Accelerated diffusion and relaxation-diffusion MRI using time-division multiplexing EPI

Area of Science:

• Magnetic Resonance Imaging
• Diffusion MRI
• Medical Physics

Background:

• Relaxation-diffusion MRI is crucial for neurological studies but is limited by long scan times.
• Conventional multi-echo echo-planar imaging (EPI) sequences are time-consuming.
• Accelerating relaxation-diffusion MRI acquisition is essential for clinical research.

Purpose of the Study:

• To develop a time-division multiplexing echo-planar imaging (TDM-EPI) sequence.
• To achieve approximately two- to threefold acceleration in joint relaxation-diffusion MRI data acquisition with multiple echo times (TEs).

Main Methods:

• The TDM-EPI sequence interleaves excitation and data collection for multiple slices at different TEs.
• Echo-shifting gradients are used to disentangle overlapping echo signals.
• Two variants, single-TE and multi-TE TDM-EPI, were developed and evaluated on a 3 Tesla scanner using phantom and in vivo human brain data.

Main Results:

• The single-TE TDM-EPI sequence can acquire 2 slices simultaneously with a maximum b-value of 3000 s/mm² and 2.5 mm isotropic resolution.
• The multi-TE TDM-EPI sequence can acquire 2 or 3 slices simultaneously with shortest TE ≈ 70 ms and ΔTE ≈ 30 ms.
• Experiments demonstrated that TDM-EPI provides comparable image quality and diffusion measures to conventional EPI while reducing scan time by two- to threefold.

Conclusions:

• TDM-EPI is a novel method for acquiring diffusion imaging data at multiple TEs.
• This technique significantly reduces acquisition time for relaxation-diffusion MRI.
• TDM-EPI removes a major barrier to the clinical research adoption of relaxation-diffusion MRI for neurological and mental disorders.