A generalized slab-wise framework for parallel transmit multiband RF pulse design.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Radiofrequency (RF) Engineering
• Medical Physics

Background:

• Simultaneous multislice (SMS) imaging enables faster MRI scans.
• Designing parallel transmit multiband pulses is crucial for SMS imaging, especially with large fields of view (FOVs).
• Current slice-wise approaches require extensive computation and B1+ mapping for each slice.

Purpose of the Study:

• To introduce a novel slab-wise framework for designing parallel transmit multiband pulses.
• To optimize pulse design for volumetric SMS imaging with extended FOVs along the slice direction.
• To enhance radiofrequency (RF) performance and efficiency in MRI.

Main Methods:

• The slab-wise framework divides the FOV into contiguous slabs and optimizes pulses per slab.
• Design parameters, including slab number and B1+ mapping slice placement, were investigated.
• Electromagnetic simulations (7T head RF array) and Bloch simulations were used for pulse design and evaluation.

Main Results:

• Increasing the number of slabs improved SAR reduction and B1+ homogenization across the brain.
• Performance gains plateaued around 12 slabs, with slab thickness around 12 mm.
• The placement of B1+ mapping slices had minimal impact on performance.

Conclusions:

• The slab-wise framework achieves comparable RF performance to slice-wise methods.
• This approach significantly reduces the number of required pulses, enhancing efficiency.
• The framework accelerates B1+ mapping, pulse calculation, and sequence preparation for faster MRI acquisition.