Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Mathematical Computing”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,063 records · Page 59Linked to original sources
PubMed1997

Calculation of multi-segment rigid body joint dynamics using MATLAB.

A computational model of the human upper limb was developed utilizing a matrix calculation software package (MATLAB) and a public domain suite of subroutines [Robotics Toolbox (1)]. An easily configurable model of a rigid body, serially linked manipulator was established, avoiding the need for complex numerical equations to be formulated. A generalized model of the upper limb was used to study throwing action of individual subjects by incorporating body segment parameters and kinematic data. Estimates of joint moments were calculated for multiple time instances. This technique can be utilized and adapted for modelling any arbitrary serially linked manipulator system. Inverse and forward kinematics and kinetics can be calculated, enabling biomechanical simulations to be undertaken.

Biomechanical Phenomena↗
PubMedDate not supplied

An application of a microcomputer compiler program to multiple logistic regression analysis.

Microcomputer programs for multiple logistic regression analysis were written in BASIC language to determine the usefulness of microcomputers for multivariate analysis, which is an important method in epidemiological studies. The program, carried out by an interpreter system, required a comparatively long computing time for a small amount of data. For example, it took approximately thirty minutes to compute the data of 6 independent variables and 63 matched sets of case and controls (1:4). The majority of the calculation time was spent computing a matrix. The matrix computation time increased cumulatively in proportion to additions in the number of subjects, and increased exponentially with the number of variables. A BASIC compiler was utilized for the program of multiple logistic regression analysis. The compiled program carried out the same computations as above, but within 4 minutes. Therefore, it is evident that a compiler can be an extremely convenient tool for computing multivariate analysis. The two programs produced here were also easily linked with spreadsheet packages to enter data.

Computers↗
PubMed2001

Force models for needle insertion created from measured needle puncture data.

The focus of this paper is to present a force-feedback model that has been developed for the epidural needle insertion procedure. The model is based on data collected from biomaterials testing studies, and consists of separate force models for each of the tissue types relevant to the epidural needle insertion procedure. These tissue force models were generalized to create force-feedback models to drive haptic devices for needle insertion simulation.

Animals↗
PubMed2001

Deficits and remedy of the standard random effects methods in meta-analysis.

The random effects model is often used in meta-analyses. A corresponding significance test based on a normal approximation has been established. Its type I error is derived in this article by theoretical considerations and computer simulations. The test can be conservative as well as unacceptably anti-conservative. The anti-conservatism increases with the increasing number of patients and the decreasing number of studies. A modification is proposed, which keeps the nominal level asymptotically as the number of patients approaches infinity. Simulations show that the modified test is often conservative, but its conservatism is small in those situations where the standard test is highly anti-conservative.

Bias↗
PubMed2003

MRI morphological and volumetric study of the cingulate gyrus and its relevance in partial epileptic patients.

The cingulate gyrus (CG) is often involved during partial epileptic seizures. The purpose of the study was to analyse the CG morphology and to measure the CG volume in epileptic patients, in order to detect subtle MRI abnormalities such as atrophy, which could be indicative of its implication in the epileptogenic area. The population consisted of 20 epileptic patients (31.2 +/- 9.4 years) and 20 normal volunteers (31.8 +/- 7.7 years). The epileptic patients underwent intracerebral recordings, and were sub-divided into five patients presenting with seizures involving the CG (CG 1), seven patients in whom the CG was only secondarily involved (CG 2) and eight patients in whom the CG was not invoved at all (CG 3). All subjects were investigated by MRI (1.5 tesla Gyroscan Philips): axial T1w 3D Gradient Echo acquisitions, thickness 1.5 mm, reconstructions in all planes. At first, we described the sulcal limits of the CG, trying to define a "normalised CG". In a second step, we segmented the CG intrasulcal grey matter using the "Surgiscope Scopeplan" (Elekta). We compared (Mann and Whitney U test [alpha=0.05]), the CG volumes of CG 1 to CG 2 + 3, and the volume of CG 1 and of CG 1 + 2 + 3 to that of normal volunteers. There was no significant difference between CG 1 and CG 2 + 3 (P= 0.89), between CG 1 and normal volunteers (P= 0.75) or between CG1 + 2 + 3 and normal volunteers (P = 0.83). The volumetric analysis showed no atrophy of the CG in epileptic patients and did not distinguish the group in whom seizures involved the CG, from the other groups.

Adult↗
PubMed1992

[Calculation of optimized and individualized hip prosthesis. A study of feasibility].

As logical consequence of a series of basic research studies on human femoral bones with unipodal support and under static stress, performed with physicomathematic modelling methods (finite-elements method) then confirmed by direct visualization of deformations resulting from such stress using holographic interferometry, the authors have worked on the definition of an optimized and individualized hip prosthesis. Thick CT sections digitized with a table and entered into a specially programmed computer allowed three-dimensional modelling of the femur as a volume, i.e. with its external contour and its medullary canal, and therefore of the implantable space. The prosthesis was then defined taking a number of hypotheses into account: necessity to regularize cortical bone spicules inside spongious bone, which are so often present opposite the rough line, partial machining at the level of the calcar, reduced tail length, presence or absence of collar. Thus an optimized and individualized prosthesis was defined. A prototype corresponding to a given femoral bone could then have been produced. However, the authors found it preferable to use simulation with computer synthetic images to check easy insertion and removal.

Acetabulum↗
PubMed2004

Averaging signals with random time shift and time scale fluctuations.

OBJECTIVES: Our main objective was to propose an alternative to the technique of signal averaging (SA) to avoid shape distortions due to jittering and scale fluctuations, leading to a mean shape signal rather than to an average one. METHODS: In case of both time shift and time scale fluctuations of the individual signals, the first point was to show what model makes it possible to interpret their expected action as a linear shift invariant filter followed by a scale invariant one. So, even in the case of equal shape signals, the average is clearly not the same shape. The second point was to propose another averaging process, using the normalized integrals and called Shape Averaging (ShA) which provides, in this case, a mean signal preserving the common shape. RESULTS: The performances of ShA were firstly shown by simulation. Shifted and scaled versions of a given signal, without and with additive noise, have been generated at random. The mean shape signal obtained by ShA was compared to the shifted and scaled signal using the exact average values of the shifts and scale factors. A very good reconstruction of the mean shape signal is obtained for SNR = 20 dB and quite good for 8 dB, especially compared to SA. The method was then applied to a series of M-waves coming from surface EMG signals. In this case, the comparison of ShA with SA makes it possible to appreciate the validity of equal shape signal hypothesis.

Algorithms↗
PubMed2004

Differentiating vascular pathophysiological states by objective analysis of flow dynamics.

BACKGROUND AND PURPOSE: There is an unmet need to classify cerebrovascular conditions physiologically and to assess cerebrovascular system performance. The authors hypothesized that by simultaneously considering the dynamic parameters of flow velocity, acceleration, and pulsatility index (PI) (impedance) in individual Doppler spectrum waveforms, they could develop an objective method to elucidate the pathophysiology of vascular conditions and classify cerebrovascular disorders. This method, dynamic vascular analysis (DVA), is described. METHODS: First, a theoretical model was developed to determine how any vascular segment and the ensemble of intracranial vascular segments could be defined according to its dynamic physiological characteristics. Next, the DVA method was applied to 847 anonymous serial complete clinical transcranial Doppler (TCD) studies of patients without regard for their diagnosis to ascertain actual reference ranges and the normality of the distribution curves for each dimension of the 3-parameter nomogram. The authors applied DVA to 2 clinical cases to see if they could track the changes in vascular performance of 2 known progressive diseases. RESULTS: The theoretical analysis identified 295,245 possible vascular states for the ensemble of vascular segments in the cerebral circulation. When applied to clinical TCD data, DVA revealed continuous, normally distributed data for the velocity, PI, and logarithm of the acceleration. CONCLUSIONS: DVA is proposed as a method for monitoring the physiological state of each cerebral artery segment individually and in ensemble. DVA evaluates the relationship among acceleration (force or pressure), velocity, and PI and provides an objective means to evaluate intracranial vascular segments using the paradigm of the well-described pressure-perfusion autoregulation relationship. DVA may be used to study cerebrovascular pathophysiology and to classify, evaluate, and monitor cerebrovascular disorders or systemic disorders with cerebrovascular effects.

Adult↗
PubMed2004

A new method for analyzing histograms of brain magnetization transfer ratios: comparison with existing techniques.

BACKGROUND AND PURPOSE: Previously reported quantitative parameters for the magnetization transfer ratio (MTR) do not give identical results, which can limit their ability to differentiate normal from diseased tissue and render them vulnerable to variations among MR systems. Our purpose was to systematically study different MTR metrics; propose a new MTR histogram parameter, AMTR(2/3); and compare AMTR(2/3) with existing parameters in a study of multiple sclerosis (MS). METHODS: Seven conventional MTR parameters were proposed: global and mean MTR; peak height and position of the histogram; and percentiles MTR25, MTR50, and MTR75. Additionally, we investigated a parameter, AMTR(2/3), to indicate the normalized pixel count (area under the histogram curve) inside the band size of two-thirds MTR histogram peak height. All parameters were measured in 10 patients with relapsing-remitting MS (group A), 10 healthy control subjects from the same imaging center as that of patients (group B), and four healthy control subjects from an outside institution (group C). Comparison of findings was performed between groups A and B to assess the discriminating ability of MTR parameters and groups B and C to evaluate intersystem variations. RESULTS: All MTR parameters differed between groups A and B, but the difference was significant for only global MTR, mean MTR, MTR25, and AMTR(2/3). With the exception of AMTR(2/3), all parameters differed significantly between the two control groups. CONCLUSION: AMTR(2/3) is less sensitive to MR imaging system variations than are other MTR parameters and was most effective in differentiating patients with MS from healthy control subjects. This finding supports the use of AMTR(2/3) in multicenter MT MR imaging studies of MS.

Adult↗
PubMed2002

Study of patient positioning on a dynamic frame for scoliosis surgery.

The goal of this clinical trial was to measure patient geometry on a dynamic positioning frame in various prone positions. Fourteen subjects (2 males and 12 females) were recruited from the scoliosis clinic at Ste-Justine Hospital on a volunteer basis. The subjects were AIS patients who were potential candidates for surgery. The Cobb angle, averaged 50 degrees (32 degrees-64 degrees). The mean age was 14.1 years (11-17). A Polaris system (Northern Digital inc, Canada) with 10 passive reflective markers was used to measure various indices of the patient's trunk geometry. Acquisitions were made while the unanaesthetized patient was in five different prone positions: I similar to the standard positioning on a Relton-Hall frame; II addition of a force applied to the ribcage at the apex of the curve; III application of a force at the apex of the curve in the lumbar region; IV, the shoulder pads were elevated to increase the patient's kyphosis; V adjustment of each pad and the application of thoracic and lumbar forces to obtain an optimal correction. The measurements of trunk geometry at each position were compared using position I as a base. A paired student t-test determined a significant difference between positions. When comparing position I to position II there was a significant difference and correction of the rib hump. There was also a significant change in shoulder angle that resulted in over correction. Position III had a significantly negative change in the rib hump. During position IV, there was a measurable increase in kyphosis. During the optimal correction, position V, a significant increase in spine length was observed as well as a significant correction in rib hump and shoulder angle. Patient trunk geometry can be improved by the application of different forces on a dynamic positioning frame. Caution is necessary as over correction and unintended negative effects were observed. The optimal patient position has not yet been found and future studies are directed at determining this.

Adolescent↗
PubMed2002

Interactive visualization of four-dimensional ultrasound data.

We present a hardware-accelerated method using three-dimensional (3D) textures to visualize four-dimensional (4D) images of the heart. Novel data subdivision and caching ideas enable interactive performance even though 4D data exceed the size of 3D texture memory. The capability to visualize 4D images is critical to continued evolution and clinical acceptance of 4D imaging.

Computers↗
PubMedDate not supplied

[The numerical Hatze-model: also qualified for calculations on children?].

The aim of this study was to find out whether the Hatze-model, which is specifically designed for adults, is suitable for calculations on children as well. By means of that program it is possible to calculate various parameters of the human body. After the collection of data and analysis of the results according to Hatze it becomes evident that this model provides good results only for the calculation of the total body mass. As regards the body segments, there are significant under- and overestimations. The same applies to the calculation of mean body density. Indeed there is a significant gender dimorphism indicating that girls have a higher fraction of body fat than boys. However, the values are far below those described in the literature. Due to the formula, the values of the centres of gravity are linear and congruent in both sides of the body. Interpretation of the results is difficult, as there are no valid reference values. Furthermore the program is not able to take characteristic shapes and proportions of children into account. For this reason 88% of the children are defined as either pregnant or obese. In summary, the study shows that the present model should not be used to calculate children and the human models have to be designed specifically for children.

Accidents, Traffic↗
PubMed2005

Genomic profiling. Interplay between clinical epidemiology, bioinformatics and biostatistics.

OBJECTIVES: The current literature on the use of microarrays to generate prognostic profiles is still a methodological wasteland. Many valid questions, such as how profiling studies should be evaluated and what conclusions can be drawn, remain unanswered. Or how can flaws in the collection, analysis and interpretation of data be detected? Undiscovered imperfections can lead to a waste of valuable resources as well as be a latent source of false conclusions. METHODS: Three seminal papers on the prognosis of breast cancer using genomic profiling will be discussed. Six principles of good experimental design will be used for methodological guidance: defining relevant endpoints, avoiding systematic bias, generalizability of results, appropriately sized samples to achieve sufficient power, simple design to improve interpretability, and avoiding artificial assumptions. RESULTS: Severe violations of at least one of the six principles of good experimental design can be found in each of the three papers. A strategy is presented to assess whether a study has achieved a high level of methodological quality. This strategy also helps to establish a suitable protocol for future profiling projects. CONCLUSIONS: Determining the design of a study in a protocol is a first step to avoid impending pitfalls. The protocol should deal with the problem of understanding the complex reality behind genomic profiling. There are basic guiding principles which can help handle the complex task of designing prognostic studies to find genomic signatures.

Biometry↗
PubMed2006

Blood-flow volume quantification in internal carotid and vertebral arteries: comparison of 3 different ultrasound techniques with phase-contrast MR imaging.

BACKGROUND AND PURPOSE: Optimal estimation of cerebral blood-flow volume (BFV) may be an important indicator for better evaluation of the patients with cerebrovascular disorders. In this study, we compared the BFV values at bilateral internal carotid and vertebral arteries of healthy volunteers obtained with color Doppler, power Doppler, and B-flow ultrasound (US) studies and tried to determine which examination is more correlated with MR phase-contrast quantification. METHODS: BFVs of the internal carotid and vertebral arteries of 40 healthy volunteers (19 men and 21 women; age range, 20-47 years) were measured by using color Doppler, power Doppler, B-flow US and MR phase-contrast imaging. The flow measurements obtained with the sonographic techniques were compared with MR phase contrast, which is accepted as the most reliable method for the estimation of cerebral BFV. RESULTS: Quantification with power Doppler imaging showed the highest values among sonography techniques, followed by color Doppler imaging, B-flow imaging (BFI), and MR phase-contrast flow quantification. There was a statistically significant difference between the flow-volume values obtained with these 4 different techniques (P < .05). BFI yielded the closest values (internal carotid arteries, 238.84 mL/min; vertebral arteries, 51.16 mL/min) to MR phase-contrast flow quantification study with higher correlation rates. CONCLUSION: Flow volumes obtained with BFI showed the highest correlation with MR phase-contrast imaging among 3 different sonography techniques. B-flow sonography may be a very effective and cost-efficient alternative for MR phase-contrast studies for the calculation of cerebral BFV.

Adult↗