Radiofrequency indicators

Figure B 1.16.9 shows background-free, pseudo-steady-state CIDNP spectra of the photoreaction of triethylamine with (a) anthroquinone as sensitizer and (b) and (c) xanthone as sensitizer. Details of the pseudo-steady-state CIDNP method are given elsewhere [22]. In trace (a), no signals from the p protons of products 1 (recombination) or 2 (escape) are observed, indicating that the products observed result from the radical ion pair. Traces (b) and (c) illustrate a usefiil feature of pulsed CIDNP net and multiplet effects may be separated on the basis of their radiofrequency (RF) pulse tip angle dependence [21]. Net effects are shown in trace (b) while multiplet effects can...

This reaction provides a third indication of the usefulness of a radiofrequency discharge in the synthesis of compounds of low thermal stability. The more-stable (CFaljTej had been prepared by the interaction of CFj radicals, formed in the pyrolysis of (CF3)2CO, with a tellurium mirror (19). The less-stable (CFsljTe was not, however, observed in that experiment. 

Because sensitivity depends on so many different experimental factors, NMR spectroscopists generally use the signal-to-noise ratio, SIN, as a figure of merit for sensitivity comparisons. For example, in a comparison between NMR probes or spectrometers from two vendors, the spectral SIN measured for a standard sample acquired with specified acquisition parameters and probe geometry would provide a direct indication of relative sensitivity. The SIN is calculated for an NMR experiment as the peak signal divided by the root mean square (RMS) noise, given by Equation 7.6, and is directly related to the performance of the radiofrequency coil [3,6]... 

Figure 11.41. Energy level diagrams and transitions for two different F-branch transitions in the YS molecule. The broken lines denote laser-induced fluorescence transitions, whilst the continuous lines indicate radiofrequency double resonance transitions observed in rotational levels of the ground electronic state [82].

Figure 3.4. H-Decoupled CNMR spectra of 35% enriched I-[ CJ- and 2-[ C]pyruvate, in the presence of (A) Mn -pyruvate carboxylase, and (B) Mg -pyruvate carboxylase. Each spectrum, except the normal Fourier transform (NFT) spectrum, is the result of applying two radiofrequency pulses to the sample the delay between them is indicated in sec. From measurements of peak heights the T, values can be calculated, and a resonance has zero intensity at about 0.69 T,. Note that Mn shortens T, and has a differential effect on the two...

Flecainide slows conduction in all cardiac cells including the anomalous pathways responsible for the Wolff-Parkinson-White (WPW) syndrome. Together with encainide and moricizine, it underwent clinical trials to establish if suppression of asymptomatic premature beats with antiarrhythmic drugs would reduce the risk of death from arrhythmia after myocardial infarction. The study was terminated after preliminary analysis of 1727 patients revealed that mortality in the groups treated with flecainide or encainide was 7.7% compared with 3.0% in controls. The most likely explanation for the result was the induction of lethal ventricular arrhythmias possibly due to ischaemia by flecainide and encainide, i.e. a proarrhythmic effect. In the light of these findings the indications for flecainide are restricted to patients with no evidence of structural heart disease. The most common indication, indeed where it is the drug of choice, is atrioventricular re-entrant tachycardia, such as AV nodal tachycardia or in the tachycardias associated with the WPW syndrome or similar conditions with anomalous pathways. This should be as a prelude to definitive treatment with radiofrequency ablation. Flecainide may also be useful in patients with paroxysmal atrial fibrillation. 

Radiofrequency thermal ablation (RFTA) S. Rossi et al. (1990, 1993) were the first to introduce this procedure. Under analgosedation and local anaesthesia, an expandable, cooled-tip needle electrode is inserted per-cutaneously into the tumour with the help of US, CT or MR guidance. There are various types of probes with some differences. Due to high-frequency alternating current (480-500 kHz), the tumour tissue is gradually heated (up to max. 105 °C). A necrosis voume of 4(-5) cm in diameter can be achieved. An indication is given for 1-3 foci, each with a maximum size of 5 cm in diameter. This also applies to compromised liver func-... 

Raised telangiectasias may become more visible in patients with thin and transparent skin. Facial telangiectasias can be electrocoagulated immediately before the phenol is applied, while the patient is under nerve-block anesthesia for the peel. An Elhnan radiofrequency unit is completely satisfactory in this indication. 

The perfluorocarbons injected into Ar LPCAT represent the case represented by Eq. (8). On injection of a perfluorocarbon, such as CF4, C2F4, etc., luminous gas jet shrinks. However, OES data indicate that there is no signal discernible to F-containing species. Radiofrequency discharge of mixtures of Ar and perfluorocarbon shows F-containing species, indicating the... 

FIGURE 6.5 Pulmonary vein (PV) isolation guided by electroan-atomical mapping. A posteroanterior view of the left atrium is displayed with locations of the PVs indicated by brown tubes. Yellow tags show locations of radiofrequency lesion around the left and right PVs. (From Ref. 182, with permission.)... 

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