Region-of-interest tomography using filtered backprojection: assessing the practical limits.

There are many cases where it is desirable to reconstruct at high resolution a small volume from a larger sample. Here we describe the outcomes of a reconstruction trial based on real samples aimed at delineating the practical limits to which a small region of interest can be viewed from a large sample. Our approach has been to artificially truncate the sinograms of whole sample scans to simulate region of interest tomography. A simple filtered back projection algorithm has been applied, with the sinograms extended laterally in a simple manner to make up for the truncated portions. The impact of the degree of truncation (from 0% down to 99%), the number of projections used, as well as the position of the region of interest, on the faithfulness of the reconstruction is evaluated for a range of sample types. We have assessed the nature of, and extent to which, artefacts are introduced and the degree to which simple strategies can minimize them to an acceptable level without the need for complex reconstruction algorithms, projection stitching strategies or very large detectors. It is found that for a wide range of objects the effect of truncation on feature detection is negligible and that excellent images can be reconstructed if the number of projections is calculated not on the basis of the number of pixels on the camera, but on the number of pixels that would be required to scan the whole sample at the chosen pixel resolution. This paper demonstrates that in many cases more sophisticated reconstruction strategies are not necessary.

[The inhibition by interferon type I of the initial phase of experimental salmonellosis]. / Ingibirovanie interferonom 1-go tipa nachal'noi fazy éksperimental'nogo sal'monelleza.

Using the bacteriological methods the level of the genus Salmonella representative histadhesion to intestinal mucosa was evaluated. Balb/c mice and Salmonella typhimurium 415 strain were used for investigation. Native homologous I type interferon was injected to experimental animals 24 before the experiment in a dose of 1000 U/mice. "False" interferon was administered to the control group animals. It was established that the level of Salmonella histadhesion in mice of the experimental group was an order less than in control. Study of the parameters of the process of Salmonella interaction with intestinal mucosa showed that the challenge dose of Salmonella typhimurium 24 after interferon injection must be 7 times higher for the control mice than for experimental ones. Thus, the barrier function of intestinal mucosa after administration of the native I type interferon in vivo increased 7 times.

[The dynamics of the formation of an infection focus in the intestines]. / Dinamika formirovaniia infektsionnogo ochaga v kishechnike.

The problem of the stability of the development of Shigella population in the intestine, depending on the dose of the infective agent, is analyzed. The agent is reproduced in the intestinal mucosa in short cycles, starting with adhesion and followed by penetration, intracellular multiplication and, finally, emission of free bacteria and hulled tops of villi with Shigella intracellular microcolonies. This form of emission maintains high concentration of bacteria and ensures, in case of the adhesion of hulled material, high local concentration provoking the repetition of the cycle. Depending on the dose, chains of cycles either progressively develop or maintain a constant level, or become extinct. Stable development of the chains of infectious cycles forms a focus of infection in the body (in the intestine). The growth of the populations of infective agents in live tissues, following the chain of cycles, produces a new type of microbial culture, differing from the types obtained by batch and flow cultivation. The aggregation and accumulation of infective agents in the hulled material is the particular case of the formation of infections, highly active particles and accumulations of infective agents, ensuring the development of infection with a relatively small number of organisms.

[The effect of subinhibitory concentrations of antibiotics on the adhesion of enterobacteria]. / Vliianie subingibiruiushchikh kontsentratsii antibiotikov na adgeziiu énterobakterii.

It is impossible to determine rigidly a net result of the influence of antibiotics on the interaction between parasite and host cells, as many factors participating in this process are not studied. Adhesion of microorganisms is one of the essential mechanisms of the above interaction. Antibiotics with a different mechanism of action in the subinhibitory concentrations affecting viability of microbes either slightly or nowise have been studied for their effect on adhesion on a model of the intestine section of human embryos and experimental animals. Most of antibiotics influenced differently adhesion of the microorganisms, that also depended on the species attribution of the latter. The accelerated selection of resistance during a successive passage via the suggested adhesion system was observed. The data obtained elucidated certain mechanisms of the effect of antibiotics on the microbial populations at the initial phase of the infectious process and under the primary contamination of mucosa.

[The role of the aggregation of microbial cells in the development of salmonellosis in mice]. / Rol' agregirovaniia mikrobnykh kletok v razvitii sal'monelleza myshei.

The dependence of the invasive action of Salmonella typhimurium in mice on the aggregation of microbial cells has been studied in vivo, as well as in vitro on explanted intestinal tissue. The aggregation of salmonellae on kaolin grains has been found to lead to an increase in the level of adhesion of salmonellae to the intestinal mucosa of mice in vitro, to the accelerated course of infection in mice and their death and to the increased contamination of the spleen. The data obtained in these experiments age indicative of the possibility of the adverse influence of some sorbents on the course of the infectious process and confirm the concept advanced by the authors on the major importance of the surface concentration of salmonellae on the mucous membrane for the effectiveness of contamination.

[Role of poliomyelitis viruses in the etiology of serous meningitis in Odessa 1979-1983]. / Rol' virusov poliomielita v étiologii seroznykh meningitov v Odesse v 1979-1983 gg.

The etiology of aseptic meningitides has been studied in the patients hospitalized in the Odessa city clinical hospital in 1979-1983. Altogether 268 strains of enteroviruses have been isolated, among them 105 poliomyelitis viruses (38.8%); 26 poliomyelitis virus strains have been isolated from the cerebrospinal fluid. Most frequently, type I poliovirus has been isolated. Poliovirus strains isolated from the cerebrospinal fluid had the genetic markers of virulent strains. The authors believe that isolation of poliomyelitis virus from the cerebrospinal fluid in aseptic meningitis proves its etiological role in the disease.

[Characteristics of the tissue population cycle of shigellae]. / Kharakteristika tkanevogo populiatsionnogo tsikla shigell.

In experiments on human fetal intestinal explants infected with shigellae the specific multiplication rate of these infective agents, found to be 0.026, and the maximum level of their accumulation in erythrocytes, reaching 22-36 microbes per cell, have been determined. These phenomena can be observed after at least 3-hour incubation and end in the release of the infective agents from the affected area with shedding epithelial elements (villi). Shigellae, aggregated in the shed villi easily adhering to the unaffected mucosa, ensure the intensive invasion of the epithelium, which leads to the continuation of the process. The regularity thus revealed indicates that the population cycle of the development of shigellae is limited by short intervals of 3-4 hours. During these intervals the repeated invasion and the release of shigellae, together with the shed epithelium, into the chyme-containing intestinal cavity occur. The conditions for the multiplication of shigellae and their specific multiplication rate in chyme are minimal (0.016).

[Dynamics of Shigella interaction with the epithelium in the infection process]. / Dinamika vzaimodeistviia shigell s épiteliem v protsesse zarazheniia.

The study of the adhesion of Shigella flexneri to intestinal mucosal explants from human postabortion fetuses, used as an experimental model, has revealed that the process of interaction between the infective agent and the epithelium develops in accordance with Langmuir's equation of the adsorption isotherm. The specific biological feature of the adhesive interaction between bacteria and the mucous membrane is the fact that the effective adhesion of microbes is possible only in case of their high concentration on the surface of the mucous membrane. In case of their low concentration in the parietal layer no microbial adhesion is observed, whereas epithelial villi infected with shigellae and fixed to the mucous membrane of the explant produce a high parietal concentration of the infective agents, which leads to the increase of adhesion by more than two orders.