Method and system for determining cannula tip location

Abstract

To provide a method and a system for determining the location of a cannula tip in a body, which provide advantages over conventional techniques.SOLUTION: A method for determining the position of a cannula tip within a body, comprising the steps of coupling an ultrasound signal into the body, receiving the ultrasound signal, wherein the ultrasound signal is received by a plurality of sensors, wherein the plurality of sensors are attached to a cannula located within the body and are arranged at a known axial distance to the cannula tip and at a known axial distance to each other along a longitudinal axis of the cannula, comparing the received ultrasound signals, and determining the position of the catheter tip relative to the ultrasound probe, wherein: And wherein the position is determined by the evaluation device depending on a comparison of signal amplitudes and signal waveforms of the received ultrasonic signals.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a method and system for determining the position of a cannula tip within the body. [Background technology]

[0002] Such procedures and systems are used, inter alia, in the field of regional anesthesia. From the prior art, a system called "OnVision" is known, which is designed to display the position of the cannula tip in the image plane of an ultrasound image. This known system is fully integrated with the underlying ultrasound imaging system. Summary of the Invention [Problem to be solved by the invention]

[0003] It is an object of the present invention to provide a method and system of the type described above that offers advantages over the prior art. [Means for solving the problem]

[0004] This object is achieved by providing a method having the features of claim 1 and a system having the features of claim 9. Advantageous embodiments are specified in the dependent claims, the language of which is incorporated by reference into the subject matter of the present specification.

[0005] The method according to the present invention is intended to determine the position of a cannula tip within a body and comprises the following steps: coupling ultrasound signals into the body along an imaging plane of an ultrasound imaging procedure with an ultrasound probe resting on the body, the imaging plane extending along depth and lateral directions; receiving ultrasound signals by a plurality of sensors attached to a cannula located within the body and positioned at known axial distances relative to the cannula tip and from each other along the longitudinal axis of the cannula; comparing the received ultrasound signals with respect to signal amplitude and signal waveform by an evaluation device connected to the sensors; optionally comparing the signal amplitude of the received ultrasound signals with the signal amplitude of an ultrasound signal applied to the ultrasound probe; and determining the position of the catheter tip relative to the ultrasound probe, the position being determined by the evaluation device in response to a comparison of the signal amplitude and signal waveform of the received ultrasound signals and optionally in response to a comparison of the received signal amplitude and the transmitted signal amplitude. The method according to the present invention has the advantage that integration into an ultrasound imaging procedure is not required. Therefore, the method according to the present invention is universally applicable. The signal amplitude applied to the ultrasound probe, i.e., the transmit signal amplitude, can be stored as a nominal value, for example, in a memory unit of the evaluation device. Therefore, connection of the ultrasound probe to the evaluation device is not necessary. The method according to the present invention allows for at least an approximate determination of the position of the catheter tip. In one embodiment, the axial distance between the cannula tip and the imaging plane is determined. In a further embodiment, alternatively or additionally, the inclination angle of the cannula in a vertical plane is determined. In a further embodiment, alternatively or additionally, the depth distance between the ultrasound probe and the cannula is determined. In a further embodiment, alternatively or additionally, the rotation angle of the cannula in a horizontal plane is determined.Based on one, several, or all of the variables listed above, the position of the catheter tip relative to the ultrasound probe can be determined, at least approximately.

[0006] In one embodiment, determining the position includes determining the axial distance between the cannula tip and the imaging plane. The axial distance is determined by the evaluation device in response to a comparison of the signal amplitudes of the received ultrasound signals and the known axial distance between the sensors. By comparing the signal amplitudes of the received ultrasound signals, it is possible to determine which of the multiple sensors is closest to the imaging plane. Placing the sensor directly within the imaging plane is expected to result in the largest received ultrasound signal. As a result, the sensor with the largest signal amplitude of the received ultrasound signal compared to the other sensors is closest to the imaging plane. Because the axial distance between the sensor and the cannula tip sensor is also known, the comparison can be used as a basis for estimating the axial distance between the cannula tip and the imaging plane. The axial distance extends along the longitudinal axis of the cannula.

[0007] In a further embodiment, the comparison of the signal amplitudes includes determining the sensor from which the largest signal amplitude is received in comparison with the other sensors. This determination is also performed by the evaluation device. Alternatively, the sensor from which the smallest signal amplitude is received in comparison with the other sensors can be determined. The sensor with the smallest signal amplitude typically has the greatest distance to the imaging plane along the longitudinal axis of the cannula.

[0008] In a further embodiment, the step of determining the position includes a step of determining an inclination angle of the cannula, where the inclination angle is projected onto a vertical plane extending along the depth direction and the longitudinal direction, and the inclination angle is determined by the evaluation device in response to a comparison of signal waveforms of received ultrasound signals and the known axial distance between the sensors. The vertical plane extends along the depth direction of the imaging plane and perpendicular to the imaging plane. The inclination angle is determined in response to a comparison of signal waveforms of received ultrasound signals and the known axial distance between the sensors. For example, based on the comparison of the signal waveforms, a phase shift and / or a propagation time difference between the received signals can be determined. This phase shift allows for inference about the propagation time difference of transmitted ultrasound signals to individual sensors. For a given frequency of ultrasound signals, the phase shift between the received signals of two or more sensors can be used to infer their distance from the ultrasound probe and / or the distance difference relative to the ultrasound probe. Alternatively or additionally, the propagation time difference is evaluated directly. The distance, or distance difference, and / or propagation time difference, together with the known axial distance between the sensor and the cannula tip, allows the tilt angle to be determined, for example, based on simple geometric relationships, particularly trigonometric relationships.

[0009] In a further embodiment, determining the tilt angle includes determining a difference in propagation time between received ultrasonic signals for at least one first sensor and one second sensor of the plurality of sensors, the difference being determined as a function of a comparison of the signal waveforms of the first and second sensors. In this embodiment of the invention, the tilt angle is determined as a function of the difference in propagation time and a known axial distance between the first and second sensors. The difference in propagation time is determined in response to a comparison of the signal waveforms of the two or more sensors. The difference in propagation time can be determined, for example, as a function of a phase shift between the ultrasonic signal received by the first sensor and the ultrasonic signal received by the second sensor. Alternatively, or in addition, the propagation time from the ultrasonic probe to each of the sensors can be measured. For this purpose, the ultrasonic imaging system can be connected to an evaluation device. Alternatively, the propagation time between the ultrasonic probe and the sensors can be determined by one or more additional sensors located directly on the ultrasonic probe or at least in the vicinity of the ultrasonic probe.

[0010] In a further embodiment, the method includes comparing the signal amplitude of the received ultrasound signal with the signal amplitude of an ultrasound signal applied to the ultrasound probe by the evaluation device, and the determining the position further includes determining a depth distance between the ultrasound probe and the cannula. The depth distance extends along a depth direction in the imaging plane. The depth distance is determined by the evaluation device in response to a comparison of the transmit signal amplitude of the ultrasound signal with the receive signal amplitude of the ultrasound signal. The greater the difference between the transmit signal amplitude of the ultrasound signal and the receive signal amplitude of the ultrasound signal, the shorter the depth distance between the cannula and the ultrasound probe. Conversely, the greater the difference between the transmit signal amplitude and the receive signal amplitude, the greater the depth distance. Ultrasound signals are attenuated within the body. This attenuation reduces the signal amplitude as the distance from the ultrasound probe in the depth direction increases. This embodiment of the present invention takes advantage of this situation. The transmit signal amplitude can be stored as a nominal value in a memory unit of the evaluation device. Alternatively, the transmit signal amplitude can be measured. Alternatively, the ultrasound probe can be connected to the evaluation device to transmit the transmit signal amplitude. In a further embodiment, the depth distance is determined as a function of propagation time. For this purpose, the transmission time of the ultrasound probe must be known. The transmission time can be determined, for example, by a sensor in the immediate vicinity of the ultrasound probe. Alternatively or additionally, the ultrasound probe can be connected to an evaluation device to transmit the transmission time to the evaluation device.

[0011] In a further embodiment, the step of determining the position includes comparing an axial profile of the received signal amplitude over the length of the cannula with reference data. Axial means along the longitudinal axis of the cannula. The reference data represents at least one profile of the signal amplitude of the ultrasound signal over the longitudinal direction, and thus perpendicular to the depth direction and perpendicular to the lateral direction of the imaging plane. The longitudinal direction should not be confused with the longitudinal axis of the cannula. The step of determining the position further includes determining a rotation angle of the cannula. The rotation angle is projected onto a horizontal plane extending along the longitudinal and lateral directions. Thus, the horizontal plane is perpendicular to the imaging plane and perpendicular to the vertical plane involved in determining the tilt angle. The rotation angle in the horizontal plane is determined by the evaluation device in response to a comparison between the axial profile of the received signal amplitude and the reference data. This embodiment of the present invention is based on the consideration that the signal amplitude of the ultrasound signal decreases as the perpendicular distance from the imaging plane, i.e., along the longitudinal direction, increases. When the rotation angle is 0°, the cannula extends longitudinally in the imaging plane. Assuming that the tilt angle is also 0°, the signal amplitude of the received ultrasound signal along the length of the cannula (i.e., along the longitudinal axis) will be approximately the same. When rotation occurs in the horizontal plane, the distance from the sensor to the imaging plane changes along the longitudinal direction. This also changes the signal amplitude profile of the received ultrasound signal along the longitudinal axis of the cannula. The comparison between the axial profile of the received signal amplitude and reference data representing the signal amplitude profile of the ultrasound signal at least along the longitudinal direction allows inferences to be made regarding the rotation angle of the cannula in the horizontal plane. The reference data is preferably stored in a memory unit of the evaluation device. In one configuration, the reference data can be selected from a reference data set containing various data for ultrasound probes with various specifications. The selection can be made by the user. In a further embodiment, the reference data is obtained from a reference measurement. Alternatively, or in addition, the reference data can represent a curve of the signal amplitude as a function of the tilt angle and / or the rotation angle.

[0012] In a further embodiment, the reference data further represents a profile of the signal amplitude of the ultrasound signal along the depth direction in the imaging plane, and the rotation angle is also determined as a function of the determined tilt angle and / or the determined depth distance. Including the tilt angle and / or the depth distance in determining the rotation angle allows for a more accurate determination of the rotation angle, and thus the position of the cannula tip, overall.

[0013] A medical system according to the present invention is configured to determine the position of a cannula tip within a body. The medical system according to the present invention includes an optional ultrasound probe, a cannula, and an evaluation device. The optional ultrasound probe is configured to couple ultrasound signals into the body. The cannula has a cannula tip and is fitted with a plurality of sensors. The sensors are each configured to receive ultrasound signals. The sensors are positioned at a known axial distance from the cannula tip and at known axial distances from each other along the longitudinal axis of the cannula. The evaluation device is connected to the sensors. This connection can be wireless or wired. The evaluation device is configured to compare the received ultrasound signals, in particular with respect to at least the signal amplitude and / or signal waveform of the received ultrasound signals. Optionally, the evaluation device is further configured to compare the signal amplitude of the received ultrasound signals with the signal amplitude of an ultrasound signal present at the ultrasound probe. The evaluation device is further configured to determine the position of the catheter tip relative to the ultrasound probe in response to a comparison of the signal amplitude and signal waveform of the received signals, and optionally in response to a comparison of the received signal amplitude and the transmitted signal amplitude. In other words, the system is configured to perform the method according to the present invention and its embodiments. In one embodiment, the medical system comprises the optional ultrasound probe already mentioned. In a further embodiment, the medical system does not have such an ultrasound probe. In this case, the ultrasound probe is not part of the medical system, but instead is part of the ultrasound imaging system. The medical system embodiments result from features of the embodiments of the method according to the invention, in particular with regard to any additional units of the evaluation device.

[0014] In a further embodiment, the evaluation device is further configured to compare the signal amplitude of the received ultrasound signal with the signal amplitude of the ultrasound signal present at the ultrasound probe, and to determine the position of the catheter tip relative to the ultrasound probe in response to the comparison of the received signal amplitude and the transmitted signal amplitude. The signal amplitude applied to the ultrasound probe may also be referred to as the transmitted signal amplitude.

[0015] Further advantages and features of the invention emerge from the claims and from the following description of preferred exemplary embodiments of the invention, which is illustrated with reference to the drawings. [Brief explanation of the drawings]

[0016] [Figure 1] 1 illustrates in a schematic block diagram an embodiment of a method according to the present invention for determining the position of a cannula tip within a body. [Figure 2] 2 shows in a schematic block diagram an embodiment of a medical system according to the invention configured to carry out the method according to FIG. 1; FIG. [Figure 3] 3 shows in a schematic simplified diagram an exemplary use of the medical system according to FIG. 2. FIG. [Figure 4] FIG. 10 is a diagram with exemplary signal waveforms that are evaluated to determine the position of the cannula tip. [Figure 5] 3 shows a further exemplary use of the medical system according to FIG. 2. [Figure 6] FIG. 10 is a further diagram with exemplary signal waveforms. [Figure 7] 3 is a further schematic diagram of an exemplary use of the medical system according to FIG. 2. [Figure 8] 3 is a further schematic diagram of an exemplary use of the medical system according to FIG. 2. [Figure 9] 3 is a further schematic diagram of an exemplary use of the medical system according to FIG. 2. [Figure 10] FIG. 10 is a diagram with further exemplary signal waveforms. [Figure 11] 3 shows in a schematic diagram a further exemplary use of the medical system according to FIG. 2. [Figure 12] FIG. 10 is a diagram with further exemplary signal waveforms. DETAILED DESCRIPTION OF THE INVENTION

[0017] According to Figure 1, a method 100 is provided for determining a position P (see Figures 3, 5, 7, 8, 9, 11) of a cannula tip 31 within a body K. The method 100 can be performed using the medical system 1 shown in Figure 2, particularly in the context of regional anesthesia. Exemplary use of the medical system 1 during the performance of the method 100 is shown in Figures 3, 5, 7-9, and 11.

[0018] The medical system 1 comprises an optional ultrasound probe 2, a cannula 3, a number of sensors 4, an evaluation device 5, and an optional display device 6. The optional ultrasound probe 2 and the optional display device 6 are not present in all embodiments.

[0019] Step 110 of method 100 provides for coupling an ultrasound signal B into a body K. The ultrasound signal B is emitted by an ultrasound probe and coupled into the body K. In use, the ultrasound probe 2 rests on the body K. Alternatively, the ultrasound probe 2 may also be inserted into an opening in the body K and positioned inside the body K. The ultrasound signal B is coupled into the body K along an imaging plane E. The imaging plane E extends along a depth direction Z and a lateral direction Y.

[0020] In the illustrated embodiment, the ultrasound probe 2 is a separate component of the ultrasound imaging system. The imaging plane E in question is the plane in which the ultrasound images of the ultrasound imaging procedure are generated / displayed. The ultrasound signals B may also be referred to as beams when the signals are combined. The term "beam" is known to those skilled in the art.

[0021] Step 120 of method 100 provides for receiving an ultrasonic signal B. The ultrasonic signal B is received using a plurality of sensors 4 attached to cannula 3 and positioned along the longitudinal axis L of cannula 3 at known axial distances relative to cannula tip 31 and at known distances from each other.

[0022] The plurality of sensors 4 are each configured to receive an ultrasonic signal B, and may also be called an ultrasonic microphone.

[0023] In the illustrated embodiment, the plurality of sensors 4 comprises a first sensor 41, a second sensor 42, and a third sensor 43. The first sensor 41 is disposed distally, in the region of the cannula tip 31. The second sensor 42 is disposed along the longitudinal axis L between the first sensor 41 and the third sensor 43 and may also be referred to as the middle sensor. The third sensor 43 is disposed proximally, in the direction of the proximal cannula end of the cannula 3, which is not shown in this case.

[0024] The number of three sensors in this case is purely exemplary: there may be more than two sensors, which is indicated in Figure 2 by further sensors drawn in dashed lines without reference numbers.

[0025] In the illustrated exemplary use situation, the sensors 41, 42, 43 receive the transmitted ultrasonic signal B. The ultrasonic signals S41, S42, S43 applied to the sensors 41, 42, 43 are hereinafter also referred to as the first ultrasonic signal S41, the second ultrasonic signal S42, and the third ultrasonic signal S43. The first ultrasonic signal S41 is applied to the first sensor 41. The second ultrasonic signal S42 is applied to the second sensor 42. The third ultrasonic signal S43 is applied to the third sensor 43. The ultrasonic signals S41, S42, S43 differ in terms of their signal amplitude and / or their signal waveform. These differences depend on the respective distances of the associated sensors 41, 42, 43 from the ultrasonic probe 2 and therefore from the ultrasonic source. Thus, evaluation of signals S41, S42, S43 allows the position P to be determined, the known distances between sensors 41, 42, 43 and the known distance to cannula tip 31 also being included in the calculation.

[0026] The method 100 provides in step 130 for a comparison of the received ultrasound signals S41, S42, S43. This comparison is carried out by the evaluation device 5. For this purpose, the evaluation device 5 is connected to the sensor 4 attached to the cannula 3 via a signal connection 7. In the illustrated embodiment, the signal connection 7 is a wired connection. In an embodiment not shown, the signal connection is a wireless connection. The signals S41, S42, S43 received by the sensors 41, 42, 43 are compared by the evaluation device 5 with respect to their amplitude and signal waveform. The signal amplitudes of the received signals S41, S42, S43 are hereinafter referred to as S'41, S'42, S'43 in single quotes and are therefore referred to as S'41, S'42, S'43.

[0027] In step 140, the method 100 provides a comparison of the signal amplitudes S'41, S'42, S'43 of the received ultrasonic signals S41, S42, S43 with the signal amplitude B' of the ultrasonic signal B applied to the ultrasonic probe 2. In one embodiment, the signal amplitude B' of the transmitted signal B is measured. In a further embodiment, the ultrasonic probe 2 transmits the signal amplitude B' to the evaluation device 5, for example, via an additional signal line 8. This additional signal line 8 is optional and is therefore shown in dashed lines in FIG. 2 . In a further embodiment, the signal amplitude B' of the combined ultrasonic signal B is provided as a nominal value for the ultrasonic probe 2. This nominal value can, for example, be input to, received from, or stored in the evaluation device 5.

[0028] The method 100 provides in step 150 for determining a position P of the catheter tip 31 relative to the ultrasound probe 2. The position P is determined as a function of a comparison of the signal amplitudes S'41, S'42, S'43 of the received ultrasound signals S41, S42, S43 with the signal waveforms and as a function of a comparison of the received signal amplitudes S'41, S'42, S'43 with the transmitted signal amplitude B' of the ultrasound signal B. The determination is performed by the evaluation device 5.

[0029] In the illustrated embodiment, the evaluation device 5 comprises a processor unit 51 and a memory unit 52. The processor unit 51 is designed to carry out the aforementioned comparisons 130, 140 and the actual determination 150 of the position P. In the illustrated embodiment, a nominal value of the signal amplitude B' of the ultrasound probe 2 is stored in the memory unit 52. This nominal value forms a kind of reference value.

[0030] The determined position P can be displayed graphically or in a different form by the display device 6. For example, the display can be output relative to the already mentioned imaging plane E. An actual ultrasound image can also be displayed by the display device 6.

[0031] The display device 6 may alternatively or additionally be designed to provide an acoustically perceptible display or output of the determined position P. For this purpose, the display device 6 may have a speaker unit. The determined position P or a change therein may be output in a manner similar to park distance control in automobiles, for example by means of an audio signal sequence, an audio signal volume, an audio signal level, etc.

[0032] The method 100 and the medical system 1 enable at least an approximate determination of the position P. Approximation means that the position P does not need to be uniquely determined with respect to all coordinate axes. For example, the method 100 and the medical system 1 may be used only to determine the axial distance between the cannula tip 31 and the imaging plane E (see FIG. 3). Alternatively or additionally, the depth direction T may be determined (see FIG. 5). As a further alternative or addition, the tilt angle α may be determined (see FIGS. 7 and 8). As a further alternative or addition, the rotation angle β may be determined (see FIGS. 9 and 11). Preferably, all of the aforementioned variables A, T, α, and β are determined so that the position P is determined as accurately and / or unambiguously as possible.

[0033] The axial distance A between the cannula tip 31 and the imaging plane E is determined based on a comparison of the signal amplitudes S'41, S'42, and S'43 of the received ultrasound signals S41, S42, and S43 and the known axial distance between the sensors 41, 42, and 43 and relative to the cannula tip 31. This determination is performed by the evaluation device 5. The determination of the axial distance A is based on the assumption that the sensor located closest to the imaging plane E produces the largest signal amplitude compared to the other sensors. In the exemplary situation shown in Figures 3 and 4, the second sensor 42 is located directly within the imaging plane E. Therefore, the second signal amplitude S'42 is largest compared to the signal amplitudes of the other sensors, particularly the signal amplitudes S'41 and S'43. In other words, to determine the axial distance A, the longitudinal position of the cannula 3 at which the beam B is located is determined. The axial distance A extends along the longitudinal axis L of the cannula 3. In the exemplary use situation shown in Fig. 3, the longitudinal axis L extends parallel to a longitudinal direction X, which is oriented orthogonal to the depth direction Z and the lateral direction Y of the imaging plane E. In the schematic diagram according to Fig. 4, an exemplary profile of the signal amplitude B' of the (transmitted) ultrasound signal B across the longitudinal direction X is plotted, as well as the signal amplitudes S'41, S'42, S'43 of the received ultrasound signals S41, S42, S43. As the distance from the imaging plane E increases, the transmitted signal amplitude B' decreases. This is due to the directivity of the beam B and / or the attenuation resulting from the properties of the body K.

[0034] The depth distance T extends along the depth direction Z in the imaging plane E (see FIG. 5 ). The depth distance T is determined by the evaluation device 5 in response to the aforementioned comparison 140 of the transmitted signal amplitude B′ with the received signal amplitudes S′ 41, S′ 42, S′ 43. The determination of the depth distance T is based on the assumption that the signal amplitude B′ of the beam B decreases with increasing depth along the depth direction Z. This decrease is shown in simplified schematic form in the exemplary diagram according to FIG. 6 , the exemplary representation being logarithmic. In the illustrated embodiment, the progression of the signal amplitude B′ over the depth direction Z is stored in the memory unit 52 of the evaluation device 5 in the form of reference data. The reference data can be determined in advance and / or only once, for example, using a reference measurement in a reference measurement setup.

[0035] If the profile of the signal amplitude B' of the transmitted ultrasound signal B over the depth direction Z is known, a comparison with the received signal amplitudes S' 41, S' 42, S' 43 can be used to estimate the depth distance T. For example, if the second sensor 42 is positioned directly in the imaging plane E, as in the exemplary use situation, the depth distance T between the second sensor 42 and the ultrasound probe 2 along the depth direction Z can be determined by a simple comparison between the second signal amplitude S' 42 and said profile of the signal amplitude B' over the depth distance Z.

[0036] When the cannula 3 is tilted at an angle (see, for example, FIG. 8), the depth distance of the cannula tip 31 can be determined based on the known distance between the sensors 41, 42, 43 and the cannula tip 31 via a simple trigonometric relationship.

[0037] The tilt angle α of the cannula 3 is projected onto a vertical plane V extending along the depth direction Z and along the longitudinal direction X (see FIGS. 7 and 8). The tilt angle α is determined depending on a comparison of the previously described signal waveforms of the received ultrasound signals S41, S42, S43 and the known axial distance between the sensors 41, 42, 43 and relative to the cannula tip 31. The tilt angle α is also determined by the evaluation device 5.

[0038] The determination of the tilt angle α is based on the assumption that different propagation times of the ultrasonic signal B are obtained depending on the distance of the sensors 41, 42, and 43 from the ultrasonic probe 2. These different propagation times are shown schematically in the form of arrows in FIGS. 7 and 8 for the first and third sensors 41 and 43, respectively. The propagation time of the ultrasonic signal B between the ultrasonic probe 2 and the first sensor 41 is designated t41. The propagation time assigned to the third sensor 43 is designated t43. In the exemplary use situation according to FIG. 7, the longitudinal axis L is oriented parallel to the longitudinal direction X, and the two sensors 41 and 43 are positioned at the same axial distance along the longitudinal axis L relative to the imaging plane E. Therefore, the propagation times t41 and t43 are identical. The distances between the ultrasonic probe 2 and the two sensors 41 and 43 are also identical. These distances, labeled with reference symbols d41 and d43 in FIG. 7, are obtained purely by calculation from the propagation time of the transmitted ultrasonic signal B and its frequency. The frequency can be determined by the evaluation device 5, for example, based on the received signals S41, S42, S43. Alternatively, or in addition, the frequency of the ultrasonic signal B can be stored as a nominal value in the memory unit 52 of the evaluation device 5. Therefore, in the exemplary use situation shown in Figure 7, there is no phase shift between the signal waveforms of the received ultrasonic signals S41, S43.

[0039] The situation is different in the use situation shown in FIG. 8. Starting from the horizontal orientation according to FIG. 7, the cannula 3 is tilted distally downward in the depth direction T. Therefore, the third sensor 43 is closer to the ultrasound probe 2 than the first sensor 41. As a result, different propagation times t41', t43' and, therefore, different distances d41', d43' are obtained. In this case, the propagation times t41, t43 or t41', t43' are not determined by direct time measurement. Instead, an indirect determination is performed by comparing the signal waveforms of the signals S41, S43 and the resulting phase difference between these two signals S41, S43. The tilt angle α can be determined based on the difference between the propagation times and a simple trigonometric relationship.

[0040] If the tilt angle α is known, the axial distance A and / or depth distance T can be determined with improved accuracy, and vice versa. This is again based on a simple trigonometric relationship and depends on the known distances between the sensors 41, 42, 43 and their distances from the cannula tip 31.

[0041] The rotation angle β (see FIG. 9) is the angle projected onto a horizontal plane H. The horizontal plane H is oriented perpendicular to the imaging plane E and the vertical plane V. Thus, the horizontal plane H extends along the longitudinal direction X and the lateral direction Y.

[0042] The ultrasonic probe 2 is depicted by dashed lines in Figures 9 and 11 and extends along a lateral direction Y. The ultrasonic probe 2 is elongated with respect to the lateral direction Y. In other words, the dimension along the lateral direction Y is significantly greater than the dimension along the longitudinal direction X.

[0043] The determination of the rotation angle β is, in turn, based on the assumption that the signal amplitude B′ of the coupled ultrasound signal B, i.e., the beam, decreases with increasing distance from the imaging plane E, i.e., along the longitudinal direction X. This exemplary decrease in signal amplitude B′ is shown schematically in FIG.

[0044] In the exemplary use situation according to Figure 9, the rotation angle β is approximately zero, and therefore the longitudinal axis L is oriented parallel to the transverse direction Y. Such longitudinal extension of the cannula 3 within the imaging plane E is also referred to as an "in-plane" arrangement. Assuming that the signal amplitude B' of the beam B in the longitudinal direction Y is constant at least over the length of the ultrasound probe 2, the "in-plane" arrangement also results in approximately identical signal amplitudes S'41, S'42, S'43 along the longitudinal axis L (see Figure 10).

[0045] As the rotation angle β increases, the difference between the signal amplitudes S'41, S'42, S'43 also increases. This difference is maximum at a rotation angle β of 90° (see the "out-of-plane" configuration in Figures 11 and 12). The rotation angle β can therefore be determined by comparing the axial profile of the received signal amplitudes S'41, S'42, S'43 over the length of the cannula 3, i.e., along the longitudinal axis L, with the profile of the signal amplitude B over the longitudinal direction X. The profile of the signal amplitude B' of the ultrasound signal B over the longitudinal direction X in this case is stored in the memory unit 52 in the form of reference data. [Explanation of symbols]

[0046] 1. Healthcare system 2 Ultrasound probes 3 Cannula 4 sensors 5 Evaluation Device 6 Display Devices 7 Signal Connections 8 Signal Lines 31 Cannula tip, catheter tip 41 First sensor, sensor 42 Second Sensor, Sensor 43 Third Sensor, Sensor 51 Processor Unit 52 Memory Unit

Claims

1. A method (100) for determining the position (P) of a cannula tip (31) within a body (K), comprising: a step (110) of coupling an ultrasound signal (B) into the body (K), the ultrasound signal (B) being coupled to the body (K) along an imaging plane (E) of an ultrasound imaging procedure with an ultrasound probe (2) resting on the body (K), the imaging plane (E) extending along a depth direction (Z) and a lateral direction (Y); a step (120) of receiving the ultrasonic signal (B), wherein the ultrasonic signal (B) is received by a plurality of sensors (41, 42, 43), the plurality of sensors (41, 42, 43) being attached to a cannula (3) located within the body and positioned at a known axial distance relative to the cannula tip (31) and at known axial distances from each other along a longitudinal axis (L) of the cannula (3); a step (130) of comparing the received ultrasonic signals (S41, S42, S43), in which the received ultrasonic signals (S41, S42, S43) are compared with respect to their signal amplitudes (S'41, S'42, S'43) and their signal waveforms by an evaluation device (5) connected to the sensors (41, 42, 43); a step (150) of determining the position (P) of the catheter tip (31) relative to the ultrasound probe (2), the position (P) being determined by the evaluation device (5) in response to the comparison of the signal amplitudes (S'41, S'42, S'43) of the received ultrasound signals (S41, S42, S43) with the signal waveforms; A method (100) comprising:

2. The step of determining the position (P) (150) comprises:

2. The method (100) of claim 1, further comprising a step of determining an axial distance (A) between the cannula tip (31) and the imaging plane (E), wherein the axial distance (A) is determined by the evaluation device (5) in response to a comparison of the signal amplitudes (S'41, S'42, S'43) of the received ultrasound signals (S41, S42, S43) and the known axial distance between the sensors (41, 42, 43).

3. The step of comparing the signal amplitudes (S'41, S'42, S'43) 3. The method of claim 2, further comprising the step of determining the sensor (42) from which the maximum signal amplitude (S'42) is received in comparison with the other sensors (41, 43).

4. The step of determining the position (P) (150) comprises:

4. The method (100) according to claim 1, further comprising a step of determining an inclination angle (α) of the cannula (3), wherein the inclination angle (α) is projected onto a vertical plane (V) extending along the depth direction (Z) and the longitudinal direction (X), and the inclination angle (α) is determined by the evaluation device (5) depending on the comparison of the signal waveforms of the received ultrasound signals (S41, S42, S43) and the known axial distance between the sensors (41, 42, 43).

5. determining the tilt angle (α) determining a difference in propagation time of the received ultrasonic signals (S41, S42, S43) for at least a first sensor (41) and a second sensor (43) of the plurality of sensors (41, 42, 43), the difference in propagation time being determined in response to the comparison of the signal waveforms of the first sensor (41) and the second sensor (43); determining the tilt angle (α) as a function of the transit time difference and the known axial distance between the first sensor (41) and the second sensor (43); The method (100) of claim 4, further comprising:

6. the additional step of comparing (140) the signal amplitudes (S'41, S'42, S'43) of the received ultrasound signals (S41, S42, S43) with the signal amplitude (B') of the ultrasound signal (B) applied to the ultrasound probe (2), said comparison (140) being performed using the evaluation device (5), The step of determining the position (P) (150) comprises:

6. The method (100) according to any one of claims 1 to 5, further comprising a step of determining a depth distance (T) between the ultrasonic probe (2) and the cannula (3), wherein the depth distance (T) in the imaging plane (E) extends along the depth direction (Z), and the depth distance (T) is determined by the evaluation device (5) in response to the comparison of the signal amplitude (B') applied to the ultrasonic probe (2) with the received signal amplitudes (S'41, S'42, S'43).

7. The step of determining the position (P) (150) comprises: comparing an axial profile of the signal amplitudes (S'41, S'42, S'43) received over the length of the cannula (3) with reference data representing at least one profile of the signal amplitudes (B') of the ultrasound signals (B) over the longitudinal direction (X); determining a rotation angle (β) of the cannula (3), the rotation angle (β) being projected onto a horizontal plane (H) extending along the longitudinal direction (X) and the transverse direction (Y), the rotation angle (β) being determined by the evaluation device (5) as a function of the comparison between the axial profile of the received signal amplitudes (S'41, S'42, S'43) and the reference data; 7. The method (100) of any one of claims 1 to 6, further comprising:

8. The method (100) according to claim 7 in combination with claim 4 and / or claim 6, wherein the reference data further represents a profile of the signal amplitude (B') of the ultrasound signal (B) along the depth direction (Z) in the imaging plane (E), and wherein the rotation angle (β) is also determined as a function of the determined tilt angle (α) and / or the determined depth distance (T), and / or vice versa.

9. A medical system (1) for determining the position (P) of a cannula tip (31) within a body (K), comprising: an ultrasound probe (2) configured to couple an ultrasound signal (B) into the body (K); a cannula (3) having the cannula tip (31) and having a plurality of sensors (41, 42, 43) configured to receive the ultrasonic signals (B) and positioned at known axial distances relative to the cannula tip (31) and from each other along a longitudinal axis (L) of the cannula (3); An evaluation device (5) connected to the sensors (41, 42, 43), the evaluation device (5) comprising: comparing (130) the received ultrasonic signals (S41, S42, S43), in particular with respect to at least their signal amplitudes (S'41, S'42, S'43) and their signal waveforms; determining (150) the position (P) of the catheter tip (31) relative to the ultrasound probe (2) in response to the comparison (130) of the signal amplitudes (S'41, S'42, S'43) of the received signals (S41, S42, S43) with the signal waveforms; An evaluation device (5) configured as follows: A medical system (1) that includes:

10. The evaluation device (5) comparing (140) the signal amplitudes (S'41, S'42, S'43) of the received ultrasonic signals (S41, S42, S43) with the signal amplitude (B') of the ultrasonic signal (B) applied to the ultrasonic probe (2); determining (150) the position (P) of the catheter tip (31) relative to the ultrasound probe (2) in response to the comparison (140) of the received signal amplitudes (S'41, S'42, S'43) and the transmitted signal amplitude (B'); The medical system (1) according to claim 9, further configured to:

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