Data processing method to reduce truncation artifacts in nuclear magnetic resonance apparatus

• US 5,345,173 A
• Filed: 07/31/1992
• Issued: 09/06/1994
• Est. Priority Date: 08/02/1991
• Status: Expired due to Term

• Current Assignee: Hitachi Medical Corporation (Hitachi, Ltd.)
• Original Assignee: Hitachi, Ltd., Hitachi Medical Corporation (Hitachi, Ltd.)
• Inventors: Bito, Yoshitaka, Suzuki, Ryuichi, Sekihara, Kensuke
• Primary Examiner(s): Tokar, Michael J.
• Assistant Examiner(s): MAH, RAYMOND
• Application Number:
  US07/922,473
• Time in Patent Office: 767 Days
• Field of Search: 324/307, 324/309, 364/413.19, 128/653.2
• US Class Current: 324/309
• CPC Class Codes: G01R 33/56545 caused by finite or discrete sampling, e.g. Gibbs ringing, truncation artefacts, phase aliasing artefacts

Abstract

A data processing method for image reconstruction in an NMR apparatus for use in the medical field which reduces a computation quantity relating to data extrapolation when truncation artifacts are reduced by data extrapolation. The data processing method is utilized with an inspection apparatus including a magnetic field generation apparatus for generating each of a static magnetic field, gradient magnetic field and RF magnetic field, a signal detection device for detecting NMR signals from an inspection object, a computer for computing detection signals of the signal detection device and for outputting the result of computation by the computer, for obtaining an image by effecting inverse Fourier transform for a measurement signal row representing data of spatial frequency space. An evaluation value representing the magnitude of ringing which occurs because a measured spatial frequency domain is limited in the spatial frequency space is utilized for comparison with a threshold value and signals are extrapolated into spatial frequency domains which are located outside of a measured spatial frequency domain by use of coefficients computed from the signals of the measured spatial frequency domain only when the evaluation is greater than the threshold value so that an image in which the ringing thereof is corrected is obtained.

Claims

1. A data processing method for use in an inspection apparatus including magnetic field generation means for generating each of a static magnetic field, a gradient magnetic field and a radio frequency (RF) magnetic field, signal detection means for detecting nuclear magnetic resonance (NMR) signals from an inspection object, a computer for computing detection signals from said signal detection means and output means for outputting the computation result of said computer, for obtaining an image by effecting inverse Fourier transform of a measurement signal row representing data of spatial frequency space, comprising:

a first step of computing an evaluation value representing the magnitude of ringing which occurs because a measured spatial frequency domain is limited in said spatial frequency space;

a second step of comparing whether or not the evaluation value obtained by said first step is greater than a predetermined threshold value; and

a third step of extrapolating signals into spatial frequency domains which are located outside of said measured spatial frequency domain by the use of coefficients computed from the signals of said measured spatial frequency domain only when said evaluation value is greater than said predetermined threshold value at said second step.

2. A data processing method for use in an inspection apparatus including magnetic field generation means for generating each of a static magnetic field, a gradient magnetic field and a radio frequency (RF) magnetic field, signal detection means for detecting a nuclear magnetic resonance (NMR) signals from an inspection object, a computer for computing detection signals from said signal detection means and output means for outputting the computation result of said computer, for obtaining an image by effecting inverse Fourier transform of a measurement signal row representing data of spatial frequency space, comprising:

a first step of computing an evaluation value representing the magnitude of ringing, which occurs because a measured spatial frequency domain is limited in said spatial frequency space, from a product signal provided by the product of a frequency offset having an origin of a signal of said measured spatial frequency domain as a reference thereof and a signal of said measured spatial frequency domain;

a second step of comparing whether or not said evaluation value obtained at said first step is greater than a predetermined threshold value; and

a third step of extrapolating signals into spatial frequency domains which are located outside of said measured spatial frequency, domain by the use of coefficients computed from the signals of said measured spatial frequency domain only when said evaluation value is greater than said predetermined threshold value at said second step in order to obtain an image ringing of which is corrected.

3. A data processing method in a nuclear magnetic resonance apparatus according to claim 2, wherein said frequency offset is determined in accordance with the formula

4. A data processing method in a nuclear magnetic resonance apparatus according to claim 2, wherein said frequency offset is determined in accordance with the formula

5. A data processing method for use in an inspection apparatus including magnetic field generation means for generating each of a static magnetic field, a gradient magnetic field and a radio frequency (RF) magnetic field, signal detection means for detection of nuclear magnetic resonance (NMR) signals from an inspection object, a computer for computing detection signals from said signal detection means and output means for outputting the computation result of said computer, for obtaining an image by effecting inverse Fourier transform of a measurement signal row representing data of spatial frequency space, comprising:

a first step of computing an evaluation value representing the magnitude of ringing which occurs because a measured spatial frequency domain is limited in said spatial frequency space, from product signal provided by the product of a frequency offset having an origin of a signal of said measured spatial frequency domain as a reference thereof and a signal of said measured spatial frequency domain, computing a value obtained by integrating said product signals in a positive direction and a value obtained by integrating said product signals in a negative direction, and computing dividedly said integration value in the positive direction and said integration value in the negative direction;

a second step of comparing whether or not said evaluation values in the positive and negative directions are greater than predetermined threshold values in the positive and negative directions, respectively; and

a third step of extrapolating signals into spatial frequency domains which are located outside of said measured spatial frequency domain in said positive and negative directions by the use of coefficients computed from the signals of said measured spatial frequency domain only when said evaluation values in said positive and negative directions are greater than said predetermined threshold values in said positive and negative directions, respectively, at said second step in order to obtain an image ringing of which is corrected.

6. A data processing method in a nuclear magnetic resonance apparatus according to claim 5, wherein said frequency offset is determined in accordance with the formula

7. A data processing method in a nuclear magnetic resonance apparatus according to claim 5, wherein said frequency offset is determined in accordance with the formula

8. A data processing method for use in an inspection apparatus including magnetic field generation means for generating each of a static magnetic field, a gradient magnetic field and a radio frequency (RF) magnetic field, signal detection means for detecting a nuclear magnetic resonance (NMR) signal from an inspection object, a computer for computing detection signals from said signal detection means and output means for outputting the computation result of said computer, for obtaining an image by effecting inverse Fourier transform of a measurement signal row representing that of spatial frequency space, comprising:

a first step of computing an evaluation value representing the magnitude of ringing which occurs because a measured spatial frequency domain is limited in said spatial frequency space, from a product signal provided by the product of a frequency offset having an origin of a signal of said measured spatial frequency domain as a reference thereof and a signal of said measured spatial frequency domain, by computing a point at which the absolute value of the signal of said measured spatial frequency domain becomes maximal, and using said point as the origin of the signal of said measured spatial frequency domain;

a second step of comparing whether or not said evaluation value obtained at said first step is greater than a predetermined threshold value; and

a third step of extrapolating signals into spatial frequency domains which are located outside of said measured spatial frequency domain by the use of coefficients computed from the signals of said measured spatial frequency domain only when said evaluation value is greater than said predetermined threshold value in order to obtain an image ringing of which is corrected.

9. A data processing method in a nuclear magnetic resonance apparatus according to claim 8, wherein said frequency offset is determined in accordance with the formula

10. A data processing method in a nuclear magnetic resonance apparatus according to claim 8, wherein said frequency offset is determined in accordance with the formula

11. A data processing method for use in an inspection apparatus including magnetic field generation means for generating each of a static magnetic field, a gradient magnetic field and a radio frequency (RF) magnetic field, signal detection means for detecting a nuclear magnetic resonance (NMR) signals from an inspection object, a computer for computing detection signals from said signal detection means and output means for outputting the computation result of said computer, for obtaining an image by effecting inverse Fourier transform of a measurement signal row representing data of spatial frequency space, comprising:

a first step of computing an evaluation value representing the magnitude of ringing which occurs because a measured spatial frequency domain is limited in said spatial frequency space, from product signals provided by the product of a frequency offset having an origin of a signal of said measured spatial frequency domain as a reference thereof and a signal of said measured spatial frequency domain, by computing a point at which the absolute value of the signal of said measured spatial frequency domain becomes maximal, and using said point as the origin of the signal of said measured spatial frequency domain, computing then a value obtained by integrating said product signals in a positive direction from said origin and a value obtained by integrating said product signals in a negative direction from said origin, and computing dividedly said integration values in said positive and negative directions as evaluation values in said positive and negative directions, respectively;

a second step of comparing whether or not said evaluation values in said positive and negative directions obtained at said first step are greater than predetermined threshold values in said positive and negative directions, respectively; and

a third step of extrapolating signals into spatial frequency domains which are located outside of said measured spatial frequency domain by the use of coefficients computed from the signals of said measured spatial frequency domain only when said evaluation values in said positive and negative directions are greater than said predetermined threshold values in said positive and negative directions, respectively, at said second step in order to obtain an image ringing of which is corrected.

12. A data processing method in a nuclear magnetic resonance apparatus according to claim 11, wherein said frequency offset is determined in accordance with the formula

13. A data processing method in a nuclear magnetic resonance apparatus according to claim 11, wherein said frequency offset is determined in accordance with the formula

14. A data processing method for use in an inspection apparatus including magnetic field generation means for generating each of a static magnetic field, a gradient magnetic field and a radio frequency (RF) magnetic field, signal detection means for detecting a nuclear magnetic resonance (NMR) signals from an inspection object, a computer for computing detection signals from said signal detection means and output means for outputting the computation result of said computer, for obtaining an image by effecting inverse Fourier transform of a measurement signal row representing data of spatial frequency domain, comprising:

a first step of computing an evaluation value representing the magnitude of ringing which occurs because a measured spatial frequency domain is limited in said spatial frequency space, from a product signal provided by the product of a frequency offset having an origin of a signal of said measured spatial frequency domain as a reference thereof and a signal of said measured spatial frequency domain;

a second step of comparing whether or not said evaluation value obtained at said first step is greater than a predetermined threshold value; and

a third step of extrapolating signals into spatial frequency domains which are located outside of said measured spatial frequency domain by the use of coefficients for data extrapolation computed from said product signal obtained at said first step, only when said evaluation value is greater than said predetermined threshold value at said second step in order to obtain an image ringing of which is corrected.

15. A data processing method in a nuclear magnetic resonance apparatus according to claim 14, wherein said frequency offset is determined in accordance with the formula

16. A data processing method in a nuclear magnetic resonance apparatus according to claim 14, wherein said frequency offset is determined in accordance with the formula

17. A data processing method for use in an inspection apparatus including magnetic field generation means for generating each of a static magnetic field, a gradient magnetic field and a radio frequency (RF) magnetic field, signal detection means for detecting a nuclear magnetic resonance (NMR) signals from an inspection object, a computer for computing detection signals from said signal detection means and output means for outputting the computation result of said computer, for obtaining an image by effecting inverse Fourier transform of a measurement signal row representing data of spatial frequency space, comprising:

a first step of computing an evaluation value representing the magnitude of ringing which occurs because a measured spatial frequency domain is limited in said spatial frequency space, from product signals provided by the product of a frequency offset having an origin of a signal of said measured spatial frequency domain as a reference thereof and a signal of said measured spatial frequency domain, computing value obtained by integrating said product signals in a positive direction and a value obtained by integrating said product signals in a negative direction, and computing dividedly said integration value in the positive direction and said integration value in the negative direction;

a second step of comparing whether or not said evaluation values in the positive and negative directions are greater than predetermined threshold values in the positive and negative directions, respectively; and

a third step of computing coefficients for data extrapolation from said product signals obtained at said first step in said positive and negative directions, respectively, and extrapolating signals into spatial frequency domains which are located outside of said measured spatial frequency domain by the use of said coefficients, only when said evaluation values in said positive and negative directions are greater than said threshold values in said positive and negative directions, respectively, at said second step in order to obtain an image ringing of which is corrected.

18. A data processing method in a nuclear magnetic resonance apparatus according to claim 17, wherein said frequency offset is determined in accordance with the formula

19. A data processing method in a nuclear magnetic resonance apparatus according to claim 17, wherein said frequency offset is determined in accordance with the formula

20. A data processing method for use in an inspection apparatus including magnetic field generation means for generating each of a static magnetic field, a gradient magnetic field and a radio frequency (RF) magnetic field, signal detection means for detecting a nuclear magnetic resonance (NMR) signals from an inspection object, a computer for computing detection signals from said signal detection means and output means for outputting the computation result of said computer, for obtaining an image by effecting inverse Fourier transform of a measurement signal row representing data of spatial frequency space, comprising:

a first step of computing an evaluation value representing the magnitude of ringing, which occurs because a measured spatial frequency domain is limited in said spatial frequency space, from a product signal provided by the product of a frequency offset having an origin of a signal of said measured spatial frequency domain as a reference thereof and a signal of said measured spatial frequency domain, by computing a point at which the absolute value of the signal of said measured spatial frequency domain becomes maximal, and using said point as the origin of the signal of said measured spatial frequency domain;

a second step of comparing whether or not said evaluation value obtained at said first step is greater than a predetermined threshold value; and

a third step of computing coefficients for data extrapolation from said product signal obtained at said first step, and extrapolating signals into spatial frequency domains which are located outside of said measured spatial frequency domain by the use of said coefficients only when said evaluation value is greater than said predetermined threshold value at said second step in order to obtain an image ringing of which is corrected.

21. A data processing method in a nuclear magnetic resonance apparatus according to claim 20, wherein said frequency offset is determined in accordance with the formula

22. A data processing method in a nuclear magnetic resonance apparatus according to claim 20, wherein said frequency offset is determined in accordance with the formula

23. A data processing method for use in an inspection apparatus including magnetic field generation means for generating each of a static magnetic field, a gradient magnetic field and a radio frequency (RF) magnetic field, signal detection means for detecting a nuclear magnetic resonance (NMR) signal from an inspection object, a computer for computing detection signals from said signal detection means and output means for outputting the computation result of said computer, for obtaining an image by effecting inverse Fourier transform of a measurement signal row representing data of spatial frequency space, comprising:

a first step of computing an evaluation value representing the magnitude of ringing which occurs because a measured spatial frequency domain is limited in said spatial frequency space, from product signals provided by the product of a frequency offset having an origin of a signal of said measured spatial frequency as a reference thereof and a signal of said measured spatial frequency domain becomes maximal, and using said point as the origin of the signal of said measured spatial frequency domain, by computing a point at which the absolute value of the signal of said measured spatial frequency domain becomes maximal, and using said point as the origin of the signal of said measured spatial frequency domain, computing then a value obtained by integrating said product signals in a negative direction from said origin, and computing dividedly said integration values in said positive and negative directions as evaluation values in said positive and negative directions as evaluation values in said positive and negative directions, respectively;

a second step of comparing whether or not said evaluation values in said positive and negative directions obtained at said first step are greater than predetermined threshold values in said positive and negative directions, respectively; and

a third step of computing coefficients for data extrapolation from said product signals obtained at said first step in said positive and negative directions, respectively, and extrapolating signals into spatial frequency domains which are located outside of said measured spatial frequency domain, only when said evaluation values in said positive and negative directions are greater than said threshold values in said positive and negative directions, respectively, at said second step in order to obtain an image ringing of which is corrected.

24. A data processing method in a nuclear magnetic resonance apparatus according to claim 23, wherein said frequency offset is determined in accordance with the formula

25. A data processing method in a nuclear magnetic resonance apparatus according to claim 23, wherein said frequency offset is determined in accordance with the formula

26. A data processing method for use in an inspection apparatus including magnetic field generation means for generating each of a static magnetic field, a gradient magnetic field and a radio frequency (RF) magnetic field, signal detection means for detecting a nuclear magnetic resonance (NMR) signals from an inspection object, a computer for computing detection signals from said signal detection means and output means for outputting the computation result of said computer, for obtaining an image by effecting inverse Fourier transform of a measurement signal row representing data of spatial frequency space, comprising:

a first step of effecting a first inverse Fourier transform in a first direction for data arrays arranged in a matrix in a measured spatial frequency domain, respectively;

a second step of computing an evaluation value representing the magnitude of ringing in a second direction orthogonal to said first direction for said data arrays subjected to inverse Fourier transform at said first step for each line;

a third step of comparing whether or not data extrapolation should be made in said second direction for each line, on the basis of said evaluation value obtained at said second step; and

a fourth step of extrapolating data into spatial frequency domains which are located outside of said measured spatial frequency domain by the use of coefficients computed from said data arrays when the result of comparison at said third step represents that extrapolation should be made, and effecting a second inverse Fourier transform in said second direction in order to obtain an image ringing of which is corrected.