IR Tomography Goes Full Color

Combining Fourier transform infrared (FTIR) spectroscopy with computed tomography creates a non-destructive, 3-D imaging technique providing full-color, molecular-level chemical information of unprecedented detail on biological and other samples with no need to stain or alter the specimens.

The work is a collaboration between researchers at Lawrence Berkeley National Laboratory and the University of Wisconsin-Milwaukee (UWM).

Spectromicrotomographic images of a human hair show absorptions of protein (red) and phospholipid (blue-green). Center, the medulla is observed to have little protein. Bottom, the medulla has higher concentrations of phospholipids.

“The notion of having the colors in a 3-D reconstructed image being tied to real chemistry is powerful,” said Berkeley Lab’s infrared imaging expert Michael C. Martin, co-author of a paper describing the research. “We’ve all seen pretty 3-D renderings of medical scans with colors — for example, bone-colored bones — but that’s simply an artistic choice. Now we can spectrally identify the specific types of minerals within a piece of bone and assign a color to each type within the 3-D reconstructed image.”

IR spectroscopy can be used to identify the chemical constituents of a sample, and the application of the Fourier transform algorithm allows all IR fingerprints to be simultaneously recorded. Along with physicist Carol J. Hirschmugl, director of the Laboratory for Dynamics and Structure at Surfaces and a principal investigator with UWM’s Synchrotron Radiation Center (SRC), Martin and colleagues combined FTIR with computed tomography, the technique for reconstructing 3-D images out of multiple cross-sectional slices, to achieve what is believed to be the first demonstration of FTIR spectromicrotomography.

Michael Martin at Berkeley Lab’s Advanced Light Source. Courtesy of Roy Kaltschmidt, Berkeley Lab.

The success of FTIR spectromicrotomography was enabled by the speed with which 2-D FTIR images could be obtained at the SRC’s Infrared Environmental Imaging (IRENI) beamline. Hundreds of 2-D spectral images were obtained as a sample was rotated in front of an IR microscope. For each wavelength, a full 3-D representation of the sample was reconstructed from computed tomography algorithms into a complete spectrum for every voxel.

The researchers applied the technique to obtain 3-D images of the molecular architecture of the cell walls in a flowering plant — zinnia — and in a woody plant — poplar.

Carol Hirschmugl at the University of Wisconsin’s Synchrotron Radiation Center.

FTIR spectromicrotomography is expected to be used in biomedical imaging, biofuel development, agriculture and even art history, where, according to Martin, different layers of paint on a painting could be revealed.

The findings were reported in Nature Methods.

For more information, visit: www.lbl.gov