Method of reducing artefacts in images formed by means of Fourier Zeugmatography

Claim 1

A method of determining a nuclear magnetic resonance distribution in a region of a body which is situated in a generated steady, uniform magnetic field, including the steps of: a) generating a high-frequency electromagnetic pulse in order to cause a precessional motion of the magnetization of nuclei in the body about the field direction of the steady magnetic field, thus generating a resonance signal, b) then applying at least one gradient magnetic field during a preparation period, c) then taking a set of (n) signal samples of the resonance signal during a measurement period, d) then repeating, each time after a waiting period, a measurement cycle comprising the steps a), b) and c) for a plurality of (n') repetitions, the integral of the intensity of at least one gradient field over the preparation period having a different value at each repetition in order to provide (n') rows of (n) signal samples in a matrix-organised storage arrangement from which, after Fourier transformation thereof, an image of the distribution of the induced nuclear magnetization is determined, characterized in that in the various measurement cycles which succeed one another with respect to a corresponding succession of values of the integral of the intensity of the gradient field over the preparation period the resonance signals are excited in such a way that between the resonance signals of said successive rows there is introduced an additional phase difference Δϕ and that the introduced additional phase differences being cancelled for Fourier transformation of values present in columns of the matrix.

Claim 2

A method of determining a nuclear magnetic resonance distribution in a region of a body which is situated in a generated steady, uniform magnetic field, including the steps of: a) generating a high-frequency electromagnetic pulse in order to cause a precessional motion of the magnetization of nuclei in the body about the field direction of the steady magnetic field, thus generating a resonance signal, b) then applying at least one gradient magnetic field during a preparation period, c) then taking a set of (n) signal samples of the resonance signal during a measurement period, d) then repeating, each time after a waiting period, a measurement cycle comprising the steps a), b) and c) for a plurality of (n') repetitions, the integral of the intensity of at least one gradient field over the preparation period having a different value at each repetition in order to provide (n') rows of (n) signal samples in a matrix-organised storage arrangement from which, after Fourier transformation thereof, an image of the distribution of the induced nuclear magnetization is determined, characterized in that in the various measurement cycles which succeed one another with respect to a corresponding succession of values of the integral of the intensity of the gradient field over the preparation period the resonance signals are excited in such a way that between the resonance signals of said successive rows there is introduced an additional phase difference Δϕ and that the introduced additional phase differences being cancelled for Fourier transformation of values present in columns of the matrix.

Claim 7

A method of determining a nuclear magnetic resonance distribution in a three-dimensional region of a body which is situated in a generated steady, uniform magnetic field, including the steps of a) generating a high-frequency electromagnetic pulse in order to cause a precessional motion of the magnetization of nuclei in the body about the field direction of the steady magnetic field, thus generating a resonance signal, b) then applying, during a preparation period, at least a first and a second preparatory gradient magnetic field whose field directions are mutually perpendicular, c) then taking, during a measurement period, a set of (n) sampling signals of the resonance signal, d) then repeating, each time after a waiting period, a measurement cycle comprising the steps a), b) and c) for a plurality of (m x n') repetitions, a first integral which comprises the integral of the intensity of the first gradient field over the preparation period having a first number (m) of different values whilst a second integral which comprises the integral of the intensity of the second gradient field over the preparation period, has a second number (n') of different values in order to provide said first number (m) of planes each with said second number (n') of rows of (n) sampling signals, in a three-dimensional matrix from which, after Fourier transformation thereof, an image of the distribution of the induced nuclear magnetization in a three-dimensional region of a body is determined, characterized in that the resonance signal is alternately excited in phase opposition in the various measurement cycles which succeed one another with respect to a corresponding succession of values of the integral of the intensity of the first gradient field over the preparation period so that between the resonance signals of said successive measurement cycles there is introduced an additional phase difference Δϕ and that the introduced additional phase differences being cancelled for Fourier transformation of values from the m planes.

Claim 8

A method of determining a nuclear magnetic resonance distribution in a three-dimensional region of a body which is situated in a generated steady, uniform magnetic field, including the steps of a) generating a high-frequency electromagnetic pulse in order to cause a precessional motion of the magnetization of nuclei in the body about the field direction of the steady magnetic field, thus generating a resonance signal, b) then applying, during a preparation period, at least a first and a second preparatory gradient magnetic field whose field directions are mutually perpendicular, c) then taking, during a measurement period, a set of (n) sampling signals of the resonance signal, d) then repeating, each time after a waiting period, a measurement cycle comprising the steps a), b) and c) for a plurality of (m x n') repetitions, a first integral which comprises the integral of the intensity of the first gradient field over the preparation period having a first number (m) of different values whilst a second integral which comprises the integral of the intensity of the second gradient field over the preparation period, has a second number (n') of different values in order to provide said first number (m) of planes each with said second number (n') of rows of (n) sampling signals, in a three-dimensional matrix from which, after Fourier transformation thereof, an image of the distribution of the induced nuclear magnetization in a three-dimensional region of a body is determined, characterized in that the resonance signal is alternately excited in phase opposition in the various measurement cycles which succeed one another with respect to a corresponding succession of values of the integral of the intensity of the first gradient field over the preparation period so that between the resonance signals of said successive measurement cycles there is introduced an additional phase difference Δϕ and that the introduced additional phase differences being cancelled for Fourier transformation of values from the m planes.

Claim 13

A method of determining a nuclear magnetic resonance distribution in a region of a body which is situated in a steady uniform magnetic field which is generated in a first direction, including the steps of: a) generating a high-frequency electromagnetic pulse in order to cause a precessional motion of the magnetization of nuclei in the body about the first field direction, thus generating a resonance signal, b) then applying, during the preparation period at least one gradient-magnetic field, c) then generating a 180 0 high-frequency electromagnetic pulse at least once in order to reverse the direction of the nuclear magnetization, thus generating a nuclear spin echo signal, a set of (n) signal samples being taken during a measurement period which succeeds the 180° pulse and which is divided into a number of sampling intervals for periodically taking the set of (n) signal samples of the nuclear spin echo signal, d) then repeating, each time after a waiting period, the steps a), b) and c) for a plurality of (n') repetitions the integral of the intensity of at least one gradient field over the preparation period then having at each repetition a different value in order to obtain a group of signal samples from which, after Fourier transformation thereof, an image of the distribution of the induced nuclear magnetization is determined, characterized in that the 180° electromagnetic pulse is alternately generated in phase opposition during the various measurement cycles which succeed one another with respect to a corresponding succession of values of the integral of the intensity of the gradient field over the preparation period.

Claim 14

A method of determining a nuclear magnetic resonance distribution in a region of a body which is situated in a steady uniform magnetic field which is generated in a first direction, including the steps of: a) generating a high-frequency electromagnetic pulse in order to cause a precessional motion of the magnetization of nuclei in the body about the first field direction, thus generating a resonance signal, b) then applying, during the preparation period at least one gradient-magnetic field, c) then generating a 180 0 high-frequency electromagnetic pulse at least once in order to reverse the direction of the nuclear magnetization, thus generating a nuclear spin echo signal, a set of (n) signal samples being taken during a measurement period which succeeds the 180° pulse and which is divided into a number of sampling intervals for periodically taking the set of (n) signal samples of the nuclear spin echo signal, d) then repeating, each time after a waiting period, the steps a), b) and c) for a plurality of (n') repetitions the integral of the intensity of at least one gradient field over the preparation period then having at each repetition a different value in order to obtain a group of signal samples from which, after Fourier transformation thereof, an image of the distribution of the induced nuclear magnetization is determined, characterized in that the 180° electromagnetic pulse is alternately generated in phase opposition during the various measurement cycles which succeed one another with respect to a corresponding succession of values of the integral of the intensity of the gradient field over the preparation period.

Claim 15

A device for determining the nuclear magnetic resonance distribution in a region of a body, comprising: a) means for generating a steady, uniform magnetic field, b) means for generating high-frequency electromagnetic radiation, c) means for generating at least one gradient magnetic field, d) sampling means for sampling a resonance signal generated by the means specified in paragraphs a) and b), after conditioning the resonance signal by means of at least one gradient magnetic field generated by the means specified in paragraph c), e) processing means for processing the signals provided by the sampling means, f) control means for controlling at least the means specified in paragraphs b) to e) for generating, conditioning, sampling and processing a plurality of resonance signals, each resonance signal being respectively conditioned during a preparation period, the control means supplying the means specified in paragraph c) with control signals for adjusting the intensity and/or theduration of at least one gradient magnetic field, the respective integral of the intensity over the duration of at least one gradient magnetic field being different after each waiting period, characterized in that the control means comprise programmed computer means for generating and applying control signals to the means for generating high-frequency magnetic radiation, said control signals being suitable for generating in accordance with a programmed schedule an excitation pulse having either a first phase or a second phase during a measurement cycle, the second phase being shifted 180° with respect to the first phase.

Claim 16

A device for determining the nuclear magnetic resonance distribution in a region of a body, comprising: a) means for generating a steady, uniform magnetic field, b) means for generating high-frequency electromagnetic radiation, c) means for generating at least one gradient magnetic field, d) sampling means for sampling a resonance signal generated by the means specified in paragraphs a) and b), after conditioning the resonance signal by means of at least one gradient magnetic field generated by the means specified in paragraph c), e) processing means for processing the signals provided by the sampling means, f) control means for controlling at least the means specified in paragraphs b) to e) for generating, conditioning, sampling and processing a plurality of resonance signals, each resonance signal being respectively conditioned during a preparation period, the control means supplying the means specified in paragraph c) with control signals for adjusting the intensity and/or theduration of at least one gradient magnetic field, the respective integral of the intensity over the duration of at least one gradient magnetic field being different after each waiting period, characterized in that the control means comprise programmed computer means for generating and applying control signals to the means for generating high-frequency magnetic radiation, said control signals being suitable for generating in accordance with a programmed schedule an excitation pulse having either a first phase or a second phase during a measurement cycle, the second phase being shifted 180° with respect to the first phase.