Low noise gradient amplification components for MR systems
Described herein are power components that may facilitate efficient, low noise operation of low-field MRI systems. In some embodiments, the power components may include switching power converters configured to switch in a manner that reduces or eliminates noise within a desired frequency band (e.g., the Larmor frequency band) due to harmonics of the switching frequency. For example, the desired frequency band may be positioned between adjacent integer harmonics of the switching frequency. In some embodiments, harmonic components generated by multiple switching power converters may destructively interfere with one another, reducing or eliminating the amplitude of the harmonic components of the switching frequency that reside in the desired frequency band. In some embodiments, the power components may include switching power converters configured in parallel without the need for active current balancing circuitry.
1. An apparatus for providing power to operate at least one gradient coil of a magnetic resonance imaging system, the apparatus comprising:
at least one switching power converter configured to provide, to the at least one gradient coil, an output signal having a characteristic frequency,
wherein a Larmor frequency associated with a B 0 field strength of the magnetic resonance imaging system is between adjacent positive integer multiples of the characteristic frequency.
2. The apparatus of claim 1 , wherein the Larmor frequency is greater than the characteristic frequency and less than twice the characteristic frequency.
3. The apparatus of claim 1 , wherein the Larmor frequency is greater than twice the characteristic frequency and less than three times the characteristic frequency.
4. The apparatus of claim 1 , wherein the output signal comprises a direct current (DC) component and an alternating current (AC) ripple component, and wherein the characteristic frequency is a frequency of the AC ripple component.
5. The apparatus of claim 4 , wherein the at least one switching converter is configured to differentially drive the at least one gradient coil, and the frequency of the AC ripple component is a differential mode component of the AC ripple component.
6. The apparatus of claim 1 , wherein the at least one switching power converter comprises a plurality of switching power converters.
7. The apparatus of claim 6 , wherein at least a first power converter of the plurality of switching power converters has a switching frequency below the characteristic frequency and greater than zero.
8. The apparatus of claim 7 , wherein the characteristic frequency is a positive integer multiple of the switching frequency.
9. The apparatus of claim 6 , wherein the plurality of switching power converters is configured to switch such that a plurality of output signals of the plurality of switching power converters have frequency components that destructively interfere with one another.
10. The apparatus of claim 6 , wherein at least two switching power converters of the plurality of switching power converters are coupled in parallel.
11. The apparatus of claim 6 , wherein at least two switching power converters of the plurality of switching power converters are configured to switch out of phase from one another.
12. The apparatus of claim 11 , wherein:
the plurality of switching power converters comprises first and second switching power converters coupled in parallel and configured to switch 90 degrees out of phase from one another, and
the first and second switching power converters are configured to switch at a second frequency that is half of the characteristic frequency.
13. The apparatus of claim 1 , wherein the at least one switching power converter comprises at least one gallium nitride transistor.
14. The apparatus of claim 13 , wherein the at least one switching power converter comprises a high-side transistor coupled between the at least one gradient coil and a first power terminal and a low-side transistor coupled between the at least one gradient coil and a second power terminal.
15. A magnetic resonance imaging system, comprising:
a B 0 magnet configured to produce a B 0 magnetic field having an associated Larmor frequency;
at least one gradient coil; and
at least one switching power converter configured to provide, to the at least one gradient coil, an output signal having a characteristic frequency,
wherein the Larmor frequency is between adjacent positive integer multiples of the characteristic frequency.
16. A method for providing power to operate at least one gradient coil of a magnetic resonance imaging system, the method comprising:
providing, to the at least one gradient coil, by at least one switching power converter, an output signal having a characteristic frequency, such that a Larmor frequency associated with a B 0 field strength of the magnetic resonance imaging system is between adjacent positive integer multiples of the characteristic frequency.
17. An apparatus for providing power to operate at least one gradient coil of a magnetic resonance imaging system, the apparatus comprising:
a first switching power converter configured to provide a first current to a first gradient coil of the at least one gradient coil; and
a second switching power converter configured to provide a second current to the first gradient coil,
wherein the first and second currents are balanced without any current-balancing circuitry.
18. The apparatus of claim 17 , wherein the first and second switching power converters are coupled in parallel.
19. The apparatus of claim 17 , wherein the first and second switching power converters are half bridges.
20. The apparatus of claim 17 , wherein the first and second switching power converters each comprise gallium nitride transistors.
21. The apparatus of claim 17 , wherein the first and second currents differ from one another in magnitude by less than 20% of a maximum output current of the first switching power converter.
22. A magnetic resonance imaging system, comprising:
a B 0 magnet;
at least one radio frequency (RF) coil configured to transmit and/or receive magnetic resonance signals;
at least one gradient coil;
a first switching power converter configured to provide a first current to a first gradient coil of the at least one gradient coil; and
a second switching power converter configured to provide a second current to the first gradient coil,
wherein the first and second currents are balanced without any current-balancing circuitry.