| Summary: | Optical methods for biomedical purposes mostly use reflected light, while few of them use the transmitted light. The blood vessels pose a challenge to these methods due to their high absorption and scattering coefficients as well as their change in size during respiration, and they are also naturally distributed in size within the body and between individuals. We suggest the full scattering profile (FSP) method in order to investigate the light at every possible exit angle. Our model of FSP successfully describes the role of the blood vessel diameter in light-tissue interaction. By means of the new point of view of FSP, we found the isobaric point, which is non-dependent on the optical properties. The uniqueness of the isobaric point is that it overcomes the shielding effect, which has known influence on the reflected light, for various vascular diameters of the same volume. We present these findings experimentally by measuring cylindrical phantoms with blood vessels in different diameters, and compare the results to our simulation results. The importance of the immunity to the shielding effect is that it allows self-calibration in clinical measurements and decreases the calibration error. In addition, by using the isobaric point we can cope with changes in blood vessel diameters and not assume microcirculation only.
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