Henricus J. C. M. Sterenborg

The determination of in vivo human tissue optical properties and absolute chromophore concentrations using spatially resolved steady-state diffuse reflectance spectroscopy

A method is described for measuring optical properties and deriving chromophore concentrations from diffuse reflection measurements at the surface of a turbid medium. The method uses a diffusion approximation model for the diffuse reflectance, in combination with models for the absorption and scattering coefficients. An optical fibre-based set-up, capable of measuring nine spectra from 400 to 1050 nm simultaneously, is used to test the method experimentally. Results of the analyses of phantom and in vivo measurements are presented. These demonstrate that in the wavelength range from 600 to 900 nm, tissue scattering can be described as a simple power dependence of the wavelength and that the tissue absorption can be accurately described by the addition of water, oxy- and deoxyhaemoglobin absorption.

Double-integrating-sphere system for measuring the optical properties of tissue

A system is described and evaluated for the simultaneous measurement of the intrinsic optical properties of tissue: the scattering coefficient, the absorption coefficient, and the anisotropy factor. This system synthesizes the theory of two integrating spheres and an intervening scattering sample with the inverse adding-doubling algorithm, which employs the adding-doubling solution of the radiative transfer equation to determine the optical properties from the measurement of the light flux within each sphere and of the unscattered transmission. The optical properties may be determined simultaneously, which allows for measurements to be made while the sample undergoes heating, chemical change, or some otherexternal stimulus. An experimental validation of the system with tissue phantoms resulted in the determination of the optical properties with a < 5% deviation when the optical density was between 1 and 10 and the albedo was between 0.4 and 0.95.

Determination of visible near-IR absorption coefficients of mammalian fat using time- and spatially resolved diffuse reflectance and transmission spectroscopy

In-vivo optical spectroscopy and the determination of tissue absorption and scattering properties have a central role in the development of novel optical diagnostic and therapeutic modalities in medicine. A number of techniques are available for the optical characterization of tissue in the visible near-IR region of the spectrum. An important consideration for many of these techniques is the reliability of the absorption spectrum of the various constituents of tissue. The availability of accurate absorption spectra in the range 600 to 1100 nm may allow for the determination of the concentration of key tissue constituents such as oxy- and deoxy-hemoglobin, water, and lipids. The objective of the current study is the determination of a reliable absorption spectrum of lipid(s) that can be used for component analysis of in-vivo spectra. We report the absorption spectrum of a clear purified oil obtained from pig lard. In the liquid phase above 36 degrees C, the oil is transparent and thus suitable for collimated transmission measurements. At room temperature, the oil is a solid grease that is highly scattering. The absorption and scattering properties in this solid phase are measured using time- and spatially resolved diffuse reflectance spectroscopy. Using these three independent measurement techniques, we have determined an accurate estimate for the absorption spectrum of mammalian fat.

In vivo measurement of the local optical properties of tissue by use of differential path-length spectroscopy

We demonstrate the capability of differential path-length spectroscopy (DPS) to determine the local optical properties of tissue in vivo. DPS measurements on bronchial mucosa are analyzed and yield information on the local blood oxygenation, blood content, average microvessel diameter, and wavelength dependence of the reduced scattering coefficient. Our data collected to date show that cancerous bronchial mucosa has a lower capillary oxygenation and a larger average capillary diameter than normal bronchial mucosa.

Performance assessment of photon migration instruments: the MEDPHOT protocol

We propose a comprehensive protocol for the performance assessment of photon migration instruments. The protocol has been developed within the European Thematic Network MEDPHOT (optical methods for medical diagnosis and monitoring of diseases) and is based on five criteria: accuracy, linearity, noise, stability, and reproducibility. This protocol was applied to a total of 8 instruments with a set of 32 phantoms, covering a wide range of optical properties.

Optical Image-Guided Cancer Surgery: Challenges and Limitations

Optical image-guided cancer surgery is a promising technique to adequately determine tumor margins by tumor-specific targeting, potentially resulting in complete resection of tumor tissue with improved survival. However, identification of the photons coming from the fluorescent contrast agent is complicated by autofluorescence, optical tissue properties, and accurate fluorescent targeting agents and imaging systems. All these factors have an important influence on the image that is presented to the surgeon. Considering the clinical consequences at stake, it is a prerequisite to answer the questions that are essential for the surgeon. What is optical image-guided surgery and how can it improve patient care? What should the oncologic surgeon know about the fundamental principles of optical imaging to understand which conclusions can be drawn from the images? And how do the limitations influence clinical decision making? This article discusses these questions and provides a clear overview of the basic principles and practical applications. Although there are limitations to the intrinsic capacity of the technique, when practical and technical surgical possibilities are considered, optical imaging can be a very powerful intraoperative tool in guiding the future oncologic surgeon toward radical resection and optimal clinical results. Clin Cancer Res; 19(14); 3745–54. ©2013 AACR.

Estimation of lipid and water concentrations in scattering media with diffuse optical spectroscopy from 900 to 1600 nm

We demonstrate a method to estimate the concentrations of water and lipid in scattering media such as biological tissues with diffuse optical spectra acquired over the range of 900 to 1600 nm. Estimations were performed by fitting the spectra to a model of light propagation in scattering media derived from diffusion theory. To validate the method, spectra were acquired from tissue phantoms consisting of lipid and water emulsions and swine tissues ex vivo with a two-fiber probe.

Measurement of the local optical properties of turbid media by differential path-length spectroscopy

We report on the development of an optical-fiber-based diagnostic tool with which to determine the local optical properties of a turbid medium. By using a single fiber in contact with the medium to deliver and detect white light, we have optimized the probability of detection of photons scattered from small depths. The contribution of scattered light from greater depths to the signal is measured and subtracted with an additional fiber, i.e., a collection fiber, to yield a differential backscatter signal. Phantoms demonstrate that, when photons have large mean free paths compared with the fiber diameter, single scattering dominates the differential backscatter signal. When photons have small mean free paths compared with the fiber diameter, the apparent path length of the photons that contribute to the differential backscatter signal becomes approximately equal to 4/5 of the fiber diameter. This effect is nearly independent of the optical properties of the sample under investigation.

Topical Application of 5‐Aminolevulinic Acid Hexyl Ester and 5‐Aminolevulinic Acid to Normal Nude Mouse Skin: Differences in Protoporphyrin IX Fluorescence Kinetics and the Role of the Stratum Corneum¶

Abstract An important limitation of topical 5-aminolevulinic acid (ALA)-based photodetection and photodynamic therapy is that the amount of the fluorescing and photosensitizing product protoporphyrin IX (PpIX) formed is limited. The reason for this is probably the limited diffusion of ALA through the stratum corneum. A solution to this problem might be found in the use of ALA derivatives, as these compounds are more lipophilic and therefore might have better penetration properties than ALA itself. Previous studies have shown that ALA hexyl ester (ALAHE) is more successful than ALA for photodetection of early (pre)malignant lesions in the bladder. However, ALA pentyl ester slightly increased the in vivo PpIX fluorescence in early (pre)malignant lesions in hairless mouse skin compared to ALA. The increased PpIX fluorescence is located in the stratum corneum and not in the dysplastic epidermal layer. In the present study, ALA- and ALAHE-induced PpIX fluorescence kinetics are compared in the normal nude mouse skin, of which the permeability properties differ from the bladder. Application times and ALA(HE) concentrations were varied, the effect of a penetration enhancer and the effect of tape stripping the skin before or after application were investigated. Only during application for 24 h, did ALAHE induce slightly more PpIX fluorescence than ALA. After application times ranging from 1 to 60 min, ALA-induced PpIX fluorescence was higher than ALAHE-induced PpIX fluorescence. ALA also induced higher PpIX production than ALAHE after 10 min of application with concentrations ranging from 0.5 to 40%. The results of experiments with the penetration enhancer and tape stripping indicated that the stratum corneum acts a barrier against ALA and ALAHE. Use of penetration enhancer or tape stripping enhanced the PpIX production more in the case of ALAHE application than in the case of ALA application. This, together with the results from the different application times and concentrations indicates that ALAHE diffuses more slowly across the stratum corneum than ALA.

Estimation of biological chromophores using diffuse optical spectroscopy: Benefit of extending the UV-VIS wavelength range to include 1000 to 1600 nm

With an optical fiber probe, we acquired spectra from swine tissue between 500 and 1600 nm by combining a silicon and an InGaAs spectrometer. The concentrations of the biological chromophores were estimated by fitting a mathematical model derived from diffusion theory. The advantage of our technique relative to those presented in previous studies is that we extended the commonly-used wavelength ranges of 500 and 1000 nm to include the range of 1000 to 1600 nm, where additional water and lipid absorption features exist. Hence, a more accurate estimation of these two chromophores is expected when spectra are fitted between 500 and 1600 nm than between 500 and 1000 nm. When extending the UV-VIS wavelength range, the estimated total amount of chromophores approached 100% of the total as present in the probed volume. The confidence levels of the water and lipid related parameters increases by a factor of four.