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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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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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Zhang H, Wang J, Zeng D, Tao X, Ma J. Regularization strategies in statistical image reconstruction of low-dose x-ray CT: A review. Med Phys 2018; 45:e886-e907. [PMID: 30098050 DOI: 10.1002/mp.13123] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 06/22/2018] [Accepted: 08/04/2018] [Indexed: 12/17/2022] Open
Abstract
Statistical image reconstruction (SIR) methods have shown potential to substantially improve the image quality of low-dose x-ray computed tomography (CT) as compared to the conventional filtered back-projection (FBP) method. According to the maximum a posteriori (MAP) estimation, the SIR methods are typically formulated by an objective function consisting of two terms: (a) a data-fidelity term that models imaging geometry and physical detection processes in projection data acquisition, and (b) a regularization term that reflects prior knowledge or expectations of the characteristics of the to-be-reconstructed image. SIR desires accurate system modeling of data acquisition, while the regularization term also has a strong influence on the quality of reconstructed images. A variety of regularization strategies have been proposed for SIR in the past decades, based on different assumptions, models, and prior knowledge. In this paper, we review the conceptual and mathematical bases of these regularization strategies and briefly illustrate their efficacies in SIR of low-dose CT.
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Affiliation(s)
- Hao Zhang
- Department of Radiation Oncology, Stanford University, Stanford, CA, 94304, USA
| | - Jing Wang
- Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX, 75390, USA
| | - Dong Zeng
- School of Biomedical Engineering, Southern Medical University, Guangzhou, 510515, China
| | - Xi Tao
- School of Biomedical Engineering, Southern Medical University, Guangzhou, 510515, China
| | - Jianhua Ma
- School of Biomedical Engineering, Southern Medical University, Guangzhou, 510515, China
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Gang GJ, Siewerdsen JH, Stayman JW. Task-Driven Optimization of Fluence Field and Regularization for Model-Based Iterative Reconstruction in Computed Tomography. IEEE TRANSACTIONS ON MEDICAL IMAGING 2017; 36:2424-2435. [PMID: 29035215 PMCID: PMC5728109 DOI: 10.1109/tmi.2017.2763538] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
This paper presents a joint optimization of dynamic fluence field modulation (FFM) and regularization in quadratic penalized-likelihood reconstruction that maximizes a task-based imaging performance metric. We adopted a task-driven imaging framework for prospective designs of the imaging parameters. A maxi-min objective function was adopted to maximize the minimum detectability index ( ) throughout the image. The optimization algorithm alternates between FFM (represented by low-dimensional basis functions) and local regularization (including the regularization strength and directional penalty weights). The task-driven approach was compared with three FFM strategies commonly proposed for FBP reconstruction (as well as a task-driven TCM strategy) for a discrimination task in an abdomen phantom. The task-driven FFM assigned more fluence to less attenuating anteroposterior views and yielded approximately constant fluence behind the object. The optimal regularization was almost uniform throughout image. Furthermore, the task-driven FFM strategy redistribute fluence across detector elements in order to prescribe more fluence to the more attenuating central region of the phantom. Compared with all strategies, the task-driven FFM strategy not only improved minimum by at least 17.8%, but yielded higher over a large area inside the object. The optimal FFM was highly dependent on the amount of regularization, indicating the importance of a joint optimization. Sample reconstructions of simulated data generally support the performance estimates based on computed . The improvements in detectability show the potential of the task-driven imaging framework to improve imaging performance at a fixed dose, or, equivalently, to provide a similar level of performance at reduced dose.
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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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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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