Fractional Perfusion: A Simple Semi-Parametric Measure for Hyperpolarized 13C MR

Hyperpolarized
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C magnetic resonance imaging is a promising tool for in-vivo metabolic interrogation of disease states and treatment efficacy assessment. The method is currently limited by the lack of good quantitative measures, particularly in humans where large variations in transport kinetics have been reported. Here, we introduce a novel model-free method for quantification of metabolic information in dynamic hyperpolarized imaging data. Fractional perfusion is defined as the metabolic conversion corrected for substrate delivery, and is achieved by scaling the area under the curve of the hyperpolarized signals with the tissue perfusion. Rats subjected to unilateral ischemia reperfusion injury (IRI) were used. The proposed fractional perfusion was investigated using hyperpolarized [1-
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C]pyruvate and α-trideuteromethyl[15N]glutamine, and then compared with 1H dynamic contrast enhanced perfusion imaging. We demonstrate that hyperpolarized
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C-metabolites can be used to quantify the energy demand by mapping both the injected biomarker perfusion and the metabolic conversion such that the pyruvate concentration curve can be a surrogate marker for perfusion in cases where other perfusion assessment is not directly obtainable. In the case of IRI, the obtained perfusion parameters allowed the fractional perfusion approach to differentiate an alteration in metabolic conversion by accounting for differences in pyruvate delivery.