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Radiation induced currents in MRI RF coils: application to linac/MRI integration
B Burke1, B G Fallone, S Rathee
1Department of Physics, University of Alberta, 11322-89th Avenue, Edmonton, Alberta T6G 2G7, Canada. bburke@phys.ualberta.ca
Physics in Medicine and Biology
|January 15, 2010
Summary
Radiation-induced currents (RIC) in magnetic resonance imaging (MRI) radiofrequency (RF) coils were measured during integrated radiotherapy. Copper windings generate RIC, which depends linearly on dose rate and may degrade MRI signal quality.
Area of Science:
- Medical Physics
- Radiotherapy Technology
- Magnetic Resonance Imaging
Background:
- Advancements in image-guided radiotherapy integrate medical linear accelerators (linac) with magnetic resonance imaging (MRI).
- Integrated linac-MRI systems offer real-time tumor localization for precise radiotherapy, potentially reducing damage to healthy tissues.
- The impact of pulsed radiation from linacs on MRI radiofrequency (RF) coils during real-time operation is currently unknown.
Purpose of the Study:
- To investigate and characterize the radiation-induced current (RIC) in MRI RF coils when exposed to pulsed radiation from a medical linear accelerator.
- To understand the fundamental properties of RIC, including its source, dependence on radiation dose rate, and the effect of shielding.
- To assess the potential impact of RIC on MRI signal quality and image artifacts in integrated radiotherapy systems.
Main Methods:
- Measurement of instantaneous RIC in two distinct MRI RF coil designs subjected to pulsed radiation.
- Calculation of frequency spectra for the measured RIC.
- Characterization of RIC by isolating the responsible coil component, assessing dose rate dependence, and evaluating the effect of wax shielding.
Main Results:
- A measurable RIC was detected in the tested MRI RF coils.
- The copper windings of the RF coils were identified as the primary source of RIC.
- RIC exhibited a linear dependence on the radiation dose rate.
- A decrease in RIC was observed with wax buildup on the coil, suggesting electronic disequilibrium as the cause.
Conclusions:
- This study confirms the presence of measurable RIC in MRI RF coils during integrated radiotherapy procedures.
- The identified source and characteristics of RIC indicate a potential for detrimental effects on MRI signal-to-noise ratio and image quality.
- Further research is warranted to mitigate RIC and ensure the integrity of MRI data in image-guided radiotherapy.
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