A T2ex MRI Dy-based contrast agent for direct pH imaging using a ratiometric approach†
pH is a critical parameter that has found unique application in magnetic resonance imaging (MRI) mapping acidity in tissues. This study reports a series of Dy-based MR probes that show innovative T2ex features, governed by proton catalyzed events. With an increase of pH from 5.5 to 8.0, the r2ex relaxivity increased dramatically, while the r1 relaxivity remained unchanged. The resulting r2ex/r1 allowed for concentration-independent and direct mapping of physiologically relevant pH ranges.