Abstract: An elongated probe suitable for lowering down a borehole for nuclear magnetic logging has a pair of similar cylindrical magnets 1 and 2 separated by a gap in which a solenoid 3 is symmetrically disposed. The solenoid has a core 4 of high permeability ferrimagnetic material and has a length preferably equal to half the length of the gap. The magnets 1 and 2 and solenoid 3 with its core 4 are contained within a hollow cylindrical casing 5 of non-magnetic material.

Abstract: Nuclear magnetic resonance (NMR) apparatus have beenproposed for examining slices or volumes of bodies, perhaps for medical examination of patients. Magnetic fields are used to induce resonance in a selected region of a body and a resonance signal is detected during a pulse of a gradient field which causes phase dispersion across the region.It is now proposed that more efficient operation of the apparatus is possible if the gradient pulse is a non-square pulse, perhaps a distorted sinusoid, and the resonance signal is sampled during that pulse at intervals such that .intg. Hdt is substantially equal between adjacent samples.

Abstract: In a medical NMR apparatus it is desirable that the axial magnetic field, Ho, is uniform. The result can in theory be obtained by accuracy of construction but in practice this cannot readily be achieved. It is now proposed to use a field sensing probe system which indicates the value of that field at a plurality of positions in the examined region and provides error signals indicating deviations from uniformity. The field is automatically corrected in response to the error signals by applying currents to field correcting coils. The errors may be considered as distinct gradient and dishing errors which are corrected individually.

Abstract: In an apparatus for examining human bodies by nuclear magnetic resonance to produce images of cross-sectional slices of such bodies, it is desirable to reduce the recovery time between scans at different angles. A suitable pulse sequence for examination with minimum dispersion is disclosed. Repetition of the sequence with inverted pulses to drive the spins back to equilibrium and reduce recovery time is also disclosed.