Hyperpolarized 13C Pyruvate MRI for In Vivo Metabolic Imaging

1-¹³C pyruvic acid (30 μL), containing 15 mM OXO63 and 2.5 mM gadolinium chelate ProHance (Bracco Diagnostics, Milano, Italy), was hyperpolarized at 3.35T and 1.4K using the Hypersense DNP polarizer (Oxford Instruments, Abingdon, UK) according to the manufacturer's instructions. After 60-90 min, the hyperpolarized sample was rapidly dissolved in 4.5 mL of a superheated alkaline buffer that consisted of 50 mM Tris(hydroxymethyl)aminomethane, 75 mM NaOH, and 100 mg/L ethylenediaminetetraacetic acid. The hyperpolarized 1-¹³C pyruvate solution (96 mM) was intravenously injected through a catheter placed in the tail vein of the mouse (12 μL/g body weight). Hyperpolarized ¹³C MRI studies were performed on a 3T scanner (MR Solutions, Guildford, UK) using a home-built ¹³C solenoid leg coil. After the rapid injection of hyperpolarized 1-¹³C pyruvate, spectra were acquired every second for 240 seconds using a single pulse sequence. Data were analyzed in a model free approach using the lactate/pyruvate ratio, calculated from the areas under the curves of the 1-¹³C lactate peak and the 1-¹³C pyruvate peak [15 (link)].