Patent Application
20220008113
The present disclosure relates generally to radiofrequency (RF) ablation systems, and more particularly to controlling temperatures in RF ablation systems.
RF nerve ablation may be used, for example, to treat osteoarthritic pain of the spine. Specifically, RF ablation therapy reduces pain through the destruction of nerves using RF energy. The RF energy may be tuned based on cannula size, target temperatures, and dwell time. For example, certain anatomical targets generally require a relatively large cannula to create a relatively large lesion, while other anatomical targets may require a relatively small cannula to limit collateral damage.
At least some known RF ablation systems use a closed-loop control scheme to control RF power to achieve a target temperature without requiring human input. Closed-loop control allows therapy to be relatively straightforward (e.g., as simple as performing an injection).
In an RF ablation system, an RF ablation generator controls operation of a cannula. Different types of RF ablation generators vary in their ability to heat cannulas with different tip sizes. However, cannulas are generally disposable components, and the size of a connected cannula tip is typically not provided to the RF ablation generator via user input or otherwise. As a result, at least some known RF ablation generators include a temperature control system that employs a “one-size fits all” approach. Such systems may perform well for mid-sized cannulas, but may underperform for relatively large and relatively small cannulas. For example, such systems may waste power and fail to heat relatively large cannulas, or may heat relatively small cannulas so fast that suboptimal lesions are generated.
Accordingly, it would be desirable to provide an RF ablation system that includes a temperature control system that automatically compensates for the size of the attached cannula.
In one embodiment, the present disclosure is directed to a temperature control system for use in a radiofrequency (RF) ablation system including a cannula. The temperature control system includes a subtractor circuit configured to calculate a temperature error as a difference between a target temperature and a measured temperature at a tip of a cannula, and a proportional-integral-derivative (PID) controller coupled to the subtractor circuit and configured to apply an RF voltage to the tip of the cannula, the PID controller configured to determine the RF voltage based on the temperature error and a proportional coefficient, an integral coefficient, and a derivative coefficient of the PID controller. The temperature control system further includes a PID coefficient controller coupled to the PID controller, the PID coefficient controller configured to dynamically adjust the proportional, integral, and derivative coefficients of the PID controller during operation of the RF ablation system.
In another embodiment, the present disclosure is directed to a radiofrequency (RF) ablation system. The RF ablation system includes a cannula including a tip, and an RF ablation generator coupled to the cannula, the RF ablation generator including a temperature control system. The temperature control system includes a subtractor circuit configured to calculate a temperature error as a difference between a target temperature and a measured temperature at a tip of a cannula, and a proportional-integral-derivative (PID) controller coupled to the subtractor circuit and configured to apply an RF voltage to the tip of the cannula, the PID controller configured to determine the RF voltage based on the temperature error and a proportional coefficient, an integral coefficient, and a derivative coefficient of the PID controller. The temperature control system further includes a PID coefficient controller coupled to the PID controller, the PID coefficient controller configured to dynamically adjust the proportional, integral, and derivative coefficients of the PID controller during operation of the RF ablation system.
In another embodiment, the present disclosure is directed to a method of controlling an RF ablation system including a cannula. The method includes calculating a temperature error as a difference between a target temperature and a measured temperature at a tip of the cannula, determining, using a proportional-integral-derivative (PID) controller, an RF voltage based on the temperature error and a proportional coefficient, an integral coefficient, and a derivative coefficient of a PID controller, applying the RF voltage to the tip of the cannula using the PID controller, and dynamically adjusting the proportional, integral, and derivative coefficients of the PID controller during operation of the RF ablation system.
The foregoing and other aspects, features, details, utilities and advantages of the present disclosure will be apparent from reading the following description and claims, and from reviewing the accompanying drawings.
Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.
The present disclosure provides systems and methods for controlling temperature in a radiofrequency (RF) ablation system. A temperature control system includes a subtractor circuit configured to calculate a temperature error as a difference between a target temperature and a measured temperature at a tip of a cannula. The temperature control system further incudes a proportional-integral-derivative (PID) controller coupled to the subtractor circuit and configured to apply an RF voltage to the tip of the cannula, the PID controller configured to determine the RF voltage based on the temperature error and a proportional coefficient, an integral coefficient, and a derivative coefficient of the PID controller. The temperature control system further includes a PID coefficient controller coupled to the PID controller, the PID coefficient controller configured to dynamically adjust the proportional, integral, and derivative coefficients of the PID controller during operation of the RF ablation system.
Referring now to the drawings, and in particular to
In the embodiment shown in
Based on the calculated difference, PID controller 204 determines an RF voltage (using the proportional, integral, and derivative coefficients), and applies the determined RF voltage to cannula 104 using a first gain circuit 206. More specifically, PID controller 204 attempts to minimize the difference between the temperature command and the measured temperature. First gain circuit 206 may be implemented, for example, using a digital to analog converter (DAC) and RF hardware. Alternatively, first gain circuit 206 may be implemented using any suitable devices.
The applied RF voltage correlates to an actual temperature experienced at tip 108. Specifically, a transfer function 208 dictates the actual temperature that results from a given RF voltage (e.g., based at least in part on an impedance 210 and an electrical current to heat conversion rate 212 of cannula 104).
Every therapy using RF ablation system 100 will have a different transfer function 208 between electrical and thermal energy that PID controller 204 must contend with to attempt to ensure that cannula 104 is properly heated. Specifically, a number of different parameters determined the particular transfer function 208. These parameters include the anatomical target of the therapy (e.g., different therapies require cannula placements in different tissues), the RF accessory used for the therapy (e.g., different therapies require different size cannulas), and the particular patient (e.g., different patients have different electrical and thermal properties).
The actual temperature at tip 108 is measured using a second gain circuit 220 to generate a measured temperature. Second gain circuit 220 may be implemented, for example, using a thermocouple, signal conditioning circuitry, and an analog to digital converter (ADC). Alternatively, second gain circuit 220 may be implemented using any suitable devices. The measured temperature is then provided to subtractor circuit 202, to effect further adjustments by PID controller 204 based on an updated temperature error. Accordingly, temperature control system 200 is a closed-loop control system.
As noted above, temperature control system 200 may perform well for some cannulas, but may underperform for other cannulas (due to variations in the transfer functions).
For example,
As shown by graph 302, for the first cannula, the temperature was increased smoothly, and the target temperature was maintained. This is not surprising, given that the proportional, integral, and derivative coefficients of PID controller 204 were fixed at values optimized for the first cannula. However, as shown by graph 304, for the second cannula, there were large oscillations in the temperature both during the increase to the target temperature and while attempting to maintain the target temperature. Accordingly, graphs 302 and 304 demonstrate that PID controller 204 (with fixed coefficients) may perform well for some cannulas, but not for all cannulas.
In contrast to temperature control system 200, temperature control system 400 dynamically adjusts the proportional, integral, and derivative coefficients of PID controller 204 during operation to ensure stable performance across a wide range of cannulas. Specifically, as shown in
By automatically adjusting the control loop during operation, temperature control system 400 enables proper operation of RF ablation system 100 for a plurality of different cannulas. Specifically, PID coefficient controller 402 automatically and dynamically adjusts the proportional, integral, and derivative coefficients to match whatever type of cannula 104 is currently attached to RF ablation generator 102. As compared to known temperature control systems, the temperature control systems described herein facilitate rapidly and reliably heating both large and small cannulas, resulting in a higher rate of therapy success.
In one embodiment, PID coefficient controller 402 initializes the proportional, integral, and derivative coefficients with values for the largest possible cannula size. Alternatively, PID coefficient controller 402 may initialize the coefficients to any suitable values. In example, the coefficients may be initialized as Kp=37.5, Ki=0.75, and Kd=56.25. Alternatively, those of skill in the art will appreciate that the coefficients may be initialized to any suitable value.
The initialized coefficients are then scaled by the number of active channels in RF ablation system 100. The number of active channels corresponds to the number of active electrodes. For example, systems with multiple channels may include multiple active electrodes on a single cannula and/or multiple active cannulas. The number of channels may be determined, for example, based on a user input received at RF ablation generator 102. Alternatively, the number of channels may be automatically determined by RF ablation generator 102 in some embodiments.
In one embodiment, the initialized coefficients are scaled according to the following Table 1:
Scaling the initialized coefficients ensures that the same amount of power is delivered across multiple channels, due to time-multiplexing schemes implemented by RF ablation generator 102. For example, when four channels are active, the same temperature error will result in doubled output voltages as compared to when only two channels are active.
During operation, PID coefficient controller 402 monitors the calculated temperature error (i.e., the difference between the temperature command and the measured temperature) at a predetermined sampling frequency (e.g., 8 Hz). The temperature error is compared to one or more threshold values, and the coefficients are adjusted accordingly, as described herein in detail.
As shown in
In this embodiment, the temperature error is compared to upper and lower thresholds that define a temperature range. If the temperature error falls outside the temperature range, the coefficients are adjusted accordingly, as described herein.
Specifically, at block 508, the temperature error is compared to the lower threshold. The lower threshold may be, for example, 1° C. If the temperature error is less than the lower threshold, flow proceeds to block 510. If the temperature error is not less than the lower threshold, flow proceeds to block 512.
At block 510, the coefficients are compared to a minimum value (also referred to as a floor value for coefficients). The floor value may be the same for each coefficient, or different coefficients may have different floor values. The floor value may be, for example, 25% of the initial value. If the coefficients are each greater than the floor value, flow proceeds to block 514. If the coefficients are not greater than the floor value, flow proceeds to block 516, and the current adjustment cycle ends (no adjustment is made in this scenario).
At block 514, the coefficients are each reduced by a predetermined amount. Specifically, the coefficients are updated by multiplying each coefficient by a first scalar (Scalar_1). The first scalar may be the same for each coefficient, or different coefficients may be multiplied by different first scalars. The first scalar may be, for example, 0.9 (i.e., reducing the coefficients by 10%). Alternatively, the first scalar may be any suitable value (e.g., 0.75, 0.5, or 0.25). Flow then proceeds to block 516, and the current adjustment cycle ends.
At block 512, the temperature error is compared to the upper threshold. The upper threshold may be, for example, 2° C. If the temperature error is greater than the upper threshold, flow proceeds to block 520. If the temperature error is not greater than the upper threshold (indicating that the temperature error falls within the temperature range), flow proceeds to block 516, and the current adjustment cycle ends.
At block 520, the coefficients are compared to a maximum value (also referred to as a ceiling value for coefficients). The ceiling value may be the same for each coefficient, or different coefficients may have different ceiling values. The ceiling value may be, for example, 110% of the initial value. If the coefficients are each less than the ceiling value, flow proceeds to block 522. If the coefficients are not less than the ceiling value, flow proceeds to block 516, and the current adjustment cycle ends (no adjustment is made in this scenario).
At block 522, the coefficients are each increased by a predetermined amount. Specifically, the coefficients are updated by multiplying each coefficient by a second scalar (Scalar_2). The second scalar may be the same for each coefficient, or different coefficients may be multiplied by different second scalars. The second scalar may be, for example, 1.1 (i.e., increasing the coefficients by 10%). Alternatively, the first scalar may be any suitable value (e.g., 1.25, 1.5, 1.75, or 2.0). Flow then proceeds to block 516, and the current adjustment cycle ends.
Using method 500, the coefficients of PID controller 204 are rapidly scaled and quickly settle to stable values, resulting in stable operation of temperature control system 400
For example,
In contrast, graph 604 simulates operation of temperature control system 400 using method 500. As shown in
As compared to at least some known temperature control systems with static PID coefficients (e.g., temperature control system 200), temperature control system 400 dynamically adjusts control loop performance (by adjusting PID coefficients) to improve cannula heating performance. As a result, temperature control system 400 is compatible with a wide range of cannulas without requiring a user input specifying the cannula size. Obviating the need for user input of the cannula size also eliminates the potential for user error.
Thus, the embodiments described herein are able to dynamically adjust PID coefficients as lesioning is performed. In contrast, at least some known systems attempt to characterize the transfer function prior to lesioning, lengthening procedure time. As such, using the systems methods described herein, clinicians (e.g., interventional anesthesiologists) may perform many RF ablations in a relatively short time period, due to the efficient workflow enabled by the temperature control systems described herein.
The embodiments described herein provide systems and methods for controlling temperature in am RF ablation system. A temperature control system includes a subtractor circuit configured to calculate a temperature error as a difference between a target temperature and a measured temperature at a tip of a cannula. The temperature control system further incudes a PID controller coupled to the subtractor circuit and configured to apply an RF voltage to the tip of the cannula, the PID controller configured to determine the RF voltage based on the temperature error and a proportional coefficient, an integral coefficient, and a derivative coefficient of the PID controller. The temperature control system further includes a PID coefficient controller coupled to the PID controller, the PID coefficient controller configured to dynamically adjust the proportional, integral, and derivative coefficients of the PID controller during operation of the RF ablation system.
Although certain embodiments of this disclosure have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this disclosure. All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are only used for identification purposes to aid the reader's understanding of the present disclosure, and do not create limitations, particularly as to the position, orientation, or use of the disclosure. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the disclosure as defined in the appended claims.
When introducing elements of the present disclosure or the preferred embodiment(s) thereof, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
As various changes could be made in the above constructions without departing from the scope of the disclosure, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
