Generation of the additional fluorescence radiation in the elastomeric shields used in computer tomography (CT).

Two commercially available (EP, Z) and eight new elastomeric composites (M1-M4, G1-G4, of thickness ≈1 mm) containing mixtures of differing proportions of heavy metal additives (Bi, W, Gd and Sb) have been synthesised and examined as protective shields. The intensity of the X-ray fluorescence radiation generated in the typical elastomeric shields for CT, containing Bi and other heavy metal additives influence on the practical shielding properties. A method for assessing the radiation shielding properties of elastomeric composites used in CT examination procedures via X-ray spectrometry has been proposed. To measure the radiation reduction ability of the protective shields, the dose reduction factor (DRF) has been determined. The lead equivalents for the examined composites were within the ranges of 0.046-0.128 and 0.048-0.130 mm for 122.1 and 136.5 keV photons, respectively. The proposed method, unlike to the common approach, includes a dose contribution from the induced X-ray fluorescence radiation of the heavy metal elements in the protective shields. The results clearly indicate that among the examined compositions, the highest values DRF have been achieved with preparations containing Bi+W, Bi+W+Gd and Bi+W+Sb mixtures with gradually decreasing content of heavy metal additives in the following order: Bi, W, Gd and Sb. The respective values of DRF obtained for the investigated composites were 21, 28 and 27 % dose reduction for a 1 mm thick shield and 39 and ~50 % for a 2 mm thick layer (M1-M4).

Low leptin mRNA level in adipose tissue and normoleptinemia in experimental chronic renal failure.

BACKGROUND: Anorexia and weight loss frequently accompany chronic renal failure (CRF). Although multiple metabolic changes occur during CRF, a bulk of evidence indicates that the decrease in caloric intake plays a major role in CRF-induced weight loss. Recently, it has been suggested that elevated plasma leptin concentrations could contribute to anorexia and to downregulation of leptin gene expression in CRF patients. However, in some CRF patients, plasma leptin concentrations have been found to be lower than one could expect. Thus we assumed that inhibition of leptin synthesis plays an important role in the regulation of plasma leptin concentrations in CRF patients. METHODS: To test this assumption, the leptin mRNA level in rat white adipose tissue from ad-libitum-fed control (sham operated), pair-fed control (sham operated) and rats with experimentally induced CRF has been measured by Northern blotting analysis. In addition, serum leptin concentration (by radioimmunoassay) was determined in all three groups of animals. RESULTS: The results of the present study indicate that in experimental CRF the leptin mRNA level is decreased by about 50% as compared to the sham-operated animals (ad-libitum-fed and pair-fed controls). The mean serum leptin concentration in CRF rats was essentially similar to the leptin concentration in sham-operated ones. CONCLUSION: The data obtained suggest that in CRF animals the serum leptin concentration might be affected not only by the decrease in leptin removal in the kidney, but also by the decrease in leptin secretion from adipose tissue. Furthermore, the results of the study suggest that leptin may be only one of many factors involved in the pathogenesis of malnutrition associated with CRF.

The power struggle: definition and evaluation of power of muscular performance.

The authors define five different measurements of power of muscular performance. Using an isokinetic dynamometer, the velocity of motion is constant and thus can be controlled. Power, therefore, can be readily assessed. The speed of muscular contraction is of physiological and functional interest. The time it takes for muscles to develop force, the rate at which muscles can contract and sustain a force throughout the range of motion, and the relationship of speed to force are all facets of power. At least five terms which connote power of muscular performances are used today. These terms are power, peak power, average power, instantaneous power, and contractile power. The current misunderstanding of the terms and their misuses are discussed. Suggestions are offered for circumventing confusion in using power to describe motor performance.