Radio-frequency coil signal chain for a low-field mri system

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.

What is claimed is: 
     
         1 - 20 . (canceled) 
     
     
         21 . A circuit configured to tune a radio frequency (RF) coil coupled to an amplifier of a low-field magnetic resonance imaging system, the circuit comprising:
 tuning circuitry coupled across inputs of the amplifier; and   active feedback circuitry coupled between an output of the amplifier and an input of the amplifier.   
     
     
         22 . The circuit of  claim 21 , wherein the active feedback circuitry includes at least one feedback capacitor. 
     
     
         23 . The circuit of  claim 21 , wherein the tuning circuitry comprises a tuning capacitor coupled across the inputs of the amplifier. 
     
     
         24 . The circuit of  claim 21 , wherein the tuning circuitry comprises a tuning/matching network including at least one capacitor and at least one inductor. 
     
     
         25 . The circuit of  claim 21 , wherein the active feedback circuitry is configured to provide a first feedback signal 90 or 270 degrees out of phase with a center frequency of the RF coil. 
     
     
         26 . The circuit of  claim 25 , wherein a gain of the amplifier is tuned to be 90 or 270 degrees out of phase with the center frequency of the RF coil. 
     
     
         27 . The circuit of  claim 25 , wherein one or more components of the active feedback circuitry is configured to produce the first feedback signal being 90 or 270 degrees out of phase with the center frequency of the RF coil. 
     
     
         28 . The circuit of  claim 25 , wherein the active feedback circuitry is configured to provide a second feedback signal 180 degrees out of phase with the center frequency of the RF coil. 
     
     
         29 . The circuit of  claim 21 , wherein the active feedback circuitry is configured to provide a feedback signal 180 degrees out of phase with a center frequency of the RF coil. 
     
     
         30 . The circuit of  claim 21 , wherein the active feedback circuitry includes mutual inductive circuitry including at least one inductor. 
     
     
         31 . The circuit of  claim 30 , wherein the at least one inductor is configured to be coupled mutually to the RF coil. 
     
     
         32 . A circuit configured to tune a radio frequency (RF) coil coupled to an amplifier of a low-field magnetic resonance imaging system, the circuit comprising:
 active feedback circuitry coupled between an output of the amplifier and an input of the amplifier to reduce a quality factor of the RF coil, wherein the active feedback circuitry is configured to provide a first feedback signal 180 degrees out of phase with a center frequency of the RF coil.   
     
     
         33 . The circuit of  claim 32 , wherein the active feedback circuitry includes at least one feedback capacitor. 
     
     
         34 . The circuit of  claim 32 , wherein the active feedback circuitry is configured to provide a second feedback signal 90 or 270 degrees out of phase with the center frequency of the RF coil. 
     
     
         35 . The circuit of  claim 34 , wherein a gain of the amplifier is tuned to be 90 or 270 degrees out of phase with the center frequency of the RF coil. 
     
     
         36 . The circuit of  claim 32 , wherein one or more components of the active feedback circuitry is configured to produce the first feedback signal being 180 degrees out of phase with the center frequency of the RF coil. 
     
     
         37 . The circuit of  claim 34 , wherein one or more components of the active feedback circuitry is configured to produce the second feedback signal being 90 or 270 degrees out of phase with the center frequency of the RF coil. 
     
     
         38 . A method of tuning a radio frequency (RF) coil coupled to an amplifier of a low-field magnetic resonance imaging system, the method comprising:
 arranging tuning circuitry across first and second inputs of the amplifier; and   coupling active feedback circuitry between an output of the amplifier and an input of the amplifier.   
     
     
         39 . The method of  claim 38 , further comprising providing, using the active feedback circuitry, a feedback signal 180 degrees out of phase with a center frequency of the RF coil. 
     
     
         40 . The method of  claim 38 , wherein the tuning circuitry comprises a tuning/matching network including at least one capacitor and at least one inductor.