A new non-invasive method to measure the optical properties of biological tissue is described. This method consists of illuminating the investigated sample with light which is spatially periodically modulated in intensity. The spatial modulation of the backscattered light and the diffuse reflectivity of the sample, both detected with an imaging technique, are used to deduce the absorption and reduced scattering coefficient from a table generated by Monte Carlo simulations. This principle has three major advantages: Firstly, it permits the immediate acquisition of the average values of the optical coefficients over a relatively large area (typ. 20 mm in diameter), thus avoiding the perturbations generated by small tissue heterogeneities; It also provides good flexibility for measuring the optical coefficients at various wavelengths and it does not require the use of a detector with a large dynamic range. The method was first validated on phantoms with known optical properties. Finally, we measured the optical properties of human skin at 400 nm, 500 nm, 633 nm and 700 nm in vivo. 相似文献
Summary: Amphiphilic polysaccharides are obtained by hydrophobic modification of a neutral bacterial polysaccharide, dextran. By reacting the polysaccharide with aliphatic epoxides (epoxyoctane and epoxydodecane) in dimethyl sulfoxide, a series of amphiphilic polymers is obtained which covers a large range of structural parameters (length of the polysaccharide, number and nature of hydrocarbon moieties). The solution behavior of dextran derivatives is first characterized by viscometric measurements in dilute and semi‐dilute domains. The effects of molecular parameters on polymer viscosity behavior are evidenced and discussed. Information on the state of aggregation of polymers is obtained by the use of static and dynamic light scattering. The presence of aggregates in the dilute domain is clearly evidenced and their structural characteristics are estimated (size, molecular weight and number of aggregation). The aggregates are shown to account for the viscometric results in the examined concentration range, relating their chemical parameters (hydrodynamic radius and molecular weight) to the macroscopic behavior of the solutions.
Summary: The equilibrium swelling degree, modulus of elasticity and the spatial inhomogeneity of poly(N,N‐dimethylacrylamide) (PDMAAm) hydrogels were investigated over the entire range of the initial monomer concentration. The degree of dilution of the networks after their preparation was denoted by ν, the volume fraction of crosslinked polymer after the gel preparation. The linear swelling ratio of the gels increased linearly with increasing ν. Depending on the value of ν, three different gel regimes were observed: (1) For ν < 0.3, increasing ν decreases the extent of cyclization during crosslinking so that the effective crosslink density of gels increases with rising ν. (2) For 0.3 < ν < 0.7, increasing ν reduces the accessibility of the pendant vinyl groups during crosslinking due to steric hindrance at high polymer concentrations. As a result, the effective crosslink density of gels decreases with increasing ν. (3) For ν > 0.7, the modulus of elasticity increases sharply with increasing ν due to the increasing extent of chain entanglements in this high concentration regime. Static light scattering measurements on the gels show that the degree of spatial gel inhomogeneity in PDMAAm gels attains a maximum value at ν = 0.06. The appearance of a maximum as well as the ν‐dependence of scattered light intensities from gels was successfully reproduced by the theory proposed by Panyukov and Rabin.
Effective crosslink density νe of the hydrogels shown as a function of ν. 相似文献
BackgroundAlthough various studies have been conducted to demonstrate the possibility of Raman spectroscopy (RS) as a diagnostic tool for prostate cancer (PC), it is difficult to use it in the real clinical area because of imitations in various research processes. Therefore, we did a systematic review and meta-analysis about the accuracy in diagnostic use of RS for PC.MethodsA literature search was done using PubMed, Embase, and Cochrane library databases in March 2019 to analyze the accuracy of RS for diagnosis of PC. The accuracy of RS for diagnosis of PC was evaluated by means of pooled sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), and summary receiver operating characteristic (SROC).ResultsFive studies were included for qualitative analysis by screening the remaining articles according to the inclusion and exclusion criteria by means of a systematic review. The pooled sensitivity and specificity of RS were 0.89 (95% CI: 0.87–0.91) and 0.91 (95% CI: 0.89–0.93), respectively. The overall PLR and NLR were 9.12 (95% CI: 4.15–20.08) and 0.14 (95% CI: 0.07–0.29), respectively. The DOR of RS demonstrated high accuracy (73.32; 95% CI: 18.43–291.73). The area under the curves (AUCs) of SROC curves was 0.93.ConclusionsRS is an optical diagnostic method with high potential for diagnosis and grading of PC and has advantages of real-time and convenient use. In order to consider real-time use of RS in an actual clinical setting, more studies for standardization and generalization of RS performance and analytical method must be conducted. 相似文献
Amphiphilic fluorinated copolymers PEGMAx-co-FAy and TEGMAx-co-FAy are prepared by activators regenerated by electron transfer atom transfer radical polymerization (ARGET-ATRP). All polymers present a reversible thermoresponsive lower critical solution temperature-type behavior, and a cloud point temperature (Tc) in the range of 30–60 °C strictly dependent on the length of the oxyethylene side chain, the content of the hydrophobic counits, and the concentration of the solution. Combined small angle X-ray scattering (SAXS) and dynamic light scattering measurements are used to study the self-assembly behavior in water, organic solvents (tetrahydrofuran [THF] and dimethylformamide [DMF]), and a fluorinated solvent (hexafluorobenzene [HFB]). SAXS confirms the formation of compact-globular single-chain self-folded unimer micelles in water below Tc, which generally presents small hydrodynamic diameters (Dh ≤ 8 nm) as a result of the folding of the hydrophobic perfluorohexylethyl acrylate counits. The copolymers are also able to form reverse unimer micelle in HFB. The copolymers are not able to self-assemble in unimer micelles in THF or DMF solutions, in which they adopt conventional random coil conformations. 相似文献
Mechanisms underlying and controlling resolution and perception in working memory are studied by means of a pulse-coupled network model. It is shown that the adaptivity, i.e. the degree to which previous activity affects the ability to fire, of the excitatory units can control several aspects of the network dynamics in a coordinated way to enable multiple items to be resolved and perceived in working memory. One basic aspect is the complexity of the dynamics that regulates the temporal resolution of several items. The slow NMDA-receptor-mediated component of synaptic couplings to excitatory units facilitates successive activations of a given item. The dimension of the activated subspace of the complete available neural representation space is gradually decreased as adaptivity is reduced. It is also shown that the formation of perception by sufficiently intense and coherent activation of different features of an object can be controlled concurrently with resolution by the adaptivity. The mechanisms derived can account for the observed capacity of working memory with respect to number of items consciously resolved and also for the observed temporal separation of different items. Numerous observations link neuromodulators to cognitive functions and to various brain disorders involving working memory. Based on the influence of various neuromodulators on neuronal adaptivity, the model can also account for neuromodulatory regulation of working memory functions. 相似文献