| 1. |
- Alerstam, Erik, et al.
(författare)
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Single-fiber diffuse optical time-of-flight spectroscopy
- 2012
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Ingår i: Optics Letters. - 0146-9592. ; 37:14, s. 2877-2879
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate interstitial diffuse optical time-of-fight spectroscopy based on a single fiber for both light delivery and detection. Detector saturation due to the massive short-time reflection is avoided by ultrafast gating of a single photon avalanche diode. We show that the effects of scattering and absorption are separable and that absorption can be assessed independently of scattering. Measurements on calibrated liquid phantoms and subsequent Monte Carlo-based evaluation illustrate that absorption coefficients can be accurately assessed over a wide range of medically relevant optical properties. Our findings pave the way to simplified and less invasive interstitial in vivo spectroscopy. (C) 2012 Optical Society of America
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| 2. |
- Andersson-Engels, Stefan, et al.
(författare)
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Preliminary evaluation of two fluorescence imaging methods for the detection and the delineation of basal cell carcinomas of the skin
- 2000
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Ingår i: Lasers in Surgery and Medicine. - 0196-8092. ; 26:1, s. 76-82
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Tidskriftsartikel (refereegranskat)abstract
- Abstract Background and ObjectiveFluorescence techniques can provide powerful noninvasive means for medical diagnosis, based on the detection of either endogenous or exogenous fluorophores. The fluorescence of δ-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) has already shown promise for the diagnosis of tumors. The aim of the study was to investigate the localization of skin tumors after the topical application of ALA, by detecting the PpIX fluorescence either in the spectral or in the time domain.Study Design/Materials and MethodsTwo fluorescence imaging systems were used to identify basal cell carcinomas of the skin in humans, after topical application of 20% ALA ointment. Both systems rely on the comparison between the exogenous and the endogenous fluorescence, performed either in the spectral domain or in the time domain. The first system works by using three images acquired through different spectral filters, whereas the second one measures the spatial map of the average fluorescence lifetime of the sample.ResultsA clear demarcation of skin malignancies was successfully performed in vivo noninvasively with both fluorescence imaging systems.ConclusionThe two complementary approaches considered in the present study show promise for skin tumor detection and delineation based on specific fluorescence features. Lasers Surg. Med. 26:76–82, 2000. © 2000 Wiley-Liss, Inc.
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| 3. |
- Bargigia, Ilaria, et al.
(författare)
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Diffuse optical techniques applied to wood characterisation
- 2013
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Ingår i: Journal of Near Infrared Spectroscopy. - : SAGE Publications. - 0967-0335 .- 1751-6552. ; 21:4, s. 259-268
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Tidskriftsartikel (refereegranskat)abstract
- We propose an optical method for non-invasive characterisation of wood samples based on two optical techniques: time-resolved diffuse optical spectroscopy and gas in scattering media absorption spectroscopy. While the latter is sensitive to gases present inside wood pores, the former extracts information on the bulk material regarding light scattering and absorption. Measurements on spruce samples, cut along different wood fibre directions, are presented to show an example of the advantages of this combined approach: by applying these two non-destructive techniques together, in fact, relevant information on wood such as porosity, permeability and moisture content can be assessed. Furthermore, the chemical composition, internal structure and the anisotropy due to the wood fibres can be investigated.
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| 4. |
- Bossi, Alessandro, et al.
(författare)
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Time domain diffuse Raman spectroscopy using single pixel detection
- 2023
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Ingår i: Biomedical Optics Express. - 2156-7085. ; 14:11, s. 5749-5763
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Tidskriftsartikel (refereegranskat)abstract
- Diffuse Raman spectroscopy (DIRS) extends the high chemical specificity of Raman scattering to in-depth investigation of thick biological tissues. We present here a novel approach for time-domain diffuse Raman spectroscopy (TD-DIRS) based on a single-pixel detector and a digital micromirror device (DMD) within an imaging spectrometer for wavelength encoding. This overcomes the intrinsic complexity and high cost of detection arrays with ps-resolving time capability. Unlike spatially offset Raman spectroscopy (SORS) or frequency offset Raman spectroscopy (FORS), TD-DIRS exploits the time-of-flight distribution of photons to probe the depth of the Raman signal at a single wavelength with a single source-detector separation. We validated the system using a bilayer tissue-bone mimicking phantom composed of a 1 cm thick slab of silicone overlaying a calcium carbonate specimen and demonstrated a high differentiation of the two Raman signals. We reconstructed the Raman spectra of the two layers, offering the potential for improved and quantitative material analysis. Using a bilayer phantom made of porcine muscle and calcium carbonate, we proved that our system can retrieve Raman peaks even in the presence of autofluorescence typical of biomedical tissues. Overall, our novel TD-DIRS setup proposes a cost-effective and high-performance approach for in-depth Raman spectroscopy in diffusive media.
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| 5. |
- Johansson, Jonas, et al.
(författare)
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Time-Resolved Studies of Light Propagation in Crassula and Phaseolus Leaves
- 1999
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Ingår i: Photochemistry and Photobiology. - 0031-8655. ; 69:2, s. 242-247
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved transmittance was used to extract in vivo optical properties of leaves of green plants experimentally. In time-resolved transmittance measurements an ultrashort light pulse is directed onto the surface of the object and the transmitted light is measured with a time resolution in the range of picoseconds. A table-top terawatt laser was used to generate 200 fs light pulses at 790 nm with a repetition rate of 10 Hz. The light pulses were focused through a cuvette filled with water to produce white light pulses and optical filters were placed in the beam path to select the wavelength of the light focused onto the leaf surface. The time profiles of the light transmitted through the leaves was recorded with a streak camera having a time resolution of about 2.5 ps. Results from Crassula falcata and Phaseolus vulgaris studied at 550, 670 and 740 nm are reported. The three selected wavelength regions represent medium, high and a low absorption of light, respectively. A library of curves was generated using Monte Carlo simulation, and the absorption and scattering coefficients were extracted by comparison of experimental curves with this library. Our results suggest that in the case of the thin (200 μm) Phaseolus leaves and certainly in the case of the thick (4 mm) Crassula leaves, light scattering plays an important role in light transport through the leaf and should also affect light flux in these leaves.
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| 6. |
- Susnjar, Stefan, et al.
(författare)
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Reconstruction of Raman spectra of two-layer diffusive media: model-based approach in time-domain
- 2023
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Ingår i: Proceedings of SPIE : Diffuse Optical Spectroscopy and Imaging IX - Diffuse Optical Spectroscopy and Imaging IX. - 1996-756X .- 0277-786X. - 9781510664654 ; 12628, s. 1-126280
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Konferensbidrag (refereegranskat)abstract
- We propose a novel analytical time-domain model for migration of Raman scattered photons in inhomogeneous two-layer diffusive media. Based on this model, the methods for reconstruction of the Raman spectra of the two layers are developed, tested in simulations and validated on phantom measurements data.
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| 7. |
- Susnjar, Stefan, et al.
(författare)
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Two-layer reconstruction of Raman spectra in diffusive media based on an analytical model in the time domain
- 2023
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Ingår i: Optics Express. - 1094-4087. ; 31:24, s. 40573-40591
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Tidskriftsartikel (refereegranskat)abstract
- We derive and validate an analytical model that describes the migration of Raman scattered photons in two-layer diffusive media, based on the diffusion equation in the time domain. The model is derived under a heuristic approximation that background optical properties are identical on the excitation and Raman emission wavelengths. Methods for the reconstruction of two-layer Raman spectra have been developed, tested in computer simulations and validated on tissue-mimicking phantom measurements data. Effects of different parameters were studied in simulations, showing that the thickness of the top layer and number of detected photon counts have the most significant impact on the reconstruction. The concept of quantitative, mathematically rigorous reconstruction using the proposed model was finally proven on experimental measurements, by successfully separating the spectra of silicone and calcium carbonate (calcite) layers, showing the potential for further development and eventual application in clinical diagnostics.
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| 8. |
- Svensson, Tomas, et al.
(författare)
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Light diffusion in quenched disorder : Role of step correlations
- 2014
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - : American Physical Society. - 1539-3755 .- 1550-2376. ; 89:2
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Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical and experimental study of light transport in disordered media with strongly heterogeneous distribution of scatterers formed via nonscattering regions. Step correlations induced by quenched disorder are found to prevent diffusivity from diverging with increasing heterogeneity scale, contrary to expectations from annealed models. Spectral diffusivity is measured for a porous ceramic where nanopores act as scatterers and macropores render their distribution heterogeneous. Results agree well with Monte Carlo simulations and a proposed analytical model.
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| 9. |
- 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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