Abstract: The invention describes an improved NMR imaging technique having particular application in imaging of solid objects using gradient echo techniques. By applying a so called 90.degree. rf pulse substantially at zero gradient crossing it is possible to obtain frequency encoded information about an object being imaged, using a so called gradient echo technique. However, profile degradation occurs as a result of the very large magnetic fields which are used which spoil the rf pulse. By shortening the length of pulses below 90.degree. it has been possible to improve gradient echo imaging. However, this has resulted in the reduction in the signal-to-noise ratio of the echo following each pulse. The present invention overcomes this problem by providing a rapidly oscillating magnetic field gradient and applying a radio frequency pulse away from a zero gradient crossing and by substantially phase rotating the resultant profile.

Abstract: Spatial NMR information is obtained from a sample by applying a magnetic field having a static component and two orthogonal periodically-varying gradient components. A recurring cycle of rf excitation pulses is applied. One of the gradient components is reduced in amplitude from its maximum to zero over a period and the other gradient component is subsequently increased from zero to its maximum over a period. The said periods are both longer than the cycle time.

Abstract: A synthetic or recombinant polypeptide displaying the antigenicity of all or an antigenic fragment of the H4 or H11 polypeptides of Toxoplasma gondii, and recombinant DNA molecules, vectors and host cells for the expression thereof. Use of the polypeptide in vaccine compositions and in diagnostic immunoassays is also disclosed.

Abstract: To derive NMR imaging information an object is subjected to a static magnetic field on which is superimposed a sinusoidally time varying magnetic gradient field. A sequence of narrow 90.degree. rf pulses are applied around the instants when the gradient field has a zero value. The rf pulses have relative phase quadrature such that excited nuclei precess with accumulated phase in each sequence.

Abstract: A sequence of a pair of r.f. pulses (90.sub.x .degree. and 90.sub.y .degree.) is applied to a solid being imaged with a time interval (.tau.) after each pulse. A static magnetic field is maintained and a magnetic gradient field is superimposed in the said time intervals, the time integrals of the gradient magnitudes of the gradient fields being equal. A free induction solid echo signal is detected at the end of the second time interval. The sequence is repeated for different values of the time integral are to obtain a set of signals and Fourier transformations with respect to the said time integral are then carried out on the set to obtain one-dimensional information. Two-dimensional information can be obtained from a plurality of sets of signals, each set being obtained in the presence of an additional orthogonal gradient field of differing value for each set.