Phantoms to Placentas: Development of an MR Method for pO2 Quantification

Kelsey Meinerz

 Insufficient oxygen (pO2) content in the body is marker of disease or disorder. A noninvasive method to map in vivo tissue oxygen tension, pO2, would aid in diagnosis and treatment planning. Magnetic resonance (MR) holds promise for mapping tissue pO2 because, in principle, the measured 1H longitudinal relaxation rate constant of tissue water, R1, is directly proportional to tissue pO2. Herein, we use relaxation tissue mimics and NMR spectroscopy to: (i) characterize/quantify the effects of physiologic confounds to the R1-based pO2 measurement (temperature, pH, and macromolecule concentration) and (ii) directly quantify the R1 vs pO2 relationship. Our data show that temperature, pH, and macromolecular concentration changes affect the R1 measurement and must therefore be either mitigated in vivo or, incorporated into a model that accounts for such effects.

The placenta is arguably the most important organ in the body, responsible for maintaining dynamic fetal homeostasis, with dysfunction of its numerous duties potentially having lifelong effects upon the health of the fetus and lasting effects upon the health of the mother. Additionally, the placenta is poorly understood and there is a severe lack of biomarkers and characterization of placental insufficiency and failure. Murine models allow for real-time monitoring of normal and pathologic placentas on relatively shorter timescales than human studies. Ongoing studies to investigate MR techniques for non-invasive biomarkers of placental function will be discussed.