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Biomedical subjects

N Pallikarakis

Publications and source records attributed to N Pallikarakis.

At least 19 recordsLinked to original sources
PubMed2001

Image quality in extended arc filtered digital tomosynthesis.

PURPOSE: To study image quality in filtered digital tomosynthesis (FDTS) tomograms as a function of their reconstruction arc, using isocentrically acquired, fluoroscopic projection data. MATERIAL AND METHODS: Both digital tomosynthesis (DTS) and cone beam CT (CBCT) reconstruction algorithms are based on backprojection and use cone beam projection data as input. Under limited angle conditions, CBCT is reduced to FDTS, where only a subset of projection data are used for reconstruction. The effect of the reconstruction arc on the spatial resolution, slice thickness, contrast sensitivity, shape distortion and artifacts, was also experimentally studied. The investigation was performed using both simulated and actual fluoroscopic images. RESULTS AND CONCLUSION: Image quality in terms of spatial resolution, slice thickness, shape distortion and artifacts, improved with increasing reconstruction arc and was optimized at 180 degrees, while contrast continued to improve as the arc was increased to 360 degrees. However, DTS was determined to be the technique of choice when reconstruction arcs of less than 40 degrees were used. Consequently, FDTS may be successfully implemented in applications involving extended arc reconstructions, in the range between 40 degrees delimiting the DTS domain and 360 degrees corresponding to CBCT.

Image Processing, Computer-Assisted↗
PubMed2000

A software data generator for radiographic imaging investigations.

A software data generation tool, intended to be used in radiographic applications, has been developed. The application integrates a phantom design module and an imaging simulator. Phantoms can be described as a set of either geometrical objects or voxels, or contours drawn on multiple tomographic slices. Radiographic projections of the phantoms are formed on the basis of a simulated irradiation process, with selectable imaging parameters. Comparison between actual projection images from a physical and a simulated phantom shows good correspondence. The application was used for digital tomosynthesis (DTS) investigations and has proven to be a useful tool in the study of tomographic noise. Further development is expected to expand the use of the application to more areas of radiological imaging research.

Algorithms↗
PubMed2000

Education in biomedical engineering: experience from a European ERASMUS program.

Based on recent advances in biomedical research and the developments of new equipment and techniques, the field of Biomedical Engineering and Health Care Telematics are currently undergoing a rapid evolution characterized by an increasing degree of specialization. This, in turns, imposes new requirements in advanced education, while the changing scene at European level, introduces a major challenge for harmonization and standardization of education with a focus on meeting the emerging needs. At the same time information technologies provide new means and tools supporting the educational and training activities. An initiative for the development of a multinational advanced course in Biomedical Engineering, is implemented in the University of Patras with extended collaboration of European Universities, providing a unique case for achievement of excellency. In order to take full advantage of this potential, a Quality Assurance system has been designed and implemented over the past four years, aiming to provide the appropriate framework for mutual recognition amongst the participating institutions. Additionally, the implementation of new telematic tools is scheduled for the near future, in order to provide the Course with teleconference facilities and allow a much larger number of students to remotely attend the lectures.

Biomedical Engineering↗
PubMed1999

An integrated system for the production of field shaping devices in radiotherapy.

A system has been developed in our department that simplifies the production processes of field shaping devices in radiotherapy, integrating an image grabbing and processing facility at a radiotherapy simulator and an automated block cutter. The data acquisition subsystem captures images, processes and corrects them for pincushion distortions, creates a composite radiograph, records user defined contours of blocks and exports data to the block cutter controller. A robotic subsystem drives and controls the polystyrene cutting unit. The system has been experimentally evaluated. Errors in contour definition were found to be less than 1 mm for a broad range of gantry angles and not exceeding 1.5 mm for those gantry orientations that present maximum magnetic field related image intensifier distortion, while the automated block cutter is capable of cutting out contours in polystyrene with an accuracy comparable to that of commercially available systems. The system is expected to contribute to the overall improvement of radiotherapy processes, particularly in low budget radiotherapy departments, introducing improvements in accuracy and efficiency at minimum costs.

Cost Control↗
PubMed1999

Three-dimensional localisation based on projectional and tomographic image correlation: an application for digital tomosynthesis.

Accurate three-dimensional tumor localisation in Radiotherapy, is critical to the treatment outcome, particularly when high dose gradients are present. A number of techniques have been proposed for the localisation of anatomical structures or markers. The present study proposes an approach to a concurrent maximisation of localisation accuracy and efficiency by correlation of tomographic and projectional images. The method introduces an element of direct verification and interactive optimisation of the process. Tomographic images are used for the identification of a point of interest. Its position is computed within the treatment co-ordinate system and verification of this position is achieved by obtaining the beam's eye view of the identified point on two projection radiographs. The key element of the approach is that all images used should be part of one single image data set. The implementation of this localisation method, as part of the functionality of a Digital Tomosynthesis prototype, has provided an integrated facility for localisation, of optimised accuracy and precision, while easy and efficient to use. The considerations are general and apply in principle to any imaging system that can augment tomographic images with projections.

Algorithms↗
PubMed1999

Monte Carlo simulation of the radiographic imaging procedure for electronically designed phantoms.

This paper presents a software simulation package of the entire X-ray projection radiography process including beam generation, absorber structure and composition, irradiation set up, radiation transport through the absorbing medium and image formation. This software tool is an augmented version of a previously presented system with expanded range of application by the implementation of Monte Carlo approach for the simulation of the radiation interaction at the absorber and the detector. Phantoms are created as composite objects from geometrical or voxelized primitives and can be subjected to simulated irradiation process. The acquired projection images represent the two dimensional spatial distribution of the energy absorbed in the detector and are formed at any geometry, taking into account energy spectrum, beam geometry and detector response.

Computer Simulation↗
PubMed1999

A protocol building software tool for medical device quality control tests.

Q-Pro is an application for Quality Control and Inspection of Medical Devices. General system requirements include friendly and comprehensive graphical environment and proper, quick, easy and intuitive user interface. Functions such as, a tool library for protocol design widely used multimedia, as well as, a support of a local database for protocol and inventory data archiving are provided by the system. In order to serve the different categories of users, involved in Quality Control procedures, the system has been split into three modules of different functionality and complexity, each of which can work as a stand-alone application. The implementation of protocols and use of the software functions, as well as, the user interface itself have been proved by the evaluators to be clear and intuitive. The software seems to adapt easily to different kinds of Quality Control procedures and objectives. Q-Pro effectively supports and enhances the processes to attain a highly tuned, professional, responsive and effective quality control and preventive maintenance procedures for biomedical equipment management.

Data Collection↗
PubMed1998

In-house development of test equipment for quality control and training. Case study: a prototype ECG simulator-tester.

The support services for biomedical technology address a variety of technical and administrative issues, concerning the safe and efficient operation of medical equipment over the period of its intended use and the training of hospital personnel in issues concerning safety and quality. Clinical Engineering Departments undertake the responsibility of developing and operating training programs in medical equipment utilisation apart from the traditional role of training and supervising technicians involved in testing, calibration and preventive/corrective maintenance of electromedical equipment. In view of the above, the Institute of Biomedical Technology and the Centre of Biomedical Engineering collaborated for the design and development of a prototype digital ECG and arrhythmia simulator. In the absence of internationally accepted inspection protocols for ECG simulators, the verification phase of the project involved mainly the inspection of the device's conformity to its initial technical specifications. The results demonstrated that this tester. due to simplicity in construction and easiness of use could be a practical, reliable and economical solution for electrocardiograph and ECG monitor testing and waveform recognition training.

Arrhythmias, Cardiac↗
PubMed1996

Volume imaging in fluoroscopy. A clinical prototype system based on a generalized digital tomosynthesis technique.

PURPOSE: This work involves the development of a new digital tomosynthesis technique into a clinical prototype imaging system for the three-dimensional visualization of patient anatomy. MATERIAL AND METHODS: The multiple projection algorithm (MPA) has been developed into a clinical prototype imaging system comprising a digital chain that is interfaced with an isocentric fluoroscopic unit to form an integrated DTS facility. Planes of varying orientations can be synthesized retrospectively on the basis of an acquired set of appropriate projection images extending over the whole volume of interest. RESULTS AND CONCLUSION: The system provides an image reconstruction and processing facility that can effectively augment fluoroscopic examinations. Reconstruction times of a few seconds per plane have been achieved. The region of interest can be approached by tracking through cross-sections with user-selected orientations. Anatomical planes of particular interest can be identified and their reconstructed images can be stored. The characteristics of the image presentation modality have the potential to extend the field of current digital tomosynthesis applications to new areas in radiology and other clinical domains.

Algorithms↗
PubMed1996

Radiographic skills learning: procedure simulation using adaptive hypermedia.

The design and development of a simulation tool supporting learning of radiographic skills is reported. This tool has by textual, graphical and iconic resources, organized according to a building-block, adaptive hypermedia approach, which is described and supported by an image base of radiographs. It offers interactive user-controlled simulation of radiographic imaging procedures. The development is based on a commercially available environment (Toolbook 3.0, Asymetrix Corporation). The core of the system is an attributed precedence (priority) graph, which represents a task outline (concept and resources structure), which is dynamically adjusted to selected procedures. The user interface imitates a conventional radiography system, i.e. operating console, tube, table, patient and cassette. System parameters, such as patient positioning, focus-to-patient distance, magnification, field dimensions, tube voltage and mAs are under user control. Their effects on image quality are presented, by means of an image base acquired under controlled exposure conditions. Innovative use of hypermedia, computer based learning and simulation principles and technology in the development of this tool resulted in an enhanced interactive environment providing radiographic parameter control and visualization of parameter effects on image quality.

Computer Simulation↗
PubMed1995

A computer program for estimating the influence of the body bicarbonate pool during CO2 breath tests.

Mathematical representation of physiological systems is a useful means of monitoring various parameters and factors of such systems. The use of compartmental models for the study of physiological systems has led to the introduction of several new techniques for solving problems, concerning the kinetics between the individual sites of these systems. The computer program, presented here, allows the calculation of the influence of a mammillary model, representing the bicarbonate pool, on the expiration rate of the label, administered during a breath test. It consists of two modules, one for performing non-linear least squares regression fitting of discrete measurements from a breath test (model output) and a second one for estimating the corresponding label released into the bicarbonate pool (model input), based on the measurements of expired air. Data, derived from metabolic studies using oral administration of naturally labelled 13C-glucose in man, under various metabolic conditions, was used as an input to this program.

Bicarbonates↗
PubMed1993

Fructose utilization during exercise in men: rapid conversion of ingested fructose to circulating glucose.

The aim of the present study was to compare the metabolic fate of repeated doses of fructose or glucose ingested every 30 min during long-duration moderate-intensity exercise in men. Healthy volunteers exercised for 3 h on a treadmill at 45% of their maximal oxygen consumption rate. "Naturally labeled" [13C]glucose or [13C]fructose was given orally at 25-g doses every 30 min (total feeding: 150 g; n = 6 in each group). Substrate utilization was evaluated by indirect calorimetry, and exogenous sugar oxidation was measured by isotope ratio mass spectrometry on expired CO2. Results were corrected for baseline drift in 13C/12C ratio in expired air due to exercise alone. Fructose conversion to plasma glucose was measured combining gas chromatography and isotope ratio mass spectrometry. Most of the ingested glucose was oxidized: 81 +/- 4 vs. 57 +/- 2 g/3 h for fructose (2P < 0.005). Exogenous glucose covered 20.8 +/- 1.4% of the total energy need (+/- 6.7 MJ) compared with 14.0 +/- 0.6% for fructose (2P < 0.005). The contribution of total carbohydrates was significantly higher and that of lipids significantly lower with glucose than with fructose. The blood glucose response was similar in both protocols. From 90 to 180 min, 55-60% of circulating glucose was derived from ingested fructose. In conclusion, when ingested repeatedly during moderate-intensity prolonged exercise, fructose is metabolically less available than glucose, despite a high rate of conversion to circulating glucose.

Adult↗