FIGURE 2.

In vivo and in vitro metabolism of hyperpolarized [1-¹³C]acetate and [1-¹³C]propionate (A and B). In vivo NMR spectra (bold gray lines) of myocardium are recorded with a 90° flip angle pulse after injecting 175-μl hyperpolarized substrate. Spectra of reactions conducted with 2 mm hyperpolarized substrate and isolated AceCS and CrAT in vitro according to the scheme in C are shown as thin black lines. Identity of in vivo metabolite signals with acyl-CoA and acyl-carnitine adducts is validated by spectral frequencies in vivo for both substrates.