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Biomedical subjects

D Meier

Publications and source records attributed to D Meier.

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

Heating effects of metallic implants by MRI examinations.

Magnetic radiofrequency fields applied in magnetic resonance imaging examinations induce electrical currents in metallic implants. These eddy currents may heat up the implants and thus may be capable of causing localized tissue heating. The rf power deposition and the joule heating of the implant can be calculated by solving Maxwell's equations for the specific problem. First, extreme in vitro worst-case experiments were performed with a large and very thin aluminum sheet, which was placed in a 1.5-T MRI device in a position parallel to the magnetic rf field. In agreement with the theoretical results the temperature rise of a thermally insulated sheet amounted to only 0.08 degrees C after a 15-min MRI examination at 64 MHz. No temperature rise in the aluminum sheet could be measured for a sheet immersed in a saline solution. Second, in vitro experiments with a hip joint prosthesis and an osteosynthetic plate were performed to confirm the theoretical results, which predict nearly no temperature rise in the metallic implants. No temperature rise in the implants could be measured.

Aluminum↗
PubMed1988

Quantitative flow measurements on phantoms and on blood vessels with MR.

A broad spectrum of MR methods has been published in the last few years for the visualization and the quantification of flow in human blood vessels. We describe the results of an extended study to measure the flow quantitatively using the MR phase modulation method. A gradient echo sequence which allows short repetition times was synchronized with the ECG. The instantaneous velocity profiles and the integrated flow rate can be determined throughout the cardiac cycle in up to 45 consecutive time intervals. The instantaneous velocity distributions can be displayed as 2D profiles over the lumen of the blood vessel. The technique has been successfully evaluated with a set of phantom experiments. Following this, quantifications of the blood flow rates in vivo were performed on the abdominal aortas of healthy volunteers. The MR flow results were compared to those obtained with conventional Doppler ultrasound examinations. The results of both methods are in good quantitative agreement.

Aorta↗
PubMed1988

T and B cell specific immune responses to purified protein derivative in the cerebrospinal cavity may be maintained and regulated independently of systemic immune control.

In vivo activated T cells could be isolated from cerebrospinal fluid (CSF) of a patient suffering from chronic meningitis of unclear origin. Although the patient's skin reactivity to purified protein derivative (PPD) was negative, and peripheral T cells did not proliferate to this antigen in vitro, the majority of T cell clones from CSF specifically recognized PPD on either autologous or allogeneic HLA class II compatible macrophages. Remarkably, peripheral blood mononuclear cells potently suppressed the PPD-specific proliferative responses of healthy donors. The selective enrichment of oligoclonal IgG in the CSF but not in the patient's serum further indicated T and B cell responses lacking systemic feedback control. Analyses of a persisting immune stimulation in the CSF provide a potent diagnostic tool and may explain neurological complications as observed in a number of autoimmune diseases and chronic infections.

Adult↗
PubMed1987

Free amino acid pattern of cerebrospinal fluid in meningeal pathology.

Free amino acid concentrations of CSF were measured in bacterial meningitis, aseptic meningitis, meningoradiculitis Garin-Bujadoux-Bannwarth, multiple sclerosis, carcinomatous meningitis, and controls. Almost all CSF amino acids were highly elevated in bacterial but not in aseptic meningitis, meningoradiculitis Garin-Bujadoux-Bannwarth or carcinomatous meningitis thus providing a laboratory tool for their differential diagnosis. In carcinomatous meningitis the amino acid pattern indicates metabolic activity of tumor cells. Minimal alterations were found in multiple sclerosis which have no diagnostic value.

Adult↗
PubMed1982

Immunoselection of oligodendrocytes by magnetic beads. II. In vitro maintenance of immunoselected oligodendrocytes.

Oligodendrocytes isolated by immunoaffinity on magnetic beads using a monoclonal antibody to oligodendrocyte cell surfaces were obtained with a purity of 91 +/- 4% [see companion paper, Meier et al, 1982]. Contaminating cells consisted mostly of tetanus toxin-positive neurons with small cell bodies. Very few glial fibrillary acidic protein-positive astrocytes and fibronectin-positive fibroblasts or fibroblast-like cells could be detected by indirect immunofluorescence. Macrophages, as identified by their characteristic morphology, were rarely detectable in the cultures. With increasing time in culture, the degree of homogeneity of the cultured oligodendrocytes increased slightly, while the cell density of oligodendrocytes decreased drastically within the first week of culture. Cultures of immunoselected oligodendrocytes with a lower degree of purity showed a better survival of oligodendrocytes, but a considerable reduction in purity after three weeks in culture, probably due to overgrowth of nonoligodendroglial elements.

Animals↗
PubMed1979

Leptomeningeal carcinomatosis with normal CSF features.

We report two cases of leptomeningeal carcinomatosis in which CSF-positive cytologic features were present but other CSF measurements were normal--a most unusual combination. In both cases, the results of the cytologic examination led to substantial therapeutic alterations. Cytologic examination of the CSF should be performed in any case with unexplained CNS symptoms or signs, regardless of the character of the CSF.

Aged↗
PubMed1978

Blunt trauma to the pancreas in children.

Sixteen children below the age of 12 were operated on for blunt injury to the pancreas during a ten-year period. Unless there was an associated injury, signs and symptoms did not immediately develop. Common to the delayed manifestation of an injury to the pancreas was history of an impaling force to the upper abdomen, abdominal tenderness, and an elevated serum amylase level. The postoperative morbidity for contusion of the pancreas was unpredictable, and a prolonged period without oral alimentation should be anticipated.

Child↗
PubMed1974

Effect of development on the translation of messenger RNA in Artemia salina embryos.

Cell-free preparations from encapsulated Artemia salina embryos readily translate poly(U), but there is no endogenous protein synthesis or translation of added natural mRNA until development resumes upon incubation in saline. High-salt-washed 80S ribosomes and highspeed supernatant (cytosol) were prepared from undeveloped eggs and from eggs allowed to develop to a stage prior to hatching. Endogenous protein synthesis occurs only with ribosomes from developed embryos, whether with undeveloped or developed cytosol. This is mainly elongation of preformed polypeptide chains, for it is largely resistant to edeine, an inhibitor of chain initiation. Edeinesensitive translation of added natural mRNA occurs with both developed and undeveloped ribosomes but requires developed cytosol. Translation of brome mosaic virus RNA is not much, if at all, further stimulated by high-saltwash of developed ribosomes, but that of globin mRNA is markedly enhanced. Levels of the chain initiation factor EIF-1 are the same before and after development. These results are consistent with the view that resumption of developemtn is triggered by transcription, with ensuing translation of the resulting messengers to yield, among other proteins, mRNA-recognizing initiation factors of the IF-3 type which are partly free in the cytosol and partly ribosome-bound. The data also suggest that different factors may be involved in the translation of brome mosaic virus RNA and globin mRNA by this system.

Animals↗