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PubMed2006

Early dynamic 201Tl SPECT in the evaluation of brain tumours.

OBJECTIVE: To estimate the usefulness of early dynamic 201Tl single photon emission computed tomography (SPECT) studies in distinguishing the histological malignancy of brain tumours. METHODS: Dynamic 201Tl SPECT was performed for 3 min per scan for 15 min immediately after the administration of 201TlCl in 110 patients with brain tumours (111 lesions). The data obtained each 3 min were used for dynamic SPECT, and the five sets of data obtained were added to acquire static SPECT data. For static SPECT, the static thallium index (STI) was calculated as the ratio of 201Tl uptake in the tumour to that of the contralateral normal brain. The ratio of the 201Tl uptake for each 3 min was defined as the dynamic thallium index (DTI). The dynamic thallium rate (DTR), as a per cent, was calculated as DTR=(DTI for every 3 min)/STI H 100. The five values were approximated as a linear function and the slope (%/min) was calculated. RESULTS: In static SPECT, there was no significant difference between the STI of malignant tumours (glioblastoma and anaplastic astrocytoma) and that of benign tumours (low-grade glioma, meningioma, pituitary adenoma, neurinoma and haemangioblastoma) (3.7+/-1.5, 5.0+/-3.5, respectively). On dynamic SPECT, DTI increased markedly over 15 min for malignant tumours. In contrast, the DTI of benign tumours increased slightly, steadily or decreased. The slope of the linear functions calculated from the DTRs was much higher in the malignant tumour group than in the benign tumour group (P<0.001). CONCLUSIONS: We suggest that the performance of 201Tl dynamic SPECT for 15 min is useful for distinguishing malignant brain tumours from benign brain tumours and reduces the examination stress of patients.

Adult↗
PubMed2006

Whole-body reaching as a measure of dynamic balance in patients with stroke.

OBJECTIVES: To investigate whether whole-body reaching (WBR) could be a task with adequate and gradable dynamic balance challenges for stroke patients. DESIGN: A total of 23 subjects with hemiplegia, after their first stroke, participated in this study. The degree of dynamic balance challenges of WBR was graded by varying the distance to the targets that the subjects had to reach. A foot-pressure measurement system was used to measure the amount of center-of-pressure shift during performance of WBR and sit-to-stand transfer. The Berg Balance Scale (BBS) was administered, and the BBS total score was calculated. Static and dynamic BBS subscores were separately calculated to further understanding of the subject performance regarding balance. Paired t tests were used to examine the effects of target distance on center-of-pressure shift. Correlations between measures of center-of-pressure shift during performance of WBR and of sit-to-stand transfer, BBS total score, BBS static subscores, and BBS dynamic subscores and measures of center-of-pressure shift during performance of sit-to-stand transfer were analyzed. RESULTS: Significant effects of distance on three of the variables representing amount of center-of-pressure shift were found (P < 0.05). The correlations between WBR and sit-to-stand transfer were positive and moderate. The correlations between WBR and sit-to-stand transfer were stronger when the subjects were reaching for a closer target than when reaching for a farther target. The correlations between WBR and BBS total score were weak to moderate; the correlations between WBR and three scores of the BBS across target distance were inconsistent; and the correlations were higher when the subjects were reaching for a farther target than when reaching for a closer target. CONCLUSIONS: WBR for targets at different distances imposed graded dynamic balance challenges on stroke patients and might be an appropriate dynamic balance measure. However, WBR, as applied in this study, showed limitations in measuring the lateral dynamic stability of stroke patients.

Disability Evaluation↗
PubMed2005

Modeling long-term HIV dynamics and antiretroviral response: effects of drug potency, pharmacokinetics, adherence, and drug resistance.

We propose a long-term HIV-1 dynamic model by considering drug potency, drug exposure, and drug susceptibility. Using a Bayesian approach, HIV-1 dynamic parameters were estimated by fitting the model to viral load data from a phase 1/2 randomized clinical study of 2 indinavir (IDV)/ritonavir (RTV)-containing highly active antiretroviral (ARV) therapy regimens in HIV-infected subjects who had previously failed protease inhibitor-containing ARV therapies. A large between-subject variation in estimated viral dynamic parameters was observed, even after accounting for variations in drug exposure and drug susceptibility, suggesting that characteristics of HIV-1 dynamics are host dependent. Significant correlations of baseline factors such as HIV-1 RNA levels and CD4 cell counts with viral dynamic parameters were found. These correlations coincide with biologic interaction mechanisms between HIV and the host immune system and also provide an explanation for the correlations between the baseline viral load and phase 1 viral decay rate, for which inconsistent results have been reported in the literature. The relations between viral dynamic parameters and virologic response were established, and these results suggest that viral dynamic parameters may play an important role in determining treatment success or failure. In particular, we estimated a drug efficacy threshold for each patient that can be used to assess whether an ARV regimen is potent enough to suppress HIV viruses in the individual patient. Our findings indicate that it is necessary to individualize the ARV regimen to treat HIV-1-infected patients. The proposed mathematic models and statistical techniques may provide a framework to simulate and predict antiviral response for individual patients.

Anti-HIV Agents↗
PubMed2006

Comparison of Gadolinium-BOPTA and Ferucarbotran-enhanced three-dimensional T1-weighted dynamic liver magnetic resonance imaging in the same patient.

OBJECTIVES: We sought to compare signal changes using Ferucarbotran and gadobenate dimeglumine (Gd-BOPTA) in dynamic 3D T1-weighted (T1w) GRE imaging of the liver. MATERIAL AND METHODS: Thirty patients were prospectively included in the study. All patients underwent 2 high-field magnetic resonance (MR) examinations: first with Gd-BOPTA (Gd) and then after a mean interval of 4 days with ferucarbotran (Feru). Dynamic MRI was obtained with a 3D T1w GRE sequence (TR 6.33, TE 2.31, flip angle 20 degrees ). Contrast enhanced scans were assessed before intravenous injection of the contrast agent (precontrast), and postcontrast during the arterial phase (30 seconds), portal venous phase (60 seconds), and equilibrium phase (120 seconds). The signal intensities (SIs) of liver, spleen, aorta, and portal vein were defined by region of interest measurements. Signal intensity changes (SICs) and percentage signal intensity change (PSIC) were calculated using the formulas SIC=(SI pre - SI post)/SI pre and PSIC=SIC x 100%. RESULTS: Positive signal enhancement was observed after intravenous injection of Feru during all dynamic measurements, whereas the mean SI values were lower compared with Gd. During the portal venous phase the mean SI of Gd was up to a factor of 2.1 higher (portal vein). The widest difference of SIC was observed during the equilibrium phase for liver parenchyma (Gd, 1.03; Feru, 0.24). The dynamic signal courses were similar for liver, portal vein and aorta. Different signal courses were obtained for the spleen. CONCLUSIONS: Feru-enhanced T1w dynamic images demonstrated significant signal increases for liver, vessels, and spleen but overall lower signal intensities than Gd-BOPTA. The dynamic signal courses of ferucarbotran were similar to that of Gd-BOPTA during ll perfusion phases except in the spleen. Thus, it may be possible to detect typical enhancement pattern of focal liver lesions with Feru-enhanced dynamic T1w MRI.

Adult↗
PubMed2006

Cervical dynamic screening in spinal clearance: now redundant.

BACKGROUND: The safest and most effective method of early cervical spine clearance in unconscious patients is the subject of intense debate. We hypothesize that helical computed tomography (CT) is a sufficiently sensitive investigation to render dynamic screening redundant. METHOD: We retrospectively reviewed the records of 839 trauma patients admitted to the intensive care unit under the orthopedic surgeons from April 1994 to September 2004. Our protocol for cervical spinal clearance in the unconscious patient involves plain radiographs, CT scanning, and dynamic screening. We recorded the presence of any unstable cervical spine injury and any cases that were missed by CT but detected by dynamic screening. RESULTS: There were 87 patients with an unstable cervical spine. Of these, 85 were detected by CT. Two cases were missed by CT (sensitivity 97.7%, specificity 100%). In one of these patients, dynamic screening detected an unstable spine and in the other patient dynamic screening missed an atlanto-occipital dislocation (sensitivity 98.8%, specificity 100%). Critical analysis of this case revealed that a powers ratio calculation on the CT scan would have detected the injury. There were no complications as a result of dynamic screening. CONCLUSION: Dynamic screening is a safe procedure but has no real advantage over helical CT. Power's ratio calculation is essential to reduce the chance of a missing an upper cervical injury. The cervical spine can be reliably cleared using helical CT alone.

Adult↗
PubMed1999

Characteristics of slow and fast ion dynamics in a lithium metasilicate glass.

Molecular dynamics simulations of lithium metasilicate (Li(2)SiO(3)) glass have been performed. The motion of lithium ions is divided into slow (A) and fast (B) categories in the glassy state. The waiting time distribution of the jump motion of each component shows power law behavior with different exponents. Slow dynamics are caused by localized jump motions and the long waiting time. On the other hand, the fast dynamics of the lithium ions in Li(2)SiO(3) are characterized as Lévy flight caused by cooperative jumps. Short intervals of jump events also occur in the fast dynamics in the short time region. Both the temporal and spatial terms contribute to the dynamics acceleration and the heterogeneity caused by these two kinds of dynamics is illustrated. The slow dynamics characteristics of the "glass transition" and in the "mixed alkali effect" are discussed.

Journal Article↗
PubMed1999

Dynamic properties of Lennard-Jones fluids and liquid metals.

The dependence of the dynamic properties of liquid metals and Lennard-Jones fluids on the characteristics of the interaction potentials is analyzed. Molecular-dynamics simulations of liquids in analogous conditions but assuming that their particles interact either through a Lennard-Jones or a liquid-metal potential were carried out. The Lennard-Jones potentials were chosen so that both the effective size of the particles and the depth of the potential well were very close to those of the liquid-metal potentials. In order to investigate the extent to which the dynamic properties of liquids depend on the short-range attractive interactions as well as on the softness of the potential cores, molecular-dynamics simulations of the same systems but assuming purely repulsive interactions with the same potential cores were also performed. The study includes both single-particle dynamic properties, such as the velocity autocorrelation functions, and collective dynamic properties, such as the intermediate scattering functions, the dynamic structure factors, the longitudinal and transverse current correlations, and the transport coefficients.

Journal Article↗
PubMed2000

Dynamics of temporal learning rules.

The changes of synaptic strength are analyzed on two time scales: the fast local field dynamics, and the slow synaptic modification dynamics. The fast dynamics are determined by the synaptic strengths and background noise in the system. The slow dynamics are determined by the functional form of a temporal learning rule. Temporal learning rules are defined to be functions yielding state dependent changes in synaptic strengths depending on the timing of pre- and postsynaptic states in the network. The evolution of local field dynamics that result from various learning rules are analyzed for a stochastic, discrete time neural model with no relative refractory period that receives a series of delayed adaptive inputs. A fixed point is found in the learning dynamics, and conditions for two types of instabilities are analyzed. Four universality classes of dynamics are found that are independent of the details of the temporal learning rules. Examples are given of biological systems in which these temporal learning rules have been identified, and their functional consequences are discussed.

Adaptation, Physiological↗
PubMed2000

Stochastic dynamics of time correlation in complex systems with discrete time

In this paper we present the concept of description of random processes in complex systems with discrete time. It involves the description of kinetics of discrete processes by means of the chain of finite-difference non-Markov equations for time correlation functions (TCFs). We have introduced the dynamic (time dependent) information Shannon entropy S(i)(t) where i=0,1,2,3,ellipsis, as an information measure of stochastic dynamics of time correlation (i=0) and time memory (i=1,2,3,ellipsis). The set of functions S(i)(t) constitute the quantitative measure of time correlation disorder (i=0) and time memory disorder (i=1,2,3,ellipsis) in complex system. The theory developed started from the careful analysis of time correlation involving dynamics of vectors set of various chaotic states. We examine two stochastic processes involving the creation and annihilation of time correlation (or time memory) in details. We carry out the analysis of vectors' dynamics employing finite-difference equations for random variables and the evolution operator describing their natural motion. The existence of TCF results in the construction of the set of projection operators by the usage of scalar product operation. Harnessing the infinite set of orthogonal dynamic random variables on a basis of Gram-Shmidt orthogonalization procedure tends to creation of infinite chain of finite-difference non-Markov kinetic equations for discrete TCFs and memory functions (MFs). The solution of the equations above thereof brings to the recurrence relations between the TCF and MF of senior and junior orders. This offers new opportunities for detecting the frequency spectra of power of entropy function S(i)(t) for time correlation (i=0) and time memory (i=1,2,3,ellipsis). The results obtained offer considerable scope for attack on stochastic dynamics of discrete random processes in a complex systems. Application of this technique on the analysis of stochastic dynamics of RR intervals from human ECG's shows convincing evidence for a non-Markovian phenomemena associated with a peculiarities in short- and long-range scaling. This method may be of use in distinguishing healthy from pathologic data sets based in differences in these non-Markovian properties.

Journal Article↗
PubMed2002

Dynamics of rarefied granular gases.

This paper presents quite general bidimensional gas-dynamic equations--derived from kinetic theory-which include the fourth cumulant kappa(r,t) as a dynamic field. The dynamics describes a low-density system of inelastic hard spheres (disks) with normal restitution coefficient r. Two illustrative examples are given and the role of kappa in them is discussed. Our general gas-dynamic equations would deal with 9 hydrodynamic fields (which corresponds to 14 in three-dimension). These fields are the standard hydrodynamic fields plus the components p(ij) of the traceless part of the pressure tensor, the energy flux vector Q and the fourth cumulant kappa. The present formulation requires no constitutive equations. The two examples are: the well-known homogeneous cooling state and a system, with and without gravity, steadily heated by two parallel walls. In the first case, the dynamics yield a description of the homogeneous cooling state consistent with known results adding extra details mainly about the transient time behavior. The steadily heated system kept in a static state gives rise to quite simple but nontrivial equations. In the case with gravity, it is shown that when kappa is included as a dynamic field, the formalism leads to a non-Fourier law already to first order in dissipation. Setting gravity g=0 a perturbative solution is shown and favorably compared with observations obtained from molecular dynamics (MD). In both cases, with and without gravity, kappa is not homogeneous. An analytic extension suggests a divergent situation for a small negative value of q, which originates in the unavoidable extension of the formalism to exothermic collisions associated with a restitution coefficient larger than one. This divergent behavior is observed in MD.

Journal Article↗
PubMed2002

Dynamical fluctuations in ion conducting glasses: slow and fast components in lithium metasilicate.

Molecular dynamics simulations of lithium metasilicate (Li2SiO3) glass have been performed. Dynamic heterogeneity of lithium ions has been examined in detail over 4 ns at 700 K. Type A particles show slow dynamics in accordance with a long tail of waiting time distribution of jump motion and localized jumps within neighboring sites (fracton), while type B particles show fast dynamics related to cooperative jumps and a strong forward correlated motion (Lévy flight). Mutual changes of two kinds of dynamics with the relatively long time scale have been observed. The changes cause an extremely large fluctuation of the mean squared displacements as well as the squared displacement of each particle, which depends on the time window of observation. Localized jump motion (fracton) cannot contribute to the long-time-translational diffusion but it can contribute to the rotational diffusion. On the other hand, forward correlated jump motion mainly contributes to long-time-translational diffusion and not to the short-time-rotational diffusion, although this can be a slower part of the rotational diffusion. These results have been compared with those of simple glass-forming liquids exhibiting the dynamic heterogeneity near T(g). The translation-rotation paradox can be explained by the characteristics of slow and fast dynamics.

Journal Article↗
PubMed2002

Sweeny and Gliozzi dynamics for simulations of Potts models in the Fortuin-Kasteleyn representation.

We compare the correlation times of the Sweeny and Gliozzi dynamics for two-dimensional Ising and three-state Potts models, and the three-dimensional Ising model for the simulations in the percolation representation. The results are also compared with Swendsen-Wang and Wolff cluster dynamics. It is found that Sweeny and Gliozzi dynamics have essentially the same dynamical critical behavior. Contrary to Gliozzi's claim [Phys. Rev. E 66, 016115 (2002)], the Gliozzi dynamics has critical slowing down comparable to that of other cluster methods. For the two-dimensional Ising model, both Sweeny and Gliozzi dynamics give good fits to logarithmic size dependences for the correlation times; for two-dimensional three-state Potts model, their dynamical critical exponent z is 0.49+/-0.01; the three-dimensional Ising model has z=0.37+/-0.02.

Journal Article↗
PubMed2005

Dynamic ultrasound radiation force in fluids.

The subject of this paper is to present a theory for the dynamic radiation force produced by dual-frequency ultrasound beams in lossless and nondispersive fluids. An integral formula for the dynamic radiation force exerted on a three-dimensional object by a dual-frequency beam is obtained stemming from the fluid dynamics equations. The static radiation force due to a monochromatic wave appears as a particular case of this theory. Dependence of the dynamic radiation force to nonlinear effects of the medium is analyzed. We calculate the dynamic radiation force exerted on solid elastic spheres of two different materials by a low-amplitude dual-frequency plane wave. The static and dynamic radiation forces exhibited approximately same magnitude. Resonance patterns observed in the dynamic radiation force are similar to those present in the static radiation force.

Journal Article↗
PubMed2006

Lattice Boltzmann scheme for fluids with dynamic heterogeneities.

We introduce and discuss a three-dimensional mesoscopic lattice Boltzmann model for the numerical simulation of strongly-interacting fluids with dynamic inhomogeneities. The model is based on an extension of the standard lattice Boltzmann dynamics in which streaming between neighboring lattice sites is constrained by the value of the nonlocal density of the surrounding fluid. The resulting dynamics exhibits typical features of dynamically heterogeneous fluids, such as long-time relaxation, non-Gaussian density distributions and dynamic heterogeneities. Due to its intrinsically parallel dynamics and absence of statistical noise, the method is expected to compute significantly faster than molecular dynamics, Monte Carlo, and lattice glass models.

Journal Article↗
PubMed2006

Structure and dynamics of colloidal depletion gels: coincidence of transitions and heterogeneity.

Transitions in structural heterogeneity of colloidal depletion gels formed through short-range attractive interactions are correlated with their dynamical arrest. The system is a density and refractive index matched suspension of 0.20 volume fraction poly(methyl methacyrlate) colloids with the nonadsorbing depletant polystyrene added at a size ratio of depletant to colloid of 0.043. As the strength of the short-range attractive interaction is increased, clusters become increasingly structurally heterogeneous, as characterized by number-density fluctuations, and dynamically immobilized, as characterized by the single-particle mean-squared displacement. The number of free colloids in the suspension also progressively declines. As an immobile cluster to gel transition is traversed, structural heterogeneity abruptly decreases. Simultaneously, the mean single-particle dynamics saturates at a localization length on the order of the short-range attractive potential range. Both immobile cluster and gel regimes show dynamical heterogeneity. Non-Gaussian distributions of single particle displacements reveal enhanced populations of dynamical trajectories localized on two different length scales. Similar dependencies of number density fluctuations, free particle number, and dynamical length scales on the order of the range of short-range attraction suggests a collective structural origin of dynamic heterogeneity in colloidal gels.

Journal Article↗
PubMed2005

Microtubule dynamics in living root hairs: transient slowing by lipochitin oligosaccharide nodulation signals.

The incorporation of a fusion of green fluorescent protein and tubulin-alpha 6 from Arabidopsis thaliana in root hairs of Lotus japonicus has allowed us to visualize and quantify the dynamic parameters of the cortical microtubules in living root hairs. Analysis of individual microtubule turnover in real time showed that only plus polymer ends contributed to overall microtubule dynamicity, exhibiting dynamic instability as the main type of microtubule behavior in Lotus root hairs. Comparison of the four standard parameters of in vivo dynamic instability--the growth rate, the disassembly rate, and the frequency of transitions from disassembly to growth (rescue) and from growth to disassembly (catastrophe)--revealed that microtubules in young root hairs were more dynamic than those in mature root hairs. Either inoculation with Mesorhizobium loti or purified M. loti lipochitin oligosaccharide signal molecules (Nod factors) significantly affected the growth rate and transition frequencies in emerging and growing root hairs, making microtubules less dynamic at a specific window after symbiotic inoculation. This response of root hair cells to rhizobial Nod factors is discussed in terms of the possible biological significance of microtubule dynamics in the early signaling events leading to the establishment and progression of the globally important Rhizobium/legume symbiosis.

Arabidopsis Proteins↗
PubMed1995

The family dynamics of childbearing and childrearing families in Finland.

Within the context of an international comparative family dynamics project, this study had two chief goals: to describe the family dynamics of childbearing and childrearing families in Finland, and to study changes in family dynamics after childbirth. The sample consisted of families expecting (n = 118) and rearing (n = 94) their first or second child in Finland. Two instruments were used in data collection, i.e. the Family Dynamics Questionnaire and the Family Dynamics Measure; both these tools have been developed in the USA. According to the results, childbearing and childrearing families were thought to function quite well. Pregnant mothers described their family dynamics in more positive terms than fathers, reporting greater flexibility and clearer communication. Similarly, mothers reported more individuation and mutuality than their partners. First-time expectant families reported more mutuality than families expecting their second child. Childrearing mothers reported more individuation, but also more role conflict than did fathers. Communication in families rearing their first child was clearer than in families rearing their second child. The birth of a child affected family dynamics by bringing about various changes such as role conflict, isolation and distorted communication.

Adaptation, Psychological↗
PubMed1998

Steady-state and dynamic behavior of ventricular repolarization and refractoriness in the dog: the effect of multiple cycle length changes and d-sotalol administration.

In anesthetized dogs with chronic, complete AV block we studied the characteristics of ventricular repolarization and refractoriness. Therefore, we determined: (1) steady-state values of ventricular effective refractory period (VERP), action potential duration (APD), and stimulus T interval (STI) before and after d-sotalol treatment at various pacing cycle lengths (PCLs); and (2) the dynamics of VERP, APD, and STI before and after d-sotalol treatment after the abrupt PCL decreases. VERP, APD, and STI showed a normal frequency dependency. All three parameters increased significantly after d-sotalol administration. During steady-state and dynamic measurements, STI was always longer than APD and APD was always longer than VERP in an individual animal, irrespective of PCL and conditions. Standard deviations of steady-state and dynamic values indicated a considerable interindividual variation. However, the dynamics of VERP, APD, and STI after an abrupt decrease in PCL were highly correlated (linear regression analysis: r2 > or = 0.93). The best mathematical model to describe these dynamics was a bi-exponential model (r2 > or = 0.98) with a very short first and a much longer second time constant. We found that there was a very consistent relation between VERP, APD, and STI, not only during steady-state but also in the dynamic situation after various abrupt PCL decreases. This relation does not change after the administration of d-sotalol. Therefore, STI could be used to predict steady-state and dynamic values of VERP and APD. Since STI can be made available online in implantable pacing systems this could lead to the development of new features in these devices.

Animals↗