Active adaptive detuning systems and methods for interventional devices
Inventors
Assignees
US Department of Health and Human Services
Publication Number
US-9486158-B2
Publication Date
2016-11-08
Expiration Date
2031-07-01
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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.
Core Innovation
Active MRI compatible interventional devices, such as catheters, include at least one RF antenna to be visible under MRI analysis. These devices have conductive transmission lines that may heat up significantly during interventional MRI procedures due to the formation of eddy currents. The electrical field coupling between the interventional devices and RF signals depends on the device's position, orientation within the bore, and insertion length.
To address the heating issue, the system detects an induced current signal during the RF transmission phase and selectively adjusts the impedance value associated with the interventional device. This adjustment is achieved using a varactor and integrated circuit components to control current levels, ensuring the induced currents remain below a threshold level, thus controlling heating in the device.
Existing decoupling circuits at the proximal end of catheters are not effective when conductor lengths exceed 80 cm, causing significant heating problems. This invention provides an adaptive detuning system and methods that iteratively adjust impedance values dynamically during an MRI procedure to maintain safe levels of induced current, thereby enabling the use of active MRI compatible interventional devices without severe heating.
Claims Coverage
The patent contains three independent claims addressing an active adaptive detuning system, an adaptive detuning circuit, and a method for adjusting impedance during MRI procedures. The inventive features focus on dynamic impedance adjustment to limit induced currents and heating in interventional devices.
Active adaptive detuning system for real-time current management
The system includes an MRI that applies and discontinues RF radiation across a subject. It comprises an interventional device with an RF antenna and inner conductor that receive and conduct induced currents. An adaptive detuning circuit iteratively adjusts the device's impedance through multiple values, determines the corresponding current magnitude for each, and selects an impedance with induced current below a threshold to limit heating. The adaptive detuning circuit includes a balun circuit, matching circuit, detuning circuit, and a control circuit that manages these adjustments based on detected induced current and threshold values stored in memory.
Adaptive detuning circuit for iterative impedance tuning
The circuit connects to the inner conductor of the interventional device and balances impedances between the device and MRI system. It dynamically varies impedance to disrupt resonance and disconnects the RF antenna in response to a DC control signal. The control circuit generates the DC signal during RF radiation, detects induced current magnitude, retrieves a threshold current level, iteratively adjusts detuning capacitance through various values, compares detected currents to the threshold, and sets the capacitance to a value ensuring induced current is below threshold to limit heating.
Method for dynamically adjusting interventional device impedance during MRI
The method involves inserting an interventional device with an inner conductor and RF antenna into a subject during MRI. It applies and discontinues RF radiation, receives induced current based on RF signals emitted by tissue when RF is off, balances impedances, disconnects the RF antenna via a DC control signal generated while RF is applied, detects induced current magnitude, retrieves a stored threshold current level, iteratively adjusts impedance by varying detuning capacitance through multiple values, determines currents corresponding to each capacitance, compares currents to the threshold, and sets the capacitance to a first value where the induced current is below the threshold, thus limiting heating.
The claims cover a system, circuit, and method that iteratively and dynamically adjust the impedance of an active MRI interventional device by detecting induced currents and ensuring these remain below a safe threshold. This is achieved using a balun, matching, and detuning circuits controlled by a control circuit that adjusts a varactor-based detuning capacitance to prevent device heating during MRI procedures.
Stated Advantages
Effectively controls and limits induced currents and voltages in interventional devices during MRI to prevent dangerous local heating and potential tissue damage.
Dynamically adjusts device impedance based on insertion length and orientation within the body, enabling safe use of active MRI compatible interventional devices without severe heating.
Iterative impedance adjustment within each MRI sequence repetition time allows quick response to varying induced currents, maintaining safety.
Documented Applications
Use with MRI-compatible interventional devices such as catheters, guidewires, and endoscopes during MRI-guided interventional and intraoperative procedures.
Enabling real-time visualization and tracking of interventional devices inside a subject undergoing MRI by incorporating an RF antenna at the device distal end.
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