Acidity in the tumor microenvironment (TME) is related to invasion, metastasis, and chemotherapeutic resistance, all of which are contributors to poor prognoses in cancer patients. In this thesis, we propose the application of Cerenkov radiation as a tool for imaging pH in vivo through the measurement of Selective Bandwidth Quenching (SBQ) and Cerenkov Radiation Energy Transfer (CRET) in triple negative human breast cancer models MDA-MB-231 and 4175-Luc+. To test the hypothesis that SBQ and CRET signals could provide measurements of TME pH in vivo, a Cerenkov-active molecule, NFbD, was conjugated and chelated with 68Ga. Cerenkov imaging was performed with NFbD-Ga in vitro to construct pH titration curves, later used to interpolate in vivo Cerenkov pH values. In vivo Cerenkov imaging was performed on athymic nude mice bearing 4175-Luc+ triple negative breast cancer xenografts after intratumoral injections of NFbD-Ga (40 μCi). CRET values obtained from in vivo Cerenkov imaging were used to estimate TME pH values, which were validated by 31P Magnetic Resonance Spectroscopy (31P MRS) following i.p. injection of 3-APP. Tissue scattering, and absorption effects were evaluated in vitro with tissue phantoms. NFbD maintained its pH-sensitivity after conjugation (pKa= 7.8, λex= 599 nm, λem= 669 nm at pH 9). SBQ and CRET were observed in vitro inter-and intramolecularly, at 600 nm and 700 nm, respectively. SBQ and CRET were also observed in vivo. CRET measurements following intratumoral injections of NFbD-Ga yielded a tumor pHCerenkov= 6.90 ± 0.16, 31P-MRS on the same tumors yielded a pHMRS= 6.92 ± 0.04. Chicken tissue phantoms provided insight on tissue attenuation effects, showing that 1 mm of tissue can attenuate 64% of the Cerenkov signal, in the absence of naphthofluorescein and further attenuation to 17% is achieved with the addition of naphthofluorescein. The synthesis and development of this Cerenkov-active, pH sensitive probe for the determination of TME pH provided detectable CRET signals in vivo, allowing Cerenkov to be used as a potential technique for non-invasive pH imaging.