Quantification of In Vivo Saturation Kinetics of Co-Polarized [2-13C]Pyruvate and [1,4-13C2]Fumarate in Rat Liver Using Dynamic 3D-Spiral CSI with Alternate Spectral Band Excitation

Dynamic metabolic imaging of co-polarized ¹³C-labeled pyruvate (Pyr) and fumarate (Fum) has shown great potential in characterizing multiple in vivo metabolic activities as demonstrated in recent animal models.^1,2 Although in these studies, both the injected substrates and downstream metabolic product can be acquired over time at relatively high spatial resolution, robust quantification and metabolic modelling remains an active area of investigation. Also, the enzyme saturation effects that are routinely seen with commonly used doses of hyperpolarized substrates are not correctly captured using approaches such as metabolite ratios, time-to-peak of metabolic products, single exchange rate constants and by constant small-flip-angle excitation. Therefore, the goal of this study is to measure the saturation kinetics of various involved enzymatic processes using effective 90° excitation of the products at clinical field strengths. This work is an extension of our method developed for dynamic metabolic imaging of co-polarized mixture of [2-¹³C]Pyr and [1,4-¹³C₂]Fum.²