PubMed Health⌕ Search

Biomedical subjects

M Avison

Publications and source records attributed to M Avison.

8 recordsLinked to original sources
PubMed2001

The use of a modified technique to reduce radioactive air contamination in aerosol lung ventilation imaging.

The aim of this study was to reduce airborne contamination resulting from the use of aerosols in lung ventilation scintigraphy. Lung ventilation imaging is frequently performed with 99mTc-diethylenetriaminepentaacetate aerosol (DTPA), derived from a commercial nebuliser. Airborne contamination is a significant problem with this procedure; it results in exposure of staff to radiation and can reduce gamma camera performance when the ventilation is performed in the camera room. We examined the level of airborne contamination resulting from the standard technique with one of the most popular nebuliser kits and tested a modification which significantly reduced airborne contamination. Air contamination was measured while ventilating 122 patients. The modified technique reduced air contamination by a mean value of 64% (p = 0.028) compared with the standard control technique. Additionally, differences in contamination were examined when a mask or mouthpiece was used as well as differences between operators. A simplified method of monitoring air contamination is presented using a commonly available surface contamination monitor. The index so derived was proportional to air contamination (r = 0.88). The problems and regulations associated with airborne contamination are discussed.

Aerosols↗
PubMed1992

Cerebral lactate turnover after electroshock: in vivo measurements by 1H/13C magnetic resonance spectroscopy.

We reported earlier that brain activation by 10 s of cortical electroshock caused prolonged elevation of brain lactate without significant change in intracellular pH, brain high-energy phosphorylated metabolites, or blood gases. The metabolic state of the elevated lactate has been investigated in further experiments using combined, in vivo 1H-observed 13C-edited nuclear magnetic resonance spectroscopy (NMRS), homonuclear J-edited 1H-NMRS, and high-resolution 1H-NMRS of perchloric acid extracts to monitor concentrations and 13C-isotopic fractions of brain and blood lactate and glucose. We now report that electroshock-elevated lactate pool in rabbit brain approaches equilibrium with blood glucose within 1 h. There was nearly complete turnover of the raised lactate pool in brain; any pool of metabolically inactive lactate could not have been > 5% of the total. In the same experiments, blood lactate underwent < 50% turnover in 1 h. The new 1H-spectroscopic methods used for these experiments are readily adaptable for the study of human brain and may be useful in characterizing the metabolic state of elevated lactate pools associated with epilepsy, stroke, trauma, tumors, and other pathological conditions.

Animals↗
PubMed1992

Hepatic perfusion index: a multicentre trial.

The reproducibility and accuracy of the hepatic perfusion index (HPI) was examined by consideration of in vitro and in vivo factors. A phantom was used to simulate liver blood flow and data acquired on nine gamma cameras. Dynamic hepatic scintigraphy was undertaken on 28 patients at two centres and values obtained for the HPI. Results from the phantom study showed good agreement between the nine cameras and also with the HPI values predicted from the measured phantom flow rates. The results of the patient study indicated a high degree of conformity between observers (r = 0.95, S.E = 0.03) but poorer correlation between the HPI values from the two centres (r = 0.67, S.E. = 0.09). These results imply that centres wishing to use HPI clinically should establish their own range of normality.

Blood Flow Velocity↗
PubMed1991

Lactate rise detected by 1H NMR in human visual cortex during physiologic stimulation.

Brain lactate concentration is usually assumed to be stable except when pathologic conditions cause a mismatch between glycolysis and respiration. Using newly developed 1H NMR spectroscopic techniques that allow measurement of lactate in vivo, we detected lactate elevations of 0.3-0.9 mM in human visual cortex during physiologic photic stimulation. The maximum rise appeared in the first few minutes; thereafter lactate concentration declined while stimulation continued. The results are consistent with a transient excess of glycolysis over respiration in the visual cortex, occurring as a normal response to stimulation in the physiologic range.

Energy Metabolism↗
PubMed1990

In vivo measurements of ethanol concentration in rabbit brain by 1H magnetic resonance spectroscopy.

In vivo 1H magnetic resonance spectroscopy was used to measure the cerebral ethanol concentration in the rabbit after both intraarterial and intragastric administration. There was good agreement between cerebral and blood ethanol concentrations at all times after administration by either route. Cerebral ethanol levels, measured using in vivo 1H spectroscopy, agreed well with those measured in perchloric acid extracts of brain, analyzed by both high-resolution 1H spectroscopy and gas chromatography. Ethanol may be useful as an indicator to measure cerebral blood flow by 1H spectroscopy and chemical shift-selective magnetic resonance imaging.

Animals↗
PubMed1986

Combined 1H and 31P nuclear magnetic resonance spectroscopic studies of bicuculline-induced seizures in vivo.

Using a 1.89-Tesla spectrometer, 1H and 31P nuclear magnetic resonance spectra were acquired from the brains of paralyzed rabbits ventilated with 30% oxygen in nitrous oxide. Intracellular pH and changes in lactate concentration in the cerebrum were monitored by nuclear magnetic resonance methods during and after bicuculline-induced seizures, together with the electroencephalogram, heart rate, and arterial blood pressure. During seizures lasting more than an hour, cerebral intracellular pH became acidic, the cerebral lactate level rose rapidly, and both changes persisted as long as 2 hours without signs of recovery. After less prolonged seizures, lactate elevations were no less persistent, despite nearly complete recovery of intracellular pH and the electroencephalogram.

Animals↗