Removal of Analyte-Irrelevant Variations in Near-Infrared Tissue Spectra (original) (raw)
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Optics Express, 2007
A method to non-invasively and quantitatively measure muscle oxygen saturation (SmO 2 ) using broadband continuous-wave diffuse reflectance near infrared (NIR) spectroscopy is presented. The method obtained SmO 2 by first correcting NIR spectra for absorption and scattering of skin pigment and fat, then fitting to a Taylor expansion attenuation model. A non-linear least squares optimization algorithm with set boundary constraints on the fitting parameters was used to fit the model to the acquired spectra. A data preprocessing/optimization scheme for accurately determining the initial values needed for the optimization was also employed. The method was evaluated on simulated muscle spectra with 4 different scattering properties, as well as on in vivo forearm spectra from 5 healthy volunteer subjects during arterial occlusion. Measurement repeatability was assessed on 24 healthy volunteers with 5 repeated measurements, each separated by at least 48 hours.
Quantification in tissue near-infrared spectroscopy
Philosophical Transactions of the Royal Society B: Biological Sciences, 1997
In near–infrared spectroscopy (NIRS) of tissue, light attenuation is due to: (i) absorption from chromophores of fixed concentration, (ii) absorption from chromophores of variable concentration, and (iii) light scatter. NIRS is usually concerned with trying to quantify the concentrations of chromophores in category (ii), in particular oxy– and deoxyhaemoglobin (HbO 2 and Hb) and cytochrome oxidase. In the absence of scatter the total light absorption in the medium is a linear sum of that due to each chromophore. In a scattering medium like tissue, this linear summation is distorted because the optical path length at each wavelength may differ. This distorted spectrum is then superimposed upon a further wavelength–dependent attenuation arising from light loss due to scatter, which is a complex function of the tissue absorption and scattering coefficients ( μ a and μ s ), scattering phase function, and tissue and measurement geometry. Consequently, quantification of NIRS data is diffi...
Journal of Biomedical Optics, 1996
The aim of this study was to clarify the influence of subcutaneous adipose tissue (AT) thickness on nearinfrared (NIR) optical density and the penetration depth of light in muscle tissue in vivo. The thickness of adipose tissue in the leg was measured using ultrasonography in 12 young subjects. Optical densities (OD) at 775, 807, and 827 nm were measured when the distance between the light source and the detector was increased from 20 to 100 mm in 10 mm steps. Ultrasonography showed that AT thickness ranged from 4 to 10 mm. The OD increased with increasing distance between the light source and the detector in all subjects. At the same distance between the light source and the detector (30 mm), the OD values correlated negatively with AT thickness (r ϭ Ϫ0.79, −0.82, and −0.79 at 775, 807, and 827 nm, respectively). Ultrasonography also showed that only the extensor hallucis longus muscle (EHL), which is under the extensor digitrum longus muscle (EDL), was activated during the flexion of the big toe. In order to evaluate the penetration depth of NIR light, the depth of EHL was measured and the OD observed before and during flexion. When the distance between the light source and detector was set at 30 mm, the OD values before exercise ranged from 0.36 to 3.18 at 775 nm, from 0.19 to 2.43 at 807 nm, and from 0.15 to 1.60 at 827 nm. Changes in OD during exercise were detectable for all subjects, and the EHLs of the subjects were located 10.0 to 20.2 mm under the detector. However, when the light source-detector distance was set at 20 mm, changes in OD during exercise were detectable for only 2 subjects, whose AT thicknesses were 4.0 or 5.0 mm, and the EHLs of the subjects were 10.0 or 11.7 mm deep. At a distance of 40 mm, 9 out of 12 subjects showed changes in OD, and their AT thicknesses and EHL locations ranged from 6.4 to 10.0 mm and from 11.4 to 20.4 mm deep, respectively. However, at this distance, OD reached our instrumental limit (4.82) and no OD change could be detected in three subjects with small AT values (4.0, 4.0, and 5.3 mm). These findings suggested that the thinner the AT, the higher the OD when the light source and detector are set a certain distance apart, and that NIR light penetrates the muscle tissue at least deep enough to reach half the distance between the light source and the detector when the AT thickness ranges from 4 to 10 mm.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2011
Near-infrared spectroscopy (NIRS) has been shown to be one of the tools that can measure oxygenation in muscle and other tissues in vivo . This review paper highlights the progress, specifically in this decade, that has been made for evaluating skeletal muscle oxygenation and oxidative energy metabolism in sport, health and clinical sciences. Development of NIRS technologies has focused on improving quantification of the signal using multiple wavelengths to solve for absorption and scattering coefficients, multiple pathlengths to correct for the influence of superficial skin and fat, and time-resolved and phase-modulated light sources to determine optical pathlengths. In addition, advances in optical imaging with multiple source and detector pairs as well as portability using small wireless detectors have expanded the usefulness of the devices. NIRS measurements have provided information on oxidative metabolism in various athletes during localized exercise and whole-body exercise, a...
Physiological Reports, 2013
The potential interference of cutaneous circulation on muscle blood volume and oxygenation monitoring by near-infrared spectroscopy (NIRS) remains an important limitation of this technique. Spatially resolved spectroscopy (SRS) was reported to minimize the contribution of superficial tissue layers in cerebral monitoring but this characteristic has never been documented in muscle tissue monitoring. This study aims to compare SRS with the standard Beer-Lambert (BL) technique in detecting blood volume changes selectively induced in muscle and skin. In 16 healthy subjects, the biceps brachii was investigated during isometric elbow flexion at 70% of the maximum voluntary contractions lasting 10 sec, performed before and after exposure of the upper arm to warm air flow. From probes applied over the muscle belly the following variables were recorded: total hemoglobin index (THI, SRS-based), total hemoglobin concentration (tHb, BL-based), tissue oxygenation index (TOI, SRS-based), and skin blood flow (SBF), using laser Doppler flowmetry. Blood volume indices exhibited similar changes during muscle contraction but only tHb significantly increased during warming (+5.2 AE 0.7 lmol/LÁcm, an effect comparable to the increase occurring in postcontraction hyperemia), accompanying a 10-fold increase in SBF. Contraction-induced changes in tHb and THI were not substantially affected by warming, although the tHb tracing was shifted upward by (5.2 AE 3.5 lmol/LÁcm, P < 0.01). TOI was not affected by cutaneous warming. In conclusion, SRS appears to effectively reject interference by SBF in both muscle blood volume and oxygenation monitoring. Instead, BL-based parameters should be interpreted with caution, whenever changes in cutaneous perfusion cannot be excluded.
The use of muscle near-infrared spectroscopy in sport
2011
Near-infrared spectroscopy (NIRS) has been shown to be one of the tools that can measure oxygenation in muscle and other tissues in vivo. This review paper highlights the progress, specifically in this decade, that has been made for evaluating skeletal muscle oxygenation and oxidative energy metabolism in sport, health and clinical sciences. Development of NIRS technologies has focused on improving quantification of the signal using multiple wavelengths to solve for absorption and scattering coefficients, multiple pathlengths to correct for the influence of superficial skin and fat, and time-resolved and phase-modulated light sources to determine optical pathlengths. In addition, advances in optical imaging with multiple source and detector pairs as well as portability using small wireless detectors have expanded the usefulness of the devices. NIRS measurements have provided information on oxidative metabolism in various athletes during localized exercise and whole-body exercise, as well as training-induced adaptations. Furthermore, NIRS technology has been used in the study of a number of chronic health conditions. Future developments of NIRS technology will include enhancing signal quantification. In addition, advances in NIRS imaging and portability promise to transform how measurements of oxygen utilization are obtained in the future.
Physics in Medicine and Biology, 1998
The absorption and transport scattering coefficients of caucasian and negroid dermis, subdermal fat and muscle have been measured for all wavelengths between 620 and 1000 nm. Samples of tissue 2 mm thick were measured ex vivo to determine their reflectance and transmittance. A Monte Carlo model of the measurement system and light transport in tissue was then used to recover the optical coefficients. The sample reflectance and transmittance were measured using a single integrating sphere 'comparison' method. This has the advantage over conventional double-sphere techniques in that no corrections are required for sphere properties, and so measurements sufficiently accurate to recover the absorption coefficient reliably could be made. The optical properties of caucasian dermis were found to be approximately twice those of the underlying fat layer. At 633 nm, the mean optical properties over 12 samples were 0.033 mm −1 and 0.013 mm −1 for absorption coefficient and 2.73 mm −1 and 1.26 mm −1 for transport scattering coefficient for caucasian dermis and the underlying fat layer respectively. The transport scattering coefficient for all biological samples showed a monotonic decrease with increasing wavelength. The method was calibrated using solid tissue phantoms and by comparison with a temporally resolved technique. ‡ Present address:
Validation of tissue optical properties measurement using diffuse reflectance spectroscopy (DRS)
Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XXVIII
The effectiveness of photodynamic treatment depends on several factors including an accurate knowledge of optical properties of the tissue to be treated. Transmittance and diffuse reflectance spectroscopic techniques are commonly used to determine tissue optical properties. Although transmittance spectroscopy technique is accurate in determining tissue optical properties, it is only valid in an infinite medium and can only be used for interstitial measurements. Diffuse reflectance spectroscopy, on the other hand, is easily adapted to most tissue geometries including skin measurements that involve semi-infinte medium. However, the accuracy of the measured optical properties can be affected by uncertainty in the measurements themselves and/or due to the uncertainty in the fitting algorithm. In this study, we evaluate the accuracy of optical properties determination using diffuse reflectance spectroscopy implemented using a contact probe setup. We characterized the error of the optical properties fitted using two fitting algorithms, a wavelength wise fitting algorithm and a full reflectance spectral fitting algorithm. By conducting systematic investigation of the measurements and fitting algorithm of DRS, we gained an understanding of the uncertainties in the measured optical properties and outlined improvement measures to minimize these errors.