Cerenkov-Specific Contrast Agents for Detection of pH In Vivo

We report the design, testing, and in vivo application of pH-sensitive contrast agents designed specifically for Cerenkov imaging. Radio-isotopes used for PET emit photons via Cerenkov radiation. The multispectral emission of Cerenkov radiation allows for selective bandwidth quenching, in which a band of photons is quenched by absorption by a functional dye. Under acidic conditions, 18F-labeled derivatives emit the full spectrum of Cerenkov light. Under basic conditions, the dyes change color and a wavelength-dependent quenching of Cerenkov emission is observed. Methods: Mono-and di-18F-labeled derivatives of phenolsulfonphthalein (phenol red) and meta-cresolsulfonphthalein (cresol purple) were synthe-sized by electrophilic fluorination. Cerenkov emission was measured at different wavelengths as a function of pH in vitro. Intramolecular response was measured in fluorinated probes and intermolecular quenching by mixing phenolphthalein with 18F-FDG. Monofluorocresol purple (MFCP