Biomedical subjects

I Magnin

Publications and source records attributed to I Magnin.

6 recordsLinked to original sources

PubMed2005

Grid-enabling medical image analysis.

Grids have emerged as a promising technology to handle the data and compute intensive requirements of many application areas. Digital medical image processing is a promising application area for grids. Given the volume of data, the sensitivity of medical information, and the joint complexity of medical datasets and computations expected in clinical practice, the challenge is to fill the gap between the grid middleware and the requirements of clinical applications. The research project AGIR (Grid Analysis of Radiological Data) presented in this paper addresses this challenge through a combined approach: on one hand, leveraging the grid middleware through core grid medical services which target the requirements of medical data processing applications; on the other hand, grid-enabling a panel of applications ranging from algorithmic research to clinical applications.

Computer Communication Networks↗

PubMed1998

Fusion of cine magnetic resonance and contrast-enhanced first-pass magnetic resonance data in patients with coronary artery disease: a feasibility study.

RATIONALE AND OBJECTIVES: The left ventricle (LV) myocardial wall contractibility can be evaluated using cine magnetic resonance imaging (MRI) in a qualitative or quantitative manner. Meanwhile, myocardial perfusion can be assessed using contrast-enhanced first-pass MRI. The authors propose a method of automatically fusing the complementary information from these two cardiac MRI modalities into one single image, from which a match or mismatch between contraction and perfusion could be extracted. METHODS: The authors developed a registration algorithm based on the combined use of the global affine transformation and intrinsic landmarks to match images from the same sequence or from two imaging sequences. Contraction and perfusion information was fused by combining a myocardial contour image and a parametric image of the slope of the intensity-time curve, respectively. The fusion paradigm was applied to four patients' data as a demonstration of feasibility of the proposed approach and as a preliminary evaluation. RESULTS: Cine MR and contrast-enhanced MR images were well aligned. The contractibility of the LV was displayed by the myocardial contour image. The parametric slope image was consistent with the known coronary artery status of each patient. The combined contraction-perfusion representation of the LV showed the correspondence between regional LV contraction and myocardial perfusion at a one slice level. CONCLUSIONS: Left ventricle contraction and myocardial perfusion can be represented conjointly in one single fused image. The fusion paradigm should be evaluated for a larger number of patients to evaluate the clinical relevance of this approach in assessing coronary artery disease.

Algorithms↗

PubMed1998

Evaluation of an automatic intraluminal edge detection technique for intravascular ultrasound images.

Intravascular ultrasound (IVUS) imaging enables detailed analysis and precise measurements of vascular cross-sections. However, to achieve a reduction in the existing level of observer variability requires the development of quantitative IVUS. We have developed a fully automatic intraluminal edge detection technique, based on adaptive active contour models and called ADDER (adaptive damping dependent on echographic regions) that allows the quantitation of the intraluminal cross-sectional area (ICSA). Using a 30-MHz mechanically rotated transducer mounted at the tip of a 3.5-F catheter, 58 normal and pathologic arterial segments (from coronary, renal, splenic, iliac, and carotid arteries) were imaged in vitro. These images were analyzed by 2 experts, E1 and E2, who manually traced the intraluminal contour twice for each image, as well as with ADDER. Intra-observer variabilities for ICSAs were found to be excellent (-1.454 +/- 3.51% for E1, 0.96 +/- 5.4% for E2). The inter-observer variability was 2.1 +/- 4.3%. The success factor for ADDER was 89%. Its intra-observer variability was null, as the method always finds a unique contour. The correlation between the automatically detected ICSA and the manual ICSA was: r = 0.99 (y = 1.03x + 0.89 mm2). Morphometric variations between manually and automatically traced contours, analyzed by the centerline method, were 100 +/- 140 mm on average. In conclusion, the ADDER automatic contour detection applied to IVUS images is robust and characterized by small systematic and random errors; therefore, quantitative IVUS is a useful tool in clinical research trials.

Blood Vessels↗

PubMed1997

Comparison between qualitative and quantitative wall motion analyses using dipyridamole stress breath-hold cine magnetic resonance imaging in patients with severe coronary artery stenosis.

Breath-hold cine magnetic resonance imaging (MRI) at rest and during dipyridamole infusion was used to study wall motion abnormalities in patients with severe coronary artery stenosis proven by coronary angiography. Sixteen patients without myocardial infarction but at least one major coronary artery with > or = 70% diameter narrowing were included. Qualitative "visual" assessment of wall motion, as well as quantitative measurement "wall thickening changes (%)" were compared using receiver operating characteristic curve analysis. 201Tl-single-photon emission computed tomography (SPECT) was also studied for comparison. Using qualitative analysis, coronary artery disease detection rate was comparable when assessing wall motion abnormalities with dipyridamole-MRI (79%) and with dipyridamole-induced perfusion defects with 201-thallium-SPECT (75%). Furthermore, sensitivity and specificity for identification of all diseased coronary territories were comparable for both imaging modalities (sensitivity of dipyridamole-MRI and 201thallium-SPECT, 80% vs. 69%; specificity, 75% vs. 80%). The quantitative method has a substantially higher sensitivity than the qualitative method in identifying all diseased territories (Az = 0.81, p < 0.01 vs. Az = 0.55 and 0.59). In addition, we demonstrated that the quantitative method had higher performance than the qualitative one in identifying the diseased vessels territories related to 1-vessel, 2-vessel, and each of individual coronary artery stenoses.

Aged↗

PubMed1997

Effects of radiofrequency catheter ablation on patients with permanent pacemakers.

The objective of this study was to assess the effects of radiofrequency energy application on implanted pacemaker functions. Radiofrequency (RF) catheter ablation may cause pacemaker dysfunction due to electromagnetic interferences. The effects of RF on pacemaker behavior were studied in a series of 38 pacemakers, implanted 18 +/- 26 months prior to a RF procedure using either a right ventricular approach (AV node ablation, n = 35) or a left ventricular approach (left concealed accessory pathway ablation, n = 1; VT ablation, n = 2). The 38 patients (mean age 65 +/- 9 years) included 20 men and 18 women. Before energy applications, the 23 different pacemaker models were programmed to the VVI mode at the lowest available rate. The continuous surface ECG was recorded throughout the procedure. Thorough testing of the devices was performed before and after each RF delivery. Unusual pacemaker responses occurred in 20 of the 38 cases studied (53%). The impact of RF delivery was unpredictable, and variable dysfunctions were observed at different times for a given patient or could vary for a given model. Unusual pacemaker responses included pacemaker inhibition (n = 8), untoggled backup mode (n = 3), electromagnetic interference noise mode (n = 3), temporary RF-induced pacemaker tachycardia (n = 2), erratic behavior (n = 1), oversensing of RF onset and offset (n = 8), and transient loss of ventricular capture, (n = 1). Postablation, most devices automatically toggled back to full functionality. The three devices in the untoggled backup mode had to be reprogrammed to obtain normal operations. At the end of the procedure, pacing thresholds remained unchanged in all but one patient, in whom the increase in ventricular threshold was due to a nicked lead. In conclusion, implanted pacemakers frequently exhibit transient, unpredictable responses to RF energy application. Although all pacemaker functions were restored postablation, some devices had to be reset manually. The anomalies observed during the RF application argue for the simultaneous use of an external pacemaker in pacing-dependent patients.

Adult↗

PubMed1993

Artifacts in intravascular ultrasound imaging: analyses and implications.

The ability of an intravascular ultrasound catheter to give cross-sectional images of vessel walls and surrounding tissues, and the behavior of ultrasound in heterogeneous media, are at the origin of degradation of image quality. Qualitative and quantitative analyses of in vivo studies are then operator-dependent and are limited by artifacts. We investigated these limitations by an in vitro study on plexiglass phantoms and segments of fresh arteries. We used a 20 MHz transducer mounted on the tip of a 4.8 F catheter and an interventional ultrasound system. The ultrasound beam is reflected onto the rotating transducer at 600 rotations per minute (RPM), creating 360 degrees real-time images (10 images/second). We then observed, analyzed and interpreted the most specific reasons for image artifacts: geometric distortions, multiple echoes, the point spread function (PSF) of the imaging system, near-field effects, "petal-shaped" effect, and ultrasound speckle. Various practical implications have resulted from this study. Only a thorough knowledge of how to avoid some of the most obvious pitfalls will enable the user to obtain maximum benefits from intravascular ultrasound imaging, and to appreciate its limitations.

Arteries↗