High Contrast Areas Research Articles

Lanthanide accumulation in the periplasmic space of Escherichia coli B

Treatment of growing Escherichia coli B with lanthanide ions [lanthanum(III), terbium(III), and europium(III)] and subsequent aldehyde-OsO4 fixation caused areas of high contrast to appear within the periplasm (the space between inner and outer membrane of the cell envelope). X-ray microanalysis of ultrathin sections of Epon-embedded or acrylic resin-embedded cells revealed the presence of the lanthanide and of phosphorus in the areas, whose contrast greatly exceeded that of other stained structures. Comparatively small amounts of the lanthanide were also present in the outer membrane and in the cytoplasm. The distribution of the periplasmic areas of high contrast was found to be random and not clustered at areas of current or future septum formation. Irregular cell shapes were observed after lanthanide treatment before onset of fixation. In contrast to glutaraldehyde-OsO4 fixation, glutaraldehyde used as the sole fixer caused a scattered distribution of the lanthanide. Cryofixation (slam-freezing) and freeze substitution revealed a lanthanum stain at both the periplasm and the outer part of the outer membrane. Deenergization of the cell membrane by either phage T4 or carbonyl cyanide m-chlorophenylhydrazone abolished the metal accumulation. Furthermore, addition of excess calcium, administered together with the lanthanide solution, diminished the quantity and size of areas of high contrast. Cells grown in media of high NaCl concentration revealed strongly stained areas of periplasmic precipitates, whereas cells grown under low-salt conditions showed very few high-contrast patches in the periplasm. Terbium treatment (during fixation) enhanced the visibility of the sites of inner-outer membrane contact (the membrane adhesion sites) in plasmolized cells, possibly as the result of an accumulation of the metal at the adhesion domains. The data suggest a rapid interaction of the lanthanides with components of the cell envelope, the periplasm, and the energized inner membrane.

Phase retrieval by Monte Carlo methods

A Monte Carlo method based on simulated annealing is investigated for phase retrieval. Its performance is found successful for reconstructing good estimates of objects with high contrast areas. This makes it attractive for calculation in fast computers.

Zonography in daily radiological practice.

In 1931, Ziedses des Plantes (6) described tomography with a small angle of tube arc as a separate and independent radiographic technic with specific advantages. To this procedure he later applied the term “zonography.” Since that time very few papers have been written on this technic or its clinical application (1–3, 5, 6). In fact, until recently most tomographic apparatuses have not provided facilities for the use of small angles. The quality of any tomographic image is essentially dependent upon three factors: blurring, definition, and contrast. Westra (5) emphasized that these three qualities of the image varied as a function of the angle described by the tube. He pointed out that zonography was superior to tomography in detail and contrast, while it produced a considerably smaller degree of blurring. He favored pluridirectional movement over the linear for zonography because of its more effective blurring. It is well established that excellent blurring of structures close to or remote from the plane of interest will be achieved with wide angles of tube movement in tomography. In zonography blurring of structures remote from the plane of interest will also be excellent, but with structures close to the plane of interest, blurring will be incomplete. In certain conditions, however, especially in the abdomen, the result will be diagnostically adequate. Since in zonography a thick layer is in focus, the film closely resembles a conventional film, and orientation and interpretation are much easier than in tomography. In contrast to Westra (5) and Littleton and Winter (2), who stated that pluridirectional movement is particularly essential to zonography, Swart (4) in an as yet unpublished communication, reports highly satisfactory and informative results in abdominal linear zonography. His paper is based on experience with 1,250 intravenous urograms and 750 intravenous cholangiograms. He examined the physical basis underlying both linear and circular zonography, employing phantoms of densities equivalent to those in the abdomen, as well as phantoms of conventional metal type. He concludes that results of studies on high-contrast metal grids are not applicable to the abdominal organs, although they have relevance to studies on bone and areas of high contrast, such as the bronchial tree. The work of Swart deserves recognition as providing a clear understanding of the place of linear zonography in roentgen procedures. Our interest has been to assess the usefulness of zonography in clinical practice. The studies reported here have been performed on a linear movement apparatus which has been simply modified to allow a 5° angle technic. Intravenous Urography Our customary technic has been to obtain zonograms during the early stages of urography, usually at three minutes.