Evaluation of a fiberoptic-based system for measurement of optical properties in highly attenuating turbid media

• Main Authors: Matchette L Stephanie, Agrawal Anant, Sharma Divyesh, Pfefer T Joshua
• Format: Article
• Language: English
• Published: BMC 2006-08-01
• Series: BioMedical Engineering OnLine
• Online Access: http://www.biomedical-engineering-online.com/content/5/1/49

<p>Abstract</p> <p>Background</p> <p>Accurate measurements of the optical properties of biological tissue in the ultraviolet A and short visible wavelengths are needed to achieve a quantitative understanding of novel optical diagnostic devices. Currently, there is minimal information on optical property measurement approaches that are appropriate for <it>in vivo </it>measurements in highly absorbing and scattering tissues. We describe a novel fiberoptic-based reflectance system for measurement of optical properties in highly attenuating turbid media and provide an extensive <it>in vitro </it>evaluation of its accuracy. The influence of collecting reflectance at the illumination fiber on estimation accuracy is also investigated.</p> <p>Methods</p> <p>A neural network algorithm and reflectance distributions from Monte Carlo simulations were used to generate predictive models based on the two geometries. Absolute measurements of diffuse reflectance were enabled through calibration of the reflectance system. Spatially-resolved reflectance distributions were measured in tissue phantoms at 405 nm for absorption coefficients (μ_a) from 1 to 25 cm^-1and reduced scattering coefficients (<m:math name="1475-925X-5-49-i1" xmlns:m="http://www.w3.org/1998/Math/MathML"><m:semantics><m:mrow><m:msub><m:msup><m:mi>μ</m:mi><m:mo>′</m:mo></m:msup><m:mtext>s</m:mtext></m:msub></m:mrow><m:annotation encoding="MathType-MTEF"> MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8akY=wiFfYdH8Gipec8Eeeu0xXdbba9frFj0=OqFfea0dXdd9vqai=hGuQ8kuc9pgc9s8qqaq=dirpe0xb9q8qiLsFr0=vr0=vr0dc8meaabaqaciaacaGaaeqabaqabeGadaaakeaacuaH8oqBgaqbamaaBaaaleaacqqGZbWCaeqaaaaa@3007@</m:annotation></m:semantics></m:math>) from 5 to 25 cm^-1. These data and predictive models were used to estimate the optical properties of tissue-simulating phantoms.</p> <p>Results</p> <p>By comparing predicted and known optical properties, the average errors for μ_aand <m:math name="1475-925X-5-49-i1" xmlns:m="http://www.w3.org/1998/Math/MathML"><m:semantics><m:mrow><m:msub><m:msup><m:mi>μ</m:mi><m:mo>′</m:mo></m:msup><m:mtext>s</m:mtext></m:msub></m:mrow><m:annotation encoding="MathType-MTEF"> MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8akY=wiFfYdH8Gipec8Eeeu0xXdbba9frFj0=OqFfea0dXdd9vqai=hGuQ8kuc9pgc9s8qqaq=dirpe0xb9q8qiLsFr0=vr0=vr0dc8meaabaqaciaacaGaaeqabaqabeGadaaakeaacuaH8oqBgaqbamaaBaaaleaacqqGZbWCaeqaaaaa@3007@</m:annotation></m:semantics></m:math> were found to be 3.0% and 4.6%, respectively, for a linear probe approach. When bifurcated probe data was included and samples with μ_avalues less than 5 cm^-1were excluded, predictive errors for μ_aand <m:math name="1475-925X-5-49-i1" xmlns:m="http://www.w3.org/1998/Math/MathML"><m:semantics><m:mrow><m:msub><m:msup><m:mi>μ</m:mi><m:mo>′</m:mo></m:msup><m:mtext>s</m:mtext></m:msub></m:mrow><m:annotation encoding="MathType-MTEF"> MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8akY=wiFfYdH8Gipec8Eeeu0xXdbba9frFj0=OqFfea0dXdd9vqai=hGuQ8kuc9pgc9s8qqaq=dirpe0xb9q8qiLsFr0=vr0=vr0dc8meaabaqaciaacaGaaeqabaqabeGadaaakeaacuaH8oqBgaqbamaaBaaaleaacqqGZbWCaeqaaaaa@3007@</m:annotation></m:semantics></m:math> were further reduced to 1.8% and 3.5%.</p> <p>Conclusion</p> <p>Improvements in system design have led to significant reductions in optical property estimation error. While the incorporation of a bifurcated illumination fiber shows promise for improving the accuracy of <m:math name="1475-925X-5-49-i1" xmlns:m="http://www.w3.org/1998/Math/MathML"><m:semantics><m:mrow><m:msub><m:msup><m:mi>μ</m:mi><m:mo>′</m:mo></m:msup><m:mtext>s</m:mtext></m:msub></m:mrow><m:annotation encoding="MathType-MTEF"> MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8akY=wiFfYdH8Gipec8Eeeu0xXdbba9frFj0=OqFfea0dXdd9vqai=hGuQ8kuc9pgc9s8qqaq=dirpe0xb9q8qiLsFr0=vr0=vr0dc8meaabaqaciaacaGaaeqabaqabeGadaaakeaacuaH8oqBgaqbamaaBaaaleaacqqGZbWCaeqaaaaa@3007@</m:annotation></m:semantics></m:math> estimates, further study of this approach is needed to elucidate the source of discrepancies between measurements and simulation results at low μ_avalues.</p>