Snapshot-CEST: Optimizing spiral-centric-reordered gradient echo acquisition for fast and robust 3D CEST MRI at 9.4 T

Area of Science:

• Magnetic Resonance Imaging
• Biomedical Engineering
• Spectroscopy

Background:

• Gradient echo (GRE) acquisition is a reliable method for chemical exchange saturation transfer (CEST) imaging, particularly at ultrahigh fields (UHF).
• Developing a rapid, volumetric CEST imaging technique is crucial for advancing UHF MRI applications.

Purpose of the Study:

• To develop and optimize a snapshot-CEST approach using GRE readout for fast and robust volumetric imaging at UHF.
• To investigate transient GRE signal characteristics and point spread functions for parameter optimization.

Main Methods:

• Simulated transient GRE signals to determine optimal sequence parameters and k-space acquisition limits.
• Analyzed point spread functions to assess k-space filtering and evaluate reordering schemes for SNR and relaxation dependence.
• Validated simulation findings with MRI measurements in healthy subjects at 9.4 T.

Main Results:

• Identified minimal repetition time (TR) as beneficial for snapshot-GRE readout, enabling acquisition of up to 562 k-space lines with TR = 4 ms and optimal flip angle.
• Demonstrated improved image quality using a rectangular spiral reordering scheme for k-space acquisition.
• Achieved excellent image quality for amide, nuclear Overhauser enhancement (NOE), and guanidyl CEST detection in human brain imaging.

Conclusions:

• The proposed snapshot-CEST sequence provides a fast and robust volumetric CEST imaging method at UHF.
• This technique is suitable for imaging known and novel exchange-weighted contrasts, advancing UHF MRI capabilities.