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Wang W, Gang GJ, Siewerdsen JH, Stayman JW. Spatial Resolution and Noise Prediction in Flat-Panel Cone-Beam CT Penalized-likelihood Reconstruction. PROCEEDINGS OF SPIE--THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING 2018; 10573. [PMID: 29622857 DOI: 10.1117/12.2294546] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Purpose Model based iterative reconstruction (MBIR) algorithms such as penalized-likelihood (PL) methods have data-dependent and shift-variant image properties. Predictors of local reconstructed noise and resolution have found application in a number of methods that seek to understand, control, and optimize CT data acquisition and reconstruction parameters in a prospective fashion (as opposed to studies based on exhaustive evaluation). However, previous MBIR prediction methods have relied on idealized system models. In this work, we develop and validate new predictors using accurate physical models specific to flat-panel CT systems. Methods Novel predictors for estimation of local spatial resolution and noise properties are developed for PL reconstruction that include a physical model for blur and correlated noise in flat-panel cone-beam CT (CBCT) acquisitions. Prospective predictions (e.g., without reconstruction) of local point spread function and and local noise power spectrum (NPS) model are applied, compared, and validated using a flat-panel CBCT test bench. Results Comparisons between prediction and physical measurements show excellent agreement for both spatial resolution and noise properties. In comparison, traditional prediction methods (that ignore blur/correlation found in flat-panel data) fail to capture important data characteristics and show significant mismatch. Conclusion Novel image property predictors permit prospective assessment of flat-panel CBCT using MBIR. Such predictors enable standard and task-based performance assessments, and are well-suited to evaluation, control, and optimization of the CT imaging chain (e.g., x-ray technique, reconstruction parameters, novel data acquisition methods, etc.) for improved imaging performance and/or dose utilization.
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Affiliation(s)
- W Wang
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD, USA 21205
| | - 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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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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Dang H, Stayman JW, Xu J, Zbijewski W, Sisniega A, Mow M, Wang X, Foos DH, Aygun N, Koliatsos VE, Siewerdsen JH. Task-based statistical image reconstruction for high-quality cone-beam CT. Phys Med Biol 2017; 62:8693-8719. [PMID: 28976368 DOI: 10.1088/1361-6560/aa90fd] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Task-based analysis of medical imaging performance underlies many ongoing efforts in the development of new imaging systems. In statistical image reconstruction, regularization is often formulated in terms to encourage smoothness and/or sharpness (e.g. a linear, quadratic, or Huber penalty) but without explicit formulation of the task. We propose an alternative regularization approach in which a spatially varying penalty is determined that maximizes task-based imaging performance at every location in a 3D image. We apply the method to model-based image reconstruction (MBIR-viz., penalized weighted least-squares, PWLS) in cone-beam CT (CBCT) of the head, focusing on the task of detecting a small, low-contrast intracranial hemorrhage (ICH), and we test the performance of the algorithm in the context of a recently developed CBCT prototype for point-of-care imaging of brain injury. Theoretical predictions of local spatial resolution and noise are computed via an optimization by which regularization (specifically, the quadratic penalty strength) is allowed to vary throughout the image to maximize local task-based detectability index ([Formula: see text]). Simulation studies and test-bench experiments were performed using an anthropomorphic head phantom. Three PWLS implementations were tested: conventional (constant) penalty; a certainty-based penalty derived to enforce constant point-spread function, PSF; and the task-based penalty derived to maximize local detectability at each location. Conventional (constant) regularization exhibited a fairly strong degree of spatial variation in [Formula: see text], and the certainty-based method achieved uniform PSF, but each exhibited a reduction in detectability compared to the task-based method, which improved detectability up to ~15%. The improvement was strongest in areas of high attenuation (skull base), where the conventional and certainty-based methods tended to over-smooth the data. The task-driven reconstruction method presents a promising regularization method in MBIR by explicitly incorporating task-based imaging performance as the objective. The results demonstrate improved ICH conspicuity and support the development of high-quality CBCT systems.
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Affiliation(s)
- Hao Dang
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205, United States of America
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Abstract
Current photon counting x-ray detector (PCD) technology faces limitations associated with spectral fidelity and photon starvation. One strategy for addressing these limitations is to supplement PCD data with high-resolution, low-noise data acquired with an energy-integrating detector (EID). In this work, we propose an iterative, hybrid reconstruction technique which combines the spectral properties of PCD data with the resolution and signal-to-noise characteristics of EID data. Our hybrid reconstruction technique is based on an algebraic model of data fidelity which substitutes the EID data into the data fidelity term associated with the PCD reconstruction, resulting in a joint reconstruction problem. Within the split Bregman framework, these data fidelity constraints are minimized subject to additional constraints on spectral rank and on joint intensity-gradient sparsity measured between the reconstructions of the EID and PCD data. Following a derivation of the proposed technique, we apply it to the reconstruction of a digital phantom which contains realistic concentrations of iodine, barium, and calcium encountered in small-animal micro-CT. The results of this experiment suggest reliable separation and detection of iodine at concentrations ≥ 5 mg/ml and barium at concentrations ≥ 10 mg/ml in 2-mm features for EID and PCD data reconstructed with inherent spatial resolutions of 176 μm and 254 μm, respectively (point spread function, FWHM). Furthermore, hybrid reconstruction is demonstrated to enhance spatial resolution within material decomposition results and to improve low-contrast detectability by as much as 2.6 times relative to reconstruction with PCD data only. The parameters of the simulation experiment are based on an in vivo micro-CT experiment conducted in a mouse model of soft-tissue sarcoma. Material decomposition results produced from this in vivo data demonstrate the feasibility of distinguishing two K-edge contrast agents with a spectral separation on the order of the energy resolution of the PCD hardware.
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Affiliation(s)
- Darin P. Clark
- Center for In Vivo Microscopy, Department of Radiology, Duke University Medical Center, Durham, NC, United States of America
| | - Cristian T. Badea
- Center for In Vivo Microscopy, Department of Radiology, Duke University Medical Center, Durham, NC, United States of America
- * E-mail:
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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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Gomes J, Gang GJ, Mathews A, Stayman JW. An Investigation of Low-Dose 3D Scout Scans for Computed Tomography. ACTA ACUST UNITED AC 2017; 10132. [PMID: 28596635 DOI: 10.1117/12.2255514] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
PURPOSE Commonly 2D scouts or topograms are used prior to CT scan acquisition. However, low-dose 3D scouts could potentially provide additional information for more effective patient positioning and selection of acquisition protocols. We propose using model-based iterative reconstruction to reconstruct low exposure tomographic data to maintain image quality in both low-dose 3D scouts and reprojected topograms based on those 3D scouts. METHODS We performed tomographic acquisitions on a CBCT test-bench using a range of exposure settings from 16.6 to 231.9 total mAs. Both an anthropomorphic phantom and a 32 cm CTDI phantom were scanned. The penalized-likelihood reconstructions were made using Matlab and CUDA libraries and reconstruction parameters were tuned to determine the best regularization strength and delta parameter. RMS error between reconstructions and the highest exposure reconstruction were computed, and CTDIW values were reported for each exposure setting. RMS error for reprojected topograms were also computed. RESULTS We find that we are able to produce low-dose (0.417 mGy) 3D scouts that show high-contrast and large anatomical features while maintaining the ability to produce traditional topograms. CONCLUSIONS We demonstrated that iterative reconstruction can mitigate noise in very low exposure CT acquisitions to enable 3D CT scout. Such additional 3D information may lead to improved protocols for patient positioning and acquisition refinements as well as a number of advanced dose reduction strategies that require localization of anatomical features and quantities that are not provided by simple 2D topograms.
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Affiliation(s)
- Juliana Gomes
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD, USA 21205
| | - Grace J Gang
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD, USA 21205
| | - Aswin Mathews
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD, USA 21205
| | - J Webster Stayman
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore MD, USA 21205
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Mathews AJ, Gang G, Levinson R, Zbijewski W, Kawamoto S, Siewerdsen JH, Stayman JW. Experimental evaluation of dual Multiple Aperture Devices for Fluence Field Modulated X-Ray Computed Tomography. PROCEEDINGS OF SPIE--THE INTERNATIONAL SOCIETY FOR OPTICAL ENGINEERING 2017; 10132:101322O. [PMID: 28603335 PMCID: PMC5464412 DOI: 10.1117/12.2255677] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Acquisition of CT images with comparable diagnostic power can potentially be achieved with lower radiation exposure than the current standard of care through the adoption of hardware-based fluence-field modulation (e.g. dynamic bowtie filters). While modern CT scanners employ elements such as static bowtie filters and tube-current modulation, such solutions are limited in the fluence patterns that they can achieve, and thus are limited in their ability to adapt to broad classes of patient morphology. Fluence-field modulation also enables new applications such as region-of-interest imaging, task specific imaging, reducing measurement noise or improving image quality. The work presented in this paper leverages a novel fluence modulation strategy that uses "Multiple Aperture Devices" (MADs) which are, in essence, binary filters, blocking or passing x-rays on a fine scale. Utilizing two MAD devices in series provides the capability of generating a large number of fluence patterns via small relative motions between the MAD filters. We present the first experimental evaluation of fluence-field modulation using a dual-MAD system, and demonstrate the efficacy of this technique with a characterization of achievable fluence patterns and an investigation of experimental projection data.
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Affiliation(s)
| | - G Gang
- Johns Hopkins University, Baltimore, MD USA
| | - R Levinson
- Global Research and Advanced Development, Philips Healthcare, Haifa, Israel
| | | | - S Kawamoto
- Johns Hopkins University, Baltimore, MD USA
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Mathews AJ, Tilley S, Gang G, Kawamoto S, Zbijewski W, Siewerdsen JH, Levinson R, Webster Stayman J. Design of dual multiple aperture devices for dynamical fluence field modulated CT. CONFERENCE PROCEEDINGS. INTERNATIONAL CONFERENCE ON IMAGE FORMATION IN X-RAY COMPUTED TOMOGRAPHY 2016; 2016:29-32. [PMID: 28361128 PMCID: PMC5370167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
A Multiple Aperture Device (MAD) is a novel x-ray beam modulator that uses binary filtration on a fine scale to spatially modulate an x-ray beam. Using two MADs in series enables a large variety of fluence profiles by shifting the MADS relative to each other. This work details the design and control of dual MADs for a specific class of desired fluence patterns. Specifically, models of MAD operation are integrated into a best fit objective followed by CMA-ES optimization. To illustrate this framework we demonstrate the design process for an abdominal phantom with the goal of uniform detected signal. Achievable fluence profiles show good agreement with target fluence profiles, and the ability to flatten projections when a phantom is scanned is demonstrated. Simulated data reconstruction using traditional tube current modulation (TCM) and MAD filtering with TCM are investigated with the dual MAD system demonstrating more uniformity in noise and illustrating the potential for dose reduction under a maximum noise level constraint.
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Affiliation(s)
- Aswin John Mathews
- Aswin John Mathews, Steven Tilley II, Grace Gang, Satomi Kawamoto, Wojciech Zbijewski, Jeffrey H. Siewerdsen and J. Webster Stayman are with the Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21212 USA. Reuven Levinson is with Philips, Haifa
| | - Steven Tilley
- Aswin John Mathews, Steven Tilley II, Grace Gang, Satomi Kawamoto, Wojciech Zbijewski, Jeffrey H. Siewerdsen and J. Webster Stayman are with the Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21212 USA. Reuven Levinson is with Philips, Haifa
| | - Grace Gang
- Aswin John Mathews, Steven Tilley II, Grace Gang, Satomi Kawamoto, Wojciech Zbijewski, Jeffrey H. Siewerdsen and J. Webster Stayman are with the Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21212 USA. Reuven Levinson is with Philips, Haifa
| | - Satomi Kawamoto
- Aswin John Mathews, Steven Tilley II, Grace Gang, Satomi Kawamoto, Wojciech Zbijewski, Jeffrey H. Siewerdsen and J. Webster Stayman are with the Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21212 USA. Reuven Levinson is with Philips, Haifa
| | - Wojciech Zbijewski
- Aswin John Mathews, Steven Tilley II, Grace Gang, Satomi Kawamoto, Wojciech Zbijewski, Jeffrey H. Siewerdsen and J. Webster Stayman are with the Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21212 USA. Reuven Levinson is with Philips, Haifa
| | - Jeffrey H Siewerdsen
- Aswin John Mathews, Steven Tilley II, Grace Gang, Satomi Kawamoto, Wojciech Zbijewski, Jeffrey H. Siewerdsen and J. Webster Stayman are with the Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21212 USA. Reuven Levinson is with Philips, Haifa
| | - Reuven Levinson
- Aswin John Mathews, Steven Tilley II, Grace Gang, Satomi Kawamoto, Wojciech Zbijewski, Jeffrey H. Siewerdsen and J. Webster Stayman are with the Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21212 USA. Reuven Levinson is with Philips, Haifa
| | - J Webster Stayman
- Aswin John Mathews, Steven Tilley II, Grace Gang, Satomi Kawamoto, Wojciech Zbijewski, Jeffrey H. Siewerdsen and J. Webster Stayman are with the Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21212 USA. Reuven Levinson is with Philips, Haifa
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