Imaging the brain in a blackout
13 June 2011
The team used an entirely new imaging method called 'functional electrical impedance tomography of evoked response' (fEITER), which enables high-speed imaging and monitoring of electrical activity deep within the brain and is designed to enable researchers to measure brain function.
The new device was developed by a multidisciplinary team drawn from the Schools of Medicine and Electrical and Electronic Engineering at The University of Manchester (UK), led by Professor Hugh McCann and with support from a Wellcome Trust Translation Award. The Manchester team is one of many worldwide groups investigating electrical impedance tomography (EIT), but this is its first application to anaesthesia. By using a carefully tuned combination of analogue and digital electronics, the state-of-the-art fEITER instrument achieves a unique combination of sensitivity and imaging speed.
The machine itself is a portable, lightweight monitor, which can fit on a small trolley. It has 32 electrodes that are fitted around the patient's head. A small, high-frequency electric current, too small to be felt or have any effect, is passed between two of the electrodes, and the voltages between other pairs of electrodes are measured in a process that takes less than one-thousandth of a second.
An electronic scan is thus carried out, and the machine does this whole imaging procedure 100 times a second. By measuring the resistance to current flow (electrical impedance), a 3D image of the changing electrical conductivity within the brain is constructed. This is thought to reflect the amount of electrical activity in different parts of the brain. The speed of operation of fEITER is such that many images of the response of the brain to an external stimulus, such as an anaesthetic drug, can be captured in rapid succession as different parts of the brain respond, thus tracking the brain's processing activity.
Using the new technique, the researchers have constructed a real-time 3D movie of the brain as it changes while an anaesthetic drug takes effect.
"We have looked at 20 healthy volunteers and are now looking at 20 anaesthetised patients scheduled for surgery," explained Brian Pollard, Professor of Anaesthesia at the University of Manchester. "We are able to see 3D images of the brain's conductivity change, and those where the patient is becoming anaesthetised are most interesting."
"We have been able to see a real-time loss of consciousness in anatomically distinct regions of the brain for the first time. We are currently working on trying to interpret the changes that we have observed. We still do not know exactly what happens within the brain as unconsciousness occurs, but this is another step in the direction of understanding the brain and its functions."
Professor Pollard said that a huge amount of research still needed to be done to fully understand the role EIT could have in medicine.
"If its power can be harnessed, then it has the potential to make a huge impact on many areas of imaging in medicine. It should help us to better understand anaesthesia, sedation and unconsciousness, although its place in medicine is more likely to be in diagnosing changes to the brain that occur as a result of, for example, head injury, stroke and dementia.
"The biggest hurdle is working out what we are seeing and exactly what it means, and this will be an ongoing challenge," he concluded.
Image: Image reconstructed from measurements recorded using fEITER during awake conditions (left) and during the onset of anaesthesia (right). Credit: University of Manchester.
