| 1. |
- Lewander, Märta, et al.
(författare)
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Clinical system for non-invasive in situ monitoring of gases in the human paranasal sinuses
- 2009
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Ingår i: Optics Express. - 1094-4087. ; 17:13, s. 10849-10863
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Tidskriftsartikel (refereegranskat)abstract
- We present a portable system for non-invasive, simultaneous sensing of molecular oxygen (O-2) and water vapor (H2O) in the human paranasal cavities. The system is based on high-resolution tunable diode laser spectroscopy (TDLAS) and digital wavelength modulation spectroscopy (dWMS). Since optical interference and non-ideal tuning of the diode lasers render signal processing complex, we focus on Fourier analysis of dWMS signals and procedures for removal of background signals. Clinical data are presented, and exhibit a significant improvement in signal-to-noise with respect to earlier work. The in situ detection limit, in terms of absorption fraction, is about 5 x 10(-5) for oxygen and 5 x 10(-4) for water vapor, but varies between patients due to differences in light attenuation. In addition, we discuss the use of water vapor as a reference in quantification of in situ oxygen concentration in detail. In particular, light propagation aspects are investigated by employing photon time-of-flight spectroscopy. (C) 2009 Optical Society of America
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| 2. |
- Lewander, Märta, et al.
(författare)
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Non-invasive diagnostics of the maxillary and frontal sinuses based on diode laser gas spectroscopy
- 2012
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Ingår i: Rhinology. - 0300-0729. ; 50:1, s. 26-32
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Tidskriftsartikel (refereegranskat)abstract
- Problem: Suspected, but objectively absent, rhinosinusitis constitutes a major cause of visits to the doctor, high health care costs, and the over-prescription of antibiotics, contributing to the serious problem of resistant bacteria. This situation is largely due to a lack of reliable and widely applicable diagnostic methods. Method: A novel method for the diagnosis of rhinosinusitis based on non-intrusive diode laser gas spectroscopy is presented. The technique is based on light absorption by free gas (oxygen and water vapour) inside the sinuses, and has the potential to be a complementary diagnostic tool in primary health care. The method was evaluated on 40 patients with suspected sinus problems, referred to the diagnostic radiology clinic for low-dose computed tomography (CT), which was used as the reference technique. Main results:The data obtained with the new laser-based method correlated well with the grading of opacification and ventilation using CT. The sensitivity and specificity were estimated to be 93% and 61%, respectively, for the maxillary sinuses, and 94% and 86%, respectively, for the frontal sinuses. Good reproducibility was shown. Principal conclusion: The laser-based technique presents real-time clinical data that correlate well to CT findings, while being non-intrusive and avoiding the use of ionizing radiation.
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| 3. |
- Lindberg, Sven, et al.
(författare)
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Method for Studying Gas Composition in the Human Mastoid Cavity by Use of Laser Spectroscopy
- 2012
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Ingår i: Annals of Otology, Rhinology & Laryngology. - 0003-4894. ; 121:4, s. 217-223
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: We evaluated a method for gas monitoring in the mastoid cavity using tunable diode laser spectroscopy by comparing it to simultaneously obtained computed tomographic (CT) scans. Methods: The presented optical technique measures free gases, oxygen (O2), and water vapor (H2O) within human tissue by use of low-power diode lasers. Laser light was sent into the tip of the mastoid process, and the emerging light at the level of the antrum was captured with a detector placed on the skin. The absorption of H2O was used to monitor the probed gas volume of the mastoid cavity, and it was compared to the CT scan measured volume. The ratio between O2 absorption and H2O absorption estimated the O2 content in the mastoid cavity and thus the ventilation. The parameters were compared to the grading of mastoid cavities based on the CT scans (n = 31). The reproducibility of the technique was investigated by measuring each mastoid cavity 4 times. Results: Both O2 and H2O were detected with good reproducibility. The H2O absorption and the CT volume correlated (r = 0.69). The average ratio between the normalized O2 absorption and the H2O absorption signals was 0.7, indicating a lower O2 content than in surrounding air (expected ratio, 1.0), which is consistent with previous findings made by invasive techniques. All mastoid cavities with radiologic signs of disease were detected. Conclusions: Laser spectroscopy monitoring appears to be a usable tool for noninvasive investigations of gas composition in the mastoid cavity, providing important clinical information regarding size and ventilation.
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| 4. |
- Persson, Linda, et al.
(författare)
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Non-intrusive optical study of gas and its exchange in human maxillary sinuses - art. no. 662804
- 2007
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Ingår i: Diagnostic Optical Spectroscopy in Biomedicine IV. - : SPIE. - 1996-756X .- 0277-786X. ; 6628, s. 62804-62804
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Konferensbidrag (refereegranskat)abstract
- We demonstrate a novel non-intrusive technique based on tunable diode laser absorption spectroscopy to investigate human maxillary sinuses in vivo. The technique relies on the fact that free gases have much sharper absorption features (typical a few GHz) than the surrounding tissue. Molecular oxygen was detected at 760 nm. Volunteers have been investigated by injecting near-infrared light fibre-optically in contact with the palate inside the mouth. The multiply scattered light was detected externally by a handheld probe on and around the cheek bone. A significant signal difference in oxygen imprint was observed when comparing volunteers with widely different anamnesis regarding maxillary sinus status. Control measurements through the hand and through the cheek below the cheekbone were also performed to investigate any possible oxygen offset in the setup. These provided a consistently non-detectable signal level. The passages between the nasal cavity and the maxillary sinuses were also non-intrusively optically studied, to the best of our knowledge for the first time. These measurements provide information on the channel conductivity which may prove useful in facial sinus diagnostics. The results suggest that a clinical trial together with an ear-nose-throat (ENT) clinic should be carried out to investigate the clinical use of the new technique.
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| 5. |
- Abrahamsson, Christoffer, et al.
(författare)
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Time and wavelength resolved spectroscopy of turbid media using light continuum generated in a crystal fiber
- 2004
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Ingår i: Optics Express. - 1094-4087. ; 12:17, s. 4103-4112
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Tidskriftsartikel (refereegranskat)abstract
- We report a novel system for time-resolved diffuse remission spectral measurements, based on short light continuum pulses generated in an index-guided crystal fiber, and a spectrometer-equipped streak camera. The system enables spectral recordings of absorption and reduced scattering coefficients of turbid media in the wavelength range 500 - 1200 nm with a spectral resolution of 5 nm and a temporal resolution of 30 ps. The optical properties are calculated by fitting the solution of the diffusion equation to the time-dispersion curve at each wavelength. Example measurements are presented from an apple, a finger and a pharmaceutical tablet. (C) 2004 Optical Society of America.
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| 6. |
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| 7. |
- Andersson, Mats, et al.
(författare)
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Flexible lock-in detection system based on synchronized computer plug-in boards applied in sensitive gas spectroscopy
- 2007
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 78:11
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Tidskriftsartikel (refereegranskat)abstract
- We present a flexible and compact, digital, lock-in detection system and its use in high-resolution tunable diode laser spectroscopy. The system involves coherent sampling, and is based on the synchronization of two data acquisition cards running on a single standard computer. A software-controlled arbitrary waveform generator is used for laser modulation, and a four-channel analog/digital board records detector signals. Gas spectroscopy is performed in the wavelength modulation regime. The coherently detected signal is averaged a selected number of times before it is stored or analyzed by software-based, lock-in techniques. Multiple harmonics of the modulation signal 1f, 2f, 3f, 4f, etc. are available in each single data set. The sensitivity is of the order of 10−5, being limited by interference fringes in the measurement setup. The capabilities of the system are demonstrated by measurements of molecular oxygen in ambient air, as well as dispersed gas in scattering materials, such as plants and human tissue.
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| 8. |
- Chauchard, F, et al.
(författare)
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Least-squares support vector machines modelization for time-resolved spectroscopy
- 2005
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Ingår i: Applied Optics. - 2155-3165. ; 44:33, s. 7091-7097
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Tidskriftsartikel (refereegranskat)abstract
- By use of time-resolved spectroscopy it is possible to separate light scattering effects from chemical absorption effects in samples. In the study of propagation of short light pulses in turbid samples the reduced scattering coefficient and the absorption coefficient are usually obtained by fitting diffusion or Monte Carlo models to the measured data by use of numerical optimization techniques. In this study we propose a prediction model obtained with a semiparametric modeling technique: the least-squares support vector machines. The main advantage of this technique is that it uses theoretical time dispersion curves during the calibration step. Predictions can then be performed by use of data measured on different kinds of sample, such as apples.
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| 9. |
- Lewander, Märta, et al.
(författare)
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Non-intrusive measurements of headspace gas composition in liquid food packages made of translucent materials
- 2011
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Ingår i: Packaging Technology & Science. - : Wiley. - 0894-3214. ; 24:5, s. 271-280
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Tidskriftsartikel (refereegranskat)abstract
- The increase in chilled food consumption requires enhanced food safety and quality assurance. Food deteriorating processes are affected by the presence of oxygen, combined with factors such as time and temperature. To slow down deterioration processes and prolong shelf life, traditional packaging methods are being replaced by Modified Atmosphere Packaging (MAP), for example. Oxygen, which is naturally present in the headspace of most food packages, is then reduced and controlled. Many sensing techniques for food quality assurance have been developed; however, almost all are intrusive, increasing the complication level and causing sample waste. The purpose of this article is to introduce a non-intrusive technique (GASMAS) for measuring gas composition in the headspace of liquid food packages. The GASMAS method uses diode laser absorption spectroscopy combined with diffuse light propagation to analyze gas located inside solids and liquids. By illuminating the package from the outside and analyzing the scattered light that emerges, the absorption from the gas inside the headspace can be studied. The GASMAS technique was evaluated on a series of carton packages with high quality orange juice and a nitrogen headspace. A clear variation in oxygen content was measured for samples with different storage times. The results demonstrate the possibility of using the GASMAS method for non-intrusive quality measurements in food products and packaging. They also indicate the potential for non-intrusive quality assurance applications without waste of samples. A further development of the technique could include “in-line” quality control of packed food items throughout the food packaging supply chain.
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| 10. |
- Somesfalean, Gabriel, et al.
(författare)
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Temporal correlation scheme for spectroscopic gas analysis using multimode diode lasers
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:18
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Tidskriftsartikel (refereegranskat)abstract
- The reliability of diode lasers used in spectroscopic applications is limited by their intrinsic multimode and mode-jump behavior when wavelength-tuned by current or temperature. We report on a scheme for gas analysis based on temporal correlation between absorption signals from an unknown external and a known reference gas concentration, simultaneously recorded when the diode laser wavelength is temperature-tuned across absorption features of the gas of interest. This procedure, which does not require any knowledge of the exact spectrum, also eliminates light intensity fluctuations due to mode competition. The method is illustrated for atmospheric oxygen absorption applied to diffusion measurements.
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