MR-guided focused-ultrasound ablation system: determination of precision and accuracy in preparation for clinical trials

The authors analyzed the accuracy and precision of focal-spot placement with a magnetic resonance-guided, focused-ultrasound system. Average absolute accuracy errors ranged from 0.2 to 1.0 mm, and average absolute individual precision errors ranged from 0.2 to 0.3 mm. To prevent damage to vital structures, single sonications and sonication grids should be placed beyond approximately 2 and 1 mm, respectively.     

Dispersion and noise of 1.3 μm multimode lasers in microwavedigital systems

The intensity noise and the performance in a 1.7 Gb/s digital system of 1.3 μm InGaAsP multilongitudinal mode lasers is discussed. The total intensity noise, mode partitioning, and the impact of dispersion on optical noise are measured. It is found that under CW conditions the total simulated emission from unpackaged lasers is inherently quiet, with an integrated optical signal-to-noise ratio (SNR) of 26.8±1.5 dB over a bandwidth of 1.5 GHz and 5 mW/facet. The optical SNR decreased as a function of increasing reflection. Intense mode partitioning decreased the SNR of the main mode by ~20 dB and reduced the effective coherence length to ~2 cm in glass fiber. At 1.7 Gb/s, the power penalities associated with laser bias and fiber dispersion are reported. The best receiver sensitivity is obtained when the laser is biased 1.3 mA below threshold. In general, it is found that as the bit rate increases, the optimum transmitter design becomes progressively more restrictive     

Effect of endogenous L-arginine on the measurement of nitric oxide synthase activity in the rat kidney

The endogenous level of L-arginine in renal cortex, outer medulla, and inner medulla and its effect on the measurement of nitric oxide synthase (NOS) activity in these regions was determined. L-Arginine was measured with an amino acid analyzer and total NOS activity was measured as the rate of formation of radiolabeled L-citrulline from L-[14C]arginine. Total NOS activity was that activity inhibited by NG-nitromonomethyl-L-arginine (300 microM). The endogenous L-arginine concentration was 452 +/- 45 (mean +/- SEM), 313 +/- 25, and 95 +/- 8 pmol/mg wet weight in the cortex, outer medulla, and inner medulla, respectively (n = 12). Total NOS activity was 61 +/- 19, 709 +/- 94, and 1347 +/- 76 pmol.h-1.mg protein-1 in the cortex, outer medulla, and inner medulla, respectively, when endogenous L-arginine was not considered in the calculation. Correcting for endogenous L-arginine gave values of 185 +/- 61, 1714 +/- 239, and 1707 +/- 104 pmol.h-1.mg protein-1, respectively. Dowex extraction to remove endogenous L-arginine from samples also increased NOS activity in cortex and medulla. The data indicate that there is a differential distribution of endogenous L-arginine in the kidney and that these levels must be taken into account when measuring NOS activity. NOS activity is also distributed differentially, with activity in the medulla being nearly 10-fold higher than in the cortex.     

Anti-thyroid isoflavones from soybean: isolation, characterization, and mechanisms of action

The soybean has been implicated in diet-induced goiter by many studies. The extensive consumption of soy products in infant formulas and in vegetarian diets makes it essential to define the goitrogenic potential. In this report, it was observed that an acidic methanolic extract of soybeans contains compounds that inhibit thyroid peroxidase- (TPO) catalyzed reactions essential to thyroid hormone synthesis. Analysis of the soybean extract using HPLC, UV-VIS spectrophotometry, and LC-MS led to identification of the isoflavones genistein and daidzein as major components by direct comparison with authentic standard reference isoflavones. HPLC fractionation and enzymatic assay of the soybean extract showed that the components responsible for inhibition of TPO-catalyzed reactions coeluted with daidzein and genistein. In the presence of iodide ion, genistein and daidzein blocked TPO-catalyzed tyrosine iodination by acting as alternate substrates, yielding mono-, di-, and triiodoisoflavones. Genistein also inhibited thyroxine synthesis using iodinated casein or human goiter thyroglobulin as substrates for the coupling reaction. Incubation of either isoflavone with TPO in the presence of H2O2 caused irreversible inactivation of the enzyme; however, the presence of iodide ion in the incubations completely abolished the inactivation. The IC50 values for inhibition of TPO-catalyzed reactions by genistein and daidzein were ca. 1-10 microM, concentrations that approach the total isoflavone levels (ca. 1 microM) previously measured in plasma from humans consuming soy products. Because inhibition of thyroid hormone synthesis can induce goiter and thyroid neoplasia in rodents, delineation of anti-thyroid mechanisms for soy isoflavones may be important for extrapolating goitrogenic hazards identified in chronic rodent bioassays to humans consuming soy products.