Wang Guangzhi

Segmentation of the Breast Region in Mammograms Using Watershed Transformation

The author proposes a new approach for the breast region segmentation for the purpose of reduction of subsequent processing calculation and removal of radiopaque artifacts. The proposed algorithm combines the global thresholding method for a coarse estimation of breast region and morphological operations for exact positioning of the breast boundary. 204 mammographic images were randomly selected from the DDSM mammogram database to test the segmenting algorithm and the segmentation results were evaluated by an experienced radiologist. Nearly 95% of the segmentation results were rated as exact segmentation

Evaluating Harris Method in Camera Calibration

In this paper, we focus on the performance of Harris feature point extraction method (Harris method) and evaluate its characteristic in some aspects. We propose a set of criteria for the evaluation: detection, accuracy, consistency, and efficiency. All of these criteria are defined theoretically and measured with different kinds of images. Especially, to verify the localization accuracy of Harris method, we synthesize a series of chessboard images in which the real coordinates of feature points could be computed. Therefore, the criteria proposed here are objective and believable

Construction of a Knowledge Center for Medical Image Processing

This article introduces a medical imaging and image processing knowledge center which serves as an e-learning platform based on network technology. This platform includes contents of medical imaging and medical image processing for the teaching activities, virtual reality tutoring system of human skeleton, medical image database, etc. The purpose of establishing this platform is to recruit and excavate information records which usually associated with the daily data exchanged in teaching and research activities. Then it will gradually form an open professional knowledge database. At present, this platform plays the role of knowledge community in the educational activities of BME program in Tsinghua University

Relationship between surface temperature distribution and internal heat source size of the in-vitro tissue

ln this paper, the relationship between surface temperature distribution and internal heat source size of the in-vitro tissue was discussed. The method of obtaining internal heat source information from surface temperature distribution will promote the application of thermography. Through approximation, the relationship between surface temperature distribution and internal beat source size of the in-vitro tissue was induced. The reasonability of the approximation was validated by the high match degree between the template generated by the approximation solution and the practical surface temperature distribution.

A multistage processing procedure for 4D breast MRI segmentation

Contrast-enhanced magnetic resonance imaging (MRI) is a novel approach to detect breast tumor, however, multiple 3D image sets need to be analyzed which causes unaffordable inspection tasks to physicians. Computer assistant detection is of great help to this situation and image segmentation is most important process of computer assistant detection. To segment the breast region from 3D MRI set, a multistage image processing procedure was proposed. Considering the morphological features of breast image, the image was divided into two parts to reduce the complexity of the segmentation procedure. For the anterior part of the image, the breast tissue was segmented from background using the region growing method. Meanwhile, the mean intensity of breast tissue was estimated. To segment the posterior part of the image, the estimated mean breast intensity was used to initialize an approximate boundary between breast and chest. The estimated intensity distribution of breast tissue was used to set the propagation term of following level set iterations. Based on this initialization, threshold-based 3D level set algorithm was used to seek the precise boundary between chest and breast. The level set algorithm achieves novel performance for the 3D segmentation of chest boundary. Based on the segmentation of one set of 3D image, the segmentation result was used as the initial boundary of following image sets to achieve automatic 4D segmentation. This multistage procedure greatly accelerates the convergence of the level set algorithm and reduces the chance of running into local minimum. Clinical data demonstrated that this processing procedure was effective for automatic segmentation of 4D breast MRI.

CCD-based system for three-dimensional real-time positioning

Based upon the direct position detection approach and pixel analysis technique, a CCD-based system has been developed for three-dimensional real-time positioning. A data sampling interface card has been designed to gather the 2D coordinates of the LED markers. The spatial positions of moving multiple spots can be obtained instantly. A calibration frame has been constructed to acquire the system parameters before detection. A modified DLT (Direct Linear Transformation) algorithm is presented to correct the nonlinear lens distortion using a planar spot-grid. The precision of the system is less than /spl plusmn/1 mm in a 500 mm/spl times/500 mm/spl times/500 mm space. This corresponds to a spatial resolution of about one part in 500 or 0.2% overall accuracy. This system has been applied in evaluating the therapeutic effect of Lumbar Spine Function in manipulative orthopedics. Some discussions about how to acquire more accurate results by modifying the system and the algorithm are also presented.

Finite Element Modeling and Biomechanical Analysis of Eyeball and Extraocular Muscles

Finite element analysis (FEA) plays an important role in the biomechanical field. In this paper, we used FEA method in the area of ophthalmology. We generated an eyeball - extraocular muscles (EOMs) model and converted it to meet the need of FEA process. We exerted outside forces on the structure for nonlinear computation and achieved the distributions of displacement, stress and strain. The results corresponded with the basic theory of ophthalmology. We also put forward some related aspects for discussion and advanced studies

Accuracy of Fiducial Marker Based Multimodal Image Registration in Image Guided Surgery

A key step in Image Guided Surgery (IGS) is the accurate preoperative registration of CT/MRI. Landmark-based registration performs much better in speed, stability and interaction than other registration methods, and the registration accuracy, which directly affects image-to-target registration in surgery, mainly depends on manually localization. In this thesis, we present an experimental technique for estimating the fiducial localization error (FLE_I) and analyzing effecting factors on FLE_I. Our study shows that theoretical localization accuracy is 0.57±0.18mm while clinic accuracy is 0.66±0.33mm (CT) and 0.98±0.38mm (MRI), from which we conclude that fiducial marker based registration method is stable and accurate enough which is an appropriate choice for an image guided surgery system.

Tele-Therapy System for Cognitive Disturbances

Stroke can cause a variety of cognitive disturbances depending on the location of the injury. It is proved by clinic that some specific cognitive training is a safe and effective method for stroke patients who are suffering from cognitive disturbances. In this paper, we designed and implemented a tele-therapy system that based on Internet, so that the patients with cognitive impairment can take the therapy at home. It might be more convenient and effective than the traditional therapy of outpatient visits to the rehabilitation hospital. The tele-therapy system is composed of the computer-assisted cognitive training system (CACT) and the tele-therapy Web on Internet for managing the system and training records