tISM - A transportable integrating sphere setup for standardized measurements of blood and tissue phantoms

The development of an optical sensor for noninvasive measurements in humans requires a test setup, where the optical properties of tissue and blood can be adjusted and measured standardized. The goal of this work is to develop a simplified device based on an integrating sphere setup to evaluate the optical properties of tissue and blood phantoms with respect to static as well as flow conditions. Furthermore, the measurement system is intended to be used at different locations such as laboratories and operating theaters. We evaluate the absorption µ_a and reduced scattering µ_s' coefficients of specimens, with the developed integrating sphere setup. The measurement is regulated by a microcontroller for averaging and processing the data. The system is housed in a lightproof box and powered by a battery and therefore transportable. Due to this construction, no calibration is necessary between transports of the system. Calculations are executed with the inverse adding doubling algorithm. In order to basically calibrate and evaluate the setup before first transportation, a dilution series with Intralipid and India ink serve for the test. The results were consistent with precedent studies (mean absolute deviation for µ_s' of 0.75 mm^-1) and demonstrate that this method might be able to produce liquids with adjustable optical properties, as required for further research. Furthermore, a first dilution series of heparinized heamoglobin (5 to 15 g/dl) with oxygen saturation of 98 % was measured with this system under flow conditions. We observed a linear increase of µ_a and µ_s' with the increment of the haemoglobin concentration. As light sources, laser diodes in the range from 780 to 980 nm were introduced. Static and flow measurements indicated that the system is capable for evaluating optical properties under the selected conditions.