Double-row dipole/loop combined array for human whole brain imaging at 7 T.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biomedical Engineering
• Physics

Background:

• Designing radiofrequency (RF) coils for ultra-high field (UHF; ≥7 Tesla) human head imaging faces challenges with transmit (Tx) RF field inhomogeneity and longitudinal coverage.
• Loop-only receive (Rx) arrays may not achieve optimal intrinsic signal-to-noise ratio (UISNR) near the brain center at UHF.
• Combining complementary conductive structures, like loops and dipoles, can improve Rx performance.

Purpose of the Study:

• To develop and evaluate a novel 32-element hybrid RF coil array for 7 Tesla (T) human head imaging.
• To address limitations in RF field homogeneity, coverage, and signal-to-noise ratio (SNR) at UHF MRI.
• To improve transmit (Tx) efficiency and simplify coil design.

Main Methods:

• Development and construction of a 32-element hybrid array comprising 16 transceiver loops and 16 Rx-only dipoles.
• Single-layer element placement to increase RF power deposition and preserve Tx-efficiency.
• Evaluation of whole brain coverage, 3D RF shimming capability, and SNR performance.

Main Results:

• The hybrid array demonstrated whole brain coverage and 3D RF shimming capability.
• Achieved approximately 15% higher SNR near the brain center compared to a commercial head array.
• Showcased 20% to 40% higher Tx-efficiency, depending on the RF shim mode.

Conclusions:

• The novel 32-element hybrid array design offers improved SNR and Tx-efficiency for 7T human head MRI.
• This design facilitates whole brain coverage and 3D RF shimming.
• The hybrid approach simplifies coil structure while enhancing imaging performance at ultra-high fields.