Spatiotemporal Encoding With Nonlinear Gradient Hardware Using Pulseq: From Principles to Practical Demonstration

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Pulse Sequence Design

Background:

• Spatiotemporal encoding (SPEN) is an advanced MRI technique.
• Conventional SPEN methods often rely on chirped-RF pulses, which can introduce limitations.

Purpose of the Study:

• To provide the theoretical basis and practical demonstration of SPEN using nonlinear gradient hardware.
• To compare a novel SPEN method with conventional techniques.

Main Methods:

• Implementation of a novel SPEN method using a custom-built matrix gradient coil for quadratic phase generation.
• Integration into a spin-echo echo-planar-imaging (SE-EPI) sequence using Pulseq.
• Comparison with conventional chirped-RF pulse methods via phantom imaging on a 3T MRI system.

Main Results:

• Successful generation of the SPEN-defining quadratic phase profile using nonlinear gradients.
• Achieved comparable image quality to conventional methods.
• Overcame specific absorption rate (SAR) and minimum echo time (TE) limitations associated with chirped-RF pulses.

Conclusions:

• Generating the SPEN quadratic phase with nonlinear gradients is a superior alternative to conventional methods.
• This nonlinear gradient approach enhances SPEN's clinical utility, particularly for 3D and high-field MRI.
• Mitigates critical safety and timing issues, paving the way for broader adoption.