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PubMed2001

Mental imagery of high- and low-resolution gratings activates area 17.

Some, but not all, previous neuroimaging studies of visual mental imagery have found that Area 17 (primary visual cortex) is activated when people visualize objects. The present study was designed to test the hypothesis that the necessary degree of resolution of the mental image is a determining factor in whether Area 17 is activated during imagery. Eight male subjects visualized and compared sets of stripes that required high or low resolution to resolve, while their brains were scanned using 15O(CO2) positron emission tomography (PET). When imagery in general (visualization of high- and low-resolution gratings stimuli combined) was compared to an auditory baseline condition where subjects did not visualize, Area 17 was activated. However, region of interest (ROI) and statistical parametric mapping (SPM) analyses revealed no difference between imagery conditions using high- and low-resolution stimuli. These results indicate that the resolution of the stimuli alone does not necessarily determine whether Area 17 will be activated during visual mental imagery.

Adolescent↗

PubMed1995

Effector functions of antibody and CD8+ cells in resolution of rotavirus infection and protection against reinfection in mice.

The importance of antibody and CD8+ cells in resolution of murine rotavirus (EDIM) infection and protection against reinfection was examined with two strains of B-cell-deficient mice. Following inoculation of one strain (JHD), rotavirus infection was resolved within days, but when later reinoculated with EDIM, these mice again shed rotavirus. Thus, effector mechanisms other than antibody resolved viral shedding in JHD mice but were insufficient to prevent reinfection. EDIM shedding in another B-cell-deficient mouse strain (microMT) diminished but was not fully resolved 93 days after the initial infection, thus demonstrating that antibody could also be important in resolution of rotavirus infection. When depleted of CD8+ cells by monoclonal antibody treatment before EDIM inoculation, JHD mice were unable to resolve shedding. Even though microMT mice did not fully resolve their initial infection, depletion of CD8+ cells 49 days after initial inoculation resulted in a burst of shedding. Thus, CD8+ cells were involved in resolution of the initial EDIM infection in both strains of B-cell-deficient mice. Finally, when microMT mice were depleted of CD8+ cells before the initial EDIM infection, gradual resolution of rotavirus shedding was still observed, suggesting a third effector mechanism was also involved in resolution of rotavirus infection in mice.

Animals↗

PubMed1979

Measurement of visual resolution at high luminance levels in patients with possible demyelinating disease.

An interferometric acuity device (Takata) has been used to study visual resolution in individuals with possible demyelinating disease. The instrument employed provides a large field with a continuous range of grid or fringe frequencies and a relatively intense (10(5) mean photopic trolands) stimulus. After a brief period of time with eyes closed, resolution thresholds of patient are repeatedly determined during a five minute period. In all individuals suspected of having a demyelinating disease tested to date, a fall off in resolution capability has been found in time when using this intense stimulus display. This occurs whether eye signs have been present, are present or have not yet been observed. Normal observers do not exhibit comparable decrements. The fall off in resolution capability may or may not occur at lower stimulus levels, and is often not revealed when testing routine Snellen acuity. Outer and inner retinal pathology (division based on vascular support) do not cause a comparable fall off in resolution in time. The interferometric acuity test is a non-invasive, easily applied test.

Adult↗

PubMed1991

Light-sense, flicker and resolution perimetry in glaucoma: a comparative study.

A total of 106 eyes of 106 patients with different types of glaucoma were examined by automated light-sense, flicker and resolution perimetry (Humphrey Field Analyzer, program 30-2; flicker perimeter as described by Lachenmayr [16, 18]; resolution perimeter as devised by Frisén [4, 6, 8-11]). The fields were classified in a masked fashion as being normal or as having purely diffuse loss, purely localized loss or diffuse as well as localized loss. As compared with light-sense perimetry, resolution perimetry had a markedly lower sensitivity in the detection of glaucomatous damage (77%) but a high specificity (93%); the comparison of resolution perimetry with flicker perimetry showed similar results (sensitivity, 75%; specificity, 85%). When flicker perimetry was compared with light-sense perimetry and vice versa, the sensitivity was high (95% and 94%, respectively), but the specificity was low (57% and 62%, respectively). The prevalence of detection of diffuse loss by both light-sense and resolution perimetry was related to visual acuity, whereas flicker perimetry did not show such a relationship.

Adult↗

PubMed1991

Simulated bipolar cells in fovea of human retina. V. Use of Fourier analysis to determine resolution.

Fourier analysis is used to study resolution of images processed by the matrix of simulated red-center (BCR) and green-center (BCG) bipolar cells (BC) of the human central fovea. Simulated achromatic and chromatic sine and square waves, and a two-bar stimulus are used to activate the BCs. Due to the "honeycomb" packing of the cones and BC matrices Fourier transforms are computed row by row using a one-dimensional FFT. Resolution computed by the Fourier transform is compared with the resolution index (RI), which is a method for determining resolution based on two-point discrimination in the space domain. In general the harmonic with the maximum amplitude gives the best correlation with RI for the three stimuli. Amplitudes at all spatial frequencies are enhanced by increasing the number of cycles in the sine and square wave gratings. Results with simulated BCs compare favorably with human and macaque psychophysics measuring contrast sensitivity. Square wave gratings are better than sine wave greetings for studying resolution.

Color Perception↗

PubMed1996

Lesion discrimination in optic neuritis using high-resolution fat-suppressed fast spin-echo MRI.

Fast spin-echo (FSE) is a new sequence with acquisition times currently down to one-sixteenth of those obtained with conventional spin-echo sequences, which allows high-resolution (512 x 512 matrix) images to be acquired in an acceptable time. We compared the higher resolution of FSE with the medium resolution of a short inversion-time inversion-recovery (STIR) sequence in depicting the optic nerves of healthy controls and patients with optic neuritis. Optic nerve MRI examinations were performed in 18 patients with optic neuritis and 10 normal controls. Two sequences were obtained coronally: fat-suppressed FSE (FSE TR 3250 ms/TEef 68 ms, echo-train length 16, 4 excitations, 24 cm rectangular field of view, 3 mm interleaved contiguous slices, in-plane resolution 0.5 x 0.5 mm) and STIR (TR 2000 ms/TE 50 ms/TI 175 ms, in-plane resolution 0.8 x 0.8 mm, slice thickness 5 mm). FSE demonstrated much more anatomical detail than STIR, e.g. distinction of optic nerve and sheath. Lesions were seen in 20 of 21 symptomatic nerves using FSE and in 18 of 21 using STIR. Nerve swelling or partial cross-sectional lesions of the optic nerve were each seen only on FSE in 3 cases. Fat-suppressed FSE imaging of the optic nerve improves anatomical definition and increases lesion detection in optic neuritis.

Adult↗

PubMed1991

Strain differences in rats with respect to speed of conflict resolution.

Speed of conflict resolution was studied in a conditioned punishment paradigm in a Skinner box and a straight runway. In both experimental situations speed of conflict resolution was defined as the latency to gain food during an approach-avoidance conflict. In the Skinner box Tryon Maze Bright rats were faster in speed of conflict resolution than Tryon Maze Dull rats, and Roman Low Avoidance rats were faster than Roman High Avoidance rats. In the runway situation, Wistar Kyoto rats were faster in solving the conflict than randomly bred Wistar Wu rats and Brown Norway rats were faster than Wistar Wu rats. Differences between the strains in speed of conflict resolution could not be consistently explained from strain differences in approach or avoidance behavior, measured separately. It is, therefore, suggested that speed of conflict resolution is a unique parameter.

Animals↗

PubMed1995

C-reactive protein as an indicator of resolution of sepsis in the intensive care unit.

OBJECTIVE: To investigate the value of decreasing plasma C-reactive protein (CRP) concentrations as an indicator or resolution of microbiologically-proven sepsis. DESIGN: Retrospective analysis of CRP concentrations measured during episodes of microbiologically-proven sepsis. A receiver-operating characteristic (ROC) curve was used to assess the usefulness of CRP as a test for resolution of sepsis. SETTING: The intensive care unit (ICU) of a teaching hospital. PATIENTS AND PARTICIPANTS: 32 episodes of microbiologically-proven sepsis occurring in 18 patients were followed from diagnosis until resolution. MEASUREMENTS AND RESULTS: Daily routine observations and blood testing were performed prospectively. The daily presence or absence of systemic inflammatory response syndrome (SIRS) was prospectively determined according to standard definitions. Concentrations of CRP were analysed retrospectively once the patients had left the ICU. A decrease in CRP by 25% or more from the previous day's level was a good indicator of resolution of sepsis, with a sensitivity of 97%, specificity of 95% and predictive value of 97%. In 13 cases (46%), a decrease in CRP preceded clinical resolution of sepsis; this was more likely to occur in patients with less severe sepsis than in those with severe sepsis or septic shock. CONCLUSION: Daily measurement of CRP is useful for monitoring the course of microbiologically-proven sepsis in ICU patients, and may be used to indicate successful treatment.

Biomarkers↗

PubMed1988

Resolution as a function of accelerating voltage in electron microscopy of semithick biological specimens.

In the past, biological sections ranging in thickness from 0.10- to 0.50-micron have usually been examined with high-voltage (greater than 500 kV) electron microscopes (HVEM). Now investigators are increasingly using intermediate voltage (200-500 kV) electron microscopes (IVEM), which are more readily available and demand less maintenance. In a study of "typical" plastic-embedded, stained sections of mouse liver ranging from 0.10 to 1.0 micron thick, we determined the resolution obtainable at 100, 200, and 1000 kV. At all three accelerating voltages the resolution (2.7 nm) for 0.10-micron sections was limited only by the sections stain granularity. For 0.25-micron thickness the resolutions were 5.8, 3.1, and 3.1 nm at 100, 200, and 1000 kV, respectively. The maximum usable thickness at 200 kV with resolution sufficient to resolve membranes clearly was between 0.75 and 1.0 micron, depending on the magnification. Resolution at 100 kV was adequate for screening sections up to 1.0-micron thick for preparation defects prior to examination with an IVEM or HVEM.

Animals↗

PubMed2002

Performance evaluation of OSEM reconstruction algorithm incorporating three-dimensional distance-dependent resolution compensation for brain SPECT: a simulation study.

UNLABELLED: Iterative reconstruction techniques such as an ordered subsets-expectation maximization (OSEM) algorithm can easily incorporated various physical models of attenuation or scatter. We implemented OSEM reconstruction algorithm incorporating compensation for distance-dependent blurring due to the collimator in SPECT. The algorithm was examined by computer simulation to estimate the accuracy for brain perfusion study. METHODS: The detector response was assumed to be a two-dimensional Gauss function and the width of the function varied linearly with the source-to-detector distance. The attenuation compensation (AC) was also included. To investigate the properties of the algorithm, we performed computer simulations with the point source and digital brain phantoms. In the point source phantom, the uniformity of FWHM for the radial, tangential and longitudinal directions was evaluated on the reconstruction image. As for the brain phantom, quantitative accuracy was estimated by comparing the reconstructed images with the true image by the mean square error (MSE) and the ratio of gray and white matter counts (G/W). Both noise free and noisy simulations were examined. RESULTS: In the point source simulation, FWHM in radial, tangential and longitudinal directions were 14.7, 14.7 and 15.0 mm at the image center and were 15.9, 9.83 and 10.6 mm at a distance of 15 cm from the center by using FBP, respectively. On the other hand, they were 8.12, 8.12 and 7.83 mm at the image center, and were 7.45, 7.44 and 7.01 mm at 15 cm from the center by OSEM with distance-dependent resolution compensation (DRC). An isotropic and stationary resolution was obtained at any location by OSEM with DRC. The spatial resolution was also improved about 6.5 mm by OSEM with DRC at the image center. In the brain phantom simulation, the blurring at the edge of the brain structure was eliminated by using OSEM with both DRC and AC. The G/W was 2.95 and 2.68 for noise free and noisy cases, respectively, when no compensation was performed. But the values for G/W without and with noise became 3.45 and 3.21 with AC only and were improved to 3.75 and 3.71 with both AC and DRC. The G/W approached the true value (4.00) by using OSEM with both AC and DRC even when there was statistical noise. CONCLUSION: In conclusion, OSEM reconstruction including the distance-dependent resolution compensation algorithm was reasonably successful in achieving isotropic and stationary resolution and improving the quantitative accuracy for brain perfusion SPECT.

Algorithms↗

PubMed1995

Interpretation of subtle interstitial chest abnormalities: conventional radiography versus high-resolution storage-phosphor radiography--a preliminary study.

To evaluate the reliability of digital chest radiography in diagnosing subtle interstitial lung abnormalities, we performed several clinical studies including a comparison of conventional screen-film radiography and storage-phosphor radiography (2 K x 2 K pixels, 10 bit), and a comparison of conventional screen-film radiography and film-digitized radiography (2 K x 2 K pixels, 10 bit). From these previous studies, a spatial resolution of 0.2-mm pixel size was considered inadequate to diagnose subtle interstitial lung diseases. Under these circumstances, the newly developed Fuji Computed Radiography system (FCR 9000; Fuji Photo Film, Tokyo, Japan) has recently become available. This system provides 0.1-mm pixel size (4 K x 5 K pixels, 10-bit depth) and life-size hard copies (14 x 17 inches). To evaluate the reliability of new high-resolution storage-phosphor radiography (FCR 9000) in diagnosing simulated subtle interstitial abnormalities (including simulated lines, micronodules, and groundglass opacities), the differences among radiologists in interpreting conventional screen-film radiographs and life-size high-resolution storage-phosphor radiographs were studied. Observation was made by eight experienced chest radiologists and receiver-operating characteristic (ROC) analysis was performed. There was no significant difference in detecting in subtle simulated interstitial abnormalities between conventional film-screen radiography and high-resolution storage-phosphor radiography. For all three types of abnormalities, there was no significant difference between conventional and storage-phosphor radiography. In conclusion, the high-resolution storage-phosphor chest radiography (0.1-mm pixel size, 10-bit depth) may be substituted for conventional chest radiography in the detection of subtle interstitial abnormalities.

Data Display↗

PubMed2000

Frequency and impact of high-resolution monitor failure in a filmless imaging department.

The purpose of this study was to assess the image quality and the rate of failure of the high-resolution (2,048 x 1536 pixel) monitors used for primary diagnosis in a filmless radiology department and to analyze the type of problems encountered as well as the action taken to repair the monitors. Data were collected from Picture Archival and Communication System (PACS) service logs to determine rates of monitor adjustment and replacement, the symptoms reported, and the action taken. Additionally, random surveys of the high-resolution monitors were performed using a standard test pattern to assess spatial and contrast resolution in the center and outer corners of the monitors. Analysis of monitor service records showed a high rate of monitor replacement (41% per year) resulting in a relatively short "life expectancy" (defined as average time required before replacement) of 2.4 years. Random surveys of monitor quality using a standard test pattern showed suboptimal image quality in approximately 54% of the monitors with moderate image quality degradation present in at least one region of 27% of the high-resolution monitors, despite our vendor's quality control program. The results of this study support our subjective impression and those of other colleagues in the PACS community of an unacceptably high monitor failure rate and persistent image quality problems with 2,000 pixel monitors used for primary diagnosis. The relatively high incidence of suboptimal quality monitors suggests that more frequent quality control should be performed using a test pattern particularly given the fact that radiologists often are unable to discern degradation of monitor performance using clinical images. The high incidence of problems with image quality on high-resolution monitors indicates that vendors need to develop better quality control in monitor design and testing. Radiologists should review briefly a test pattern on each monitor at the beginning of each day. A computer program should be incorporated into the PACS, which asks radiologists to evaluate a test pattern and records the results in a central database, which is communicated to the service engineers. Further studies should be evaluated to determine the clinical impact of monitor image degradation, which is relatively easily seen using a test pattern but may be difficult to discern on clinical images. Requests for proposals (RFPs) for PACS and service contracts must specify carefully requirements for monitor image quality and conditions under which the vendor is required to replace these monitors.

Computer Terminals↗

PubMed1997

The laser film digitizer: density, contrast, and resolution.

This work evaluates differences in density linearity, contrast, and resolution of digital images acquired from a laser film scanner. A calibrated photographic step tablet tested linearity of diffuse optical density (OD). It was digitized within center openings of a dark and light film. The 14- x 17-inch films were scanned into 1024 x 1280 picture elements of 8 bits. A photographic tapered resolution guide evaluated the scanner's detail resolution. A single characteristic curve adequately represents the rate of change of OD per pixel value, but two piecewise linear functions are better. One ranges in light OD and a second in dark OD. Contrast shows a steeper slope in a light film rather than a dark film, yet a greater difference exists between two identical digitizers. The resolution test diminishes at 1.3 line pairs per mm (LP/mm), which compares to a Nyquist limit of 1.44 LP/mm. Such density, contrast, and resolution tests yield a benchmark to assure quality operations.

Humans↗

PubMed2000

[Optimizing temporal resolution in CT with retrospective ECG gating].

PURPOSE: Spiral CT of the heart using the established ways of ECG synchronization is hampered by the relatively long acquisition times of 250 to 500 ms. This only allows to acquire diastolic images in patients with moderate heart rates. In this work, algorithms for time-optimized retrospective cardiac gating are presented, and their potential to improve temporal resolution is investigated. MATERIAL AND METHODS: These algorithms use data from multiple gantry rotations for image reconstruction, which is possible for multi-scans at fixed slice positions as well as for overlapping spiral scans. Temporal resolution was quantified using computer simulations and compared to experimental data from pigs. RESULTS: Using a conventional sub-second CT scanner, considerably higher temporal resolutions are possible with spiral scanning. A temporal resolution of 170 ms already provides systolic images with little motion artifacts. Higher temporal resolutions of up to 70 ms are demonstrated for multi-scans, which allows to depict ventricle wall movement over the complete cardiac cycle. DISCUSSION: The method of time-optimized retrospective cardiac gating broadens the spectrum of conventional spiral-CT for cardiac imaging. It can be directly transferred to multi-slice scanners. Here it can be used clinically because of reduced scan time. Potential applications are the determination of functional cardiac parameters like ejection fraction and the detection of disorders of ventricle wall movement.

Algorithms↗

PubMed2001

Structural analysis of high resolution in vitro MR images compared to stained grindings.

The recent advancement of high resolution magnetic resonance imaging has opened up new avenues for the determination of structural characteristics of the trabecular network, which may significantly improve the diagnosis of osteoporosis. An analysis of the calcaneus in healthy women has shown similar age-related changes when comparing structural parameters in high resolution MR images and BMD as measured by DXA [1]. Here we undertook an in vitro study to further compare structural measurements in MR images with those from stained grindings. A 3D gradient echo sequence on a 1.5 T scanner was used to obtain four contiguous sagittal MR images with a slice thickness of 1 mm and an in plane pixel size of 195 microns. Twenty-one stained grindings with a slice thickness of 1 micron each were obtained from a 3 mm thick slab of the same volume investigated by MR. The stack of stained grindings was also used to simulate the influence of variations in slice thickness and in plane resolution. Results for structural parameters derived from the high resolution MR images differed considerably from those derived from the stained grindings because the MR images are heavily influenced by partial volume artifacts. This finding was supported by simulations which also revealed that even at a slice thickness of 500 microns and an in plane pixel size of 13 microns, accurate results could not be obtained when a histomorphometric type analysis was applied. Results also depended strongly on the segmentation method. However, contrary to the stained grindings, images averaged over several slices reveal the three-dimensional network character of the trabecular structure. New efforts should be undertaken to develop analysis strategies that are more adequate for in vivo high resolution images instead of using analysis techniques applied in classical histomorphometry.

Cadaver↗

PubMed2001

Does the "keyhole" technique improve spatial resolution in MRI perfusion measurements? A study in volunteers.

We examined the potential of the 'keyhole' technique to improve spatial resolution in perfusion-weighted MRI on whole-body imagers with standard gradient hardware. We examined 15 healthy volunteers. We acquired a high-resolution image with 256 phase-encoding steps before a bolus-tracking procedure. For the dynamic series we collected only 34 lines in the center of k-space. Data reconstruction was performed by both zero-filling and keyhole methods. The dynamic datasets, concentration-time curves calculated from user-defined regions and maps of the cerebrovascular parameters using both reconstruction methods were compared. Using keyhole series, anatomical structures could easily be defined which were not seen on the original dynamic series because of blurring due to ringing artefacts. Comparison of signal-time curves in large regions yielded no significant difference in signal loss during bolus passage. In the parameter maps truncation artefacts were significantly reduced using keyhole reconstruction. The keyhole method is appropriate for enhancing image quality in perfusion-weighted imaging on standard imagers without sacrificing time resolution or information about transitory susceptibility changes. However, it should be applied carefully, because the spatial resolution of the dynamic signal change and the cerebrovascular parameters is less than that afforded by the spatial resolution of the reconstructed images.

Brain↗

PubMed2004

High-resolution MR imaging of the elbow using a microscopy surface coil and a clinical 1.5 T MR machine: preliminary results.

OBJECTIVE: To obtain high-resolution MR images of the elbow using a microscopy surface coil with a 1.5 T clinical machine and to evaluate the feasibility of its use for elbow injuries. DESIGN AND PATIENTS: Five asymptomatic normal volunteers and 13 patients with elbow pain were prospectively studied with MR imaging using a microscopy surface coil 47 mm in diameter. High-resolution MR images using a microscopy coil were obtained with fast spin echo (FSE) proton density-weighted sequence, gradient recalled echo (GRE) T2*-weighted sequence, and short tau inversion recovery (STIR) sequence, with a 1-2 mm slice thickness, a 50-70 mm field of view, an imaging matrix of 140-224 x 512 using zero fill interpolation, and 2-6 excitations. RESULTS: High-resolution MR images of normal volunteers using a microscopy coil clearly showed each structure of the medial and lateral collateral ligaments on GRE T2*-weighted images and FSE proton-density weighted images. Partial medial collateral ligament injury, a small avulsion of the medial epicondyle, and osteochondritis dissecans were well demonstrated on high-resolution MR images. CONCLUSION: High-resolution MR imaging of the elbow using a microscopy surface coil with a 1.5 T clinical machine is a promising method for accurately characterizing the normal anatomy of the elbow and depicting its lesions in detail.

Adolescent↗

PubMed2002

Quantification of dopamine transporters in the mouse brain using ultra-high resolution single-photon emission tomography.

Functional imaging of small animals, such as mice and rats, using ultra-high resolution positron emission tomography (PET) and single-photon emission tomography (SPET), is becoming a valuable tool for studying animal models of human disease. While several studies have shown the utility of PET imaging in small animals, few have used SPET in real research applications. In this study we aimed to demonstrate the feasibility of using ultra-high resolution SPET in quantitative studies of dopamine transporters (DAT) in the mouse brain. Four healthy ICR male mice were injected with (mean+/-SD) 704+/-154 MBq [(99m)Tc]TRODAT-1, and scanned using an ultra-high resolution SPET system equipped with pinhole collimators (spatial resolution 0.83 mm at 3 cm radius of rotation). Each mouse had two studies, to provide an indication of test-retest reliability. Reference tissue kinetic modeling analysis of the time-activity data in the striatum and cerebellum was used to quantitate the availability of DAT. A simple equilibrium ratio of striatum to cerebellum provided another measure of DAT binding. The SPET imaging results were compared against ex vivo biodistribution data from the striatum and cerebellum. The mean distribution volume ratio (DVR) from the reference tissue kinetic model was 2.17+/-0.34, with a test-retest reliability of 2.63%+/-1.67%. The ratio technique gave similar results (DVR=2.03+/-0.38, test-retest reliability=6.64%+/-3.86%), and the ex vivo analysis gave DVR=2.32+/-0.20. Correlations between the kinetic model and the ratio technique ( R(2)=0.86, P<0.001) and the ex vivo data ( R(2)=0.92, P=0.04) were both excellent. This study demonstrated clearly that ultra-high resolution SPET of small animals is capable of accurate, repeatable, and quantitative measures of DAT binding, and should open up the possibility of further studies of cerebral binding sites in mice using pinhole SPET.

Animals↗