Peter Mansfield

Multi-planar image formation using NMR spin echoes

A new method of two- or three-dimensional spin density imaging by nuclear magnetic resonance (NMR) is proposed, which exploits the properties of spin echoes in time- dependent magnetic field gradients. An analysis shows that simultaneous observation and differentiation of signals, arising from all spins distributed in a plane or set of planes within the specimen, is possible. The method is thus capable of producing visual pictures faster than previously described planar imaging methods.

NMR 'diffraction' in solids?

A new approach to the study of structure in solids by NMR is described. Multiple-pulse line-narrowing sequences and an applied magnetic field gradient are used. The theoretical analysis highlights the analogy with X-ray diffraction. Experimental results from a model one-dimensional lattice are presented.

Medical imaging by NMR

Application of the new nuclear magnetic resonance (NMR) method of fast scan proton imaging is described. Cross sectional proton scans of a human finger in vivo are measured and reveal considerable anatomical detail, particularly of the soft tissue regions. Imaging of tumour tissue is also briefly discussed.

Biological and medical imaging by NMR

Abstract Several methods of producing NMR images are discussed and examples of biological application are given. The discussion emphasizes spin density projections as an introduction to the new method of echo-planar imaging, which is fully described. An example showing the first picture produced by this method is presented. The problems of scaling up medical imaging experiments to whole-body size are also discussed and the type of image expected from such experiments is anticipated by constructing crosssectional water content maps of a human subject.

Image formation in NMR by a selective irradiative process

A new method of image formation by NMR is described. It is based on selective RF irradiation of the sample in switched magnetic field gradients. Selective irradiation may be achieved by tailored (or simple) excitation or tailored (or simple) saturation. Preliminary experiments illustrating various aspects of the method are described, and a two dimensional picture or image of a simple object is presented.

Symmetrized pulse sequences in high resolution NMR in solids

A systematic approach is developed for the improvement of the line narrowing efficiency of multipulse cycle sequences. This is based on the symmetrization of pulse cycles and exploits the useful properties of reflection symmetry subcycles. An example of a new pulse sequence is given which removes the dipolar interaction to third order in the time expansion of the logarithmic operator. Ways are discussed for compensating multipulse cycles for the effects of finite rf pulse width and rf inhomogeneity and a fully compensated version of the new pulse sequence is given.

Structure and behaviour in hydrophilic matrix sustained release dosage forms: 2. NMR-imaging studies of dimensional changes in the gel layer and core of HPMC tablets undergoing hydration

Abstract The swelling of hydrating HPMC tablets has been studied by NMR microscopy. The technique is non-invasive and has allowed both dimensional changes in the core and in the developing surface hydrated layer to be studied. Hydration at the edges of the tablet occurred to a greater extent than in the centre of the table surfaces, giving rise to a convex shaped hydrated layer. Gel layer development occurred to the same extent in both axial and radial directions, and was similar in all HPMC types. The predominantly axial swelling reported for all HPMC types, was shown to result almost equally from growth of the hydrated surface gel layer and expansion of the ungelled tablet core. The smaller axial expansion observed in E4M tablets was not a result of slower gel layer growth, but was entirely due to a smaller expansion of the core.

Fast scan proton density imaging by NMR

A new fast scanning method of producing proton density images by NMR is described which could be useful for the examination of plants as well as biological tissue in vivo. Examples are given of images produced from small samples of plant and biological material. Calculations show that imaging equipment, if scaled to deal with objects of human proportions, could under ideal conditions produce pictures close to television quality in times ranging down to a few minutes by this method.

Active magnetic screening of coils for static and time-dependent magnetic field generation in NMR imaging

A new method is introduced for screening or reducing extraneous magnetic fields outside coil structures. The method utilises a set of current-carrying conductors or a discrete wire array to simulate the induced surface currents which occur in superconducting magnetic screens or which occur in high conductivity thick metal screens when placed around coils producing time-dependent fields or field gradients. The active screens have the advantage that they work at any frequency including DC. Field gradient coil structures utilising the principle can be compact and of low inductance. Strong external fields can be made arbitrarily low thus making it feasible to generate large rapidly switched gradients within and in close proximity to a superconductive magnet. Such gradients can be especially useful in the implementation of high speed NMR imaging methods.

Improvements in snap-shot nuclear magnetic resonance imaging

New variants of the ultra-high-speed echo-planar imaging technique have been used to obtain snap-shot images of adult patients and volunteers at 0.1 T. Modified pulsed-gradient sequences together with non-linear signal sampling and activity screened gradients have greatly improved the image quality obtainable by single-shot methods. A particular variant, modulus blipped echo-planar single-pulse technique (MBEST), although slightly slower than the blipped echo-planar single-pulse technique (BEST), is experimentally more robust and incorporates intrinsic T2 weighting. An account of these improvements together with some experimental results is presented.