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13 Sep 2007
US scientists have developed a simple and inexpensive optical imaging system that provides real-time mapping of animals' internal organs.
The new system, which researchers Elizabeth Hillman of Columbia University and Anna Moore of the Harvard Medical School have dubbed a dynamic fluorescence molecular (DFM) imager, is currently being used to monitor the organs of laboratory mice. Hillman is now collaborating with Cambridge Research & Instrumentation to develop a commercial imaging platform that could have applications in drug testing and in the search for tumour-killing cancer treatments.
"It's quite amazing how this system came about," Hillman told optics.org. "At the time, Anna Moore was working on labelling and tracking pancreatic islet cells that had been transplanted into the kidney of a mouse, and she needed an accurate way to identify and verify the location of the kidneys of lab mice."
"Unfortunately, the only systems capable of doing this are very complex and expensive – like combined optical and X-ray tomography and micro-computed tomography (micro-CT). I set about working on the problem, and put together a basic imaging system with off-the-shelf components."
The prototype imager works by tracking a fluorescent dye that is injected into the animal. The dye is excited by two laser diodes that deliver 160 mW of diffused near infrared light at 785 nm, and the fluorescence is then captured with a CCD camera with a 830-870 nm bandpass emission filter. A motion picture of the dye's movement through the animal can be formed by taking a number of images in quick succession.
"Although a still photograph may be good enough for visualizing a labelled region of the tissue, it provides little additional information," said Hillman. "So I decided to look at a video of the dye's movement instead."
Hillman observed the dye moving through the body: starting from the heart, it went to the lungs, then the brain and kidneys, then the small intestines and finally ending up in the liver. "I realized that with some basic image processing, we could generate an accurate map of the internal organs of that particular lab animal".
According to the researchers, this technique could offer an alternative to existing CT-based imaging systems. "With this imager, you get both the molecular sensitivity of the dye and the ability to simultaneously track multiple organs, making it a much cheaper alternative X-ray and micro-CT imagers," said Hillman. "A lot of information can be gleaned non-invasively through this system."
Their work was published in Nature Photonics.
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