Development of a dynamic test phantom for optical topography.

Optical topography (OT) is a near infrared spectroscopy (NIRS) technique that provides spatial maps of haemodynamic and oxygenation changes. When developing, testing and calibrating OT systems it is often necessary to use tissue simulating phantoms that are capable of providing realistic changes in attenuation properties. We present a novel dynamic tissue phantom that enables spatially and temporally varying tissue properties to be reproduced in a controlled manner. This new dynamic test phantom consists of a modified liquid crystal display (LCD) (enabling flexible and rapid changes in attenuation across different regions of the phantom) sandwiched between two layers Of tissue Simulating epoxy resin (providing static and homogeneous optical absorption and scattering). By activating different pixels in the liquid crystal display it is possible to produce highly localised and dynamic changes in attenuation which call be used to Simulate the changes associated with the cerebral haemodynamic response to functional activation. The reproducibility Of the dynamic phantom will be described with examples of its use with all OT system.