B1 field-insensitive transformers for RF-safe transmission lines.

Area of Science:

• Medical Imaging
• Biomedical Engineering
• Electromagnetics

Background:

• Radiofrequency (RF)-induced heating is a critical safety concern in Magnetic Resonance Imaging (MRI).
• Conventional transformer coils can cause artifacts and heating, limiting their integration into medical devices.
• Minimizing RF field coupling is essential for safe and effective MRI-guided interventions.

Purpose of the Study:

• To evaluate the performance of novel figure-of-eight-shaped transformer coils compared to conventional loop coils.
• To assess the reduction in RF-induced heating and MRI artifacts with the new transformer design.
• To investigate the safety and signal transmission properties for active tracking applications.

Main Methods:

• Comparative analysis of transmission properties between figure-of-eight and loop transformer coils.
• Quantification of B1 field decoupling effects.
• Temperature measurements to assess RF-induced heating.
• Active tracking experiments to evaluate localization accuracy.

Main Results:

• Figure-of-eight coils demonstrated an 18 dB reduction in B1 field coupling compared to loop coils.
• Significantly reduced MRI artifacts were observed with figure-of-eight coils.
• Comparable signal transmission properties were maintained.
• Maximal temperature increases were 30 K (unsegmented) and 3.5 K (segmented), indicating effective heating reduction.
• Successful localization of a robotic assistance system using active tracking with a segmented transmission line.

Conclusions:

• The figure-of-eight transformer design effectively suppresses RF field coupling and reduces MRI artifacts.
• This design offers improved safety and potentially less obscuration of anatomical structures near the device.
• The findings support the integration of these transformers into devices like intravascular catheters for enhanced MRI-guided procedures.