Figure 4.

Distinguishing Identical Nanoparticles with Phase-Encoded Hyperpolarization. (a) Schematic representation of functionalized nanoparticles targeting tumors both actively and passively. Active targeting in the vasculature relies on specific interactions between ligands on the nanoparticle surface and receptors expressed on the surface of, for instance, endothelial cells adjacent to tumors. Passive targeting is nonspecific to nanoparticle functionalization and can occur via the enhanced permeability and retention effect in regions of leaky vasculature at tumor sites. Potentially, phase-encoded hyperpolarization can distinguish between these two regimes. (b) Direction of hyperpolarized ¹³C magnetization versus the pump frequency. (c) Phantom schematic showing two 2 μm diamond samples (yellow and green) in a tube of water (blue). Teflon walls of the tubes containing diamond are also shown (pink). The sample shown in yellow was hyperpolarized at 80.87 GHz (f = ω_e − ω_n) for 20 minutes before transfer to the imager. The diamond sample shown in green was subsequently hyperpolarized at 80.94 GHz (f = ω_e + ω_n) for 4 minutes before transfer to the hyperpolarizer. (d) Imaging of the phantom described in (c). Overlaid ¹³C magnitude (left) and phase (right) colormaps are shown with masks applied to regions with less than 8 times the root mean square value of the background signal. Small black spots in gray-scale ¹H magnitude image are bubbles adhered to surfaces in the phantom. Scale bar is 3 mm in length.