Experimental test of theoretical models for time-resolved reflectance
ABSTRACT Four different expressions, derived from the diffusion theory or the random walk model, were used to fit time-resolved reflectance data for the evaluation of tissue optical properties. The experimental reflectance curves were obtained from phantoms of known optical parameters (absorption and transport scattering coefficients) covering the range of typical values for biological tissues between 600 and 900 nm. The measurements were performed using an instrumentation for time-correlated single-photon counting. The potential of the four methods in the assessment of the absorption and transport scattering coefficients was evaluated in terms of absolute error, linearity error, and dispersion of data. Each method showed different performances depending on the optical properties of the sample and the experimental conditions. We propose some criteria for the optimal choice of the fitting method to be used in different applications.
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- "The trailing flank is cut where the photon count drops below 1% of the peak count. Discussions on appropriate fit regions are found in Hielscher et al (1995) and Cubeddu et al (1996). The best fit is reached iteratively using a "
ABSTRACT: In recent years, extensive efforts have been made in developing near-infrared optical techniques to be used in detection and diagnosis of breast cancer. Variations in optical properties of normal breast tissue set limits to the performance of such techniques and must therefore be thoroughly examined. In this paper, we present intra- and intersubject as well as contralateral variations of optical and physiological properties in breast tissue as measured by using four-wavelength time-resolved spectroscopy (at 660, 786, 916 and 974 nm). In total, 36 volunteers were examined at five regions at each breast. Optical properties (absorption, mu(a), and reduced scattering, mu'(s)) are derived by employing diffusion theory. The use of four wavelengths enables determination of main tissue chromophores (haemoglobin, water and lipids) as well as haemoglobin oxygenation. Variations in all evaluated properties seen over the entire breast are approximately twice those for small-scale heterogeneity (millimetre scale). Intrasubject variations in optical properties are almost in all cases below 20% for mu'(s), and 40% for mu(a). Overall variations in water, lipid and haemoglobin concentrations are all in the order of 20%. Oxygenation is the least variable of the quantities evaluated, overall intrasubject variations being 6% on average. Extracted physiological properties confirm differences between pre- and post-menopausal breast tissue. Results do not indicate systematic differences between left and right breasts.Physics in Medicine and Biology 07/2005; 50(11):2559-71. DOI:10.1088/0031-9155/50/11/008 · 2.92 Impact Factor
- Department of Physics, Lund University, , Degree: PhD
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ABSTRACT: The objective is derived from the need for a reliable absorption spectrum of lipids for component analysis of in vivo tissue spectra. NIR in vivo spectroscopy enables to derive the concentration of the key tissue constituents absorbing in the 600-1100 nm range, that is oxy- and deoxy- hemoglobin, water and lipids. Yet, although the first three constituents are already well characterized in literature, quite few data are available on mammalian lipids. In the present proceeding we report the absorption spectrum of a clear purified oil obtained from pig lard. Absorption coefficients were measured with time resolved and spatially resolved diffuse reflectance spectroscopy techniques. At temperatures of 37 °C and higher it is a clear transparent liquid thus suitable for collimated transmission measurements. In total three independent measurement techniques were employed the determine the absorption coefficients of mammalian lipids. The absorption spectra obtained from NIR spectroscopic techniques are supposed to be a linear combination of the absorption spectra of the chromophores present in the tissue. Decomposition of the measured absorption spectra into its components can be used to quantify absolute tissue chromophore concentrations. Furthermore, tissue oxygenation and total haemoglobin content can be calculated from these quantities. It is therefore essential to have detailed knowledge of the intrinsic absorption spectra of these 4 components. Oxy, de-oxy hemoglobin spectra and water are well-quantified en commonly applied. A basic tissue fat spectrum however has not been determined so far. The fat spectra used for spectral decomposition vary among the different research groups. These spectra all differ from each other with respect to their spectral shape as well as the magnitude of the main absorption peaks and may contain chlorophylls, making absolute comparison and interpretation of results and techniques impossible. The reason for the absence of a basic fat spectrum in the literature is that saturated mammalian fat is not available as a pure clear liquid. In the present paper we report the absorption spectrum of a clear oil obtained from mammalian pig lard. At room temperature this oil is a solid grease that displays strong scattering properties. Absorption and scattering properties of this solid grease were measured using time resolved and spatially resolved diffuse reflectance spectroscopy (TRS and DRS). At temperatures of 37°C and higher it is a clear liquid with only minimal scattering properties. Hence, an independent measurement of the absorption spectrum can be made using collimated transmission measurements.