Abstract: A method of examining a slice of a body by nuclear magnetic resonance in which a steady magnetic field, and a gradient field G.sub.z along the same axis define the slice to be examined. A periodic magnetic field H.sub.1 at the Larmor frequency for the slice is applied in two distinct pulses 1, 2 each in conjunction with the gradient field. The total field integral of the two pulses is chosen to be sufficient to rotate spin vectors of nuclei in the field through an angle of .pi./2 radians. Between the two pulses 1, 2, a further pulse 3 is applied in the absence of the gradient field G.sub.z, which has a field integral sufficient to rotate the spin vectors through an angle of .pi. radians.

Abstract: Nuclear magnetic resonance methods have been proposed for examination of large bodies, including medical examination of patients. These include so-called steady state free precession methods. Such methods involve alternating excitation of a region of the body in such a way that an equilibrium condition is established at which a mean resonance signal is detectable. Typically for excitation of a planar region a radio frequency excitation field is provided in the presence of a field having an alternating gradient so that equilibrium is only reached in the plane. It is now proposed to achieve the same result by the application of two radio frequency fields having opposing gradients and pulsed in alternation to balance substantially only in the plane and provide equilibrium only there. The fields are provided by respective sets of saddle shaped coils divided into pairs of unequal dimension (1a, 1b, 2a, 2b) to provide the respective gradients.

Abstract: In Nuclear Magnetic Resonance (NMR) imaging systems it is known to excite resonance in a slice of a body and to sample the resonance signals in the presence of a field gradient across the slice. The gradient field is pulsed. Where such systems analyse the signal to be for many sets of strips in the slice, each set in a different direction, for analysis by techniques used in computerized tomography (CT) X-ray systems, it is now proposed that the field gradient pulsed should reach a maximum after not more than one third of its total duration to balance the spatial frequency emphasis (FIG. 1e) in the CT processing.

Abstract: In nuclear magnetic resonance (NMR) imaging systems it is known to excite resonance in a slice of a body and then to sample the resonance signals in the presence of a field gradient across the slice. It has been proposed that the signals should be sampled at intervals such that there is equal field integral (for the field gradient) in each interval. It is now proposed to use outputs from two NMR probes in the slice and on opposite sides of the body. The phase difference between the two probes is measured and samples are taken when the phase difference reaches a predetermined value. Preferably the samples are taken when a gate detects zero-crossing of the output of a demodulator providing the phase difference. Two probes only may be rotated around the patient as the field gradient rotates or four may be used, two orthogonally disposed pairs and one or other appropriately weighted output used.

Abstract: In NMR imaging systems a pulsed field gradient may be applied across an excited slice (1) and the resonance signal detected during the field gradient pulse. It has been usual to demodulate the resonance signal at the Larmor frequency for a strip at the center of the slice, at which generally the field gradient has a zero-crossing. It has, however, been proposed to put the zero-crossing outside the slice, still demodulating at the slice Larmor frequency. In this invention demodulation is actually at the frequency for a probe (12) which is necessarily outside the patient. This makes the demodulation independent of errors in a local oscillator frequency. Demodulation may be for a probe effect to give a frequency for a strip outside the slice or the probe may be perpendicular to the gradient to give the zero-crossing frequency.

Abstract: The invention concerns the production of gradient fields for nuclear magnetic resonance apparatus particularly imaging apparatus. It has been earlier proposed that samples of the resonance signal be taken at intervals such that the field gradient integrals in each such interval are the same. This sampling is at unequal time intervals. It is now proposed to provide the gradient fields in discrete pulses with spaces in between at which samples can be taken. It is then straightforward to make the pulses of equal field integral or to provide an extra small pulse in one or both of the orthogonal gradients if the field integral should need adjusting before the next sample.

Abstract: The invention is suitable for a small nuclear magnetic resonance pulse head applicable to a part of the body in the manner of ultrasonic systems. The arrangement generates a field which varies in amplitude with distance from the head, being uniform at surfaces which intrude into the body. Resonance is excited in one such surface and a gradient restricts resonance to one line therein. The phase is then dispersed along the line and the signal sensed as a function of position therealong.

Abstract: The invention provides RF field coils and detector coils for an NMR machine. The two coils are specially designed for their respective purpose, the transmit coil (5, 6) being rectangular and the received coil (7-11) substantially elliptical with defined axis ratios and spacing in the z-direction being by projection of equi-spaced conductors on to the ellipse.

Abstract: The invention provides an investigation of chemical shift for an element, for example phosphorus, in a region of a body, in one example resonance is preferentially in a line in a slice of the body. Frequency dispersion down the line is produced by a pulsed field having a switched gradient so that the frequency distribution is in steps. This allows a chemical dispersion in each limited region of the line without overlap with adjacent regions. The measured FID signals are Fourier transformed to give a spatial and chemical analysis of the line.Alternatively resonance is excited in a slice and lines selected by a pulsed gradient which gives chemical dispersion as well as spatial dispersion between the lines after Fourier Transformation. This is repeated for many different directions of the pulsed gradient to allow analysis of a chemical line by convolution techniques to give a picture for the slice.

Abstract: The invention is related to the so-called "echo-planar" method of NMR imaging. In that method a resonance is first excited in a slice and then two orthogonal gradients provided dispersion in the slice. One gradient is pulsed to space the frequencies of spins in adjacent strips allowing the other gradient to provide dispersion down the strips. It is now proposed to pulse the second gradient so that the dephasing down each strip is also in steps. The FID signals (including rephasing signals) for each distinct element so produced can then be put in an array and two-dimensionally Fourier transformed to yield the desired output for each element.

Abstract: In an NMR examining arrangement for producing an image of a region, generally a planar slice, of a body, it has been suggested to derive, from the resonance signals, a plurality of values, for strips in the slice, and then to convolve them with a convolution function to be suitable for back projection in the manner known for x-ray signals. In this invention it is proposed to modulate the resonance signals with a suitable function and then to Fourier transform them but not to convolve them. The modulation function is chosen to give after Fourier transformation the same effect as the convolution would have given. It is suggested that the modulation function should be the inverse Fourier Transform of the desired convolution function.

Abstract: For NMR purposes a uniform magnetic field has been produced by field coils. It is known to use a cosinusoidal distribution to produce a uniform field. However, a large-diameter low-inductance coil is required for NMR and it is difficult to wind a small number of turns cosinusoidally. It is proposed to use two cosinusoidal coils providing unequal and opposing fields, the required field being the resultant and the combined inductance being less than either coil individually. The coils may have different winding densities or may be at different radii or both.

Abstract: In a NMR pulse sequence dispersion caused by inhomogeneity in the steady axial magnetic field may be reduced by applying a 180.degree. `spin-echo` RF pulse. However, whereas it is possible in known pulse sequences to apply a 90.degree. RF pulse in the presence of a selected gradient and to phase correct it adequately, this is not true for the 180.degree. pulse needed in a simple echo system (or the multiple pulses of more complex systems). It has been thought that a 180.degree. pulse could not then be use. It is proposed to apply the 90.degree. H.sub.1 pulse in the absence of an axial field gradient. For this purpose it is desirable to apply the RF field and sense the resonance with different coils. The RF coils should be of substantially greater extent in the axial direction than the resonance sensing coils.