Microscope yields sharp 3-D images.

By adapting optical methods used in astronomy and medicine, scientists have developed a computer-assisted microscope that makes high-resolution three-dimensional images of living cells in dim light.

"This method lets us observe live specimens with a resolution far higher than that of ordinary light microscopes," says Walter A. Carrington, an imaging researcher at the University of Massachusetts Medical School in Worcester. "The technique doesn't damage the cells. They remain alive and intact."

Carrington and his coworkers describe the technique in the June 9 Science.

With ordinary light microscopes, attempts to increase magnification beyond a certain point cause blurring, says coauthor Fredric S. Fay. Moreover, an optical microscope creates a sharp image only of objects that lie in the flat focal plane, making it difficult to see a three-dimensional structure--especially if the object is alive.

To solve these problems, the researchers joined a charge-coupled device to an optical microscope, then devised computer algorithms to correct the blurriness caused by the microscope optics at high magnification. The method is similar to the procedure astronomers used to correct images from the flawed optics of the Hubble Space Telescope before its repair. Using a second computer procedure, the microscope scans many focal planes and builds a three-dimensional image of the object, much as CAT scans do.

The researchers have imaged organelles without killing cells or cutting them into slivers, says Fay. The final resolution is four times greater than that provided by an unaided light microscope.

"An electron microscope would provide higher resolution," says Carrington. "But then the specimen would be dead."