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James F Dempsey - One of the best experts on this subject based on the ideXlab platform.

  • tu h bra 01 the physics of high power radiofrequency isolation in a novel compact Linear Accelerator based mri guided radiation therapy system
    Medical Physics, 2016
    Co-Authors: J Lamb, D Low, S Mutic, S Shvartsman, T Chmielewski, G Fought, A Sharma, James F Dempsey
    Abstract:

    Purpose: To develop a method for isolating the radiofrequency waves emanating from Linear Accelerator components from the magnetic resonance imaging (MRI) system of an integrated MRI-linac. Methods: An MRI-guided radiation therapy system has been designed that integrates a Linear Accelerator with simultaneous MR imaging. The radiofrequency waves created by the accelerating process would degrade MR image quality, so a method for containing the radiofrequency waves and isolating the MR imager from them was developed. The Linear Accelerator radiofrequency modulator was placed outside the room, so a filter was designed to eliminate the radiofrequency corresponding to the proton Larmour frequency of 14.7 MHz. Placing the radiofrequency emitting components in a typical Faraday cage would have reduced the radiofrequency emissions, but the design would be susceptible to small gaps in the shield due to the efficiency of the Faraday cage reflecting internal radiofrequency emissions. To reduce internal radiofrequency reflections, the Faraday cage was lined with carbon fiber sheets. Carbon fiber has the property of attenuating the radiofrequency energy so that the overall radiofrequency field inside the Faraday cage is reduced, decreasing any radiofrequency energy emitted from small gaps in the cage walls. Results: Within a 1.2 MHz band centered on the Larmor frequency, the radiofrequency (RF) leakage from the Faraday cage was measured to be −90 dB with no RF on, −40 dB with the RF on and no shield, returning to −90 dB with the RF on and shields in place. The radiofrequency filter attenuated the Linear Accelerator modulator emissions in the 14.7 MHz band by 70 dB. Conclusions: One of the major challenges in designing a compact Linear Accelerator based MRI-guided radiation therapy system, that of isolating the high power RF system from the MRI, has been solved. The measured radiofrequency emissions are sufficiently small to enable system integration. This research was funded by ViewRay, Inc., Oakwood, OH

  • tu h bra 02 the physics of magnetic field isolation in a novel compact Linear Accelerator based mri guided radiation therapy system
    Medical Physics, 2016
    Co-Authors: D Low, S Mutic, S Shvartsman, T Chmielewski, G Fought, A Sharma, James F Dempsey
    Abstract:

    Purpose: To develop a method for isolating the MRI magnetic field from field-sensitive Linear Accelerator components at distances close to isocenter. Methods: A MRI-guided radiation therapy system has been designed that integrates a Linear Accelerator with simultaneous MR imaging. In order to accomplish this, the magnetron, port circulator, radiofrequency waveguide, gun driver, and Linear Accelerator needed to be placed in locations with low magnetic fields. The system was also required to be compact, so moving these components far from the main magnetic field and isocenter was not an option. The magnetic field sensitive components (exclusive of the waveguide) were placed in coaxial steel sleeves that were electrically and mechanically isolated and whose thickness and placement were optimized using E&M modeling software. Six sets of sleeves were placed 60° apart, 85 cm from isocenter. The Faraday effect occurs when the direction of propagation is parallel to the magnetic RF field component, rotating the RF polarization, subsequently diminishing RF power. The Faraday effect was avoided by orienting the waveguides such that the magnetic field RF component was parallel to the magnetic field. Results: The magnetic field within the shields was measured to be less than 40 Gauss, significantly below the amount needed for the magnetron and port circulator. Additional mu-metal was employed to reduce the magnetic field at the Linear Accelerator to less than 1 Gauss. The orientation of the RF waveguides allowed the RT transport with minimal loss and reflection. Conclusion: One of the major challenges in designing a compact Linear Accelerator based MRI-guided radiation therapy system, that of creating low magnetic field environments for the magnetic-field sensitive components, has been solved. The measured magnetic fields are sufficiently small to enable system integration. This work supported by ViewRay, Inc.

Brian W Pogue - One of the best experts on this subject based on the ideXlab platform.

  • time gated cherenkov emission spectroscopy from Linear Accelerator irradiation of tissue phantoms
    Biomedical optics, 2012
    Co-Authors: Rongxiao Zhang, Adam K Glaser, Scott C Davis, David J Gladstone, Brian W Pogue
    Abstract:

    A time-gated-acquisition method is introduced to measure the Cherenkov emission from Linear Accelerator (LINAC) in tissue mimic phantom and shown to be an effective way to enhance the intensity of the Cherenkov emission over the ambient light.

  • time gated cherenkov emission spectroscopy from Linear Accelerator irradiation of tissue phantoms
    Optics Letters, 2012
    Co-Authors: Adam K Glaser, Rongxiao Zhang, Scott C Davis, David J Gladstone, Brian W Pogue
    Abstract:

    Radiation from a Linear Accelerator induces Cherenkov emission in tissue, which has recently been shown to produce biochemical spectral signatures that can be interpreted to estimate tissue hemoglobin and oxygen saturation or molecular fluorescence from reporters. The Cherenkov optical light levels are in the range of 10−6 to 10−9  W/cm2, which limits the practical utility of the signal in routine radiation therapy monitoring. However, due to the fact that the radiation is pulsed, gated-acquisition of the signal allows detection in the presence of ambient lighting, as is demonstrated here. This observation has the potential to significantly increase the value of Cherenkov emission spectroscopy during radiation therapy to monitor tissue molecular events.

D Low - One of the best experts on this subject based on the ideXlab platform.

  • tu h bra 01 the physics of high power radiofrequency isolation in a novel compact Linear Accelerator based mri guided radiation therapy system
    Medical Physics, 2016
    Co-Authors: J Lamb, D Low, S Mutic, S Shvartsman, T Chmielewski, G Fought, A Sharma, James F Dempsey
    Abstract:

    Purpose: To develop a method for isolating the radiofrequency waves emanating from Linear Accelerator components from the magnetic resonance imaging (MRI) system of an integrated MRI-linac. Methods: An MRI-guided radiation therapy system has been designed that integrates a Linear Accelerator with simultaneous MR imaging. The radiofrequency waves created by the accelerating process would degrade MR image quality, so a method for containing the radiofrequency waves and isolating the MR imager from them was developed. The Linear Accelerator radiofrequency modulator was placed outside the room, so a filter was designed to eliminate the radiofrequency corresponding to the proton Larmour frequency of 14.7 MHz. Placing the radiofrequency emitting components in a typical Faraday cage would have reduced the radiofrequency emissions, but the design would be susceptible to small gaps in the shield due to the efficiency of the Faraday cage reflecting internal radiofrequency emissions. To reduce internal radiofrequency reflections, the Faraday cage was lined with carbon fiber sheets. Carbon fiber has the property of attenuating the radiofrequency energy so that the overall radiofrequency field inside the Faraday cage is reduced, decreasing any radiofrequency energy emitted from small gaps in the cage walls. Results: Within a 1.2 MHz band centered on the Larmor frequency, the radiofrequency (RF) leakage from the Faraday cage was measured to be −90 dB with no RF on, −40 dB with the RF on and no shield, returning to −90 dB with the RF on and shields in place. The radiofrequency filter attenuated the Linear Accelerator modulator emissions in the 14.7 MHz band by 70 dB. Conclusions: One of the major challenges in designing a compact Linear Accelerator based MRI-guided radiation therapy system, that of isolating the high power RF system from the MRI, has been solved. The measured radiofrequency emissions are sufficiently small to enable system integration. This research was funded by ViewRay, Inc., Oakwood, OH

  • tu h bra 02 the physics of magnetic field isolation in a novel compact Linear Accelerator based mri guided radiation therapy system
    Medical Physics, 2016
    Co-Authors: D Low, S Mutic, S Shvartsman, T Chmielewski, G Fought, A Sharma, James F Dempsey
    Abstract:

    Purpose: To develop a method for isolating the MRI magnetic field from field-sensitive Linear Accelerator components at distances close to isocenter. Methods: A MRI-guided radiation therapy system has been designed that integrates a Linear Accelerator with simultaneous MR imaging. In order to accomplish this, the magnetron, port circulator, radiofrequency waveguide, gun driver, and Linear Accelerator needed to be placed in locations with low magnetic fields. The system was also required to be compact, so moving these components far from the main magnetic field and isocenter was not an option. The magnetic field sensitive components (exclusive of the waveguide) were placed in coaxial steel sleeves that were electrically and mechanically isolated and whose thickness and placement were optimized using E&M modeling software. Six sets of sleeves were placed 60° apart, 85 cm from isocenter. The Faraday effect occurs when the direction of propagation is parallel to the magnetic RF field component, rotating the RF polarization, subsequently diminishing RF power. The Faraday effect was avoided by orienting the waveguides such that the magnetic field RF component was parallel to the magnetic field. Results: The magnetic field within the shields was measured to be less than 40 Gauss, significantly below the amount needed for the magnetron and port circulator. Additional mu-metal was employed to reduce the magnetic field at the Linear Accelerator to less than 1 Gauss. The orientation of the RF waveguides allowed the RT transport with minimal loss and reflection. Conclusion: One of the major challenges in designing a compact Linear Accelerator based MRI-guided radiation therapy system, that of creating low magnetic field environments for the magnetic-field sensitive components, has been solved. The measured magnetic fields are sufficiently small to enable system integration. This work supported by ViewRay, Inc.

Rongxiao Zhang - One of the best experts on this subject based on the ideXlab platform.

  • time gated cherenkov emission spectroscopy from Linear Accelerator irradiation of tissue phantoms
    Biomedical optics, 2012
    Co-Authors: Rongxiao Zhang, Adam K Glaser, Scott C Davis, David J Gladstone, Brian W Pogue
    Abstract:

    A time-gated-acquisition method is introduced to measure the Cherenkov emission from Linear Accelerator (LINAC) in tissue mimic phantom and shown to be an effective way to enhance the intensity of the Cherenkov emission over the ambient light.

  • time gated cherenkov emission spectroscopy from Linear Accelerator irradiation of tissue phantoms
    Optics Letters, 2012
    Co-Authors: Adam K Glaser, Rongxiao Zhang, Scott C Davis, David J Gladstone, Brian W Pogue
    Abstract:

    Radiation from a Linear Accelerator induces Cherenkov emission in tissue, which has recently been shown to produce biochemical spectral signatures that can be interpreted to estimate tissue hemoglobin and oxygen saturation or molecular fluorescence from reporters. The Cherenkov optical light levels are in the range of 10−6 to 10−9  W/cm2, which limits the practical utility of the signal in routine radiation therapy monitoring. However, due to the fact that the radiation is pulsed, gated-acquisition of the signal allows detection in the presence of ambient lighting, as is demonstrated here. This observation has the potential to significantly increase the value of Cherenkov emission spectroscopy during radiation therapy to monitor tissue molecular events.

Adam K Glaser - One of the best experts on this subject based on the ideXlab platform.

  • time gated cherenkov emission spectroscopy from Linear Accelerator irradiation of tissue phantoms
    Biomedical optics, 2012
    Co-Authors: Rongxiao Zhang, Adam K Glaser, Scott C Davis, David J Gladstone, Brian W Pogue
    Abstract:

    A time-gated-acquisition method is introduced to measure the Cherenkov emission from Linear Accelerator (LINAC) in tissue mimic phantom and shown to be an effective way to enhance the intensity of the Cherenkov emission over the ambient light.

  • time gated cherenkov emission spectroscopy from Linear Accelerator irradiation of tissue phantoms
    Optics Letters, 2012
    Co-Authors: Adam K Glaser, Rongxiao Zhang, Scott C Davis, David J Gladstone, Brian W Pogue
    Abstract:

    Radiation from a Linear Accelerator induces Cherenkov emission in tissue, which has recently been shown to produce biochemical spectral signatures that can be interpreted to estimate tissue hemoglobin and oxygen saturation or molecular fluorescence from reporters. The Cherenkov optical light levels are in the range of 10−6 to 10−9  W/cm2, which limits the practical utility of the signal in routine radiation therapy monitoring. However, due to the fact that the radiation is pulsed, gated-acquisition of the signal allows detection in the presence of ambient lighting, as is demonstrated here. This observation has the potential to significantly increase the value of Cherenkov emission spectroscopy during radiation therapy to monitor tissue molecular events.