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At least 1,153 records · Page 64Linked to original sources

PubMed1996

Standard and high resolution magnetic resonance imaging of glomus tumors of toes and fingertips.

BACKGROUND: High-resolution magnetic resonance imaging (MRI) of subungual glomus tumors has been recently reported. OBJECTIVE: Our purpose was to compare high-resolution MRI and standard MRI for the diagnosis of 44 glomus tumors of the toes and fingertips. METHODS: Glomus tumors (11 cases) were first examined by MRI with a commercial surface coil (set 1). Thirty-three other glomus tumors and one tumor from set 1 were then examined with a high-resolution module designed for skin imaging (set 2). RESULTS: All 44 glomus tumors were identified with MRI. The limits of the tumors were detected in 54% of set 1 and 100% of set 2. A capsule was present in most cases, but was incomplete or absent in eight cases. Subtypes of glomus tumors were more easily differentiated in set 2. CONCLUSION: Standard MRI was adequate to detect glomus tumors, but high-resolution MRI assessed tumor characteristics more accurately.

Adolescent↗

PubMed2003

Prognostic value of ST-segment resolution-when and what to measure.

AIMS: Analyses of ST-segment resolution during acute myocardial infarction has, during recent years, challenged coronary angiography as gold-standard for predicting myocardial reflow and future risk. We have previously reported that continuous ST-monitoring can be done accurately in the clinical setting. We now set out to compare the prognostic value of previously suggested cut-offs for ST-segment resolution, and determine the times to measure these. METHODS AND RESULTS: We analysed 752 patients with ST-elevation infarction, from the second Assessment of Safety and Efficacy of a New Thrombolytic (ASSENT 2) and ASSENT-PLUS studies, either with vectorcardiography or continuous 12-lead ST-monitoring. All analyses were made blindly by two independent observers. Times to 20, 30, 50 and 70% ST-segment resolution were examined in relation to 30-day mortality.The optimal cut-off for ST-segment resolution analyses was found to be 50%, measured at 60 min. We could hereby identify a large low-risk group, 40% of the population, with only 1.4% 30-day mortality. Furthermore, 88% of deaths were correctly predicted within 1h of observation and treatment. CONCLUSION: Continuous ST-monitoring of patients with acute myocardial infarction yields important prognostic information after 60 min of observation and should be used for very early-risk stratification in these patients.

Aged↗

PubMedDate not supplied

High-resolution computed tomography of the temporal bone: its role in the evaluation of middle ear disease.

High-resolution computed tomography (CT) was performed on the temporal bones of 93 patients in conjunction with pluridirectional tomography. The majority of the patients were scanned on the prototype Pfizer 0200 FS second-generation scanner, modified to meet the demands of high-resolution scanning. Images from this relatively economical scanner are almost comparable to those obtainable with the GE CT/T 8800 scanner in spatial and contrast resolution. CT scans of the temporal bone were found to be more sensitive than pluridirectional tomography in visualizing fractures and soft tissue masses in the middle ear, including fluid levels and tympanic membrane swelling. It is concluded that high-resolution CT of the temporal bone will probably soon entirely replace pluridirectional tomography.

Cholesteatoma↗

PubMed1997

Rapid measurement of the spatial resolution of colour flow scanners.

An acoustic grid for rapid measurement of the spatial resolution of colour velocity images is described. The grid is composed of alternate widths of acoustic window and acoustic attenuator. Attenuation is provided by the use of a layer of waterproof paper, which is wrapped in close contact with a tube of a flow phantom. The colour image consists of several closely spaced lines. When the grid line spacing is less than the spatial resolution, the colour lines cannot be separately visualised. The use of several grids of different spacing provides a measure of the spatial resolution. It is shown that the spatial resolution is dependent on the position of the focal zone.

Blood Flow Velocity↗

PubMed2002

Initial resolution measurements of miniaturized electrostatic lenses for LVSEM.

Theoretical and experimental investigations on miniaturized electrostatic lenses for high-resolution low-voltage scanning electron microscopical applications are presented. The electron optical column consists of a Schottky emitter including the extraction anode and a miniaturized three electrode lens consisting of conventional (electron microscopical) platinum apertures. The lens has been optimized with respect to resolution and a value of about 5 nm at a working distance of 1 mm and a beam energy of 1 keV is predicted by simulation. Details on the resolution measurements are presented. An initial experimental value amounts to 31 nm. Specific problems encountered during building and alignment of the lens and measuring the resolution are discussed as well.

Journal Article↗

PubMed1979

High resolution SEM of bacterial virus T7.

High resolution "low-loss" scanning electron microscopy is a relatively new technique which permits an investigator to examine structures that were formerly visualized exclusively by transmission electron microscopy [1]. This paper presents some images of intact bacterial virus T7, viewed at the ultrastructural level. Due to the high resolution capibility of this technique, and the demanding physical prerequisites for visualization of the specimen, current specimen preparation techniques were modified in order to permit 1--2 nm resolution in surface mode. Using this method of microscopy, it is possible to view clearly this small bacteriophage (the smallest of the T-coliphages), adsorbed to its host bacterium, in a scanning mode at magnification (and resolution) comparable to TEM without resorting to the use of replicas, or reconstruction of a two-dimensional image.

Capsid↗

PubMed2000

Upper limits for the residual aberrations of a high-resolution aberration-corrected STEM

The development of correctors for electron optical systems has already brought the improvement of resolution for a low-voltage scanning electron microscope and a commercially available transmission electron microscope and is anticipated in the near future for a dedicated scanning transmission electron microscope (STEM). The resolution attainable especially of a probe-forming system at 200 kV cannot only be estimated from calculations ignoring all non-rotationally symmetric axial aberrations in an electron optical system. For a certain resolution, one would like to attain, the influence of the deviations from the ideal, aberration-free system has to be investigated. Therefore, in the following we have carried out the evaluation of the required accuracy for the compensation of the various residual aberrations in order to achieve a resolution in the sub-Angstrom regime with a probe-forming system.

Journal Article↗

PubMed2003

Rippled-spectrum resolution dependence on level.

Rippled-density resolution of a rippled sound spectrum (probe band) in both the presence and absence of another band (masker) was studied as a function of sound level in normal listeners. The resolvable ripple density in the probe band was measured by finding the highest ripple density at which an interchange of ripple peak and valley positions was detectable (the phase-reversal test). Probe bands were 0.5 oct wide with center frequencies of 1, 2, and 4 kHz. In the control condition (no masker), the ripple-density resolution was almost independent of sound level within a range of 40-90 dB SPL. When an on-frequency masker coincided with the probe band (that resulted in reduced ripple depth), resolution decreased slightly relative to the control condition but remained little dependent on level. With an off-frequency low-side masker, the ripple-density resolution was a little less than in the control but almost independent of level within a range of 40-60 dB SPL and progressively decreased with level increase from 70 to 90 dB SPL. The dependence on level was qualitatively similar at all probe frequencies and at various widths and positions of the low-side off-frequency masker band.

Acoustic Stimulation↗

PubMed2000

High-resolution segmented EPI in a motor task fMRI study.

A high-resolution gradient echo, multi-slice segmented echo planar imaging method was used for functional MRI (fMRI) using a motor task at 1.5 Tesla. Functional images with an in-plane resolution of 1 mm and slice thickness of 4 mm were obtained with good white-gray matter contrast. The multi-shot approach, combined with a short total readout period of 82 ms, limits blurring effects for short T(2)(*) tissues (such as gray matter), assuring truly high-resolution images. In all subjects, motor functions were clearly depicted in the contralateral central sulcus over several slices and sometimes activation was detected in the supplementary motor area and/or ipsilateral central sulcus. The average signal change of 11+/-3% was much higher than in standard low-resolution fMRI EPI experiments, as a result of larger relative blood fractions.

Adult↗

PubMed2002

Investigation of insect morphology by MRI: assessment of spatial and temporal resolution.

Classically, the investigation of the internal morphology of insects relies on histologic methods, e.g., the preparation of thin tissue sections. However, the preparation of serial sections is time consuming and means the irreversible loss of the animal. In the present investigation, we have analyzed the potential of NMR imaging as a tool for the morphologic classification of insects with sufficient spatial resolution. With a 512 matrix, 15 mm FOV, 200 microm slice thickness, images with an in-plane spatial resolution of 30 microm are obtained with a signal-to-noise ratio of 70. These conditions require only seven averages, resulting in an experimental time of only 50 min. Such image quality already permits the differentiation of fine structural and morphologic details such as e.g., intestinal tracts and copulation organ in a beetle. Also, wing controlling dorsal muscle groups as well as leg structures and joints are clearly distinguishable. We conclude that the spatial resolution and contrast condition of MR imaging are quite promising for the new approach of zoological insect classification using NMR imaging. Further principally available technical enhancement of sensitivity and spatial resolution will provide an attractive alternative to invasive techniques for the classification of, sometimes, rare and precious insect specimen.

Animals↗

PubMed2003

Improved spectral quality for 3D MR spectroscopic imaging using a high spatial resolution acquisition strategy.

Spectral quality in (1)H MR spectroscopic imaging (MRSI) of the brain is often significantly degraded in regions subject to local magnetic susceptibility variations, which results in broadened and distorted spectral lineshapes. In this report, a modified acquisition strategy for volumetric echo-planar spectroscopic imaging (3D EPSI) is presented that extends the region of the brain that can be observed. The data are sampled at higher spatial resolution, then corrected for local B(0) shifts and reconstructed such that the final spatial resolution matches that of 3D EPSI data acquired with the conventional lower spatial resolution. Comparison of in vivo data obtained at 1.5 T with these two acquisition schemes shows that the high spatial resolution acquisition provides considerable reduction of spectral linewidths in many problematic brain regions, though with a reduction in signal-to-noise ratio by a factor of approximately 1.4 to 1.6 for the matrix sizes used in this study. However, the effect of the increased noise was largely offset by the improved spectral quality, leading to an overall improvement of the metabolite image quality obtained using automated spectral analysis.

Brain↗

PubMed1999

High-resolution imaging using Hadamard encoding.

High-resolution imaging techniques using noninvasive modalities such as magnetic resonance (MR) imaging are being pursued as in vivo cancer screening techniques in an attempt to eliminate the invasive nature of surgical biopsy. When acquiring high-resolution MR images for tissue screening, image fields of view have in the past been limited by the matrix sizes available in conventional MR scanners. We present here a technique that uses aliasing to produce high resolution images with larger matrix sizes than are currently available. The image is allowed to alias in both the frequency encoding and phase encoding dimensions, and the individual, aliased fields of view are recovered by Hadamard encoding methods. These fields may then be tiled to obtain a composite image with high spatial resolution and a large field of view. The technique is demonstrated using two-dimensional and three-dimensional in vivo imaging of the human brain and breast.

Brain↗

PubMed2000

Variable heating rate thermogravimetric analysis as a mechanism to improve efficiency and resolution of the weight loss profiles of three model pharmaceuticals.

The effect of variable heating rates on the efficiency or resolution of the derivative of the thermogravimetry profiles of three model pharmaceutical compounds was investigated. The variable heating system utilized computer controlled algorithms for the evaluation of crystalline sodium warfarin, DuP 532 and hydrated DuP 925 as model compounds with one, two and three step weight loss profiles, respectively. As the heating modes were increased through each of the eight settings, the minimum heating rate decreased while the efficiency and resolution and the analysis times increased. The observed weight loss remained relatively constant for each of the model compounds as the heating modes were increased. The efficiency of the derivative of the weight loss profile of crystalline sodium warfarin increased from 121 to 621 as the heating mode increased. The resolution between the two steps of the derivative of the weight loss profile of DuP 532 increased from 1.73 to 3.88 as the heating mode increased. For hydrated DuP 925, the resolution increased from 1.49 to 5.46 between steps 1 and 2 of the derivative of the weight loss profile and from 1.87 to 3.24 between steps 2 and 3 of the derivative of the weight loss profile. Variable heating rates provided a valuable aid in obtaining high efficiency/resolution thermograms. The enhanced efficiency/resolution permitted greater separation of the volatilization process, especially for samples with multi-step weight loss profiles. Increasing the heating mode afforded higher efficiencies/resolutions that typically reached a maximum value at mode 6.

Algorithms↗

PubMed1999

The significance of persistent ST elevation versus early resolution of ST segment elevation after primary PTCA.

OBJECTIVES: To determine the prevalence and clinical significance of early ST segment elevation resolution after primary percutaneous transluminal coronary angioplasty (PTCA) for acute myocardial infarction (AMI). BACKGROUND: Despite angiographically successful restoration of coronary flow early during AMI, adequate myocardial reperfusion might not occur in a substantial portion of the jeopardized myocardium due to microvascular damage. This phenomenon comprises the potentially beneficial effect of early recanalization of the infarct related artery (IRA). METHODS: Included in the study were 117 consecutive patients who underwent angiographically successful [Thrombolysis in Myocardial Infarction (TIMI III)] primary PTCA. The patients were classified based on the presence or absence of reduction > or =50% in ST segment elevation in an ECG performed immediately upon return to the intensive cardiac care unit after the PTCA in comparison with ECG before the intervention. RESULTS: Eighty-nine patients (76%) had early ST segment elevation resolution (Group A) and 28 patients (24%) did not (Group B). Group A and B had similar clinical and hemodynamic features before referring to primary PTCA, as well as similar angiographic results. Despite this, ST segment elevation resolution was associated with better predischarge left ventricular ejection fraction (LVEF) (44.7 +/- 8.0 vs. 38.2 +/- 8.5, p < 0.01). Group B patients, as compared with those of Group A, had a higher incidence of in-hospital mortality (11% vs. 2%, p = 0.088), congestive heart failure (CHF) [28% vs. 19%, odds ratio (OR) = 4, 95% confidence interval (CI) 1 to 15, p = 0.04], higher long-term mortality (OR = 7.3, 95% CI 1.9 to 28, p = 0.004 with Cox proportional hazard regression analysis) and long-term CHF rate (OR = 6.5, 95% CI 1.3 to 33, p = 0.016 with logistic regression). CONCLUSIONS: Absence of early ST segment elevation resolution after angiographically successful primary PTCA identifies patients who are less likely to benefit from the early restoration of flow in the IRA, probably because of microvascular damage and subsequently less myocardial salvage.

Angioplasty, Balloon, Coronary↗

PubMed1987

Optical resolution of silicone and polymethylmethacrylate intraocular lenses.

The optical resolution and contrast of 18 silicone and 18 polymethylmethacrylate (PMMA) intraocular lenses were determined before implantation in and after removal from rabbit eyes. A specially designed microphotographic system that allows documentation and comparison of the image quality of different lens types was used. Silicone intraocular lenses showed a mean axial resolution of 1.25, PMMA lenses showed 1.60, of an optotype analogous resolution target (1.0 = 20/20) at a 3 mm pupil opening preoperatively. At one to 16 weeks postoperatively, both types of IOLs demonstrated nearly unchanged resolution. Contrast, however, decreased to between 60% and 85% of the preoperative 100% standard. This decrease was due to precipitates deposited on the lens surface, to posterior capsule opacification, and to lens decentration.

Animals↗

PubMed2000

Clinically and mammographically occult breast lesions: detection and classification with high-resolution sonography.

With recent significant advances in ultrasound technology, the potential of high-resolution sonography to improve the sensitivity of cancer diagnosis in women with dense breasts has become a matter of interest for breast imagers. To determine how often physician-performed high-resolution sonography can detect nonpalpable breast cancers that are not revealed by mammography, 8,970 women with breast density grades 2 through 4 underwent high-resolution sonography as an adjunct to mammography. All sonographically detected, clinically and mammographically occult breast lesions that were not simple cysts were prospectively classified into benign, indeterminate, or malignant categories. Diagnoses were confirmed by ultrasound-guided fine-needle aspiration, core-needle biopsy, or surgical biopsy. In 8,103 women with normal findings at mammography and physical examination, 32 cancers and 330 benign lesions were detected in 273 patients with sonography only. Eight additional cancers were found in 867 patients with a malignant (n = 5) or a benign (n = 3) palpable or mammographically detected index lesion. The overall prevalence of cancers detected with screening sonography was 0.41%, and the proportion of sonographically detected cancers to the total number of nonpalpable cancers was 22%. The mean size of invasive cancers detected only by sonography was 9.1 mm, and was not statistically different from the mean size of invasive cancers detected by mammography. The sensitivity of prospective sonographic classification for malignancy was 100%, and the specificity was 31%. In conclusion, the use of high-resolution sonography as an adjunct to mammography in women with dense breasts may lead to detection of a significant number of otherwise occult cancers that are no different in size from nonpalpable mammographically detected cancers. Prospective classification of these lesions based on sonographic characteristics resulted in an acceptable benign-to-malignant biopsy rate of 6.3:1.

Adult↗

PubMed2000

Multiple-quantum MAS NMR of quadrupolar nuclei. Do five-, seven- and nine-quantum experiments yield higher resolution than the three-quantum experiment?

The question of whether or not higher-order (five-, seven- and nine-quantum) multiple-quantum magic angle spinning (MQMAS) experiments yield isotropic NMR spectra of half-integer quadrupolar nuclei with higher resolution than the basic three-quantum MAS experiment is examined. The frequency dispersion is shown theoretically to be greatly increased in higher-order MQMAS spectra, but it is argued that whether or not this translates into an increase in resolution depends upon the ratio of the homogeneous to inhomogeneous contributions to the isotropic linewidth. Experimentally, it is demonstrated using three-, five- and seven-quantum 45Sc MAS NMR and three- and five-quantum 27Al MAS NMR of crystalline samples that higher-order MQMAS experiments can yield a real and useful increase in resolution but that, owing to the presence of inhomogeneous broadening in the isotropic spectra, this increase is less than the theoretically predicted value. A number of practical issues relating to resolution in MQMAS NMR are also pointed out.

Aluminum↗

PubMed1991

Clinical utility of high-resolution portal films.

We have evaluated the film quality and overall clinical utility of a unique high-resolution portal film system which utilizes high contrast graphics art film. A total of 127 unselected patients had their conventional portal films and high-resolution films of the same site, compared and graded subjectively for a variety of parameters by an independent panel of radiotherapists and radiographers. Although consistent improvements in most aspects of image quality were noted, improved overall clinical usefulness of the high-resolution portal film system in comparison to the conventional films, when subjected to multiple regression analysis, was confined to lateral neck views only. High-resolution portal film utility was also found to depend significantly on field size with areas less than 110 cm2 having a markedly worse clinical utility score.

Humans↗