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PubMed1990

How to study the kinetic depth effect experimentally.

Sperling, Landy, Dosher, and Perkins (1989) proposed an objective 3D shape identification task with 2D artifactual cues removed and with full feedback (FB) to the subjects to measure KDE and to circumvent algorithmically equivalent KDE-alternative computations and artifactual non-KDE processing. (1) The 2D velocity flow-field was necessary and sufficient for true KDE. (2) Only the first-order (Fourier-based) perceptual motion system could solve our task because the second-order (rectifying) system could not simultaneously process more than two locations. (3) To ensure first-order motion processing, KDE tasks must require simultaneous processing at more than two locations. (4) Practice with FB is essential to measure ultimate capacity (aptitude) and, thereby, to enable comparisons with ideal observers. Experiments without FB measure ecological achievement--the ability of subjects to extrapolate their past experience to the current stimuli.

Algorithms↗
PubMed1992

Prenatal screening for Down's syndrome with use of maternal serum markers.

BACKGROUND: Approximately 35 percent of all cases of Down's syndrome in fetuses can be detected by measuring maternal serum alpha-fetoprotein during the second trimester in the general population of pregnant women. Recent case-control studies indicate that this detection rate could be approximately doubled by measuring serum levels of unconjugated estriol and chorionic gonadotropin, which are abnormally low and abnormally high, respectively, in women carrying fetuses affected by Down's syndrome. METHODS: We prospectively screened 25,207 women and adolescents in the second trimester of pregnancy and assigned each a risk of fetal Down's syndrome with an algorithm that took into account measurements of all three serum markers in combination with maternal age. On this basis, 1661 subjects (6.6 percent) were initially assigned a second-trimester risk of fetal Down's syndrome of at least 1 in 190, and 962 (3.8 percent) were offered amniocentesis for chromosomal analysis after verification of gestational age. Gestational age was determined on the basis of the first day of the last menstrual period or, when available, by ultrasonography. RESULTS: Among the 760 women and adolescents who chose amniocentesis, 20 cases of fetal Down's syndrome were detected, along with 7 other chromosomal disorders. There was 1 additional case of fetal Down's syndrome among the 202 women who chose not to have amniocentesis. The rate of detection of Down's syndrome was thus 58 percent (21 of 36 expected cases), and the frequency of identifying a fetus with Down's syndrome in women undergoing amniocentesis was 1 per 38 amniocenteses (95 percent confidence interval, 1 in 25 to 1 in 62). CONCLUSIONS: Measuring serum alpha-fetoprotein, chorionic gonadotropin, and estriol is more effective in screening for fetal Down's syndrome than measuring maternal serum alpha-fetoprotein alone. Such an expanded protocol can readily be incorporated into existing prenatal screening programs.

Adolescent↗
PubMed1986

Two-view motion analysis: a unified algorithm.

We present a linear algorithm for determining the three-dimensional rotation and translation of a rigid object from two time-sequential perspective views using point correspondences. The algorithm is different from existing ones in two respects. First, various measures for combating noise are incorporated. Second, the algorithm is unified in the sense that, assuming that the surface assumption holds, it can handle both the case of nonzero translation and the case of zero translation.

Algorithms↗
PubMed1994

Machine scoring of somatosensory evoked potentials.

A machine-scoring algorithm was developed for automatic identification and measurement of the positive and negative peaks of short-latency somatosensory evoked potentials (SEPs). The algorithm enables objective and consistent identification and naming of specific components with minimal operator involvement, avoiding inaccuracies and variability resulting from differences in the criteria used by different operators, or by the same operator at different times. The algorithm is based on finite impulse response filtering of wave forms from 4 conventional recording channels at a bandpass of 90-240 Hz. The bandpass was based on the major lobe in power spectra of multiple records and was verified as effective by application to numerous wave forms. Peak identification is based on identifying the peak at its optimal channel and verifying its consistency with corresponding peaks in the other channels. The machine-scoring algorithm was validated on SEPs from 120 subjects. The machine-scored peak latencies obtained with this procedure were significantly correlated with their manually measured counterparts.

Adult↗
PubMed1990

Simultaneous measurements of blood pH, pCO2, pO2 and concentrations of hemoglobin and its derivates--a multicenter study.

During the last few years a need for simultaneous measurements of pH, pCO2, pO2, total hemoglobin concentration, oxygen saturation, carboxyhemoglobin, and methemoglobin has been emphasized. Besides the direct use of such measured quantities a series of algorithms has been developed, especially to describe series of oxygen parameters of the blood. A multicenter study involving 20 hospital centers in Denmark and Sweden was conducted. ABL pH/blood gas analyzers and OSM3 HEMOXIMETERs from Radiometer A/S, Denmark were used. Each center was requested to perform daily quality control procedures using the QUALICHECK quality control system from RADIOMETER. Blood samples were analyzed simultaneously on both types of analyzers using local procedures. During the study 11,700 blood data sets were collected. The quality control procedures showed that the analyzers performed according to specifications with a few exceptions during the study. Measured values of hematocrit were obtained for some samples allowing for calculation of a regression equation for hematocrit and total hemoglobin. Average values for total hemoglobin from arterial and venous samples showed 7.2 mmol/L which is well below the typical normal value of 9.3 mmol/L. This was reflected in the calculated value for total oxygen (oxygen content). The measured quantities made calculation of 2,3-diphosphoglycerate, cDPG, possible. Based on the DPG results, an internal quality procedure has been suggested. Oxygen saturation was calculated based on actual values of pH and pO2 and the standard oxyhemoglobin dissociation curve, and then compared to the measured oxygen saturation. The discrepancy between the calculated and measured values for the different types of blood samples showed that calculation of oxygen saturation should be used with great care for pO2 values below 10 kPa and especially for capillary and umbilical blood samples.

2,3-Diphosphoglycerate↗
PubMed1992

Image comparison techniques for use with megavoltage imaging systems.

In this paper we describe software facilities for enabling patient positioning studies using the megavoltage imaging system developed at the Royal Marsden Hospital and Institute of Cancer Research. The study focuses on the use of the system for three purposes: patient position verification (by comparing images taken at treatment simulation with megavoltage images taken at treatment time); reproducibility studies (by analysing a set of megavoltage images); and set-up correction (by adjusting the set-up until the megavoltage image obtained at treatment registers with the simulation image). The need is discussed for suitably presented simulator images, a method of determining field boundaries and the possibility of delineating soft-tissue interfaces. Several algorithms of different types, developed specifically for the purpose of intercomparison of planar projection images, are presented. The techniques employed and their usefulness, in both the qualitative and the quantitative sense, are discussed. The results are presented of a phantom and clinical study, to evaluate the rigour and reproducibility of the algorithms. These results indicate that measurements can be made to an accuracy of about 1-2 mm, with a similar value for interobserver reproducibility for the best image comparison techniques available.

Algorithms↗
PubMed1995

[Assessment of right ventricular function by magnetic resonance imaging of old myocardial infarction].

The usefulness of magnetic resonance imaging (MRI) for estimating right ventricular function and the influence of left ventricular dysfunction on the performance of the right ventricle were assessed in 43 patients with chronic myocardial infarction (MI) and 14 control subjects (N) using electrocardiography-gated MRI and cardiac catheterization. Patients with MI were divided into three groups according to the location of the coronary lesions; 22 patients with left coronary artery lesion (LCA group), 13 with right coronary artery lesion (RCA group), and 8 with both left and right coronary artery lesions (L+R group). The right ventricular end-diastolic volume (RVEDV) and right ventricular ejection fraction (RVEF) were measured by Simpson's rule algorithm on transverse images of the right ventricle obtained at the end-systolic and end-diastolic phases. In 34 of the 43 patients, the same parameters of right ventricular function were calculated by the thermodilution method using a Swan-Ganz catheter with rapid response thermistor. Left ventricular ejection fraction (LVEF) and end-diastolic volume were determined from left ventriculography. The intraobserver reproducibility (11 cases, r = 0.97) and interobserver reproducibility (11 cases, r = 0.92) of RVEF measured by MRI were excellent. The RVEF and RVEDV determined from MRI were significantly correlated with those from the thermodilution method (RVEF: r = 0.56, RVEDV: r = 0.52). There was no difference in right ventricular end-diastolic volume index in any patient group. The RVEF was decreased in the L+R (41.0 +/- 4.5%, p < 0.01) and RCA (45.9 +/- 6.6%) groups, but there was no difference between the LCA (50.6 +/- 6.6%) and N (48.9 +/- 4.3%) groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

Correcting for the thermodynamic characteristics of a body plethysmograph.

A constant volume body plethysmograph is used to measure changes in total body volume by relating pressure changes measured inside a closed chamber to changes in its volume. The relationship between pressure and volume, however, is complicated by the fact that rapid changes in pressure are accompanied by changes in the temperature of the gas in the plethysmograph. The rate at which the temperature of the gas subsequently approaches that of the environment affects the frequency response of the plethysmograph as a volume measuring instrument. In this paper it is shown that the transient response in plethysmograph pressure to a step change in volume must be a multi-component function, due to the gas near the walls of the plethysmograph approaching thermal equilibrium with the environment at a faster rate than gas near the center. The step response of a 200 L plethysmograph was determined experimentally and found to be well described empirically by a sum of two decaying exponential functions of time. The fitted exponentials were used to construct an algorithm for digitally correcting a measured pressure signal for the effects of the plethysmograph response. When applied to a hypothetical volume waveform over a single breath, an almost perfect correction was obtained.

Animals↗
PubMed1989

Using composite health status measures to assess the nation's health.

Research in progress at the National Center for Health Statistics for evaluating the usefulness of composite measures of health status for assessing the nation's health is described. Three measures suitable for use in the general population, the Health Insurance Experiment-Functional Limitations (HIE-FL), the Health Utility Index (HUI), and the Quality of Well-being (QWB) scale, have been mapped to data collected in the 1980 National Health Interview Survey (NHIS). Analysis using current algorithms for making composite function status measures according to the QWB methods suggests that traditional single indicators of health tend to overestimate the level of health by about 10%. When symptoms and problems are added to the composite function score, the overestimate as measured by the single indicator is at least 50%. The authors are continuing to validate these algorithms, to develop similar ones for the HIE-FL and HUI, and to extend the analysis to data collected in 1977, 1979, and 1984. Current results indicate that to realize fully the benefits of composite measures, well-established, valid, and reliable measures of health-related quality of life should be included as part of the regular NHIS data collection procedures.

Activities of Daily Living↗
PubMed1987

Skeletal measurements using a flying spot digital imaging device.

A flying spot digital imaging unit was devised to measure skeletal length and angles. This device uses a spinning chopper wheel and fixed slit collimator in front of a conventional X-ray tube to produce a scanning pencil beam that passes through the patient and onto an electronic detector. The beam scans the patient transversely and the device moves longitudinally, creating a digital image with a skin dose of less than 2 mrad (0.02 mGy). Patients can be imaged both when upright and when recumbent. A large field of view makes it possible for the entire length of the spine or lower extremities to be included in a single image. Built-in computer algorithms are used to make measurements of skeletal lengths and angles. The accuracy of the digital device was tested by making measurements of known angles and lengths using protractors and rulers. Skeletal measurements were then made on a number of patients. Interobserver error was tested using both patient and nonpatient images. The following patient measurements were made: Cobb angle in 166 patients with scoliosis; knee joint angles in 120 patients undergoing knee surgery; lower extremity lengths in 78 patients with length inequalities; bony fragment angulation and displacement in 30 patients with healing fractures. These studies have shown the device to be accurate with low interobserver error, while delivering much lower patient dose than more conventional methods. The ability to manipulate window levels and widths enables visualization of thick and thin body parts on the same image. Our experience both in the laboratory and with patients has been encouraging, and the method appears to have several advantages over more conventional techniques.

Bone and Bones↗
PubMed1995

Depth dose under narrow shielding blocks: a comparison of measured and calculated dose.

This paper describes measurements done to investigate the accuracy of dose calculation algorithms when used to calculate the dose under shielding blocks. Because the prescribed dose is sometimes limited by the dose to organs at risk within the irradiated volume, it is important to know the dose under a block accurately. Five different algorithms from four treatment planning systems were used to calculate the dose under two narrow lead alloy blocks each placed centrally in a 15 x 15-cm beam of 6- and 18-MV X-rays, respectively. Measurements were done in a water phantom with the same geometrical set-up. All measured data have a common feature; a high surface dose (up to about 20%) decreasing linearly within the first 1-2 cm to a minimum ranging from 13 to 6.5%, and then increasing to a maximum depending on the X-ray energy and block width. Beyond the maximum, the dose decreases approximately linearly due to absorption of the primary beam. The first part of the curve is due essentially to secondary electrons. Beyond the minimum, the X-ray scatter dose component increases, due to increasing phantom scatter, to a maximum which is greater for 6 MV than for 18 MV X-rays. Most algorithms could not reproduce measured data accurately.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1992

Hemodynamic and oxygen transport patterns for outcome prediction, therapeutic goals, and clinical algorithms to improve outcome. Feasibility of artificial intelligence to customize algorithms.

A generalized decision tree or clinical algorithm for treatment of high-risk elective surgical patients was developed from a physiologic model based on empirical data. First, a large data bank was used to do the following: (1) describe temporal hemodynamic and oxygen transport patterns that interrelate cardiac, pulmonary, and tissue perfusion functions in survivors and nonsurvivors; (2) define optimal therapeutic goals based on the supranormal oxygen transport values of high-risk postoperative survivors; (3) compare the relative effectiveness of alternative therapies in a wide variety of clinical and physiologic conditions; and (4) to develop criteria for titration of therapy to the endpoints of the supranormal optimal goals using cardiac index (CI), oxygen delivery (DO2), and oxygen consumption (VO2) as proxy outcome measures. Second, a general purpose algorithm was generated from these data and tested in preoperatively randomized clinical trials of high-risk surgical patients. Improved outcome was demonstrated with this generalized algorithm. The concept that the supranormal values represent compensations that have survival value has been corroborated by several other groups. We now propose a unique approach to refine the generalized algorithm to develop customized algorithms and individualized decision analysis for each patient's unique problems. The present article describes a preliminary evaluation of the feasibility of artificial intelligence techniques to accomplish individualized algorithms that may further improve patient care and outcome.

Algorithms↗
PubMed1986

Estimation of drug binding parameters.

Many methods have been suggested and tested to estimate the association constants and binding capabilities of ligand-macromolecule interactions from experimental data. This problem is a subset of the general problem of parameter estimation for nonlinear algebraic models where both the independent and dependent variables are subject to measurement error. It is often difficult to anticipate the effect on the parameter estimates that is caused by error in the primary measurements. In this work, a computer algorithm is described which finds the maximum likelihood estimate for the true values of the parameters and also estimates for the values of the measurements. It is applied to experimental binding data in two examples for fitting the association constants and binding capacities.

Dicumarol↗
PubMedDate not supplied

Investigation of an FFT-based correlation technique for verification of radiation treatment setup.

Electronic portal imaging devices that capture an image of a patient's treatment field electronically by means of a computer data acquisition system operating in real time are becoming available. This paper reports on a study of a field verification correlation algorithm that can compare each treatment portal image to an image of the correct treatment field positioning. The algorithm requires no human intervention or analysis of the images but rather uses fast Fourier transforms to produce a correlation distribution. The position and amplitude of the correlation distribution maximum were tested as objective measures of translational and rotational differences of subject positions between pairs of images. The concept was tested by using a prototype algorithm to obtain the correlation distributions for images of an Alderson Rando head phantom. Images of the phantom setup with various errors were compared with an image of the phantom in the initial, correct treatment position. Translations, in-plane and out-of-plane rotations, and combinations of translations and rotations were studied. The algorithm accurately measured translations. The value of the correlation distribution maximum was found to be a reasonable candidate for an alignment parameter for which tolerable error thresholds might be established.

Algorithms↗
PubMed1989

Accuracy and reproducibility of clinically acquired two-dimensional echocardiographic mass measurements.

Left ventricular mass (LVM) measurements made by the truncated ellipsoid algorithm from clinical two-dimensional echocardiograms (2DE) were compared to autopsy weights in 37 patients. All six 2DE instruments were calibrated with an ultrasound phantom to standardize LVM measurements. Measurements were made by an experienced echocardiographer (LVME) and by an echocardiographer (LVMN) newly trained in LVM measurement from clinical 2DE tapes of patients with LV weights later confirmed at autopsy. LVME (r = 0.91, SEE +/- 41 gm) were more accurate than LVMN for all 2DE, but LVMN equalled LVME in accuracy for technically good 2DE. Interobserver variability was 36 gm, or 17% of LVM for all 2DE, and fell to 27 gm, or 12% of LVM for technically good 2DE. Segmental wall motion abnormalities and time from 2DE to death did not influence measurement accuracy significantly. LVM measurements by the 2DE truncated ellipsoid formula are accurate and reproducible in patients with normal and abnormal hearts.

Adult↗
PubMed1990

Physics of gamma knife approach on convergent beams in stereotactic radiosurgery.

The Presbyterian-University Hospital of Pittsburgh installed the first clinically designated Leksell gamma knife in the U.S. in August 1987. Gamma knife radiosurgery involves stereotactic target localization with the Leksell frame and subsequent closed-skull single-treatment session irradiation of a lesion with multiple highly focused gamma ray beams produced from 60Co sources. The hemispherical array of sources, the large number of small-diameter beams, and the steep dose gradients surrounding a targeted lesion make physical characterization of the radiation field complex. This paper describes the physical features and the operation of the gamma knife as well as the calibration procedures of the very small, well-collimated beams. The results of studies using in-phantom ion chamber, diode, film, and lithium fluoride thermoluminescent dosimetry were all in close agreement. Both single-beam and multiple-beam dose profiles were measured and reported for the interchangeable helmets, which have 4-, 8-, 14-, and 18-mm-diameter collimators. We also describe the dose calculation and treatment planning algorithm in the treatment planning system. Measurements of the accuracy of mechanical and radiation alignment are also performed and discussed.

Brain Diseases↗
PubMed2026

PaNDA: Efficient Optimization of Phylogenetic Diversity in Networks.

Phylogenetic diversity (PD) plays an important role in biodiversity, conservation, and evolutionary studies by measuring the diversity of a set of taxa based on their phylogenetic relationships. In phylogenetic trees, a subset of k taxa with maximum PD can be found by a simple and efficient greedy algorithm. However, this algorithmic tractability is lost when considering phylogenetic networks, which incorporate reticulate evolutionary events such as hybridization and horizontal gene transfer. To address this challenge, we introduce PaNDA (Phylogenetic Network Diversity Algorithms), the first software package and interactive graphical user-interface for exploring, visualizing, and maximizing diversity in phylogenetic networks. PaNDA includes a novel algorithm to find a subset of k taxa with maximum diversity, running in polynomial time for networks of bounded scanwidth, a measure of tree-likeness of a network that grows slower than the well-known level measure. This algorithm considers the variant of PD on networks in which the branch lengths of all paths from the root to the selected taxa contribute towards their diversity. We demonstrate the scalability of this algorithm on simulated networks, successfully analyzing level-15 networks with up to 200 taxa in seconds. We also provide a proof-of-concept analysis using a phylogenetic network on Xiphophorus species, illustrating how the tool can support diversity studies based on real genomic data. The software is easily installable and freely available at https://github.com/nholtgrefe/panda. Additionally, we extend the definition of PD to semi-directed phylogenetic networks, which are mixed graphs increasingly used in phylogenetic analysis to model uncertainty of the root location. We prove that finding a subset of k taxa with maximum diversity remains NP-hard on semi-directed networks, but do present a polynomial-time algorithm for networks with bounded level.

network↗
PubMed1991

Critically ill patients have high basal growth hormone levels with attenuated oscillatory activity associated with low levels of insulin-like growth factor-I.

OBJECTIVE: The aim was to study the relationship between growth hormone (GH) and insulin-like growth factor-I (IGF-I) in critically ill patients. DESIGN: Case-control study of critically ill patients admitted to the intensive care unit was carried out. PATIENTS: Six critically ill patients (51-78 years) who required ventilation and parenteral nutrition and six age, weight, height, and sex-matched healthy adults were studied. MEASUREMENTS: The patients and controls were studied for two 24-hour periods; the patients before and after starting parenteral feeding, and the controls during a 36-hour fast and when taking meals equivalent in calories and protein to the patients' parenteral feed. Serum GH was measured at 20-minute intervals and analysed by a pulse detection algorithm (Pulsar) and Fourier transformation. IGF-I was measured at 0, 12, and 24 hours. RESULTS: Patients had low serum IGF-I levels compared with controls, whether fasted or fed, despite having mean GH levels similar to fasted controls. For fasted patients vs fasted controls the mean (+/- 1 SD) GH levels were 4.5 +/- 2.0 vs 4.0 +/- 2.4 mU/l respectively, and IGF-I levels at the end of the fast were 0.17 +/- 0.11 vs 0.78 +/- 0.29 U/ml (P = 0.003). Patients showed elevated baseline GH levels compared with controls when fasted and during parenteral feeding (patients vs controls fasted 3.1 +/- 1.9 vs 0.8 +/- 0.5 mU/l, P = 0.01; patients vs controls fed 4.2 +/- 4.5 vs 0.5 +/- 0.04 mU/l, P = 0.028). Fourier transformation confirmed oscillatory GH levels in the controls, fasted or fed, but this activity was attenuated in the patients. Parenteral feeding had no effect on the GH profiles or IGF-I levels of patients, but controls showed greater mean GH levels during their fast than when fed. CONCLUSIONS: We have demonstrated that critically ill patients have low IGF-I levels associated with augmented baseline GH levels which show reduced oscillatory activity. The results would be compatible with the hypothesis that there is an adaptive change in critically ill patients away from the indirect effects of GH (stimulation of IGF-I production and anabolism) and toward the direct effects (lipolysis and insulin antagonism) which increase the availability of energy substrates. The pattern of GH levels seen in our patients may be important in this adaptation.

Abdomen↗