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At least 901 records · Page 50Linked to original sources
PubMed2000

Uncommon left hepatic duct injury during laparoscopic cholecystectomy.

Laparoscopic cholecystectomy is currently the gold standard in the treatment of symptomatic gallstones but has been shown to have a higher incidence of biliary tree lesions (0.3-1%) compared with reported traditional open approaches. Loss of three-dimensional view and of depth perception is the main limit of the laparoscopic approach, especially if particular risk factors are associated (e.g., postinflammatory fibrosis, anatomic variations). Moreover, inadequate training may justify the increase of biliary tract lesions. The authors describe a unique case of left hepatic duct clipped without section of the duct itself during an otherwise "easy" operation. At the reintervention, because of the favorable local condition, a reconstruction was possible after a small duct resection with a ductal-hepatic anastomosis over a T-tube. This was removed after 8 months because of the good patency of the biliary tree and the absence of cholestasys. A long-term follow-up is mandatory for a complete functional evaluation.

Adult↗
PubMed2000

Independent component analysis applied to feature extraction from colour and stereo images.

Previous work has shown that independent component analysis (ICA) applied to feature extraction from natural image data yields features resembling Gabor functions and simple-cell receptive fields. This article considers the effects of including chromatic and stereo information. The inclusion of colour leads to features divided into separate red/green, blue/yellow, and bright/dark channels. Stereo image data, on the other hand, leads to binocular receptive fields which are tuned to various disparities. The similarities between these results and the observed properties of simple cells in the primary visual cortex are further evidence for the hypothesis that visual cortical neurons perform some type of redundancy reduction, which was one of the original motivations for ICA in the first place. In addition, ICA provides a principled method for feature extraction from colour and stereo images; such features could be used in image processing operations such as denoising and compression, as well as in pattern recognition.

Algorithms↗
PubMed2001

Stereoscopic x-ray image processing.

A three-step stereoscopic image-processing algorithm is proposed in order to improve image quality and depth perception of stereoscopic radiographs taken with C-arm equipment. The steps include illumination correction, geometry conversion and screen parallax adjustment. Flipping of stereoscopic radiographs is also discussed.

Computer Simulation↗
PubMed2001

Hierarchical processing of horizontal disparity information in the visual forebrain of behaving owls.

According to their restricted receptive fields and input-filter characteristics, disparity-sensitive neurons at early processing levels of the visual system perform rather ambiguous computations; they respond vigorously to disparity in false-matched images and show multiple response peaks in their disparity-tuning profiles. On the other hand, the perception of depth from binocular disparity is reliable, thus raising the question as to where and how in the brain additional processing is accomplished leading toward behaviorally relevant disparity detection. To address this issue, tuning data during stimulation with correlated and anticorrelated random-dot stereograms (a-RDS) were obtained from 52 disparity-sensitive visual Wulst neurons in three behaving owls. From the disparity-tuning curves, several quantitative measures were derived that allowed to determine the response ambiguity of a cell. A systematic decline of response ambiguities with increasing response latencies was observed. An increase in response latencies of neurons was correlated with a decrease of the strength of responses to a-RDS. Declining responses to a-RDS are expected for global detectors, because an owl was not able to discriminate depth in psychophysical tests with a-RDS. In addition, suppression of response side peaks was increased and disparity tuning was enhanced with growing response latencies. These results suggest a functional hierarchy of disparity processing in the owl's forebrain, leading from spatial filters to more global disparity detectors that may be able to solve the correspondence problem. Nonlinear threshold operations and inhibition are proposed as candidate mechanisms to resolve coding ambiguities.

Action Potentials↗
PubMedDate not supplied

Modeling V1 neuronal responses to orientation disparity.

The contribution of interocular orientation differences to depth perception, at either the neuronal or the psychophysical level, is unclear. To understand the responses of binocular neurons to orientation disparity, we extended the energy model of Ohzawa et al. (1990) to incorporate binocular differences in receptive-field orientation. The responses of the model to grating stimuli with interocular orientation differences were examined, along with the responses to random dot stereograms (RDS) depicting slanted surfaces. The responses to combinations of stimulus orientations in the two eyes were left-right separable, which means there was no consistent response to the binocular orientation difference. All existing neuronal data concerning orientation disparity can be well described by this type of model (even a version with no disparity selectivity). The disparity sensitive model is nonetheless sensitive to changes in RDS slant, although it requires narrow orientation bandwidth to produce substantial modulation. The disparity-insensitive model shows no selectivity to slant in this stimulus. Several modifications to the model were attempted to improve its selectivity for orientation disparity and/or slant. A model built by summing several disparity-sensitive models showed left-right inseparable responses, responding maximally to a consistent orientation difference. Despite this property, the selectivity for slant in RDS stimuli was no better than the simple disparity-selective model. The range of models evaluated here demonstrate that interocular orientation differences are neither necessary nor sufficient for signaling slant. In contrast, within the framework of the energy model, positional disparity sensitivity appears to be both necessary and sufficient.

Animals↗
PubMed2002

Feasibility of off-pump ASD closure using real-time 3-D echocardiography.

BACKGROUND: If surgeons could "see " through blood and cardiac chamber walls, it would ultimately be unnecessary to open the heart or use cardiopulmonary bypass to perform procedures such as atrial septal defect (ASD) closure or mitral valve repair. Conventional echocardiography generates cross-sectional images that are not satisfactory as the only visualization for surgical procedures, and current 3-Dimensional (3-D) CT and echo systems take several minutes to compose and process a single still frame. Recently, however, the first system for real-time 3-D echocardiography has been developed. This study examines whether real-time 3-D echocardiography can provide images of sufficient anatomic definition, depth perception, and image resolution to substitute for optical visualization in performing ASD closures. METHODS: A prototype Volumetrics 3-D echocardiographic system was evaluated in a water bath on a complex-surfaced standard reference model to determine the image resolution and define the ideal imaging parameters. A static image and views of sutures being placed with an endoscopic needle driver and two commercial suture placement devices were evaluated at multiple angles and distances from the target. The resulting images were graded by a blinded reviewer. Once the best imaging parameters were determined, five porcine ASDs were closed with interrupted sutures, running sutures, or a pursestring suture using only echo visualization. RESULTS: The highest quality images were obtained with the probe at a distance of 4-6 cm and at angles perpendicular or 45 degrees forward to the target. Spatial and temporal resolutions were adequate to suture all ASDs closed under only echo guidance. CONCLUSIONS: The evaluated real-time 3-D echo system provided adequate spatial and temporal information to act as a guide for surgical procedures.

Animals↗
PubMed1992

Complications of laparoscopic cholecystectomy.

Laparoscopic cholecystectomy has proven popular with both surgeons and patients. The rapid adoption of laparoscopic surgery has resulted in a number of new operative complications, including problems related to distension of the peritoneal cavity, a lack of depth perception afforded by the video image, and new instruments used with this technique. Few reports deal with complications associated with laparoscopic biliary tract surgery. This report discusses the problems that have occurred most frequently in my region as well as problems related to me in discussions with other experienced laparoscopic surgeons; it also presents methods of recognizing such injuries and preventing them.

Cholecystectomy, Laparoscopic↗
PubMed1992

Relationships between surgical ability ratings and spatial abilities and personality.

Twenty-two trainee surgeons were tested on high level tests of intelligence, a detailed battery of paper-and-pencil and computerized spatial ability tests, and personality tests. They were also rated for operating ability, clinical decision-making ability, and for overall performance by consultant surgeons who knew them well. Ability ratings were high, indicating very little dissatisfaction with the performance of trainee surgeons. There were no significant correlations between surgical ability ratings and intelligence test scores. The only significant correlation between spatial ability and ability ratings was with one subtest, and was in the opposite direction to that expected. Trends in the data suggested that those trainees rated as superior tended to be more introverted and conscientious, and tended to have better stereoscopic depth perception. The discussion questions the necessity for aptitude testing in surgery and points out some statistical pitfalls in the area. It is concluded that little advance may be made with the application of aptitude testing in the selection of surgeons until there are more objective criteria of surgical ability in different surgical specialties.

Adult↗
PubMed2000

Stereoscopic visual impairment in vascular dementia.

Binocular depth perception is mediated by neural pathways that involve thalamic nuclei, the posterior parietal lobe and adjacent gyri, and white matter projections connecting these regions. Vascular dementia results from a variety of pathologic syndromes that can affect these areas, and in the current study is shown to produce associated impairment of stereoacuity or complete stereoblindness. Stereoacuity was relatively more impaired by right than left hemisphere pathology, by cortical than subcortical vascular processes, and by lesions that involved the parietal lobe. The extent of impairment was related to dementia severity as reflected by measures of intelligence, memory, and visual-spatial function. Stereoacuity was unimpaired in age-matched patients with depressive disorders.

Journal Article↗
PubMed2000

Familial Creutzfeldt-Jakob disease: a neuropsychological case study.

The spectrum of neuropsychological features of familial Creutzfeldt-Jakob disease (CJD) have seldom been reported, possibly because of (a) the rarity of this hereditary form of prion disease; (b) frequent delays in diagnosis, and; (c) the typically rapid demise of the patient, which affords little opportunity for comprehensive testing or serial analysis. Here we describe the neurobehavioral characteristics of a 48-year-old right-handed male (JD) who presented with complaints of poor depth perception, unsteady gait, and unusual sensory experiences in his face and neck. JD was followed serially over the final 4 months of his 5-month illness. Immediately following hospital admission, he underwent a neuropsychological evaluation that revealed moderate to severe impairment of delayed (30-minute) verbal memory, tactual performance in his right hand, and word-finding ability. In contrast, other abilities that are commonly classified within the verbal, visuospatial, and memory domains showed minimal or no compromise. Parallel studies of electroencephalographic activity revealed diffuse slowing and, later, 1-Hz rhythmical discharges over the left hemisphere, and mild prominence of the lateral ventricles and cerebral sulci on magnetic resonance imaging. Autopsy revealed spongiform changes and reactive astrocytosis, and genetic testing demonstrated a codon 200 mutation in the prion protein gene. These findings indicate that CJD can result in clinical manifestations compatible with multifocal asymmetric cerebral involvement before more diffuse neurodegeneration ensues, providing a strong impetus for the study of additional cases. This long-term understanding can help to determine whether the multiple loci of clinical involvement are specified by genetic or epigenetic factors, or both.

Clinical Conference↗
PubMed1999

Astereopsis caused by traumatic brain injury.

Impaired depth perception (astereopsis) has been observed in a variety of cerebral pathologies affecting the posterior parietal lobe. In the current study of 93 consecutive head trauma admissions, 24% had complete astereopsis and 41% performed more than 2 SDs below the orthopedic control group mean. Degree of impairment was related to Glascow Coma Scale score, length of posttraumatic amnesia, reduced visuospatial and memory abilities, and the presence of intracranial pathology of the parietal lobes. Impairment was also related to trauma severity in patients without any visualized intracranial pathology, presumably due to diffuse axonal shearing. Clinically meaningful impairment was observed in 25% of this group; 10% had complete astereopsis. Stereoacuity screening requires 1 to 2 minutes. Undetected astereopsis may increase risk for subsequent motor vehicle accidents or falls.

Journal Article↗
PubMed1992

Development of binocular vision in the kitten's striate cortex.

Studies of the development and plasticity of the visual pathway are well documented, but a basic question remains open: what is the physiological status of the system prior to extensive visual experience? Somewhat conflicting answers have been put forward, and in a major area, binocular vision, reports have ranged from severe immaturity to well-developed maturity. This is an important question to resolve since binocular cells in the visual cortex are thought to be the neural substrate for stereoscopic depth perception. We have addressed this question by recording from single cells in the striate cortex of kittens at postnatal ages 2, 3, and 4 weeks and from adults for comparison. Gratings with sinusoidal luminance distribution are presented to left, right, or both eyes. For each cell, we determine optimal values for orientation and spatial frequency. Relative phase (retinal disparity) is then varied in a dichoptic sequence so that binocular interaction may be studied. Results are as follows. In the normal adult, we have shown in previous work that most binocular interaction in the visual cortex can be accounted for on the basis of linear summation. Results from 3 and 4 week postnatal kittens are closely similar to those from adults. All types of binocular interaction found in adults are present in kittens. This includes phase-specific and non-phase-specific suppression or facilitation. Furthermore, monocular and binocular tuning characteristics are comparable in kittens and adults. The clear changes that occur with age are optimal spatial frequencies and peak responses. In addition, at 2 weeks, there is a substantially higher proportion of monocular cells compared to other ages and correspondingly, lower relative numbers of cells that exhibit phase-specific or suppressive binocular interactions. From increases in optimal spatial frequency and interpupillary distance with age, we calculated predicted changes in binocular disparity thresholds (stereo acuity) with age. Although there are methodological limits with respect to the behavioral testing of young kittens, the predicted results are comparable to some of the values obtained. Considered together, our results show that the physiological apparatus for binocular vision is functional at an early stage in postnatal development. It is possible that the connections that underlie this function are developed rapidly during early postnatal experience. An alternative possibility is that there is an elaborate genetic organization of binocular vision, but our study does not address this issue directly. A combination of these factors may be applicable.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed2003

Major review: The underutilization of vision screening (for amblyopia, optical anomalies and strabismus) among preschool age children.

BACKGROUND: Nearly 80% of preschool age children never get an eye examination (1). Many "back to school" physical exams do not test for common vision disorders. Untreated eye and vision problems can interfere with most life experiences. The prevalence of undetected vision problems among preschool age children is estimated to be 5% to 10% (2). Failure to detect visual impairment early may have a permanent effect on long term vision outcomes, education achievement, and self esteem (3). The most common vision disorders among children are strabismus, amblyopia and optical problems impairing visual acuity and depth perception. Various professional organizations, including the American Academy of Pediatrics (AAP), advise preschool vision screening to detect and correct vision problems before school entry. The AAP also recommends that children continue to receive periodic eye and vision examinations throughout childhood. However, resources for this level of care are rarely available. As such, only 21% of preschool age children receive vision screening and even fewer children get a comprehensive eye examination (1). PURPOSE: The purpose of this review is to determine, through a critical review of the literature, the social, economic, and political barriers which contribute to the underutilization of vision screening among preschool age children. A secondary aim is to identify gaps in the literature base that may be needed to complete a public policy response to this problem. METHOD: A comprehensive review and analysis of the pertinent available literature. RESULTS: A variety of barriers exist which prevent children from receiving proper vision screening. They include social, economic and even political problems. Social contextual barriers include ignorance, inconvenience, language, and a lack of providers. Financial barriers affect low income families. Political barriers reside in the disproportionately meager funding of preventative medicine. Moreover there are additional factors which put preventative medicine for vision at a disadvantage compared to other pediatric demands like immunizations, such as the danger to both the individual and society from the medical condition being prevented. CONCLUSION: Even considering large gaps in the literature concerning this topic, it is clear that low income, minority, uninsured families are at high risk of not utilizing vision screening. Ignorance remains a major problem at all levels so improvements in the distribution of information and education are needed and should yield improvement. Additional funding is necessary to pay for these remedies. Titration and direction of available resources to those at highest risk will create the greatest return on such efforts.

Amblyopia↗
PubMed2003

[Study of multi-factor cognition evoked by binocular disparity].

It is the aim of studies in cognitive process to understand how the impressive cognitive capacity of the human mind is uninterruptedly developed and how the process is controlled. We have been focusing attention on the central question with stereoscopic research. A multi-channel EEG data acquisition system is constructed for cognition studies which not only works perfectly in the EEG collection and signal processing of stereoscopic visual evoked potentials(VEP) but also is suitable for investigative and clinical use. We have identified the fact that the processing of stereoscopic depth information is done in the cortical advance functional areas with labeled characteristic signaling of the depth related VEP and the results were shown to be of no difference when compared with the ones of other investigations. We believe, the stereoscopic depth cognition is both a dynamic multi-factor processing process and a consequence of depth perception in advanced cortical areas through biological feedback to the whole process of visual signal processing. It is our novel and significant supposition in the psychophysical study, and the experimental results of the VEP are presented in this article.

Adult↗
PubMed1992

Cardiopulmonary bypass in the successful resuscitation of a 28-year-old woman with cardiac arrest.

This patient remained hospitalized for several weeks, and her stay was relatively uneventful. She extubated herself 2 days after admission, after an operative procedure to remove the cannulas and repair the right femoral cutdown site. A fasciotomy of her right calf was done for compartment syndrome. The patient had minor neurologic deficits of short-term memory loss and spatial depth perception loss. These deficits, attributed to postresuscitative hypoxia, eventually resolved. Extensive cardiac testing performed to pinpoint the underlying cause of her cardiac dysfunction were inconclusive. Because no cause was found, an automatic implantable cardiodefribrillator was recommended to prevent future cardiac events. The patient agreed and the device was implanted before her discharge. With expert occupational therapy, physical rehabilitation, nursing care, and medical treatment the patient regained her previous level of functioning. Her October wedding was postponed to December, but she was able to return to work in November 1990.

Adult↗
PubMedDate not supplied

Training and assessment of laparoscopic skills.

Laparoscopic surgery is gaining popularity among the surgical community. While its prevalence expands, the need for reliable training and assessment tools is becoming increasingly important. Laparoscopic skills are not an innate behavior, nor can they be easily mimicked, and can only be acquired through hands-on training. A consensus exists among physicians that establishment and evaluation of technical skill in surgical training programs are inadequate and in need of improvement. A validated, reliable bench model that could train and assess could be standardized and provide numerous benefits including determination of which medical students should consider a career in surgery, valuable feedback to residents, a tracking mechanism of resident performance, a possible certification and recertification tool, and to allow for interinstitutional comparison. To this end, several potentially successful bench models testing dexterity, hand-eye coordination, and depth perception have been developed. A few models have been proven to be both valid and reliable indicators of technical skill. Although the future remains uncertain, enough groundwork has been laid to begin incorporating technical skill training and assessment into surgical training programs.

Clinical Competence↗
PubMed2002

Evaluation of visualization techniques for image-guided navigation in liver surgery.

A substantial component of an image-guided surgery system (IGSS) is the kind of three-dimensional (3D) presentation to the surgeon because the visual depth perception of the complex anatomy is of significant relevance for orientation. Therefore, we examined in this contribution four different visualization techniques, which were evaluated by eight surgeons. The IGSS developed by our group supports the intraoperative orientation of the surgeon by depicting a visualization of the spatially tracked surgical instruments with respect to intrahepatic vessels that have to be conserved vitally, the tumor, and preoperatively calculated resection planes. In the prelimenary trial presented here we examined the human ability to percept an intraoperative virtual scene and to solve given navigation tasks. The focus of the experiments was to measure the ability of eight surgeons to orientate intrahepaticaly and to transfer the percepted spatial relation to movements in real space. An autostereoscopic visualization with a prism-based display yielded that the navigation can be performed faster and more accurately than with the other visualization techniques.

Anatomy, Regional↗