Oxyhemoglobin saturation measurements by green spectral shift

From an analysis of new hemoglobin solution transmission spectra at various oxygen saturations (SO2), path lengths, and pH, we find the determination of SO2 by using the classical oximetry technique to be poorly calibrated. We used this data set to develop a proposed method for SO2 determination based on the spectral shift of the hemoglobin transmission minimum between 475 and 510 nm. The method does not require accurate knowledge of hemoglobin extinction coefficients and is linear in relation to SO2 despite changes in path length, pH, or hemoglobin concentration.     

Correlation of static speckle with sample properties in optical coherence tomography

We present theoretical calculations, based on a random phasor sum model, which show that the optical coherence tomography speckle contrast ratio is dependent on the local density of scattering particles in a sample, provided that the effective number of scatterers in the probed volume is less than about five. We confirm these theoretical predictions experimentally, using suspensions of microspheres in water. The observed contrast ratios vary in value from the Rayleigh limit of 0.52 to in excess of 2, suggesting that the contrast ratio could be useful in optical coherence tomography, particularly when imaging in ultrahigh-resolution regimes.     

Redox history effects accompanying the electrochemical cycling of poly(vinylferrocene)

Cyclic voltammetric studies of poly(vinylferrocene), PVF, in aqueous sodium perchlorate, sodium p-toluenesulfonate, and sodium naphthalenesulfonate solutions revealed unexpected history effects. The films contain redox sites in two local environments. One type of ferrocene site is in a compact, unsolvated environment; it undergoes redox switching in NaClO₄ with only the transfer of counter ions. The other type of ferrocene site is in a more diffuse environment; it undergoes redox switching with the transfer of perchlorate counter ion and water. Only the latter sites can accommodate large anions (toluenesulfonate or naphthalenesulfonate), and therefore undergo redox switching in such media. Upon multiple redox cycling, these large anions get progressively locked into the structure, thereby blocking the diffuse sites. Upon transfer back to NaClO₄ solution, only the compact sites are able to undergo redox switching.Contribution to the 3^rd Baltic Conference on Electrochemistry, Gdask-Sobieszewo, 23–26 April 2003.Dedicated to the memory of Harry B. Mark, Jr. (February 28^th, 1934 – March 3^rd, 2003).     

Spatially resolved Fourier holographic light scattering angular spectroscopy

We show for what is the first time to our knowledge that digital Fourier holography can be used to record spatially resolved angular light scattering spectra from microscopically structured samples. This is achieved in one or a few digital image captures over large millimeter-scale fields of view. Such spectra are a sensitive measure of microscopic morphology, with wide applications in biological and medical imaging. We demonstrate good agreement between results of experiment and Mie theory for the angular scattering spectra of microspheres in water extracted from local regions within reconstructed 2 x 1 millimeter image sets.     

Perfect and Acyclic Subgroups of Finitely Presentable Groups

Acyclic groups of low dimension are considered. To indicatethe results simply, let G' be the nontrivial perfect commutatorsubgroup of a finitely presentable group G. Then def(G)1. Whendef(G)=1, G' is acyclic provided that it has no integral homologyin dimensions above 2 (a sufficient condition for this is thatG' be finitely generated); moreover, G/G' is then Z or Z². Naturalexamples are the groups of knots and links with Alexander polynomial1. A further construction is given, based on knots in S²x S¹.In these geometric examples, G' cannot be finitely generated;in general, it cannot be finitely presentable. When G is a 3-manifoldgroup it fails to be acyclic; on the other hand, if G' is finitelygenerated it has finite index in the group of a Q-homology 3-sphere.     

Uniqueness and wavelength optimization in continuous-wave multispectral diffuse optical tomography

We derive conditions for the unique and simultaneous recovery of chromophore concentrations and scattering coefficients in multispectral continuous-wave diffuse optical tomography. These conditions depend strongly on measurement wavelengths. We introduce and demonstrate a general methodology for choosing those wavelengths, which yields superior separation of scattering from absorption and superior separation of one chromophore from another. Application of these concepts should significantly improve the fidelity of continuous-wave diffuse near-infrared optical tomography in tissues.