Novel approach for the Monte Carlo calculation of free-air chamber correction factors

A self-consistent approach for the Monte Carlo calculation of free-air chamber (FAC) correction factors needed to convert the chamber reading into the quantity air-kerma at the point of measurement is introduced, and its implementation in the new EGSnrc user code egs_fac is discussed. To validate the method, comparisons between computed and measured FAC correction factors for attenuation Ax, scatter (Ascat), and electron loss (Aeloss) are performed in the medium energy range where the experimental determination is believed to be accurate. The Monte Carlo calculations utilize a full simulation of the x-ray tube with BEAMnrc and a detailed model of the parallel-plate FAC. Excellent agreement between the computed Ascat and Aeloss and the measured values for these correction factors currently used in the National Research Council (NRC) of Canada primary FAC standard is observed. Our simulations also agree with previous Monte Carlo results for Ascat and Aeloss for the 135 and 250 kVp Consultative Committee for Ionizing Radiation reference beam qualities. The computed attenuation correction agrees with the measured Aatt within the stated uncertainties, although the authors' simulations demonstrate that the evacuated-tube technique employed at NRC to measure the attenuation correction slightly overestimates Aatt in the medium energy range. The newly introduced corrections for backscatter, beam geometry, and lack of charged particle equilibrium along the beam axis are found to be negligible. On the other hand, the correction for photons leaking through the FAC aperture, currently ignored in the NRC standard, is shown to be significant.     

The rise of [Na+]i during ischemia and reperfusion in the rat heart—underlying mechanisms

Intracellular Na⁺ concentration ([Na⁺]_i) rises in the heart during ischemia, and on reperfusion, there is a transient rise followed by a return toward control. These changes in [Na⁺]_i contribute to ischemic and reperfusion damage through their effects on Ca²⁺ overload. Part of the rise of [Na⁺]_i during ischemia may be caused by increased activity of the cardiac Na⁺/H⁺ exchanger (NHE1), activated by the ischemic rise in [H⁺]_i. In support of this view, NHE1 inhibitors reduce the [Na⁺]_i rise during ischemia. Another possibility is that the rise of [Na⁺]_i during ischemia is caused by Na⁺ influx through channels. We have reexamined these issues by use of two different NHE1 inhibitors, amiloride, and zoniporide, in addition to tetrodotoxin (TTX), which blocks voltage-sensitive Na⁺ channels. All three drugs produced cardioprotection after ischemia, but amiloride (100 μM) and TTX (300 nM) prevented the rise in [Na⁺]_i during ischemia, whereas zoniporide (100 nM) did not. Both amiloride and zoniporide prevented the rise of [Na⁺]_i on reperfusion, whereas TTX was without effect. In an attempt to explain these differences, we measured the ability of the three drugs to block Na⁺ currents. At the concentrations used, TTX reduced the transient Na⁺ current (I _Na) by 11 ± 2% while amiloride and zoniporide were without effect. In contrast, TTX largely eliminated the persistent Na⁺ current (I _Na,P) and amiloride was equally effective, whereas zoniporide had a substantially smaller effect reducing I _Na,P to 41 ± 8%. These results suggest that part of the effect of NHE1 inhibitors on the [Na⁺]_i during ischemia is by blockade of I _Na,P. The fact that a low concentration of TTX eliminated the rise of [Na⁺]_i during ischemia suggests that I _Na,P is a major source of Na⁺ influx in this model of ischemia.     

Influence of rBAT-mediated amino acid transport on cytosolic pH

rBAT, together with its subunit b(0,+) AT mediates the hetero- and homoexchange of neutral and dibasic amino acids. Since the heteroexchange of dibasic amino acids against neutral amino acids is coupled to net transport of positive charge, this transport is electrogenic. Extracellular addition of histidine could create an inward or an outward current depending on extracellular pH (pH(e)) and cell membrane potential. It has been concluded that histidine may be transported in both its protonated and its neutral form. In this study measurements of cytosolic pH (pH(i)) were performed to test this hypothesis. As a result, addition of protonated histidine at acidic pH(e) to Xenopus oocytes expressing rBAT creates an inward current which is paralleled by cytosolic acidification. Both can be reduced by increase of pH(e). At alkaline pH(e) and simultaneous depolarization of the cell membrane the effect of histidine on pH(i) is virtually abolished. The neutral amino acid leucine does not alter cytosolic pH at neither pH 6.0 nor at pH 8.0. In conclusion, histidine can be transported in either its neutral or its protonated form. Transport of the protonated form is facilitated by extracellular acidification and hyperpolarization of the cell membrane.     

Induction of interleukin-6 by hepatitis C virus core protein in hepatitis C-associated mixed cryoglobulinemia and B-cell non-Hodgkin's lymphoma.

PURPOSE: Chronic hepatitis C carries the risk to develop mixed cryoglobulinemia (MC) and B-cell non-Hodgkin's lymphoma (B-NHL), possibly because viral antigens stimulate the host's inflammatory response via extracellular pattern recognition receptors (PRR). To clarify this issue, we studied whether recognition of hepatitis C virus (HCV) proteins by PRR is involved in the pathogenesis of HCV-associated MC or B-NHL. EXPERIMENTAL DESIGN: Peripheral blood mononuclear cells of patients with HCV-associated B-NHL (n = 12), MC (n = 14), uncomplicated hepatitis C (n = 12), and healthy volunteers (n = 12) were incubated with the recombinant HCV proteins E2, core, and NS3 to study induction of cytokine production, stimulation of B-cell proliferation, and immunoglobulin secretion. In addition, serum levels of interleukin-6 (IL-6) were measured by ELISA. RESULTS: HCV core was the only studied protein, which induced production of IL-6 and IL-8 in CD14(+) cells. IL-6 induction was mediated via Toll-like receptor 2 (TLR2) and lead to increased B-cell proliferation in vitro. TLR2 expression on monocytes and IL-6 serum concentrations were increased in all groups of HCV-infected patients compared with healthy controls and were highest in MC (P < 0.05). CONCLUSIONS: Increased secretion of IL-6 via stimulation of TLR2 by HCV core protein may play a role in the pathogenesis of hepatitis C-associated MC and B-NHL.     

Reaktionen von 1-Phenyl-1-cyan-2-aminoäthen mit substituierten Acetaldehyden 21. Mitt über Untersuchungen an Acyl-enaminen

Reactions of 1-Phenyl-1-cyano-2-aminoethene with Substituted Acetaldehydes 3-Azapenta-1,4-diene derivatives 4a, b and c were prepared from 1-phenyl-1-cyano-2-aminoethene (2) and substituted acetaldehydes (3a, b, c). Catalytic hydrogenation led to 3-azapentene-1-or -4-derivatives (5, 7, 13, 15) , whose structures were established by independent synthesis or by hydrolysis.     

Background on methods of stimulation in galvanic-induced body sway in young healthy adults

The aim of this study was to develop a standardized procedure for reproducible quantification of galvanic-induced body sway (GBS). This was a prospective experimental study conducted in a tertiary referral centre. An exploratory study was first conducted to define the galvanic vestibular stimulation (GVS) method that resulted in the best reproducible responses. Ten subjects underwent computer-controlled GVS using five different types of monaural and binaural stimulation with 2-mA currents. Cosinusoidal stimulation gave the most reproducible responses. The frequency and current variability of this stimulus type were then tested in the same 10 subjects. A monaural continuous 1-cosinusoidal current of 0.5 Hz and 2 mA gave the most reproducible responses (< 20% test-retest variation) and the largest GBS amplitude. The other (sinusoidal) stimuli resulted in variabilities exceeding 50%. This stimulus was thus used for further testing in our normative study. In this study we measured GBS amplitude at 0.5 Hz in 60 subjects, with eyes closed and an inter-feet distance of 0 cm, using a force platform. In addition to body sway, responses included slight dizziness, taste sensations and a tingling sensation at the site of stimulation. Habituation to the applied stimulus was seen. Binaural prestimulation, performed in 50/60 test subjects, is necessary to reduce habituation and achieve optimal reproducibility in order to be able to compare the sensitivity of the left and right vestibular systems. The test-retest variability was determined in detail in 12 additional subjects. Prestimulation reduced habituation, but improved the sensitivity of the method; some test-retest variability persisted (< 20%).     

Ultrastructural MR imaging techniques of the knee articular cartilage: problems for routine clinical application

The high incidence of cartilage lesions together with new surgical treatment techniques have necessitated the development of noninvasive cartilage evaluation techniques. Although arthroscopy has been the standard for cartilage evaluation, MR imaging has emerged as the imaging method of choice, allowing morphological evaluation of cartilage and cartilage repair tissue, as well as evaluation of its biochemical content. This article deals with current ultrastructural MR imaging techniques for cartilage evaluation, indicating the advantages as well as the drawbacks for routine clinical application.