Method of determining the spectral distribution of the nuclear magnetization in a limited volume, and device for performing the method

Claim 1

A method of determining the nuclear magnetisation distribution in a limited volume by means of a plurality of sequences, three r.f. pulses being applied to an examination zone in each sequence in the presence of a steady, uniform magnetic field, the first and the second r.f. pulse cooperating with a respective one of two magnetic fields whose gradients extend perpendicularly with respect to one another, stimulated echo signals generated in each sequence being added and subjected to a Fourier transformation, characterized in that each sequence comprises a sub-sequence (HF1' . . . HF3') which precedes the three r.f. pulses (HF1 . . . HF3) and which dephases the nuclear magnetisation everywhere outside a layer (S) in said examination zone which extends parallel to the plane defined by the two gradient directions (Gy, Gz), the sequences taking place in cycles, the sequences being repeated n times in each cycle, where n is larger than or equal to 3, all sequences of a cycle being distinct from one another as regards the phase difference between the first and the second r.f. pulse by 360°/n or an integer multiple thereof which is not zero, the spin resonance signals generated by the sequences being added so that FID signals produced by the third r.f. pulse (HF3) compensate for one another.

Claim 2

A method of determining the nuclear magnetisation distribution in a limited volume by means of a plurality of sequences, three r.f. pulses being applied to an examination zone in each sequence in the presence of a steady, uniform magnetic field, the first and the second r.f. pulse cooperating with a respective one of two magnetic fields whose gradients extend perpendicularly with respect to one another, stimulated echo signals generated in each sequence being added and subjected to a Fourier transformation, characterized in that each sequence comprises a sub-sequence (HF1' . . . HF3') which precedes the three r.f. pulses (HF1 . . . HF3) and which dephases the nuclear magnetisation everywhere outside a layer (S) in said examination zone which extends parallel to the plane defined by the two gradient directions (Gy, Gz), the sequences taking place in cycles, the sequences being repeated n times in each cycle, where n is larger than or equal to 3, all sequences of a cycle being distinct from one another as regards the phase difference between the first and the second r.f. pulse by 360°/n or an integer multiple thereof which is not zero, the spin resonance signals generated by the sequences being added so that FID signals produced by the third r.f. pulse (HF3) compensate for one another.

Claim 21

A device for determining the nuclear magnetization distribution in a limited volume by means of a plurality of sequences applied to an examination zone comprising a magnet for generating a uniform, steady magnetic field in said examination zone, an r.f. coil system for generating an r.f. coil system with r.f. pulses, a gradient coil system for generating magnetic fields which extend in the direction of the steady magnetic field and which comprise gradients in different directions, generators for powering the gradient coils, a control unit for controlling the r.f. generator and the generators, and an arithmetic device for processing the stimulated r.f. signal, characterized in that the control unit is programmed so that it generates a plurality of sequences, each of which includes a sub-sequence (HF1' . . . HF3') whereby the nuclear magnetisation is dephased everywhere outside a layer (S), after which three r.f. pulses (HF1 . . . HF3) are generated, the first and the second r.f. pulse acting on the examination zone in the presence of a magnetic field having gradients (Gy, Gz) which extend perpendicularly to one another and to the layer, there being generated cycles comprising n sequences, where n is larger than or equal to 3, in which the phase difference between the first and the second r.f. pulse after the subsequence deviates by 360°/n, the arithmetic device being programmed so that the spin resonance signals generated by the individual sequences are added so that FID signals generated by the third r.f. pulse compensate for one another.

Claim 22

A device for determining the nuclear magnetization distribution in a limited volume by means of a plurality of sequences applied to an examination zone comprising a magnet for generating a uniform, steady magnetic field in said examination zone, an r.f. coil system for generating an r.f. coil system with r.f. pulses, a gradient coil system for generating magnetic fields which extend in the direction of the steady magnetic field and which comprise gradients in different directions, generators for powering the gradient coils, a control unit for controlling the r.f. generator and the generators, and an arithmetic device for processing the stimulated r.f. signal, characterized in that the control unit is programmed so that it generates a plurality of sequences, each of which includes a sub-sequence (HF1' . . . HF3') whereby the nuclear magnetisation is dephased everywhere outside a layer (S), after which three r.f. pulses (HF1 . . . HF3) are generated, the first and the second r.f. pulse acting on the examination zone in the presence of a magnetic field having gradients (Gy, Gz) which extend perpendicularly to one another and to the layer, there being generated cycles comprising n sequences, where n is larger than or equal to 3, in which the phase difference between the first and the second r.f. pulse after the subsequence deviates by 360°/n, the arithmetic device being programmed so that the spin resonance signals generated by the individual sequences are added so that FID signals generated by the third r.f. pulse compensate for one another.