A method for accurate pH mapping with chemical exchange saturation transfer (CEST) MRI

Area of Science:

• Biomedical Imaging
• Magnetic Resonance Imaging (MRI)
• Chemical Exchange Saturation Transfer (CEST)

Background:

• Chemical exchange saturation transfer (CEST) MRI is promising for pH imaging but faces challenges from confounding factors.
• Conventional ratiometric CEST (RCEST) MRI is limited to agents with multiple exchangeable groups.
• RF power-based ratiometric CEST (PRCEST) imaging was proposed but remains dependent on parameters like relaxation time and chemical shift due to RF saturation.

Purpose of the Study:

• To develop and validate a novel RF power-based ratiometric analysis of RF spillover effect-corrected inverse CEST asymmetry (PRICEST) for enhanced pH measurement.
• To improve the accuracy and reduce confounding factors in CEST-based pH imaging.
• To achieve concentration-independent pH mapping using MRI.

Main Methods:

• Numerical simulations to verify the proposed PRICEST method.
• Experimental validation using an in vitro phantom.
• Comparison of pH determination accuracy between PRCEST and PRICEST imaging against electrode measurements.

Main Results:

• PRICEST imaging demonstrated significantly higher accuracy in pH determination compared to PRCEST imaging (0.04 ± 0.03 vs. 0.12 ± 0.13 pH unit difference).
• The exchange rate showed a pH-dependent, base-catalyzed relationship, independent of creatine concentration.
• The labile proton ratio linearly scaled with creatine concentration, indicating concentration dependence.

Conclusions:

• PRICEST MRI provides a more accurate and robust method for pH imaging compared to PRCEST.
• The developed PRICEST method offers concentration-independent pH mapping, overcoming limitations of previous CEST techniques.
• This advancement significantly augments quantitative CEST MRI for precise pH mapping in biomedical applications.