High-resolution gradient-recalled echo imaging at 9.4T using 16-channel parallel transmit simultaneous multislice...

Area of Science:

• Magnetic Resonance Imaging
• High-Field MRI

Background:

• High-field MRI at 9.4T offers superior signal-to-noise and contrast-to-noise ratios.
• Challenges include B1+ inhomogeneity and long acquisition times for high-resolution 2D gradient-recalled echo (GRE) imaging.

Purpose of the Study:

• To address B1+ inhomogeneity and reduce acquisition time in high-resolution 2D GRE imaging at 9.4T.
• To enable full benefit from improved image quality at ultra-high fields.

Main Methods:

• Developed slice-specific simultaneous multislice (SMS) parallel transmission (pTx) 3-spoke pulses.
• Utilized magnitude least-squares optimization for pulse design and simulations for optimal spoke placement.
• Applied slice-specific radiofrequency scaling factors to sinc waveforms on a per-channel basis.

Main Results:

• Demonstrated improved flip angle homogenization with 3-spoke pulses compared to conventional methods (NRMSE 0.119-0.137).
• Achieved comparable excitation homogeneity across single-band and SMS acquisitions.
• Reduced scan duration by 50% in a 48-slice GRE protocol (0.28x0.28mm resolution), achieving a total acquisition time of 6:52 min.

Conclusions:

• Successfully implemented time-efficient, flip angle-homogenized high-resolution GRE imaging at 9.4T.
• Slice-specific SMS-pTx spokes excitations are effective for overcoming B1+ inhomogeneity and reducing scan times.
• This technique enhances the utility of ultra-high-field MRI for detailed anatomical imaging.