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Results for “Convergence”

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At least 613 records · Page 34Linked to original sources

PubMed1999

[Determination of focal distance and convergence assessment in collimators with focalized geometry].

OBJECTIVE: A method to calculate intrinsic parameters of fan beam collimators is presented. This method allows us to determine focal length and to assess the convergence of the collimator on a single focus line. MATERIAL AND METHODS: Images of a radioactive source located successively in a series of known coordinate positions are acquired. To determine the focal distance, a method has been developed that minimizes the sum of the distances between the experimental image point and the theoretical ones. Collimator convergence was evaluated by the intersections between all the pairs of lines drawn between the source location and its experimental image point. RESULTS: The results found between the two collimators showed that the actual focal length deviates 1.5% from the real focal value and the nominal focal length. The results also indicate that the collimator holes do not converge on a single focal line but rather on a focal area, with average deviations in regards to the real focus being *x = 2.5 mm and *z = 7.1 mm. CONCLUSIONS: The errors in regards to the original values and the extension of the focal zone make it possible to conclude that the quality of the collimators used is acceptable.

Mathematics↗

PubMed2000

Convergent inputs from thalamic motor nuclei and frontal cortical areas to the dorsal striatum in the primate.

Current models of basal ganglia circuitry primarily associate the ventral thalamic nuclei with relaying basal ganglia output to the frontal cortex. However, some studies have demonstrated projections from the ventral anterior (VA) and ventral lateral (VL) thalamic nuclei to the striatum, suggesting that these nuclei directly modulate the striatum. VA/VL nuclei have specific connections with primary, supplementary, premotor, and cingulate motor cortices indicating their involvement in motor function. These areas mediate different aspects of motor control such as movement execution, motor learning, and sensorimotor integration. Increasing evidence indicates that functionally related motor areas have convergent projections to the dorsal striatum, suggesting that integration of different aspects of motor control occur at the level of the striatum. This study examines the organization of VA/VL thalamic inputs to the dorsal "motor" striatum to determine how this afferent projection is organized with respect to corticostriatal afferents from motor, premotor, and cingulate motor areas. Motor cortical projections to specific dorsal striatal regions arose from multiple areas, including components from primary motor, premotor, supplementary, and cingulate motor areas. Diverse motor cortical projections to a given dorsal striatal region indicated convergence of functionally related corticostriatal motor pathways. Most dorsal striatal sites received dense thalamic inputs from the VL pars oralis nucleus. Additional thalamostriatal projections arose from VA, VL pars caudalis, and ventral posterior lateral pars oralis nuclei and Olszewski's Area X. Our results provide evidence for convergent striatal projections from interconnected ventral thalamic and cortical motor areas, suggesting that these afferents modulate the same striatal output circuits.

Animals↗

PubMed2001

[Validation of quantitative parameters of paraprosthetic mitral valve regurgitation of the zone of convergence by transthoracic echocardiography].

The study of the convergence zone by echocardiography is a validated method of quantification of native valve mitral regurgitation. However, there is little data concerning its applications to paraprosthetic mitral regurgitation. The aim of this study was to evaluate the method in this indication. Thirty consecutive patients (21 mechanical and 9 bioprostheses) with paraprosthetic mitral regurgitation quantified by transoesophageal echocardiography were included: 4 mild, 13 moderate and 13 severe. The regurgitant volume RV) and the regurgitant surface area (RSA) were calculated by the following formulae: RV = 2 pi.r2.Va.t.alpha/180 and RSA = RV/VTI (r: mid systolic radius of the convergence zone, Va: aliasing velocity, t: regurgitation time, alpha/180: the angular correction due to parietal stress, VTI: velocity time integral of the regurgitant flow). The feasibility of the calculation of the RV and RSA was 93 and 63% respectively. There was a statistically significant correlation between the RV and transoesophageal echocardiography (r: 0.85, p < 0.001), between RSA and transoesophageal echocardiography (r: 0.67, p < 0.05) and between RV and RSA (r: 0.95, p < 0.001). When severe paraprosthetic regurgitation was defined by a RV greater than 60 ml and RSA greater than 40 mm2, the concordance between RV, RSA and transoesophageal echocardiography was 75% and 74% respectively. Therefore, the study of the convergence zone provides an accurate evaluation of paraprosthetic mitral regurgitation by transthoracic echocardiography.

Adult↗

PubMed1999

[The value of "blood vessel convergency" sign in the diagnosis of small peripheral lung cancer].

OBJECTIVE: To evaluate blood vessel convergency (BVC) sign in the radiologic diagnosis of small peripheral lung cancer. METHODS: A prospective thin-section CT-pathology comparative study was done in 123 cases with solitary pulmonary nodules less than 3 cm in diameter including 83 peripheral lung cancera (adenocarcinoma 46, squamous-cell carcinoma 21, bronchiolo-alveolar-cell carcinomas 7, undifferentiated carcinoma 6, adenosquamous carcinoma 3) and 40 benign lesions. They were pathologically and clinically confirmed. Serial transverse sections of the surgically resected specimens were examined microscopically in 91 cases. Attention was focused on the imaging and histological manifestations of BVC. RESULTS: BVC was found in 54 (65.1%) peripheral lung cancers and in 8(20%) benign nodules (chi 2 = 22.75, P < 0.001). Histologically, the convergent vessels were shown to be dilated arterioles or venules. CONCLUSION: Blood vessel convergency can be regarded as a valuable sign for the diagnosis of small peripheral lung cancers.

Adult↗

PubMed1993

[The convergence angle of crown preparations with clinically satisfactory retention].

A method was developed to measure the convergence angle on dies of complete crown preparations. The 132 dies measured revealed a surprising range in the convergence angles (15.5 to 30.2 degrees). The mandibular molar preparations had the greatest convergence angle. The design of mandibular molar preparations should be the subject of additional research.

Crowns↗

PubMed2002

Dynamin-dependent endocytosis is necessary for convergent-extension movements in Xenopus animal cap explants.

Cadherin cell-cell adhesion molecules are important determinants of morphogenesis and tissue patterning. C-cadherin plays a key role in the cell-upon-cell movements seen during Xenopus gastrulation. In particular, regulated changes in C-cadherin adhesion critically influence convergence-extension movements, thereby determining organization of the body plan. It is also predicted that remodelling of cadherin adhesive contacts is important for such cell-on-cell movements to occur. The recent demonstration that Epithelial (E-) cadherin is capable of undergoing endocytic trafficking to and from the cell surface presents a potential mechanism for rapid remodelling of such adhesive contacts. To test the potential role for C-cadherin endocytosis during convergence-extension, we expressed in early Xenopus embryos a dominantly-inhibitory mutant of the GTPase, dynamin, a key regulator of clathrin-mediated endocytosis. We report that this dynamin mutant significantly blocked the elongation of animal cap explants in response to activin, accompanied by inhibition of C-cadherin endocytosis. We propose that dynamin-dependent endocytosis of C-cadherin plays an important role in remodelling adhesive contacts during convergence-extension movements in the early Xenopus embryo.

Animals↗

PubMed1993

On regional convergence in a transitional economy: the roles of migration and wages.

The role of migration in influencing convergence between regions at different levels of economic development is analyzed using the example of Germany following reunification, with particular reference to the impact of migration on wages. "Several ways of regional wage formation are investigated, among them a full employment wage mechanism as well as a fast regional convergence of wages which is independent of productivity movements. The conclusion is that the impact of wage mechanisms on the convergence of per capita output is ambiguous. However social costs in terms of unemployment are high in case of a wage adjustment which is regardless of productivity growth." (SUMMARY IN GER)

Demography↗

PubMed2003

Convergence and interaction of hippocampal and amygdalar projections within the prefrontal cortex in the rat.

The orbital and medial prefrontal cortex (OMPFC) receives inputs from the CA1/subicular (CA1/S) region of the ventral hippocampus and the basolateral nucleus of the amygdala (BLA). Despite many studies about these projections, little is known as to how CA1/S and BLA inputs converge and interact within the OMPFC. Extracellular recordings of single-unit activity in the OMPFC were performed in sodium pentobarbitone-anesthetized rats. OMPFC neurons driven by CA1/S or BLA stimulation were more frequently encountered in the ventral portion of the prelimbic (v-PrL) and infralimbic cortex (IL). OMPFC neurons showing excitatory convergence of both inputs from the CA1/S and BLA were also located predominantly in the v-PrL and IL. The excitatory latencies of these neurons from both the CA1/S and BLA revealed almost identical values. Excitatory responses of OMPFC neurons to CA1/S (or BLA) stimulation were markedly augmented by simultaneous BLA (or CA1/S) stimulation, whereas the inhibitory influence of the BLA (or CA1/S) on CA1/S-induced (or BLA-induced) excitation was apparent when BLA (or CA1/S) stimulation was given 20-40 msec before CA1/S (or BLA) stimulation. Similar results were also observed when reciprocal connections between the CA1/S and BLA were severed to exclude the influences of these connections on one another. From these studies, we concluded that excitatory and inhibitory inputs from the hippocampus and amygdala converge and interact in the v-PrL and IL. Furthermore, the results indicate that simultaneous activation of hippocampal and amygdalar neurons may be important for amplification of OMPFC neuronal activity.

Action Potentials↗

PubMed2005

Comparison of convergence angles achieved in posterior teeth prepared for full veneer crowns.

This study compares the convergence angle of preparations for posterior gold crowns made by fourth/ fifth year undergraduate dental students, clinical teaching staff and general dental practitioners. Sixty dies were cast from impressions previously taken of clinical preparations by clinicians within each of the four groups. Each die was trimmed and sectioned in both mesio-distal and bucco-lingual planes before being projected using an overhead projector, thereby enabling the convergence angle silhouette to be measured. The results show the greatest convergence angle range to be produced by the least experienced students (10 degrees - 82 degrees). However, no significant difference (p > 0.05) was found when students with one further year of experience were compared to experienced staff. The degree of conformity to the ideal taper (4 degrees - 14 degrees) was no greater than 50% for any of the groups.

Analysis of Variance↗

PubMed1989

[Convergence of preganglionic fibers on neurons of the rabbit superior cervical ganglion].

Responses of neurons of the rabbit superior cervical ganglion to stimulation of the fascicles of preganglionic fibres and tonic activity of these neurons were recorded with intracellular electrodes in vitro and in situ, respectively. Marked convergence of preganglionic fibres onto ganglion cells was found: 8.5 +/- 1.2 fibres, on the average, converged on each cell. It was found that each ganglionic neuron received two preganglionic inputs: single and multiple. The single input was formed by a single preganglionic fibre which evoked EPSP strong enough to trigger a postsynaptic spike. The multiple input was formed by two or more converging preganglionic fibres which could trigger a postsynaptic spike only through summation of the EPSPs they evoked. The interspike intervals for these two preganglionic inputs in tonic activity of neurons were described by distributions of different types: Gaussian and Poisonian ones. Those two distributions were typical of single and multiple inputs, respectively.

Action Potentials↗

PubMed1983

Infantile convergence-evoked nystagmus.

A case of convergence-evoked nystagmus in a healthy 15-month-old boy is presented. This is clinically demonstrated to be induced by fusional convergence, and not related to accommodative, tonic, or proximal convergence. The lack of neurological or ophthalmic abnormalities supports the classification of a "congenital" type of this rare phenomenon. A differential diagnosis is also discussed.

Accommodation, Ocular↗

PubMed1984

Convergence insufficiency in patients taking medicines.

The incidence of convergence insufficiency in patients taking medicines is compared with its incidence in patients taking no therapeutic drugs, in a sample of 648 taken from a normal optometric practice. It is found that the incidence was significantly higher in those patients on medicines considering the group as a whole. It is also found to be higher in older patients, and that most of the older patients were taking medicines whilst the younger patients were not. However, the increase in the incidence of convergence insufficiency in the older patients taking medicines was disproportionately high. It is concluded that age is not the only factor in the increased incidence, and that the taking of medicines as a possible indicator of poor general health, is also an important factor in the cause of convergence difficulties.

Age Factors↗

PubMed1994

Squirrel monkey lateral thalamus. II. Viscerosomatic convergent representation of urinary bladder, colon, and esophagus.

The response properties of 106 visceroceptive lateral thalamic neurons were investigated in anesthetized squirrel monkeys. Most neurons were located in the ventral posterior lateral nucleus (VPL), and a smaller number of cells was also found in a variety of thalamic nuclei around VPL. Ninety (85%) of these cells responded to distension of the urinary bladder, the distal colon, and/or the lower esophagus. The majority of the visceral-responsive cells also had convergent somatic and multivisceral responses (71% of the 85%). A small population (6%) was visceral specific; that is, these neurons were not activated with somatic stimuli. Visceral responses were excitatory, inhibitory, or mixed, and most were either visceral nociceptive specific (65%) or visceral wide-dynamic-range type (34%). Very few visceral responses (1%) could be classified as low threshold. The incidence of these response types were highly dependent on the specific viscus stimulated. Most visceral responses were able to code stimulus duration and intensity. The majority (69%) of the visceroceptive neurons had somatic low-threshold convergent input mainly from the surface of the lower body. The somatic receptive field locations and the somatic response properties seem unrelated to the convergent visceral input and the visceral response properties, although there were some exceptions. No obvious viscerotopical organization was found in VPL. The results lead us to propose two different modes of representation for processing of and distinguishing between visceral and somatic inputs: a distributed population code for visceral inputs, and a local code for somatic inputs. Based on these codes, we discuss a new hypothesis for referred pain.

Animals↗

PubMed1993

[Search for convergence between values of indicators for evaluating oral cavity status as recommended by WHO and presence of fungi or Trichomonas tenax].

There is a lack in the literature of publications analyzing values of indicators for evaluation of oral cavity status, namely: PUW number (cariogenic indicator), Russell's indicator (changes in the paradontium) and Greene-Vermillion indicator (hygiene) recommended by WHO. This prompted the study for search of convergence between values of listed indicators and presence of fungi in ontocenosis of oral cavity in patients reporting to the stomatologist because of several reasons. Among 355 patients in oral cavity of whom presence of fungi was detected, the highest frequency of this invasion was noted in patients with diseases of the paradontium, while lowest percentage was noted in patients with confirmed caries. Convergence between values of tested indicators and presence of fungi was evaluated by application of convergence coefficient of Yule and the Pearson's test (Chi2). No significant correlation between presence of fungi and changes in the oral cavity was found.

Animals↗

PubMedDate not supplied

[Surgical treatment of paralytic convergent strabismus using a modification of Jensen's method].

Surgical treatment of paralytic convergent strabismus using the modified Jensen's is method was performed in 35 patients. The full success (orthophoria) was achieved in 51.5% and satisfying (approximately orthophoria) in 25.7% of cases. The six-year follow up of patients showed that surgical effect was permanent in 71.4% of cases. The most common cause of paralytic convergent strabismus has been trauma (71.4%), and, that, traffic accidents in 45.7%. According to communications and available literature this modified treatment of paralytic convergent strabismus for the first time in Yugoslavia has been applied in the Military Medical Academy.

Adolescent↗

PubMed1993

Rapidly converging iterative reconstruction algorithms in single-photon emission computed tomography.

Iterative reconstruction algorithms with markedly different convergence rates have been proposed in single-photon emission computed tomography (SPECT). Several new iterative reconstruction methods are described in this investigation. Differences between the methods include whether a ramp filter was used during backprojection, the type of backprojection weighting and whether camera and collimator blur were employed in the projection step. Simulated and real cylindrical phantoms with rod inserts were used to compare the properties of convergence and resolution following reconstruction by maximum likelihood (ML), iterative-Chang and the newly proposed reconstruction methods. Resolution was assessed after kernel-sieve regularization to achieve the same signal-to-noise ratio for all methods. Compared with maximum-likelihood reconstruction, methods employing a ramp converged much faster. One such method resulted in images with the same resolution and noise as ML, thus permitting termination of reconstruction at 14 iterations rather than the 1000 iterations required with ML. The major determinants of resolution were found to be use of an accurate model of the gamma camera imaging process in the projection step and inclusion of attenuation weighting and depth-dependent blur in the backprojection step. In summary, a new iterative reconstruction method was developed incorporating attenuation and blur and using a ramp filter that achieved results comparable to maximum-likelihood reconstruction in a fraction of the time.

Algorithms↗

PubMed1993

Convergent force fields organized in the frog's spinal cord.

Microstimulation of the gray matter of the frog's spinal cord was used to elicit motor responses. Force responses were recorded with the frog's ankle clamped while EMG activity was monitored. The collections of force patterns elicited at different leg configurations were summarized as force fields. These force fields showed convergence to an equilibrium point. The equilibrium paths were calculated from the force fields with the leg clamped. These paths predicted free limb motion in 75% of trials. The force fields were separated into active and prestimulation resting responses. The active force field responses had a fixed position equilibrium. These active force fields were modulated in amplitude over time, although the balance and orientations of forces in the pattern remained fixed. The active fields grouped into a few classes. These included both convergent and parallel fields. The convergent force fields (CFFS) could be observed in deafferented preparations. Motoneuron (MN) activity underlying the force fields was marked using sulforhodamine. The marked activity covered several segments. Several simulations and MN stimulations show that topography, limb geometry, and random activation could not account for the results. It is likely that propriospinal interneurons distribute the activity that underlies the responses observed here. Experiments showed that CFFs that resemble those elicited by microstimulation also underlie natural behaviors. The full variety of fields revealed by microstimulation was larger than the repertoire elicited by cutaneous stimulation. It was concluded that fixed-pattern force fields elicited in the spinal cord may be viewed as movement primitives. These force fields could form building blocks for more complex behaviors.

Animals↗

PubMedDate not supplied

[Efferent-afferent convergence as a structural-functional basis for a mechanism of an acceptor of action results].

In investigation data illustrating neurophysiological features efferent-afferent convergence in CNS are presented. Possibility of involvement of the efferent-afferent convergence mechanism in development of the acceptor of action results apparatus is considered. The role of parietal associative cortex as the integrative zone and zone of interaction the collateral pyramidal excitations with the nature afferent excitations is also discussed. The functional role of efferent-afferent convergence and interaction within the cyclic outline: motor cortex-parietal associative cortex-caudate nucleus-pallidum-thalamus-frontal cortex-motor cortex is analysed.

Afferent Pathways↗