A dynamic phantom brain model for near-infrared spectroscopy

This report describes the construction, fluid dynamics and optical properties of an in vitro model of the neonatal brain for testing near-infrared spectroscopy (NIRS) instruments. The brain model is a solid plastic structure containing a vascular network perfused with blood equilibrated with O2, N2 and CO2 in a closed circuit. The oxygenation state and haemoglobin concentration of the perfusate can be regulated and measured with a co-oximeter, providing a means to compare NIRS measurements of oxy-, deoxy- and total haemoglobin concentrations and haemoglobin O2 directly with a validated standard method. Fluid dynamic experiments revealed that the model's vasculature remains stable over time with minimal haemolysis. The model's optical properties were characterized by time-resolved and continuous wave NIRS between 670 and 850 nm as perfusate saturation was varied in the range 0-100%. Optical properties of the neonatal piglet brain were also determined by similar methods. No significant differences were found between the model and piglet brain in absorption coefficients, reduced scattering coefficients and optical pathlengths, indicating that the model optically simulates the piglet brain over a wide range of oxygenation states. These results demonstrate the potential utility of this dynamic phantom brain for testing NIRS instruments for accuracy and reliability.