We describe a method for the preparation of a polyurethane phantom to simulate the optical properties of biologic tissues at two wavelengths in the visible and near-infrared spectral range. We characterize the addition of added molecular absorbers with relatively narrow absorption bands [full width at half maximum (FWHM) 32 and 76 nm for Epolight 6084 and 4148, respectively] for independent absorption at 690 nm for absorption up to 5 cm–1, and 830 nm for absorptions up to 3 cm–1. Absorption by both dyes is linear with concentration in these respective regions and is consistent in polyurethane both before and after curing. The dyes are stable over long durations with no more than 4% change. The absorption of visible light by polyurethane decreases with time and is stable by one year with a drop of 0.03±0.003 cm–1 from 500 to 830 nm. The scattering properties are selected by the addition of TiO2 particles to the polyurethane, which we functionally describe for the 690- and 830-nm wavelengths as related to the weight per volume. We demonstrate that the variation in absorption and scattering properties for large batch fabrication (12 samples) is ±3%. The optical properties of the phantoms have not significantly changed in a period of exceeding one year, which makes them suitable for use as a reference standard.
We report on the development of an optical-fiber-based diagnostic instrument to determine the local optical properties of a turbid media. The system relies on making differential diffuse reflection measurements. We present a method to correct for the variations in the spectral characteristics of the two spectrometers. We also introduce a novel method to evaluate the differential reflectance by encoding a relative wavelength sensitivity constant into the signal processing to account for differences in the spectral sensitivity between spectrometers. This method allows us to record differential reflectance without needing to make additional reference measurements before an experiment to account for spectral variation of the lamp.
A single fiber may be employed to emit and collect light from a optically diffusing medium such as biological tissues. However, the light collected by the fiber consists of two components: diffusely scattered light from within the tissue and specularly reflected light from the surfaces. Only the diffuse reflection contains the desired information regarding the optical absorption and scattering properties of the tissue, but the specular component is comparable in magnitude to the diffuse reflection with visible light. The refractive index mismatch between the fiber and tissue account for a portion of the specular reflection. However, imperfect contact of the fiber with the surface of tissue creates additional boundaries and thus additional specular reflections. Experiments are performed with a 200 micron diameter fiber and a 632.8 nm He-Ne source to characterize the specular reflection collected through the same fiber using water as a coupling medium. The angular collection efficiency is measured for a fiber in contact with the surface on a glass substrate (specular reflection only) and an epoxy resin tissue phantom (specular and diffuse reflection components). Next, the collection efficiency is measured for a separation between the fiber and the samples for perpendicular illumination to the surface, 14 degrees, and 25 degrees from normal. Imperfect contact is demonstrated to vary the amount of specular reflection collected using a single fiber where changes in angle greater than 4 degrees or a separation between the fiber and the surface in excess of 400 micron caused a minimum of 7 percent reduction of the collected specular reflection.
A new method for tissue soldering using an argon ion beam coagulator (ABC) and human serum albumin is presented. The ABC is widely used in surgery and provides a fast and precise means of achieving hemostasis. In this paper, the mechanical properties of liver and denatured albumin (solder) were measured and the failure methods of liver repaired with albumin were identified. The ultimate tensile strength was measured for healthy liver (N=37) and thermally damaged liver (N=32). The ultimate tensile strength was measured for three concentrations of coagulated albumin (25, 38 and 53%) in a single layer and for two layers of denatured 38% albumin. Failure under tension of argon beam coagulator soldered liver on the parenchymal surface (N=30) with 38% albumin in two layers had a 70% occurrence for tearing at a mean stress of 39 kPa and a 23% occurrence for shearing at a mean stress of 7 kPa. Liver repaired on the interior surface (N=11) failed in tension by tearing (64%) at a mean stress of 34 kPa and by shearing (36%) at a mean stress of 6 kPa. Argon beam coagulator soldering with 38% albumin took 6 s/cm2 for two layers of solder and gave the best balance of usability and strength.
Sized-fiber reflectometry describes a device and method for measuring absorption and reduced scattering of tissue using optical fibers with different diameters. The device used in this paper consists of two fibers with diameters of 200 and 600 microns. Each fiber emits and collects its own backscattered light. Monte Carlo simulations tabulating the diffuse reflectance collected by 200 and 600 micron fibers in a semi-infinite homogenous media are presented for an absorption, (mu) a range of 0.2-30 cm-1 and a reduced scattering, (mu) s range of 10-200 cm-1. The diffuse reflectance collected by a 600 micron fiber may be approximated by a near relation to the 200 micron fiber. An empirical relation is derived relating the reduced scattering coefficient to the diffuse reflectance collected with 200 and 600 micron fibers. The sensitivity of the relation is determined for changes in each fiber measurement. Finally, in vivo diffuse reflection measurements and reduced scattering coefficient of skin are presented using the aforementioned fiber sizes with a wavelength range of 400-800 nm.
Sized-fiber array spectroscopy describes a device for measuring the absorption and reduced scattering properties of tissue. The device consists of two fibers with different diameters that measure the amount of light back-scattered into each fiber. Only one fiber emits and collects light at a time. Recent innovations allow for spatially limited measurement diffuse reflectance over a wavelength range of 500-800 nm. Reflection spectra of in vitro an din vivo porcine tissue are presented for a device with 200 and 600 micrometers fibers to demonstrate its performance.