Less is more? Performance of loops without distributed capacitors for 7 T MRI applications.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Radiofrequency (RF) Coil Engineering
• Biomedical Engineering

Background:

• Conventional RF coils for 7 Tesla (7T) MRI often involve complex designs with distributed capacitors.
• There is a need for simpler, more robust, and flexible RF coil designs for ultra-high field MRI applications.
• Plain loops, lacking distributed capacitors, are being explored as a potential alternative.

Purpose of the Study:

• To evaluate the suitability of plain loops as RF coils for 7T MRI applications.
• To compare the performance of circular and elliptical plain loops against conventional loops and dipoles.
• To provide insights into the benefits, limitations, and fabrication of plain loops for RF coil arrays.

Main Methods:

• Characterization of RF coils based on surface current distribution, transmit efficiency, and robustness to loading.
• Assessment of specific absorption rate (SAR), coupling (S21), and 'flexibility' (S11 after deformation).
• Comparative analysis of round plain loops, elongated plain loops, conventional loops, and dipoles.

Main Results:

• A 12 cm round plain loop demonstrated flexibility and similar transmit properties to a conventional loop, with significantly lower coupling.
• An elongated plain loop showed greater robustness to coil-load distance and lower worst-case maxSAR10g compared to a dipole, with comparable transmit efficiency.
• Plain loops exhibit distinct characteristics in terms of flexibility, coupling, and SAR, offering a trade-off compared to conventional designs.

Conclusions:

• Plain loops are viable alternatives for RF coil construction in 7T MRI, offering advantages in flexibility and coupling.
• The study provides foundational data for optimizing plain loop designs in ultra-high field MRI coil arrays.
• Further research can leverage these findings to develop more efficient and adaptable MRI coil systems.