Your search for ""P C Lauterbur"" returned 16 results

A description is given of a microprocessor-based device for controlling magnetic field gradients in three dimensions, including the design logic, the interface to a minicomputer and a nuclear magnetic resonance spectrometer, and the mathematical basis for a two-stage reconstruction method that may be implemented with such a controller. Two examples of the resulting complete 3D nuclear magnetic resonance zeugmatographic images are presented as sets of thin slices or tomograms.

The NMR zeugmatographic projections obtained from Fourier transforms of free induction decays require certain corrections before they can be used for image reconstruction. Software methods for making automatic correction of these errors are proposed, and simple procedures for performing such corrections are described and illustrated.

Nuclear magnetic resonance (NMR) zeugmatographic imaging may become a safe and versatile alternative to medical imaging techniques that employ ionising and ultrasonic radiation. Most of the techniques that have been described for obtaining NMR images use single point, line, or plane scans to give a single slice, or reconstruct only a two-dimensional projection, and are relatively inefficient, complex, or difficult to scale up for use on the human body. There are a number of advantages to scanning simultaneously an approximately spherical volume to obtain a true three-dimensional image. A simple two-stage reconstruction method is described for obtaining such images efficiently with isotropic resolution, and examples are presented to demonstrate the validity and usefulness of this mode. The feasibility of high-resolution imaging on large objects is also discussed.

This review presents the physical foundations of NMR introscopy, a method of obtaining images by nuclear magnetic resonance. We describe various methods of producing NMR images and compare their characteristics. We discuss the technical, instrumentation, and applied aspects of NMR introscopy, and in particular the prospects for applying it in biology and medicine.

Computer-aided tomography (CAT) is a method of laminar reconstruction of the structure of an inhomogeneous and generally asymmetric three-dimensional object from a set of measured projections. Recently CAT has been widely used, not only in medical diagnostics, where most brilliant and impressive results have been achieved, but also in various areas in physics. Physical and technical applications of CAT are the topic of the present review. The basic principles of tomography research are described, CAT problems are classified from the point of view of integral geometry, and the main algorithms used in computational data processing are briefly commented upon. Particular attention is devoted to possible CAT applications to defectoscopy, microscopy, solid state physics, geophysics, Earth and planetary atmospheric physics, aeroand hydrodynamics, and plasma physics. The main developmental directions of theoretical and technical CAT in the near future are noted in conclusion.

CONTENTS I. Introduction 243 II. Homocyclic silicon compounds 244 III. Heterocyclic silicon compounds 245 IV. Mixed cyclic silicon compounds 257 V. Polycyclic silicon compounds 259

CONTENTS I. Introduction 477 II. Investigation of structure 477 III. Preparation and properties 479 IV. π-Allyl complexes in organic syntheses 491

The NMR spectroscopic data for organometallic allyl and related derivatives have been examined. It is suggested that allyl compounds of transition metals be classified solely as σ- and π-derivatives and NMR spectroscopic criteria for the assignment of the test compounds to one of these types have been formulated. The effects of the structural non-equivalence of allyl ligands in a series of compounds, certain types of isomerism of allyl derivatives and also their possible lack of stereochemical rigidity have been considered. The validity, from the standpoint of NMR experiments, of the hypothesis of the σ–π transformations of allyl derivatives of transition metals in the presence of bases has been discussed. Hypotheses have been put forward concerning the geometry of the allyl compounds of certain non-transition metals. The bibliography includes 171 references.

In its electronic effect phosphorus(III) is usually regarded as an analogue of tervalent nitrogen. However, in recent years it has been shown that substituents with phosphorus(III) do not exhibit a π-donor effect, which is characteristic to a greater or smaller extent of groups containing the elements in Periods II and III with lone pairs of electrons. On the other hand, substituents with phosphorus(III) exhibit a π-acceptor effect, characteristic of meta-orienting groups, and probably due to the interaction with the vacant orbitals of phosphorus. Thus, in contrast to elements of Periods II and III with lone electron pairs, phosphorus(III) is incapable of p–π conjugation. The absence of the capacity of the lone electron pair of phosphorus to undergo delocalisation (or the presence of only insignificant capacity of this kind) has been explained by an enhanced s-character of the lone pair orbital, which is confirmed by data for the valence angles in phosphorus(III) compounds. The physical and chemical properties of phosphorus(III) compounds in which there is a possibility of p–π conjugation are discussed in the review from this standpoint. All the properties are consistent with the hypothesis of the predominant s-character of the lone electron pair of phosphorus. The bibliography includes 361 references.

Results obtained for complexes of transition metals with unusual organic ligands — trimethylenemethane, tetramethyleneethane, pentadienyl, and benzyl — are summarised. The chief structural and chemical features of these compounds are discussed. A list of 169 references is included.