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Biomedical subjects

C Segebarth

Publications and source records attributed to C Segebarth.

At least 37 records · Page 2Linked to original sources
PubMed1995

Intracranial gradient-echo and spin-echo functional MR angiography in humans.

PURPOSE: To investigate the predominance of venous signal intensity at 1.5-T gradient-echo (GRE) functional magnetic resonance (MR) imaging of motor activity and to demonstrate the contribution from task-induced changes in flow velocity to the functional MR imaging signal intensity. MATERIALS AND METHODS: Functional MR imaging of motor activity was performed in healthy volunteers. In a first examination, conventional two-dimensional GRE blood oxygenation level-dependent (BOLD) functional MR imaging techniques were used, and the image planes were carefully positioned with respect to the veins that responded to the motor task. In a second examination, two-dimensional spin-echo (SE) techniques were used, and the image planes were oriented axially and measured in a sequential multisection manner. The areas of hyperintensity on functional MR images were eventually processed by means of maximum intensity projection. RESULTS: Functional MR angiograms were obtained in both examinations. The possibility to generate SE functional MR angiograms demonstrates that venous inflow effects may contribute substantially to signal intensity in conventional two-dimensional GRE BOLD functional MR imaging of motor activity. CONCLUSION: Veins have a substantial role in BOLD functional MR imaging of motor activity.

Adult↗
PubMed1994

Functional MRI of the human brain: predominance of signals from extracerebral veins.

This study demonstrates the predominance of extracerebral vascular signals in gradient-echo functional magnetic resonance imaging of motor activity at 1.5 Tesla. The demonstration is based upon a novel experimental approach. Maximum intensity projection images are derived from a large set of contiguous 2D functional MR images, and compared with MR angiograms obtained from the volume covered by the set of functional MR images. The comparison shows that the hyperintensities in the functional MR images cover extensive areas, which can be superimposed with a number of veins in the MR angiograms. These results should trigger a general caution in interpretation of the observations in 1.5 Tesla functional MRI.

Brain↗
PubMed1994

Early MR detection of cortical and subcortical hypoxic-ischemic encephalopathy in full-term-infants.

Four observations illustrate the potential of MR imaging in the early depiction of multiple types of neuropathologic lesions which may coexist in the full-term newborn, upon severe hypoxic-ischemic encephalopathy (HIE). In particular, diffuse, postnatal involvement of cerebral cortex and subcortical white matter (WM) is demonstrated. Cortical hyperintensity on both proton-density- and T1-weighted images is probably related to cellular necrosis which is distributed diffusely or parasagittally. Hyperintense, frontal, subcortical WM edging on proton-density-weighted images results from the increase of water concentration, induced either by infarct or by edema. Diffuse WM areas of low intensity on T1-weighted images and of high intensity on T2-weighted images are presumably related to cytotoxic and/or vasogenic edema, proportional to the underlying damaged tissues. On follow-up MR examinations, several months later, the importance of cortical atrophy and of the myelination delay appeared related to the importance of the lesions detected during the postnatal period.

Brain Ischemia↗
PubMed1994

Three-dimensional reconstruction of the in vivo human diaphragm shape at different lung volumes.

The ability of the diaphragm to generate pressures at different lung volumes (VLs) in humans may be determined by the following factors: 1) its in vivo three-dimensional shape, radius of curvature, and tension according to Laplace law; 2) the relative degree to which it is apposed to the rib cage (i.e., zone of apposition) and lungs (i.e., diaphragm dome); and 3) its length-force properties. To gain more insight into these factors we have reconstructed from nuclear magnetic images the three-dimensional shape of the diaphragm of four normal subjects under supine relaxed conditions at four different VLs: residual volume, functional residual capacity, functional residual capacity plus one-half of the inspiratory capacity, and total lung capacity. Under our experimental conditions the shape of the diaphragm changes substantially in the anteroposterior plane but not in the coronal one. Multivariate regression analysis indicates that the zone of apposition is dependent on both diaphragm shortening and lower rib cage widening with lung inflation, although much more on the first of these two factors. Because of the changes in anteroposterior shape and expansion of the insertional origin at the costal margin with lung inflation, the data therefore suggest that the diaphragm may be more accurately modeled by a "widening piston" (Petroll's model) than a simple "piston in a cylinder" model. A significant portion of the muscular surface is lung apposed, suggesting that diaphragmatic force has radial vectors in the dome and vectors along the body axis in the zone of apposition. The muscular surface area of the diaphragm decreased linearly by approximately 41% with VL from residual volume to total lung capacity. Diaphragmatic fibers may shorten under physiological conditions more than any other skeletal muscle. The large changes in fiber length combined with limited shape changes with lung inflation suggest that the length-twitch force properties of the diaphragm may be the most important factor for the pressure-generating function of this respiratory muscle in response to bilateral phrenic shocks at different VLs.

Diaphragm↗
PubMed1993

MRI in seven cases of Rathke's cleft cyst in infants and children.

Seven MRI observations of presumed Rathke's cleft cysts in infants and children are reported. Age ranged between 6 months and 13 years. Size of the cysts ranged between 4 and 20 mm. While 3 small cysts were detected incidentally, 4 were large enough to cause symptoms secondary to compression of the pituitary gland and suprasellar components. The MRI appearance of the Rathke's cleft cysts varied according to their nature. MRI provides a major contribution to the diagnosis of these lesions; nevertheless, it often remains difficult to differentiate complex Rathke's cleft cysts from cystic craniopharyngiomas. The difficulties related to this differentiation are discussed.

Adolescent↗
PubMed1992

Mechanical implications of in vivo human diaphragm shape.

Using magnetic resonance imaging, we measured the three-dimensional form of the diaphragm in vivo in four supine relaxed subjects at functional residual capacity and calculated its total surface area, the right and left surface areas in the zone of apposition, and the principal radii of curvature as a function of height. The area of apposition comprised 45 +/- 1.5% (SE) of the total surface area of the diaphragm. Available data on the area of the central tendon indicate that a considerable part of the muscular part of the diaphragm is lung apposed. The curvature was linearly related to height over 7 cm of the posterior half of each hemidiaphragm. From the linear portion of this graph and assuming a vertical gradient of transdiaphragmatic pressure of 0.75 cmH2O/cm, we applied the Laplace law and calculated tensions of 54 and 32 g/cm for right and left sides, respectively. We conclude that the shape of at least part of the posterior half of the relaxed human diaphragm in the supine position at functional residual capacity can be explained by the Laplace law, suggesting that both the lung and abdominal contents behave sufficiently as fluids so that they do not impose their shape on the diaphragm. Because diaphragm muscle is partly lung apposed, it is unlikely that the diaphragm functions simply as a piston.

Adult↗
PubMed1990

Mapping of normal brain maturation in infants on phase-sensitive inversion--recovery MR images.

It is illustrated that phase-sensitive inversion-recovery MR images are particularly well suited for the monitoring of brain maturation and myelination in the neonate and young infant. Provided appropriate timings are applied with the inversion-recovery MR pulse sequence, the myelinated areas show up as bright spots in the phase-sensitive images. The chronology of the appearance, and the location of these hyperintense zones correlate well with the chronology of brain maturation, as assessed by other means. In particular, the progressive functional capabilities of the infant correlate well with the progress of myelination, as exhibited by the MR images.

Brain↗
PubMed1990

Neuroradiologic findings in leptomeningeal carcinomatosis: the value interest of gadolinium-enhanced MRI.

Four patients with leptomeningeal metastases documented by neuroradiological examinations are reported. All had central nervous system or systemic neoplasms and showed clinical signs of carcinomatous meningitis. Gadolinium-enhanced MRI (Gd-MRI) disclosed for each patient pathological foci, allowing delineation of the extent of meningeal disease. Although non-specific, these findings, combined with the clinical context and CSF analysis, may lead to a rapid diagnosis and treatment of carcinomatous meningitis, even when malignant cells are not detected in the cerebrospinal fluid.

Adult↗
PubMed1990

[Contribution of MRI in 5 cases of central diabetes insipidus].

Five cases of central diabetes insipidus demonstrate the potential of MRI to explore the hypothalamohypophysial axis. The diversity of the detected pathologies are illustrated: abnormal signal of the posterior pituitary in an idiopathic diabetes insipidus, lobar prosencephaly, malignant teratoma (embryonal carcinoma), histiocytosis X, craniopharyngioma.

Child↗
PubMed1989

Gd-DTPA-enhanced MR in thoracic disc herniations.

The Gd-DTPA-enhanced magnetic resonance findings in two patients with herniated thoracic intervertebral discs are reported. The first patient was a 56-year-old woman with a small subligamentous T6-7 disc herniation, slightly lateralized to the right. The second patient was a 51-year-old man with a central and right posterolateral disc herniation, including a large calcified fragment, at the T8-9 level. The nonenhanced MR examination revealed the presence of an extradural mass lesion in both patients, impinging upon the dural sac and compressing and displacing the spinal cord posteriorly. The lesion was slightly hypointense on both T1- and T2-weighted spin echo sequences. Following intravenous injection of Gd-DTPA in a dosage of 0.1 mmol/kg body weight, enhancement of the posterior longitudinal ligament was noted and triangular areas of contrast uptake were seen to occur in the epidural space above and below the herniated disc. At surgery, they were found to correspond to dilated and congested epidural veins.

Contrast Media↗
PubMed1989

Gd-DTPA-enhanced MR imaging of spinal tumors.

Forty-eight Gd-DTPA-enhanced MR examinations of the spine were performed in 40 patients referred for MR because of clinically suspected spinal tumor or for further evaluation of an expanded cord. The study group consisted of 32 patients with spinal tumors (seven ependymomas; seven astrocytomas; four hemangioblastomas; two arteriovenous malformations; two unidentified intramedullary neoplasms; four meningiomas; and single cases of metastatic breast carcinoma, cavernous hemangioma with associated hematomyelia, neurinoma, angiolipoma, drop metastasis from medulloblastoma, and epidermoid with diastematomyelia). In the remaining eight patients, other diagnoses were established: thoracic disk herniation (two patients), lumbosacral meningocele (one), syringomyelia secondary to arachnoiditis (four), and expanded cord secondary to gliotic tissue (one). All but two diagnoses were proved histologically by biopsy, surgery, or autopsy; in the two patients with arteriovenous malformations, the definitive diagnosis was made by spinal angiography. Contrast enhancement occurred in 30 of the 32 spinal tumors, and Gd-DTPA-enhanced T1-weighted images proved helpful in defining and outlining intra- and extramedullary spinal neoplasms. All ependymomas and astrocytomas (including low-grade astrocytomas) enhanced. In meningiomas, an immediate and uniform contrast uptake was demonstrated. Additional advantages of Gd-DTPA MR include the differentiation of solid tumor components vs syrinx or cyst or pseudotumoral areas of cord expansion, and the differentiation of residual or recurrent tumor from scar tissue in postoperative patients. Our results suggest that IV-injected Gd-DTPA improves MR sensitivity and specificity in the evaluation of spinal lesions.

Astrocytoma↗
PubMed1989

[Neoplastic invasion of the pulmonary arteries. Evaluation by MRI. Preliminary experience].

Bronchial tumors invading the mediastinum are no longer systematically regarded as inoperable. Curative surgery has produced a significant survival rate and led to the adaptation of the TNM classification. The degree of invasion of the pulmonary artery is a criterion of operability. The authors are trying to assess the role of MRI with regard to CT and DSA for the measurement of invasion. Their study deals with the prospective assessment of ten patients. The MRI examinations have been carried out with a 0.5 and 1.5 T supraconductive magnet (Philips Gyroscan). Cardiac gating has been used for acquisition. The planes of section are axial, transverse or oblique along the greater axis of the pulmonary arteries. CT examinations in 9-mm thick sections with and IV contrast injection demonstrate the contact of the tumor with the mediastinum. The digital angiograms have been taken with an intravenous injection into a vein of the bend of the elbow or into a femoral vein. Six cases have been verified at surgery. In all cases, the invasion predicted with MRI proved to be correctly assessed. In three cases, MRI provides additional information to the combined findings of CT and DSA. MRI is a good complement for the preoperative assessment of patients with large tumors invading the mediastinum but for which curative surgery is indicated.

Bronchial Neoplasms↗
PubMed1988

Non-obstructive kidney transplant dysfunction: magnetic resonance evaluation.

The value of magnetic resonance imaging in the differential diagnosis of non-obstructive dysfunction of renal allografts was studied in a series of 58 examinations at 0.5 T. Four parameters were evaluated: the corticomedullary differentiation; the relative thickness of the cortex; the evolution, with echo number, of the relative signal intensities of kidney parenchyma and adjacent fatty tissue on images generated by a long time to repeat multiecho sequence; and the proximal vascularization. The loss of corticomedullary differentiation is the major finding in acute rejection, but it is not specific as it is also observed in chronic rejection and in the much rarer acute glomerulonephritis. Thickening of the cortex is helpful for the detection of rejected transplants with visible corticomedullary delineation (26% of the cases). Uncomplicated acute tubular necrosis appears as a normal transplant.

Adolescent↗