SEARCH · PubMed Health

Results for “Resolution”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38Linked to original sources

PubMed2000

Liquid chromatographic resolution of 2-hydroxycarboxylic acids on a new chiral stationary phase derived from (S)-leucine.

Enantiomers of racemic 2-hydroxycarboxylic acids have been resolved as their O-ethoxycarbonyl pi-basic anilide derivatives on a new chiral stationary phase (CSP) derived from N-(3,5-dinitrobenzoyl)leucine N-phenyl N-alkylamide and the resolution results have been compared with those on various commercial pi-acidic CSPs. The resolution results demonstrate that the new CSP derived from N-(3,5-dinitrobenzoyl)leucine N-phenyl N-alkylamide is most effective among the five CSPs tested for the resolution of 2-hydroxycarboxylic acid derivatives. In order to elucidate the chiral recognition mechanism exerted by the new CSP, the resolution of slightly differently modified derivatives of 2-hydroxycarboxylic acids on the new CSP has been investigated. Based on the resolution results, a chiral recognition mechanism utilizing three simultaneous interactions such as the face to face pi-pi interaction and the two hydrogen bonding interactions between the CSP and the more retained enantiomer of the analyte has been proposed.

Chemical Phenomena↗

PubMed2003

Atomic resolution structures of native copper nitrite reductase from Alcaligenes xylosoxidans and the active site mutant Asp92Glu.

We provide the first atomic resolution (<1.20 A) structure of a copper protein, nitrite reductase, and of a mutant of the catalytically important Asp92 residue (D92E). The atomic resolution where carbon-carbon bonds of the peptide become clearly resolved, remains a key goal of structural analysis. Despite much effort and technological progress, still very few structures are known at such resolution. For example, in the Protein Data Bank (PDB) there are some 200 structures of copper proteins but the highest resolution structure is that of amicyanin, a small (12 kDa) protein, which has been resolved to 1.30 A. Here, we present the structures of wild-type copper nitrite reductase (wtNiR) from Alcaligenes xylosoxidans (36.5 kDa monomer), the "half-apo" recombinant native protein and the D92E mutant at 1.04, 1.15 and 1.12A resolutions, respectively. These structures provide the basis from which to build a detailed mechanism of this important enzyme.

Alcaligenes↗

PubMed1990

Three-dimensional electron diffraction of PhoE porin to 2.8 A resolution.

A three-dimensional set of electron diffraction intensities of PhoE porin embedded in trehalose extending to 2.8 A resolution has been collected and analyzed. The strongest high-resolution intensities are distributed as a figure of revolution about the z*-axis and are located primarily in a resolution range of 4.5 A to 5.0 A. Within this region, centered near 4.8 A resolution the brightest intensities are clustered about inclination angles of 35 degrees and 0 degrees from the a*, b* plane. This distribution of intensities indicates that the beta-sheet in PhoE porin is arranged to form a cylinder-like structure that contains major populations of beta-sheet strands tilted an average of 35 degrees and 0 degrees with respect to the membrane plane normal. This cylindrical structure has been seen previously in the high-resolution projection map of PhoE as an elliptical ring of high density.

Bacterial Outer Membrane Proteins↗

PubMed1981

Image resolution in dental and maxillofacial radiography with the conventional and "free focus" imaging concepts.

An investigation of the resolution capability of conventional and "free focus" dental radiography on non screen film was completed. The over-all imaging performance of conventional and "free focus" radiography exposed with three types of dental x-ray machines was comparable. Conventional "long-cone" radiography produced better resolution than "short-cone" radiography. "Short-cone" radiography exposed with conventional compact dental x-ray machines provided similar or better image resolution than those exposed with larger, high-energy machines. The miniaturized dental x-ray machines used in "free focus" radiography for periapical type exposures gave a resolution which was similar to or up to 100 percent higher than in conventional "long-cone" periapical radiographs. Differences in path length of the x-ray beam during clinical applications of conventional and "free focus" radiography indicated a higher potential for image noise and degradation in conventional films. A potential for segmental variation in image resolution in surveys of the dentition was seen only in the conventional techniques. These characteristics must be balanced against a tendency to variable segmental magnification in free focus radiography. Indications, however, are that applications of "free focus" radiography may be able to improve the early diagnosis of dental disease. Periapical type surveys of the dentition produced by "free focus" radiography may require only two exposures instead of the 14 to 20 required in conventional periapical surveys and may contain characteristics of periapical as well as bitewing films. "Free focus" radiography represents an attractive alternative that may be able to accomplish substantial time savings in the practice of dental radiography.

Face↗

PubMed1999

Spatial attention improves performance in spatial resolution tasks.

This study used peripheral precueing to explore the effect of covert transient attention on performance in spatial resolution tasks. Experiments 1 (Landolt-square) and 2 ('broken-line') measured gap resolution and Experiment 3 measured vernier resolution. In all three tasks the target was presented alone in a large number of possible locations, ranging from 1.5-6 degrees of eccentricity in the vertical or horizontal axes. The precue indicated the target location but did not convey information regarding the correct response. Performance decreased as the gap size or the vernier offset size decreased and as target eccentricity increased. Precueing improved performance in terms of RT and accuracy in all three tasks; the eccentricity effect decreased in the cued trials of the gap resolution tasks. These findings support the idea that the performance improvement at attended locations results, to some extent, from an enhanced spatial resolution at the cued location, and not just from distractor exclusion, diminished uncertainty, or decisional factors.

Attention↗

PubMed1999

Temporal resolution deficits in the visual fields of MS patients.

We assessed the relationship between temporal resolution and MS-induced neuropathy. A diagnostic strategy comprising assessments of temporal resolution at 16 points in the extra-foveal visual field up to 12 degrees from the fovea was first compared with foveal temporal resolution and with a standard VEP procedure in the same MS patients. At the group level, foveal temporal resolution was less sensitive to demyelination than the 16-point diagnostic strategy, the detection rate of which was comparable to that of the VEP procedure. Cross-sensitivity of the VEP and the 16-point diagnostic procedure was low. Subsequently, the average severity of MS-induced temporal resolution deficits was studied at three retinal loci of the same size but different eccentricities. Foveal deficits were not significantly greater than more peripheral deficits within the central 12 degrees.

Adult↗

PubMed1997

Rapid resolution of symptomatic acute subdural hematoma: case report.

BACKGROUND: Only a few cases showing spontaneous resolution of acute subdural hematoma (ASDH) have been reported. Several possible mechanisms of spontaneous resolution of ASDH have been reported. Two possible hypotheses have been suggested: (1) the hematoma is diluted by cerebrospinal fluid (CSF) due to tearing of the arachnoid membrane and is washed out, (2) the hematoma is compressed by the pressure produced by acute brain swelling and redistributed. In this article, we report a patient with a rapid spontaneous resolution of an ASDH and discuss the mechanisms. METHODS: We experienced a case of a spontaneous resolution of symptomatic ASDH within only 3 hours. Characteristic serial changes on computed tomography (CT) corresponding to neurologic changes were obtained. RESULTS: Serial CT findings showing changes corresponding to neurologic fluctuation were obtained. The characteristic features of the CT findings are as follows: (1) participation of CSF at the lateral portion of the hematoma was recognized during the early period after injury, (2) no cerebral contusion was identified, (3) acute cerebral swelling was not identified, (4) when the neurologic state deteriorated, the hematoma had not enlarged, but there was an increase in the low-density area corresponding to participation of the CSF and midline shift was recognized. CONCLUSION: Spontaneous resolution of ASDH depends on both dilution due to CSF participation and redistribution of the blood; but acute cerebral swelling is not a necessary condition. Elasticity of the brain and absence of cerebral contusion obstructing the outflow of the cerebrospinal fluid is optimal.

Acute Disease↗

PubMed1997

A high-resolution, confocal laser-scanning microscope and flash photolysis system for physiological studies.

We describe the construction of a high-resolution confocal laser-scanning microscope, and illustrate its use for studying elementary Ca2+ signalling events in cells. An avalanche photodiode module and simple optical path provide a high efficiency system for detection of fluorescence signals, allowing use of a small confocal aperture giving near diffraction-limited spatial resolution (< 300 nm lateral and < 400 nm axial). When operated in line-scan mode, the maximum temporal resolution is 1 ms, and the associated computer software allows complete flexibility to record line-scans continuously for long (minutes) periods or to obtain any desired pixel resolution in x-y scans. An independent UV irradiation system permits simultaneous photolysis of caged compounds over either a uniform, wide field (arc lamp source) or at a tightly focussed spot (frequency-tripled Nd:YAG laser). The microscope thus provides a versatile tool for optical studies of dynamic cellular processes, as well as excellent resolution for morphological studies. The confocal scanner can be added to virtually any inverted microscope for a component cost that is only a small fraction of that of comparable commercial instruments, yet offers better performance and greater versatility.

Animals↗

PubMed1994

3D computed X-ray tomography of human cancellous bone at 8 microns spatial and 10(-4) energy resolution.

Human cancellous bone was imaged and its absorptive density accurately measured in three dimensions (3D), nondestructively and at high spatial resolution by means of computerized microtomography (microCT). Essential for achieving the resolution and accuracy was the use of monoenergetic synchrotron radiation (SR) which avoided beam hardening effects, secured excellent contrast conditions including the option of energy-modulated contrast, and yet provided high intensity. To verify the resolution, we selected objects of approximately 8 micron size that could be observed on tomograms and correlated them in a unique manner to their counter images seen in histological sections prepared from the same specimen volume. Thus we have shown that the resolution expected from the voxel size of 8 microns used in the microCT process is in effect also attained in our results. In achieving the present results no X-ray-optical magnification was used. From microCT studies of composites (Bonse et al., X-ray tomographic microscopy (XTM) applied to carbon-fibre composites. In: Materlik G, ed. HASYLAB Jahresbericht 1990. Hamburg: DESY, 1990; 567-568) we know that by including X-ray magnification a resolution below 2 microns is obtained. Therefore, with foreseeable development of our microCT method, the 3D and nondestructive investigation of structures in mineralized bone on the 2 micron level is feasible. For example, it should be possible to study tomographically the 3D distribution and amount of osteoclastic resorption in the surrounding bone structure.

Aged↗

PubMed1997

Resolution requirements for digital images in dermatology.

BACKGROUND: The digital image has become an important tool in dermatology because of the rapid development of computer hardware, networks, and the World Wide Web. OBJECTIVE: Our purpose was to examine the resolution requirements for digital images. METHODS: Slides of eight selected images showing characteristic lesions were produced in five different resolutions each, ranging from 192 x 128 x 24 (192 pixels x, 128 pixels y, and 24-bit color depth) up to 3072 x 2048 x 24. They were compared side by side by a group of six experienced dermatologists using a standardized questionnaire. RESULTS: Images at the resolution of 768 x 512 x 24 were perceived as equivalent to higher resolutions, whereas a clear difference was visible between 768 x 512 x 24 and 384 x 256 x 24. The slide projector had a significant influence on the rating of the images. CONCLUSION: For digital images in dermatology a resolution of 768 x 512 x 24 is suitable to recognize the relevant details of the source image.

Dermatology↗

PubMed2001

High-resolution functional imaging with ultrasound contrast agents based on RF processing in an in vivo kidney experiment.

Knowledge of the relative tissue perfusion distribution is valuable in the diagnosis of numerous diseases. Techniques for the assessment of the relative perfusion distribution, based on ultrasound (US) contrast agents, have several advantages compared to established nuclear techniques. These are, among others, a better spatial and temporal resolution, the lack of exposure of the patient to ionizing radiation and the relatively low cost. In the present study, US radiofrequency (RF) image sequences are acquired, containing the signal intensity changes associated with the transit of a bolus contrast agent through the microvasculature of a dog kidney. The primary objective is to explore the feasibility of calculating functional images with high spatial resolution. The functional images characterize the transit of the contrast agent bolus and represent distributions of peak time, peak value, transit time, peak area, wash-in rate and wash-out decay constant. For the evaluation of the method, dog experiments were performed under optimized conditions where motion artefacts were minimized and an IA injection of the contrast agent Levovist was employed. It was demonstrated that processing of RF signals obtained with a 3.5-MHz echo system can provide functional images with a high spatial resolution of 2 mm in axial resolution, 2 to 5 mm in lateral resolution and a slice thickness of 2 mm. The functional images expose several known aspects of kidney perfusion, like perfusion heterogeneity of the kidney cortex and a different peripheral cortical perfusion compared to the inner cortex. Based on the findings of the present study, and given the results of complimentary studies, it is likely that the functional images reflect the relative perfusion distribution of the kidney.

Animals↗

PubMed2002

Axial resolution in elastography.

The limits and trade-offs of the axial resolution in elastography were investigated using a controlled simulation study. The axial resolution in elastography was estimated as the distance between the full widths at half-maximum of the strain profiles of two equally stiff lesions embedded in a softer homogeneous background. The results show that the upper bound of the axial resolution in elastography is controlled by the physical wave parameters of the ultrasound (US) system used to acquire the data (transducer center frequency and band- width). However, an inappropriate choice of the parameters used to process the US data (cross-correlation window length and shift between consecutive windows) may compromise the best resolution attainable. The measured elastographic axial resolution was found to be on the order of the ultrasonic wavelength.

Computer Simulation↗

PubMed2003

Lateral resolution in elastography.

The factors that control the lateral resolution in elastography were investigated using a simulation study. The lateral resolution was estimated from the simulated axial strain elastograms as the smallest measurable distance between two equally stiff lesions embedded in a homogeneously softer background. The lesions were symmetrically positioned lateral to the center of the target, at the focus of the transducer. Ultrasound (US) systems with different transducer frequencies, bandwidths and f-numbers were simulated. The effects of the ultrasonic parameters, the lateral spacing between adjacent echo signals, the cross-correlation window length, the lesion/background elastic contrast and the lateral motion of scatterers on the estimated lateral resolution were investigated. The results show that the lateral resolution in elastography is proportional to the beam width of the US system used to acquire the data, and is on the same order as the sonographic lateral resolution.

Computer Simulation↗

PubMed2003

Improving energy resolution of EELS spectra: an alternative to the monochromator solution.

In this paper, we propose a numerical method which can routinely improve the energy resolution down to 0.2-0.3eV of electron energy-loss spectra acquired in a transmission electron microscope. The method involves measurement of the point-spread function (PSF) corresponding to the spectrometer aberration and to the incident energy spread, and then an inversion of this PSF so as to restore the spectrum. The chosen algorithm is based on an iterative calculation of the maximum likelihood solution known to be very robust against small errors in the PSF used. Restorations have been performed on diamond and graphite C-K edges acquired with an initial energy resolution of around 1eV. After reconstruction, the sharp core exciton lines become clearly visible for both compounds and the final energy resolution is estimated to be about 200-300meV. In the case of graphite, restorations involving both energy resolution and angular resolution have been successfully conducted. Finally, restorations of Fe L(2,3) and O-K edges measured for various iron oxides will be shown.

Journal Article↗

PubMed1982

Factors related to the resolution of treated hand infections.

One hundred thirty-eight patients with acute hand infection (81% deep) treated from 1970 to 1980 in hospital were reviewed. Resolution time of infection was slow, 8 days or longer in 57% of 135 patients and 15 days or longer in 28%. Such slow resolution occurred in infection of closed anatomical spaces and included 50% of all pulp space and joint infections, 23% of tenosynovitis, and 24% of subcutaneous dorsal had infections. There was a direct correlation between increasing treatment delay and slower resolution of infections in pulp spaces, palmar spaces, joints, and tendon sheaths. If the mean treatment delay was greater than a brief 2 1/2 days, 69% of tenosynovitis showed delayed resolution. Other factors associated with the rate of resolution were adequacy of surgical drainage, efficacy of antibiotics, and associated diabetes mellitus.

Acute Disease↗

PubMed2001

The effect of masking noise on rippled-spectrum resolution.

Ripple-density resolution in a rippled sound spectrum (probe band) under the effect of another band (masker) was studied in normal listeners. The resolvable ripple density in the probe band was measured using a phase-reversal test. The principle of the test was to find the highest ripple density at which an interchange of mutual peak and valley position (the ripple phase reversal) was detectable. Probe bands were 0.5 octave (oct) wide with center frequencies of 1, 2, and 4 kHz. When a masker band was below the probe one (a low-frequency masker), it markedly reduced the ripple-density resolution. The effect of the low-frequency masker enhanced (ripple-density resolution decreased) with decreasing the stop-band (frequency spacing) between the probe and masker bands. The strongest masker effect was observed at zero spacing between the probe and masker bands. However, when the probe band overlapped the masker one so that no masker power was below the probe band, the masker effect diminished (ripple-density resolution partially released). Increase of the masker bandwidth above 0.5 oct by shifting its lower boundary downwards did not enhance the masker effect. Masker bands above the probe one (high-frequency maskers) did not influence the ripple-density resolution.

Acoustic Stimulation↗

PubMed1998

Estimating spatial resolution of in vivo MR images using spatial modulation of magnetization.

Spatial Modulation of Magnetization is shown to provide a means of estimating perceived spatial resolution directly in vivo. On the first magnetic resonance system tested, resolution in conventional spin echo images was found to be stability limited in the phase encoding direction and voxel limited (via the Nyquist sampling theorem) in the frequency encoding direction both in vitro and in vivo. As the voxel size approaches half the stripe separation, fringes of resolved and unresolved stripes are formed across the image. This phenomenon is explained and described mathematically. On a second magnetic resonance scanner, resolution in the phase encoding direction of fast spin echo images with centrically ordered phase encoding is shown to be voxel limited in substances with long T2, with poorer resolution in substances with short T2. Resolution in fast spin echo images with linearly ordered phase encoding was shown to be voxel limited in the phase encoding direction.

Artifacts↗

PubMed1990

Optical resolution of foldable intraocular lenses.

Recently manufactured intraocular lenses (IOLs) (STAAR AA 4203 made of silicone and IOGEL PC-12 made of polyHEMA) were tested before and after implantation simulation for axial optical resolution (model eye), for optical surface quality (photokeratoscope), and for surface microtrauma (scanning electron microscopy). At a 3 mm pupillary opening, both lens types achieved a mean axial resolution of 1.25 (range 1.0 to 1.5) on an optotype analogous resolution target. When the pupillary opening was increased to 6 mm, polymacon IOLs showed only a moderate resolution decrease (up to one line) and loss of contrast (up to 30%); silicone IOLs showed almost no decrease. Photokeratoscopic evaluation revealed that a circular optical nonhomogeneity at the peripheral optical zone of the hydrogel IOLs is the source of this impairment. Groove-like surface deformities occasionally observed by scanning electron microscopy did not detectably decrease resolution or contrast.

Humans↗