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Objective: The purpose of this work was to develop an electronically tunable resonator operating at 750 MHz for continuous-wave electron paramagnetic resonance (CW-EPR) imaging of a mouse tumor-bearing leg. Methods: The resonator had a multi-coil parallel-gap structure with a sample space of 16 mm in diameter and 20 mm in length. Microstrip line couplers were used in conjunction with varactor diodes to enable resonance frequency adjustment and to reduce the nonlinear effects of the varactor diodes. The resonator was modeled by the finite-element method and a microwave circuit simulation was performed to clarify its radiofrequency characteristics. Results: A tunable resonator was evaluated in terms of its resonance frequency, tunable frequency band, and conversion efficiency of the RF magnetic field. The developed resonator provided a tunable frequency band of 4 MHz at a central frequency of 747 MHz and a conversion efficiency of 34 mu T/W-1/2. To demonstrate the application of this tunable resonator to EPR imaging, three-dimensional EPR images of a sample solution and a mouse tumor-bearing leg were obtained. Conclusion: The developed tunable resonator satisfied our initial requirements for in vivo EPR imaging and may be able to be further improved using the present finite-element and circuit models if any problems arise during future practical applications. Significance: This work may help to promote EPR imaging of tumor-bearing mice in cancer-related studies.

A 750-MHz electronically tunable resonator was investigated in terms of the sensitivity of electron paramagnetic resonance (EPR) signal detection. The conversion efficiency of the radio-frequency magnetic field was calculated for resonators with 50- and 100-Omega coaxial coupling lines using three-dimensional (3D) microwave field and microwave circuit simulators. Based on the simulation results, two tunable resonators were physically constructed and compared in terms of EPR signal sensitivity using a nitroxyl radical solution. While the resonator with 100-Omega coaxial lines provided 14% greater signal intensity, its signal-to-noise ratio was lower than that of the resonator with 50-Omega lines. To demonstrate the capability of the constructed tunable resonator for EPR imaging experiments, a solution of nitroxyl radical and the leg of a tumor-bearing mouse were visualized.

Objective: The purpose of this work was to develop an electronically tunable resonator operating at 750 MHz for continuous-wave electron paramagnetic resonance (CW-EPR) imaging of a mouse tumor-bearing leg. Methods: The resonator had a multi-coil parallel-gap structure with a sample space of 16 mm in diameter and 20 mm in length. Microstrip line couplers were used in conjunction with varactor diodes to enable resonance frequency adjustment and to reduce the nonlinear effects of the varactor diodes. The resonator was modeled by the finite-element method and a microwave circuit simulation was performed to clarify its radiofrequency characteristics. Results: A tunable resonator was evaluated in terms of its resonance frequency, tunable frequency band, and conversion efficiency of the RF magnetic field. The developed resonator provided a tunable frequency band of 4 MHz at a central frequency of 747 MHz and a conversion efficiency of 34 mu T/W-1/2. To demonstrate the application of this tunable resonator to EPR imaging, three-dimensional EPR images of a sample solution and a mouse tumor-bearing leg were obtained. Conclusion: The developed tunable resonator satisfied our initial requirements for in vivo EPR imaging and may be able to be further improved using the present finite-element and circuit models if any problems arise during future practical applications. Significance: This work may help to promote EPR imaging of tumor-bearing mice in cancer-related studies.

A 750-MHz electronically tunable resonator was investigated in terms of the sensitivity of electron paramagnetic resonance (EPR) signal detection. The conversion efficiency of the radio-frequency magnetic field was calculated for resonators with 50- and 100-Omega coaxial coupling lines using three-dimensional (3D) microwave field and microwave circuit simulators. Based on the simulation results, two tunable resonators were physically constructed and compared in terms of EPR signal sensitivity using a nitroxyl radical solution. While the resonator with 100-Omega coaxial lines provided 14% greater signal intensity, its signal-to-noise ratio was lower than that of the resonator with 50-Omega lines. To demonstrate the capability of the constructed tunable resonator for EPR imaging experiments, a solution of nitroxyl radical and the leg of a tumor-bearing mouse were visualized.

Objective: The purpose of this work was to develop an electronically tunable resonator operating at 750 MHz for continuous-wave electron paramagnetic resonance (CW-EPR) imaging of a mouse tumor-bearing leg. Methods: The resonator had a multi-coil parallel-gap structure with a sample space of 16 mm in diameter and 20 mm in length. Microstrip line couplers were used in conjunction with varactor diodes to enable resonance frequency adjustment and to reduce the nonlinear effects of the varactor diodes. The resonator was modeled by the finite-element method and a microwave circuit simulation was performed to clarify its radiofrequency characteristics. Results: A tunable resonator was evaluated in terms of its resonance frequency, tunable frequency band, and conversion efficiency of the RF magnetic field. The developed resonator provided a tunable frequency band of 4 MHz at a central frequency of 747 MHz and a conversion efficiency of 34 mu T/W-1/2. To demonstrate the application of this tunable resonator to EPR imaging, three-dimensional EPR images of a sample solution and a mouse tumor-bearing leg were obtained. Conclusion: The developed tunable resonator satisfied our initial requirements for in vivo EPR imaging and may be able to be further improved using the present finite-element and circuit models if any problems arise during future practical applications. Significance: This work may help to promote EPR imaging of tumor-bearing mice in cancer-related studies.

A 750-MHz electronically tunable resonator was investigated in terms of the sensitivity of electron paramagnetic resonance (EPR) signal detection. The conversion efficiency of the radio-frequency magnetic field was calculated for resonators with 50- and 100-Omega coaxial coupling lines using three-dimensional (3D) microwave field and microwave circuit simulators. Based on the simulation results, two tunable resonators were physically constructed and compared in terms of EPR signal sensitivity using a nitroxyl radical solution. While the resonator with 100-Omega coaxial lines provided 14% greater signal intensity, its signal-to-noise ratio was lower than that of the resonator with 50-Omega lines. To demonstrate the capability of the constructed tunable resonator for EPR imaging experiments, a solution of nitroxyl radical and the leg of a tumor-bearing mouse were visualized.

Objective: The purpose of this work was to develop an electronically tunable resonator operating at 750 MHz for continuous-wave electron paramagnetic resonance (CW-EPR) imaging of a mouse tumor-bearing leg. Methods: The resonator had a multi-coil parallel-gap structure with a sample space of 16 mm in diameter and 20 mm in length. Microstrip line couplers were used in conjunction with varactor diodes to enable resonance frequency adjustment and to reduce the nonlinear effects of the varactor diodes. The resonator was modeled by the finite-element method and a microwave circuit simulation was performed to clarify its radiofrequency characteristics. Results: A tunable resonator was evaluated in terms of its resonance frequency, tunable frequency band, and conversion efficiency of the RF magnetic field. The developed resonator provided a tunable frequency band of 4 MHz at a central frequency of 747 MHz and a conversion efficiency of 34 mu T/W-1/2. To demonstrate the application of this tunable resonator to EPR imaging, three-dimensional EPR images of a sample solution and a mouse tumor-bearing leg were obtained. Conclusion: The developed tunable resonator satisfied our initial requirements for in vivo EPR imaging and may be able to be further improved using the present finite-element and circuit models if any problems arise during future practical applications. Significance: This work may help to promote EPR imaging of tumor-bearing mice in cancer-related studies.

A 750-MHz electronically tunable resonator was investigated in terms of the sensitivity of electron paramagnetic resonance (EPR) signal detection. The conversion efficiency of the radio-frequency magnetic field was calculated for resonators with 50- and 100-Omega coaxial coupling lines using three-dimensional (3D) microwave field and microwave circuit simulators. Based on the simulation results, two tunable resonators were physically constructed and compared in terms of EPR signal sensitivity using a nitroxyl radical solution. While the resonator with 100-Omega coaxial lines provided 14% greater signal intensity, its signal-to-noise ratio was lower than that of the resonator with 50-Omega lines. To demonstrate the capability of the constructed tunable resonator for EPR imaging experiments, a solution of nitroxyl radical and the leg of a tumor-bearing mouse were visualized.

Objectives The aim of this study was to demonstrate the feasibility of in vivo three-dimensional (3D) relaxation time T-2* mapping of a dicarboxy-PROXYL radical using continuous-wave electron paramagnetic resonance (CW-EPR) imaging. Materials and methods Isotopically substituted dicarboxy-PROXYL radicals, 3,4-dicarboxy-2,2,5,5-tetra(H-2(3)) methylpyrrolidin-( 3,4-H-2(2))-(1-N-15)-1-oxyl (H-2, N-15-DCP) and 3,4-dicarboxy-2,2,5,5-tetra(H-2(3)) methylpyrrolidin-(3,4-H-2(2))1- oxyl (H-2-DCP), were used in the study. A clonogenic cell survival assay was performed with the H-2-DCP radical using squamous cell carcinoma (SCC VII) cells. The time course of EPR signal intensities of intravenously injected H-2, N-15-DCP and H-2-DCP radicals were determined in tumor-bearing hind legs of mice (C3H/HeJ, male, n = 5). CW-EPR-based single-point imaging (SPI) was performed for 3D T-2* mapping. Results H-2-DCP radical did not exhibit cytotoxicity at concentrations below 10 mM. The in vivo half-life of H-2, N-15-DCP in tumor tissues was 24.7 +/- 2.9 min (mean +/- standard deviation [SD], n = 5). The in vivo time course of the EPR signal intensity of the H-2, N-15-DCP radical showed a plateau of 10.2 +/- 1.2 min (mean +/- SD) where the EPR signal intensity remained at more than 90% of the maximum intensity. During the plateau, in vivo 3D T-2* maps with H-2, N-15-DCP were obtained from tumor-bearing hind legs, with a total acquisition time of 7.5 min. Conclusion EPR signals of H-2, N-15-DCP persisted long enough after bolus intravenous injection to conduct in vivo 3D T-2* mapping with CW-EPR-based SPI.

In this paper, we introduce a procedure for the reconstruction of spectral-spatial EPR images using projections acquired with the constant sweep of a magnetic field. The application of a constant field-sweep and a predetermined data sampling rate simplifies the requirements for EPR imaging instrumentation and facilitates the backprojection-based reconstruction of spectral-spatial images. The proposed approach was applied to the reconstruction of a four-dimensional numerical phantom and to actual spectral-spatial EPR measurements. Image reconstruction using projections with a constant field sweep was three times faster than the conventional approach with the application of a pseudo-angle and a scan range that depends on the applied field gradient. Spectral-spatial EPR imaging with a constant field-sweep for data acquisition only slightly reduces the signal-to-noise ratio or functional resolution of the resultant images and can be applied together with any common backprojection-based reconstruction algorithm. (C) 2017 Elsevier Inc. All rights reserved.

In this paper, we introduce a procedure for the reconstruction of spectral-spatial EPR images using projections acquired with the constant sweep of a magnetic field. The application of a constant field-sweep and a predetermined data sampling rate simplifies the requirements for EPR imaging instrumentation and facilitates the backprojection-based reconstruction of spectral-spatial images. The proposed approach was applied to the reconstruction of a four-dimensional numerical phantom and to actual spectral-spatial EPR measurements. Image reconstruction using projections with a constant field sweep was three times faster than the conventional approach with the application of a pseudo-angle and a scan range that depends on the applied field gradient. Spectral-spatial EPR imaging with a constant field-sweep for data acquisition only slightly reduces the signal-to-noise ratio or functional resolution of the resultant images and can be applied together with any common backprojection-based reconstruction algorithm. (C) 2017 Elsevier Inc. All rights reserved.

Objectives The aim of this study was to demonstrate the feasibility of in vivo three-dimensional (3D) relaxation time T-2* mapping of a dicarboxy-PROXYL radical using continuous-wave electron paramagnetic resonance (CW-EPR) imaging. Materials and methods Isotopically substituted dicarboxy-PROXYL radicals, 3,4-dicarboxy-2,2,5,5-tetra(H-2(3)) methylpyrrolidin-( 3,4-H-2(2))-(1-N-15)-1-oxyl (H-2, N-15-DCP) and 3,4-dicarboxy-2,2,5,5-tetra(H-2(3)) methylpyrrolidin-(3,4-H-2(2))1- oxyl (H-2-DCP), were used in the study. A clonogenic cell survival assay was performed with the H-2-DCP radical using squamous cell carcinoma (SCC VII) cells. The time course of EPR signal intensities of intravenously injected H-2, N-15-DCP and H-2-DCP radicals were determined in tumor-bearing hind legs of mice (C3H/HeJ, male, n = 5). CW-EPR-based single-point imaging (SPI) was performed for 3D T-2* mapping. Results H-2-DCP radical did not exhibit cytotoxicity at concentrations below 10 mM. The in vivo half-life of H-2, N-15-DCP in tumor tissues was 24.7 +/- 2.9 min (mean +/- standard deviation [SD], n = 5). The in vivo time course of the EPR signal intensity of the H-2, N-15-DCP radical showed a plateau of 10.2 +/- 1.2 min (mean +/- SD) where the EPR signal intensity remained at more than 90% of the maximum intensity. During the plateau, in vivo 3D T-2* maps with H-2, N-15-DCP were obtained from tumor-bearing hind legs, with a total acquisition time of 7.5 min. Conclusion EPR signals of H-2, N-15-DCP persisted long enough after bolus intravenous injection to conduct in vivo 3D T-2* mapping with CW-EPR-based SPI.

Objectives The aim of this study was to demonstrate the feasibility of in vivo three-dimensional (3D) relaxation time T-2* mapping of a dicarboxy-PROXYL radical using continuous-wave electron paramagnetic resonance (CW-EPR) imaging. Materials and methods Isotopically substituted dicarboxy-PROXYL radicals, 3,4-dicarboxy-2,2,5,5-tetra(H-2(3)) methylpyrrolidin-( 3,4-H-2(2))-(1-N-15)-1-oxyl (H-2, N-15-DCP) and 3,4-dicarboxy-2,2,5,5-tetra(H-2(3)) methylpyrrolidin-(3,4-H-2(2))1- oxyl (H-2-DCP), were used in the study. A clonogenic cell survival assay was performed with the H-2-DCP radical using squamous cell carcinoma (SCC VII) cells. The time course of EPR signal intensities of intravenously injected H-2, N-15-DCP and H-2-DCP radicals were determined in tumor-bearing hind legs of mice (C3H/HeJ, male, n = 5). CW-EPR-based single-point imaging (SPI) was performed for 3D T-2* mapping. Results H-2-DCP radical did not exhibit cytotoxicity at concentrations below 10 mM. The in vivo half-life of H-2, N-15-DCP in tumor tissues was 24.7 +/- 2.9 min (mean +/- standard deviation [SD], n = 5). The in vivo time course of the EPR signal intensity of the H-2, N-15-DCP radical showed a plateau of 10.2 +/- 1.2 min (mean +/- SD) where the EPR signal intensity remained at more than 90% of the maximum intensity. During the plateau, in vivo 3D T-2* maps with H-2, N-15-DCP were obtained from tumor-bearing hind legs, with a total acquisition time of 7.5 min. Conclusion EPR signals of H-2, N-15-DCP persisted long enough after bolus intravenous injection to conduct in vivo 3D T-2* mapping with CW-EPR-based SPI.

In this paper, we introduce a procedure for the reconstruction of spectral-spatial EPR images using projections acquired with the constant sweep of a magnetic field. The application of a constant field-sweep and a predetermined data sampling rate simplifies the requirements for EPR imaging instrumentation and facilitates the backprojection-based reconstruction of spectral-spatial images. The proposed approach was applied to the reconstruction of a four-dimensional numerical phantom and to actual spectral-spatial EPR measurements. Image reconstruction using projections with a constant field sweep was three times faster than the conventional approach with the application of a pseudo-angle and a scan range that depends on the applied field gradient. Spectral-spatial EPR imaging with a constant field-sweep for data acquisition only slightly reduces the signal-to-noise ratio or functional resolution of the resultant images and can be applied together with any common backprojection-based reconstruction algorithm. (C) 2017 Elsevier Inc. All rights reserved.

Objectives The aim of this study was to demonstrate the feasibility of in vivo three-dimensional (3D) relaxation time T-2* mapping of a dicarboxy-PROXYL radical using continuous-wave electron paramagnetic resonance (CW-EPR) imaging. Materials and methods Isotopically substituted dicarboxy-PROXYL radicals, 3,4-dicarboxy-2,2,5,5-tetra(H-2(3)) methylpyrrolidin-( 3,4-H-2(2))-(1-N-15)-1-oxyl (H-2, N-15-DCP) and 3,4-dicarboxy-2,2,5,5-tetra(H-2(3)) methylpyrrolidin-(3,4-H-2(2))1- oxyl (H-2-DCP), were used in the study. A clonogenic cell survival assay was performed with the H-2-DCP radical using squamous cell carcinoma (SCC VII) cells. The time course of EPR signal intensities of intravenously injected H-2, N-15-DCP and H-2-DCP radicals were determined in tumor-bearing hind legs of mice (C3H/HeJ, male, n = 5). CW-EPR-based single-point imaging (SPI) was performed for 3D T-2* mapping. Results H-2-DCP radical did not exhibit cytotoxicity at concentrations below 10 mM. The in vivo half-life of H-2, N-15-DCP in tumor tissues was 24.7 +/- 2.9 min (mean +/- standard deviation [SD], n = 5). The in vivo time course of the EPR signal intensity of the H-2, N-15-DCP radical showed a plateau of 10.2 +/- 1.2 min (mean +/- SD) where the EPR signal intensity remained at more than 90% of the maximum intensity. During the plateau, in vivo 3D T-2* maps with H-2, N-15-DCP were obtained from tumor-bearing hind legs, with a total acquisition time of 7.5 min. Conclusion EPR signals of H-2, N-15-DCP persisted long enough after bolus intravenous injection to conduct in vivo 3D T-2* mapping with CW-EPR-based SPI.

In this paper, we introduce a procedure for the reconstruction of spectral-spatial EPR images using projections acquired with the constant sweep of a magnetic field. The application of a constant field-sweep and a predetermined data sampling rate simplifies the requirements for EPR imaging instrumentation and facilitates the backprojection-based reconstruction of spectral-spatial images. The proposed approach was applied to the reconstruction of a four-dimensional numerical phantom and to actual spectral-spatial EPR measurements. Image reconstruction using projections with a constant field sweep was three times faster than the conventional approach with the application of a pseudo-angle and a scan range that depends on the applied field gradient. Spectral-spatial EPR imaging with a constant field-sweep for data acquisition only slightly reduces the signal-to-noise ratio or functional resolution of the resultant images and can be applied together with any common backprojection-based reconstruction algorithm. (C) 2017 Elsevier Inc. All rights reserved.