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Design of An MR Compatible Rotating Anode X-Ray Tube

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P Lillaney

P Lillaney*, M Shin, W Hinshaw, R Fahrig, Stanford University, Stanford, CA

WE-C-217BCD-2 Wednesday 10:30:00 AM - 12:30:00 PM Room: 217BCD

Purpose: To design a rotating anode X-ray tube capable of operating in strong magnetic field environments. This tube design can be used in 'close proximity' hybrid X-ray/MR system geometries where the imaging fields of view are separated by only ~1.2 meters.

Methods: Existing rotating anode X-ray tube designs fail in strong magnetic field environments because the fields alter the electron trajectories in the tube and act as a brake on the induction motor, reducing the rotation speed of the anode. We propose an X-ray tube design that utilizes optimized resistive coils to shield a fraction of the MR fringe field. The remainder of the correction is performed using bias voltages on electrodes adjacent to the x-ray tube filament. Furthermore, we replace the induction motor with a novel motor design that is analogous to a three-phase brushed DC motor with the MR fringe field serving as the stator field.

Results: Space charge simulations of the electron optics show that the combined magnetostatic/electrostatic method can correct for a magnetic field strength of 152 mT with approximately 590 A/cm² applied to the shielding coils and a 35 kV potential difference applied to the bias electrodes. A prototype of the motor design was machined and assembled. The performance of this prototype motor was evaluated at various magnetic field strengths, and was found to accelerate to the minimum operating speed of 3000 rpm in 10 seconds for an external field of 60 mT.

Conclusions: The space charge simulations validate that the electron trajectories can be controlled using our combined approach. Testing of the motor prototype demonstrates that our design outperforms existing induction motors in strong magnetic field environments. Integrating this design with our modified flat panel detector will allow, for the first time, a 'close proximity' hybrid system in which imaging performance is not compromised.

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