Multi-port-driven birdcage coil for multiple-mouse MR imaging at 7 T

Area of Science:

• Medical Imaging
• Biomedical Engineering
• Radiofrequency Coil Design

Background:

• Ultra-high field (UHF) magnetic resonance imaging (MRI) for multiple mice (MM-MRI) faces challenges with radiofrequency (RF) coil hardware, imaging protocols, and experimental setups.
• Transmit (Tx) (|B1+|)-field inhomogeneity is a persistent problem in UHF MM-MRI due to shortened RF wavelengths, impacting image quality.
• Existing MM-MRI studies have explored single-channel or multi-channel phased array coils, but B1+ inhomogeneity remains a significant hurdle.

Purpose of the Study:

• To propose and evaluate a novel multiple birdcage (MBC) coil design for improved MM-MRI at UHF.
• To address the critical issue of Tx (|B1+|)-field inhomogeneity in UHF MM-MRI.
• To enhance the signal-to-noise ratio (SNR) for higher-resolution MR images of multiple mice.

Main Methods:

• Electromagnetic (EM) simulations using the finite-difference time-domain (FDTD) method were employed to analyze |B1|-field distribution.
• A single birdcage (SBC) high-pass filter (HPF) configuration (SBC_HPF) was investigated for its |B1|-field intensity.
• A triple-SBC_HPF configuration with decoupling techniques was developed as the MBC_HPF coil for simultaneous imaging of three mice.

Main Results:

• The SBC_HPF configuration, without an RF shield, demonstrated higher |B1|-field intensity compared to low-pass (LPF) and band-pass (BPF) filter configurations.
• Experimental 7-T MRI results showed the SBC_HPF configuration achieved the highest signal-to-noise ratio (SNR), indicating superior coil performance.
• The developed MBC_HPF coil enabled simultaneous image acquisition of three mice, showcasing its practical application in MM-MRI.

Conclusions:

• The proposed smaller individual Tx-only coils within an MBC configuration effectively mitigate Tx (|B1+|)-field inhomogeneity in UHF MM-MRI.
• The SBC_HPF configuration offers superior |B1|-field intensity and SNR performance compared to other tested RF coil designs.
• The MBC_HPF coil represents a significant advancement for simultaneous, high-resolution imaging of multiple mice in UHF MRI.