Processing

Please wait...

Settings

Settings

Goto Application

1. WO2020139476 - CORRECTING FOR HYSTERESIS IN MAGNETIC RESONANCE IMAGING

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

[ EN ]

CLAIMS

What is claimed is:

1. An apparatus for controlling at least one gradient coil of a magnetic resonance imaging (MRI) system, the apparatus comprising:

at least one computer hardware processor; and

at least one computer-readable storage medium storing processor executable instructions that, when executed by the at least one computer hardware processor, cause the at least one computer hardware processor to perform a method comprising:

receiving information specifying at least one target pulse sequence;

determining a corrected pulse sequence to control the at least one gradient coil based on the at least one target pulse sequence and a hysteresis model of induced magnetization in the MRI system caused by operation of the at least one gradient coil; and

controlling, using the corrected pulse sequence, the at least one gradient coil to generate one or more gradient pulses for imaging a patient.

2. The apparatus of claim 1, wherein the corrected pulse sequence includes a corrected gradient pulse sequence and controlling the at least one gradient coil comprises driving the at least one gradient coil with the corrected gradient pulse sequence such that a strength of a gradient field formed in at least a portion of an imaging region of the MRI system is substantially equal to a target magnetic field strength that the target pulse sequence is designed to achieve.

3. The apparatus of claim 1 or any other preceding claim, wherein determining the corrected pulse sequence is further based on a current state of the hysteresis model.

4. The apparatus of claim 1 or any other preceding claim, wherein the hysteresis model comprises a plurality of weights, a respective plurality of lower magnetic field strength values and a respective plurality of upper magnetic field strength values, wherein each of the plurality of weights is associated with a respective one of the plurality of lower magnetic field strength values and a respective one of the upper magnetic field strength values.

5. The apparatus of claim 4 or any other preceding claim, wherein the hysteresis model comprises a Preisach model.

6. The apparatus of claim 4 or any other preceding claim, wherein each of the plurality of weights is determined using at least one previously-obtained hysteresis measurement obtained with a multi-element probe.

7. The apparatus of claim 1 or any other preceding claim, wherein the MRI system includes a ferromagnetic yoke, and wherein the hysteresis model represents effects of hysteresis induced at least in the ferromagnetic yoke by operation of the at least one gradient coil.

8. The apparatus of claim 1 or any other preceding claim, wherein determining the corrected pulse sequence comprises iteratively determining the corrected pulse sequence.

9. The apparatus of claim 8 or any other preceding claim, wherein iteratively

determining the corrected pulse sequence comprises:

determining an initial corrected pulse sequence based on the target pulse sequence and the hysteresis model; and

determining a final corrected pulse sequence based on the initial corrected pulse sequence and the hysteresis model,

wherein controlling the at least one gradient coil comprises driving the at least one gradient coil with a final gradient pulse sequence of the final pulse sequence such that a strength of a gradient field formed in at least a portion of an imaging region of the MRI system is substantially equal to a target magnetic field strength value.

10. The apparatus of claim 1 or any other preceding claim, wherein determining the corrected pulse sequence comprises adjusting an amplitude of a pulse within a target gradient pulse sequence of the target pulse sequence.

11. The apparatus of claim 10 or any other preceding claim, wherein:

the target pulse sequence comprises a target gradient pulse sequence comprising a plurality of target gradient pulses;

determining the corrected pulse sequence comprises determining a plurality of corrected pulse amplitudes for a plurality of corrected gradient pulses of a corrected gradient pulse sequence; and

determining a first corrected pulse amplitude of a first corrected gradient pulse is based on at least a second corrected pulse amplitude of a second corrected gradient pulse that occurs earlier in the corrected gradient pulse sequence than the first corrected gradient pulse.

12. The apparatus of claim 11 or any other preceding claim, wherein determining the corrected gradient pulse sequence comprises determining an amplitude of every pulse of the corrected pulse sequence by iterating from a beginning gradient pulse of the corrected gradient pulse sequence to a final gradient pulse of the corrected gradient pulse sequence, wherein the amplitude of a particular corrected gradient pulse of the corrected gradient pulse sequence is based on at least one previous corrected gradient pulse of the corrected gradient pulse sequence.

13. The apparatus of claim 1 or any other preceding claim, wherein determining the corrected pulse sequence comprises determining a corrected transmit radio frequency (RF) pulse sequence used to control a RF transmit coil and/or a corrected receive RF pulse sequence used to control a RF receive coil.

14. The apparatus of claim 13 or any other preceding claim, wherein:

determining a corrected transmit RF pulse sequence comprises adjusting a center frequency or phase of a transmit RF pulse of the corrected transmit RF pulse sequence; and determining a corrected receive RF pulse sequence comprises adjusting a center frequency or phase of a receive RF pulse of the corrected receive RF pulse sequence.

15. The apparatus of claim 1 or any other preceding claim, further comprising the MRI system.

16. The apparatus of claim 15 or any other preceding claim, further comprising the at least one gradient coil.

17. The apparatus of claim 15 or any other preceding claim, wherein the MRI system comprises a ferromagnetic yoke.

18. The apparatus of claim 17 or any other preceding claim, wherein the ferromagnetic yoke comprises:

a first plate comprising ferromagnetic material;

a second plate comprising ferromagnetic material; and

a frame comprising ferromagnetic material coupled to the first plate and the second plate.

19. The apparatus of claim 18 or any other preceding claim, wherein the frame comprising a plurality of supports, each of the plurality of supports comprising ferromagnetic material and spaced apart from an adjacent support by a gap.

20. The apparatus of claim 19 or any other preceding claim, wherein the frame comprises a first arm portion comprising ferromagnetic material coupled to the first plate and a second arm portion comprising ferromagnetic material coupled to the second plate, and wherein the plurality of supports are coupled between the first arm portion and the second arm portion.

21. The apparatus of claim 19 or any other preceding claim, wherein the gap is an air gap.

22. The apparatus of claim 18 or any other preceding claim, wherein the frame is substantially C-shaped.

23. The apparatus of claim 18 or any other preceding claim, wherein the first plate and the second plate are substantially circular.

24. The apparatus of claim 17 or any other preceding claim, wherein the ferromagnetic yoke comprises at least one portion made from low carbon steel, cobalt steel (CoFe) and/or silicon steel.

25. The apparatus of claim 15 or any other preceding claim, wherein the MRI system is a low-field MRI system.

26. The apparatus of claim 25 or any other preceding claim, wherein a Bo magnet field strength of the MRI system is equal to or less than approximately 0.2 T.

27. The apparatus of claim 26 or any other preceding claim, wherein a Bo magnet field strength of the MRI system is equal to or less than approximately 0.1 T and greater than or equal to approximately 50 mT.

28. The apparatus of claim 26 or any other preceding claim, wherein a Bo magnet field strength of the MRI system is equal to or less than approximately 20 mT and greater than or equal to approximately 10 mT.

29. A method of controlling at least one gradient coil of a magnetic resonance imaging (MRI) system, the method comprising, with at least one computer hardware processor:

receiving information specifying at least one target pulse sequence;

determining a corrected pulse sequence to control the at least one gradient coil based on the at least one target pulse sequence and a hysteresis model of induced magnetization in the MRI system caused by operation of the at least one gradient coil; and

controlling, using the corrected pulse sequence, the at least one gradient coil to generate one or more gradient pulses for imaging a patient.

30. The method of claim 29 or any other preceding claim, wherein the corrected pulse sequence includes a corrected gradient pulse sequence and controlling the at least one gradient coil comprises driving the at least one gradient coil with the corrected gradient pulse sequence such that a strength of a gradient field formed in at least a portion of an imaging region of the MRI system is substantially equal to a target magnetic field strength that the target pulse sequence is designed to achieve.

31. The method of claim 29 or any other preceding claim, wherein determining the corrected pulse sequence is further based on a current state of the hysteresis model.

32. The method of claim 29 or any other preceding claim, wherein the hysteresis model comprises a plurality of weights, a respective plurality of lower magnetic field strength values and a respective plurality of upper magnetic field strength values, wherein each of the plurality of weights is associated with a respective one of the plurality of lower magnetic field strength values and a respective one of the upper magnetic field strength values.

33. The method of claim 32 or any other preceding claim, wherein the hysteresis model comprises a Preisach model.

34. The method of claim 32 or any other preceding claim, wherein each of the plurality of weights is determined using at least one previously-obtained hysteresis measurement obtained with a multi-element probe.

35. The method of claim 29 or any other preceding claim, wherein the MRI system includes a ferromagnetic yoke, and wherein the hysteresis model represents effects of hysteresis induced at least in the ferromagnetic yoke by operation of the at least one gradient coil.

36. The method of claim 29 or any other preceding claim, wherein determining the corrected pulse sequence comprises iteratively determining the corrected pulse sequence.

37. The method of claim 36 or any other preceding claim, wherein iteratively determining the corrected pulse sequence comprises:

determining an initial corrected pulse sequence based on the target pulse sequence and the hysteresis model; and

determining a final corrected pulse sequence based on the initial corrected pulse sequence and the hysteresis model,

wherein controlling the at least one gradient coil comprises driving the at least one gradient coil with a final gradient pulse sequence of the final pulse sequence such that a strength of a gradient field formed in at least a portion of an imaging region of the MRI system is substantially equal to a target magnetic field strength value.

38. The method of claim 29 or any other preceding claim, wherein determining the corrected pulse sequence comprises adjusting an amplitude of a pulse within a target gradient pulse sequence of the target pulse sequence.

39. The method of claim 38 or any other preceding claim, wherein:

the target pulse sequence comprises a target gradient pulse sequence comprising a plurality of target gradient pulses;

determining the corrected pulse sequence comprises determining a plurality of corrected pulse amplitudes for a plurality of corrected gradient pulses of a corrected gradient pulse sequence; and

determining a first corrected pulse amplitude of a first corrected gradient pulse is based on at least a second corrected pulse amplitude of a second corrected gradient pulse that occurs earlier in the corrected gradient pulse sequence than the first corrected gradient pulse.

40. The method of claim 39 or any other preceding claim, wherein determining the corrected gradient pulse sequence comprises determining an amplitude of every pulse of the corrected pulse sequence by iterating from a beginning gradient pulse of the corrected gradient pulse sequence to a final gradient pulse of the corrected gradient pulse sequence, wherein the amplitude of a particular corrected gradient pulse of the corrected gradient pulse sequence is based on at least one previous corrected gradient pulse of the corrected gradient pulse sequence.

41. The method of claim 29 or any other preceding claim, wherein determining the corrected pulse sequence comprises determining a corrected transmit radio frequency (RF) pulse sequence used to control a RF transmit coil and/or a corrected receive RF pulse sequence used to control a RF receive coil.

42. The method of claim 41 or any other preceding claim, wherein:

determining a corrected transmit RF pulse sequence comprises adjusting a center frequency or phase of a transmit RF pulse of the corrected transmit RF pulse sequence; and determining a corrected receive RF pulse sequence comprises adjusting a center frequency or phase of a receive RF pulse of the corrected receive RF pulse sequence.

43. The method of claim 29 or any other preceding claim, wherein the MRI system comprises a ferromagnetic yoke.

44. The method of claim 43 or any other preceding claim, wherein the ferromagnetic yoke comprises:

a first plate comprising ferromagnetic material;

a second plate comprising ferromagnetic material; and

a frame comprising ferromagnetic material coupled to the first plate and the second plate.

45. The method of claim 44 or any other preceding claim, wherein the frame comprising a plurality of supports, each of the plurality of supports comprising ferromagnetic material and spaced apart from an adjacent support by a gap.

46. The method of claim 45 or any other preceding claim, wherein the frame comprises a first arm portion comprising ferromagnetic material coupled to the first plate and a second arm portion comprising ferromagnetic material coupled to the second plate, and wherein the plurality of supports are coupled between the first arm portion and the second arm portion.

47. The method of claim 45 or any other preceding claim, wherein the gap is an air gap.

48. The method of claim 44 or any other preceding claim, wherein the frame is substantially C-shaped.

49. The method of claim 44 or any other preceding claim, wherein the first plate and the second plate are substantially circular.

50. The method of claim 43 or any other preceding claim, wherein the ferromagnetic yoke comprises at least one portion made from low carbon steel, cobalt steel (CoFe) and/or silicon steel.

51. The method of claim 29 or any other preceding claim, wherein the MRI system is a low-field MRI system.

52. The method of claim 51 or any other preceding claim, wherein a Bo magnet field strength of the MRI system is equal to or less than approximately 0.2 T.

53. The method of claim 52 or any other preceding claim, wherein a Bo magnet field strength of the MRI system is equal to or less than approximately 0.1 T and greater than or equal to approximately 50 mT.

54. The method of claim 51 or any other preceding claim, wherein a Bo magnet field strength of the MRI system is equal to or less than approximately 20 mT and greater than or equal to approximately 10 mT.

55. At least one computer-readable storage medium storing processor executable instructions that, when executed by at least one computer hardware processor, cause the at least one computer hardware processor to perform a method of controlling at least one gradient coil of a magnetic resonance imaging (MRI) system, the method comprising:

receiving information specifying at least one target pulse sequence;

determining a corrected pulse sequence to control the at least one gradient coil based on the at least one target pulse sequence and a hysteresis model of induced magnetization in the MRI system caused by operation of the at least one gradient coil; and

controlling, using the corrected pulse sequence, the at least one gradient coil to generate one or more gradient pulses for imaging a patient.

56. The at least one computer-readable storage medium of claim 1, wherein the corrected pulse sequence includes a corrected gradient pulse sequence and controlling the at least one gradient coil comprises driving the at least one gradient coil with the corrected gradient pulse sequence such that a strength of a gradient field formed in at least a portion of an imaging region of the MRI system is substantially equal to a target magnetic field strength that the target pulse sequence is designed to achieve.

57. The at least one computer-readable storage medium of claim 55 or any other preceding claim, wherein determining the corrected pulse sequence is further based on a current state of the hysteresis model.

58. The at least one computer-readable storage medium of claim 55 or any other preceding claim, wherein the hysteresis model comprises a plurality of weights, a respective plurality of lower magnetic field strength values and a respective plurality of upper magnetic field strength values, wherein each of the plurality of weights is associated with a respective one of the plurality of lower magnetic field strength values and a respective one of the upper magnetic field strength values.

59. The at least one computer-readable storage medium of claim 58 or any other preceding claim, wherein the hysteresis model comprises a Preisach model.

60. The at least one computer-readable storage medium of claim 58 or any other preceding claim, wherein each of the plurality of weights is determined using at least one previously-obtained hysteresis measurement obtained with a multi-element probe.

61. The at least one computer-readable storage medium of claim 55 or any other preceding claim, wherein the MRI system includes a ferromagnetic yoke, and wherein the hysteresis model represents effects of hysteresis induced at least in the ferromagnetic yoke by operation of the at least one gradient coil.

62. The at least one computer-readable storage medium of claim 55 or any other preceding claim, wherein determining the corrected pulse sequence comprises iteratively determining the corrected pulse sequence.

63. The at least one computer-readable storage medium of claim 62 or any other preceding claim, wherein iteratively determining the corrected pulse sequence comprises: determining an initial corrected pulse sequence based on the target pulse sequence and the hysteresis model; and

determining a final corrected pulse sequence based on the initial corrected pulse sequence and the hysteresis model,

wherein controlling the at least one gradient coil comprises driving the at least one gradient coil with a final gradient pulse sequence of the final pulse sequence such that a strength of a gradient field formed in at least a portion of an imaging region of the MRI system is substantially equal to a target magnetic field strength value.

64. The at least one computer-readable storage medium of claim 55 or any other preceding claim, wherein determining the corrected pulse sequence comprises adjusting an amplitude of a pulse within a target gradient pulse sequence of the target pulse sequence.

65. The at least one computer-readable storage medium of claim 64 or any other preceding claim, wherein:

the target pulse sequence comprises a target gradient pulse sequence comprising a plurality of target gradient pulses;

determining the corrected pulse sequence comprises determining a plurality of corrected pulse amplitudes for a plurality of corrected gradient pulses of a corrected gradient pulse sequence; and

determining a first corrected pulse amplitude of a first corrected gradient pulse is based on at least a second corrected pulse amplitude of a second corrected gradient pulse that occurs earlier in the corrected gradient pulse sequence than the first corrected gradient pulse.

66. The at least one computer-readable storage medium of claim 65 or any other preceding claim, wherein determining the corrected gradient pulse sequence comprises determining an amplitude of every pulse of the corrected pulse sequence by iterating from a beginning gradient pulse of the corrected gradient pulse sequence to a final gradient pulse of the corrected gradient pulse sequence, wherein the amplitude of a particular corrected gradient pulse of the corrected gradient pulse sequence is based on at least one previous corrected gradient pulse of the corrected gradient pulse sequence.

67. The at least one computer-readable storage medium of claim 55 or any other preceding claim, wherein determining the corrected pulse sequence comprises determining a corrected transmit radio frequency (RF) pulse sequence used to control a RF transmit coil and/or a corrected receive RF pulse sequence used to control a RF receive coil.

68. The at least one computer-readable storage medium of claim 67 or any other preceding claim, wherein:

determining a corrected transmit RF pulse sequence comprises adjusting a center frequency or phase of a transmit RF pulse of the corrected transmit RF pulse sequence; and determining a corrected receive RF pulse sequence comprises adjusting a center frequency or phase of a receive RF pulse of the corrected receive RF pulse sequence.

69. The at least one computer-readable storage medium of claim 55 or any other preceding claim, wherein the MRI system comprises a ferromagnetic yoke.

70. The at least one computer-readable storage medium of claim 69 or any other preceding claim, wherein the ferromagnetic yoke comprises:

a first plate comprising ferromagnetic material;

a second plate comprising ferromagnetic material; and

a frame comprising ferromagnetic material coupled to the first plate and the second plate.

70. The at least one computer-readable storage medium of claim 69 or any other preceding claim, wherein the frame comprising a plurality of supports, each of the plurality of supports comprising ferromagnetic material and spaced apart from an adjacent support by a gapĀ·

71. The at least one computer-readable storage medium of claim 70 or any other preceding claim, wherein the frame comprises a first arm portion comprising ferromagnetic material coupled to the first plate and a second arm portion comprising ferromagnetic material coupled to the second plate, and wherein the plurality of supports are coupled between the first arm portion and the second arm portion.

72. The at least one computer-readable storage medium of claim 70 or any other preceding claim, wherein the gap is an air gap.

73. The at least one computer-readable storage medium of claim 70 or any other preceding claim, wherein the frame is substantially C-shaped.

74. The at least one computer-readable storage medium of claim 69 or any other preceding claim, wherein the first plate and the second plate are substantially circular.

75. The at least one computer-readable storage medium of claim 69 or any other preceding claim, wherein the ferromagnetic yoke comprises at least one portion made from low carbon steel, cobalt steel (CoFe) and/or silicon steel.

76. The at least one computer-readable storage medium of claim 55 or any other preceding claim, wherein the MRI system is a low-field MRI system.

77. The at least one computer-readable storage medium of claim 76 or any other preceding claim, wherein a Bo magnet field strength of the MRI system is equal to or less than approximately 0.2 T.

78. The at least one computer-readable storage medium of claim 77 or any other preceding claim, wherein a Bo magnet field strength of the MRI system is equal to or less than approximately 0.1 T and greater than or equal to approximately 50 mT.

79. The at least one computer-readable storage medium of claim 77 or any other preceding claim, wherein a Bo magnet field strength of the MRI system is equal to or less than approximately 20 mT and greater than or equal to approximately 10 mT.

80. A method of measuring hysteresis in a magnetic resonance imaging (MRI) system comprising at least one gradient coil, the method comprising:

controlling the at least one gradient coil using a first pulse sequence comprising a first plurality of pulses;

measuring, using a multi-element RF probe placed in an imaging region of the MRI system, a first plurality of magnetic field strengths in the imaging region of the MRI system, each of the first plurality of magnetic field strengths resulting, at least in part, from a respective one of the first plurality of pulses of the first pulse sequence;

estimating parameters of a hysteresis model based on the measured first plurality of magnetic field strengths; and

storing the parameters of the hysteresis model.

81. The method of claim 80 or any other preceding claim, further comprising accessing at least one parameter value specifying the first pulse sequence.

82. The method of claim 80 or any other preceding claim, wherein measuring the first plurality of magnetic field strengths is performed after controlling the at least one gradient coil using the first pulse sequence such that the at least one gradient coil is not generating a magnet field while measuring the first plurality of magnetic field strengths.

83. The method of claim 80 or any other preceding claim, wherein at least some of the first plurality of pulses decrease in amplitude over time.

84. The method of claim 83 or any other preceding claim, wherein at least some of the first plurality of pulses increase in amplitude over time.

85. The method of claim 80 or any other preceding claim, wherein storing the parameters of the hysteresis model comprises storing a plurality of weights based on the first plurality of magnetic field strengths, a plurality of lower magnetic field strength values, and a plurality of upper magnetic field strength values, wherein each weight of the plurality of weights is associated with one of the plurality of lower magnetic field strength values and one of the plurality of upper magnetic field strength values.

86. The method of claim 85 or any other preceding claim, wherein estimating the weights of the hysteresis model comprises estimating each weight of the plurality of weights based on a difference between the first magnetic field strength and a target magnetic field strength.

87. The method of claim 86 or any other preceding claim, further comprising, after measuring the first plurality of magnetic field strengths:

controlling the at least one gradient coil with a second pulse sequence comprising a second plurality of pulses;

measuring, using the multi-element probe, a second plurality of magnetic field strengths in the imaging region, each of the second plurality of magnetic field strengths resulting, at least in part, from a respective one of the second plurality of pulses of the second pulse sequence; and

updating the plurality of weights based on the second magnetic field strengths.

88. The method of claim 85 or any other preceding claim, further comprising:

iteratively controlling the at least one gradient coil with a subsequent pulse sequence comprising a plurality of pulses, wherein a first iteration comprises controlling the at least one gradient coil with the first pulse sequence;

iteratively measuring, using the multi-element probe, a subsequent plurality of magnetic field strengths, each of the subsequent plurality of magnetic field strengths resulting from a respective one of the plurality of pulses in the subsequent pulse sequence; and

iteratively updating the plurality of weights based on the subsequent plurality of magnetic field strengths.

89. The method of claim 80 or any other preceding claim, further comprising controlling a radio frequency (RF) coil of the MRI system with an RF driving pulse prior to each one of the first plurality of pulses of the first pulse sequence.

90. The method of claim 89 or any other preceding claim, further comprising including a readout window after each RF driving pulse and the respective pulse of the first plurality of driving pulses of the first pulse sequence.

91. The method of claim 80 or any other preceding claim, wherein the at least one gradient coil comprises an x-gradient coil, a y-gradient coil, and a z-gradient coil.

92. The method of claim 91 or any other preceding claim, wherein first pulse sequence comprises a sub-sequence of x-gradient driving pulses, a sub-sequence of y-gradient driving pulses, and a sub- sequence of z-gradient driving pulses.

93. The method of claim 80 or any other preceding claim, further comprising placing the multi-element RF probe at the isocenter of the MRI system.

94. The method of claim 80 or any other preceding claim, wherein the multi-element RF probe comprises a plurality of RF receiving elements.

95. The method of claim 94 or any other preceding claim, wherein each of the plurality of RF receiving elements comprises a coil.

96. The method of claim 95 or any other preceding claim, wherein the multi-element RF probe comprises a plurality of liquid samples, wherein each of the plurality of liquid samples is contained within a respective coil of the plurality of RF receiving elements.

97. The method of claim 96 or any other preceding claim, wherein at least one of the liquid samples comprises agar.

98. The method of claim 96 or any other preceding claim, wherein at least one of the liquid samples comprises copper sulfate.

99. The method of claim 96 or any other preceding claim, wherein at least one of the liquid samples comprises mineral oil.

100. The method of claim 96 or any other preceding claim, wherein at least one of the liquid samples is a gel sample.

101. The method of claim 95 or any other preceding claim, wherein each coil of the plurality of RF receiving elements comprises a two-layer Litz solenoid.

102. The method of claim 95 or any other preceding claim, wherein the multi-element probe comprises an RF transmit coil.

103. The method of claim 102 or any other preceding claim, wherein the RF transmit coil is a cylindrical coil larger than each of the plurality of RF receiving elements.

104. The method of claim 102 or any other preceding claim, wherein the plurality of RF receiving elements are positioned within the RF transmit coil.

105. At least one computer-readable storage medium storing processor executable instructions that, when executed by at least one computer hardware processor, cause the at least one computer hardware processor to perform a method of measuring hysteresis in a magnetic resonance imaging (MRI) system comprising at least one gradient coil, the method comprising:

controlling the at least one gradient coil using a first pulse sequence comprising a first plurality of pulses;

measuring, using a multi-element RF probe placed in an imaging region of the MRI system, a first plurality of magnetic field strengths in the imaging region of the MRI system, each of the first plurality of magnetic field strengths resulting, at least in part, from a respective one of the first plurality of pulses of the first pulse sequence;

estimating parameters of a hysteresis model based on the measured first plurality of magnetic field strengths; and

storing the parameters of the hysteresis model.

106. The at least one computer-readable storage medium of claim 105 or any other preceding claim, wherein the method further comprises accessing at least one parameter value specifying the first pulse sequence.

107. The at least one computer-readable storage medium of claim 105 or any other preceding claim, wherein measuring the first plurality of magnetic field strengths is performed after controlling the at least one gradient coil using the first pulse sequence such that the at least one gradient coil is not generating a magnet field while measuring the first plurality of magnetic field strengths.

108. The at least one computer-readable storage medium of claim 105 or any other preceding claim, wherein at least some of the first plurality of pulses decrease in amplitude over time.

109. The at least one computer-readable storage medium of claim 108 or any other preceding claim, wherein at least some of the first plurality of pulses increase in amplitude over time.

110. The at least one computer-readable storage medium of claim 105 or any other preceding claim, wherein storing the parameters of the hysteresis model comprises storing a plurality of weights based on the first plurality of magnetic field strengths, a plurality of lower magnetic field strength values, and a plurality of upper magnetic field strength values, wherein each weight of the plurality of weights is associated with one of the plurality of lower magnetic field strength values and one of the plurality of upper magnetic field strength values.

111. The at least one computer-readable storage medium of claim 110 or any other preceding claim, wherein estimating the weights of the hysteresis model comprises estimating each weight of the plurality of weights based on a difference between the first magnetic field strength and a target magnetic field strength.

112. The at least one computer-readable storage medium of claim 111 or any other preceding claim, wherein the method further comprises, after measuring the first plurality of magnetic field strengths:

controlling the at least one gradient coil with a second pulse sequence comprising a second plurality of pulses;

measuring, using the multi-element probe, a second plurality of magnetic field strengths in the imaging region, each of the second plurality of magnetic field strengths resulting, at least in part, from a respective one of the second plurality of pulses of the second pulse sequence; and

updating the plurality of weights based on the second magnetic field strengths.

113. The at least one computer-readable storage medium of claim 110 or any other preceding claim, wherein the method further comprises:

iteratively controlling the at least one gradient coil with a subsequent pulse sequence comprising a plurality of pulses, wherein a first iteration comprises controlling the at least one gradient coil with the first pulse sequence;

iteratively measuring, using the multi-element probe, a subsequent plurality of magnetic field strengths, each of the subsequent plurality of magnetic field strengths resulting from a respective one of the plurality of pulses in the subsequent pulse sequence; and

iteratively updating the plurality of weights based on the subsequent plurality of magnetic field strengths.

114. The at least one computer-readable storage medium of claim 105 or any other preceding claim, wherein the method further comprises controlling a radio frequency (RF) coil of the MRI system with an RF driving pulse prior to each one of the first plurality of pulses of the first pulse sequence.

115. The at least one computer-readable storage medium of claim 114 or any other preceding claim, wherein the method further comprises including a readout window after each RF driving pulse and the respective pulse of the first plurality of driving pulses of the first pulse sequence.

116. The at least one computer-readable storage medium of claim 105 or any other preceding claim, wherein the at least one gradient coil comprises an x-gradient coil, a y-gradient coil, and a z-gradient coil.

117. The at least one computer-readable storage medium of claim 116 or any other preceding claim, wherein first pulse sequence comprises a sub- sequence of x-gradient driving pulses, a sub-sequence of y-gradient driving pulses, and a sub-sequence of z-gradient driving pulses.

118. The at least one computer-readable storage medium of claim 105 or any other preceding claim, wherein the method further comprises placing the multi-element RF probe at the isocenter of the MRI system.

119. The at least one computer-readable storage medium of claim 105 or any other preceding claim, wherein the multi-element RF probe comprises a plurality of RF receiving elements.

120. The at least one computer-readable storage medium of claim 119 or any other preceding claim, wherein each of the plurality of RF receiving elements comprises a coil.

121. The at least one computer-readable storage medium of claim 120 or any other preceding claim, wherein the multi-element RF probe comprises a plurality of liquid samples, wherein each of the plurality of liquid samples is contained within a respective coil of the plurality of RF receiving elements.

122. The at least one computer-readable storage medium of claim 121 or any other preceding claim, wherein at least one of the liquid samples comprises agar.

123. The at least one computer-readable storage medium of claim 121 or any other preceding claim, wherein at least one of the liquid samples comprises copper sulfate.

124. The at least one computer-readable storage medium of claim 121 or any other preceding claim, wherein at least one of the liquid samples comprises mineral oil.

125. The at least one computer-readable storage medium of claim 121 or any other preceding claim, wherein at least one of the liquid samples is a gel sample.

126. The at least one computer-readable storage medium of claim 120 or any other preceding claim, wherein each coil of the plurality of RF receiving elements comprises a two-layer Litz solenoid.

127. The at least one computer-readable storage medium of claim 120 or any other preceding claim, wherein the multi-element probe comprises an RF transmit coil.

128. The at least one computer-readable storage medium of claim 127 or any other preceding claim, wherein the RF transmit coil is a cylindrical coil larger than each of the plurality of RF receiving elements.

129. The at least one computer-readable storage medium of claim 127 or any other preceding claim, wherein the plurality of RF receiving elements are positioned within the RF transmit coil.

130. An apparatus for controlling at least one gradient coil of a magnetic resonance imaging (MRI) system, the apparatus comprising:

at least one computer hardware processor; and

at least one computer-readable storage medium storing processor executable instructions that, when executed by the at least one computer hardware processor, cause the at least one computer hardware processor to perform a method comprising:

controlling the at least one gradient coil using a first pulse sequence comprising a first plurality of pulses;

measuring, using a multi-element RF probe placed in an imaging region of the MRI system, a first plurality of magnetic field strengths in the imaging region of the MRI system, each of the first plurality of magnetic field strengths resulting, at least in part, from a respective one of the first plurality of pulses of the first pulse sequence; estimating parameters of a hysteresis model based on the measured first plurality of magnetic field strengths; and

storing the parameters of the hysteresis model.

131. The apparatus of claim 130 or any other preceding claim, wherein the method further comprises accessing at least one parameter value specifying the first pulse sequence.

132. The apparatus of claim 130 or any other preceding claim, wherein measuring the first plurality of magnetic field strengths is performed after controlling the at least one gradient coil using the first pulse sequence such that the at least one gradient coil is not generating a magnet field while measuring the first plurality of magnetic field strengths.

133. The apparatus of claim 130 or any other preceding claim, wherein at least some of the first plurality of pulses decrease in amplitude over time.

134. The apparatus of claim 133 or any other preceding claim, wherein at least some of the first plurality of pulses increase in amplitude over time.

135. The apparatus of claim 130 or any other preceding claim, wherein storing the parameters of the hysteresis model comprises storing a plurality of weights based on the first plurality of magnetic field strengths, a plurality of lower magnetic field strength values, and a plurality of upper magnetic field strength values, wherein each weight of the plurality of weights is associated with one of the plurality of lower magnetic field strength values and one of the plurality of upper magnetic field strength values.

136. The apparatus of claim 135 or any other preceding claim, wherein estimating the weights of the hysteresis model comprises estimating each weight of the plurality of weights based on a difference between the first magnetic field strength and a target magnetic field strength.

137. The apparatus of claim 136 or any other preceding claim, wherein the method further comprises, after measuring the first plurality of magnetic field strengths:

controlling the at least one gradient coil with a second pulse sequence comprising a second plurality of pulses;

measuring, using the multi-element probe, a second plurality of magnetic field strengths in the imaging region, each of the second plurality of magnetic field strengths resulting, at least in part, from a respective one of the second plurality of pulses of the second pulse sequence; and

updating the plurality of weights based on the second magnetic field strengths.

138. The apparatus of claim 135 or any other preceding claim, wherein the method further comprises:

iteratively controlling the at least one gradient coil with a subsequent pulse sequence comprising a plurality of pulses, wherein a first iteration comprises controlling the at least one gradient coil with the first pulse sequence;

iteratively measuring, using the multi-element probe, a subsequent plurality of magnetic field strengths, each of the subsequent plurality of magnetic field strengths resulting from a respective one of the plurality of pulses in the subsequent pulse sequence; and

iteratively updating the plurality of weights based on the subsequent plurality of magnetic field strengths.

139. The apparatus of claim 130 or any other preceding claim, wherein the method further comprises controlling a radio frequency (RF) coil of the MRI system with an RF driving pulse prior to each one of the first plurality of pulses of the first pulse sequence.

140. The apparatus of claim 139 or any other preceding claim, wherein the method further comprises including a readout window after each RF driving pulse and the respective pulse of the first plurality of driving pulses of the first pulse sequence.

141. The apparatus of claim 130 or any other preceding claim, wherein the at least one gradient coil comprises an x-gradient coil, a y-gradient coil, and a z-gradient coil.

142. The apparatus of claim 141 or any other preceding claim, wherein first pulse sequence comprises a sub-sequence of x-gradient driving pulses, a sub-sequence of y-gradient driving pulses, and a sub- sequence of z-gradient driving pulses.

143. The apparatus of claim 130 or any other preceding claim, wherein the method further comprises placing the multi-element RF probe at the isocenter of the MRI system.

144. The apparatus of claim 130 or any other preceding claim, wherein the multi-element RF probe comprises a plurality of RF receiving elements.

145. The apparatus of claim 144 or any other preceding claim, wherein each of the plurality of RF receiving elements comprises a coil.

146. The apparatus of claim 145 or any other preceding claim, wherein the multi-element RF probe comprises a plurality of liquid samples, wherein each of the plurality of liquid samples is contained within a respective coil of the plurality of RF receiving elements.

147. The apparatus of claim 146 or any other preceding claim, wherein at least one of the liquid samples comprises agar.

148. The apparatus of claim 146 or any other preceding claim, wherein at least one of the liquid samples comprises copper sulfate.

149. The apparatus of claim 146 or any other preceding claim, wherein at least one of the liquid samples comprises mineral oil.

150. The apparatus of claim 146 or any other preceding claim, wherein at least one of the liquid samples is a gel sample.

151. The apparatus of claim 145 or any other preceding claim, wherein each coil of the plurality of RF receiving elements comprises a two-layer Litz solenoid.

152. The apparatus of claim 145 or any other preceding claim, wherein the multi-element probe comprises an RF transmit coil.

153. The apparatus of claim 152 or any other preceding claim, wherein the RF transmit coil is a cylindrical coil larger than each of the plurality of RF receiving elements.

154. The apparatus of claim 152 or any other preceding claim, wherein the plurality of RF receiving elements are positioned within the RF transmit coil.

155. A multi-element probe for measuring hysteresis in a magnetic resonance imaging (MRI) system, the multi-element probe comprising:

an RF transmit coil;

a plurality of RF receiving elements; and

a plurality of liquid samples, each liquid sample contained within a respective coil of the plurality of RF receiving elements.

156. The multi-element probe of claim 155, wherein each of the plurality of RF receiving elements comprises a coil.

157. The multi-element probe of claim 155 or any other preceding claim, wherein at least one of the liquid samples comprises agar.

158. The multi-element probe of claim 155 or any other preceding claim, wherein at least one of the liquid samples comprises copper sulfate.

159. The multi-element probe of claim 155 or any other preceding claim, wherein at least one of the liquid samples and a respective RF receiving element are disposed in epoxy.

160. The multi-element probe of claim 155 or any other preceding claim, wherein each coil of the plurality of RF receiving elements comprises a two-layer Litz solenoid.

161. The multi-element probe of claim 155 or any other preceding claim, wherein the RF transmit coil is a cylindrical coil larger than each of the plurality of RF receiving elements.

162. The multi-element probe of claim 155 or any other preceding claim, wherein each of the plurality of RF receiving elements is electrically connected to a Litz twisted pair cable.

163. The multi-element probe of claim 155 or any other preceding claim, wherein the plurality of RF receiving elements are disposed within the RF transmit coil.

164. The multi-element probe of claim 163 or any other preceding claim, further comprising a housing, wherein the plurality of RF receiving elements and the RF transmit coil are contained within the housing.

165. The multi-element probe of claim 164 or any other preceding claim, wherein the housing comprises a fastener configured to mount the multi-element probe in the MRI system.

166. The multi-element probe of claim 165 or any other preceding claim, wherein the fastener is configured to mount the multi-element probe in the isocenter of the MRI system.

167. The multi-element probe of claim 164 or any other preceding claim, wherein the housing is substantially cylindrical in shape.

168. The multi-element probe of claim 155 or any other preceding claim, wherein the RF transmit coil defines an internal volume and the RF receiving elements are disposed in the internal volume.

169. A method of measuring hysteresis in a magnetic resonance imaging (MRI) system comprising at least one electromagnet, the method comprising:

measuring the magnetic field in an imaging region of the MRI system using a multi element probe, the multi-element probe comprising:

an RF transmit coil;

a plurality of RF receiving elements; and

a plurality of liquid samples, each liquid sample contained within a respective coil of the plurality of RF receiving elements.

170. The method of claim 169, wherein each of the plurality of RF receiving elements comprises a coil.

171. The method of claim 169 or any other preceding claim, wherein at least one of the liquid samples comprises agar.

172. The method of claim 169 or any other preceding claim, wherein at least one of the liquid samples comprises copper sulfate.

173. The method of claim 169 or any other preceding claim, wherein at least one of the liquid samples and a respective RF receiving element are disposed in epoxy.

174. The method of claim 169 or any other preceding claim, wherein each coil of the plurality of RF receiving elements comprises a multilayer Litz solenoid.

175. The method of claim 169 or any other preceding claim, wherein the RF transmit coil is a cylindrical coil larger than each of the plurality of RF receiving elements.

176. The method of claim 169 or any other preceding claim, wherein each of the plurality of RF receiving elements is electrically connected to a Litz twisted pair cable.

177. The method of claim 169 or any other preceding claim, wherein the plurality of RF receiving elements are disposed within the RF transmit coil.

178. The method of claim 177 or any other preceding claim, further comprising a housing, wherein the plurality of RF receiving elements and the RF transmit coil are contained within the housing.

179. The method of claim 178 or any other preceding claim, further comprising placing the multi-element probe in the MRI system.

180. The method of claim 179 or any other preceding claim, wherein placing the multi element probe in the MRI system comprises mounting, using a fastener, the multi-element probe in the isocenter of the MRI system.

181. The method of claim 177 or any other preceding claim, wherein the housing is substantially cylindrical in shape.

182. The method of claim 169 or any other preceding claim, wherein the RF transmit coil defines an internal volume and the RF receiving elements are disposed in the internal volume.

183. The method of claim 169, wherein the at least one electromagnet comprises at least one gradient coil, the method further comprising:

controlling the at least one gradient coil using a first pulse sequence comprising a first plurality of pulses, wherein

measuring the magnetic field in an imaging region comprises measuring a first plurality of magnetic field strengths in the imaging region of the MRI system, each of the first plurality of magnetic field strengths resulting, at least in part, from a respective one of the first plurality of pulses of the first pulse sequence.

184. The method of claim 183, further comprising:

estimating parameters of a hysteresis model based on the measured first plurality of magnetic field strengths.

storing the parameters of the hysteresis model.

185. The method of claim 184, further comprising accessing at least one parameter value specifying the first pulse sequence.

186. The method of claim 184 or any other preceding claim, wherein measuring the first plurality of magnetic field strengths and controlling the at least one gradient coil using the first pulse sequence are performed simultaneously

187. The method of claim 184 or any other preceding claim, wherein at least some of the first plurality of driving pulses decrease in amplitude over time.

188. The method of claim 187 or any other preceding claim, wherein at least some of the first plurality of driving pulses increase in amplitude over time.

189. The method of claim 184 or any other preceding claim, wherein storing the parameters of the hysteresis model comprises storing a plurality of weights based on the first plurality of magnetic field strengths, a plurality of lower magnetic field strength values, and a plurality of upper magnetic field strength values, wherein each weight of the plurality of weights is associated with one of the plurality of lower magnetic field strength values and one of the plurality of upper magnetic field strength values.

190. The method of claim 189 or any other preceding claim, wherein estimating the weights of the hysteresis model comprises estimating each weight of the plurality of weights based on a difference between the first magnetic field strength and a target magnetic field strength.

191. The method of claim 189 or any other preceding claim, further comprising, after measuring the first plurality of magnetic field strengths:

driving the at least one gradient coil with a second pulse sequence comprising a second plurality of driving pulses;

measuring, using the multi-element probe, a second plurality of magnetic field strengths in the imaging region, each of the second plurality of magnetic field strengths resulting, at least in part, from a respective one of the second plurality of driving pulses of the second pulse sequence; and

updating the plurality of weights based on the second magnetic field strengths.

192. The method of claim 189 or any other preceding claim, further comprising:

iteratively driving the at least one gradient coil with a subsequent pulse sequence comprising a plurality of driving pulses, wherein a first iteration comprises driving the at least one gradient coil with the first pulse sequence;

iteratively measuring, using the multi-element probe, a subsequent plurality of magnetic field strengths, each of the subsequent plurality of magnetic field strengths resulting from a respective one of the plurality of driving pulses in the subsequent pulse sequence; and iteratively updating the plurality of weights based on the subsequent plurality of magnetic field strengths.

193. The method of claim 182 or any other preceding claim, further comprising driving a radio frequency (RF) coil of the MRI system with an RF driving pulse prior to each one of the first plurality of driving pulses of the first pulse sequence.

194. The method of claim 193 or any other preceding claim, further comprising including a readout window after each RF driving pulse and the respective driving pulse of the first plurality of driving pulses of the first pulse sequence.

195. The method of claim 184 or any other preceding claim, wherein the at least one gradient coil comprises an x-gradient coil, a y-gradient coil, and a z-gradient coil.

196. The method of claim 195 or any other preceding claim, wherein first pulse sequence comprises a sub-sequence of x-gradient driving pulses, a sub-sequence of y-gradient driving pulses, and a sub- sequence of z-gradient driving pulses.