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PubMed2003

Multidetector-row cardiac CT: diagnostic value of calcium scoring and CT coronary angiography in patients with symptomatic, but atypical, chest pain.

The aim of this study was to investigate the accuracy of multidetector-row cardiac CT (MDCT), calcium scoring (Ca-Sc), and MDCT coronary angiography (MD CTA) in the assessment of coronary atherosclerosis. Thirty-eight patients underwent invasive coronary angiography (CA) and MDCT (collimation 4x1 mm, pitch 1.5 mm, TI 500 ms, 120 kV, 300 mAs, and retrospective ECG-gating). Calcium scoring was calculated for the total coronary artery territory and for RCA, LCA, and LCX separately. The MD CTA served to assess the degree and the localization of stenoses. All findings were compared to invasive coronary angiography. Approximately 68.4% (390 of 570) of all coronary segments could be visualized by MDCT. Correlation coefficient for MD CTA and CA amounted to r=0.58, showing distinct differences for the individual segments. Proximal segments generally showed better correlation (range 0.81-0.77) than medial segments (range 0.91-0.20), distal segments (range 0.55-0.04), or side branches (range 0.76-0.00). Patients with hemodynamically relevant (>75%) stenoses were detected by MD CTA with 72.2% sensitivity (13 of 18) and 100% specificity (20 of 20). For Ca-Sc sensitivity ranged between 94.7% (17 of 18) and 66.7% (12 of 18), specificity between 20% (4 of 20) and 80% (16 of 20) respectively, depending on the prevailing cutoff value. Combination of both methods led to 83.3% sensitivity (15 of 18) and 100% specificity (20 of 20), reaching no level of significance as compared with Ca-Sc (p=0.73) or MD CTA (p=0.23) alone. Calcium scoring as a single method showed highest sensitivity in the detection of coronary atherosclerosis but at the expense of low specificity. In patients with no or moderate calcifications, combination with MD CTA helped to distinctly increase specificity and NPV.

Adult↗
PubMed2005

Evaluation of the cavotricuspid isthmus and right atrium by multidetector-row computed tomography in patients with common atrial flutter.

The sizes of the right atrium (RA), cavotricuspid isthmus, and Eustachian valve are predictors of success of radiofrequency catheter ablation for atrial flutter (AFL). We examined the relationship between the sizes of cavotricuspid isthmus as measured by multidetector-row computed tomography (MDCT) and fluoroscopy. We used eight-detector MDCT to measure the tricuspid isthmus of 23 patients prior to linear ablation for common AFL. One patient with a deep pouch in the RA was excluded. Parameters measured were (1) the length of the trace of isthmus (Ti), which was equivalent to the blocking line; (2) the size of the tricuspid isthmus (DTi); and (3) the distance from the tricuspid valve and inferior vena cava (IVC) (LDTi). DTi and LDTi indicate the size of the RA, reflecting the appropriately sized steerable ablation catheter, respectively. Of the 22 patients, 21 were ablated successfully without recurrence of AFL, and clinical success was achieved in one additional patient despite failure to obtain a bidirectional block. Ti, DTi, and LDTi were correlated with fluoroscopy time (r = 0.84, r = 0.88, and r = 0.88, respectively; P < 0.0001), total delivered energy (r = 0.81, r = 0.80, and r = 0.83, respectively; P < 0.0001), and application time (r = 0.84, r = 0.80, and r = 0.87, respectively; P < 0.0001). Measurement of the tricuspid isthmus by MDCT may noninvasively provide important information for successful linear ablation.

Atrial Fibrillation↗
PubMed2003

Left atrial appendage morphology: comparison of transesophageal images and postmortem casts.

BACKGROUND: Aim of the study was to compare 1) transesophageal echocardiographic (TEE) measurements of the left atrial appendage (LAA) with postmortem casts and 2) the TEE with the postmortem diagnosis of LAA thrombi. METHODS: From the TEE images and LAA casts length, orifice, diameter and number of branches were assessed. LAA area was measured by TEE and LAA volume from the cast. RESULTS: In 12 patients who underwent TEE and autopsy, measurements of LAA length and area correlated well with the cast volume ( r=0.6 to r=0.93). The agreement between TEE and LAA casts, concerning the number of branches, was only moderate. In one patient, a false positive diagnosis of a LAA thrombus occurred. CONCLUSIONS: LAA size and orifice diameter can be assessed reliably by TEE. The complex LAA morphology hampers measurements of LAA length, branches, course and diagnosis of thrombi.

Acrylic Resins↗
PubMed1991

Sample size and dimensionality in multivariate classification: implications for body surface potential mapping.

This paper presents empirically determined guidelines for specifying the number of features appropriate for multivariate classification studies for given sample sizes. Sample size was considered adequate if the mean distance between two sample sets, taken from the same continuous multivariate distribution and projected onto the best separating direction, remained below a prescribed level. To quantitate the sample size requirement, homogeneity of sample set pairs of equal size. N, taken from the same continuous multivariate distribution was studied as a function of dimensionality. M. Homogeneity was characterized by the maximum absolute distances (Dmax) between the corresponding pairs of empirical cumulative probability distributions on the best separating projection. Computer generated data sets were used to estimate the cumulative probability distribution, P(D)M.N, for sample sizes, N, ranging from 5 to 100 and the dimensionality, M, ranging from 1 to 4. An empirical relationship between the estimated step-polygons and the Kolmogorov type one dimensional limiting distribution L(z) has been established. Based on the sample size data of 34 key papers on clinical body surface potential mapping (BSPM) it is noted that in 30% of the cases only one, and in 6% of the cases only two parameters could be used for statistical group representation to ensure a reasonable reliability (Dmax less than 0.2). In 56% of the published cases the sample sizes could not guarantee this reliability even for one feature or parameter.

Computer Simulation↗
PubMed1987

Limiting efficiencies of the non-parametric median method for A exp(-kt) data.

Weighted least squares analysis and the median method are used to extract A and k from simulated single exponential decays. The standard deviations of these parameters (sigma p) depend upon the method of analysis. The sigma p are compared as efficiencies (= sigma 2p[least squares]/sigma 2p[median]). These efficiencies depend upon the range of the decay and the underlying error structure. These include errors independent of the data, approximately equal to the data and approximately equal to the square root of the data. Some efficiencies fall well below 25% for the median method. Such instances reflect the large cost of not knowing or not using the weights; they amount to ignoring greater than 75% of the data we strive to collect.

Computer Simulation↗
PubMed1988

Computer simulation of neuronal circuit models of rhythmic behavior in the electroencephalogram.

A computer program for modeling some features of the electroencephalogram (EEG) recorded by scalp electrodes in terms of the time- and space-dependent interactions of populations of neurons in different hypothetical brain configurations was developed. The input of the model consists of: (1) geometric and anatomic data characterizing the brain configuration; (2) physiologic features characterizing neurons; and (3) functions describing the time-dependent afferent impulses to the brain configuration under study. The output of the model consists of plots of selected intracellular and extracellular potentials as a function of time. In application of the model to various brain configurations, some configurations were sufficiently compact spatially that propagation times of action potentials between elements were either taken to be constant or were nearly independent of distance within the accuracy of the calculations. Other configurations represented cerebral cortex alone or a combined thalamocortical system in which many elements interacted via global interconnections. The basic requirement for rhythmic behavior is the existence of circuits containing inhibitory neurons. The characteristic frequencies of rhythmic oscillations are primarily determined by the local circuit parameters and are relatively independent of global circuit parameters.

Action Potentials↗
PubMed1996

Bone feature analysis using image processing techniques.

In order to establish the correlation between bone structure and age, and information about age-related bone changes, it is necessary to study microstructural features of human bone. Traditionally, in bone biology and forensic science, the analysis if bone cross-sections has been carried out manually. Such a process is known to be slow, inefficient and prone to human error. Consequently, the results obtained so far have been unreliable. In this paper we present a new approach to quantitative analysis of cross-sections of human bones using digital image processing techniques. We demonstrate that such a system is able to extract various bone features consistently and is capable of providing more reliable data and statistics for bones. Consequently, we will be able to correlate features of bone microstructure with age and possibly also with age related bone diseases such as osteoporosis. The development of knowledge-based computer vision-systems for automated bone image analysis can now be considered feasible.

Adult↗
PubMed1994

Assessing the effect of a treatment when subjects are growing at different rates.

The analysis of covariance is often used in the context of premeasure/postmeasure designs to compare treatment and control groups in both randomized [1] and nonrandomized [2] studies. The intent is to adjust the difference between the changes in the 2 groups for any difference which might exist at baseline, i.e., for any difference between the premeasures in the 2 groups. An important assumption underlying the use of the analysis of covariance is that the slopes of the lines for the regression of the postmeasure on the premeasure in the 2 groups are equal. In this paper we describe a program which can be used to test the hypothesis of equal slopes; and performs an alternative analysis which does not depend on this assumption. This is done in the context of comparing treatment and control groups with respect to a measurement subject to natural maturation as in [3]. Equal slopes in this context means equal growth rates; unequal slopes implies that the 2 groups are growing at different rates. The method, known as the Johnson-Neyman procedure [4] is, however, more general than this, and can be used in any two-sample comparison where an alternative to the usual analysis of covariance is deemed appropriate. The procedure identifies a 'region of significance' which is especially useful in practice. This region consists of a set of values of the premeasure for which the treatment and the control groups are significantly different with respect to the postmeasure.

Analysis of Variance↗
PubMed1990

Computer aided stress analysis of long bones utilizing computed tomography.

A computer aided analysis method has been developed which utilizes computed tomography (CT) and a finite element (FE) computer program to determine the stress-displacement pattern in a long bone section. The CT data file provides the geometry, the apparent density and the elastic properties for the three-dimensional FE model. A developed pre-processor generates the FE model of a human diaphyseal tibia section which is then analyzed by the SAP IV finite element program. The results obtained are sorted and displayed by a developed post-processor and compared with stresses and deformations from the literature. The model generation method was verified by applying it to a model of simple geometry and boundary conditions, then comparing the results with the analytical solution of the same problem. The convergence behavior of nodal displacements was tested as a function of mesh refinement. This method provides an automatic, versatile, non-invasive and accurate tool of long bone modeling for finite element stress analysis.

Algorithms↗
PubMed1987

Buoyant density and molecular weight calculations on an Apple II microcomputer from equilibrium banding experiment on analytical ultracentrifuge.

Buoyant density is one of the non-destructive measurements of viruses, nucleic acids etc. which help in characterizing these entities in terms of their chemical composition and physical conformation. In recent years equilibrium sedimentation in CsCl buoyant density gradient has been proved to be a powerful tool for genome characterization. The method enables one to obtain information such as the absolute and the relative buoyant density of the material and its molecular weight. This communication describes a program in BASIC which calculates these parameters from the raw data obtained directly from the experiment. The program is fully interactive, user-oriented, and written keeping in view biologists and biochemists as the main users. The program has a built-in option to calculate either the absolute or the relative buoyant density and the molecular weight.

Algorithms↗
PubMed1990

A simple algorithm for generating neuronal dendritic trees.

A simple, efficient algorithm is presented for generating the codewords of all neuronal dendritic trees with a given number of terminal nodes. Furthermore, a procedure is developed for deciding if different codewords respond to topologically equivalent trees.

Algorithms↗
PubMed1991

Analysis of multiple-choice items.

This paper deals with scoring and analysis of multiple-choice exam questions. Data may be read by an optical mark reader scanner or from a file created by a system editor and stored in a format convenient to be analysed by a specially designed program 'MCQ'. In addition the data file created can be linked with the package SPSSx for pertinent statistical methods or SPSS Graphics for illustration of score and item distributions. The MCQ program comprises: (1) scoring; (2) item analysis: difficulty and discrimination indices; (3) testing the goodness of alternatives attached to each question. The method is applicable to multiple-choice questions with 4.5 greater than 5; true/false and combined exam questions. The method should prove useful for instructors to build up a balanced discriminant questions bank.

Computer Graphics↗
PubMed1994

The graduation of secondary structure elements.

A method of graduating (i.e., least-squares fitting) a smooth polynomial curve through long elements of protein secondary structure is described. It uses the Chebyshev polynomials of a discrete (integer) variable with several restraints to prevent artifactual curvatures. A new recursion formula is given which allows the evaluation of the polynomials on rational-number points as well as on the integer points. High-order splines suitable for interpolation between integer points are also discussed. The new method finds applications in graphics and in structural analysis.

Computer Graphics↗
PubMed2006

Initial construct validation of frequently employed ANAM measures through structural equation modeling.

ANAM measures were based on procedures used in both clinical and performance assessment. This paper reviews data from studies designed to delineate specific neurocognitive functions assessed by more commonly used ANAM measures. Data are brought together from both exploratory and confirmatory analyses. Current findings support the use of these measures for assessing aspects of attention, processing efficiency, and working memory. Recommendations for further research include the need for larger samples and the inclusion of specific marker variables.

Cognition Disorders↗
PubMed2005

Machine learning in bioinformatics: a brief survey and recommendations for practitioners.

Machine learning is used in a large number of bioinformatics applications and studies. The application of machine learning techniques in other areas such as pattern recognition has resulted in accumulated experience as to correct and principled approaches for their use. The aim of this paper is to give an account of issues affecting the application of machine learning tools, focusing primarily on general aspects of feature and model parameter selection, rather than any single specific algorithm. These aspects are discussed in the context of published bioinformatics studies in leading journals over the last 5 years. We assess to what degree the experience gained by the pattern recognition research community pervades these bioinformatics studies. We finally discuss various critical issues relating to bioinformatic data sets and make a number of recommendations on the proper use of machine learning techniques for bioinformatics research based upon previously published research on machine learning.

Algorithms↗
PubMed2005

Quantitation of mitral valve tenting in ischemic mitral regurgitation by transthoracic real-time three-dimensional echocardiography.

OBJECTIVES: We sought to investigate the geometric changes of the mitral leaflets and annulus, clarify the maximum tenting site of the leaflets, and quantify the valve tenting in ischemic mitral regurgitation (MR) using three-dimensional (3D) echocardiography. BACKGROUND: Although the understanding of the mechanisms of ischemic MR has advanced recently, the geometric changes of the mitral leaflets and annulus have been assessed by two-dimensional echocardiography in the clinical setting, despite the unique configuration of the leaflets and annulus. METHODS: Utilizing real-time 3D echocardiography, we obtained transthoracic volumetric images in 12 patients with ischemic MR presenting with global left ventricular dysfunction and in 10 controls. Original software was used to crop the 3D data into 18 radial planes, and we marked the mitral annulus and leaflets in each plane in mid-systole. The 3D images of the leaflets and annulus were reconstructed for the quantitative measurements. RESULTS: In ischemic MR, the annulus flattened with apparent tenting of the leaflets. Maximum and mean tenting length were longer and tenting volume was larger in ischemic MR than control subjects (maximum tenting length: 9.8 +/- 2.0 mm vs. 3.1 +/- 1.2 mm, p < 0.0001, mean tenting length: 3.7 +/- 0.9 mm vs. 0.7 +/- 0.5 mm, p < 0.0001, tenting volume: 4.09 +/- 1.22 ml vs. 0.45 +/- 0.29 ml, p < 0.0001). The maximum tenting site was located in anterior leaflet in all patients. CONCLUSIONS: We clearly demonstrated 3D geometric deformity of the mitral leaflets and annulus in ischemic MR using novel software for creating images by 3D echocardiography. This technique will be helpful in making a proper decision for the surgical strategy in each patient.

Aged↗
PubMed2006

Fast computation of a gated dipole field.

We address the need to develop efficient algorithms for numerical simulation of models, based in part or entirely on adaptive resonance theory. We introduce modifications that speed up the computation of the gated dipole field (GDF) in the Exact ART neural network. The speed increase of our solution amounts to at least an order of magnitude for fields with more than 100 gated dipoles. We adopt a 'divide and rule' approach towards the original GDF differential equations by grouping them into three categories, and modify each category in a separate way. We decouple the slow-dynamics part - the neurotransmitters from the rest of system, solve their equations analytically, and adapt the solution to the remaining fast-dynamics processes. Part of the node activations are integrated by an unsophisticated numerical procedure switched on and off according to rules. The remaining activations are calculated at equilibrium. We implement this logic in a Generalized Net (GN) - a tool for parallel processes simulation which enables a fresh look at developing efficient models. Our software implementation of generalized nets appears to add little computational overhead.

Algorithms↗
PubMed2004

Statistical parametric mapping applied to an autoradiographic study of cerebral activation during treadmill walking in rats.

Autoradiographs are conventionally analyzed by a region-of-interest (ROI) analysis. However, definition of ROIs on an image set is labor intensive, is subject to potential inter-rater bias, and is not well suited for anatomically variable structures that may not consistently correspond to specific ROIs. Most importantly, the ROI method is poorly suited for whole-brain analysis, where one wishes to detect all activations resulting from an experimental paradigm. A system developed for analysis of imaging data in humans, Statistical Parametric Mapping (SPM), avoids some of these limitations but has not previously been adapted as a tool for the analysis of autoradiographs. Here, we describe the application of SPM to an autoradiographic data set mapping cerebral activation in rats during treadmill walking. We studied freely moving, non-tethered rats that received injections of the cerebral blood flow tracer [14C]-iodoantipyrine, while they were performing a treadmill task (n = 7) or during a quiescent control condition (n = 6). Results obtained with SPM were compared to those previously reported using a standard ROI-based method of analysis [J. Cereb. Blood Flow Metab. 23(2003) 925]. The SPM method confirmed most areas detected as significant using the ROI approach. However, in the subcortex, SPM detected additional significant regions that, because of their irregular structures, fell short of statistical significance when analyzed by ROI. The SPM approach offers the ability to perform a semi-automated whole-brain analysis, and coupled with autoradiography, provides an effective means to globally localize functional activity in small animals.

Animals↗