Quantitative pulsed CEST-MRI at a clinical 3T MRI system.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biomedical Engineering
• Quantitative Imaging

Background:

• Chemical Exchange Saturation Transfer (CEST) MRI is a promising technique for assessing biochemical environments.
• Accurate quantification of CEST parameters like chemical exchange rate and proton concentration is crucial for clinical translation.
• Existing CEST quantification methods require validation on clinical scanners.

Purpose of the Study:

• To quantify CEST parameters, including chemical exchange rate and fractional concentration of exchanging protons, using a clinical 3T MRI scanner.
• To compare two CEST quantification approaches: the AREX metric and the AREX-based Ω-plot method.
• To evaluate two pulsed radiofrequency irradiation schemes: Gaussian-shaped and spin-lock pulses.

Main Methods:

• Numerical simulations using the Bloch-McConnell equations with a two-pool exchange model.
• In vitro MRI experiments on a clinical 3T scanner using phantoms with creatine solutions at varying pH and concentrations.
• Application and comparison of the AREX metric and the Ω-plot method with Gaussian and spin-lock pulse sequences.

Main Results:

• The validity of both the AREX approach and the Ω-plot method for quantitative CEST parameter determination was confirmed.
• The Ω-plot method, particularly when combined with spin-lock preparation, yielded especially promising results.
• CEST parameters could be reliably determined in phantom studies.

Conclusions:

• Pulsed CEST MRI at 3T enables quantification of exchange rate constants and concentrations of protons exchanging with water.
• This technique holds potential for future in vivo assessment of biochemical substance exchange rates and concentrations in human tissues.
• The Ω-plot method with spin-lock preparation is a robust approach for quantitative CEST imaging.