In the past, even modern technologies have failed to produce high-resolution fluorescence images from this depth because of the strong scattering of light. In the Nature Photonics journal, the Munich researchers describe how they can reveal genetic expression within live fly larvae and fish by "listening to light". In the future this technology may facilitate the examination of tumors or coronary vessels in humans.
Since the dawn of the microscope scientists have been using light to scrutinize thin sections of tissue to ascertain whether they are healthy or diseased or to investigate cell function. However, the penetration limits for this kind of examination lie between half a millimeter and one millimeter of tissue. In thicker layers light is diffused so strongly that all useful details are obscured.
Together with his research team, Professor Vasilis Ntziachristos, director of the Institute of Biological and Medical Imaging of the Helmholtz Zentrum Mnchen German Research Center for Environmental Health and chair for biological imaging at the Technische Universitt Mnchen, has now broken through this barrier and rendered three-dimensional images through at least six millimeters of tissue, allowing whole-body visualization of adult zebra fish.
To achieve this feat, Prof. Ntziachristos and his team made light audible. They illuminated the fish from multiple angles using flashes of laser light that are absorbed by fluorescent pigments in the tissue of the genetically modified fish. The fluorescent pigments absorb the light, a process that causes slight local increases temperature, which in turn result in tiny local volume expansions. This happens very quickly and creates small shock waves. In effect, the short laser pulse gives rise to an ultrasound wave that the researchers pick up with an ultrasound microphone.
The real power of the technique, however, lies in specially developed mathematical formulas used to analyze t
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Helmholtz Zentrum Mnchen - German Research Center for Environmental Health