Warming up for Magnetic Resonance Imaging

In the technique known as "temperature-controlled molecular depolarization gates," an atom of hyperpolarized xenon from the pool at left enters a cryptophane cage, center, which is part of a biosensor attached to a specific molecular target. A burst of tuned rf energy depolarizes the xenon, which is then ejected back into the pool by chemical exchange with the next incoming xenon atom. Depolarized xenon (right) stands out in the larger hyperpolarized pool and thus enhances the contrast of the nearby target molecule. At top, a phantom half-filled with agarose beads, to which biosensors are attached, shows how image contrast can be enhanced and controlled by temperature: a 6-K temperature increase quickly depolarizes the xenon in the vicinity of the target beads.