A Prototype Hadamard Imaging System

Abstract

The purpose of this thesis was to investigate the possibility of creating an inexpensive imaging system that would be suitable for imaging small animals, either the skin of mice for skin cancer studies, or potentially whole animal imaging. In this optical system the light is collected by an array of 31 optical fibers. In more advanced systems one can envision 1024, or even more fibers being used to increase the resolution of the image. The principle novelty of this system is that Hadamard encoding enabled only one photodetector to be used for the whole system rather than one detector for each fiber. There are two important advantages that can be obtained by using this strategy. First, especially with large numbers of fibers, the overall signal to noise ratio of the system can be improved. Second, the cost and complexity of the system can be greatly reduced. In cases where the signal to noise ratio is low, such as fluorescence detection, designing a system that has only one detector has substantial advantages. This system can also be applied to other sensor applications with large numbers of inputs. To our knowledge Hadamard imaging has not been applied to macroscopic imaging applications, or to small animal imagining.

Plastic fiber optics are used to gather and pixilate the spatially dependent inputs from the light source. The optical fibers were then switched on and off using a rotating mask encoded with a Hadamard matrix by drilling holes in the mask. The encoded light was then detected with an inexpensive photodetector and decoded using a desktop computer. The system is automated by using a BASIC Stamp to control the stepper motors and LabVIEW. Future improvements such as a stationary MEMS mask and glass optical fibers that could improve the system by making it more efficient and smaller in size are discussed.