PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Photogrammetry”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 865 records · Page 48Linked to original sources
PubMed1994

Growth as a parameter of inflammation in Crohn's disease, using roentgen stereophotogrammetric analysis.

Growth rate was measured in 12 children with Crohn's disease and growth retardation, using roentgen stereophotogrammetric analysis. The method was chosen as it provides an opportunity to record growth rate accurately during short periods of time. Growth was followed at variable intervals of 4-12 weeks depending on the clinical situation. Growth rate was shown to correlate with symptoms, laboratory tests and nitrogen balance. These findings indicate that growth, when it is affected, fluctuates in a similar way as albumin, acute phase proteins and symptoms, all assumed to reflect the disease activity. Short-term growth measurements appear to be helpful in monitoring the disease progress or response to therapy in children with Crohn's disease, particularly when growth retardation is the only manifestation of the disease.

Adolescent↗
PubMed1998

Age changes in bone.

Changes in bone structure as a function of age have been studied by simple inspection, x-ray imaging, stereo-photography, deep field optical microscopy, circularly polarised light microscopy, and scanning electron microscopy (SEM), including both topographic and compositional backscattered electron (BSE) imaging modes. The study of bone as a three-dimensional object, rather than in thin sections, enables us to envisage modelling and remodelling processes in context. The study of ultra-flat block surfaces permits the acquisition of data from an effectively very thin layer in the block face, and to examine bone as a spectrum of tissue types varying in the degree of mineralisation. Particular attention has been paid in our earlier studies to the iliac crest, lumbar vertebral bodies, femoral mid-shaft, neck and head and parietal and frontal skull bones. Recently, we have compared findings from these sites with observations on the mandible. We conclude, from our new imaging data, that common generalisations about the changes in bone in ageing and osteoporosis are too simplified, and that the mandible differs sufficiently from post-cranial skeletal sites that it would be unwise to extrapolate from findings in the jaw to the circumstances elsewhere.

Age Factors↗
PubMed1980

Demonstration of glaucomatous optic disc changes by electronic subtraction.

We describe a new method, the electronic subtraction, for objective two-dimensional detection, demonstration and recording of glaucomatous optic disc changes. Siemens subtraction unit M 707 A, based on a double videochain and originally developed for the study of roentgenograms, was used. The results show that this technique is useful in demonstrating the progressive damage of neural tissue of the disc and associated alterations in the course of the vessels. Further development of the electronic subtraction method for glaucomatous optic disc evaluation is discussed.

Aged↗
PubMed1982

Changes in optic disc drusen. Demonstration by stereophotographs and electronic subtraction.

As a part of more comprehensive examination of 180 patients with optic disc drusen, fundus photographs of 159 cases were evaluated. There were 70 patients whose optic discs were photographed two or more times during the years from 1967 to 1981. Four patients were selected to present the changes which can take place in optic discs with drusen and the alterations are demonstrated by autofluorescence pictures, stereophotographs, and electronic subtraction method.

Adolescent↗
PubMed1989

Measuring short-term rates of milk synthesis in breast-feeding mothers.

A Moire contouring method was used to measure changes in the volume of the breast between infant feeds. A tungsten-halogen light source obliquely illuminated the breast through a moving Moire grid to produce contour shadows on the breast. Photographs of the Moire topographs were analysed to obtain three-dimensional co-ordinates of transverse sections through the breast. The cross-sectional areas were calculated using the trapezoidal rule and volumes were calculated by multiplying these areas by their vertical separation. The precision of the method was found to be dependent on the subject repositioning accurately. With careful control over subject posture and position the relative standard deviation was 1.8%, but without careful repositioning the relative standard deviation was 10%. The Moire topography method was accurate; the mean difference between changes in the volume of the breast after breast feeding as measured by the Moire topography method and test weighing was 0.34 +/- 7.26 ml (n = 21). For two women, the rate of increase in the volume of the right breast was found to range from 13 to 40 ml/h.

Adult↗
PubMed2001

Dynamic in vitro quantification of bioprosthetic heart valve leaflet motion using structured light projection.

Quantification of heart valve leaflet deformation during the cardiac cycle is essential in understanding normal and pathological valvular function, as well as in the design of replacement heart valves. Due to the technical complexities involved, little work to date has been performed on dynamic valve leaflet motion. We have developed a novel experimental method utilizing a noncontacting structured laser-light projection technique to investigate dynamic leaflet motion. Using a simulated circulatory loop, a matrix of 150-200 laser light points were projected over the entire leaflet surface. To obtain unobstructed views of the leaflet surface, a stereo system of high-resolution boroscopes was used to track the light points at discrete temporal points during the cardiac cycle. The leaflet surface at each temporal point was reconstructed in three dimensions, and fit using our biquintic hermite finite element approach (Smith et al., Ann. Biomed. Eng. 26:598-611, 2001). To demonstrate our approach, we utilized a bovine pericardial bioprosthetic heart valve, which revealed regions of complex flexural deformation and substantially different shapes during the opening and closing phases. In conclusion, the current method has high spatial and temporal resolution and can reconstruct the entire surface of the cusp simultaneously. Because it is completely noncontacting, this approach is applicable to studies of fatigue and bioreactor technology for tissue engineered heart valves.

Algorithms↗
PubMed2004

How cyclic loading affects the migration of radio-opaque markers attached to tendon grafts using a new method: a study using roentgen stereophotogrammetric analysis (RSA).

An increase in anterior laxity following reconstruction of the anterior cruciate ligament (ACL) can result from lengthening of the graft construct in either the regions of fixation and/or the region of the graft substance between the fixations. RSA could be a useful technique to determine lengthening in these regions if a method can be devised for attaching radio-opaque markers to soft tissue grafts so that marker migration from repeated loading of the graft is limited. Therefore, the objectives of this study were 1) to develop a method for attaching radio-opaque markers to an ACL graft that limits marker migration within the graft, 2) to characterize the error of an RSA system used to study migration, and 3) to determine the maximum amount of migration and the time when it occurs during cyclic loading of ACL grafts. Tendon markers were constructed from a 0.8-mm tantalum ball and a stainless steel suture. Ten double-looped tendon grafts were passed through tibial tunnels drilled in bovine tibias and fixed with a tibial fixation device. Two tendon markers were sewn to one tendon bundle of each graft and the grafts were cyclically loaded for 225,000 cycles from 20 N to 170 N. At specified intervals, simultaneous radiographs were obtained of the tendon markers and a radiographic standard of known length. The bias and imprecision in measuring the length of the radiographic standard were 0.0 and 0.046 mm respectively. Marker migration was computed as the change in distance between the two tendon markers along the axis of the tibial tunnel. Marker migration was greatest after 225,000 cycles with a root mean square (RMS) value of less than 0.2 mm. Because the RMS value indicates the error introduced into measurements of lengthening and because this error is small, the method described for attaching markers to an ACL graft has the potential to be useful for determining lengthening of ACL graft constructs in in vivo studies in humans.

Animals↗
PubMed2005

Simultaneous measurement of three-dimensional joint kinematics and ligament strains with optical methods.

The objective of this study was to assess the precision and accuracy of a nonproprietary, optical three-dimensional (3D) motion analysis system for the simultaneous measurement of soft tissue strains and joint kinematics. The system consisted of two high-resolution digital cameras and software for calculating the 3D coordinates of contrast markers. System precision was assessed by examining the variation in the coordinates of static markers over time. Three-dimensional strain measurement accuracy was assessed by moving contrast markers fixed distances in the field of view and calculating the error in predicted strain. Three-dimensional accuracy for kinematic measurements was assessed by simulating the measurements that are required for recording knee kinematics. The field of view (190 mm) was chosen to allow simultaneous recording of markers for soft tissue strain measurement and knee joint kinematics. Average system precision was between +/-0.004 mm and +/-0.035 mm, depending on marker size and camera angle. Absolute error in strain measurement varied from a minimum of +/-0.025% to a maximum of +/-0.142%, depending on the angle between cameras and the direction of strain with respect to the camera axes. Kinematic accuracy for translations was between +/-0.008 mm and +/-0.034 mm, while rotational accuracy was +/-0.082 deg to +/-0.160 deg. These results demonstrate that simultaneous optical measurement of 3D soft tissue strain and 3D joint kinematics can be performed while achieving excellent accuracy for both sets of measurements.

Elasticity↗
PubMed2005

Migration of radio-opaque markers injected into tendon grafts: a study using roentgen stereophotogrammetric analysis (RSA).

An increase in anterior laxity following reconstruction of the anterior cruciate ligament (ACL) can result from lengthening of the graft construct either at the sites of fixation and/or between the sites of fixation (i.e., graft substance). Roentgen stereophotogrammetric analysis (RSA), which requires that radio-opaque markers be attached to the graft, has been shown to be a useful technique in determining lengthening in these regions. Previous methods have been used for attaching radio-opaque markers to the graft, but they all have limitations particularly for single-loop grafts. Therefore, the objective of this study was to evaluate injecting markers directly into the substance of a tendon as a viable method for measuring lengthening of single-loop graft constructs by determining the maximum amount of migration after cyclic loading. Tantalum spheres of 0.8 mm diameter were used as tendon markers. Ten single-loop tendon grafts were passed through tibial tunnels drilled in calf tibias and fixed with a tibial fixation device. Two tendon markers were inserted in one tendon bundle of each graft and the grafts were cyclically loaded for 225,000 cycles from 20 N to 170 N. At specified intervals, simultaneous radiographs were obtained of the tendon markers. Marker migration was computed as the change in distance between the two tendon markers parallel to the axis of the tibial tunnel. Marker migration had a root mean square (RMS) value of less than 0.1 mm. Because the RMS value indicates the error introduced into measurements of lengthening and because this error is negligible, the method described for attaching markers to single-loop ACL grafts has the potential to be useful for determining lengthening of single-loop ACL graft constructs in in vivo studies in humans.

Animals↗
PubMedDate not supplied

Design of hearing aid shells by three dimensional laser scanning and mesh reconstruction.

Hearing aid shells (or earmolds) must couple the hearing aid with the user's ear. Earmolds have to fit the subject's outer ear canal properly to ensure a good performance of the aid. Because of the great variability in the anatomical pattern of the ear, earmolds are custom made. At present, an impression of the subject's ear canal is taken and used to fabricate the silicon-made mold. The postimpression activities that typically are performed during the fabrication process modify the physical dimensions of the resulting earmold and thus affect the fit of the product. A novel system for 3-D laser scanning and mesh reconstruction of the surface of ear canal impressions is presented. The reconstructed impression can be digitally stored and passed directly to dedicated CAD 3-D printing machines to model the silicon earmold and thus achieve the best possible fit. The proposed system is based on a couple of cameras and a commercial laser for the surface digitization and on a straightforward algorithm, based on the deformation of a geometric model, for the reconstruction of the acquired surface. Measurements on objects of well-known geometric features and dimensions are performed to assess the accuracy and repeatability levels of this 3-D acquisition system. Robustness to noise of the proposed reconstruction algorithm is determined by simulations with a synthetic test surface. Finally, the first measurements (acquisition+reconstruction) of closed surfaces from ear canal impressions are reported.

Algorithms↗
PubMed2002

The effects of stereo shift angle, geometric magnification and display zoom on depth measurements in digital stereomammography.

We are developing virtual three-dimensional (3-D) cursors for measuring depths in digital stereomammograms. We performed a study to investigate the effects of stereo shift angle, geometric magnification, and display zoom on the accuracy of depth measurements made with a virtual 3-D cursor. A phantom containing 50 low contrast fibrils at depths ranging from 1 to 11 mm was imaged with a full-field digital mammography system. Left- and right-eye images were generated at stereo shift angles of +/-3 degrees and +/-6 degrees, using either contact or 1.8x geometric magnification geometry. The images were viewed on a high-resolution stereoscopic display system in normal and 2x zoom mode. Observers viewed the images with stereo glasses and adjusted the depth of a cross-shaped virtual cursor to best match the perceived depth of each fibril. The results for two trained observers with excellent stereo acuity were nearly identical when viewing the same images. The average root mean square errors for the two observers were 1.2 mm (+/-3 degrees contact, no zoom), 1.3 mm (+/-3 degrees contact zoom), 0.8 mm (+/-6 degrees contact, no zoom), 0.6 mm (+/-6 degrees contact, zoom), 0.8 mm (+/-3 magnification, no zoom), 0.7 mm (+/-3 degrees magnification, zoom), and 0.2 mm (+/-6 degrees magnification, no zoom). One observer repeated the entire study for two additional fibril phantom configurations. Combining all the results, we found that for the contact geometry increasing the stereo shift angle from +/-3 degrees to +/-6 degrees improved the depth measurement accuracy by factors of about 1.2-4.0. Zooming did not provide observable improvement in the depth measurement accuracy; sometimes having no effect, sometimes improving the accuracy, and other times reducing the accuracy, with no general trends. Its effect is likely within experimental errors. However, the stereo effect was more readily visualized in the zoom mode. Geometric magnification improved the depth measurement accuracy. The best accuracy among all cases was about 0.2 mm, obtained with geometric magnification using a stereo angle of +/-6 degrees. This is the mode we recommend for obtaining accurate depth measurements with virtual cursors in stereomammograms.

Computer Graphics↗
PubMed2003

Incorporation of a laser range scanner into image-guided liver surgery: surface acquisition, registration, and tracking.

As image guided surgical procedures become increasingly diverse, there will be more scenarios where point-based fiducials cannot be accurately localized for registration and rigid body assumptions no longer hold. As a result, procedures will rely more frequently on anatomical surfaces for the basis of image alignment and will require intraoperative geometric data to measure and compensate for tissue deformation in the organ. In this paper we outline methods for which a laser range scanner may be used to accomplish these tasks intraoperatively. A laser range scanner based on the optical principle of triangulation acquires a dense set of three-dimensional point data in a very rapid, noncontact fashion. Phantom studies were performed to test the ability to link range scan data with traditional modes of image-guided surgery data through localization, registration, and tracking in physical space. The experiments demonstrate that the scanner is capable of localizing point-based fiducials to within 0.2 mm and capable of achieving point and surface based registrations with target registration error of less than 2.0 mm. Tracking points in physical space with the range scanning system yields an error of 1.4 +/- 0.8 mm. Surface deformation studies were performed with the range scanner in order to determine if this device was capable of acquiring enough information for compensation algorithms. In the surface deformation studies, the range scanner was able to detect changes in surface shape due to deformation comparable to those detected by tomographic image studies. Use of the range scanner has been approved for clinical trials, and an initial intraoperative range scan experiment is presented. In all of these studies, the primary source of error in range scan data is deterministically related to the position and orientation of the surface within the scanner's field of view. However, this systematic error can be corrected, allowing the range scanner to provide a rapid, robust method of acquiring anatomical surfaces intraoperatively.

Aged↗
PubMed2003

A stereotactic method for the three-dimensional registration of multi-modality biologic images in animals: NMR, PET, histology, and autoradiography.

The objective of this work was to develop and then validate a stereotactic fiduciary marker system for tumor xenografts in rodents which could be used to co-register magnetic resonance imaging (MRI), PET, tissue histology, autoradiography, and measurements from physiologic probes. A Teflon fiduciary template has been designed which allows the precise insertion of small hollow Teflon rods (0.71 mm diameter) into a tumor. These rods can be visualized by MRI and PET as well as by histology and autoradiography on tissue sections. The methodology has been applied and tested on a rigid phantom, on tissue phantom material, and finally on tumor bearing mice. Image registration has been performed between the MRI and PET images for the rigid Teflon phantom and among MRI, digitized microscopy images of tissue histology, and autoradiograms for both tissue phantom and tumor-bearing mice. A registration accuracy, expressed as the average Euclidean distance between the centers of three fiduciary markers among the registered image sets, of 0.2 +/- 0.06 mm was achieved between MRI and microPET image sets of a rigid Teflon phantom. The fiduciary template allows digitized tissue sections to be co-registered with three-dimensional MRI images with an average accuracy of 0.21 and 0.25 mm for the tissue phantoms and tumor xenografts, respectively. Between histology and autoradiograms, it was 0.19 and 0.21 mm for tissue phantoms and tumor xenografts, respectively. The fiduciary marker system provides a coordinate system with which to correlate information from multiple image types, on a voxel-by-voxel basis, with sub-millimeter accuracy--even among imaging modalities with widely disparate spatial resolution and in the absence of identifiable anatomic landmarks.

Algorithms↗
PubMed2003

Effects of quantum noise and binocular summation on dose requirements in stereoradiography.

In the case of a quantum-noise limited detector, signal detection theory suggests that stereoradiographic images can be acquired with one half of the per-image dose needed for a standard radiographic projection, as information from the two stereo images can be combined. Previously, film-screen stereoradiography has been performed using the same per-image dose as in projection radiography, i.e., doubling the total dose. In this paper, the assumption of a possible decrease in dose for stereoradiography was tested by a series of contrast-detail experiments, using phantom images acquired over a range of exposures. The number of visible details, the effective reduction of the dose, and the effective decrease in the threshold signal-to-noise ratio were determined using human observers under several display and viewing conditions. These results were averaged over five observers and compared with multiple readings by a single observer and with the results of an additional observer with limited stereoscopic acuity. Experimental results show that the total dose needed to produce a stereoradiographic image pair is approximately 1.1 times the dose needed for a single projection in standard radiography, indicating that under these conditions the human visual system demonstrates almost ideal binocular summation.

Depth Perception↗
PubMed2004

Determination of projection geometry from quantitative assessment of the distortion of spherical references in single-view projection radiography.

A method is introduced, inferring the three-dimensional (3-D) location from the 2-D radiographic shadow of an opaque spherical reference body of known radius by considering its elliptical distortion, the 2-D shadow location and a known source-to-receptor distance. Three noncollinear spheres fixed to a rigid object constitute all possible degrees of freedom, i.e., the entire 3-D imaging geometry. The method may be used (a) to determine the 3-D imaging geometry from a single 2-D view and (b) to correct for foreshortening of object distances coplanar with the plane defined by the sphere triplet. Apart from the mathematical background the article describes a small feasibility experiment, performed with four different sphere diameters and a commercial dental ccd-receptor system (pixel length: 0.0195 mm). The mouse-cursor based image evaluation revealed an average underestimation of the critical depth- (x-) coordinate decreasing with increasing radius (-30.3% for r=0.5 mm to 2.8% for r=2.5 mm). Intraobserver reliability (the standard deviation between three single cursor-based assessments) ranged between 0% and 8% of the actual true depth. The main source of the input error is associated with the assessment of the amount of elliptical distortion, where subpixel accuracy is demanded. Consequently, software-based automated image evaluation is required using available methods for pattern recognition and point-spread correction. Provided sufficient accuracy, the method provides an important tool for foreshortening correction, depth assessment, motion analysis, and 3-D reconstruction from two or more 2-D views.

Algorithms↗
PubMed2006

Accuracy of treatment planning based on stereolithography in computer assisted surgery.

Three-dimensional stereolithographic models (SL models), made of solid acrylic resin derived from computed-tomography (CT) data, are an established tool for preoperative treatment planning in numerous fields of medicine. An innovative approach, combining stereolithography with computer-assisted point-to-point navigation, can support the precise surgical realization of a plan that has been defined on an SL model preoperatively. The essential prerequisites for the application of such an approach are: (1) The accuracy of the SL models (including accuracy of the CT scan and correspondence of the model with the patient's anatomy) and (2) the registration method used for the transfer of the plan from the SL model to the patient (i.e., whether the applied registration markers can be added to the SL model corresponding to the markers at the patient with an accuracy that keeps the "cumulative error" at the end of the chain of errors, in the order of the accuracy of contemporary navigation systems). In this study, we focus on these two topics: By applying image-matching techniques, we fuse the original CT data of the patient with the corresponding CT data of the scanned SL model, and measure the deviations of defined parameter (e.g., distances between anatomical points). To evaluate the registration method used for the planning transfer, we apply a point-merge algorithm, using four marker points that should be located at exactly corresponding positions at the patient and at connective bars that are added to the surface of the SL model. Again, deviations at defined anatomical structures are measured and analyzed statistically. Our results prove sufficient correspondence of the two data sets and accuracy of the registration method for routine clinical application. The evaluation of the SL model accuracy revealed an arithmetic mean of the relative deviations from 0.8% to 5.4%, with an overall mean deviation of 2.2%. Mean deviations of the investigated anatomical structures ranged from 0.8 mm to 3.2 mm. An overall mean (comprising all structures) of 2.5 mm was found. The fiducial registration error of the point-merge algorithm ranged from 1.0 mm to 1.4 mm. The evaluated chain of errors showed a mean deviation of 2.5 mm. This study verifies that preoperative planning on SL models and intraoperative transfer of this plan with computer assisted navigation is a suitable and sufficiently reliable method for clinical applications.

Algorithms↗