Fig. 1.

(a) The pulsed gradient double spin echo sequence used for diffusion weighting of hyperpolarized ¹³C metabolites. Diffusion gradients (G) are placed symmetrically around the adiabatic 180° refocusing pulses, with a duration δ and a separation Δ. A crusher gradient after the readout ensures no transverse magnetization carries-over to subsequent scans. The excitation flip angle θ was either 15° or 30°. (b) The diffusion gradient array used to measure the extra- and intracellular weighted diffusion coefficients of hyperpolarized ¹³C metabolites. Every third scan (small boxes) was used to normalize adjacent diffusion weighted scans (large boxes), thereby removing the effects of T₁ relaxation and metabolism on the signal change from that due to the diffusion weighting. (c) The gradient array used to measure the change in the total (small boxes) and the intracellular weighted (large boxes) hyperpolarized ¹³C metabolite pools over time. See methods for a more detailed description of these two acquisition schemas.