Failsafe protection from induced RF current for MRI RF coil assembly having transmit functionality

Patent metadata

Field	Value
Publication number	US-9366737-B2
Application number	US-201514851969-A
Country	US
Kind code	B2
Filing date	Sep 11, 2015
Priority date	Jun 1, 2010
Publication date	Jun 14, 2016
Grant date	Jun 14, 2016

Abstract

An electrically-controlled failsafe switch is included in an MRI transmit-and-receive RF coil assembly so as to protect it from induced RF currents in the event it is disconnected from an MRI system, but inadvertently left linked to strong MRI RF fields during imaging procedures using other RF coils.

First claim

What is claimed is:

1. An MRI RF coil assembly having RF transmit functionality and RF receive functionality, and which is connectable to an MRI system, said RF coil assembly comprising:
an MRI RF coil configured to electromagnetically transmit MRI RF fields to an object being imaged in an MRI system gantry when MRI RF current is passed through said coil;
RF feed circuitry configured to feed MRI RF current to said coil from a connection interface with an MRI system; and
a variable impedance electrically connected within or to at least one of said RF coil and said feed circuitry, said variable impedance protecting the coil assembly from damage due to induced RF current flow when the coil assembly is not connected to the MRI system, wherein
the variable impedance is configured so that an impedance state thereof adapts to three operational modes of:
a first mode in which the RF coil assembly is not connected to the MRI system;
a second mode in which the RF coil assembly is connected to the MRI system and the RF transmit functionality operates; and
a third mode in which the RF coil assembly is connected to the MRI system and the RF receive functionality operates, wherein the first mode provides a high impedance causing substantial attenuation of induced RF current flow and the second and third modes provide low impedance permitting substantially unimpeded flow of MRI RF imaging currents between the RF feed circuitry and the coil.

2. An MRI RF coil assembly as in claim 1 , wherein said variable impedance is connected serially within an RF coil element.

3. An MRI RF coil assembly as in claim 1 , wherein said variable impedance is connected serially at a feed point of an RF coil element.

4. An MRI RF coil assembly as in claim 1 , wherein said variable impedance is connected to said RF feed circuitry between a feed point of an RF coil element and said connection interface.

5. An MRI RF coil assembly as in claim 1 further comprising:
a transmit/receive switch disposed as part of said RF feed circuitry between said connection interface and an RF coil element; and
RF receive amplifier circuitry connected between said transmit/receive switch and said connection interface thereby providing a transmit/receive MRI RF coil assembly.

6. An MRI RF coil assembly as in claim 5 constituting a birdcage coil assembly comprising a plurality of said RF coils, each with its own respectively associated (a) RF feed circuitry, and (b) variable impedance which changes between different impedance values when the coil assembly is disconnected from an MRI system.

7. An MRI coil assembly as in claim 1 , wherein said variable impedance comprises an electrically-controlled switch having at least two back-to-back serially connected diodes.

8. An MRI RF coil assembly as in claim 1 , comprising an array of said RF coils, variable impedances and RF feed circuitry.

9. An MRI RF coil assembly as in claim 1 , wherein said variable impedance comprises an electrically controlled switch and said RF feed circuitry includes a DC bias current path extending from said connection interface with said MRI system to at least said electrically-controlled switch.

10. An MRI RF coil assembly as in claim 1 , wherein said variable impedance comprises:
a parallel LC circuit resonant at an RF operating frequency of said MRI system;
at least one pair of back-to-back connected diodes connected across at least a portion of said parallel LC circuit and configured to:
(a) present a lowered RF impedance which detunes said LC circuit from resonance in the presence of a bias control current forward biasing said diodes, thus permitting MR RF imaging currents to flow substantially unimpeded to an RF coil element, and
(b) otherwise, when not forward biased, leaving said LC circuit to present a substantial parallel resonant impedance which substantially obstructs the flow of induced RF currents in the event that said RF coil assembly is not electrically connected to said MRI system, but the RF coil assembly nevertheless remains in an MRI system location where the RF coil assembly can be exposed to MRI system RF transmit fields which induce RF current in said RF coil assembly.

11. An MRI RF coil assembly as in claim 1 , wherein said variable impedance comprises:
a plurality of serially connected back-to-back diodes configured to:
(a) present a lowered RF impedance in the presence of a bias control current forward biasing said diodes, thus permitting MR RF imaging currents to flow substantially unimpeded to an RF coil element, and
(b) otherwise, when not forward biased, present a substantial impedance which substantially obstructs the flow of induced RF currents in the event that said coil assembly is not electrically connected to said MRI system, but the RF coil assembly nevertheless remains in an MRI system location where the RF coil assembly can be exposed to MRI system RF transmit fields which induce RF current in said RF coil assembly.

12. An MRI RF coil assembly as in claim 11 , further comprising: a resistance connected in parallel across each said diode, said resistances being of substantially equal resistance values so as to establish substantially equal voltage drops across said diodes when reverse biased by induced RF current.

13. An MRI system comprising said MRI RF coil assembly as in claim 1 .

14. An MRI RF coil assembly having RF transmit functionality and RF receive functionality, and which is connectable to an MRI system, said RF coil assembly comprising:
MRI RF coil circuitry configured to electromagnetically transmit RF fields to an object being imaged in an MRI system gantry; and
means connected to said RF coil circuitry for substantially impeding the flow of induced RF current within said coil assembly when the coil assembly is not connected to an MRI system, wherein
the means is configured so as to adapt to three operational modes of the RF coil assembly:
a first mode in which the RF coil assembly is not connected to the MRI system;
a second mode in which the RF coil assembly is connected to the MRI system and the RF transmit functionality operates; and
a third mode in which the RF coil assembly is connected to the MRI system and the RF receive functionality operates, wherein the first mode provides a high impedance causing substantial attenuation of induced RF current flow and the second and third modes provide low impedance permitting substantially unimpeded flow of MRI RF imaging currents between the RF feed circuitry and the coil.

15. An MRI RF coil assembly as in claim 14 , wherein said RF coil circuitry comprises:
a transmit/receive switch connected to RF receive amplifier circuitry, to said RF coil circuitry and to a connection interface with an MRI system, said transmit/receive switch and said RF receive amplifier circuitry including a DC bias current circuit configured to pass DC bias control current from a connected MRI system to said means for substantially impeding the flow of induced RF current.

16. An MRI RF coil assembly as in claim 14 , wherein said means for impeding the flow of induced RF current is serially connected between an RF coil and an electrical interface to an MRI system.

17. An MRI RF coil assembly as in claim 16 , wherein said means for impeding the flow of induced RF current is connected at a feed point of said RF coil.

18. An MRI RF coil assembly as in claim 14 , wherein said means for impeding the flow of induced RF current is serially connected within an RF coil.

19. A method of protecting a connectable MRI RF coil assembly havi

Assignees

• Quality Electrodynamics Llc
• Toshiba Medical Sys Corp

Inventors

• Hamamura Yoshinori
• Yang Xiaoyu
• Castrilla Nicholas
• Allen Christopher J
• Mitsui Shinji

Classifications

• G01R33/365

  Decoupling of multiple RF coils wherein the multiple RF coils have the same function in MR, e.g. decoupling of a receive coil from another receive coil in a receive coil array, decoupling of a transmission coil from another transmission coil in a transmission coil array · CPC title

• G01R33/3664 Primary

  Switching for purposes other than coil coupling or decoupling, e.g. switching between a phased array mode and a quadrature mode, switching between surface coil modes of different geometrical shapes, switching from a whole body reception coil to a local reception coil or switching for automatic coil selection in moving table MR or for changing the field-of-view (G01R33/3671 takes precedence) · CPC title

• G01R33/3628

  Tuning/matching of the transmit/receive coil · CPC title

• G01R33/3642 Primary

  Mutual coupling or decoupling of multiple coils, e.g. decoupling of a receive coil from a transmission coil, or intentional coupling of RF coils, e.g. for RF magnetic field amplification · CPC title

• G01R33/543

  Control of the operation of the MR system, e.g. setting of acquisition parameters prior to or during MR data acquisition, dynamic shimming, use of one or more scout images for scan plane prescription (G01R33/546 takes precedence) · CPC title