Method of internal magnetic resonance imaging and spectroscopic analysis and associated apparatus

• US 5,699,801 A
• Filed: 06/01/1995
• Issued: 12/23/1997
• Est. Priority Date: 06/01/1995
• Status: Expired due to Term

• Current Assignee: Johns Hopkins University
• Original Assignee: Johns Hopkins University
• Inventors: Atalar, Ergin, Bottomley, Paul A., Zerhouni, Elias A.
• Primary Examiner(s): Smith, Ruth S.
• Application Number:
  US08/457,833
• Time in Patent Office: 936 Days
• Field of Search: 128/653.2, 128/653.5, 128/653.1, 324/307, 324/309, 324/318, 324/322
• US Class Current: 600/410
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: G01R 33/34007 Manufacture of RF coils, e.g. using printed circuit board technology; additional hardware for providing mechanical support to the RF coil assembly or to part thereof, e.g. a support for moving the coil assembly relative to the remainder of the MR system
• CPC Class Codes: G01R 33/34084 implantable coils or coils being geometrically adaptable to the sample, e.g. flexible coils or coils comprising mutually movable parts
• CPC Class Codes: G01R 33/341 comprising surface coils
• CPC Class Codes: G01R 33/3657 Decoupling of multiple RF coils wherein the multiple RF coils do not have the same function in MR, e.g. decoupling of a transmission coil from a receive coil
• CPC Class Codes: G01R 33/3678 involving quadrature drive or detection, e.g. a circularly polarized RF magnetic field

Abstract

The invention provides a method for magnetic resonance imaging and spectroscopic analysis of the interior of a specimen which includes positioning the specimen within a main magnetic field, introducing an invasive probe having an elongated receiver coil into or adjacent to the specimen with the coil having at least one pair of elongated electrical conductors, preferably, generally parallel to each other disposed within a dielectric material and having a pair of ends electrically connected to each other. RF pulses are provided to the region of interest to excite magnetic resonance signals, gradient magnetic pulses are applied to the region of interest with the receiver coil receiving magnetic resonance signals and emitting responsive output signals which may be processed by a computer to provide image information for display in a desired manner. The method in a preferred form involves employing a flexible receiver coil which has uniform sensitivity along the coil and may be operated even when the magnetic resonance signal is in an oblique position. Tuning capacitance may be distributed along the length of the coil and/or a Faraday screen provided to minimize dielectric losses between the coil and the surrounding material of the specimen. The method may be used on a wide variety of specimens and in a preferred use is introduced into small blood vessels of a patient to facilitate determination of atherosclerotic plaque. Medical intervention procedures, such as plaque removal, may be employed generally simultaneously with the imaging of the present invention. Corresponding apparatus is provided.

Claims

1. A method of internal magnetic resonance analysis of a specimen comprising

positioning said specimen within a main magnetic field,

introducing an invasive probe having an elongated receiver coil into said specimen,

employing as said receiver coil a resiliently flexible coil having at least one pair of elongated electrical conductors disposed within a resiliently flexible dielectric material and having a pair of ends electrically connected to each other,

maintaining the spacing between said pair of elongated electrical conductors substantially uniform throughout said analysis,

imposing said main magnetic field on region of interest of said specimen,

applying RF pulses to said region of interest to excite magnetic resonance signals within said specimen,

applying gradient magnetic pulses to said region of interest to spatially encode the magnetic resonance signals,

said receiver coil receiving said magnetic resonance signals and emitting responsive output signals,

processing means for receiving and processing said output signals and converting them into MR information, and

employing display means for receiving MR information from said processing means and displaying the same as an image or as chemical shift spectra.

2. The method of claim 1 including

employing in said coil said conductors which are generally parallel to each other.

3. The method of claim 2 including

including in said receiver output signals spatially localized chemical shift information,

employing said processing means to convert said chemical shift information into chemical shift spectra, and

employing said display means to receive and display said chemical shift spectra.

4. The method of claim 3 including

employing said method in one-dimensional chemical shift imaging, wherein said chemical shift information is spatially resolved in a direction substantially along the length of said receiver coil at the region of interest in said specimen.

5. The method of claim 2 including

employing said processing means to convert said receiver coil output signals into image information, and

employing said display means to receive and display said image information.

6. The method of claim 2 including

employing as said receiver coil a coil having a conductor length measured along the portion of said conductor thereof disposed within said dielectric material of about 2 cm to 50 cm.

7. The method of claim 6 including

employing as said coil a coil having a length of about 5 cm to 20 cm.

8. The method of claim 7 including

employing as said coil a coil having a maximum width of about 0.5 mm to 15 mm.

9. The method of claim 6 including

employing as said coil a coil having a maximum width of about 0.5 mm to 2 cm.

10. The method of claim 6 including

employing as said coil a coil having substantially uniform sensitivity along the coil.

11. The method of claim 2 including

delivering said receiver coil within said probe which is a catheter, into a blood vessel.

12. The method of claim 11 including

inserting said coil containing catheter within veins to image and acquire MR chemical shift information about atherosclerotic plaques.

13. The method of claim 12 including

employing said method generally simultaneous with plaque removal from said blood vessel.

14. The method of claim 12 including

employing as said coil a coil which remains sensitive to magnetic resonance signals even at oblique positions.

15. The method of claim 14 including

said coil having the length measured along one leg thereof within said dielectric material of about 2 cm to 50 cm, and

a maximum width of about 0.5 mm to 2 cm.

16. The method of claim 2 including

employing as a said receiver coil a coil having two said pairs of electrical conductors embedded in a dielectric material with conductors within said pair being electrically connected to each other.

17. The method of claim 2 including

employing a decoupling circuit disposed intermediate said receiver coil and said processing means to resist current induction during said RF pulses.

18. The method of claim 2 including

employing a Faraday shield around said receiver coil to resist undesired dielectric losses.

19. The method of claim 18 including

employing as said Faraday shield a plurality of electrically conductive ting-like elements secured to the dielectric material of said coil in relatively axially spaced position from adjacent said ting-like elements.

20. The method of claim 18 including

employing as said Faraday shield a plurality of elongated electrically conductive elements secured to said dielectric material.

21. The method of claim 2 including

employing said coil as an RF pulse transmitting source in addition to said employment as a receiver coil.

22. The method of claim 2 including

securing said receiver coil to said invasive probe, wherein said invasive probe is an endoscope.

23. The method of claim 2 including

securing said receiver coil to the exterior of said invasive probe, wherein said invasive probe is a magnetic resonance compatible biopsy needle.

24. The method of claim 2 including

employing said method in vitro on a specimen which has been removed from a patient.

25. The method of claim 2 including

employing said method in vivo on a patient.

26. The method of claim 25 including

employing said process on a human being.

27. The method of claim 26 including

employing said method in a natural opening in said human being.

28. The method of claim 2 including

employing a tuning/matching circuit electrically interposed between said receiver coil and said processing means to enhance RF power transfer and MR signal-to-noise ratio from said receiver coil, and

performing said analysis without adjusting said tuning/matching circuit immediately prior to probe introduction into said specimen or during the period said receiver coil is in said specimen.

29. The method of claim 28 including

employing as said tuning/matching circuit a plurality of capacitors of fixed capacitance.

30. The method of claim 2 including

employing a plurality of capacitors relatively spaced along said receiver coil and secured to a flexible substrate thereof.

31. The method of claim 30 including

electrically connecting said capacitors to a common capacitance rail.

32. The method of claim 30 including

tuning said receiver coil by altering the length thereof.

33. The method of claim 30 including

establishing said plurality of capacitors by providing a plurality of relatively spaced electrically conductive elements each of which cooperate with another of said elements to function as a capacitor.

34. The method of claim 30 including

creating said plurality of capacitors by etching an electrical conductor which was previously secured to a dielectric substrate.

35. The method of claim 34 including

employing as said dielectric substrate a flexible material.

36. The method of claim 30 including

creating said plurality of capacitors by depositing electrically conductive material on a flexible dielectric material.

37. The method of claim 2 including

employing said coil in multislice imaging of said specimen without requiring movement of said receiver coil.

38. The method of claim 2 including

employing computer means as said processing means.

39. The method of claim 1 including

said electrical conductors in said coil being helically intertwined with each other, whereby induction of undesired eddy currents is resisted.

40. The method of claim 1 including

employing a patient as said specimen, and

performing generally simultaneously with said imaging a medical procedure on said patient.

41. The method of claim 1 including

locating the coil position with respect to said main magnetic field by said processing means,

calculating by said computer means the sensitivity map of said coil, and

employing said sensitivity map to enhance the display of the acquired images.

42. Magnetic resonance specimen analysis apparatus comprising

magnetic field generating means for establishing a main magnetic field on said specimen,

magnetic field gradient generating means for establishing gradients in said main magnetic field,

RF signal generating means for emitting pulsed RF signals to at least portions of said specimen disposed within said main magnetic field,

an elongated receiver coil having at least a pair of elongated electrical conductors disposed within a dielectric material and having a pair of ends electrically connected to each other and having means for receiving signals emitted from said specimen responsive to said RF pulses and emitting responsive output signals,

processing means for receiving and processing said output signals from said receiver coil and creating MR information related thereto,

visual display means for displaying said MR information received from said processing means as an image or as chemical shift spectra, and

probe means for positioning said receiver coil with respect to said specimen for insertion of said receiver coil into said specimen.

43. The magnetic resonance specimen imaging apparatus of claim 42 including

said pair of conductors disposed generally parallel to each other.

44. The apparatus of claim 43 including

said processing means having means for converting said output signals into spatially localized chemical shift spectra, and

said visual display means having means for displaying said spectra.

45. The apparatus of claim 44 including

said magnetic field gradient generating means has means for generating a magnetic field gradient substantially parallel to said receiver coil over a region of interest of said specimen in order to generate one-dimensional resolved chemical shift spectra that are spatially resolved substantially along the direction of the receiver coil in a region of interest in said specimen.

46. The apparatus of claim 44 including

said receiver coil having a conductor length measured along the portion of said conductor disposed within said dielectric material of about 2 cm to 50 cm.

47. The apparatus of claim 46 including

said receiver coil having a length of about 5 cm to 20 cm.

48. The apparatus of claim 46 including

said receiver coil having a maximum width of about 0.5 mm to 2 cm.

49. The apparatus of claim 44 including

said receiver coil being secured within catheter means,

said catheter means having an external diameter structured to be received within the blood vessel of a patient, and

said processing means having means for imaging and spectroscopically analyzing said output signals.

50. The apparatus of claim 49 including

said receiver coil having a length which facilitates multislice imaging without moving said coil.

51. The apparatus of claim 44 including

said receiver coil being flexible, whereby said receiver coil may assume a tortuous path upon insertion into said specimen.

52. The apparatus of claim 44 including

said receiver coil being structured to remain sensitive to magnetic resonance signals even when disposed at oblique angles with respect to the main magnetic field.

53. The apparatus of claim 52 including

said receiver coil having substantially uniform sensitivity along the length of said receiver coil.

54. The apparatus of claim 44 including

said receiver coil having two said pairs of electrical conductors with conductors within each of said pairs being electrically connected to each other.

55. The apparatus of claim 54 including

said coil having the length measured along the portion of one conductor thereof disposed within said dielectric material of about 2 cm to 50 cm, and

a diameter of about 0.5 mm to 2 cm.

56. The apparatus of claim 44 including

decoupling circuit means disposed intermediate said receiver coil means and said processing means to resist undesired current induction during said RF pulses.

57. The apparatus of claim 56 including

a Faraday shield disposed around said receiver coil to resist undesired dielectric losses.

58. The apparatus of claim 57 including

said Faraday shield including a plurality of electrically conductive ring-like elements secured to the dielectric material of said receiver coil in relatively axially spaced position from each other.

59. The apparatus of claim 57 including

said Faraday shield having a plurality of elongated conductive elements secured to said dielectric material.

60. The apparatus of claim 44 including

said receiver coil means having means to function as an RF pulse transmitting source to excite MR signals.

61. The apparatus of claim 44 including

said probe being an endoscope, and

said receiver coil being secured to the exterior thereof.

62. The apparatus of claim 44 including

said probe being a magnetic resonance compatible biopsy needle, and

said receiver coil being secured to the exterior of said biopsy needle.

63. The apparatus of claim 44 including

said probe being structured to be received within a naturally occurring opening in a human being.

64. The apparatus of claim 44 including

a tuning/matching circuit electrically interposed between said receiver coil and said processing means for enhancing RF power transfer from said receiver coil.

65. The apparatus of claim 64 including

said tuning/matching circuit having capacitor means electrically connected to said receiving coil to enhance the MR signal-to-noise ratio.

66. The apparatus of claim 65 including

said tuning/matching circuit having a plurality of capacitors.

67. The apparatus of claim 44 including

said receiver coil having a plurality of capacitors relatively spaced along said coil and secured to a flexible substrate, whereby the presence of said capacitors will not preclude flexing of said receiver coil.

68. The magnetic apparatus of claim 67 including

said capacitors being electrically connected to a common capacitance rail.

69. The apparatus of claim 67 including

said coil being tunable by adjusting the length thereof.

70. The apparatus of claim 67 including

said coil having as said plurality of capacitors a plurality of relatively spaced electrically conductive elements each of which cooperate with another of said elements to function as a capacitor.

71. The apparatus of claim 67 including

said capacitors having a plurality of electrically conductive elements secured to a dielectric said substrate.

72. The apparatus of claim 71 including

said electrically conductive elements having etched edges.

73. The apparatus of claim 67 including

said plurality of spaced capacitors having a plurality of axially spaced ring shaped capacitors.

74. The apparatus of claim 42 including

said electrical conductors in said receiver coil means being helically intertwined with each other, whereby said MR response signals may be enhanced.

75. The apparatus of claim 42 including

said processing means having means for locating the receiver coil position with respect to said receiver main magnetic field,

calculating the sensitivity map of said coil, and

means for employing said sensitivity map to enhance the display of acquired images.

76. A magnetic resonance coil assembly comprising

a resiliently flexible elongated receiver coil for internal magnetic resonance analysis of a region of interest of a specimen by insertion of the receiver coil into the specimen to receive magnetic energy emitted by nuclei disposed within a specimen which is positioned within a main magnetic field responsive to bursts of radio frequency energy and gradient magnetic pulses which are both applied to the specimen and emitting responsive signals, and

said receiver coil having at least one pair of elongated electrically connected conductors disposed within a flexible dielectric material and having means for receiving signals emitted from a specimen and emitting responsive output signals.

77. The coil assembly of claim 76 including

said coil having a plurality of capacitors spaced along said coil and secured to a flexible substrate thereof.

78. The coil assembly of claim 77 including said coil being tunable by adjusting the length thereof.

79. The coil assembly of claim 77 including

said coil having as said plurality of capacitors a plurality of relatively spaced electrically conductive elements each of which cooperate with another of said elements to function as a capacitor.

80. The coil assembly of claim 77 including

said capacitors having a plurality of electrically conductive elements secured to a dielectric substrate.

81. The coil assembly of claim 80 including

said electrically conductive elements having etched edges.

82. The coil assembly of claim 77 including

said plurality of spaced capacitors having a plurality of axially spaced ring shaped capacitors.

83. The coil assembly of claim 77 including

said coil having a length disposed within said dielectric material of about 2 cm to 50 cm, and

a maximum width of about 0.5 to 2 cm.

84. The coil assembly of claim 77 including

said coil assembly having a fixed capacitance tuning/matching circuit operatively associated thereof electrically connected to said elongated conductors.

85. The coil assembly of claim 84 including

a decoupling circuit operatively associated with said tuning/matching circuit.