Most clinically used magnetic resonance imaging (MRI) contrast agents have been developed and used to enhance the signal from water protons in close proximity. However, these contrast agents (e.g. gadolinium (Gd) chelates) being active all the time (always �ON�) can only distinguish diseased from healthy tissue by degree of accumulation, which limits sensitivity of disease detection. In order to maximize signal from the target and minimize signal from the background, we designed activatable MRI probes that are only active under disease-related conditions. Our strategy involves suppressing the MRI signal of Gd-based contrast agents by encapsulating them in bioresponsive and hydrophobic polymeric nanoparticles. Encapsulation limits water availability and hence their relaxation enhancement capabilities. Polymer degradation, in response to biochemical cues of disease, activates the silenced MRI probes by releasing them from the particle, allowing greater interaction with water protons and faster relaxation.

Turning MRI contrast ON through disease-triggered release from polymeric particles

245th National Meeting (2013)

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