Of mice and magnets

One of the things I saw during my visit to the Queensland Brain Institute was a mouse having an MRI (Magnetic Resonance Imaging) scan. The selected subject was, Dr Hamlin told me, a rather elderly mouse that was not part of any other experiment. Marianne, the MRI technician, placed him in a container that looked a bit like a large Tupperware salad bowl with a clear lid, and he happily ran around inside the chamber while a mixture of anaesthetic (similar to the pre-meds that you get when you're about to go into surgery, that make you drowsy and relaxed) was pumped in through a tube. Gradually, the little brown patient slowed his running, then lay down to sleep. When he was quite relaxed, Marianne carefully picked him up and laid him in a special contraption that looked like a long piece of plastic pipe that had been cut in half.

To keep his head still and in position during the scan, at one end of the pipe was a small tongue with a hole in it for the mouse's teeth to slot into. A little cowling fitted over his head, continuing to supply the anaesthetic for as long as the scan lasted. Once the sleeping mouse was strapped into position, the whole pipe (with the anaesthetic tubes attached) was placed inside the 16 Tesla MRI imager and Marianne fired up the computer monitors so we could see it working.

An MRI works, Adam and Marianne explained to me – and if I get this wrong, I hope Adam will correct my mistakes – by producing strong magnetic fields so that the hydrogen atoms in the body of the subject all line up and vibrate in a particular direction. Even using the massive magnetic fields this particular machine generates, a detailed image of a one-centimetre-wide mouse brain still takes around four hours to make, during which time the mouse must be kept perfectly still. Even its breathing interrupts the imaging process.

One computer monitor showed the mouse's respiration as a line rising and falling with every movement of its chest. Not just to monitor the mouse's vital signs, this also enable Marianne to time the imaging process so that it only occurred at the same point in the breathing cycle: she would image the brain for a fraction of a second at a time, between each breath in and out.

After several minutes, the first images of the mouse's brain appeared on another monitor. Looking at the magnified images on the screen, and seeing the details that appeared, it was difficult to remember that the brain in question was such a tiny thing residing in such a tiny creature. The purpose of this experiment, Marianne said, was to try to reduce the length of time required to get the level of detail that the neuroscientists needed in the images. By working together, she and Adam hoped to cut half an hour off the time required to image a live mouse's brain.

Adam and I left Marianne to finish the imaging, replacing our watches and credit cards (which had to be left outside so that the magnet didn't fry them) and returning to the QBI lab. Later in the day, when the imaging process was over, our little furry patient would also be returned, to sleep off the effects of his anaesthetic.