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Tackling tuberculosis using new optical imaging technology

BioPhotonics
Jul 2008
Gary Boas

The World Health Organization lists tuberculosis as one of the most serious infectious diseases: It currently affects the lives of almost one-third of the world’s population. Because of the various severe and drug-resistant strains that exist, the need for more effective diagnostic and therapeutic procedures is especially urgent.

Jeffrey D. Cirillo and colleagues at Texas A&M Health Science Center College of Medicine in College Station have been studying tuberculosis for about 20 years. For much of that time, they could not image this or any other infectious disease in live animals or in patients. In recent years, however, the development of ultrasensitive camera systems and reporter systems has enabled them to do so.

They now are collaborating with Washington University in St. Louis and with Stanford University School of Medicine in California on the study of tuberculosis infection in live animals using in vivo imaging. To this end, in late 2007, they purchased an IVIS Spectrum imaging system made by Caliper Life Sciences Inc. of Hopkinton, Mass.

TSTubber_Fluorescence1.jpg

Researchers are using a new imaging system to study tuberculosis in animal models. It facilitates both luminescence and fluorescence measurements, which allows them to image disease progression through tissue and in real time.

The device is the most advanced version of the IVIS product line. Initially, the instruments offered the ability to measure luminescence as a means to generate high sensitivity. “The Spectrum represented an attempt to leverage the effective sensitivity of luminescence measurements,” said Mark T. Roskey, vice president of reagents and applied biology at the company, “but also to be able to start looking at fluorescence as well.” Key changes made this possible: the addition of multiple excitation and emission filters, a wider range of wavelengths and the ability to look at multiple fluors at different wavelengths using spectral unmixing.

He also noted advances in the system that reduce autofluorescence; e.g., it enables the use of either epi- or transillumination. Transillumination significantly reduces autofluorescence from deep-tissue in vivo fluorescent sources. Using the combination of structured light and transillumination sources, scientists can determine source localization and concentration by 3-D diffuse fluorescence tomography.

Thus the system enables use of bioluminescent and fluorescent reporters from the blue to the near-infrared regions and single-view 3-D tomography for both types of reporters that can be analyzed in an anatomical context using a proprietary Digital Mouse Atlas.

They chose the system because of its luminescence and fluorescence detection capabilities, which allow them to image the progression of tuberculosis and the efficacy of treatment in real time. “Having had prior experience with the system at Stanford, I felt that the software developed for it was superior to that of many other systems,” Cirillo said.

Using the system, they imaged nonrecombinant tuberculosis in the lungs of mice, facilitating visualization of disease progression and impact of potential therapies in real time. These capabilities will contribute to more effective treatments for the disease as well as to more rapid progress in the research laboratory.

The researchers currently are working to improve the sensitivity of the system by optimizing the imaging methods, by using multiple levels of signal amplification and by optimizing reporter expression. “The ultimate goal is to be able to detect single bacteria in the lungs,” Cirillo said. “Obviously, that’s a very ambitious goal with the technology we’re using. It may be fine for a plate reader, but when you’re going through tissue, it’s a totally different ballgame.”

Contact: Jeffrey D. Cirillo, Texas A&M Health Science Center College of Medicine; e-mail: jdcirillo@medicine.tamhsc.edu; Mark Roskey, Caliper Life Sciences Inc.; e-mail: mark.roskey@caliperls.com.


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