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Biomedical subjects

O Ratib

Publications and source records attributed to O Ratib.

At least 19 recordsLinked to original sources
PubMed1996

In-house access to PACS images and related data through World Wide Web.

The development of a hospital wide PACS is in progress at the University Hospital of Geneva and several archive modules are operational since 1992. This PACS is intended for wide distribution of images to clinical wards. As the PACS project and the number of archived images grow rapidly in the hospital, it was necessary to provide an easy, more widely accessible and convenient access to the PACS database for the clinicians in the different wards and clinical units of the hospital. An innovative solution has been developed using tools such as Netscape navigator and NCSA World Wide Web server as an alternative to conventional database query and retrieval software. These tools present the advantages of providing a user interface which is the same, independent of the platform being used (e.g. Mac, Windows, UNIX), and an easy integration of different types of documents (e.g. text, images). A strict access control has been added to this interface. It allows user identification and access rights checking, as defined by the in-house hospital information system, before allowing the navigation through patient data records.

Computer Communication Networks↗
PubMed1995

Standard views in cardiac multimodality tomographic imaging.

In cardiology, it is often necessary to acquire more than one type of image to investigate a given clinical problem of a single patient. Images obtained from different imaging modalities are usually recorded and displayed in different orientations, at different positions, and at different scale factors. It is then necessary for the physician to mentally integrate the image information from the different imaging modalities. This phenomenon is particularly true with tomographic imaging techniques that allow complete freedom of the acquisition plane. In particular, when comparing images obtained from ultrasound, computed tomography, magnetic resonance imaging, positron-emission tomography, and single-photon emission computed tomography. The purpose of this article is to propose a standard set of slice orientations that could be easily applied to all modalities. Such common views could greatly facilitate the user's perception of the regional abnormalities observed in the different imaging modalities. This standardization is certainly useful for clinical application but also for every research study that requires a comparative evaluation of the different imaging modalities. Although exact registration of the images from the different modalities requires sophisticated computer programs, the simple reference method in plane positioning proposed here based on plane orientation according to the cardiac geometry can certainly provide a practical and convenient method for the reasonably accurate image registration required for visual comparative studies.

Diagnostic Imaging↗
PubMed1994

[Architecture and organization of PACS workstations: a critical overview].

The development and implementation of a workstation capable of handling medical images and data from different imaging modalities require a particular user-interface design so that it is easily accessible by clinical and non-computer-oriented users. Appropriate management of medical images from different imaging modalities is the first step toward the integration of multimedia information in a coherent computerized medical record. It is also the most challenging part because the amount of data obtained in the form of images is much greater than the text, graphic or sound elements. The proportion of clinical investigations based on imaging modalities is also constantly increasing. The goal of this paper is to review some important design concepts of imaging workstations and to explore the needs and requirements of medical image display and manipulation.

Computer Graphics↗
PubMed1993

Cine gradient-echo MR imaging in the evaluation of cardiovascular diseases.

The contributions of cine gradient-echo (GRE) magnetic resonance imaging were compared with those of spin-echo (SE) imaging for the evaluation of morphologic, functional, and flow alterations in 78 cases of congenital and acquired cardiac diseases. High temporal and spatial resolution cine GRE images (256 phase-encoding steps, 256 x 256 acquisition matrix interpolated to 512 x 512 for display, 16-64 frames per cycle) and SE images were acquired in each case. Cine GRE images provided a better diagnostic evaluation than SE images in several cases: (a) both masses and thrombi could be differentiated from flow artifacts; (b) abnormalities in cardiac function, such as infarction, abnormal wall motion, and ventricular dysfunction, could be evaluated; (c) small defects, shunts, and abnormal communications could be clearly seen; and (d) valvular regurgitations, poststenotic flow alterations, and aortic coarctation could be assessed. Cine GRE imaging was also valuable for postoperative evaluations. The authors believe that cine GRE imaging is a useful addition to SE sequences, especially for the assessment of blood flow and cardiac function.

Adolescent↗
PubMed1993

Regional myocardial blood flow and glucose utilization in symptomatic patients with hypertrophic cardiomyopathy.

BACKGROUND: Previous studies suggested the presence of myocardial ischemia in symptomatic patients with hypertrophic cardiomyopathy. Positron emission tomography, a technique that can identify metabolic consequences of ischemia in coronary artery disease, permits the noninvasive measurements of regional myocardial blood flow and glucose metabolism. This new quantitative imaging approach should therefore be suitable for detecting a possible enhancement of glucose utilization in myocardium of patients with hypertrophic cardiomyopathy and thus may help to elucidate the pathomechanism of ischemia in this disease. METHODS AND RESULTS: In 13 symptomatic patients with hypertrophic cardiomyopathy, myocardial blood flow and glucose utilization were measured with intravenous N-13-ammonia and F-18 deoxyglucose at rest and, in four patients, again during supine bicycle exercise. At rest, blood flow was significantly lower in hypertrophied than in normal myocardium (0.78 +/- 0.19 versus 0.99 +/- 0.13 mL.min-1.g-1, p < 0.025), whereas rates of glucose utilization were similar (0.88 +/- 0.31 versus 0.87 +/- 0.35 mumol.min-1.g-1). With exercise, blood flow and glucose utilization failed to increase in hypertrophic and normal segments but became more heterogeneously distributed throughout the left ventricular myocardium. Blood flow-metabolism mismatches indicative of myocardial ischemia were noted in three patients at rest and in three of the four patients during exercise and were due to reduced flow in the presence of maintained glucose uptake. The discordance between flow and glucose metabolism in hypertrophied myocardium was significantly more prominent in younger than in older patients. CONCLUSIONS: Normal or even elevated rates of glucose utilization and the presence of diminished blood flow in hypertrophied relative to normal myocardium suggest the presence of myocardial ischemia in symptomatic hypertrophic cardiomyopathy. The age dependence of blood flow metabolism disparity suggests differences in the underlying pathophysiology or severity of disease.

Adult↗
PubMed1992

Portable image-manipulation software: what is the extra development cost?

A hospital-wide picture archiving and communication system (PACS) project is currently under development at the University Hospital of Geneva. The visualization and manipulation of images provided by different imaging modalities constitutes one of the most challenging component of a PACS. It was necessary to provide this visualization software on a number of types of workstations because of the varying requirements imposed by the range of clinical uses it must serve. The user interface must be the same, independent of the underlying workstation. In addition to a standard set of image-manipulation and processing tools, there is a need for more specific clinical tools that can be easily adapted to specific medical requirements. To achieve this goal, it was elected to develop a modular and portable software called OSIRIS. This software is available on two different operating systems (the UNIX standard X-11/OSF-Motif based workstations and the Macintosh family) and can be easily ported to other systems. The extra effort required to design such software in a modular and portable way was worthwhile because it resulted in a platform that can be easily expanded and adapted to a variety of specific clinical applications. Its portability allows users to benefit from the rapidly evolving workstation technology and to adapt the performance to suit their needs.

Costs and Cost Analysis↗
PubMed1992

Detection of coronary artery disease with positron emission tomography and rubidium 82.

Myocardial blood flow was evaluated in 31 subjects with not only visual but also, for the first time, circumferential profile analysis of rubidium 82 (82Rb) images acquired with positron emission tomography. Fifteen were control subjects and 16 subjects had significant coronary artery disease, defined as 50% or greater diameter stenosis in a major coronary artery or a first-order branch. Simultaneous 82Rb images at three myocardial levels were obtained before and after intravenous dipyridamole plus handgrip stress. In patients with significant coronary artery disease, visual analysis correctly identified significant disease in 26 (76%) of 34 arteries and its absence in 12 (86%) of 14 normal arteries. According to circumferential profile analysis, these numbers were 91% and 86%, respectively. Thus circumferential analysis of 82Rb images, obtained before and after intravenous dipyridamole plus handgrip stress, yielded improved sensitivity and comparable specificity compared with visual analysis.

Coronary Disease↗
PubMed1992

Overview of CAPACITY data.

This paper presents an overview of the data from 15 cases collected with the CAPACITY software for cost analysis of PACS. The data suggest that both hospital wide and partial PACS implementations do not pay back yet. Only Nuclear Medicine PACS systems may be introduced cost-neutral in the near future. Because of the assumed price drop of hardware components of 5-25% per year, hospital wide and partial PACS may allow cost savings within the next 10-20 years. There are major differences in viewpoints concerning the required PACS configurations and their costs. The experiences with the CAPACITY software suggest the need for the establishment of key rules, for designing a PACS configuration and for estimating PACS costs.

Computer Systems↗
PubMed1992

Current views on the functionalities of PACS.

The concept of PACS has evolved from a central storage of medical images to a distributed data and image management system. The trend and evolution of the definition and design of PACS systems is described in this paper. Special emphasis on the concept of distributed and open architecture is given with a discussion of the advantages and disadvantages of each approach. A hospital-wide PACS system designed based on a distributed architecture integrated with a Hospital Information System (HIS) at the University Hospital of Geneva is further described.

Computer Systems↗
PubMed1992

Semiquantitative assessment of myocardial blood flow and viability using polar map displays of cardiac PET images.

Preserved glucose metabolism in ischemically injured, dysfunctional myocardial tissue as demonstrated on PET imaging predicts functional improvement after revascularization. To characterize more precisely the relationship between regional myocardial blood flow, viability and extent and severity of flow and metabolism abnormalities, we developed a PC-based semiquantitative analysis technique using 13N-ammonia and 18F-deoxyglucose polar map displays. A data base for mean values (m) and standard deviations (s.d.) for relative 13N activities reflecting regional myocardial blood flow, relative 18F activities normalized to normal flow regions reflecting regional glucose utilization and the difference of normalized 18F and 13N activities as an index of a flow-metabolism mismatch was established in 11 normals. Parametric polar maps were derived by comparing patient data to a normal range defined as greater than m - 2 s.d. for relative myocardial blood flow and less than m + 2 s.d. for both relative glucose utilization and the difference between normalized 18F and 13N activities. Semiquantitative indices of extent and severity of blood flow defects, of relative increases in glucose utilization and of flow-metabolism mismatch areas are generated for the entire myocardium and the three coronary territories. The approach promises to be clinically useful to confirm presence and absence of flow and metabolic abnormalities and to assess their extent as a potential predictor of functional outcome after therapy.

Adult↗
PubMed1991

Noninvasive detection of functionally significant coronary artery stenoses with exercise and positron emission tomography.

Positron emission tomography has been employed in vivo to assess flow using N-13 (nitrogen-13) ammonia and glucose metabolism, with the glucose analog F-18 (fluorine-18) fluorodeoxyglucose. Flow metabolism mismatches in which glucose metabolism is increased with respect to flow have been used to define ischemic, but viable myocardium. The feasibility of detecting exercise-induced ischemia using this technique was explored. Eleven normal volunteers and 16 patients who had undergone coronary arteriography were studied with N-13 ammonia at rest and with bicycle exercise, and with F-18 fluorodeoxyglucose in the postexercise period. Each image was divided into 16 sectors. Comparison of absolute net extractions of N-13 ammonia at rest and with exercise was not sensitive in detecting functionally significant coronary artery lesions. Myocardial uptakes of F-18 fluorodeoxyglucose and exercise N-13 ammonia were normalized to the sector with the highest N-13 ammonia uptake (corresponding to the highest flow rate). The differences and ratios of these normalized uptakes were successfully used to objectively define flow metabolism mismatches and to identify functionally significant coronary artery disease. Our data suggest that exercise flow and metabolic imaging are superior to rest and exercise flow imaging, particularly in patients with prior myocardial infarctions.

Ammonia↗
PubMed1991

A quantitative index of regional blood flow in canine myocardium derived noninvasively with N-13 ammonia and dynamic positron emission tomography.

To derive a quantitative index of regional myocardial blood flow, the arterial input function of the flow tracer N-13 ammonia and the regional myocardial N-13 activity concentrations were noninvasively determined in 29 experiments in eight dogs. N-13 ammonia was administered intravenously and cross-sectional images were acquired dynamically using an ECAT III positron emission tomograph with an effective in-plane resolution of 13.46 mm full-width half-maximum. Time-activity curves were derived from the serial images by assigning regions of interest to the left ventricular myocardium and left ventricular blood pool. Tracer net extractions were estimated from the myocardial time-activity concentrations at various times after tracer injection and the integral of the arterial input function. Myocardial blood flow was altered by intravenous dipyridamole, morphine, propranolol and partial or complete occlusion of the left anterior descending coronary artery, and ranged from 9 to 860 ml/min per 100 g. Estimates of tracer net extractions were most accurate when determined from the myocardial N-13 activity concentrations at 60 s divided by the integral of the arterial input function to that time. These estimates correlated with regional myocardial blood flows determined independently by the microsphere technique by y = x (1 - 0.64(e-114/x); SEE = 22.9; r = 0.94). First pass extraction fractions of N-13 ammonia determined noninvasively with this approach declined with higher flows in a nonlinear fashion and were similar to those determined invasively by direct intracoronary N-13 ammonia injections. The findings indicate that an accurate index of regional myocardial blood flow can be obtained noninvasively by high temporal sampling of arterial and myocardial tracer activity concentrations with positron emission tomography. They also provide a basis for the in vivo application of tracer kinetic principles to derive quantitatively and noninvasively regional rates of functional processes in human myocardium.

Ammonia↗
PubMed1991

Metabolic and functional recovery of ischemic human myocardium after coronary angioplasty.

Although revascularization of hypoperfused but metabolically active human myocardium improves segmental function, the temporal relations among restoration of blood flow, normalization of tissue metabolism and recovery of segmental function have not been determined. To examine the effects of coronary angioplasty on 13 asynergic vascular territories in 12 patients, positron emission tomography and two-dimensional echocardiography were performed before and within 72 h of revascularization. Ten patients underwent late echocardiography (67 +/- 19 days) and eight underwent a late positron emission tomographic study (68 +/- 19 days). The extent and severity of abnormalities of wall motion, perfusion and glucose metabolism were expressed as wall motion scores, perfusion defect scores and perfusion-metabolism mismatch scores. Angioplasty significantly increased mean stenosis cross-sectional area (from 0.95 +/- 0.9 to 2.7 +/- 1.4 mm2) and mean cross-sectional luminal diameter (from 0.9 +/- 0.6 to 1.9 +/- 0.5 mm) (both p less than 0.001). Perfusion defect scores in dependent vascular territories improved early after angioplasty (from 116 +/- 166 to 31 +/- 51, p less than 0.002) with no further improvement on the late follow-up study. The mean perfusion-metabolism mismatch score decreased from 159 +/- 175 to 65 +/- 117 early after angioplasty (p less than 0.01) and to 26 +/- 29 at late follow-up (p less than 0.001 vs. before angioplasty; p = NS vs. early after angioplasty). However, absolute rates of glucose utilization remained elevated early after revascularization, normalizing only at late follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)

Angioplasty, Balloon, Coronary↗
PubMed1991

NMINT--introductory courseware for nuclear medicine: database design.

Computer-Aided Instruction (CAI) provides a dynamic and self-paced learning experience to the medical trainee. Microcomputer based hypermedia systems integrate text, graphics, and image information. We present the design of an introductory CAI course for nuclear medicine called NMINT and elaborate on the underlying relational database that contains clinically relevant information and links to local or remote image storage over high speed networks. The IBM PS/2 Windows system uses Toolbook software augmented by C language modules for image and image-overlay database access. The current implementation stores text, graphical lesson material, and image index information on microcomputer magnetic disk; image data are stored on the attached optical disk. The storage architecture is described in detail. We emphasize its multi-access methods and its expandability into department-wide image networks.

Computer Graphics↗
PubMed1989

Radionuclide evaluation of right ventricular wall motion after surgery in tetralogy of Fallot.

Regional wall motion patterns in tetralogy of Fallot and its postoperative modifications by electrical and hemodynamic factors were assessed by Fourier analysis of gated radionuclide angiograms in 24 studies performed in children after surgical correction of tetralogy of Fallot. The range of right ventricular (RV) phase angles (standard deviation of the peak [SDP] of RV) as well as the difference between RV and LV (delta MPh) were used as indices of the synchronicity of wall motion and were correlated with RV apical electrical activation time determined by endocardial electrical mapping. Postoperative studies were divided into two groups according to apical activation: (a) those involving right bundle branch block (RBBB) (nine patients), and (b) those involving distal RBBB (15 patients). delta MPh was longer in proximal than in distal RBBB. Best discrimination between the two groups was obtained with SDP of RV (proximal = 24 degrees +/- 3 degrees, and distal = 17 degrees +/- 2 degrees; p less than 0.0001). These results showed that the range of ventricular phases measured by the SD of the phase distribution of the right ventricle is a good index for distinguishing between proximal and distal RBBB after cardiac surgery.

Adolescent↗
PubMed1989

Noninvasive quantitation of regional myocardial oxygen consumption in vivo with [1-11C]acetate and dynamic positron emission tomography.

The usefulness of [1-11C]acetate as a tracer of overall myocardial oxidative metabolism for use with positron emission tomography has been investigated in 12 closed-chest dogs. Myocardial 11C activity clearance kinetics after intravenous administration of [1-11C]acetate in dogs have been determined noninvasively by positron emission tomography. Biexponential fitting of regional myocardial 11C time-activity curves was performed to give clearance half-times and fractional distribution. The rate constant k1 for the early rapid phase of 11C activity clearance was found to correlate linearly with myocardial oxygen consumption (y = 0.0156x + 0.039; SEE = 0.023; r = 0.95). k1 was approximately 7% lower in septal sectors compared with the left ventricular free wall, suggesting that regional oxygen consumption in the septum was lower; a concomitant regional attenuation of blood flow in the septum relative to the left ventricular free wall was also observed. In dogs using carbohydrates as the predominant fuel, k1 oxygen consumption was somewhat more than in dogs using predominantly free fatty acids (0.021 +/- 0.002 compared with 0.018 +/- 0.002, p less than 0.01), indicating that increased carbohydrate consumption is associated with a small increase in k1 at constant oxygen consumption. It is concluded that measurement of myocardial [1-11C]acetate kinetics allows noninvasive determination of cardiac oxygen consumption by positron emission tomography and that the technique is relatively insensitive to myocardial fuel selection.

Acetates↗
PubMed1989

13N ammonia myocardial imaging at rest and with exercise in normal volunteers. Quantification of absolute myocardial perfusion with dynamic positron emission tomography.

Positron emission tomography (PET) was applied to the measurement of myocardial perfusion using the perfusion tracer 13N-labeled ammonia. 13N ammonia was delivered intravenously to 13 healthy volunteers both at rest and during supine bicycle exercise. Dynamic PET imaging was obtained in three cross-sectional planes for 10 minutes commencing with each injection. The left ventricle was divided into eight sectors, and a small region of interest was assigned to the left ventricular blood pool to obtain the arterial input function. The net extraction of 13N ammonia was obtained for each sector by dividing the tissue 13N concentration at 10 minutes by the integral of the input function from the time of injection to 10 minutes. With this approach for calculating net extractions, rest and exercise net extractions were not significantly different from each other. To obviate possible overestimation of the true 13N ammonia input function by contamination by 13N-labeled compounds other than 13N ammonia or by spillover from myocardium into blood pool, the net extractions were calculated using only the first 90 seconds of the blood and tissue time-activity curves. This approach for calculating net extractions yielded significant differences between rest and exercise, with an average ratio of exercise to rest of 1.38 +/- 0.34. Nonetheless, the increase was less than predicted from the average 2.7-2.8-fold increase in double product at peak exercise or the 1.7-fold increase in double product at 1 minute after exercise. However, when the first 90 seconds of dynamic data were fit with a two compartment tracer kinetic model, average perfusion rates of 0.75 +/- 0.43 ml/min/g at rest and 1.50 +/- 0.74 ml/min/g with exercise were obtained. This average increase in perfusion of 2.2-fold corresponded to similar average increases in double product. Thus, the noninvasive technique of PET imaging with 13N ammonia shows promise for future applications in determining absolute flows in patients with coronary artery disease.

Adult↗