Scattering media characterization with phase-only wavefront modulation.

A new experimental approach is demonstrated to probe the scattering properties of complex media. Using phase-only modulation of the light illuminating a random scattering sample, we induce and record fluctuations in the reflected speckle patterns. Using predictions from diffusion theory, we obtain the scattering and absorption coefficients of the sample from the average change in the speckle amplitude. Our approach, which is based on interference, is in principle able to give better signal to noise ratio as compared to an intensity modulation approach. We compare our results with those obtained from a knife-edge illumination method and enhanced back-scattering cone. Our work can find application in the non-invasive study of biological specimens as well as the study of light propagation in random scattering devices like solar cells or LEDs.

Picture archiving and communications systems (PACS).

Although there has been a recent increase in interest in picture archiving and communications systems (PACS) topics, little has been published to assist the non-technical person in understanding the complexities of the technologies required for a PACS implementation. This issue of Current Problems in Radiology defines each PACS component and explains why each is important in a system design. PACS installations at the University of Florida are used as examples to tie the concepts together. The infrastructure required for PACS consists of the information system interfaces, networks, and databases. Information system interfaces guarantee consistent patient data across all platforms and reduce labor requirements by eliminating duplicate data entry. Data networks move information from the originating location to users around the hospital, clinic, campus, city, or world. In the PACS environment, the data consist of patient and study information as well as images and information about these images. Databases organize the data from multiple sources into a coherent package that can be queried for many different purposes, such as retrieving images, reviewing patient and study information, studying practice statistics, and performing outcomes analysis. PACS components consist of acquisition nodes, archives, and output devices. Acquisition nodes may include "digital modalities" such as CT, MRI, nuclear medicine, and computed radiography (CR), along with devices to convert from analog to digital, such as digitizers and frame grabbers. Options for archives are discussed along with configuration schemes. Output devices include both hard copy (film and paper prints) and soft copy (workstations for display and diagnosis). Finally, a description of the PACS installations at the University of Florida is presented, with comments on some of the difficulties and complexities encountered. A discussion of the cost and benefits of PACS is included, along with a forecast of the future of PACS.

The human brain: localized H-1 MR spectroscopy at 1.0 T.

Localized H-1 magnetic resonance (MR) spectroscopy of the human brain in vivo was performed at a field strength of 1.0 T. Investigations with the stimulated echo acquisition mode included studies in the right frontoparietal area, occipital lobe, cerebellum, and pons of healthy volunteers, as well as studies in two patients with astrocytomas. Prior to the acquisition of the H-1 MR spectra, all examinations included fast low angle shot MR imaging in three orientations to select the volumes of interest. The tumor spectra confirmed previous findings at higher field strengths by producing characteristic alterations from the spectra of normal brain tissue: markedly reduced resonances of N-acetyl-aspartate and creatine, increased signal intensities of cholines, and a strong resonance from lactate. The authors conclude that the results of this study clearly demonstrate the feasibility of H-1 MR spectroscopy at 1.0 T without significant losses in relative spectral resolution and signal-to-noise ratio of major metabolites with singlet resonances, compared with previous studies at 1.5 and 2.0 T.

Magnetic resonance angiography.

Magnetic resonance imaging allows the visualization of vascular structures without the use of contrast agents. With three-dimensional imaging techniques, based on gradient echo sequences, up to 128 slices can be acquired within a maximum acquisition time of 21 minutes at a spatial resolution of approximately 1 mm. This allows the carotid arteries and major intracerebral vascular structures to be displayed. From the primary three-dimensional data set, projective images at arbitrary projection angles can be calculated. This technique is extremely helpful for assigning spatially complex vascular structures and identifying vascular disease. As a result of rapid technologic advances in magnetic resonance angiography, it is now necessary to assess its clinical utility for identifying atherosclerotic stenoses, aneurysms, and arteriovenous malformations. Limited experience to date has shown that magnetic resonance angiography, because of its high sensitivity to these vascular diseases, may play a clinically important role as a screening method.

Rhizocticin A, an antifungal phosphono-oligopeptide of Bacillus subtilis ATCC 6633: biological properties.

Rhizocticin A, the main component of the antifungal, hydrophilic phosphono-oligopeptides of Bacillus subtilis ATCC 6633, was used for sensitivity testing and experiments into the molecular mechanism of the antibiotic action. Budding and filamentous fungi as well as the cultivated nematode Caenorhabditis elegans were found to be sensitive, whereas bacteria and the protozoon Paramecium caudatum were insensitive. Rhizoctonia solani was inhibited in agar dilution tests but not in diffusion tests. The antifungal effect of rhizocticin A was neutralized by a variety of amino acids and oligopeptides. Oligopeptide influence was mainly understood as transport antagonism, and it was concluded that the antibiotic enters the recipient cell via the peptide transport system. L- and D-cystine were also identified as potent, general antagonists of the oligopeptide transport. The rhizocticin-antagonism of four other amino acids was taken as a clue to the site of action. Provided that rhizocticin A is split by peptidases of the target cell into inactive L-arginine and toxic L-2-amino-5-phosphono-3-cis-pentenoic acid (L-APPA), the latter may interfere with the threonine or threonine-related metabolism.

Fengycin--a novel antifungal lipopeptide antibiotic produced by Bacillus subtilis F-29-3.

Fengycin is an antifungal lipopeptide complex produced by Bacillus subtilis strain F-29-3. It inhibits filamentous fungi but is ineffective against yeast and bacteria. The inhibition is antagonized by sterols, phospholipids and oleic acid, whereas two other unsaturated fatty acids increase the antifungal effect. Fengycin consists of two main components differing by one amino acid exchange. Fengycin A is composed of 1 D-Ala, 1 L-Ile, 1 L-Pro, 1 D-allo-Thr, 3 L-Glx, 1 D-Tyr, 1 L-Tyr, 1 D-Orn, whereas in fengycin B the D-Ala is replaced by D-Val. The lipid moiety of both analogs is more variable, as fatty acids have been identified as anteiso-pentadecanoic acid (ai-C15), iso-hexadecanoic acid (i-C16), n-hexadecanoic acid (n-C16), and there is evidence for further saturated and unsaturated residues up to C18.

Influence of magnetic field strength on image contrast.

In magnetic resonance imaging (MRI) S/N increases with magnetic field strength. The curve, however, flattens out at higher fields, resulting in diminishing gains as the field strength is increased.

Proton chemical shift imaging.

Proton resonance spectra contain two broad classes of hydrogen-containing compounds: those that are fat-like and those that are water-like. Proton chemical shift imaging is a means to produce water or fat proton images. Three methods of proton chemical shift imaging are discussed.

Physical principles of NMR tomography.

Using nuclear magnetic resonance tomography it is possible to produce sectional images of the density and relaxation times of the protons within the human body. After a review of the general principles of nuclear magnetic resonance it is explained how this physical effect can be used for generating tomographic images in medical diagnosis. The major components of an imaging system and the physical and technical potentials and limitations of this new method are described. The different appearance of tissue and body fluids in spin-density, T1 and T2 images, as well as resulting problems of interpretation are discussed with typical examples.

[Nuclear magnetic resonance tomography]. / Kernspin-Tomographie.

Imaging methods based on nuclear magnetic resonance allow the production of sectional images of the human body without ionizing radiation. It is possible to measure the density and relaxation times of the water protons in body fluids or tissue. This allows not only to obtain morphological information but also to get some insight into the spatial distribution of physiological data. Starting with a review of the principles of nuclear magnetic resonance it is explained how the measured signal can be associated with an image point; it is also explained what type of apparatus is necessary and what the physical limitations are. Possible risks the patient may be exposed to in an examination using nuclear magnetic resonance are discussed. The present state of the technical development enables the production of whole-body sectional images of a living person within about one minute. By means of some typical examples the nature and properties of these images are explained. Although extensive clinical studies will be necessary before a more general assessment can be made of this method, an outlook is provided on expected further developments and possible future fields of application.

Metabolic products of microorganisms. 196 The structure of ethericin B, a new diphenylether antibiotic.

Ethericin B(Ia) was isolated together with ethericin A1) from fermentations of Aspergillus funiculosus Tü 680. The structure of ethericin B was established as 4-carbethoxy-5,5'-dihydro-xy-3,3'-dimethyl-diphenyl ether by chemical degradation, mass spectrometry, 1H-NMR and comparison with synthetic 4-carbethoxy-5,5'-dimethoxy-3,3'-dimethyl-diphenyl ether.

[Genetic aspects of opportunistic fungi]. / Aspects génétiques des champignons opportunistes.

The etiologic agents of human mycoses are discussed in taxonomic order. Some fungal genera are used as examples to describe the general genetical behavior of the various groups. Special features of probable genetical and etiological relevance are mentioned.

Ophiocordin, an antifungal antibiotic of Cordyceps ophioglossoides.

An unknown antibiotic, ophiocordin, C21H22N2O8, MW: 430, was isolated from submerged cultures of Cordyceps ophioglossoides, strain TU 276, grown in a glycerol soybean meal medium at 27 degrees C. The antibiotic was extracted from acidified culture fluids with n-butanol and purified by subsequent column chromatography on DEAE-Sephadex and cellulose. Studies including nuclear magnetic resonance and mass spectrometry resulted in proposals of partial structures of the molecule. Inhibition by ophiocordin could be demonstrated for a small number of fungi belonging to different taxonomic groups. Bacteria were not inhibited. The antifungal effect was antagonized by ammonia and nitrate ions and by certain amino acids.