Figure 2.

Dynamic nuclear hyperpolarisation theory: in a magnetic field, nuclei behave like bar magnets aligning with or against the applied field. The tiny difference in these two populations at thermal equilibrium produces a small MR signal (polarisation of 0.0005%). DNP magnifies the difference in these two populations and hence the MR signal >10 000 fold. This is achieved by mixing the ¹³C containing nuclei with a source of free electrons (a radical) at very low temperature (~1 Kelvin). At these low temperatures, free radical polarisation reaches 100%, and microwaves are used to transfer this electron polarisation to the nuclear spins. Dissolution is rapid to ensure the signal is maintained long enough to allow injection into the patient and in vivo metabolism to be observed.