Landmark Selection Research Articles

Comparison of landmark position between conventional cephalometric radiography and CT scans projected to midsagittal plane

Objective: The purpose of this study is to compare landmark position between cephalometric radiography and midsagittal plane projected images from 3 dimensional (3D) CT. Methods: Cephalometric radiographs and CT scans were taken from 20 patients for treatment of mandibular prognathism. After selection of landmarks, CT images were projected to the midsagittal plane and magnified to 110% according to the magnifying power of radiographs. These 2 images were superimposed with frontal and occipital bone. Common coordinate system was established on the base of FH plane. The coordinate value of each landmark was compared by paired t test and mean and standard deviation of difference was calculated. Results: The difference was from −0.14 ± 0.65 to −2.12 ± 2.89 mm in X axis, from 0.34 ± 0.78 to −2.36 ± 2.55 mm (6.79 ± 3.04 mm) in Y axis. There was no significant difference only 9 in X axis, and 7 in Y axis out of 20 landmarks. This might be caused by error from the difference of head positioning, by masking the subtle end structures, identification error from the superimposition and error from the different definition. Conclusions: This study revealed innate shortcomings of radiography. For the development of 3D ceph

Landmark Selection for Task-Oriented Navigation

Many vision-based navigation systems are restricted to the use of only a limited number of landmarks when computing the camera pose. This limitation is due to the overhead of detecting and tracking these landmarks along the image sequence. A new algorithm is proposed for subset selection from the available landmarks. This algorithm searches for the subset that yields minimal uncertainty for the obtained pose parameters. Navigation tasks have different types of goals: moving along a path, photographing an object for a long period of time, etc. The significance of the various pose parameters differs for different navigation tasks. Therefore, a requirements matrix is constructed from a supplied severity function, which defines the relative importance of each parameter. This knowledge can then be used to search for the subset that minimizes the uncertainty of the important parameters, possibly at the cost of greater uncertainty in others. It is shown that the task-oriented landmark selection problem can be defined as an integer-programming problem for which a very good approximation can be obtained. The problem is then translated into a semi-definite programming representation which can be rapidly solved. The feasibility and performance of the proposed algorithm is studied through simulations and lab experimentation.

Clinical neuroanatomy module 5 years’ experience at the School of Medicine of Padova

Macroscopic anatomy of the brain is scheduled during the last meeting of the Short Course of Dissection, an optional course for second-year medical students at the School of Medicine of Padova, following the official 44 h of lectures of Neuroanatomy. The aim of the present study was to ascertain the value of brain dissection in retention of neuroanatomical knowledge by medical students. An anatomical questionnaire was given to second-year students in the years 2002-2006, aiming at evaluating their initial neuroanatomical background. Administered twice, at the beginning and end of the last meeting of the optional course, the questionnaire consisted of three diagrams, showing the base, the convexity of the brain, and an axial section of the cerebrum. For each diagram, ten anatomical structures were selected, according to their clinical importance. Students then followed a worksheet for external examination of the brain and cutting. The teacher presented three examples of pathologies causing elevated intracranial pressure, and indicated their locations on the relative cerebral structures. At the end of the meeting, the same questionnaire was given again. To evaluate long-term retention of information, it was also given to third-year students. The questionnaire revealed improved knowledge of neuroanatomy in a mean of 57% of students, especially as regards the axial section (72%), with respect to that of the brain base (43%) and convexity (40%). After 1 year, long-term assessment of information retention showed that 65% of the group which had followed the dissection course correctly answered with respect to the control group (40%), and even better (87.5%) as regards anatomical details presented in their clinical aspects. The main guidelines in planning the clinical neuroanatomy module were: (1) selection of anatomical landmarks of importance from the clinical viewpoint; (2) identification of pathologies which involve the above anatomical landmarks; (3) relationships between morphology and pathology enhancing anatomo-clinical importance.

Computerassistierte radiologische Diagnostik arthritischer Gelenkveränderungen

Computer assisted diagnosis (CAD) schemes are currently used in the field of musculoskeletal diseases to quantitatively assess vertebral fractures, joint space narrowing, andr erosion. Most systems work semi-automatically, i.e. they are operator dependent in the selection of anatomical landmarks. Fully automatic programs are currently under development. Some CAD products have already been successfully used in clinical trials.

Movement and Native American Landscapes: A Comparative Approach

Landscapes are created by people through their experience and engagement with the world around them and through their activities and movements on the ground. Human groups humanize an environment by mapping themselves onto the landscape using their knowledge of specific landforms and waterways, resources including minerals, plants and animals, and human settlements. Once established, this human imprint transforms the natural landscape into a cultural landscape and establishes a pattern of land use which can persist for generations, if not millennia. The objective of this paper is to examine and compare native perceptions and uses of landscapes using historic maps, established travel and trade routes, and ethnographic data on settlement locations for groups occupying the boreal forest and northwesern Plains of Canada. The data indicate that native perceptions of the landscape are rooted in the landforms and vegetation present in an area as well as the transportation technology available to the group. Although movement and vegetation influence the selection of landmarks on the landscape, mythology and oral traditions describe the origin and spiritual relationships of features on the landscape.

Registration of in vivo magnetic resonance T1-weighted brain images to triphenyltetrazolium chloride stained sections in small animals

Signal changes observed in high-resolution in vivo magnetic resonance (MR) images acquired during cerebral ischemia in small animal models must be correlated to molecular indicators of tissue damage obtained from digitized histological brain sections. An effective image registration technique that incorporates both a linear and non-linear thin plate spline transform was developed to compensate the distortions that occur in the brain during the extraction, fixation, and staining process. Features in different layers of the brain were utilized in conjunction with a radial guideline-assisted landmark selection method to register tissue layers with few distinguishing characteristics. Quantitative analysis using simulated data demonstrated average registration error of 400 μm (corresponding to ∼2.5 pixels in the MR images) when ≥50 landmark points are used. Visual agreement was obtained between T 1-weighted MR images and 2,3,5-triphenyltetrazolium chloride stained histology. These methods will allow accurate registration of in vivo images with histology to correlate in vivo surrogate markers of tissue damage with specific histological indicators of disease.

Landmark Selection for Vision-Based Navigation

Recent work in the object recognition community has yielded a class of interest-point-based features that are stable under significant changes in scale, viewpoint, and illumination, making them ideally suited to landmark-based navigation. Although many such features may be visible in a given view of the robot's environment, only a few such features are necessary to estimate the robot's position and orientation. In this paper, we address the problem of automatically selecting, from the entire set of features visible in the robot's environment, the minimum (optimal) set by which the robot can navigate its environment. Specifically, we decompose the world into a small number of maximally sized regions, such that at each position in a given region, the same small set of features is visible. We introduce a novel graph theoretic formulation of the problem, and prove that it is NP-complete. Next, we introduce a number of approximation algorithms and evaluate them on both synthetic and real data. Finally, we use the decompositions from the real image data to measure the localization performance versus the undecomposed map

Automatic extraction of the mid-facial plane for cranio-maxillofacial surgery planning

Recently developed computer applications provide tools for planning cranio-maxillofacial interventions based on 3-dimensional (3D) virtual models of the patient's skull obtained from computed-tomography (CT) scans. Precise knowledge of the location of the mid-facial plane is important for the assessment of deformities and for planning reconstructive procedures. In this work, a new method is presented to automatically compute the mid-facial plane on the basis of a surface model of the facial skeleton obtained from CT. The method matches homologous surface areas selected by the user on the left and right facial side using an iterative closest point optimization. The symmetry plane which best approximates this matching transformation is then computed. This new automatic method was evaluated in an experimental study. The study included experienced and inexperienced clinicians defining the symmetry plane by a selection of landmarks. This manual definition was systematically compared with the definition resulting from the new automatic method: Quality of the symmetry planes was evaluated by their ability to match homologous areas of the face. Results show that the new automatic method is reliable and leads to significantly higher accuracy than the manual method when performed by inexperienced clinicians. In addition, the method performs equally well in difficult trauma situations, where key landmarks are unreliable or absent.

Alignment of gas chromatography–mass spectrometry data by landmark selection from complex chemical mixtures

Analyzing the response of analytical sensors to complex chemical mixtures is difficult, as signals may overlap and may vary between experiments. The analysis and comparison of data files depends on their repeatability, and misaligned signals will not be directly comparable. We present a method for aligning chromatographic data by the selection of landmarks, the matching of these landmarks across chromatograms, the calculation of a functional approximation describing the amount of shift of the landmarks between files using cubic spline interpolation, and the subsequent shifting of the data by the application of this functional approximation so that the two files are aligned. We demonstrate the effect of this alignment on subsequent principal component analysis.

A New Concept of Indexing Tibiofibular Torsion

A newly developed clinical method of indexing tibial torsion uses the medial surface of the tibia as the proximal reference; however, the selection of a specific landmark on the medial surface has not been justified. Three different surfaces relating to the tibial tuberosity were tested using 24 dry tibial bones to determine which provides the most accurate and reliable landmark for use as the proximal reference. The medial surface of the tibia at the inferior point of the tibial tuberosity was the most reliable proximal reference that yielded the highest level of association between the newly developed clinical method and true tibial torsion (r = 0.77). The new method has the potential to describe the anatomy of the leg and to improve the clinical measurement of tibiofibular torsion.

Intraobserver Errors in Obtaining Visually Selected Anatomic Landmarks During Registration Process in Nonimage-based Navigation-assisted Total Knee Arthroplasty: A Cadaveric Experiment

This study investigated the intraobserver errors in obtaining visually selected anatomic landmarks that were used in registration process in a nonimage-based computer-assisted total knee replacement (TKR) system. The landmarks studied were center of distal femur, medial and lateral femoral epicondyle, center of proximal tibia, medial malleolus, and lateral malleolus. Repeated registration in the above sequence was done for 100 times by a single surgeon. The maximum combined errors in the mechanical axis of the lower limb were only 1.32° (varus/valgus) in the coronal plane and 4.17° (flexion/extension) in the sagittal plane. The maximum error in transepicondylar axis was 8.2°. The errors using the visual selection of anatomic landmarks for the registration technique of bony landmarks in nonimage-based navigated TKR did not introduce significant error in the mechanical axis of the lower limb in the coronal plane. However, the error in the transepicondylar axis was significant in the “worst-case scenario.”

A high accuracy, landmark-based, sub-pixel level image registration method

Many medical applications require high-accuracy registration of images. In this paper, we present a landmark-based method for registering images that allows for scaling, translation, and rotation. The method is applied to register high-resolution (HR) Visible Human Male cryosection images with their corresponding registered low-resolution (LR) images. The difference in resolution presents difficulty in landmark selection. The solution for this requires equalizing pixel sizes of images from both sets. Registering HR images to LR images, already registered to each other, results in a registered set of HR images. The accuracy of the registration algorithm is evaluated by registering an image transformed with preset factors and comparing it to the original image. The accuracy of registration is calculated as 10 −3 HR pixels for scaling, 10 −3 degrees for rotation and 10 −7 HR pixels for translation. Once the HR set is registered and segmented it is possible to generate 3D virtual models of anatomical structures for other applications.

2A1-S-016 軌道評価に基づく特徴LandMark選定による走行軌道補正の検証(車輪移動ロボット3,生活を支援するロボメカ技術のメガインテグレーション)

2A1-S-016 軌道評価に基づく特徴LandMark選定による走行軌道補正の検証(車輪移動ロボット3,生活を支援するロボメカ技術のメガインテグレーション)

Otolith shape contour analysis using affine transformation invariant wavelet transforms and curvature scale space representation

Fish otolith morphology has been closely related to landmark selection in order to establish the most discriminating points that can help to differentiate or find common characteristics in sets of otolith images. Fourier analysis has traditionally been used to represent otolith images, since it can reconstruct a version of the contour that is close to the original by choosing a reduced set of harmonic terms. However, it is difficult to locate the contour’s singularities from this spectrum. As an alternative, wavelet transform and curvature scale space representation allow us to quantify the irregularities of the contour and determine its precise position. These properties make these techniques suitable for pattern recognition purposes, ageing, stock determination and species identification studies. In the present study both techniques are applied and used in an otolith classification system that shows robustness against affine image transformations, shears and the presence of noise. The results are interpreted and discussed in relation to traditional morphology studies.

Perceptually relevant and piecewise linear matching of silhouettes

In this paper, a novel alignment method for silhouettes is proposed. This method is based on the establishment of correspondences between landmarks on their boundaries and, in turn, on the establishment of correspondences of the boundary pieces in between these landmarks. The method yields more correct correspondences than conventional methods that scale the arc-length descriptions of silhouettes to align them. The selection of landmarks is investigated as to the robustness of their localization and their perceptual relevance. Matching of silhouettes is then achieved by quantifying the dissimilarity of a pair of silhouette boundaries, based on a novel dissimilarity metric. The matching procedure is evaluated, based on retrieval experiments, and it is concluded that the precision of the results is higher than that obtained by conventional pointwise comparison methods.

Automatic noise robust registration of radiographs for subtraction using strategic local correlation: an application to radiographs of dental implants

Most of digital subtraction methods in dental radiography are based on registration using manual landmarks. We have developed an automatic registration method without using the manual selection of landmarks. By restricting a geometrical matching of images to a region of interest (ROI), we compare the cross-correlation coefficient only between the ROIs. The affine or perspective transform parameters satisfying maximum of cross-correlation between the local regions are searched iteratively by a fast searching strategy. The parameters are searched on the 1 4 scale image coarsely and then, the fine registration is performed on the original scale image. The developed method can match the images corrupted by Gaussian noise with the same accuracy for the images without any transform simulation. The registration accuracy of the perspective method shows a 17% improvement over the manual method. The application of the developed method to radiographs of dental implants provides an automatic noise robust registration with high accuracy in almost real time.

Appearance based landmark selection and reliability evaluation for topological navigation

In this paper we propose two algorithms for selecting landmarks, and methods to measure the reliability of the selected landmarks, that will be used in future work to optimize topological navigation of a blimp. The first algorithm evaluates image similarities between possible landmarks. The second one, which can also be used for online landmark selection, uses Incremental Principal Component Analysis and a measure of how good a new landmark can be expressed in the existing eigenspace.

Automatic noise robust registration of dental radiographs for implants using strategic local correlation

We have developed an automatic registration method without using the manual selection of landmarks. By restricting a geometrical matching of images to a region of interest (ROI), we compare the cross-correlation coefficient only between the ROIs. The transform parameters satisfying maximum of cross-correlation between the local regions are searched iteratively by a fast searching strategy. The developed method can match the images corrupted by Gaussian noise with the same accuracy for the images without any transform simulation. The application of the developed method to radiographs of dental implants provides an automatic noise robust registration with high accuracy in almost real time.

Development of a three-dimensional treatment planning system based on computed tomographic data

Abstract.Current surgical treatment planning systems predict three-dimensional (3D) corrections from two-dimensional (2D) data and are inadequate for complex movements. In this paper, we present a 3D planning system based on computed tomographic (CT) data.A three-dimensional CT scan of the craniofacial skeleton forms the database. Software developed in the Harvard Surgical Planning Laboratory was modified for the craniofacial skeleton. Reproducible skeletal landmarks are identified for superimposition. A ‘cutting tool’ is used to segment the mandible and segments are moved to their predicted positions. A ‘collision tool’, alerts the operator of skeletal interferences. An analysis of selected scans is used to demonstrate the system.Three-dimensional visualization of the facial skeleton, selection of landmarks, measurement of angles and distances, simulation of osteotomies, repositioning of bones, detection of collisions and super-imposition of scans were accomplished.In an illustrative case of Hemifacial Microsomia, predicted and actual 3D corrective movements of the entire mandible were documented. Analysis of scans indicated that 3D planning can prevent insufficient jaw lengthening or other surgical inaccuracies which occur with standard 2D methods.Software demonstrated here will allow the surgeon to accurately plan treatment and evaluate craniomaxillofacial surgery outcomes. Future applications may include surgical navigation.

Visual Navigation in Natural Environments: From Range and Color Data to a Landmark-Based Model

This paper concerns the exploration of a natural environment by a mobile robot equipped with both a video color camera and a stereo-vision system. We focus on the interest of such a multi-sensory system to deal with the navigation of a robot in an a priori unknown environment, including (1) the incremental construction of a landmark-based model, and the use of these landmarks for (2) the 3-D localization of the mobile robot and for (3) a sensor-based navigation mode. For robot localization, a slow process and a fast one are simultaneously executed during the robot motions. In the modeling process (currently 0.1 Hz), the global landmark-based model is incrementally built and the robot situation can be estimated from discriminant landmarks selected amongst the detected objects in the range data. In the tracking process (currently 4 Hz), selected landmarks are tracked in the visual datas the tracking results are used to simplify the matching between landmarks in the modeling process. Finally, a sensor-based visual navigation mode, based on the same landmark selection and tracking, is also presenteds in order to navigate during a long robot motion, different landmarks (targets) can be selected as a sequence of sub-goals that the robot must successively reach.