Rapid and quantitative CEST-MRI sequence using water presaturation.

Area of Science:

• Biomedical Engineering
• Magnetic Resonance Imaging
• Metabolic Imaging

Background:

• Chemical Exchange Saturation Transfer (CEST) MRI holds promise for in vivo metabolic imaging.
• Current CEST MRI techniques are limited by long scan times and inaccurate quantification due to signal contaminations.
• Accelerating CEST imaging and improving quantification are crucial for its clinical and preclinical applications.

Purpose of the Study:

• To develop a novel CEST MRI method to suppress signal contaminations between different frequencies.
• To shorten the repetition time (TR) for faster CEST imaging.
• To enable accurate quantification of metabolic parameters in CEST MRI.

Main Methods:

• A novel Water-Presaturation CEST (WPS CEST) sequence was developed, incorporating a water-presaturation module at the start of each TR.
• This module rapidly diminishes residual signals from prior TRs, allowing magnetization to reset to zero.
• WPS CEST was validated using simulations, a creatine phantom, and human brain scans at 3T.

Main Results:

• WPS CEST enabled accurate estimation of the exchange rate (ksw) with shorter delay times (Td) and saturation times (Ts) compared to conventional CEST.
• Simulations confirmed consistent spin-lock relaxation (R1ρ) values with WPS CEST across varied Td and Ts.
• Human scans showed that WPS CEST yielded identical R1ρ values for different Td/Ts settings, unlike conventional sequences which showed significant differences.

Conclusions:

• WPS CEST provides accurate quantification within a shorter TR compared to conventional CEST sequences.
• This method facilitates rapid quantitative CEST imaging.
• WPS CEST has the potential to significantly advance in vivo metabolic imaging applications.