Modified optical coefficient measurements using a single high-NA fiber with detection parameter changes at a tip

To avoid the instability of an optical coefficient measurement using sliced tissue preparation, an attenuation coefficient measurement by puncturing an optical fiber in bulk tissue have been reported. We proposed a modified puncturing method to obtain an absorption coefficient and scattering coefficient by increasing optical information. We used the light intensity measurement through a single high-NA fiber puncturing into an optically thick bulk tissue varying detection parameters, the depth and field of view (FOV), at the tip. The light intensity measurement and ray trace calculation using the Monte Carlo method (inverse or normal) were employed. We constructed the measurement system which can change the FOV at the fiber tip inside the bulk tissue using the variable aperture outside the bulk tissue. A 200 μmΦ NA:0.5 fiber installed in a 21G needle was punctured down to surface of the bulk tissue to measure light intensity in the bulk tissue. Using homogeneous optical model solution, the accuracy about attenuation coefficients of the constructed experimental system was confirmed. The error in the attenuation coefficient was up to 1.4%. We demonstrated the optical coefficient measurement of porcine myocardium using the proposed method. To fit dependence of the measured attenuation coefficients on FOV, we decided that the absorption coefficient, the scattering coefficient, and anisotropic parameter were 0.2 mm^-1, 10 mm^-1, and 0.96, respectively. We proposed modified puncturing optical coefficient measurement varying depth and FOV. We demonstrated its usefulness on myocardium.