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PubMed1995

[The spatial resolution of the digital storage phosphor system. The monitor and film compared].

The physical characteristics of radiographic images, namely spatial resolution and contrast, have obvious effects upon diagnostic image usefulness. We investigated the spatial resolution of both radiographs and magnified digital obtained with a storage phosphor system, in comparison with a film-screen combination. This study was carried out on the conventional radiographs of a phantom grid 0.5 mm thick, with resolution ranging from 0.5 to 10 lp/mm. Each examination was compared at naked eye and with the electronic evaluation of a region of interest on both standard and magnified views or by digitization with a charge coupled detector (CCD) television camera followed by the computing of the modulation transfer function curve. Our results demonstrate a higher spatial resolution of direct magnification, on both digital and film-screen pictures (over 5 lp/mm). On the contrary, the electronic magnification on the monitor yields the same spatial resolution as non-magnified digital images (up to 4.3 lp/mm). By selecting appropriate regions of interest, we could demonstrate the compression of the non-magnified images on the monitor. The modulation transfer curves show that direct magnification yields higher spatial resolution than electronic magnification and non-magnified views. Viewing electronically magnified images on the monitor yields the same resolution as contact radiographs: the monitor offers the advantage of an easier study of the regions of interest.

Evaluation Studies as Topic↗

PubMed1993

Resolution of synthetic chi structures by the FLP site-specific recombinase.

The FLP site-specific recombinase is encoded by the two micron circle, an endogenous plasmid of Saccharomyces cerevisiae. FLP-mediated recombination in vitro proceeds via a short-lived Holliday (chi) intermediate. We have made a synthetic chi structure containing two FLP recognition target (FRT) sequences in order to investigate resolution by purified FLP protein. We found that incubation of this model substrate with FLP generated two pairs of linear products in equal quantities. Thus, resolution was equally likely to occur in either direction. Alteration of FLP binding sites, so as to inhibit binding, affected the direction of resolution; cleavage was reduced adjacent to the altered binding site. The overall efficiency of resolution increased when one FLP binding site was mutated. In investigating the series of mutated chi structures we found that resolution requires only two intact FLP binding sites. However, the non-specific protein-DNA interaction of additional FLP molecules may also be required. Thus, resolution is more tolerant of the loss of FLP binding sites than is the complete recombination reaction.

Base Sequence↗

PubMed1993

The influence of image resolution on the positron emission tomographic measurement of caudate glucose consumption.

The aim of this study was to investigate the influence of image resolution on (a) relative and absolute values of caudate glucose consumption (rCMRGlc) determined by positron emission tomography (PET), and (b) the detection of significant differences in these metabolic values between groups of subjects. For this purpose, raw data of cerebral accumulation of fluorine-18 fluorodeoxyglucose (FDG) obtained in 11 normal subjects and in nine patients with unilateral thalamic infarction were reconstructed using filtered backprojection with four different cut-off frequencies (CFs), yielding images with a transaxial resolution of 5.7, 7.1, 8.9 and 11 mm (full-width at half-maximum; FWHM). Absolute values of caudate rCMRGlc decreased significantly by more than 30% over the range of image resolutions studied. Bilateral ratios of caudate rCMRGlc were insensitive to variations in image resolution. Levels of significance assessing the differences in mean metabolic values between patients and controls were all below 0.01. They were, however, slightly better at image resolutions of 7.1 and 8.9 mm than at a resolution of 5.7 mm. These data indicate (a) that relative values of rCMRGlc are better suited to compare quantitative results from different PET cameras than are absolute values, and (b) that the CF used for the filtered back-projection exerts a small but not negligible influence on levels of significance assessing differences in metabolic values between groups of subjects.

Adult↗

PubMed1995

Influence of transcription and replication on the in situ resolution of immunoglobulin heavy-chain constant region genes: an interphase cytogenetics analysis.

An interphase cytogenetics analysis was performed to investigate whether replication and transcription could influence in situ resolution of immunoglobulin (Ig) heavy chain constant region genes. A plasmid probe recognizing five C gamma segments separated by known linear DNA distances was hybridized in situ and visualized by digital fluorescence microscopy. In interphase nuclei from phytohemagglutinin (PHA)-stimulated lymphocytes, the gamma genes were resolved as one to three signals per allele in the majority of nuclei, whereas in a minority, complex patterns of several signals per allele could be observed. The latter were restricted to nuclei in an early stage of the S phase, as assessed by hybridization experiments performed in cells grown in the presence of bromodeoxyuridine. To investigate whether the in situ resolution of the C gamma segments could vary as a function of the transcription activity of the locus, the C gamma probe was subsequently hybridized to nuclei from a mature B cell line (JVM-2), which produces gamma transcripts as shown by in situ RNA hybridization experiments. Primary human fibroblasts were further used as representative of a non-lymphoid cell type with transcriptionally inactive Ig genes. When Gl nuclei from the three cell types were compared in terms of the in situ resolution of the C gamma locus, JVM-2 cells were found to include the highest percentage of higher resolution patterns (three to five signals per allele in 28% of nuclei), fibroblasts the lowest (three signals per allele, 2%), while PHA-stimulated lymphocytes occupied an intermediate position between the other two cell types (three or four signals per allele, 15%). The data show that the in situ resolution of Ig C gamma genes varies throughout the cell cycle and is influenced by the transcriptional activity of the locus. The variability of the resolution patterns observed appears to reflect different levels of chromatin packaging, which in turn are likely to influence the probe accessibility to its target. These observations are relevant for the interpretation of data from interphase cytogenetics analysis of independent, but closely spaced, DNA segments.

Cells, Cultured↗

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↗

PubMed1993

Prospects for using an IVEM with a FEG for imaging macromolecules towards atomic resolution.

Specimen preparation and imaging techniques for biological macromolecules have been improved to the point where attention to the electron-optical imaging conditions becomes a significant factor for achieving high resolution. A field emission gun (FEG) can provide an illumination source with a better spatial and temporal coherence suitable for imaging near atomic resolution. Our computational analysis of carbon film images taken between Scherzer focus and 1.1 microns underfocus (20x Scherzer focus) with the Hitachi 200 kV microscope with a cold field emission gun shows detectable contrast beyond 3.5 A resolution. In biological imaging, a large defocus is often used to optimize the low-resolution contrast in order to facilitate the subsequent steps in computer reconstruction. An intermediate-voltage electron microscope (IVEM) would optimize the contrast at high resolution by reducing the temporal coherent effects. In theory, the IVEM would give a greater depth of field so that large macromolecular assemblies such as viruses and cellular structures can be interpreted and reconstructed reliably using the projection approximation. These experimental and theoretical considerations provide a rationale for designing a future IVEM with a FEG suitable for biological macromolecule imaging close to atomic resolution.

Fourier Analysis↗

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↗

PubMed1993

Low resolution spin echo: a simple timesaving technique for MRI liver exams.

MR evaluation of the liver at mid-field strength requires relatively lengthy T2-weighted sequences (T2W) for differentiation of benign cavernous hemangiomas from malignant lesions. A short duration T2W, which maintains standard signal-to-noise ratio and also contrast relationships, can be easily implemented by increasing the pixel size in the phase-encoding direction (thus reducing spatial resolution) and proportionally decreasing the number of phase-encoding steps in the matrix (thus reducing acquisition time). Blinded interpretations of a quick (4 min), low resolution (3.4 mm x 1.7 mm pixel) T2W sequence (matrix 64 x 256, FOV 21.7 cm phase x 43.5 cm frequency) were compared to the 17 min standard resolution (1.7 mm x 1.7 mm) T2W sequence (256 x 256 matrix, FOV 43 x 43 cm) in 25 patients suspected of having liver metastasis. Lesions felt to be cavernous hemangiomas showed a 100% (24/24) agreement for interpreter "A" and 96% (22/23) agreement for interpreter "B" when 4 min low resolution T2W was compared to the standard 17 min sequence. Sensitivity (for all types of lesions) of the low resolution T2W sequence ranged from 100% (31/31) for interpreter "A" to 80% (28/35) for interpreter "B." Missed lesions (interpreter "B") were either partially obscured by excessive fat (wrap around) (N = 4), less than 1 cm in size (N = 2), or degraded by motion artifact (N = 1). Thus in many situations low resolution T2 may provide a substantial timesaving alternative to standard T2W particularly where T2W is used primarily for lesion classification in normal sized patients.

Adult↗

PubMed1994

Improved endocardial border resolution during dobutamine stress echocardiography with intravenous sonicated dextrose albumin.

OBJECTIVES: The purpose of this study was to determine whether intravenous sonicated dextrose albumin could improve endocardial border resolution during dobutamine stress echocardiography. BACKGROUND: Sonicated albumin improves endocardial border resolution in patients undergoing exercise stress echocardiography. Because a sonicated mixture of albumin with dextrose results in better transpulmonary passage than sonicated albumin alone, this agent could be utilized to further improve endocardial border resolution during dobutamine stress echocardiography. METHODS: We gave intravenous injections of sonicated dextrose and albumin to 50 patients undergoing dobutamine stress echocardiography. Left ventricular video intensity, contrast agent persistence (in seconds), number of contrast agent-enhanced cardiac cycles and improvement in endocardial border resolution were assessed from the apical four-chamber view at baseline, low dose (10 micrograms/kg body weight per min) and peak dobutamine infusion. RESULTS: There was significantly better left ventricular peak video intensity at peak dobutamine infusion than after the same injection at baseline (p < 0.005, analysis of variance). The number of contrast agent-enhanced cardiac cycles in the left ventricular cavity was also significantly longer at peak infusion. Endocardial border resolution was improved (mainly in lateral segments) in 93% of patients at low dose and 95% of patients at peak infusion. CONCLUSIONS: Intravenous sonicated dextrose albumin improves endocardial border resolution during dobutamine stress echocardiography.

Aged↗

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↗

PubMed1993

Two-dimensional crystallization of Escherichia coli-expressed bacteriorhodopsin and its D96N variant: high resolution structural studies in projection.

Highly ordered two-dimensional (2-D) crystals of Escherichia coli-expressed bacteriorhodopsin analog (e-bR) and its D96N variant (e-D96N) reconstituted in Halobacterium halobium lipids have been obtained by starting with the opsin protein purified in the denaturing detergent sodium dodecyl sulfate. These crystals embedded in glucose show electron diffraction in projection to better than 3.0 A at room temperature. This is the first instance that expressed bR or a variant has been crystallized in 2-D arrays showing such high order. The crystal lattice is homologous to that in wild-type bR (w-bR) in purple membranes (PM) and permit high resolution analyses of the structure of the functionally impaired D96N variant. The e-bR crystal is isomorphous to that in PM with an overall averaged fractional change of 12.7% (26-3.6-A resolution) in the projection structure factors. The projection difference Fourier map e-bR-PM at 3.6-A resolution indicates small conformational changes equivalent to movement of approximately < 7 C-atoms distributed within and in the neighborhood of the protein envelope. This result shows that relative to w-bR there are no global structural rearrangements in e-bR at this 3.6 A resolution level. The e-D96N crystal is isomorphous to the e-bR crystal with a smaller (9.2%) overall averaged fractional change in the structure factors. The significant structural differences between e-D96N and e-bR are concentrated at high resolution (5-3.6 A); however, these changes are small as quantified from the 3.6 A resolution e-D96N-e-bR Fourier difference map. The difference map showed no statistically significant peaks or valleys within 5 A in projection from the site of D96 substitution on helix C. Elsewhere within the protein envelope the integrated measure of peaks or valleys was < approximately 3 C-atom equivalents. Thus, our results show that for the isosteric substitution of Asp96 by Asn, the molecular conformation of bR in its ground state is essentially unaltered. Therefore, the known effect of D96N on the slowed M412 decay is not due to ground-state structural perturbations.

Bacteriorhodopsins↗

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↗