Reducing MRI RF-induced heating for the external fixation using capacitive structures.

Area of Science:

• Biomedical Engineering
• Medical Imaging Physics
• Materials Science

Background:

• External fixation devices are essential in orthopedic treatments but pose risks during MRI due to RF-induced heating.
• Existing methods for mitigating RF heating are often device-specific and may not be universally applicable.

Purpose of the Study:

• To develop and validate a generic method for reducing radiofrequency (RF)-induced heating in external fixation devices during MRI procedures.
• To investigate the use of capacitive reactance to mitigate electromagnetic coupling between fixation devices and MRI RF fields.

Main Methods:

• Developed a simplified equivalent circuit model to analyze RF field interactions with external fixation devices.
• Designed and integrated mechanical structures with capacitive reactance into fixation device joints (clamp-pin and rod-clamp).
• Validated the circuit model and method effectiveness through numerical simulations and experimental studies at 1.5 T and 3 T.

Main Results:

• Numerical simulations showed significant reductions in peak specific absorption rate (SAR1g) near pin tips (e.g., from 760.4 W/kg to 12.0 W/kg at 1.5 T).
• Experimental results demonstrated substantial decreases in RF-induced heating (e.g., from 7.85 °C to 1.01 °C at 1.5 T).
• The capacitive structures effectively detuned the coupling between the device and MRI RF fields.

Conclusions:

• The proposed generic method using capacitive structures effectively reduces RF-induced heating in external fixation devices during MRI.
• This approach enhances patient safety by mitigating thermal risks associated with MRI in patients with external fixation.
• Thorough testing of final device designs is crucial due to the device-specific nature of RF-induced heating.