The oxygen content of the venous blood in the cerebral efferent vessels is a physiological parameter for the assessment of the perfusion, metabolism and the oxygenation of the brain. There is no near infrared spectroscopy (NIRS) system available to measure this parameter non-invasively. We present a phantom based on a three layer model to simulate the anatomical target region and made a first attempt to measure concentration changes inside a measurement cell, representing a vessel. Our sensor consisted of one LED with the wavelength of 850 nm in combination with two photo diodes to detect the reflective signals. The inflow and outflow of Intralipid (IL) and Indocyanine green (ICG) in different concentrations could be detected inside of the cell. The results illustrate the capability to measure the target values in a specific vessel, represented by the measurement cell. Based on these first measurments a next generation sensor was designed which is geometrically aligned with the three layer phantom model and provides the opportunity to investigate several wavelengths and photodiode distances.