Monte Carlo studies of x-ray energy absorption and quantum noise in megavoltage transmission radiography.

The subject contrast of bony anatomy in megavoltage medical radiographs is very low, making detection of bony landmarks difficult if additional noise sources are introduced into the images. One source of noise, which is inherent to the x-ray detection process, is x-ray energy absorption noise. X-ray energy absorption noise results from variations in the amount of energy deposited in the imaging detector per interacting x ray.

Building clinical classifiers using incomplete observations--a neural network ensemble for hepatoma detection in patients with cirrhosis.

One objective of liver transplant evaluation is to identify patients that harbor a hepatoma, but standard screening techniques are not sensitive enough. We trained neural network ensembles to predict the presence of hepatoma in patients with cirrhosis, based on information collected at the time of transplant evaluation. Network architecture and training were modified to handle missing observations.

Influence of the RpoS (KatF) sigma factor on maintenance of viability and culturability of Escherichia coli and Salmonella typhimurium in seawater.

The sigma factor RpoS is essential for stationary-phase-specific, multiple-stress resistance. We compared the viabilities (direct viable counts) and culturabilities (colony counts) in seawater of Escherichia coli and Salmonella typhimurium strains and those in which rpoS was deleted or which were deficient in guanosine 3',5'-bispyrophosphate (ppGpp) synthesis (relA spoT). RpoS, possibly via ppGpp regulation, positively influenced the culturability of these bacteria in oligotrophic seawater.

Tests for evaluating laser film digitizers.

A number of tests to evaluate the image transfer characteristics of laser film digitizers have been developed and these tests have been used to evaluate the performance of a Konica KFDR-S laser film digitizer. These tests were designed to be simple in nature and to use materials readily available in clinical departments. The tests examined (i) the geometric accuracy of the laser film digitizer; (ii) the linearity of the digitizer's characteristic curve; (iii) the temporal/spatial response of the digitizer to abrupt changes in optical density; and (iv) the noise added by the digitizer to the digitized images.

Portal Imaging Technology: Past, Present, and Future.

Many different electronic portal imaging devices (EPIDs) have been developed to improve geometric accuracy in radiation therapy. This article describes the two types of EPIDs that have become available commercially-the television camera-based EPID and the matrix ion chamber EPID-as well as describing the amorphous silicon array, a device that may become available in the future for portal imaging. In addition, the various image registration techniques that identify geometric errors from the portal images are described.

Optimal radiographic magnification for portal imaging.

Two approaches to estimate the optimal radiographic magnification for a TV camera-based portal imaging system and portal films have been used. The first approach optimizes signal transfer while the second optimizes signal-to-noise ratio (SNR) transfer. In order to perform these optimization calculations, the physical characteristics of the imaging system (modulation transfer function and noise power spectrum) as well as the sizes of the radiation sources of our medical linear accelerators have been measured.

A semiautomatic method for registration of portal images.

A method to register pairs of portal images quickly and accurately has been developed. The approach uses a cross-correlation operator to find the optimal match between corresponding anatomic regions that have been selected by a user on pairs of portal images. The cross-correlation operator determines the translation that best registers each pair of anatomic features independently, and then the images are translated, rotated, and scaled so that the least squares difference between the coordinates of all of the paired regions is minimized.

Effect of thermal, oxidative, acidic, osmotic, or nutritional stresses on subsequent culturability of Escherichia coli in seawater.

Survival of stressed Escherichia coli with or without the rpoS gene was assessed after 2 and 6 days in sterile seawater. Cells were submitted to thermal (48°C), acidic (pH 5.1), oxidative (H2O2 1mM), nutritional (C, N, P starvation), or osmotic (NaCl 0.

Seawater effects on various Vibrio species.

This study compared the effects of sea water on Vibrio cholerae and six other Vibrio spp. Survival in seawater microcosms as well as uptake of a carbonated substrate in marine or non-marine conditions were investigated. Except for V.

X-ray scatter in megavoltage transmission radiography: physical characteristics and influence on image quality.

The physical characteristics of x rays scattered by the patient and reaching the imaging detector, as well as their effect on verification (portal) image quality, were investigated for megavoltage (0.1-20 MeV) x-ray beams. Monte Carlo calculations and experimental measurements were used to characterize how the scatter and primary fluences at the detector plane were influenced by scattering geometry and the energy spectrum of the incident beam.

Extraocular muscle problems in thyroid eye disease.

In this paper methods of visualisation of the extraocular muscle changes in thyroid eye disease are discussed. The histopathology of extraocular muscle biopsies has been studied by both light and electron microscopy to show the type of cellular infiltration and the amorphous material in the extracellular matrix. A series of questions to which answers have not yet been found concerning thyroid eye disease are posed which may help to direct new research projects.

Detection of pneumothorax by accident and emergency officers and radiologists on single chest films.

To assess whether an accurate diagnosis of pneumothorax can be made on a single chest film, 233 pairs of inspiratory (I) and expiratory (E) chest films taken in an accident and emergency (A&E) department for suspected pneumothorax were reviewed by two A&E officers and three radiologists. The films were assessed for the presence of pneumothorax by viewing the I film in isolation and, after an interval, by viewing the paired I and E films together. Fifty-four of the patients had a pneumothorax.

X-ray sources of medical linear accelerators: focal and extra-focal radiation.

A computerized tomography (CT) reconstruction technique has been used to make quantitative measurements of the size and shape of the focal spot in medical linear accelerators. Using this technique, we have measured the focal spots in a total of nine accelerators, including (i) two Varian Clinac 2100c's, (ii) two Atomic Energy of Canada Ltd. (AECL) Therac-25's, (iii) two AECL Therac 6's, (iv) a Siemens KD-2, (v) a Varian Clinac 600c (4 MV), and (vi) an AECL Therac-20.

The loss of culturability by Escherichia coli cells in seawater depends on availability of phosphate ions and phosphate transport systems.

Using strains with or without the PhoE porin or different components of the phosphate regulon, we determined that maintenance of the culturability of Escherichia coli in seawater depended significantly on the presence of structures allowing access of phosphate ions to the periplasm, then to the cytoplasm of cells. Cells totally deprived of the two main phosphate transport systems (Pit, Pst) exhibited the highest loss of culturability. Most of this effect resulted from the loss of the high-affinity Pst system, and more specifically that of the periplasmic phosphate-binding protein PhoS.

The proton NMR spectrum in acute EAE: the significance of the change in the Cho:Cr ratio.

We have studied by nuclear magnetic resonance spectroscopy the evolution of the proton spectral changes in acute experimental allergic encephalomyelitis. We found an in vivo elevation in the ratio between the peaks assigned to "choline containing compounds" (Cho) and creatine plus phosphocreatine (Cr). This was associated with an increase in choline, betaine, and phosphorylcholine (PC) as well as a reduction in N-acetylaspartate (NAA), aspartate, N-acetylaspartatylglutamate and inositol in vitro.

Glutamate uptake and synthesis by Escherichia coli cells in seawater: effects on culturability loss and glycinebetaine transport.

In filtered natural seawater supplemented with potassium glutamate, the ability of Escherichia coli MC4100 cells to grow on a complex medium was enhanced as a logarithmic function of the external glutamate concentration. By comparison, a glutamate-respiring strain of E. coli exhibited a greater decline in culturability in seawater, suggesting a protective influence of the accumulated amino acid.

Dynamic gender-related differences in dichotic listening performance.

This experiment investigated dynamic gender-related differences in perceptual asymmetry (PA) in a dichotic task. Twenty right-handed males and 20 right-handed females performed a 200 trial directed attention dichotic listening task using consonant-vowel-consonant nonsense syllables. Men showed a greater right-ear advantage (REA) at the beginning of the test than did women.

Functional properties of retinal Müller cells following transplantation to the anterior eye chamber.

Two types of glial cells occur in the retina, Müller cells and astrocytes. These cells share several structural features such as extending endfeet onto blood vessels of the retina. Retinal vessels express a tight blood-retinal barrier which is comparable to the blood-brain barrier (BBB) of the CNS.

Display equalization: a new display method for portal images.

A method of displaying portal images which permits the user to optimize the display contrast (windowing and leveling) without clipping parts of the image has been developed. The method finds the average signal (brightness) in small regions of the image, generally 1/64th of the total image area. The difference between the average signal in each small region and the global average over the entire image is subtracted from the original image.

Sensitivity of Escherichia coli cells to seawater closely depends on their growth stage.

Sensitivity of Escherichia coli cells in seawater, considered in terms of culturability loss, was examined after different growth periods in a mineral medium supplemented with glucose (M9) at 37 degrees C under aerobic or anaerobic conditions. Their sensitivity varied considerably during the different growth phases and differed when cells were grown under aerobic or anaerobic conditions. Sensitivity of aerobic cells rapidly increased during the lag phase, then decreased during the exponential phase and became minimal during the stationary phase.

OmpC and OmpF porins influence viability and culturability of Escherichia coli cells incubated in seawater.

The contribution of the major outer membrane porins OmpF and OmpC to the maintenance of viability and culturability of Escherichia coli cells in seawater was analyzed using isogenic mutant strains lacking one or both porins. Cells that possessed OmpF and OmpC survived better than those lacking one or both of them. However, the results differed, depending on whether the cells were adapted to high osmolarity or not before transfer to seawater.

Study of high-affinity interactions by quantitative affinity chromatography. Analytical expressions in terms of total ligand concentration.

Analytical expressions are derived for the description of ligand-facilitated and ligand-retarded desorption of partitioning solute in terms of total ligand concentration in quantitative affinity chromatography. Their application is then illustrated by consideration of results from recycling partition equilibrium studies of the heparin-facilitated desorption of thrombin from heparin-Sepharose, and of the competition between methyl-alpha-D-mannoside and p-nitrophenyl-alpha-D- mannoside for concanavalin A immobilized on CPG-170. Finally, published frontal affinity chromatographic data for the NADH-dependent elution of rabbit muscle lactate dehydrogenase from oxamate-Sepharose are reanalysed using these equations to demonstrate the characterization of a system reflecting the binding of a solute-ligand complex to an affinity matrix.

Daily monitoring and correction of radiation field placement using a video-based portal imaging system: a pilot study.

We have developed a video-based portal imaging system for radiotherapy localization. The system can acquire high quality portal images automatically using short (1-3 monitor unit) irradiations and immediately display the images. The major advantage of the imaging system is that it can be used routinely to check and correct patient positioning before much of the daily irradiation has been delivered.

Metabolically dependent blood-brain barrier breakdown in chronic relapsing experimental allergic encephalomyelitis.

We have studied chronic relapsing experimental allergic encephalomyelitis (CREAE), a model of immune-mediated demyelination, using gadolinium (Gd)-enhanced magnetic resonance imaging in vivo and the blood-brain barrier (BBB) markers, lanthanum nitrate and Gd nitrate, histologically. In regions of the spinal cord showing Gd enhancement, there was evidence for vesicular transport as a mechanism of BBB breakdown in CREAE, shown by an increased number of endothelial vesicles containing lanthanide (lanthanum or Gd, whichever had been perfused) and deposition of tracer in the perivascular space; tight interendothelial junctions remained intact. Prior perfusion with 2,4-dinitrophenol, a metabolic inhibitor, suppressed the appearance of endothelial vesicles containing lanthanide and tracer in the perivascular space.