A flexible 8.5 MHz litz wire receive array for field-cycling imaging

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Coil Design and Optimization
• Low-Frequency Applications

Background:

• Low-frequency coils face significant signal-to-noise ratio (SNR) degradation due to loop and component losses.
• Minimizing these losses is crucial for effective low-field MRI, where SNR is often a limiting factor.
• Array coils offer potential for enhanced SNR, coverage, and imaging speed if inter-loop interactions are managed.

Purpose of the Study:

• To investigate methods for characterizing and preserving SNR in a low-frequency coil array.
• To develop a geometrically conforming array coil for rapid, no-tune application across various anatomies.
• To optimize low-noise preamplifiers and interfacing electronics for a 6-channel flex array coil.

Main Methods:

• Construction and loss characterization of single and multi-turn litz wire loops (16.2 cm diameter).
• Acquisition and characterization of low-noise preamplifiers and development of interfacing electronics.
• Implementation of a bench-level SNR test to evaluate tuning and loading effects on individual coils.

Main Results:

• Ultra-fine strand litz wire demonstrated lower losses and provided necessary mechanical flexibility compared to solid wire.
• Single-turn loops showed dominant losses, while 2 and 3-turn loops exhibited body loss dominance under specific loading.
• A 6-channel flex array coil (3 anterior, 3 posterior) was constructed, conforming to anatomies and yielding consistent volunteer study results.

Conclusions:

• Body loss dominance was achieved with 16.2 cm loops at 8.5 MHz, demonstrating optimized SNR preservation.
• Low-noise interfacing electronics were developed and tested, characterizing SNR penalties related to tuning and loading.
• The resulting flexible 6-channel array coil supports field-cycling MRI studies requiring adaptable and quickly deployable coils.