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Schwarz A, Shemer A, Danan Y, Bar-Shalom R, Avraham H, Zlotnik A, Zalevsky Z. Gamma Radiation Imaging System via Variable and Time-Multiplexed Pinhole Arrays. SENSORS 2020; 20:s20113013. [PMID: 32466401 PMCID: PMC7313691 DOI: 10.3390/s20113013] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Revised: 05/20/2020] [Accepted: 05/21/2020] [Indexed: 11/16/2022]
Abstract
Biomedical planar imaging using gamma radiation is a very important screening tool for medical diagnostics. Since lens imaging is not available in gamma imaging, the current methods use lead collimator or pinhole techniques to perform imaging. However, due to ineffective utilization of the gamma radiation emitted from the patient’s body and the radioactive dose limit in patients, poor image signal to noise ratio (SNR) and long image capturing time are evident. Furthermore, the resolution is related to the pinhole diameter, thus there is a tradeoff between SNR and resolution. Our objectives are to reduce the radioactive dose given to the patient and to preserve or improve SNR, resolution and capturing time while incorporating three-dimensional capabilities in existing gamma imaging systems. The proposed imaging system is based on super-resolved time-multiplexing methods using both variable and moving pinhole arrays. Simulations were performed both in MATLAB and GEANT4, and gamma single photon emission computed tomography (SPECT) experiments were conducted to support theory and simulations. The proposed method is able to reduce the radioactive dose and image capturing time and to improve SNR and resolution. The results and method enhance the gamma imaging capabilities that exist in current systems, while providing three-dimensional data on the object.
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Affiliation(s)
- Ariel Schwarz
- Department of Electrical and Electronics Engineering, Azrieli College of Engineering, Jerusalem 9103501, Israel; (A.S.); (Y.D.)
| | - Amir Shemer
- Department of Electrical and Electronics Engineering, Azrieli College of Engineering, Jerusalem 9103501, Israel; (A.S.); (Y.D.)
- Correspondence:
| | - Yossef Danan
- Department of Electrical and Electronics Engineering, Azrieli College of Engineering, Jerusalem 9103501, Israel; (A.S.); (Y.D.)
| | - Rachel Bar-Shalom
- Shaare Zedek Medical Center, Jerusalem 9103102, Israel; (R.B.-S.); (H.A.)
| | - Hemy Avraham
- Shaare Zedek Medical Center, Jerusalem 9103102, Israel; (R.B.-S.); (H.A.)
| | - Alex Zlotnik
- Faculty of Engineering, Bar-Ilan University, Ramat-Gan 5290002, Israel; (A.Z.); (Z.Z.)
| | - Zeev Zalevsky
- Faculty of Engineering, Bar-Ilan University, Ramat-Gan 5290002, Israel; (A.Z.); (Z.Z.)
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Lin A, Kupinski MA, Peterson TE, Shokouhi S, Johnson LC. Task-based design of a synthetic-collimator SPECT system used for small animal imaging. Med Phys 2018; 45:2952-2963. [PMID: 29734479 DOI: 10.1002/mp.12952] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Revised: 02/12/2018] [Accepted: 02/25/2018] [Indexed: 11/08/2022] Open
Abstract
PURPOSE In traditional multipinhole SPECT systems, image multiplexing - the overlapping of pinhole projection images - may occur on the detector, which can inhibit quality image reconstructions due to photon-origin uncertainty. One proposed system to mitigate the effects of multiplexing is the synthetic-collimator SPECT system. In this system, two detectors, a silicon detector and a germanium detector, are placed at different distances behind the multipinhole aperture, allowing for image detection to occur at different magnifications and photon energies, resulting in higher overall sensitivity while maintaining high resolution. The unwanted effects of multiplexing are reduced by utilizing the additional data collected from the front silicon detector. However, determining optimal system configurations for a given imaging task requires efficient parsing of the complex parameter space, to understand how pinhole spacings and the two detector distances influence system performance. METHODS In our simulation studies, we use the ensemble mean-squared error of the Wiener estimator (EMSEW ) as the figure of merit to determine optimum system parameters for the task of estimating the uptake of an 123 I-labeled radiotracer in three different regions of a computer-generated mouse brain phantom. The segmented phantom map is constructed by using data from the MRM NeAt database and allows for the reduction in dimensionality of the system matrix which improves the computational efficiency of scanning the system's parameter space. To contextualize our results, the Wiener estimator is also compared against a region of interest estimator using maximum-likelihood reconstructed data. RESULTS Our results show that the synthetic-collimator SPECT system outperforms traditional multipinhole SPECT systems in this estimation task. We also find that image multiplexing plays an important role in the system design of the synthetic-collimator SPECT system, with optimal germanium detector distances occurring at maxima in the derivative of the percent multiplexing function. Furthermore, we report that improved task performance can be achieved by using an adaptive system design in which the germanium detector distance may vary with projection angle. Finally, in our comparative study, we find that the Wiener estimator outperforms the conventional region of interest estimator. CONCLUSIONS Our work demonstrates how this optimization method has the potential to quickly and efficiently explore vast parameter spaces, providing insight into the behavior of competing factors, which are otherwise very difficult to calculate and study using other existing means.
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Affiliation(s)
- Alexander Lin
- College of Optical Sciences, University of Arizona, 1630 E. University Ave, Tucson, AZ, USA
| | - Matthew A Kupinski
- College of Optical Sciences, University of Arizona, 1630 E. University Ave, Tucson, AZ, USA
| | - Todd E Peterson
- Department of Radiology and Radiological Sciences, Institute of Imaging Science, Vanderbilt University Medical Center, 1161 21st Avenue South, Nashville, TN, USA
| | - Sepideh Shokouhi
- Department of Radiology and Radiological Sciences, Institute of Imaging Science, Vanderbilt University Medical Center, 1161 21st Avenue South, Nashville, TN, USA
| | - Lindsay C Johnson
- Department of Radiology, University of Pennsylvania, 3620 Hamilton Walk, Philadelphia, PA, USA
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Zeraatkar N, Farahani MH, Rahmim A, Sarkar S, Ay MR. Design and assessment of a novel SPECT system for desktop open-gantry imaging of small animals: A simulation study. Med Phys 2016; 43:2581. [DOI: 10.1118/1.4947127] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
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Van Audenhaege K, Van Holen R, Vandenberghe S, Vanhove C, Metzler SD, Moore SC. Review of SPECT collimator selection, optimization, and fabrication for clinical and preclinical imaging. Med Phys 2015; 42:4796-813. [PMID: 26233207 PMCID: PMC5148182 DOI: 10.1118/1.4927061] [Citation(s) in RCA: 81] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Revised: 07/07/2015] [Accepted: 07/08/2015] [Indexed: 01/23/2023] Open
Abstract
In single photon emission computed tomography, the choice of the collimator has a major impact on the sensitivity and resolution of the system. Traditional parallel-hole and fan-beam collimators used in clinical practice, for example, have a relatively poor sensitivity and subcentimeter spatial resolution, while in small-animal imaging, pinhole collimators are used to obtain submillimeter resolution and multiple pinholes are often combined to increase sensitivity. This paper reviews methods for production, sensitivity maximization, and task-based optimization of collimation for both clinical and preclinical imaging applications. New opportunities for improved collimation are now arising primarily because of (i) new collimator-production techniques and (ii) detectors with improved intrinsic spatial resolution that have recently become available. These new technologies are expected to impact the design of collimators in the future. The authors also discuss concepts like septal penetration, high-resolution applications, multiplexing, sampling completeness, and adaptive systems, and the authors conclude with an example of an optimization study for a parallel-hole, fan-beam, cone-beam, and multiple-pinhole collimator for different applications.
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Affiliation(s)
- Karen Van Audenhaege
- Department of Electronics and Information Systems, MEDISIP-IBiTech, Ghent University-iMinds Medical IT, De Pintelaan 185 block B/5, Ghent B-9000, Belgium
| | - Roel Van Holen
- Department of Electronics and Information Systems, MEDISIP-IBiTech, Ghent University-iMinds Medical IT, De Pintelaan 185 block B/5, Ghent B-9000, Belgium
| | - Stefaan Vandenberghe
- Department of Electronics and Information Systems, MEDISIP-IBiTech, Ghent University-iMinds Medical IT, De Pintelaan 185 block B/5, Ghent B-9000, Belgium
| | - Christian Vanhove
- Department of Electronics and Information Systems, MEDISIP-IBiTech, Ghent University-iMinds Medical IT, De Pintelaan 185 block B/5, Ghent B-9000, Belgium
| | - Scott D Metzler
- Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Stephen C Moore
- Division of Nuclear Medicine, Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, 75 Francis Street, Boston, Massachusetts 02115
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Johnson LC, Shokouhi S, Peterson TE. Reducing multiplexing artifacts in multi-pinhole SPECT with a stacked silicon-germanium system: a simulation study. IEEE TRANSACTIONS ON MEDICAL IMAGING 2014; 33:2342-2351. [PMID: 25055382 PMCID: PMC4565520 DOI: 10.1109/tmi.2014.2340251] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In pinhole single photon emission computed tomography (SPECT), multi-pinhole collimators can increase sensitivity but may lead to projection overlap, or multiplexing, which can cause image artifacts. In this work, we explore whether a stacked-detector configuration with a germanium and a silicon detector, used with 123I (27-32, 159 keV), where little multiplexing occurs in the Si projections, can reduce image artifacts caused by highly-multiplexed Ge projections. Simulations are first used to determine a reconstruction method that combines the Si and Ge projections to maximize image quality. Next, simulations of different pinhole configurations (varying projection multiplexing) in conjunction with digital phantoms are used to examine whether additional Si projections mitigate artifacts from the multiplexing in the Ge projections. Reconstructed images using both Si and Ge data are compared to those using Ge data alone. Normalized mean-square error and normalized standard deviation provide a quantitative evaluation of reconstructed images' error and noise, respectively, and are used to evaluate the impact of the additional nonmultiplexed data on image quality. For a qualitative comparison, the differential point response function is used to examine multiplexing artifacts. Results show that in cases of highly-multiplexed Ge projections, the addition of low-multiplexed Si projections helps to reduce image artifacts both quantitatively and qualitatively.
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Affiliation(s)
- Lindsay C. Johnson
- Vanderbilt University Institute of Imaging Science and the Department of Radiology and Radiological Sciences, Nashville, TN 37232 USA
| | - Sepideh Shokouhi
- Vanderbilt University Institute of Imaging Science and the Department of Radiology and Radiological Sciences, Nashville, TN 37232 USA
| | - Todd E Peterson
- Vanderbilt University Institute of Imaging Science, the Department of Physics and Astronomy, and the Department of Radiology and Radiological Sciences Nashville, TN 37232 USA
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Bowen JD, Huang Q, Ellin JR, Lee TC, Shrestha U, Gullberg GT, Seo Y. Design and performance evaluation of a 20-aperture multipinhole collimator for myocardial perfusion imaging applications. Phys Med Biol 2013; 58:7209-26. [PMID: 24061162 PMCID: PMC3855225 DOI: 10.1088/0031-9155/58/20/7209] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Single photon emission computed tomography (SPECT) myocardial perfusion imaging remains a critical tool in the diagnosis of coronary artery disease. However, after more than three decades of use, photon detection efficiency remains poor and unchanged. This is due to the continued reliance on parallel-hole collimators first introduced in 1964. These collimators possess poor geometric efficiency. Here we present the performance evaluation results of a newly designed multipinhole collimator with 20 pinhole apertures (PH20) for commercial SPECT systems. Computer simulations and numerical observer studies were used to assess the noise, bias and diagnostic imaging performance of a PH20 collimator in comparison with those of a low energy high resolution (LEHR) parallel-hole collimator. Ray-driven projector/backprojector pairs were used to model SPECT imaging acquisitions, including simulation of noiseless projection data and performing MLEM/OSEM image reconstructions. Poisson noise was added to noiseless projections for realistic projection data. Noise and bias performance were investigated for five mathematical cardiac and torso (MCAT) phantom anatomies imaged at two gantry orbit positions (19.5 and 25.0 cm). PH20 and LEHR images were reconstructed with 300 MLEM iterations and 30 OSEM iterations (ten subsets), respectively. Diagnostic imaging performance was assessed by a receiver operating characteristic (ROC) analysis performed on a single MCAT phantom; however, in this case PH20 images were reconstructed with 75 pixel-based OSEM iterations (four subsets). Four PH20 projection views from two positions of a dual-head camera acquisition and 60 LEHR projections were simulated for all studies. At uniformly-imposed resolution of 12.5 mm, significant improvements in SNR and diagnostic sensitivity (represented by the area under the ROC curve, or AUC) were realized when PH20 collimators are substituted for LEHR parallel-hole collimators. SNR improves by factors of 1.94-2.34 for the five patient anatomies and two orbital positions studied. For the ROC analysis the PH20 AUC is larger than the LEHR AUC with a p-value of 0.0067. Bias performance, however, decreases with the use of PH20 collimators. Systematic analyses showed PH20 collimators present improved diagnostic imaging performance over LEHR collimators, requiring only collimator exchange on existing SPECT cameras for their use.
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Affiliation(s)
- Jason D. Bowen
- Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, California, USA
| | - Qiu Huang
- Shanghai Jiaotong University, Shanghai, China
| | - Justin R. Ellin
- Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, California, USA
| | - Tzu-Cheng Lee
- Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, California, USA
| | - Uttam Shrestha
- Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, California, USA
| | - Grant T. Gullberg
- Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, California, USA
- Department of Radiotracer Development and Imaging Technology, Lawrence Berkeley National Laboratory, Berkeley, California, USA
| | - Youngho Seo
- Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, California, USA
- Department of Radiation Oncology, University of California, San Francisco, California, USA
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Van Audenhaege K, Vandenberghe S, Deprez K, Vandeghinste B, Van Holen R. Design and simulation of a full-ring multi-lofthole collimator for brain SPECT. Phys Med Biol 2013; 58:6317-36. [PMID: 23966017 DOI: 10.1088/0031-9155/58/18/6317] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Currently, clinical brain single photon emission computed tomography (SPECT) is mostly performed using rotating dual-head gamma cameras equipped with low-energy-high-resolution parallel-beam collimators (LEHR PAR). The resolution of these systems is rather poor (8-10 mm) and the rotation of the heavy gamma cameras can introduce misalignment errors. Therefore, we designed a static full-ring multi-lofthole brain SPECT insert for an existing ring of LaBr3 (5% Ce) detectors. The novelty of the design is found in the shutter mechanism that makes the system very flexible and eliminates the need for rotating parts. A stationary SPECT insert is not only more robust, it is also easier to integrate in a magnetic resonance imaging system (MRI) for simultaneous SPECT-MRI. The target spatial resolution of our design is 6 mm. In this study we used analytical calculations to optimize the collimator for an existing ring of LaBr3 (5% Ce) detectors. We fixed the target spatial resolution at 6 mm in the center of the field-of-view and maximized the volume sensitivity by changing the collimator radius, the aperture and the number of loftholes. Based on these optimal parameters we simulated phantom data and evaluated the image quality of our multi-lofthole system. We simulated a noiseless uniform and Defrise phantom to assess artifacts and sampling completeness and a noiseless hot-rod phantom to assess the reconstructed spatial resolution. We visually evaluated a simulated noisy Hoffman phantom with two lesions. Then, we evaluated the non-prewhitening matched filter signal-to-noise ratio (NPW-SNR) in two lesion detectability phantoms: one with hot lesions and one with cold lesions. Finally, a contrast-to-noise (CNR) study was performed on a phantom with both hot and cold lesions of different sizes (6-16 mm). All results were compared to a LEHR PAR system. The optimization resulted in a final collimator design with a volume sensitivity of 1.55 × 10(-4) cps Bq(-1), which is 2.5 times lower than the sensitivity of a dual-head system with LEHR PAR collimators. Spatial resolution, on the other hand, has clearly improved compared to LEHR PAR: with the multi-lofthole system we successfully reconstructed 4 mm hot rods. Although this improved resolution did not result in an unambiguous improvement in CNR or NPW-SNR, we believe that the flexibility of the shutter mechanism opens interesting perspectives toward time-multiplexing and integration with MRI.
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Affiliation(s)
- Karen Van Audenhaege
- Ghent University-iMinds, Department of Electronics and Information Systems, MEDISIP-IBiTech, De Pintelaan 185 block B/5, B-9000 Ghent, Belgium.
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Havelin RJ, Miller BW, Barrett HH, Furenlid LR, Murphy JM, Dwyer RM, Foley MJ. Design and performance of a small-animal imaging system using synthetic collimation. Phys Med Biol 2013; 58:3397-412. [PMID: 23618819 DOI: 10.1088/0031-9155/58/10/3397] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
This work outlines the design and construction of a single-photon emission computed tomography imaging system based on the concept of synthetic collimation. A focused multi-pinhole collimator is constructed using rapid-prototyping and casting techniques. The collimator projects the centre of the field of view (FOV) through 46 pinholes when the detector is adjacent to the collimator, with the number reducing towards the edge of the FOV. The detector is then moved further from the collimator to increase the magnification of the system. The object distance remains constant, and each new detector distance is a new system configuration. The level of overlap of the pinhole projections increases as the system magnification increases, but the number of projections subtended by the detector is reduced. There is no rotation in the system; a single tomographic angle is used in each system configuration. Image reconstruction is performed using maximum-likelihood expectation-maximization and an experimentally measured system matrix. The system matrix is measured for each configuration on a coarse grid, using a point source. The pinholes are individually identified and tracked, and a Gaussian fit is made to each projection. The coefficients of these fits are used to interpolate the system matrix. The system is validated experimentally with a hot-rod phantom. The Fourier crosstalk matrix is also measured to provide an estimate of the average spatial resolution along each axis over the entire FOV. The 3D synthetic-collimator image is formed by estimating the activity distribution within the FOV and summing the activities in the voxels along the axis perpendicular to the collimator face.
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Affiliation(s)
- R J Havelin
- School of Physics, National University of Ireland Galway, Ireland
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Abstract
Preclinical SPECT of rodents is both in demand and very demanding. The need for high spatial resolution in combination with good sensitivity has given rise to considerable innovation in the areas of detectors, collimation, acquisition geometry, and image reconstruction. Some of the developments described herein are beginning to carry over into clinical imaging as well.
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Affiliation(s)
- Todd E Peterson
- Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee 37232-2310, USA
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