3D gradient echo snapshot CEST MRI with low power saturation for human studies at 3T.

ABSTRACT:

Purpose

For clinical implementation, a chemical exchange saturation transfer (CEST) imaging sequence must be fast, with high signal-to-noise ratio (SNR), 3D coverage, and produce robust contrast. However, spectrally selective CEST contrast requires dense sampling of the Z-spectrum, which increases scan duration. This article proposes a compromise: using a 3D snapshot gradient echo (GRE) readout with optimized CEST presaturation, sampling, and postprocessing, highly resolved Z-spectroscopy at 3T is made possible with 3D coverage at almost no extra time cost.

Methods

A 3D snapshot CEST sequence was optimized for low-power CEST MRI at 3T. Pulsed saturation was optimized for saturation power and saturation duration. Spectral sampling and postprocessing (B₀ correction, denoising) was optimized for spectrally selective Lorentzian CEST effect extraction. Reproducibility was demonstrated in 3 healthy volunteers and feasibility was shown in 1 tumor patient.

Results

Low-power saturation was achieved by a train of 80 pulses of duration t_p  = 20 ms (total saturation time t_sat = 3.2 seconds at 50% duty cycle) with B₁ = 0.6 ?T at 54 irradiation frequency offsets. With the 3D snapshot CEST sequence, a 180 × 220 × 54 mm field of view was acquired in 7 seconds per offset. Spectrally selective CEST effects at +3.5 and -3.5 ppm were quantified using multi-Lorentzian fitting. Reproducibility was high with an intersubject coefficient of variation below 10% in CEST contrasts. Amide and nuclear overhauser effect CEST effects showed similar correlations in tumor and necrosis as show in previous ultra-high field work.

Conclusion

A sophisticated CEST tool ready for clinical application was developed and tested for feasibility.

SUBMITTER: Deshmane A 

PROVIDER: S-EPMC6718050 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature