A T_2ex MRI Dy-based contrast agent for direct pH imaging using a ratiometric approach

Area of Science:

• Biomedical Imaging
• Chemical Biology
• Materials Science

Background:

• pH is a critical physiological parameter influencing biological processes.
• Magnetic Resonance Imaging (MRI) offers potential for non-invasive acidity mapping in tissues.
• Developing targeted MR probes is essential for advanced MRI applications.

Purpose of the Study:

• To develop and characterize novel Dysprosium (Dy)-based MR probes for pH sensing.
• To investigate the pH-dependent relaxivity properties of these Dy-based probes.
• To establish a method for direct and concentration-independent pH mapping using MRI.

Main Methods:

• Synthesis and characterization of a series of Dy-based MR contrast agents.
• Measurement of longitudinal (r1) and exchange relaxivity (r2ex) at varying pH levels (5.5-8.0).
• Evaluation of the r2ex/r1 ratio for pH-dependent signal changes.

Main Results:

• The Dy-based probes exhibited pH-sensitive T2ex relaxation.
• r2ex relaxivity increased significantly with pH from 5.5 to 8.0.
• r1 relaxivity remained largely unaffected by pH changes.
• The r2ex/r1 ratio provided a direct measure of pH, independent of probe concentration.

Conclusions:

• Dy-based MR probes can be designed to report on pH through proton-catalyzed exchange mechanisms.
• The r2ex/r1 ratio offers a robust metric for accurate, concentration-independent pH mapping in physiologically relevant ranges.
• These findings pave the way for advanced MRI-based diagnostics of tissue acidity.