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M Amiel

Publications and source records attributed to M Amiel.

At least 55 records · Page 3Linked to original sources
PubMed1993

Contrast-enhanced magnetic resonance tomoangiography: a new imaging technique for studying thoracic great vessels.

The authors propose a new imaging approach for studying thoracic great vessels, using high-speed MR imaging combined with intravenous rapid bolus injection of a paramagnetic contrast media. The decrease of the T1 relaxation time of flowing blood induced by the contrast agent (Gd-DOTA) caused an increased signal intensity within the vessel lumen for a time period allowing multiplanar imaging of various vascular structures. The intraluminal signal enhancement is mainly related to the blood concentration of the contrast agent as in conventional X-ray angiography. Information on the aorta and pulmonary arteries obtained by the so-called contrast-enhanced magnetic resonance tomoangiography appears complementary to that obtained with other vascular MR imaging procedures such as cine-MRI and magnetic resonance angiography (MRA).

Aortic Dissection↗
PubMed1993

Superparamagnetic iron oxide particles and positive enhancement for myocardial perfusion studies assessed by subsecond T1-weighted MRI.

Superparamagnetic iron oxide particles (SPIOs) are usually referred to as T2 MR contrast agents, reducing signal intensity (SI) on T2-weighted MR images (negative enhancement). This study reports the original use of SPIOs as T1-enhancing contrast agents, primarily assessed in vitro, and then applied to an in vivo investigation of a myocardial perfusion defect. Using a strongly T1-weighted subsecond MR sequence with SPIOs intravenous (IV) bolus injection, MR imaging of myocardial vascularization after reperfusion was performed, on a dog model of coronary occlusion followed by reperfusion. Immediately after the intravenous bolus injection of 20 mumol/kg of SPIOs, a positive signal intensity enhancement was observed respectively, in the right and left ventricular cavity and in the nonischemic left myocardium. Moreover, compared to normal myocardium, the remaining ischemic myocardial region (anterior wall of the left ventricle) appeared as a lower and delayed SI enhancing area (cold spot). Mean peak SIE in the nonischemic myocardium (posterior wall) was significantly higher than in the ischemic myocardium (anterior wall) (110 +/- 23% vs. 74 +/- 22%, Mann-Whitney test alpha < 1%, n1 = 6, n2-n1 = 0, U > 2). In conclusion, the T1 effect of SPIOs at low dose, during their first intravascular distribution, suggests their potential use as positive markers to investigate the regional myocardial blood flow and some perfusion defects such as the "no-reflow phenomenon."

Animals↗
PubMed1993

[Value and role of echo-Doppler in the screening of renovascular hypertension. A prospective study of 144 arteries with reference to angiography].

The purpose of the study is a rigorous validation of different ultrasonic criteria of renal artery stenosis, and the presentation of the performances of duplex sonography in renal artery stenosis screening. Sixty seven patients have been investigated by ultrasonic techniques, and the results of duplex compared with intraarterial or intravenous digital subtraction angiography. Two kinds of ultrasonic investigations have been defined: complete explorations when the renal artery ostium is accessible, incomplete explorations in other cases. The main difficulty preventing the exploration from being complete is obesity: all patient with an overweight of more than 20% of their theoretical weight have an incomplete exploration of at least one of their renal arteries. Furthermore, duplex sonography was not able to demonstrate polar artery in any case. When the exploration is complete, maximum systolic frequency (F max) recorded on the renal artery course, and the systolic frequency ratio of renal and aortic recordings (RAR) are two valuable criteria of significant stenosis (> 50%): mean difference between normal and stenosed arteries for these two variables is statistically significant (p < 0.01). To obtain a good specificity, pathological threshold have been fixed at F max > 3,500 Hz and RRA > 2.5. When the exploration in incomplete, ascending time (asc. T) and resistance index (RI) of doppler recording obtained in the renal hilum are two valuable criteria for severe stenosis (> 80%), or occlusion: the mean between stenosed and non stenosed arteries is statistically different (p < 0.001 and p < 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiography↗
PubMed1993

[Intravascular echographic imaging: experimental validations and limits. An in vitro study].

Intravascular ultrasound is a new method of visualizing details of vascular pathology, providing (real time) high resolution images of vascular walls. Most of the research on the technique has explored its qualitative and quantitative capabilities to improve the assessment of atherosclerotic vascular disease in vivo. Intravascular ultrasound differs from angiography and angioscopy in its ability to penetrate below the surface of the vessel lumen, demonstrating specific appearances of the distribution and composition of plaque. Image analysis is operator dependent. Although this technology is very promising limitations such as artefacts and loss of image quality in heavily calcified vessels hinder its use. There is hope that this imaging technique may ultimately improve the results of endovascular interventions.

Arteries↗
PubMed1992

[Technique for measuring the atheroma volume in men].

The evaluation of the impact of therapy on the evolution of atherosclerotic lesions or restenosis after angioplasty requires the use of techniques of vascular imaging. The reference invasive method is digital angiography although it does not provide data on the arterial wall thickness. This parameter can be approached however by intravascular ultrasound imaging, a technique which has a number of important practical limitations. Of the non-invasive techniques available, Doppler ultrasonography is the only one that can be used in clinical trials. Nuclear magnetic resonance imaging is the object of much research and is without doubt the technique of the future. The choice of model of atherosclerosis influences that of the imaging technique: cineangiography for coronary arteries, digital angiography or Doppler ultra sonography for lower limb arteries and Doppler ultrasonography for the carotid arteries. Interpretation of angiography is now performed quantitatively by videodensitometry. Interpretation of other techniques should be performed by a second independent observer and "blinded" with respect to the order in which the investigations were performed and to the treatment administered. The criteria of judgment may be qualitative (progression, stabilisation, regression) or quantitative, the latter having a number of advantages over the former. Of the quantitative criteria, the percentage stenosis, though widely used, does not fully answer the question posed, and neither does the diameter of the stenosis. The volume of the arterial lumen calculated from videodensitometric data would seem to be the best, by its sensitivity and additivity, current angiographic parameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiography, Digital Subtraction↗
PubMed1992

Disturbances caused by dental materials in magnetic resonance imaging.

Nuclear Magnetic Resonance (NMR) is the latest addition to medical imaging technology. This technique plays an important role in head and neck diagnosis. Radiologists may encounter patients with fixed dental prostheses that may produce image distortion on MRI scans of the face. The MRI appearances of dental prosthetic materials was studied in vitro, including precious alloys, non-precious alloys, ceramic prostheses, dental amalgam and composite materials. It was found that non-precious alloys produce large image deformations, whereas precious alloys had no effect on MRI images. An in vivo study showed the anatomical zones that were most affected on MRI scans.

Ceramics↗
PubMed1991

Dental materials and magnetic resonance imaging.

Radiologists may encounter patients with fixed dental prostheses that may produce image distortion on MRI scans of the face and jaw. In this work, we assessed the MRI appearances of dental prosthetic materials in vitro, including precious alloys, nonprecious alloys, ceramic prostheses, dental amalgam, and composite materials. For in vivo studies, these materials were placed in the patient's mouth. Nonprecious alloys produce large image deformations, whereas precious alloys had no effect on MRI images. The in vivo study showed the anatomical zones that were most affected on MRI scans. The size of these zones produced by the presence of nonprecious alloys is influenced by the volume of the prosthesis and is related to the scanning sequence used.

Adult↗
PubMed1991

Quantitation of reperfused myocardial infarction by Gd-DOTA-enhanced magnetic resonance imaging. An experimental study.

Because there is evidence that myocardial infarct size is modified by coronary artery reperfusion, an ex vivo experimental model of myocardial infarction was developed to determine the influence of the timing of gadolinium-tetraazacyclododecane tetraacetic acid (Gd-DOTA)-enhanced magnetic resonance imaging (MRI) on the accuracy of infarct size quantitation. Eighteen dogs underwent a 2-hour coronary occlusion followed by 1 (n = 6), 6 (n = 6), or 48 (n = 6) hours of reperfusion. Gd-DOTA was injected 10 minutes before the dogs were killed. T1 (SE 250/26) and T2 (SE 1500/78) weighted images were performed on excised hearts. Gd-DOTA concentration was measured in myocardium by atomic emission spectrometry, and correlated with myocardial blood flow evaluated by radioactive microspheres. All dogs presented with myocardial infarction (mean size 20.4% +/- 3.1% of the left ventricle), and a corresponding area of increased signal intensity on T1-weighted MR images. In none of the three groups did the area of high signal intensity correlate with the ischemic area. By contrast, after 6 and 48 hours of reperfusion, the high signal intensity area (17.9% +/- 2.4%) closely matched the area of nonreversible jeopardized tissue (16.4% +/- 2.5%), as determined on tetrazolium-stained heart slices. Although a noreflow phenomenon was observed in the jeopardized tissue, Gd-DOTA concentration was higher in the subendocardial central ischemic zone than in normally perfused myocardium. Gd-DOTA imaging enhancement seems to be the consequence of a delayed clearance of the agent from the injured tissue. Gd-DOTA-enhanced MRI accurately quantitates the size of reperfused myocardial infarction on the ex vivo heart for more than 6 hours after the beginning of reperfusion. It remains to be determined whether the in vitro results obtained here can be applied to assess the myocardial infarct size in vivo.

Animals↗
PubMed1991

[Obstruction of pulmonary arteries. Contribution of the scanner and MRI. Apropos of 10 cases].

We present a retrospective study of ten patients presenting non specific clinical manifestations in whom the diagnosis of pulmonary embolism was documented by CT scan and/or MRI. Results of CT scan and/or MRI were compared to DSA bi-selective pulmonary angiography findings. In a large number of cases, CT scan and MRI allowed the detection of the obstruction within the right and left pulmonary arteries (RPA and LPA). Although these techniques did not permit the diagnosis of peripheral clots, pulmonary infarcts were usually depicted by these two procedures. CT scan and/or MRI could be performed as first-line investigations in case of atypical clinical symptoms because of their high relevance for proximal pulmonary artery obstruction, although these two non-invasive procedures cannot indicate the aetiology of the obstruction etiology.

Evaluation Studies as Topic↗
PubMed1990

Reliability of phlebography in the assessment of venous thrombosis in a clinical trial.

In the frame of a multicenter controlled study comparing the efficacy of low-molecular-weight heparin to standard heparin in the prevention of postsurgical thrombosis, 94 phlebograms were centrally evaluated by two independent radiologists. Three months after the first central evaluation, a new reading was performed with the same radiologists, and discrepancies were adjudicated by a senior radiologist. The number of discrepancies between the first and the second evaluation was high: 33 interpretations (35%) had a least one difference, including 14 (14.9%) discrepancies regarding the main issue, i.e. the presence of venous thrombosis. After the adjudication by the senior radiologist, this number decreased but was still large: 22 films (23.4%) with at least one discrepant item in all and 11 related to the presence of venous thrombosis. This report shows that venous thrombosis assessed by phlebography, which is usually considered as a golden standard in clinical trials, deserves a thorough quality control procedure.

Double-Blind Method↗
PubMed1990

[Perforation of a loop of the small intestine by a Kim-Ray Greenfield endocaval filter. Report of a case].

Kim-Ray filter complications are usually benign, such as angulation or slight migration. We report and compare with the literature one case of vena cava perforation associated with a small bowel lesion. The follow-up with regular abdominal plain X-rays allows detection of filter angulation, the first step before vena cava perforation. Cavography or CT scan depicts this perforation. Complete or partial surgical removal of the filter may be necessary.

Adult↗
PubMed1990

[An attempt to quantify myocardial ischemia by selective coronary arteriography: determination of a new score. An initial study].

An original model for estimating myocardial ischaemia from coronary arteriography is proposed. Four parameters are taken into consideration: anatomical variations, the myocardial mass perfused, the degree of reduction of basal flow across the stenosis, the eventual summation of several successive stenotic lesions. This scoring system was tested by simulation on a computer and evaluated in 100 anginal patients. Analysis of our preliminary results shows statistically significant differences in the score between the following groups of patients: patients with normal and those with abnormal LV wall motion; patients with and those without previous myocardial infarction; patients with Class II stable angina and those with other forms (III, IV and unstable angina).

Adult↗