Q-factor control for use with retained surgical article detection system

Abstract

An interrogation and detection system for detecting a surgical instrument within a patient, the interrogation and detection system comprising: an RF tag configured to transmit a return signal when energized; a signal generator configured to generate an energization signal for the RF tag; an antenna operably coupled to the signal generator and configured to receive the return signal transmitted by the RF tag; a processor; and a memory. The memory includes instructions stored thereon that, when executed by the processor, cause the system to: receive the return signal; detecting an impedance of the antenna based on the return signal; and determining a ratio of the real impedance to the reactive impedance based on the detected impedance.

Description

Technical Field

[0001] The present disclosure relates generally to interrogation and detection systems for radio frequency (RF) tags, and more particularly, to interrogation, detection, and inventory systems for radio frequency (RF) tags used within a surgical site. Background Art

[0002] Before completing a surgical procedure, it is often useful to determine whether an object associated with the surgical procedure is present in the patient's body. Such objects can take various forms. For example, the object can take the form of an instrument, such as a scalpel, scissors, forceps, hemostats, and / or clamps. And, for example, the object can take the form of related accessories and / or disposable objects, such as surgical sponges, gauze, and / or pads. Failure to locate an object before suturing may require additional surgical procedures and may have undesirable medical consequences in some cases.

[0003] Accordingly, there is a need for technology that can provide presence detection and tagged surgical item / instrument identification capabilities and inventory control of such tagged items / instruments in a medical environment. Specifically, detecting the presence of, identifying, and maintaining inventory of tagged surgical items and materials used during the performance of medical procedures. Existing technologies can accomplish these functions either individually or in combination with one another, but the methods and packaging of the discrete solutions used are not ideal for the application. More specifically, the components attached or attached to the item being tracked are either too bulky, present a cumbersome or impediment when performing the procedure, or the detection and identification performance of the solution may degrade rapidly in the presence of variable and uncontrolled dielectric or conductive materials.

[0004] Accordingly, there is a need for improved presence detection, tagged item identification, and inventory capabilities in healthcare environments. Summary of the invention

[0005] The present disclosure relates to systems for detecting surgical objects and devices used in body cavities during surgical procedures, and in particular to systems and methods for controlling the electrical damping factor (Q factor) of antennas used in such systems.

[0006] According to various aspects of the present disclosure, an interrogation and detection system for detecting surgical instruments in a patient is proposed. The system includes: an RF tag configured to transmit a return signal when powered on; a signal generator configured to generate a power-on signal for the RF tag; an antenna operably coupled to the signal generator and configured to receive the return signal transmitted by the RF tag; a processor; and a memory. The memory includes instructions stored thereon, which, when executed by the processor, cause the system to: receive the return signal; detect the impedance of the antenna based on the return signal, the impedance including a real impedance and a reactive impedance; and determine the ratio of the real impedance to the reactive impedance based on the detected impedance.

[0007] In one aspect of the disclosure, the instructions, when executed by the processor, may further cause the system to set the ratio to a predetermined constant value based on the determined ratio of the real impedance to the reactive impedance.

[0008] In another aspect of the present disclosure, the instructions, when executed by the processor, may further cause the system to set the ratio within a predetermined range of values ​​based on the determined ratio of the real impedance to the reactive impedance.

[0009] In yet another aspect of the present disclosure, setting the ratio to a predetermined value may be performed by adjusting a real element and / or a reactive element of the antenna.

[0010] In yet another aspect of the present disclosure, impedance may be detected based on current passing through the antenna.

[0011] In one aspect of the disclosure, the adjustment may be performed by varying the current through the antenna.

[0012] In another aspect of the present disclosure, the adjustment may be performed by varying a tuning voltage to a voltage controlled resistor.

[0013] In yet another aspect of the present disclosure, the current may be measured by a root mean square (RMS) converter.

[0014] In another aspect of the present disclosure, the instructions, when executed by the processor, may further cause the system to determine whether a return signal is received via the antenna from an RF tag marking a surgical instrument used in the procedure.

[0015] In one aspect of the disclosure, the instructions, when executed by the processor, may further cause the system to send information to a display configured to display information associated with the RF tag.

[0016] According to various aspects of the present disclosure, an interrogation and detection system for detecting surgical instruments in a patient is proposed. The interrogation and detection system includes: an RF tag configured to transmit a return signal when powered on; a signal generator configured to generate a power-on signal for the RF tag; an antenna operably coupled to the signal generator and configured to receive the return signal transmitted by the RF tag; a processor; and a memory. The memory includes instructions stored thereon, which, when executed by the processor, cause the system to: measure a current through the antenna; determine a Q factor of the antenna based on the measured current; and compare the determined Q factor with a predetermined value.

[0017] In yet another aspect of the disclosure, the instructions, when executed by the processor, cause the system to adjust a Q factor of the antenna based on the comparison.

[0018] In one aspect of the disclosure, the adjustment may be performed by varying the current through the antenna.

[0019] In another aspect of the present disclosure, the adjustment may be performed by varying a tuning voltage to a voltage controlled resistor.

[0020] In yet another aspect of the present disclosure, the current may be measured by an RMS converter.

[0021] In one aspect of the present disclosure, a computer-implemented method for detecting a surgical instrument in a patient is provided. The method includes: generating, by a signal generator, a power-on signal for an RF tag attached to the surgical instrument; receiving a return signal from the RF tag by an antenna operably coupled to the signal generator; measuring a current through the antenna; determining a Q factor of the antenna based on the measured current; comparing the determined Q factor with a predetermined value; and adjusting the Q factor of the antenna based on the comparison.

[0022] In another aspect of the present disclosure, the adjustment may be performed by varying the current through the antenna.

[0023] In yet another aspect of the present disclosure, the method may further include determining whether a return signal is received via the antenna from an RF tag marking a surgical instrument used in the procedure.

[0024] In yet another aspect of the present disclosure, the current may be measured by an RMS converter.

[0025] In one aspect of the present disclosure, the method may further include sending information to a display configured to display information related to the RF tag. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In the drawings, the same reference numerals represent similar elements or actions. The sizes and relative positions of the elements in the drawings are not necessarily drawn to scale. For example, the shapes and angles of various elements are not drawn to scale, and some of these elements are arbitrarily enlarged or reduced and positioned to improve the readability of the drawings. In addition, the particular shapes of the drawn elements are not intended to convey any information about the actual shape of the particular element, but are merely selected for ease of identification in the drawings.

[0027] Various aspects of the presently disclosed antennas, RF tags, and articles containing the same are described below with reference to the accompanying drawings.

[0028] Figure 1 is a schematic diagram showing an interrogation and detection system configured to detect an RF-tagged object within a patient's body according to one illustrated aspect;

[0029] Figure 2 is configured according to an embodiment of the present disclosure Figure 1 A functional block diagram of a controller used with an interrogation and detection system;

[0030] Figure 3A According to an embodiment of the present disclosure, Figure 1 A schematic diagram of a control loop used with an interrogation and detection system;

[0031] Figure 3B According to the embodiments of the present disclosure Figure 1 A schematic diagram of a nested control loop used with an interrogation and detection system;

[0032] Figure 4 According to the embodiments of the present disclosure Figure 3A Schematic diagram of the resistance factor control circuit of the control loop;

[0033] Figure 5 According to the embodiments of the present disclosure Figure 3A Schematic diagram of the loop filter of the control loop;

[0034] Figure 6 is a flow chart of a computer-implemented method for detecting a surgical instrument being used within a surgical site within a patient; and

[0035] Figure 7 It is a graph of the resistance damping factor versus frequency as the real component of a tuned circuit increases. DETAILED DESCRIPTION

[0036] In the following description, certain specific details are set forth in order to provide a thorough understanding of the disclosed aspects. However, one skilled in the relevant art will recognize that the aspects may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other cases, well-known structures associated with transmitters, receivers, or transceivers are not shown or described in detail to avoid unnecessarily obscuring the description of the aspects.

[0037] References throughout this specification to "one aspect" or "an aspect" refer to specific features, structures, or characteristics described in conjunction with an aspect that is included in at least one aspect. Thus, the phrases "in one aspect" or "in an aspect" appearing in various places throughout this specification are not necessarily all referring to the same aspect. Furthermore, in one or more aspects, specific features, structures, or characteristics may be combined in any suitable manner.

[0038] In interrogation and detection systems, the electrical damping factor (Q factor) can significantly affect the matching network. The matching network is necessary to present an output impedance to the RF amplifier that matches the impedance of the antenna's input so that electrical reflections are minimized. If the Q factor of the load can be fixed, the matching network can be greatly simplified or eliminated. When the antenna is waved over a patient, the dielectric constant of the patient's tissue can change the Q factor and / or the tuning of the antenna. Since the Q factor can be a variable amount or value, the present disclosure describes a circuit that controls the Q factor and achieves consistency in power delivery to the antenna.

[0039] Figure 1 An interrogation and detection system 10 is depicted for detecting a radio frequency (RF) tag to determine whether an item, implement, or object 100a is present in a patient 18. The interrogation and detection system 10 generally includes a signal generator 300 and an antenna 110 coupled to the signal generator 300 via one or more communication paths (e.g., a coaxial cable 122). In one aspect of the interrogation and detection system 10, the antenna 110 can be handheld or embedded in a base pad.

[0040] The object 100a can take various forms, such as instruments, accessories and / or disposable objects useful in performing surgical procedures. For example, the object 100a can take the form of a scalpel, scissors, tweezers, hemostats and / or clamps. And, for example, the object 100a can take the form of surgical sponges, gauze and / or pads. The object 100a is marked, carried, attached or otherwise coupled to the RF tag 100. The various aspects of the inquiry and detection system 10 disclosed herein are particularly suitable for operating with one or more RF tags 100, which are not accurately tuned to the selected or selected resonant frequency. Therefore, the RF tag 100 does not require high manufacturing tolerances or expensive materials, and therefore the manufacturing cost may be low. The RF tag may include an inductor and a capacitor forming a resonant tank, or may include an RFID tag, which includes an inductor and a capacitor and a circuit for enabling an ID function.

[0041] In use, the medical provider 12 may use the detection system 10 to detect one or more RF tags 100 and, therefore, the presence of an object 100a in a patient 18. For a detailed description of an exemplary interrogation and detection system, reference may be made to commonly owned U.S. Patent Application Publication No. 2004 / 0250819, entitled “Apparatus and Method For Detecting Objects Using Tags and Wideband Detection Device,” filed on March 29, 2004, by Blair et al., the entire contents of which are hereby incorporated herein by reference.

[0042] In various aspects, the signal generator 300 may generate a power-on signal for the RF tag 100. The RF tag 100 may be attached to a surgical instrument. The antenna 110 may receive a return signal from the RF tag 100. The controller 200 may determine whether a return signal is received from the RF tag 100 via the antenna 110, which marks the surgical instrument used in the procedure. The controller may then send information to the display 140 to display information related to the RF tag 100.

[0043] Reference now Figure 2, the controller 200 includes a processor 220 connected to a computer-readable storage medium or memory 230. The computer-readable storage medium or memory 230 may be a volatile type of memory, such as RAM, or a non-volatile type of memory, such as flash media, disk media, etc. In various aspects of the present disclosure, the processor 220 may be another type of processor, such as a digital signal processor, a microprocessor, an ASIC, a graphics processing unit (GPU), a field programmable gate array (FPGA), or a central processing unit (CPU). In certain aspects of the present disclosure, as opposed to a processor, network inference may also be accomplished in a system that implements weights as memristors, chemically, or in other inference calculations.

[0044] In various aspects of the present disclosure, the memory 230 may be a random access memory, a read-only memory, a magnetic disk memory, a solid-state memory, an optical disk memory, and / or another type of memory. In some aspects of the present disclosure, the memory 230 may be separate from the controller 200 and may communicate with the processor 220 via a communication bus of a circuit board and / or via a communication cable (such as a serial ATA cable or other type of cable). The memory 230 includes computer-readable instructions that can be executed by the processor 220 to operate the controller 200. In other aspects of the present disclosure, the controller 200 may include a network interface 240 to communicate with other computers or servers. The storage device 210 may be used to store data. The disclosed method may be run on the controller 200 or on a user device, including, for example, on a mobile device, an IoT ("Internet of Things") device, or a server system.

[0045] Figure 3A 1 shows a block diagram of a control loop 400 of the interrogation and detection system 10. The control loop 400 includes a Q factor control circuit 500, a controller 200, and a low pass filter 600 ( Figure 5 ). The Q factor control circuit 500 generally includes a sensor 420 and a voltage controlled resistor 410 ( Figure 4 ). The voltage controlled resistor 410 (VCR) is typically a three terminal active device with one input port and two output ports. The input port voltage controls the value of the resistor between the output ports. The voltage controlled resistor is most often constructed from a field effect transistor (FET), such as a JFET and / or a MOSFET. The junction capacitance of the voltage controlled resistor 410 can limit the speed at which the resistance can be adjusted and the real part of the impedance that can be adjusted by the VCR. The voltage controlled resistor 410 can include one or more devices connected in series.

[0046] The control loop 400 is configured to measure the current in series with the antenna 110 and adjust the channel impedance of one or more series voltage-controlled resistors 410 in order to maintain a constant current through the antenna 110 .

[0047] The sensor 420 is configured to sense a signal (e.g., an electrical parameter, such as current and / or voltage) and transmit the electrical parameter to the controller 200. The sensor 420 may include a root mean square (RMS) converter. To measure AC current, the signal is usually converted to an equivalent value of DC current, i.e., root mean square (RMS).

[0048] The controller 200 determines whether the ratio of the real impedance to the reactive impedance is within a desired predetermined value range (eg, window) based on the sensed signal. If the ratio is outside the value range, an error current and / or voltage may be generated by the controller 200 and transmitted to the low pass filter 600.

[0049] In various aspects, the interrogation and detection system 10 may include nested control loops.

[0050] Figure 3B It shows that it can include Figure 3A The nested control loop 400' is a block diagram of a portion of a control loop of FIG. The nested control loop 400' generally includes Figure 3A The nested control loop 400' is configured to provide a "fast loop" and a "slow loop" corresponding to the control loop of the antenna. The "slow loop" includes a programmable high voltage direct current (HVDC) power supply 430 and an amplifier 440. The nested control loop 400' is configured to serve the voltage amplitude of the antenna source RF signal to minimize the thermal load on the VCR 410 and adjust the bias point of the Q factor controller to achieve maximum Q factor control over the dynamic range. During transient events, the thermal load on the VCR 410 may exceed the rated voltage amplitude. The "slow loop" is configured to reduce the dissipated heat by reducing the amplifier 440 output power in the event that the antenna Q factor becomes high during use.

[0051] refer to Figure 4 , showing Figure 3A The Q-factor control circuit 500 of the control loop of FIG. The Q-factor control circuit 500 generally includes a voltage-controlled resistor 502, an RF matching network 506, and a sense resistor 504. The sense resistor is generally a relatively small value resistor, such as about 0.5 ohms, and is configured to sense the antenna current (I 天线 ). The Q-factor control circuit 500 may include other filtering components (such as inductors and / or capacitors) to process the control voltage.

[0052] Typically, the body or tissue of the patient 18 presents an electrical impedance to the antenna 110, and when the antenna 110 is moved closer to the patient 18 ( Figure 1 ), the impedance increases and vice versa. Signal generator 300 ( Figure 1The total impedance seen by the output of ) is the sum of the antenna impedance and the impedance of one or more voltage-controlled resistors 502 in the Q-factor control circuit 500. The RF matching network 506 can be used to match the antenna impedance to the impedance of the signal generator 300. By modulating the impedance of the voltage-controlled resistor 502, the impedance of the signal generator 300 ( Figure 1 ) the total impedance seen by the device is more or less constant.

[0053] For maximum power transfer, the signal generator 300 ( Figure 3A ) should be a relatively constant impedance. This constant impedance enables any RF matching network 506 to be substantially minimized or eliminated. In addition, the transmit power of the signal generator 300 can be constant (or at least maintained within a small range of values), which has the benefit of meeting regulatory agency requirements.

[0054] The control loop may have a loop bandwidth of approximately 1 / 100 ms.

[0055] Figure 5 yes Figure 3A Schematic diagram of an exemplary loop filter of a control loop. Low pass filter 600 ( Figure 5 ) is configured to integrate the error current to generate a Q factor which is transmitted to the Q factor control circuit 500 ( Figure 4 ) of the Q factor control voltage. Loop filter 600 can be an active filter or a passive filter. An active loop filter includes active devices (such as an operational amplifier) ​​and generally has a high input impedance. Loop filter 600 can include one or more poles.

[0056] Now refer to Figure 6 , showing the operation of detecting a surgical instrument in a patient. In various embodiments, the interrogation and detection system 10 ( Figure 1 ) to execute Figure 6 In various embodiments, the operation may be performed by another type of system and / or during another type of procedure. Figure 6 The following description will refer to the interrogation and detection system, but it will be understood that such description is exemplary and does not limit the scope of the present disclosure and applicability to other systems and programs.

[0057] Initially, at step 602, the signal generator 300 generates a signal for the RF tag 100 ( Figure 1 ) power-on signal. The RF tag 100 can be attached to a surgical instrument. When the antenna 110 is within the patient 18 ( Figure 1 ) when waved over the tissue, the dielectric constant of the tissue can change the Q factor and / or tuning of the antenna 110.

[0058] Next, at step 604 , the controller 200 receives a return signal from the RF tag through the antenna 110 operably coupled to the signal generator 300 .

[0059] Next, at step 606, the controller 200 measures the current through the antenna 110. The current may be measured by an RMS converter and / or sensor 420 ( Figure 3A ) measurement. For example, a current of about 425 mA RMS (600 mA pp) may be measured. The current may be measured across a series resistor such as sense resistor 504. The measured antenna current (I 天线 )( Figure 4 ) will be transmitted to the controller 200. In various aspects, the RMS current may fall between about 0.7A-2A to maximize read distance (associated with the tag) and regulatory compliance, but other currents are also contemplated.

[0060] Next, at step 608, the controller 200 determines the Q factor of the antenna 110 based on the measured current. The Q factor of the antenna 110 is the ratio of the reactive part of the impedance to the real part of the impedance (Q=X L / R L ). For example, the ratio may be about 30:1. Although 30:1 is used as an example, other ratios are also contemplated. The antenna may have, for example, an inductance of about 1.68 uH, a real impedance R of about 5 ohms, and a L and an operating frequency of about 13.56MHz, which will have a reactive part X L The impedance is about 143 ohms. The Q factor (or determined Q) will be about 29 (Q = 143 ohms / 5 ohms).

[0061] Next, at step 620, the controller 200 compares the determined Q with a predetermined value of Q. For example, the predetermined value may be Q=35. The predetermined value 35 may be compared with the determined (or measured) value 29. The controller 200 may adjust the Q factor of the antenna 110 based on the comparison. For example, by changing the tuning voltage of the voltage-controlled resistor 410, the controller 200 may adjust the voltage-controlled resistor 410 ( Figure 3A ) to increase or decrease resistance in response to the detected impedance of antenna 110. The change in resistance will increase or decrease the Q of antenna 110. For example, the value of voltage controlled resistor 410 can be reduced to about 4 ohms, which will result in a Q factor of about 35.

[0062] In various aspects, the controller 200 may detect the impedance of the antenna based on the return signal. The impedance may include real impedance and reactive impedance. The impedance may be detected based on the current passing through the antenna 110.

[0063] Setting the ratio to a predetermined value may be performed by adjusting the real element and / or reactive element of the antenna. For example, by changing the tuning voltage of the voltage controlled resistor 410, the controller 200 may adjust the voltage controlled resistor 410 to increase or decrease the resistance in response to the detected impedance of the antenna 110. Figure 1 ) current to perform this adjustment.

[0064] In various aspects, the controller 200 may determine a ratio of real impedance to reactive impedance based on the detected impedance. The controller 200 may set the ratio to a predetermined constant value (eg, approximately + / - 0.1 ohms) based on the determined ratio of real impedance to reactive impedance.

[0065] The controller 200 can set the ratio within a predetermined range of values ​​based on the determined ratio of the real impedance to the reactive impedance. The ratio is a unitless number (ohm / ohm). For example, the controller 200 can maintain a value (ratio) of 10 ohms-20 ohms per ohm, depending on the final application. An uncompensated (no Q-factor control) resonant inductive antenna can have a Q-factor offset from >30 to <10, resulting in a field strength reduction of up to 70% in the presence of tissue loading when compared to free space. When the antenna is loaded by tissue, the Q-factor control circuit 500 intentionally reduces the free space field strength (reduces the Q-factor) in order to obtain a "working space" (return Q-factor). Using the disclosed technology, the "return Q-factor" operation can be performed very quickly and with low computational overhead, which is one of the features that makes the Q-factor control circuit 500 so effective. Alternatively, taking away the Q-factor (such as quickly transitioning from patient load to free space) is also very fast, allowing compliance with radio regulations in the free space case while maximizing the field strength (still compliant) in the loaded case.

[0066] refer to Figure 7 , shows a graph of Q factor versus frequency as the real component of the tuned circuit increases. As the real component of the antenna increases, the Q factor is a lower value. Although described as an element of an RF tag based system, it is contemplated that the Q factor control concepts described herein extend to any inductive (coil) antenna based system where field strength is directly related to energization / detection performance.

[0067] Although various aspects of the disclosure have been shown in the accompanying drawings, it is not intended to limit the disclosure thereto, as it is intended that the disclosure be as broad as the art will allow and that the specification should be read in the same manner. Therefore, the above description should not be construed as limiting, but merely as an illustration of particular aspects. Those skilled in the art will be able to envision other modifications within the scope and spirit of the claims appended hereto.

Claims

1. An interrogation and detection system for detecting a surgical instrument in a patient, the interrogation and detection system comprising: an RF tag configured to transmit a return signal when powered; a signal generator configured to generate a power-on signal for the RF tag; an antenna operably coupled to the signal generator, the antenna being configured to receive the return signal transmitted by the RF tag; processor; and a memory including instructions stored thereon that, when executed by the processor, cause the system to: receiving the return signal; detecting an impedance of the antenna based on the return signal, wherein the impedance includes a real impedance and a reactive impedance; and A ratio of the real impedance to the reactive impedance is determined based on the detected impedance. 2 . The system of claim 1 , wherein the instructions, when executed by the processor, further cause the system to set the ratio to a predetermined constant value based on the determined ratio of the real impedance to the reactive impedance. 3 . The system of claim 1 , wherein the instructions, when executed by the processor, further cause the system to set the ratio within a predetermined range of values ​​based on the determined ratio of real impedance to reactive impedance. 4 . The system of claim 3 , wherein setting the ratio to a predetermined value is performed by adjusting at least one of a real element or a reactive element of the antenna. The system of claim 4 , wherein the impedance is detected based on a current through the antenna. The system of claim 5 , wherein the adjusting is performed by varying the current through the antenna.

7. The system of claim 4, wherein the adjusting is performed by varying a tuning voltage to a voltage controlled resistor.

8. The system of claim 5, wherein the current is measured by a root mean square (RMS) converter.

9. The system of claim 1, wherein the instructions, when executed by the processor, further cause the system to determine whether a return signal is received via the antenna from an RF tag marking a surgical instrument used in a procedure.

10. The system of claim 9, wherein the instructions, when executed by the processor, further cause the system to: Information is sent to a display configured to display information associated with the RF tag.

11. An interrogation and detection system for detecting a surgical instrument in a patient, the interrogation and detection system comprising: an RF tag configured to transmit a return signal when powered; a signal generator configured to generate a power-on signal for the RF tag; an antenna operably coupled to the signal generator, the antenna being configured to receive the return signal transmitted by the RF tag; processor; and a memory including instructions stored thereon that, when executed by the processor, cause the system to: measuring a current through the antenna; determining an electrical damping factor (Q factor) of the antenna based on the measured current; as well as The determined Q factor is compared with a predetermined value.

12. The system of claim 11, wherein the instructions, when executed by the processor, further cause the system to adjust the Q factor of the antenna based on the comparison.

13. The system of claim 11, wherein the adjusting is performed by varying the current through the antenna.

14. The system of claim 11, wherein the adjusting is performed by varying a tuning voltage to a voltage controlled resistor.

15. The system of claim 11, wherein the current is measured by an RMS converter.

16. A computer-implemented method for detecting a surgical instrument within a patient, the method comprising: generating, by a signal generator, a power-on signal for an RF tag attached to a surgical instrument; receiving a return signal from the RF tag by an antenna operably coupled to the signal generator; measuring a current through the antenna; determining a Q factor of the antenna based on the measured current; comparing the determined Q factor with a predetermined value; as well as The Q factor of the antenna is adjusted based on the comparison.

17. The computer-implemented method of claim 16, wherein the adjusting is performed by varying the current through the antenna.

18. The computer-implemented method of claim 17, further comprising: A determination is made as to whether a return signal is received via the antenna from the RF tag marking a surgical instrument used in a procedure.

19. The computer implemented method of claim 17, wherein the current is measured by an RMS converter.

20. The computer-implemented method of claim 17, further comprising: Information is sent to a display configured to display information associated with the RF tag.

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