Probing cardiac metabolism by hyperpolarized 13C MR using an exclusively endogenous substrate mixture and photo-induced nonpersistent radicals

To probe the cardiac metabolism of carbohydrates and short chain fatty acids simultaneously in vivo following the injection of a hyperpolarized javax.xml.bind.JAXBElement@47d46327 C-labeled substrate mixture prepared using photo-induced nonpersistent radicals. Droplets of mixed [1- javax.xml.bind.JAXBElement@f125d2a C]pyruvic and [1- javax.xml.bind.JAXBElement@3a61d95c C]butyric acids were frozen into glassy beads in liquid nitrogen. Ethanol addition was investigated as a means to increase the polarization level. The beads were irradiated with ultraviolet light and the radical concentration was measured by ESR spectroscopy. Following dynamic nuclear polarization in a 7T polarizer, the beads were dissolved, and the radical-free hyperpolarized solution was rapidly transferred into an injection pump located inside a 9.4T scanner. The hyperpolarized solution was injected in healthy rats to measure cardiac metabolism in vivo. Ultraviolet irradiation created nonpersistent radicals in a mixture containing javax.xml.bind.JAXBElement@2f4af5f8 C-labeled pyruvic and butyric acids, and enabled the hyperpolarization of both substrates by dynamic nuclear polarization. Ethanol addition increased the radical concentration from 16 to 26 mM. Liquid-state javax.xml.bind.JAXBElement@4b63666d C polarization was 3% inside the pump at the time of injection, and increased to 5% by addition of ethanol to the substrate mixture prior to ultraviolet irradiation. In the rat heart, the in vivo javax.xml.bind.JAXBElement@56058926 C signals from lactate, alanine, bicarbonate, and acetylcarnitine were detected following the metabolism of the injected substrate mixture. Copolarization of two different javax.xml.bind.JAXBElement@629a1183 C-labeled substrates and the detection of their myocardial metabolism in vivo was achieved without using persistent radicals. The absence of radicals in the solution containing the hyperpolarized javax.xml.bind.JAXBElement@1a07cd1d C-substrates may simplify the translation to clinical use, as no radical filtration is required prior to injection.