Resonant circuit-based vascular monitor and related systems and methods

Abstract

Systems and methods for control and signal processing in a variable inductance, resonant circuit monitoring device are disclosed, including improved techniques for exciting a sensor resonant circuit using an excitation signal frequency sweep, techniques for verifying sensor readings and characterizing the sensor frequency output as a measured physical parameter, and improved techniques for isolating background electromagnetic noise and distinguishing known items from sensor measurement signals.

Description

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 934,399, filed on November 12, 2019, entitled “Resonant Circuit-Based Monitors and Related Systems and Methods,” which is incorporated herein by reference.

[0003] field

[0004] The present disclosure relates to improvements in wireless vascular monitors, and more particularly to resonant circuit-based monitors and related systems and methods.

[0005] background

[0006] A resonant circuit (RC) based sensor is one in which the resonant frequency changes due to a change in a physical parameter in the surrounding environment, which causes the resonant frequency generated by the circuit within the device to change. When the circuit is excited, the change in resonant frequency can be detected as a "ring-back" signal, which is indicative of the parameter or change being sensed therein. As is well known, a basic resonant circuit comprises an inductor and a capacitor. In most available RC sensing devices, the change in resonant frequency is caused by a change in the capacitance of the circuit. A well-known example of such a device is a pressure sensor, where the plates of a capacitor move together or apart in response to changes in pressure. Less commonly, the change in resonant frequency is based on a change in the inductance of the circuit.

[0007] The applicant has filed multiple patent applications that disclose novel RC monitoring devices that use variable inductance to monitor the dimensions of blood vessels and determine physiological parameters such as the patient's fluid status based thereon. See, for example, PCT / US17 / 63749, filed on November 29, 2017, entitled "Wireless Resonant Circuit and Variable Inductance Vascular Implants for Monitoring Patient Vasculature and Fluid Status and Systems and Methods Employing Same," published as WO2018 / 102435, and PCT / US19 / 34657, filed on May 30, 2019, entitled "Wireless Resonant Circuit and Variable Inductance Vascular Monitoring Implants and Anchoring Structures Therefore," published as WO2019 / 232213, each of which is incorporated herein by reference, which disclose many different embodiments and techniques related to such devices.

[0008] While these prior disclosures represent advances in the art, improvements can still be made to the control and signal processing of such devices. Accordingly, the present disclosure provides solutions to some of the unique problems described herein, which were encountered only after the introduction and testing of the new RC monitoring devices described above.

[0009] Public Overview

[0010] In one implementation, the present disclosure relates to a method for controlling a wireless resonant circuit sensor, the sensor comprising a variable inductance coil that changes resonant frequency in response to changes in a monitored physical parameter and, when energized, generates a ringback signal at a frequency related to the physical parameter. The method comprises outputting at least one excitation frequency sweep, the excitation frequency sweep comprising a predetermined number of transmit pulses at a predetermined frequency within a range of resonant frequencies of an intended implant; receiving a ringback signal for each of the sequentially output transmit pulses; transmitting at least one initial transmit pulse within a predetermined initial period, wherein the at least one initial transmit pulse comprises one of the following: a pulse frequency corresponding to the highest amplitude ringback signal received from the at least one frequency sweep; or a plurality of excitation frequency sweeps; receiving a plurality of test ringback signals in response to the at least one initial transmit pulse transmitted within the initial period; identifying an initial ringback signal corresponding to a preferred excitation pulse frequency; and selecting the preferred excitation pulse frequency as a measurement transmit pulse frequency; and outputting a measurement transmit pulse at the measurement transmit pulse frequency during a subsequent measurement period.

[0011] In another embodiment, the present disclosure relates to a control system for a wireless resonant circuit sensor, the sensor including a variable inductance coil that changes resonant frequency in response to changes in a monitored physical parameter and, when excited, generates a ringback signal at a frequency related to the physical parameter. The control system includes: a transmit / receive switch configured to control the transmission of signals to and reception of signals from an antenna; a signal generation module configured to generate an excitation signal, wherein the transmit / receive switch controls the transmission of the generated signal to the antenna; and a receiver-amplifier module configured to receive and process the ringback signal, which is received by the antenna and transmitted to the receiver-amplifier module via the transmit / receive switch in communication with a processor configured to execute program instructions, characterized in that the system is configured to: output at least one excitation frequency sweep comprising a predefined frequency sweep within a range of expected implant resonant frequencies. a preset number of transmit pulses; receiving a ringback signal for each of the sequentially output transmit pulses; transmitting at least one initial transmit pulse within a predetermined initial period, wherein the at least one initial transmit pulse includes one of the following: a pulse frequency corresponding to the highest amplitude ringback signal received from the at least one frequency sweep; or a plurality of excitation frequency sweeps; receiving a plurality of test ringback signals in response to the at least one initial transmit pulse transmitted within the initial period; identifying the initial ringback signal corresponding to a preferred excitation pulse frequency; selecting the preferred excitation pulse frequency as the measurement transmit pulse frequency; and outputting the measurement transmit pulse at the measurement transmit pulse frequency within a subsequent measurement period.

[0012] In yet another implementation, the present disclosure relates to a method for characterizing a resonant circuit sensor to correlate a sensor output with a measured physical parameter, wherein the sensor includes a variable inductance coil that, when energized, changes its resonant frequency in response to changes in the physical parameter by generating a ringback signal at a frequency related to the physical parameter. The method includes determining physical parameter value versus frequency data for at least one sensor within a range of parameter values ​​and frequencies prior to placement within a patient; and creating a characterization curve for the at least one sensor by plotting a curve using a curve fitting or interpolation technique using the data.

[0013] In yet another embodiment, the present disclosure relates to a method for evaluating electromagnetic background noise before outputting an excitation signal for measurement with a resonant circuit sensor, wherein the sensor includes a variable inductance coil that changes its resonant frequency in response to changes in a physical parameter by generating a ringback signal at a frequency related to the physical parameter when excited. The method includes transmitting a predetermined test pulse at a test frequency, wherein the test frequency is selected to be sufficiently far from an expected sensor excitation frequency so as not to excite the sensor; receiving the test signal with a sensor ringback signal receiver, wherein the received test signal is composed of the test pulse and background electromagnetic noise; defining the background electromagnetic noise based on the received test signal as a signal component different from the known test pulse; and modulating the signal processing of the received measurement ringback signal to eliminate or reduce the effect of the defined background electromagnetic noise.

[0014] In another implementation, the present disclosure relates to a method for verifying a sensor signal in a resonant circuit sensor, wherein the sensor includes a variable inductance coil that changes its resonant frequency in response to changes in a physical parameter by generating a ringback signal at a frequency related to the physical parameter when energized. The method includes transmitting a known fixed frequency and fixed amplitude signal; capturing the known signal as part of a captured signal that includes the ringback signal generated by the sensor; comparing the captured known signal portion with the transmitted known signal; and verifying the sensor ringback signal when the captured known signal portion matches the transmitted known signal within predetermined limits. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] For the purpose of illustrating the invention, the drawings show several aspects of one or more embodiments of the invention. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown in the drawings, in which:

[0017] Figure 1 is a schematic system overview of an embodiment of a wireless vascular monitoring system employing a resonant circuit-based sensor implant.

[0018] Figure 2 is a block diagram of an embodiment of a control system for the wireless vascular monitoring system disclosed herein.

[0019] Figure 3A 、 Figure 3B and Figure 3C Shown are signals obtained in in vivo preclinical experiments using a prototype RC-WVM system as disclosed herein.

[0020] Figure 4A and Figure 4B Shown are exemplary ringback signals received in a bench top test via a control system receiver-amplifier module without and with transmit-to-receive stimulus signal leakage according to embodiments disclosed herein.

[0021] Figure 5 is an example of a sensor characterization curve.

[0022] Detailed description

[0023] The unique physiology of the inferior vena cava (IVC) presents some unique challenges in attempts to detect and interpret changes in IVC size caused by changes in a patient's fluid status. For example, the IVC walls in the typical monitoring region (i.e., between the hepatic and renal veins) are relatively compliant compared to other blood vessels, which means that changes in vessel volume can result in different relative distance changes between the anterior-posterior walls compared to the lateral-medial walls. Therefore, it is very typical that changes in fluid volume will result in paradoxical changes in the geometry and motion of the vessel; that is, as blood volume decreases, the IVC tends to get smaller and collapse with respiration, and as blood volume increases, the IVC tends to get larger and collapse less with respiration. The present applicants have developed new wireless sensor implants and related systems and methods to address these challenges and provide clinically effective wireless vascular monitors ("WVMs"). In one such embodiment, the WVM includes a resonant circuit ("RC-WVM") configured as a coil that can be implanted in a patient's vasculature. Detailed examples of embodiments of the RC-WVM, systems, and methods are disclosed, inter alia, in co-pending U.S. patent application Ser. No. 17 / 018,194, filed by the applicant on September 11, 2020, entitled “Wireless Resonant Circuit and Variable Inductance Vascular Monitoring Implants and Anchoring Structures Therefore,” which is incorporated herein by reference in its entirety.

[0024] In the course of working with the RC-WVM embodiments described in the aforementioned applications, the applicants have developed a number of new embodiments, as disclosed herein, that further improve the accuracy and usability of the RC-WVM implants, systems, and methods described above. These new embodiments are described below after a basic overview discussion of an example of the RC-WVM system and its operation.

[0025] Figure 1 An overview of an RC-WVM system 10 to which embodiments disclosed herein apply is provided. As shown therein, such a system may generally include an RC-WVM implant 12 configured for placement in a patient's inferior vena cava (IVC), a control system 14, an antenna module 16, and one or more remote systems 18, such as a processing system, a user interface / display, a data storage device, etc., which communicate with the control and communication module via one or more data links 26. The data link 26 may be a wired or remote / wireless data link. In many implementations, the remote system 18 may include a computing device and user interface, such as a laptop, tablet, or smartphone, serving as an external interface device.

[0026] The RC-WVM implant 12 generally comprises a variable inductance, constant capacitance, resonant LC circuit formed as a collapsible and expandable coil structure that, when positioned at a monitoring location within a patient's IVC, moves with the IVC wall as it expands and contracts due to changes in fluid volume. The variable inductance is provided by the implant's coil structure such that as the size of the coil (e.g., the area enclosed by the coil or "sensing area") changes as the IVC wall moves, the inductance also changes. The capacitive element of the circuit can be provided by discrete capacitors or by a specially designed inherent capacitance of the implant structure itself. When an excitation signal is directed toward the RC-WVM implant, the resonant circuit generates a "ringback" signal at a frequency characteristic of the circuit. The characteristic frequency changes based on the change in the size of the inductor (i.e., coil) as it moves with the vessel wall. Because the inductance value depends on the geometry of the implant, which changes as described above based on dimensional changes of the IVC in response to fluid status, heart rate, etc., the ringback signal can be interpreted by the control system 14 to provide information about the geometry of the IVC, thereby providing information about fluid status and other physiological information such as respiration and heart rate.

[0027] The control system 14 includes functional modules for signal generation, signal processing, and power supply (typically including excitation and feedback monitoring ("EFM") circuits, and is represented as module 20, which includes a signal generation module 20a and a receiver-amplifier module 20b, such as Figure 2) and a communication and data acquisition module 22 to facilitate communication and data transmission to various external or remote systems 18 via a data link 26 and optionally other local or cloud-based networks 28. After analyzing the signals received from the RC-WVM implant 12, the results may be communicated manually or automatically to the patient, caregiver, medical professional, health insurance company, and / or any other desired and authorized party via the external or remote system 18 in any suitable manner (e.g., verbally, by printing a report, by sending a text message or email, or otherwise). Figure 2 As shown, components of the control system 14 may include a transmit / receive (T / R) switch 92, a transmitter tuning and matching circuit 94, a receiver tuning and matching circuit 96, a direct digital synthesizer (DDS) 98, an anti-aliasing filter 100, a preamplifier 102, an output amplifier 104, a single-ended to differential input amplifier (SE to DIFF) 106, a variable gain amplifier (VGA) 108, a filter amplifier (e.g., an active bandpass filter-amplifier) ​​110, an output filter (e.g., a passive high-order low-pass filter) 112, a high-speed analog-to-digital converter (ADC) 114, a microcontroller 116, and a communication submodule 118. Signal identification, selection, and other signal processing functions following amplification and filtering may be embedded within the microcontroller 116, or may be performed in an external interface device 18, such as an external computing system executing program instructions for performing the steps disclosed herein.

[0028] The antenna module 16 is connected to the control system 14 via a power and communication link 24, which can be a wired or wireless connection. The antenna module 16 generates a suitably shaped and oriented magnetic field around the RC-WVM implant 12 based on the signal provided by the signal generation module 20a of the control system 14 to excite the resonant circuit as described above. The antenna module 16 thus provides both a receive function / antenna and a transmit function / antenna. In some embodiments, the transmit and receive functions are performed by a single antenna, which is switched between transmit and receive modes, for example, by a transmit / receive switch 92 (which can be a single-pole double-throw switch). In other embodiments, each function is performed by a separate antenna.

[0029] As those skilled in the art will appreciate, optimal excitation of an LC resonant circuit occurs when the excitation signal is delivered at the circuit's natural frequency. However, in the RC-WVM implant 12 described herein, because the RC-WVM sensor size varies depending on its intended use, the circuit's natural frequency at any given time is unknown a priori. In one embodiment, a typical sensor is suitable for patients with IVC diameters nominally ranging from approximately 14 mm to approximately 28 mm. This means that the overall sensor diameter range will be from slightly less than approximately 14 mm to slightly greater than 28 mm in order to detect variations in IVC size above and below the nominal size range. When the sensor diameter is at the lower end of this size range, for example, below approximately 19 mm or even below approximately 15 mm, the amplitude of the ringback signal that can be generated by the sensor will be relatively low due to reduced inductive coupling, and thus can pose challenges for detection and accurate signal analysis. Another challenge in determining an appropriate excitation signal may be imposed by regulatory requirements, which generally require that any such signal have limited bandwidth and power. These challenges can be addressed in a variety of ways.

[0030] In one embodiment, the excitation signal provided by the signal generation module 20a and delivered by the antenna module 16 can be configured as a predefined transmit pulse (e.g., a single frequency burst) to excite the RC-WVM sensor. In this embodiment, because smaller sensor diameters produce lower ringback signal amplitudes, the transmit pulse frequency is selected to optimally excite the sensor assuming the sensor is within a smaller diameter range. Alternatively, the transmit pulse frequency can be selected assuming the sensor is at its smallest diameter, which will have the lowest ringback signal amplitude and therefore require optimal excitation to ensure the ringback signal is at a sufficiently detectable level to obtain a reliable reading. The same predefined transmit pulse frequency is used to excite the sensor for the duration of the signal measurement, e.g., 60 seconds. However, as the blood vessel dilates, the optimal excitation frequency changes, and the amplitude of the ringback signal may decrease, resulting in a less reliable reading.

[0031] In another embodiment, a frequency sweep function can be used to more reliably transmit the excitation signal at or near the optimal frequency. In one example, the signal generation module 20a performs the frequency sweep function by outputting a preset number of transmit pulses (in one example, five transmit pulses) in a predefined frequency sequence within the expected implant's natural frequency range. The ringback sensor signals captured during the frequency sweep function are processed by the receiver-amplifier module 20b, the communication and data acquisition module 22, and the optional external device 18. All ringback signals (corresponding to the preset number of transmit pulses) are received and processed. From the resonant frequencies detected in the preset number of transmit pulses sent, the frequency with the highest amplitude is selected as the optimal transmit frequency. The optimal excitation frequency is then used as the excitation transmit pulse to excite the sensor for the duration of the signal measurement (e.g., 60 seconds). Note that depending on the size of the sensor during the transmit pulse sweep, all ringback signals from the preset number of transmit pulses can be detected, and any ringback signal can be used as the optimal resonant frequency.

[0032] In the frequency sweep method described above, the system selects the frequency with the highest amplitude detected during the execution of the frequency sweep function. As explained, the amplitude of the resulting resonant frequency depends on the size (e.g., area or diameter) of the IVC at the monitoring location, with larger sizes producing larger signal amplitudes. Using this approach, the system may therefore tend to select excitation frequencies that are more favorable for larger sensor sizes. Subsequently, during signal acquisition, as the size of the vessel decreases (e.g., due to respiratory failure), the excitation may become suboptimal, potentially resulting in low or insufficient signal quality when the vessel collapses. Alternative excitation frequency determination methods can be utilized to address this issue.

[0033] In another such alternative embodiment, a two-tier approach is used to determine the excitation frequency. First, the initial excitation frequency is determined using, for example, the above-mentioned frequency sweep function. Therefore, the signal generation module 20a is configured to transmit during an initial observation period at a frequency determined by means of the frequency sweep function, which should be long enough to cover at least one respiratory cycle. During this period, the sensor resonant frequency is assessed, and the highest detection frequency is subsequently selected as the excitation frequency for the signal measurement remainder. This method can be conducive to selecting a higher frequency, corresponding to a smaller sensor area (which may be the worst case for signal quality), and therefore more reliable excitation can be provided.

[0034] The limitations of the method described in the previous paragraph are envisioned when considering the case of significant IVC collapse due to respiration. In this case, because the initial frequency sweep will tend to pick resonant frequencies corresponding to larger sensor / vessel sizes, by the time the IVC reaches its maximum level of collapse, the sensor's resonant frequency can deviate significantly from the excitation frequency, resulting in suboptimal excitation. This, coupled with the reduced amplitude of the sensor response (due to the small sensor area), can lead to unreliable resonant frequency detection (due to low signal quality) and potentially incorrect excitation frequency determination.

[0035] To overcome this problem, a further improvement can be employed in which the system repeatedly performs the frequency sweep function described above during a period of predefined length, which should be long enough to cover at least one respiratory cycle. Because the excitation frequency is sequentially varied between predefined frequencies (including the frequency corresponding to the smallest sensor area), more optimal excitation is achieved in the case of large IVC collapse and small sensors. As with the above method, the system selects the highest observed resonant frequency as the excitation frequency for the remainder of the signal measurement.

[0036] In another implementation, the frequency of the excitation signal is dynamically adjusted during signal acquisition. In one embodiment, the amplitude or signal-to-noise ratio (SNR) of the response signal from the RC-WVM sensor is continuously or periodically monitored (for each sample). If the signal amplitude is detected to be below a predefined threshold (e.g., due to a greater collapse of the IVC), a new frequency sweep is performed (using any of the methods described previously), allowing retuning to the latest sensor resonant frequency.

[0037] In another embodiment, the output frequency of signal generation module 20a is continuously adjusted after each measurement point. In this case, the sensor's resonant frequency is calculated for each sample acquired between sample acquisitions. Therefore, the excitation frequency for the next sample is adjusted to the most recently measured resonant frequency. As long as the system's sampling rate is faster than the dynamics of IVC collapse, this approach will always ensure optimal excitation.

[0038] The embodiments described above require a signal processing algorithm for frequency detection that can be executed in real time in the communication and data acquisition module 22. A Fast Fourier Transform (FFT) can be used for this purpose. However, if a high resolution of the detected IVC size is required, the required FFT length may result in high computation time and, therefore, is not suitable for frequency determination between sample acquisitions. Alternatively, a variation of the conventional FFT, such as the Zoom FFT, can be used. This technique allows the analysis to be focused on a given portion of the frequency spectrum, thereby reducing the length of the FFT and, therefore, its computation time, without compromising the resolution of the detected frequencies.

[0039] Given that the amount of RF power that can be transmitted via antenna 16 will be subject to limits imposed by applicable regulations designed to ensure efficient use of the spectrum, determining the optimal transmit frequency using any of the methods described above is key to providing effective excitation of the RC-WVM sensor. As an additional means of minimizing the level of intended RF emissions, the dependency between the RC-WVM sensor area and the sensor response signal strength can be considered. As previously discussed, a larger sensor area will generally result in greater mutual inductance (and therefore magnetic field coupling) between antenna 16 and the RC-WVM sensor. To account for this, signal generation module 20a can be controlled in a manner that adjusts the output RF power as a function of the output frequency. In particular, the maximum power is transmitted when the sensor's detected resonant frequency is at the high end of the intended sensor bandwidth, which corresponds to the smallest sensor area and, therefore, the weakest response. Thus, the output power decreases monotonically as the frequency decreases, thereby facilitating compliance with applicable radio regulations.

[0040] In another implementation, the amplitude of the RC-WVM sensor response signal is monitored, and the transmitter output is dynamically adjusted, for example, to achieve a constant signal amplitude (similar to an automatic gain control application). As described in the previous paragraph, this approach can allow for tighter control of the transmitted RF power. Additionally, this approach provides a means of ensuring that the amplitude of the received signal does not lead to saturation of the receiver stage, which would otherwise result in inaccuracies in the signal processing algorithms subsequently used to determine the sensor's fundamental components.

[0041] Figure 3A 、 Figure 3B and Figure 3C Examples of signals from in vivo testing are shown, which are the original ringback signal, the detection of the resonant frequency, and the conversion to the IVC size using the reference characterization curve, respectively. Figure 3A The raw ringback signal showing the decay of the resonant response of the RC-WVM implant over time is shown in the time domain. Modulation of the implant geometry results in a change in the resonant frequency due to the change in the IVC shape, which can be seen as the difference between two different plotted traces. Figure 3B Shows the Figure 3A The RC-WVM implant signal is converted into the frequency domain and plotted over time. Figure 3A The resonant frequency of the IVC is determined (e.g., using a fast Fourier transform) and plotted over time. Larger, slower modulations of the signal (i.e., three broader peaks) indicate respiratory-induced motion of the IVC wall, while faster, smaller modulations overlaid on this signal indicate motion of the IVC wall in response to the cardiac cycle. Figure 3C Shown in Figure 3AThe frequency modulation plotted in is converted to a graph of sensor area versus time. (In this case, the conversion is based on a characterization curve determined by benchtop testing on a range of sample diameter cavities following standard laboratory / test procedures.) Therefore, Figure 3C The changes in IVC size at the monitoring location in response to the respiratory and cardiac cycles are shown.

[0042] As one of ordinary skill will recognize, Figures 3A-3C Accurate and reliable interpretation of the complex signals shown in requires good signal fidelity and confidence for both the excitation signal and the ringback signal from the RC-WVM. Therefore, the embodiments disclosed herein provide solutions to potential problems to help ensure the best possible signal fidelity and confidence.

[0043] One way signal fidelity can be compromised is when defective hardware within the control system leads to inaccurate readings. Therefore, a mechanism is needed to verify the accuracy of the data generated by the system. In one embodiment, data accuracy can be verified by reading the known frequency signal generated by the signal generation module 20a with the receiver-amplifier module 20b and confirming that the system's output matches the known input. Therefore, in one embodiment, a known fixed frequency and amplitude signal portion is included in the captured signal to allow offline verification of the raw data file. Once the transmit cycle begins, the receiver-amplifier 20b, along with the communication and data acquisition submodule 22, begins capturing the generated signal. The transmit signal has a large amplitude, thus generating a small leakage signal through the transmit / receive (T / R) switch 92 that reaches the receiver channel. Because the latter has very large gain, the resulting signal at the receiver's output can be detected and processed to determine its frequency, which is known a priori because the transmitter has been programmed to generate such a frequency. In another alternative, a known or fixed frequency signal portion can be included in the sensor raw data capture by allowing the transmit / receive switch 92 to briefly leak a known excitation signal from the transmit side to the receive side when switching from transmit to receive.

[0044] In this way, when the receiver-amplifier module 20b begins to acquire the received signal, the first part of the signal is the known frequency part. Figure 4A and Figure 4B Illustrates a brief signal leak. Figure 4A 1 shows the ringback signal that may be received by the control system after the RC-WVM sensor is excited by a signal from the transmit side in typical operation without any signal leakage through the T / R switch 92. Figure 4AThe signal in Figure 1 starts at maximum amplitude on the left when the RC-WVM coil is first excited and decays over time as the energy dissipates. Note that in this example, the ringback signal begins at time 14 μs, which represents the time delay between the transmit signal being sent and exciting the sensor. (The excitation signal begins at time 0, which is in the Figure 4A Not shown in , but in Figure 4B .) Figure 4B The signal in Figure 1 shows the received signal when leakage through the switch is allowed, as described in the previous embodiment. The leakage portion of the signal (LS) begins at approximately time zero because there is no delay waiting for the sensor to be energized. However, by limiting the leakage signal (LS) to the time before the expected sensor ringback signal, the leakage signal does not interfere with the sensor reading while providing a known frequency verification signal that can be checked against the control system output.

[0045] In one embodiment, the process of providing the leakage signal as a known frequency hardware verification signal may include the following steps:

[0046] 1. The RF transmitter outputs a known pulse via the antenna to excite the sensor.

[0047] 2. The transmit / receive switch is configured to allow signal leakage from the transmit side to the receive side. When the transmitter is activated, the receiver electronics begins capturing receiver data.

[0048] 3. The transmit / receive switch completely changes the antenna connection to the receiver electronics to detect the sensor RF response.

[0049] 4. The receiver electronics continues to capture the sensor signal via the ADC.

[0050] 5. The captured ADC data is stored in the microcontroller and sent to the laptop for long-term storage. This data now includes the transmit portion of the transmit / receive cycle within the data packet. The data packet also includes the frequency programmed into the RF transmitter.

[0051] 6. The data can then be verified by comparing the frequency and amplitude of the transmitted portion of the data signal data to the programmed frequency and predefined thresholds for expected amplitude.

[0052] Another issue that can arise with systems of the type described herein is interference from background noise. Excessive electromagnetic noise or external electromagnetic interference from nearby devices can cause the system to detect readings that are unrelated to the sensor signal. During normal operation, the system attempts to detect signals induced by the sensor in response to the excitation signal delivered to the sensor during the transmit cycle. A sufficiently strong external signal can couple into the system and mask the sensor signal, potentially leading to incorrect measurements.

[0053] According to the present disclosure, this problem can be solved by providing a mechanism for evaluating the electromagnetic background noise before starting the measurement. In one embodiment, the system operates in normal mode, that is, the transmit mode is turned on and a known test frequency is transmitted that is sufficiently far away from the expected sensor bandwidth / excitation frequency. In this way, the sensor is not excited and therefore does not generate a ringback signal response. The control system then switches to the receiver mode in normal operation and records any received signal. Since the sensor does not respond (due to the "detuned" transmit frequency), the received signal consists entirely of background electromagnetic noise. Appropriate corrections or adjustments can then be made in the signal processing based on the detected background noise. In one option, the control system evaluates the power of the largest component of the background noise signal. This process is repeated a predefined number of times and an average value is obtained for a more consistent metric. The calculated signal level is then defined as the background noise.

[0054] The background noise assessment process described above is not limited to being performed before the sensor signal recording begins. In other embodiments, the background noise assessment may also be performed at different stages or multiple points during the sensor signal acquisition process to mitigate risks associated with intermittent noise sources or increased noise coupling due to patient movement.

[0055] After evaluating the background noise, the sensor signal is identified through a frequency sweep. Once the sensor response signal is detected, its amplitude is evaluated and compared to the previously measured background noise amplitude, effectively calculating the signal-to-noise ratio (SNR). A minimum threshold level is established for the SNR. Any SNR below this limit indicates that external interference is high enough to inhibit reliable measurement. This, in turn, can alert the user to change location or eliminate any potential sources of interference in order to continue using the system.

[0056] Combined with the above Figure 3A and Figure 3C The use of characterization curves to convert the raw signal output of an RC-WVM sensor into physiologically relevant readings regarding blood vessel size and size changes is discussed. Generally, the art understands the need to characterize raw sensor signals to provide physiologically relevant readings useful to healthcare providers. However, RC-WVM sensors, as described herein, can present unique characterization challenges because their characteristic inductance is intentionally varied by design. Furthermore, the inductive and capacitive properties that define the resonant circuit vary due to variability in sensor manufacturing. To address these challenges in characterizing RC-WVM sensors, a number of new and different approaches can be employed.

[0057] In one embodiment, a sensor characterization curve is created by sequentially passing the RC-WVM sensor through a series of increasingly larger tubes of known area and recording the corresponding frequencies, such as Figure 5A unique curve can then be generated from these area-frequency measurements using a number of methods. For example, a curve fitting method can be employed, in which a curve is fitted to the original data by minimizing the error between the fit and the original data. Curve fitting can be performed using a number of different fit types, including but not limited to exponential and logarithmic fits based on the following function:

[0058] Logarithm: y = c1 ln(x) + c2

[0059] index:

[0060] In another example, interpolation can be used, where a curve is created by interpolating between the recorded area-frequency data. Many interpolation methods can be used, including linear interpolation functions such as:

[0061] Linear interpolation:

[0062] In addition to the curve type selected, characterization curves can be generated from single sensor specific area-frequency data or from averaged area-frequency data from a batch of sensors.

[0063] Typically, each RC-WVM sensor characterization curve is determined in a cleanroom during sensor manufacturing. However, these curves can shift slightly after the manufacturing and sterilization processes. Because sensors for clinical use cannot be recharacterized after sterilization, sensor / batch-specific manufacturing curves can only be created before sterilization. Alternatively, reference characterization curves can be generated from independent sensors that are not intended for clinical use after sterilization; as long as they are manufactured and sterilized in a similar manner to the clinical sensors, they can be used as a reference.

[0064] In another embodiment, greater characterization accuracy can be achieved as follows. First, during manufacturing, area versus frequency data is determined for each sensor. Before or after sterilization, a characterization curve is created from the sensor or batch specific area-frequency data by curve fitting or interpolation as described above. Then, sensor measurements are taken and the results are converted to IVC dimensions using the characterization curve created in the previous steps. Thus, by using sensor or batch specific characterization curves, measurement errors caused by manufacturing variability are minimized. Use of a predetermined characterization curve allows for more accurate measurements over a wider range of sizes and can avoid the need for in vivo calibration for imaging modalities such as intravascular ultrasound (IVUS), which have other inherent accuracy issues.

[0065] Additional features, advantages, and limitations of the embodiments disclosed herein are listed in the following numbered subparagraphs:

[0066] 1. A method and system for validating a sensor signal received from a resonant circuit based sensor, comprising including a known fixed frequency and amplitude portion of a signal within an output signal captured from the sensor to allow validation of raw data received from the sensor, wherein the validation can optionally be performed offline.

[0067] 2. A method and system for determining an optimal transmit frequency for exciting a resonant circuit sensor, comprising outputting a plurality of predefined transmit pulses to excite the sensor within an expected sensor frequency range; determining the highest amplitude sensor signal received corresponding to the optimal excitation frequency; and exciting the sensor at the determined optimal transmit frequency for a duration of signal measurement, wherein the duration can optionally be approximately 60 seconds.

[0068] 3. A method and system for characterizing a size-related output signal of a sensor, comprising determining size versus frequency data of the sensor during sensor manufacturing; creating a sensor or batch-specific characterization curve of the size-frequency data by curve fitting or interpolation before or after sterilization of the corresponding one or more sensors; taking measurements with the sensor; converting the sensor results to a desired size using the created characterization curve; minimizing size measurement errors caused by manufacturing variability by using the sensor or batch-specific characterization curve; wherein, optionally, the use of a predetermined characterization curve allows accurate measurements over a large size range.

[0069] 4. A method and system for evaluating electromagnetic background noise in a sensor system, comprising operating the sensing system in a normal mode, e.g., with a transmitter engaged, and transmitting a test frequency that is sufficiently far from an expected sensor bandwidth so as not to excite the sensor and cause a sensor response; switching the sensor to a receiver mode and recording a received signal with the sensing system, wherein the received signal consists of background electromagnetic noise; evaluating the power of a maximum component of the background noise signal; optionally repeating the process a predefined number of times to obtain an average; and defining a calculated signal level, which is then defined as the background noise.

[0070] The foregoing is a detailed description of illustrative embodiments of the present invention. Note that in this specification and the claims appended hereto, unless expressly stated or indicated otherwise, conjunction language such as used in the phrases "at least one of X, Y, and Z" and "one or more of X, Y, and Z" should be understood to mean that each item in the conjunction list may be expressed as any number excluding all other items in the list or as any number in conjunction with any or all other items in the conjunction list, and each item may also be expressed as any number. Applying this general rule, in the foregoing examples where the conjunction list consists of X, Y, and Z, the conjunction phrases should each include: one or more of X; one or more of Y; one or more of Z; one or more of X and one or more of Y; one or more of Y and one or more of Z; one or more of X and one or more of Z; and one or more of X, one or more of Y, and one or more of Z.

[0071] Various modifications and additions may be made without departing from the spirit and scope of the present invention. The features of each of the various embodiments described above may be appropriately combined with the features of the other described embodiments to provide a variety of feature combinations in associated new embodiments. In addition, although the foregoing describes a plurality of separate embodiments, what is described herein is merely an illustration of the application of the principles of the present invention. Furthermore, although the specific methods herein may be illustrated and / or described as being performed in a particular order, it is within the skill of the art that the ordering is highly variable to implement aspects of the present disclosure. Therefore, this description is intended to be made by way of example only and not to limit the scope of the present invention in any other way.

[0072] Exemplary embodiments have been disclosed above and shown in the accompanying drawings. Those skilled in the art will appreciate that various changes, omissions, and additions may be made to the embodiments specifically disclosed herein without departing from the spirit and scope of the present invention.

[0073] Aspects of the present invention may be implemented in one or more of the following embodiment items.

[0074] Item 1). A method for controlling a wireless resonant circuit sensor, the sensor comprising a variable inductance coil, the variable inductance coil varying its resonant frequency in response to changes in a monitored physical parameter and generating a ringback signal at a frequency related to the physical parameter when energized, the method comprising:

[0075] outputting at least one excitation frequency sweep comprising a preset number of transmit pulses at a predefined frequency within a range of expected implant resonant frequencies;

[0076] receiving a ringback signal of each transmission pulse in the sequentially output transmission pulses;

[0077] At least one initial transmit pulse is transmitted within a predetermined initial period, wherein the at least one initial transmit pulse comprises one of the following:

[0078] a pulse frequency corresponding to the highest amplitude ringback signal received from the at least one excitation frequency sweep; or

[0079] a plurality of said excitation frequency sweeps;

[0080] receiving a plurality of initial ringback signals in response to the at least one initial transmit pulse transmitted during the initial period;

[0081] identifying an initial ringback signal corresponding to a preferred excitation pulse frequency; and

[0082] Selecting the preferred excitation pulse frequency as the measurement transmission pulse frequency;

[0083] In the subsequent measurement cycle, the measurement transmission pulses are output at the measurement transmission pulse frequency.

[0084] Item 2). The method according to item 1), further comprising:

[0085] receiving a measurement ringback signal generated by the sensor in response to the measurement transmit pulse during the measurement period; and

[0086] The measured ringback signal is analyzed to determine a characteristic of the monitored physical parameter.

[0087] Item 3). The method according to item 1) or item 2), wherein:

[0088] The transmitting of the at least one initial transmit pulse during the initial period comprises:

[0089] Identifying the ringback signal with the highest amplitude;

[0090] Selecting the transmission pulse frequency corresponding to the ringback signal with the highest amplitude as the initial transmission pulse frequency; and

[0091] transmitting a plurality of initial transmit pulses at the initial transmit pulse frequency; and

[0092] The receiving of a plurality of initial ringback signals and the identifying of the initial ringback signal include:

[0093] exciting the sensor at the initial transmit pulse frequency during the initial period;

[0094] receiving the initial ringback signal from the sensor during the initial period; and

[0095] The initial transmission pulse frequency that generates the initial ringback signal having the highest frequency is selected as the measurement transmission pulse frequency.

[0096] Item 4). The method according to item 1) or item 2), wherein:

[0097] said transmitting said at least one initial transmit pulse during said initial period comprises outputting a repetitive excitation frequency sweep during said initial period; and

[0098] The identifying an initial ringback signal includes identifying a highest observed ringback signal frequency generated by the repeated excitation frequency sweep as the preferred excitation pulse frequency.

[0099] Item 5). The method according to any one of items 1) to 4), wherein the predetermined initial period comprises a time long enough to include at least one breathing cycle.

[0100] Item 6). The method according to any one of items 1) to 5) further includes dynamically adjusting the frequency of the transmit pulse during acquisition of the corresponding ringback signal.

[0101] Item 7). The method according to item 6), wherein the dynamic adjustment comprises:

[0102] monitoring at least one of an amplitude or a signal-to-noise ratio of a corresponding ringback signal; and

[0103] In response to detecting that the ringback signal amplitude is below a predefined threshold, a new excitation frequency sweep is output to identify a new measurement transmit pulse frequency.

[0104] Item 8). The method according to any one of items 2) to 7), further comprising calculating a new measurement pulse signal for each measurement transmit pulse after receiving the measurement ringback signal during the measurement period.

[0105] Item 9). The method according to any one of items 1) to 8) further includes adjusting the transmit pulse output power according to the transmit pulse output frequency.

[0106] Item 10). The method according to Item 9), wherein the adjustment comprises monotonically reducing the transmit pulse output power as the transmit pulse frequency decreases.

[0107] Item 11). The method according to any one of items 1) to 8), further comprising:

[0108] monitoring a ringback signal generated by the sensor; and

[0109] The transmit pulse output is dynamically adjusted based on the monitored ringback signal to achieve a substantially constant ringback signal amplitude.

[0110] Item 12). The method according to any one of items 1) to 11), further comprising:

[0111] Transmit a known signal of fixed frequency and fixed amplitude;

[0112] capturing the known signal as part of a captured ringback signal;

[0113] The signal processing is verified by comparing the captured portion of the known signal with the transmitted known signal.

[0114] Item 13). The method according to Item 12), wherein transmitting and capturing the known signal includes allowing the signal to leak through a transmit / receive switch of a signal generation and reception control system.

[0115] Item 14). The method according to any one of items 2)-13), further comprising evaluating electromagnetic background noise before outputting the at least one excitation frequency sweep, and adjusting signal processing based on the calculated background noise signal level.

[0116] Item 15). The method according to Item 14), wherein the evaluating electromagnetic background noise comprises:

[0117] transmitting a predetermined test pulse at a test frequency, wherein the test frequency is selected to be sufficiently far from an expected sensor excitation frequency so as not to excite the sensor;

[0118] Receive a test signal using a sensor ringback signal receiver, wherein the received test signal consists of the test pulse and background electromagnetic noise;

[0119] defining the background electromagnetic noise based on the received test signal; and

[0120] The signal processing of the received measurement ringback signal is modulated to eliminate or reduce the influence of the defined background electromagnetic noise.

[0121] Item 16). The method according to any one of items 1) to 15), further comprising:

[0122] determining physical parameter versus frequency data for at least one of said sensors prior to placement in a patient;

[0123] creating a characterization curve for said at least one said sensor by curve fitting or interpolation;

[0124] taking measurements with the sensor; and

[0125] The sensor measurements are converted to values ​​of the physical parameters using the characterization curve.

[0126] Item 17). The method according to item 16), wherein said at least one sensor comprises a sensor batch, and said frequency data comprises batch-specific parameter-frequency data.

[0127] Item 18). The method according to item 16) or item 17), further comprising minimizing physical parameter measurement errors caused by sensor manufacturing variability by using sensor or sensor batch specific characterization curves.

[0128] Item 19). The method of any preceding item, wherein the sensor is configured for placement in the patient's vascular system and the physical parameter is blood vessel size.

[0129] Item 20). The method according to Item 19), wherein the sensor is specifically configured for placement in the vena cava, and the vessel size is the area or diameter of the vena cava.

[0130] Item 21). The method according to Item 20) further includes correlating the measured area or diameter of the vena cava with the patient's fluid status.

[0131] Item 22. A control system for a wireless resonant circuit sensor, the sensor including a variable inductance coil that changes its resonant frequency in response to changes in a monitored physical parameter and, when energized, generates a ringback signal at a frequency related to the physical parameter. The control system includes: a transmit / receive switch configured to control signal transmission to and reception from an antenna; a signal generation module configured to generate an excitation signal, wherein the transmit / receive switch controls transmission of the generated signal to the antenna; and a receiver-amplifier module configured to receive and process the ringback signal, the ringback signal being received by the antenna and transmitted to the receiver-amplifier module via the transmit / receive switch in communication with a processor configured to execute program instructions. The control system is configured to:

[0132] outputting at least one excitation frequency sweep comprising a preset number of transmit pulses at a predefined frequency within a range of expected implant resonant frequencies;

[0133] receiving a ringback signal of each transmission pulse in the sequentially output transmission pulses;

[0134] At least one initial transmit pulse is transmitted within a predetermined initial period, wherein the at least one initial transmit pulse comprises one of the following:

[0135] a pulse frequency corresponding to the highest amplitude ringback signal received from the at least one excitation frequency sweep; or

[0136] a plurality of said excitation frequency sweeps;

[0137] receiving a plurality of initial ringback signals in response to the at least one initial transmit pulse transmitted during the initial period;

[0138] identifying an initial ringback signal corresponding to a preferred excitation pulse frequency;

[0139] Selecting the preferred excitation pulse frequency as the measurement transmission pulse frequency; and

[0140] In the subsequent measurement cycle, the measurement transmission pulses are output at the measurement transmission pulse frequency.

[0141] Item 23). A control system according to Item 22), further characterized in that the control system is configured to receive a measurement ringback signal generated by the sensor in response to the measurement transmit pulse during the measurement cycle, and analyze the measurement ringback signal to determine the characteristics of the monitored physical parameter.

[0142] Item 24). The control system according to item 22) or item 23), wherein the control system is configured to:

[0143] identifying a ringback signal having the highest amplitude from the at least one excitation frequency scan, and selecting a transmit pulse frequency corresponding to the highest amplitude ringback signal as an initial transmit pulse frequency;

[0144] transmitting an excitation signal at the initial transmission pulse frequency during the initial period;

[0145] receiving the initial ringback signal from the sensor during the initial period; and

[0146] The initial transmission pulse frequency that generates the initial ringback signal having the highest frequency is selected as the measurement transmission pulse frequency.

[0147] Item 25). The control system according to item 22) or item 23), further characterized in that the control system is configured to transmit the at least one initial transmit pulse during the initial period by outputting a repeated excitation frequency sweep during the initial period; and

[0148] The initial ringback signal is identified by identifying the highest observed ringback signal frequency generated by the repeated excitation frequency sweep as the preferred excitation pulse frequency.

[0149] Item 26). A control system according to any one of Items 22)-25), further characterized in that the control system is configured to dynamically adjust the frequency of the transmit pulse during the acquisition of the corresponding ringback signal by monitoring at least one of the amplitude or signal-to-noise ratio of the corresponding ringback signal and outputting a new excitation frequency scan to identify a new measurement transmit pulse frequency in response to detecting that the amplitude of the ringback signal is lower than a predefined threshold.

[0150] Item 27). A control system according to any one of Items 22)-26), further characterized in that the control system is configured to adjust the transmit pulse output power according to the transmit pulse output frequency by monotonically reducing the transmit pulse output power as the transmit pulse frequency decreases.

[0151] Item 28). A control system according to any one of Items 22)-27), further characterized in that the control system is configured to monitor the ringback signal generated by the sensor and dynamically adjust the transmit pulse output based on the monitored ringback signal to achieve a substantially constant ringback signal amplitude.

[0152] Item 29. A method for characterizing a resonant circuit sensor to correlate a sensor output with a measured physical parameter, wherein the sensor includes a variable inductance coil that changes its resonant frequency in response to changes in the physical parameter by generating a ringback signal at a frequency related to the physical parameter when energized, the method comprising:

[0153] determining physical parameter value versus frequency data for at least one of the sensors within a range of parameter values ​​and frequencies prior to placement within the patient; and

[0154] A characterization curve for said at least one said sensor is created by plotting a curve with said data using curve fitting or interpolation techniques.

[0155] Item 30). The method according to Item 29), wherein the physical parameter is the internal vascular cavity size, the internal vascular cavity size including the cavity diameter or area, the sensor can be implanted in the vascular cavity and can expand and contract accordingly, characterized in that the determination includes sequentially placing the sensor in a series of gradually increasing or decreasing tubes of known sizes, and recording the corresponding ringback signal frequency when the sensor is excited in each tube of different sizes.

[0156] Item 31). The method according to Item 30), further comprising:

[0157] During manufacturing, determining a blood vessel size versus frequency dataset for each sensor in a batch of sensors; and

[0158] Prior to sensor sterilization, the characterization curve is created from the sensor batch vessel size-frequency data by curve fitting or interpolation.

[0159] Item 32). The method according to Item 30), further comprising:

[0160] manufacturing and sterilizing a batch of the sensors;

[0161] selecting a group of sensors from a sterilized batch of sensors;

[0162] designating the selected set of sensors as sensors not intended for clinical use; and

[0163] performing said determining step only on said set of sensors designated not for clinical use; and

[0164] The characterization curve for the sterilized batch of sensors is generated based on size versus frequency data generated using the group of sensors designated not for clinical use.

[0165] Item 33. A method for evaluating electromagnetic background noise before outputting an excitation signal for measurement with a resonant circuit sensor, wherein the sensor includes a variable inductance coil that changes its resonant frequency in response to changes in a physical parameter by generating a ringback signal at a frequency related to the physical parameter when excited, the method comprising:

[0166] transmitting a predetermined test pulse at a test frequency, wherein the test frequency is selected to be sufficiently far from an expected sensor excitation frequency so as not to excite the sensor;

[0167] Receive a test signal using a sensor ringback signal receiver, wherein the received test signal consists of the test pulse and background electromagnetic noise;

[0168] defining the background electromagnetic noise based on the received test signal as a signal component other than known test pulses; and

[0169] The received measurement ringback signal is modulated by signal processing to eliminate or reduce the influence of the defined background electromagnetic noise.

[0170] Item 34) A method for verifying a sensor signal in a resonant circuit sensor, wherein the sensor includes a variable inductance coil that changes a resonant frequency in response to a change in a physical parameter by generating a ringback signal at a frequency related to the physical parameter when energized, the method comprising:

[0171] Transmit a known signal of fixed frequency and fixed amplitude;

[0172] capturing the known signal as part of a captured signal including a ringback signal generated by the sensor;

[0173] comparing the captured portion of the known signal to the transmitted known signal; and

[0174] When the captured known signal portion matches the transmitted known signal within predetermined limits, the sensor ringback signal is validated.

[0175] Item 35). A method according to Item 34), wherein transmitting and capturing a known signal includes allowing leakage of the signal through a transmit / receive switch of a signal generation and reception control system.

Claims

1. A method for controlling a wireless resonant circuit sensor, the sensor comprising a variable inductance coil, the variable inductance coil changing a resonant frequency in response to changes in a monitored physical parameter and generating a ringback signal at a frequency related to the physical parameter when excited, the method comprising: outputting at least one excitation frequency sweep comprising a preset number of transmit pulses at a predefined frequency within an expected implant resonant frequency range; receiving a ringback signal of each transmission pulse in the sequentially output transmission pulses; determining a pulse frequency of the transmit pulses corresponding to a highest amplitude ringback signal received from the at least one excitation frequency sweep; transmitting at least one initial transmission pulse at the determined pulse frequency within a predetermined initial period; receiving a plurality of test ringback signals in response to the at least one initial transmit pulse transmitted during the initial period; identifying a ringback signal having a highest frequency among the received plurality of test ringback signals; selecting the frequency of the identified ringback signal as the measurement transmission pulse frequency; as well as In the subsequent measuring cycle, the measuring transmit pulses are output at the measuring transmit pulse frequency.

2. The method according to claim 1, further comprising: receiving a measurement ringback signal generated by the sensor in response to the measurement transmit pulse during the measurement period; and The measured ringback signal is analyzed to determine a characteristic of the monitored physical parameter.

3. The method according to claim 1 or claim 2, wherein: The transmitting of the at least one initial transmit pulse during the initial period comprises: identifying the ringback signal having the highest amplitude; Selecting the transmission pulse frequency corresponding to the ringback signal with the highest amplitude as the initial transmission pulse frequency; and The at least one initial transmit pulse is transmitted at the initial transmit pulse frequency during the initial period.

4. The method according to claim 1 or claim 2, wherein: Transmitting the at least one initial transmit pulse during the initial period includes outputting a repetitive excitation frequency sweep during the initial period; and Identifying a ringback signal having a highest frequency among the received plurality of test ringback signals includes identifying a highest observed ringback signal frequency generated by the repeated excitation frequency sweep.

5. The method according to any one of claims 1 to 4, wherein: The predetermined initial period comprises a time long enough to include at least one breathing cycle.

6. The method according to any one of claims 1-5, further comprising dynamically adjusting the frequency of the transmit pulses during acquisition of the corresponding ringback signal.

7. The method according to claim 6, wherein: The dynamic adjustment includes: monitoring at least one of an amplitude or a signal-to-noise ratio of a corresponding ringback signal; and In response to detecting that the ringback signal amplitude is below a predefined threshold, a new excitation frequency sweep is output to identify a new measurement transmit pulse frequency.

8. The method of claim 2, further comprising calculating a new measurement pulse signal for each measurement transmit pulse after receiving the measurement ringback signal during the measurement period.

9. The method according to any one of claims 1-8, further comprising adjusting the transmit pulse output power according to the transmit pulse output frequency.

10. The method according to claim 9, wherein: The adjustment includes monotonically reducing the transmit pulse output power as the transmit pulse frequency decreases.

11. The method according to any one of claims 1 to 8, further comprising: monitoring a ringback signal generated by the sensor; and The transmit pulse output is dynamically adjusted based on the monitored ringback signal to achieve a substantially constant ringback signal amplitude.

12. The method according to any one of claims 1 to 11, further comprising: Transmit a known signal of fixed frequency and fixed amplitude; capturing the known signal as part of a captured ringback signal; Signal processing is verified by comparing the captured known signal portion with the transmitted known signal.

13. The method according to claim 12, wherein: The transmitting and acquiring of the known signal includes allowing the signal to leak through a transmit / receive switch of a signal generation and reception control system.

14. The method of claim 2 or 8, further comprising evaluating electromagnetic background noise prior to outputting the at least one excitation frequency sweep, and adjusting signal processing based on the calculated background noise signal level.

15. The method according to claim 14, wherein: The evaluating electromagnetic background noise comprises: transmitting a predetermined test pulse at a test frequency, wherein the test frequency is selected to be sufficiently far from an expected sensor excitation frequency so as not to excite the sensor; Utilizing a sensor ringback signal receiver to receive a test signal, wherein the received test signal consists of the test pulse and background electromagnetic noise; defining the background electromagnetic noise based on the received test signal; and The signal processing of the received measurement ringback signal is modulated to eliminate or reduce the influence of the defined background electromagnetic noise.

16. The method according to any one of claims 1 to 15, further comprising: determining physical parameter versus frequency data for at least one of the sensors prior to placement in a patient; creating a characterization curve for said at least one said sensor by curve fitting or interpolation; Taking measurements with the sensor; and The sensor measurements are converted to values ​​of the physical parameter using the characterization curve.

17. The method according to claim 16, wherein: Said at least one of said sensors comprises a sensor batch, and said frequency data comprises batch-specific parameter-frequency data.

18. The method of claim 16 or claim 17, further comprising minimizing physical parameter measurement errors caused by sensor manufacturing variability by using a sensor or sensor batch specific characterization curve.

19. A method according to any preceding claim, wherein: The sensor is configured for placement in a patient's vascular system, and the physical parameter is a blood vessel dimension.

20. The method according to claim 19, wherein: The sensor is specifically configured for placement in the vena cava, and the vessel dimension is the area or diameter of the vena cava.

21. The method of claim 20, further comprising correlating the measured area or diameter of the vena cava with patient fluid status.

22. A control system for a wireless resonant circuit sensor, the sensor comprising a variable inductance coil, the variable inductance coil varying its resonant frequency in response to changes in a monitored physical parameter and generating a ringback signal at a frequency related to the physical parameter when excited, the control system comprising: a transmit / receive switch configured to control transmission of signals to and reception of signals from the antenna; a signal generation module configured to generate an excitation signal, wherein the transmit / receive switch controls the transmission of the generated signal to the antenna; and a receiver-amplifier module configured to receive and process a ringback signal, the ringback signal being received by the antenna and transmitted to the receiver-amplifier module through the transmit / receive switch in communication with a processor configured to execute program instructions, wherein the control system is configured to: outputting at least one excitation frequency sweep comprising a preset number of transmit pulses at a predefined frequency within an expected implant resonant frequency range; receiving a ringback signal of each transmission pulse in the sequentially output transmission pulses; determining a pulse frequency of the transmit pulses corresponding to the highest amplitude ringback signal received from the at least one excitation frequency sweep; transmitting at least one initial transmission pulse at the determined pulse frequency within a predetermined initial period; receiving a plurality of test ringback signals in response to the at least one initial transmit pulse transmitted during the initial period; identifying a ringback signal having a highest frequency among the received plurality of test ringback signals; selecting the frequency of the identified ringback signal as the measurement transmit pulse frequency; and In the subsequent measuring cycle, the measuring transmit pulses are output at the measuring transmit pulse frequency.

23. The control system according to claim 22, further characterized in that: The control system is configured to receive a measurement ringback signal generated by the sensor in response to the measurement transmit pulse during the measurement period and to analyze the measurement ringback signal to determine a characteristic of the monitored physical parameter.

24. A control system according to claim 22 or claim 23, further characterized in that: The control system is configured to: identifying the ringback signal having the highest amplitude from the at least one excitation frequency scan, and selecting the transmit pulse frequency corresponding to the highest amplitude ringback signal as the initial transmit pulse frequency; The excitation signal is transmitted at the initial transmission pulse frequency during the initial period.

25. The control system according to claim 22 or claim 23, further characterized in that: The control system is configured to transmit the at least one initial transmit pulse during the initial period by outputting a repeated excitation frequency sweep during the initial period; and A ringback signal having a highest frequency among the received plurality of test ringback signals is identified by identifying a highest observed ringback signal frequency generated by the repeated excitation frequency sweep.

26. The control system according to any one of claims 22 to 25, further characterized in that: The control system is configured to dynamically adjust the frequency of the transmit pulses during acquisition of the corresponding ringback signal by monitoring at least one of the amplitude or the signal-to-noise ratio of the corresponding ringback signal and outputting a new excitation frequency scan to identify a new measured transmit pulse frequency in response to detecting that the ringback signal amplitude is below a predefined threshold.

27. The control system according to any one of claims 22 to 26, further characterized in that: The control system is configured to adjust the transmit pulse output power according to the transmit pulse output frequency by monotonically decreasing the transmit pulse output power as the transmit pulse frequency decreases.

28. The control system according to any one of claims 22 to 27, further characterized in that: The control system is configured to monitor a ringback signal generated by the sensor and dynamically adjust the transmit pulse output based on the monitored ringback signal to achieve a substantially constant ringback signal amplitude.

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