First 3-D images set cell biology in a spin

A new imaging technique has allowed scientists to create the first 3D images of a living cell, using a method similar to the X-ray CT scans doctors use to see inside the body.

MIT professor Michael Feld, right, and colleagues Wonshik Choi and Kamran Badizadegan, have found a way to create 3D images of the inner workings of cells.

The technique could produce the most detailed images yet of what goes on inside a living cell without the help of fluorescent markers or other externally added contrast agents.

Michael Feld, director of MIT’s George R. Harrison Spectroscopy Laboratory who carried out the research, said: “Accomplishing this has been my dream, and a goal of our laboratory, for several years. For the first time the functional activities of living cells can be studied in their native state.”
The researchers based their technique on the same concept used to create three-dimensional CT (computed tomography) images of the human body. CT images are generated by combining a series of two-dimensional X-ray images taken as the X-ray source rotates around the object.
The researchers made their measurements using a technique known as interferometry, in which a light wave passing through a cell is compared with a reference wave.

To create a 3D image, the researchers combined 100 two-dimensional images taken from different angles. The resulting images are essentially 3D maps of the refractive index of the cell’s organelles. The entire process took about 10 seconds, but the researchers recently reduced this time to 0.1 seconds.

“One key advantage of the new technique is that it can be used to study live cells without any preparation,” said Kamran Badizadegan, principal research scientist in the Spectroscopy Laboratory and one of the authors of the paper. “With essentially all other 3D imaging techniques, the samples must be fixed with chemicals, frozen, stained with dyes, metallised or otherwise processed to provide detailed structural information.”

The current resolution of the new technique is about 500nm, or billionths of a meter, but the team is working on improving the resolution. “We are confident that we can attain 150nm, and perhaps higher resolution is possible,” Feld said.