ACTIVE ADAPTIVE DETUNING SYSTEMS AND METHODS FOR INTERVENTIONAL DEVICES

• US 20130172729A1
• Filed: 07/01/2011
• Published: 07/04/2013
• Est. Priority Date: 07/02/2010
• Status: Active Grant

• Current Assignee: United States Secretary of Health and Human Services is the head of the United States Department of Health and Human Services
• Original Assignee: Government of the United States of America
• Inventors: Kocaturk, Ozgur
• Granted Patent: US 9,486,158 B2
• Time in Patent Office: Days
• US Class Current: 600/411
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: G01R 33/285 Invasive instruments, e.g. catheters or biopsy needles, specially adapted for tracking, guiding or visualization by NMR
• CPC Class Codes: G01R 33/34084 implantable coils or coils being geometrically adaptable to the sample, e.g. flexible coils or coils comprising mutually movable parts
• CPC Class Codes: 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

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.

Claims

1. A system for use during a magnetic resonance imaging procedure, the system comprising:

a magnetic resonance imaging device to selectively;

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.

2. The system of claim 1 wherein the adaptive detuning circuit comprises:

a balun circuit to balance impedances between the interventional device and the magnetic resonance imaging device;

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 device in response to a DC control signal; and

a control circuit to generate the DC control signal when a magnetic resonance imaging device applies the radio frequency radiation signal.

3. The system of claim 2 wherein control circuit is further configured to:

detect the magnitude of the induced current in the inner conductor;

retrieve the threshold current level from a memory; and

adjust the impedance value by adjusting an adaptive detuning capacitance of the adaptive detuning circuit based on the detected magnitude of the induced current.

4. The system of claim 3 wherein the control circuit is configured to:

iteratively adjust the impedance value by adjusting the detuning capacitance value through a series of detuning capacitance values;

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 a 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.

5. The system of claim 4 wherein the control circuit adjusts a varactor to adjust the detuning capacitance value.

6. The system of claim 4 wherein the series of detuning capacitance values includes at least eight different detuning capacitance values.

7. The system of claim 1 wherein the inner conductor is a microcoaxial cable.

8. 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 selectively 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 comprising:

a connector to connect to the inner conductor; and

a control 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.

9. The adaptive detuning circuit of claim 8 wherein the adaptive detuning circuit further comprises:

a balun circuit to balance impedances between the interventional device and the magnetic resonance imaging device;

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 device in response to a DC control signal; and

wherein the control circuit is further configured to generate the DC control signal when the when a magnetic resonance imaging device applies the radio frequency radiation signal.

10. The adaptive detuning circuit of claim 8 wherein control circuit is further configured to:

detect the magnitude of the induced current in the inner conductor;

retrieve the threshold current level from a memory; and

adjust the impedance value by adjusting the adaptive detuning capacitance value of the adaptive detuning circuit based on the detected magnitude of the induced current.

11. The adaptive detuning circuit of claim 10 wherein control circuit is configured to:

iteratively adjust the impedance value by adjusting the detuning capacitance value through a series of detuning capacitance values;

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 a 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.

12. The adaptive detuning circuit of claim 10 wherein the control circuit adjusts a varactor to adjust the detuning capacitance value.

13. The adaptive detuning circuit of claim 11 wherein the series of detuning capacitance values includes at least eight different detuning capacitance values.

14. The adaptive detuning circuit of claim 8 wherein the inner conductor is a microcoaxial cable.

15. 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 device;

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;

iteratively adjusting an impedance value of the interventional device through a plurality of impedance values;

determining a corresponding magnitude of the induced current in the inner conductor for each of the plurality of impedance values; and

setting 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.

16. The method of claim 15 further comprising:

balancing impedances between the interventional device and the magnetic resonance imaging system;

generating a DC control signal when the radio frequency radiation signal is being applied; and

disconnecting the radio frequency antenna from the magnetic resonance imaging device in response to a DC control signal.

17. The method of claim 15 further comprising:

retrieving the threshold current level from a memory; and

adjusting an adaptive detuning capacitance value based on the detected magnitude of the induced current to adjust the impedance value.

18. The method of claim 17 wherein iteratively adjusting the impedance value includes adjusting the detuning capacitance value through a series of detuning capacitance values and the method further comprises:

determining the 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 a threshold current value; and

setting 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.

19. The method of claim 17 further comprising adjusting a varactor to adjust the detuning capacitance value.

20. The method of claim 18 wherein the series of detuning capacitance values includes at least eight different detuning capacitance values.