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Toews AR, Lee PK, Nayak KS, Hargreaves BA. Comprehensive assessment of nonuniform image quality: Application to imaging near metal. Magn Reson Med 2024. [PMID: 38997797 DOI: 10.1002/mrm.30222] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2024] [Revised: 06/06/2024] [Accepted: 06/26/2024] [Indexed: 07/14/2024]
Abstract
PURPOSE Comprehensive assessment of image quality requires accounting for spatial variations in (i) intensity artifact, (ii) geometric distortion, (iii) signal-to-noise ratio (SNR), and (iv) spatial resolution, among other factors. This work presents an ensemble of methods to meet this need, from phantom design to image analysis, and applies it to the scenario of imaging near metal. METHODS A modular phantom design employing a gyroid lattice is developed to enable the co-registered volumetric quantitation of image quality near a metallic hip implant. A method for measuring spatial resolution by means of local point spread function (PSF) estimation is presented and the relative fitness of gyroid and cubic lattices is examined. Intensity artifact, geometric distortion, and SNR maps are also computed. Results are demonstrated with 2D-FSE and MAVRIC-SL scan protocols on a 3T MRI scanner. RESULTS The spatial resolution method demonstrates a worst-case error of 0.17 pixels for measuring in-plane blurring up to 3 pixels (full width at half maximum). The gyroid outperforms a cubic lattice design for the local PSF estimation task. The phantom supports four configurations toggling the presence/absence of both metal and structure with good spatial correspondence for co-registered analysis of the four quality factors. The marginal scan time to evaluate one scan protocol amounts to five repetitions. The phantom design can be fabricated in 2 days at negligible material cost. CONCLUSION The phantom and associated analysis methods can elucidate complex image quality trade-offs involving intensity artifact, geometric distortion, SNR, and spatial resolution. The ensemble of methods is suitable for benchmarking imaging performance near metal.
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Affiliation(s)
- Alexander R Toews
- Radiology, Stanford University, Stanford, California, USA
- Electrical Engineering, Stanford University, Stanford, California, USA
| | - Philip K Lee
- Radiology, Stanford University, Stanford, California, USA
| | - Krishna S Nayak
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California, USA
| | - Brian A Hargreaves
- Radiology, Stanford University, Stanford, California, USA
- Electrical Engineering, Stanford University, Stanford, California, USA
- Bioengineering, Stanford University, Stanford, California, USA
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2
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Spronk T, Kraff O, Schaefers G, Quick HH. Numerical approach to investigate MR imaging artifacts from orthopedic implants at different field strengths according to ASTM F2119. MAGMA (NEW YORK, N.Y.) 2023; 36:725-735. [PMID: 36933090 PMCID: PMC10504103 DOI: 10.1007/s10334-023-01074-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2022] [Revised: 02/24/2023] [Accepted: 02/26/2023] [Indexed: 03/19/2023]
Abstract
OBJECTIVE This study presents an extended evaluation of a numerical approach to simulate artifacts of metallic implants in an MR environment. METHODS The numerical approach is validated by comparing the artifact shape of the simulations and measurements of two metallic orthopedic implants at three different field strengths (1.5 T, 3 T, and 7 T). Furthermore, this study presents three additional use cases of the numerical simulation. The first one shows how numerical simulations can improve the artifact size evaluation according to ASTM F2119. The second use case quantifies the influence of different imaging parameters (TE and bandwidth) on the artifact size. Finally, the third use case shows the potential of performing human model artifact simulations. RESULTS The numerical simulation approach shows a dice similarity coefficient of 0.74 between simulated and measured artifact sizes of metallic implants. The alternative artifact size calculation method presented in this study shows that the artifact size of the ASTM-based method is up to 50% smaller for complex shaped implants compared to the numerical-based approach. CONCLUSION In conclusion, the numerical approach could be used in the future to extend MR safety testing according to a revision of the ASTM F2119 standard and for design optimization during the development process of implants.
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Affiliation(s)
- Tobias Spronk
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Kokereiallee 7, Building C84, 45141, Essen, Germany.
- High-Field and Hybrid MR Imaging, University Hospital Essen, University Duisburg-Essen, Essen, Germany.
- MRI-STaR Magnetic Resonance Institute for Safety GmbH, Technology and Research GmbH, Gelsenkirchen, Germany.
| | - Oliver Kraff
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Kokereiallee 7, Building C84, 45141, Essen, Germany
| | - Gregor Schaefers
- MRI-STaR Magnetic Resonance Institute for Safety GmbH, Technology and Research GmbH, Gelsenkirchen, Germany
- MR:Comp GmbH, Testing Services for MR Safety and Compatibility, Gelsenkirchen, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Kokereiallee 7, Building C84, 45141, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, University Duisburg-Essen, Essen, Germany
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Wu JK, Yu MC, Chen SH, Liao SH, Wang YJ. Low cost multifunctional 3D printed image quality and dose verification phantom for an image-guided radiotherapy system. PLoS One 2022; 17:e0266604. [PMID: 35385553 PMCID: PMC8986000 DOI: 10.1371/journal.pone.0266604] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2021] [Accepted: 03/23/2022] [Indexed: 11/18/2022] Open
Abstract
Purpose Image-guided radiation therapy (IGRT) is used to precisely deliver radiation to a tumour to reduce the possible damage to the surrounding normal tissues. Clinics use various quality assurance (QA) equipment to ensure that the performance of the IGRT system meets the international standards set for the system. The objective of this study was to develop a low-cost and multipurpose module for evaluating image quality and dose. Methods A multipurpose phantom was designed to meet the clinical requirements of high accuracy, easy setup, and calibration. The outer shell of the phantom was fabricated using acrylic. Three dimensional (3D) printing technology was used to fabricate inner slabs with the characteristics of high spatial resolution, low-contrast detectability, a 3D grid, and liquid-filled uniformity. All materials were compatible with magnetic resonance (MR). Computed tomography (CT) simulator and linear accelerator (LINAC) modules were developed and validated. Results The uniformity slab filled with water is ideal for the assessment of Hounsfield units, whereas that filled with wax is suitable for consistency checks. The high-spatial-resolution slab enables measurements with a resolution up to 5 lp/cm. The low-contrast detectability slab contains rods of 5 different sizes that can be clearly visualised. These components meet the American College of Radiology (ACR) standards for QA of CT simulators and LINACs. Conclusions The multifunctional phantom module meets the ACR recommended QA guidelines and is suitable for both LINACs and CT-sim. Further measurements in an MR simulator and an MR linear accelerator (MR-LINAC) will be arranged in the future.
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Affiliation(s)
- Jian-Kuen Wu
- Division of Radiation Oncology, Departments of Oncology, National Taiwan University Hospital, Taipei, Taiwan
| | - Min-Chin Yu
- Department of Radiation Oncology, Taipei Medical University Hospital, Taipei, Taiwan
| | - Shih-Han Chen
- Department of Medical Imaging, National Taiwan University Cancer Center, Taipei, Taiwan
| | - Shu-Hsien Liao
- Institute of Electro-Optical Science and Technology, National Taiwan Normal University, Taipei, Taiwan
| | - Yu-Jen Wang
- Department of Radiation Oncology, Fu Jen Catholic University Hospital, New Taipei City, Taiwan
- School of Medicine, College of Medicine, Fu Jen Catholic University, New Taipei City, Taiwan
- * E-mail:
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Yamashiro A, Saito T, Miyati T. Development of a novel task-based functional magnetic resonance imaging phantom based on a bubble-compression approach. Med Phys 2022; 49:3717-3728. [PMID: 35287246 DOI: 10.1002/mp.15599] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Revised: 01/25/2022] [Accepted: 03/02/2022] [Indexed: 11/12/2022] Open
Abstract
PURPOSE Phantoms used in previous functional magnetic resonance imaging (fMRI) studies have drawbacks, such as a complicated circuit and equipment use, a single signal-change rate, and T2 * values that do not correspond to those of living human brains. We aimed to develop a phantom for use in task-based fMRI studies (gradient-echo echo-planar imaging; GRE-EPI) with bioequivalent T1 and T2 * values, using an innovative method to control the rate of signal change. METHODS A gel phantom with T1 and T2 * values equivalent to that of the living brain gray matter was fixed in a 150 mm diameter container, with five holes, each of which could hold a 30-mL syringe. The gel phantom contained microscopic air bubbles; this made it possible to control the percent signal change by injector-induced water pressure changes. Using this phantom, we investigated the percent signal change, derived an equation that can approximately reproduce an arbitrary percent signal change, compared different gel phantom samples, investigated the change in relaxation time and bubble size during signal change, and assessed the change in values in each sample over time. RESULTS The relaxation time of the gel phantom was similar to the literature values for gray matter. The percent signal change achieved was approximately 0-13.51% and was dependent on the water pressure change. The derived equation was y = 0.000008x3 - 0.000771x2 + 0.034222x - 0.026054, with y being the percent signal change and x being the pressure in kPa; the reproducibility was high. No significant difference was detected among samples of gray matter gel phantoms (P > 0.05). The change in the rate of signal change with the change in water pressure was due to the change in T2 * value with the change in bubble size. With pressure increasing from 0 to 151.7 kPa, the T2 * value increased from 52 ms to 85 ms. The newly developed gel phantom was stable for 60 days, but its bubble size changed after 21 days. CONCLUSION We developed a novel phantom for use in fMRI, which could reproduce minute signal changes similar to the blood-oxygen-level-dependent effect and with bioequivalent T1 and T2 * values, and used an innovative method to control the percent signal change by compressing the air contained in the phantom for validation of fMRI using GRE-EPI. This phantom reproduced the percent signal change due to changes in T2 * values, which is very similar to scanning a human body. This phantom is expected to be a powerful tool for advancing the study of task-based fMRI. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Akihiro Yamashiro
- Department of Radiology, Nagano Red Cross Hospital, 5-22-1 Wakasato, Nagano-City, Nagano, 380-8582, Japan.,Division of Health Sciences, Graduate School of Medical Sciences, Kanazawa University, 5-11-80 Kodatuno, Kanazawa-City, Ishikawa, 920-0942, Japan
| | - Takaaki Saito
- Department of Radiology, Iiyama Red Cross Hospital, 226-1 Iiyama, Iiyama-City, Nagano, 389-2295, Japan
| | - Tosiaki Miyati
- Division of Health Sciences, Graduate School of Medical Sciences, Kanazawa University, 5-11-80 Kodatuno, Kanazawa-City, Ishikawa, 920-0942, Japan
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5
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Development and evaluation of a numerical simulation approach to predict metal artifacts from passive implants in MRI. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2021; 35:485-497. [PMID: 34655346 PMCID: PMC9188622 DOI: 10.1007/s10334-021-00966-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 09/27/2021] [Accepted: 10/01/2021] [Indexed: 11/08/2022]
Abstract
Objective This study presents the development and evaluation of a numerical approach to simulate artifacts of metallic implants in an MR environment that can be applied to improve the testing procedure for MR image artifacts in medical implants according to ASTM F2119. Methods The numerical approach is validated by comparing simulations and measurements of two metallic test objects made of titanium and stainless steel at three different field strengths (1.5T, 3T and 7T). The difference in artifact size and shape between the simulated and measured artifacts were evaluated. A trend analysis of the artifact sizes in relation to the field strength was performed. Results The numerical simulation approach shows high similarity (between 75% and 84%) of simulated and measured artifact sizes of metallic implants. Simulated and measured artifact sizes in relation to the field strength resulted in a calculation guideline to determine and predict the artifact size at one field strength (e.g., 3T or 7T) based on a measurement that was obtained at another field strength only (e.g. 1.5T). Conclusion This work presents a novel tool to improve the MR image artifact testing procedure of passive medical implants. With the help of this tool detailed artifact investigations can be performed, which would otherwise only be possible with substantial measurement effort on different MRI systems and field strengths.
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Jenista ER, Jensen CJ, Wendell D, Spatz D, Darty S, Kim HW, Parker M, Klem I, Chen EL, Kim RJ, Rehwald WG. Double spectral attenuated inversion recovery (DSPAIR)-an efficient fat suppression technique for late gadolinium enhancement at 3 tesla. NMR IN BIOMEDICINE 2021; 34:e4580. [PMID: 34251717 DOI: 10.1002/nbm.4580] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Revised: 06/11/2021] [Accepted: 06/12/2021] [Indexed: 06/13/2023]
Abstract
Despite clinical use of late gadolinium enhancement (LGE) for two decades, an efficient, robust fat suppression (FS) technique still does not exist for this CMR mainstay. In ischemic and non-ischemic heart disease, differentiating fibrotic tissue from infiltrating and adjacent fat is crucial. Multiple groups have independently developed an FS technique for LGE, double spectral attenuated inversion recovery (DSPAIR), but no comprehensive evaluation was performed. This study aims to fill this gap. DSPAIR uses two SPAIR pulses and one non-selective IR pulse to enable FS LGE, including compatibility with phase sensitive inversion recovery (PSIR). We implemented a magnitude (MAGN) and a PSIR variant and compared them with LGE without FS (CONTROL) and with spectral presaturation with inversion recovery (SPIR) in simulations, phantoms, and patients. Fat magnetization by SPIR, MAGN DSPAIR, and PSIR DSPAIR was simulated as a function of pulse B1 , readout (RO) pulse number, and fat TI . A phantom with fat, fibrosis, and myocardium compartments was imaged using all FS methods and modifying pulse B1 , RO pulse number, and heart rate. Signal was measured in SNR units. Fat, myocardium, and fibrosis SNR and fibrosis-to-fat CNR were obtained. Patient images were acquired with all FS techniques. Fat, myocardium, and fibrosis SNR, fibrosis-to-fat CNR, and image and FS quality were assessed. In the phantom, both DSPAIR variants provided superior FS compared with SPIR, independent of heart rate and RO pulse number. MAGN DSPAIR reduced fat signal by 99% compared with CONTROL, PSIR DSPAIR by 116%, and SPIR by 67% (25 RO pulses). In patients, both DSPAIR variants substantially reduced fat signal (MAGN DSPAIR by 87.1% ± 10.0%, PSIR DSPAIR by 130.5% ± 36.3%), but SPIR did not (35.8% ± 25.5%). FS quality was good to excellent for MAGN and PSIR DSPAIR, and moderate to poor for SPIR. DSPAIR provided highly effective FS across a wide range of parameters. PSIR DSPAIR performed best.
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Affiliation(s)
- Elizabeth R Jenista
- Duke Cardiovascular MR Center, Duke Heart Center, Duke University Medical Center, Durham, North Carolina, USA
| | - Christoph J Jensen
- Duke Cardiovascular MR Center, Duke Heart Center, Duke University Medical Center, Durham, North Carolina, USA
| | - David Wendell
- Duke Cardiovascular MR Center, Duke Heart Center, Duke University Medical Center, Durham, North Carolina, USA
| | - Deneen Spatz
- Duke Cardiovascular MR Center, Duke Heart Center, Duke University Medical Center, Durham, North Carolina, USA
- Department of Internal Medicine, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Stephen Darty
- Duke Cardiovascular MR Center, Duke Heart Center, Duke University Medical Center, Durham, North Carolina, USA
| | - Han W Kim
- Duke Cardiovascular MR Center, Duke Heart Center, Duke University Medical Center, Durham, North Carolina, USA
| | - Michele Parker
- Duke Cardiovascular MR Center, Duke Heart Center, Duke University Medical Center, Durham, North Carolina, USA
| | - Igor Klem
- Duke Cardiovascular MR Center, Duke Heart Center, Duke University Medical Center, Durham, North Carolina, USA
| | - Enn-Ling Chen
- Duke Cardiovascular MR Center, Duke Heart Center, Duke University Medical Center, Durham, North Carolina, USA
| | - Raymond J Kim
- Duke Cardiovascular MR Center, Duke Heart Center, Duke University Medical Center, Durham, North Carolina, USA
| | - Wolfgang G Rehwald
- Duke Cardiovascular MR Center, Duke Heart Center, Duke University Medical Center, Durham, North Carolina, USA
- Siemens Medical Solutions North America, Malvern, Pennsylvania, USA
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Michael Gach H, Curcuru AN, Kim T, Yang D. Technical Note: Effects of rotating gantry on magnetic field and eddy currents in 0.35 T MRI-guided radiotherapy (MR-IGRT) system. Med Phys 2021; 48:7228-7235. [PMID: 34520081 DOI: 10.1002/mp.15226] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Revised: 07/19/2021] [Accepted: 09/04/2021] [Indexed: 01/03/2023] Open
Abstract
PURPOSE The purpose of this study was to identify the cause of severe image artifacts that occurred during gantry rotation in a 0.35 T MRI-Linac by comparing measurements of eddy currents, center frequency, and field inhomogeneities made with the gantry in motion and stationary. METHODS Gradient and B0 eddy currents were calculated from the free induction decays (FIDs) resulting from selective excitation at a temporal resolution of 200 ms/measurement. B0 eddy currents were also calculated from FIDs acquired with nonselective excitation at a temporal resolution of 100 ms/measurement. Center frequencies and B0 inhomogeneities were measured by acquiring FIDs with a repetition time (TR) of 290 ms. Cartesian and radial 2D true fast imaging with steady-state precession (TrueFISP) pulse sequences used in real-time MRI-guided radiation therapy (MR-IGRT) were acquired. To assess artifact severity, the normalized root mean square error (nRMSE) was calculated between a reference MRI (static gantry) and MRIs acquired during gantry rotation for each serial acquisition. Image artifacts were qualitatively graded as nominal, minor, or severe. Measurements were conducted while the gantry was rotated through its entire range for both clockwise and counterclockwise. Measurements during gantry rotation were compared to measurements with a stationary gantry (every 30°). RESULTS Severe image artifacts were observed 22-35% of the time while the gantry was rotating. Short time constant eddy currents were not affected by gantry rotation. The peak to peak center frequency and FWHM rose by factors of 13.2-14.5 and 1.1-1.6, respectively, for the rotating versus stationary gantry. The magnitude of the center frequency offset and field inhomogeneities depended on the direction of the gantry rotation. CONCLUSIONS Image artifacts during gantry rotation were primarily caused by center frequency variations and field inhomogeneities. Therefore, dynamic B0 compensation techniques should be able to reduce artifacts during gantry rotation.
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Affiliation(s)
- H Michael Gach
- Departments of Radiation Oncology, Radiology, and Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Austen N Curcuru
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Taeho Kim
- Department of Radiation Oncology, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Deshan Yang
- Departments of Radiation Oncology and Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
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Wexler AD, Woisetschläger J, Reiter U, Reiter G, Fuchsjäger M, Fuchs EC, Brecker L. Nuclear Magnetic Relaxation Mapping of Spin Relaxation in Electrically Stressed Glycerol. ACS OMEGA 2020; 5:22057-22070. [PMID: 32923764 PMCID: PMC7482076 DOI: 10.1021/acsomega.0c02059] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Accepted: 08/06/2020] [Indexed: 06/11/2023]
Abstract
This work discusses nuclear magnetic relaxation effects in glycerol subject to a strong electric field. The methods used are 1.5 T magnetic resonance imaging (MRI), referenced by 9.4 T nuclear magnetic resonance (NMR). While MRI allows a glycerol probe to be sampled with a high voltage (HV) of 16 kV applied to the probe, NMR provides precise molecular data from the sample, but the sample cannot be tested under HV. Using MRI, the recording of magnetic relaxation times was possible while HV was applied to the glycerol. NMR spectroscopy was used to confirm that MRI provides a reasonably accurate estimation of temperature. The applied HV was observed to have a negligible effect on the spin-lattice relaxation time T 1, which represents the energy release to the thermal bath or system enthalpy. In contrast to that, the spin-spin relaxation time T 2, which does represent the local entropy of the system, shows a lower response to temperature while the liquid is electrically stressed. These observations point toward a proton population in electrically stressed glycerol that is more mobile than that found in the bulk, an observation that is in agreement with previously published results for water.
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Affiliation(s)
- Adam D. Wexler
- Wetsus
European Centre of Excellence for Sustainable Water Technology, Leeuwarden 8911MA, The Netherlands
| | - Jakob Woisetschläger
- Institute
for Thermal Turbomachinery and Machine Dynamics, Working Group Metrology
− Laser Optical Metrology, Graz University
of Technology, Inffeldgasse 25A, Graz 8010, Austria
| | - Ursula Reiter
- Division
of General Radiology, Department of Radiology, Medical University of Graz, Graz 8036, Austria
| | - Gert Reiter
- Division
of General Radiology, Department of Radiology, Medical University of Graz, Graz 8036, Austria
- Research
& Development, Siemens Healthcare Diagnostics
GmbH, Graz 8054, Austria
| | - Michael Fuchsjäger
- Division
of General Radiology, Department of Radiology, Medical University of Graz, Graz 8036, Austria
| | - Elmar C. Fuchs
- Wetsus
European Centre of Excellence for Sustainable Water Technology, Leeuwarden 8911MA, The Netherlands
| | - Lothar Brecker
- Department
of Organic Chemistry, University of Vienna, 1090 Vienna, Austria
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Gach HM, Curcuru AN, Mutic S, Kim T. B 0 field homogeneity recommendations, specifications, and measurement units for MRI in radiation therapy. Med Phys 2020; 47:4101-4114. [PMID: 32472707 DOI: 10.1002/mp.14306] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Revised: 05/11/2020] [Accepted: 05/24/2020] [Indexed: 12/20/2022] Open
Abstract
PURPOSE The purpose is: (a) Relate magnetic resonance imaging (MRI) quality recommendations for radiation therapy (RT) to B0 field homogeneity; (b) Evaluate manufacturer specifications of B0 homogeneity for 34 commercial whole-body MRI systems based on the MRI quality recommendations and RT application; (c) Measure field homogeneity in five commercial MRI systems and one commercial MRI-Linac used in RT and compare the results with their B0 homogeneity specifications. METHODS Magnetic resonance imaging quality recommendations for spatial integrity, image blurring, fat saturation, and null banding in RT were developed based on the literature. Guaranteed (maximum) and typical B0 field homogeneity specifications for various diameter spherical volumes (DSVs) were provided by GE, Philips, Siemens, and Canon. For each system, the DSV that conforms to each MRI quality recommendation and anatomical RT application was estimated based on the manufacturer specifications. B0 field homogeneity was measured on six MRI systems including Philips (1.5 T), Siemens (1.5 and 3 T), and ViewRay MRI (0.35 T) systems using 24 and 35 cm DSV spherical phantoms. Two measurement techniques were used: (a) MRI using phase contrast field mapping to measure peak-to-peak (pk-pk), volume root mean square (VRMS), and standard deviation (SD); and (b) Magnetic resonance (MR) spectroscopy by acquiring a volumetric free induction decay (FID) to measure full width at half maximum (FWHM). The measurements were used to assess: (a) conformance with the manufacturer specifications; and (b) the relationship between the various field homogeneity measurement units. Measurements were made with and without gradient shimming (gradshim) or second-order active shimming. Multiple comparisons, analysis of variance (ANOVA), and Pearson correlations were performed to assess the dependence of pk-pk, VRMS, SD, and FWHM measurements of field homogeneity on shim volume, level of shim, and MRI system. RESULTS For a 40 cm DSV, the B0 homogeneity specifications ranged from 0.35 to 5 ppm (median = 0.75 ppm) VRMS for 1.5 T systems and 0.2 to 1.4 ppm (median = 0.5 ppm) VRMS for 3 T systems. The usable DSVs ranged from 16 to 49 cm (median = 35 cm) based on the image quality recommendations and the manufacturer specifications. There was general compliance between the six measured field homogeneities and manufacturer specifications although signal dephasing was observed in two systems at < 35 cm DSV. The relationships between pk-pk, VRMS, SD, and FWHM varied based on MRI system, shim volume, and quality of shim. However, VRMS and SD measurements were highly correlated. CONCLUSIONS The delineation of the diseased lesion from organs at risk is the main priority for RT. Therefore, field homogeneity performance for RT must minimize image blurring and image artifacts (null bands and signal dephasing) while optimizing spatial integrity and fat saturation. Based on the specifications and recommendations for field homogeneity, some MRI systems are not well suited to meet the strict demands of RT particularly for the large imaging volumes used in body MRI. VRMS and SD measurements of B0 field homogeneity tend to be more stable and sensitive to field inhomogeneities in RT applications than pk-pk and FWHM.
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Affiliation(s)
- H Michael Gach
- Departments of Radiation Oncology, Radiology, and Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, 63110, USA
| | - Austen N Curcuru
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, 63110, USA
| | - Sasa Mutic
- Department of Radiation Oncology, Washington University in St. Louis, St. Louis, MO, 63110, USA
| | - Taeho Kim
- Department of Radiation Oncology, Washington University in St. Louis, St. Louis, MO, 63110, USA
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10
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Sindi R, Wong YH, Yeong CH, Sun Z. Development of patient-specific 3D-printed breast phantom using silicone and peanut oils for magnetic resonance imaging. Quant Imaging Med Surg 2020; 10:1237-1248. [PMID: 32550133 DOI: 10.21037/qims-20-251] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Background Despite increasing reports of 3D printing in medical applications, the use of 3D printing in breast imaging is limited, thus, personalized 3D-printed breast model could be a novel approach to overcome current limitations in utilizing breast magnetic resonance imaging (MRI) for quantitative assessment of breast density. The aim of this study is to develop a patient-specific 3D-printed breast phantom and to identify the most appropriate materials for simulating the MR imaging characteristics of fibroglandular and adipose tissues. Methods A patient-specific 3D-printed breast model was generated using 3D-printing techniques for the construction of the hollow skin and fibroglandular region shells. Then, the T1 relaxation times of the five selected materials (agarose gel, silicone rubber with/without fish oil, silicone oil, and peanut oil) were measured on a 3T MRI system to determine the appropriate ones to represent the MR imaging characteristics of fibroglandular and adipose tissues. Results were then compared to the reference values of T1 relaxation times of the corresponding tissues: 1,324.42±167.63 and 449.27±26.09 ms, respectively. Finally, the materials that matched the T1 relaxation times of the respective tissues were used to fill the 3D-printed hollow breast shells. Results The silicone and peanut oils were found to closely resemble the T1 relaxation times and imaging characteristics of these two tissues, which are 1,515.8±105.5 and 405.4±15.1 ms, respectively. The agarose gel with different concentrations, ranging from 0.5 to 2.5 wt%, was found to have the longest T1 relaxation times. Conclusions A patient-specific 3D-printed breast phantom was successfully designed and constructed using silicone and peanut oils to simulate the MR imaging characteristics of fibroglandular and adipose tissues. The phantom can be used to investigate different MR breast imaging protocols for the quantitative assessment of breast density.
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Affiliation(s)
- Rooa Sindi
- Discipline of Medical Radiation Sciences, School of Molecular and Life Sciences, Curtin University, Perth, WA, Australia.,Radio-diagnostic and Medical Imaging Department, Medical Physics Section, King Fahd Armed Forces Hospital, Jeddah, Kingdom of Saudi Arabia
| | - Yin How Wong
- School of Medicine, Faculty of Health and Medical Sciences, Taylor's University, Subang Jaya, Selangor, Malaysia
| | - Chai Hong Yeong
- School of Medicine, Faculty of Health and Medical Sciences, Taylor's University, Subang Jaya, Selangor, Malaysia
| | - Zhonghua Sun
- Discipline of Medical Radiation Sciences, School of Molecular and Life Sciences, Curtin University, Perth, WA, Australia
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