X-Message-Number: 3502 From: Brian Wowk <> Date: Sun, 18 Dec 94 01:24:08 CST Subject: SCI.CRYONICS Magnetite and Brain Mapping In response to Thomas Donaldson's recent speculations about engineering bacteria to contain magnetite to enhance MRI visibility: Such bacteria exist naturally. There is a species of bacteria found in some swamps (I can't remember the name) that contains enough magnetite to actually orient and change swimming direction according to the Earth's magnetic field. The magnetite particles are prominently visible on electron micrographs of these bacteria. In fact recent research is revealing magnetite-based navigation to be nearly ubiquitous in the animal kingdom. For some reason only primates seem to have lost this natural internal compass. No trace of magnetite has ever been found in human brains. Although I sometimes wonder whether the intense vertigo some people (like me) experience in high magnetic fields could be caused be a residual field orientation sense. Getting back to MRI, magnetite-labelled antibodies are a hot new research area in MRI contrast agents right now. People want to use these molecules as probes for (among other things) determining the efficacy of gene therapy in treating conditions like familial hypercholesterolemia. Even a tiny trace of ferromagnetic particles in tissue produces a field inhomogeneity and signal loss in MRI images. If I remember right, as few as 1000 five nanometer wide magnetite particles will produce a detectable signal loss in a 1mm wide voxel of tissue. From this we can infer that even *ONE* magnetite containing bacterium would be easily detectable with MRI. How this might be used for brain mapping I will leave to the imagination of others. --- Brian Wowk Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=3502