Ultra sensitive MRI

researchers have developed a technique for Magnetic Resonance Imaging (MRI) that can detect molecules at 10,000 times lower concentrations than conventional MRI techniques.

The US Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California at Berkeley developed the method. Called HYPER-CEST, for hyperpolarised xenon chemical exchange saturation transfer, it holds great promise for molecular imaging, in which the spatial distribution of specific molecules is detected within an organism. Ultimately, HYPER-CEST could become a valuable tool for medical diagnosis, including the early detection of cancer.

In the technique xenon atoms that have been hyperpolarised with laser light to enhance their MRI signal are incorporated into a biosensor and linked to specific protein or ligand targets. These hyperpolarised xenon biosensors generate highly selective contrast at sites where they are bound, dramatically boosting the strength of the MRI signal and resulting in spatial images of the chosen molecular or cellular target.

Other molecular MRI contrast agents provide small changes in big MRI signals, making the changes difficult to detect when the amount of contrast agent binding is small. The HYPER-CEST contrast agent provides a big change in the xenon MRI signal, which means it is much easier to detect even though the xenon MRI signals are rather small.

In addition to its intrinsically higher contrast, another advantage with the HYPER-CEST technique is that its effects can be 'multiplexed', meaning that the polarised xenon biosensors can be targeted to detect different proteins at the same time in a single sample. This capability, which is not shared by most conventional molecular MRI contrast agents, opens up a number of possibilities for future diagnostics.

This would mean, for example, that multiple virtual biopsies on a single tissue sample could be performed, using different biosensors to screen for each potential form of cancer.

Another advantage is that there is no xenon naturally present in body, so scientists do not have to distinguish a small change in an MRI signal with a high background like other MRI contrast agents.

The Berkeley HYPER-CEST technique not only provides a bright image with high contrast, but also speeds up the image acquisition process by more than 3,000-fold relative to directly detecting the xenon biosensor.