Magnetic resonance imaging method and apparatus

Claim 2

A magnetic resonance imaging method comprising the step of generating a static magnetic field, gradient magnetic fields and a radio-frequency magnetic field; the step of measuring an NMR signal from an object to-be-examined on an arbitrary partial region which is so determined that, in the partial region of a measurement region required for obtaining both a real part and an imaginary part of a reconstructed image at a desired resolution, said partial region itself and a region obtained by moving said partial region in point symmetry with respect to an origin of a measurement space include the whole measurement region when combined; and the step of reconstructing the image by combining the measured signals and phase information on the reconstructed image.

Claim 3

An MR imaging method according to Claim 1, wherein the signals measured on said partial region are subjected to Fourier transformation and then corrected with the phase information on an image space, whereupon the corrected signals are subjected to inverse Fourier transformation to be brought back onto said measurement space again, thereby to obtain estimated values of unmeasured signals, and the reconstructed image is obtained using the estimated values.

Claim 4

An MR imaging method according to Claim 1, wherein estimated values of unmeasured signals and the signals measured on said partial region are subjected to Fourier transformation and then corrected with the phase information on an actual space, whereupon the corrected signals are subjected to inverse Fourier transformation to be brought back onto said measurement space again, thereby to update the estimated values of the measured signals, and the reconstructed image is obtained using the estimated values obtained lastly by sequential repetition of the updating.

Claim 5

An MR imaging method according to Claim 2 or Claim 3, wherein the phase information is a phase image which expresses phase values of various points of the reconstructed image, and the correction is to take complex conjugate values of the Fourier-transformed signals and thereafter rotate phases thereof double the phase values.

Claim 6

An MR imaging method according to Claim 2 or Claim 3, wherein the correction with the phase information is a correction in which phase values of data after the Fourier transformation of the measured signals are replaced with phase information on the image to-be-reconstructed.

Claim 7

An MR imaging method according to Claim 4 or Claim 5, wherein the phase image is estimated and obtained from the signals measured on said partial region neighboring the origin of said measurement space.

Claim 8

An MR imaging method according to any of Claims 2 - 6, wherein when the reconstucted image has at least two dimensions, the measured signals are Fourier-transformed in relation to variables of respective axes except only a variable of one axis, and a result obtained is subjected to one of the processes of Claims 2 - 6 in relation to the variable of one axis.

Claim 9

An MR imaging method according to claim 7, wherein said processes are applied for estimating unmeasured data in such a way that, in estimating the image from measured data of a measured part of a measurement space and phase information of the image, the measured data is first subjected to one-dimensional Fourier transformation in a readout direction and thereafter subjected to a reconstructing process in only a phase encode direction.

Claim 10

An MR imaging method comprising the step of generating a static magnetic field, gradient magnetic fields and a radio-frequency magnetic field; the step of measuring some of all echo signals which need to be measured for imparting a desired resolution to an image reconstructed by a Fourier transformation method, in such a way that a radio-frequency magnetic field is applied to an object to-be-examined under a static magnetic field so as to cause nuclear magnetic resonance, followed by application of a phase encoding gradient magnetic field, that a gradient magnetic field having a gradient in a readout direction is thereafter applied so as to measure an echo signal, and that all the echo signals and a total amount of application which is an amount of application of gradient magnetic fields necessary for measuring all the echo signals are subjected to any of the following substeps (1) - (4); the step of reconstructing an image by the use of the measured signals; and the step of extracting an image of a blood stream part from the reconstructed image: (1) the substep of applying the gradient magnetic field having the gradient in the readout direction, less than a half of the total amount of application, and subsequently applying a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the former gradient magnetic field, simultaneously with the measurement of the echo signal, (2) the substep of applying the gradient magnetic field having the gradient in the readout direction and a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the former gradient magnetic field, at least once so that a summation of amounts of application of both the gradient magnetic fields may be less than a half of the total amount of application, and thereafter applying a gradient magnetic field in the readout direction, simultaneously with the measurement of the echo signal, (3) the substep of applying the gradient magnetic field having the gradient in the readout direction, less than a half of the total amount of application, subsequently applying a magnetization inverting radio-frequency magnetic field, and subsequently applying a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the gradient magnetic field applied first, simultaneously with the measurement of the echo signal, and (4) the substep of applying a magnetization inverting radio-frequency magnetic field, applying the gradient magnetic field having the gradient in the readout direction and a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the former gradient magnetic field, at least once before and after the magnetization inverting radio-frequency magnetic field so that a difference between a summation of amounts of application before the radio-frequency magnetic field and a summation of amounts of application after the radio-frequency magnetic field may be less than a half of the total amount of application, and thereafter applying a gradient magnetic field having a gradient in the readout direction, simultaneously with the measurement of the echo signal.

Claim 11

An MR imaging method comprising the step of generating a static magnetic field, gradient magnetic fields and a radio-frequency magnetic field; the step of measuring some of all echo signals which need to be measured for imparting a desired resolution to an image reconstructed by a Fourier transformation method, in such a way that a radio-frequency magnetic field is applied to an object to-be-examined under a static magnetic field so as to cause nuclear magnetic resonance, followed by application of a phase encoding gradient magnetic field, that a gradient magnetic field having a gradient in a readout direction is thereafter applied so as to measure an echo signal, and that all the echo signals and a total amount of application which is an amount of application of gradient magnetic fields necessary for measuring all the echo signals are subjected to any of the following substeps (1) - (4); the step of reconstructing an image by the use of the measured signals; and the step of extracting an image of a blood stream part from the reconstructed image: (1) the substep of applying the gradient magnetic field having the gradient in the readout direction, less than a half of the total amount of application, and subsequently applying a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the former gradient magnetic field, simultaneously with the measurement of the echo signal, (2) the substep of applying the gradient magnetic field having the gradient in the readout direction and a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the former gradient magnetic field, at least once so that a summation of amounts of application of both the gradient magnetic fields may be less than a half of the total amount of application, and thereafter applying a gradient magnetic field in the readout direction, simultaneously with the measurement of the echo signal, (3) the substep of applying the gradient magnetic field having the gradient in the readout direction, less than a half of the total amount of application, subsequently applying a magnetization inverting radio-frequency magnetic field, and subsequently applying a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the gradient magnetic field applied first, simultaneously with the measurement of the echo signal, and (4) the substep of applying a magnetization inverting radio-frequency magnetic field, applying the gradient magnetic field having the gradient in the readout direction and a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the former gradient magnetic field, at least once before and after the magnetization inverting radio-frequency magnetic field so that a difference between a summation of amounts of application before the radio-frequency magnetic field and a summation of amounts of application after the radio-frequency magnetic field may be less than a half of the total amount of application, and thereafter applying a gradient magnetic field having a gradient in the readout direction, simultaneously with the measurement of the echo signal.

Claim 12

An MR imaging method according to Claim 9, wherein an image reconstructing method is applied in which the image having the desired resolution is reconstructed from some of all the echo signals and information on phases of the image.

Claim 13

An MR imaging method according to Claim 10, wherein the image of the blood stream part is extracted from the reconstructed image by executing a subtraction between reconstructed images obtained in such a way that the application of the gradient magnetic fields is made different when these reconstructed images are to be obtained.

Claim 14

An MR imaging apparatus comprising means to generate a static magnetic field, gradient magnetic fields and a radio-frequency magnetic field; means to measure an NMR signal from an object to-be-examined on an optional partial region which is so determined that, in the partial region of a measurement region required for obtaining both a real part and an imaginary part of a reconstructed image at a desired resolution, said partial region itself and a region obtained by moving said partial region in point symmetry with respect to an origin of a measurement space include the whole measurement region when combined; and means to reconstruct the image by combining the measured signals and phase information on the reconstructed image.

Claim 15

An MR imaging apparatus comprising means to generate a static magnetic field, gradient magnetic fields and a radio-frequency magnetic field; means to measure an NMR signal from an object to-be-examined on an optional partial region which is so determined that, in the partial region of a measurement region required for obtaining both a real part and an imaginary part of a reconstructed image at a desired resolution, said partial region itself and a region obtained by moving said partial region in point symmetry with respect to an origin of a measurement space include the whole measurement region when combined; and means to reconstruct the image by combining the measured signals and phase information on the reconstructed image.

Claim 16

An MR imaging apparatus comprising means to generate a static magnetic field, gradient magnetic fields and a radio-frequency magnetic field; measurement means to detect nuclear magnetic resonance signals from an object to-be-examined; and means to reconstruct an image by estimating unknown measurement data in such a way that, in estimating the image from measured data of a measured part of a measurement space and phase information of the image obtained beforehand, the measured data is first subjected to one-dimensional Fourier trans formation in a readout direction and thereafter subjected to a reconstructing process in only a phase encode direction.

Claim 17

An MR imaging apparatus comprising means to generate a static magnetic field, gradient magnetic fields and a radio-frequency magnetic field; measurement means to detect nuclear magnetic resonance signals from an object to-be-examined; and means to reconstruct an image by estimating unknown measurement data in such a way that, in estimating the image from measured data of a measured part of a measurement space and phase information of the image obtained beforehand, the measured data is first subjected to one-dimensional Fourier trans formation in a readout direction and thereafter subjected to a reconstructing process in only a phase encode direction.

Claim 18

An MR imaging apparatus comprising means to generate a static magnetic field, gradient magnetic fields and a radio-frequency magnetic field; means to measure some of all echo signals which need to be measured for imparting a desired resolution to an image reconstructed by a Fourier transformatiom method, in such a way that a radio-frequency magnetic field is applied to an object to-be-examined so as to cause nuclear magnetic resonance, followed by application of a phase encoding gradient magnetic field, that a gradient magnetic field having a gradient in a readout direction is thereafter applied so as to measure an echo signal, and that all the echo signals and a total amount of application which is an amount of application of gradient magnetic fields necessary for measuring all the echo signals are subjected to any of the following substeps (1) - (4); the step of reconstructing an image by the use of the measured signals; and the step of extracting an image of a blood stream part from the reconstructed image: (1) the substep of applying the gradient magnetic field having the gradient in the readout direction, less than a half of the total amount of application, and subsequently applying a gradient magnetic field having a gradient in the readout direction and being opposite to the former gradient magnetic field, simultaneously with the measurement of the echo signal, (2) the substep of applying the gradient magnetic field having the gradient in the readout direction and a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the former gradient magnetic field, at least once so that a summation of amounts of application of both the gradient magnetic fields may be less than a half of the total amount of application, and thereafter applying a gradient magnetic field in the readout direction, simultaneously with the measurement of the echo signal, (3) the substep of applying the gradient magnetic field having the gradient in the readout direction, less than a half of the total amount of application, subsequently applying a magnetization inverting radio-frequency magnetic field, and subsequently applying a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the gradient magnetic field applied first, simultaneously with the measurement of the echo signal, and (4) the substep of applying a magnetization inverting radio-frequency magnetic field, applying the gradient magnetic field having the gradient in the readout direction and a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the former gradient magnetic field, at least once before and after the magnetization inverting radio-frequency magnetic field so that a difference between a summation of amounts of application before the radio-frequency magnetic field and a summation of amounts of application after the radio-frequency magnetic field may be less than a half of the total amount of application, and thereafter applying a gradient magnetic field having a gradient int he readout direction, simultaneously with the measurement of the echo signal.

Claim 19

An MR imaging apparatus comprising means to generate a static magnetic field, gradient magnetic fields and a radio-frequency magnetic field; means to measure some of all echo signals which need to be measured for imparting a desired resolution to an image reconstructed by a Fourier transformatiom method, in such a way that a radio-frequency magnetic field is applied to an object to-be-examined so as to cause nuclear magnetic resonance, followed by application of a phase encoding gradient magnetic field, that a gradient magnetic field having a gradient in a readout direction is thereafter applied so as to measure an echo signal, and that all the echo signals and a total amount of application which is an amount of application of gradient magnetic fields necessary for measuring all the echo signals are subjected to any of the following substeps (1) - (4); the step of reconstructing an image by the use of the measured signals; and the step of extracting an image of a blood stream part from the reconstructed image: (1) the substep of applying the gradient magnetic field having the gradient in the readout direction, less than a half of the total amount of application, and subsequently applying a gradient magnetic field having a gradient in the readout direction and being opposite to the former gradient magnetic field, simultaneously with the measurement of the echo signal, (2) the substep of applying the gradient magnetic field having the gradient in the readout direction and a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the former gradient magnetic field, at least once so that a summation of amounts of application of both the gradient magnetic fields may be less than a half of the total amount of application, and thereafter applying a gradient magnetic field in the readout direction, simultaneously with the measurement of the echo signal, (3) the substep of applying the gradient magnetic field having the gradient in the readout direction, less than a half of the total amount of application, subsequently applying a magnetization inverting radio-frequency magnetic field, and subsequently applying a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the gradient magnetic field applied first, simultaneously with the measurement of the echo signal, and (4) the substep of applying a magnetization inverting radio-frequency magnetic field, applying the gradient magnetic field having the gradient in the readout direction and a gradient magnetic field having a gradient in the readout direction and being opposite in polarity to the former gradient magnetic field, at least once before and after the magnetization inverting radio-frequency magnetic field so that a difference between a summation of amounts of application before the radio-frequency magnetic field and a summation of amounts of application after the radio-frequency magnetic field may be less than a half of the total amount of application, and thereafter applying a gradient magnetic field having a gradient int he readout direction, simultaneously with the measurement of the echo signal.