A specific absorption rate reduction method for simultaneous multislice magnetic resonance imaging.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Pulse Sequence Design
• Biomedical Engineering

Background:

• Simultaneous multi-slice (SMS) imaging accelerates MRI acquisition but often increases specific absorption rate (SAR).
• Optimizing radio frequency (RF) pulse design is crucial for balancing imaging speed, SAR, and image quality in SMS MRI.
• Existing methods for SMS RF pulse synthesis may not sufficiently address SAR reduction and artifact control.

Purpose of the Study:

• To develop a modified Shinnar-Le Roux method for synthesizing low-SAR, low-ripple RF pulses for 2D gradient echo (GRE) based SMS MRI.
• To introduce formulas for estimating relative SAR values of SMS pulses.
• To evaluate the performance of the proposed method against typical RF pulses in phantom and human brain imaging.

Main Methods:

• Modified Shinnar-Le Roux method incorporating thinner slice bandwidth and lower multislice offset frequencies.
• Weighted Parks-McClellan algorithm for sidelobe reduction.
• Formulas for relative SAR value estimation and experimental validation using phantom and in-vivo imaging.

Main Results:

• Synthesized SMS RF pulses achieved significantly lower SAR values (32% and 28% of standard pulses) in simultaneous 5-slice and 3-slice imaging, respectively.
• The proposed method demonstrated comparable image quality to standard pulses while reducing SAR.
• The method effectively reduces sidelobes and out-of-slice ripple.

Conclusions:

• The modified Shinnar-Le Roux method provides an effective approach for synthesizing low-SAR, high-quality RF pulses for 2D GRE-based SMS MRI.
• This technique offers substantial SAR reduction, making SMS MRI safer and more efficient.
• The method is broadly applicable to synthesizing typical SMS RF pulses for significant SAR reduction.