Metabolic clearance rate modeling: A translational approach to quantifying cerebral metabolism using hyperpolarized pyruvate.

Hyperpolarized carbon-13 MRI is a promising technique for in vivo metabolic interrogation of alterations between health and disease. This study introduces a model-free formalism for quantifying the metabolic information in hyperpolarized imaging. This study investigated a novel model-free perfusion and metabolic clearance rate (MCR) model in pre-clinical stroke and in the healthy human brain. Simulations showed that the proposed model was robust to perturbations in T1, transmit B1, and kPL. A significant difference in ipsilateral vs contralateral pyruvate derived cerebral blood flow (CBF) was detected in rats (140 {+/-} 2 vs 89 {+/-} 6 mL/100g/min, p < 0.01, respectively) and pigs (139 {+/-} 12 vs 95 {+/-} 5 mL/100g/min, p = 0.04, respectively), along with an increase in fractional metabolism (26 {+/-} 5 vs 4 {+/-} 2 %, p < 0.01, respectively) in the rodent brain. In addition, a significant increase in ipsilateral vs contralateral MCR (0.034 {+/-} 0.007 vs 0.017 {+/-} 0.02 s-1, p = 0.03, respectively) and a decrease in mean transit time (MTT) (31 {+/-} 8 vs 60 {+/-} 2, p = 0.04, respectively) was observed in the porcine brain. In conclusion, MCR mapping is a simple and robust approach to the post-processing of hyperpolarized magnetic resonance imaging.