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Dharmadhikari S, James JR, Nyenhuis J, Bansal N. Evaluation of radiofrequency safety by high temperature resolution MR thermometry using a paramagnetic lanthanide complex. Magn Reson Med 2015; 75:2121-9. [DOI: 10.1002/mrm.25792] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Revised: 05/05/2015] [Accepted: 05/06/2015] [Indexed: 11/09/2022]
Affiliation(s)
- Shalmali Dharmadhikari
- School of Health Sciences, Purdue University; West Lafayette Indiana USA
- Department of Radiology and Imaging Sciences; Indiana University School of Medicine; Indianapolis Indiana USA
| | - Judy R. James
- Department of Radiology; Mayo Clinic, Scottsdale; Arizona USA
| | - John Nyenhuis
- Department of Electrical and Computer Engineering; Purdue University; West Lafayette Indiana USA
| | - Navin Bansal
- Department of Radiology and Imaging Sciences; Indiana University School of Medicine; Indianapolis Indiana USA
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In E, Naguib H, Haider M. Mechanical stability analysis of carrageenan-based polymer gel for magnetic resonance imaging liver phantom with lesion particles. J Med Imaging (Bellingham) 2014; 1:035502. [PMID: 26158073 PMCID: PMC4478721 DOI: 10.1117/1.jmi.1.3.035502] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2014] [Accepted: 11/24/2014] [Indexed: 11/14/2022] Open
Abstract
Medical imaging is an effective technique used to detect and prevent disease in cancer research. To optimize medical imaging, a calibration medium or phantom with tissue-mimicking properties is required. Although the feasibility of various polymer gel materials has previously been studied, the stability of the gels' properties has not been investigated. In this study, we fabricated carrageenan-based polymer gel to examine the stability of its properties such as density, conductivity, permittivity, elastic modulus, and [Formula: see text] and [Formula: see text] relaxation times over six weeks. We fabricated eight samples with different carrageenan and agar concentrations and found that the density, elastic modulus, and compressive strength fluctuated with no specific pattern. The elastic modulus in sample 4 with 3 wt. % carrageenan and 1.5 wt. % agar fluctuated from 0.51 to 0.64 MPa in five weeks. The [Formula: see text] and [Formula: see text] relaxation times also varied by 23% to 29%. We believe that the fluctuation of these properties is related to the change in water content of the sample due to cycles of water expulsion and absorption in their containers. The fluctuation of the properties should be minimized to achieve accurate calibration over the shelf life of the phantom and to serve as the standard for quality assurance. Furthermore, a full liver phantom with spherical lesion particles was fabricated to demonstrate the potential for phantom production.
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Affiliation(s)
- Eunji In
- University of Toronto, Smart and Adaptive Polymer Laboratory, Department of Mechanical & Industrial Engineering, 5 King’s College Road, Toronto M5S 3G8, Canada
| | - Hani Naguib
- University of Toronto, Smart and Adaptive Polymer Laboratory, Department of Mechanical & Industrial Engineering, 5 King’s College Road, Toronto M5S 3G8, Canada
- University of Toronto, Department of Materials Science and Engineering, Wallberg Building, 184 College Street, Toronto M5S 3E4, Canada
- University of Toronto, The Institute of Biomaterials and Biomedical Engineering, 164 College Street, Toronto M5S 3G9, Canada
| | - Masoom Haider
- University of Toronto, Department of Radiology, 263 McCaul Street, Toronto M5T 1W7, Canada
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Carluccio G, Erricolo D, Oh S, Collins CM. An approach to rapid calculation of temperature change in tissue using spatial filters to approximate effects of thermal conduction. IEEE Trans Biomed Eng 2013; 60:1735-41. [PMID: 23358947 DOI: 10.1109/tbme.2013.2241764] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
We present an approach to performing rapid calculations of temperature within tissue by interleaving, at regular time intervals, 1) an analytical solution to the Pennes (or other desired) bioheat equation excluding the term for thermal conduction and 2) application of a spatial filter to approximate the effects of thermal conduction. Here, the basic approach is presented with attention to filter design. The method is applied to a few different cases relevant to magnetic resonance imaging, and results are compared to those from a full finite-difference (FD) implementation of the Pennes bioheat equation. It is seen that results of the proposed method are in reasonable agreement with those of the FD approach, with about 15% difference in the calculated maximum temperature increase, but are calculated in a fraction of the time, requiring less than 2% of the calculation time for the FD approach in the cases evaluated.
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Oh S, Webb AG, Neuberger T, Park B, Collins CM. Experimental and numerical assessment of MRI-induced temperature change and SAR distributions in phantoms and in vivo. Magn Reson Med 2010; 63:218-23. [PMID: 19785018 DOI: 10.1002/mrm.22174] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
It is important to accurately characterize the heating of tissues due to the radiofrequency energy applied during MRI. This has led to an increase in the use of numerical methods to predict specific energy absorption rate distributions for safety assurance in MRI. To ensure these methods are accurate for actual MRI coils, however, it is necessary to compare to experimental results. Here, we report results of some recent efforts to experimentally map temperature change and specific energy absorption rate in a phantom and in vivo where the only source of heat is the radiofrequency fields produced by the imaging coil. Results in a phantom match numerical simulation well, and preliminary results in vivo show measurable temperature increase. With further development, similar methods may be useful for verifying numerical methods for predicting specific energy absorption rate distributions and in some cases for directly measuring temperature changes and specific energy absorption rate induced by the radiofrequency fields in MRI experiments.
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Affiliation(s)
- Sukhoon Oh
- Department of Radiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA
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Yoshida A, Kato H, Kuroda M, Hanamoto K, Yoshimura K, Shibuya K, Kawasaki S, Tsunoda M, Kanazawa S, Hiraki Y. Development of a phantom compatible for MRI and hyperthermia using carrageenan gel—relationship betweenT1andT2values and NaCl concentration. Int J Hyperthermia 2009; 20:803-14. [PMID: 15764343 DOI: 10.1080/0265673042000199268] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
The authors developed a phantom, designated as the CAGN phantom, compatible for MRI and hyperthermia that is useful in the fundamental studies of non-invasive MR thermometry. The ingredients of this phantom are carrageenan, GdCl3 as a T1 modifier, agarose as a T2 modifier, NaCl as a conductivity modifier, NaN3 as an antiseptic and distilled water. Another phantom that was developed, the CAG phantom, has relaxation times that are adjustable to those of any human tissue. To use this phantom for electromagnetic heating, NaCl was added to change the conductivity of the phantom and clarified the relationship between the conductivity and NaCl concentration. This study examined the relationship between relaxation times and NaCl concentration of the CAGN phantom. The results showed that both T1 and T2 values were affected by NaCl and the experimental results led to the empirical formulae expressing the relationship between the relaxation rates (1/T1, 1/T2) and the concentrations of GdCl3, agarose and NaCl. The appropriate concentrations of T1 and T2 modifiers were calculated from these empirical formulae when making a specified phantom that has the required relaxation times and NaCl concentration.
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Affiliation(s)
- A Yoshida
- Department of Radiology, Okayama University Medical School, 2-5-1 Shikata-cho, Okayama 700-8558, Japan.
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Liu HL, Chen HM, Wu YC, Lim SN, Huang CM, Hsu YY, Wai YY, Wu T. False-positive analysis of functional MRI during simulated deep brain stimulation: a phantom study. J Magn Reson Imaging 2008; 27:1439-42. [PMID: 18504733 DOI: 10.1002/jmri.21222] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
PURPOSE To investigate the false-positive activations/deactivations in functional MRI (fMRI) of deep brain stimulation (DBS) using a phantom. MATERIALS AND METHODS fMRI experiments were performed on a 1.5T scanner using a single-shot gradient-echo echo-planar imaging (GE-EPI) sequence (TR/TE/FA = 6000 msec/60 msec/90 degrees ) on an agar-gel phantom inserted with DBS electrodes. During the experimental blocks, two-second stimuli were delivered during the interscan waiting time (ISWT), which was adjusted by changing the number of slices acquired within the TR (3500 msec with 30 slices and 5160 msec with 10 slices). Data were analyzed using SPM2 software, and the false-positive voxels were detected with five different P-value thresholds. RESULTS The number of false-positive voxels in experimental conditions had no significant differences from those in control conditions with either long or short ISWT, which increased with the P-value threshold from zero at P < 0.0001 to approximately 40 at P < 0.05. The pattern of increasing number of false-positive reactions along with P-value was similar between all conditions. CONCLUSION False-positive findings from fMRI with similar experimental design can be well controlled with a statistical threshold of P < 0.001 or tighter. The short ISWT of 3500 msec did not increase false-positive reactions compared to the long ISWT of 5160 msec.
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Affiliation(s)
- Ho-Ling Liu
- Department of Medical Imaging and Radiological Sciences, Chang Gung University, Taoyuan, Taiwan
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OHNO S, KATO H, HARIMOTO T, IKEMOTO Y, YOSHITOMI K, KADOHISA S, KURODA M, KANAZAWA S. Production of a Human-Tissue-Equivalent MRI Phantom: Optimization of Material Heating. Magn Reson Med Sci 2008; 7:131-40. [DOI: 10.2463/mrms.7.131] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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Shapiro EM, Borthakur A, Shapiro MJ, Reddy R, Leigh JS. Fast MRI of RF heating via phase difference mapping. Magn Reson Med 2002; 47:492-8. [PMID: 11870836 PMCID: PMC2855824 DOI: 10.1002/mrm.10067] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A method is presented for the rapid acquisition of temperature maps derived from phase difference maps. The temperature-dependent chemical shift coefficients (TDCSCs) of various concentrations of aqueous cobalt and dysprosium-based compounds were measured. The largest TDCSC calculated was for 100 mM DyEDTA, which had a TDCSC of -0.09 PPM/K; 160 mM CoCl2 had a TDCSC of -0.04 PPM/K. These temperature-dependent chemical shifts (TDCSs) result in phase changes in the MR signal with changing temperature. Agarose phantoms were constructed with each paramagnetic metal. A fast gradient-echo (FGRE) MR image was acquired to serve as the baseline image. A "test" MRI procedure was then performed on the phantom. Immediately afterwards, a second FGRE MR image was acquired, serving as the probing image. Proper image processing as a phase difference map between the probing image and the baseline image resulted in an image which quantitatively described the temperature increase of the phantom in response to a particular "test" imaging experiment. Applications of this technique in assessing the safety of pulse sequences and MR coils are discussed.
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Affiliation(s)
- Erik M Shapiro
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
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Cassidy PJ, Grieve S, Clarke K, Edwards DJ. Electromagnetic characterisation of MR RF coils using the transmission-line modelling method. MAGMA (NEW YORK, N.Y.) 2002; 14:20-9. [PMID: 11796249 DOI: 10.1007/bf02668183] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The Transmission-Line Modelling (TLM) method is applied to the electromagnetic characterisation of RF coils and samples for magnetic resonance imaging MRI. Theoretical verification was performed using a simple surface coil. Experimental verification was performed using Alderman-Grant and birdcage coils constructed for use on a 7 T micro-imaging system. The modelling method enabled electromagnetic characteristics of frequency response, electromagnetic field generation, energy stored and power loss to be determined. From these parameters, coil resonant modes, B1 field profiles, voltages, currents, quality factor (Q), pi/2 pulse length, and the equivalent lumped-element circuit components of resistance, inductance and capacitance were calculated. Equations are presented that enable a comprehensive electromagnetic characterisation of the RF coil and sample to be achieved based on the results of the TLM simulations. The use of the TLM method is extended to include the design of safe arbitrary multi-nuclear pulse sequences such that the specific absorption rate (SAR) of tissue, and RF coil component safety limits are not exceeded.
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Affiliation(s)
- P J Cassidy
- British Heart Foundation Molecular Cardiology Group, Department of Biochemistry, University of Oxford, South Parks Road, OX1 3QU, Oxford, UK.
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Abstract
MR temperature measurements are important for applications such as the evaluation of thermal therapies and radiofrequency (RF) coil heating effects. In this work the spherical mean value (SMV) method has been applied to significantly improve the precision of MR temperature mapping in a homogeneous gel phantom. Temperature-increase maps of the phantom were obtained with three-dimensional (3D) MR phase difference mapping after heating with the RF coil. The temperature-increase distribution in most regions in the phantom is a harmonic function with the mean value property. Based on this property, the precision of temperature-increase maps was improved up to sixfold with the SMV method. Comparison of this method with conventional smoothing, further precision improvement, and the in vivo application of the SMV method are discussed.
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Affiliation(s)
- L Li
- Department of Radiology, Metabolic Magnetic Resonance Research and Computing Center, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
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