Dendritic PARACEST contrast agents for magnetic resonance imaging

Area of Science:

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

Background:

• Chemical exchange-dependent saturation transfer (CEST) MRI contrast agents, particularly Ytterbium(III)DOTAM complexes, show promise for pH mapping.
• Developing advanced MRI contrast agents with enhanced sensitivity and tunable properties is crucial for improved diagnostic capabilities.

Purpose of the Study:

• To synthesize Ytterbium(III)DOTAM-functionalized poly(propylene imine) dendrimers as novel PARACEST MRI agents.
• To evaluate the applicability of these dendritic agents for pH mapping using both high-field NMR and clinical MRI scanners.
• To investigate the impact of dendrimer generation on the sensitivity and pH-responsive behavior of the MRI contrast agents.

Main Methods:

• Synthesis of Ytterbium(III)DOTAM-functionalized poly(propylene imine) dendrimers.
• Evaluation of pH mapping capabilities on a 7 T NMR spectrometer and a 3 T clinical MRI scanner.
• Comparison of detection limits and pH dependence with a mononuclear reference complex.

Main Results:

• The synthesized dendritic PARACEST agents demonstrated effective pH mapping capabilities.
• Lower detectable concentrations were observed for dendritic agents (4x and 16x lower for 1st and 3rd generation, respectively) compared to a mononuclear complex.
• The pH dependence of the CEST effect shifted towards lower pH values with increasing dendrimer generation, enabling fine-tuning of the responsive pH region.

Conclusions:

• Yb(III)DOTAM-functionalized dendrimers represent a promising class of PARACEST MRI agents for pH mapping.
• Varying the dendritic framework allows for fine-tuning the pH sensitivity, offering potential for targeted diagnostic applications.
• These agents exhibit improved sensitivity compared to mononuclear counterparts, enhancing their utility in MRI-based pH measurements.