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Monte Carlo simulations of backscattered light intensity from convex and concave surfaces with an optical fiber array sensor
Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
Linköping University, Department of Biomedical Engineering, Biomedical Instrumentation. Linköping University, The Institute of Technology.
2006 (English)In: Proceedings of the SPIE - Optical Interactions with Tissue and Cells XVII, SPIE - International Society for Optical Engineering, 2006, Vol. 6084, 8-18 p.Conference paper, Published paper (Other academic)
Abstract [en]

In a previous study, we presented a new technique for representationof the shape of a scattering surface. A sensor basedon two parallel fiber arrays yielded a source-detector intensity matrix(SDIM). In that study, it was shown that convex andconcave polyacetal plastic (Delrin) surfaces could be accurately distinguished usingthe proposed technique. A simplified simulation model for calculating theSDIM was used, assuming that backscattered light was generated byLambertian sources in the illuminated surface. These simulations showed discrepanciescompared to measurements, probably due to the absence of lightscattering in the model.Here, we will present an improved model,based on the Monte Carlo technique for light transport inturbid media. The optical properties of the Delrin phantoms wereestimated by means of different measurement techniques. The optical propertiesand the geometry of the Delrin phantoms were implemented inthe model along with the spatial distribution of the sourceand detector fibers of the sensor. The SDIM was extractedfrom backscattered photons exiting the turbid medium from the curvedsurface. The SDIM:s obtained with the Monte Carlo model, showeda much closer agreement with the measurements than those obtainedwith the Lambertian model. The small discrepancies observed are probablydue to spatially varying optical properties of the plastic phantoms.Measurements, using the previously described sensor, of the SDIM fromDelrin pieces with convex and concave surfaces, are compared tothe SDIM extracted from simulations using the Monte Carlo model.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2006. Vol. 6084, 8-18 p.
Series
Proceedings of SPIE (Progress in biomedical optics and imaging), ISSN 1605-7422 ; 6084
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-13010DOI: 10.1117/12.659550ISI: 000237158300002OAI: oai:DiVA.org:liu-13010DiVA: diva2:17660
Conference
Optical Interactions with Tissue and Cells XVII, 21 January 2006, San Jose, CA, USA
Available from: 2008-03-20 Created: 2008-03-20 Last updated: 2014-01-31Bibliographically approved
In thesis
1. Optical Methods for Tympanic Membrane Characterisation: Towards Objective Otoscopy in Otitis Media
Open this publication in new window or tab >>Optical Methods for Tympanic Membrane Characterisation: Towards Objective Otoscopy in Otitis Media
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Otitis media, which is an upper respiratory tract infection that affect the middle ear, is the second most common disease in childhood, outnumbered in prevalence only by the common cold. Diagnosis of middle ear inflammation is often performed in the primary healthcare where the normal procedure involves anamnesis and physical examination of the tympanic membranes (TM) of the patient, usually be means of otoscopy. The general aim of this thesis was to develop optical methods that enable quantification of TM characteristics associated with otitis media. Diffuse reflectance spectroscopy was applied to quantify TM erythema using previously suggested erythema detection algorithms. Healthy TM:s were significantly distinguished from TM:s with induced erythema (p < 0.01) and from TM:s in ears with mucous middle ear effusion (p < 0.05). A new technique for surface shape assessment based on an on-axis dual fibre array incorporated in an otoscope was developed and evaluated in ear models and on tympanic membranes from harvested temporal bones. The technique utilises the combined effects of source-detector fibre separation and fibre-to-sample distance on the detected light intensity.

Optical phantoms, both polyacetal plastic solids and latex membranes, were utilised to demonstrate the ability of the surface shape assessment technique to differentiate between convex and concave surfaces – as a bulging tympanic membrane is typically associated with acute otitis media whereas a retracted eardrum is associated with otitis media with effusion. Monte Carlo simulations of the surface shape data were performed in order to validate the experimental results with a theoretical model that are consistent with light transport theory. Retracted and bulging tympanic membranes from harvested temporal bones could be separated with a single measurement, given that variations in measurement distance were accounted for and that measurement from normally positioned tympanic membranes were used for signal normalization. In conclusion, the studies implicate that for individual otitis diagnosis, the hyperaemic tympanic membrane was separated from the healthy by application of erythema indices using diffuse reflectance spectroscopy. Moreover, bulging and retracted positions of the tympanic membrane were separable by means of the source-detector intensity matrix. For further clinical studies it is reasonable to assume that data from both methods are needed for diagnosis.

Place, publisher, year, edition, pages
Institutionen för medicinsk teknik, 2008. 97 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1173
Keyword
Optical Methods, Spectroscopy, Surface Curvature, Monte Carlo, Tympanic Membrane, Otitis Media
National Category
Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:liu:diva-11246 (URN)978-91-7393-933-1 (ISBN)
Public defence
2008-04-11, Berzeliussalen, Ingång 65, plan 9, Campus US, Linköpings universitet, Linköping, 13:00 (English)
Opponent
Supervisors
Available from: 2008-03-20 Created: 2008-03-20 Last updated: 2009-05-14

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Sundberg, MikaelLindbergh, TobiasStrömberg, Tomas

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