Ultra-Fast Lasers for Imaging Brain Tissue

The technique was described in the July 3, 2002, issue of Neuron.

Previously, to obtain microscopic images of the brain, researchers had to manually cut thin slices of frozen brain and view them through a light microscope. In the new technique, the tissue is imaged and ablated, or vaporized, in successive iterations. The ablation requires a femtosecond laser, which produces light pulses lasting one quadrillionth of a second. This is as short in comparison with a second, as a second is in comparison with all of human history. After each ablation, the newly uncovered tissue is labeled with a fluorescent dye, and lower-intensity laser light is used to take an image of the surface. Successive snapshots of each layer can be recombined to create a 3-D image of the tissue.

The new technique can be used to automate and modernize histology, aid the study of tissues at the microscopic level, and map the production of neurotransmitters and other proteins involved in communication between cells and normal cell function.

One special application of the new technique is to image brains of animals that have ben genetically engineered to produce a fluorescent protein in certain cells. By studying 3-D images of the brains of mice that produced fluorescent protein in the blood vessels of the brain, the research team was able to determine the volume of the blood vessels relative to the rest of the brain.

"This new technique is able to more precisely measure structures in the brain and do it without the tedious and laborious methods of thin slicing sections of the brain,” said David Kleinfeld, professor of physics at the University of California, San Diego (UCSD, USA). "It solves a big problem and it potentially changes the way a lot of science is done today.”




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