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PubMed1993

Dynamic MR imaging of hepatoma treated by transcatheter arterial embolization therapy. Assessment of treatment effect.

The effect of transcatheter arterial chemo-embolization therapy (TACE) for hepatoma was evaluated with dynamic MR imaging with Gd-DTPA in 37 patients (44 tumors). TACE was performed using Lipiodol/cis-platinum and gelatin sponge (or microspheres) as an embolic material. All patients were examined with dynamic CT and MR imaging before and after treatment. On conventional spin echo images, changes of signal intensity after treatment varied regardless of presence of Lipiodol. Dynamic MR imaging revealed changes of tumor vascularity before and after treatment. On histologic correlation, areas of persistent tumor enhancement on dynamic MR imaging corresponded to areas of viable tumor cells while areas of non-enhancement corresponded to areas of necrosis. Dynamic MR imaging was superior in contrast resolution and was not influenced by the presence of Lipiodol compared with dynamic CT, and therefore residual viable tumors were better defined by dynamic MR imaging.

Adult↗
PubMed1996

[Perimetry with normal Octopus technique and Weber 'dynamic' technique. Initial results with reference to reproducibility of measurements in glaucoma patients].

UNLABELLED: There is ample reason to strive for a shorter test without losing solid and reproducible information on the function of the eye. The purpose of this study was to compare the standard Octopus strategy with the 'dynamic strategy' of Weber in terms of time requirement and reproducibility of results, i.e., short-term as well as long-term fluctuations in glaucoma. MATERIALS AND METHODS: On an Octopus 1-2-3 automated perimeter, 23 experienced glaucoma patients with predominantly local loss completed three test sessions, each consisting of a short training test followed by six visual fields, i.e., the first 'stage' (16 test locations) of program GIX, beginning at random with one strategy, then alternating the strategies. RESULTS: The deviation from normal values of the 1104 test locations obtained with the standard and the dynamic strategy (mean +/- SD) was 5.2 +/- 7.5 dB and 4.6 +/- 7.3 dB (P < 0.02), respectively. The short-term fluctuation (given as variance) with the standard and the dynamic strategy averaged 8.3 +/- 5.9 dB2 and 10.2 +/- 5.8 dB2 (p < 0.02), respectively. The long-term fluctuation, i.e., 'test-to-test' variation (given as variance), with the standard and the dynamic strategy was 6.4 +/- 16.5 dB2 and 7.89 +/- 19.2 dB2 (P < 0.22), respectively. The total long-term fluctuation of the index mean defect, MD, averaged 1.8 +/- 2.7 dB2 and 1.3 +/- 1.7 dB2 (P = 0.69), respectively, with the standard and the dynamic strategy. The number or stimuli required with the standard and the dynamic strategy averaged 5.6 +/- 1.4 and 3.0 +/- 1.0 (P < 0.001), respectively. CONCLUSIONS: The dynamic strategy required 43% fewer stimuli and presented 23% (significantly) higher short-term fluctuation, but long-term fluctuations were similar for both strategies. The two strategies were comparable regarding the respective reproducibility of the results. However, further studies may investigate the sensitivity and the specificity of either strategy to distinguish disease from normal, or, change during a follow-up of a disease, and, may elucidate whether the observed differences between the two strategies are due to the modified step size, or, to the single (versus double) crossing of the threshold.

Adult↗
PubMed1997

Comparison of two-dimensional time-of-flight dynamic magnetic resonance angiography with digital subtraction angiography in popliteal artery entrapment syndrome.

OBJECTIVE: To assess dynamic magnetic resonance angiography (MRA) as an alternative to catheter angiography in patients with popliteal artery entrapment syndrome (PAES). PATIENTS AND METHODS: Nine patients with surgically proven PAES underwent provocation digital subtraction angiography (DSA) and 2-dimensional time-of-flight dynamic MRA of the popliteal fossae (total of 17 limbs). Eight normal volunteers also underwent dynamic MRA (total of 16 limbs). Two observers blinded to the surgical findings and the results of DSA independently evaluated the 33 limbs of the 17 subjects on the basis of maximum-intensity projection images and transverse MRA source images. The degree of stenosis was graded and compared with that indicated by DSA. RESULTS: Among the 17 limbs of patients with surgically proven PAES, dynamic MRA suggested the correct diagnosis in 13 (76%) by indicating stenosis greater than 50%. Dynamic MRA indicated stenosis of 1% to 50% for 4 (25%) of the 16 normal limbs and no stenosis in the other 12 normal limbs (i.e., no false positive results). CONCLUSION: Catheter angiography is not necessary if dynamic MRA indicates stenosis of greater than 50% in patients with clinical suspicion of PAES, but is recommended if dynamic MRA indicates stenosis of 1% to 50%.

Adolescent↗
PubMed1997

Dynamic and conventional spin-echo MR of pituitary microlesions.

PURPOSE: To determine whether dynamic traditional spin-echo MR imaging, with the use of routine T1 parameters during contrast infusion, is superior to standard MR imaging after contrast administration for detecting microlesions of the pituitary gland. METHODS: Sixty-four patients with pituitary microlesions 3 to 10 mm in diameter were examined with a dynamic traditional spin-echo technique; that is, a typical T1 spin-echo sequence of 500-600/20-25/2 (repetition time/echo time/excitations), 3-mm-thick sections, 16-cm field of view, 256 x 128 matrix, and a scan time ranging from 2 minutes to 2 minutes 40 seconds during contrast infusion. In addition, standard imaging with unenhanced and contrast-enhanced spin-echo sequences were obtained. The three sequences were evaluated retrospectively and graded for gland-lesion contrast conspicuity, lesion homogeneity, and delineation of lesion margin. RESULTS: The dynamic sequence was judged to be better than the standard enhanced sequence for depicting microlesions in 42% to 47% of patients. Lesions were identified only on the dynamic study in an additional 1% to 14% of patients. Lesions were seen equally well on the standard and dynamic sequences only in 16% to 23% of cases. The standard postcontrast sequence was judged better in 12.5% to 17% of cases, with lesions identified only on the standard sequence in an additional 8% to 9%. CONCLUSION: Dynamic traditional spin-echo MR imaging improved lesion detection and provided increased clarity over standard sequences after contrast infusion. Both sequences are important, since lesions were detected only on the dynamic sequence in 11% to 14% of patients and only on the standard sequence in 8% to 9% of patients.

Adenoma↗
PubMed1997

[Dynamic magnetic resonance of the knee. Considerations on techniques and anatomy with a magnetic resonance system with open magnet].

MRI is currently considered the best technique to study the joints--knee joints in particular. Most studies are performed with the knee straightened out or slightly flexed, which position is mandatory with contemporary MR units. Recently, however, the MR equipment for limb studies and the larger tunnels of total body magnets have permitted partially dynamic knee studies, up to 30-40 degrees flexion; this joint excursion cannot be exceeded. In 1996, Muhle and Niitsu demonstrated that dynamic MRI can be useful to study cruciate ligament injuries, some types of meniscal injuries, all femoropatellar conditions and, mostly, cruciate ligament reconstruction. We used an open magnet MR unit for thorough functional dynamic knee studies, acquiring the images at 0-120 degrees flexion. The open magnet MR unit permits free joint movements. We examined 25 subjects: 10 healthy volunteers and 15 patients with meniscal, capsuloligamentous, femoropatellar or synovial conditions. This technique schedules axial, coronal or sagittal images, according to the diagnostic suspicion, suitably directed with the patient in lateral decubitus and with the knee flexed to maximum joint excursion. Dynamic MR findings are easily transferred to an X-ray film, so that the radiologist can send them to the orthopedist with no need of any videotape or TV take. The current cine MR programs display the dynamic images of the moving joint on an MR monitor, but this option is not yet widely available. The quality of dynamic MR studies is exactly the same as that of conventional images, with a particular emphasis on the small diagnostic details of the injuries. We report our preliminary experience with this technique, indicating some possible clinical applications of dynamic MRI which permits thorough studies of knee flexion-extension.

Humans↗
PubMed2005

Periodic dynamics in a two-stage Allee effect model are driven by tension between stage equilibria.

Single species difference population models can show complex dynamics such as periodicity and chaos under certain circumstances, but usually only when rates of intrinsic population growth or other life history parameter are unrealistically high. Single species models with Allee effects (positive density dependence at low density) have also been shown to exhibit complex dynamics when combined with over-compensatory density dependence or a narrow fertility window. Here we present a simple two-stage model with Allee effects which shows large amplitude periodic fluctuations for some initial conditions, without these requirements. Periodicity arises out of a tension between the critical equilibrium of each stage, i.e. when the initial population vector is such that the adult stage is above the critical value, while the juvenile stage is below the critical value. Within this area of parameter space, the range of initial conditions giving rise to periodic dynamics is driven mainly by adult mortality rates. Periodic dynamics become more important as adult mortality increases up to a certain point, after which periodic dynamics are replaced by extinction. This model has more realistic life history parameter values than most 'chaotic' models. Conditions for periodic dynamics might arise in some marine species which are exploited (high adult mortality) leading to recruitment limitation (low juvenile density) and might be an additional source of extinction risk.

Ecosystem↗
PubMed2026

Dynamic Fusion of Genomics and Functional Network Connectivity in UK Biobank Reveals Schizophrenia-Related SNP Manifolds.

Many mental disorders show strong genetic influence. In parallel, dynamic functional network connectivity (dFNC) has shown high sensitivity to brain changes related to mental disorders. However, previous studies linking dFNC to genetics largely follow a paradigm to identify associations between one set of genetic factors and multiple sets of connectivity features from different dFNC states, ignoring the potential variability in genetic correlates across states. We propose a novel joint ICA (jICA)-based "dynamic fusion" framework to identify dynamically tuned genetic manifolds. A sliding window approach was utilized to estimate four dFNC states and compute subject-level state-average dFNC (sa-dFNC) features. The sa-dFNC features of each state were combined with schizophrenia risk single nucleotide polymorphisms (SNPs) within a jICA fusion framework, resulting in four parallel fusions in 32,861 individuals of the UK Biobank cohort. The extracted four sets of joint SNP-dFNC components were further validated for clinical relevance in a combined schizophrenia cohort of 820 individuals (348 patients). The similarity of SNP-dFNC components across four parallel fusions was evaluated as a measure of state variability. We observed a mixture of "state-invariant" and "state-variant" components for SNP and dFNC modalities. Particularly, the schizophrenia-related state-variant SNP components, or manifolds, complemented each other by capturing different SNPs involved in the same biological functions, revealing a partition of genomic risk particularly elicited by the dynamics of brain function. By augmenting the SNP factors to state-variant manifolds, this dynamic fusion framework promises additional insights into the underlying genetic risk of disease-related alterations in dynamic brain function.

Humans↗
PubMed2000

Effects of patch number and dispersal patterns on population dynamics and synchrony.

In this paper, we examine the effects of patch number and different dispersal patterns on dynamics of local populations and on the level of synchrony between them. Local population renewal is governed by the Ricker model and we also consider asymmetrical dispersal as well as the presence of environmental heterogeneity. Our results show that both population dynamics and the level of synchrony differ markedly between two and a larger number of local populations. For two patches different dispersal rules give very versatile dynamics. However, for a larger number of local populations the dynamics are similar irrespective of the dispersal rule. For example, for the parameter values yielding stable or periodic dynamics in a single population, the dynamics do not change when the patches are coupled with dispersal. High intensity of dispersal does not guarantee synchrony between local populations. The level of synchrony depends also on dispersal rule, the number of local populations, and the intrinsic rate of increase. In our study, the effects of density-independent and density-dependent dispersal rules do not show any consistent difference. The results call for caution when drawing general conclusions from models of only two interacting populations and question the applicability of a large number of theoretical papers dealing with two local populations.

Animals↗
PubMed2002

Interplay between local dynamics and dispersal in discrete-time metapopulation models.

The effects of synchronous dispersal on discrete-time metapopulation dynamics with local (patch) dynamics of the same (compensatory or overcompensatory) or mixed (compensatory and overcompensatory) types are explored. Single-species metapopulation models behave as single-species single-patch models, whenever all local patches are governed by compensatory dynamics. Dispersal gives rise to multiple attractors with complex basin structures, whenever some local patches are under overcompensatory dynamics. In mixed systems, dispersal is capable of altering the local dynamics from compensatory to overcompensatory dynamics and vice versa. Examples are provided of metapopulation models supporting multiple attractors with intermingled basins of attraction.

Animals↗
PubMed2001

The dynamics of two diffusively coupled predator-prey populations.

I analyze the dynamics of predator and prey populations living in two patches. Within a patch the prey grow logistically and the predators have a Holling type II functional response. The two patches are coupled through predator migration. The system can be interpreted as a simple predator-prey metapopulation or as a spatially explicit predator-prey system. Asynchronous local dynamics are presumed by metapopulation theory. The main question I address is when synchronous and when asynchronous dynamics arise. Contrary to biological intuition, for very small migration rates the oscillations always synchronize. For intermediate migration rates the synchronous oscillations are unstable and I found periodic, quasi-periodic, and intermittently chaotic attractors with asynchronous dynamics. For large predator migration rates, attractors in the form of equilibria or limit cycles exist in which one of the patches contains no prey. The dynamical behavior of the system is described using bifurcation diagrams. The model shows that spatial predator-prey populations can be regulated through the interplay of local dynamics and migration.

Animals↗
PubMed2006

Sex differences in perception of emotion intensity in dynamic and static facial expressions.

Most research on the perception of emotional expressions is conducted using static faces as stimuli. However, facial displays of emotion are a highly dynamic phenomenon and a static photograph is its very unnatural representation. The goal of the present research was to assess the role of stimuli dynamics as well as subjects' sex in the perception of emotional expressions. In the experiment, subjects rated the intensity of expressions of anger and happiness presented as photographs (static stimuli) and animations (dynamic stimuli). The impact of both stimulus dynamics and emotion type on the perceived intensity was observed. The emotions on 'angry faces' were judged as more intense than on 'happy faces' and the intensity ratings were higher in the case of animation rather than photography. Moreover, gender differences in the rated intensity were found. For male subjects higher intensity ratings for dynamic than for static expressions were noted in the case of anger, whereas in the case of happiness, no differences were observed. For female subjects, however, differences for both anger and happiness were significant. The results suggest that the dynamic characteristic of facial display is an important factor in the perception of the intensity of emotional expressions. Its effect, however, depends on the subjects' sex and emotional valence.

Adult↗
PubMed2006

Stochastic models for mainland-island metapopulations in static and dynamic landscapes.

This paper has three primary aims: to establish an effective means for modelling mainland-island metapopulations inhabiting a dynamic landscape; to investigate the effect of immigration and dynamic changes in habitat on metapopulation patch occupancy dynamics; and to illustrate the implications of our results for decision-making and population management. We first extend the mainland-island metapopulation model of Alonso and McKane [Bull. Math. Biol. 64:913-958, 2002] to incorporate a dynamic landscape. It is shown, for both the static and the dynamic landscape models, that a suitably scaled version of the process converges to a unique deterministic model as the size of the system becomes large. We also establish that, under quite general conditions, the density of occupied patches, and the densities of suitable and occupied patches, for the respective models, have approximate normal distributions. Our results not only provide us with estimates for the means and variances that are valid at all stages in the evolution of the population, but also provide a tool for fitting the models to real metapopulations. We discuss the effect of immigration and habitat dynamics on metapopulations, showing that mainland-like patches heavily influence metapopulation persistence, and we argue for adopting measures to increase connectivity between this large patch and the other island-like patches. We illustrate our results with specific reference to examples of populations of butterfly and the grasshopper Bryodema tuberculata.

Algorithms↗
PubMed1994

The brain as a dynamic physical system.

The brain is a dynamic system that is non-linear at multiple levels of analysis. Characterization of its non-linear dynamics is fundamental to our understanding of brain function. Identifying families of attractors in phase space analysis, an approach which has proven valuable in describing non-linear mechanical and electrical systems, can prove valuable in describing a range of behaviors and associated neural activity including sensory and motor repertoires. Additionally, transitions between attractors may serve as useful descriptors for analysing state changes in neurons and neural ensembles. Recent observations of synchronous neural activity, and the emerging capability to record the spatiotemporal dynamics of neural activity by voltage-sensitive dyes and electrode arrays, provide opportunities for observing the population dynamics of neural ensembles within a dynamic systems context. New developments in the experimental physics of complex systems, such as the control of chaotic systems, selection of attractors, attractor switching and transient states, can be a source of powerful new analytical tools and insights into the dynamics of neural systems.

Action Potentials↗
PubMed2006

The impact of ejection fraction on outcomes after percutaneous coronary intervention in patients with congestive heart failure: an analysis of the National Heart, Lung, and Blood Institute Percutaneous Transluminal Coronary Angioplasty Registry and Dynamic Registry.

BACKGROUND: Patients with congestive heart failure (CHF) have higher rates of adverse outcomes after percutaneous coronary intervention (PCI). A comprehensive analysis of outcomes in patients with CHF in the current era has not been done. We studied the outcomes of patients with CHF who underwent PCI in the National Heart, Lung, and Blood Institute-sponsored Percutaneous Transluminal Coronary Angioplasty (PTCA) and Dynamic registries. METHODS: We evaluated demographic and angiographic characteristics and the clinical outcomes of patients with CHF in the Dynamic Registry and the PTCA Registry, excluding patients with acute myocardial infarction. In the Dynamic Registry, patients with CHF (n = 503) were compared with patients without CHF (n = 4194), and patients with CHF with a preserved ejection fraction (EF) (n = 134) were compared with patients with CHF who have a reduced EF (n = 199). The patients with CHF in the 1997 through 2001 Dynamic Registry (n = 236) were then similarly compared with patients with CHF in the earlier PTCA Registry (n = 117). RESULTS: In the Dynamic Registry, compared with patients without CHF, patients with CHF had a higher-risk clinical and angiographic profile, and a higher mortality rate both inhospital (2.6% vs 0.4%, P < or = .001) and at 1 year (13.1% vs 3.0%, P < .001). Patients with reduced EF had higher inhospital mortality rates and a trend toward higher mortality at 1 year. The patients with CHF in the Dynamic Registry compared with those in the PTCA Registry had a higher risk profile yet had significantly higher procedural success rates and improved clinical outcomes. CONCLUSIONS: Although CHF remains a strong predictor of adverse outcomes after PCI, significant improvement seen in the past decade is likely related to improved procedural techniques and improved medical therapy.

Aged↗
PubMed2024

Advances in solid-state NMR methods for studying RNA structures and dynamics.

Ribonucleic acid (RNA) structures and dynamics play a crucial role in elucidating RNA functions and facilitating the design of drugs targeting RNA and RNA-protein complexes. However, obtaining RNA structures using conventional biophysical techniques, such as X-ray crystallography and solution nuclear magnetic resonance (NMR), presents challenges due to the inherent flexibility and susceptibility to degradation of RNA. In recent years, solid-state NMR (SSNMR) has rapidly emerged as a promising alternative technique for characterizing RNA structure and dynamics. SSNMR has several distinct advantages, including flexibility in sample states, the ability to capture dynamic features of RNA in solid form, and suitability to character RNAs in various sizes. Recent decade witnessed the growth of 1H-detected SSNMR methods on RNA, which targeted elucidating RNA topology and base pair dynamics in solid state. They have been applied to determine the topology of RNA segment in human immunodeficiency virus (HIV) genome and the base pair dynamics of riboswitch RNA. These advancements have expanded the utility of SSNMR techniques within the RNA research field. This review provides a comprehensive discussion of recent progress in 1H-detected SSNMR investigations into RNA structure and dynamics. We focus on the established 1H-detected SSNMR methods, sample preparation protocols, and the implementation of rapid data acquisition approaches.

Dynamics↗
PubMed1994

Role of chaotic dynamics in neural plasticity.

Mathematical models are essential for the study of complex neural systems at all levels of the hierarchy from macromolecules through neurons to brain systems. ANN are readily available, but most of them are inappropriate for modeling brain function in normal behavior, because they stem from studies of neural systems in anesthetized or paralyzed animals which are capable only of reflux output. That class of models lacks the goal-directed, self-organizing properties of neural systems in behaving animals. In contrast to the stability of ANN and their reliance on asymptotic convergence to steady states (point attractors) and periodic oscillations (limit cycle attractors), BNN are intrinsically unstable. They continuously generate 'spontaneous' aperiodic activity that manifests the operation of chaotic dynamics undergoing repeated state transitions. Observations on the activity patterns of sensory cortex reveal that the perceptual outputs of BNN are by construction of spatial patterns and dynamic trajectories and not by computation using symbolic representations. Chaotic dynamics plays essential roles both in the construction of perceptions and in the continuing update of cortical populations, which requires selective synaptic modification during associative learning and habituation. Simultaneous multichannel recording from the olfactory bulb and cortex has given the following experimental results. (1) The cortical activity that relates to the perception of a sensory stimulus is carried macroscopically by a smaller number of single neurons e.g. 'units', 'feature detectors'. (2) The macroscopic activity reflects the meaning and significance of the stimulus for the experimental subject and not the stimulus as it is known to the observer. (3) The activity carries the meaning in spatial patterns, not in time series (the difference between a phonograph or radio and movie or TV). (4) The spatial patterns of activity that accompany previously learned stimuli or responses are changed by the introduction of new stimuli and also by modifications in reinforcement contingencies. There is no invariance in the memory store within the populations. (5) The patterns of activity are created by dynamic neural interactions in sensory cortex, not by registration or filtering of stimuli. There is no evidence for storage, retrieval, cross-correlation or logical tree search. (6) The dynamics is chaotic, not merely noisy, so that each act of perception involves a new construction by the cortex not by mere information processing. From these findings we infer that chaotic dynamics plays a crucial role in the construction of the associational contexts comprising the memory systems of experimental subjects.

Animals↗
PubMed1997

Non-linear dynamics of alpha and theta rhythm: correlation dimensions and Lyapunov exponents from healthy subject's spontaneous EEG.

The aim of the present paper was to analyze some non-linear dynamic properties of the resting EEG from healthy subjects under eyes closed conditions. For this purpose we digitally filtered the spontaneous EEG in the theta (3-8 Hz) and alpha frequency range (8-13 Hz) and considered these independent rhythms as signals from a deterministic system. Under certain conditions non-linear dynamic systems are able to generate deterministic chaos, which means that similar causes do not produce similar effects. This phenomenon is called sensitive dependence on initial conditions. From different lead positions (F3, F4, Cz, P3, P4, O1 and O2) we calculated the so-called correlation dimension D2, which is assumed to be an estimation of the system's complexity, and the Lyapunov exponent L, which appears to be a measure of the sensitive dependence on initial conditions. Our investigations revealed that the dimensionality of the theta- and alpha-rhythm varies within subjects across the experimental session in wide ranges. The degrees of freedom of the alpha and theta rhythms across the scalp are in the same order, indicating dynamic processes which can not be differentiated by applying the Grassberger-Procaccia algorithm. The Lyapunov-exponents, indicating 'how chaotic a deterministic process is', are in general smaller for the theta than for the alpha activity. Across the scalp there is no evidence for different dynamics of the theta rhythm. The dynamics of the alpha rhythm, on the contrary, appears to be different at various lead positions. It appears justified to state that the dynamics of the frontal alpha activity is functionally different from the alpha activity recorded at other topographic locations.

Algorithms↗
PubMed1999

Dynamics underlying rhythmic and non-rhythmic variants of abnormal, waking delta activity.

OBJECT: We applied a new test, nonlinear cross prediction (NLCP), to investigate whether or polymorphic delta activity (PDA) and frontal intermittent rhythmic delta activity (FIRDA) reflect linear or nonlinear brain dynamics. Furthermore realistic models were constructed to explain the dynamical properties of PDA and FIRDA. METHODS: Forty-nine EEG time series with FIRDA and 40 time series with PDA were studied with the NLCP algorithm. This characterizes a time series in terms of its predictability, amplitude asymmetry, and time asymmetry, with the latter two measures reflecting nonlinearity. Parameters of an EEG model proposed by Lopes da Silva were adjusted to obtain time series resembling PDA and FIRDA. RESULTS: FIRDA was more predictable than PDA. Most PDA segments could not be distinguished from linearly filtered noise. In contrast, FIRDA activity showed strong evidence of nonlinear dynamics. These dynamical properties of PDA and FIRDA could be reproduced by the Lopes da Silva model. PDA and FIRDA reflect a point attractor and a limit cycle attractor, respectively, perturbed by dynamical noise. CONCLUSION: Experimental analysis and modeling of the data suggest that PDA and FIRDA reflect fundamentally different types of brain dynamics. While PDA is filtered noise, reflecting low-level, random input to cortical networks, FIRDA may reflect limit-cycle oscillations due to increased excitation.

Adult↗