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PubMed2004

Comparison of outcomes between overlapping structure-based and non-overlapping structure-based optimization for simultaneous integrated boost IMRT for malignant gliomas.

BACKGROUND: Intensity-modulated radiotherapy (IMRT) can deliver different doses to two target volumes with high conformity. The purpose of the present study was to compare outcomes provided by two different optimization methods, overlapping structure-based and non-overlapping structure-based methods, for simultaneous integrated boost (SIB)-IMRT for malignant gliomas. METHODS: Treatment plans for three glioblastomas and one anaplastic astrocytoma were analyzed in the present study. The planning protocol was to deliver 70 Gy/28 fractions (fr) to the gross tumor volume (GTV) and 56 Gy/28 fr to the surrounding edema. Two different optimization methods were tested for optimizing dose distribution to the GTVand the surrounding edema. One method was the "including method", an overlapping structure-based (GTV and the clinical target volume [CTV]) optimization method. The other method was the "annulus method", a non-overlapping structure-based (GTV and the subtracted volume) optimization method. Dosimetric indexes derived from dose-volume histograms (DVHs) were used for the analysis. RESULTS: There was no significant difference between the two methods in the mean doses of the target volumes and the doses delivered to the 5% or 95% target volumes (D05 or D95). The mean dose to the brain by the including method was significantly higher than that delivered by the annulus method (P = 0.0001). The D05 of the brain showed no significant difference between the two methods. CONCLUSION: The two optimization methods provided comparable dose distributions within the target volumes and normal brain.

Brain Neoplasms↗

PubMed2007

Prevalence of treatment optimism-related risk behavior and associated factors among men who have sex with men in 11 states, 2000-2001.

Sustainable behavior change among men who have sex with men (MSM) may be threatened by optimistic beliefs about HIV treatments: treatment optimism has been associated with high risk sexual behaviors. We used data from behavioral surveys of MSM attending gay bars in 11 states from 2000-2001 to describe the prevalence and correlates of being less careful with sex or drugs because of treatment optimism (optimism-related risk behavior). Fifteen percent of 1477 HIV-negative or -untested MSM reported optimism-related risk behavior. Optimism-related risk behavior was reported more often by Black and Hispanic MSM (versus white), more often by MSM with a high school education or less (versus college), and less often by MSM in some states. HIV prevention programs should address treatment optimism and related behavioral risks by providing culturally appropriate information, accessible to MSM with lower educational attainment, about the limitations of current therapies.

AIDS Serodiagnosis↗

PubMed2006

Quality of life in cancer patients: The role of optimism, hopelessness, and partner support.

The interaction of optimism, hopelessness and social support as predictors of Health-Related Quality of Life (HRQL) among seriously ill people is not well understood. Also, the impact of partner characteristics on patient quality of life has often been overlooked. In this study the relationships between optimism, hopelessness, partner support and HRQL were investigated in 155 cancer patients and their partners. Special attention was given to the effects of optimism and hopelessness as mediators and moderators in the partner support-HRQL relationship. The impact of partner optimism and hopelessness on perceived partner support and patient HRQL was also studied. The results indicated substantial gender differences in the relationships between the study variables. High levels of partner support were associated with female patients' optimistic appraisals, and together they predicted better HRQL at 8 months follow-up. Partial support was found for the effect of optimism as a mediator. For male patients, low hopelessness was the key variable predicting good HRQL. Clear evidence for the moderator effects of optimism/hopelessness was not found, and the expected impact of partner's characteristics on partner support or patient HRQL could not be confirmed. Although partner support, patient optimism and hopelessness all appeared to be important determinants of HRQL in cancer patients, the relationships between these variables differed by gender. The proposed mediation and moderation models needs to be confirmed in future studies.

Affect↗

PubMed2006

Optimal wavelets for biomedical signal compression.

Signal compression is gaining importance in biomedical engineering due to the potential applications in telemedicine. In this work, we propose a novel scheme of signal compression based on signal-dependent wavelets. To adapt the mother wavelet to the signal for the purpose of compression, it is necessary to define (1) a family of wavelets that depend on a set of parameters and (2) a quality criterion for wavelet selection (i.e., wavelet parameter optimization). We propose the use of an unconstrained parameterization of the wavelet for wavelet optimization. A natural performance criterion for compression is the minimization of the signal distortion rate given the desired compression rate. For coding the wavelet coefficients, we adopted the embedded zerotree wavelet coding algorithm, although any coding scheme may be used with the proposed wavelet optimization. As a representative example of application, the coding/encoding scheme was applied to surface electromyographic signals recorded from ten subjects. The distortion rate strongly depended on the mother wavelet (for example, for 50% compression rate, optimal wavelet, mean+/-SD, 5.46+/-1.01%; worst wavelet 12.76+/-2.73%). Thus, optimization significantly improved performance with respect to previous approaches based on classic wavelets. The algorithm can be applied to any signal type since the optimal wavelet is selected on a signal-by-signal basis. Examples of application to ECG and EEG signals are also reported.

Algorithms↗

PubMed1989

The optimism bias and traffic accident risk perception.

Research suggests that people are excessively and unrealistically optimistic when judging their driving competency and accident risk. In this study, college-age drivers compared their risk of being involved in a variety of described traffic accidents relative to their peers. They also rated each of the accidents along a number of dimensions hypothesized as being related to optimism. In addition, subjects provided global estimates of their driving safety, skill, and accident likelihood. Significant optimism was evident for both the accidents and the global ratings. Optimism increased with driving experience and marginally with age. Those with more driving experience considered human factors to be more important in accident causation; those assigning more importance to human factors also rated themselves as more skillful drivers. For the specific accidents, perceived controllability was a strong predictor of optimism. The findings for controllability are interpreted in terms of other recent data and hypothesized explanations of the optimism bias. In general, it appears that optimism arises because people persistently overestimate the degree of control that they have over events.

Accidents, Traffic↗

PubMed1984

Comparison of optimal scalar electrocardiographic, orthogonal electrocardiographic and vectorcardiographic criteria for diagnosing inferior and anterior myocardial infarction.

A scalar electrocardiogram (ECG), orthogonal ECG and vectorcardiogram (VCG) were recorded in 46 normal persons, 38 patients with inferior myocardial infarction (MI) and 22 patients with anterior MI proved at cardiac catheterization. The diagnostic information provided by the scalar ECG, orthogonal ECG and VCG was quantitatively analyzed and the optimal criteria for diagnosing inferior and anterior MI exhibited by each method were identified. The optimal scalar electrocardiographic, orthogonal electrocardiographic and vectorcardiographic criteria, respectively, are: For inferior MI: initial superior duration in lead aVF greater than 30 ms (sensitivity 63%, specificity 100%), superior/inferior amplitude ratio in lead Y greater than or equal to 0.2 (sensitivity 63%, specificity 96%), initial superior duration greater than 29 ms or initial superior distance greater than 0.4 mV in the frontal plane loop (sensitivity 68%, specificity 100%). For anterior MI: initial anterior duration in lead V2 less than 20 ms or initial anterior duration in lead V3 less than 25 ms (sensitivity 91%, specificity 100%), anterior/posterior duration ratio in lead Z less than 0.3 (sensitivity 73%, specificity 98%), initial anterior duration less than 15 ms in the transverse plane loop (sensitivity 64%, specificity 98%). There were no significant differences among the performances of the optimal scalar ECG, orthogonal ECG and the VCG for diagnosing inferior MI. However, the performance of the optimal scalar ECG was superior to that of the optimal orthogonal ECG and the optimal VCG for diagnosing anterior MI (chi-square = 5.20, p less than 0.02 and chi-square = 7.14, p greater than 0.01, respectively).

Adult↗

PubMed1978

Experimental optimization of the detection limit of one-step solid-phase radioimmunoassay.

The minimal detection limit and the conditions of maximal sensitivity of a one-step solid-phase inhibition radioimmunoassay for human immunoglobulin A have been determined by application of statistical methods of experimental optimization. The choice of the optimal combination of qualitative variables, such as the origin of the antibody and the nature of the solid phase, was made by the study of a covariable under non-optimal conditions of the quantitative variables, such as the amount of antibody. The covariable was the avidity of the antibody, which is expected to have a large influence on the sensitivity. Only the difference in avidity between two immunosorbents with cellulose or Sepharose as solid-phase material proved to be statistically significant, and further study was done with cellulose. The experimental optimization of the sensitivity as a function of five quantitative variables yielded a reduction of the detection limit by a factor 5.6 (from 23.5 to 4.2 ng IgA). The variables determining the amount of insolubilized antibody in the assay had the largest influence on the value of the detection limit. The conditions of optimal sensitivity did agree with the predictions by a physical model of radioimmunoassay. The results are discussed in relation to the assay parameters such as the amount and the avidity of the insolubilized antibody and the initial percentage of binding, and in relation with theoretical optimization of the sensitivity.

Animals↗

PubMed1989

Mathematical shape optimization of hip prosthesis design.

The long-term success of artificial-joint replacement depends partly on the chances for acrylic cement failure and interface disruption. These chances can be diminished by an optimal load-transfer mechanism, whereby stress concentrations are avoided. The present paper introduces a method for numerical shape optimization, whereby the finite element method is used iteratively to determine optimal prosthetic designs, which minimize interface stresses. The method is first applied in a simplified one-dimensional model of a cemented femoral stem fixation, using acrylic cement. The results show that 30-70% cement and interface stress reductions can be obtained in principle with an optimized design. Although the actual optimal shape is susceptible to the characteristics of the joint load, the stem length, stem modulus, cement modulus and bone properties, its general geometrical characteristics are consistent, featuring proximal and distal tapers, and a belly-shaped middle region. These general characteristics are confirmed in a more realistic two-dimensional FEM model. It is concluded that this method of shape optimization can provide a meaningful basis for prosthetic design and analysis activities in general.

Bone Cements↗

PubMed1989

Linear optimization of predictors for secondary structure. Application to transbilayer segments of membrane proteins.

Sliding-window averaging of amino acid properties is a standard method for predicting protein secondary structure. For example, transmembrane segments are predicted to occur near the peaks in a hydropathy plot of a membrane protein. Such a scheme (linear convolutional recognizer, LCR) assigns a number (weight) to each type of monomer, and then convolutes some window function with the sequence of weights. The window has commonly been rectangular, and the weights derived from singlet amino acid frequencies in proteins of known secondary structure or from physical properties of amino acids. The accuracy of the windows and weights have remained unknown. We use linear optimization theory to develop a general method for approximating the optimal window and weights for a LCR. The method assumes that one knows the sequences of one or more chains and the locations of their "features", regions having the secondary structure of interest. We present formulae for quantifying the accuracy of predictors. We show why the optimal LCR is more accurate than methods based on the differences between singlet monomer frequencies inside and outside features. The advantage of an optimal LCR is that its weights inherently include correlations between nearby monomer positions. The optimal predictor is not perfect though. We argue that its inaccuracy is an intrinsic limitation of linear predictors based on monomer weights. As a practical example, we study predictors for transbilayer segments of membrane proteins. We estimate the optimal weights and windows for the two bacterial photosynthetic reaction centers whose three-dimensional structures are known. The resultant LCR, which is more accurate than previous ones, is still inexact. We apply it to bacteriorhodopsin and halorhodopsin. Several non-linear generalizations are examined as possible improvements to the LCR method: non-linear combinations of linear predictors and windowed Fourier transforms of the weight sequences. The former do not significantly increase the accuracy, while the latter reveal a weak negative correlation between the segments and periodic variations of the weights.

Amino Acids↗

PubMed1993

The optimal dosage of (-)deprenyl for increasing superoxide dismutase activities in several brain regions decreases with age in male Fischer 344 rats.

We previously reported that the optimal dosage of (-)deprenyl to increase superoxide dismutase (SOD) activities in striatum in rats differs 10 fold between young male and female rats (1). Furthermore, in female rats the optimal dosage increased with age (1). In the present study in order to clarify how the optimal dosage of this effect changes with age in male rats, we examined the effects of four different dosages of deprenyl on SOD enzyme activities in striatum and several other tissues in old (28-29-month-old) male Fischer 344 (F-344) rats. Continuous s.c. infusion of deprenyl for 3 wks increased activities of SOD and catalase (CAT) in striatum, substantia nigra and cortical regions but not in hippocampus, cerebellum or the liver. The dose of 0.5 mg/kg/day was found to be most effective, while higher (1.0, 2.0 mg/kg/day) or lower (0.1 mg/kg/day) dosages were less effective. This value of 0.5 mg/kg/day was 4 fold lower than the dosage of 2.0 mg/kg/day which was most effective in increasing SOD and CAT activities in young (5-7 month old) male rats of the same strain (1,2). The decline of the optimal dosage with age found in male rats is best explained by a possible decline with age in the hepatic microsomal monooxygenase enzyme activities that are involved with the metabolism of deprenyl. In view of the large differences in the optimal dosages shown among different sexes and ages of rats, future studies regarding the unique effect of this drug in prolonging the life span of rats must be carefully investigated with the caution in mind that the optimal dosage for the life prolonging effect may well differ depending on sex, age and possibly strain and species of animal model used.

Aging↗

PubMed1991

On the optimal policies of cancer screening.

Some problems of optimal screening are considered. A screening strategy is allowed to be nonperiodic. Two approaches to screening optimization are used: the minimum delay time approach and the minimum cost approach. Both approaches are applied to the analysis of an optimization problem when the natural history of the disease is known and when it is unknown (a minimax problem). The structure of optimal screening policies is investigated as well as the benefit they can provide compared to the periodic screening policy. The detection probability is assumed to depend only on the stage of the disease, though it may not be constant throughout each stage. It is shown that periodic screening appears to be optimal when one has no information on the natural history of the disease, the minimum delay time criterion being used for optimization. Some applications to lung cancer screening are presented.

Costs and Cost Analysis↗

PubMed1993

Optimal kinetic design of enzymes in a linear metabolic pathway.

The rate equations for a sequence of enzymic reactions conforming to Michaelis-Menten kinetics have been analyzed in order to establish what kinetic design optimizes the steady-state reaction flux for a given total concentration of enzymes and a given average magnitude of true and apparent first-order rate constants in the reaction system. Analytical solutions are presented which have been derived with the assumptions that the concentration of the first substrate in the pathway represents a fixed parameter and that no diffusional constraints come into operation. The solutions prescribe that reaction flux in the examined system becomes optimal when all of the enzymes are present at equal active-site concentrations. The optimal kinetic design of each enzyme reaction is characterized by forward (true or apparent) first-order rate constants of equal magnitude and reverse rate constants of equal magnitude. This means that the optimal kinetic design of the examined pathway is highly uniform, individual enzymes being likely to exhibit optimal V values differing by a factor less than 5 and optimal Km/[S] values falling within the range 0.3-2.

Binding Sites↗

PubMed1993

Optimized low dose rate pellet configurations for intravaginal brachytherapy.

PURPOSE: The objective was to identify configurations of low dose rate pellet sources that optimize short treatment length brachytherapy dose distributions for a set of four intravaginal applicators. METHODS AND MATERIALS: The method of simulated annealing was used. Dose rates at calculation points on the surface of 2.0, 2.5, 3.0, and 3.5 cm diameter applicators along a fixed 3.0 cm treatment length were optimized for Cs-137 sources of strengths 0.74 and 0.63 GBq in trains having maximum lengths of 3.0, 3.5 and 4.0 cm. Variations in the optimization algorithm involving two different objective functions and different combinations of selectable parameters were investigated in an effort to standardize the approach. RESULTS: An objective function based on the maximum dose rate difference at the calculation points in conjunction with a single parameter set proved suitable for all applicators. Optimized solutions involving both a single configuration of sources and a combination of two such configurations were successfully identified. The latter consistently afforded superior dose rate uniformity, particularly for the smaller diameter applicators. A maximum source train length of 3.5 cm was found to provide a good compromise between attaining dose rate uniformity along the 3.0 cm treatment length and minimizing irradiation of adjacent normal tissues. For each applicator, an optimized 3.5 cm pellet train yielded better surface dose rate uniformity than a corresponding optimum-length linear source. CONCLUSION: Pellet configurations that optimize dose distributions for intravaginal brachytherapy applicators can be reliably identified with modest computational effort using the method of simulated annealing. The method is therefore suitable for use in routine clinical treatment planning for this site.

Algorithms↗

PubMed1980

Obstetrical condition and neonatal neurological morbidity. An analysis with the help of the optimality concept.

In order to increase understanding of the origin of neonatal neurological morbidity, the relationship between the obstetrical and neonatal neurological conditions was studied in a 3-year cohort containing 3162 singleton infants. The infants were neurologically examined at term age according to the technique described by Prechtl. Obstetrical data were documented extensively. Prechtl's optimality concept was applied in the analysis. A statistically significant relationship was found between the obstetrical and neonatal neurological optimality scores. There was no sex difference in the obstetrical optimality, whereas there was in the neurological optimality, to the advantage of the girls. It could be shown that obstetrical conditions such as acidemia, preterm birth and intrauterine growth retardation have a stronger relationship to neurological morbidity when the accompanying obstetrical optimality is lower. In obstetrical practice the application of the optimality concept to obstetrical and neurological data is a helpful complementary refinement.

Female↗

PubMed2004

Effect of optimizing the VV interval on left ventricular contractility in cardiac resynchronization therapy.

Simultaneous biventricular pacing improves left ventricular (LV) function in patients with heart failure and LV asynchrony. Proper timing of the interventricular pacing interval (VV interval) may further optimize LV function. We investigated the acute hemodynamic response of changing the VV interval using maximum LV dP/dt (LV dP/dt(max)) as a parameter for LV function. A biventricular pacemaker was implanted in 53 patients with severely impaired LV function, New York Heart Association class III and IV heart failure, left bundle branch block, LV asynchrony, and a QRS interval >150 ms. Optimization of the atrioventricular and VV intervals was based on measurement of LV dP/dt(max) by a 0.014-in sensor-tipped pressure guidewire. Measurement of LV dP/dt(max) was obtained without complications in all patients. In patients in sinus rhythm with ischemic cardiomyopathy or idiopathic dilated cardiomyopathy, mean improvements by simultaneous biventricular pacing were 17% and 18%, respectively. Patients in atrial fibrillation showed an improvement of 21%. Optimizing the VV interval resulted in further absolute increases of 8%, 7%, and 3%, respectively, in dP/dt(max) in the 3 groups. Maximum dP/dt was achieved with LV pacing first in 44 patients, simultaneous right and left ventricular pacing in 6 patients, and right ventricular pacing first in 3 patients. The mean optimal VV intervals were 37 +/- 32 ms in the atrial fibrillation group, 28 +/- 30 ms in the idiopathic dilated cardiomyopathy group, and 52 +/- 31 ms in the ischemic cardiomyopathy group. Optimization of the VV interval significantly increased LV dP/dt(max) compared with simultaneous biventricular pacing, and such optimization could be easily, accurately, and reliably evaluated by a 0.014-in sensor-tipped pressure guidewire.

Aged↗

PubMed2004

Finding optimal decision scores by evolutionary strategies.

OBJECTIVE: Severeness of illness is often rated by physicians at admission time. For this purpose, medical scores have been developed as 'objective' rating methods. When considering their classification performance, it is not assumed that such an expert-driven score is an optimal one. Our aim is to design an optimized data-driven score. In particular, we compare classical scores with a new data-driven score for abdominal septic shock patients. METHODS AND MATERIAL: Medical scores are used as ratings for different aspects of a patient's health status. The medical score indicates either a more critical or a healthier condition. For example, physicians rate organ conditions for different organs. We consider four different scores, SOFA, APACHE II, SAPS II, and MODS. Beyond the use of such classical scores, we propose an evolutionary strategy, that is suitable for score design, to find optimized data-driven scores. A database of 282 patients is used to optimize a new score for abdominal septic shock patients. Classification performance is compared by a ROC analysis. RESULTS: We give a general instruction for building optimized scores, i.e. we define individuals and operators for the evolutionary score design task. We apply this instruction to abdominal septic shock patient data. When compared to the SOFA score, it has similar classification performance, but it is more performant than APACHE II, SAPS II, and MODS. It can be used as a daily bedside score. CONCLUSIONS: We argue that evolutionary strategies should be used for optimizing purposes in the medical score design process. Using abdominal septic shock patient data, we show that evolutionary score design is a feasible and performant method that can complement or replace expert knowledge, provided that qualitative data is available.

Abdomen↗

PubMedDate not supplied

A theory of optimal differential gene expression.

We investigate a model of optimal regulation, intended to describe large-scale differential gene expression. Relations between the optimal expression patterns and the function of genes are deduced from an optimality principle: the regulators have to maximise a fitness function which they influence directly via a cost term, and indirectly via their control on important cell variables, such as metabolic fluxes. According to the model, the optimal linear response to small perturbations reflects the regulators' functions, namely their linear influences on the cell variables. The optimal behaviour can be realised by a linear feedback mechanism. Known or assumed properties of response coefficients lead to predictions about regulation patterns. A symmetry relation predicted for deletion experiments is verified with gene expression data. Where the optimality assumption is valid, our results justify the use of expression data for functional annotation and for pathway reconstruction and suggest the use of linear factor models for the analysis of gene expression data.

Adaptation, Physiological↗

PubMed2005

Robustness, evolvability, and optimality of evolutionary neural networks.

In a typical optimization problem, the main goal is to search for the appropriate values of the variables that provide the optimal solution of the given function. In artificial neural networks (ANN), this translates to the minimization of the error surface during training such that misclassification is minimized during generalization. However, since optimal training performance does not necessarily imply optimal generalization due to the possibility of overfitting or underfitting, we developed SEPA (Structure Evolution and Parameter Adaptation) which addressed these issues by simultaneously evolving ANN structure and weights. Since SEPA primarily relies on the perturbation function to bring variation in its population, this follow-up study aims to find out SEPAs evolvability, optimality, and robustness in other perturbation functions. Our findings indicate that SEPAs optimal generalization performances are stable and robust from the effect of the different perturbation functions. This is due to the feedback loop between its architecture evolution and weight adaptation such that any shortcoming of the former is compensated by the latter, and vice versa. Our results strongly suggest that proper ANN design requires simultaneous adaptation of ANN structure and weights to avoid one-sided or bias convergence to either the weight or architecture space.

Algorithms↗