Topologies of the Mind  

Magnetic Resonance Imaging (MRI)

Structural MRI scan of Carol Vorderman

©Dr Mark Lythgoe.

Structural MRI

At the centre of every hydrogen atom in every water molecule in the human body, there lies a tiny magnet. In everyday life, since these small magnets are weak and relatively very far apart, they are unaware of each other’s presence and point randomly in all directions. However, when the body is placed in the strong magnetic field of an MRI scanner (where the magnetic field is about 30,000 times stronger than the Earth’s natural magnetic field), these tiny magnets line up with the strong field, in the same way a compass needle points to North.

If you push a compass needle away from North, as soon as you let go it will swing back to its original orientation. A similar situation exists for the magnetisation of the human body when it is lying in an MRI scanner. Applying a burst of radio waves while someone is inside the MR scanner causes an electromagnetic force to push the body’s magnetisation out of alignment with the scanner’s magnetic field. Like the compass needle, this is an unnatural state for the body’s magnetisation, and so it quickly returns back to its original position. As it does so, it sends out radio waves, and these are detected and form the signal that makes the final MR image.

Text modified from MRI by David Thomas in Mapping Perception

Images of the Mind: Functional MRI (fMRI)

Brain activity can be imaged using a technique called functional magnetic resonance imaging (fMRI). fMRI scans of the brain produce images that "light up" when a subject thinks, identifying particular areas of brain activity.   When we think, the area of the brain that is working needs more oxygen and the blood supply increases to supply the extra demand.  The change in the amount of blood oxygenation causes an increase in the MRI signal intensity where the brain is thinking (coloured area) in the functional MRI image.   By acquiring a series of images over time, a picture can be constructed of the activated regions of the brain.

Dr. Mark Lythgoe is a Neurophysiologist at the Institute of Child Health and Great Ormond Street Hospital.  Mark uses Magnetic Resonance Imaging (MRI) techniques for investigating brain function and developing possible therapies for children suffering from stroke.  Mark has been involved in several science–art collaborations, notable directing the film ‘Mapping Perception’ with Andrew Kotting which premiered in 2002. He is currently working towards a production with the London International Festival of Theatre (LIFT) for 2004. Carol's scans will also star in forthcoming lectures by Dr Lythgoe, an extension of the Visions of Science Photographic Awards, backed by The Telegraph, Novartis and Nesta. 

Special thanks: Brian Butterworth, Elizabeth Isaacs, Chloe Hutton, Joey Tang, Fulvia Castelli, Hugo Critchley, David Thomas, David Gadian, Roger Ordidge

Mark Lythgoe and Angela Palmer ©2003