Method of magnetic resonance imaging and spectroscopic analysis and associated apparatus employing a loopless antenna

• US 5,928,145 A
• Filed: 04/25/1996
• Issued: 07/27/1999
• Est. Priority Date: 04/25/1996
• Status: Expired due to Term

• Current Assignee: Johns Hopkins University
• Original Assignee: Johns Hopkins University
• Inventors: Ocali, Ogan, Atalar, Ergin
• Primary Examiner(s): Smith, Ruth S.
• Application Number:
  US08/638,934
• Time in Patent Office: 1,188 Days
• Field of Search: 128/653.2, 128/653.5, 324/307, 324/309, 324/318, 324/322, 600/410, 600/411, 600/423
• US Class Current: 600/410
• CPC Class Codes: A61B 10/0275 with sample notch, e.g. on the side of inner stylet
• CPC Class Codes: A61B 2090/374 NMR or MRI
• 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

Abstract

The invention provides a method for magnetic resonance imaging and spectroscopic analysis of a specimen which includes positioning the specimen within a main magnetic field and introducing an antenna having a loopless antenna portion in close proximity to the specimen. Radio frequency 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 antenna receiving magnetic resonance signals and emitting responsive output signals. A processor processes the responsive output signals to provide image information for display in a desired manner. The method in a preferred form involves employing a flexible antenna. The method in another preferred form involves employing an impedance matching circuit electrically interposed between the loopless antenna and the processor to enhance radio frequency power transfer and magnetic resonance signal-to-noise ratio from the loopless antenna to the processor. 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 and magnetic resonance antenna assembly are provided.

Claims

1. A method of magnetic resonance analysis of a specimen, said method comprising

positioning said specimen within a main magnetic field,

introducing a loopless antenna in close proximity to said specimen,

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

applying radio frequency 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 said magnetic resonance signals,

employing a coaxial cable with an outer shield and an inner conductor,

employing a portion of said outer shield and a portion of said inner conductor as an antenna portion of said loopless antenna for receiving said magnetic resonance signals and employing another portion of said coaxial cable for emitting responsive output signals,

employing processing means for receiving and processing said responsive output signals and converting them into magnetic resonance information, and

employing display means for receiving said magnetic resonance 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 a dipole antenna portion of said loopless antenna for receiving said magnetic resonance signals, and

employing said another portion of said coaxial cable as a connection portion for emitting said responsive output signals.

3. The method of claim 2 including

employing said antenna portion having a length of about 3 cm to about 20 cm, and having a maximum width of about 0.3 mm to about 1.0 cm.

4. The method of claim 1 including

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

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

5. The method of claim 1 including

including in said responsive 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.

6. The method of claim 1 including

employing an impedance matching circuit electrically interposed between said loopless antenna and said processing means to enhance radio frequency power transfer and magnetic resonance signal-to-noise ratio from said loopless antenna to said processing means.

7. The method of claim 6 including

employing said coaxial cable as a first coaxial cable,

employing a second coaxial cable electrically interposed between said processing means and said impedance matching circuit, and

said impedance matching circuit matching the impedance of said loopless antenna to the impedance of said second coaxial cable.

8. The method of claim 7 including

employing said coaxial cable with an inner conductor and an outer shield, and

employing a matching capacitor in said impedance matching circuit electrically interposed between said inner conductor and said outer shield.

9. The method of claim 8 including

employing diode means electrically interposed between said impedance matching circuit and said processing means, and

employing a blocking capacitor in said impedance matching circuit electrically interposed between said diode means and said loopless antenna.

10. The method of claim 9 including

employing said blocking capacitor electrically interposed between said diode means and said matching capacitor.

11. The method of claim 1 including

employing said responsive output signals as first responsive output signals,

employing at least one receiver coil with said loopless antenna,

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

employing said processing means for receiving and processing said first and second responsive output signals and combining them into said magnetic resonance information.

12. The method of claim 1 including

employing said antenna portion with a maximum width of about 0.3 mm to about 1.0 cm.

13. The method of claim 1 including

employing said loopless antenna as an invasive probe, and

delivering said invasive probe into a blood vessel of a patient.

14. The method of claim 13 including

inserting said invasive probe within blood vessels to acquire magnetic resonance image information thereof.

15. The method of claim 13 including

inserting said invasive probe within blood vessels to acquire magnetic resonance chemical shift spectra or magnetic resonance image information thereof.

16. The method of claim 13 including

employing said method generally simultaneous with an interventional procedure on the patient.

17. The method of claim 1 including

employing said loopless antenna in vivo in a patient.

18. The method of claim 17 including

employing said loopless antenna in a human being.

19. The method of claim 1 including

employing said loopless antenna as a magnetic resonance biopsy needle.

20. The method of claim 1 including

employing a patient as said specimen, and

performing generally simultaneously with said magnetic resonance analysis a medical procedure on said patient.

21. The method of claim 1 including

employing said loopless antenna in multislice imaging of said specimen without requiring movement of said loopless antenna.

22. The method of claim 1 including

employing computer means as said processing means.

23. The method of claim 1 including

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

24. The method of claim 1 including

employing said method substantially simultaneously with surgical procedures on a patient.

25. The method of claim 1 including

employing said loopless antenna as a radio frequency pulse transmitting source in addition to employment as a receiver antenna.

26. The method of claim 1 including

employing said loopless antenna as an invasive probe, and

introducing said invasive probe into said specimen to conduct internal magnetic resonance analysis thereof.

27. The method of claim 1 including

employing said loopless antenna as an invasive probe, and

introducing said invasive probe into said specimen to conduct internal magnetic resonance analysis thereof.

28. The method of claim 1 including

electrically connecting a magnetic resonance biopsy needle to said portion of said inner conductor.

29. The method of claim 1 including

said antenna portion and said coaxial cable having a combined length of up to about 2 m.

30. A method of magnetic resonance analysis of a specimen, said method comprising

positioning said specimen within a main magnetic field,

introducing an antenna in close proximity to said specimen,

employing as said antenna a loopless antenna,

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

applying radio frequency 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 said magnetic resonance signals,

said antenna receiving said magnetic resonance signals and emitting responsive output signals,

employing processing means for receiving and processing said responsive output signals and converting them into magnetic resonance information,

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

employing said antenna as a magnetic resonance biopsy needle,

employing a coaxial cable with said antenna, with said coaxial cable having an outer shield and an inner conductor, and

employing said inner conductor as said biopsy needle.

31. A method of magnetic resonance analysis of a specimen, said method comprising

positioning said specimen within a main magnetic field,

introducing an antenna in close proximity to said specimen,

employing as said antenna a loopless antenna,

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

applying radio frequency 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 said magnetic resonance signals,

said antenna receiving said magnetic resonance signals and emitting responsive output signals,

employing processing means for receiving and processing said responsive output signals and converting them into magnetic resonance information,

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

employing a dipole antenna portion of said loopless antenna for receiving said magnetic resonance signals,

employing a connection portion of said loopless antenna for emitting said responsive output signals,

employing said antenna as an invasive probe,

introducing said invasive probe into said specimen to conduct internal magnetic resonance analysis thereof,

employing a coaxial cable with an outer shield and an inner conductor, and

employing a portion of said outer shield and a portion of said inner conductor as said dipole antenna portion of said loopless antenna for receiving said magnetic resonance signals.

32. The method of claim 31 including

employing said portion of said outer shield operatively associated with a first pole of said loopless antenna, and

employing said portion of said inner conductor operatively associated with a second pole of said loopless antenna.

33. The method of claim 32 including

employing balancing transformer means operatively associated with said portion of said outer shield.

34. The method of claim 33 including

delivering said antenna into a blood vessel, and

employing an insulator in said balancing transformer means with a dielectric constant about equal to a dielectric constant of blood in said blood vessel.

35. A method of magnetic resonance analysis of a specimen, said method comprising

positioning said specimen within a main magnetic field,

introducing an antenna in close proximity to said specimen,

employing as said antenna a loopless antenna,

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

applying radio frequency 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 said magnetic resonance signals,

said antenna receiving said magnetic resonance signals and emitting responsive output signals,

employing processing means for receiving and processing said responsive output signals and converting them into magnetic resonance information,

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

employing a dipole antenna portion of said loopless antenna for receiving said magnetic resonance signals,

employing a connection portion of said loopless antenna for emitting said responsive output signals,

employing a coaxial cable as said connection portion of said loopless antenna for emitting said responsive output signals,

employing said coaxial cable with an outer shield and an inner conductor,

employing said outer shield as a first pole of said loopless antenna, and

employing said inner conductor as a second pole of said loopless antenna.

36. The method of claim 35 including

employing said antenna with a length of up to about 2 m.

37. Magnetic resonance analysis apparatus for a specimen, said 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,

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

a loopless antenna assembly comprising

a coaxial cable having an outer shield and an inner conductor, with a portion of said outer shield and a portion of said inner conductor of said coaxial cable forming an antenna portion of said loopless antenna assembly at least for receiving signals emitted from said specimen responsive to said pulsed radio frequency signals, and with another portion of said coaxial cable for emitting responsive output signals,

processing means for receiving and processing said responsive output signals from said loopless antenna assembly and creating magnetic resonance information related thereto, and

display means for displaying said magnetic resonance information received from said processing means as an image or as chemical shift spectra.

38. The apparatus of claim 37 including

said loopless antenna is a dipole antenna.

39. The apparatus of claim 38 including

said dipole antenna is inserted in said specimen, and

said magnetic field gradient generating means generating a magnetic field gradient over a region of interest of said specimen in order to generate spatially resolved chemical shift spectra in the region of interest in said specimen.

40. The apparatus of claim 37 including

said loopless antenna is a dipole antenna having an external diameter structured to be received within a blood vessel of a patient,

said processing means converting said responsive output signals into magnetic resonance spectroscopic information or magnetic resonance image information, and

said display means displaying said magnetic resonance spectroscopic information or said magnetic resonance image information in order to image said blood vessel.

41. The apparatus of claim 37 including

said antenna portion is flexible, whereby the same may assume a tortuous path upon insertion into said specimen.

42. The apparatus of claim 37 including

said loopless antenna is a dipole antenna,

said antenna portion is a dipole antenna portion,

said dipole antenna portion having a length of about 3 cm to about 20 cm, and

said dipole antenna portion having a maximum width of about 0.3 mm to about 1.0 cm.

43. The apparatus of claim 37 including

said antenna portion is structured to be received within a naturally occurring passageway in a human being.

44. The apparatus of claim 37 including

said antenna portion is structured as an invasive probe and is introduced into said specimen to conduct internal magnetic resonance analysis thereof.

45. The apparatus of claim 37 including

said loopless antenna is a dipole antenna,

said antenna portion is a dipole antenna portion for receiving said signals emitted from said specimen responsive to said pulsed radio frequency signals, and

said coaxial cable having a connection portion for emitting said responsive output signals.

46. The apparatus of claim 37 including

said processing means including impedance matching means electrically interposed between said coaxial cable and said processing means for enhancing radio frequency power transfer and magnetic resonance signal-to-noise ratio from said antenna portion to said processing means.

47. The apparatus of claim 46 including

said coaxial cable means electrically interposed between said loopless antenna and said impedance matching means.

48. The apparatus of claim 46 including

said loopless antenna and said coaxial cable means each having an external diameter structured to be received within at least one of a pancreatic duct, a bile duct, a urethra, and a ureter of a patient.

49. The apparatus of claim 46 including

said specimen is a blood vessel of a patient,

said antenna portion is positionable within said blood vessel, and

said impedance matching means is positionable external to said blood vessel.

50. The apparatus of claim 49 including

said antenna portion having a length of about 3 cm to about 20 cm, and

a maximum width of about 0.3 mm to about 1.0 cm.

51. The apparatus of claim 37 including

said antenna portion having a length which facilitates multislice imaging without moving said antenna portion.

52. The apparatus of claim 37 including

said radio frequency signal generating means also having means for sourcing radio frequency pulses to said antenna portion, and

said antenna portion also for transmitting said radio frequency pulses in order to excite magnetic resonance signals.

53. The apparatus of claim 37 including

said loopless antenna is a dipole antenna structured as a biopsy needle.

54. The apparatus of claim 37 including

said loopless antenna is a dipole antenna, and

said dipole antenna having a length of about 3 cm to about 20 cm.

55. The apparatus of claim 37 including

said outer shield having an outer surface, an inner surface, and balancing transformer means for impeding current flow on said outer surface without significantly impeding current flow on said inner surface.

56. The apparatus of claim 37 including

said coaxial cable having a dielectric portion which electrically insulates said inner conductor from said outer shield, and

a biopsy needle is electrically connected to said portion of said inner conductor and is electrically insulated from said outer shield by the dielectric portion.

57. Magnetic resonance analysis apparatus for a specimen, said 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,

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

antenna means having a loopless antenna at least for receiving signals emitted from said specimen responsive to said pulsed radio frequency signals and emitting responsive output signals,

said loopless antenna is a dipole antenna having a first pole and a second pole,

processing means for receiving and processing said responsive output signals from said antenna means and creating magnetic resonance information related thereto,

display means for displaying said magnetic resonance information received from said processing means as an image or as chemical shift spectra,

said antenna means including impedance matching means electrically interposed between said loopless antenna and said processing means for enhancing radio frequency power transfer and magnetic resonance signal-to-noise ratio from said loopless antenna to said processing means, and said antenna means also including coaxial cable means for emitting said responsive output signals, with said coaxial cable means electrically interposed between said loopless antenna and said impedance matching means,

said coaxial cable means having an outer shield and an inner conductor,

said outer shield having a portion thereof operatively associated with said first pole of said dipole antenna, and

said inner conductor having a portion thereof operatively associated with said second pole of said dipole antenna.

58. The apparatus of claim 57 including

said portion of said outer shield operatively associated with said first pole having an inner primary shield and an outer secondary shield, with each of said inner primary shield and said outer secondary shield being coaxial with said inner conductor, and

said coaxial cable means also having an insulator between said inner primary shield and said outer secondary shield,

with said insulator, said inner primary shield and said outer secondary shield forming a balancing transformer means operatively associated with said first pole.

59. The apparatus of claim 58 including

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

said balancing transformer means having an insulator with a dielectric constant about equal to a dielectric constant of blood in said blood vessel.

60. Magnetic resonance analysis apparatus for a specimen, said 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,

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

antenna means having a loopless antenna at least for receiving signals emitted from said specimen responsive to said pulsed radio frequency signals and emitting responsive output signals, said loopless antenna is a dipole antenna having a first pole and a second pole, said antenna means also including coaxial cable means for emitting said responsive output signals, said coaxial cable means having an outer shield, and said outer shield having balancing transformer means operatively associated with said first pole,

processing means for receiving and processing said responsive output signals from said antenna means and creating magnetic resonance information related thereto, and

display means for displaying said magnetic resonance information received from said processing means as an image or as chemical shift spectra.

61. Magnetic resonance analysis apparatus for a specimen, said 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,

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

antenna means having a loopless antenna at least for receiving signals emitted from said specimen responsive to said pulsed radio frequency signals and emitting responsive output signals, said loopless antenna is a dipole antenna having a first pole and a second pole,

processing means for receiving and processing said responsive output signals from said antenna means and creating magnetic resonance information related thereto,

display means for displaying said magnetic resonance information received from said processing means as an image or as chemical shift spectra,

said antenna means including impedance matching means electrically interposed between said loopless antenna and said processing means for enhancing radio frequency power transfer and magnetic resonance signal-to-noise ratio from said loopless antenna to said processing means, and said antenna means also including coaxial cable means for emitting said responsive output signals, with said coaxial cable means electrically interposed between said loopless antenna and said impedance matching means, said coaxial cable means having an outer shield and an inner conductor, with said outer shield as the first pole of said loopless antenna and said inner conductor as the second pole of said loopless antenna.

62. The apparatus of claim 61 including

said dipole antenna and said coaxial cable means having a length of up to about 2 m.

63. A magnetic resonance loopless antenna assembly comprising

a coaxial cable having an outer shield and an inner conductor, with a portion of said outer shield and a portion of said inner conductor forming an antenna portion of said loopless antenna assembly,

said antenna portion at least for receiving magnetic resonance signals emitted from a specimen, with another portion of said coaxial cable for emitting responsive output signals.

64. The loopless antenna assembly of claim 63 including

said antenna portion is resiliently flexible.

65. The loopless antenna assembly of claim 63 including

said antenna portion and said coaxial cable having a combined length of up to about 2 m.

66. The loopless antenna assembly of claim 63 including

said antenna portion has a cylindrical conductor electrically interconnected with said portion of said inner conductor.

67. The loopless antenna assembly of claim 63 including

said portion of said outer shield having an inner primary shield and an outer secondary shield, with each of said inner primary shield and said outer secondary shield being coaxial with said inner conductor, and

said coaxial cable also having an electrical insulator between said inner primary shield and said outer secondary shield,

with said insulator, said inner primary shield and said outer secondary shield forming balancing transformer means.

68. The loopless antenna assembly of claim 67 including

said coaxial cable having an external diameter structured to be received within a blood vessel of a patient, and

said insulator having a dielectric constant about equal to a dielectric constant of blood in said blood vessel.

69. A magnetic resonance antenna assembly comprising

an antenna having loopless antenna means at least for receiving magnetic resonance signals emitted from a specimen and emitting responsive output signals,

said loopless antenna means is a dipole antenna having a first pole and a second pole,

said antenna also having a coaxial cable, with said coaxial cable having an outer shield and an inner conductor for emitting said responsive output signals,

said outer shield having a portion thereof operatively associated with said first pole, and

said inner conductor having a portion thereof operatively associated with said second pole.

70. The antenna assembly of claim 69 including

said portion of said outer shield operatively associated with said first pole having an inner primary shield and an outer secondary shield, with each of said inner primary shield and said outer secondary shield being coaxial with said inner conductor, and

said coaxial cable also having an insulator between said inner primary shield and said outer secondary shield,

with said insulator, said inner primary shield and said outer secondary shield forming a balancing transformer means operatively associated with said first pole.

71. The antenna assembly of claim 70 including

said coaxial cable having an external diameter structured to be received within a blood vessel of a patient, and

said insulator having a dielectric constant about equal to a dielectric constant of blood in said blood vessel.

72. A magnetic resonance antenna assembly comprising

an antenna having loopless antenna means at least for receiving magnetic resonance signals emitted from a specimen and emitting responsive output signals, said loopless antenna means is a dipole antenna having a first pole and a second pole,

said antenna also having a coaxial cable, with said coaxial cable having an outer shield and an inner conductor for emitting said responsive output signals, with said outer shield as the first pole of said loopless antenna means and said inner conductor as the second pole of said loopless antenna means.

73. The antenna assembly of claim 72 including said antenna having a length of up to about 2 m.