Biomedical subjects

G Zacharakis

Publications and source records attributed to G Zacharakis.

6 recordsLinked to original sources

PubMed2005

Optical characterization of thin female breast biopsies based on the reduced scattering coefficient.

One of the main goals in optical characterization of biopsies is to discern between tissue types. Usually, the theory used for deriving the optical properties of such highly scattering media is based on the diffusion approximation. However, biopsies are usually small in size compared to the transport mean free path and thus cannot be treated with standard diffusion theory. To account for this, an improved theory was developed, by the authors, that can correctly describe light propagation in small geometries (Garofalakis et al 2004 J. Opt. A: Pure Appl. Opt. 6 725-35). The theory's limit was validated by both Monte Carlo simulations and experiments performed on tissue-like phantoms, and was found to be two transport mean free paths. With the aid of this theory, we have characterized 59 samples of breast tissue including cancerous samples by retrieving their reduced scattering coefficients from time-resolved transmission data. The mean values for the reduced scattering coefficients of the normal and the tumour tissue were measured to be 9.7 +/- 2.2 cm(-1) and 10.8 +/- 1.8 cm(-1), respectively. The correlation with age was also investigated.

Adipose Tissue↗

PubMed2001

Artificial neural networks for discriminating pathologic from normal peripheral vascular tissue.

The identification of the state of human peripheral vascular tissue by using artificial neural networks is discussed in this paper. Two different laser emission lines (He-Cd, Ar+) are used to excite the chromophores of tissue samples. The fluorescence spectrum obtained, is passed through a nonlinear filter based on a high-order (HO) neural network neural network (NN) [HONN] whose weights are updated by stable learning laws, to perform feature extraction. The values of the feature vector reveal information regarding the tissue state. Then a classical multilayer perceptron is employed to serve as a classifier of the feature vector, giving 100% successful results for the specific data set considered. Our method achieves not only the discrimination between normal and pathologic human tissue, but also the successful discrimination between the different types of pathologic tissue (fibrous, calcified). Furthermore, the small time needed to acquire and analyze the fluorescence spectra together with the high rates of success, proves our method very attractive for real-time applications.

Arteriosclerosis↗

PubMed2001

In vitro optical characterization and discrimination of female breast tissue during near infrared femtosecond laser pulses propagation.

Ultrashort infrared laser pulses were transmitted through excised female breast tissue. The resulted signal was recorded by a streak camera with a time resolution of the order of a few ps. Experimental data of the temporal spread of the ultrashort pulse during the transmission through the tissue have been analyzed using the Patterson analytical expression derived from the diffusion theory. This resulted in the calculation of the absorption and reduced scattering coefficients, which are related to the optical characteristics of each type of tissue. The goal of the study was to use the theoretical values of the coefficients to discriminate different kinds of tissue.

Breast Neoplasms↗

PubMed2000

Single and double wavelength excitation of laser-induced fluorescence of normal and atherosclerotic peripheral vascular tissue.

Laser-induced fluorescence spectra were recorded from the exposure of peripheral vascular tissue to both helium-cadmium and argon-ion laser radiation. Spectral analysis was based on simple algebraic expressions constructed using the intensity difference of the various spectral regions. The above methods were developed in order to determine the degree of atherosclerosis according to the laser-induced fluorescence signal. Similar results with single wavelength excitation were observed during in vivo irradiation of peripheral vessels.

Arteries↗

PubMed1999

Absence of the negative strand of GBV-C/HGV RNA from the liver.

BACKGROUND/AIMS: The pathogenic role of the human virus GBV-C/HGV remains unclear as information on tissue specific tropism and sites of replication of GBV-C/HGV is limited and controversial. The aim of this study was to determine whether the liver is the site of GBV-C/HGV replication. METHODS: We utilized the strand-specific Tth RT-PCR assay to investigate the presence of the positive- and negative-strand of GBV-C/HGV RNA in liver and serum samples from 12 patients with chronic GBV-C/HGV infection; four were infected with GBV-C/HGV alone, six were coinfected with HCV and two with HBV. A control group of six patients infected with HCV alone was included. The presence of the positive- and negative-strand of HCV RNA was also investigated in the same samples. RESULTS: All liver specimens were negative for the presence of the replicating negative-strand of GBV-C/HGV RNA. Positive-strand GBV-C/HGV RNA was found in 6 of the 12 liver samples and was detectable only at low levels, most probably reflecting serum contamination. By contrast, the negative strand of HCV RNA was detected in high titers in the liver of all HCV-infected and -coinfected subjects with less than a 100-fold difference from the positive strand. In serum samples only the positive strands of GBV-C/HGV and HCV RNA were detected in comparable titers. CONCLUSIONS: The results of this study suggest that GBV-C/HGV is not replicating in the liver and, taken together with the bulk of evidence against hepatopathogenicity, they argue against the new agent being a hepatotropic virus. We suggest that the acronymic term of this agent GBV-C/HGV is used with the understanding that it is not a hepatitis virus.

Flaviviridae↗

PubMed1998

Effect of liquid-nitrogen and formalin-based conservation in the in vitro measurement of laser-induced fluorescence from peripheral vascular tissue.

In order to investigate the effects of conservation in liquid nitrogen and formalin on peripheral vascular tissue (abdominal aortic, femoral, flank, ham, fibular and tibial artery tissue), laser-induced fluorescence spectra have been recorded during the exposure of these tissues to helium-cadmium and argon ion radiation. The spectral distribution of tissue fluorescence allows the development of simple algorithms based on the intensity difference in order to discriminate the tissue samples when they are fresh and after they have been stored for 24 and 28 h in liquid nitrogen or formalin.

Arteries↗