In vivo time course of 13C hyperpolarized TFPP signal decay after intracardiac injection of 1mL 13 mM TFPP in a LDLR mouse corresponding to Fig. 3D. Each spectrum (temporal resolution is 1.78 s) is an average of 12 individual scans acquired using 1H/13C double resonance volume coil (Doty Scientific, South Carolina, USA) at 4.7 T. Acquisition parameters: excitation pulse = 10°, spectral width=4,000 Hz, acquisition time=128 ms, repetition time = 148 ms. MR scan # 1 (first) and #300 (last) were recorded 15 s and 60 s after injection respectively.