5. Another Reason to Brush. Before a patient is seated in the MEG unit, every piece of metal on his or her body must be demagnetized. Otherwise, the merest jiggle would break the magnetic calm. MEG technician Nancy Lopez has a handheld demagnetizer for this purpose; it’s powerful enough to neutralize even a patient’s dental fillings.
6. Sound Check. The first step in a MEG exam is to plumb the patient’s brain for fixed reference points, needed later to align the MEG data with MRI images and reckon the locations of electrical disturbances. Lopez outfits a subject with headphones so that she can administer a series of tones, which cause the brain’s auditory centers to sprout magnetic fields. These centers – which are well-known landmarks in the brain, always located on specific folds in the right and left temporal lobes – show up clearly on the MEG unit’s computer readout.
7. Electric Dreams. For the next hour or two, the patient must sit absolutely still – it’s okay to doze off – while the detector array observes the brain’s spontaneous electromagnetic activity.
8. Number Cruncher. Each of the SQUIDs sends its readings to a separate board in the MEG unit’s main computer, a refrigerator-sized behemoth across the room from the MEG chamber.
9. Skull Cap. At a bank of desktop and laptop computers adjacent to the main computer, Lopez and Sutherling open windows depicting the MEG unit’s measurements graphically. A map caricaturing a top view of the subject’s head, complete with a tiny triangular nose and elephant ears, shows the detectors’ locations around the skull as red circles. In another window, the changing readings from each individual detector are expressed as squiggly, EEG-like lines. The relatively flat readings from this healthy volunteer indicate that she’s asleep.
10. A Passing Storm. Conditions are quite different during a seizure. To illustrate, Sutherling calls up the records of an actual epilepsy patient examined in HMRI’s MEG unit before surgery. Rather than wait for a patient to have a spontaneous seizure during the exam, doctors implant a grid of electrodes just inside the skull, over the region of the brain thought to be affected. A jolt from these electrodes induces a miniseizure whose magnetic signature can then be recorded in detail. The individual SQUID readings from these small seizures are translated by software into a schematic showing where the strongest magnetic fields emanate from the skull.
Pointing to the three views of the head at the top of the screen, Sutherling explains that the magnetic readings are mathematically transformed into three dimensions and overlaid on MRI images of the patient’s brain. The stark yellow markings then guide surgeons to the wellsprings of a patient’s epileptic seizures – usually tiny bits of scar tissue.
Sutherling recalls one lifelong epilepsy sufferer whose seizures struck every two hours. EEGs showed unusual activity across the man’s frontal lobes, but MEG images traced the problem to a single spot in the left frontal lobe, near the speech center. Surgeons excised most of the scarred tissue while avoiding cuts that might have affected the man’s ability to speak. After the operation, he experienced only minor seizures. “Ideally, we want to make certain that the area that’s removed has zero function – that it’s just scar tissue – and that the removal is complete,” says Sutherling. “The goal is to make people seizure-free, so that they’re able to drive and able to work.”