Supercooled lead hats aid brain scans
It's all about the Meissner effect
Magnetic brain scans look set to get more accurate, thanks to medical physicists at Los Alamos. The researchers have said they can filter out electronic background noise during measurements of brain activity if the patient wears a lead helmet.
Taking direct measurements of brain activity can only be done using Magnetoencephalography (MEG). It measures the magnetic fields generated by current flowing in and around neurons. These fields are tiny: around 10-14 to 10-13 Tesla, and detecting them is no mean feat. An MEG scanner uses superconducting quantum interference device (SQUID) sensors to measure them. However, because the fields are so small, it doesn't take much to disrupt or overwhelm the signal.
So, how do you keep out electronic background noise that interferes with the signals from the brain? You use a tin foil hat on steroids.
The hat is actually made from lead, chilled until it becomes superconducting. A liquid helium cryostat keeps it below eight kelvin. It takes advantage of the tendency of superconducting materials to actively exclude magnetic fields from their interior, known as the Meissner Effect. So external magnetic fields won't get in and, researchers say, the helmet won't affect the currents in the brain.
Early tests suggest interference can be reduced by six orders of magnitude, or a million times. The team is still working to improve the shielding, however, as noise levels are still high around the brim. ®