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

Area of Science:

• Magnetic Resonance Imaging
• Biomedical Engineering
• Medical Physics

Background:

• Chemical Exchange Saturation Transfer (CEST) MRI is valuable for clinical applications, requiring fast imaging, high signal-to-noise ratio (SNR), and 3D coverage.
• Traditional CEST sequences necessitate dense Z-spectrum sampling, leading to extended scan durations, which is a limitation for clinical implementation.

Purpose of the Study:

• To develop and validate a fast 3D Chemical Exchange Saturation Transfer (CEST) imaging sequence for clinical use at 3 Tesla (3T).
• To achieve highly resolved Z-spectroscopy with 3D coverage without significantly increasing scan time, optimizing contrast and SNR.

Main Methods:

• A 3D snapshot gradient echo (GRE) readout was combined with optimized CEST presaturation, spectral sampling, and postprocessing techniques (including B0 correction and denoising).
• Low-power pulsed saturation (80 pulses, 20 ms duration, 0.6 μT B1) was applied across 54 frequency offsets.
• The sequence was tested for reproducibility in healthy volunteers and feasibility in a tumor patient.

Main Results:

• The optimized 3D snapshot CEST sequence acquired a 180 × 220 × 54 mm field of view in 7 seconds per offset.
• Spectrally selective CEST effects at +3.5 and -3.5 ppm were accurately quantified using multi-Lorentzian fitting.
• High reproducibility was observed, with intersubject coefficient of variation below 10% for CEST contrasts. Amide and nuclear Overhauser effect CEST effects showed correlations in tumor and necrosis consistent with prior ultra-high field studies.

Conclusions:

• A sophisticated and feasible 3D CEST MRI tool has been developed and validated for potential clinical implementation.
• The optimized sequence enables rapid, high-resolution Z-spectroscopy with 3D coverage, overcoming previous time constraints of CEST imaging.