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A A Farag

Publications and source records attributed to A A Farag.

8 recordsLinked to original sources
PubMed2006

Cerebrovascular segmentation from TOF using stochastic models.

In this paper, we present an automatic statistical approach for extracting 3D blood vessels from time-of-flight (TOF) magnetic resonance angiography (MRA) data. The voxels of the dataset are classified as either blood vessels or background noise. The observed volume data is modeled by two stochastic processes. The low level process characterizes the intensity distribution of the data, while the high level process characterizes their statistical dependence among neighboring voxels. The low level process of the background signal is modeled by a finite mixture of one Rayleigh and two normal distributions, while the blood vessels are modeled by one normal distribution. The parameters of the low level process are estimated using the expectation maximization (EM) algorithm. Since the convergence of the EM is sensitive to the initial estimate of the model parameters, an automatic method for parameter initialization, based on histogram analysis, is provided. To improve the quality of segmentation achieved by the proposed low level model especially in the regions of significantly vascular signal loss, the high level process is modeled as a Markov random field (MRF). Since MRF is sensitive to edges and the intracranial vessels represent roughly 5% of the intracranial volume, 2D MRF will destroy most of the small and medium sized vessels. Therefore, to reduce this limitation, we employed 3D MRF, whose parameters are estimated using the maximum pseudo likelihood estimator (MPLE), which converges to the true likelihood under large lattice. Our proposed model exhibits a good fit to the clinical data and is extensively tested on different synthetic vessel phantoms and several 2D/3D TOF datasets acquired from two different MRI scanners. Experimental results showed that the proposed model provides good quality of segmentation and is capable of delineating vessels down to 3 voxel diameters.

Algorithms↗
PubMed2003

Video reconstructions in dentistry.

OBJECTIVES: To present two practical techniques for three-dimensional (3D) modeling of the human jaw from a sequence of intra-oral images. DESIGN: A data acquisition system consists of: 3D digitizing arm, CCD camera and a laser projector in addition to a software module of two 3D modeling techniques; shape from shading (SFS) and space carving (SC). SETTING AND SAMPLE POPULATION: Several experiments have been conducted on a sample of students at the Computer Vision and Image Processing (CVIP) Laboratory at the University of Louisville, Louisville, KY. Other experiments were performed on solid models of human jaw. EXPERIMENTAL VARIABLE: The SFS technique, using perspective projection and camera calibration, extracts the 3D information from a sequence of two-dimensional images of the jaw. Data fusion of range data and 3D registration techniques develop the complete jaw model. The SC approach is implemented on a sequence of calibrated images. On the two reconstructions, we fit a mesh model to the data, in order to create a solid 3D model. OUTCOME MEASURE: The accuracy of the reconstructed 3D model of human jaw is calculated based on the measurements on real jaws. RESULTS: The SFS-based technique seems to provide more faithful information about the shape of the tooth tops. However, the SC algorithm successfully reconstructed 3D models of the human jaw with sub-millimeter accuracy, which is as accurate as (or even better than) the first technique without using any range measurements or laser projectors. The average error in distance calculation was found to be 0.74 mm, which is an acceptable resolution for many orthodontics and maxillofacial applications. CONCLUSION: Accurate 3D reconstruction of the human jaw enables many orthodontics and dental imaging research findings to be applied directly to a digital jaw model--not to a cast--using computer vision and medical imaging tools.

Algorithms↗
PubMed2000

A 3-D reconstruction system for the human jaw using a sequence of optical images.

This paper presents a model-based vision system for dentistry that will assist in diagnosis, treatment planning, and surgical simulation. Dentistry requires an accurate three-dimensional (3-D) representation of the teeth and jaws for diagnostic and treatment purposes. The proposed integrated computer vision system constructs a 3-D model of the patient's dental occlusion using an intraoral video camera. A modified shape from shading (SFS) technique, using perspective projection and camera calibration, extracts the 3-D information from a sequence of two-dimensional (2-D) images of the jaw. Data fusion of range data and 3-D registration techniques develop the complete jaw model. Triangulation is then performed, and a solid 3-D model is reconstructed. The system performance is investigated using ground truth data, and the results show acceptable reconstruction accuracy.

Algorithms↗
PubMed1993

Teleradiology for dentistry.

As the world enters the "telecosm," the importance of rapid information transfer will grow. It is not unusual for the average American to have a beeper on his or her belt, a cellular telephone in the car, a telephone with remote access answering machine, voice mail, call forwarding, a home fax, and a personal computer networked with a commercial purchasing and information retrieval service such as CompuServe or Prodigy. Conventional cellular telephones, introduced in 1983, numbered approximately 6.4 million in the United States by January, 1992. This is a measure of the importance placed on rapid interpersonal communication. Undoubtedly, patients will begin to expect at least the same degree of efficiency in communications on the part of health care providers, including dentists. There are great potentials for expediting prior approval and reducing costs for dental care as dentists obtain new, lower-priced, direct digital imaging systems, especially as ISDN and electronic mail systems become more available and less costly. It should be possible to reduce insurance costs by minimizing the numbers of clerical staff needed to open, check, and return submitted radiographs. Centralized diagnostic centers for second or expert opinions both for the dental profession and for the insurance carriers are additional pluses. There are potential savings in mailing costs and in reducing travel required of the patient living in a remote region to obtain a second opinion. Transmission using commercially available access to Internet/NSFNET is already possible for a small monthly fee. Nothing, other than a basic personal computer with graphics capabilities, is needed to transmit and receive files once the image is in a digital form. Electronic imaging and image transmission are here.

Computer Communication Networks↗
PubMed1992

Expediting prior approval and containing third-party costs for dental care.

Dental insurance carriers frequently require referral of radiographs for determination of prior approval. Radiographs are also often used for obtaining expert opinions before finalizing diagnoses and establishing treatment plans. Traditionally, such referrals have been carried out using the original or duplicate films transmitted through the postal system. Studies concerning alternative communication media for data transmission are presented, namely, the use of switched-digital telephone lines and of electronic mail networks.

Computer Communication Networks↗
PubMed1992

Communication in digital radiology.

The long-distance transfer of dental radiographs was explored as early as the 1920s. The practicality of such image transfer has improved through advances in telecommunications and computer networks (both hardware and software) and the emerging trends towards direct and indirect digital imaging techniques for recording oral and maxillofacial radiographs. This paper reviews the current status of communication in digital dental radiology. It is illustrated by personal observations from a variety of demonstration projects.

Computer Communication Networks↗
PubMedDate not supplied

Detection of pulse and respiratory signals from the wrist using dry electrodes.

A dry, tetrapolar electrode array was used to detect the differential impedance signal at the wrists of 11 adult human subjects. Experiments were conducted to determine the importance of potential-sensing electrode spacing to detect each wearer's pulse rate and respiratory rate. The current-injecting electrodes were at the sides of the wrist; the potential-sensing electrodes were on the volar wrist surface. The bandwidth-filtered root-mean-square amplitudes of the pulse and respiratory components were computed and found to increase with increasing electrode spacing. Optimum spacings were slightly different for the pulse and respiration and were slightly different in the male and female subjects. A spacing for the potential electrodes of about 60% of the wrist hemicircumference is a good compromise for detecting respiration and pulse.

Adult↗