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Results for “Optimism”

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At least 253 records · Page 14Linked to original sources

PubMed2005

Temporo-spatial IMRT optimization: concepts, implementation and initial results.

With the recent availability of 4D-CT, the accuracy of information on internal organ motion during respiration has improved significantly. We investigate the utility of organ motion information in IMRT treatment planning, using an in-house prototype optimization system. Four approaches are compared: (1) planning with optimized margins, based on motion information; (2) the 'motion kernel' approach, in which a more accurate description of the dose deposit from a pencil beam to a moving target is achieved either through time-weighted averaging of influence matrices, calculated for different instances of anatomy (subsets of 4D-CT data, corresponding to various phases of motion) or through convolution of the pencil beam kernel with the probability density function describing the target motion; (3) optimal gating, or tracking with beam intensity maps optimized independently for each instance of anatomy; and (4) optimal tracking with beam intensity maps optimized simultaneously for all instances of anatomy. The optimization is based on a gradient technique and can handle both physical (dose-volume) and equivalent uniform dose constraints. Optimization requires voxel mapping from phase to phase in order to score the dose in individual voxels as they move. The results show that, compared to the other approaches, margin expansion has a significant disadvantage by substantially increasing the integral dose to patient. While gating or tracking result in the best dose conformation to the target, the former elongates treatment time, and the latter significantly complicates the delivery procedure. The 'motion kernel' approach does not provide a dosimetric advantage, compared to optimal tracking or gating, but might lead to more efficient delivery. A combination of gating with the 'motion kernel' or margin expansion approach will increase the duty cycle and may provide one with the most efficient solution, in terms of complexity of the delivery procedure and dose conformality to the target.

Algorithms↗

PubMed2005

High-resolution temperature-based optimization for hyperthermia treatment planning.

In regional hyperthermia, optimization techniques are valuable in order to obtain amplitude/phase settings for the applicators to achieve maximal tumour heating without toxicity to normal tissue. We implemented a temperature-based optimization technique and maximized tumour temperature with constraints on normal tissue temperature to prevent hot spots. E-field distributions are the primary input for the optimization method. Due to computer limitations we are restricted to a resolution of 1 x 1 x 1 cm3 for E-field calculations, too low for reliable treatment planning. A major problem is the fact that hot spots at low-resolution (LR) do not always correspond to hot spots at high-resolution (HR), and vice versa. Thus, HR temperature-based optimization is necessary for adequate treatment planning and satisfactory results cannot be obtained with LR strategies. To obtain HR power density (PD) distributions from LR E-field calculations, a quasi-static zooming technique has been developed earlier at the UMC Utrecht. However, quasi-static zooming does not preserve phase information and therefore it does not provide the HR E-field information required for direct HR optimization. We combined quasi-static zooming with the optimization method to obtain a millimetre resolution temperature-based optimization strategy. First we performed a LR (1 cm) optimization and used the obtained settings to calculate the HR (2 mm) PD and corresponding HR temperature distribution. Next, we performed a HR optimization using an estimation of the new HR temperature distribution based on previous calculations. This estimation is based on the assumption that the HR and LR temperature distributions, though strongly different, respond in a similar way to amplitude/phase steering. To verify the newly obtained settings, we calculate the corresponding HR temperature distribution. This method was applied to several clinical situations and found to work very well. Deviations of this estimation method for the AMC-4 system were typically smaller than 0.2 degrees C in the volume of interest, which is accurate enough for treatment planning purposes.

Body Burden↗

PubMed1998

The transepicondylar axis approximates the optimal flexion axis of the knee.

The traditional understanding of knee kinematics holds that no single fixed axis of rotation exists in the knee. In contrast, a recent hypothesis suggests that knee kinematics are better described simply as two simultaneous rotations occurring about fixed axes. Knee flexion and extension occurs about an optimal flexion axis fixed in the femur, whereas tibial internal and external rotations occur about a longitudinal rotation axis fixed in the tibia. No other translations or rotations exist. This hypothesis has been tested. Tibiofemoral kinematics were measured for 15 cadaveric knees undergoing a realistic loadbearing activity (simulated squatting). An optimization technique was used to identify the locations of the optimal flexion and longitudinal rotation axes such that simultaneous rotations about them could best represent the measured kinematics. The optimal flexion axis was compared with the transepicondylar axis defined by bony landmarks. The longitudinal rotation axis was found to pass through the medial joint compartment. The optimal flexion axis passed through the centers of the posterior femoral condyles. No significant difference was found between the optimal flexion and transepicondylar axes. To an average accuracy of better than 3.4 mm in translation, and 2.9 degrees in orientation, knee kinematics were represented successfully by simple rotations about the optimal flexion and longitudinal rotation axes. The optimal flexion axis is fixed in the femur and can be considered the true flexion axis of the knee. The transepicondylar axis axis, which is identified easily by palpation, closely approximates the optimal flexion axis.

Adult↗

PubMed2004

A longitudinal study of the association between treatment optimism and sexual risk behavior in young adult gay and bisexual men.

To determine whether optimism about highly active antiretroviral therapy is associated with sexual risk behavior among young adult HIV-negative gay and bisexual men, and to test 2 alternative explanations for this association: that treatment optimism leads to increased sexual risk or that treatment optimism is the result of previous sexual risk. Data on sexual risk behavior, treatment optimism, and perceived susceptibility to HIV infection were obtained from a sample of 538 HIV-negative or untested gay and bisexual men (ages 18-30) who were not in monogamous relationships. Follow-up data were collected 18 months later. In the cross-sectional data, treatment optimism was associated with the 2-month cumulative incidence of unprotected anal intercourse (UAI) with nonprimary partners; however, this effect was observed only among men who felt highly susceptible to HIV infection. Longitudinal analyses revealed that treatment optimism did not predict subsequent UAI, but UAI did predict later treatment optimism. Treatment optimism is associated with sexual risk behavior among young adult gay and bisexual men. However, these data suggest that optimism may result from, rather than precede, sexual risk.

Adolescent↗

PubMed2004

Optimal restraint reduces the risk of abdominal injury in children involved in motor vehicle crashes.

BACKGROUND: The American Academy of Pediatrics has established guidelines for optimal, age-appropriate child occupant restraint. While optimal restraint has been shown to reduce the risk of injuries overall, its effect on specific types of injuries, in particular abdominal injuries, has not been demonstrated. METHODS: Cross-sectional study of children aged younger than 16 years in crashes of insured vehicles in 15 states, with data collected via insurance claims records and a telephone survey. A probability sample of 10927 crashes involving 17132 restrained children, representing 210926 children in 136734 crashes was collected between December 1, 1998 and May 31, 2002. Restraint use was categorized as optimal or suboptimal based on current American Academy of Pediatrics guidelines. The outcome of interest, abdominal injury, was defined as any reported injury to an intra-abdominal organ of Abbreviated Injury Scale >or=2 severity. RESULTS: Among all restrained children, optimal was noted in 59% (n = 120473) and suboptimal in 41% (n = 83555). An associated abdominal organ injury was noted in 0.05% (n = 62) of the optimal restrained group and 0.17% (n = 140) of the suboptimal group. After adjusting for age and seating position (front vs. rear), optimally restrained children were more than 3 times less likely [odds ratio 3.51 (95% confidence interval, 1.87-6.60, P < 0.001)] as suboptimally restrained children to suffer an abdominal injury. Of note, there were no abdominal injuries reported among optimally restrained 4- to 8-year-olds. CONCLUSIONS: Optimally restrained children are at a significantly lower risk of abdominal injury than children suboptimally restrained for age. This disparity emphasizes the need for aggressive education efforts aimed not only at getting children into restraint systems, but also the importance of optimal, age-appropriate restraint.

Abdominal Injuries↗

PubMed1998

Optimal CT scanning plan for long-bone 3-D reconstruction.

Digital computed tomographic (CT) data are widely used in three-dimensional (3-D) reconstruction of bone geometry and density features for 3-D) modeling purposes. During in vivo CT data acquisition the number of scans must be limited in order to protect patients from the risks related to X-ray absorption. Aim of this work is to automatically define, given a finite number of CT slices, the scanning plan which returns the optimal 3-D) reconstruction of a bone segment from in vivo acquired CT images. An optimization algorithm based on a Discard-Insert-Exchange technique has been developed. In the proposed method the optimal scanning sequence is searched by minimizing the overall reconstruction error of a two-dimensional (2-D) prescanning image: an anterior-posterior (AP) X-ray projection of the bone segment. This approach has been validated in vitro on three different femurs. The 3-D reconstruction errors obtained through the optimization of the scanning plan on the 2-D) prescanning images and on the corresponding 3-D data sets have been compared. Two-dimensional and 3-D data sets have been reconstructed by linear interpolation along the longitudinal axis. Results show that direct 3-D optimization yields root mean square reconstruction errors which are only 4%-7% lower than the 2-D-optimized plan, thus proving that 2-D-optimization provides a good suboptimal scanning plan for 3-D reconstruction. Further on, 3-D reconstruction errors given by the optimized scanning plan and a standard radiological protocol for long bones have been compared. Results show that the optimized plan yields 20%-50% lower 3-D reconstruction errors.

Algorithms↗

PubMed1999

Multiobjective genetic optimization of diagnostic classifiers with implications for generating receiver operating characteristic curves.

It is well understood that binary classifiers have two implicit objective functions (sensitivity and specificity) describing their performance. Traditional methods of classifier training attempt to combine these two objective functions (or two analogous class performance measures) into one so that conventional scalar optimization techniques can be utilized. This involves incorporating a priori information into the aggregation method so that the resulting performance of the classifier is satisfactory for the task at hand. We have investigated the use of a niched Pareto multiobjective genetic algorithm (GA) for classifier optimization. With niched Pareto GA's, an objective vector is optimized instead of a scalar function, eliminating the need to aggregate classification objective functions. The niched Pareto GA returns a set of optimal solutions that are equivalent in the absence of any information regarding the preferences of the objectives. The a priori knowledge that was used for aggregating the objective functions in conventional classifier training can instead be applied post-optimization to select from one of the series of solutions returned from the multiobjective genetic optimization. We have applied this technique to train a linear classifier and an artificial neural network (ANN), using simulated datasets. The performances of the solutions returned from the multiobjective genetic optimization represent a series of optimal (sensitivity, specificity) pairs, which can be thought of as operating points on a receiver operating characteristic (ROC) curve. All possible ROC curves for a given dataset and classifier are less than or equal to the ROC curve generated by the niched Pareto genetic optimization.

Algorithms↗

PubMed2005

Evolutionary optimization of a hierarchical object recognition model.

A major problem in designing artificial neural networks is the proper choice of the network architecture. Especially for vision networks classifying three-dimensional (3-D) objects this problem is very challenging, as these networks are necessarily large and therefore the search space for defining the needed networks is of a very high dimensionality. This strongly increases the chances of obtaining only suboptimal structures from standard optimization algorithms. We tackle this problem in two ways. First, we use biologically inspired hierarchical vision models to narrow the space of possible architectures and to reduce the dimensionality of the search space. Second, we employ evolutionary optimization techniques to determine optimal features and nonlinearities of the visual hierarchy. Here, we especially focus on higher order complex features in higher hierarchical stages. We compare two different approaches to perform an evolutionary optimization of these features. In the first setting, we directly code the features into the genome. In the second setting, in analogy to an ontogenetical development process, we suggest the new method of an indirect coding of the features via an unsupervised learning process, which is embedded into the evolutionary optimization. In both cases the processing nonlinearities are encoded directly into the genome and are thus subject to optimization. The fitness of the individuals for the evolutionary selection process is computed by measuring the network classification performance on a benchmark image database. Here, we use a nearest-neighbor classification approach, based on the hierarchical feature output. We compare the found solutions with respect to their ability to generalize. We differentiate between a first- and a second-order generalization. The first-order generalization denotes how well the vision system, after evolutionary optimization of the features and nonlinearities using a database A, can classify previously unseen test views of objects from this database A. As second-order generalization, we denote the ability of the vision system to perform classification on a database B using the features and nonlinearities optimized on database A. We show that the direct feature coding approach leads to networks with a better first-order generalization, whereas the second-order generalization is on an equally high level for both direct and indirect coding. We also compare the second-order generalization results with other state-of-the-art recognition systems and show that both approaches lead to optimized recognition systems, which are highly competitive with recent recognition algorithms.

Algorithms↗

PubMed1999

Optimal diversity-dependent contributions of genotypes to mixtures.

Deployment of genotypes to a production population decisively depends on the measure of diversity, a consideration that parallels genetic gain in the management of genotype mixtures. Optimal diversity-dependent deployment has been developed in this study for a family of diversity indices in the genetical and ecological context. The optimal solution at given diversity was expressed as the relationship between genotype contributions and their genetic performances, which maximized genetic gain. Numerical calculations were performed by using genotypes generated from normal order statistics. An optimal deployment in one situation could be nonoptimum in another. Classical uniform deployment, where superior genotypes equally contribute to the mixtures, was the limit of optimal deployment. Comparisons were made between optimal and uniform deployment and between optimal and nonoptimal deployment where genotypes contributed proportionally to the mixtures in accordance to their genetic superiority. The superiority in gain of optimal deployment over that of uniform deployment increased as the difference between the diversity measure under optimal deployment and the contributing number (N) of genotypes under uniform deployment became large and as the diversity measure and N under optimal deployment increased. The superiority over nonoptimal deployment increased rapidly at low diversity, reaching a maximum somewhere at diversity between 1 and N. Scale of superiority depended on the similitude between optimum and nonoptimum deployment; the larger the distinctiveness, the greater the superiority.

Agriculture↗

PubMed2004

Optimization of submerged culture requirements for the production of mycelial growth and exopolysaccharide by Cordyceps jiangxiensis JXPJ 0109.

AIMS: The objective of the present study was to investigate the optimal culture requirements for mycelial growth and exopolysaccharide production by Cordyceps jiangxiensis JXPJ 0109 in submerged culture. METHODS AND RESULTS: The effects of medium ingredients (i.e. carbon and nitrogen sources, and growth factor) and other culture requirements (i.e. initial pH, temperature, etc.) on the production of mycelia and exopolysaccharide were observed using a one-factor-at-a-time method. More suitable culture requirements for mycelial growth and exopolysaccharide production were proved to be maltose, glycerol, tryptone, soya bean steep powder, yeast extract, medium capacity 200 ml in a 500-ml flask, agitation rate 180 rev min(-1), seed age 4-8 days, inoculum size 2.5-7.5% (v/v), etc. The optimal temperatures and initial pHs for mycelial growth and exopolysaccharide production were at 26 degrees C and pH 5 and at 28 degrees C and pH 7, respectively, and corresponding optimal culture age were observed to be 8 and 10 days respectively. According to the primary results of the one-factor-at-a-time experiments, the optimal medium for the mycelial growth and exopolysaccharide production were obtained using an orthogonal layout method to optimize further. Herein the effects of medium ingredients on the mycelial growth of C. jiangxiensis JXPJ 0109 were in the order of yeast extract > tryptone > maltose > CaCl2 > glycerol > MgSO4 > KH2PO4 and the optimal concentration of each composition was 15 g maltose (food-grade), 10 g glycerol, 10 g tryptone, 10 g yeast extract, 1 g KH2PO4, 0.2 g MgSO4, and 0.5 g CaCl2 in 1 l of distilled water, while the order of effects of those components on exopolysaccharide production was yeast extract > maltose > tryptone > glycerol > KH2PO4 > CaCl2 > MgSO4, corresponding to the optimal concentration of medium was as follows: 20 g maltose (food-grade), 8 g glycerol, 5 g tryptone, 10 g yeast extract, 1 g KH2PO4, and 0.5 g CaCl2 in 1 l of distilled water. CONCLUSIONS: Under the optimal culture requirements, the maximum exopolysaccharide production reached 3.5 g l(-1) after 10 days of fermentation, while the maximum production of mycelial growth achieved 14.5 g l(-1) after 8 days of fermentation. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report on the submerged culture requirements for mycelial growth and exopolysaccharide in C. jiangxiensis, and this two-step optimization strategy in this study can be widely applied to other microbial fermentation processes.

Carbon↗

PubMed1995

Choosing the optimal monophasic and biphasic waveforms for ventricular defibrillation.

INTRODUCTION: The truncated exponential waveform from an implantable cardioverter defibrillator can be described by three quantities: the leading edge voltage, the waveform duration, and the waveform time constant (tau s). The goal of this work was to develop and test a mathematical model of defibrillation that predicts the optimal durations for monophasic and the first phase of biphasic waveforms for different tau s values. In 1932, Blair used a parallel resistor-capacitor network as a model of the cell membrane to develop an equation that describes stimulation using square waves. We extended Blair's model of stimulation, using a resistor-capacitor network time constant (tau m), equal to 2.8 msec, to explicitly account for the waveform shape of a truncated exponential waveform. This extended model predicted that for monophasic waveforms with tau s of 1.5 msec, leading edge voltage will be constant for waveforms 2 msec and longer; for tau s of 3 msec, leading edge voltage will be constant for waveforms 3 msec and longer; for tau s of 6 msec, leading edge voltage will be constant for waveforms 4 msec and longer. We hypothesized that the best phase 1 of a biphasic waveform is the best monophasic waveform. Therefore, the optimal first phase of a biphasic waveform for a given tau s is the same as the optimal monophasic waveform. METHODS AND RESULTS: We tested these hypotheses in two animal experiments. Part I: Defibrillation thresholds were determined for monophasic waveforms in eight dogs. For tau s of 1.5 msec, waveforms were truncated at 1, 1.5, 2, 2.5, 3, 4, 5, and 6 msec. For tau s of 3 msec, waveforms were truncated at 1,2,3,4,5,6, and 8 msec. For tau s of 6 msec, waveforms were truncated at 2,3,4,5,6,8, and 10 msec. For waveforms with tau s of 1.5, leading edge voltage was not significantly different for the waveform durations of 1.5 msec and longer. For waveforms with tau s of 3 msec, leading edge voltage was not significantly different for waveform durations of 2 msec and longer. For waveforms with tau s of 6 msec, there was no significant difference in leading edge voltage for the waveforms tested. Part II: Defibrillation thresholds were determined in another eight dogs for the same three tau s values. For each value of tau s, six biphasic waveforms were tested: 1/1, 2/2, 3/3, 4/4, 5/5, and 6/6 msec. For waveforms with tau s of 1.5 msec, leading edge voltage was a minimum for the 2/2 msec waveform. For waveforms with tau s of 3 msec, leading edge voltage was a minimum for the 3/3 msec waveform. For waveforms with tau s of 6 msec, leading edge voltage was a minimum and not significantly different for the 3/3, 4/4, 5/5, and 6/6 msec waveforms. CONCLUSIONS: The model predicts the optimal monophasic duration and the first phase of a biphasic waveform to within 1 msec as tau s varies from 1.5 to 6 msec: for tau s equal to 1.5 msec, the optimal monophasic waveform duration and the optimal first phase of a biphasic waveform is 2 msec, for tau s equal to 3.0 msec, the optimal duration is 3 msec, and for tau s equal to 6 msec, the optimal duration is 4 msec. For both monophasic and biphasic waveforms, optimal waveform duration shortens as the waveform time constant shortens.

Animals↗

PubMed1999

Prediction of antagonistic muscle forces using inverse dynamic optimization during flexion/extension of the knee.

This paper examined the feasibility of using different optimization criteria in inverse dynamic optimization to predict antagonistic muscle forces and joint reaction forces during isokinetic flexion/extension and isometric extension exercises of the knee. Both quadriceps and hamstrings muscle groups were included in this study. The knee joint motion included flexion/extension, varus/valgus, and internal/external rotations. Four linear, nonlinear, and physiological optimization criteria were utilized in the optimization procedure. All optimization criteria adopted in this paper were shown to be able to predict antagonistic muscle contraction during flexion and extension of the knee. The predicted muscle forces were compared in temporal patterns with EMG activities (averaged data measured from five subjects). Joint reaction forces were predicted to be similar using all optimization criteria. In comparison with previous studies, these results suggested that the kinematic information involved in the inverse dynamic optimization plays an important role in prediction of the recruitment of antagonistic muscles rather than the selection of a particular optimization criterion. Therefore, it might be concluded that a properly formulated inverse dynamic optimization procedure should describe the knee joint rotation in three orthogonal planes.

Algorithms↗

PubMed2003

Therapeutic treatment plan optimization with probability density-based dose prescription.

The dose optimization in inverse planning is realized under the guidance of an objective function. The prescription doses in a conventional approach are usually rigid values, defining in most instances an ill-conditioned optimization problem. In this work, we propose a more general dose optimization scheme based on a statistical formalism [Xing et al., Med. Phys. 21, 2348-2358 (1999)]. Instead of a rigid dose, the prescription to a structure is specified by a preference function, which describes the user's preference over other doses in case the most desired dose is not attainable. The variation range of the prescription dose and the shape of the preference function are predesigned by the user based on prior clinical experience. Consequently, during the iterative optimization process, the prescription dose is allowed to deviate, with a certain preference level, from the most desired dose. By not restricting the prescription dose to a fixed value, the optimization problem becomes less ill-defined. The conventional inverse planning algorithm represents a special case of the new formalism. An iterative dose optimization algorithm is used to optimize the system. The performance of the proposed technique is systematically studied using a hypothetical C-shaped tumor with an abutting circular critical structure and a prostate case. It is shown that the final dose distribution can be manipulated flexibly by tuning the shape of the preference function and that using a preference function can lead to optimized dose distributions in accordance with the planner's specification. The proposed framework offers an effective mechanism to formalize the planner's priorities over different possible clinical scenarios and incorporate them into dose optimization. The enhanced control over the final plan may greatly facilitate the IMRT treatment planning process.

Algorithms↗

PubMed2005

Optimizing the automatic segmentation of the left ventricle in magnetic resonance images.

Automatic segmentation of the left ventricular (LV) myocardial borders in cardiovascular MR (CMR) images allows a significant speed-up of the procedure of quantifying LV function, and improves its reproducibility. The automated boundary delineation is usually based on a set of parameters that define the algorithms. Since the automatic segmentation algorithms are usually sensitive to the image quality and frequently depend heavily on the acquisition protocol, optimizing the parameters of the algorithm for such different protocols may be necessary to obtain optimal results. In other words, using a default set of parameters may be far from optimal for different scanners or protocols. For the MASS-software, for example, this means that a total of 14 parameters need to be optimized. This optimization is a difficult and labor-intensive process. To be able to more consistently and rapidly tune the parameters, an automated optimization system would be extremely desirable. In this paper we propose such an approach, which is based on genetic algorithms (GAs). The GA is an unsupervised iterative tool that generates new sets of parameters and converges toward an optimal set. We implemented and compared two different types of the genetic algorithms: a simple GA (SGA) and a steady state GA (2SGA). The difference between these two algorithms lies in the characteristics of the generated populations: "nonoverlapping populations" and "overlapping populations," respectively "nonoverlapping" population means that the two populations are disjoint, and "overlapping" means that the best parameters found in the previous generation are included in the present population. The performance of both algorithms was evaluated on twenty routinely obtained short-axis examinations (eleven examinations acquired with a steady-state free precession pulse sequence, and nine examinations with a gradient echo pulse sequence). The optimal parameters obtained with the GAs were used for the LV myocardial border delineation. Finally, the automatically outlined contours were compared to the gold standard--manually drawn contours by experts. The result of the comparison was expressed as a degree of similarity after a processing time of less than 72 h to a 59.5% of degree of similarity for SGA and a 66.7% of degree of similarity for 2SGA. In conclusion, genetic algorithms are very suitable to automatically tune the parameters of a border detection algorithm. Based on our data, the 2SGA was more suitable than the SGA method. This approach can be generalized to other optimization problems in medical image processing.

Algorithms↗

PubMed1998

Evaluation of the OptiMAL test for rapid diagnosis of Plasmodium vivax and Plasmodium falciparum malaria.

The development of rapid and specific diagnostic tests to identify individuals infected with malaria is of paramount importance in efforts to control the severe public health impact of this disease. This study evaluated the ability of a newly developed rapid malaria diagnostic test, OptiMAL (Flow Inc., Portland, Oreg.), to detect Plasmodium vivax and Plasmodium falciparum malaria during an outbreak in Honduras. OptiMAL is a rapid (10-min) malaria detection test which utilizes a dipstick coated with monoclonal antibodies against the intracellular metabolic enzyme parasite lactate dehydrogenase (pLDH). Differentiation of malaria parasites is based on antigenic differences between the pLDH isoforms. Since pLDH is produced only by live Plasmodium parasites, this test has the ability to differentiate live from dead organisms. Results from the OptiMAL test were compared to those obtained by reading 100 fields of traditional Giemsa-stained thick-smear blood films. Whole-blood samples were obtained from 202 patients suspected of having malaria. A total of 96 samples (48%) were positive by blood films, while 91 (45%) were positive by the OptiMAL test. The blood films indicated that 82% (79 of 96) of the patients were positive for P. vivax and 18% (17 of 96) were infected with P. falciparum. The OptiMAL test showed that 81% (74 of 91) were positive for P. vivax and 19% (17 of 91) were positive for P. falciparum. These results demonstrated that the OptiMAL test had sensitivities of 94 and 88% and specificities of 100 and 99%, respectively, when compared to traditional blood films for the detection of P. vivax and P. falciparum malaria. Blood samples not identified by OptiMAL as malaria positive normally contained parasites at concentrations of less than 100/microl of blood. Samples found to contain P. falciparum were further tested by two other commercially available rapid malaria diagnostic tests, ParaSight-F (Becton Dickinson, Cockeysville, Md.) and ICT Malaria P.f. (ICT Diagnostics, Sydney, Australia), both of which detect only P. falciparum. Only 11 of the 17 (65%) P. falciparum-positive blood samples were identified by the ICT and ParaSight-F tests. Thus, OptiMAL correctly identified P. falciparum malaria parasites in patient blood samples more often than did the other two commercially available diagnostic tests and showed an excellent correlation with traditional blood films in the identification of both P. vivax malaria and P. falciparum malaria. We conclude that the OptiMAL test is an effective tool for the rapid diagnosis of malaria.

Humans↗

PubMed1993

Constrained optimization of ventricular efficiency in normal and failing hearts.

Optimal ventriculoarterial coupling, in terms of maximal energetic efficiency, was recently analyzed by analytic and experimental studies. Whereas for normal hearts the analytic predictions agreed well with measured data, failing hearts were found to operate remote from the predicted optimal conditions. An analysis of optimal coupling is developed in the present study, based on constrained optimization. The constraints are based on the concept that the system must comply with physiological requirements (restrictions) under all conditions. Optimization using the mean pressure as a constraint yielded results similar to the unconstrained case in the normal heart but different with the failing heart: in the failing heart the optimal arterial elastance was found to be larger than the ventricular elastance, whereas the opposite was predicted by the unconstrained optimization. If an additional constraint on the end-systolic pressure is used, a unique solution of the coupling state is obtained. The predicted coupling ratio was found to match published data from normal subjects and heart failure patients, where in the latter group it was found to be remote from the optimal efficiency state. An increase in ventricular contractility and reduction in afterload were shown to shift the nonoptimal coupling state toward the optimal one. This prediction complies with the use of inotropic agents and vasodilators as the mainstay of heart failure treatment. This study may provide a convenient framework of analysis for the assessment of the ventriculoarterial coupling and for the evaluation of the cardiovascular effects of specific drug treatments.

Blood Pressure↗

PubMed2006

Dispositional optimism and health behaviour in community-dwelling older people: associations with healthy ageing.

OBJECTIVE: Dispositional optimism measured with the Life Orientation Test has been associated with a variety of health outcomes. We assessed whether optimism was related to indices of healthy ageing, and if effects were mediated through health behaviours. METHOD: A community sample of 128 men and women aged 65 to 80 years was recruited from general practice lists. Optimism and health behaviours were assessed by questionnaire, and healthy ageing indexed by physical health summary scores from the Short Form 36, and by self-rated health. RESULTS: Optimism was associated with not smoking, moderate alcohol consumption, brisk walking, and vigorous physical activities (women only), independently of socio-demographic factors and clinical condition. Physical health status was associated with optimism, independently of socio-demographic factors, clinical condition, negative affectivity, and body mass. This effect was attenuated when health behaviours were taken into account. Self-rated health was also positively related to optimism, and this association was not mediated by health behaviours. Neither the optimism nor pessimism subscales of the Life Orientation Test showed as consistent effects as the full scale. CONCLUSIONS: We conclude that dispositional optimism is associated with healthy ageing. The relationship between optimism and healthy ageing was only partly mediated by the health behaviours assessed in this sample.

Affect↗

PubMedDate not supplied

Optimization of temperature distributions in scanned, focused ultrasound hyperthermia.

Scanned, focused ultrasound systems (SFUS) have considerable flexibility in shaping the power deposition field during hyperthermia treatments. When utilizing this adaptability many complicated, interacting decisions must be made to obtain an optimal steady-state temperature distribution. This optimization problem is studied using a 3-D, radially symmetric simulation program which searches for a set of optimal scan parameters. The conjugate-gradient optimization technique with a golden section search was used to obtain the optimal temperature distributions attainable with a single circular scan of a tumour. The variable scan parameters of the single transducer heating system optimized (and under the control of the therapist) are: transducer tilt and rotation angles, focal depth, output acoustical power, and scan radius. This single scan study includes the effects of tumour and normal tissue blood perfusions, tumour depth, skin temperature boundary condition, as well as tumour size and shape. A similar, but less comprehensive, study was done for larger tumours using two concentric circular scans. The results show that (1) the optimization process can produce a set of scan parameters that give a considerably better temperature distribution than could be obtained ad hoc, and (2) the optimal scan parameter configuration obtained produces a close-to-ideal tumour temperature distribution for a wide variety of clinically relevant conditions. Thus, when extended to include data from individual patients such optimization should be a very useful tool in patient treatment planning, and should enhance the present capabilities of clinical scanned, focused ultrasound systems.

Body Temperature↗