Stimulating the brain to focus on a specific subject during MRI scans proved a challenge to German researchers, who combined two technologies to project images inside a scanner. Stuart Nathan reports.

The use of magnetic resonance imaging to study the brain is a rapidly-developing area which presents an unusual problem. To observe the brain 'working' it has to be stimulated, which means the test subject having to think — often about something very specific. Unfortunately the inside of an MRI scanner is a far from stimulating place.

To solve this problem, researchers at the Fraunhofer Institute for Applied Optics and Precision Engineering have developed a system which projects images to the person being scanned. The device could also have applications for imaging systems other than medical, according to lead researcher Stefan Riehemann.

The system, known as functional MRI (fMRI) combines two different scanning techniques. It provides the normal MRI images of bone and soft tissue, showing the positions of the various structures within the brain. But it also follows the concentration of oxygen in blood and tissues, showing which parts of the brain are active at the time of the scan.

Over time, it builds up an image of how the brain processes particular tasks. Usually, these are presented as a series of visual images: a maths problem, for example, or a series of pictures which might give an emotional response.

This presented a series of challenges. First, the subject had to be able to see the images clearly within the narrow and constrained tube of an MRI scanner. Second, the system is so sensitive that any other brain activity — even movement — would confuse the result, so the subject could not move. This meant that a compact projection system was necessary.

As fMRI is a magnetic technique, the system could not contain ferromagnetic materials, as they would distort the magnetic field. It also had to be able to work within the strong magnetic field without distortions, which ruled out anything based on a cathode ray tube or other electrostatic technology.

So Riehmann turned to organic light-emitting diodes (OLEDs) for his system. The OLEDs are contained within a pair of separate eyepieces, which gives the system — which can be run off a standard PC graphics card — two valuable properties. it can project slightly different images to each eye, allowing a 3D effect, and it can track which part of the image each eye is looking at, providing more information for neurological studies.

The system is being built by Norwegian fMRI specialist, NordicNeuroLab, which commissioned the original research. 'There is a growing need for projection systems for medical applications, and also for use in virtual reality systems,' said Riehmann. 'We are often asked to design such specialised systems — especially for cases where it is not possible to use conventional hardware.'