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Results for “Photogrammetry”

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At least 145 records · Page 8Linked to original sources

PubMed1985

A photogrammetric method to measure fluid movement across isolated frog retinal pigment epithelium.

Bullfrog retinal pigment epithelium (RPE)/choroid explants were mounted in an Ussing chamber modified so that the side bathing the choroid was completely sealed. Net fluid movement across the RPE and into or out of the sealed side of the chamber forced the tissue to assume a convex or concave shape. Photogrammetry was used to measure this tissue bowing by analyzing the displacement of the image produced on the RPE surface by an off-axis laser. Under baseline conditions, measured net fluid movements were always in the retina-to-choroid direction with a mean of 7.6 microliter cm-2 h-1. Potential artifacts from a variety of sources have been examined and shown to be insignificant.

Animals↗

PubMed1998

Functional and morphological evaluation of different polypropylene-mesh modifications for abdominal wall repair.

Modern surgical hernia repair depends increasingly on synthetic meshes for the reconstruction of the abdominal wall. Despite the undisputed advantages of the polypropylene (PP) meshes currently available (Marlex, Prolene), reports of complications after implantation are increasing. Although, serious complications such as perforation and fistula formation are rare, minor and local complaints such as seromas, misfeelings and a decreased abdominal wall mobility are observed in about one-half of the patients. In regard to the exaggerated strength of the currently available mesh modifications a reduction of the material should improve the integration of the meshes into the artificial abdominal wall. In the present study, the commercially available basic mesh Prolene has been compared to two newly constructed PP-mesh modifications with reduced amounts of PP. The modifications have gradually been adopted to the physiological requirements of abdominal wall stability and mobility by reducing the amount of PP to 64% (E-BLUE) and 24% (variant A) of the Prolene mesh (developed by ETHICON, Norderstedt, Germany). All PP-mesh variants have been implanted in a rat model and studied by 3D-photogrammetry, tensiometry, light- and electron microscopy, as well as morphometry over implantation intervals of 3, 7, 14, 21 and 90 days. The data show that current constructions of PP-meshes are oversized and definitely restrict abdominal wall mobility in the present model. Sufficient stability of the artificial abdominal wall is even guaranteed by PP-mesh modifications with a reduction of PP-quantity to about 25% of the Prolene mesh. The degree of fibrosis directly correlated with abdominal wall restriction, whereas the formation of connective tissue in the interface PP-fibre/host-issue depends on the amount and activity of the inflammatory reaction. The quantity and quality of inflammation, again, directly relies to the amount of PP and to the surface area in contact with the recipient tissues. Altogether, the present study suggests that a modification of the PP-meshes could be helpful to prevent major and minor complications of surgical PP-meshes.

Abdominal Muscles↗

PubMed1985

Measurements of reversibility of optic disc cupping and pallor in ocular hypertension and glaucoma.

Four cases are presented of young and elderly glaucoma patients who had both surgical and medical therapy and showed reversal of cupping and pallor of the optic disc. The cupping was measured by photogrammetry and the pallor by computerized image analysis from photographs of the optic disc. Two patients showed regression of visual field loss. The optic disc and visual field changes corresponded to the changes in ocular pressures, generally showing worsening with an increase in ocular pressure. With a decrease in ocular pressure there was regression of visual field loss and a decrease in cupping; pallor did not decrease consistently. The changes in cupping and pallor in some patients followed similar courses but in others behaved in an independent manner. It is proposed that these new sensitive and reproducible techniques for measuring changes in the optic disc may allow the detection of disc changes early in the disease, prior to visual field loss. If treatment is begun at this time, reversal of optic disc changes may occur.

Aged↗

PubMed2000

Real-time three-dimensional motion analysis for patient positioning verification.

BACKGROUND AND PURPOSE: This paper describes the technology and methods involved in a system for automatically checking the position of patients at radiotherapy units. This is proposed for improving the accuracy in the irradiation geometrical set-up, which is a crucial factor in radiotherapy quality control. MATERIALS AND METHODS: The system is based on real-time opto-electronics and close-range photogrammetry and detects multiple passive markers placed on selected patient skin landmarks. Patient alignment and position monitoring is carried out by comparing the current three-dimensional positions of the markers with those of an initial reference position acquired during the simulation procedure and/or the first irradiation session. The system was used to measure the accuracy of conventional laser centering techniques for patient repositioning. Inaccuracies due to breathing and random movements were also taken into account. Professional technicians were asked to reposition three volunteer subjects carefully using a traditional laser centering procedure. RESULTS: The results revealed significant repositioning errors even in highly controlled conditions, affecting particularly body areas relatively far from the skin reference points used for laser alignment. CONCLUSIONS: The outcome of the experimental application of this technology confirms its potential as a tool for patient repositioning and automatic detection of any errors caused by breathing or other unpredictable movements. The real-time feedback on the patient's position given by the system provides operators with appropriate visual indices and allows them to take suitable countermeasures in case of significant failures. In addition, the use of the system output for automatic position control is envisaged.

Artifacts↗

PubMed1975

A transverse loading system applied to a modified Harrington instrumentation.

Observations using standard Harrington Instrumentation revealed that while maximal distractive forces are applied it is possible to produce further correction of spinal deformity by applying a lateral force. Modifications to the standard Harrington Instrumentation by applying a transverse loading system have been made in order to produce this added correction. The transverse load is applied as nearly as possible in the same plane as the bearing points of hooks, i.e., below the axis of the rods. Transverse loading helps to reduce the distance from the apex of the curve to the midline, thereby producing a more stable spine as well as providing additional support on the convex side. The system is ideal for flexible curves with little kyphosis. Photogrammetry reveals that there was no significant rotation occurring after the application of the transverse load. To date, Instrumentation has been used in 10 patients with success.

Adolescent↗

PubMed1997

Methods to objectify reversibility of glaucomatous cupping.

Lowering intraocular pressure in adults with glaucoma may be associated with an improvement in appearance of the optic nerve head. The stage of disease, the amount of intraocular pressure reduction, and the age of the patient probably influence the occurrence of this event. The clinical relevance of "reversal" has not been established with certainty. The reversibility of glaucomatous cupping can be detected by subjective and qualitative means (examination of the patient or of fundus photographs) or by quantitative techniques such as photogrammetry, computerized image analysis, and scanning laser tomography. Clinical and experimental studies are providing new information about the behavior of the optic nerve head tissues in response to changes in intraocular pressure.

Adult↗

PubMed1997

Corneal topography.

In the review period, limitations of individual Placido disk-based topography systems have been studied and new principles, such as raster photogrammetry, pancorneal slit topography, laser holographic interferometry, and confocal laser scanning topography, have been introduced for laboratory or clinical work. Both Fourier analysis and Zernike decomposition of topographic height data seem to be powerful new tools for cross-sectional analysis of complex topographic corneal images, such as after cataract surgery, penetrating keratoplasty, and refractive surgery, as well as for longitudinal studies of corneal changes, such as in schoolchildren. Subdividing into rational optical components may improve consistency and standardization of topography data from different systems. Topography-based flying-spot-mode excimer laser photoablation after Zernike decomposition of topography height data has been proposed for correction of irregular corneal astigmatism. Topography-based central power measurements are of increasing value for intraocular lens power calculation before cataract surgery in eyes with irregular corneal surfaces, such as in keratoconus or after refractive surgery procedures. Quantitative and qualitative classification of corneal topography maps after corneal transplantation following conventional mechanical and nonmechanical trephination or after refractive surgery may lead to a better understanding of impaired visual acuity despite a clear graft or despite significantly reduced ametropia or corneal astigmatism.

Cornea↗

PubMed1992

The computer synthesis of expressive faces.

This paper presents a methodology for the computer synthesis of realistic faces capable of expressive articulations. A sophisticated three-dimensional model of the human face is developed that incorporates a physical model of facial tissue with an anatomical model of facial muscles. The tissue and muscle models are generic, in that their structures are independent of specific facial geometries. To synthesize specific faces, these models are automatically mapped onto geometrically accurate polygonal facial representations constructed by photogrammetry of stereo facial images or by non-uniform meshing of detailed facial topographies acquired by using range sensors. The methodology offers superior realism by utilizing physical modelling to emulate complex tissue deformations in response to coordinated facial muscle activity. To provide realistic muscle actions to the face model, a performance driven animation technique is developed which estimates the dynamic contractions of a performer's facial muscles from video imagery.

Computer Graphics↗

PubMed1999

Alignment of adjacent picture frames captured by a CLSM.

Mosaicking a picture from its adjacent parts (called picture frames or tiles) is encountered in different fields of research and technology, e.g., photogrammetry, remote sensing, microscopy, etc. It is applied whenever the object of investigation is too large for the field of view of the sensor, e.g. a microscope. We describe mosaicking with a confocal laser-scanning microscope (CLSM) Bio-Rad, MRC 600 (U.K.). Aligning neighboring picture tiles was accomplished by registering the overlapped border areas of these tiles. Such registration procedures are constrained by: 1) the limited size of the registered samples (windows); 2) anisotropy of the form of the windows (usually narrow rectangles); and 3) the content of the windows, including changes of their intensity scale. Focusing on the latter problem, methods of registration were discussed and the robustness of the following three similarity based methods was studied with regard to the distortions of the intensity scales of the tiles to be registered: 1) the sum of absolute valued differences (SAVD); 2) normalized correlation coefficient (NCC); and 3) the mutual information function (MIF). Pilot experiments were extended to three-dimensional (3-D) stacks of pictures encountered in the framework of 3-D object rendering and visualization. MIF was found in most cases to be the most robust; however, it also demanded the most computational power. It is discussed how to choose a cost-effective method of the registration with regard to the content (texture, contrast, intensity scale distortion) of the tiles.

Microscopy, Confocal↗

PubMed1995

Decrease of optic disc cupping and pallor of ocular hypertensives with timolol therapy.

PURPOSE: The purpose of this study was to determine whether timolol drops compared to placebo drops had a significant effect on optic disc cupping and pallor in ocular hypertensives. METHODS: Thirty-seven ocular hypertensives were randomly assigned to placebo or 0.5% timolol drops to both eyes in a double masked clinical trial. Measurements of ocular pressure and photographs of the optic disc for cupping by photogrammetry and pallor by computerized image analysis were made at about 3 month intervals, for 18 to 24 months of follow-up. RESULTS: None of the subjects developed visual field loss when tested with the Goldmann perimeter by kinetic and static means at six month intervals. Subjects treated with timolol developed a significant decrease in ocular pressure and a significant decrease in optic disc cupping with a smaller decrease in pallor compared to subject treated with placebo. Multivariate analyses indicated that the decrease of optic disc cupping and pallor was not associated with the ocular pressure on treatment or the decrease in ocular pressure during the trial. CONCLUSION: Timolol treatment was associated with a decrease in optic disc cupping and pallor. The effect of timolol appears to be related to mechanisms other than the decrease in ocular pressure.

Double-Blind Method↗

PubMed1976

The effect of oral physiotherapy on dilantin gingival hyperplasia.

Gingival hyperplasia was studied in 13 boys with epilepsy living in a state hospital. Boys were selected on the basis of having gingival hyperplasia, having all teeth between cuspids (upper and lower), having no occlusal abnormality and being cooperative. After gingivectomy, regrowth of gingiva was compared around lateral incisors on one side of the mouth having operator-assisted oral hygiene with that around lateral incisors on the other side of the mouth without operator-assisted oral hygiene. Regrowth of tissue was documented by precise photogrammetry. Oral hygiene, gingival inflammation and crevicular fluid were monitored. Less inflammation, less crevicular fluid and less regrowth of gingival tissues occurred around teeth subjected to good oral hygiene. Precise periodic photographic documentation of the clinical status of patients during studies such as this is considered very valuable.

Adolescent↗

PubMed1999

Joint surface modeling with thin-plate splines.

Mathematical joint surface models based on experimentally determined data points can be used to investigate joint characteristics such as curvature, congruency, cartilage thickness, joint contact areas, as well as to provide geometric information well suited for finite element analysis. Commonly, surface modeling methods are based on B-splines, which involve tensor products. These methods have had success; however, they are limited due to the complex organizational aspect of working with surface patches, and modeling unordered, scattered experimental data points. An alternative method for mathematical joint surface modeling is presented based on the thin-plate spline (TPS). It has the advantage that it does not involve surface patches, and can model scattered data points without experimental data preparation. An analytical surface was developed and modeled with the TPS to quantify its interpolating and smoothing characteristics. Some limitations of the TPS include discontinuity of curvature at exactly the experimental surface data points, and numerical problems dealing with data sets in excess of 2000 points. However, suggestions for overcoming these limitations are presented. Testing the TPS with real experimental data, the patellofemoral joint of a cat was measured with multistation digital photogrammetry and modeled using the TPS to determine cartilage thicknesses and surface curvature. The cartilage thickness distribution ranged between 100 to 550 microns on the patella, and 100 to 300 microns on the femur. It was found that the TPS was an effective tool for modeling joint surfaces because no preparation of the experimental data points was necessary, and the resulting unique function representing the entire surface does not involve surface patches. A detailed algorithm is presented for implementation of the TPS.

Algorithms↗

PubMedDate not supplied

The PAR Technology Corneal Topography System.

BACKGROUND: Computer-assisted videokeratography has emerged as a useful clinical and research tool. All of the currently available commercial units utilize a modified placido disk image and require a smooth reflective surface. The PAR Technology Corneal Topography System (PAR CTS) is a prototype of a new computer-assisted corneal imaging device. The system produces a true topographic map (elevation map) by analyzing a projected grid on the corneal surface, as opposed to a placido disk reflection, and utilizes the technique of raster photogrammetry to define elevation points on the corneal surface. Because the system defines elevation points, not curvature, mathematical modeling is easily accomplished. Current software displays include a true topographic map, a spherical subtraction map in both relative and absolute scales, and a meridian analysis that is adapted to display refractive photoablative surgery. METHODS: We evaluated the accuracy of this device by analyzing three calibrated test spheres (55.76, 42.21, and 33.55 diopters). The test spheres were steel balls coated with a thin white silicone polyester coating that was necessary for grid projection. The test spheres were measured by a Taylor-Hobson contact profilometer possessing submicron accuracy. To determine the reproducibility of the system, three investigators measured three noncalibrated balls (20 mm, 18 mm, and 12 mm). The optical system was purposely decentered and refocused after each reading. RESULTS: Utilizing the CTS custom optics, system accuracy at the 8-millimeter test area was 0.03 (SD 0.03), 0.00, (SD 0.02), and 0.07 (SD 0.01) D respectively. Smaller diameter test areas resulted in a predicted loss of accuracy. Maximum intraobserver variability was 0.09, 0.06, and 0.11 D respectively, and maximum interobserver variability measured 0.18, 0.12, and 0.16 D. CONCLUSIONS: These data demonstrate that the PAR CTS is both highly accurate and reproducible in determining topography of spheres that approximate the curvature of the human cornea.

Algorithms↗

PubMedDate not supplied

Wear measurements in clinical studies of composite resin restorations in the posterior region: a review.

During the last twenty years, wear-evaluation methods have changed, with newer techniques developed to determine the extent of loss of material in posterior composite resin restorations functioning in the mouth. These included: direct clinical evaluation; marginal evaluation on models; heights of exposed cavity walls; volumetric assessment of impressions; profilometry and artificial or natural references; section measurements; coordinate measuring device, contact and noncontact scanning; measuring microscope; photogrammetry; moiré topography; laser interferometry; scanning electron microscopy; and optical scanning. A laser scanning technique appears to hold great potential in clinical research.

Bicuspid↗

PubMed1990

Breast form changes resulting from a certain brassière.

Eleven adult female subjects aged 22-39 years wore a certain brassière for 3 months while anthropometry and moiré fringe photographs on the anterior trunk were taken regularly once a week. After the 3 months, the brassière was not worn for another 3 months. Then the measurements and photogrammetry were repeated for comparison using superimposed moiré configurations. The results are summarized as follows. Regardless of slim or obese trunk, subjects with pendent breasts showed the highest degree of breast form "correction" from wearing the brassière. In all subjects, after 3 months of brassière constraint, the underbust circumference was smaller but the chest circumference became enlarged, the distance between the right and left nipples became wider, and the breasts tended to hang down. This change was more marked in obese subjects with pendent breasts. And when this type of subject wore a "well-fitted" brassière for a long time, her breast form became developed; that is, her breasts hung down more.

Adaptation, Physiological↗

PubMed1990

[The spread of the backspray under different working conditions].

The use of high- and highest-speed preparation instruments and the therefore required intensive spray cooling results not only in more efficient working possibilities but also in an increased infection hazard, especially for the dentist and his assistance caused by the spray rebound. Simulated preparations were carried out on different tooth surfaces at different positions of the patient with or without exhaust under clinical conditions to objectify the space spreading of the spray rebound. The arrangement of the equipment has been objectified by photogrammetry so that the measurement data could be clearly classified. The use of the spraying mist exhaust reduces the spray rebound between 50 and 65%.

Aerosols↗

PubMed1989

[Dynamic study of the optic papilla].

There are several methods of accurately measuring the contours of the papilla and rim. Of these methods, photogrammetry and its refinements are known to provide reproducible results. Unfortunately, there is a discrepancy between the accuracy of these methods and the biological "background noise". This noise does not allow the precision of these methods to be improved beyond a certain level. This also applies for determination of the color of the papilla. An alternative to this problem is to use the "provocation" test. In this article, we try to show the importance of the dynamic test of the papilla (dynamic provoked circulatory response): measuring the change in pallor of the rim during an artificial increase in the intraocular pressure.

Glaucoma↗

PubMed1989

New methods for quantitative and qualitative facial studies: an overview.

The clinical study of birth defects has traditionally followed the Gestalt approach, with a trend, in recent years, toward more objective delineation. Data collection, however, has been largely restricted to measurements from X-rays and anthropometry. In other fields, new techniques are being applied that capitalize on the use of modern computer technology. One such technique is that of remote sensing, of which photogrammetry is a branch. Cartographers, surveyors and engineers, using specially designed cameras, have applied geometrical techniques to locate points on an object precisely. These techniques, in their long-range application, have become part of our industrial technology and have assumed great importance with the development of satellite-borne surveillance systems. The close-range application of similar techniques has the potential for extremely accurate clinical measurement. We are currently evaluating the application of remote sensing to facial measurement using three conventional 35 mm still cameras. The subject is photographed in front of a carefully measured grid, and digitization is then carried out on 35-mm slides specific landmarks on the cranioface are identified, along with points on the background grid and the four corners of the slide frame, and are registered as xy coordinates by a digitizer. These coordinates are then converted into precise locations in object space. The technique is capable of producing measurements to within 1/100th of an inch. We suggest that remote sensing methods such as this may well be of great value in the study of congenital malformations.

Cephalometry↗