Active adaptive detuning systems and methods for interventional devices

Patent metadata

Field	Value
Publication number	US-9486158-B2
Application number	US-201113805454-A
Country	US
Kind code	B2
Filing date	Jul 1, 2011
Priority date	Jul 2, 2010
Publication date	Nov 8, 2016
Grant date	Nov 8, 2016

Abstract

Active MRI compatible interventional devices, such as catheters, include at least one RF antenna so that they are visible under MRI analysis. However, metallic structures within intravascular devices may heat up significantly during interventional MRI procedures due to eddy current formation over the conductive transmission lines. The electrical field coupling that occurs between interventional devices and RF signals depend on the position and orientation of interventional device within the bore and the insertion length of the interventional device. The system detects an induced current signal during RF transmission phase and selectively adjusts the impedance value associated with the interventional device by using a varactor and integrated circuit components in such a manner that the currents induced in the interventional device are below a threshold current level, thereby controlling current levels and heating in the interventional device.

First claim

What is claimed is:

1. An active adaptive detuning system for use during a magnetic resonance imaging procedure, the system comprising:
a magnetic resonance imaging system to:
apply a radio frequency radiation signal across a selected portion of a subject; and
discontinue application of the radio frequency radiation signal across the selected portion of the subject;

an interventional device for insertion into the subject and proximate to the selected portion of the subject, the interventional device comprising:
a radio frequency antenna at a distal end of the interventional device to receive an induced current based on another radio frequency signal emitted from tissue surrounding the radio frequency antenna when the interventional device is inserted in the subject; and
an inner conductor along a length of the interventional device and connected to the radio frequency antenna to conduct the induced current;

an adaptive detuning circuit connected to the inner conductor to:
iteratively adjust an impedance value of the interventional device through each of a plurality of impedance values;
determine a corresponding magnitude of the induced current in the inner conductor for each of the plurality of impedance values; and
set the impedance value of the interventional device to a first one of the plurality of impedance values where the corresponding magnitude of the induced current is below a threshold current level to limit heating of the interventional device when inserted within the subject;
the adaptive detuning circuit comprising:
a balun circuit to balance impedances between the interventional device and the magnetic resonance imaging system;
a matching circuit to dynamically vary the impedance value of the inner conductor to disrupt resonant conditions;
a detuning circuit to connect and disconnect the radio frequency antenna from the magnetic resonance imaging system in response to a DC control signal; and

a control circuit to:
generate the DC control signal when the magnetic resonance imaging system applies the radio frequency radiation signal;
detect the magnitude of the induced current in the inner conductor;
retrieve the threshold current level from a memory;
iteratively adjust the impedance value by adjusting an adaptive detuning capacitance of the adaptive detuning circuit through a series of detuning capacitance values based on the detected magnitude of the induced current;
determine the corresponding magnitude of the induced current in the inner conductor for each of the detuning capacitance values;
compare the corresponding magnitude of each induced current to the threshold current value; and
set the detuning capacitance value to a first one of the detuning capacitance values where the corresponding magnitude of the induced current is below the threshold current level.

2. The active adaptive detuning system of claim 1 wherein the control circuit adjusts a varactor to adjust the detuning capacitance value.

3. The active adaptive detuning system of claim 1 wherein the series of detuning capacitance values includes at least eight different detuning capacitance values.

4. The active adaptive detuning system of claim 1 wherein the inner conductor is a microcoaxial cable.

5. An adaptive detuning circuit for use in a magnetic resonance system during insertion of an interventional device into a subject during a magnetic resonance imaging procedure, wherein the magnetic resonance imaging system applies and discontinues application of a radio frequency radiation signal across a selected portion of a subject, and wherein the interventional device comprises a radio frequency antenna to receive an induced current based on another radio frequency signal emitted from tissue proximate to the radio frequency antenna and an inner conductor connected to the radio frequency antenna to conduct the induced current conductor, the adaptive detuning circuit to:
iteratively adjust an impedance value of the interventional device through each of a plurality of impedance values;
determine a corresponding magnitude of the induced current in the inner conductor for each of the plurality of impedance values; and
set the impedance value of the interventional device to a first one of the plurality of impedance values where the corresponding magnitude of the induced current is below a threshold current level to limit heating of the interventional device when inserted within the subject;
wherein the adaptive detuning circuit comprises:
a connector to connect to the inner conductor;
a balun circuit to balance impedances between the interventional device and the magnetic resonance imaging system;
a matching circuit to dynamically vary the impedance value of the inner conductor to disrupt resonant conditions; and
a detuning circuit to disconnect the radio frequency antenna from the magnetic resonance imaging system in response to a DC control signal; and
a control circuit to:
generate the DC control signal when the magnetic resonance imaging system applies the radio frequency radiation signal;
detect the magnitude of the induced current in the inner conductor;
retrieve a threshold current level from a memory;
iteratively adjust the impedance value by adjusting an adaptive detuning capacitance value of the adaptive detuning circuit through a series of detuning capacitance values based on the detected magnitude of the induced current;
determine a corresponding magnitude of the induced current in the inner conductor for each of the detuning capacitance values;
compare the corresponding magnitude of each induced current to the threshold current value; and
set the detuning capacitance value of the interventional device to a first one of the detuning capacitance values where the corresponding magnitude of the induced current is below the threshold current level.

6. The adaptive detuning circuit of claim 5 wherein the control circuit adjusts a varactor to adjust the detuning capacitance value.

7. A method for adjusting an impedance value associated with an interventional device during insertion of the interventional device into a subject during a magnetic resonance imaging procedure, the method comprising:
inserting an interventional device having an inner conductor and a radio frequency antenna into the subject;
applying a radio frequency radiation signal across a selected portion of a subject via a magnetic resonance imaging system;
discontinuing application of the radio frequency radiation signal across the selected portion of the subject;
receiving an induced current in the conductor via the radio frequency antenna based on another radio frequency signal emitted from tissue surrounding the radio frequency antenna when application of the radio frequency radiation signal is discontinued;
balancing impedances between the interventional device and magnetic resonance imaging system;
disconnecting the radio frequency antenna from the magnetic resonance imaging system in response to a DC control signal;
generating the DC control signal when the radio frequency radiation signal is being applied;
detecting the magnitude of the induced current in the inner conductor;
retrieving a threshold current level from a memory, wherein the threshold current level limits heating of the interventional device when inserted within the subject;
iteratively adjusting an impedance value of the interventional device by adjusting an adaptive detuning capacitance value through a series of detuning capacitance values based on the detected magnitude of the induced current;
determining a corresponding magnitude of the induced current in the inner conductor for each of the detuning capacitance values;
comparing the corresponding magnitude of each induced current to the

Assignees

• Kocaturk Ozgur
• Us Health

Inventors

• Kocaturk Ozgur

Classifications

• G01R33/3657 Primary

  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 · CPC title

• A61B5/055 Primary

  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging · CPC title

• G01R33/34084

  implantable coils or coils being geometrically adaptable to the sample, e.g. flexible coils or coils comprising mutually movable parts · CPC title

• G01R33/285

  Invasive instruments, e.g. catheters or biopsy needles, specially adapted for tracking, guiding or visualization by NMR · CPC title