Investigation of optical properties of dissected and homogenized biological tissue

Abstract

Knowledge of tissue optical properties, in particular the absorption μ a and the reduced scattering coefficient μ 0 s , is required for diagnostic and therapeutic applications in which the light distribution during treatment has to be known. As it is generally very difficult to obtain this information with sufficient accuracy in vivo, optical properties are often approximately determined on ex vivo tissue samples. In this case, the obtained optical properties may strongly depend on the sample preparation. The extent of the expectable preparationdependent differences was systematically investigated in comparative measurements on dissected and homogenized porcine tissue samples (liver, lung, brain, and muscle). These measurements were performed at wavelengths 520, 635, 660, and 785 nm, using a dual-step reflectance device and at a spectral range of 515 to 800 nm with an integrating sphere setup. In a third experiment, the density of tissue samples (dissected and homogenized) was investigated, as the characteristic of the packaging of internal tissue structures strongly influences the absorption and scattering. The standard errors of the obtained absorption and reduced scattering coefficients were found to be reduced in case of homogenized tissue. Homogenizing the tissues also allows a much easier and faster sample preparation, as macroscopic internal tissue structures are destroyed in the homogenized tissue so that a planar tissue sample with well-defined thickness can easily and accurately be prepared by filling the tissue paste into a cuvette. Consequently, a better reproducibility result was obtained when using homogenized samples. According to the density measurements accomplished for dissected and homogenized tissue samples, all types of tissues, except lung, showed a decrease in the density due to the homogenization process. The presented results are in good agreement for μ 0 s regardless of the preparation procedure, whereas μ a differs, probably influenced by blood content and dehydration. Because of faster and easier preparation and easier sample positioning, homogenization prior to measurement seems to be suitable for investigating the optical properties ex vivo. Additionally, by means of using the homogenization process, the sample size and thickness do not need to be particularly large, as is the case for most biopsies from the OR.

Optimization of anastomotic technique and gastric conduit perfusion with hyperspectral imaging in an experimental model for minimally invasive esophagectomy

“…Spectral reflectance was clearly different with a double-peak between 550 and 590 nm and higher values at 680 nm for physiological tissue compared to non-perfused gastric tissue as seen in Figure 2. These findings are in line with the descriptions of optical properties of oxygenated and deoxygenated hemoglobin in current literature [36][37][38] . This initial analysis serves as a reference point for the subsequent experiments as spectral reflectance of the critically perfused areas on the gastric conduit next to the stapling site is expected to be similar compared to the spectral reflectance of non-perfused gastric tissue.…”

Fluorescence and Treatment Light Monitoring for Interstitial Photodynamic Therapy

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Effects and side effects of plasmonic photothermal therapy in brain tissue

“…In particular, for small heterogeneous samples from biopsies or resections. However, homogenization of brain tissue is reported to cause an increase in absorption and decrease in scattering coefficients, which is attributed to the more even distribution of hemoglobin and to the destruction of membranes and other cellular structures when blending the tissue 24,25 . Furthermore, our storage of tissue may have altered the optical properties of the samples, as there are indications that refrigerating for 24-48 hours can cause a decrease in absorption and an increase in scattering of homogenized porcine liver tissue.…”