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PubMed1992

Phosphorylation-induced conformational changes in the phosphorylase ab hybrid as revealed by resolution of pyridoxal 5'-phosphate with imidazole citrate and cysteine.

The accessibility of pyridoxal 5'-phosphates of the phosphorylase ab hybrid to resolution by imidazole citrate and cysteine was studied and compared with that of the b and a forms. Promotion of resolution of phosphorylated forms by raising the temperature or in the presence of glycogen indicates that the resistance of phosphorylase a and ab to resolution at 0 degrees C is due rather to their tetrameric state than their phosphorylation-related active conformation. The pattern of resolution of the ab hybrid was similar to that of the a and differed from that of the b forms in that it occurred at 30 degrees C and 37 degrees C but not at 0 degrees C, moreover, it did not show first-order kinetics. On the other hand, inhibition of resolution by ligands binding to the nucleotide site of phosphorylase reflected an intermediate sensitivity of the ab form between that of the b and a forms. We conclude that partial phosphorylation of phosphorylase b elicits conformational change(s) in both subunits which influence the monomer-monomer interactions and resolution of pyridoxal 5'-phosphates. Resistance of ab hybrid to monomerizing agents as imidazole citrate, comparable to that of other forms, argues for its stability, ruling out its reshuffling into mixtures of phosphorylase b and a.

Adenosine Monophosphate↗

PubMed1981

Resolution and accuracy in two dimensional echocardiography.

The resolution and accuracy of commercially available two dimensional echocardiographic systems were tested by imaging two types of in vitro test objects. One consisted of a series of fine parallel threads spaced at known intervals and the other was a tissue phantom in which a series of holes of known size had been cut. The echocardiographic systems tested included a mechanical single element sector scanner, a three element rotary sector scanner and a phased array system. Azimuthal resolution, lateral resolution and accuracy of horizontal distance measurements were assessed at depths of 2 and 6 cm. For each system, azimuthal resolution was better than lateral resolution, especially when assessed with use of the parallel threads. When the tissue phantom was imaged, the best resolution (2 mm in azimuthal and lateral directions) was obtained with the highest frequency transducer tested (3.5 MHz). The apparent size of a tissue defect was sensitive to gain settings, especially at a depth of 2 cm with lower frequency transducers; at a depth of 6 cm, echographic measurements of defect size were accurate to within 2.5 mm. Recent applications of two dimensional echocardiography require near the apparent limits of current equipment. It is recommended that the highest frequency transducer and lowest possible gain settings be used in these situations.

Cardiomyopathies↗

PubMed1987

Resolution of the enantiomers of various alpha-substituted ornithine and lysine analogs by high-performance liquid chromatography with chiral eluant and by gas chromatography on Chirasil-Val.

A reversed-phase high-performance liquid chromatography method, with L-proline and copper as chiral mobile phase, is described for the enantiomeric resolution of various alpha-substituted ornithine and lysine analogs. Although ornithine gives no separation with the chiral eluant used, excellent resolutions are obtained for various alpha-alkyl-, alpha-halogenomethyl-, alpha-vinyl-, and alpha-ethynyl-substituted ornithines. Similar separations are also observed for the dehydroornithine and lysine analogs. Gas chromatography on a chiral stationary phase, Chirasil-Val, allows the resolution of the ornithine and lysine analogs after derivatization into the monofluoroacyl derivatives of their corresponding lactams. No resolution or only a poor resolution is obtained by GC on Chirasil-Val for the dehydroornithine analogs as their di-N-perfluoroacyl alkyl esters. The chiral eluant HPLC procedure is easily scaled up for the semipreparative resolution of several ornithine analogs, i.e., alpha-fluoromethylornithine, alpha-difluoromethylornithine, alpha-chlorofluoromethylornithine, and alpha-fluoromethyldehydroornithine, which are known as potent ornithine decarboxylase inhibitors in vitro and in vivo.

Chromatography, Gas↗

PubMed1987

High resolution autoradiography at the regional topographic level with [14C]2-deoxyglucose and [3H]2-deoxyglucose.

After injection of 2-deoxyglucose (2-DG) labeled with tritium or carbon-14, autoradiograms were produced by thaw-mounting 4 micron frozen sections of rat brains on nuclear emulsion-coated slides. The results show that the distribution of radioactivity among different brain regions was similar and that the resolution at the regional topographical level was virtually identical for both compounds. The resolution obtained with the thaw-mounting of thin frozen sections onto nuclear emulsion was considerably greater than the resolution demonstrated in published results in the literature, when carbon-14 or tritium-labeled 2-deoxyglucose were used with 20 micron frozen sections and X-ray film or tritium-sensitive film. The results indicate that section thickness, detection medium and intimacy of contact between section and photographic emulsion influence resolution. At the regional level, the detection medium apparently influences resolution to a greater extent than the energy differences of the beta particles emitted from 14C or 3H. Although diffusion of radiolabeled 2-deoxyglucose and metabolites during the thaw-mounting process precludes single cell resolution of these autoradiograms, the improvement of visualizing regional topographic detail demonstrates that the described technique is a valuable approach with which to study regional 2-DG uptake.

Animals↗

PubMed1992

Emission microscopy and related techniques: resolution in photoelectron microscopy, low energy electron microscopy and mirror electron microscopy.

A unified treatment of the resolution of three closely related techniques is presented: emission electron microscopy (particularly photoelectron microscopy, PEM), low energy electron microscopy (LEEM), and mirror electron microscopy (MEM). The resolution calculation is based on the intensity distribution in the image plane for an object of finite size rather than for a point source. The calculations take into account the spherical and chromatic aberrations of the accelerating field and of the objective lens. Intensity distributions for a range of energies in the electron beam are obtained by adding the single-energy distributions weighted according to the energy distribution function. The diffraction error is taken into account separately. A working resolution is calculated that includes the practical requirement for a finite exposure time, and hence a finite non-zero current in the image. The expressions for the aberration coefficients are the same in PEM and LEEM. The calculated aberrations in MEM are somewhat smaller than for PEM and LEEM. The resolution of PEM is calculated to be about 50 A, assuming conventional UV excitation sources, which provide current densities at the specimen of 5 x 10(-5) A/cm2 and emission energies ranging up to 0.5 eV. A resolution of about 70 A has been demonstrated experimentally. The emission current density at the specimen is higher in LEEM and MEM because an electron gun is used in place of a UV source. For a current density of 5 x 10(-4) A/cm2 and the same electron optical parameters as for PEM, the resolution is calculated to be 27 A for LEEM and 21 A for MEM.

Mathematics↗

PubMed1994

Capillary zone electrophoresis of peptides: prediction of the electrophoretic mobility and resolution.

The determination of the pKa values of some selected peptides of similar size was performed by microtitration, which makes possible an accurate determination of the peptide charge as a function of the solution pH. Capillary zone electrophoresis separation of these peptides on modified capillaries at acidic pH showed that the electrophoretic mobility correlates with the peptide charge. This observation suggests that when an appropriate charge value is used, the basic electrophoretic equation is respected and, at least at a peptide charge value less than 1, the utilization of alternative semi-empirical predictions is not necessary. As a general rule, a peptide separation at acidic pH values is to be preferred to that at basic pH values. In fact, at basic pH a separation in the absence of both electroosmotic flow and of spurious interactions between the peptides and the inner wall of the capillary is difficult, owing to the instability of capillary modification. Further, from the differences in the peptide charge, a prediction of the best resolution as a function of the pH could be obtained; in fact, the resolution, for peptides of similar size and in the absence of electroosmotic flow, is connected to a simple equation, where the principal term depends on the effective charge of the peptides, which is a function of the pH of the solution and the pKa values of the peptides. The predictions of resolution at acidic pH agreed well with the experimental results; the spatial resolution measured in the separation of met- and leu-enkephalin was virtually coincident with the predicted resolution; in the case of a mixture of four model tetrapeptides of sequence GGNA, GGQA, GGDA and GGEA some anomalous results with respect to the predicted resolutions were observed. Nevertheless, an acceptable prediction can also be made in this case.

Amino Acid Sequence↗

PubMed1995

Poly(ethyleneoxide) for high-resolution and high-speed separation of DNA by capillary electrophoresis.

Capillary electrophoresis (CE) with polyacrylamide gels has already been demonstrated to allow single-base resolution of single-stranded DNA. However, linear polyacrylamide is not an ideal matrix because of a high viscosity and difficulties in preparing the polymer with well defined pore sizes. Alternatively, poly(ethyleneoxide) (PEO) with a large range of molecular masses from 300,000 to 8,000,000 is available commercially. In addition, it is easy to prepare homogeneous solutions to provide highly reproducible separation performance with sufficient resolution. Single-base resolution of double-stranded DNA between 123 and 124 base pairs can be achieved by the use of homogeneous matrices prepared from PEO (2.5% M(r) 8,000,000), and even better resolution is achieved by using mixed polymer matrices. With further work, it should be possible to change the fractions and the total amounts of polymers to achieve even higher resolution for different samples with different size ranges of fragments. Another advantage of mixed polymer matrices is that relatively high resolution can be obtained while maintaining a relatively low viscosity compared to linear polyacrylamide with identical contents of formamide and urea, which makes it easier to fill these matrices into small capillaries.

DNA↗

PubMed1995

Time course of resolution of persistent air leak in spontaneous pneumothorax.

Persistent air leak (PAL) following tube drainage for spontaneous pneumothorax (SP) is a potentially troublesome complication. The optimum time to intervene surgically is not known. We therefore investigated the rate of resolution of PAL (defined as continued air leak at 2 days after tube insertion) in patients treated medically. We retrospectively reviewed the records of 214 patients presenting with SP over 5 yr. One hundred and forty-two (67%) had tube drainage and in 73 (51%) of these a PAL developed. Overall median time to resolution in the 43 patients with PAL treated medically was 8 days from tube insertion, but PAL resolution was longer in those with underlying lung disease (n = 19) than those without such disease (11 days vs. 7 days, P = 0.05). In patients with normal lungs 20/24 had resolved by 9 days but subsequently the rate of resolution was much slower. In those with abnormal lungs only 8/19 had resolved by 9 days (P < 0.05 compared with those with normal lungs) but the rate of resolution in such patients appeared to change little subsequently. The size of the initial SP did not influence the rate of resolution of PAL. For patients with PAL and normal lungs, surgery at 7-9 days from tube insertion would provide a reasonable opportunity for the PAL to resolve with medical treatment. For those with underlying lung disease there is no clear optimal time and decisions need to be taken on an individual basis.

Adolescent↗

PubMed1988

Silicone intraocular lens resolution in air and in water.

The resolution efficiencies of 31 biconvex silicone intraocular lenses, ranging in power from 16.0 to 23.5 diopters, were tested in air and in water to see if a predictable relationship existed as previously reported with polymethylmethacrylate lenses. Resolution efficiency is defined as the percentage ratio of the actual resolving power of a lens to that of a perfect lens of the same focal length which is only limited in resolution by diffraction. The lenses ranged from 29% to 58% resolution efficiency in air. No lenses exhibiting multiple images were included. All 31 lenses achieved at least 73% resolution efficiency in water, and one lens achieved 82%. Based on these findings, a biconvex silicone lens that exceeds 30% resolution efficiency in air and does not produce multiple images can perform near its diffraction limit when implanted in the eye.

Air↗

PubMed1995

The 70S Escherichia coli ribosome at 23 A resolution: fitting the ribosomal RNA.

BACKGROUND: The ribosome--essential for protein synthesis in all organisms--has been an evasive target for structural studies. The best available structures for the 70S Escherichia coli ribosome or its 30S and 50S subunits are based on electron microscopical tilt experiments and are limited in resolution to 28-55 A. The angular reconstitution approach, which exploits the random orientations of particles within a vitreous ice matrix, can be used in conjunction with cryo-electron microscopy to yield a higher-resolution structure. RESULTS: Our 23 A resolution map of the 70S ribosome elucidates many structural details, such as an extensive system of channels within the 50S subunit and an intersubunit gap ideally shaped to accommodate two transfer RNA molecules. The resolution achieved is sufficient to allow the preliminary fitting of double-helical regions of an earlier three-dimensional ribosomal RNA model. CONCLUSIONS: Although we are still a long way from attaining an atomic-resolution structure of the ribosome, cryo-electron microscopy, in combination with angular reconstitution, is likely to yield three-dimensional maps with gradually increasing resolution. As exemplified by our current 23 A reconstruction, these maps will lead to progressive refinement of models of the ribosomal RNA.

Escherichia coli↗

PubMed1995

Fibrinogen and markers of fibrinolysis and endothelial damage following resolution of critical limb ischaemia.

OBJECTIVES: To assess the effects of resolution of critical limb ischaemia on the elevated plasma fibrinogen, cross-linked fibrin degradation products (FDP), and von Willebrand factor antigen (vWF) levels, reported in peripheral arterial occlusive disease. DESIGN: A prospective study of patients undergoing surgery for chronic critical limb ischaemia. SETTING: Two vascular surgery units providing tertiary referral services for the West of Scotland. MATERIALS: Venous blood samples were assayed for plasma fibrinogen, FDP D-dimer, and vWF levels, prior to surgery, together with fibrinolytic and rheological parameters, in 82 patients. Sampling was repeated 4 months after resolution of critical limb ischaemia. OUTCOME MEASURES: Levels of these parameters following successful resolution of critical limb ischaemia were compared with pre-operative levels, and with an age-matched random population sample. MAIN RESULTS: Plasma fibrinogen and vWF levels were significantly lower (both p < 0.005, Wilcoxon matched pairs) following successful resolution of critical limb ischaemia in the 56 patients available for review, although levels remained higher than in population controls (p < 0.01, Mann-Whitney U-test). FDP levels were unchanged following surgery, remaining higher than in age-matched population controls (p < 0.01). CONCLUSIONS: Resolution of critical limb ischaemia fails to reduce plasma fibrinogen, fibrin turnover, and vWF levels to those seen in population controls. This implies that increased fibrinogen and fibrin turnover in peripheral arterial disease is not solely a consequence of tissue ischaemia, while the persisting prothrombotic state following resolution of critical limb ischaemia has potentially important implications for graft and patient survival.

Aged↗

PubMed1987

Video-endoscopes in comparison with fiberscopes: quantitative measurement of optical resolution.

The subject of this study was the optical performance of video-endoscopic systems (VE) in terms of maximal resolving power and resolvable picture elements. Olympus, Toshiba/Machida, Fujinon, and Welch Allyn video gastroscopes were tested. A GIF Q 10 fiberscope from Olympus was also included for comparison. The resolution measurements were made at various distances using two independent methods--electronic analysis of the TV signal, and visual evaluation of the resolution, of a standardized test target. The results obtained with the two methods were in perfect agreement. The resolution of fine details clearly depends on the distance between the distal end and the target because of decreasing image scale. Depending on the individual optical design, the various VE's show maxima at different distances. At shorter distances, the image is degraded by defocusing. An optimal distance which is as small as possible is desired for clinical routine. Apart from the fiberscope this requirement is best met by the Fuji system. The greatest resolution is obtained with the Toshiba system but at the cost of the viewing angle which is the smallest of all the systems. Fuji combines relatively high resolution with a large viewing angle. Because of the widely varying viewing angle a comparison based solely on resolution cannot represent the true imaging capability of the system. We therefore eliminated purely optical parameters and calculated the number of resolvable picture elements per line. We regard this number to be a fair characterization of both TV and fiber systems.

Fiber Optic Technology↗

PubMed1987

Influence of zoom factor on centre-of-rotation of the SPECT system and on the resolution of tomographic images.

The influence of zooming on centre-of-rotation (COR) of the rotating camera-based SPECT system and on the resolution of tomographic images was investigated. COR values were measured as a function of zoom factor varying from x1.0 to x3.0. Measurements were performed using two SPECT systems collimated with three collimators. In this study, the COR was observed to shift linearly with zoom factor. The influence of zooming on COR depends on the location and the deviation of the COR from the axis-of-rotation (AOR). We recommend that the deviation of the COR from the AOR be kept to within 0.4 pixels corresponding to 2.4 mm. Unlike zooming, the magnitude of COR shift is uncorrelated to the type of collimator used. Contrast and spatial resolution variations of the tomographic images were quantitated as a function of COR shift for clinical data acquired using no zoom factor and a zoom factor of 2.50. The resolution indices were observed to be more sensitive to COR shift for clinical data acquired using no zoom factor. The sensitivity appeared to be inversely dependent on the zoom factor utilized. However, zooming was found not to preserve the same resolution degradation. Optimum resolution images can be reconstructed by requiring the COR be determined and clinical study be acquired using the same zoom factor and collimator. For qualitative evaluation of tomographic images, the zoom factor requirement can be removed provided that the deviation of the COR from the AOR is within the recommended limit. This limit allows for a maximum spatial resolution degradation of 5%.(ABSTRACT TRUNCATED AT 250 WORDS)

Image Enhancement↗

PubMed1992

High-resolution scanning electron microscopy of frozen-hydrated cells.

Cryo-fixed yeast Paramecia and sea urchin embryos were investigated with an in-lens type field-emission SEM using a cold stage. The goal was to further develop and investigate the processing of frozen samples for the low-temperature scanning electron microscope (LTSEM). Uncoated frozen-hydrated samples were imaged with the low-voltage backscattered electron signal (BSE). Resolution and contrast were sufficient to visualize cross-fractured membranes, nuclear pores and small vesicles in the cytoplasm. It is assumed that the resolution of this approach is limited by the extraction depth of the BSE which depends upon the accelerating voltage of the primary beam (V0). In this study, the lowest possible V0 was 2.6 kV because below this value the sensitivity of the BSE detector is insufficient. It is concluded that the resolution of the uncoated specimen could be improved if equipment were available for high-resolution BSE imaging at 0.5-2 kV. Higher resolution was obtained with platinum cryo-coated samples, on which intramembranous particles were easily imaged. These images even show the ring-like appearance of the hexagonally arranged intramembranous particles known from high-resolution replica studies. On fully hydrated samples at high magnification, the observation time for a particular area is limited by mass loss caused by electron irradiation. Other potential sources of artefacts are the deposition of water vapour contamination and shrinkage caused by the sublimation of ice. Imaging of partially dehydrated (partially freeze-dried) samples, e.g. high-pressure frozen Paramecium and sea urchin embryos, will probably become the main application in cell biology. In spite of possible shrinkage problems, this approach has a number of advantages compared with any other electron microscopy preparation method: no chemical fixation is necessary, eliminating this source of artefacts; due to partial removal of the water additional structures in the cytoplasm can be investigated; and finally, the mass loss due to electron beam irradiation is greatly reduced compared to fully frozen-hydrated specimens.

Animals↗

PubMed1989

High resolution scanning electron microscopy of the cell.

The scanning electron microscope (SEM) has become a powerful tool for ultrastructural research with improvement of the instrument's resolution and progress in specimen preparation techniques. With regard to resolution, it has been improved step-by-step in this decade and, in 1985, an ultra-high resolution SEM (UHS-T1) was developed, with a resolution of 0.5 nm. Concerning specimen preparation, the osmium-DMSO-osmium method, which is effective for revealing intracellular structures, has come to be widely used. Techniques for observing smaller objects, such as bacteriophages, viruses, and biological macromolecules, have also been devised in recent years. As a result of these preparation techniques and the availability of the ultra-high resolution SEM, the application of SEM in biology is expanding rapidly. In this paper, an outline of the ultra-high resolution SEM, techniques for specimen preparation, findings of some biological materials by these techniques, and guidelines to making the specimens, are described.

Animals↗

PubMed1967

Visual resolution when light enters the eye through different parts of the pupil.

1. Threshold contrasts for resolution of sinusoidal gratings imaged on to the retina through a decentred 2 mm pupil were measured.2. No loss in resolution was found when the pupil was decentred parallel to the lines of the gratings. A loss in resolution by a factor of 3 occurred when the pupil was decentred by 3 mm perpendicular to the lines of the gratings.3. The effects of focus on the threshold contrast for a grating viewed through a centred and decentred pupil were used to show that at least a portion of the loss in resolution is due to optical aberrations.4. Using a neon-helium gas laser as a coherent light source, interference fringes were produced on the retina directly. Threshold contrasts for resolution of the fringes were determined for different positions of entry of the beams of light through the pupil. When the Stiles-Crawford brightness effect was compensated for, no loss in resolution was found to occur for decentred entry of the beams.5. It is concluded that the off-axis loss of visual acuity is wholly due to optical aberrations in the eye.6. The ratios between the threshold contrasts for sinusoidal gratings and for interference fringes are used to calculate the optical transfer functions of the off-axis aberrations of the eye.

Humans↗

PubMed1991

Human peripheral spatial resolution for achromatic and chromatic stimuli: limits imposed by optical and retinal factors.

1. The aim of this study was to determine whether optical, receptoral or higher-order neural properties limit spatial resolution (acuity) in human vision, especially in the peripheral regions of the visual field. 2. Both achromatic and chromatic stimuli were used, and measures were taken to ensure that the resolution estimates were not contaminated by the detection of spatial sampling artifacts. Spatial contrast sensitivity functions were measured at retinal locations from 0 to 55 deg along the naso-temporal meridian for: (i) discriminating the direction of drift of luminance-modulated (black-white) sinusoidal stimuli drifting at 8 Hz (achromatic task); and (ii) for detecting isoluminant red-green sinusoidal stimuli drifting at 0.4 Hz (chromatic task). Achromatic contrast sensitivity functions were also measured along the vertical meridian for eccentricities of 8 and 40 deg. Each achromatic function was extrapolated to a contrast sensitivity of one (100% contrast) to estimate achromatic acuity. Chromatic acuities were obtained by expressing chromatic contrast in terms of cone contrasts and using the same method of extrapolation. We compared the results with recent data on human optical properties and retinal anatomy. 3. Both achromatic and chromatic acuity decline with distance from the fovea, but at a faster rate than that dictated by the known optical and/or receptoral properties of the human eye. We conclude that, for stimuli of either achromatic or chromatic contrast, peripheral spatial resolution is limited by post-receptoral mechanisms. Also, chromatic acuity declines more steeply than luminance acuity with eccentricity suggesting that there are additional post-receptoral limitations on colour resolution in the periphery. 4. A clear naso-temporal asymmetry is seen in the resolution whose dependence is qualitatively, but not quantitatively, similar to the Nyquist limits imposed by the asymmetric density of human retinal ganglion cells. We discuss the possibility that in peripheral vision (beyond the optic nerve head) the spacing of ganglion cells may pose a fundamental limit on the resolution of achromatic stimuli, but not chromatic stimuli.

Color Perception↗

PubMedDate not supplied

Localized in vivo high-resolution NMR imaging using gradient subencoding technique.

A new spatial localization technique for in vivo high-resolution imaging is presented here. In contrast to other localization techniques that use a series of rf pulses to define a volume of interest, only one rf pulse is utilized in the proposed method for selection of a region to be imaged. Instead of rf pulses for region selection, subencoding gradient pulses are used for the localization together with a convolution process on each phase-encoding gradient by a set of additional gradients (e.g., y direction). Then the 2-D localization is completed by restricting the bandwidth in the readout direction (e.g., x direction). The latter is simply achieved by using a low-pass filter in the receiver system. By applying this technique on a human body, localized in vivo high-resolution images are obtained for the knee with much improved resolution. 100 x 100 microns in-plane (x,y plane) resolution images obtained from the human knee demonstrate that localized in vivo high-resolution imaging for both human and animals is possible with an in-plane resolution of below 100 microns.

Image Processing, Computer-Assisted↗