Dynamic coil selection for real-time imaging in interventional MRI.

MR-guided intravascular interventions require image update rates of up to 10 images per second, which can be achieved using parallel imaging. However, parallel imaging requires many coil elements, which increases reconstruction times and thus compromises real-time image reconstruction. In this study a dynamic coil selection (DCS) algorithm is presented that selects a subset of receive coils to reduce image reconstruction times. The center-of-sensitivity coordinates and the relative signal intensities are determined for each coil in a prescan. During the intervention m coils are selected for reconstruction using a coil ranking based on the distance to the current slice or catheter position. In a phantom experiment for m = 6, an optimal signal-to-background ratio (SBR) was achieved and foldover artifacts were avoided. In three animal experiments involving catheter manipulation in the aorta and the right heart chamber, the anatomy was successfully visualized at frame rates of about 5 Hz using active catheter tracking.     

Toxicity of polymethylmethacrylate thermodegradation products

Polymethylmethacrylate was thermally degraded in air at 300° C and the volatile decomposition products studied with gas chromatography-mass spectrometry. The main product was monomeric methacrylate, although many other compounds existed among the products. Electron spin resonance spectroscopy revealed the presence of free radicals. Wistar rats were exposed to the fumes of the plastic (300° C) and their lungs and brain studied for biochemical effects. In the lung, the activity of 7-ethoxycoumarin O-deethylase decreased and an initial inhibition of glutathione peroxidase and superoxide dismutase was observed. The contents of reduced nonprotein sulfhydryl groups were decreased in the lung and brain. The exposures enhanced the activities of acetylcholine esterase, creatine kinase and NADPH-diaphorase in the brain. Scanning electron microscopy of the exposed lungs showed disorganization of ciliated cells, and the epithelial serous cells (Clara cells) were damaged.     

How does interferon exert its cell growth inhibitory effect?

Abstract: The interferons (IFNs) have become accepted therapy in a range of haematological and non-haematological malignancies. The mechanism behind IFN's antitumour action is, however, unclear. Interferons (IFNs) are capable of modulating a variety of cellular responses. One prominent effect of IFNs is their cell growth inhibitory activity, which has also been suggested to be of major importance in their antitumour action. In the present review we will discuss the cellular events leading to a decreased number of cells following IFN treatment, the molecular mechanisms underlying these phenomena, and the importance of these effects in a clinical perspective.     

Dental fluorosis among participants in a non-supervised fluoride tablet program

The aim of the present study was to describe the intraoral pattern of dental fluorosis among fluoride tablet consumers. One hundred and forty-two children, of whom 56 had participated in a fluoride tablet program of 0.5/1.0 mg NaF per day were examined blindly for possible fluoride-induced enamel changes. A low prevalence of dental fluorosis was found among non-participants. The later in life the tooth was formed, the higher was the prevalence. The subjects who had participated in the fluoride tablet program showed a significantly higher prevalence of fluorosis. They could be divided into three groups: Group 1 exhibited a tooth prevalence pattern not statistically different from that of the non-participants, group 2 showed dental fluorosis in almost all teeth except in those formed before the start of the tablet program. In group 3 the early and the late formed teeth showed very little fluorosis while those formed in the few years just after the initiation of the fluoride tablet intake were affected by fluorosis.     

Ketamine and midazolam decrease cerebral blood flow and consequently their own rate of transport to the brain: An application of mass balance pharmacokinetics with a changing regional blood flow

Mass balance pharmacokinetics, with simultaneous blood sampling from an artery and the internal jugular vein, was used to characterize the cerebral uptake of ketamine, norketamine, and midazolam in normoventilated pigs. Intravenous injections of ketamine or midazolam decreased the cerebral blood flow (CBF)by one third, as measured by intermittent ¹³³Xewashout. By means of pharmacodynamic models, the effects on the CBFcould be predicted from the arterial drug concentrations. The high-resolution CBFvs. time curves thus generated allowed the calculation of cerebral drug levels from arteriovenous concentration gradients in spite of a continuously changing regional blood flow. By their effects on the CBF,ketamine and midazolam decreasetheir own rateof transport to the brain, the immediate 30-35% drops in CBFgiving similar reductions in initial net influx of drug. Physiological pharmacokinetic models assuming a constant regional blood flow are therefore not appropriate. Under clinical conditions, the CBFis determined mainly by the effects of the anesthetics and by the arterial CO ₂ tension. CBFchanges in either direction influence the transport of drugs to the brain and may consequently result in impaired or exaggerated drug effects.The study was supported by grants from the Swedish Medical Research Council (B91-14X-00084-27A), the Medical Faculty at Lund University, Malmö General Hospital, The Tore Nilsson Foundation for Medical Research, Warner-Lambert Scandinavia AB, Roche-Produkter AB, and the Laerdal Foundation for Acute Medicine.     

The accessory optic system in the frog, Rana pipiens: An electron microscopic study of the retinal afferents utilizing the anterograde tracer biocytin

The retinal afferents to the basal optic nucleus in the frog, Rana Pipiens, were labeled anterogradely with biocytin and subsequently studied at the electron microscopic level. Labeled synaptic terminals in the nucleus varied in size from 0.5 μm to 2.0 μm and made symmetric synaptic contacts with large and small dendrites, although very rare axospinous and axosomatic contacts were also demonstrated.     

Antagonism of Reserpine-Induced Suppression of Spontaneous Motor Activity by Stimulation of 5-HT1A Receptors in Rats

Abstract: The 5-HT_1A and the DA D₂ receptor agonists 8-OH-DPAT (0.05–3.2 mg kg^–1 subcutaneously, –20 min.) and quinpirole (0.08–1.25 mg kg^–1 subcutaneously, –20 min.), respectively, both partially antagonized reserpine-induced (5 mg kg^–1 subcutaneously, –16 hr) suppression of spontaneous motor activity in the rat. Four different aspects of the spontaneous motor activity were recorded in a photocell-equipped open-field (8x8 photocells, 90 mm apart, defining two horizontal planes): locomotor activity (all photocell counts at the lower level); rearing (all photocell counts at the upper level); forward locomotion (the proportion movements across the arena); peripheral activity (the proportion locomotor activity as picked up by the photocell beam closest to the wall, i.e. 25 mm). As denned by these variables, the pattern of activity produced by 8-OH-DPAT or quinpirole were indistinguishable, The effects produced by 8-OH-DPAT were fully antagonized by the 5-HT₁ antagonist (–) pindolol (4 mg kg^–1 subcutaneously, –30 min.), but not by the DA D₂ receptor antagonist raclopride (2 mg kg^–1 subcutaneously, –30 min.) nor by the 5-HT₂ receptor antagonist ritanserin (2 mg kg^–1 subcutaneously, –30 min.), whereas effects produced by quinpirole were fully antagonized by raclopride (2 mg kg^–1 subcutaneously, –30 min.). Effects produced by quinpirole, but not 8-OH-DPAT, were potentiated by administration of the DA D₁ agonist SKF-38,393 (3 mg kg^–1 subcutaneously, –20 min.). It is concluded that effects by 8-OH-DPAT on spontaneous motor activity in the reserpine treated rat primarily are due to stimulation of postsynaptic 5-HT_1A receptors.     

A case of high mercury exposure from dental amalgam

This report describes a patient who suffered from several complaints, which by herself were attributed to her amalgam fillings. Analysis of mercury in plasma and urine showed unexpectedly high concentrations. 63 and 223 nmol/l. respectively. Following removal of the amalgam fillings, the urinary excretion of mercury became gradually normalized, and her symptoms declined.     

The Effect of Chronic Lithium Treatment on the Sialic Acid Content in Rat Brain Synaptosomes

Abstract: Rats were fed a lithium-containing diet for five weeks (40 mmol LiCl/kg fodder). Plasma lithium concentration was 0.44 mmol Li⁺/1 plasma. The synaptosomes were isolated and incubated with ³H-glucosamine for 60 min. The glycopeptides and the gangliosides were extracted and the sialic acid content and the ³H-sialic acid content were measured. The lithium treatment produced an increase in the synaptosomal glycopeptide content. The sialic acid content was simultaneously increased in glycopeptides as well as gangliosides. The specific activity of sialic acid was reduced to 75% of the control value in the sialoglycopeptide fraction.