| 261. |
- Svensson, Tomas, et al.
(författare)
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VCSEL-based oxygen spectroscopy for structural analysis of pharmaceutical solids
- 2008
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 90:2, s. 345-354
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Tidskriftsartikel (refereegranskat)abstract
- We present a minimalistic and °exible single-beam instrumen- tation based for sensitive tunable diode laser absorption spectroscopy (TD- LAS) and its use in structural analysis of highly scattering pharmaceu- tical solids. By utilising a vertical-cavity surface emitting laser (VCSEL) for sensing of molecular oxygen dispersed in tablets, we address structural properties such as porosity. Experiments involve working with unknown pathlengths, severe backscattering and di®use light. These unusual experi- mental conditions has lead to the use of the term gas in scattering media absorption spectroscopy (GASMAS). By employing fully digital wavelength modulation spectroscopy and coherent sampling, system sensitivity in am- bient air experiments reaches the 10¡7 range. Oxygen absorption exhibited by our tablets, being in°uenced by both sample porosity and scattering, were in the range 8 £ 10¡5 to 2 £ 10¡3, and corresponds to 2-50 mm of pathlength through ambient air (Leq). The day-to-day reproducibility was on average 1.8% (0.3 mm Leq), being limited by mechanical positioning. This is the ¯rst time sub-millimetre sensitivity is reached in GASMAS. We also demonstrate measurements on gas transport on a 1 s timescale. By employing pulsed illumination and time-correlated single photon counting, we reveal that GASMAS exhibits excellent correlation with time-domain photon migration. In addition, we introduce an optical measure of porosity by relating oxygen absorption to average photon time-of-°ight. Finally, the simplicity, robustness and low cost of this novel TDLAS instrumentation provides industrial potential.
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| 262. |
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| 263. |
- Swartling, Johannes, et al.
(författare)
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Changes in tissue optical properties due to radio-frequency ablation of myocardium
- 2003
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Ingår i: Medical & Biological Engineering & Computing. - 0140-0118. ; 41:4, s. 403-409
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Tidskriftsartikel (refereegranskat)abstract
- The optical properties of pig heart tissue were measured after in vivo ablation therapy had been performed during open-heart surgery. In vitro samples of normal and ablated tissue were subjected to measurements with an optically integrating sphere set-up in the region 470-900nm. Three independent measurements were made: total transmittance, total reflectance and collimated transmittance, which made it possible to extract the absorption and scattering coefficients and the scattering anisotropy factor g, using an inverse Monte Carlo model. Between 470 and 700nm, only the reduced scattering coefficient and absorption could be evaluated. The absorption spectra were fitted to known tissue chromophore spectra, so that the concentrations of haemoglobin and myoglobin could be estimated. The reduced scattering coefficient was compared with Mie computations to provide Mie equivalent average radii. Most of the absorption was from myoglobin, whereas haemoglobin absorption was negligible. Metmyoglobin was formed in the ablated tissue, which could yield a spectral signature to distinguish the ablated tissue with a simple optical probe to monitor the ablation therapy. The reduced scattering coefficient increased by, on average, 50% in the ablated tissue, which corresponded to a slight decrease in the Mie equivalent radius.
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| 264. |
- Swartling, Johannes, et al.
(författare)
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Comparison of spatially and temporally resolved diffuse-reflectance measurement systems for determination of biomedical optical properties
- 2003
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Ingår i: Applied Optics. - 2155-3165. ; 42:22, s. 4612-4620
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved and spatially resolved measurements of the diffuse reflectance from biological tissue are two well-established techniques for extracting the reduced scattering and absorption coefficients. We have performed a comparison study of the performance of a spatially resolved and a time-resolved instrument at wavelengths 660 and 785 nm and also of an integrating-sphere setup at 550-800 nm. The first system records the diffuse reflectance from a diode laser by means of a fiber bundle probe in contact with the sample. The time-resolved system utilizes picosecond laser pulses and a single-photon-counting detection scheme. We extracted the optical properties by calibration using known standards for the spatially resolved system, by fitting to the diffusion equation for the time-resolved system, and by using an inverse Monte Carlo model for the integrating sphere. The measurements were performed on a set of solid epoxy tissue phantoms. The results showed less than 10% difference in the evaluation of the reduced scattering coefficient among the systems for the phantoms in the range 9-20 cm(-1), and absolute differences of less than 0.05 cm(-1) for the absorption coefficient in the interval 0.05-0.30 cm(-1). (C) 2003 Optical Society of America.
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| 265. |
- Swartling, Johannes, et al.
(författare)
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Estimation of depth of fluorescing lesions in tissue from changes in fluorescence spectra
- 2005
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Ingår i: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 5693:1, s. 225-231
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Konferensbidrag (refereegranskat)abstract
- We present a novel method for estimating the depth of a fluorescent lesion in tissue based on measurements of the fluorescence signal in different wavelength bands. The measured fluorescence spectrum following irradiation by excitation light at the surface is a function of several parameters, because the fluorescence light has to pass through tissue with characteristic scattering and absorption properties. Thus, the intrinsic fluorescence spectrum will be altered, in a way determined by the tissue optical properties, the depth of the fluorophore, and also by the geometry of the light irradiation and the detection system. By analyzing the ratio between the signals at two wavelengths we show that it is possible to estimate the depth of the lesion. We have performed Monte Carlo simulations and measurements on an Intralipid phantom in the wavelength range 850 - 1000 nm. By taking the ratio between the signals at the wavelengths 875 and 930 nm the depth of a fluorescing layer could be determined with 0.8 mm accuracy down at least a depth of 10 mm. Monte Carlo simulations were also performed for different tissue types with various composition. The results indicate that depth estimation of a lesion is possible with no assumptions made about the optical properties for a wide range of tissues
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| 266. |
- Swartling, Johannes, et al.
(författare)
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Fluorescence spectra provide information on the depth of fluorescent lesions in tissue
- 2005
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Ingår i: Applied Optics. - 2155-3165. ; 44:10, s. 1934-1941
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Tidskriftsartikel (refereegranskat)abstract
- The fluorescence spectrum measured from a fluorophore in tissue is affected by the absorption and scattering properties of the tissue, as well as by the measurement geometry. We analyze this effect with Monte Carlo simulations and by measurements on phantoms. The spectral changes can be used to estimate the depth of a fluorescent lesion embedded in the tissue by measurement of the fluorescence signal in different wavelength bands. By taking the ratio between the signals at two wavelengths, we show that it is possible to determine the depth of the lesion. Simulations were performed and validated by measurements on a phantom in the wavelength range 815-930 nm. The depth of a fluorescing layer could be determined with 0.6-mm accuracy down to at least a depth of 10 mm. Monte Carlo simulations were also performed for different tissue types of various composition. The results indicate that depth estimation of a lesion should be possible with 2-3-mm accuracy, with no assumptions made about the optical properties, for a wide range of tissues.
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| 267. |
- Swartling, Johannes, et al.
(författare)
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Rigorous characterization of time-resolved diffuse spectroscopy systems for measurements of absorption and scattering properties using solid phantoms
- 2003
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 5138, s. 80-87
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Konferensbidrag (refereegranskat)abstract
- Two systems for measurements of absorption and scattering properties, based on picosecond-pulse lasers and single-photon counting detection, were characterized using a detailed protocol. The first system utilizes diode lasers at 660, 785, 910 and 974 nm as light sources. The second employs a Ti:sapphire and a mode-locked dye laser to produce tunable pulses in the range 610 - 1000 nm. Using solid tissue phantoms, the systems were rigorously characterized and compared in terms of absolute accuracy of the measured scattering and absorption coefficients, the linearity over the parameter range, the precision with respect to injected light energy, the stability over time, and the reproducibility of the results. The phantoms were made of epoxy resin with TiO as scatterer and black toner powder as absorber.
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| 268. |
- Swartling, Johannes, et al.
(författare)
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System for interstitial photodynamic therapy with online dosimetry: first clinical experiences of prostate cancer.
- 2010
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Ingår i: Journal of Biomedical Optics. - : SPIE-Intl Soc Optical Eng. - 1083-3668 .- 1560-2281. ; 15:5
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Tidskriftsartikel (refereegranskat)abstract
- The first results from a clinical study for Temoporfin-mediated photodynamic therapy (PDT) of low-grade (T1c) primary prostate cancer using online dosimetry are presented. Dosimetric feedback in real time was applied, for the first time to our knowledge, in interstitial photodynamic therapy. The dosimetry software IDOSE provided dose plans, including optical fiber positions and light doses based on 3-D tissue models generated from ultrasound images. Tissue optical property measurements were obtained using the same fibers used for light delivery. Measurements were taken before, during, and after the treatment session. On the basis of these real-time measured optical properties, the light-dose plan was recalculated. The aim of the treatment was to ablate the entire prostate while minimizing exposure to surrounding organs. The results indicate that online dosimetry based on real-time tissue optical property measurements enabled the light dose to be adapted and optimized. However, histopathological analysis of tissue biopsies taken six months post-PDT treatment showed there were still residual viable cancer cells present in the prostate tissue sections. The authors propose that the incomplete treatment of the prostate tissue could be due to a too low light threshold dose, which was set to 5 J∕cm2.
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| 269. |
- Thompson, Alex, et al.
(författare)
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Hyperspectral fluorescence lifetime fibre probe spectroscopy for use in the study and diagnosis of osteoarthritis and skin cancer
- 2011
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Ingår i: Optical Biopsy IX. - : SPIE. - 1605-7422. - 9780819484321 ; 7895
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Konferensbidrag (refereegranskat)abstract
- We present the application of two fibre-optic-coupled time-resolved spectrofluorometers and a compact steady-state diffuse reflected light/fluorescence spectrometer to in vivo and ex vivo studies of skin cancer and osteoarthritis. In a clinical study of skin cancer, 27 lesions on 25 patients were investigated in vivo before surgical excision of the region measured. Preliminary analysis reveals a statistically significant decrease in the autofluorescence lifetime of basal cell carcinomas compared to neighbouring healthy tissue. A study of autofluorescence signals associated with the onset of osteoarthritis indicates autofluorescence lifetime changes associated with collagen degradation.
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| 270. |
- Thompson, Alex J., et al.
(författare)
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In vivo measurements of diffuse reflectance and time-resolved autofluorescence emission spectra of basal cell carcinomas
- 2012
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Ingår i: Journal of Biophotonics. - : Wiley. - 1864-063X. ; 5:3, s. 240-254
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present a clinical investigation of diffuse reflectance and time-resolved autofluorescence spectra of skin cancer with an emphasis on basal cell carcinoma. A total of 25 patients were measured using a compact steady-state diffuse reflectance/fluorescence spectrometer and a fibre-optic-coupled multispectral time-resolved spectrofluorometer. Measurements were performed in vivo prior to surgical excision of the investigated region. Singular value decomposition was used to reduce the dimensionality of steady state diffuse reflectance and fluorescence spectra. Linear discriminant analysis was then applied to the measurements of basal cell carcinomas (BCCs) and used to predict the tissue disease state with a leave-one-out methodology. This approach was able to correctly diagnose 87% of the BCCs. With 445 nm excitation a decrease in the spectrally averaged fluorescence lifetime was observed between normal tissue and BCC lesions with a mean value of 886 ps. Furthermore, the fluorescence lifetime for BCCs was lower than that of the surrounding healthy tissue in all cases and statistical analysis of the data revealed that this decrease was significant (p = 0.002). (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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