Method of obtaining internal information of a measuring target from the out-side by the application of a nuclear magnetic resonance phenomenon

• US 3,932,805 A
• Filed: 08/09/1973
• Issued: 01/13/1976
• Est. Priority Date: 02/02/1973
• Status: Expired due to Term

• Current Assignee: Kichizo Niwa
• Original Assignee: Kichizo Niwa
• Inventors: Hotta, Masao, Imai, Masaaki, Tanaka, Kunio, Abe, Zenuemon
• Primary Examiner(s): Smith, Alfred E.
• Assistant Examiner(s): Tokar, Michael J.
• Application Number:
  US05/387,138
• Time in Patent Office: 887 Days
• Field of Search: 324/.5 R, 324/.5 A, 324/.5 B
• US Class Current: 324/309
• CPC Class Codes: G01F 1/716 using electron paramagnetic resonance [EPR] or nuclear magnetic resonance [NMR]
• CPC Class Codes: G01R 33/3808 Magnet assemblies for single-sided MR wherein the magnet assembly is located on one side of a subject only; Magnet assemblies for inside-out MR, e.g. for MR in a borehole or in a blood vessel, or magnet assemblies for fringe-field MR
• CPC Class Codes: G01R 33/445 MR involving a non-standard magnetic field B0, e.g. of low magnitude as in the earth's magnetic field or in nanoTesla spectroscopy, comprising a polarizing magnetic field for pre-polarisation, B0 with a temporal variation of its magnitude or direction such as field cycling of B0 or rotation of the direction of B0, or spatially inhomogeneous B0 like in fringe-field MR or in stray-field imaging
• CPC Class Codes: G01R 33/48 NMR imaging systems

Abstract

This invention relates to a method of obtaining internal information of the body to be investigated (target) by the application to the target of a nuclear magnetic resonance phenomenon, in which the measuring target is placed in a homogeneous magnetic field Ho and a static or scanning magnetic field H_s is superimposed on the homogenous magnetic field Ho within a specified area of the target; from the inside or outside thereof. A high frequency field H₁ of a frequency determined by the static field H_o +ΔH_s in the measuring target area (MT) is applied uniformly to the body thereby obtaining information of a nuclear magnetic substance disposed within the specified area of the body, i.e., the measuring target in accordance with detection of a resonance frequency defined by H_o +ΔH_s. Alternatively, the scanning field ΔH_s may be applied to the body only outside of the target region and a resonance frequency defined by H_o only then is detected as to the target MT. The high frequency field may be constant or pulsed.

Claims

1. A method of obtaining internal information of a specified area of a measuring target by use of a nuclear magnetic resonance phenomenon, including the steps of:

providing a homogeneous magnetic field H₀,

disposing the measuring target in said homogeneous magnetic field,

generating a scanning magnetic field Δ

H_s and applying said scanning magnetic field Δ

H_s in superimposed relationship with said homogeneous magnetic field H₀ to establish a level of field intensity in the specified area to be examined which differs substantially from the level of field intensity of the remaining portion of the measuring target,

providing a high-frequency magnetic field H₁ of a resonance frequency of a nuclear magnetic substance in the measuring target area, said high-frequency being determined by the level of field intensity in the said target area, and applying the high-frequency magnetic field in a direction perpendicular to the field H₀ so as to encompass at least said specified area of the measuring target and regions adjacent said specified area of said measuring target, to produce a signal representative of a nuclear magnetic substance in said specified area, and detecting and processing said signal for obtaining information of said nuclear magnetic substance of said specified area of said measuring target.

2. A method according to claim 1 wherein the step of generating and applying said magnetic field Δ

H_s comprises;

generating and applying a magnetic field Δ

H_s of a field intensity Δ

H_s = 0 to said specified area of said measuring target, and

generating and applying said scanning magnetic field Δ

H_s of a substantially different level in the remainder of the measuring target, including the said regions adjacent the said specified area.

3. A method according to claim 1 wherein the step of generating the scanning magnetic field comprises generating a scanning field Δ

H_s having an intensity value equal to that of said homogeneous magnetic field H₀ but of opposite sense, and

applying said scanning magnetic field Δ

H_s to said specified area to be examined so as to establish a field intensity of the superimposed fields H_o and Δ

H_s in the said specified area which is substantially lower than that of the intensity of the homogeneous magnetic field H₀ as applied to the remainder of the measuring target.

4. A method as recited in claim 1 wherein said homogeneous magnetic field H₀ is reduced to a very low intensity,

said scanning magnetic field Δ

H_s is applied only to the measuring target area to be examined,

whereby the field intensity in the measuring target area is substantially greater than that in the remainder of the measuring target.

5. A method as recited in claim 1 wherein said scanning magnetic field and said measuring target are moved relatively one to the other to apply the scanning magnetic field Δ

H_s selectively to different, specified areas of the measuring target.

6. A method as recited in claim 5 wherein said scanning magnetic field is generated by selective energization of a plurality of coils, including the step of sequentially and selectively changing the ampere turns of the coils to effect movement of said scanning field relatively to said measuring target thereby to selectively apply said scanning field to selected areas of the measuring target.

7. A method according to claim 1 including the step of providing an injection device having scanning field generating means, and manipulating said injection device to introduce said scanning field generating means into selected portions of said measuring target for applying said scanning magnetic field to said selected areas.

8. A method as recited in claim 1 wherein the scanning magnetic field is generated by a plurality of pairs of electrodes disposed exteriorally of the measuring target, including the step of selectively energizing said plurality of pairs of electrodes at selected current intensities for applying said scanning magnetic field to a desired, specified area of the measuring target.

9. A method as recited in claim 1 wherein the generating and applying of said scanning magnetic field is performed by introducing a ferromagnetic powder into said specified area of the measuring target, said homogeneous magnetic field H₀ applied to said measuring target including said specified area thereof, causing said ferromagnetic powder introduced therein to respond thereto and to generate the scanning magnetic field Δ

H_s in said specified area.

10. A method as recited in claim 1 wherein the step of detecting the signal representative of a nuclear magnetic substance in said specified area includes introducing a ferromagnetic substance into the specified area of the measuring target for altering the relaxation time of the said specified area, detecting a signal from the said specified area and detecting a signal from regions of said measuring target outside of said specified area, and said processing step includes processing the signals detected for the said specified area and for the said outside regions of said measuring target and determining the relative relaxation times represented thereby.

11. A method as recited in claim 1 wherein the generation of the homogeneous magnetic field includes the use of a ferromagnetic substance, and wherein the homogeneous magnetic field is generated to have magnetic symmetry, and the scanning magnetic field is generated to have magnetic symmetry, and the said scanning and homogeneous magnetic fields are applied to the measuring target with the symmetries of the respective fields coinciding.

12. A method according to claim 1 wherein said measuring target includes a moving member and including the step of applying a high-frequency magnetic field to said moving member to produce a nuclear magnetic resonance phenomenon in said moving member and wherein said detecting step includes detecting the presence of said nuclear magnetic resonance phenomenon in said moving member at a remote location from where said high-frequency field is applied for measuring said phenomenon.

13. A method according to claim 12 wherein said high-frequency magnetic field is applied in the form of a pulse.

14. A method according to claim 12 including the step of exposing the moving member to a static magnetic field at a position upstream of the measuring point where said homogeneous magnetic field is applied and of greater strength than said homogeneous magnetic field for increasing the signal received during said detecting step and rotating the angle N+90°

by a pulsed field, where N is an integral number, to facilitate the measuring of said phenomenon.

15. A method according to claim 1 wherein said measuring target includes both stationary and moving protons, including the steps of applying a selected high-frequency magnetic field to a region adjacent the specified area including said protons, permitting said moving protons to leave said specified area, and measuring the nuclear magnetic resonance phenomenon of the stationary protons remaining in said specified area to thereby obtain information on said stationary protons.

16. A method as recited in claim 1 further including the step of producing mechanical vibrations in the measuring target area of a given frequency thereby to produce motion of a nuclear magnetic substance in the measuring target area having a frequency correspoding to the frequency of the said produced mechanical vibrations, and the step of detecting includes selectively amplifying the said signal representative of a nuclear magnetic substance in said specified area at the said magnetic vibration frequency thereby to enhance the signal to noise ratio of the detected signal.

17. A method as recited in claim 16 including the step of generating a plurality of ultrasonic beams and applying the said beams so as to cross one another in the said measuring target area, the generating of the ultrasonic beams including controlling the relative phases of the beams thereby to effect corresponding control of the combination of the ultrasonic beams in the said measuring target area and corresponding vibration of protons in the said measurihg target area, the vibrating protons in the magnetic target area in accordance with the homogenous magnetic field H₀ thereby generating the said scanning field Δ

H_s for application thereof to the said measuring target area.

18. A method as recited in claim 1 providing compensation for pseudo-signals derived from regions of said measuring target other than the said specified measuring target area, including

detecting pseudo-signals from regions of said measuring target other than the said specified measuring target area at two positions exteriorly of the said measuring target wherein the pseudo-signals are of the same polarity and the resulting output signals are opposite in polarity, and said processing includes combining the outputs from the detectors so as to cancel the pseudo-signals and improve the signal to noise ratio of the said signal representative of a nuclear magnetic substance in said specified area.

19. A method according to claim 1 wherein said scanning magnetic field generating step is carried out by generating a plurality of magnetic fields and synthesizing said plurality of magnetic fields to provide a scanning magnetic field intensity of zero at a central space in said measuring target area.

20. A method according to claim 19 wherein said measuring target includes a moving member and including the step of applying a pulsed high frequency field to the measuring target except in the measuring target specified area whereby the total rotated angle of the moving member is an integral multiple of 180°

.

21. A method according to claim 1 including the step of applying a high intensity field in the vicinity of the specified area to strongly magnetize that area for raising the signal level of the specified area in the measuring target and detecting the resonance signal determined by a homogeneous magnetic field superimposed on said high intensity magnetic field.

22. A method according to claim 1 including the step of applying a strong magnetic field and an adjacent, homogeneous, low magnetic field, providing a ferromagnetic substance and shielding said strong and low magnetic fields from each other with said ferromagnetic substance.

23. A method according to claim 1 including the step of providing a short-circuit coil and shielding the specified area of said measuring target with said short-circuit coil.

24. A method as recited in claim 1, wherein said scanning magnetic field is applied statically to the said specified area.

25. A method as recited in claim 1 wherein said scanning magnetic field is scanned across the said specified area.

26. A method as recited in claim 2 wherein the step of generating and applying said scanning magnetic field comprises generating a scanning magnetic field of substantially spherical configuration and applying said magnetic field to a corresponding spherical, predetermined volume comprising the specified area of said measuring target.

27. A method as recited in claim 2 wherein the step of generating and applying said scanning magnetic field comprises generating a scanning magnetic field of substantially cylindrical configuration and applying said magnetic field to a corresponding cylindrical, predetermined volume comprising the specified area of said measuring target.

28. A method as recited in claim 2 wherein the intensity of the scanning magnetic field is generated to be substantially zero in the said specified area and wherein the differential synthesis of the scanning magnetic field and the homogeneous magnetic field in the remaining regions of the measuring target establish an intensity of the magnetic field in the said remaining regions of the measuring target such that the intensity of the field in the said specified area is substantially lower than that of the remaining regions of the measuring target.

29. A method as recited in claim 11 wherein the said symmetry is plane symmetry.

30. A method as recited in claim 11 wherein the said symmetry is line symmetry.

31. A method as recited in claim 11 wherein the said symmetry is dot symmetry.

32. The method as recited in claim 16 wherein the said mechanical vibration is produced by respiration of a living body comprising the measuring target.

33. A method as recited in claim 16 wherein the said corresponding vibration of the nuclear magnetic substance comprises rippling of the moving protons therein.

34. A method as recited in claim 1 wherein the step of applying said scanning magnetic field includes applying a strong said scanning magnetic field to the said specified area thereby to raise the signal level of the nuclear magnetic substance in the said specified area of the measuring target and, thereafter, removing the said scanning magnetic field and detecting the resulting signal from the measuring target area as established by the said superimposed homogeneous and high frequency magnetic fields.