NMR scanner with motion zeugmatography

• US 4,516,075 A
• Filed: 01/04/1983
• Issued: 05/07/1985
• 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:
  US06/455,596
• Time in Patent Office: 854 Days
• Field of Search: 324/300, 324/307, 324/309, 324/306, 324/312
• US Class Current: 324/309
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• 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 which 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:

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 which 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 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 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 of the magnetic field gradient F; and

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

7. A method for producing a FID signal which contains motion information, 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 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 time period 2T is substantially zero; and

sensing 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; 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.

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.