Nonlinear image labeling for multivalued segmentation.

We describe a framework for multivalued segmentation and demonstrate that some of the problems affecting common region-based algorithms can be overcome by integrating statistical and topological methods in a nonlinear fashion. We address the sensitivity to parameter setting, the difficulty with handling global contextual information, and the dependence of results on analysis order and on initial conditions. We develop our method within a theoretical framework and resort to the definition of image segmentation as an estimation problem. We show that, thanks to an adaptive image scanning mechanism, there is no need of iterations to propagate a global context efficiently. The keyword multivalued refers to a result property, which spans over a set of solutions. The advantage is twofold: first, there is no necessity for setting a priori input thresholds; secondly, we are able to cope successfully with the problem of uncertainties in the signal model. To this end, we adopt a modified version of fuzzy connectedness, which proves particularly useful to account for densitometric and topological information simultaneously. The algorithm was tested on several synthetic and real images. The peculiarities of the method are assessed both qualitatively and quantitatively.

[The application of fractal technics for the enhancement of radiographic images]. / Applicazione di tecniche frattali per la discriminazione di immagini radiografiche.

This paper deals with digital radiological image processing, with a special emphasis on quantitative measurement extraction aimed at discriminating different lung pathologies. Texture analysis of these images, not easily performed by the human eye, can be carried out by means of fractal techniques, which allow different textures to be characterized by a single parameter--i.e. the fractal dimension. To extract the fractal dimension of an image, the so-called "blanket" method is employed, which allows the average fractal dimension of an image area to be evaluated. The result of this processing is a new image whose points are assigned the average fractal dimension value of the area they belong to. The behaviors of fractal dimension histograms related to various simulations of lung pathologies are notably different, which allows such pathologies to be effectively characterized and differentiated on a quantitative basis. The radiographic images the "blanket" method was applied to are related to simulations of both pathological and healthy tissues. The behaviors of fractal dimension histograms and the average fractal dimension values allow the characterization of the different pathologies both for single tissues and in case of superimposition of a healthy tissue on a pathological one. The promising simulation results have encouraged us to carry out the present experimental investigation in the field of lung neoplasms.

Nuclear pores and interphase chromatin: high-resolution image analysis and freeze etching.

Computer-enhanced analysis of electron micrographs of thin-sectioned rat liver nuclei, combined with three-dimensional reconstruction of the same Feulgen-stained nuclei, points to a unique clustering of chromatin DNA fibres near the nuclear border. Computer-enhanced image analysis has been applied to electron micrographs of the envelopes of the same rat liver nuclei prepared by freeze etching and a few essential geometrical parameters characterizing the pores and their distribution have been determined. During interphase, clusters of nuclear pores, closely paralleling the clustering of membrane-attached chromatin fibres, have been identified on the envelope, the number of these being similar to the number of homologus pairs of metaphase chromosomes. Furthermore, rapid changes induced in chromatin distribution appear to be associated with rapid changes in pore number, but not in the number of pore clusters.

[Digital radiography]. / Radiografia digitale.

The reliability of radiographical information may be improved by a) standardised radiography (exposure-development); b) transformation of the original image into a densitometric image and equalization with a reference wedge made of Ergal. The linear absorption coefficient of Ergal in terms of photon X energy is almost identical to the average coefficient of the bone mineral matrix; c) processing the densitometric image for additional information. An automatic image analyser controlled by a computer is used. The first osteological results showing the correspondence between the densitometric measurements provided by the analyser and the actual bone mineral content revealed by chemical analysis are presented.