Efficient Spectroscopic Imaging Demonstrated In Vivo
WEST LAFAYETTE, Ind., Nov. 2, 2015 — Although optical spectroscopy is routinely used study molecules in cell samples, it is currently not practical to perform in vivo. Now, a converted Raman spectroscopy system has been used to reveal the chemical composition of living tissues in seconds.
In vivo vibrational spectroscopic imaging is inhibited by relatively slow spectral acquisition on the second scale. Another limitation is low photon-collection efficiency for a highly scattering system, such as living tissue.
Researchers from Purdue University have demonstrated vibrational imaging by spatial frequency multiplexing of incident photons and single-photodiode detection of a stimulated Raman spectrum within 60 μs. Compared with conventional spectroscopy, the method improves photon-collection efficiency by two orders of magnitude for highly scattering specimens.
Ji-Xin Cheng leads a Purdue team demonstrating spectroscopic imaging technology that could enable advanced medical diagnostics. Courtesy of Vincent Walter/Purdue University.
The technique works by coding individual photons from a pulsing laser with a megahertz radio frequency and then collecting those photons with a detector after they have interacted with tissue. The system was demonstrated in human breast cancer detection; ordinarily, cancer tissue samples would have to be processed for histological examination, which could take up to a week. The Purdue technology yields results in about 2 s.
The technique also was used to map vitamin E in the skin of laboratory mice.
"People use vitamin E on their skin as a topical treatment, and, like any drug, we would like to know where it goes after it is applied to study drug delivery mechanisms," said professor Ji-Xin Cheng, who is also the scientific director of the Label-Free Imaging Lab at Purdue’s Discovery Park.
The label-free detection system doesn’t require use of fluorescent dyes or other preparations to detect structures and features. Such processing can kill living tissue and is time-consuming; this system allows the study of unaltered living tissues and cells, making for more rapid and accurate studies, Cheng said.
Future research using the technology will explore development of an "imaging pen" to quickly analyze surfaces for traces of explosives for homeland security applications, to monitor human tissue for disease and infection, and to help surgeons determine whether any diseased tissue remains after cancer surgery.
The work was published in Science Advances (doi: 0.1126/sciadv.1500738) and was supported by a grant from the W.M. Keck Foundation.
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