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Biomedical subjects

S C Orphanoudakis

Publications and source records attributed to S C Orphanoudakis.

At least 19 recordsLinked to original sources
PubMed1997

Pre-hospital health emergency management as an integrated service of the Regional Health Telematics Network of Crete.

In this paper, a Pre-hospital Health Emergency Management System (PHEMS) is presented, which is being developed on the basis of a common reference architecture that has been defined at a European level by partners from ten EU member states in the course of the ongoing HECTOR project. The PHEMS, which is implemented as an autonomous system, will be integrated as an added-value service into the Regional Health Telematics Network of Crete. The PHEMS architecture is based on a 'perception-cognition-action' paradigm.

Expert Systems↗
PubMed1997

DIPE: a distributed environment for medical image processing.

DIPE is a distributed environment that provides image processing services over integrated teleradiology services networks. DIPE integrates existing and new image processing software and employs sophisticated execution scheduling mechanisms for the efficient management of computational resources within a distributed environment. It can also be extended to provide various added-value services, such as management and retrieval of image processing software modules, as well as advanced charging procedures based on quality of service. DIPE can be viewed as the natural evolution of the legacy field of medical image processing towards a service over the emergent health care telematics networks.

Computer Communication Networks↗
PubMed1996

Technological advances in teleradiology.

Teleradiology consists of a set of added-value telematic services, implemented over an advanced telecommunications infrastructure and supported by different information technologies and related applications. The main goal of teleradiology is to provide different levels of support for remote diagnostic imaging procedures. This paper considers technological advances in this important area, including a discussion of the various added-value telematic services, applications supporting these services, and the required information technology and telecommunications infrastructure. Teleradiology is also considered in the general context of an integrated regional health telematics network, emphasizing its role and its interaction with other information and networking services.

Computer Communication Networks↗
PubMed1987

An estimation and correction scheme for system imperfections in multiple-echo magnetic resonance imaging.

Multiecho sequences are widely used in MRI because they are an efficient means of acquiring data and they can be used to quantitatively estimate T2. However, the uniformity of each image and the accuracy of each T2 estimate may be corrupted by several instrumental factors such as rf pulse imperfections and static field inhomogeneities. We propose a scheme based on our prior knowledge of the effects of such factors and using the Levenberg-Marquardt method of nonlinear estimation that produces accurate estimates of T2 even in the presence of substantial system imperfections and improves the image quality of later echo images in a multiecho sequence. A further extension of this scheme permits mapping the distribution of the static magnetic field from a single multiecho imaging study of a uniform object. Simulations have been performed to test the efficacy of this scheme and the results are substantiated with experiments performed on a whole-body imager operating at 6.35 MHz.

Algorithms↗
PubMed1986

Errors in the measurements of T2 using multiple-echo MRI techniques. I. Effects of radiofrequency pulse imperfections.

In principle, multiple-echo magnetic resonance imaging (MRI) can be used to estimate the spin-spin relaxation time, T2, which can then be used for quantitative tissue characterization. Although multiple echoes can be used to enhance the signal-to-noise ratio in an image, by echo addition, rf pulse imperfections modify the echo amplitudes resulting in significant errors in the estimate of T2. Imperfect 180 degree pulses do not completely invert the transverse magnetization so that the magnitude of the transverse component is reduced and a longitudinal component is generated. Successive application of such imperfect pulses generates many components that interact in a complex manner. The amplitudes of successive echoes are affected whenever the transverse components refocus, whereas the longitudinal components may be rotated into the transverse plane by subsequent pulses and may often add to the image signal or give rise to an image artifact. These effects have been analyzed theoretically and have been demonstrated for a wide range of rf pulse imperfections using both simple and composite pulses, through computer simulations based on the numerical solution of the Bloch equations. The theoretical and simulation results have been substantiated through experiments performed on a mineral oil phantom using a resistive prototype MR scanner operating at 6.35 MHz. In this paper we report the effects of improper pulse amplitude or duration for nonselective rf pulses on resonance. We separately describe the other types of imperfections caused by off-resonance effects and the use of selective pulses.

Humans↗
PubMed1986

Errors in the measurements of T2 using multiple-echo MRI techniques. II. Effects of static field inhomogeneity.

The accurate estimation of the spin-spin relaxation time T2 is an important goal in magnetic resonance imaging particularly because it can be used for quantitative tissue characterization. The spin-spin relaxation time T2 may be estimated using multiecho pulse sequences, but the accuracy of the estimate is dependent on the fidelity of the spin-echo amplitudes, which may be severely compromised by rf pulse and static field imperfections. In this paper, the effects of static field inhomogeneities are investigated. The propagation of the errors introduced by off-resonance effects are analyzed through computer simulations and analytical solutions of the Bloch equations. A series of experiments performed on a simple tissue phantom using a whole-body imaging system operating at 6.35 MHz corroborates the simulation and analytical results. For accurate measurements of T2 using a whole-body imaging system it is necessary to correct for these inhomogeneities. A correction scheme which would enable a more accurate estimate of T2 is currently under investigation.

Biometry↗
PubMed1983

Fluoroscopic dose reduction using a digital television noise-reduction device.

A digital video image processor, connected to a video system in a conventional pediatric fluoroscopy room, was used to determine whether the device could provide satisfactory fluoroscopic images during routine examinations when the x-ray tube was operated at substantially lower than normal radiation-dose levels. A 50% reduction resulted in image quality which was indistinguishable from conventional fluoroscopic views.

Child↗
PubMed1982

A simulation study of motion artefacts in computed tomography.

In order to increase understanding of artefacts caused by patient motion in computed tomography, rigid translational and rotational motions in the plane of reconstruction have been considered. Motion artefacts were simulated on a digital computer and demonstrated in actual CT scans of a phantom. The types of motion artefacts observed included streaking, boundary splitting and subtle distortions of shape. A method for removing artefacts from a CT image without rescanning the patient is discussed, and some examples of possible improvement are shown using the simulation model. It is assumed that perfect knowledge of patient motion is known since this represents the theoretical limit on possible improvement to the degraded image. A qualitative discussion of streaking, the most common type of motion artefact, is also included.

Humans↗
PubMed1982

The effect of a television digital noise reduction device on fluoroscopic image quality and dose rate.

In conventional fluoroscopy, the current, and therefore the dose rate, is usually determined by the level at which the radiologist visualizes a just tolerable amount of photon "mottle" on the video monitor. In this study, digital processing of the analogue video image reduced noise and generated a television image at half the usual exposure rate. The technique uses frame delay to compare an incoming frame with the preceding output frame. A first-order recursive filter implemented under a motion-detection scheme operates on the image of a point-by-point basis. This effective motion detection algorithm permits noise suppression without creating noticeable lag in moving structures. Eight radiologists evaluated images of vesicoureteral reflux in the pig for noise, contrast, resolution, and general image quality on a five-point preferential scale. They rated the digitally processed fluoroscopy images equivalent in diagnostic value to unprocessed images.

Animals↗
PubMed1980

Assessment of bone mass in the radius by computed tomography.

A reproducible method for quantitative analysis of computed tomographic cross-sections of the distal radius of patients with various metabolic bone diseases is described. A statistically significant correlation between the CT measurements in the radius and quantitative histomorphometric measurement of the trabecular bone volume of corresponding transilial bone biopsies is demonstrated. Selected longitudinal studies are presented to demonstrate the possible clinical applications of this type of CT analysis.

Adult↗
PubMed1978

Small hemorrhages vs. small calcifications in brain tumors: difficulty in differentiation by computed tomography.

The difficulty in differentiating multiple small hemorrhages from multiple small calcifications in brain tumors by computed tomography (CT) is discussed. Illustrative CT scans are presented and the theoretical basis for this problem is elaborated. The difficulty is attributed to the relatively large size of the voxel and the ensuing partial volume effect, particularly with small intraparenchymal lesions of different sizes and attenuations.

Adult↗
PubMedDate not supplied

I2Cnet: Content-based similarity search in geographically distributed repositories of medical images.

The retrieval of images by content is rapidly gaining acceptance as an important function of image database systems. This paper discusses the architecture of I2Cnet, a network of servers which provide content-based query services through a WWW browser. In I2Cnet, algorithms for the representation, storage, and retrieval of medical images based on different descriptions of image content are implemented using description types. AttributeMatch, a description type supported by I2Cnet, aims to capture the knowledge of medical experts in queries by using a similarity criterion which can be tailored to user preferences. We present results showing the query response time of AttributeMatch, obtained with image classes of various sizes, and the degree of similarity of retrieved images to the query image under different similarity criteria.

Algorithms↗
PubMedDate not supplied

Bone mineral analysis using single-energy computed tomography.

We present a new method for evaluating in vivo changes in bone mineralization in the peripheral skeleton, using computed tomography (CT). A set of bone mineralization indices are generated from numerous CT images of the patient's distal radius. The cross-sectional anatomy displayed by the CT scan allows for separate evaluation of the cortical and trabecular bone. Correction for possible drift of the CT number scale (Hounsfield scale) is achieved by scanning standard solutions of dipotassium hydrogen phosphate simultaneously with the forearm. Preliminary data indicate that this is a precise method for evaluating in vivo changes in bone mineralization.

Adolescent↗
PubMedDate not supplied

Mathematical model of conventional tomography.

A Fourier decomposition approach is used to study the imaging properties of conventional tomography. Spatial frequency response curves (MTFs) are calculated for both linear and axial transverse tomography. These curves depend on the product of the spatial frequency of the sinusoidal density variations in thin layers parallel to the tomographic plane and the distance between such layers and the tomographic plane. Based on the spatial frequency response curves, a quantitative definition of tomographic layer thickness is given. Furthermore, the spatial frequency response curves suggest that unattenuated low-frequency information from outside the tomographic layer limits the resolution in conventional tomograms and that high-pass spatial filtering of the image may substantially improve the diagnostic quality of tomographic images, particularly in the identification of boundaries.

Mathematics↗
PubMedDate not supplied

Linearizing mechanisms in conventional tomographic imaging.

Implicit in the concept of conventional tomography and in any attempt to characterize the tomographic process by a modulation transfer function is the assumption that the tomographic process is linear. A Fourier decomposition approach and an analysis of nonlinear contributions to the integrated tomographic image intensity are used in this paper to establish the validity of this assumption and to determine the mechanisms by which the tomographic process is effectively linearized.

Energy Transfer↗
PubMedDate not supplied

Preliminary evaluation of display format effects on perceptibility in a low contrast ultrasound test object.

A phantom consisting of a gel closely resembling human liver on B-mode scanning, and containing a rounded zone of decreased echogenicity, was used to create a series of B-mode ultrasonic images containing simulated "lesions" in random locations on the final recorded image. A homogeneous gel phantom was used to create a series of blank images. Images were recorded in three display formats: conventional white on black background, conventional black on white background, and black on a white background with luminance normalized to that of the conventional white on black image. Six subjects were presented with a randomized series of scans in the 3 display formats, and receiver operating characteristic analysis was used to assess the effect of display format on low-contrast detectability. Detectability of low-contrast "lesions" was lower in a high contrast image with black on white background compared to the medium contrast image in white on black format. Detectability with the black on white format having normalized luminance was generally intermediate between that observed for the two conventional formats.

Evaluation Studies as Topic↗
PubMedDate not supplied

I2C: a system for the indexing, storage, and retrieval of medical images by content.

Image indexing, storage, and retrieval based on pictorial content is a feature of image database systems which is becoming of increasing importance in many application domains. Medical image database systems, which support the retrieval of images generated by different modalities based on their pictorial content, will provide added value to future generation picture archiving and communication systems (PACS), and can be used as a diagnostic decision support tools and as a tool for medical research and training. We present the architecture and features of I2C, a system for the indexing, storage, and retrieval of medical images by content. A unique design feature of this architecture is that it also serves as a platform for the implementation and performance evaluation of image description methods and retrieval strategies. I2C is a modular and extensible system, which has been developed based on object-oriented principles. It consists of a set of cooperating modules which facilitate the addition of new graphical tools, image description and matching algorithms. These can be incorporated into the system at the application level. The core concept of I2C is an image class hierarchy. Image classes encapsulate different segmentation and image content description algorithms. Medical images are assigned to image classes based on a set of user-defined attributes such as imaging modality, type of study, anatomical characteristics, etc. This class-based treatment of images in the I2C system achieves increased accuracy and efficiency of content-based retrievals, by limiting the search space and allowing specific algorithms to be fine-tuned for images acquired by different modalities or representing different parts of the anatomy.

Abstracting and Indexing↗