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At least 343 records · Page 19Linked to original sources
PubMed2005

[Location and frequency of visual field defects as measured by SITA (Swedish Interactive Threshold Algorithm) strategy in primary open angle glaucoma].

PURPOSE: To evaluate the frequency, location and pattern of visual field defects as measured by SITA strategy in primary open angle glaucoma (POAG). METHODS: Six thousand and two-hundred charts were reviewed. One hundred and fifty two patients who fulfilled the inclusion criteria were included. They were stratified according to severity into early, moderate and severe. The following visual field defects were defined: nasal step, paracentral scotomata, arcuate defect, Seidel scotomata, temporal defect, general reduction of sensitivity, annular scotomata and central island. Each examination was divided into sectors corresponding to optic disc regions. Student's t test was used to compare differences in frequency. RESULTS: In the early glaucoma group, the nasal superior step was the most frequent visual field defect, followed by paracentral scotoma and inferior nasal step. General reduction of sensitivity was noted in 7.8%. Defects were more common in the superior hemifield (p<0.05). CONCLUSION: The superior nasal step and paracentral scotoma were the most commun visual field defects in early primary open angle glaucoma as evaluated by SITA strategy, and the superior hemifield comprises most of the defects. General reduction of sensitivity was an early and rare visual field defect.

Adult↗
PubMed2001

Measurement of cortical thickness using an automated 3-D algorithm: a validation study.

A validation study was conducted to assess the accuracy of the algorithm developed by MacDonald et al. (1999) for measuring cortical thickness. This algorithm automatically determines the cortical thickness by 3-D extraction of the inner and outer surfaces of the cerebral cortex from an MRI scan. A manual method of tagging the grey-csf and grey-white interface was used on 20 regions (10 cortical areas found in each hemisphere) in 40 MRIs of the brain to validate the algorithm. The regions were chosen throughout the cortex to get broad assessment of the algorithm's performance. Accuracy was determined by an anatomist tagging the csf-grey and grey-white borders of selected gyri and by allowing the algorithm to determine the csf-grey and grey-white borders and the corresponding cortical thickness of the same region. Results from the manual and automatic methods were statistically compared using overall ANOVA and paired t tests for each region. The manual and automatic methods were in agreement for all but 4 of the 20 regions tested. The four regions where there were significant differences between the two methods were the insula left and right, the right cuneus, and the right parahippocampus. We conclude that the automatic algorithm is valid for most of the cortex and provides a viable alternative to manual methods of determining cortical thickness in vivo. However, caution should be taken when measuring the regions mentioned previously where the results of the algorithm can be biased by surrounding grey structures.

Adult↗
PubMed2005

Efficient multi-modal dense field non-rigid registration: alignment of histological and section images.

We describe a new algorithm for non-rigid registration capable of estimating a constrained dense displacement field from multi-modal image data. We applied this algorithm to capture non-rigid deformation between digital images of histological slides and digital flat-bed scanned images of cryotomed sections of the larynx, and carried out validation experiments to measure the effectiveness of the algorithm. The implementation was carried out by extending the open-source Insight ToolKit software. In diagnostic imaging of cancer of the larynx, imaging modalities sensitive to both anatomy (such as MRI and CT) and function (PET) are valuable. However, these modalities differ in their capability to discriminate the margins of tumor. Gold standard tumor margins can be obtained from histological images from cryotomed sections of the larynx. Unfortunately, the process of freezing, fixation, cryotoming and staining the tissue to create histological images introduces non-rigid deformations and significant contrast changes. We demonstrate that the non-rigid registration algorithm we present is able to capture these deformations and the algorithm allows us to align histological images with scanned images of the larynx. Our non-rigid registration algorithm constructs a deformation field to warp one image onto another. The algorithm measures image similarity using a mutual information similarity criterion, and avoids spurious deformations due to noise by constraining the estimated deformation field with a linear elastic regularization term. The finite element method is used to represent the deformation field, and our implementation enables us to assign inhomogeneous material characteristics so that hard regions resist internal deformation whereas soft regions are more pliant. A gradient descent optimization strategy is used and this has enabled rapid and accurate convergence to the desired estimate of the deformation field. A further acceleration in speed without cost of accuracy is achieved by using an adaptive mesh refinement strategy.

Algorithms↗
PubMed2005

Influence of aging on thermal and vibratory thresholds of quantitative sensory testing.

Quantitative sensory testing has become a common approach to evaluate thermal and vibratory thresholds in various types of neuropathies. To understand the effect of aging on sensory perception, we measured warm, cold, and vibratory thresholds by performing quantitative sensory testing on a population of 484 normal subjects (175 males and 309 females), aged 48.61 +/- 14.10 (range 20-86) years. Sensory thresholds of the hand and foot were measured with two algorithms: the method of limits (Limits) and the method of level (Level). Thresholds measured by Limits are reaction-time-dependent, while those measured by Level are independent of reaction time. In addition, we explored (1) the correlations of thresholds between these two algorithms, (2) the effect of age on differences in thresholds between algorithms, and (3) differences in sensory thresholds between the two test sites. Age was consistently and significantly correlated with sensory thresholds of all tested modalities measured by both algorithms on multivariate regression analysis compared with other factors, including gender, body height, body weight, and body mass index. When thresholds were plotted against age, slopes differed between sensory thresholds of the hand and those of the foot: for the foot, slopes were steeper compared with those for the hand for each sensory modality. Sensory thresholds of both test sites measured by Level were highly correlated with those measured by Limits, and thresholds measured by Limits were higher than those measured by Level. Differences in sensory thresholds between the two algorithms were also correlated with age: thresholds of the foot were higher than those of the hand for each sensory modality. This difference in thresholds (measured with both Level and Limits) between the hand and foot was also correlated with age. These findings suggest that age is the most significant factor in determining sensory thresholds compared with the other factors of gender and anthropometric parameters, and this provides a foundation for investigating the neurobiologic significance of aging on the processing of sensory stimuli.

Adult↗
PubMed2006

Performance evaluation of algorithms for SAW-based temperature measurement.

Whenever harsh environmental conditions such as high temperatures, accelerations, radiation, etc., prohibit usage of standard temperature sensors, surface acoustic wave-based temperature sensors are the first choice for highly reliable wireless temperature measurement. Interrogation of these sensors is often based on frequency modulated or frequency stepped continuous wave-based radars (FMCW/FSCW). We investigate known algorithms regarding their achievable temperature accuracy and their applicability in practice. Furthermore, some general rules of thumb for FMCW/FSCW radar-based range estimation by means of the Cramer-Rao lower bound (CRLB) for frequency and phase estimation are provided. The theoretical results are verified on both simulated and measured data.

Acoustics↗
PubMed2006

State estimation approach for determining composition and growth rate of Si1-xGex chemical vapor deposition utilizing real-time ellipsometric measurements.

We present an algorithm that simultaneously deduces from real-time ellipsometric measurements both the growth rate and the composition of Si1-xGex films deposited via chemical vapor deposition. The heart of the algorithm is a dynamic, first-principles model of the deposition system and the ellipsometric sensor. The model predicts the ellipsometric parameters psi and Delta during film growth. An extended Kalman filter is developed that utilizes the sensor model and infers both the growth rate and the Ge composition of the deposited film in real time. Two simulations demonstrating the effectiveness of the algorithm are evaluated.

Journal Article↗
PubMed2005

Automatic measurement of skin wheals provoked by skin prick tests.

Skin prick tests (SPT) represent the standard method for the diagnosis of type-1 allergies. The skin wheals provoked by the SPTs are considered positive above certain cut-off diameters, usually 3 mm. At present their size is mostly estimated by measuring the diameter with rulers. Since the shape of wheals usually is not circular, the measurement of diameters leads to imprecise results. Therefore, we developed an algorithm for precisely measuring the wheals' area in mm(2) automatically. The average deviation of the automatic measurement on a test set achieved with the developed algorithm was 6.9 %. Compared to the maximum standard deviation of 6.59 % when measuring the manually redrawn outlines, the automatic method works sufficiently well.

Algorithms↗
PubMed2002

[New algorithm for oscillometric noninvasive automatic arterial pressure measurement in patients with atrial fibrillation].

Oscillometric noninvasive arterial pressure monitoring devices frequently fail to measure pressure precisely in patients with arrhythmia, such as atrial fibrillation, because beat-by-beat changes in pulse pressure and mean pressure level distort the relation between cuff pressure and oscillometric wave amplitude. To overcome this problem, we developed a new algorithm for oscillometric measurement in which oscillometric wave amplitude is corrected according to changes in pulse pressure and mean arterial pressure level. In 7 patients with atrial fibrillation, we compared systolic pressure thus estimated with that simultaneously measured invasively in the radial artery and averaged during oscillometric measurement. Correction based on invasively obtained beat-by-beat pulse pressure and mean pressure level decreased the ratio of unmeasurable cases from 11 to 4%. Correction based on plethysmographically estimated pulse pressure decreased unmeasurable cases to 6% (P < 0.01). Standard error of systolic pressure estimates was 6.44 +/- 1.83, 4.10 +/- 0.85, and 4.75 +/- 1.26 mmHg with no, invasive, and plethysmographical correction in this order (P < 0.01). We conclude that oscillometric wave amplitude correction based on beat-by-beat pulse pressure and mean arterial pressure level lessened the number of unmeasurable cases and improved measurement precision in patients with atrial fibrillation.

Algorithms↗
PubMedDate not supplied

Left ventricular ejection fraction and volumes from gated blood pool tomography: comparison between two automatic algorithms that work in three-dimensional space.

BACKGROUND: Two different algorithms, which are fast and automatic and which operate in 3-dimensional space, were compared in the same group of patients to compute left ventricular ejection fraction (LVEF) and volumes from gated blood pool tomography. One method, developed at Cedars-Sinai Medical Center (CS), was dependent on surface detection, whereas the other method, developed at the Free University of Brussels (UB), used image segmentation. METHODS AND RESULTS: Gated blood pool tomograms were acquired in 92 consecutive patients after injection of 740 MBq of technetium 99m-labeled human serum albumin. After reconstruction and reorientation according to the left ventricular long axis, LVEF and left ventricular volumes were measured with the CS and UB algorithms. Measurements of LVEF were validated against planar radionuclide angiocardiography (PRNA) results. The success rates of the algorithms were 87% for CS and 97% for UB. Agreement between LVEF measured with CS and UB (LVEF(CS) = 0.91. LVEF(UB) - 0.85; r = 0.87) and between LVEF measured with CS and PRNA (LVEF(CS) = 1.04. LVEF(PRNA) - 4.75; r = 0.80) and UB and PRNA (LVEF(UB) = 0.98. LVEF(PRNA) + 4.42; r = 0.82) was good. For left ventricular volumes, linear regression analysis showed good correlation between both methods with regard to end-diastolic volumes (r = 0.81) and end-systolic volumes (r = 0.91). On average, end-diastolic volumes were similar and end-systolic volumes were slightly higher with CS than with UB. Consequently, significantly lower LVEFs were observed with CS than with UB. CONCLUSIONS: Good correlation was observed between CS and UB for both left ventricular volumes and ejection fraction. In addition, measurements of LVEF obtained with both algorithms correlated fairly well with those obtained from conventional PRNA over a wide range of values.

Adult↗
PubMed2003

Analysis of associations with change in a multivariate outcome variable when baseline is subject to measurement error.

A simple general algorithm is described for correcting for bias caused by measurement error in independent variables in multivariate linear regression. This algorithm, using standard software, is then applied to several approaches to the analysis of change from baseline as a function of baseline value of the outcome measure plus other covariates, any of which might have measurement error. The algorithm may also be used when the independent variables differ by component of the multivariate independent variable. Simulations indicate that under various conditions bias is much reduced, as is mean squared error, and coverage of 95 per cent confidence intervals is good.

Algorithms↗
PubMedDate not supplied

Error measures for objective assessment of scene segmentation algorithms.

Scene segmentation is an important element in pattern recognition problems. Previous efforts to evaluate and compare scene segmentation procedures have been largely subjective. Quantitative error measures would facilitate objective comparison of scene segmentation algorithms. A theoretical discussion leading to a new generalized quantitative error measure, G2, based on comparison of both pixel class proportions and spatial distributions of "true" and test segmentations, is presented. This error measure was tested on 14 manual segmentations and 40 gynecologic cytology specimens segmented with five different scene segmentation techniques. Results indicate that G2 seems to have the desirable properties of correlation with human observation, categorization of error allowing for weighting, invariance with picture size and ease of computation necessary for a useful scene segmentation error measure.

Autoanalysis↗
PubMed2006

Metric for measuring the effectiveness of clustering of DNA microarray expression.

BACKGROUND: The recent advancement of microarray technology with lower noise and better affordability makes it possible to determine expression of several thousand genes simultaneously. The differentially expressed genes are filtered first and then clustered based on the expression profiles of the genes. A large number of clustering algorithms and distance measuring matrices are proposed in the literature. The popular ones among them include hierarchal clustering and k-means clustering. These algorithms have often used the Euclidian distance or Pearson correlation distance. The biologists or the practitioners are often confused as to which algorithm to use since there is no clear winner among algorithms or among distance measuring metrics. Several validation indices have been proposed in the literature and these are based directly or indirectly on distances; hence a method that uses any of these indices does not relate to any biological features such as biological processes or molecular functions. RESULTS: In this paper we have proposed a metric to measure the effectiveness of clustering algorithms of genes by computing inter-cluster cohesiveness and as well as the intra-cluster separation with respect to biological features such as biological processes or molecular functions. We have applied this metric to the clusters on the data set that we have created as part of a larger study to determine the cancer suppressive mechanism of a class of chemicals called retinoids.We have considered hierarchal and k-means clustering with Euclidian and Pearson correlation distances. Our results show that genes of similar expression profiles are more likely to be closely related to biological processes than they are to molecular functions. The findings have been supported by many works in the area of gene clustering. CONCLUSION: The best clustering algorithm of genes must achieve cohesiveness within a cluster with respect to some biological features, and as well as maximum separation between clusters in terms of the distribution of genes of a behavioral group across clusters. We claim that our proposed metric is novel in this respect and that it provides a measure of both inter and intra cluster cohesiveness. Best of all, computation of the proposed metric is easy and it provides a single quantitative value, which makes comparison of different algorithms easier. The maximum cluster cohesiveness and the maximum intra-cluster separation are indicated by the metric when its value is 0.We have demonstrated the metric by applying it to a data set with gene behavioral groupings such as biological process and molecular functions. The metric can be easily extended to other features of a gene such as DNA binding sites and protein-protein interactions of the gene product, special features of the intron-exon structure, promoter characteristics, etc. The metric can also be used in other domains that use two different parametric spaces; one for clustering and the other one for measuring the effectiveness.

Algorithms↗
PubMed1990

Transducer characterization from pressure amplitude distribution measurements using a Kalman filter as parameter estimation algorithm.

The amplitude and frequency contents of a received ultrasound pulse depends on the spatial pressure amplitude distribution of the sound field, as produced by the transducer in the medium, and on the position and orientation of the reflecting surface in this field. Often, the geometry of the reflecting surface and the acoustical properties of the medium are known or can be estimated. Then it is practical to determine the transducer parameters in order to calculate the distortion of a reflected ultrasound pulse. Apart from geometrical parameters such as size and mechanical focusing, the surface velocity amplitude distribution (SVAD) of a transducer is of major importance. For some transducer configurations this SVAD may be described with a limited number of parameters. This paper presents a method, based on a Kalman filter algorithm, to assess the transducer parameters by measurement of the spatial sound field pressure amplitude distribution in various planes for different emission frequencies. Comparison of the measured pressure amplitudes with those calculated using the estimated values of the parameters shows that this method yields reliable results.

Acoustics↗
PubMedDate not supplied

[A computer arterial pressure measuring device].

The paper describes a non-invasive oscillometric blood pressure (BP) measuring device. It provides an algorithm for the automatic measurement of systolic and diastolic BP values. A variant of assessing the BP measurement stability is proposed and the results of this assessment are given for 3 devices made by different firms. The total errors made by the studied device that functions as part of a physician's computer monitor are defined. Health institutions, resuscitation units, operating rooms for children and adults are an application sphere of the device.

Adolescent↗
PubMed2004

Blood pressure measurement and the guidelines: a proposed new algorithm for the diagnosis of hypertension.

Current hypertension guidelines continue to base management decisions on the office BP as recorded by mercury sphygmomanometry. The imminent disappearance of mercury from the workplace for environmental and safety reasons provides an opportunity to re-assess how a diagnosis of hypertension is made. There are now several validated, automated BP recording devices available to replace mercury sphygmomanometers in the office setting. Self/home and 24-hour ambulatory BP monitoring should now become an integral part of the diagnostic algorithm for hypertension in view of their superior ability to predict clinical outcomes when compared to traditional office BP measurements.

Algorithms↗
PubMed1995

Depth profiling by ARXPS in surface analysis.

A method of nondestructive depth profiling in near surface regions of solids is described. Models have been discussed from which algorithms for evaluation of measured data are obtained. The algorithms, based on standard profiles with free parameters, have been adjusted to the data resulting from angle resolved XPS (ARXPS) by means of least squares fits. Depth profile analyses and segregation studies were performed on Pt-Ni and Fe-S specimens.

Journal Article↗
PubMed2005

Recursive estimation of 3D motion and surface structure from local affine flow parameters.

A recursive structure from motion algorithm based on optical flow measurements taken from an image sequence is described. It provides estimates of surface normals in addition to 3D motion and depth. The measurements are affine motion parameters which approximate the local flow fields associated with near-planar surface patches in the scene. These are integrated over time to give estimates of the 3D parameters using an extended Kalman filter. This also estimates the camera focal length and, so, the 3D estimates are metric. The use of parametric measurements means that the algorithm is computationally less demanding than previous optical flow approaches and the recursive filter builds in a degree of noise robustness. Results of experiments on synthetic and real image sequences demonstrate that the algorithm performs well.

Algorithms↗
PubMed2006

Delineation of T-wave in ECG by wavelet transform using multiscale differential operator.

This paper proposes an improved wavelet-based method for the delineation of T wave in the electrocardiogram by using multiscale dif-operator (MDO). MDO was employed to automatically categorize the T wave into one of the three categories of T wave morphologies and to improve the precision of T wave delineation for each category. The new algorithm was evaluated on QT database (QTDB) and new annotations of 2160 beats from QTDB were performed by two cardiologists. To evaluate the performance of the wave delineation, the time differences between automatic detection versus cardiologists' annotations and intercardiologist differences were measured. The new algorithm can attain better results than the previous methods by achieving the smallest standard deviation of the differences and qualifying the strict error criterion for T-off measurement. This new algorithm also exhibited excellent T wave categorization agreement with the cardiologists, resulting in kappa values above 0.75.

Algorithms↗