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Electrostatic focal spot correction for x-ray tubes operating in strong magnetic fields
Prasheel Lillaney1, Mihye Shin2, Waldo Hinshaw3
1Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California 94107.
Medical Physics
|November 6, 2014
Summary
This study developed an electrostatic correction method to shield x-ray tubes from magnetic resonance fringe fields in hybrid XMR imaging systems. The technique successfully compensates for orthogonal magnetic fields up to 65 mT, enabling closer proximity imaging.
Area of Science:
- Medical Imaging Physics
- Biomedical Engineering
- X-ray Tube Technology
Background:
- Hybrid X-ray/Magnetic Resonance (XMR) imaging systems offer advantages for advanced medical imaging.
- Current XMR systems have large separation distances, limiting integrated system design.
- Magnetic Resonance (MR) fringe fields pose a significant challenge to co-locating X-ray tubes and MR systems.
Purpose of the Study:
- To design an x-ray tube immune to magnetic resonance fringe fields for close-proximity XMR systems.
- To develop a method for correcting electron drift caused by MR fringe fields impacting the x-ray tube focal spot.
Main Methods:
- Proposed an electrostatic correction method using biased electrodes adjacent to the cathode to counteract electron drift.
- Derived and simulated a focusing cup assembly design considering MR fringe field strength and high voltage standoff.
- Utilized Monte Carlo simulations to assess the impact on the x-ray energy spectrum.
Main Results:
- Electrostatic correction compensated for orthogonal fringe fields up to 65 mT with specific bias voltages.
- A hybrid approach combining active shielding coils and bias electrodes achieved full correction at 88.1 mT.
- Monte Carlo simulations showed no significant change in mean x-ray energy but a 7.5% reduction in output flux.
Conclusions:
- The electrostatic correction method is effective for orthogonal magnetic fields up to 65 mT.
- Pure electrostatic correction is limited by dielectric strength and parallel magnetic fields.
- A hybrid correction approach is necessary for stronger and complex magnetic field conditions in close-proximity XMR systems.
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