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At least 469 records · Page 26Linked to original sources
PubMed1998

A digital method for computing target margins in radiotherapy.

Computer methods for determining the planning target volume from the gross tumor volume for both conventional and conformal radiotherapy are presented. Production of a two-dimensional (2D) treatment plan is assisted by projecting outlines of the gross tumor onto a single transverse plane, so that the total extent of the tumor can be easily visualized. A 2D margin can then be added to the resulting outline, so as to account for microscopic tumor spread, organ motion, and setup uncertainty. The margin may be anisotropic to account for the known differences in setup accuracy in the anterior, posterior, left and right directions. For three-dimensional (3D) treatment planning, it is necessary to add a 3D margin to the gross tumor volume to define the planning target volume, the anisotropy of the margin now being allowed to extend to the superior and inferior directions also. Robust methods for automatically calculating these regions are described, and illustrated for the case of a prostate tumor. It is demonstrated that while a slicewise 2D margin is adequate for 2D planning, a fully 3D margin must be used for 3D conformal planning to avoid underdosing the superior and inferior extremities of the clinical target volume.

Biophysical Phenomena↗
PubMed1998

A method of computationally enhanced detection of chromatogram regions with apparent high relative agonist activity.

An occasional but difficult problem arises in drug discovery during a chromatographic analysis in which high background activity is associated with the presence of most eluting molecular species. This makes the isolation of material of high relative activity difficult. A computational method is shown that clarifies the identification of regions of the chromatogram of interest. The data for bioactivity and absorbance are normalized to percent of maximal response, filtered to raise very small or zero values to a minimal level, and the activity/absorbance ratio is plotted per fraction. The fractions with relatively high activity become evident. This technique is a helpful adjunct to existing graphical methods and provides an objective relationship between the data sets. It is simple to implement with Visual Basic and spreadsheet data, making it widely accessible.

Animals↗
PubMed2004

The molecular structures of pentaborane(9) with halogen substituents in apical and basal positions, determined by electron diffraction and theoretical calculations.

The molecular structures of 1-bromo-pentaborane(9) and 2-bromo-pentaborane(9) in the gas phase have been determined by electron diffraction and ab initio and DFT computational methods. Computational methods have also been applied to the fluoro and chloro analogues, to 1,2-dibromo-pentaborane(9), and to the parent unsubstituted borane. The electronic effects of halogen substitution on the borane cage are remarkably small, particularly for chlorine and bromine substituents, and steric effects are also minimal, even in the compound with two bromine atoms. The largest effects are (a) lengthening of B((base))-B((apex)) bonds adjacent to the halogen in the 2-isomers, with an associated shortening of the opposite base-apex bond, (b) shortening of the B((base))-B((apex)) bond in the 1-fluoro compound, and (c) increase of the B((base))-B((apex))-F angle in 1-F-B(5)H(8), but a decrease in this angle in the 2-bromo compounds.

Journal Article↗
PubMed1995

A fast method to compute surface potentials generated by dipoles within multilayer anisotropic spheres.

Berg and Scherg's fast computation method is extended to multilayer anisotropic spheres. The Berg parameters can be dependent upon a dipole radial parameter or not, depending on the actual sphere conductivities and the layer the dipole is within. To find the Berg parameters, no specific electrode locations are required. Berg and Scherg's method is generally applicable whenever de Munck and Peters's addition-subtraction method can be used.

Anisotropy↗
PubMed1984

Microcomputer analysis of indicator dilution curves to determine Qp/Qs.

We developed and tested, in an animal model, a method for collecting and analyzing indicator dilution curves to determine the pulmonary-to-systemic flow ratio (Qp/Qs) using a programmable microcomputer. Curves were digitized in real time by an analog to digital converter. A gamma variate curve fitting algorithm, similar to that used in nuclear cardiology, was used to determine the area under primary and recirculation portions of a single cardiogreen dye curve. A ratio of these areas was used as a measure of Qp/Qs. In an animal model simulating patent ductus arteriosus, there was close correlation of Qp/Qs measured by the Fick method and by the microcomputer method (computer Qp/Qs = 0.95 X Fick Qp/Qs + 0.22, R = 0.97, N = 14, SEE = 0.14). The computer method of measuring Qp/Qs is rapid, easily repeatable, and does not require catheter manipulation. Therefore, it may be particularly useful in the clinical cardiac catheterization laboratory for studying the effects of interventions on Qp/Qs.

Animals↗
PubMed2004

Synthesis, biological properties, and molecular modeling investigations of novel 3,4-diarylpyrazolines as potent and selective CB(1) cannabinoid receptor antagonists.

A series of novel 3,4-diarylpyrazolines was synthesized and evaluated in cannabinoid (hCB(1) and hCB(2)) receptor assays. The 3,4-diarylpyrazolines elicited potent in vitro CB(1) antagonistic activities and in general exhibited high CB(1) vs CB(2) receptor subtype selectivities. Some key representatives showed potent pharmacological in vivo activities after oral dosing in both a CB agonist-induced blood pressure model and a CB agonist-induced hypothermia model. Chiral separation of racemic 67, followed by crystallization and an X-ray diffraction study, elucidated the absolute configuration of the eutomer 80 (SLV319) at its C(4) position as 4S. Bioanalytical studies revealed a high CNS-plasma ratio for the development candidate 80. Molecular modeling studies showed a relatively close three-dimensional structural overlap between 80 and the known CB(1) receptor antagonist rimonabant (SR141716A). Further analysis of the X-ray diffraction data of 80 revealed the presence of an intramolecular hydrogen bond that was confirmed by computational methods. Computational models and X-ray diffraction data indicated a different intramolecular hydrogen bonding pattern in the in vivo inactive compound 6. In addition, X-ray diffraction studies of 6 revealed a tighter intermolecular packing than 80, which also may contribute to its poorer absorption in vivo. Replacement of the amidine -NH(2) moiety with a -NHCH(3) group proved to be the key change for gaining oral biovailability in this series of compounds leading to the identification of 80.

Administration, Oral↗
PubMed1998

[Methods of computer-assisted molecular modeling].

We present an overview on modern computer methods of molecular modelling. After treating three main steps of drug evaluation, namely target identification, lead identification and lead optimisation, we shortly discuss molecular graphics, molecular mechanics, molecular orbital and molecular dynamics methods. These are suitable for the more-or-less adequate modelling of real molecular processes both at the microscopic and the macroscopic levels. Molecular graphics provides beautiful pictures for the specialist that allow inspection and manipulation of detailed molecular models. An especially useful tool for the visualisation of molecular entities is the display of various properties on the molecular surface that allows rapid recognition of important relationships. Molecular mechanics is able to predict properties (e.g. geometric parameters, conformer stability) of several classes of molecules with an accuracy close to the experimental one, therefore it plays an important role in complementing molecular graphics. The performance of molecular orbital methods increased considerably in the last decade thus we can calculate parameters for isolated or interacting molecules that are not easily amenable to experiment (e.g. structure and energetics of unstable species or activation energies of elementary processes). Computer simulation methods provide a link between gas-phase models of microscopic structures or processes and macroscopic properties or events that may be derived from the former. Thus, it became possible to apply computerised methods for an adequate simulation of important events, like chemical and biochemical reactions, drug-target interactions, drug delivery and the similar that determine drug action. It is stressed that the hardware and software for computer-aided molecular modelling may not be absent from the arsenal of a drug designer.

Computer Graphics↗
PubMed2005

Accurate, efficient, and simple forces computed with quantum Monte Carlo methods.

Computation of ionic forces using quantum Monte Carlo methods has long been a challenge. We introduce a simple procedure, based on known properties of physical electronic densities, to make the variance of the Hellmann-Feynman estimator finite. We obtain very accurate geometries for the molecules H(2), LiH, CH(4), NH(3), H(2)O, and HF, with a Slater-Jastrow trial wave function. Harmonic frequencies for diatomics are also in good agreement with experiment. An antithetical sampling method is also discussed for additional reduction of the variance.

Journal Article↗
PubMed1991

[Quantitative analysis of coronary arteriogram by a computer-assisted method].

A computer-assisted method for quantitating coronary arteriograms was applied to measure the diameter of major epicardial coronary arteries in 58 normal subjects and 25 hypertensive patients, and to determine the percentage of relative stenosis of coronary lesions in 109 patients with coronary artery disease. Average coronary size was larger than normal in patients with hypertension. The left coronary artery was larger than the right coronary artery in the majority of patients. The degree of coronary stenosis can be measured accurately with good reproducibility. Thus this inexpensive microprocessor system provides rapid quantitation of coronary artery diameter and lesions.

Angina Pectoris↗
PubMed1994

A fast method for forward computation of multiple-shell spherical head models.

Using a combination of 3 suitably located dipoles in a homogeneous sphere, the scalp potential due to a dipole source in a 4-shell spherical head model can be approximated with a high degree of precision and a more than 30-fold increase in computing speed. Magnitudes and locations of the 3 equivalent dipoles can be fitted in a homogeneous sphere to data generated from a source at one location in a 4-shell head model. The resulting parameters are used to compute scalp potentials for sources at other locations and orientations. Residual variance measures showed close agreement between the new approximation and a standard 4-shell computation method. Further tests of the method used scalp data from 500 randomly selected pairs of sources generated by the standard 4-shell computation and fitted using, for forward computations, the new approximation and the single-shell Ary-corrected head model. Errors with the new approximation were marginally larger than with the standard computation, but sources were located within 0.5 mm and 0.6 degrees of the original position in 99% of the fits. 99% error limits for the Ary model were up to 18 mm and 25 degrees and depended on the head model parameters.

Brain↗
PubMedDate not supplied

Combination of multiple pencil-beam imaging to computed storage phosphor radiography: a new method.

Computed radiography (CR) with storage phosphors offers a wide dynamic range and improved sensitivity compared to film-screen technology. CR was combined in this study with a prototype multiple pencil-beam (MPB) imaging device which has been shown to be very effective in scatter reduction. The combination was analyzed and compared to the standard technique of grid screening in two ways: a free-response ROC (FROC) analysis was first performed followed by a blinded test arrangement for visual analysis of image quality in a series of computed radiography of the lumbar spine by both the MPB and grid modalities. The results of the FROC study showed a statistically significant (P less than or equal to 0.01) improvement in signal detection. The MPB-CR images of the lumbar spine had more contrast but also a slightly mottled or grainy appearance. Image quality was found good but contrast processing was criticized because it seemed to result in a too steep display of contrast in MPB imaging. This should be avoidable by changing the image processing parameters.

Adult↗
PubMedDate not supplied

[Comparative evaluation of visual function computer examining methods for early diagnosis of glaucoma].

Computer methods for examining the visual functions are compared: computer-aided campymetry from the time of the sensorimotor reaction, computer-aided color campymetry, visocontrastometry, and threshold static perimetry (program 24-2) with Humphrey's visual field analyzer. These methods were used in examinations of 65 patients (105 eyes) with primary open-angle glaucoma at various stages of the disease. A complex of sufficiently sensitive psychophysical methods for examination of the visual functions has been defined, including computer-aided campymetry and visocontrastometry, which may be used for early diagnosis of glaucoma.

Aged↗
PubMedDate not supplied

[Research on the factors determining cellular clonogenic capacity following fractional irradiation by the method of computer simulation modelling].

Methods of multifactor dispersion analysis of variance of the results of imitation model tests were used to estimate the factors that influence the clonogenic capacity of cells after fractionated irradiation. The "interval between fractions" and "the share of cells at G0" were the major factors at different ratios between radioresistance and efficiency of repair of resting and proliferating cells.

Animals↗
PubMed1980

[Effectiveness of computer-assisted methods of evaluation of serial cerebral scintigrams (radionuclide angiography) (author's transl)].

A validation was made of various published methods of computer processing of radionuclide angiography studies of the brain: qualitative and quantitative evaluation of count-rate curves from regular and irregular regions of interest, evaluation of images of the arterial, capillary and venous phase of the tracer transit and the evaluation of function images of the slope, the height of the maximum and the time of the maximum of the regional countrate curves. By logical combination of results from various methods, an attempt was made to improve the final diagnosis in terms of higher sensitivity and simultaneously higher overall accuracy. It was found that the logical "OR" combination of slope function images, qualitative comparison of curves from irregular ROIs and quotient of the maxima of these curves is an "acceptable" processing method for clinicians with average experience in nuclear medicine. This was demonstrated by a comparison of ROC curves.

Brain↗
PubMed1997

A computer-based method for cause of death classification in stillbirths and neonatal deaths.

BACKGROUND: In large-scale epidemiological studies of stillbirths and neonatal deaths a method is needed to replace detailed medical record audits in order to determine the cause of death. METHODS: A computer-based method is presented for determination of the cause of death in stillbirths and in neonatal deaths. It utilizes information in the Swedish medical registries. The study comprises 6044 dead infants born in Sweden from 1983-1990. For each infant the program determines 31 basic characteristics which are important in deciding the cause of death. Based on these characteristics a modified Wigglesworth's classification is used to find the cause of death. The validity of the method was checked by comparing the computer generated information with information obtained by scrutinizing medical records for a 10% representative sample (603 infants). RESULTS: Specificity and sensitivity for each basic characteristic varied, but for the modified Wigglesworth cause of death classification the concordance was 88%. The weakest data refer to intrauterine deaths, where pertinent information was often missing in the medical registries. CONCLUSION: The method can be used for large-scale epidemiological studies.

Cause of Death↗
PubMed1999

Breast cancer: computer simulation method for estimating optimal intervals for screening.

PURPOSE: To develop and evaluate a mathematic method that can be used to determine the optimal screening interval for detection of breast cancer prior to distant metastatic spread. MATERIALS AND METHODS: A computer simulation was developed with the use of biologically based data from the literature on the rates of tumor growth and spread, which can be used to calculate the course of breast cancer growth and metastasis. RESULTS: On the basis of the data available at this time, the results of the simulations suggested that a screening interval of 2 years would result in a 22% reduction in the rate of distant metastatic disease, an interval of 1 year would result in a 51% reduction, and an interval of 6 months would result in an 80% reduction. CONCLUSION: These findings suggest that more frequent screening could dramatically reduce the death rate from breast cancer.

Appointments and Schedules↗
PubMed1995

Blood volume change and redistribution after change in posture.

A computational method developed by LaForte et al., 1992, and Lee, 1994, uses changes in hematocrit, plasma protein concentration, plasma density, or blood density to calculate the fluid restitution from the tissues to the blood, as well as the volume shift from micro- to macrocirculation; this microvascular volume shift is not taken into account by the preexisting methods for computing fluid shifts between the tissues and the blood based on changes in hematocrit. The new computational method was applied to published data obtained in two studies of posture change in humans by Hagan et al., 1978, and by Hinghofer-Szalkay and Moser, 1986. The results support the hypothesis that the microvasculature has the capacity to dilate or constrict so as to absorb a large part of the change in the total blood volume induced by posture change, thus ensuring minimal change in the filling of the macrocirculation.

Blood Proteins↗