Steer-PROP: a GRASE-PROPELLER sequence with interecho steering gradient pulses.

Area of Science:

• Magnetic Resonance Imaging
• Medical Physics
• Radiology

Background:

• Gradient and spin echo (GRASE) sequences are susceptible to phase errors and long imaging times.
• Single-shot echo planar imaging (SS-EPI) can produce image distortions, particularly in diffusion imaging.
• PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) sequences offer motion robustness but can be time-consuming.

Purpose of the Study:

• To introduce and evaluate a novel MRI pulse sequence, Steer-PROP, designed to reduce imaging times and correct phase errors inherent in GRASE sequences.
• To assess the feasibility of Steer-PROP as an alternative to SS-EPI for acquiring distortion-free diffusion images.
• To demonstrate the effectiveness of Steer-PROP in mitigating motion-induced phase inconsistencies.

Main Methods:

• Developed Steer-PROP, a GRASE-based sequence utilizing blip gradient pulses to acquire multiple k-space blades per repetition time.
• Implemented a phase correction algorithm to address GRASE and motion-induced phase errors.
• Evaluated Steer-PROP on phantoms and human subjects at 1.5T and 3.0T for T2- and diffusion-weighted imaging.

Main Results:

• Steer-PROP achieved image quality comparable to conventional FSE-based PROPELLER but with approximately one-third of the scan time.
• The sequence demonstrated robustness against motion, similar to FSE-based PROPELLER.
• High-quality, distortion-free diffusion images were acquired in all planes from human subjects, surpassing SS-EPI performance.

Conclusions:

• Steer-PROP substantially reduces scan times compared to FSE-based PROPELLER while maintaining adequate image quality.
• The novel k-space sampling strategy enables integrated phase correction and minimizes echo spacing.
• Steer-PROP is a viable alternative to SS-EPI for reducing image distortion across all imaging planes.