Abstract. Most methods for measuring light-tissue interaction focus on volume reflectance, while very few measure light transmission. In a previous work, we suggested investigating the influence of blood vessel diameter on photons exiting the tissue at all exit angles to receive the full scattering profile. By this method, we have shown that there is a central angle, i.e., the isobaric point, independent of blood vessel diameter. The vessel diameter changes the effective reduced scattering coefficient. However, both the scattering profile and the value of the isobaric point strongly depend on optical properties and the exact geometry of the tissue. In this study, we investigate the dependency of the isobaric point on tissue diameter and scattering coefficient in both two-dimensional and three-dimensional simulations. We show that the value of this point linearly depends on tissue diameter. The findings of this work solve the dilemma of whether to measure transmission or reflection since the isobaric point reduces by half the total amount of exiting photons. Furthermore, the full scattering profile is sensitive to changes in the scattering properties, but a single isobaric point to these changes is expected. If this point is not found, it is a diagnostic indication of an unexpected change in the tissue.

Optical methods for monitoring physiological tissue state are important and useful because they are non-invasive and sensitive. Experimental measurements of the full scattering profile of circular phantoms are presented. We report, for the first time, an experimental observation of a typical reflected light intensity behavior for a circular structure characterized by the isobaric point. We previously suggested a new theoretically method for measuring the full scattering profile, which is the angular distribution of light intensity, of cylindrical tissues. In this work we present that the experimental result match the simulation results. We show the isobaric point at 105° for a cylindrical phantom with a 7mm diameter, while for a 16mm diameter phantom the isobaric point is at 125°. Furthermore, the experimental work present a new crossover point of the full scattering profiles of subjects with different diameters of the cylindrical tissues.

In optical sensing, to reveal the chemical composition of tissues, the main challenge is isolating absorption from scattering. Most techniques use multiple wavelengths, which adds an error due to the optical pathlength differences. We suggest using a unique measurement angle for cylindrical tissues, the iso-pathlength (IPL) point, which depends on tissue geometry only (specifically the effective radius). We present a method for absorption assessment from a single wavelength at multiple measurement angles. The IPL point presented similar optical pathlengths for different tissues, both in simulation and experiments, hence it is optimal. Finally, in vivo measurements validated our proposed method.

Human tissue is one of the most complex optical media since it is turbid and nonhomogeneous. We suggest a new optical method for sensing physiological tissue state, based on the collection of the ejected light at all exit angles, to receive the full scattering profile. We built a unique set-up for noninvasive encircled measurement. We use a laser, a photodetector and finger tissues-mimicking phantoms presenting different optical properties. Our method reveals an isobaric point, which is independent of the optical properties. We compared the new finger tissues-like phantoms to others samples and found the linear dependence between the isobaric point's angle and the exact tissue geometry. These findings can be useful for biomedical applications such as non-invasive and simple diagnostic of the fingertip joint, ear lobe and pinched tissues.

Abstract. 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.