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At least 991 records · Page 55Linked to original sources
PubMed2005

Internal model of gravity for hand interception: parametric adaptation to zero-gravity visual targets on Earth.

Internal model is a neural mechanism that mimics the dynamics of an object for sensory motor or cognitive functions. Recent research focuses on the issue of whether multiple internal models are learned and switched to cope with a variety of conditions, or single general models are adapted by tuning the parameters. Here we addressed this issue by investigating how the manual interception of a moving target changes with changes of the visual environment. In our paradigm, a virtual target moves vertically downward on a screen with different laws of motion. Subjects are asked to punch a hidden ball that arrives in synchrony with the visual target. By using several different protocols, we systematically found that subjects do not develop a new internal model appropriate for constant speed targets, but they use the default gravity model and reduce the central processing time. The results imply that adaptation to zero-gravity targets involves a compression of temporal processing through the cortical and subcortical regions interconnected with the vestibular cortex, which has previously been shown to be the site of storage of the internal model of gravity.

Adaptation, Physiological↗
PubMed2003

[Virtual colonoscopy in real life--is it that good?].

BACKGROUND: Colon cancer is the main cause of mortality among the gastrointestinal cancers in Israel. Early detection of the average risk population is recommended from the age of 50 to 75 years. Private departments of radiology aggressively advertise virtual colonoscopy for the early detection of colon cancer, although it is not recognised as such in any country. METHODS: We collected all cases in which virtual colonoscopy was followed by endoscopic colonoscopy in the same patient from four medical centers in Israel. RESULTS: Total discrepancy between the results of the two examinations was found in 2/3 of the patients. In some cases colon cancer was missed. CONCLUSIONS: The results presented herein, raise many questions and "red lights" as to the use of virtual colonoscopy in its present form for screening purposes in Israel unless it is in the setting of clinical research.

Advertising↗
PubMed2004

Male sexual dysfunctions: immersive virtual reality and multimedia therapy.

The study describes a therapeutic approach using psycho-dynamic psychotherapy integrating virtual environment (VE) for resolving impotence or better erectile dysfunction (ED) of presumably psychological or mixed origin and premature ejaculation (PE). The plan for therapy consists of 12 sessions (15 if a sexual partner was involved) over a 25-week period on the ontogenetic development of male sexual identity, and the methods involved the use of a laptop PC, joystick, Virtual Reality (VR) helmet with miniature television screen showing a new specially-designed CD-ROM programs using Virtools with Windows 2000 and an audio CD. This study was composed of 30 patients, 15 (10 suffering from ED and 5 PE) plus 15 control patients (10 ED and 5 PE), that underwent the same therapeutic protocol but used an old VR helmet to interact with the old VE using a PC Pentium 133 16 Mb RAM. We also compared this study with another study we carried out on 160 men affected by sexual disorders, underwent the same therapeutic protocol, but treated using a VE created (in Superscape VRT 5.6) using always Windows 2000 with portable tools. Comparing the groups of patients affected by ED and PE, there emerged a significant positive results value without any important differences among the different VE used. However, we had a % increase of undesirable physical reactions during the more realistic 15-minute VR experience using Virtools development kit. Psychotherapy alone normally requires long periods of treatment in order to resolve sexual dysfunctions. Considering the particular way in which full-immersion VR involves the subject who experiences it (he is totally unobserved and in complete privacy), we hypothesise that this methodological approach might speed up the therapeutic psycho-dynamic process, which eludes cognitive defences and directly stimulates the subconscious, and that better results could be obtained in the treatment of these sexual disorders. This method can be used by any psychotherapist and it can be used alone or associated with pharmacotherapy prescribed by the urologist/andrologist as part of a therapeutic alliance.

CD-ROM↗
PubMed1987

Gene synthesis, expression, structures, and functional activities of site-specific mutants of ubiquitin.

To study the structure and function of ubiquitin we have chemically synthesized a ubiquitin gene that encodes the amino acid sequence of animal ubiquitin, inserting a series of restriction enzyme sites that divide the gene into eight "mutagenesis modules." A series of site-specific mutations were constructed to selectively perturb various regions of the molecule. The mutant genes were expressed in a large quantity of Escherichia coli, and the modified proteins were purified. To determine the structural effects of the amino acid substitutions, the solution structure of ubiquitin was investigated by two-dimensional NMR and each of the mutant proteins were screened for structural perturbations. With one exception, virtually no changes were seen other than at the point of mutation. Functional studies of the mutant proteins with the ubiquitin-activating enzyme E1 and in the reticulocyte protein degradation assay were used to identify regions of the molecule important to ubiquitin's activity in intracellular proteolysis.

Amino Acid Sequence↗
PubMed2002

Considering virtual colonoscopy.

Virtual colonoscopy continues to show promise as a colorectal cancer screening test and is technically evolving rapidly. It has particular advantages with regard to acceptability by both radiologists and patients. Important steps to achieve implementation include clear delineation of all of the technical components necessary to produce consistent high performance and development of clear-cut recommendations for interpretation and management of polyps of various sizes and the range of extracolonic findings identified. Development of an effective methodology to perform the test without bowel preparation or demonstration of cost-effectiveness for identification and treatment of one or more significant extracolonic diseases would be major breakthroughs, provided they are still accompanied by effective detection of significant colon neoplasms. Issues regarding general effectiveness and cost-effectiveness must be resolved before virtual colonoscopy is endorsed for widespread colorectal cancer screening or utilized for that purpose.

Colonic Polyps↗
PubMed1977

Effect of virtual image projection distance on the accomodative response of the eye.

Virtual image displays utilize either aircraft-mounted or helmet-mounted beam splitters, or combining screens. The effect on the accomodative response of the projection distance of the virtual image was measured by photographing the first and fourth Purkinje images of a source. The results indicate possible effect on the accomodation response. Further exploration of the problem is indicated.

Accommodation, Ocular↗
PubMed2006

A virtual active compound produced from the negative image of a ligand-binding pocket, and its application to in-silico drug screening.

We developed a new structure-based in-silico screening method using a negative image of a ligand-binding pocket and a multi-protein-compound interaction matrix. Based on the structure of the ligand pocket of the target protein, we designed a negative image, which consists of virtual atoms whose radii are close to those of carbon atoms. The virtual atoms fit the pocket ideally and achieve an optimal Coulomb interaction. A protein-compound docking program calculates the protein-compound interaction matrix for many proteins and many compounds including the negative image, which can be treated as a virtual compound. With specific attention to a vector of docking scores for a single compound with many proteins, we selected a compound whose score vector was similar to that of the negative image as a candidate hit compound. This method was applied to representative target proteins and showed high database enrichment with a relatively quick procedure.

Binding Sites↗
PubMed2006

Impairment on the hippocampal-dependent virtual Morris water task in schizophrenia.

Traditional neuropsychological tests of visual and verbal memory have been used to evaluate memory deficits in schizophrenia. However, these tests cannot be used in non-human animal research, which is important for the discovery of treatments that will improve cognition and for study of the etiology of schizophrenia. To help bridge the gap between human and non-human animal research on hippocampal function in schizophrenia, this study sought to characterize the behavioral performance exhibited by patients using the Morris water task (MWT). The MWT has been shown in human and non-human animal studies to be hippocampus-dependent. In the virtual MWT, human subjects navigate a computer-generated on-screen environment to escape from the "water" by locating a platform. Patients with schizophrenia and controls performed two versions of the virtual MWT: a hippocampal-dependent hidden-platform version, relying on allocentric navigational abilities, and a non-hippocampal-dependent visible-platform version, relying on cued-navigational abilities. Patients traveled further and took longer to find the hidden platform over training blocks and spent less time in the correct quadrant during a probe trial. There was no deficit in the visible-platform condition. These findings identify a behavioral impairment on a hippocampal-dependent task in schizophrenia and support using the MWT in testing animal models of schizophrenia.

Adult↗
PubMed2003

Prediction of aqueous solubility of a diverse set of compounds using quantitative structure-property relationships.

"Fail early and fail fast" is the current paradigm that the pharmaceutical industry has adopted widely. Removing non-drug-like compounds from the drug discovery lifecycle in the early stages can lead to tremendous savings of resources. Thus, fast screening methods are needed to profile the large collection of synthesized and virtual libraries involved in the early stage. Solubility is one of the filters that are applied extensively to ensure that the compounds are reasonably soluble so that synthesis of the compounds and assay studies of pharmacokinetics and toxicity are feasible. To address this need, we have developed a fast quantitative structure-property relationship (QSPR) model for the prediction of aqueous solubility (at 298 K, unbuffered solution) from the molecular structures. Multiple linear regressions and genetic algorithms were used to develop the models. The model was based on a set of diverse compounds including small organic molecules and drug and drug-like species. The predicted solubility for the training and test sets agrees well with the experimental values. The coefficient of determination is R(2) = 0.84 for the training set of 775 compounds and the RMS error = 0.87. This model was validated on four sets of compounds. The RMS error for the 1665 compounds from the four validation data sets (including compounds from the Physician's Desk References and Comprehensive Medicinal Chemistry databases) is 1 log unit and the unsigned error is 0.77. This model does not require 3-D structure generation which is rather time-consuming. Using 2-D structure as input, this model is able to compute solubility for 90 000-700 000 compounds/h on a SGI Origin 2000 workstation. This kind of fast calculation allows the model to be used in data mining and screening of large synthesized or virtual libraries.

Databases, Factual↗
PubMed2003

Tumor detection in the bladder wall with a measurement of abnormal thickness in CT scans.

Virtual cystoscopy is a developing technique for bladder cancer screening. In a conventional cystoscopy, an optical probe is inserted into the bladder and an expert reviews the appearance of the bladder wall. Physical limitations of the probe place restrictions on the examination of the bladder wall. In virtual cystoscopy, a computed tomography (CT) scan of the bladder is acquired and an expert reviews the appearance of the bladder wall as shown by the CT. The task of identifying tumors in the bladder wall has often been done without extensive computational aid to the expert. We have developed an image processing algorithm that aids the expert in the detection of bladder tumors. Compared with an expert observer reading the CT, our algorithm achieves 89% sensitivity, 88% specificity, 48% positive predictive value, and 98% negative predictive value.

Anatomy, Cross-Sectional↗
PubMed1998

Global spatial sampling with isotropic virtual planes: estimators of length density and total length in thick, arbitrarily orientated sections.

Existing design-based direct length estimators require random rotation around at least one axis of the tissue specimen prior to sectioning to ensure isotropy of test probes. In some tissue it is, however, difficult or even impossible to define the region of interest, unless the tissue is sectioned in a specific, nonrandom orientation. Spatial uniform sampling with isotropic virtual planes circumvents the use of physically isotropic or vertical sections. The structure that is contained in a thick physical section is investigated with software-randomized isotropic virtual planes in volume probes in systematically sampled microscope fields using computer-assisted stereological analysis. A fixed volume of 3D space in each uniformly sampled field is probed with systematic random, isotropic virtual planes by a line that moves across the computer screen showing live video images of the microscope field when the test volume is scanned with a focal plane. The intersections between the linear structure and the virtual probes are counted with columns of two dimensional disectors. Global spatial sampling with sets of isotropic uniform random virtual planes provides a basis for length density estimates from a set of parallel physical sections of any orientation preferred by the investigator, i.e. the simplest sampling scheme in stereology. Additional virtues include optimal conditions for reducing the estimator variance, the possibility to estimate total length directly using a fractionator design and the potential to estimate efficiently the distribution of directions from a set of parallel physical sections with arbitrary orientation. Other implementations of the basic idea, systematic uniform sampling using probes that have total 3D x 4pi freedom inside the section, and therefore independent of the position and the orientation of the physical section, are briefly discussed.

Journal Article↗
PubMed1994

Screening for cancer susceptibility in children.

Epidemiologic studies have demonstrated that virtually every form of human cancer may aggregate in families. Genetic susceptibility plays an important role in the development of many of these cancers, yet until very recently genes associated with this susceptibility had not been identified. Over the last several years, the class of genes known as tumor suppressor genes has been most consistently implicated in hereditary cancers. Recently, genes associated with childhood tumors including retinoblastoma, Wilms' tumor, as well as with adult-onset tumors such as breast cancer and colon cancer have been either cloned or localized to specific chromosomal sites. Their isolation has encouraged the development of techniques with which to analyze cancer-prone individuals and families for the presence of germline, or constitutional, alterations of genes that may place them at high cancer risk. In the past year, the benefits and pitfalls of some of these screening assays have been studied. Also, the literature has indicated the importance of considering both ethical and psychosocial implications of our growing ability to perform predictive testing for cancer.

Child↗
PubMed2004

Magnetic resonance colonography: a promising new technique.

Colorectal carcinoma is still the second leading cause of cancer-related death, although it arises mostly from benign adenomas. Numerous screening methods are available, but none of them is accepted as ideal. Ultrafast three-dimensional data sets acquired by cross-sectional imaging modalities (CT or magnetic resonance ) in combination with new post-processing modes, known as virtual colonoscopy, have led to a new discussion of screening tests for colorectal cancer. Recently published results indicate a high sensitivity for CT colonography and for MR-based colonography (MRC), with detection rates of greater than 90% for colorectal lesions greater than 10 mm in size. Three-dimensional data acquisition for MRC is performed in less than 1 minute, and no severe complications have been reported. The main advantages of MRC are the lack of ionizing radiation, the low risk of the procedure, and low patient discomfort. MRC has become an attractive diagnostic procedure for colorectal lesions that can also be used as a screening method.

Colonoscopy↗
PubMed1994

[The parameters of image quality of a novel ultra high resolution film-screen system].

A film/screen system is described where the light emission of the intensifying screen is in the UV, which is more efficiently absorbed by the film, and hence print-through is virtually eliminated. In addition, because of significantly higher UV absorption within the screen, MTF is superior to conventional systems based on visible light. Thus the overall UV film/screen system has imaging efficiency and quality, as measured by the Detective Quantum Efficiency (DQE) and the Noise Equivalent Quantum Efficiency (NEQ), with superior characteristics to those of conventional systems. These imaging characteristics of the novel systems are described here and are compared with those of some conventional systems.

Humans↗
PubMed2006

Evaluation of an indirect immunofluorescence assay for strongyloidiasis as a tool for diagnosis and follow-up.

The diagnostic accuracy of an indirect immunofluorescence antibody test (IFAT) for Strongyloides stercoralis at different serum antibody titers was evaluated. To assess diagnostic sensitivity, sera from 156 patients with known strongyloidiasis were collected. Negative control sera were obtained from a composite group of 427 subjects (blood donors and hospitalized patients). With an area under the receiver-operating characteristic plot of 0.98, the IFAT showed a high level of diagnostic accuracy for strongyloidiasis. An antibody titer of > or = 1:20, with 97% sensitivity and 98% specificity, was identified as the diagnostic threshold with the best overall performance. Cross-reactions were evaluated with 41 additional samples from patients with other known helminth infections, and the IFAT detected low-titer positivity in only one subject with filariasis. A positive IFAT result at an antibody dilution of > or = 1:80 was virtually 100% specific, with 71% sensitivity. To test the usefulness of the IFAT as a monitoring tool, the changes in specific-antibody titers after treatment in a group of 155 patients were evaluated. Seroreversion or a decrease in antibody titer of twofold or more was observed in 60% of the patients. Response to treatment was directly correlated to the initial antibody titer, and a baseline titer of > or = 1:80 was identified as the best predictor of response. In conclusion, a positive IFAT result at an antibody dilution of >/=1:20 is the optimal cutoff for screening. A titer of > or = 1:80, with virtually no false-positive result, is a reliable cutoff for a serological assessment of treatment efficacy and for inclusion in clinical trials.

Aged↗
PubMed2005

[Screen of differentially expressed genes between gastrula embryos and tail bud embryos in gynogenetic gibel carp (Carassius auratus gibelio)].

Suppression subtractive hybridization (SSH) cDNA plasmid libraries were constructed between gastrula embryos and tail bud embryos in gynogenetic gibel carp (Carassius auratus gibelio). 739 and 816 PCR positive clones were respectively selected to perform dot blot, and 72 dot blot positive clones and 98 dot blot positive clones were obtained from the SSH plasmid libraries specific for gastrula embryos and tail bud embryos. Sequencing analysis and database searches indicated that there were 19 known genes and 31 unknown/cDNA fragments in the sequenced 72 dot blot positive clones specific for gastrula embryos, and 52 known genes and 37 unknown cDNA fragments in the sequenced 98 dot blot positive clones specific for tail bud embryos. Moreover,specific expressions of partial genes were further confirmed by virtual Northern blots and RT-PCR. The screen of these differentially expressed genes will help us to understand the molecular mechanism in gibel carp embryogenesis.

Animals↗
PubMed2006

Functional genomic approaches in C. elegans.

The nematode Caenorhabditis elegans is an extraordinarily powerful model organism for the application of functional genomic approaches. Two such approaches, whole genome microarray analysis and genome-wide RNA interference (RNAi)-mediated phenotypic screening, are highly advanced and can be used by virtually any laboratory to study biological processes of interest. Using studies of the osmotic stress response in C. elegans as an example, this chapter describes methods for conducting whole genome microarray experiments and for carrying out genome-wide reverse-genetic screens using a commercially available C. elegans bacterial RNAi feeding library. Both approaches are complimentary and can be used to rapidly gain genome-wide insights into the genes and gene networks controlling specific physiological processes.

Animals↗
PubMed2002

Development and validation of virtual driving simulator for the spinal injury patient.

We developed a virtual reality (VR) driving simulator in order to safely evaluate and improve the driving ability of spinal injury patients. The simulator is composed of an actual car, a beam projector, and a large screen. For the interface of our driving simulator, an actual car was adapted and then connected to a computer. We equipped the car with hand control driving devices especially adapted for spinal injury patients. A beam projector was used so that the subjects could see the virtual scene on a large screen set up in front of them. The virtual environment (VE) consisted of 18 sections (e.g., a speed-limited road, a straight road, a curved road, a left turn) and each section was linked naturally to the next. The subjects selected for this trial were 10 normal drivers with valid driving licenses and 15 patients with thoracic or lumbar cord injuries who had prior driving experience. For evaluation, five driving skills were measured, including average speed, steering stability, centerline violations, traffic signal violations, and driving time in various road conditions such as straight and curved roads. The normal subjects manipulated the gas pedal and the brake with their feet, while the patients manipulated a hand control with their hands. After they finished driving the whole course, the participants answered the questions such as "How realistic did the virtual reality driving simulator seem to you?" and "How much was your fear reduced?" In this study, we found that the difference in manipulation method (i.e., the patient group's hand control versus the normal driver's foot controls) does not seem to influence relative performance in the VR driving simulator, though training to improve the use of hand controls in the VR driving simulator would be useful to reduce the fear that the patients feel while driving.

Adult↗