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Does the Shape of the Brain Matter?

Roger Hult
Centre for Image Analysis
Uppsala University
June 2002


My research examines the brain surface from three-dimensional images (volume-images) of the brain using a technology similar to X-rays. I program my computer to extract a three-dimensional image that contains only the brain surface from these images. Then I investigate how the brain is shaped. Psychiatrists are interested in whether or not the shape of the brain is different among people with certain mental diseases. My research will give them the tools to examine the shape of the brain.

Psychiatrists are investigating whether the shape of the brain changes due to mental diseases, such as schizophrenia. Currently, schizophrenia is diagnosed mainly through interviews intended to determine if the patients meet certain diagnostic criteria. Perhaps in the near future, doctors might be able to use images of the brain's surface to help them diagnose mental diseases. There is also research on using genes, drawn from blood samples, to diagnose mental diseases. Other research tries to determine how the activity in the brain might be changed in people with schizophrenia. All in all, there is a lot of research on the brain in the study of mental diseases.

There are several techniques that can be used to see the inside of a brain, one of which is Magnetic Resonance Imaging, or MRI. This method enables us to see the anatomy of the brain. The person is placed in a strong magnetic field that is turned on and off rapidly. Tissues that contain water act as radio-transmitters when the magnetic field is off and an image can be calculated from these signals. Computerised image analysis of a brain scanned in an MRI-camera can be used to make a diagnosis. In this way, computers can aid doctors in finding diagnosis based upon image analysis.

I try to find structures in the brain using three-dimensional images acquired with an MRI camera. To extract a picture of the brain surface I first examine dark and light intensities in the image that correspond to different kinds of tissues. Brain tissue is either grey or white matter. The grey matter can be looked at as the processor in a computer and the white matter like wires connected to other parts of the computer. Tissues have different intensities in the image: air, bone and fluids appear dark, while grey matter, white matter and flesh or fat appear lighter. Because some surrounding tissue has a similar shade on the image as the brain matter, I program the computer, using my knowledge of brain anatomy, to remove undesired areas from the image.

Once a picture of the whole brain is extracted, the surface of the brain can be converted into a three-dimensional model that only describes the surface and contains no information about the underlying structures. This means that the surface of the brain is described as a shell of the brain. This is similar to the models that are used in computer-animated movies like "Toy Story" and "Jurassic Park." In those movies, the characters are modelled as geometric objects with properties of the surface only. From the model of the brain surface one can then examine the curvature and changes in certain areas of the brain.

To provide a proper frame of reference, it is necessary to be able to compare different brains. This task is simplified if the brains are arranged so that they are oriented in the same direction with differences in size compensated for. It is interesting to examine both the size of an area and the curvature of the surface in the area. There is a standardised coordinate system called the Talairach atlas, which defines different areas in the brain with the use of a grid. These areas can be seen as boxes, and one of these boxes is called the frontal lobe. Psychiatrists have a theory that this part of the brain is smaller if the patient suffers from schizophrenia.

There is an interest in diagnosing mental diseases in an accurate way. One way of achieving this is through the use of a computer to assist the psychiatrists in proposing the correct diagnosis. The computer in this case investigates a three-dimensional image of the brain, detects the surface and converts the surface into a geometric model. The surface is then compared with other brains to see if some changes are more likely among people who suffer from schizophrenia. So shape may truly matter when it comes to brains!