GRADIENT WAVEFORM DESIGN FOR LOW-FIELD MAGNETIC RESONANCE IMAGING SYSTEMS
Systems and methods for generating a gradient waveform for use by a low-field MRI system to generate a gradient magnetic field are provided herein. The gradient waveform can be determined using first information indicative of the gradient waveform and second information indicative of hardware constraints of the low-field MRI system including a maximum voltage of the gradient power amplifier, a maximum slew rate of the gradient coil, a resistance of the gradient coil, and an inductance of the gradient coil. In some embodiments, the gradient waveform can be a trapezoidal gradient waveform determined to have a non-linear ramp-up portion and/or a non-linear ramp-down portion.
1 . A method of generating a gradient waveform for use by a low-field magnetic resonance imaging (MRI) system to generate a gradient magnetic field, the low-field MRI system comprising a gradient coil and a gradient power amplifier for driving the gradient coil, the method comprising:
accessing first information indicative of the gradient waveform;
accessing second information indicative of hardware constraints of the low-field MRI system, the second information including one of:
(i) information indicative of a maximum voltage of the gradient power amplifier, a maximum slew rate of the gradient coil, a resistance of the gradient coil, and an inductance of the gradient coil, or
(ii) information indicative of a maximum voltage of the gradient power amplifier, a maximum slew rate of the gradient coil, and a voltage induced in the gradient coil in response to an applied current,
determining the gradient waveform using the first information and the second information; and
generating the gradient waveform.
2 . The method of claim 1 , further comprising:
generating the gradient magnetic field by using the gradient power amplifier and the gradient waveform to drive the gradient coil.
3 . The method of claim 1 , wherein determining the gradient waveform is performed using a ratio of the resistance of the gradient coil and the inductance of the gradient coil.
4 . The method of claim 1 , wherein determining the gradient waveform comprises determining gradient waveform parameters subject to hardware constraints specified using a differential equation, the differential equation specified in part using the second information.
5 . The method of claim 1 , wherein accessing the first information comprises accessing information including a moment of the gradient magnetic field, a duration of the gradient magnetic field, and/or a maximum value of the gradient magnetic field.
6 . The method of claim 1 , wherein accessing the first information comprises accessing a pre-determined gradient waveform.
7 . The method of claim 1 , further comprising:
after determining the gradient waveform, rotating a frame of reference of the gradient waveform to match a frame of reference of the low-field MRI system.
8 . The method of claim 1 , wherein the gradient waveform is a trapezoidal gradient waveform having a ramp-up portion, a top portion, and a ramp-down portion.
9 . The method of claim 8 , wherein determining the gradient waveform comprises determining a shape of the ramp-up portion and/or the ramp-down portion using the first information and the second information.
10 . The method of claim 1 , wherein the maximum slew rate has a magnitude in a range from 10 T/m/s to 80 T/m/s.
11 . The method of claim 1 , wherein the maximum slew rate has a magnitude in a range from 25 T/m/s to 65 T/m/s.
12 . The method of claim 1 , wherein the maximum voltage of the gradient power amplifier has a magnitude in a range from 20 V to 120 V.
13 . The method of claim 1 , wherein the maximum voltage of the gradient power amplifier has a magnitude in a range from 40 V to 60 V.
14 . The method of claim 1 , wherein the low-field MRI system further comprises at least one permanent magnet configured to generate a B 0 magnetic field having a strength less than 0.2 T.
15 . The method of claim 1 , wherein the low-field MRI system further comprises at least one permanent magnet configured to generate a B 0 magnetic field having a strength in a range from 50 mT to 0.1 T.
16 . At least one non-transitory computer-readable storage medium storing processor-executable instructions that, when executed by a low-field magnetic resonance imaging (MRI) system, cause the low-field MRI system to perform a method of generating a gradient waveform for use by the low-field MRI system to generate a gradient magnetic field, the low-field MRI system comprising a gradient coil and a gradient power amplifier for driving the gradient coil, the method comprising:
accessing first information indicative of the gradient waveform;
accessing second information indicative of hardware constraints of the low-field MRI system, the second information including one of:
(i) information indicative of a maximum voltage of the gradient power amplifier, a maximum slew rate of the gradient coil, a resistance of the gradient coil, and an inductance of the gradient coil, or
(ii) information indicative of a maximum voltage of the gradient power amplifier, a maximum slew rate of the gradient coil, and a voltage induced in the gradient coil in response to an applied current,
determining the gradient waveform using the first information and the second information; and
generating the gradient waveform.
17 . A low-field magnetic resonance imaging (MRI) system, comprising:
a magnetics system comprising a plurality of magnetics components configured to produce magnetic fields for performing magnetic resonance imaging, the plurality of magnetics components comprising a gradient coil and a gradient power amplifier for driving the gradient coil; and
at least one controller configured to operate one or more of the plurality of magnetics components, wherein the at least one controller is configured to:
access first information indicative of a gradient waveform;
access second information indicative of hardware constraints of the low-field MRI system, the second information including one of:
(i) information indicative of a maximum voltage of the gradient power amplifier, a maximum slew rate of the gradient coil, a resistance of the gradient coil, and an inductance of the gradient coil, or
(ii) information indicative of a maximum voltage of the gradient power amplifier, a maximum slew rate of the gradient coil, and a voltage induced in the gradient coil in response to an applied current,
determine the gradient waveform using the first information and the second information; and
generate the gradient waveform.
18 . The low-field MRI system of claim 17 , wherein the at least one controller is further configured to:
generate a gradient magnetic field by using the gradient power amplifier and the gradient waveform to drive the gradient coil.
19 . The low-field MRI system of claim 17 , wherein the at least one controller is further configured to determine the gradient waveform by using a ratio of the resistance of the gradient coil and the inductance of the gradient coil.
20 . The low-field MRI system of claim 17 , wherein the at least one controller is further configured to determine the gradient waveform by determining gradient waveform parameters subject to hardware constraints specified using a differential equation, the differential equation specified in part using the second information.