Closest Point Distance Research Articles

Esthetic outcome of immediately placed and nonfunctionally loaded implants in the anterior maxilla utilizing a definitive abutment: A pilot clinical trial

Immediate dental implants placement and loading utilizing definitive abutments might save time and cost when an esthetic final result is anticipated. The objective of this prospective clinical trial was to evaluate the esthetic outcome of immediate implantation and immediate nonfunctional loading utilizing definitive abutments, with and without bony substitutes filling the peri-implant gap. In this clinical trial study a total of 11 implants were placed utilizing a flapless immediate post extraction approach in the maxilla (second premolar to second premolar). Atraumatic extraction was performed and implants were immediately placed. The gap was either left without grafting or filled with particulate bone material. Immediate nonfunctional loading was performed utilizing a definitive abutment. The pink esthetic scores (PESs) were assessed preoperatively, at 1- and 2-year follow-up periods. Dental casts were obtained at respective time intervals; scanned, registered, and closest point distances were measured. For all statistical tests, value of P = 0.05 was set as a statistical significance level. The mean of PES at baseline was 9.4 ± 1.69, at 1 year was 9.5 ± 2.07, at 2 years was 10.2 ± 2.75, for the graft group 10.3 ± 2.8, and for nongrafting group was 10.2 ± 2.59. There were no statistically significant differences in PESs at baseline when compared to 1- and 2-year intervals, and for grafting group versus nongrafting group (P = 0.24). Distances between the two time points for all cases were <1 mm in all reference planes. Immediate placement and nonfunctional loading utilizing a definitive abutment appear to result in a stable result as far as esthetic outcome and alveolar process sufficiency are concerned.

Application of Areal Change Detection Methods Using Point Clouds Data

Surveying techniques such as Terrestrial Laser Scanner have recently been used to measure surface changes via 3D point cloud (PC) comparison. Since there are no signalized points when using laser scanners and no identical points between two epochs, judging an object change detection can only be based on areal methods. A surface based analysis is able to detect changes that are unknown and spread along the whole surface. Existing methods for point cloud comparison and the source of uncertainties are reviewed in the first part of the paper. Current comparison methods are based on a closest point distance or require at least one of the point cloud to be meshed. Better results can be achieved with using Least Square Adjustment of polynomial surfaces (planes and quadric height functions) applied on point cloud data. Examples for change detection based on measurements obtained from terrestrial laser scanning for a double-arc object are given. Two areal methods for comparing two point clouds are used and the obtained results are analyzed.

Accurate 3D comparison of complex topography with terrestrial laser scanner: Application to the Rangitikei canyon (N-Z)

Surveying techniques such as terrestrial laser scanner have recently been used to measure surface changes via 3D point cloud (PC) comparison. Two types of approaches have been pursued: 3D tracking of homologous parts of the surface to compute a displacement field, and distance calculation between two point clouds when homologous parts cannot be defined. This study deals with the second approach, typical of natural surfaces altered by erosion, sedimentation or vegetation between surveys. Current comparison methods are based on a closest point distance or require at least one of the PC to be meshed with severe limitations when surfaces present roughness elements at all scales. To solve these issues, we introduce a new algorithm performing a direct comparison of point clouds in 3D. The method has two steps: (1) surface normal estimation and orientation in 3D at a scale consistent with the local surface roughness; (2) measurement of the mean surface change along the normal direction with explicit calculation of a local confidence interval. Comparison with existing methods demonstrates the higher accuracy of our approach, as well as an easier workflow due to the absence of surface meshing or Digital Elevation Model (DEM) generation. Application of the method in a rapidly eroding, meandering bedrock river (Rangitikei River canyon) illustrates its ability to handle 3D differences in complex situations (flat and vertical surfaces on the same scene), to reduce uncertainty related to point cloud roughness by local averaging and to generate 3D maps of uncertainty levels. We also demonstrate that for high precision survey scanners, the total error budget on change detection is dominated by the point clouds registration error and the surface roughness. Combined with mm-range local georeferencing of the point clouds, levels of detection down to 6mm (defined at 95% confidence) can be routinely attained in situ over ranges of 50m. We provide evidence for the self-affine behaviour of different surfaces. We show how this impacts the calculation of normal vectors and demonstrate the scaling behaviour of the level of change detection. The algorithm has been implemented in a freely available open source software package. It operates in complex 3D cases and can also be used as a simpler and more robust alternative to DEM differencing for the 2D cases.

Automated tongue area detection for computer‐aided diagnosis based on ASM and GA

PurposeThe human tongue is a unique organ that can be stuck out of the body for physical examination, and tongue diagnosis is very important in traditional Chinese medicine. Automated tongue area detection is crucial and indispensable for computer‐aided tongue diagnosis, but it is difficult to implement because of the physiological properties of the tongue. For example, as a non‐rigid organ, the tongue has a high degree of variability in size, shape, color, and texture. The purpose of this study is to address this problem.Design/methodology/approachThis paper presents a hybrid framework for tongue area detection based on active shape model and genetic algorithm with the prior knowledge of tongue shape deformation.FindingsA set of 612 tongue images was collected from both healthy and sick subjects. Using these images, the proposed method was compared with state‐of‐the‐art methods. The proposed method achieved an improvement of about 10 percent, 36 percent, and 6 percent over the existing methods in terms of mean Hausdorff distance, mean closest point distance, and Williams Index, respectively. The results demonstrate the efficacy of our proposed method in terms of both robustness and accuracy.Originality/valueThe proposed method gives a new approach for computer‐aided tongue diagnosis in medicine.

SU-FF-J-42: Analytical Image Guided Radiotherapy for Head and Neck

Purpose: Present a general cost-effective robust clinical process that can analytically evaluate and correct patient setup error for head and neck radiotherapy by comparing orthogonal megavoltage portal images (PI) with corresponding digitally reconstructed radiographs (DRR). Method and Materials: Adobe Photoshop CS2 is used to interactively segment images. Scripts are available to automate many steps, including image enhancement. MATLAB is a software package with many features for rapid matrix computations and image analysis. The closest point distance (CPD) for each PI point to a DRR point forms a set of homologous points. The translation T that aligns the PI to the DRR is equal to the difference in centers of mass. The original PI points are transformed and the process repeated with an Iterative Closest Point (ICP) algorithm. Analytical results are displayed as a cumulative histogram of the percentage of points exceeding CPD. The total area Σ under the histogram is a general error metric. A color coded image is provided to display the anatomical location of the PI points with respect to the DRR and their CPD. Results: The ICP algorithm always converged. The integral Σ was consistently lower for the analytical IGRT, with a mean reduction of 16%. The process was tested retrospectively by three users. Typical user dependence was below 0.5 mm. The time for segmentation of two images and computations was under ten minutes. The process has been integrated with a Visual Basic Toolbox that guides the user through the required all the steps from importing the daily Portal Image, segmentation, computing the translation, and printing a standard report. Conclusion: Inexpensive commercial software has been shown to be useful for on line analytical IGRT. The process developed is robust, consistently better then IGRT, provides documented error metrics, and can be customized by the user for individual applications.

Amplitude fluctuations of decimeter and centimeter radio waves emmitted by the Venera-15 and Venera-16 space probes during propagation through the solar plasma

Results are presented of investigations into the fluctuations of centimeter and decimeter radio waves in the solar plasma. The experimental dependence of the scintillation index on distance of closest point of approach in the range 2.3-100 solar radii is given. Dependence of the scintillation index on wavelength and solar activity is discussed. The dependence of the variance of the fluctuations of the electron concentration on distance to the sun is obtained. It is shown that there is a continuously present region of heightened plasma inhomogeneity in the region of space around the sun.