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At least 235 records · Page 13Linked to original sources
PubMed1984

[Systems theory of ultrasound pulse echo technic (2)].

Part two explains the terms, spatial resolution, range ambiguity and maximum frame rate of diagnostic pulse echo systems. Then the idealised system described in part one is completed by incorporating various band pass filters, which represent the effects of resonant piezoelectric transducers and electric filters of the TGC amplifiers. The influence of such band limiting components on spatial resolution and dynamic range are shown by numerical examples. Mathematical derivations are restricted to the necessary minimum and all formulae are illustrated by means of a substantial number of graphs.

Humans↗
PubMed1997

The temporolimbic system theory of positive schizophrenic symptoms.

This article proposes that subtle structural and functional disturbance of limbic key structures in the medial temporal lobe-especially of the left hippocampal formation and parahippocampal gyrus-can explain the so-called positive symptoms of schizophrenia. After presenting pathophysiological considerations linking limbic dysfunction to schizophrenia, the article reviews evidence from structural, biochemical, and functional studies supporting the theory. Also discussed here are neurodevelopmental and laterality aspects, as well as predictions, questions, and future tasks derived from the theory.

Brain Mapping↗
PubMed1991

Biochemical systems theory: increasing predictive power by using second-order derivatives measurements.

Models based on the power-law formalism provide a useful tool for analyzing metabolic systems. Within this methodology, the S-system variant furnishes the best strategy. In this paper we explore an extension of this formalism by considering second-order derivative terms of the Taylor series which the power-law is based upon. Results show that the S-system equations which include second-order Taylor coefficients give better accuracy in predicting the response of the system to a perturbation. Hence, models based on this new approach could provide a useful tool for quantitative purposes if one is able to measure the required derivatives experimentally. In particular we show the utility of this approach when it comes to discriminating between two mechanisms that are equivalent in the S-system a representation based on first-order coefficients. However, the loss of analytical tractability is a serious disadvantage for using this approach as a general tool for studying metabolic systems.

Kinetics↗
PubMed1998

Influence of pulse angle variations on stimulated echo acquisition mode proton nuclear magnetic resonance spectra of AB spin systems: theory and experiments with citrate.

The influence of pulse angle variations in the localization sequence stimulated echo acquisition mode (STEAM) on the signal of strongly coupled AB spin systems has been examined. Experimental 1H nuclear magnetic resonance (NMR) spectra of citrate were recorded on a 1.5 T whole-body imager. Theoretically calculated spectra were generated, with good correlation to experimental results. The dependence of the signal intensity on sequence timing and pulse angles was calculated analytically. For longer sequence timings, the ratio of the signal intensity from citrate to the signal intensity from uncoupled nuclei depends strongly on the applied flip angles. The shape of spectra also changes with varying flip angles. These effects are clearly less pronounced for STEAM than for point resolved spectroscopy (PRESS). The results have to be considered for quantitative measurements of citrate in spectroscopic investigations as, e.g. of prostate neoplasms.

Acetic Acid↗