3D Images of Living Cell Generated

A newly developed imaging method has allowed scientists to create the first three-dimensional (3D) images of a living cell, using a technique similar to computed tomography (CT) scans utilized to see inside the body.

The technique, described in a study published in the August 12, 2007, online issue of the journal Nature Methods, could be used to generate the most detailed images to date of what goes on inside a living cell without the help of fluorescent markers or other externally added contrast agents, according to Dr. Michael Feld, director of the Massachusetts Institute of Technology's (MIT; Cambridge, MA, USA) George R. Harrison Spectroscopy Laboratory and a professor of physics.

Accomplishing this has been my dream, and a goal of our laboratory, for several years, said Dr. Feld, senior author of the study. For the first time the functional activities of living cells can be studied in their native state.

Using the new technique, Dr. Feld's team has created 3D images of cervical cancer cells, showing internal cell structures. They have also imaged Caenorhabditis elegans (a nematode or roundworm), as well as several other cell types. The researchers based their technique on the same concept used to create three-dimensional CT images of the human body, which allow clinicians to diagnose and treat medical conditions. CT images are generated by combining a series of two-dimensional X-ray images captured as the X-ray source rotates around the object.

You can reconstruct a 3D representation of an object from multiple images taken from multiple directions, said Dr. Wonshik Choi, lead author of the study and a spectroscopy laboratory postdoctoral associate.

Cells do not absorb much visible light, therefore, the researchers instead created their images by taking advantage of a property known as refractive index. Every substance has a well-defined refractive index, which is a measure of how much the speed of light is reduced as it passes through the material. The higher the index, the slower the light travels.

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 that does not pass through it. A 2D image containing data about refractive index is thus obtained.

To create a 3D image, the researchers combined 100 two-dimensional images taken from different angles. The resulting images are basically 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. The investigators' image of a cervical cancer cell revealed the cell nucleus, the nucleolus, and a number of smaller organelles in the cytoplasm.


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