In vivo pH mapping of injured lungs using hyperpolarized [1-13C]pyruvate

PURPOSE To optimize the production of hyperpolarized 13 C-bicarbonate from the decarboxylation of hyperpolarized [1-13 C]pyruvate and use it to image pH in the lungs and heart of rats with acute lung injury. METHODS Two forms of catalysis are compared calorimetrically to maximize the rate of decarboxylation and rapidly produce hyperpolarized bicarbonate from pyruvate while minimizing signal loss. Rats are injured using an acute lung injury model combining ventilator-induced lung injury and acid aspiration. Carbon images are obtained from both healthy (n = 4) and injured (n = 4) rats using a slice-selective chemical shift imaging sequence with low flip angle. pH is calculated from the relative HCO3- and CO2 signals using the Henderson-Hasselbalch equation. RESULTS It is demonstrated that base catalysis is more effective than metal-ion catalysis for this decarboxylation reaction. Bicarbonate polarizations up to 17.2% are achieved using the base-catalyzed reaction. A mean pH difference between lung and heart of 0.14 pH units is measured in the acute lung injury model. A significant pH difference between injured and uninjured lungs is also observed. CONCLUSION It is demonstrated that hyperpolarized 13 C-bicarbonate can be efficiently produced from the base-catalyzed decarboxylation of pyruvate. This method is used to obtain the first regional pH image of the lungs and heart of an animal. Magn Reson Med 78:1121-1130, 2017. © 2016 International Society for Magnetic Resonance in Medicine.