# US 10,871,530 B2 · Radio-frequency coil signal chain for a low-field MRI system

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- Number: US 10,871,530 B2
- Document ID: US10871530B2
- Status: Granted
- Kind: B2
- Application number: 16/418,397
- Filed: 2019-05-21
- Published: 2019-11-21
- Granted: 2020-12-22
- Earliest claimed: 2018-05-21
- Assignees: Hyperfine Research, Inc.
- Applicants: Hyperfine Research, Inc.
- Inventors: Hadrien A. Dyvorne; Todd Rearick
- Web page: https://patentgrep.com/patent/US10871530B2

## CPC

- G01R 33/34007: {Manufacture of RF coils, e.g. using printed circuit board technology; additional hardware for providing mechanical support to the RF coil assembly or to part thereof, e.g. a support for moving the coil assembly relative to the remainder of the MR system}
- G01R 33/34053: {Solenoid coils; Toroidal coils}
- G01R 33/341: comprising surface coils
- G01R 33/3657: {Decoupling of multiple RF coils wherein the multiple RF coils do not have the same function in MR, e.g. decoupling of a transmission coil from a receive coil}
- G01R 33/445: {MR involving a non-standard magnetic field B0, e.g. of low magnitude as in the earth's magnetic field or in nanoTesla spectroscopy, comprising a polarizing magnetic field for pre-polarisation, B0 with a temporal variation of its magnitude or direction such as field cycling of B0 or rotation of the direction of B0, or spatially inhomogeneous B0 like in fringe-field MR or in stray-field imaging}
- G01R 33/0029: {Treating the measured signals, e.g. removing offset or noise}
- G01R 33/3614: {RF power amplifiers}
- G01R 33/3628: {Tuning/matching of the transmit/receive coil}
- G01R 33/3854: {means for active and/or passive vibration damping or acoustical noise suppression in gradient magnet coil systems}
- G01R 33/565: Correction of image distortions, e.g. due to magnetic field inhomogeneities
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

Methods and apparatus for reducing noise in RF signal chain circuitry for a low-field magnetic resonance imaging system are provided. A switching circuit in the RF signal chain circuitry may include at least one field effect transistor (FET) configured to operate as an RF switch at an operating frequency of less than 10 MHz. A decoupling circuit may include tuning circuitry coupled across inputs of an amplifier and active feedback circuitry coupled between an output of the amplifier and an input of the amplifier, wherein the active feedback circuitry includes a feedback capacitor configured to reduce a quality factor of an RF coil coupled to the amplifier.

## Claims

### Claim 1

A switching circuit configured to be coupled to a radio-frequency (RF) coil of a low-field magnetic resonance imaging system, the switching circuit comprising:
at least one field-effect transistor (FET) configured to operate as an RF switch at an operating frequency of less than 10 MHz, wherein the at least one FET has a parasitic drain-source capacitance of less than 15 picoFarads.

### Claim 2 (depends on 1)

The switching circuit of claim 1, wherein the at least one FET comprises at least one gallium nitride (GaN) FET.

### Claim 3 (depends on 2)

The switching circuit of claim 2, wherein the at least one GaN FET comprises a first GaN FET and a second GaN FET, wherein the first GaN FET and the second GaN FET are arranged to receive a same gate voltage.

### Claim 4 (depends on 1)

The switching circuit of claim 1, wherein the at least one FET has an on-state resistance of less than 1 ohm.

### Claim 5 (depends on 1)

The switching circuit of claim 1, further comprising:
driving circuitry configured to apply a gate voltage to the at least one FET, wherein the driving circuitry includes at least one isolation element configured to isolate a voltage source from the at least one FET.

### Claim 6 (depends on 5)

The switching circuit of claim 5, wherein the at least one isolation element comprises a transformer.

### Claim 7 (depends on 6)

The switching circuit of claim 6, wherein the transformer is an air core transformer.

### Claim 8 (depends on 5)

The switching circuit of claim 5, wherein the driving circuitry comprises an AC voltage source coupled to a gate of the at least one FET via a transformer.

### Claim 9

A switching circuit configured to be coupled to a radio-frequency (RF) coil of a low-field magnetic resonance imaging system, the switching circuit comprising:
at least one field-effect transistor (FET) configured to operate as an RF switch at an operating frequency of less than 10 MHz; and
driving circuitry configured to apply a gate voltage to the at least one FET, wherein the driving circuitry includes at least one isolation element configured to isolate a voltage source from the at least one FET, wherein the at least one isolation element comprises at least one resistor.

### Claim 10

A switching circuit configured to be coupled to a radio-frequency (RF) coil of a low-field magnetic resonance imaging system, the switching circuit comprising:
at least one field-effect transistor (FET) configured to operate as an RF switch at an operating frequency of less than 10 MHz; and
driving circuitry configured to apply a gate voltage to the at least one FET, wherein the driving circuitry includes at least one isolation element configured to isolate a voltage source from the at least one FET, wherein the driving circuitry comprises a diode coupled between the at least one isolation element and a gate of the at least one FET, wherein the diode is configured to rectify an input AC voltage to provide a DC voltage at the gate of the at least one FET.

### Claim 11

A switching circuit configured to be coupled to a radio-frequency (RF) coil of a low-field magnetic resonance imaging system, the switching circuit comprising:
at least one field-effect transistor (FET) configured to operate as an RF switch at an operating frequency of less than 10 MHz; and
driving circuitry configured to apply a gate voltage to the at least one FET, wherein the driving circuitry includes at least one isolation element configured to isolate a voltage source from the at least one FET, wherein the driving circuitry comprises an inductor coupled to the RF coil, wherein the inductor is configured to drive a gate of the at least one FET based on a transmit pulse sensed by the inductor.

### Claim 12

A drive circuit configured to apply a gate voltage to at least one field-effect transistor (FET) configured to operate as a radio-frequency switch in a low-field magnetic resonance imaging system, the drive circuit comprising:
at least one isolation element configured to isolate a voltage source from the at least one FET, wherein the at least one isolation element comprises at least one resistor.

### Claim 13 (depends on 12)

The drive circuit of claim 12, further comprising:
an AC voltage source coupled to a gate of the at least one FET via a transformer.

### Claim 14

A drive circuit configured to apply a gate voltage to at least one field-effect transistor (FET) configured to operate as a radio-frequency switch in a low-field magnetic resonance imaging system, the drive circuit comprising:
at least one isolation element configured to isolate a voltage source from the at least one FET; and
a diode coupled between the at least one isolation element and a gate of the at least one FET, wherein the diode is configured to rectify an input AC voltage to provide a DC voltage at the gate of the at least one FET.

### Claim 15 (depends on 14)

The drive circuit of claim 14, wherein the at least one isolation element comprises an air core transformer.

### Claim 16

A drive circuit configured to apply a gate voltage to at least one field-effect transistor (FET) configured to operate as a radio-frequency switch in a low-field magnetic resonance imaging system, the drive circuit comprising:
at least one isolation element configured to isolate a voltage source from the at least one FET; and
an inductor coupled to the RF coil, wherein the inductor is configured to drive a gate of the at least one FET based on a transmit pulse sensed by the inductor.