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R Sigal

Publications and source records attributed to R Sigal.

At least 73 records · Page 4Linked to original sources
PubMed1987

The potential for community level evaluations based on loop analysis.

In this paper we present results obtained with a computer simulation in which a community, described by Levins in his presentation of loop analysis (Levins, R., 1975, Evolution in communities near equilibrium, in: Ecology and Evolution of Communities, M.L. Cody and J.M. Diamond (eds) (Harvard University Press, Cambridge, Mass.) pp. 16-50), is analysed. We show how our simulation accurately reproduces Levins' calculations and further, (i) how our simulation can be used to answer questions raised by Levins but never answered, (ii) how the simulation can be used to dissect a community in order to analyse the roles played by the various entities, and (iii) how predictions relating to the evolution of this community, proposed by Levins, can be analysed with some interesting and unexpected results. In particular, it becomes clear that discussion of the type of selection that may take place needs to be done in the framework of the community in which it occurs.

Biological Evolution↗
PubMed1986

Nuclear magnetic resonance proton imaging of bone pathology.

Thirty-two patients with diversified pathology were examined with a supraconductive NMR imager using spin echo with different TR and TE to obtain T1 and T2 weighted images. They included 20 tumors (12 primary, eight metastasis), six osteomyelitis, three fractures, two osteonecrosis, and one diffuse metabolic (Gaucher) disease. In all cases except for the stress fractures, the bone pathology was clearly visualized in spite of the normal lack of signal from the compact cortical bone. Nuclear magnetic resonance (NMR) imaging proved to be at least as sensitive as radionuclide scintigraphy but much more accurate than all other imaging procedures including computed tomography (CT) and angiography to assess the extension of the lesions, especially in tumors extended to soft tissue. This is due both to easy acquisition of sagittal and coronal sections and to different patterns of pathologic modifications of T1 and T2 which are beginning to be defined. It is hoped that more experience in clinical use of these patterns will help to discriminate between tumor extension and soft-tissue edema. We conclude that while radionuclide scintigraphy will probably remain the most sensitive and easy to perform screening test for bone pathology, NMR imaging, among noninvasive diagnostic procedures, appears to be at least as specific as CT. In addition, where the extension of the lesions is concerned, NMR imaging is much more informative than CT. In pathology of the spine, the easy visualization of the spinal cord should decrease the need for myelography.

Adolescent↗
PubMed1986

MRI and CT scan compared with microscopic histopathology in osteogenic sarcoma of the proximal tibia.

The authors report the case of a 15-year-old female who presented with a history of vague but constant pain about the medial aspect of her right knee. X-ray established the presence of an expanding lesion in the medial tibial plateau. Computerized axial tomography (CT) and magnetic resonance imaging (MRI) were used in the evaluation of the lesion. The authors compare the preoperative CT and MRI findings with the microscopic histopathology of the amputation specimen and note that the CT scan underestimated the extent of the microscopic tumor boundaries, whereas MRI showed altered activity beyond these boundaries.

Adolescent↗
PubMed1986

[Larrey and Egyptian ophthalmia].

During the napoleonic expedition to Egypt (1798-1801), a new ophthalmic disease, the "egyptian ophthalmia", was discovered by the french physicians. We analysed a contemporary study published by the surgeon Jean-Dominique Larrey. The accuracy of the clinical description enables us to suggest hypotheses upon the origin if the egyptian ophthalmia: Weeks' conjunctivitis, gonorrheal conjunctivitis, trachoma. Treatments are also reviewed. Larrey is to be seen as a symbol of the transition from the old medical vision to modern clinical medicine.

Egypt↗
PubMed1985

[2 trials of measuring the flow of the intraorbital ophthalmic artery using pulsed Doppler].

We studied the flow pattern of the ophthalmic artery by pulsed doppler. The technique of visualization of the artery using bidimensional echography and the method of flow calculation by pulsed doppler are described in this preliminary report. This direct, non-invasive and readily feasible technique may play a prominent role in the clinical diagnosis of ophthalmic artery diseases.

Blood Flow Velocity↗
PubMed1985

Nuclear magnetic resonance imaging of liver hemangiomas.

Nine patients with cavernous hemangioma of the liver were examined by nuclear magnetic resonance imaging (MRI) with a 0.5 T superconductive magnet. Spin-echo technique was used with varying time to echo (TE) and repetition times (TR). Results were compared with 99mTc red blood cell (RBC) scintigraphy, computed tomography (CT), echography, and arteriography. Four illustrated cases are reported. It was possible to establish a pattern for MRI characteristics of cavernous hemangiomas; rounded or smooth lobulated shape, marked increase in T1 and T2 values as compared with normal liver values. It is concluded that, although more experience is necessary to compare the specificity with that of ultrasound and CT, MRI proved to be very sensitive for the diagnosis of liver hemangioma, especially in the case of small ones which may be missed by 99mTc-labeled RBC scintigraphy.

Adolescent↗
PubMedDate not supplied

Correlation between nodal density in contrasted scans and response to cisplatin-based chemotherapy in head and neck squamous cell cancer: a prospective validation.

This prospective study was done to validate an earlier retrospective study demonstrating a relationship between complete response to chemotherapy and nodal density as estimated in contrasted computed tomography (CT scans) in head and neck squamous cell carcinoma (HNSCC). CT scans of 36 patients were evaluated by two radiologists blinded to therapeutic outcome. The density of the largest node (> 2 cm) was compared to that of nuchal muscles. A node was classified as hypodense if more than 33% of the nodal surface area consisted of hypodense zones. Density and nodal staging were related: 67% (10 of 15) of patients with N3 disease but only 29% (six of 21) with N1-N2 exhibited isodensity, p < 0.05. Complete response to chemotherapy was noted in 63% (10 of 16) of the isodense group but only in 15% (three of 20) of the hypodense group, p < 0.01. We believe that nodal density can be used for therapeutic decision-making in high nodal volume HNSCC.

Adult↗
PubMedDate not supplied

Post-traumatic diabetes insipidus: MR demonstration of pituitary stalk rupture.

We report the magnetic resonance findings in a case of post-traumatic diabetes insipidus (DI). They consisted of pituitary stalk rupture shown on both coronal and sagittal planes with associated disappearance of the normal high signal intensity of the posterior lobe on T1 images. This last sign, previously described in nontraumatic DI, appears to represent a finding indicating nonfunctioning neurohypophysis.

Adult↗
PubMedDate not supplied

Aneurysmal bone cysts of the jaws: CT and MR findings.

Two cases of aneurysmal bone cyst of the jaws, one in the mandible and the other in the maxilla, are reported in young girls 7 and 15 years old. One was a primary lesion; the other was associated with fibrous dysplasia. In both cases CT and MR demonstrated characteristic fluid-fluid levels. The diagnosis was confirmed after biopsy and surgical resection of the lesions.

Adolescent↗
PubMedDate not supplied

Synovial sarcomas of the head and neck: CT and MR findings.

The authors present three cases of histologically proved synovial sarcoma. CT is useful in assessing erosive or destructive changes in bone, and in demonstrating calcifications. MR characteristics are nonspecific; calcifications within these tumors can be missed on MR. MR can help to assess tumor extension, vascular invasion, and hemorrhage within the tumor.

Adolescent↗
PubMedDate not supplied

Ventriculus terminalis of the conus medullaris: MR imaging in four patients with congenital dilatation.

MR findings in four patients with MR evidence of congenital cystic dilatation of the ventriculus terminalis were reviewed retrospectively. The ventriculus terminalis is a small cavity of the conus medullaris that forms during embryonic development as result of canalization and retrogressive differentiation. The dilated ventriculus terminalis appears on MR images as a small ovoid cavity with regular margination; intralesional fluid resembles cerebrospinal fluid on all MR sequences. After injection of contrast material, MR imaging shows no enhancement of the cyst or its wall, and thus differentiates congenital dilatation of the ventriculus terminalis from cystic tumors, which occur more frequently in this region.

Adult↗