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Results for “Model interpretability”

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At least 397 records · Page 22Linked to original sources
PubMed2001

Pore-to-pore hopping model for the interpretation of the pulsed gradient spin echo attenuation of water diffusion in cell suspension systems.

A simplified pore-to-pore hopping model for the two-phase diffusion problem is developed for the analysis of the pulsed gradient spin echo (PGSE) attenuation of water diffusion in the condensed cell suspension systems. In this model, the two phases inside and outside the cells are treated as two different kinds of pores, and the spin-bearing molecules perform hopping diffusion between them. The size and the orientations of those two respective pores are considered, and then the diffraction pattern of the PGSE attenuation may be well simulated. Nevertheless, the intensity of the characteristic peak decreases with increasing membrane permeability, from which the exchange time may be estimated. We then analyze the experimental 1H PGSE results of the erythrocytes suspension system. The water-residence lifetime in the erythrocyte is obtained to be 10 ms, which is the same as that estimated from the two-region approximation. Furthermore, the PGSE attenuation curve of addition of p-Chloromercuribenzenesulfonate (p-CMBS) is also discussed. It predicts that the alignment of erythrocytes will become normal to the magnetic field direction after the addition of p-CMBS, and inspection using a light microscope confirms that result.

4-Chloromercuribenzenesulfonate↗
PubMed1989

Role of models in understanding and interpreting clinical Doppler ultrasound.

Mathematical and physical models are essential tools in both fundamental and clinically applied Doppler ultrasound research. In this paper we illustrate a variety of models and show how they can be used to understand and interpret clinical Doppler ultrasound signals, particularly from stenosed arteries. The physical models discussed include both steady and pulsatile flow systems, and also a flow visualization technique that can be used to interpret the Doppler signals at a fundamental hemodynamic level. The mathematical models deal with three different aspects of the Doppler signal: models that describe the mechanism of ultrasound scattering by blood, a model to stimulate the returned Doppler signal and a model that may be used to aid in the analysis of clinical recordings. Each of these models provides a more complete understanding of blood flow through normal and stenosed vessels and contributes to the interpretation of clinical Doppler signals.

Computer Simulation↗
PubMed2001

Estimating the percentage of Papanicolaou smears that can be reproducibly identified: modeling Papanicolaou smear interpretation based on multiple blinded rescreenings.

BACKGROUND: Multiple blinded rescreenings of Papanicolaou (Pap) smears for litigation purposes is based on the assumption that a subset of Pap smears can be reproducibly identified. The size of this subset is not known. METHODS: To estimate the size of the subset of Pap smears that can be reproducibly identified, a model was constructed based on the results of repeated blinded screenings in the AutoPap Primary Screening System Trial. Additional analysis came from data in the literature. RESULTS: Routine and AutoPap-assisted screening both have a detection rate for all detected abnormal cases of < 50%. Models with only two subsets or types of slides each with a different detection rate correlated well with the available data. Data from multiple rapid reviews strongly supported the existence of additional definable subsets. Although the percentage of cases with an expected detection rate of 100% in a three-subset model might have been as high as 30% of the abnormal cases detected in a single review, all estimates that included a second subset of slides with at least a 50% detection rate limited the percentage of slides in the 100% sensitive subset of slides to < 2% of all abnormal slides and < 6% of all abnormal slides detected by a single screening. CONCLUSIONS: Repeated screenings of Pap smears allowed more accurate models of the sensitivity of Pap-smear screening and the overall incidence of abnormal cases. The data strongly supported the existence of multiple subsets of Pap smears, which can be defined by repeated blinded rescreenings. The percentage of slides that can be reproducibly identified was small.

Data Interpretation, Statistical↗
PubMedDate not supplied

Considerations for the design, implementation, and interpretation of animal models of fetal alcohol effects.

Animal models have provided clear insights into the clinical manifestations of fetal alcohol syndrome (FAS) and fetal alcohol effects (FAE). The value of such models depends upon the strengths of the experimental procedures. Researchers interested in fetal alcohol effects must be aware of issues and considerations which strengthen their investigations and those issues which place limitations upon interpretations. Methodological considerations associated with the use of animal models, choice of a test animal, method of ethanol administration, control groups, and data analysis are discussed.

Alcohol Drinking↗
PubMed1997

Contribution of mathematical modelling to the interpretation of bedside tests of cerebrovascular autoregulation.

OBJECTIVES: Cerebral haemodynamic responses to short and longlasting episodes of decreased cerebral perfusion pressure contain information about the state of autoregulation of cerebral blood flow. Mathematical simulation may help to elucidate which of the indices, that can be derived using transcranial Doppler ultrasonography and trends of intracranial pressure and blood pressure, are useful in clinical tests of autoregulatory reserve. METHODS: Time dependent interactions between pressure, flow, and volume of cerebral blood and CSF were modelled using a set of non-linear differential equations. The model simulates changes in arterial blood inflow and storage, arteriolar and capillary blood flow controlled by cerebral autoregulation, venous blood storage and venous outflow modulated by changes in ICP, and CSF storage and reabsorption. The model was used to simulate patterns of blood flow during either short or longlasting decreases in cerebral perfusion pressure. These simulations can be considered as clinically equivalent to a short compression of the common carotid artery, systemic hypotension, and intracranial hypertension. Simulations were performed in autoregulating and non-autoregulating systems and compared with recordings obtained in patients. RESULTS: After brief compression of the common carotid artery, a subsequent transient hyperaemia can be interpreted as evidence of intact autoregulation. During longlasting sustained hypoperfusion, a gradual increase in the systolic value of the blood flow velocity waveform along with a decrease in the diastolic value is specific for an autoregulating cerebrovascular system. CONCLUSION: Modelling studies help to interpret both clinical and experimental cerebral haemodynamic phenomena and their dependence on the state of autoregulation.

Blood Flow Velocity↗
PubMed1988

Nonequivalent cylinder models of neurons: interpretation of voltage transients generated by somatic current injection.

1. Numerical methods were used to simulate the voltage responses to an intrasomatic current step of neuronal models that incorporated tapering dendrites, dendrites of unequal electrotonic length, nonlinear membrane properties, and regional differences in specific membrane resistivity (Rm). A "peeling" technique was used to estimate the time constants (tau 0 and tau 1) and coefficients (a0 and a1) of the first two exponential terms of the series of exponential terms whose sum represented the slope of the voltage response. 2. The electrotonic structure of models with a uniform Rm was calculated using equations derived by Rall or Johnston or Brown et al. The adequacy of these methods were tested using a wide variety of models that conformed to the equivalent cylinder approximation of Rall. Johnston's method provided the most reliable estimate of electrotonic length (L) and the ratio of the dendritic conductance to the somatic conductance (rho). However, if L exceeded 2 and rho was eight or larger, the equations derived by Johnston could frequently not be solved due to small errors in the peeled values of tau 0, tau 1, a0, and a1. Although the method suggested by Brown et al. could be applied to all models, this method invariably underestimated L and rho. These errors were particularly large for model neurons with L values of 1.5 or larger and rho values of four or larger. Estimates of L using Rall's method were only reliable if rho was large and L was two or less. 3. Changing the geometry of the dendritic tree (dendritic tapering or dendrites of unequal L) or the addition of a time- and voltage-dependent conductance designed to mimic a sag process commonly seen in spinal motoneurons caused systematic changes in tau 0, tau 1, a0, and a1. The sag process always led to an underestimate of tau 0 even after applying a correction procedure. On the other hand, the ratio, tau 0/tau 1, was not affected by the sag process or dendritic tapering.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMedDate not supplied

Non-random sampling in human genetics: estimation of familial correlations, model testing, and interpretation.

By choice or necessity, human geneticists and genetic epidemiologists often design studies that involve non-random sampling of clusters of individuals, and yet address hypotheses appropriate to the population as a whole. Failure to adjust for the non-randomness of data often leads to biased parameter estimates and misspecification of predictive models that cause familial resemblance of traits. We develop an approach to adjust for common forms of non-randomness in the context of estimating familial correlation with minimal distributional assumptions and discuss its implications in connection with adjustments for concomitant variables.

Analysis of Variance↗
PubMed1998

Fluorescence quenching data interpretation in biological systems. The use of microscopic models for data analysis and interpretation of complex systems.

In micro-heterogeneous media (e.g. membranes, micelles and colloidal systems), the fluorescence decay in the absence of quencher is usually intrinsically complex, e.g. due to the existence of several sub-populations with different micro-environments. In this case it is impossible to analyze data in detail (accounting for transient effects) and simpler formalisms are needed. The objective of the present work is to present and discuss such simpler formalisms. The goal is to achieve simple data analysis and meaningful, clear data interpretation in complex systems using microscopic models that consider several sub-populations of chromophores. Two points are dealt with in detail. (i) It is shown that the approximation of the transient effects by the quenching sphere-of-action model is not always possible. The quenching sphere-of-action concept can be regarded as a valuable tool, although crude, only in a limited range of experimental conditions, namely time resolution. (ii) The Stern-Volmer equation usually used for data analysis is only valid for a limited range of small and moderate equilibrium association constants, Ka, although this is frequently overlooked in the literature. Self-consistency criteria are presented for the proposed methods. The well-known downward curvature due to a fraction of fluorophores which is not accessible to the quencher is only a limiting case from a set of possible situations which result in deviations to linearity. A systematic classification of the different types of quenching is presented.

Data Interpretation, Statistical↗
PubMed2006

Theoretical model for the interpretation of BMD scans in patients stopping strontium ranelate treatment.

UNLABELLED: Strontium ranelate is a new treatment for osteoporosis that results in large increases in BMD, much of which is an artefact caused by high bone strontium content. We used clinical trial data and a model of long-term strontium kinetics to estimate the effect of past strontium treatment on future BMD measurements. INTRODUCTION: The oral administration of strontium ranelate causes a clinically significant overestimation of BMD because of the high attenuation of X-rays by strontium atoms in bone. As more patients are treated with strontium ranelate, questions will arise about the correct interpretation of their future BMD measurements. We performed a theoretical study to calculate the long-term effect of strontium treatment on BMD and establish the duration of past treatment for which the remaining bone strontium content (BSC) has a negligible effect on BMD. MATERIALS AND METHODS: The BMD changes measured at the spine and hip during strontium ranelate treatment were interpolated from clinical trial data. The long-term retention of strontium in bone was estimated using the International Commission on Radiological Protection (ICRP) strontium retention function modified for use in postmenopausal women. Estimates of the strontium BMD artefact after treatment has stopped were performed on the assumption that the BSC effect accounts for 75% of the total measured BMD change at 3 years. RESULTS: If 75% of the BMD changes are explained by BSC, in the average patient, 3-year treatment leads to a spine BMD artefact of 11.2%, decreasing to 3.8% 10 years after stopping treatment. The BMD artefacts at the total hip and femoral neck sites are smaller by factors of 0.65 and 0.53, respectively. If pre- and post-therapy BMD measurements are available, these predictions can be tailored to the individual patient. On average, 6-month treatment is required for the spine BMD artefact to exceed 3%, the figure adopted as the maximum BMD change caused by bone strontium that has a negligible effect on scan interpretation. Ten years after stopping treatment, 28 months of treatment are required for the residual BMD artefact to still exceed the 3% threshold. CONCLUSIONS: Strontium ranelate treatment lasting for >6 months can affect BMD measurements for many years afterward.

Bone Density↗
PubMed2001

A knowledge model for the interpretation and visualization of NLP-parsed discharged summaries.

At our institution, a Natural Language Processing (NLP) tool called MedLEE is used on a daily basis to parse medical texts including complete discharge summaries. MedLEE transforms written text into a generic structured format, which preserves the richness of the underlying natural language expressions by the use of concept modifiers (like change, certainty, degree and status). As a tradeoff, extraction of application-specific medical information is difficult without a clear understanding of how these modifiers combine. We report on a knowledge model for MedLEE modifiers that is helpful for a high level interpretation of NLP data and is used for the generation of two distinct views on NLP-parsed discharge summaries: A physician view offering a condensed overview of the severity of patient problems and a data mining view featuring binary problem states useful for machine learning.

Artificial Intelligence↗
PubMed1987

Feasibility of the homogeneous head model in the interpretation of neuromagnetic fields.

During the past few years it has been demonstrated that active areas in the human brain can be located by measuring the magnetic fields arising from the electric currents in the neurons. An established model for the conductivity geometry of the head in these studies is the layerwise homogeneous sphere. If, however, the measurement grid is too large or the local radius of curvature of the head is changing rapidly in the measurement area, this simple model may become inadequate. In this paper we investigate the feasibility of replacing the conducting sphere by a homogeneous body having the shape of the brain. We show by a semi-quantitative argument that the homogeneous body model is justified. A numerical procedure for the calculation of the magnetic field is presented with examples of the accuracy that can be obtained. An example of significant differences between the predictions of the homogeneous and sphere models is discussed.

Animals↗
PubMed2003

[Dynamic biliary manometry: display modelling and graphic interpretation].

Tendencies of development of biliary manometry have been analyzed. Key advantages and problems of manometric investigation of biliary tracts have been summarized. New method of graphic registration and pressure monitoring in biliary tracts called biliary manometry has been suggested. Characteristic types of manometric curves were determined using stand modelling, their physical and mathematical analysis was conducted, clinical analogues have been suggested. The emphasis has been made on expediency of its further elaboration and clinical application.

Bile Duct Diseases↗
PubMed1991

Application of the LQ model to the interpretation of absorbed dose distribution in the daily practice of radiotherapy.

In 1991, the vast majority of radiotherapy centers are implemented with computer treatment planning systems (TPS), and it has become routine practice to compute full absorbed dose distribution (ADD) in almost all treatment situations. Usually the target is covered by the 100% isodose and the surrounding normal tissues receive a lesser dose than the tumor. It implies, that, as the dose per fraction of, say, 2 Gy is prescribed at the 100%, normal tissues receive a daily dose different than 2 Gy. The absorbed doses delivered at different organs have therefore not the same biological effectiveness and must be corrected according to the actual dose per fraction for a proper interpretation of the treatment planning. This is of great importance since most of the "tolerance levels" used in the practice have been determined for doses per fraction around 1.8-2 Gy. The linear-quadratic (LQ) model provides a simple method for establishing biological equivalencies and has been used throughout this article to establish the difference between the absorbed dose computed by the TPS and its biological equivalent. It is shown that normal tissues receiving less than 100% of the daily dose are relatively more protected than suggested by the ADD, and, inversely, that normal structures overdosed and thus receiving more than the 100% daily dose are relatively more at risk for complications than suggested from the ADD.

Bronchial Neoplasms↗