Optical phantoms mimicking spectral properties of laboratory mouse biotissues D.A. Loginova1,2, E.A. Sergeeva1, P.D. Agrba2, and M. Yu. Kirillin1 1 Institute of Applied Physics RAS, Nizhny Novgorod, Russia 2 Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia  

Introduction Optical measurements in visible and NIR wavelengths are widely applied in biomedical diagnostics due to the ability of visible and NIR light to non-destructively penetrate into a tissue to a depth of several centimeters Optical methods advantages Non-invasive and safe Highly spatial resolution Actual problems: approbation approaches calibration of optical systems comparison of the different systems efficiencies .

Optical phantoms Optical phantoms, stable medium with known optical properties close to those of biological tissues, are necessary to approbate and calibrate optical measurements. Phantoms are also used in diffuse optical tomography for filling cells with small laboratory animals, for example, to suppress the effect of complex boundaries. Usually the main phantom components are Intralipid (or Lipofundin) and black India ink, however, usage of only these components doesn’t allow designing phantoms simulating the optical characteristics in wide spectral range. The aim of this study was measuring the optical properties of murine biotissues ex vivo in the visible and IR regions and developing optical phantoms mimicking their optical properties in a wide spectral range.

Spectrophotometry measurements [1] Integrating sphere Spectral range: 380-1100nm Sphere diameter: 75 мmm material: spectralon The spectral dependences of collimated transmittance Tc, diffuse transmittance Td, and diffuse reflectance Rd were measured within the range 400 – 1100 nm using an Analytikjena Specord 250 plus spectrophotometer equipped with an integrating sphere. [1] R. R. Anderson and J. A. Parrish, The Science of Photomedicine , Plenum Press, New York, 1982, pp. 147–194.

Determination methods of optical properties Theoretical models are used for the optical characteristics reconstruction: The diffusion approximation. Reconstruction was carried out in accordance with the relations from [1]. This method is applicable for samples with weak absorption ( ) The low-order backward scattering approximation[2]. This method is applicable for samples with a thickness smaller than or of the order of the transport length for samples whose absorption coefficient is comparable with the backscattering scattering coefficient (scattering to the backward hemisphere). [1] Krainov A.D., Mokeeva A.M., Sergeeva E.A., Agrba P.D., Kirillin M.Yu. Opt. Spektrosk., 115 (2), 47 (2013). [2] Sergeeva E.A., Krainov A.D., Agrba P.D., Kirillin M.Yu. Metodika GSSSD ME 217-2014 (FGUP Standartinform,26.03.2014, No. 911a – 2014).

The low-order backward scattering approximation The relations used in this method are based on the modified Bouguer – Lambert – Beer (BLB) law. Absorption coefficient: Scattering coefficient: Applicability: Estimation: Sergeeva E.A., Krainov A.D., Agrba P.D., Kirillin M.Yu. Metodika GSSSD ME 217-2014 (FGUP Standartinform,26.03.2014, No. 911a – 2014).

Spectral properties of murine brain The spectral dependences of the optical properties of mouse brain biotissue ex vivo were determined from the measured spectral characteristics Tc, Td and Rd in the low-order backward scattering approximation and compared to results of other groups. [1] [2] [1] [1] M. Mesradi, A. Genoux, V. Cuplov, D. A. Haidar, S. Jan, I. Buvat and F. Pain  J. Biomed. Opt. 18 (11), 117010 (2013) [2] Moy A.J., Capulong B.V., Saager R.B., Wiersma M.P., Lo P.C., Durkin A.J., Choi B. J. Biomed. Opt., 20(9), 095010, (2015).

Spectral properties of murine muscle The spectral dependences of the optical properties of mouse muscle biotissue ex vivo were determined from the measured spectral characteristics Tc, Td and Rd in the low-order backward scattering approximation . [1] [1] [1] M. Mesradi, A. Genoux, V. Cuplov, D. A. Haidar, S. Jan, I. Buvat and F. Pain  J. Biomed. Opt. 18 (11), 117010 (2013)

Optical properties of phantom components In this study the phantoms are composed of aqueous solutions of Lipofundin MCT/LCT 20% and inks with different absorption characteristics. 1 – blue Ink 2 – red Ink 3 – fuchsia Ink Lipofundin absorption is considerably weaker than scattering, and Lipofundin parameters were reconstructed using the diffusion approximation of the radiation transfer theory. The optical properties of inks were reconstructed in the low-order backscattering approximation because the absorption coefficient for the considered concentrations significantly exceeded the total scattering coefficient. Lipofundin MCT/LCT

Brain phantom for 480-1000 nm. Comparison of the spectral properties b – brain p - phantom

Muscle phantom for 530-779 nm. Comparison of the spectral properties m – muscle, p - phantom

Summary Optical properties of murine brain and muscle biotissues ex vivo were measured in the range of 400-1100 nm Separately, the spectral characteristics of model medium chosen as phantom components were studied. Comparison of the optical properties measured immediately after phantom preparation and after chosen time intervals showed that these properties differ by no more than 5 %, which characterizes phantoms as stable optical media Comparison of the spectral characteristics of the brain biotissue of four mice in work [1] showed that the variation in the coefficients for different individuals can reach 30 %. Thus, we mimic the optical properties with a discrepancy no larger than the variations of optical properties from object to object. [1] M. Mesradi, A. Genoux, V. Cuplov, D. A. Haidar, S. Jan, I. Buvat and F. Pain  J. Biomed. Opt. 18 (11), 117010 (2013)

Acknowledgements The study is supported by Russian Foundation for Basic Research (grants No. 15-02-04270 and 15-32-20227)