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Biomedical subjects

J F Le Bas

Publications and source records attributed to J F Le Bas.

At least 91 records · Page 5Linked to original sources
PubMed1988

[Spontaneous dissecting aneurysm of the internal carotid artery. Magnetic resonance imaging].

A man underwent Magnetic Resonance Imaging (MRI) of the left carotid artery 11 days after a spontaneous dissection of this vessel. T1 weighed images were obtained in the frontal and axial planes. There was a hyperintense lesion expanding the arterial wall due to the hematoma. The image of the lumen was narrowed. These findings corresponded to the angiographic abnormalities. In this case MRI was able to diagnose specifically and non invasively carotid artery dissections. Its sensitivity remains to be evaluated.

Aortic Dissection↗
PubMed1988

[The MRI sites functioning in 1987 in France. Results of a survey].

A study of the 23 MRI sites functioning in France at the end of 1987 provides an overall view of the organizational and economic aspects of these sites as well as an initial assessment of their activity in terms of the types of equipment used and the institutions, private or public, within which they have been set up.

Costs and Cost Analysis↗
PubMed1988

[Magnetic resonance imaging in horizontal oculomotor paralysis caused by infarction].

Four patients with focal brainstem ischemic strokes and various types of horizontal oculomotor disturbances have been studied clinically and radiologically. One had a six nerve palsy, one a unilateral internuclear ophthalmoplegia, one a Fisher's one-and-a-half syndrome, and one a paramedian pontine reticular formation syndrome with a sixth nerve palsy. In all patients a C.T. Scan and a Magnetic Resonance Imaging (MRI) were obtained. The MRI study was performed on a CGR Magniscan 5000 with a superconducting magnet of 0.5 Tesla. In all patients a hypersignal in T2 weighted images was shown and corresponded to the brainstem infarct. MRI allowed accurate delineation of the lesion and clinico-radiologic correlations in three patients. But the low specificity of MRI does not permit to distinguish edema from necrosis, gliosis or demyelination in a region with a pathological MRI signal. In one patient this low specificity and perhaps partial volume effects decreased the accuracy of the clinico-topographic correlation.

Abducens Nerve↗
PubMed1988

[Magnetic resonance imaging and laterobulbar infarction].

Six patients with a clinical diagnosis of lateral medullary infarction have been studied by CT scan and Magnetic Resonance Imaging (MRI). The MRI study was performed on a CGR Magniscan 5000 with a superconducting magnet of 5 Tesla. In all patients T2 weighted images (TR = 2000, TE 60, 120) in joined section of 9 or 6 mm thickness were obtained in the axial plane. Three patients were also studied in T1 weighted sequences (TR = 500, TE = 28). A lateral medullary infarct was shown in 5 patients. MRI findings were consistent with a hemorrhagic infarct in one case. Occlusion of a vertebral artery was suggested in 2 cases and was confirmed by angiography. In 3 cases, an associated ipsilateral cerebellar infarct was demonstrated. The CT scan had only shown bleeding in the medulla oblongata in the hemorrhagic infarction case, and a cerebellar infarction in another case. Some clinical manifestations are discussed with regard to the results of MRI. MRI appears as the best current method to improve clinico-topographic correlations in medullary infarcts.

Aged↗
PubMed1987

The mediastinum in sagittal sectioning. Anatomy and magnetic resonance imaging (MRI).

Ten volunteers with a normal mediastinum were investigated by magnetic resonance using a 0.5 Tesla CGR imager with a supraconducting magnet. The reconstruction matrix consisted of a 256 X 256 grating for a field of the order of 420 mm, with a spatial resolution of 1.6 X 1.6 mm2. The sections, balanced in T1, were performed in synchronization with the ECG. The successive sagittal sections were correlated with sagittal sections made on a single embalmed frozen subject. The MRI and anatomic sections were made at 5 mm intervals and located in relation to the median sagittal plane of the mediastinum. Examples of structural variations, malformations or tumours studied in sagittal sections, and taken from investigation of over 170 patients, demonstrate the importance of this investigational technique.

Electrocardiography↗
PubMed1987

Magnetic resonance imaging of the liver by frontal (coronal) sections.

In general, frontal sections of the liver in magnetic resonance imaging are used less than sections passing through other planes of space. Frontal sections of the trunk in magnetic resonance imaging involving the liver, performed in over 80 patients for various reasons, were compared with frontal sections of the trunk made in 10 cadavers. A general schema was established of the anatomy of the liver studied in the frontal plane. Frontal sections in magnetic resonance imaging make it possible to form a very good estimate of the structure and size of the liver, and to recognize individual variations. They clearly show certain inferior relations of the liver. In particular, frontal sections in magnetic resonance imaging make it possible to identify most of the main veins of the liver, the main lobar veins and branches of the portal vein, and to properly study the entire retrohepatic portion of the inferior vena cava. Some of the vascular images were found almost constantly in the sections of the various subjects. The right lobe of the liver is more accessible to such study than the left by reason of its structure and its venous arrangements. Frontal sections of the liver in magnetic resonance imaging constitute a preferential method for studying the anatomy of the liver. Together with transverse sections, they make it possible to specify the site and venous relations of a pathologic process within the liver, with a view to hepatectomy.

Fatty Liver↗
PubMed1987

[Multiple correlative studies of stereotaxic biopsies of brain tumors].

The opportunity of having several samples at the same site which could be spatially localized allows an intensive exploitation of stereotactic biopsies of brain tumors: the pathological data may be correlated to other measures, performed at the same site (electrical impedance X ray absorption coefficient) or on other samples (NMR relaxation times, water content, nucleic acids). These samples are available for oncology experiments in cellular biology (cell cultures, grafts on nude mice) or in molecular biology (DNA and RNA hybridization with specific nucleic acid probes). We were therefore able: 1) to study the diagnostic homologies between pathology and histology examinations; 2) to show that T1 and T2 NMR relaxation times are 2 times longer in tumor tissues than in normal brain; 3) to show that the electrical impedance is decreased by a factor 2 in brain tumors; 4) to show the absence of integrated viral genomic sequences and the existence of oncogenes association patterns in brain tumors by hybridization of specific sequences; 5) to establish permanent cell lines, the tumorigenicity of which is assayed by grafting on nude mice. Therefore, stereotactic biopsies appear to be, provided they are intensively and rationally exploited, a major research tool in an area which remains unsensitive to the various therapeutic approaches.

Animals↗
PubMed1987

31P nuclear magnetic resonance in vivo spectroscopy of the metabolic changes induced in the awake rat brain during KCN intoxication and its reversal by hydroxocobalamine.

Radiofrequency surface coils were chronically implanted in rats, which were subsequently subjected to 31P nuclear magnetic resonance (NMR) investigations at 4.7 T. The implanted coil allowed study of the animals without need for anesthesia, which is a prerequisite for studies of normal brain metabolism. The animals may be kept in the NMR probe for several hours. During subsequent experiments, they may be placed in the same position, therefore allowing follow-up studies for periods as long as 2 months. This method has been used in the study of sublethal KCN intoxication. KCN, a cytochrome c oxidase inhibitor, induces a blockade of cell respiratory processes, which is reflected, in a dose-dependent manner, by a decrease in phosphocreatine content and pH and an increase in inorganic phosphate content, whereas ATP levels remain constant until high doses of KCN (6 mg/kg i.p.) are reached. 31P NMR allows the time course of these metabolic changes to be followed. For high KCN doses, a new peak, termed X, is observed, which is interpreted as being due to a pool of inorganic phosphate at very low pH (5.65), corresponding to a subset of cells that did not survive KCN injury. Hydroxocobalamine, a specific antidote of KCN, suppresses the metabolic changes due to 6 mg/kg of KCN.

Animals↗
PubMed1987

MRI contribution to the stereotactic management of cerebral tumours.

Of 67 patients with cerebral tumours studied by MRI, 60 underwent stereotactic biopsy for histological diagnosis. The data from MRI were compared with those obtained from the CT scan with regard to the pathological diagnosis. The tumoural nature and extent of a lesion were better revealed by MRI. The single or multiple localization of the process was also seen better by MRI. Moreover, the sagittal-plane views shown by MRI provide much more accurate target placement and probe guiding for an orthogonal stereotactic approach. Finally, a post-biopsy MRI can show the biopsy site in relation to the tumour better.

Biopsy↗
PubMed1987

[MRI of the cervical spine. Creation of a surface coil. Technical and clinical results].

Cervical myelopathy represents a good indication for study by Magnetic Resonance Imaging (MRI). The MRI examination may be performed without hospitalisation and without any pain or risk for the patient. It often gives sufficient information to decide whether to proceed with surgical intervention, after imaging on standard plain films and ever before cervical myelography. An efficient study of the cervical spinal cord requires special surface coils adapted to this region. We have developed a surface coil, working as a receiver, inductively coupled, tuned and matched all at once, and easy to use. The concave form of this coil has been studied so as to be comfortable for all patients. It can be directly connected to our Thomson CGR machines (Magniscan 5000). In continuous routine use for 6 months, without any problems, it has been found to be very reliable. We present here some results on different types of myelopathy and discuss methodological aspects concerning the choice of acquisition parameters in the examinations. The simplicity of its realisation and the low cost leads us to believe that it will be possible to construct other surface coils convenient on many other parts of the body.

Cervical Vertebrae↗
PubMed1987

[Phosphorus-31 NMR spectrometry of the calf muscles in patients with arterial claudication. Preliminary results].

Phosphorus NMR spectrometry allows non-invasive exploration in vivo of certain aspects of muscle energy metabolism. A study was conducted in 10 healthy volunteers and 12 patients with lower limb affections (stage II claudication) to define a precise methodology and to discuss perspectives offered by this new method, in the light of preliminary findings. Changes with time of amplitude of peaks of phosphocreatine (Pcr), inorganic phosphorus (Pi) and ATP, and of intracellular pH, showed that recovery of 80% of resting value of the ratio Pcr/Pi + Pcr after quantified exercise is a very discriminatory parameter correlated with severity of arteriographic findings in patients with claudication.

Energy Metabolism↗
PubMed1987

[MRI and tumors of the mediastinum. Correlation with CT x-ray].

This correlative study concerns the investigation of 22 mediastinal tumors by MRI and CT, subsequently verified by biopsies or surgery. It allows us to better define the technical aspects in the realization of MRI, including an assessment of the use of ECG gating. It also permits an appreciation of the respective performances of these 2 imaging methods: there is a good correlation between the two technics for both the positive and etiologic diagnosis of mediastinal tumors: in etiologic diagnosis, the same limitations were encountered with the two technics. However, MRI offers some advantages in the evaluation of tumoral extension. So, we suggest once a mediastinal mass has been shown using plain films, when available, MRI alone should be performed.

Adult↗
PubMed1986

[Effects of the magnetic field in magnetic resonance imaging on 15 tested cardiac valve prostheses].

The effects of static magnetic fields used in MR imaging at 0.5 Tesla have been studied on 15 different types of cardiac valves. The displacement of the valves was insignificant at 0.5 Tesla. No significant heating effects was observed with the standard sequences used in cardiac imaging. The image artefacts remain confined to the area immediately surrounding these different valves. It seems possible to perform MRI examinations on patient with the prosthetic heart valves without any risk.

Electromagnetic Fields↗