Magnetostatic focal spot correction for x-ray tubes operating in strong magnetic fields using iterative optimization

Area of Science:

• Medical Imaging Physics
• Interventional Radiology
• Electromagnetism

Background:

• Integrating X-ray fluoroscopy and Magnetic Resonance (MR) imaging systems is crucial for advanced interventional procedures.
• Magnetic fields from MR systems pose a significant challenge to the stability and performance of X-ray tubes.
• Developing magnetic field-immune X-ray tubes is essential for co-located imaging systems.

Purpose of the Study:

• To design active shielding coils that minimize magnetic field effects on the X-ray tube focal spot.
• To optimize coil design for reduced power consumption and enhanced magnetic field homogeneity.
• To investigate the use of permanent magnets to improve shielding efficiency and operational duration.

Main Methods:

• An iterative optimization algorithm combining linear and nonlinear programming was used to design active shielding coils.
• Finite element space charge simulations validated the effectiveness of the designed coils.
• A lumped parameter model assessed the thermal dynamics and operational limits of the shielding coils.
• Neodymium permanent magnets were incorporated to mitigate heating and enhance performance.

Main Results:

• Optimized active shielding coils achieved a current density of 588 A/cm² at 88 mT, with a 15-minute continuous operation time.
• Incorporating a neodymium magnet reduced current density to 337 A/cm², extending operation to 59 minutes.
• Simulations confirmed coil effectiveness but noted focal spot distortions in oblique X-ray tube geometries.

Conclusions:

• Active shielding is a viable strategy for mitigating magnetic field interference in co-located X-ray and MR systems.
• The inclusion of permanent magnets in active shielding designs offers a practical method for achieving longer operational times during fluoroscopic procedures.