NMR scanner with motion zeugmatography

• US RE32,701 E
• Filed: 04/08/1987
• Issued: 06/21/1988
• Est. Priority Date: 01/04/1983
• Status: Expired due to Term

• Current Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Original Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Inventors: Moran, Paul R.
• Primary Examiner(s): Tokar, Michael J.
• Application Number:
  US07/036,103
• Time in Patent Office: 440 Days
• Field of Search: 324/300, 324/307, 324/309, 324/312, 324/306
• US Class Current: 324/309
• CPC Class Codes: G01R 33/56308 Characterization of motion or flow; Dynamic imaging
• CPC Class Codes: G01R 33/56316 involving phase contrast techniques

Abstract

An NMR zeugmatographic scanner is modified to produce flow images. A motion sensitizing gradient field is applied to the gyromagnetic nuclei after transverse excitation and prior to emission measurement. The motion sensitized free induction signal which results is processed using an inverse Fourier transformation to produce a number of useful images.

Claims

1. In a gyromagnetic resonance instrument .Iadd.for producing an image of an extended subject which contains both stationary gyromagnetic material and moving gyromagnetic material, in .Iaddend.which .Iadd.the instrument .Iaddend.performs a measurement cycle by applying a transverse excitation signal to a gyromagnetic material and to thereby impart a transverse magnetic moment thereto, and which produces a FID signal responsive to emissions by the transversely magnetized gyromagnetic material, the improvement comprising:

.Iadd.means for locating the position of the gyromagnetic material within the extended subject which is producing a FID signal;

.Iaddend.

means for motion sensitizing a FID signal in which a motion sensitizing magnetic field gradient F is applied to the gyromagnetic material for a period of time 2T after its transverse excitation and prior to the production of the FID signal, and wherein the motion sensitizing magnetic field gradient F has alternating polarity with respect to the gyromagnetic material such that its integral over the time period 2T is substantially zero; and

detector means for receiving the FID signal and producing therefrom a signal S₁ (t) which is phase-referenced to the cosine phase of the transverse excitation signal and a signal S₂ (t) which is phase-referenced to the sine phase of the transverse excitation signal.

2. The instrument as recited in claim 1 in which the motion sensitizing magnetic field gradient F is substantially anti-symmetrical with respect to time T during the time period 2T.

3. The instrument as recited in claim 1 .Iadd.in .Iaddend.which .Iadd.the means for locating .Iaddend.includes means for applying a magnetic field gradient G to the gyromagnetic material such that the FID signals which are emitted from a selected location .[.therein.]. .Iadd.in the extended subject .Iaddend.are .[.frequency.]. encoded during each measurement cycle and the motion sensitized FID signals are thereby also position sensitized.

4. The instrument as recited in claim 3 in which the means for generating said field gradients G and F both employ the same set of gradient coils which are positioned around the gyromagnetic material.

5. The instrument as recited in claim 1 which includes:

processor means for performing an inverse Fourier transform on the S₁ (t) and S₂ (t) signals to produce data indicative of motion intensity in the direction of the magnetic field gradient F.

6. The instrument as recited in claim 1 in which the .[.direction and magnitude.]. .Iadd.value .Iaddend.of the motion sensitizing magnetic field gradient F is altered for successive measurement cycles to produce a corresponding set of motion sensitized FID signals, and corresponding sets of S₁ (t) and S₂ (t) signals, and which includes:

processor means for receiving the sets of S₁ (t) and S₂ (t) signals and performing an inverse Fourier transform thereon to produce a corresponding set of output data indicative of motion intensity in the .[.directions.]. .Iadd.direction .Iaddend.of the magnetic field gradient F; and

display means connected to receive the output data and produce an image.

16. The NMR scanner as recited in claim 14 which includes processor means for receiving said image data and being operable to produce a first data file containing data for the production of an image related to the density distribution of the gyromagnetic phenomena, and being operable to produce a second data file containing data for the production of an image related to the density distribution of the gyromagnetic phenomena modulated by the motion of the gyromagnetic material. .Iadd.17. The instrument as recited in claim 1 in which the motion sensitizing magnetic field gradient F is substantially symmetrical with respect to time T during the time period 2T. .Iaddend. .Iadd.18. An NMR scanner, the combination comprising:

means for generating a polarizing magnetic field B₀ within a gyromagnetic material;

means for generating an excitation magnetic field B₁ which produces a transverse magnetic moment in the gyromagnetic material;

means for sensing both the amplitude and phase of a FID signal produced by the gyromagnetic material excited by said excitation magnetic field B₁ ;

means for generating a magnetic field gradient to produce a position phase sensitizing field gradient G which imparts a first phase component in the FID signal that indicates the position of the gyromagnetic material which is producing the FID signal;

means for generating a magnetic field gradient to produce a motion phase sensitizing field gradient F which imparts a second phase component in the FID signal that indicates the motion of the gyromagnetic material which is producing the FID signal; and

processor means for receiving such sensed FID signal and separating the phase component therein indicative of gyromagnetic material position from the phase component therein indicative of gyromagnetic material motion such that accurate images may be reconstructed therefrom. .Iaddend.

7. A method for producing .Iadd.from a gyromagnetic material .Iaddend.a FID signal which contains .[.motion.]. information .Iadd.pertaining to the density of the gyromagnetic material and information pertaining to the acceleration of the gyromagnetic material, which information may be used to reconstruct an image.Iaddend. , the steps comprising:

applying a polarizing magnetic field to the gyromagnetic material;

exciting the gyromagnetic material with a magnetic field B₁ to produce a transverse magnetic moment M₁ therein;

applying a motion sensitizing magnetic field gradient F to the gyromagnetic material for a period .Iadd.of time from 0 to .Iaddend.2T after its transverse excitation, wherein the polarity of the field gradient F alternates with respect to the gyromagnetic material such that the integral of the field gradient F over the period 2T is substantially zero;

.Iadd.and such that the field gradient F is symmetrical about the time T;

.Iaddend.and

sensing .Iadd.both the amplitude and the phase of .Iaddend.the FID signal produced by the transversely excited gyromagnetic material over a period of time after the time .[.period.]. 2T.

8. The method as recited in claim 7 in which a position sensitizing magnetic field gradient G is applied to the gyromagnetic material while the FID signal is being produced.

9. The method as recited in claim 7 which includes:

processing the FID signal by performing an inverse Fourier transform thereon; and

displaying the processed FID signal.

10. An NMR scanner, the combination comprising:

means for generating a polarizing magnetic field B₀ within a gyromagnetic material;

means for generating an excitation magnetic field B₁ which produces a transverse magnetic moment in the gyromagnetic material;

means for sensing a FID signal produced by the gyromagnetic material excited by said excitation magnetic field B₁ ;

means for generating a position magnetic field gradient G in the gyromagnetic material to position sensitize the sensed FID signal and to thereby link the sensed FID signal to a location within the gyromagnetic material;

means for generating a motion magnetic field gradient F in the gyromagnetic material to motion sensitize the sensed FID signal and to thereby link the sensed FID signal to the motion of the gyromagnetic material at said location; and

processor means for receiving sensed FID signals and producing an image which is modulated by the motion of the gyromagnetic material.

11. The NMR scanner as recited in claim 10 which includes control means for cyclically generating a series of said FID signals, said control means including:

means for altering the position magnetic field gradient G during successive cycles to link the series of FID signals with a succession of different locations in the gyromagnetic material.

12. The NMR scanner as recited in claim 11 in which the control means alters the motion sensitizing magnetic field gradient F during successive cycles to link a series of FID signals at a specific location in the gyromagnetic material to a succession of different motion values.

13. The NMR scanner as recited in claim 10 in which the means for generating the motion sensitizing magnetic field gradient F includes control means for producing the field F during each measurement cycle over a period of time 2T with alternating polarity such that the integral of F over the time period 2T is substantially zero.

14. In an NMR scanner which produces images related to the density distribution of a gyromagnetic phenomena is a gyromagnetic material, the improvement therein comprising:

means for motion sensitizing NMR signals produced by the gyromagnetic material, such sensitizing including the application of a magnetic field gradient F of alternating polarity .Iadd.with respect to the gyromagnetic material.Iaddend.; and

means for receiving the motion sensitized NMR signals and producing image data which is related to the density distribution of the gyromagnetic phenomena in the material and which is modulated by the motion of the gyromagnetic material.

15. The NMR scanner as recited in claim 14 which includes processor means for receiving said image data and producing an image which is related to the motion of the gyromagnetic material, but which is substantially independent of the density distribution of the gyromagnetic phenomena.

18. which is employed to reconstruct an image. .Iaddend. .Iadd.25. The NMR scanner as recited in claim 24 in which the motion field gradient F is substantially anti-symmetrical with respect to time T during said time period. .Iaddend. .Iadd.26. The NMR scanner as recited in claim 24 in which the motion field gradient F is substantially symmetrical with respect to time T during said time period. .Iaddend. .Iadd.27. The NMR scanner as recited in claim 24 in which the image reconstructed from said data indicates the density of said gyromagnetic material at the positions indicated by the position sensitized FID signals. .Iaddend. .Iadd.28. In a gyromagnetic resonance instrument for producing an image of an extended subject which contains both stationary gyromagnetic material and moving gyromagnetic material, in which the instrument performs a cycle with a measurement period between the time of initial excitation T_A and the time of FID acquisition T_B by applying a transverse excitation field to the gyromagnetic material to thereby impart a transverse excited magnetization therein, and receiving a FID signal responsive to the transverse excited magnetization, the improvement comprising:

means for applying a magnetic field gradient to the gyromagnetic material during a cycle such that the FID signal which is received is both position and motion sensitized in accordance with the following expression;

space="preserve" listing-type="equation">S(t)=∫

∫

M.sub.1 (r,v)e.sup.2π

iγ

[G·

rt+F·

v(T).spsp.2.sup.] drdv

wherein F is the element of the field gradient which is applied during the measurement period for a time 2T, which has alternating polarity with respect to the gyromagnetic material and which has a first integral over the time 2T of zero;

wherein G is the element of the field gradient which is applied during the cycle; and

which has a first integral over the cycle which is not zero;

wherein phase factor r is the average position vector during the time when the G element of the field gradient is actively applied;

wherein phase factor v is the average motion vector during the time when the F element of the field gradient is actively applied; and

wherein M₁ (r,v) is the gyromagnetic material density of a resolvable volume located at r and having the motion v;

detector means for receiving the FID signal S(t) and producing therefrom a signal S₁ (t) which is phase-coherently referenced to the cosine-phase of the transverse excitation field and a signal S₂ (t) which is phase-coherently referenced to the sine-phase of the transverse excitation field; and

processor means for performing an inverse Fourier transform on the complex-pair represented by S₁ (t)+iS₂ (t) to produce p₀ (r) from which an image is reconstructed that indicates the density of the

17. Iadd. 9. The NMR scanner as recited in claim 18 in which the means for generating the motion sensitizing field gradient F includes control means for producing the field F over a period 2T after application of the excitation magnetic field B₁ and the polarity of the field gradient F alternates with respect to the gyromagnetic material such that the integral of the field gradient F over the time period 2T is substantially zero. .Iaddend. .Iadd.20. The NMR scanner as recited in claim 18 which includes control means for cyclically generating a series of said FID signals, said control means including:

means for altering the position field gradient G during successive cycles to produce a series of FID signals indicative of the gyromagnetic material at a succession of different locations. .Iaddend. .Iadd.21. The NMR scanner as recited in claim 20 in which the processor means performs an inverse Fourier transform on the series of sensed FID signals. .Iaddend. .Iadd.22. The NMR scanner as recited in claim 20 in which a plurality of cycles are performed for each value of the position field gradient G and the value of the motion field gradient F is altered during each of said plurality of cycles. .Iaddend. .Iadd.23. The NMR scanner as recited in claim 19 in which the phase component in the FID signal due to motion is a function of the magnitude of the motion field gradient F, the duration of period 2T and the magnitude of the motion in the direction of the field gradient F, and in which the phase component in the FID signal due to position is a function of the integral of the position field gradient G over the time period between generation of the excitation magnetic field B₁ and the specific sampling time during the sensing of the FID signal. .Iaddend. .Iadd.24. An NMR scanner for producing an image, the combination comprising;

means for generating a polarizing magnetic field B₀ within a gyromagnetic material;

means for applying an excitation magnetic field B₁ to the gyromagnetic material which produces a transverse magnetic moment in the gyromagnetic material;

means for sensing both the amplitude and phase of a FID signal produced by the gyromagnetic material excited by said excitation magnetic field B₁ ;

means for generating a position field gradient G which position sensitizes the FID signal to indicate the position of the gyromagnetic material which is producing the FID signal;

means for generating a motion field gradient F which is applied to the gyromagnetic material for a period of time from zero to 2T after the application of the excitation magnetic field B₁ and prior to the production of the FID signal, and wherein the motion field gradient F alternates in polarity with respect to the gyromagnetic material at least twice during said time period and the integral of the motion field gradient F over said time period is substantially zero; and

processor means for receiving the sensed FID signal and producing data

19. gyromagnetic material. .Iaddend. .Iadd.29. The gyromagnetic resonance instrument as recited in claim 28 in which said processor means also produces data p₀ (r,v) from which an image is reconstructed that indicates the density of the gyromagnetic material, modulated by the resolvable volume average value of motion in the direction of the magnetic field gradient producing the F element. .Iaddend. .Iadd.30. The gyromagnetic resonance instrument as recited in claim 28 in which the F element of the field gradient alternates in polarity a plurality of times during the period 2T. .Iaddend.