Biomedical subjects

Frank Scheffold

Publications and source records attributed to Frank Scheffold.

4 recordsLinked to original sources

PubMed2006

Quantitative modeling of laser speckle imaging.

We have analyzed the image formation and dynamic properties in laser speckle imaging (LSI) both experimentally and with Monte Carlo simulation. We show for the case of a liquid inclusion that the spatial resolution and the signal itself are both significantly affected by scattering from the turbid environment. Multiple scattering leads to blurring of the dynamic inhomogeneity as detected by LSI. The presence of a nonfluctuating component of scattered light results in the significant increase in the measured image contrast and complicates the estimation of the relaxation time. We present a refined processing scheme that allows a correct estimation of the relaxation time from LSI data.

Computer Simulation↗

PubMed2006

Multiple-scattering suppression in dynamic light scattering based on a digital camera detection scheme.

We introduce a charge-coupled device (CCD) camera-based detection scheme in dynamic light scattering that provides information on the single-scattered autocorrelation function even for fairly turbid samples. It is based on the single focused laser beam geometry combined with the selective cross-correlation analysis of the scattered light intensity. Using a CCD camera as a multispeckle detector, we show how spatial correlations in the intensity pattern can be linked to single- and multiple-scattering processes. Multiple-scattering suppression is then achieved by an efficient cross-correlation algorithm working in real time with a temporal resolution down to 0.02 s. Our approach allows access to the extensive range of systems that show low-order scattering by selective detection of the singly scattered light. Model experiments on slowly relaxing suspensions of titanium dioxide in glycerol were carried out to establish the validity range of our approach. Successful application of the method is demonstrated up to a scattering coefficient of more than micro(S) = 5 cm(-1) for the sample size of L = 1 cm.

Complex Mixtures↗

PubMed2004

Depolarization of backscattered linearly polarized light.

We formulate a quantitative description of backscattered linearly polarized light with an extended photon diffusion formalism taking explicitly into account the scattering anisotropy parameter g of the medium. From diffusing wave spectroscopy measurements, the characteristic depolarization length for linearly polarized light, lp , is deduced. We investigate the dependence of this length on the scattering anisotropy parameter g spanning an extended range from -1 (backscattering) to 1 (forward scattering). Good agreement is found with Monte Carlo simulations of multiply scattered light.

Journal Article↗

PubMed2001

Diffusing-Wave Spectroscopy of Concentrated Alumina Suspensions during Gelation.

Using diffusing-wave spectroscopy, we followed the aggregation and gelation of concentrated (30 vol%) alumina suspensions. The suspensions were destabilized by either shifting the pH to the isoelectric point or by increasing the ionic strength. Both effects can be achieved continuously and homogeneously by using an enzyme-catalyzed internal chemical reaction. Based on the light-scattering data, we could derive quantitative information about the sol-gel transition and the viscoelastic properties of the gels, as well as a characterization of changes in the microstructure. The elastic moduli determined from light scattering are found to be in good agreement with rheological measurements. Copyright 2001 Academic Press.

Journal Article↗