Optical Projection Moves from VIS to IR

A new imaging method enables optical projection tomography to be extended from the visible to the near-IR spectrum, allowing the study of different types of cells in one preparation and the use of different contrast agents. The findings could be used to study insulin-producing cells in diabetics.

Initially, optical projection tomography (OPT) could be used only on relatively small preparations, but five years ago scientists at Umeå Center for Molecular Medicine were able to adapt the technology to studying whole organs, including the pancreas of adult mice. Now, they have taken the technology a step further by extending it into the near-IR spectrum, whose longer wavelengths more easily penetrate tissue.

Near-infrared optical projection tomography enables the visualization of several cell types in large preparations. The image of a pancreas from a mouse with type-1 diabetes shows the insulin-producing islets of Langerhans in blue, blood vessels in red, and infiltrating autoimmune cells that break down the insulin-producing cells in green. Images courtesy of Umeå University.

An international commitment has been made to the development of noninvasive imaging methods for studying the number of remaining insulin cells in patients with developing diabetes. Currently, these cells can be studied only indirectly; the stumbling block has been finding contrast agents that bind specifically to insulin-producing cells of the pancreas and that also permit imaging.

The Umeå near-IR OPT technology meets the challenge as it enables the evaluation of new contrast agents. It could simultaneously track the insulin-producing islets of Langerhans as well as the autoimmune infiltrating cells and the distribution of blood vessels in a model system for type-1 diabetes. It may also be used as a tool to calibrate the noninvasive readout by, for example, magnetic resonance imaging.

The enhanced technology allows new types of analyses, such as the possibility of evaluating preclinical samples for the purpose of developing better strategies for transplanting islets of Langerhans in diabetics. The image shows a liver from a mouse (gray) into which islets of Langerhans (blue) have been transplanted. By visualizing several markers in an organ, it is possible to see directly where the islets of Langerhans wind up in the blood vessel tree.

With a broader range of the light spectrum, it is possible to study larger samples, for example the rat pancreas; this is important because a rat is thought to be physiologically more similar to a human than a mouse is.

The technology is now being tested in a newly launched Marie Curie project, “European Training Network for Excellence in Molecular Imaging in Diabetes,” which links together five major European Union-funded research consortia.

The study appears in the form of a video in the The Journal of Visualized Experiments (doi: 10.3791/50238).

For more information, visit: www.umu.se