Array-optimized composite pulse for excellent whole-brain homogeneity in high-field MRI

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biophysics
• Radiofrequency Engineering

Background:

• Improving excitation homogeneity is crucial for high-field MRI.
• Existing methods often utilize separate control of radiofrequency (RF) coils in transmit arrays.
• Limitations exist in achieving uniform signal intensity distribution across the entire brain volume with current techniques.

Purpose of the Study:

• To demonstrate a novel method for achieving superior excitation homogeneity in high-field MRI.
• To combine accurate RF field calculations with Bloch equation simulations.
• To introduce the concept of array-optimized composite pulses for enhanced MRI.

Main Methods:

• Utilized accurate radiofrequency (RF) field calculations.
• Employed the Bloch equation for simulations.
• Developed and simulated a sequence of pulses with individually optimized current distributions (array-optimized composite pulse).

Main Results:

• Achieved remarkably homogeneous signal intensity distributions over the entire brain volume.
• Demonstrated superior homogeneity compared to single optimized (RF shimmed) pulses or standard composite pulse arrangements.
• Simulations confirmed excellent whole-brain excitation homogeneity at up to 600 MHz with a simple array-optimized composite pulse.

Conclusions:

• Array-optimized composite pulses offer a highly effective strategy for improving excitation homogeneity in high-field MRI.
• This approach surpasses conventional RF shimming techniques in achieving uniform signal intensity.
• The method shows promise for enhancing brain imaging quality at high magnetic field strengths.