The Jasanoff lab has been working on improving MRI for a while, using such cool terms as ‘molecular fMRI’. They are really attempting to push the technology by designing molecular agents to help with the imaging. For instance, they have sensors that can respond to kinase activity or to amines like dopamine.
MRI works by sending powerful magnetic fields at a tissue such as the brain, and measuring the time it takes for molecules in this tissue to ‘relax’ to its previous state. In order to detect molecules such as dopamine, they modified magnetized proteins to bind specifically to those molecules. The relaxation occurs in a specific ‘communication channel’ called T1, as opposed to the T2 ‘channel’ that is used to detect changes in blood flow for fMRI. Since the proteins have different relaxation times depending on whether they are bound or unbound, MRI can be used to measure when there is more or less dopamine in the tissue.
Although I’ve been hearing about these sensors for a few years (the dopamine one came out in a paper four years ago, the kinase one six), I hadn’t seen a paper that really used them until now. The Jasanoff lab has now shown that if you stimulate the nerves that release dopamine, their sensors can indeed detect it. Problem is: they have to inject the sensor directly into the brain. This means, first of all, that they probably aren’t able to measure dopamine activity across the whole brain using this technique. I’m not sure, but I imagine they can image the level of the sensor that is at any given point? But that level is going to affect the signal that they get. Further, someone suggested that because the sensor is large and polar, it’s not going to cross the blood-brain barrier so it’s not a plausible way to image dopamine release in humans. The field will just have to stick with PET imaging for now.
Finally, a personal complaint: they kept claiming they were measuring ‘phasic’ activity of the dopamine (ie, transient). Although they were stimulating the dopamine neurons phasically, I didn’t see any control to measure the tonic level of dopamine! I’m not sure I would have allowed them to get away with that if I were a reviewer. Still, it’s a cool technique that has a lot of potential in the years ahead. It should be exciting to see how it gets developed.
Unrelated, but the Jasanoff lab page claims they are doing MRI in flies. In flies! But I can’t find any papers that do this; anyone know about that?