Quantified pH detection with hyperpolarized 13C-Bicarbonate

Abstract

Event Abstract Back to Event Quantified pH detection with hyperpolarized 13C-Bicarbonate Johannes Scholz1, 2*, Martin A. Janich2, Angela M. Otto1, Franz Schilling1, Axel Haase1 and Marion I. Menzel2 1 Technische Universität München, Physics, Germany 2 GE Global Research Center, Germany Background and aim. pH plays a crucial role in several diseases, such as cancer, hypoxia, inflammation etc., and it is therefore desirable to detect pH in vivo. Ideally, the detection should be noninvasive and spatially localized. Despite the medical impact, a clinical tool for pH mapping is not yet available. Different approaches in pH detection were made in NMR e.g. with 31P and CEST.[1] A promising candidate to achieve pH mapping in vivo is 13C metabolic magnetic resonance (13CMMR). This technique enhances the signal of 13C-labeled bicarbonate using dissolution dynamic nuclear polarization (DNP) and then probes the pH by measuring the ratio of 13C bicarbonate and 113CO2 [2]. Methods. Hyperpolarization is achieved using dissolution DNP Hypersense polarizer. The MR acquisition is performed on pH phantoms and mammary carcinoma cell spheroids (MCF-7) using a 3T MR system (GE Signa HDx) and a 14T Bruker spectrometer. Relaxation time analysis was additionally performed with a 1T Bruker Minispec mq40 NMR analyzer. Results. In vitro tests using hyperpolarized sodium bicarbonate and phosphate buffers and pH-phantoms showed good correlation between the derived pH value and the reference pH (+/- 0.03) obtained with a pH electrode. An analysis of the signal dynamics revealed that the correct bicarbonate to CO2 signal ratio is established after 40 seconds without adding carbonic anhydrases. In tumor cell systems (MCF-7 spheroids), T1 times of bicarbonate and CO2 were determined for different field strengths (1T, 3T, 14T) and different pH values in the biological range (6-8). Comparison of the values achieved with and without tumor spheroids show the impact of the spheroids on the hyperpolarized signal. Acknowledgements This research was partly funded by BMBF grant 01EZ1114A.