System and method for robust flow measurement in blood vessels

Abstract

The invention provides a system and method for calculating flow parameters based on a plurality of ultrasound reflections received from a plurality of distances along a blood vessel. A first flow parameter (41) at a first location (z1) and a second flow parameter (42) at a second location (z2) are calculated from a first ultrasound signal associated with ultrasound reflections at the first location and a second ultrasound signal associated with ultrasound reflections at the second location, respectively. A composite flow parameter (50) is calculated based on the first flow parameter and the second flow parameter, which is then output to a user interface (6).

Description

Technical Field

[0001] This invention relates to systems for measuring flow and methods for measuring flow in anatomical structures. Background Technology

[0002] Assessing the hemodynamic significance of cardiovascular and peripheral vascular diseases through intravascular flow measurements is beneficial in guiding the management of circulatory system disorders. In particular, for coronary arteries, large clinical trials have demonstrated that decision-making based on pressure and flow measurements improves clinical outcomes compared to angiography alone. Flow measurements are especially valuable in cases of non-obstructive coronary artery disease (i.e., angina pectoris presenting with no visible blockage in the large arteries). Furthermore, flow measurements in other areas of peripheral vascular disease, such as peripheral vascular disease, can be helpful in quantifying the impact of atherosclerosis on blood supply to the foot and in defining the endpoints of endovascular treatments (e.g., stenting, blockage resection). Additionally, in interventional oncology, blood flow monitoring during embolization can potentially aid in assessing the extent of embolism and preventing embolization of healthy tissue (e.g., in transarterial chemoembolization).

[0003] Guidewires for blood flow velocity measurement have been developed, equipped with a single-element ultrasonic transducer at their distal end. These devices allow for the transmission and reception of ultrasonic pulses. Blood flow velocity can be derived by analyzing the received signals, for example, through pulse-wave Doppler processing.

[0004] One of the challenges is the often limited signal-to-noise ratio (SNR) and robustness of the measurement, which can lead to inaccurate results, especially when the guidewire is not optimally positioned within the blood vessel.

[0005] Therefore, there is a need to improve the robustness of flow measurements in anatomical structures such as blood vessels. Summary of the Invention

[0006] According to an example of one aspect of the invention, an apparatus for measuring flow in blood vessels is provided, the apparatus including a processor configured to:

[0007] A first ultrasound signal and a second ultrasound signal are obtained from an ultrasound transducer of an interventional device, wherein the first ultrasound signal is associated with an ultrasound reflection at a first location in a blood vessel separated from the location of the ultrasound transducer, and the second ultrasound signal is associated with an ultrasound reflection at a second location in a blood vessel separated from the location of the ultrasound transducer.

[0008] The first flow parameter at the first location and the second flow parameter at the second location are determined based on the first ultrasonic signal and the second ultrasonic signal, respectively.

[0009] The composite flow parameters are determined based on the first flow parameters and the second flow parameters;

[0010] The composite flow parameters are output to the user interface.

[0011] The interventional device (which may be any intravascular device (e.g., guidewire, catheter) or interventional needle (e.g., a needle for percutaneous access to a blood vessel)) includes an ultrasound transducer at its distal portion, configured for introduction into the patient's anatomy. The device may be configured to generate multiple electrical pulses to be emitted to the ultrasound transducer, which converts the electrical pulses into ultrasound pulses that propagate into the anatomy (e.g., a blood vessel, a heart chamber) or a medium (e.g., blood) within the anatomy, and the ultrasound transducer receives multiple echo signals, which are reflected ultrasound pulses or ultrasound waves. Upon impact with the ultrasound pulses, the ultrasound echo signals originate from a first measurement position at a distance from the transducer, and are therefore separate from or different from the position of the ultrasound transducer, and from a second measurement position separate from or different from the position of the ultrasound transducer. The first and second positions are different and therefore separated from each other by a distance. In some embodiments, the separation is in the direction of transmission / reception of the ultrasound pulses emitted / received by the transducer. The processor is configured to calculate a first flow parameter at the first location and a second flow parameter at the second location based on the received echo signal, and subsequently calculate a composite flow parameter based on the first and second flow parameters. The advantage of the composite flow parameter is that it depends less on the position and / or orientation of the ultrasound transducer relative to the anatomical structure. Furthermore, the calculation of the composite parameter can improve signal quality by reducing the variance of the flow parameters, which overall improves the robustness of flow velocity measurements.

[0012] In some embodiments, the flow parameter is a velocity parameter, such as a Doppler spectrum (amplitude and / or power), instantaneous peak velocity, or average peak velocity, and the composite flow parameter is a composite velocity parameter. In other embodiments, the flow parameter is a volumetric flow rate, and the composite flow parameter is a composite volumetric flow rate.

[0013] In embodiments of the device, the first location includes a first distance interval, and the second location includes a second distance interval. The first and second distance intervals can be selected by a user (e.g., via a user interface input) or can be predefined based on clinical applications that benefit flow measurement (e.g., in cardiac chambers, flow is less affected by the presence of interventional devices, and the distance interval can be selected to be larger than in coronary artery applications, as the anatomy of the heart wall is far from the ultrasound transducer; whereas in small vessels, the presence of interventional devices interferes with flow in their immediate vicinity, and the vessel wall is closer to the ultrasound transducer). The advantage of having distance intervals for the respective locations is that flow parameters can be calculated over the sampling distance or sampling volume defined by the corresponding distance interval, which improves the reliability of flow measurement. Furthermore, having distance intervals for the respective locations provides additional flexibility in calculating the composite flow parameters by dynamically adjusting the distance intervals or their contribution to the composite flow parameters, which may be required or caused by changes in the environment (e.g., due to a beating heart).

[0014] In some embodiments, the first distance interval and the second distance interval are spatially aligned along the ultrasonic transmission and / or reception axis of the ultrasonic transducer. In embodiments, the first distance interval and the second distance interval are consecutive distance intervals, and in alternative embodiments, the first distance interval and the second distance interval partially overlap. Whether the first distance interval and the second distance interval partially overlap can be selected by the user (e.g., via user interface input) or can be predefined based on clinical applications that benefit from flow measurements. Generally, adjacent or partially overlapping sampling volumes ensure the continuity of measurements used to calculate the composite flow parameters, thus preventing significant differences between measurements that would occur between two more distantly separated sampling distances or volumes. Advantageously, this provides greater flexibility in selecting the appropriate distance interval.

[0015] In any of the disclosed embodiments of the device, the processor can be configured to calculate the composite flow parameters based on a first weighting factor applied to the first flow parameter and a second weighting factor applied to the second flow parameter. The weight or weighting factor values ​​can vary, for example, as a function of any of the following: distance range, time, Doppler frequency, Doppler amplitude spectrum data, and background information (e.g., user input or input from an additional imaging source). The advantage is that clinical application specificity and robustness can be optimized for the calculation of the composite flow parameters.

[0016] In some embodiments, the first weighting factor and the second weighting factor are automatically determined by the processor. The first weighting factor and the second weighting factor may be determined based on the correlation between the Doppler amplitude spectra for the corresponding distance intervals, preferably based on optimization using the minimum variance of the combined Doppler amplitude spectrum across the corresponding distance intervals. This optimally reduces the variance in the composite Doppler amplitude spectrum, which generally improves the robustness of flow velocity measurements.

[0017] In an alternative embodiment, the weighting factor is determined based on the gradient of the Doppler amplitude spectrum for the corresponding distance interval. This is particularly advantageous when the goal is to derive the instantaneous maximum blood flow velocity present in the vessel, such as the instantaneous peak velocity (IPV), from the Doppler amplitude spectrum. This is, for example, the case in Doppler ultrasound coronary flow reserve (CFR) measurements. The confidence level for estimating the IPV depends on the intensity difference between the desired blood flow signal and the background noise. In an embodiment, this confidence level can be quantified by the difference or gradient of the Doppler amplitude spectrum with frequency at the detected IPV. One can evaluate the extent to which the individual Doppler amplitude spectrum contributes to the difference or gradient of the composite Doppler amplitude spectrum and optimize the weights such that the difference or gradient is maximized. This optimization can be implemented as an iterative process of initializing the weights (e.g., uniform weights). The iterative process begins by calculating the composite Doppler amplitude spectrum. Next, the IPV is evaluated, and the difference or gradient of the individual amplitude spectrum at the IPV is evaluated. The weights are optimized based on the difference or gradient values, and the iterative process returns to its starting point. The iterative process can be stopped whenever a satisfactory difference or gradient value is found in the composite Doppler amplitude spectrum, when the increase of the difference or gradient value is below a threshold, when the absolute or relative change of IPV is below a threshold, when the weight reaches the upper / lower limit of the allowable value, when a local optimum is found with a given specific step size, or when the maximum number of iterations is reached.

[0018] In another alternative embodiment, the processor is configured to receive position and / or orientation information of the ultrasonic transducer's ultrasonic emission and / or reception axes relative to the anatomical structure of the blood vessel from which the flow measurement is performed, and the processor is further configured to calculate the first weighting factor and the second weighting factor based on the position and / or orientation information. This allows for the dynamic recording of the distance from the blood flow velocity measurement to the location of the blood vessel, thereby improving the robustness of the blood flow velocity measurement, particularly in motion.

[0019] In any embodiment of the device, the processor may be configured to calculate the composite flow parameters based on the average Doppler amplitude spectrum after scaling the different Doppler amplitude spectra at various distance intervals such that the background noise values ​​across the various distance intervals are brought to substantially equal values. This minimizes the noise variance in the average Doppler amplitude spectrum and highlights those distance intervals characterized by the highest velocity signal energy.

[0020] In any embodiment of the device, the processor may be configured to acquire additional ultrasonic signals associated with ultrasonic reflections at corresponding locations at respective distances from the ultrasonic transducer, wherein the multiple locations are spatially aligned along the ultrasonic transmission and / or reception axes of the ultrasonic transducer. Covering the additional multiple locations allows for selection and / or weighting to maximize signal quality (e.g., maximizing the confidence / reliability of the estimated IPV).

[0021] According to another aspect of the invention, a system is provided, the system comprising: an apparatus according to any embodiment of the invention; the interventional device including an ultrasonic transducer in its distal portion; and the user interface for outputting the composite flow parameters.

[0022] In another aspect of the invention, a flow measurement method is provided, the flow measurement method comprising:

[0023] A first ultrasound signal and a second ultrasound signal are obtained from an ultrasound transducer of an interventional device, wherein the first ultrasound signal is associated with an ultrasound reflection at a first location in a blood vessel separated from the location of the ultrasound transducer, and the second ultrasound signal is associated with an ultrasound reflection at a second location in a blood vessel separated from the location of the ultrasound transducer.

[0024] The first flow parameter at the first location and the second flow parameter at the second location are determined based on the first ultrasonic signal and the second ultrasonic signal, respectively.

[0025] The composite flow parameters are determined based on the first flow parameters and the second flow parameters;

[0026] The composite flow parameters are output to the user interface.

[0027] In an optional embodiment, the method may include the processor performing the operations mentioned in any embodiment of the apparatus according to the invention.

[0028] In another aspect of the invention, a computer program is provided, wherein, when the computer program is run on a computer, the computer program code modules of the computer program are adapted to implement any method of the method according to the invention on any system of the system according to the invention.

[0029] These and other aspects of the invention will become apparent from the embodiments described below and will be explained with reference to the embodiments described below. Attached Figure Description

[0030] Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

[0031] Figure 1 An example of an interventional device in a blood vessel is shown;

[0032] Figure 2 An example of a sampling volume for flow measurement in blood vessels is shown;

[0033] Figure 3 An example of flow measurement displayed on the user interface is shown;

[0034] Figure 4 An example is shown of an incorrect orientation of an interventional device used for flow measurement in blood vessels;

[0035] Figure 5 An exemplary illustration shows the correct orientation of an interventional device for measuring flow in a blood vessel;

[0036] Figure 6 A schematic representation of flow measurement in blood vessels is shown;

[0037] Figure 7 An embodiment of a system for flow measurement is illustrated schematically;

[0038] Figure 8 The Doppler amplitude spectrum at various measurement depths is shown;

[0039] Figure 9 The gray-scale encoded Doppler spectra at various depth intervals as a function of time, obtained in vivo, are shown.

[0040] Figure 10 It shows the average Figure 9 The composite Doppler spectrum obtained from the spectrum shown;

[0041] Figure 11 It is an angiographic image showing blood vessels, flow sensing interventional devices, and flow measurement fields; and

[0042] Figure 12 An exemplary method for measuring flow is illustrated. Detailed Implementation

[0043] It should be understood that the detailed descriptions and specific examples are intended for illustrative purposes only and are not intended to limit the scope of the invention when indicating exemplary embodiments of the apparatuses, systems, and methods. These and other features, aspects, and advantages of the apparatuses, systems, and methods of the present invention will become better understood from the following description, claims, and drawings. The invention will be described with reference to the accompanying drawings.

[0044] To assess blood flow, interventional device 1 is equipped with a single-unit ultrasonic transducer 2 in its distal portion, such as... Figure 1 As illustrated, ultrasound pulses are transmitted and received by ultrasound transducer 2. Based on analysis of the received signals, blood flow velocity in a specific sampling area can be inferred. Intravascular devices (e.g., catheters and guidewires) are interventional devices specifically designed to measure blood flow velocity in various vessels 20 of a patient's circulatory system; however, other interventional devices (such as interventional needles) can be equipped with ultrasound transducers for detecting vessels in a patient's anatomy based on ultrasound Doppler measurements. Philips Volcano commercializes Doppler ultrasound guidewires such as FloWire and ComboWire, which are commonly used for measuring blood flow velocity in the coronary arteries.

[0045] In ultrasound Doppler and imaging, ultrasound transducer 2 transmits burst pulses at a controlled rate and pulse repetition frequency (PRF). After each pulse is transmitted, the transducer switches to receiving mode, and the so-called radio frequency (RF) line can be measured after each pulse transmission. The RF line includes the echo signal caused by the reflection of the transmitted pulse by blood cells 22, which essentially reflect the pulse as if by... Figure 1 The blood cells move in the direction 21 indicated by the exemplary and illustrative symbols; however, depending on the insertion site of the interventional device in the blood vessel, the blood cells may move substantially in the opposite direction of the arrows. These blood cells together form a single acquisition, in which the RF line is measured over a time span of several microseconds. It is typically a band-limited signal with frequency content primarily at the frequency of the transmitted pulse. The time between transmission and reception for each acquisition (referred to as the “fast time”) reflects the distance between the transducer and the scatterer; the fast time is the distance divided by twice the speed of ultrasound propagation. The complex amplitude (and / or phase) of the signal varies as a function of time and is used in ultrasound imaging (amplitude) and Doppler (phase) applications. In the example, the PRF is provided by hardware (e.g., an ultrasound console connected to the interventional device). In some examples, the PRF is 50 kHz.

[0046] In Doppler applications, desired information is extracted through continuous acquisition, which provides a complex amplitude signal that is a function of distance (“fast time”) and acquisition time (“slow time”), namely, the so-called in-phase and quadrature (IQ) signal. The so-called “Doppler signal” is obtained by... Figure 2 The complex signal, obtained by sampling within a distance range of 3 shown in the diagram, is only considered as a function of slow time. The frequency content of the Doppler signal is displayed in the spectral Doppler. This is actually implemented by performing a Fourier transform on a fixed number of slow-time samples (or pulsed emissions) of the complex amplitude signal. The frequency distribution in the Doppler signal, obtained from the amplitude or power spectrum of the Doppler signal, is correlated with the velocity distribution within the sampling volume through analysis of the Doppler equation (i.e., without calibration): . Doppler frequency f D Depends on axial velocity v Ultrasonic propagation speed c (Assuming it is constant in blood, 1566 m / s), ultrasound frequency f c (Determined by the system, e.g., 12 MHz), and the angle between the ultrasonic beam and the flow. θ (“Doppler angle”). For intravascular flow measurement, it is assumed that... θ It can be ignored, therefore cos( θ =1.

[0047] The processing routines used in spectral Doppler are summarized below:

[0048] - Demodulation (e.g., phase quadrature demodulation) converts the RF signal into an IQ signal;

[0049] - (e.g., via a high-pass filter) Clutter filtering is used to reduce low-frequency content in the Doppler signal. Depending on the application, clutter filtering mainly consists of signals from slowly moving tissue (e.g., in the case of FloWire, this often involves blood vessel wall motion).

[0050] Gating (or grouping) is used to sample and integrate the Doppler signal over a specific distance range, thus providing a gated IQ signal. By increasing the gate length (or duration), the Doppler signal is integrated over a longer depth range, thereby increasing the signal-to-noise ratio (SNR) of the Doppler signal at the expense of spatial resolution. The optimal gate duration is equal to the transmit pulse duration, as this maximizes the SNR: a longer gate does not further improve the SNR. The Doppler spectrum can be estimated using a Fast Fourier Transform (FFT) on the gated IQ signal. The amplitude or power of the Doppler spectrum is calculated (the phase spectrum is typically not used).

[0051] Figure 3 An example of velocity determination using pulsed ultrasound Doppler methods (e.g., spectral Doppler) via an interventional device (e.g., FloWire) is illustrated. This method dynamically estimates the distribution of flow velocity 30 in sample region 3 as a function of time. In this way, it provides not directly flow rate or velocity, but rather the distribution of all flow velocities present within the sample volume, thus providing a wealth of information that needs to be aggregated to facilitate clinical decision-making. By doing so, the entire velocity distribution is characterized as a dynamic flow velocity characteristic (DFVF).

[0052] For intravascular flow velocity measurement, instantaneous peak velocity (IPV) is used as DFVF, as shown by the dashed line 32.

[0053] This is based on the idea that in any blood vessel, flow velocity will exhibit a distribution between zero and IPV. Typically, the highest flow velocity exists at the center of the vessel, while the velocity tends to zero near the vessel wall. Therefore, there will be a clear change in the velocity distribution around the IPV, from a significant value to zero. Depending on the signal-to-noise ratio, there will be a variation in the Doppler spectrum from the signal spectral amplitude to the background noise. The brightness of region 31 below the dashed line 32 indicates the density of the velocity distribution. This applies as long as the interventional device (e.g., FloWire) is positioned such that its sampling volume 3 includes the location of the highest flow velocity (e.g., in…). Figure 2 and Figure 5 In the case of [the situation described], changes can be clearly identified from the detected velocity distribution. In some embodiments, the IPV value can be averaged over time (e.g., across a predetermined number of cardiac cycles) to derive the average peak velocity (APV).

[0054] In various other applications, other DFVFs are estimated, such as the instantaneous mean velocity (i.e., the mean of the instantaneous velocity distribution), which is commonly used in ultrasound color Doppler imaging. In power Doppler, total power is used as the DFVF, which is less quantitative but more sensitive. Another alternative DFVF is the power-velocity integral, as this can be estimated more efficiently without first having to estimate the complete velocity distribution. However, the mean flow velocity is highly dependent on the transducer's position within the vessel, which is difficult to control and maintain steadily, and therefore, the measured mean flow velocity is highly unreproducible. In ultrasound power Doppler, the presence of flow is indicated only by calculating the total power in the velocity distribution (i.e., without calculating any velocity).

[0055] One of the challenges with intravascular spectral Doppler methods is the often limited SNR and robustness of measurements. This can lead to inaccurate and inconsistent results, especially when the interventional device (e.g., FloWire) is not optimally positioned within the vessel. Figure 4An example of this is illustrated. Misalignment of the distal tip of an interventional device in a blood vessel can lead to suboptimal sampling of the highest velocity in the vessel. This can result in a suboptimal signal-to-noise ratio, making peak velocity calculation more difficult, or even impossible, if the sampling area or volume does not contain the highest velocity. Given that the position and / or orientation of the interventional device tip can change dynamically during measurement, particularly in coronary arteries located within a beating heart, this misalignment can make it difficult to obtain a reliable peak velocity signal. Figure 5 The diagram illustrates a scenario that leads to more reliable flow measurements, where the sampling volume includes the central region of the vascular lumen.

[0056] The signal quality of the Doppler spectrum can be further improved. As previously mentioned, gating is performed to improve the SNR, where the optimal gate length / duration is given by the transmit pulse length. Therefore, any further improvement in SNR by extending the gate length will require a longer transmit pulse length (e.g., by increasing the number of cycles). However, if longer pulses are to be emitted, it will be necessary in practice to reduce the transmit pulse amplitude to avoid exceeding ultrasonic safety regulations (specifically, time-averaged acoustic energy). Furthermore, longer transmit pulses will increase the period during transducer emission and therefore cannot be used to receive ultrasonic signals.

[0057] In spectral Doppler images, such as... Figure 3 As shown in Figure 30, each pixel is calculated as a complex amplitude spectrum (corresponding to the Doppler signal intensity at a specific Doppler frequency), the real and imaginary parts of which are distorted by additive white (Gaussian) noise with a mean of 0 (in the case of noise) and a standard deviation of σ. The resulting amplitude is characterized by having a mean of 0. and standard deviation The noise follows a Rayleigh distribution (with parameter σ). This particular form of noise is not restrictive and is used here as an example.

[0058] The two related effects can be mathematically utilized as follows:

[0059] - Over a relatively short distance, the Doppler signal is averaged in the time domain, which reduces the standard deviation σ by a factor proportional to the square root of the duration (K) during which the signal is averaged. );

[0060] Over relatively long distances, the Doppler amplitude spectrum can be averaged across different distance ranges. Since the Doppler amplitude spectrum is obtained from different locations, i.e., independently, the noise across different distance ranges is uncorrelated. Thus, averaging will not affect the mean, but will reduce the standard deviation. For equally distributed signals (with equal variance across distance ranges), the variance of the combined spectrum is determined by the number of distance ranges across which the Doppler amplitude spectrum is averaged (…). NThe variance reduction is achieved by averaging across the square root of the variance. If there are differences in variance across different distance ranges, the variance reduction achieved by averaging across the distance ranges will be even smaller. This causes a combined effect, where the noise level will have a mean of 1 / 2. and standard deviation Therefore, the benefit of adding a combined Doppler amplitude spectrum across different depth ranges is that it reduces the standard deviation in the Doppler image. The end result is increased uniformity in the spectral Doppler image, which provides a clearer contrast between signal and noise.

[0061] Figure 6 An interventional device 1 for measuring flow within a blood vessel is schematically shown. Although the interventional device is schematically aligned with the central axis 23 of the blood vessel 20, this is not necessary, as it is sufficient to have a first ultrasound signal 12 associated with ultrasound reflection from a first position (z1) of the transducer and a second ultrasound signal 13 associated with ultrasound reflection from a second position (z2) of the ultrasound transducer. The ultrasound transducer generates multiple ultrasound pulses 11 and receives multiple echo signals 12 from a first measurement position at a first distance z1 from the device, and multiple echo signals 13 from a second measurement position at a second distance z2 from the device. The multiple echo signals 12 from the first measurement position are used to form a first Doppler signal, and the multiple echo signals 13 from the second measurement position are used to form a second Doppler signal.

[0062] In this embodiment, the first position and the second position are spatially aligned along the ultrasonic transmitting and / or receiving axis of the ultrasonic transducer. The first position and the second position are separated by a distance x.

[0063] Interventional device 1 is connected to device 5, such as a control console, via a wired or wireless connection. Figure 7As illustrated, the console can provide electrical excitation pulses to the ultrasound transducer. Alternatively, the electrical excitation pulses can be provided by an autonomous electrical component integrated in the proximal portion of the interventional device, wherein the proximal portion of the interventional device is held outside the patient's body 7 during flow measurements using the distal portion of the interventional device inserted into the patient's anatomy. In another alternative, a power supply is integrated in the proximal portion of the interventional device and configured to communicate with an application-specific integrated circuit (ASIC) located near the ultrasound transducer in the distal portion of the interventional device, which then provides electrical excitation pulses for the ultrasound transducer. Optionally, measurement data can be directly wirelessly transmitted to a user interface (e.g., display 6). In any embodiment, the processor relates to processing the measurement data to output the results of the flow measurement. The processor can be integrated in at least one of the following: a console, a display, and the proximal portion of the interventional device (e.g., a handheld device). The measurement results can be presented on the user interface in the form of a visual representation (e.g., graphics and / or numbers), or they can be presented as an acoustic signal, wherein the acoustic characteristics of the signal vary according to the output flow results.

[0064] exist Figure 7 The system 10, schematically illustrated in the diagram, may include the following components in various alternative configurations:

[0065] - An interventional device, wherein a processor is integrated within the proximal portion of the interventional device, and a user interface for outputting flow results is also included, wherein the processor communicates with the user interface wirelessly.

[0066] - An intervention device that communicates with a console, including a processor, via wired or wireless communication, and outputs streaming results to a user interface that may be separate from or integrated into the console.

[0067] In any of the embodiments, the system may further include at least an external device 8 adapted to provide at least one of the following imaging modalities: X-ray angiography, computed tomography, ultrasound imaging, and magnetic resonance imaging.

[0068] exist Figure 8 The graphical representation 40 shows an example of in vivo Doppler spectra sampled simultaneously at different depth ranges. It should be noted that by averaging the amplitude spectra obtained at different depth ranges, the variance of both the Doppler signal and the background noise can be reduced. This results in improved homogeneity and therefore increased contrast between the signal and noise. Figure 9 Graphical representation of Doppler spectra at various distance ranges (e.g., 41, 42) and Figure 10A comparison with the graphical representations in the text allows for further visualization of the effects. In this particular example, after scaling the different Doppler spectra across various distance ranges to equalize the background noise, the composite Doppler spectrum 50 is calculated using a simple average of the Doppler amplitude spectra (before conversion to dB) (i.e., the arithmetic mean), as shown below. Figure 10 As shown. Several advanced options exist that can be considered in alternative embodiments for combining information (e.g., geometric mean, median, etc.) from individual Doppler spectra from each associated depth interval (or range). In some embodiments, instead of using individual Doppler spectra obtained from subsequent distance ranges (whether adjacent to each other), superimposed distance ranges (e.g., 2-3 mm, 2.5-3.5 mm, 3-4 mm, etc.) can be considered for calculating the composite Doppler spectrum.

[0069] In some embodiments, a module is provided for selecting and / or weighting the combined Doppler amplitude spectrum. This is advantageous because not all amplitude spectra across different ranges comprise exactly the same velocity distribution. Weighting (which, in the case of binary weighting, is equivalent to the selection of the range) can be based on several inputs. Weighting / selection can be performed dynamically by the processor, or it can be determined by the system user by indicating the weights it wants to associate with the Doppler spectrum belonging to a specific range, or by selecting the desired range on the user interface, which is then considered for calculating the composite Doppler spectrum. The weights can vary as a function of the range, time, and Doppler frequency.

[0070] In some embodiments, prior assumptions (e.g., the type of clinical application) may be used. The configuration of a measurement system that inserts a flow-sensing interventional device (e.g., a guidewire) into a blood vessel can have some consequences for the flow velocity profile within the vessel. In particular, the presence of the guidewire disrupts the flow velocity profile near its distal tip, such that the axial velocity measured at a distance range near the distal tip is slightly lower than that measured at a more distant distance. The distance at which this effect is significant depends on the vessel diameter and flow rate. Based on this, the distance range very close to the distal tip of the interventional device (e.g., closer than 2 mm) may be ignored, or low weighting factor values ​​may be associated for calculating the composite Doppler amplitude spectrum. For example, the reduced weighting can be attributed to the distance range very close to the distal tip compared to the Doppler spectrum associated with distance intervals located further from the distal tip of the interventional device. In additional or alternative embodiments, distal ranges that are too far from the ultrasound transducer and where the available Doppler signal has too low quality may similarly be ignored, or the Doppler spectra belonging to those distance ranges may be associated with low weighting factor values. This is advantageous because the finite penetration depth of ultrasound in the measurement medium (e.g., blood or tissue) is related to the ultrasound frequency, and therefore the contribution of the corresponding distance range can be minimized or ignored. Furthermore, the ultrasound beam diverges with penetration depth unless it is a focused ultrasound beam, and at a certain penetration depth, the ultrasound beam becomes wider than the diameter of the blood vessel, and the contribution of the distance intervals around and beyond that particular penetration depth only adds clutter to the measurement and almost no usable velocity signal. Focusing the ultrasound beam used for the ultrasound transducer onto interventional devices (e.g., guidewires or interventional needles) is problematic due to their cross-sectional dimensions, especially when the ultrasound transducer is integrated into the distal end of the interventional device.

[0071] In another alternative embodiment, imaging modalities (e.g., angiography) can provide insight into how well the flow velocity profile (inside the blood vessel) is covered at different distance ranges. Angiography can be used in conjunction with a vascular navigation system, such as... Figure 11 As shown. You can ask about Figure 7 The processor in any of the disclosed system embodiments provides information about the optimal distance for flow measurement, based on which it provides automatic optimization of Doppler spectral weighting for various distance ranges to calculate the composite Doppler spectrum. The interventional device can be presented as an image formed by an imaging system at a location within the blood vessel (e.g., in...). Figure 11(The situation in the image). Additionally or alternatively, the interventional device can be navigated to the desired measurement location. Co-registration can be used to track the distal region of the interventional device relative to the morphology of the vessel obtained from the imaging system (e.g., by using radiopaque markers on the interventional device or by electromagnetic tracking through coils in the distal portion of the device). In some embodiments, the processor can be configured to automatically magnify the location of the distal portion of the interventional device without initiating a flow measurement. In some embodiments, the distal portion of the interventional device is highlighted in the presented image. In other embodiments, both the distal portion of the interventional device and the vascular anatomy are enhanced in the presented image. In some embodiments, the measurement field 4 of the ultrasound transducer is visualized relative to the vascular anatomy (e.g., the wall). The ultrasound measurement field or ultrasound transducer beam profile can be known based on the manufacturing and calibration measurements of the ultrasound transducer integrated into the interventional device. The ultrasound measurement field or ultrasound transducer beam profile may depend on the frequency and excitation pulse and may have been implemented to be recorded in a library stored on a memory device. By coupling a specific interventional device for measurement, the processor automatically selects the corresponding ultrasound measurement field or ultrasound transducer beam profile from the library and overlays it onto the image including the vascular anatomy and the interventional device. Furthermore, in some embodiments, the processor may be configured to allow flow measurement only when the ultrasound measurement field or ultrasound transducer beam profile does not intersect the vessel wall. In another embodiment, the processor is configured to automatically select a distance interval for the sampling range based on the distance interval within the ultrasound measurement field or ultrasound transducer beam profile within the vessel lumen at a predetermined lateral distance from the vessel wall. In yet another embodiment, the processor may be configured to output the ultrasound measurement field or ultrasound transducer beam profile to a display differently when the position and / or orientation of the ultrasound measurement field relative to the vessel wall is suitable for flow measurement, compared to when the environment would not allow for reliable flow measurement. In examples, suitable and unsuitable environments for flow measurement may be represented using different colors, such as green for suitable conditions and orange to red for unsuitable conditions. Optionally, the ultrasound measurement field or ultrasound beam profile may be represented differently for distance intervals suitable or unsuitable for flow measurement (e.g., shaded lines or colors).

[0072] In alternative approaches, the interventional device can be presented against a dynamic coronary artery pathway map, for example, as described in the article by Piayda et al. (Eur J Med Res (2018) 23:36 (https: / / doi.org / 10.1186 / s40001-018-0333-x)). Figure 1 and Figure 2 Content described in a particularly relevant way.

[0073] Alternatively, in addition to or replacing X-ray angiography, other imaging modalities that can provide anatomical information along with information on the location and / or orientation of the interventional device can be used in the system. Imaging systems 8 are contemplated herein, providing ultrasound imaging, magnetic resonance imaging (MRI), or computed tomography (CT). These imaging modalities can provide three-dimensional (3D) information to better assess the orientation of the flow velocity measurement field 4 of the ultrasound transducer in conjunction with anatomical structures (e.g., blood vessels 24). Alternatively or additionally, the location and / or orientation of the distal tip of the interventional device 1 can be tracked using ultrasound localization techniques or via optical fibers integrated within the interventional device, as known to those skilled in the art from patent literature.

[0074] In some embodiments, the selection and / or weighting of the Doppler amplitude spectrum can be based on the content of the spectrum itself (i.e., data-driven). This can be implemented in various ways:

[0075] - A general data adaptation method can be used to optimally utilize the correlation between the Doppler amplitude spectra obtained at different distance ranges. The weights can be based on the actual correlation between the amplitude spectra measured at different distance ranges;

[0076] - Adaptive algorithms can be used to determine the weights for optimizing a cost function, such as minimizing the variance of a combined Doppler amplitude spectrum;

[0077] - Selection and / or weights can be determined for the purpose of optimizing the accuracy of DFVF estimation. Weights for different distance ranges can be determined based on how much the Doppler amplitude spectrum at a specific distance range contributes to the accuracy of DFVF estimation; for example, if the Doppler amplitude spectrum at a specific distance range would contain only noise, then the contribution would be negative, and this distance range would preferably not be considered in DFVF estimation. To illustrate how this method can be implemented, an IPV is used as an example DFVF, and the contribution of the distance range to the DFVF estimation is measured using the gradient of the Doppler amplitude spectrum at the IPV as a feature. Figure 8As shown in the example Doppler amplitude spectrum, a significant negative gradient exists in the amplitude spectrum between 8 and 10 kHz (i.e., within the frequency range corresponding to IPV tracking 43). The strength of this gradient is a measure of how accurately the IPV can be estimated. Alternatively, other features (e.g., SNR) can be used for this purpose. Thus, an algorithm for iterative optimization of the weights (e.g., starting with uniform weights) can be used, including: calculation of the weighted combined amplitude spectrum; estimation of the IPV; testing whether the IPV is sufficiently accurate: if so, then stop; if not, then continue calculating the gradient of the IPV for all amplitude spectra; updating the weights for all amplitude spectra based on the gradient and returning to the first step of calculating the weighted combined amplitude spectrum. The confidence level for estimating the IPV depends on the difference in strength between the expected blood flow signal and the background noise. In an embodiment, this confidence level can be quantified by the difference or gradient of the Doppler amplitude spectrum with frequency at the detected IPV. One can evaluate the extent to which individual Doppler amplitude spectra contribute to the difference or gradient of the composite Doppler amplitude spectrum and optimize the weights such that this difference or gradient is maximized. This optimization can be implemented as an iterative process where weights are initialized (e.g., uniform weights). The iterative process begins by calculating the composite Doppler amplitude spectrum. Next, the IPV is evaluated, and the differences or gradients of the individual amplitude spectra at the IPV are assessed. Weights are optimized based on the differences or gradient values, and the iterative process returns to its starting point. The iterative process can stop whenever a satisfactory difference or gradient value in the composite Doppler amplitude spectrum is found, when the increase in the difference or gradient value is below a threshold, when the absolute or relative change in IPV is below a threshold, when the weights reach an upper / lower bound of the allowable value, when a local optimum is found for a given step size, or when the maximum number of iterations is reached.

[0078] In any embodiment of the interventional device, the ultrasound transducer may include multiple ultrasound transducer elements, in which case the ultrasound pulses can be guided using electron beam steering and / or electron beam focusing to include a sampling volume from the central region of the vascular lumen with the maximum flow velocity. In this way, the measurement results can be made less sensitive to the orientation of the interventional device. In some embodiments of the system, electron beam steering and focusing can be applied to optimally align the ultrasound beam with the flow direction. The ultrasound beam angle can be optimized to maximize the intensity of the Doppler signal. Beam angle optimization can be performed iteratively and / or adaptively. Any transducer in the interventional device can be a conventional ultrasound transducer including PZT or PVDF, or it can be a micromechanical ultrasound transducer (capacitive or piezoelectric).

[0079] In another aspect of the invention, a method 100 for measuring flow is provided, comprising:

[0080] 101 First ultrasonic signal and second ultrasonic signal are obtained from the ultrasonic transducer of the interventional device, wherein the first ultrasonic signal is associated with ultrasonic reflection at a first position at a first distance from the ultrasonic transducer, and the second ultrasonic signal is associated with ultrasonic reflection at a second position at a second distance from the ultrasonic transducer.

[0081] Determine the first flow parameter at the first position and the second flow parameter at the second position;

[0082] The composite flow parameters of 103 are determined based on the first flow parameter and the second flow parameter.

[0083] Output 104 composite flow parameters to the user interface.

[0084] In an optional embodiment, the method may include a processor that performs the operations mentioned in any embodiment of the apparatus according to the invention, for example, as an option, applying various weighting factors of 105 to the contributions of the Doppler spectrum over various distance ranges for calculating the composite Doppler spectrum.

[0085] Furthermore, a computer program including code modules is provided, which, when run on a computer, implements any of the methods according to the invention on any system in the system to output composite flow parameters, such as composite Doppler spectra, instantaneous peak velocities, and average peak velocities. The computer program can be stored / distributed on a suitable medium, such as an optical storage medium or solid-state medium provided together with or as part of other hardware, but the computer program can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0086] By studying the accompanying drawings, description, and appended claims, those skilled in the art can understand and implement other variations of the disclosed embodiments in practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the words "a" or "an" do not exclude a plurality. Although specific measures are recited in dissimilar dependent claims, this does not indicate that combinations of these measures cannot be advantageously used. Any reference numerals in the claims should not be construed as limiting the scope.

Claims

1. A device (5) for measuring flow in a blood vessel (20), comprising a processor configured to: A first ultrasonic signal (12) and a second ultrasonic signal (13) are obtained from the ultrasonic transducer (2) of the interventional device (1), wherein, The first ultrasonic signal is associated with an ultrasonic reflection at a first position (z1) separate from the position of the ultrasonic transducer, and the second ultrasonic signal is associated with an ultrasonic reflection at a second position (z2) separate from the position of the ultrasonic transducer. The first flow parameter (41) at the first position and the second flow parameter (42) at the second position are determined based on the first ultrasonic signal and the second ultrasonic signal, respectively. The composite flow parameter (50) is determined based on the first flow parameter and the second flow parameter. The composite flow parameters are output to the user interface (6).

2. The apparatus according to claim 1, wherein, The first position includes a first distance interval, and the second position includes a second distance interval.

3. The apparatus according to claim 2, wherein, The first distance interval and the second distance interval are spatially aligned along the ultrasonic transmitting and / or receiving axis of the ultrasonic transducer.

4. The apparatus according to claim 3, wherein, The first distance interval and the second distance interval are consecutive distance intervals.

5. The apparatus according to claim 3, wherein, The first distance interval and the second distance interval partially overlap.

6. The apparatus according to any one of the preceding claims, wherein, The flow parameters include at least one of the following: Doppler spectrum, instantaneous peak velocity, and average peak velocity.

7. The apparatus according to claim 6, wherein, The flow parameters include the Doppler amplitude spectrum.

8. The apparatus according to any one of claims 1-5 and 7, wherein, The processor is configured to calculate the composite flow parameters based on a first weighting factor applied to the first flow parameter and a second weighting factor applied to the second flow parameter.

9. The apparatus according to claim 8, wherein, The first weighting factor and the second weighting factor are automatically determined by the processor.

10. The apparatus according to claim 9, wherein, The first weighting factor and the second weighting factor are determined based on the correlation between the Doppler amplitude spectra for the corresponding distance intervals.

11. The apparatus according to claim 10, wherein, The first weighting factor and the second weighting factor are determined based on optimization using the minimum variance of the combined Doppler amplitude spectrum across the respective distance intervals.

12. The apparatus according to claim 9, wherein, The first weighting factor and the second weighting factor are determined based on the gradient of the Doppler amplitude spectrum for the corresponding distance interval.

13. The apparatus according to claim 9, wherein, The processor is configured to receive position and / or orientation information of the ultrasonic transmission and / or reception axis of the ultrasonic transducer relative to the anatomical structure of the blood vessel to which the flow measurement is performed, and wherein the processor is further configured to determine the first weighting factor and the second weighting factor based on the position and / or orientation information.

14. The apparatus according to any one of claims 1-5, 7 and 9-13, wherein, The processor is configured to determine the composite flow parameters based on the average Doppler amplitude spectrum after scaling different Doppler amplitude spectra at various distance intervals so that the background noise values ​​across the various distance intervals are brought to substantially equal values.

15. A system (10) for measuring flow in blood vessels, comprising: The apparatus according to any one of the preceding claims; The interventional device (1) includes an ultrasonic transducer (2) on its distal portion; and The user interface (6) is used to output the composite flow parameters (50).

16. A method for measuring flow in blood vessels (100), comprising: (101) A first ultrasonic signal (12) and a second ultrasonic signal (13) are obtained from the ultrasonic transducer of the interventional device, wherein the first ultrasonic signal is associated with an ultrasonic reflection at a first position (z1) separated from the position of the ultrasonic transducer, and the second ultrasonic signal is associated with an ultrasonic reflection at a second position (z2) separated from the position of the ultrasonic transducer. The first flow parameter (41) at the first position and the second flow parameter (42) at the second position are determined based on the first ultrasonic signal and the second ultrasonic signal, respectively. The composite flow parameter (50) is determined based on the first flow parameter and the second flow parameter (103). Output the composite flow parameters (104) to the user interface.

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