Applications - Small Animal Imaging

Noninvasive longitudinal investigations of laboratory animals are increasingly gaining favor among the biotechnology and pharmaceutical industries. The information derived is often far more relevant than can be gained from acute terminal studies, and in many instances the number of animals and associated costs is significantly reduced. In recent years optical studies with live animals has gained favor as a tool to explore molecular expression. Among the molecular imaging methods being employed, reporter gene studies with Luciferin or Green Fluorescent Protein are now widely used. While effective, this approach does not lend itself to translation to human trials. On the other hand, measurements based on the hemoglobin signal are fully translatable. We believe that, in many instances, the hemoglobin signal can be used as a surrogate marker for factors that ultimately impact on cell metabolism. Another argument supporting use of NIRS in animal studies is its ability to directly assess whether candidate drugs have desirable or undesirable effects on bloo d flo w. Given the central role of hemoglobin to body function and the integrated nature of vascular reactivity, the merits of this measure hold whether or not the considered drug is vasoactive.

Small Animal Imaging 

Rat imaging software

A four-wavelength small animal imager is available that can be easily adapted to explore various target tissues in mice, rats and other small animals. Notably the particular measuring head developed for rat brain studies is MR compatible.

A photograph of the measuring head is shown above.  The unit features a three point stereotactic holder with optical fibers being introduced into the mouth, ears and from the top of the head. The top array is effectively spring loaded to ensure good tissue contact and has two axes of motion. An example of the 3D image quality achieved of the rat head and new image display capabilities is shown to the right. Seen is volume rendered image based on a 7-tissue segmented finite element mesh of the rat head depicting the response to a 3 second forepaw stimulation at 10 Hz. New image display capabilities include an interactive MatLAB based 3-axis orthogonal views, user directed exploded views, among other features.

Value / Advantages

NIRS offers a low cost solution to molecular imaging and evaluating of effects of investigative drugs. Currently available are costum configured and MR compatible measuring heads for brain and abdominal investigations that are suitable for animals ranging in size from mice to guinea pigs.