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G Marchal

Publications and source records attributed to G Marchal.

At least 181 records · Page 10Linked to original sources
PubMed1995

Three-dimensional CT-imaging of the ossicular chain.

In eight patients, with a known air-conduction hearing loss, three-dimensional images of the ossicular chain were constructed based on heavily overlapping high resolution CT-slices, obtained from a spiral CT data set. High quality three-dimensional images could be obtained in all eight patients. Supplementary information was derived from these three-dimensional images in three patients; in one, this supplementary information had therapeutic importance. The slight image quality loss in spiral-CT of the temporal bone, compared with conventional CT, is in some cases largely compensated by the possibility of rendering high quality secondary reconstructions.

Adult↗
PubMed1995

Cloning, sequencing, and expression of the apa gene coding for the Mycobacterium tuberculosis 45/47-kilodalton secreted antigen complex.

Effective protection against a virulent challenge with Mycobacterium tuberculosis is induced mainly by previous immunization with living attenuated mycobacteria, and it has been hypothesized that secreted proteins serve as major targets in the specific immune response. To identify and purify molecules present in culture medium filtrate which are dominant antigens during effective vaccination, a two-step selection procedure was used to select antigens able to interact with T lymphocytes and/or antibodies induced by immunization with living bacteria and to counterselect antigens interacting with the immune effectors induced by immunization with dead bacteria. A Mycobacterium bovis BCG 45/47-kDa antigen complex, present in BCG culture filtrate, has been previously identified and isolated (F. Romain, A. Laqueyrerie, P. Militzer, P. Pescher, P. Chavarot, M. Lagranderie, G. Auregan, M. Gheorghiu, and G. Marchal, Infect. Immun. 61:742-750, 1993). Since the cognate antibodies recognize the very same antigens present in M. tuberculosis culture medium filtrates, a project was undertaken to clone, express, and sequence the corresponding gene of M. tuberculosis. An M. tuberculosis shuttle cosmid library was transferred in Mycobacterium smegmatis and screened with a competitive enzyme-linked immunosorbent assay to detect the clones expressing the proteins. A clone containing a 40-kb DNA insert was selected, and by means of subcloning in Escherichia coli, a 2-kb fragment that coded for the molecules was identified. An open reading frame in the 2,061-nucleotide sequence codes for a secreted protein with a consensus signal peptide of 39 amino acids and a predicted molecular mass of 28,779 Da. The gene was referred to as apa because of the high percentages of proline (21.7%) and alanine (19%) in the purified protein. Southern hybridization analysis of digested total genomic DNA from M. tuberculosis (reference strains H37Rv and H37Ra) indicated that the apa gene was present as a single copy on the genome. The N-terminal identity or homology of the M. tuberculosis and M. bovis BCG purified molecules and their similar global and deduced amino acid compositions demonstrated the perfect correspondence between the molecular and chemical analyses. The presence of a high percentage of proline (21.7%) was confirmed and explained the apparent higher molecular mass (45/47 kDa) determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis resulting from the increased rigidity of molecules due to proline residues.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1995

Sequential studies of severely hypometabolic tissue volumes after permanent middle cerebral artery occlusion. A positron emission tomographic investigation in anesthetized baboons.

BACKGROUND AND PURPOSE: In the positron emission tomography literature, markedly hypometabolic brain tissue (oxygen metabolism < 1.3 to 1.7 mL.100 g-1.min-1) has often been equated with irreversible damage in the human brain. By serial positron emission tomography measurements, we investigated the temporal evolution of the volume of severely hypometabolic brain tissue after permanent middle cerebral artery occlusion in anesthetized baboons with, as a perspective, the development of rational therapeutic strategies. METHODS: Seven anesthetized and ventilated baboons underwent sequential positron emission tomography examinations with the 15O steady-state technique before and 1, 4, 7, and 24 hours and 14 to 29 days after occlusion. In each baboon the infarct volume was calculated by quantitative histological procedures after 19 to 41 days of occlusion. RESULTS: The sequential measurement of regional oxygen metabolism demonstrated an extension (for > or = 24 hours) of the volume of severely hypometabolic tissue as defined by both absolute and relative metabolic thresholds, and this profile of evolutivity is observed no matter the threshold used. Mean (+/- SEM) infarction volume of 2.4 +/- 0.6 cm3 was comparable to a tissue volume with oxygen consumption < 40% of contralateral metabolism. The volume of hypometabolic tissue was essentially stable at the 1-, 4-, and 7-hour postocclusion studies, increased markedly at the 24-hour study point, and increased even further in the chronic-stage study (on average, 17 days after occlusion). The tissue that eventually displayed a severely hypometabolic state at the final measurement showed a significant decrease of oxygen metabolism and cerebral blood flow at each time analyzed. In that tissue, the oxygen extraction fraction increased significantly at 1 hour (although not thereafter). CONCLUSIONS: The extension of severely hypometabolic volume after middle cerebral artery occlusion reinforces the concept of a dynamic penumbra and suggests the existence of a relatively large window of therapeutic opportunity in which it may be possible to develop neuroprotective strategies. Our study suggests that maximum infarct volume is determined at some time between 24 hours and 17 days after permanent middle cerebral artery occlusion in anesthetized baboons.

Animals↗
PubMed1995

Experimental teleradiology. Novel telematics services using image processing, hypermedia and remote cooperation to improve image-based medical decision making.

We illustrate the possible impact of information technology on digital radiology using two pilot projects. The first aimed to improve the transfer of radiological information and the interaction between radiologist and referring physician, using hypermedia documents and hypermedia electronic mail. During a 12-month evaluation period, approximately 100 hypermedia reports were generated and distributed to hepatologists and neurosurgeons. The second project aimed to improve planning of orthopaedic surgery, using an image processing service for three-dimensional visualization and a conferencing system to support active cooperation. Over two months, 12 routine cases were reconstructed in three dimensions and conferencing was carried out between surgeons and radiologists in hospitals 15 km apart. Initial results were encouraging. Telematics may be valuable in reconciling the growing need for multidisciplinary cooperation with the growing geographical and organizational separation of different experts. We conclude that to benefit from information technology, the focus should not be on a direct translation of traditional working methods, but rather on possibilities that were not available in the film-based environment.

Belgium↗
PubMed1995

Time-of-flight MR angiography of the brain: comparison of acquisition techniques in healthy volunteers.

OBJECTIVE: The saturation phenomenon that limits vessel visibility in unenhanced time-of-flight MR angiograms can be overcome by the injection of MR contrast agents that shorten the T1 of the blood. Unlike the situation with unenhanced MR angiographic acquisitions, in which the MR parameters must be carefully adjusted to reduce saturation effects, optimization procedures for contrast-enhanced MR angiography focus on the acquired shortening of the T1 of the blood and the time evolution of the T1 over the entire measurement. To improve the quality of contrast-enhanced time-of-flight MR angiographic acquisitions in the brain, we compared different acquisition techniques that exploit shortening of the T1 of the blood. SUBJECTS AND METHODS: High-resolution MR angiographic examinations were done with a 1-T MR system for 12 healthy volunteers. Doses of 0.1 and 0.2 mmol of gadopentetate dimeglumine per kilogram of body weight were injected on two separate days to allow for identical timing of the comparative studies after contrast material injection. The effects of dose of contrast material, MR parameters (TR and flip angle), method of injecting the contrast material (monophasic, biphasic, or continuous slow injection), and K-space acquisition schemes (regular schemes versus collecting the central K-space lines near the beginning or the end of the acquisition) were studied. RESULTS: Higher doses provided better MR angiograms. The flip angle and the TR had to be adjusted on the basis of the Ernst equation and therefore depended on an estimation of the averaged T1 value over the entire measurement. Comparison of the different K-space acquisition schemes confirmed that the evolution of the T1 of the blood over the entire measurement time is important, especially for longer measurements. There was no noticeable difference between the MR angiograms acquired with monophasic or biphasic injections. These injection schemes provided more detailed MR angiograms than did continuous slow injection over the entire measurement. CONCLUSION: Our results show that the quality of contrast-enhanced MR angiograms can be remarkably increased when acquisition techniques that exploit the short T1 of the blood are used.

Adult↗
PubMed1995

Helical CT for the preoperative localization of islet cell tumors of the pancreas: value of arterial and parenchymal phase images.

OBJECTIVE: In two-phase helical CT, organs are scanned in both the arterial and the parenchymal phase after IV injection of contrast material. The purpose of our study was to evaluate the usefulness of two-phase helical CT for the preoperative localization of pancreatic islet cell tumors. MATERIALS AND METHODS: Ten patients with 11 surgically proven islet cell tumors were included in the study. Helical CT scans of the pancreas were obtained with 5-mm collimation and overlapping image reconstruction. Images were obtained in the arterial and parenchymal phases after contrast material injection. A test bolus was used for tailored bolus timing. Images were analyzed by two observers. If a tumor was detected, its density relative to the surrounding parenchyma was scored by consensus, using a five-point scale. RESULTS: Nine of 11 tumors could be located using two-phase helical CT (sensitivity, 82%), including one 4-mm gastrinoma. Two lesions smaller than 5 mm could not be visualized. Two tumors were easier to detect (n = 1) or could only be detected on parenchymal-phase images (n = 1). Tumor conspicuity was better on arterial-phase images in two patients. CONCLUSION: Our results show that obtaining CT scans in both the arterial and the parenchymal phase leads to improved detection of pancreatic islet cell tumors.

Adenoma, Islet Cell↗
PubMed1995

The use of magnetic resonance angiography in stereotactic neurosurgery.

The authors discuss the advantages and disadvantages of the use of magnetic resonance (MR) angiography images in stereotactic neurosurgery. Current computer programs designed to assist the neurosurgeon in the planning of stereotactic neurosurgical interventions use intraarterial digital subtraction angiography images to visualize the blood vessels. Magnetic resonance angiography is a recent technique with a number of advantages over the digital subtraction method: it is less invasive and less prone to complications; it provides truly three-dimensional data sets that can be viewed from any direction; and it can visualize both stationary and flowing tissues with the same imaging device and localizer frame. Although digital subtraction images are still superior in contrast and vascular detail, state-of-the-art high-resolution MR angiography sequences provide sufficient vascular detail for planning surgery. Contrast-enhanced MR angiography images were acquired using adapted gradient-echo sequences to compensate for flow-induced distortions; postacquisition distortion correction was not necessary. Five methods to integrate and inspect a possible trajectory in the MR angiography data are discussed. Initial clinical experience with eight patients led to the conclusion that MR angiography is a valuable imaging modality that can be integrated reliably into a stereotactic neurosurgery planning procedure.

Adult↗
PubMed1995

Abdominal pain in the postpartum: role of imaging.

The post-delivery evaluation of the obstetric patient presenting with severe abdominal pain can be a challenge to the obstetrician, the internist, and the radiologist. Besides non-pregnancy-related causes of abdominal pain, several pregnancy-related complications should be included in the list of differential diagnoses. Based on pathogenesis, these conditions can be divided in four categories: thromboembolic disease, infectious complications, mechanical complications, and complications of preeclampsia. Most disease processes can be adequately visualized with sonography. CT can be indicated for the evaluation of the extent of ovarian vein thrombosis and for depiction of deep abdominal collections in obese patients or in cases of abundant overlying abdominal gas. MRI can be useful to provide the specific diagnosis of hemorrhagic liver infarction in the clinical setting of a HELLP syndrome.

Abdominal Pain↗
PubMed1995

[Spiral CT of the renal blood vessels].

Spiral CT angiography has been successfully applied to the detection and grading of renal artery stenoses. In this manuscript the technique, the diagnostic accuracy and the advantages and limitations of this new method are discussed.

Angiography↗
PubMed1995

[Clinical application of three-dimensional spiral CT in skeletal disorders].

Three-dimensional (3D) computed tomographic reformations are used as an adjunct to standard axial computed tomography (CT) in the evaluation of disorders affecting areas of complex anatomy such as the skull, the spine, the pelvis, hands and feet. 3D-CT can provide a clear impression of lesion extent, pattern, shape and proximity to adjacent structures. This unique spatial information potentially has a significant impact on decisions regarding resectability, surgical approach and repair. The basic requirements for high-quality 3D-reformations are an absence of patient movement and narrow-width transaxial sections. Spiral CT significantly contributes to fulfilling these requirements. In addition, spiral CT scan data can be used to produce the ultimate representation of the third dimension: a life-size palpable medical model. In this review we describe the process of three-dimensional reconstruction and highlight potential problems arising during 3D-imaging processing. Useful clinical applications of spiral CT for 3D-visualization of skeletal pathology are discussed.

Bone Diseases↗
PubMed1995

[Spiral CT angiography].

Spiral CT angiography (CTA) is a promising technique for the evaluation of vascular lesions. We review some important technical aspects in CTA such as longitudinal resolution, determination of injection scan interval and limitations of three-dimensional rendering techniques. Several current and potential applications are discussed.

Angiography↗
PubMed1995

[Spiral CT of cerebral aneurysms].

Spiral CT was performed in 9 patients with 13 cerebral aneurysms known from angiography. All lesions were detected by spiral CT, the smallest lesion measuring 3 mm in diameter. The neck of the aneurysm and the anatomical relations could be determined very accurately in all cases. Advantages of spiral CT over magnetic resonance angiography include: the short examination time, the independence of flow rate and cardiac output, and the excellent visualisation of calcification, thrombus and the bony landmarks. Disadvantages are the necessity of iodinated contrast media, the long postprocessing and reconstruction time and the possibility of overlap from bone and venous blood.

Cerebral Angiography↗
PubMed1995

[Application of spiral CT in the head and neck region].

In comparison with other regions of the body, spiral CT has only been recently applied in the radiological evaluation of the head and neck region. Some interesting applications seem to emerge. The fast data acquisition allows to examine children (e.g. temporal bone examinations) without sedation, to reduce patient moving artefacts in adults, and to limit the dose of injected contrast material in enhanced studies. Furthermore, without additional irradiation, images with a very small table increment can be calculated out of the volumetric data set, allowing generation of high quality secondary reconstructions.

Ear Ossicles↗
PubMed1995

[Spiral CT of the liver: detection of focal liver lesions].

The advantages of spiral CT mainly reside in the possibility to scan the entire liver volume in a single period of about 20 to 30 seconds, while the patient holds his breath. This high acquisition speed allows to selectively evaluate the entire liver during the arterial and/or portal venous phase. In addition, spiral CT is a true volumetric technique that allows a posteriori calculation of perfectly contiguous or even overlapping slices. These two specifications, high acquisition speed and the absence of data gaps improves the detection of focal liver lesions.

Humans↗
PubMed1995

[Spiral CT of the pancreas].

Spiral CT allows rapid acquisition of axial images during a single breath-hold. This results in optimal vascular and parenchymal opacification and eliminates respiratory misregistration. These factors also contribute to high quality multiplanar displays. Double phase spiral CT allows repeated scanning in the vascular (arterial) phase and in the parenchymal phase after contrast injection, resulting in optimal detection of parenchymal as well as vascular lesions. The advantages and applications of spiral scanning for imaging the pancreas are discussed.

Acute Disease↗