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PubMed1986

Preferential looking as a measure of visual resolution in infants and toddlers: a comparison of psychophysical methods.

We used preferential looking to estimate the monocular visual resolution of children 6-36 months old and compared results from 3 psychophysical methods: Taylor and Creelman's PEST staircase, our modification of the PEST procedure, and the method-of-constant stimuli. Estimates of visual resolution for 48 children tested with the original and modified PEST procedures and for 50 children tested with the method-of-constant stimuli and the modified PEST procedure showed excellent agreement across procedures, with the modified PEST procedure requiring the fewest trials and the least time. Results from the modified PEST procedure for 168 children with normal eye alignment and minimal refractive errors indicated that monocular visual resolution improves from 6.5 min at 6 months to 1.2 min at 36 months. Preferential looking combined with the shortened PEST procedure should be useful for testing the visual resolution of preverbal children with eye problems.

Child Development↗

PubMed2004

Expression of matrix metalloproteinase-2 and -14 persists during early resolution of experimental liver fibrosis and might contribute to fibrolysis.

BACKGROUND/AIMS: Resolution of liver fibrosis is possible but the identity of the matrix metalloproteinases (MMPs) which degrade the accumulated collagens is uncertain. We examined MMP-2 and MMP-14 expression in established and resolving fibrosis to assess their role in resolution of liver fibrosis. METHODS: MMP and tissue inhibitor of metalloproteinase (TIMP)-2 expression in liver extracts was examined by ribonuclease protection assay, Western blotting and gelatin zymography. MMP activity was examined by (14)C gelatin degradation. RESULTS: In human cirrhotic liver, MMP-14 mRNA was increased to 230-330% of normal liver expression. Both 63 kDa proenzyme and 60 kDa activated form were present. Cirrhotic livers had 270-320% of normal liver expression of MMP-2 protein with 20-25% being the 62 Da activated form. Protein and mRNA for MMP-2 and MMP-14 progressively increased during 8 weeks of CCl(4) treatment in rats. Between 3 and 7 days of resolution from CCl(4) liver fibrosis, MMP-2 and MMP-14 persisted at elevated levels. Gelatinolytic activity in liver homogenates peaked at 7 days of recovery, being 140% above that in livers at peak fibrosis. CONCLUSIONS: Increased expression and activation of MMP-2 and -14 occurs even under conditions of elevated TIMPs during liver fibrogenesis. During liver fibrosis resolution, as TIMP expression decays, the persistence of MMP-2 and MMP-14 may permit collagen degradation.

Adult↗

PubMed1993

What triggers the resolution of alcohol problems without treatment.

This study investigated natural recoveries (self-change) from alcohol problems, and overcame several methodological problems that affected the few previous studies of this phenomenon. Three groups of individuals who had resolved an alcohol problem without treatment were interviewed about their drinking history, life events that occurred during the year prior to their resolution, and factors that helped maintain their resolution. As a control for prevalence of life events, a control group of nonresolved, nontreated alcohol abusers were interviewed about events in a randomly selected year. Collaterals were interviewed for all subjects. No life event or constellation of events was differentially associated with the resolutions across the three resolved groups or differentiated the resolved and nonresolved groups. Interviews with resolved subjects were qualitatively analyzed-the majority (57%) of recoveries were characterized as involving a "cognitive evaluation" or appraisal of the pros and cons of drinking. Spousal support was reported by the greatest number of resolved subjects as having helped them maintain their resolution. Findings from this study may provide direction for developing new treatment strategies and for accelerating self-change among problem drinkers in the community. The study also demonstrates the importance of using a control group, without which very different conclusions might have been drawn.

Adult↗

PubMed2004

Radiographic resolution of community-acquired bacterial pneumonia in the elderly.

OBJECTIVES: To investigate the radiographic clearance of proven community-acquired nontuberculous bacterial pneumonia in nonimmunocompromised older patients to provide working estimates of the rate of radiographic resolution as a function of the patient cumulative comorbidities, extent of initial radiographic involvement, functional status, and causative pathogens. DESIGN: A prospective study. PARTICIPANTS: Seventy-four patients aged 70 and older, consecutively admitted to a hospital for community-acquired bacterial pneumonia. SETTING: A university-affiliated teaching hospital. MEASUREMENTS: Chest radiographs were performed every 3 weeks from the date of admission for a total period of 12 weeks or until all radiographic abnormalities had resolved or returned to baseline. RESULTS: Sixty-four patients (86%) completed the study. The rate of radiographic clearance was estimated at 35.1% within 3 weeks, 60.2% within 6 weeks, and 84.2% within 12 weeks. Radiographic resolution was significantly slower for those with high comorbidity index, bacteremia, multilobar involvement, and enteric gram-negative bacilli pneumonias. Multivariate regression analysis demonstrated that the comorbidity index (relative risk for clearance=0.67 per class index, P<.001) and multilobar disease (relative risk for clearance=0.24 for more than one lobe, P<.001) had independent predictive value (Cox proportional hazards regression model) on the rate of resolution. CONCLUSION: The radiographic resolution of nontuberculous bacterial pneumonia in the elderly should take into account the extent of lobar disease and the burden of underlying illnesses. A waiting period of 12 to 14 weeks is recommended for slowly resolving pneumonia to be considered nonresolving.

Aged↗

PubMed2000

Diagnosis and ablation of atrial flutter using a high resolution, noncontact mapping system.

The ablation of atrial flutter can sometimes be time consuming and unsuccessful using conventional catheter techniques especially in patients with recurrences after previous ablation procedures. Simultaneous high resolution mapping from multiple sites may overcome some of the limitations. Therefore, a new high resolution noncontact mapping system was used for diagnosis and ablation of atrial flutter in 15 patients. The mapping system consists of a catheter-mounted multielectrode array, an amplifier, and a computer workstation. Far-field potentials recorded by the multielectrode catheter are amplified, digitized, and sampled at 1.2 kHz, and digitally filtered to construct high resolution activation maps during tachycardia. Ablation catheters can be steered to target sites without fluoroscopy. In 12 of the 15 patients the analysis of the activation sequence during tachycardia showed a counter-clockwise, and in 1 of 15 patients a clockwise, rotating wavefront using the isthmus as part of the reentrant circuit. In two patients no tachycardia could be induced. In 3 of the 15 patients with previous conventional ablation procedures the gap in the line of block in the isthmus region was identified and marked on the animation model. The isthmus in the right atrium was ablated and isthmus block verified by the mapping system in all patients. No complications were observed. No recurrences of atrial flutter occurred during follow-up of 4 +/- 1.7 months. The total procedure and fluoroscopy time was 171 +/- 50.0 minutes and 24 +/- 12.7 minutes, respectively. In conclusion, the use of the new high resolution noncontact mapping system in patients with right atrial flutter is safe and highly effective. In patients with previously failed conventional ablation procedures the use of a noncontact mapping system may facilitate the identification of the gap in the line of block in the isthmus region and reablation of atrial flutter.

Adult↗

PubMed1996

Routine low and high resolution typing of the HLA-DRB gene using the PCR-MPH (microtitre plate hybridization) method.

We describe HLA-DRB1 typing using polymerase chain reaction-based microtitre plate hybridization (PCR-MPH), which can process large numbers of samples. MPH typing is similar to an enzyme-linked immunosorbent assay (ELISA), in which a tandemly ligated sequence-specific oligonucleotide is immobilized on microtitre wells. The typing procedure consisted of two steps. In the first, PCR-MPH with 16 probes was performed to determine the specificities of the serological levels (DR1, DR2, DR3, DR4, DR11, DR12, DR13, DR14, DR7, DR8, DR9 and DR10) after generic amplification ("low resolution typing'). In the second step, DR1, DR2, DR4, DR12/8 and DR3/11/13/14 were group-specifically amplified based on the results of the first PCR-MPH, and microtitre plate hybridization proceeded in a similar manner to the first step ("high resolution typing'). Low resolution typing was completed within 2 h after generic amplification, and the results of high resolution typing were obtained in another 3.5 h after amplification. The allelic types classified using PCR-MPH were completely concordant with those obtained by PCR-single-strand conformation polymorphism or PCR-restriction fragment length polymorphism.

HLA-DR Antigens↗

PubMed1989

Working memory, comprehension ability and the resolution of text anomaly.

This article examines possible working memory deficits in 7-8-year-olds who are accurate readers but relatively poor comprehenders. In Expt 1, poor comprehenders scored below good comprehenders on a non-linguistic test of working memory (reading series of digits and recalling the last digit in each series) on the more taxing items. Experiment 2 examined the relationship between working memory and text comprehension using an anomaly resolution task. Good and poor comprehenders heard stories describing an adult's anomalous emotional response to a child's action, some of which contained information to resolve the anomaly. The load on working memory imposed by the need to integrate the resolution with the anomaly was varied in two ways: the resolution was presented immediately next to, or two sentences distant from, the anomaly, and appeared either before or after the anomaly. Poor comprehenders were worse than good ones at anomaly resolution only when the anomalous and resolving information were separated. The results support the hypothesis that text processing is influenced by working memory demands and suggest that children's comprehension is related to the efficiency of a general non-linguistic working memory system.

Attention↗

PubMed2003

Modified laser speckle imaging method with improved spatial resolution.

A two-dimensional map of blood flow is crucial for physiological studies. We present a modified laser speckle imaging method (LSI) that is based on the temporal statistics of a time-integrated speckle. A model experiment was performed for the validation of this technique. The spatial and temporal resolutions of this method were studied in theory and compared with current laser speckle contrast analysis (LASCA); the comparison indicates that the spatial resolution of the modified LSI is five times higher than that of current LASCA. Cerebral blood flow under different temperatures was investigated by our modified LSI. Compared with the results obtained by LASCA, the blood flow map obtained by the modified LSI possessed higher spatial resolution and provided additional information about changes in blood perfusion in small blood vessels. These results suggest that this is a suitable method for imaging the full field of blood flow without scanning and provides much higher spatial resolution than that of current LASCA and other laser Doppler perfusion imaging methods.

Algorithms↗

PubMedDate not supplied

Evaluating the lateral resolution of the adaptive optics scanning laser ophthalmoscope.

We present a statistical assessment of the lateral resolution of the adaptive optics scanning laser ophthalmoscope (AOSLO). We adopt a 2-D Gaussian function to approximate the AOSLO point spread function (PSF), which is dominated by the residual wavefront aberration and characterized by the Strehl ratio. Thus, we derive the lateral resolution in the presence of residual wave aberrations, which is inversely proportional to square root of the Strehl ratio. The modeling, while not sufficient in describing the fine structure of the real PSF, demonstrates good conformance to the lateral cross section of the real PSF. With this model, the lateral resolution of our current AOSLO was computed to be 1.65 to 2.33 microm, which agreed well with the actual result. We also reveal the relationships among the lateral resolution and other three measures of the AOSLO imaging property including the Strehl ratio, the PSF, and the root mean square (rms) of wavefront aberration.

Benchmarking↗

PubMedDate not supplied

Effect of optical tissue clearing on spatial resolution and sensitivity of bioluminescence imaging.

In vivo bioluminescence imaging (BLI) is a powerful method of in vivo molecular imaging based on the use of optically active luciferase reporter genes. Although this method provides superior sensitivity relative to other in vivo imaging methods, spatial resolution is poor due to light scattering. The objective of this study was to use hyperosmotic agents to reduce the scattering coefficient and hence improve spatial resolution of the BLI method. A diffusing fiber tip was used to simulate an isotropic point source of bioluminescence emission (550 to 650 nm). Mouse skin was treated in vitro and in vivo with glycerol (50%, 30 min) and measurements of optical properties, and imaging photon counts were made before, during, and after application of glycerol to the skin sample. Glycerol application to mouse skin had little effect on the absorption coefficient but reduced the reduced scattering coefficient by more than one order of magnitude. This effect was reversible. Consequently, the spot size (i.e., spatial resolution) of the bioluminescence point source imaged through the skin decreased by a factor of 2 (550-nm light) to 3 (650-nm light) after 30 min. Simultaneously, an almost twofold decrease in the amount of light detected by the BLI system was observed, despite the fact that total transmission increased 1.7 times. We have shown here that multiply scattered light is responsible for both observations. We have shown that applying a hyperosmotic clearing agent to the skin of small rodents has the potential to improve spatial resolution of BLI owing to a reduction in the reduced scattering coefficient in the skin by one order of magnitude. However, reducing the scattering coefficient reduces the amount of light reaching the camera due to a reduction in the amount of multiply scattered light that reaches the camera aperture and thus reducing the sensitivity of the method.

Administration, Topical↗

PubMed2000

A variable resolution x-ray detector for computed tomography: II. Imaging theory and performance.

A computed tomography (CT) imaging technique called variable resolution x-ray (VRX) detection provides variable image resolution ranging from that of clinical body scanning (1 cy/mm) to that of microscopy (100 cy/mm). In this paper, an experimental VRX CT scanner based on a rotating subject table and an angulated storage phosphor screen detector is described and tested. The measured projection resolution of the scanner is > or = 20 lp/mm. Using this scanner, 4.8-s CT scans are made of specimens of human extremities and of in vivo hamsters. In addition, the system's projected spatial resolution is calculated to exceed 100 cy/mm for a future on-line CT scanner incorporating smaller focal spots (0.1 mm) than those currently used and a 1008-channel VRX detector with 0.6-mm cell spacing.

Algorithms↗

PubMed2000

A variable resolution x-ray detector for computed tomography: I. Theoretical basis and experimental verification.

A computed tomography imaging technique called variable resolution x-ray (VRX) detection provides detector resolution ranging from that of clinical body scanning to that of microscopy (1 cy/mm to 100 cy/mm). The VRX detection technique is based on a new principle denoted as "projective compression" that allows the detector resolution element to scale proportionally to the image field size. Two classes of VRX detector geometry are considered. Theoretical aspects related to x-ray physics and data sampling are presented. Measured resolution parameters (line-spread function and modulation-transfer function) are presented and discussed. A VRX image that resolves a pair of 50 micron tungsten hairs spaced 30 microns apart is shown.

Algorithms↗

PubMed2001

Spatial resolution measurements in quasimonochromatic x rays with mosaic crystals for mammography application.

A novel x-ray source for mammography application is being investigated. Quasimonochromatic x rays have been produced via Bragg diffraction with a W-anode x-ray tube and a graphite mosaic crystal array. The system provides 18 keV x rays with an energy resolution deltaE/E approximately equals 0.12. A thorough analysis of the spatial resolution of the system has been performed in order to understand and quantify the effect of the introduction of an active optical element such as a mosaic crystal in the x-ray path. The focal spot of the source and its emission properties have been studied by using the slit camera method. Experiments have shown that the introduction of a mosaic crystal in the optical path modifies the resolution properties of the Bragg diffraction-based radiography system. Along the direction perpendicular to the diffraction plane the resolution properties of the imaging system mainly depend on the x-ray tube focal spot size and position. Along the diffraction plane the focal spot size depends on mosaic characteristics and on the geometrical setup. Hence, it could be modified by setting the appropriate experimental conditions.

Mammography↗

PubMed2001

High-resolution polymer gel dosimetry by parameter selective MR-microimaging on a whole body scanner at 3T.

High dose variations across small spatial distances, as present in brachytherapeutic applications or radiosurgery and especially gamma-knife therapy, are difficult to quantify by standard dosimetry. We demonstrate the possibility to obtain planar spatial resolutions for dose imaging at pixel sizes below 200 microm within multislice parameter selective MR imaging on polymer gels. The sensitivity of the transversal and longitudinal relaxation time as well as diffusivity on dose is shown. High spatial resolution is achieved by parameter selective microimaging of polymer gels on a high-field (3 T) whole-body MR system equipped with a dedicated strong gradient system and a small probe head matched to the sample size. In addition to the spin-spin relaxation rate R2 = 1/T2 we investigate the sensitivity of the longitudinal relaxation rate R1 = 1/T1 and the diffusivity Dapp in acrylic polymer gels on irradiation up to dose levels of about 20 Gy. Dose images are obtained after calibration of the corresponding MR parameters by known dose levels of gamma irradiation. Also the MR-parameter T1 may be used for dose imaging. The impact of all of the three parameters T1, T2, and diffusivity on obtained signal intensities in irradiated regions has to be taken into account in nonoptimized pulse sequences. Further, very high spatial resolution imposes several restrictions on the evaluation of R2, which have to be considered for quantitative dosimetry. These restrictions are discussed in detail. We also demonstrate the importance of such a high spatial resolution in case of a set of differently sized gamma-knife stereotactic irradiation schemes. Gel dosimetry based on MR parameter selective microimaging represents a potent alternative for the detection of dose distributions characterized by steep dose gradients, typical in brachytherapeutic and radiosurgical applications.

Calibration↗

PubMed2003

Accuracy of CT-based thickness measurement of thin structures: modeling of limited spatial resolution in all three dimensions.

Measurement of the width of thin structures such as the cortical shell of the vertebral body or femoral neck with computed tomography (CT) is limited by the spatial resolution of the CT system. Limited spatial resolution exists both within the CT image plane and perpendicular to it and can be described by the in-plane point spread function (PSF) and the across-plane slice sensitivity profile (SSP), respectively. The goal of this study was to confirm that errors of thickness measurement of thin structures critically depend on the spatial positioning of the object and the spatial resolution limitations of CT in all three dimensions, and to assess the size of the errors themselves. We compared computer models that incorporated both effects to experimentally assessed cortical thicknesses of the European Spine Phantom. Analysis included varying CT slice width, the orientation of measurement and angle beta of misalignment of longitudinal scanner and phantom axes. Agreement of models with measurements was good in all configurations with an overall error of 0.17 mm. This showed that PSF and SSP are adequate system characteristics to predict deviation of measured values from true widths. Errors between measurements and true cortical thickness values delta(true) averaged to 1.5 mm were strongly positively correlated with slice width d and beta. When the across-plane partial volume effect was eliminated, limited in-plane resolution still accounted for overestimation of delta(true) by 0.68 (137%), 0.27 (27%), and 0.06 mm (4%) for delta(true)=0.5, 1.0, and 1.5 mm, respectively. For delta(true) of 1.0 mm and above, it was shown that although the absolute cortical thickness values might not be accurately measurable, relative differences between two values are reflected in measurement. Implications for cortical thickness measurement are that the spinal cortical shell is too thin, whereas accurate assessment at locations of the femoral neck exhibiting a thicker cortical shell of both difference and absolute values should be possible with CT even for larger misalignment angles, especially when a smaller CT slice width is chosen.

Computer Simulation↗

PubMed2004

Solid-state fluoroscopic imager for high-resolution angiography: physical characteristics of an 8 cm x 8 cm experimental prototype.

In this paper, the performance of an 8 cm x 8 cm three-side buttable charge-coupled device (CCD)-based imager specially designed for high-resolution fluoroscopy and operating in fluoroscopic (30 frames/second) mode is presented in terms of the presampling modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE). The 8 cm x 8 cm CCD imager is coupled to a 450 microm thick CsI:Tl scintillator by nondemagnifying (straight, 1:1) fiberoptics. The CCD imager has a fundamental pixel pitch of 39 microm and incorporates an optically opaque interline (data) channel. The CCD imager was operated at 156 microm pixel pitch by binning 4 x 4 adjacent pixels prior to readout. The fluoroscopic image lag was measured and accounted for in the DQE estimate to provide lag-corrected DQE. The measured limiting spatial resolution at 10% presampling MTF with the imager operated at 156 microm pixel pitch (Nyquist sampling limit: 3.21 cy/mm) was 3.6 cy/mm. In the pulsed fluoroscopic mode, the first-frame image lag was less than 0.9%. The lag-corrected DQE(0) of approximately 0.62 was achieved even at a low fluoroscopic exposure rate of 1 microR/frame. Grid phantom measurements indicate no appreciable distortion. Results from DQE and image lag measurements at fluoroscopic exposure rates combined with the high spatial resolution observed from the MTF suggest that this type of imager or its variants may be a potential candidate for high-resolution neuro-interventional imaging, cardiovascular imaging, pediatric angiography, and small animal imaging. Since the CCD is three-side buttable, four such CCD modules can be joined to form a 2 x 2 matrix providing a field of view of 16 cm x 16 cm.

Angiography↗

PubMed2004

Effects of the intensity levels and beam map resolutions on static IMRT plans.

In this study we focus on how the intensity level and multileaf collimator (MLC) resolution affect the quality of IMRT plans using the static MLC delivery technique. The planning process is based on a least-square dose-based quadratic function and uses a simulated annealing algorithm to sample the discrete variables. Three clinical cases are studied empirically: a medulloblastoma, a prostate, and an oropharyngeal carcinoma. The intensity levels used are 3, 5, 10, 20, and continuous; the map resolution varies from 0.15-1.5 cm, with the leaf width equal to the step size. The influence of these two parameters are studied by comparing the cost value and the cost of delivery time from a trade-off point of view. An "efficient frontier" is drawn by connecting the plans with the lowest cost value at any given resolutions. For each case, a practical delivery region is defined by doubling the delivery time needed at a normal setting (five levels, 1.0 cm). Within this region, the "efficient frontier" demonstrates that the plans with five intensity levels are the most efficient comparing with plans with higher levels. This is a confirmation of the conclusion from Keller-Reichenbecher et al. [Int. J. Radiat. Oncol., Biol., Phys. 45, 1315-1324 (1999)]. It indicates that to further improve the plan quality with the minimal cost of extra delivery time, the most economical way is to improve the resolution rather than using higher intensity levels.

Algorithms↗

PubMed2005

Density resolution of proton computed tomography.

Conformal proton radiation therapy requires accurate prediction of the Bragg peak position. Protons may be more suitable than conventional x-rays for this task since the relative electron density distribution can be measured directly with proton computed tomography (CT). However, proton CT has its own limitations, which need to be carefully studied before this technique can be introduced into routine clinical practice. In this work, we have used analytical relationships as well as the Monte Carlo simulation tool GEANT4 to study the principal resolution limits of proton CT. The noise level observed in proton CT images of a cylindrical water phantom with embedded tissue-equivalent density inhomogeneities, which were generated based on GEANT4 simulations, compared well with predictions based on Tschalar's theory of energy loss straggling. The relationship between phantom thickness, initial energy, and the relative electron density resolution was systematically investigated to estimate the proton dose needed to obtain a given density resolution. We show that a reasonable density resolution can be achieved with a relatively small dose, which is comparable to or even lower than that of x-ray CT.

Algorithms↗