| 1. |
- Alerstam, Erik, et al.
(författare)
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Improved accuracy in time-resolved diffuse reflectance spectroscopy.
- 2008
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Ingår i: Optics Express. - 1094-4087. ; 16:14, s. 10440-10454
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Tidskriftsartikel (refereegranskat)abstract
- Significant improvements in the accuracy of time-resolved diffuse reflectance spectroscopy are reached by using a Monte Carlo scheme for evaluation of measured photon time-of-flight distributions. The use of time-resolved diffusion theory of photon migration, being the current standard scheme for data evaluation, is shown defective. In particular, the familiar problem sometimes referred to as absorption-to-scattering coupling or crosstalk, is identified as an error related to the breakdown of the diffusion approximation. These systematic errors are investigated numerically using Monte Carlo simulations, and their influence on data evaluation of experimental recordings are accurately predicted. The proposed Monte Carlo-based data evaluation avoids these errors, and can be used for routine data evaluation. The accuracy and reproducibility of both MC and diffusion modeling are investigated experimentally using the MEDPHOT set of solid tissue-simulating phantoms, and provides convincing arguments that Monte Carlo-based evaluation is crucial in important ranges of optical properties. In contrast to diffusion-based evaluation, the Monte Carlo scheme results in optical properties consistent with phantom design. Since the MEDPHOT phantoms are used for international comparisons and performance assessment, the performed characterization is carefully reported.
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| 2. |
- Alerstam, Erik, et al.
(författare)
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Observation of anisotropic diffusion of light in compacted granular porous materials
- 2012
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Ingår i: Physical Review E (Statistical, Nonlinear, and Soft Matter Physics). - 1539-3755. ; 85:4
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Tidskriftsartikel (refereegranskat)abstract
- By analyzing spatio-temporal characteristics of short optical pulses diffusively transmitted through compacted granular materials, we reveal that powder compaction can give rise to strongly anisotropic light diffusion. Our disclosure represents a revision of the understanding of optics of powder compacts. Routes to material characterization and investigation of compression-induced structural anisotropy are opened, and the falsification of isotropic models have implications for quantitative spectroscopy of powder compacts (e.g., pharmaceutical tablets).
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| 3. |
- Alerstam, Erik, et al.
(författare)
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Parallel computing with graphics processing units for high-speed Monte Carlo simulation of photon migration.
- 2008
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Ingår i: Journal of Biomedical Optics. - : SPIE-Intl Soc Optical Eng. - 1083-3668. ; 13:6
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Tidskriftsartikel (refereegranskat)abstract
- General-purpose computing on graphics processing units (GPGPU) is shown to dramatically increase the speed of Monte Carlo simulations of photon migration. In a standard simulation of time-resolved photon migration in a semi-infinite geometry, the proposed methodology executed on a low-cost graphics processing unit (GPU) is a factor 1000 faster than simulation performed on a single standard processor. In addition, we address important technical aspects of GPU-based simulations of photon migration. The technique is expected to become a standard method in Monte Carlo simulations of photon migration.
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| 4. |
- 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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| 5. |
- Alerstam, Erik, et al.
(författare)
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White Monte Carlo for time-resolved photon migration.
- 2008
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Ingår i: Journal of Biomedical Optics. - : SPIE-Intl Soc Optical Eng. - 1083-3668. ; 13:4
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Tidskriftsartikel (refereegranskat)abstract
- A novel scheme for fully scalable White Monte Carlo (WMC) has been developed and is used as a forward solver in the evaluation of experimental time-resolved spectroscopy. Previously reported scaling problems are avoided by storing detection events individually, turning spatial and temporal binning into post-simulation activities. The approach is suitable for modeling of both interstitial and noninvasive settings (i.e., infinite and semi-infinite geometries). Motivated by an interest in in vivo optical properties of human prostate tissue, we utilize WMC to explore the low albedo regime of time-domain photon migration--a regime where the diffusion approximation of radiative transport theory breaks down, leading to the risk of overestimating both reduced scattering (mu(s)') and absorption (mu(a)). Experimental work supports our findings and establishes the advantages of Monte Carlo-based evaluation.
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| 6. |
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| 7. |
- Lindahl, Göran, et al.
(författare)
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Centrala Jönköping : Den Nordiska Trästaden
- 1972
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Rapport (populärvet., debatt m.m.)abstract
- Konsthögskolans Arkitektur skola har under studieåret 1971-72 behandlat förnyelseproblemen i centrala Jönköping. Huvudvikten har lagts vid de problem som uppstått vid över gången från 60-talets överhettade konjunktur till 70-talets mera dämpade. I denna situation framstår det som naturligt att begränsa eller hejda den omdaningsprocess i Jönköpings centrala delar, som i så hög grad varit ett uttryck för de expansiva årens förväntningar. Denna typ av restriktiv planering förutsätter en mycket detaljerad kunskap om den befintliga bebyggelsen och dess utnyttjande. Föreliggande arbete bygger således på inventeringar, genomförda på platsen, och på tillgängligt utredningsmaterial som förmedlats av kommunens tjänstemän. Studierna har koncentrerats till två områden i staden, som representerar var sitt skede i Jönköpings byggnadshistoria, och som också bedömts möjliga att bevara.
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| 8. |
- Svensson, Tomas, et al.
(författare)
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Disordered, strongly scattering porous materials as miniature multipass gas cells
- 2011
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 107:14
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the interaction of light and gas in strongly scattering nano- and macroporous media. Manufacturing and structural characterization of ZrO2, Al2O3 and TiO2 ceramics with different pore sizes, measurements of optical properties using photon time-of-flight spectroscopy, and high-resolution laser spectroscopy of O 2 at 760 nm are reported. We show that extreme light scattering can be utilized to realize miniature spectroscopic gas cells. Path length enhancement factors up to 750 are reached (5.4 m path through gas for light transmitted through a 7 mm ZrO2 with 49% porosity and 115 nm pores). © 2011 American Physical Society.
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| 9. |
- 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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| 10. |
- Svensson, Tomas, et al.
(författare)
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Near-infrared photon time-of-flight spectroscopy of turbid materials up to 1400 nm
- 2009
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 80:6
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Tidskriftsartikel (refereegranskat)abstract
- Photon time-of-flight spectroscopy (PTOFS) is a powerful tool for analysis of turbid materials. We have constructed a time-of-flight spectrometer based on a supercontinuum fiber laser, acousto-optical tunable filtering, and an InP/InGaAsP microchannel plate photomultiplier tube. The system is capable of performing PTOFS up to 1400 nm, and thus covers an important region for vibrational spectroscopy of solid samples. The development significantly increases the applicability of PTOFS for analysis of chemical content and physical properties of turbid media. The great value of the proposed approach is illustrated by revealing the distinct absorption features of turbid epoxy resin. Promising future applications of the approach are discussed, including quantitative assessment of pharmaceuticals, powder analysis, and calibration-free near-infrared spectroscopy.
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