Abstract: A magnetic coil, especially for use as an r.f. transmit/receive coil in NMR apparatus, comprises a continuous closed conductive loop would round a former 1. A pair of external terminals 2 and 3 both lie in a plane 4 constituting a plane of symmetry and the coil is would so that there is mirror symmetry about this plane. There are two electrically parallel paths between terminals 2 and 3 each restricted to one side of the plane of symmetry 4 and the resultant magnetic field when a potential difference is applied between terminals 2 and 3 is such that equal magnetic fields are produced on both sides of the plane of symmetry 4.

Abstract: A set of NMR free induction signals generated in nuclei in a sample are recorded in the presence of a magnetic field gradient to a static magnetic field in which the sample is positioned. Prior to recording a magnetic field gradient orthogonal to the said gradient is applied to phase-encode the signals. The individual signals of a set are differentiated by being recorded after different time integrals of the phase encoding gradient. The magnitudes of successive time integrals have a non-monotonic relationship with each other so that sufficient signal data is recorded to enable the Fourier transform operation to commence before half or less of the set of signals has been recorded. Preferably the relationship between the magnitudes of successive time integrals corresponds to a numerical sequence represented by a monotonic sequence of binary numbers re-arranged in bit-reversed order.

Abstract: A method of deriving three dimensional image information from an object using nuclear magnetic resonance signals is described. The method comprises subjecting the object to a continuous, static magnetic field and carrying out the following set of sequential steps.1. Exciting nuclear spins in a volume;2. applying non-aligned first, second and third gradients of the magnetic field;3. causing the spins to rephase periodically in the presence of the first gradient;4. phase encoding the spins in the direction of the second gradient prior to every read-out of the rephased FIS from the object;and then successively repeating the above set of steps with different values of gradient of the third gradient (G.sub.z.sup.(2)), there being a recovery interval between the repetition of successive sets of steps.