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At least 721 records · Page 40Linked to original sources

Computer-generated diagnostic correction of anterior diastemas.

A technique for pretreatment estimation of appearance following cosmetic change to the anterior teeth by using a computer-generated image has been described. Patients should be advised that the generated projection is an estimation. As with a diagnostic set-up, a computer-generated result can only approximate final treatment. The patient must understand that the result could vary for reasons that might include (1) restorative material, (2) functional occlusal needs, (3) gingival tissue irritability, (4) artificial versus outdoor light, and (5) the angle at which the photograph was made. As technology advances, there will undoubtedly be other applications for computer graphics. The authors have successfully estimated outcomes for prosthodontic, orthodontic, and orthognathic surgical treatment. If properly used, color computer estimations can be successfully integrated in a dental office as a communication tool for the dentist, patient, and laboratory technician.

Cuspid↗

Rietveld analysis and Fourier maps of hydroxyapatite.

Rietveld analysis was applied to the X-ray powder diffraction data of well-crystallized hydroxyapatites synthesized at 80 degrees C and pH 7.4. The least-squares refinement program adopted for Rietveld analysis showed good pattern fitting with the calculated profile. The a- and c-axis dimensions, a-0.943046 + 0.000126 nm and c-0.687485 +/- 0.000104 nm, were obtained and compared with the data estimated from a single peak. The lattice dimensions obtained by Rietveld analysis were much closer to the values of a single crystal, a = 0.9432 nm and c-0.6881nm. Fourier analysis was also performed. The maps of electron densities expressed the existing possibility of each atom composing hydroxyapatite in the crystal structure. In particular, columnar calcium and screw-axis calcium were clearly revealed. These data agreed well with the computer graphics model of hydroxyapatite reported previously.

Computer Simulation↗

Virtual reality exposure therapy for PTSD Vietnam Veterans: a case study.

Virtual reality (VR) integrates real-time computer graphics, body tracking devices, visual displays, and other sensory input devices to immerse a participant in a computer-generated virtual environment that changes in a natural way with head and body motion. VR exposure (VRE) is proposed as an alternative to typical imaginal exposure treatment for Vietnam combat veterans with posttraumatic stress disorder (PTSD). This report presents the results of the first Vietnam combat veteran with PTSD to have been treated with VRE. The patient was exposed to two virtual environments, a virtual Huey helicopter flying over a virtual Vietnam and a clearing surrounded by jungle. The patient experienced a 34% decrease on clinician-rated PTSD and a 45% decrease on self-rated PTSD. Treatment gains were maintained at 6-month follow-up.

Humans↗

Fast generation of digitally reconstructed radiographs using attenuation fields with application to 2D-3D image registration.

Generation of digitally reconstructed radiographs (DRRs) is computationally expensive and is typically the rate-limiting step in the execution time of intensity-based two-dimensional to three-dimensional (2D-3D) registration algorithms. We address this computational issue by extending the technique of light field rendering from the computer graphics community. The extension of light fields, which we call attenuation fields (AFs), allows most of the DRR computation to be performed in a preprocessing step; after this precomputation step, DRRs can be generated substantially faster than with conventional ray casting. We derive expressions for the physical sizes of the two planes of an AF necessary to generate DRRs for a given X-ray camera geometry and all possible object motion within a specified range. Because an AF is a ray-based data structure, it is substantially more memory efficient than a huge table of precomputed DRRs because it eliminates the redundancy of replicated rays. Nonetheless, an AF can require substantial memory, which we address by compressing it using vector quantization. We compare DRRs generated using AFs (AF-DRRs) to those generated using ray casting (RC-DRRs) for a typical C-arm geometry and computed tomography images of several anatomic regions. They are quantitatively very similar: the median peak signal-to-noise ratio of AF-DRRs versus RC-DRRs is greater than 43 dB in all cases. We perform intensity-based 2D-3D registration using AF-DRRs and RC-DRRs and evaluate registration accuracy using gold-standard clinical spine image data from four patients. The registration accuracy and robustness of the two methods is virtually identical whereas the execution speed using AF-DRRs is an order of magnitude faster.

Algorithms↗

The use of virtual reality exposure in the treatment of anxiety disorders.

One possible alternative to standard in vivo exposure may be virtual reality exposure. Virtual reality integrates real-time computer graphics, body tracking devices, visual displays, and other sensory input devices to immerse a participant in a computer-generated virtual environment. Virtual reality exposure (VRE) is potentially an efficient and cost-effective treatment of anxiety disorders. VRE therapy has been successful in reducing the fear of heights in the first known controlled study of virtual reality in the treatment of a psychological disorder. Outcome was assessed on measures of anxiety, avoidance, attitudes, and distress. Significant group differences were found on all measures such that the VRE group was significantly improved at posttreatment but the control group was unchanged. The efficacy of virtual reality exposure therapy was also supported for the fear of flying in a case study. The potential for virtual reality exposure treatment for these and other disorders is explored.

Anxiety Disorders↗

Virtual reality exposure therapy.

It has been proposed that virtual reality (VR) exposure may be an alternative to standard in vivo exposure. Virtual reality integrates real-time computer graphics, body tracking devices, visual displays, and other sensory input devices to immerse a participant in a computer-generated virtual environment. Virtual reality exposure is potentially an efficient and cost-effective treatment of anxiety disorders. VR exposure therapy reduced the fear of heights in the first controlled study of virtual reality in treatment of a psychiatric disorder. A case study supported the efficacy of VR exposure therapy for the fear of flying. The potential for virtual reality exposure treatment for these and other disorders is explored, and therapeutic issues surrounding the delivery of VR exposure are discussed.

Fear↗

Three-dimensional display in the evaluation and performance of neurosurgery without a stereotactic frame: more than a pretty picture?

Display of three-dimensionally rendered images derived from radiological data sets is often suggested to be useful for surgical and radiation treatment planning in neurosurgery. Nevertheless, physicians will often note (off the record) that these rendered images are 'just a pretty picture' and are not clinically useful. This paper will discuss our three-dimensional rendering and quantitative analysis software and its primary use in evaluating and utilizing frameless stereotactic methodologies. A variety of concepts and techniques will be discussed. Specifically, a computer graphic and statistical-based technique will be presented that enables timely and measurable image registration between radiological image space and the coordinate system of computer-driven surgical devices in the operating room. This technique may be utilized to maintain a surgeon's orientation and to quantitatively and graphically monitor the position of probes and instruments in the surgical field. Three-dimensional quantitative results of phantom testing will be presented. Correlation to and validation against stereotactic imaging calculations using the compass stereotactic system will also be discussed. These computer graphic/statistical-based techniques are applicable for evaluating the accuracy of any frameless stereotactic device including, but not limited to robotic arms, spark gap, LED and magnetic field digitizers.

Evaluation Studies as Topic↗

Stereoscopic visualization of three-dimensional ultrasonic data applied to breast tumours.

OBJECTIVE: This paper presents a technique for stereoscopic visualization applied to three-dimensional (3D) ultrasonic breast data. METHODS: A motorized acquisition system has been designed to translate regularly a linear-phased array transducer, in order to provide a series of parallel echographic slices of the breast. During acquisition, the breast is compressed between a plane support and a plexiglass plate to avoid breast motion. A window in this plate provides access for ultrasonic exploration. From the series of cross-sectional scans, a 3D volume is formed by interpolation between the successive ultrasonic images. A stereoscopic computer-graphic method has been developed to visualize these 3D ultrasonic data. Two conical transparent projections of the volume are computed from two slightly different viewpoints. These two projections make up the stereoscopic pair. This pair is displayed on a stereoscopic monitor for the visualization of the 3D data with the depth dimension. RESULTS: The acquisition system and the method for computing the stereo-echograms were validated using an agar gel phantom. In vivo breast experiments were also performed. CONCLUSION: Visualization of stereo-echographic projections improves the perception of depth and shape of breast tumours.

Breast Diseases↗

Virtual reality exposure therapy for Vietnam veterans with posttraumatic stress disorder.

BACKGROUND: Virtual reality (VR) integrates real-time computer graphics, body-tracking devices, visual displays, and other sensory input devices to immerse a participant in a computer-generated virtual environment that changes in a natural way with head and body motion. VR exposure (VRE) is proposed as an alternative to typical imaginal exposure treatment for Vietnam combat veterans with posttraumatic stress disorder (PTSD). METHOD: This report presents the results of an open clinical trial using VRE to treat Vietnam combat veterans who have DSM-IV PTSD. In 8 to 16 sessions, 10 male patients were exposed to 2 virtual environments: a virtual Huey helicopter flying over a virtual Vietnam and a clearing surrounded by jungle. RESULTS: Clinician-rated PTSD symptoms as measured by the Clinician Administered PTSD Scale, the primary outcome measure, at 6-month follow-up indicated an overall statistically significant reduction from baseline (p = .0021) in symptoms associated with specific reported traumatic experiences. All 8 participants interviewed at the 6-month follow-up reported reductions in PTSD symptoms ranging from 15% to 67%. Significant decreases were seen in all 3 symptom clusters (p < .02). Patient self-reported intrusion symptoms as measured by the Impact of Event Scale were significantly lower (p < .05) at 3 months than at baseline but not at 6 months, although there was a clear trend toward fewer intrusive thoughts and somewhat less avoidance. CONCLUSION: Virtual reality exposure therapy holds promise for treating PTSD in Vietnam veterans.

Follow-Up Studies↗

Tri-meridional analysis using arbitrary meridians.

The evaluation of the sphero-cylindrical components of curvature or refraction from measurements taken along three distinct meridians has been solved for various sets of three fixed meridians. A constraint of those solutions has been that the meridians of measurement are necessarily predetermined, which introduces an unwelcome restriction in experimental or clinical applications of tri-meridional analysis. A new solution is presented (in three formats: analogue computer, graphical and algebraic), which enables any set of three meridians to be used for tri-meridional analysis. A computer program listing (in BASIC) is included.

Computers, Analog↗

On the existence of limit cycles in motion field.

In this paper we show the existence of limit cycles in the vector field generated by the perspective projection on the image plane of the velocity field of a moving surface. The existence of limit cycles is proved with the Poincaré-Bendixon theorem, in the case of a rotating smooth non-planar surface and illustrated with computer graphics. The structural stability of the limit cycles is also discussed.

Computer Simulation↗

Utilization of radioligands in schizophrenia research.

Interest in the role of monoaminergic mechanisms in schizophrenia has stimulated the development of specific radioligands that allow PET analysis of quantitative aspects of monoamine receptor subtypes in the living human brain. Clinical studies with such ligands have not consistently demonstrated specific alterations of the total populations of D1 and D2 dopamine receptors in the caudate putamen complex of drug-naive schizophrenic patients. However, recent studies using [11C]SCH 23390, a specific D1 dopamine receptor ligand, disclosed a highly significant reduction of ligand binding in pixel elements of the basal ganglia that normally contain high activity. This finding may be related to reduced D1 dopamine regulated transmission in subsets of neuronal pathways within the basal ganglia. D3, D4, and D5 receptor subtypes constitute minor fractions of the total number of dopamine receptors in the human brain. However, efforts to find selective ligands for D3 and D4 subtypes also show promise. Radioligands for monoamine receptors have also been used to follow drug effects on receptor subtypes in schizophrenic patients treated with different types of antipsychotic drugs. Such studies have allowed the analysis of relationships between occupancy of dopamine receptor subtypes and some clinical manifestations of drug treatment. Such studies with the selective D2 antagonist raclopride indicated quantitative relationships between the degree of D2 dopamine receptor occupancy in the basal ganglia and the extrapyramidal manifestations, as well as the antipsychotic action. Some of the currently available antipsychotic drugs also induced significant occupancy of D1 dopamine receptors. However, the selective D1 antagonist SCH 39166 in doses inducing a more than 70% occupancy of D1 dopamine receptors in the caudate putamen failed to induce an antipsychotic action. This indicates that, in contrast to D2 blockade, selective antagonism of D1-regulated pathways does not mediate antipsychotic action in schizophrenia. Some but not all antipsychotic drugs also induced high occupancy of neocortical 5HT2A receptors. Because selective 5HT2A antagonism does not appear to be an efficient treatment for schizophrenia, it seems most likely that 5HT2A receptors and, perhaps, D1 receptors act in concert to modify aspects of the mandatory D2 blockade to induce antipsychotic actions. Computer graphic methods for image analysis add new dimensions to brain imaging research, allowing three-dimensional visualization of receptor populations computed from molecular PET data. This will make possible further exploration of the detailed molecular compartmentalization of the human brain using radioligand binding.

Brain↗

A desk top computer program for visualized statistical analysis of lesional images in intracerebral hemorrhage.

Statistically identified information on the relationships between the sites of lesions in intracerebral hemorrhage (ICH), risk factors such as a smoking or drinking habit, anamnesis, and biochemical data through blood tests will extend assistance to neuromedical clinicians on their daily clinical duties. It will provide them with a useful guide to determine the method of treatment. Also, it will be a basic research material for their clinical studies on diagnosis, progress, or prognosis in ICH. In order to obtain such statistics with the help of the computer, we need to have a computationally effective image database system. As is generally known, medical image data especially requires a great amount of storage; high-speed processing techniques are therefore also needed to deal with such data effectively. In addition, it is desired that we have outputs from the analysis edited with well-visualized effect, using 3D computer graphics, etc. These are why most existing image processing systems have been designed to work on comparatively large-scale computers. So far as we know, it is hard to find a practical and inexpensive personal computer-based application system for visualized statistical analysis of lesional images in ICH. We have developed a desk top computer-based program for statistical analysis of lesional image data of ICH. With this system, we can organize a medical image database that consists of the personal data of patients with ICH (sex, age, occupation, diagnosis, symptoms, part of physical disorder, etc.), risk factors, anamnesis (cerebral apoplexy, hypertension, hypotension, corpulence, diabetes, hyperlipidemia, atrial fibrillation, valvular endocarditis, etc.), biochemical data of blood, and lesional image data from CT or MRI. This system consists of the following components: 1) database management, 2) information retrieval (IR), 3) lesional image processing, 4) statistical analysis, and 5) prognostic prediction. The images are drawn manually on prescribed data sheets by tracing CT or MRI films and are read through the image scanner; then the compressed data of the digitized images is recorded in the database. Each recorded image data consists of the following two components: the frame image that corresponds to the contour of tissues of interest on the corresponding sliced section, and the actual image that corresponds to the lesion itself. In our system, these two images are separately stored and managed so that we can effectively perform subsequent image analysis. Other variables in the database (risk factors, anamnesis, etc.) are mainly used as search keys for making the aggregate of image data by the IR subsystem. In any aggregate, its elements, namely image data, have common medical background descriptions with the search keys. These aggregates can be used as input for the lesional image processing subsystem. With this subsystem, we can obtain the accumulated distribution of frequencies within a specified range of any sliced section, display planar color maps and profiles associated with the distribution, reconstruct it in 3D form, perform transformations of 3D images (zooming, enhancement, rotation, etc.), and test the significant difference of frequencies between any two different sites. We have been making practical use of this system to find the neurological relationship between the symptom (dysarthria, and paralysis of upper/lower limbs) and the site of lesion with cerebral infarction in pons. This study is quite important since the distributions of pyramidal tract related to the above symptom in pons are not well-known compared to those in cerebral cortex, internal capsule, or cerebral peduncle. With our system, we have obtained several findings expected to be helpful for this study. However, since this study is still in the initial phases, we will only present the outcome as a working example of our system. Our system was originally developed for analyzing lesional images with ICH. However, it could

Cerebral Hemorrhage↗

Three-dimensional molecular distribution in single cells analysed using the digital imaging microscope.

Cellular changes in molecular distribution are believed to underly a wide range of cell functions. In order to investigate changes in molecular distribution in single cells utilizing fluorescent probes we have developed a digital imaging microscope. The system, consisting of both hardware and software, automatically acquires 3-D data sets consisting of optical sections and then processes such data to facilitate the analysis of molecular distribution in single cells. The first major step in processing reverses distortion introduced principally by the optics of the fluorescent microscope. Various procedures for accomplishing this task are compared and a method based on regularization theory is shown to give superior results for several different 3-D images. Following this step features of interest are automatically extracted from 3-D images utilizing an artificial 3-D visual system. This artificial visual system utilize a system of spatial filters to identify regional characteristics of images, the information obtained from these filters being used to identify and characterize clusters of molecules within the image. This information is then utilized to construct a 3-D graphical model of molecular distribution in single cells. Such models are displayed in 3-D and may further analysed utilizing interactive 3-D computer graphics. These methods are illustrated by results obtained regarding alpha-actinin distribution in single smooth muscle cells.

Actinin↗

Virtual Reality Simulation of Gynecologic Laparoscopy

Realistic virtual simulation of gynecologic laparoscopy would permit the surgeon to practice any procedure, with any degree of pathology, at any time and as many times as necessary to achieve proficiency before attempting it in the operating room. Effective computer simulation requires accurate anatomy, realistic three-dimensional computer graphics, the ability to cut and deform tissue in response to instruments, and an appropriate hardware interface. The Visible Human Project from the National Library of Medicine has made available extremely accurate, three-dimensional, digital data that computer animation companies have begun to transform to three-dimensional graphic images. The problem of tissue deformation and movement is approached by a software package called TELEOS. Hardware consisting of two scissor-grip laparoscopic handles mounted on a sensor can interface with any simulation program to simulate a multiplicity of laparoscopic instruments. The next step will be to combine TELEOS with the three-dimensional anatomy data and configure it for gynecologic surgery.

Journal Article↗

The effect of neodymium: YAG capsulotomy on contrast sensitivity and the evaluation of methods for its assessment.

OBJECTIVE: To determine the most appropriate method for measuring the effect on contrast sensitivity of neodymium:YAG (Nd:YAG) posterior capsulotomy for early posterior capsular opacification (PCO). DESIGN: Prospective comparison of five different methods for luminous contrast sensitivity testing in patients undergoing capsulotomy. PARTICIPANTS: Sixteen patients with PCO involving the visual axis and visual acuities of 20/40 or better were recruited sequentially. INTERVENTION: All patients were tested with each of the five tests before and after Nd:YAG capsulotomy. MAIN OUTCOME MEASURES: The contrast sensitivity function was measured with variable contrast sine wave gratings using the Vistech VCTS 6500, Mentor B-VAT-II and a computer graphics system. Peak contrast sensitivity at 3 cyc/deg was compared with two letter tests, the Pelli-Robson chart, and a computer that generated optotypes. RESULTS: Significant generalized improvement that was not frequency selective was measured over the entire contrast sensitivity function after capsulotomy. The five tests did not significantly differ (P > 0.05) in their measurement of peak contrast sensitivity (3 cyc/deg) improvement after capsulotomy. Letter-based tests showed better agreement and lower variance than gratings tests. Visual acuity and contrast sensitivity improvement were poorly correlated. CONCLUSIONS: This study shows that contrast sensitivity is adequately documented by a single measurement at 3 cyc/deg, is an informative supplement to visual acuity, and that little extra information is to be gained by measuring further spatial frequencies in eyes with PCO. Peak contrast sensitivity is best determined using a letter-based test.

Aged↗

[Tridimensional radiation treatment planning].

The effectiveness of radiotherapy and the possibility that the patient will be cured are basically determined by the accuracy of the therapy planning and the treatment. The tumour with its environment is a three-dimensional (3D) phenomenon, and therefore 3D radiation treatment planning and performance are needed for adequate coverage of the target volume (tumour+safety zone). The prerequisities of the elaboration of the 3D radiotherapy planning were as follows: the availability of high-performance hardware, the establishment of interactive computer graphics, and the development and direct integration into the therapy planning process of the digitalized information derived from diagnostic imaging, and especially computer tomography. The introduction of 3D treatment planning will mean the modernization of the radiotherapy, the accuracy of which may permit more cures, i. e. more patients will recover their ability to work.

Dose-Response Relationship, Radiation↗

Computer assisted unit data acquistion/reduction.

A computer system for unit data acquisition and reduction (CAUDAR) is presented. This system digitally processes uninterrupted, continuous unit data with attention to waveform detail. Several units in a multiunit field are recognized by evaluation of spike waveform and amplitude. High-speed computer graphics provides almost instantaneous figures of good quality for illustration. The system affords a great economy of the user's time because the computer performs all data processing.

Computers↗