Interferometric Tissue Characterization: I: Theory

Паез, Гонзало; Strojnik, Marija; Scholl, M. K.

doi:10.1117/12.621274

Cited by 11 publications

(5 citation statements)

References 1 publication

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“…If there are M different tissue components with different attenuation coefficients, then there is attenuation inside the material i of length x i , with attenuation coefficient µ i . 13,14 Figure 1 depicts the light path through the target (biological tissue in this case). We assume that the beam pass through the M materials in the sample sequentially in time, and the output beam has less intensity (it is attenuated).…”

Section: Intensity Attenuation Through Tissuementioning

confidence: 99%

Development of noise-immune oximetry: theory and measurement

2006

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We examine the feasibility of applying oximetry for the assessment of the degree of brain activity. Changes in concentration of oxygenated and deoxygenated hemoglobin may be used to determine the activity levels through differential attenuation in red and infrared (IR) spectral lines. We extend the classical mathematical model for oxygen saturation to include multiplicative and additive noises, signal gain, and detector responsivity. We perform temporal correlation between two signals (red and IR) to increase immunity to noise. This is particularly important when we consider dynamic biological processes and that the movement is always present. In the literature the difficulty of movement (differences in optical paths) is resolved with electronic solutions. We improve the effect of time displacement between signals at the level of equations. The considerations of noise in the saturation expression are significant when the signal levels approach zero.

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Section: Intensity Attenuation Through Tissuementioning

confidence: 99%

Development of noise-immune oximetry: theory and measurement

2006

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“…7-9 Therefore, we have proposed a biomedical technique that focuses on the utilization of pass-through photons to perform analysis. [10][11][12] In the following section, we review practical and theoretical aspects of the method we propose for the isolation of passthrough photons. The need of MC analysis for determining the temporal behavior of such radiation is established in the third part of this work.…”

Section: Tissue Entropy and Information Of Pass-through Photonsmentioning

confidence: 99%

Monte-Carlo simulation of photon trans-illumination time of flight

Vacas-Jacques

Strojnik

Паез

2007

Novel Optical Instrumentation for Biomedical Applications III

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We present a Monte Carlo (MC) program for determining the temporal behavior of radiation in turbid media, in general, and a tissue, in particular. An object-oriented MC program with flexibility for parallel implementation, and for performing stochastic analysis, is described. We determine the temporal probability distribution functions for three tissues: I ) a lipid-based tissue phantom, II ) a healthy dental tissue, and III ) a dental tissue with caries. The expected time of flight for transmitted radiation is calculated. Signal-to-noise ratios (SNR) are then obtained for several temporal thresholds. By restraining the time threshold, a two orders of magnitude increase in SNR is predicted. A multivariate analysis is finally proposed to complement the discrimination process, necessary for trans-illumination interferometry. Tissue entropy and information of pass-through photonsThe relevance of any diagnostic technique, including the biomedical ones, resides in its capacity to provide specific information concerning the phenomenon under study. For example, in order to recognize certain types of tissues (those not possessing intrinsic luminescent characteristics) when performing fluorescence microscopy, extrinsic fluorophores are necessary. 1-3 In this case, without the addition of such fluorophores, fluorescence microscopy yields no usable information. That is to say, fluorescence microscopy is irrelevant until extrinsic fluorophores that bind to the tissue of interest are utilized. The importance of this example is that every diagnostic technique should seek to maximize the return of useful information.First, though, it is necessary to establish means to assess the amount of information that a certain technique may unveil. The mathematical formulation of information theory presents a firm foundation to achieve this task. 4,5 In order to fathom the concept of information, probability theory is necessary since both are closely interrelated. Our intuitive notion of information is as follows: events that are highly unlikely (i.e., less probable) to occur reveal much information, whereas events that arise frequently (i.e., highly probable) are less informative. Therefore, a method of diagnosis that seeks to maximize information, would theoretically focus on the assessment of physical phenomena that are less likely to occur. Speaking of entropy rather than information, we would say that diagnostic techniques that center their attention on characteristics that are less likely to arise, generate diagnoses with more informative content as compared to those approaches studying the complementary physical characteristics.Taking this short intuitive discussion as background, we may reflect upon the phenomena that occur frequently in radiation-tissue interactions. Instantaneously scattering and absorption events come to mind. These two phenomena arise very frequently in tissue optics. Figure 1 depicts a Monte Carlo (MC) simulation evidencing such recurrent events in a layered tissue-like configuration.To illustrate qualitativel...

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“…It is indispensable (both ballistic and forward-scattered radiation are transmitted) to identify a process for discriminating between scattered and ballistic radiation. 1,2 In this paper, we present a mathematical model, considering an interferometric setup, to separate the ballistic from the scattered radiation. Furthermore, our experimental results demonstrate that this separation of signal from noise is feasible.…”

Section: Transillumination Interferometry and Current Diagnostic Techmentioning

confidence: 99%

Reduced coherence and calibration optimization for transillumination interferometry

2007

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We compare the detected signal in the radiometric transillumination experiment for two sources: a gas laser with high coherence, and an LED with low coherence. Detected signal is significantly improved when a low-coherent light source is utilized, allowing us to clearly separate ballistic photons from those that undergo multiple scattering. The preliminary experimental results confirm the feasibility of the concept, requiring precise matching of the source coherence with the scattering behavior of the tissue (phantom) under study.

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Interferometric Tissue Characterization: I: Theory

Cited by 11 publications

References 1 publication

Development of noise-immune oximetry: theory and measurement

Development of noise-immune oximetry: theory and measurement

Monte-Carlo simulation of photon trans-illumination time of flight

Reduced coherence and calibration optimization for transillumination interferometry

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