We used phosphorus NMR spectroscopy to study 16 patients with muscular enzyme deficiencies affecting glycogenolysis and glycolysis. Study of phosphomonoester (Pm) kinetics and intracellular pH during exercise and recovery provided criteria for the distinction of these metabolic myopathies by NMR spectroscopy. The Pm peak was undetectable in patients lacking debrancher enzyme or phosphorylase. By contrast, in phosphofructokinase (PFK) or phosphoglycerate kinase (PGK) deficiency, the Pm peak was larger than that of inorganic phosphate in exercise, whereas it was always smaller in normal subjects. During recovery, the disappearance of Pm was slower in PGK than in PFK deficiency.
The influence of a 2-T static magnetic field on the cardiac rhythm was studied with 24-hour electrocardiographic monitoring in 12 healthy volunteers for 1 hour before exposure, 1 hour during exposure, and 22 hours after exposure. Four other subjects were exposed to 1 T, and nine control subjects were exposed to 0 T. In the 2-T group, the mean cardiac cycle length (CCL) was 912 msec +/- 83 before exposure. A significant 17% increase in CCL was observed after 10 minutes of exposure. No further significant variation was observed during exposure, and the CCL was back to preexposure values 10 minutes after exposure. No other arrhythmogenic effect was noted during the 24-hour monitoring. No statistically significant change was observed at either 0 or 1 T. The magnetically induced blood-flow potentials superimposed on the T wave were observed. The CCL increase during exposure could reflect a direct or indirect effect of magnetic fields on the sinus node, which is probably harmless in healthy subjects. However, its safety in dysrhythmic patients remains to be determined.
Gradient pulses used in most localization techniques induce time-dependent shifts in B0 that strongly distort NMR signals. A postprocessing correction method requiring no additional hardware is proposed. The phase shift produced by the B0 shift is calculated from a reference free induction decay (FID) and used to correct any FID acquired with the same sequence.
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