CHEmical-shift selective Adiabatic Pulse (CHEAP): fast and high resolution downfield 3D 1H-MRSI at 7T

Abstract

Purpose

The downfield resonances in the human brain remain elusive or challenging to detect with traditional ¹H-MRSI. Conventional in vivo 3D ¹H-MRSI faces several challenges, including low signal-to-noise ratio (SNR) and magnetization transfer effects with water, which can lead to prolonged measurement times and reduced spatial resolution. To address these limitations, we propose a downfield 3D-MRSI method aimed at measuring downfield metabolites with enhanced spatial resolution, and speed acceptable for clinical practice at 7T.

Methods

The CHEmical-shift selective Adiabatic Pulse (CHEAP) technique was integrated into echo-planar spectroscopic imaging (EPSI) readout sequence for downfield metabolite and water reference 3D-MRSI. Five healthy subjects and two glioma patients were scanned to test the feasibility.

Results

In this work, CHEAP-EPSI technique achieves a high spatial resolution of 0.37 ml with a 10.5-min scan time. Its distinct advantages include relative insensitivity to transmit B₁⁺ inhomogeneity through adiabatic refocusing, effective suppression of water and lipid signals, and minimal baseline distortions, making it a valuable tool for research or potentially diagnostic purposes.

Conclusions

CHEAP-EPSI allows the rapid mapping of multiple downfield metabolites such as N-acetyl-aspartate (DF7.82) and DF8.18, and offers new possibilities for the study of metabolism in healthy and diseased brain.