Molecular imaging with endogenous substances

Dynamic nuclear polarization has enabled hyperpolarization of nuclei such as C-13 and N-15 in endogenous substances. The resulting high nuclear polarization makes it possible to perform subsecond C-13 MRI. By using the dynamic nuclear polarization hyperpolarization technique, 10% polarization was obtained in an aqueous solution of 100 mM C-13-labeled urea, ready for injection. The in vivo T, relaxation time of C-13 in the urea solution was determined to 20 +/- 2 s. Due to the long relaxation time, it is possible to use the hyperpolarized substance for medical imaging. A series of high-resolution (approximate to1-mm) magnetic resonance images were acquired, each with a scan time of 240 ms, 0-5 s after an i.v. injection of the hyperpolarized aqueous [C-13]urea solution in a rat. The results show that it is possible to perform C-13 angiography with a signal-to-noise ratio of approximate to275 in approximate to0.25 s. Perfusion studies with endogenous substances may allow higher spatial and/or temporal resolution than is possible with current proton imaging techniques