The effect of blood content on the optical and dielectric skin properties.

A wearable system incorporating sensors for dielectric and optical spectroscopy was used to study skin properties and their dependence on the cutaneous blood content (CBC). Simultaneous measurements with both modalities were carried out on the upper arm during blood perfusion-provoking exercises performed by four subjects in four separate sets of experiments. By relating changes in the attenuation of green (central wavelength λ(c) = 568 nm) and infrared (λ(c) = 798 nm) light, the ratio of mean pathlengths travelled by photons in the skin blood plexus was obtained. The pathlength for infrared light is found to be 3.85 times larger than for green. Combining signals of two wavelengths and accounting for pathlength difference, we quantitatively characterize the CBC as a cumulative optical thickness of red blood cells in the skin plexus. The dielectric spectra of skin in the MHz range were fitted with the Cole-Cole model and the changes of parameters were quantitatively related to the optically derived changes in CBC using a linear regression analysis. The positive correlation with CBC is obtained for the dispersion exponent (R(2) = 0.68), and the negative-for the dispersion time (R(2) = 0.40). Thus dielectric dispersion of the skin gets broader and shifts towards lower frequencies with an increase of CBC.

Noise in laser speckle correlation and imaging techniques.

We study the noise of the intensity variance and of the intensity correlation and structure functions measured in light scattering from a random medium in the case when these quantities are obtained by averaging over a finite number N of pixels of a digital camera. We show that the noise scales as 1/N in all cases and that it is sensitive to correlations of signals corresponding to adjacent pixels as well as to the effective time averaging (due to the finite integration time) and spatial averaging (due to the finite pixel size). Our results provide a guide to estimation of noise levels in such applications as multi-speckle dynamic light scattering, time-resolved correlation spectroscopy, speckle visibility spectroscopy, laser speckle imaging etc.

Full-field optical coherence tomography for the rapid estimation of epidermal thickness: study of patients with diabetes mellitus type 1.

Changes in morphology of the skin are an important factor that can affect non-invasive measurements performed through this organ, in particular for glucose monitoring in e.g. patients with diabetes mellitus. A characterization technique for non-contact in vivo profiling of the superficial skin layers can be beneficial for evaluation of the performance of such measurement systems. We applied a full-field optical coherence tomography (OCT) system followed by the fully automatic processing for this task. With the developed procedure, non-invasive quantification of the skin morphology can be performed within a few minutes. The dorsal skin of the upper arm of 22 patients with Type 1 Diabetes Mellitus was investigated with an OCT system and with a commercially available dermatological laser scanning confocal microscope (CM) as a reference method. The estimates of epidermal thickness from OCT were compared with the results of expert-assisted analysis of confocal images. The highest correlation with the CM measurements has been obtained for the distance from the entrance peak to the first minimum of the OCT reflection profile (R2 = 0.657, p < 0.0001). In this specific patient group, we have observed a statistically significant correlation of the subjects' body mass index with the distance from the entrance peak to the dermal reflection peak in the OCT profile (p = 0.010). Furthermore, the same OCT parameter is negatively correlated with age with marginal statistical significance (p = 0.062). At the same time, no relation of diabetes-related parameters (duration of disease and concentration of glycated haemoglobin) to the skin morphology observed with the OCT and CM was found.

A wearable diffuse reflectance sensor for continuous monitoring of cutaneous blood content.

An optical diffuse reflectance sensor for characterization of cutaneous blood content and optimized for continuous monitoring has been developed as part of a non-invasive multisensor system for glucose monitoring. A Monte Carlo simulation of the light propagation in the multilayered skin model has been performed in order to estimate the optimal geometrical separation of the light source and detector for skin and underlying tissue. We have observed that the pathlength within the upper vascular plexus of the skin which defines the sensor sensitivity initially grows with increasing source-detector distance (SDD) before reaching a maximum at 3.5 mm and starts to decay with further increase. At the same time, for distances above 2.4 mm, the sensor becomes sensitive to muscle blood content, which decreases the specificity to skin perfusion monitoring. Thus, the SDDs in the range from 1.5 mm to 2.4 mm satisfy the requirements of sensor sensitivity and specificity. The hardware implementation of the system has been realized and tested in laboratory experiments with a venous occlusion procedure and in an outpatient clinical study in 16 patients with type 1 diabetes mellitus. For both testing procedures, the optical sensor demonstrated high sensitivity to perfusion change provoking events. The general build-up of cutaneous blood under the sensor has been observed which can be associated with pressure-induced vasodilation as a response to the sensor application.

Dynamic laser speckle imaging of cerebral blood flow.

Laser speckle imaging (LSI) based on the speckle contrast analysis is a simple and robust technique for imaging of heterogeneous dynamics. LSI finds frequent application for dynamical mapping of cerebral blood flow, as it features high spatial and temporal resolution. However, the quantitative interpretation of the acquired data is not straightforward for the common case of a speckle field formed by both by moving and localized scatterers such as blood cells and bone or tissue. Here we present a novel processing scheme, we call dynamic laser speckle imaging (dLSI), that can be used to correctly extract the temporal correlation parameters from the speckle contrast measured in the presence of a static or slow-evolving background. The static light contribution is derived from the measurements by cross-correlating sequential speckle images. In-vivo speckle imaging experiments performed in the rodent brain demonstrate that dLSI leads to improved results. The cerebral hemodynamic response observed through the thinned and intact skull are more pronounced in the dLSI images as compared to the standard speckle contrast analysis. The proposed method also yields benefits with respect to the quality of the speckle images by suppressing contributions of non-uniformly distributed specular reflections.

Photocount statistics in mesoscopic optics.

We report the first observation of the impact of mesoscopic fluctuations on the photocount statistics of coherent light scattered in a random medium. A Poisson photocount distribution of the incident light widens and gains additional asymmetry upon transmission through a suspension of small dielectric spheres. The effect is only appreciable when the average number n of photocounts becomes comparable or larger than the effective dimensionless conductance g of the sample.

Multispeckle diffusing-wave spectroscopy with a single-mode detection scheme.

We present a detection scheme for diffusing-wave spectroscopy (DWS) based on a two-cell geometry that allows efficient ensemble averaging. This is achieved by putting a fast rotating diffuser in the optical path between laser and sample. We show that the recorded (multispeckle) correlation echoes provide an ensemble averaged signal that does not require additional time averaging. Furthermore, combined with traditional two-cell DWS, the full intensity autocorrelation function can be measured with a single experimental setup. The scheme provides access to a large range of correlation times thus opening an experimental window for the study of slowly relaxing and arrested systems, such as viscoelastic complex fluids, colloidal glasses, and gels.

Laser speckle imaging with an active noise reduction scheme.

We present an optical scheme to actively suppress statistical noise in Laser Speckle Imaging (LSI). This is achieved by illuminating the object surface through a diffuser. Slow rotation of the diffuser leads to statistically independent surface speckles on time scales that can be selected by the rotation speed. Active suppression of statistical noise is achieved by accumulating data over time. We present experimental data on speckle contrast and noise for a dynamically homogenous and a heterogeneous object made from Teflon. We show experimentally that for our scheme spatial and temporal averaging provide the same statistical weight to reduce the noise in LSI: The standard deviation of the speckle contrast value scales with the effective number N of independent speckle as 1/ radicalN.

Low-intensive lasers in the treatment of peptic gastric and duodenal ulcers.

Pharmacochemical achievements have brought about considerable improvement in treating peptic ulcers. But possible side effects demand a very cautious approach to the administration of every new drug, and stimulate the search for nontraditional treatment. In 638 patients who were treated by semiconductor laser transcutaneously (external irradiation), an average term of ulcer healing was 11.5 days, that is, half the time required for controls. The healing process under laser therapy depends on the disease gravity as well as the diameter and depth of the ulcer. Morphologically, we noted a quick restoration of microvessels in the ulcer area. The most optimal parameters of laser irradiation are chosen with the help of biophotometry.

[The phototherapy of peptic ulcer patients using a semiconductor laser]. / Fototerapiia bol'nykh iazvennoi bolezn'iu s pomoshch'iu poluprovodnikogo lazera.

External semiconductor laser treatment was realized in 470 patients with peptic ulcer. The average time of ulcer healing was twice shorter than in control cases. Ulcer epithelialization depended on the severity of the disease, diameter and depth of the ulcer defect. Prophylactic treatment is recommended to reduce the number of recurrences.

[Morphologic diagnosis of the initial stages of stomach cancer (an analysis of 252 cases)]. / Morfologichesdkaia diagnostika nachal'nykh stadii raka zheludka (analiz 252 nabliudenii).

Cancer involvement of the stomach diagnosed in 225 patients appeared limited to tela submucosa in 252 cases and mucosa in 64.5% of cases. Early diagnosis of metachromatic postoperative cancer was established in 7.6% of patients. Macroscopic forms of the tumors varied. Adenocarcinoma prevailed histologically, its well-differentiated forms occurring in superficial twice as often as in invasive cancer. In 71.8% of patients tumor growth was accompanied by epithelial dysplasia varying in degree. Severe dysplasia was more common in superficial cancer. Carcinomas of exclusively mucosal localization are usually small-sized, differentiated, more distinctly associated with precancer conditions.

[Clinical and diagnostic characteristics of the early forms of stomach cancer]. / Osobennosti kliniki i diagnostiki rannikh form raka zheludka.

Clinical and diagnostic problems of early stomach cancer were considered for 157 patients with diagnosis confirmed after operation. Gastroenterological diseases were not mentioned in the past medical history of 22.9% of the patients only. 48.4% of the patients had the so-called stomach precancerous diseases, 28.7% other diseases of the alimentary tract. At diagnosis of carcinoma, 51.6% of the patients had clinical signs of previous diseases. The importance of prophylactic medical examination in the diagnosis of early stomach cancer was emphasized (cancer was detected actively in 84.7%). Since the gross appearance of early stomach cancer looks like benign lesions, the x-ray and endoscopic methods might not be quite informative. Morphological examination of the spot biopsy material raised preoperative diagnostic accuracy up to 92.3%.