attenuation-based beam modulation using a translating bowtie filter and (2) dynamic beam modulation using multiple aperture devices (MADs)-an emerging beam filtration strategy based on binary filtration of the x-ray beam using variable width slits in a high-density beam blocker. Improved dose utilization and more consistent image performance with respect to an unmodulated baseline (static filter) are demonstrated for miscentered objects and dynamic beam filtration in physical experiments. For a homogeneous object miscentered by 4 cm, the dynamic filter reduced the maximum regional noise and dose penalties (compared with a centered object) from 173% to 16% and 42% to 14%, respectively, for a traditional bowtie, 29% to 8% and 24% to 15%, respectively, for a single MAD, and 275% to 11% and 56% to 18%, respectively, for a dual-MAD filter. The proposed methodology has the potential to relax patient centering requirements within the scanner, reduce setup time, and facilitate additional CT dose reduction.
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Affiliation(s)
- Andrew Mao
- Johns Hopkins University, Department of Biomedical Engineering, Baltimore, Maryland, United States
| | - Grace J. Gang
- Johns Hopkins University, Department of Biomedical Engineering, Baltimore, Maryland, United States
| | - William Shyr
- Johns Hopkins University, Department of Biomedical Engineering, Baltimore, Maryland, United States
| | - Reuven Levinson
- Philips Healthcare, Global Research and Advanced Development, Haifa, Israel
| | - Jeffrey H. Siewerdsen
- Johns Hopkins University, Department of Biomedical Engineering, Baltimore, Maryland, United States
- Johns Hopkins University, Department of Radiology, Baltimore, Maryland, United States
| | - Satomi Kawamoto
- Johns Hopkins University, Department of Radiology, Baltimore, Maryland, United States
| | - J. Webster Stayman
- Johns Hopkins University, Department of Biomedical Engineering, Baltimore, Maryland, United States
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11
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Zhang R, Cruz-Bastida JP, Gomez-Cardona D, Hayes JW, Li K, Chen GH. Quantitative accuracy of CT numbers: Theoretical analyses and experimental studies. Med Phys 2018; 45:4519-4528. [PMID: 30102414 DOI: 10.1002/mp.13119] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Revised: 07/26/2018] [Accepted: 07/27/2018] [Indexed: 12/22/2022] Open
Abstract
PURPOSE The CT number accuracy, that is, CT number bias, plays an important role in clinical diagnosis. When strategies to reduce radiation dose are discussed, it is important to make sure that the CT number bias is controlled within an acceptable range. The purpose of this paper was to investigate the dependence of CT number bias on radiation dose level and on image contrast (i.e., the difference in CT number between the ROI and the background) in Computed Tomography (CT). METHODS A lesion-background model was introduced to theoretically study how the CT number bias changes with radiation exposure level and with CT number contrast when a simple linear reconstruction algorithm such as filtered backprojection (FBP) is used. The theoretical results were validated with experimental studies using a benchtop CT system equipped with a photon-counting detector (XC-HYDRA FX50, XCounter AB, Sweden) and a clinical diagnostic MDCT scanner (Discovery CT750 HD, GE Healthcare, Waukesha, WI, USA) equipped with an energy-integrating detector. The Catphan phantom (Catphan 600, the Phantom Laboratory, Salem, NY, USA) was scanned at different mAs levels and 50 scans were performed for each mAs. The bias of CT number was evaluated for each combination of mAs and ROIs with different contrast levels. An anthropomorphic phantom (ATOM 10-year-old phantom, Model 706, CIRS Inc. Norfolk, VA, USA) with much more heterogeneous object content was used to test the applicability of the theory to the more general image object cases. RESULTS Both theoretical and experimental studies showed that the CT number bias is inversely proportional to the radiation exposure level yet linearly dependent on the CT number contrast between the lesion and the background, that is, Bias ( μ ^ 1 FBP ) = α mAs ( 1 + β Δ H U ) . CONCLUSIONS The quantitative accuracy of CT numbers can be problematic and thus needs some extra attention when radiation dose is reduced. In this work, we showed that the bias of the FBP reconstruction increases as mAs is reduced; both positive and negative bias can be observed depending on the contrast difference between a targeted ROI and its surrounding background tissues.
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Affiliation(s)
- Ran Zhang
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison, WI, 53705, USA
| | - Juan P Cruz-Bastida
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison, WI, 53705, USA
| | - Daniel Gomez-Cardona
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison, WI, 53705, USA
| | - John W Hayes
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison, WI, 53705, USA
| | - Ke Li
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison, WI, 53705, USA.,Department of Radiology, University of Wisconsin School of Medicine and Public Health, 600 Highland Avenue, Madison, WI, 53792, USA
| | - Guang-Hong Chen
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison, WI, 53705, USA.,Department of Radiology, University of Wisconsin School of Medicine and Public Health, 600 Highland Avenue, Madison, WI, 53792, USA
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Dedes G, Johnson RP, Pankuch M, Detrich N, Pols WMA, Rit S, Schulte RW, Parodi K, Landry G. Experimental fluence‐modulated proton computed tomography by pencil beam scanning. Med Phys 2018; 45:3287-3296. [DOI: 10.1002/mp.12989] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 05/14/2018] [Accepted: 05/14/2018] [Indexed: 01/22/2023] Open
Affiliation(s)
- George Dedes
- Department of Medical Physics Faculty of Physics Ludwig‐Maximilians‐Universität München (LMU Munich) 85748 Garching b. München Germany
| | | | - Mark Pankuch
- Northwestern Medicine Chicago Proton Center Warrenville IL 60555 USA
| | - Nick Detrich
- IBA and Northwestern Medicine Chicago Proton Center Warrenville IL 60555 USA
| | - Willemijn M. A. Pols
- Department of Medical Physics Faculty of Physics Ludwig‐Maximilians‐Universität München (LMU Munich) 85748 Garching b. München Germany
| | - Simon Rit
- Université de Lyon CREATIS CNRS UMR5220 Inserm U1044 INSA‐Lyon Université Lyon 1 F69373 Lyon France
| | - Reinhard W. Schulte
- Division of Radiation Research Loma Linda University Loma Linda CA 92354 USA
| | - Katia Parodi
- Department of Medical Physics Faculty of Physics Ludwig‐Maximilians‐Universität München (LMU Munich) 85748 Garching b. München Germany
| | - Guillaume Landry
- Department of Medical Physics Faculty of Physics Ludwig‐Maximilians‐Universität München (LMU Munich) 85748 Garching b. München Germany
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13
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Larsen TC, Gopalakrishnan V, Yao J, Nguyen CP, Chen MY, Moss J, Wen H. Optimization of a secondary VOI protocol for lung imaging in a clinical CT scanner. J Appl Clin Med Phys 2018; 19:271-280. [PMID: 29785839 PMCID: PMC6036356 DOI: 10.1002/acm2.12354] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Revised: 04/02/2018] [Accepted: 04/10/2018] [Indexed: 11/10/2022] Open
Abstract
We present a solution to meet an unmet clinical need of an in-situ "close look" at a pulmonary nodule or at the margins of a pulmonary cyst revealed by a primary (screening) chest CT while the patient is still in the scanner. We first evaluated options available on current whole-body CT scanners for high resolution screening scans, including ROI reconstruction of the primary scan data and HRCT, but found them to have insufficient SNR in lung tissue or discontinuous slice coverage. Within the capabilities of current clinical CT systems, we opted for the solution of a secondary, volume-of-interest (VOI) protocol where the radiation dose is focused into a short-beam axial scan at the z position of interest, combined with a small-FOV reconstruction at the xy position of interest. The objective of this work was to design a VOI protocol that is optimized for targeted lung imaging in a clinical whole-body CT system. Using a chest phantom containing a lung-mimicking foam insert with a simulated cyst, we identified the appropriate scan mode and optimized both the scan and recon parameters. The VOI protocol yielded 3.2 times the texture amplitude-to-noise ratio in the lung-mimicking foam when compared to the standard chest CT, and 8.4 times the texture difference between the lung mimicking and reference foams. It improved details of the wall of the simulated cyst and better resolution in a line-pair insert. The Effective Dose of the secondary VOI protocol was 42% on average and up to 100% in the worst-case scenario of VOI positioning relative to the standard chest CT. The optimized protocol will be used to obtain detailed CT textures of pulmonary lesions, which are biomarkers for the type and stage of lung diseases.
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Affiliation(s)
- Thomas C Larsen
- National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Vissagan Gopalakrishnan
- National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD, USA.,Rush Medical College, Chicago, IL, USA
| | - Jianhua Yao
- Department of Radiology, Hatfield Clinical Center, National Institutes of Health, Bethesda, MD, USA
| | - Catherine P Nguyen
- National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Marcus Y Chen
- National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Joel Moss
- National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD, USA
| | - Han Wen
- National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD, USA
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Gang GJ, Mao A, Siewerdsen JH, Stayman JW. Implementation and Assessment of Dynamic Fluence Field Modulation with Multiple Aperture Devices. CONFERENCE PROCEEDINGS. INTERNATIONAL CONFERENCE ON IMAGE FORMATION IN X-RAY COMPUTED TOMOGRAPHY 2018; 2018:47-51. [PMID: 30506056 PMCID: PMC6261319] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
This work reports experimental results of dynamic fluence field modulation (FFM) using a dual multiple aperture devices (MAD) system. MAD filters use Moiré patterns produced by relative motions between two sets of thin, highly attenuating tungsten bars of varying widths and spacings. Each MAD was affixed to a linear actuator and installed on an experimental cone-beam CT bench. Phantom-specific FFM profiles were designed based on a flatness and minimum mean variance objectives and realized through a combination of MAD translations and pulse width modulation at a constant tube current. To properly correct for gains associated with the MAD filters, a correction algorithm was designed to account for focal spot shifts during scanning, as well as spectral effects from incomplete blockage of x-rays by the tungsten bars. The FFM designs were demonstrated in an elliptical phantom (25.8×14.1 cm). Variance and noise power spectrum (NPS) analysis was performed on the resulting reconstructions. While conventionalgain correction produced reconstructions with high frequency ring artifacts in axial slices, the proposed correction algorithm effectively removed such artifacts while preserving phantom details. Fluence field designs for the elliptical phantom were achievedusing relative MAD motions over a 0.44 mm range, and measured beam profiles closely approximated the theoretically computed target profiles. The noise properties of the resulting reconstructions behave as expected: a flat detected fluence criterion yields nearly isotropic NPS and more homogeneous variance across the reconstruction as compared to an unmodulated scan; the minimum mean variance FFM results in lower mean variance compared to both the unmodulated and flat-field patterns at approximately matched total bare-beam fluence. These results suggest that a dual-MAD CT is an effective approach to provide fluence and image quality control and that can potentially accommodate a wide range of phantoms and design objectives.
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Affiliation(s)
- Grace J Gang
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205 USA (, , , )
| | - Andrew Mao
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205 USA (, , , )
| | - Jeffrey H Siewerdsen
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205 USA (, , , )
| | - J Webster Stayman
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205 USA (, , , )
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Dekker KH, Hazarika R, Silveira MA, Jordan KJ. Fixed, object-specific intensity compensation for cone beam optical CT radiation dosimetry. Phys Med Biol 2018; 63:06NT02. [PMID: 29547397 DOI: 10.1088/1361-6560/aab17f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Optical cone beam computed tomography (CT) scanning of radiochromic gel dosimeters, using a CCD camera and a low stray light convergent source, provides fast, truly 3D radiation dosimetry with high accuracy. However, a key limiting factor in radiochromic gel dosimetry at large (⩾10 cm diameter) volumes is the initial attenuation of the dosimeters. It is not unusual to observe a 5-10× difference in signal intensity through the dosimeter center versus through the surrounding medium in pre-irradiation images. Thus, all dosimetric information in a typical experiment is measured within the lower 10%-20% of the camera sensor's range, and re-use of gels is often not possible due to a lack of transmission. To counteract this, in this note we describe a simple method to create source compensators by printing on transparent films. This technique, which is easily implemented and inexpensive, is an optical analogue to the bowtie filter in x-ray CT. We present transmission images and solution phantom reconstructions to demonstrate that (1) placing compensators beyond the focal zone of the imaging lens prevents high spatial frequency features of the printed films from generating reconstruction artifacts, and (2) object-specific compensation considerably reduces the range of intensities measured in projection images. This will improve the measurable dose range in optical CT dosimetry, and will enable imaging of larger gel volumes (∼15 cm diameter). Additionally, it should enable re-use of dosimeters by printing a new compensator for a second experiment.
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Affiliation(s)
- Kurtis H Dekker
- Department of Medical Biophysics, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada
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16
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Gang GJ, Stayman JW. Joint Optimization of Fluence Field Modulation and Regularization for Multi-Task Objectives. PROCEEDINGS OF SPIE--THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING 2018; 10573:1057313. [PMID: 29622856 PMCID: PMC5881947 DOI: 10.1117/12.2294950] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
This work investigates task-driven optimization of fluence field modulation (FFM) and regularization for model-based iterative reconstruction (MBIR) when different imaging tasks are presented by different organs. Example applications of the design framework were demonstrated in an abdomen phantom where the task of interest in the liver is a low-contrast, low-frequency detection task while that in the kidney is a high-contrast, high-frequency discrimination task. The global performance objective is based on maximizing local detectability index (d') at a discrete set of locations. Two objective functions were formulated based on different imaging needs: 1) a maxi-min objective where all tasks are equally important, and 2) a region-of-interest (ROI) objective to maximize imaging performance in an ROI while maintaining a minimum level of performance elsewhere. The FFM pattern for the maxi-min objective is determined by the most challenging task in the liver where both angular and spatial modulation resulted in a ~35% improvement in d' compared to an unmodulated case. The FFM for the ROI objective prescribes the most fluence to the organs of interest, boosting d' by ~59%, but manages to achieve the minimum d' target elsewhere. A spatially varying regularization was found to be important when tasks of different frequency content are present in different parts of the image - the optimal regularization strength for the two studied tasks differed by two orders of magnitude. Initial investigations in this work demonstrated that a multi-task objective is potentially important in shaping the optimal FFM and MBIR regularization, and that these tools may help to generalize task-based acquisition and reconstruction design for more complex diagnostic scenarios.
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Affiliation(s)
- Grace J Gang
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, U.S.A
| | - J Webster Stayman
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, U.S.A
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17
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Dedes G, De Angelis L, Rit S, Hansen D, Belka C, Bashkirov V, Johnson RP, Coutrakon G, Schubert KE, Schulte RW, Parodi K, Landry G. Application of fluence field modulation to proton computed tomography for proton therapy imaging. ACTA ACUST UNITED AC 2017; 62:6026-6043. [DOI: 10.1088/1361-6560/aa7734] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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18
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Gang GJ, Siewerdsen JH, Webster Stayman J. Task-driven optimization of CT tube current modulation and regularization in model-based iterative reconstruction. Phys Med Biol 2017. [PMID: 28362638 DOI: 10.1088/1361-6560/aa6a97/meta] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/30/2023]
Abstract
Tube current modulation (TCM) is routinely adopted on diagnostic CT scanners for dose reduction. Conventional TCM strategies are generally designed for filtered-backprojection (FBP) reconstruction to satisfy simple image quality requirements based on noise. This work investigates TCM designs for model-based iterative reconstruction (MBIR) to achieve optimal imaging performance as determined by a task-based image quality metric. Additionally, regularization is an important aspect of MBIR that is jointly optimized with TCM, and includes both the regularization strength that controls overall smoothness as well as directional weights that permits control of the isotropy/anisotropy of the local noise and resolution properties. Initial investigations focus on a known imaging task at a single location in the image volume. The framework adopts Fourier and analytical approximations for fast estimation of the local noise power spectrum (NPS) and modulation transfer function (MTF)-each carrying dependencies on TCM and regularization. For the single location optimization, the local detectability index (d') of the specific task was directly adopted as the objective function. A covariance matrix adaptation evolution strategy (CMA-ES) algorithm was employed to identify the optimal combination of imaging parameters. Evaluations of both conventional and task-driven approaches were performed in an abdomen phantom for a mid-frequency discrimination task in the kidney. Among the conventional strategies, the TCM pattern optimal for FBP using a minimum variance criterion yielded a worse task-based performance compared to an unmodulated strategy when applied to MBIR. Moreover, task-driven TCM designs for MBIR were found to have the opposite behavior from conventional designs for FBP, with greater fluence assigned to the less attenuating views of the abdomen and less fluence to the more attenuating lateral views. Such TCM patterns exaggerate the intrinsic anisotropy of the MTF and NPS as a result of the data weighting in MBIR. Directional penalty design was found to reinforce the same trend. The task-driven approaches outperform conventional approaches, with the maximum improvement in d' of 13% given by the joint optimization of TCM and regularization. This work demonstrates that the TCM optimal for MBIR is distinct from conventional strategies proposed for FBP reconstruction and strategies optimal for FBP are suboptimal and may even reduce performance when applied to MBIR. The task-driven imaging framework offers a promising approach for optimizing acquisition and reconstruction for MBIR that can improve imaging performance and/or dose utilization beyond conventional imaging strategies.
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Affiliation(s)
- Grace J Gang
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205, United States of America
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Gang GJ, Siewerdsen JH, Webster Stayman J. Task-driven optimization of CT tube current modulation and regularization in model-based iterative reconstruction. Phys Med Biol 2017; 62:4777-4797. [PMID: 28362638 DOI: 10.1088/1361-6560/aa6a97] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Tube current modulation (TCM) is routinely adopted on diagnostic CT scanners for dose reduction. Conventional TCM strategies are generally designed for filtered-backprojection (FBP) reconstruction to satisfy simple image quality requirements based on noise. This work investigates TCM designs for model-based iterative reconstruction (MBIR) to achieve optimal imaging performance as determined by a task-based image quality metric. Additionally, regularization is an important aspect of MBIR that is jointly optimized with TCM, and includes both the regularization strength that controls overall smoothness as well as directional weights that permits control of the isotropy/anisotropy of the local noise and resolution properties. Initial investigations focus on a known imaging task at a single location in the image volume. The framework adopts Fourier and analytical approximations for fast estimation of the local noise power spectrum (NPS) and modulation transfer function (MTF)-each carrying dependencies on TCM and regularization. For the single location optimization, the local detectability index (d') of the specific task was directly adopted as the objective function. A covariance matrix adaptation evolution strategy (CMA-ES) algorithm was employed to identify the optimal combination of imaging parameters. Evaluations of both conventional and task-driven approaches were performed in an abdomen phantom for a mid-frequency discrimination task in the kidney. Among the conventional strategies, the TCM pattern optimal for FBP using a minimum variance criterion yielded a worse task-based performance compared to an unmodulated strategy when applied to MBIR. Moreover, task-driven TCM designs for MBIR were found to have the opposite behavior from conventional designs for FBP, with greater fluence assigned to the less attenuating views of the abdomen and less fluence to the more attenuating lateral views. Such TCM patterns exaggerate the intrinsic anisotropy of the MTF and NPS as a result of the data weighting in MBIR. Directional penalty design was found to reinforce the same trend. The task-driven approaches outperform conventional approaches, with the maximum improvement in d' of 13% given by the joint optimization of TCM and regularization. This work demonstrates that the TCM optimal for MBIR is distinct from conventional strategies proposed for FBP reconstruction and strategies optimal for FBP are suboptimal and may even reduce performance when applied to MBIR. The task-driven imaging framework offers a promising approach for optimizing acquisition and reconstruction for MBIR that can improve imaging performance and/or dose utilization beyond conventional imaging strategies.
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Affiliation(s)
- Grace J Gang
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205, United States of America
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De Man B, Uribe J, Baek J, Harrison D, Yin Z, Longtin R, Roy J, Waters B, Wilson C, Short J, Inzinna L, Reynolds J, Neculaes VB, Frutschy K, Senzig B, Pelc N. Multisource inverse-geometry CT. Part I. System concept and development. Med Phys 2017; 43:4607. [PMID: 27487877 DOI: 10.1118/1.4954846] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE This paper presents an overview of multisource inverse-geometry computed tomography (IGCT) as well as the development of a gantry-based research prototype system. The development of the distributed x-ray source is covered in a companion paper [V. B. Neculaes et al., "Multisource inverse-geometry CT. Part II. X-ray source design and prototype," Med. Phys. 43, 4617-4627 (2016)]. While progress updates of this development have been presented at conferences and in journal papers, this paper is the first comprehensive overview of the multisource inverse-geometry CT concept and prototype. The authors also provide a review of all previous IGCT related publications. METHODS The authors designed and implemented a gantry-based 32-source IGCT scanner with 22 cm field-of-view, 16 cm z-coverage, 1 s rotation time, 1.09 × 1.024 mm detector cell size, as low as 0.4 × 0.8 mm focal spot size and 80-140 kVp x-ray source voltage. The system is built using commercially available CT components and a custom made distributed x-ray source. The authors developed dedicated controls, calibrations, and reconstruction algorithms and evaluated the system performance using phantoms and small animals. RESULTS The authors performed IGCT system experiments and demonstrated tube current up to 125 mA with up to 32 focal spots. The authors measured a spatial resolution of 13 lp/cm at 5% cutoff. The scatter-to-primary ratio is estimated 62% for a 32 cm water phantom at 140 kVp. The authors scanned several phantoms and small animals. The initial images have relatively high noise due to the low x-ray flux levels but minimal artifacts. CONCLUSIONS IGCT has unique benefits in terms of dose-efficiency and cone-beam artifacts, but comes with challenges in terms of scattered radiation and x-ray flux limits. To the authors' knowledge, their prototype is the first gantry-based IGCT scanner. The authors summarized the design and implementation of the scanner and the authors presented results with phantoms and small animals.
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Affiliation(s)
- Bruno De Man
- CT Systems and Applications Laboratory, GE Global Research, Niskayuna, New York 12309
| | - Jorge Uribe
- Functional Imaging Laboratory, GE Global Research, Niskayuna, New York 12309
| | - Jongduk Baek
- School of Integrated Technology, Yonsei University, Incheon 406-840, South Korea
| | - Dan Harrison
- CT Systems and Applications Laboratory, GE Global Research, Niskayuna, New York 12309
| | - Zhye Yin
- CT Systems and Applications Laboratory, GE Global Research, Niskayuna, New York 12309
| | - Randy Longtin
- Mechanical Systems Technologies, GE Global Research, Niskayuna, New York 12309
| | - Jaydeep Roy
- Mechanical Systems Technologies, GE Global Research, Niskayuna, New York 12309
| | - Bill Waters
- Design and Development Shops, GE Global Research, Niskayuna, New York 12309
| | - Colin Wilson
- High Energy Physics Laboratory, GE Global Research, Niskayuna, New York 12309
| | - Jonathan Short
- Detector Laboratory, GE Global Research, Niskayuna, New York 12309
| | - Lou Inzinna
- High Energy Physics Laboratory, GE Global Research, Niskayuna, New York 12309
| | - Joseph Reynolds
- High Frequency Power Electronics Laboratory, GE Global Research, Niskayuna, New York 12309
| | - V Bogdan Neculaes
- High Energy Physics Laboratory, GE Global Research, Niskayuna, New York 12309
| | - Kristopher Frutschy
- Mechanical Systems Technologies, GE Global Research, Niskayuna, New York 12309
| | - Bob Senzig
- Molecular Imaging and Computed Tomography, GE Healthcare, Waukesha, Wisconsin 53188
| | - Norbert Pelc
- Department of Radiology, Stanford University, Stanford, California 94305
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Variation in CT Number and Image Noise Uniformity According to Patient Positioning in MDCT. AJR Am J Roentgenol 2017; 208:1064-1072. [PMID: 28267350 DOI: 10.2214/ajr.16.17215] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
OBJECTIVE Many algorithms for clinical decision making rely on assessment of the CT number (expressed as Hounsfield units); however, to our knowledge, few, if any, studies have addressed how CT numbers change as a function of patient positioning within the scanner. MATERIALS AND METHODS An anthropomorphic phantom underwent imaging with varying amounts of vertical orientation misalignment with respect to isocenter. CT number and noise were measured using ROIs in the upper thorax, mid thorax, and abdomen. The degree of noise nonuniformity and changes in the CT number were assessed by comparing values obtained in the anterior versus posterior ROIs. To add clinical relevance, data on vertical mispositioning were collected from 20,316 clinical abdominal CT scans. Box-and-whisker plot analysis was used to identify the range of patient positioning. RESULTS Absolute CT number changes of more than 20 HU were observed for some ROIs at phantom positions of 10 cm from isocenter, with important differences noted between the thoracic and abdominal regions. Noise uniformity varied by more than twofold for all regions at 10 cm below isocenter. On clinical CT examinations, off-centering of more than 1, 2, 4, and 6 cm occurred for 41%, 19%, 1.9%, and 0.3% of patients, respectively. CONCLUSION Radiologists should treat CT number measurements with caution when patients are grossly mispositioned in the scanner. The substantial changes in attenuation values shown in the present study are large enough to warrant further investigation.
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Gang GJ, Siewerdsen JH, Stayman JW. Joint Optimization of Fluence Field Modulation and Regularization in Task-Driven Computed Tomography. PROCEEDINGS OF SPIE--THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING 2017. [PMID: 28626290 PMCID: PMC5470723 DOI: 10.1117/12.2255517] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/30/2023]
Abstract
PURPOSE This work presents a task-driven joint optimization of fluence field modulation (FFM) and regularization in quadratic penalized-likelihood (PL) reconstruction. Conventional FFM strategies proposed for filtered-backprojection (FBP) are evaluated in the context of PL reconstruction for comparison. METHODS We present a task-driven framework that leverages prior knowledge of the patient anatomy and imaging task to identify FFM and regularization. We adopted a maxi-min objective that ensures a minimum level of detectability index (d') across sample locations in the image volume. The FFM designs were parameterized by 2D Gaussian basis functions to reduce dimensionality of the optimization and basis function coefficients were estimated using the covariance matrix adaptation evolutionary strategy (CMA-ES) algorithm. The FFM was jointly optimized with both space-invariant and spatially-varying regularization strength (β) - the former via an exhaustive search through discrete values and the latter using an alternating optimization where β was exhaustively optimized locally and interpolated to form a spatially-varying map. RESULTS The optimal FFM inverts as β increases, demonstrating the importance of a joint optimization. For the task and object investigated, the optimal FFM assigns more fluence through less attenuating views, counter to conventional FFM schemes proposed for FBP. The maxi-min objective homogenizes detectability throughout the image and achieves a higher minimum detectability than conventional FFM strategies. CONCLUSIONS The task-driven FFM designs found in this work are counter to conventional patterns for FBP and yield better performance in terms of the maxi-min objective, suggesting opportunities for improved image quality and/or dose reduction when model-based reconstructions are applied in conjunction with FFM.
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Affiliation(s)
- G J Gang
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD, USA 21205
| | - J H Siewerdsen
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD, USA 21205
| | - J W Stayman
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD, USA 21205
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Xu J, Sisniega A, Zbijewski W, Dang H, Stayman JW, Wang X, Foos DH, Aygun N, Koliatsos VE, Siewerdsen JH. Evaluation of detector readout gain mode and bowtie filters for cone-beam CT imaging of the head. Phys Med Biol 2016; 61:5973-92. [PMID: 27435162 DOI: 10.1088/0031-9155/61/16/5973] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The effects of detector readout gain mode and bowtie filters on cone-beam CT (CBCT) image quality and dose were characterized for a new CBCT system developed for point-of-care imaging of the head, with potential application to diagnosis of traumatic brain injury, intracranial hemorrhage (ICH), and stroke. A detector performance model was extended to include the effects of detector readout gain on electronic digitization noise. The noise performance for high-gain (HG), low-gain (LG), and dual-gain (DG) detector readout was evaluated, and the benefit associated with HG mode in regions free from detector saturation was quantified. Such benefit could be realized (without detector saturation) either via DG mode or by incorporation of a bowtie filter. Therefore, three bowtie filters were investigated that varied in thickness and curvature. A polyenergetic gain correction method was developed to equalize the detector response between the flood-field and projection data in the presence of a bowtie. The effect of bowtie filters on dose, scatter-to-primary ratio, contrast, and noise was quantified in phantom studies, and results were compared to a high-speed Monte Carlo (MC) simulation to characterize x-ray scatter and dose distributions in the head. Imaging in DG mode improved the contrast-to-noise ratio (CNR) by ~15% compared to LG mode at a dose (D 0, measured at the center of a 16 cm CTDI phantom) of 19 mGy. MC dose calculations agreed with CTDI measurements and showed that bowtie filters reduce peripheral dose by as much as 50% at the same central dose. Bowtie filters were found to increase the CNR per unit square-root dose near the center of the image by ~5-20% depending on bowtie thickness, but reduced CNR in the periphery by ~10-40%. Images acquired at equal CTDIw with and without a bowtie demonstrated a 24% increase in CNR at the center of an anthropomorphic head phantom. Combining a thick bowtie filter with a short arc (180° + fan angle) scan centered on the posterior of the head reduced dose to the eye lens by up to 90%. Acquisition in DG mode (without a bowtie filter) was beneficial to the detection of small, low contrast lesions (e.g. subtle ICH) in CBCT. While bowtie filters were found to reduce dose, mitigate sensor saturation at the periphery in HG mode, and improve CNR at the center of the image, the image quality at the periphery was slightly reduced compared to DG mode, and the use of a bowtie required careful implementation of the polyenergetic flood-field correction to avoid artifacts.
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Affiliation(s)
- Jennifer Xu
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205, USA
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Gang GJ, Siewerdsen JH, Stayman JW. Task-Based Design of Fluence Field Modulation in CT for Model-Based Iterative Reconstruction. CONFERENCE PROCEEDINGS. INTERNATIONAL CONFERENCE ON IMAGE FORMATION IN X-RAY COMPUTED TOMOGRAPHY 2016; 2016:407-410. [PMID: 28066840 PMCID: PMC5217752] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
A task-driven imaging framework for prospective fluence field modulation (FFM) is developed in this paper. The design approach uses a system model that includes a parameterized FFM acquisition and model-based iterative reconstruction (MBIR) for image formation. Using prior anatomical knowledge (e.g. from a low-dose 3D scout image), accurate predictions of spatial resolution and noise as a function of FFM are integrated into a task-based objective function. Specifically, detectability index (d'), a common metric for task-based image quality assessment, is computed for a specific formulation of the imaging task. To optimize imaging performance in across an image volume, a maximin objective function was adopted to maximize the minimum detectability index for many locations sampled throughout the volume. To reduce the dimensionality, FFM patterns were represented using wavelet bases, the coefficients of which were optimized using the covariance matrix adaptation evolutionary strategy (CMA-ES) algorithm. The optimization was performed for a mid-frequency discrimination task involving a cluster of micro-calcifications in an abdomen phantom. The task-driven design yielded FFM patterns that were significantly different from traditional strategies proposed for FBP reconstruction. In addition to a higher minimum d' consistent with the objective function, the task-driven approach also improved d' to a greater extent over a larger area of the phantom. Results from this work suggests that FFM strategies suitable for FBP reconstruction need to be reevaluated in the context of MBIR and that a task-driven imaging framework provides a promising approach for such optimization.
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Affiliation(s)
- Grace J Gang
- G. J. Gang, J. W. Stayman, and J. H. Siewerdsen are with the Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205 USA
| | - Jeffrey H Siewerdsen
- G. J. Gang, J. W. Stayman, and J. H. Siewerdsen are with the Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205 USA
| | - J Webster Stayman
- G. J. Gang, J. W. Stayman, and J. H. Siewerdsen are with the Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205 USA
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Hsieh SS, Peng MV, May CA, Shunhavanich P, Fleischmann D, Pelc NJ. A prototype piecewise-linear dynamic attenuator. Phys Med Biol 2016; 61:4974-88. [PMID: 27284705 DOI: 10.1088/0031-9155/61/13/4974] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The piecewise-linear dynamic attenuator has been proposed as a mechanism in CT scanning for personalizing the x-ray illumination on a patient- and application-specific basis. Previous simulations have shown benefits in image quality, scatter, and dose objectives. We report on the first prototype implementation. This prototype is reduced in scale and speed and is integrated into a tabletop CT system with a smaller field of view (25 cm) and longer scan time (42 s) compared to a clinical system. Stainless steel wedges were machined and affixed to linear actuators, which were in turn held secure by a frame built using rapid prototyping technologies. The actuators were computer-controlled, with characteristic noise of about 100 microns. Simulations suggest that in a clinical setting, the impact of actuator noise could lead to artifacts of only 1 HU. Ring artifacts were minimized by careful design of the wedges. A water beam hardening correction was applied and the scan was collimated to reduce scatter. We scanned a 16 cm water cylinder phantom as well as an anthropomorphic pediatric phantom. The artifacts present in reconstructed images are comparable to artifacts normally seen with this tabletop system. Compared to a flat-field reference scan, increased detectability at reduced dose is shown and streaking is reduced. Artifacts are modest in our images and further refinement is possible. Issues of mechanical speed and stability in the challenging clinical CT environment will be addressed in a future design.
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Affiliation(s)
- Scott S Hsieh
- Departments of Radiology, Stanford University, Stanford, CA 94305, USA. Departments of Electrical Engineering, Stanford University, Stanford, CA 94305, USA
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Stayman JW, Mathews A, Zbijewski W, Gang G, Siewerdsen J, Kawamoto S, Blevis I, Levinson R. Fluence-Field Modulated X-ray CT using Multiple Aperture Devices. PROCEEDINGS OF SPIE--THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING 2016; 9783. [PMID: 27110052 DOI: 10.1117/12.2214358] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
We introduce a novel strategy for fluence field modulation (FFM) in x-ray CT using multiple aperture devices (MADs). MAD filters permit FFM by blocking or transmitting the x-ray beam on a fine (0.1-1 mm) scale. The filters have a number of potential advantages over other beam modulation strategies including the potential for a highly compact design, modest actuation speed and acceleration requirements, and spectrally neutral filtration due to their essentially binary action. In this work, we present the underlying MAD filtration concept including a design process to achieve a specific class of FFM patterns. A set of MAD filters is fabricated using a tungsten laser sintering process and integrated into an x-ray CT test bench. A characterization of the MAD filters is conducted and compared to traditional attenuating bowtie filters and the ability to flatten the fluence profile for a 32 cm acrylic phantom is demonstrated. MAD-filtered tomographic data was acquired on the CT test bench and reconstructed without artifacts associated with the MAD filter. These initial studies suggest that MAD-based FFM is appropriate for integration in clinical CT system to create patient-specific fluence field profile and reduce radiation exposures.
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Affiliation(s)
| | - Aswin Mathews
- Biomedical Engineering, Johns Hopkins Univ., Baltimore, MD
| | | | - Grace Gang
- Biomedical Engineering, Johns Hopkins Univ., Baltimore, MD
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Parsons D, Robar JL. Volume of interest CBCT and tube current modulation for image guidance using dynamic kV collimation. Med Phys 2016; 43:1808. [DOI: 10.1118/1.4943799] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
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Hermus JR, Szczykutowicz TP. Two-dimensional dynamic fluid bowtie attenuators. J Med Imaging (Bellingham) 2016; 3:013502. [PMID: 26835499 DOI: 10.1117/1.jmi.3.1.013502] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2015] [Accepted: 12/11/2015] [Indexed: 11/14/2022] Open
Abstract
Fluence field modulated (FFM) CT allows for improvements in image quality and dose reduction. To date, only one-dimensional modulators have been proposed, as the extension to two-dimensional (2-D) modulation is difficult with solid-metal attenuation-based fluence field modulated designs. This work proposes to use liquid and gas to attenuate the x-ray beam, as unlike solids, these materials can be arranged allowing for 2-D fluence modulation. The thickness of liquid and the pressure for a given path length of gas were determined that provided the same attenuation as 30 cm of soft tissue at 80, 100, 120, and 140 kV. Liquid iodine, zinc chloride, cerium chloride, erbium oxide, iron oxide, and gadolinium chloride were studied. Gaseous xenon, uranium hexafluoride, tungsten hexafluoride, and nickel tetracarbonyl were also studied. Additionally, we performed a proof-of-concept experiment using a 96 cell array in which the liquid thickness in each cell was adjusted manually. Liquid thickness varied as a function of kV and chemical composition, with erbium oxide allowing for the smallest thickness. For the gases, tungsten hexaflouride required the smallest pressure to compensate for 30 cm of soft tissue. The 96 cell iodine attenuator allowed for a reduction in both dynamic range to the detector and scatter-to-primary ratio. For both liquids and gases, when k-edges were located within the diagnostic energy range used for imaging, the mean beam energy exhibited the smallest change with compensation amount. The thickness of liquids and the gas pressure seem logistically implementable within the space constraints of C-arm-based cone beam CT (CBCT) and diagnostic CT systems. The gas pressures also seem logistically implementable within the space and tube loading constraints of CBCT and diagnostic CT systems.
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Affiliation(s)
- James R Hermus
- University of Wisconsin-Madison , Department of Biomedical Engineering, 1415 Engineering Drive, Madison, Wisconsin 53706, United States
| | - Timothy P Szczykutowicz
- University of Wisconsin-Madison, Department of Biomedical Engineering, 1415 Engineering Drive, Madison, Wisconsin 53706, United States; University of Wisconsin-Madison, Department of Medical Physics, 1005 WIMR, 1111 Highland Avenue, Madison, Wisconsin 53705, United States; University of Wisconsin-Madison, Department of Radiology, 1005 WIMR, 1111 Highland Avenue, Madison, Wisconsin 53705, United States
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Szczykutowicz TP, Hermus J, Geurts M, Smilowitz J. Realization of fluence field modulated CT on a clinical TomoTherapy megavoltage CT system. Phys Med Biol 2015; 60:7245-57. [DOI: 10.1088/0031-9155/60/18/7245] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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De Man B, Wu M, FitzGerald P, Kalra M, Yin Z. Dose reconstruction for real-time patient-specific dose estimation in CT. Med Phys 2015; 42:2740-51. [PMID: 25979072 DOI: 10.1118/1.4921066] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Many recent computed tomography (CT) dose reduction approaches belong to one of three categories: statistical reconstruction algorithms, efficient x-ray detectors, and optimized CT acquisition schemes with precise control over the x-ray distribution. The latter category could greatly benefit from fast and accurate methods for dose estimation, which would enable real-time patient-specific protocol optimization. METHODS The authors present a new method for volumetrically reconstructing absorbed dose on a per-voxel basis, directly from the actual CT images. The authors' specific implementation combines a distance-driven pencil-beam approach to model the first-order x-ray interactions with a set of Gaussian convolution kernels to model the higher-order x-ray interactions. The authors performed a number of 3D simulation experiments comparing the proposed method to a Monte Carlo based ground truth. RESULTS The authors' results indicate that the proposed approach offers a good trade-off between accuracy and computational efficiency. The images show a good qualitative correspondence to Monte Carlo estimates. Preliminary quantitative results show errors below 10%, except in bone regions, where the authors see a bigger model mismatch. The computational complexity is similar to that of a low-resolution filtered-backprojection algorithm. CONCLUSIONS The authors present a method for analytic dose reconstruction in CT, similar to the techniques used in radiation therapy planning with megavoltage energies. Future work will include refinements of the proposed method to improve the accuracy as well as a more extensive validation study. The proposed method is not intended to replace methods that track individual x-ray photons, but the authors expect that it may prove useful in applications where real-time patient-specific dose estimation is required.
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Affiliation(s)
- Bruno De Man
- Image Reconstruction Laboratory, GE Global Research, Niskayuna, New York 12309
| | - Mingye Wu
- X-ray and CT Laboratory, GE Global Research, Shanghai 201203, China
| | - Paul FitzGerald
- Radiation Systems Laboratory, GE Global Research, Niskayuna, New York 12309
| | - Mannudeep Kalra
- Divisions of Thoracic and Cardiac Imaging, Massachusetts General Hospital, Boston, Massachusetts 02114
| | - Zhye Yin
- Image Reconstruction Laboratory, GE Global Research, Niskayuna, New York 12309
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Szczykutowicz TP, Hermus J. Creation of an atlas of filter positions for fluence field modulated CT. Med Phys 2015; 42:1779-86. [DOI: 10.1118/1.4915123] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Lu W, Yan H, Gu X, Tian Z, Luo O, Yang L, Zhou L, Cervino L, Wang J, Jiang S, Jia X. Reconstructing cone-beam CT with spatially varying qualities for adaptive radiotherapy: a proof-of-principle study. Phys Med Biol 2014; 59:6251-66. [PMID: 25255957 PMCID: PMC4197814 DOI: 10.1088/0031-9155/59/20/6251] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
With the aim of maximally reducing imaging dose while meeting requirements for adaptive radiation therapy (ART), we propose in this paper a new cone beam CT (CBCT) acquisition and reconstruction method that delivers images with a low noise level inside a region of interest (ROI) and a relatively high noise level outside the ROI. The acquired projection images include two groups: densely sampled projections at a low exposure with a large field of view (FOV) and sparsely sampled projections at a high exposure with a small FOV corresponding to the ROI. A new algorithm combining the conventional filtered back-projection algorithm and the tight-frame iterative reconstruction algorithm is also designed to reconstruct the CBCT based on these projection data. We have validated our method on a simulated head-and-neck (HN) patient case, a semi-real experiment conducted on a HN cancer patient under a full-fan scan mode, as well as a Catphan phantom under a half-fan scan mode. Relative root-mean-square errors (RRMSEs) of less than 3% for the entire image and ~1% within the ROI compared to the ground truth have been observed. These numbers demonstrate the ability of our proposed method to reconstruct high-quality images inside the ROI. As for the part outside ROI, although the images are relatively noisy, it can still provide sufficient information for radiation dose calculations in ART. Dose distributions calculated on our CBCT image and on a standard CBCT image are in agreement, with a mean relative difference of 0.082% inside the ROI and 0.038% outside the ROI. Compared with the standard clinical CBCT scheme, an imaging dose reduction of approximately 3-6 times inside the ROI was achieved, as well as an 8 times outside the ROI. Regarding computational efficiency, it takes 1-3 min to reconstruct a CBCT image depending on the number of projections used. These results indicate that the proposed method has the potential for application in ART.
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Affiliation(s)
- Wenting Lu
- Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX 75390, USA
- Department of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, 510515, China
| | - Hao Yan
- Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | - Xuejun Gu
- Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | - Zhen Tian
- Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | - Ouyang Luo
- Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | - Liu Yang
- Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX 75390, USA
- Department of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, 510515, China
| | - Linghong Zhou
- Department of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, 510515, China
| | - Laura Cervino
- Center for Advanced Radiotherapy Technologies, Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, CA 92037, USA
| | - Jing Wang
- Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | - Steve Jiang
- Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX 75390, USA
| | - Xun Jia
- Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX 75390, USA
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