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Biomedical subjects

I Pitas

Publications and source records attributed to I Pitas.

12 recordsLinked to original sources
PubMed2004

Marginal median SOM for document organization and retrieval.

The self-organizing map algorithm has been used successfully in document organization. We now propose using the same algorithm for document retrieval. Moreover, we test the performance of the self-organizing map by replacing the linear Least Mean Squares adaptation rule with the marginal median. We present two implementations of the latter variant of the self-organizing map by either quantifying the real valued feature vectors to integer valued ones or not. Experiments performed using both implementations demonstrate a superior performance against the self-organizing map based method in terms of the number of training iterations needed so that the mean square error (i.e. the average distortion) drops to the e(-1) = 36.788% of its initial value. Furthermore, the performance of a document organization and retrieval system employing the self-organizing map architecture and its variant is assessed using the average recall-precision curves evaluated on two corpora; the first comprises of manually selected web pages over the Internet having touristic content and the second one is the Reuters-21578, Distribution 1.0.

Algorithms↗
PubMed2000

The use of 3D computerized reconstruction for the study of coronal microleakage.

AIM: The purpose of this study was to evaluate a new method for studying coronal microleakage associated with root-filled teeth. METHODOLOGY: Twenty human mandibular posterior teeth were prepared chemomechanically with the stepback technique and then divided into two groups of 10 teeth each. The canals were filled using lateral condensation of gutta-percha points; Roth's 801 was used as a sealer for the first group, and Ketac-Endo for the second. After 48 h, the temporary fillings in the access cavities were removed, the roots coated with three layers of nail polish and then the teeth were exposed to artificial saliva for 40 days. Subsequently, the crowns of the teeth were placed into Indian ink for 4 days before the coating was removed and the teeth embedded in a two-phase polyester resin. Serial cross sections were taken from each specimen using a microtome, and each cross section photographed under a stereoscopic microscope. The photographs of the cross sections were digitized using an image scanner and the contours of the external surface of the teeth, the obturated root canals and the boundaries of dye penetration were followed. Finally, a three-dimensional surface representation was achieved using the triangulation method. RESULTS: Although the sample size and the experimental methods were not designed to form valid groups, the results showed that all roots obturated with Ketac-Endo sealer had dye microleakage, whilst only three teeth of the Roth's 801 group had dye microleakage. CONCLUSIONS: The 3D reconstruction of dye microleakage proved to be an interesting method and a useful tool for the evaluation of coronal microleakage when using different types of root canal sealers.

Bicuspid↗
PubMed2000

Three-dimensional reconstruction: a new method for the evaluation of apical microleakage.

The purpose of this study was the evaluation of a new method for studying apical microleakage by using a three-dimensional (3-D) reconstruction method. Fourteen human single-rooted mandibular teeth were used for this work. The canals were prepared with hand instruments by using the step-back technique. To supply a focus to the study of the method, the teeth were divided into two groups that were obturated using two different sealers. India ink was used for passive stain. Serial cross-sections 0.75 mm thick were taken from each specimen by using a special microtome. Each section was photographed under a stereoscopic microscope. Each photograph was digitized and processed to obtain a 3-D reconstruction of the external surface of the teeth, their corresponding prepared root canals, and their apical microleakage. Sample size and experimental methods were not designed to make valid groups; however, apical microleakage was observed in both groups ranging between 2.25 to 8.25 mm height. The 3-D reconstruction method has proved to be a useful tool in the study of apical microleakage.

Carbon↗
PubMed2000

Interpolation of 3-D binary images based on morphological skeletonization.

In this paper, the morphological skeleton interpolation (MSI) algorithm is presented. It is an efficient, shape-based interpolation method used for interpolating slices in a three-dimensional (3-D) binary object. It is based on morphological skeletonization, which is used for two-dimensional (2-D) slice representation. The proposed morphological skeleton matching process provides translation, rotation, and scaling information at the same time. The interpolated slices preserve the shape of the original object slices, when the slices have similar shapes. It can also modify the shape of an object when the successive slices do not have similar shapes. Applications on artificial and real data are also presented.

Algorithms↗
PubMed1999

3D computer-aided reconstruction of six teeth with morphological abnormalities.

AIM: The purpose of this study was the 3D reconstruction of six teeth with morphological peculiarities using serial cross-sections. METHODOLOGY: All the teeth were put in 3% NaOCl solution after extraction, washed under running water and air-dried. They were then embedded in a two-phase polyester resin and serial cross-sections were produced from each specimen using a special microtome. The thickness of each section was 0.75 mm. Each section was photographed under a stereoscopic microscope. The photographs of the cross-sections were digitized and the external contours of the teeth and the root-canal outline were annotated for each section. Semiautomatic alignment of the sections was achieved with the use of image-processing techniques. Three dimensional surface representation was used in this project to reconstruct the inner and outer surface of the teeth. RESULTS: The results showed in detail the internal morphology of the teeth under investigation. The fact that it was possible to observe and study these teeth from different angles is one of the main advantages of this method as the three dimensional anatomy of these teeth was apparent. CONCLUSIONS: The 3D reconstructing method is a useful tool for the study of the morphology of the teeth.

Anatomy, Cross-Sectional↗
PubMed1997

3D reconstruction of two C-shape mandibular molars.

Two mandibular second molars, with an indication of C-shape morphology were processed for 3-D reconstruction. After serial cross sectioning, photographs of the sections were digitized and by using surface representation, 3D reconstruction was achieved. The first molar as the 3D reconstruction showed was single rooted with one C-shaped root canal with two foramens, while the second one was double rooted with two root canals, one C-shaped and one thin, having a common foramen.

Anatomy, Cross-Sectional↗
PubMed1997

Computerized 3-D reconstruction of two "double teeth".

"Double teeth" is a root malformation in the dentition and the purpose of this study was to reconstruct three-dimensionally the external and internal morphology of two "double teeth". The first set of "double teeth" was formed by the conjunction of a mandibular molar and a premolar, and the second by a conjunction of a maxillary molar and a supernumerary tooth. The process of 3-D reconstruction included serial cross-sectioning, photographs of the sections, digitization of the photographs, extraction of the boundaries of interest for each section, surface representation using triangulation and, finally, surface rendering using photorealistic effects. The resulting three-dimensional representations of the two teeth helped us visualize their external and internal anatomy. The results showed: a) in the first case, fusion of the radical and coronal dentin, as well as fusion of the pulp chambers; and b) in the second case, fusion only of the radical dentin and the pulp chambers.

Anatomy, Cross-Sectional↗
PubMed1996

Non-linear algorithms for processing biological signals.

This paper illustrates different approaches to the analysis of biological signals based on non-linear methods. The performance of such approaches, despite the greater methodological and computational complexity is, in many instances, more successful compared to linear approaches, in enhancing important parameters for both physiological studies and clinical protocols. The methods introduced employ median filters for pattern recognition, adaptive segmentation, data compression, prediction and data modelling as well as multivariate estimators in data clustering through median learning vector quantizers. Another approach described uses Wiener-Volterra kernel technique to obtain a satisfactory estimation and causality test among EEG recordings. Finally, methods for the assessment of non-linear dynamic behaviour are discussed and applied to the analysis of heart rate variability signal. In this way invariant parameters are studied which describe non-linear phenomena in the modelling of the physiological systems under investigation.

Algorithms↗
PubMed1995

Three computer methods to reconstruct pulpal blood vessels and nerves.

This study describes three methods of computerized three-dimensional reconstruction of the main neurovascular pulpal bundle of human teeth, using serial cross-paraffin sections, digital image processing, and three-dimensional computer graphics. These methods are surface representation, representation by means of a stack of slices, and volume representation.

Adolescent↗
PubMed1995

Computerized reconstruction of TEM examined pulpal blood vessels and nerves.

Five healthy premolars were used for transmission electron microscopy examination and three-dimensional (3D) reconstruction of pulpal blood vessels and their surrounding nerves. Serial Epon thin sections were taken from specimens. After a series of preprocessing steps that included digitization, contrast enhancement, slice alignment, segmentation and interpolation, three dimensional surface representation was performed using the triangulation method. The findings showed that vessels were usually accompanied by a number of myelinated and unmyelinated nerves. The nerves shared a more or less common course with the vessels. Small arteries presented greater number of nerves in their vicinity, compared to small veins. In the sections examined, no direct contact between the nerve trunks and the wall of the vessels was found; the closest distance measured was approximately 67 microns. The common course of vessels and nerves suggested autonomic innervation on part of the myelinated axons.

Adult↗
PubMed1992

Optimum nonlinear signal detection and estimation in the presence of ultrasonic speckle.

A unified approach to the design of nonlinear filters for speckle suppression in ultrasound B-mode images is presented. The detection of the (lesion) signal is formulated as a binary hypothesis-testing problem. The structure of the optimal decision rules is derived both in the case where the lesion signal is assumed either a constant or random variable. In the case of a constant signal, the maximum likelihood (ML) estimator and the optimal L-estimator are derived. In the case of a random lesion signal, the maximum a posteriori probability estimator of the lesion signal has also been found. Experimental results verify the superiority of the proposed ML-estimator and the L-estimator over the straightforward choice of an arithmetic mean for speckle filtering in simulated tissue mimicking phantom ultrasound B-mode images.

Equipment Design↗