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Development of an MR compatible rotating anode x-ray tube

In order to achieve a truly hybrid, high quality X-ray/MR system one must have a rotating anode x-ray source as close as possible to the bore of the high-field MR magnet. Full integration between a closed bore MR system and an x-ray fluoroscopy system presents two main challenges that must be addressed: x-ray tube motor operation and efficiency in an external field, and focal spot deflection. Regarding the first challenge our results have shown that an AC induction motor operating in external fields will experience a drop off in efficiency. Specifically, fields on the order of 100 Gauss perpendicular to the rotor decrease the rotation speed from 2450 RPM to below 1800 RPM. We are currently developing an alternate brushless DC motor design that would exploit the presence of the external MR fringe field and our initial finite element results indicate that the necessary amount of torque is produced. Regarding the second challenge our results show that an external field of 195 Gauss perpendicular to the anode-cathode axis (BR direction) produces a focal spot deflection of 5 mm. For the fields at which we want to operate the x-ray tube (~to 1000 Gauss along BR) this deflection will be significantly larger than 5 mm and must be corrected for. We propose a design that includes active deflection coils which serve to counteract the presence of the external field and reduce the focal spot deflection to less than 1 mm in our simulations.