SEARCH · PubMed Health

Results for “scale-space”

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 37 records · Page 2Linked to original sources

PubMed2001

Automatic recognition of biological shapes using the Hotelling transform.

We present two contour-based techniques, for computerized object recognition that avoid the difficulties due to translations, rotations and scaling. Our techniques do not require any shape representation. The first technique uses the scale-space filtered coordinate functions of contours and their "largest diameters". The second, uses the Hotelling transform of the vector representations of the points of contours. We applied both techniques to recognize human corneal endothelial cells, embedded in a sample of tissue. The results obtained using the Hotelling transform represent a considerable improvement when compared to those previously obtained using the coordinate functions, the curvature function and Fourier descriptors as representations of shape.

Artificial Intelligence↗

PubMed1999

Automatic segmentation of contours of corneal cells.

A fully automatic computerized method for segmenting contours of corneal endothelial cells is proposed. As part of the method, scale-space filtering (i.e. Gaussian filtering) is used to achieve tasks different from noise removal. This type of filtering is applied making use of the separability property of Gaussian kernels, avoiding the erosion of images. A variant of unsharp masking is used to considerably increase the visibility of dark areas of images. It is shown how the overflow that occurs when two images are subtracted can be handled to produce better results than normal unsharp masking. The method is exemplified with a low quality specular micrograph. To test the performance of the method, its output is used to automatically calculate the average cell size of images of different samples of tissue and different visual quality. The obtained results are successfully compared to those obtained with a manual semi-automatic method. A method for reading the segmented contours is suggested as well as two shape representations to achieve morphometric analysis of individual cells.

Algorithms↗

PubMed2000

Wavelet transforms in estimating scatterer spacing from ultrasound echoes.

Ultrasound echoes from organs such as the liver display resolvable periodicity due to regular scattering centers within tissue. The spacing among such scattering centers has been proposed as a signature to characterize diffuse and focal diseases of the liver. Even though it is highly desirable to be able to estimate an inter-scatterer-spacing (ISS) distribution, current methods can estimate only the mean value of scatterer spacing (MSS) over a tissue length. In this paper, we propose a wavelet transform-based technique that is capable of estimating the location of each scattering center, making it possible to obtain the ISS distribution. We represent liver tissue with a point scatterer model, and show, via computer simulations, that the use of multi-scale information in the wavelet scale-space allows us to estimate the locations of regular scattering centers. We show that both the observation noise and random ultrasound returns from unresolvable tissue microstructure can be removed successfully in the wavelet domain via the properties of the modulus maxima sequence of observation across different scales.

Computer Simulation↗

PubMedDate not supplied

Detecting the edge of the tongue: a tutorial.

The goal of this paper is to provide a tutorial introduction to the topic of edge detection of the tongue from ultrasound scans for researchers in speech science and phonetics. The method introduced here is Active Contours (also called snakes), a method for searching for an edge, assuming that it is a smooth curve in the image data. The advantage of this approach is that it is robust to the noisy speckle that clouds edges. This method has been implemented in several software packages currently used for detecting the edge of the tongue in ultrasound images. The tutorial concludes with an overview of the scale-space and Kalman filter approaches, state-of-the-art developments in image processing that will likely influence work on tongue edge detection in the coming years.

Humans↗

PubMed2002

Wavelet analysis of vortex tubes in experimental turbulence.

This paper proposes a method to study vortex tubes in one-dimensional velocity data of experimental turbulence. Vortex tubes are detected as local maxima on the scale-space plot of wavelet transforms of the velocity data. Then it is possible to extract a typical velocity pattern. The result for data obtained in a wind tunnel is consistent with those of three-dimensional direct numerical simulations.

Journal Article↗

PubMed2001

Algorithm for data clustering in pattern recognition problems based on quantum mechanics.

We propose a novel clustering method that is based on physical intuition derived from quantum mechanics. Starting with given data points, we construct a scale-space probability function. Viewing the latter as the lowest eigenstate of a Schrödinger equation, we use simple analytic operations to derive a potential function whose minima determine cluster centers. The method has one parameter, determining the scale over which cluster structures are searched. We demonstrate it on data analyzed in two dimensions (chosen from the eigenvectors of the correlation matrix). The method is applicable in higher dimensions by limiting the evaluation of the Schrödinger potential to the locations of data points.

Journal Article↗

PubMed2002

Parameter space warping: shape-based correspondence between morphologically different objects.

This paper presents a novel and comprehensive method for the automated determination of correspondences between two morphologically different two-dimensional (2-D) or three-dimensional (3-D) objects. Correspondences are determined by warping parametric representations of the objects to be matched. The warp is guided by the minimization of a similarity criterion function that measures features related to structural correspondence, including Euclidian point-to-point distance and differences in normals and curvature. The method uses a continuous harmonic parameterization for both the object and the warp, which provides: 1) a high degree of computational efficiency; 2) robust extraction of differential features, not subject to discretization errors or noise amplification in differentiation; 3) direct formulation of constraints to avoid overlaps in the resulting correspondence set; and 4) a scale-space paradigm of object shape and warp. The new method does not search for individual landmarks, but operates with a complete, integrated representation of the object geometry. The method was tested on 2-D and 3-D objects with substantial shape differences. Results demonstrated substantial improvements of 2%-33% in correspondence accuracy and 15%-59% in correspondence quality compared with direct registration methods.

Algorithms↗

PubMed2006

Movie and video scale-time equalization application to flicker reduction.

Image flicker is a general film effect, which can be observed in videos as well as in old films, and consists of fast variations of the frame contrast and brightness. Reducing flicker of a sequence improves its visual quality and can be an essential first treatment before ulterior manipulations. This paper presents an axiomatic analysis of the problem, which leads to a global and fast method of "de-flicker," based on the scale-space theory. The stability of this process, called scale-time equalization, is ensured by the scale-time framework. Results on different sequences are given and show great visual improvement.

Algorithms↗

PubMed2006

Shape representation and recognition through morphological curvature scale spaces.

A multiscale, morphological method for the purpose of shape-based object recognition is presented. A connected operator similar to the morphological hat-transform is defined, and two scale-space representations are built, using the curvature function as the underlying one-dimensional signal. Each peak and valley of the curvature is extracted and described by its maximum and average heights and by its extent and represents an entry in the top or bottom hat-transform scale spaces. We demonstrate object recognition based on hat-transform scale spaces for three large data sets, a set of diatom contours, the set of silhouettes from the MPEG-7 database and the set of two-dimensional views of three-dimensional objects from the COIL-20 database. Our approach outperforms other methods for which comparative results exist.

Algorithms↗

PubMed2006

The multiscale hermite transform for local orientation analysis.

The efficient representation of local differential structure at various resolutions has been a matter of great interest for adaptive image processing and computer vision tasks. In this paper, we derive a multiscale model to represent natural images based on the scale-space representation: a model that has an inspiration in the human visual system. We first derive the one-dimensional case and then extend the results to two and three dimensions. The operators obtained for analysis and synthesis stages are derivatives of the Gaussian smoothing kernel, so that, for the two-dimensional case, we can represent them either in a rotated coordinate system or in terms of directional derivatives. The method to perform the rotation is efficient because it is implemented by means of the application of the so-called generalized binomial filters. Such a family of discrete sequences fulfills a number of properties that allows estimating the local orientation for several image structures. We also define the discrete counterpart in which the coordinate normalization of the continuous case is approximated as a subsampling of the discrete domain.

Algorithms↗

PubMed2002

Deformable triangular surfaces using fast 1-D radial Lagrangian dynamics--segmentation of 3-D MR and CT images of the wrist.

We developed a new triangulated deformable surface model, which is used to detect the boundary of the bones in three-dimensional magnetic resonance (MR) and computed tomography (CT) images of the wrist. This surface model is robust to initialization and provides wide geometrical coverage and quantitative power. The surface is deformed by applying one-dimensional (1-D) radial Lagrangian dynamics. For initialization a tetrahedron is placed within the bone to be segmented. This initial surface is inflated to a binary approximation of the boundary. During inflation, the surface is refined by the addition of vertices. After the surface is fully inflated, a detailed, accurate boundary detection is obtained by the application of radial scale-space relaxation. In this optimization stage, the image intensity is filtered with a series of 1-D second-order Gaussian filters. The resolution of the triangulated mesh is adapted to the width of the Gaussian filter. To maintain the coherence between the vertices, a resampling technique is applied which is based on collapsing and splitting of edges. We regularized the triangulated mesh by a combination of volume-preserving vertex averaging and equi-angulation of edges. In this paper, we present both qualitative and quantitative results of the surface segmentations in eight MR and ten CT images.

Algorithms↗

PubMed2003

Chromosome image enhancement using multiscale differential operators.

Chromosome banding patterns are very important features for karyotyping, based on which cytogenetic diagnosis procedures are conducted. Due to cell culture, staining, and imaging conditions, image enhancement is a desirable preprocessing step before performing chromosome classification. In this paper, we apply a family of differential wavelet transforms (Wang and Lee, 1998), (Wang, 1999) for this purpose. The proposed differential filters facilitate the extraction of multiscale geometric features of chromosome images. Moreover, desirable fast computation can be realized. We study the behavior of both banding edge pattern and noise in the wavelet transform domain. Based on the fact that image geometrical features like edges are correlated across different scales in the wavelet representation, a multiscale point-wise product (MPP) is used to characterize the correlation of the image features in the scale-space. A novel algorithm is proposed for the enhancement of banding patterns in a chromosome image. In order to compare objectively the performance of the proposed algorithm against several existing image-enhancement techniques, a quantitative criteria, the contrast improvement ratio (CIR), has been adopted to evaluate the enhancement results. The experimental results indicate that the proposed method consistently outperforms existing techniques in terms of the CIR measure, as well as in visual effect. The effect of enhancement on cytogenetic diagnosis is further investigated by classification tests conducted prior to and following the chromosome image enhancement. In comparison with conventional techniques, the proposed method leads to better classification results, thereby benefiting the subsequent cytogenetic diagnosis.

Algorithms↗

PubMed2003

A primal sketch of the cortex mean curvature: a morphogenesis based approach to study the variability of the folding patterns.

In this paper, we propose a new representation of the cortical surface that may be used to study the cortex folding process and to recover some putative stable anatomical landmarks called sulcal roots usually buried in the depth of adult brains. This representation is a primal sketch derived from a scale space computed for the mean curvature of the cortical surface. This scale-space stems from a diffusion equation geodesic to the cortical surface. The primal sketch is made up of objects defined from mean curvature minima and saddle points. The resulting sketch aims first at highlighting significant elementary cortical folds, second at representing the fold merging process during brain growth. The relevance of the framework is illustrated by the study of central sulcus sulcal roots from antenatal to adult age. Some results are proposed for ten different brains. Some preliminary results are also provided for superior temporal sulcus.

Adult↗

PubMed2005

Robust anisotropic Gaussian fitting for volumetric characterization of pulmonary nodules in multislice CT.

This paper proposes a robust statistical estimation and verification framework for characterizing the ellipsoidal (anisotropic) geometrical structure of pulmonary nodules in the Multislice X-ray computed tomography (CT) images. Given a marker indicating a rough location of a target, the proposed solution estimates the target's center location, ellipsoidal boundary approximation, volume, maximum/average diameters, and isotropy by robustly and efficiently fitting an anisotropic Gaussian intensity model. We propose a novel multiscale joint segmentation and model fitting solution which extends the robust mean shift-based analysis to the linear scale-space theory. The design is motivated for enhancing the robustness against margin-truncation induced by neighboring structures, data with large deviations from the chosen model, and marker location variability. A chi-square-based statistical verification and analytical volumetric measurement solutions are also proposed to complement this estimation framework. Experiments with synthetic one-dimensional and two-dimensional data clearly demonstrate the advantage of our solution in comparison with the gamma-normalized Laplacian approach (Linderberg, 1998) and the standard sample estimation approach (Matei, 2001). A quasi-real-time three-dimensional nodule characterization system is developed using this framework and validated with two clinical data sets of thin-section chest CT images. Our experiments with 1310 nodules resulted in (1) robustness against intraoperator and interoperator variability due to varying marker locations, (2) 81% correct estimation rate, (3) 3% false acceptance and 5% false rejection rates, and (4) correct characterization of clinically significant nonsolid ground-glass opacity nodules. This system processes each 33-voxel volume-of-interest by an average of 2 s with a 2.4-GHz Intel CPU. Our solution is generic and can be applied for the analysis of blob-like structures in various other applications.

Algorithms↗

PubMed2000

Multiresolution spot detection by means of entropy thresholding.

Many imaging applications deal with the detection of small targets or spots embedded within an inhomogeneous background. We present a method that accomplishes a multiresolution detection on the wavelet-transformed image. The targets are separated from the background by the exploitation of Renyi's information, which is evaluated at the different decomposition levels of the wavelet transform. The scale-dependent candidate detections are successively combined by means of majority voting for final detection. Connections with results provided in different fields such as multifractal analysis, generalized information measures in scale-space, and cross-entropy analysis in fine-to-coarse transformations are discussed. Detection performance is investigated through an example from medical image analysis.

Diagnostic Imaging↗

PubMed2000

Color image segmentation based on fuzzy rule-based reasoning applied to colonoscopic images.

A fuzzy color segmentation approach is developed for the analysis of colonoscopic images. The segmentation is made up of two phases: segmentation through histogram space filtering and region merging using fuzzy rule-base reasoning. The first phase involves using a scale-space filter to analyze the hue, saturation, and intensity (HSI) histograms to determine the number of classes and construct a 3-D class grid. The color image is then segmented based on the class grid. In the second phase, region merging based on applying the fuzzy rule-base is employed to guide the combining process of the segmented regions. For fuzzy reasoning, three criteria are evaluated, namely, the edge strength along the boundary, color similarity, and spatial connectivity of adjoining regions. Experimental testing of the proposed method applied on colonoscopic images was conducted, and the results are encouraging.

Colonoscopy↗

PubMed2004

Catheter simulation system CathI: from patient data generation to cardiological training systems.

In this paper we discuss a new approach to generate 3D models for a simulation system for training an angioplasty. The underlying data for these models are obtained from angiograms that are captured during routine interventions in cardiology. For the extraction of the arteries we use a non-linear classificatory with features based on vesselness information (using a scale-space approach), the gray value, and motion information of the arteries. As result we can correctly find 80% of the arteries in the image and we have 4% pixels incorrectly classified as arteries. These models serve for a virtual catheter laboratory that is based on original instruments like catheters, wires, control instruments for the X-ray, syringes, and pressure pumps for the balloon catheter but instead of a patient an input instrument is used. This instrument sends positional and pressure data to a PC that simulates the patient. The cardiologist then obtains the visual and haptic feedback as if we operated a real patient.

Cardiac Catheterization↗

PubMed1998

Detection of MRI brain contour using isotropic and anisotropic diffusion filter. A comparative study.

Reconstructed brain surface from MRI are still based on either interactive or manual edge detection methods which are time consuming and subjective. In order to overcome such inadequate result, the scale-space technique was applied using isotropic and anisotropic diffusion filter. Isotropic diffusion was not adequate because it did not allow locally adaptive blurring. On the contrary, stopping the anisotropic diffusion process at the best time of diffusion, edge detector provided the true location and morphology of the sulci and gyri. Although some sulci appeared open curves this one didn't have to be considered as failure of anisotropic diffusion because it was related to the resolution of the original MR image. Nevertheless the human vision subjectively made explicit their closure.

Anisotropy↗