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PubMed2006

Optimal pulse durations for the treatment of leg telangiectasias with a neodymium YAG laser.

BACKGROUND: Leg veins can be effectively treated with lasers. However, the optimal pulse duration for small leg veins has not been established in human studies with a Nd:YAG laser. OBJECTIVES: The purpose of this study was to investigate a range of pulse durations to determine an optimal pulse duration for clearance of leg veins. STUDY DESIGN/MATERIALS AND METHODS: After mapping and photo documentation of the leg veins to be treated, a variable pulse duration Neodymium:Yttrium Aluminum Garnet (Nd:YAG) laser (3-100 milliseconds) was used in a single test site session. Pulse durations of 3, 20, 40, 60, 80, and 100 milliseconds were used. At the 3-week follow-up, the optimal pulse duration was defined as that pulse duration which resulted in the most complete clearance of vessels with the least side effects. Up to 20 vessels were then treated using the established "optimal" pulse duration. Final evaluation was at 16 weeks after the initial visit. Three blinded observers rated the percent of vessels completely cleared based on initial and final photographs. RESULTS: Eighteen patients completed the study. Fluence thresholds for immediate vessel changes varied depending on spot size and vessel diameter, with larger fluences required for smaller spot sizes and smaller vessels. Shorter pulse durations (< or =20 milliseconds) were associated with occasional spot sized purpura and spot sized post-inflammatory hyperpigmentation. Longer pulse durations (40-60 milliseconds) achieved superior vessel elimination with less post-inflammatory hyperpigmentation. With a single laser treatment, 71% of the treated vessels cleared. CONCLUSIONS: Compared to shorter pulses (<20 milliseconds), longer pulses may provide gentler heating of the vessel and a greater ratio of contraction to thrombosis.

Adult↗

PubMed2004

Subzero water transport characteristics of boar spermatozoa confirm observed optimal cooling rates.

Incomplete understanding of the water transport parameters (reference membrane permeability, L(pg), and activation energy, E(Lp)) during freezing in the presence of extracellular ice and cryoprotective agents (CPAs) is one of the main limiting factors in reconciling the difference between the numerically predicted value and the experimentally determined optimal rates of freezing in boar (and in general mammalian) gametes. In the present study, a shape-independent differential scanning calorimeter (DSC) technique was used to measure the water transport during freezing of boar spermatozoa. Water transport data during freezing of boar sperm cell suspensions were obtained at cooling rates of 5 and 20 degrees C/min in the presence of extracellular ice and 6% (v/v) glycerol. Using previously published values, the boar sperm cell was modeled as a cylinder of length 80.1 microm and a radius of 0.31 microm with an osmotically inactive cell volume, V(b), of 0.6 V(o), where V(o) is the isotonic cell volume. By fitting a model of water transport to the experimentally obtained data, the best-fit water transport parameters (L(pg) and E(Lp)) were determined. The "combined-best-fit" parameters at 5 and 20 degrees C/min for boar spermatozoa in the presence of extracellular ice are: L(pg) = 3.6 x 10(-15) m(3)/N. s (0.02 microm/min-atm) and E(Lp) = 122.5 kJ/mole (29.3 kcal/mole) (R(2) = 0.99); and the corresponding parameters in the presence of extracellular ice and glycerol are: L(pg)[cpa] = 0.90 x 10(-15) m(3)/N. s (0.005 microm/min-atm) and E(Lp)[cpa] = 75.7 kJ/mole (18.1 kcal/mole) (R(2) = 0.99). The water transport parameters obtained in the present study are significantly different from previously published parameters for boar and other mammalian spermatozoa obtained at suprazero temperatures and at subzero temperatures in the absence of extracellular ice. The theoretically predicted optimal rates of freezing using the new parameters ( approximately 30 degrees C/min) are in close agreement with previously published but experimentally determined optimal cooling rates. This analysis reconciles a long-standing difference between theoretically predicted and experimentally determined optimal cooling rates for boar spermatozoa.

Animals↗

PubMed2003

Optimization of localized 19F magnetic resonance spectroscopy for the detection of fluorinated drugs in the human liver.

Fluorine MR spectroscopy ((19)F MRS) is an indispensable tool for assessing the pharmacokinetics of fluorinated drugs. Since the metabolism of 5-fluorouracil (5FU), a frequently used cytotoxic drug, is expected to be different in normal liver and in tumor tissue, spatial localization is required for detection by MRS. In this study, three independent signal-to-noise ratio (SNR) optimizations were combined to enable chemical shift imaging (CSI) as a localization method in the detection of 5FU and its metabolites in tumor tissue. First, the hardware was optimized by using circularly polarized coils together with integrated preamplifiers. Second, the optimal pulse angle (Ernst angle) was determined on the basis of T(1) relaxation time measurements of 5FU. Finally, averaging of CSI phase-encoding steps was optimized by using the applied Hamming filter as a weighting function. The combination of these three methods enables the in vivo detection of 5FU and alpha-fluoro-beta-alanine (FBAL) by (19)F MRS, localized in three dimensions in tumor and liver tissue at a time resolution of 4 min at 1.5 Tesla.

Antimetabolites, Antineoplastic↗

PubMed1986

Optimization of signal-to-noise ratio in calculated T1 images derived from two spin-echo images.

A simplified model relating signal intensity in an MR image to spin-lattice relaxation time (T1), repetition time (TR), number of signal averages and the average tip angle (-alpha) of the protons within the slice has been developed. This model has been used to select the optimal repetition times of two spin-echo images for a fixed total imaging time to maximize signal to noise in calculated T1 images. Theoretical predictions of T1 are virtually identical to spectroscopically measured values, and the relative noise (delta T1) in T1 images calculated from two measured spin-echo images is in good agreement with the theoretically predicted values of delta T1/T1. This model predicts that: (a) for a T1 of approximately 500 ms, the least T1 image noise is obtained with one of the spin-echo images collected with a TR of 400-500 ms. The longer the TR of the other spin-echo image, the lower the T1 image noise, but past a TR of approximately 1400 ms, T1 image signal/noise is optimized for the same total imaging time by increasing the number of averages in the shorter TR spin-echo image rather than increasing the TR of the second spin-echo image. (b) The error is reduced and the optimum TR1 is reduced as -alpha is increased from 63 to 90 degrees. (c) For a range of T1, optimal selection of TR1 and TR2 based on an intermediate value of T1, results in relatively little increase over optimal values in delta T1/T1 for the entire T1 range.

Humans↗

PubMed1988

Optimization of MR protocols: a statistical decision analysis approach.

A new method of optimizing MRI data acquisition protocols is presented. Tissues are modeled with probability density functions (PDFs) of tissue parameter values (such as T1, T2). The imaging data acquisition process is modeled as a mapping from a tissue parameter space to a signal strength space. Tissue parameter PDFs are mapped to signal strength PDFs for each tissue in a clinical problem. The efficacy of an MRI protocol is evaluated using the methods of statistical decision analysis applied to the signal strength PDFs, including the propagation of noise. This procedure evaluates the ability to discriminate different tissues based on the signal strengths produced with the protocol. The model can incorporate an arbitrary number of tissues, parameters, and pulse sequences in the protocol. The multivariate nature of MRI and the observed broad distribution of tissue parameter values makes this model more appropriate for optimizing data acquisition protocols than methods which maximize the signal-difference-to-noise ratio between discrete values of the tissue parameters. It is shown that these two methods may calculate different optimal protocols. The method can be used to optimize data acquisition for quantitative computer-based tissue classification, as well as imaging. Data acquisition and image processing philosophies are discussed in light of the method.

Computer Simulation↗

PubMed1996

Design of adiabatic selective pulses using optimal control theory.

Optimal control theory has been applied in the past for the design of RF pulses for selective excitation. This was the outcome of having established the controllability of the MR spin system for the selective excitation problem. "Minimum distance" was the main formulation used for the solution. Because of their robust behavior in the presence of inhomogeneous RF fields, adiabatic pulses play an important role in spin inversion and excitation. In this study, we present a method for incorporating adiabaticity into the optimal control problem by enhancing the cost functional with an appropriate term. Two different types of adiabatic terms are proposed. Furthermore, two methods are used to solve the optimal control problem, namely the Hamiltonian approach and the solution by mathematical programming. Design examples include both a frequency selective pulse for performing fat suppression by inversion and a regular inversion pulse. It is shown that, in the course of optimization, the pulse designer can trade-off slice resolution against pulse adiabaticity.

Humans↗

PubMed2006

Optimal acquisition schemes for in vivo quantitative magnetization transfer MRI.

This paper uses the theory of Cramer-Rao lower bounds (CRLB) to obtain optimal acquisition schemes for in vivo quantitative magnetization transfer (MT) imaging, although the method is generally applicable to any multiparametric MRI technique. Quantitative MT fits a two-pool model to data collected at different sampling points or settings of amplitude and offset frequency in the MT saturation pulses. Here we use simple objective functions based on the CRLB to optimize sampling strategies for multiple parameters simultaneously, and use simulated annealing to minimize these objective functions with respect to the sampling configuration. Experiments compare optimal schemes derived for quantitative MT in the human white matter (WM) at 1.5T with previously published schemes using both synthetic and human-brain data. Results show large reductions in error of the fitted parameters with the new schemes, which greatly increases the clinical potential of in vivo quantitative MT. Since the sampling-scheme optimization requires specific settings of the MT parameters, we also show that the optimum schemes are robust to these settings within the range of MT parameters observed in the brain.

Adult↗

PubMed2005

The mediating role of appraisal and coping in the relationship between optimism-pessimism and quality of life.

Longitudinal data from 165 women diagnosed and treated for breast cancer were used to investigate if the relationship between optimism-pessimism and quality of life (QOL) is attributed to the appraisal and coping strategies. The women completed the Life Orientation Test-Revised (LOT-R), as a measurement of optimism-pessimism, the Mental Adjustment to Cancer (MAC) Scale, as a measure for coping, a VAS for appraisal and the EORTC QLQ-C30, as a measure for QOL at two time points: at diagnosis and 12-months after breast cancer surgery. Optimism-pessimism had both a direct and indirect influence on QOL. Two coping strategies were particularly strong mediators for the indirect influence: fighting spirit and hopeless/helpless. Optimists responded with fighting spirit, which had a positive effect on their QOL. On the other hand, pessimists responded with hopeless/helplessness, which had a negative effect on their QOL. The relationship between pessimism and QOL at time of diagnosis was also mediated by appraisal, such as threat. The two coping strategies remained fairly stable over the 12 months within the optimists and pessimists.The results suggest that the influence of optimism and pessimism on QOL appears to be mediated by coping both before and after treatment for breast cancer. Fighting spirit and hopeless/helplessness appear to reflect the characteristic coping strategies for optimists and pessimists.

Adaptation, Psychological↗

PubMed2006

Optimism, social support and psychosocial functioning among women with breast cancer.

Personality, psychosocial, demographic and medical variables have been identified as correlates of adjustment to breast cancer and quality of life (QoL). Most studies have examined relationships between personality, social support and adjustment to cancer in predominantly middle-class Caucasian samples, thus limiting the generalizability of their findings. Eighty-one female outpatients at a medical oncology breast clinic in a county general hospital serving primarily indigent Hispanic and African-American patients completed measures assessing demographic and medical information, health-related QoL, cancer-specific distress, mood disturbance, dispositional optimism and satisfaction with social support. Older age, receipt of treatment and greater optimism accounted for 41% of the variance in emotional well-being (p<0.01). Absence of family history of breast cancer, receipt of treatment and optimism accounted for 43% of the variance in functional well-being (p<0.01). Optimism and satisfaction with social support accounted for 43% of the variance in social/family well-being (p<0.01). Absence of treatment (not yet treated) and pessimism accounted for 31% of the variance in cancer-specific distress (p<0.01). Finally, family history of breast cancer and pessimism accounted for 48% of the variance in mood disturbance (p<0.001). Family history of breast cancer and pessimism were related to mood disturbance (p<0.001). No between-group differences were found for race/ethnicity for any of the variables. Encouraging positive expectations and facilitating social support may help women in public sector medical settings cope with the stressful demands of diagnosis and treatment of breast cancer regardless of race/ethnicity.

Adaptation, Psychological↗

PubMed1997

Optimization of the electrostatic interactions between ionized groups and peptide dipoles in proteins.

The three-dimensional optimization of the electrostatic interactions between the charged amino acid residues and the peptide partial charges was studied by Monte-Carlo simulations on a set of 127 nonhomologous protein structures with known atomic coordinates. It was shown that this type of interaction is very well optimized for all proteins in the data set, which suggests that they are a valuable driving force, at least for the native side-chain conformations. Similar to the optimization of the charge-charge interactions (Spassov VZ, Karshikoff AD, Ladenstein R, 1995, Protein Sci 4:1516-1527), the optimization effect was found more pronounced for enzymes than for proteins without enzymatic function. The asymmetry in the interactions of acidic and basic groups with the peptide dipoles was analyzed and a hypothesis was proposed that the properties of peptide dipoles are a factor contributing to the natural selection of the basic amino acids in the chemical composition of proteins.

Amino Acids↗

PubMed2004

Optimizing physical energy functions for protein folding.

We optimize a physical energy function for proteins with the use of the available structural database and perform three benchmark tests of the performance: (1) recognition of native structures in the background of predefined decoy sets of Levitt, (2) de novo structure prediction using fragment assembly sampling, and (3) molecular dynamics simulations. The energy parameter optimization is based on the energy landscape theory and uses a Monte Carlo search to find a set of parameters that seeks the largest ratio deltaE(s)/DeltaE for all proteins in a training set simultaneously. Here, deltaE(s) is the stability gap between the native and the average in the denatured states and DeltaE is the energy fluctuation among these states. Some of the energy parameters optimized are found to show significant correlation with experimentally observed quantities: (1) In the recognition test, the optimized function assigns the lowest energy to either the native or a near-native structure among many decoy structures for all the proteins studied. (2) Structure prediction with the fragment assembly sampling gives structure models with root mean square deviation less than 6 A in one of the top five cluster centers for five of six proteins studied. (3) Structure prediction using molecular dynamics simulation gives poorer performance, implying the importance of having a more precise description of local structures. The physical energy function solely inferred from a structural database neither utilizes sequence information from the family of the target nor the outcome of the secondary structure prediction but can produce the correct native fold for many small proteins.

Algorithms↗

PubMed2001

Optimizing the hydrogen-bond network in Poisson-Boltzmann equation-based pK(a) calculations.

pK(a) calculation methods that are based on finite difference solutions to the Poisson-Boltzmann equation (FDPB) require that energy calculations be performed for a large number of different protonation states of the protein. Normally, the differences between these protonation states are modeled by changing the charges on a few atoms, sometimes the differences are modeled by adding or removing hydrogens, and in a few cases the positions of these hydrogens are optimized locally. We present an FDPB-based pK(a) calculation method in which the hydrogen-bond network is globally optimized for every single protonation state used. This global optimization gives a significant improvement in the accuracy of calculated pK(a) values, especially for buried residues. It is also shown that large errors in calculated pK(a) values are often due to structural artifacts induced by crystal packing. Optimization of the force fields and parameters used in pK(a) calculations should therefore be performed with X-ray structures that are corrected for crystal artifacts.

Amino Acid Sequence↗

PubMed2005

Design of combinatorial protein libraries of optimal size.

In this article we introduce a computational procedure, OPTCOMB (Optimal Pattern of Tiling for COMBinatorial library design), for designing protein hybrid libraries that optimally balance library size with quality. The proposed procedure is directly applicable to oligonucleotide ligation-based protocols such as GeneReassembly, DHR, SISDC, and many more. Given a set of parental sequences and the size ranges of the parental sequence fragments, OPTCOMB determines the optimal junction points (i.e., crossover positions) and the fragment contributing parental sequences at each one of the junction points. By rationally selecting the junction points and the contributing parental sequences, the number of clashes (i.e., unfavorable interactions) in the library is systematically minimized with the aim of improving the overall library quality. Using OPTCOMB, hybrid libraries containing fragments from three different dihydrofolate reductase sequences (Escherichia coli, Bacillus subtilis, and Lactobacillus casei) are computationally designed. Notably, we find that there exists an optimal library size when both the number of clashes between the fragments composing the library and the average number of clashes per hybrid in the library are minimized. Results reveal that the best library designs typically involve complex tiling patterns of parental segments of unequal size hard to infer without relying on computational means.

Amino Acid Sequence↗

PubMed2007

A novel synthetic peptide vector system for optimal gene delivery to bone marrow stromal cells.

A 23-amino acid, bifunctional, integrin-targeted synthetic peptide was evaluated for ex vivo gene delivery to rabbit bone marrow stromal cells (BMSCs). The peptide (K)(16)GRGDSPC consists of an amino terminal domain of 16 lysines for electrostatic binding of DNA, and a 7-amino acid integrin-binding domain at the carboxyl terminal. PcDNA3-EGFP plasmids were transfected into BMSCs by (K)(16)GRGDSPC and the positive cells gave out a bright green fluorescence. High levels of gene delivery of pcDNA3-TGF-beta1 plasmids were obtained with 2 to 4 microg/ml DNA concentration, with (K)(16)GRGDSPC at an optimal peptide: DNA w/w ratio of 3:1, with a required exposure time of more than 4 h but shorter than 24 h for BMSC exposure to the peptide/DNA complexes with completely absent serum in the initial stage; with 100 microM chloroquine and at least 8 h exposure for BMSC exposure to chloroquine; with a fusogenic peptide at an optimal (K)(16)GRGDSPC/DNA/fusogenic peptide w/w ratio of 3:1:5; and with Lipofectamine 2000 at an optimal (K)(16)GRGDSPC/DNA/Lipofectamine 2000 w/w ratio of 3:1:2 at a constant DNA concentration of 2 microg/ml. Chloroquine, the fusogenic peptide and Lipofectamine 2000 all significantly promoted gene delivery, but chloroquine was more effective than the fusogenic peptide and had obvious synergistic effects with Lipofectamine 2000. Under optimal conditions, TGF-beta1 gene was transfected into BMSCs without observable toxicity, and the stable expression was examined by RT-PCR and Western blot analysis. The stable transgenic cells showed obvious bands. This novel synthetic peptide, providing a new way for the use of polylysine and RGD motif in DNA vector system, is potentially well suited to ex vivo gene delivery to BMSCs for experimental and clinical applications in the field of bone tissue engineering.

Animals↗

PubMed2006

Automated method for measuring globin adducts of acrylamide and glycidamide at optimized Edman reaction conditions.

The general population is exposed to acrylamide, a potential human carcinogen, through food and cigarette smoke. The assessment of human exposure to acrylamide is important in the evaluation of health risks associated with this chemical. Hemoglobin adducts of acrylamide (AA-Hb) and its primary metabolite glycidamide (GA-Hb) are established biomarkers of acrylamide exposure and methods to measure these biomarkers using modified Edman reaction are described. Only limited information about the optimal Edman reaction conditions such as pH or temperature is available for these adducts and the existing methods do not allow automation needed in biomonitoring studies. In this study, the yield of Edman products of AA-Hb and GA-Hb between pH 3-10 and at 35-55 degrees C at different time intervals, and the applicability of liquid-liquid extraction on diatomaceous earth for analyte extraction, were assessed and results were used in a new optimized method. The applicability of our optimized method was assessed by comparing results obtained with a convenience sample from 96 individuals with a conventional method. Maximum yield of Edman products was obtained between pH 6-7, heating the reaction solution at 55 degrees C for 2 h resulted in the same yields as with conventional conditions, and use of diatomaceous earth was found suitable for automated analyte extraction. Using these conditions, no difference was observed between our optimized and a conventional method. The median globin adduct values in the convenience sample are 129 pmol/g globin (range: 27-453 pmol/g globin) and 97 pmol/g globin (range: 27-240 pmol/g globin) for AA-Hb and GA-Hb, respectively. The GA-Hb/AA-Hb ratio decreases significantly with increasing AA-Hb values indicating that measurement of AA-Hb as well as GA-Hb are needed to appropriately assess human exposure to acrylamide.

Acrylamides↗

PubMed1991

Determination of optimal designs using linear models in crossover trials.

This study determines the optimal designs for crossover trials with fixed size of population, in order to estimate contrasts between two treatment effects, for various numbers of periods. The problem is approached in the framework of a linear model, taking into consideration the structure of a variance matrix constructed from two random sources: linked-to-subject random effect and linked-to-measurement random error. Different models, as well as different optimality criteria, are considered. For example, when two periods are planned, for the criterion of the minimization of the variance of the treatment-effect estimator, in the presence of residual effect, the optimal design corresponds to four groups of sequences, (T1, T2), (T2, T1), (T1, T1), (T2, T2); without residual effect it corresponds to two groups, (T1, T2), (T2, T1). Optimal designs are given for the comparison of two treatments when using three or four periods.

Clinical Trials as Topic↗

PubMed1995

Determination of optimally resolving gel concentration and migration time (path) in gel electrophoresis.

The notion of a mathematically defined optimally resolving gel concentration for components of a pair of molecular species of any given size was developed by Rodbard et al. (Electrophoresis and Isoelectric Focusing on Polyacrylamide Gel, pp. 28-62, de Gruyter, Berlin, 1974) 21 years ago. The mathematical treatment was incorporated into a computer program (T-OPT) for mainframe computers which upon input of the slope and intercept on the mobility axis of the Ferguson plots of the two components, electrophoresis time and temperature, yielded plots of resolution vs gel concentration. The same algorithms were later incorporated into the program ELPHOFIT for personal computers. Ideality of diffusion spreading and zero initial zone width were assumed along with a Gaussian peak distribution and an equal area for both components. Moreover, these programs failed to respond to the practical question of the migration time (or path) required for the resolution at the optimal gel concentration, although an independent program predicting the course of resolution under the assumption of free diffusion band spreading in gels (DAR-001) had been devised by Rodbard for application in preparative elution-PAGE. The present work advances the technology for predicting resolving conditions by presenting a computer program which allows the user (i) to predict the gel concentration which is optimal for obtaining the desired degree of resolution at any migration time, (ii) to prescribe the minimal degree of resolution between two band distributions one wishes to achieve, and (iii) to predict the migration time (or path) required at the optimal gel concentration for the resolution of the two components. The program is written in MATLAB and can be used by any computer that supports MATLAB language.

Algorithms↗

PubMed1998

A search for the optimal stimulus.

How do stimulus size and item number relate to the magnitude and direction of error on center estimation and line cancellation tests? How might this relationship inform theories concerning spatial neglect? These questions were addressed by testing twenty patients with right hemisphere lesions, eleven with left hemisphere lesions and eleven normal control subjects on multiple versions of center estimation and line cancellation tests. Patients who made large errors on these tests also demonstrated an optimal or pivotal stimulus value, i.e., a particular size center estimation test or number of lines on cancellation that either minimized error magnitude relative to other size stimuli (optimal) or marked the boundary between normal and abnormal performance (pivotal). Patients with right hemisphere lesions made increasingly greater errors on the center estimation test as stimuli were both larger and smaller than the optimal value, whereas those with left hemisphere lesions made greater errors as stimuli were smaller than a pivotal value. In normal subjects, the direction of errors on center estimation stimuli shifted from the right of true center to the left as stimuli decreased in size (i.e., the crossover effect). Right hemisphere lesions exaggerated this effect, whereas left hemisphere lesions diminished and possibly reversed the direction of crossover. Error direction did not change as a function of stimulus value on cancellation tests. The demonstration of optimal and pivotal stimulus values indicates that performances on center estimation and cancellation tests in neglect are only relative to the stimuli used. In light of other studies, our findings indicate that patients with spatial neglect grossly overestimate the size of small stimuli and underestimate the size of large stimuli, that crossover represents an "apparent" shift in error direction that actually results from normally occurring errors in size perception, and that the left hemisphere is specialized for one aspect of size estimation, whereas the right performs dual roles.

Aged↗