Method for determining the position of a catheter tip

Abstract

The invention relates to a method for determining the position of a catheter tip inside a body, comprising the steps of: measuring an intravascular ECG signal between the catheter tip and a surface electrode, wherein the surface electrode is arranged at a defined surface position of the body;Computer-aided calculation of a virtual intravascular ECG lead between a virtual catheter tip and a virtual surface electrode, wherein the calculation is performed using a numerical simulation model that models physical properties of the body, the surface position of the surface electrode, electrical cardiac activity and an electric field resulting from the electrical cardiac activity, wherein a modeled electrical cardiac activity underlying the numerical simulation model is modeled and / or corrected depending on the measured ECG lead, wherein the modeled electrical cardiac activity is adjusted to the actual electrical cardiac activity that caused the measured ECG lead, and wherein the calculation is performed for several different virtual positions of the virtual catheter tip;Comparing the measured ECG lead with the calculated virtual ECG lead, comparing the multiple virtual positions of the virtual catheter tip; determining the position of the catheter tip based on the comparison.

Description

The invention relates to a method for determining a position of a catheter tip in the interior of a body. The invention also relates to a medical system configured to carry out such a method.Catheters are well known in medicine. When a catheter is put on, its catheter tip is introduced into a body-side access and advanced to a desired location. The placement of the catheter is also referred to as catheter installation.Central venous catheters are usually introduced into the venous system via a vein of the upper half of the body. The catheter tip is usually advanced to the right atrium region. Misdirected advancement and insufficiently accurate positioning of the catheter tip can lead to problems. To counteract such problems, control of the position of the catheter tip is required. At best, such a determination takes place in real time, i.e. already during the catheter installation. Different methods are known for this purpose in clinical practice.In a known method, after or already during the catheter installation, the position of the catheter tip is recorded by X-ray analysis. The radiation exposure associated therewith carries health risks and is therefore contrary to a broad application. In addition, X-ray methods are complicated in terms of apparatus and comparatively time-consuming and cost-intensive.In a further known method, electrocardiography position control is carried out (e.g. W. Schummer et al.: "Optimized positioning of central venous catheters by a modified application of intravascular electrocardiography", Anesthesist 54 (2005), pp. 983-990). An ECG signal is thereby derived between a surface electrode attached to the body surface of the patient and a guide wire of the catheter. Said ECG signal can also be referred to as intravascular ECG derivation. The known method makes use of the fact that the P-wave of the intravascular ECG lead changes as a function of the advance of the catheter tip. As the catheter tip enters the atrium, a characteristic change in the P wave occurs. The position control is effected by observing the said change. The known electrocardiograph method only allows confirmation of correct positioning in front of the right atrium. It is not possible to determine the position of the catheter tip even in areas remote from the atrium.Moreover, a medical system is known under the name "Shear 3CG™ Tip Confirmation System", which provides for the position of the catheter tip to be determined by means of magnetic field sensors.It is an object of the invention to provide a method and a medical system of the type mentioned at the beginning which offer advantages over the prior art.To achieve this object, the invention provides a method having the features of claim 1 and a medical system having the features of claim 4. Advantageous embodiments are specified in the dependent claims. The wording of all claims is made the content of the description by reference.The method according to the invention comprises: metrological detection of an intravascular ECG lead between the catheter tip and a surface electrode, wherein the surface electrode is arranged at a defined surface position of the body; computer-aided calculation of a virtual intravascular ECG lead between a virtual catheter tip and a virtual surface electrode, wherein the calculation is carried out using a numerical simulation model which models physical properties of the body, the surface position of the surface electrode, an electrical cardiac activity and an electric field resulting from the electrical cardiac activity, wherein a modeled electrical cardiac activity on which the numerical simulation model is based is modeled and / or corrected as a function of the ECG lead recorded by measurement, wherein the modeled electrical cardiac activity is matched to the actual electrical cardiac activity which is causative of the ECG lead recorded by measurement, and wherein the calculation is carried out for a plurality of different virtual positions of the virtual catheter tip; comparing the ECG lead recorded by measurement technology with the calculated virtual ECG lead, wherein the comparison is made for the plurality of virtual positions of the virtual catheter tip; determining the position of the catheter tip as a function of the comparison. The solution according to the invention makes it possible to dispense with the use of X-ray or electromagnetic radiation for determining the position of the catheter tip. This prevents radiation exposure of the patient. On the other hand, the apparatus complexity can be saved. In contrast to methods known from the prior art, the position determination can also be carried out away from the atrium with sufficient accuracy, in particular in the region of the extremities. The invention is based on the finding that the electric field resulting from the electrical cardiac activity increasingly distorts in the interior and at the surface of the body in the region of the body extremities. Due to this distortion, a sufficiently accurate position determination is not readily possible with methods known from the prior art. The solution according to the invention takes into account said field distortion in the context of computer-assisted calculation, i.e. using said numerical simulation model.The measurement of the intravascular ECG lead is carried out in a manner known to the person skilled in the art. Intravascular ECG derivation may also be referred to as catheter derivation. The catheter can be derived in a wired or wireless manner. For example, the catheter can be discharged via a distal end face of a guide wire or other wire. Alternatively, the catheter tip may be provided with a catheter electrode. Further alternatively, the catheter can be discharged via a catheter lumen filled with electrically conductive liquid, in particular saline solution. The surface electrode can also be referred to as a skin electrode and is arranged at a defined position of the body surface (surface position). The catheter lead is detected for at least one cycle of the patient's cardiac activity, i.e. for at least one heart beat and / or one complete circulation of the so-called ECG vector.Computer-aided calculation of the virtual intravascular ECG lead is performed using the numerical simulation model. The virtual intravascular ECG lead is also referred to below as virtual and / or simulated catheter lead. The numerical simulation model used for calculating the virtual catheter lead depicts the measurement of the (real / actual) catheter lead in a model-based manner. The numerical simulation model is preferably based on fundamentally known nonlinear differential equations and a discretizing method suitable for solving such equations, for example a finite element method or a finite difference method. The numerical simulation model depicts the relevant problem area in a model-like manner, in this case the patient's body and its relevant physical properties. The surface position of the (actual) surface electrode, an electrical activity of the heart (electrical heart activity) and the electrical field resulting from the heart activity in the interior of the body and on the body surface are depicted further by way of model. The electric field (approximated) is calculated. Finally, the virtual catheter lead can be calculated on this basis. The virtual catheter lead is determined for at least one cycle of electrical heart activity, i.e. for at least one heart beat and / or one complete circulation of the so-called ECG vector. The virtual catheter derivation is calculated for different virtual positions of the virtual catheter tip. Consequently, the position of the virtual catheter tip is changed, in particular stepwise, in the course of the computer-assisted calculation, for example along a plausible feed path within the body. The computerized calculation thus provides an associated virtual catheter lead for each virtual position of the catheter tip. The modeled electrical heart activity on which the simulation model is based is modeled and / or corrected as a function of the ECG lead recorded by measurement, the modeled electrical heart activity being matched to an actual electrical heart activity which is causative of the ECG lead recorded by measurement. In other words, a correction and / or adaptation takes place between the measured catheter lead and the calculated catheter lead. Such a correction and / or adaptation can basically take place in different ways. In this embodiment of the invention, however, the correction and / or adaptation is particularly advantageously carried out on the basis of the measured ECG vector. This represents the actual electrical cardiac activity of the patient. If the modeled electrical heart activity on which the numerical simulation model is based is modeled on the basis of the actual heart activity, deviations between the measurement-technology detection and the computer-assisted calculation can be avoided and improved accuracy can be achieved. When simulating cardiac activity, the electric field must be "corrected" by the real cardiac activity. In one embodiment, the electric field is calculated and corrected subsequently using the ECG signal recorded by measurement technology, in particular by the / a measured ECG vector. In a further embodiment, the electric field for the actually measured, real ECG signal is calculated.The comparing provides a matching of the measured catheter lead with the calculated catheter leads for the different positions of the virtual catheter tip. For this purpose, for example, the measured catheter lead may be subtracted from each of the calculated catheter leads, or vice versa. On the basis of such a difference formation, for example, a difference value can be determined which represents the deviation between calculated and measured catheter derivation. Further, for example, a mean square error (MSE) may be calculated, which represents a deviation between the calculated and the measured catheter derivatives.The position is determined as a function of the comparison. If a difference value or a mean quadratic deviation are determined, the position of the actual catheter tip lies approximately in the region of that virtual position of the virtual catheter tip at which the said determined variable assumes an extreme value, in particular becomes minimal.The method according to the invention is particularly advantageously suitable for determining the position of central vein catheters, PICCs (Peripherally Inserted Central Venous Catheter) and so-called midlines. The solution according to the invention is not, however, restricted to such catheters, but is also advantageously suitable for pulmonaryis catheters, dialysis catheters and / or arterial catheters, for example.In one embodiment of the invention, the metrological detection and the computer-assisted calculation are carried out for different surface positions of the surface electrode and / or for a plurality of differently positioned surface electrodes, and the comparison of the metrologically detected ECG derivatives and the calculated virtual ECG derivatives is carried out for the different surface positions of the surface electrode and / or for the plurality of differently positioned surface electrodes. In this embodiment of the invention, therefore, not only the (virtual) position of the virtual catheter tip is changed during the computer-assisted calculation. Rather, the position of the surface electrode is additionally changed and / or a plurality of differently positioned surface electrodes are used. This is the case both in measurement and computer-assisted calculation. This makes it possible to achieve an even improved accuracy. Preferably, at least three differently positioned surface electrodes are used for measuring catheter derivation and computer-assisted calculation thereof.In a further embodiment of the invention, the physical properties of the body on which the numerical simulation model is based comprise at least one body dimension, a mass of the body and / or a body fat fraction. In this embodiment of the invention, the numerical simulation model is adapted to the real conditions in an improved manner by relevant physical properties of the body being taken into account during the modeling. For example, the at least one body dimension, for example the body length, the body mass (weight) and / or the body fat fraction. The aforementioned properties have an influence on the field magnitudes resulting from the electrical heart activity and thus on the accuracy of the calculated virtual catheter derivatives.The medical system according to the invention is configured to carry out a method according to the preceding description. The medical system according to the invention has a measuring device and a calculating device. The measuring device is configured for metrologically detecting an intravascular ECG lead between a catheter tip and a surface electrode, wherein the surface electrode is provided for arranging at a defined surface position of the body. The calculation device is configured for computer-assisted calculation of a virtual intravascular ECG lead, for comparison of the ECG lead recorded by measurement technology with the calculated virtual ECG lead and for ascertaining the position of the catheter tip as a function of the comparison. This is in each case according to the preceding description of the method according to the invention. To avoid repetitions, express reference is made and referred to to the description of the method according to the invention and its configurations. What has been said there also applies, mutatismutatally, to the medical system according to the invention. Embodiments of the medical system are directly and unambiguously evident from the disclosure of the embodiments of the method according to the invention.Further advantages and features of the invention are evident from the claims and from the following description of a preferred exemplary embodiment of the invention, which is illustrated on the basis of the drawings. FIG. 1 shows a schematically simplified representation of an embodiment of a medical system according to the invention, FIGS. 2, 3 show an exemplary situation of use of the medical system according to FIG. 1 and FIG. 4 shows a schematic block diagram of an embodiment of a method according to the invention using the medical system according to FIG. 1.According to FIGS. 1 to 3, a medical system 1 is provided for ascertaining a position P of a catheter tip 5. The position determination or also localization takes place in the present case in the interior of a body K. The body K can be a human or animal body. The catheter tip 5 to be localized is in the present case part of a central venous catheter 4. Instead of a central venous catheter 4, for example a PICC catheter or a so-called midline can be located.The medical system 1 has a measuring device 2 and a calculating device 3.In the embodiment shown here, the medical system 1 also comprises the central venous catheter 4 to be localized.The measuring device 2 is arranged for metrologically detecting an intravascular ECG lead E between the catheter tip 5 and at least one surface electrode 7. The attachment is carried out in a manner known to the person skilled in the art. In the situation of use shown with reference to FIG. 2, the catheter tip 5 is located inside the body K. The catheter installation can be carried out in a manner known to the person skilled in the art, for example by means of the Seldinger technique. The intravascular ECG lead E can also be referred to as catheter lead, wherein both terms are used interchangeably hereinafter.In the embodiment shown, the central venous catheter 4 is provided with a catheter electrode 6 in the region of its distal catheter tip 5. The catheter electrode 6 is connected to the measuring device 2 via a signal line 61. The surface electrode 7 is connected to the measuring device 2 by a signal line 71.The measured catheter lead E results from a potential difference between the catheter electrode 6 and the surface electrode 7. In this case, field lines L of the electric field F for an imaginary time of the electrical heart activity HA are drawn in by way of example and schematically in a greatly simplified manner in FIG. 2. It is understood that the field lines L change during a cycle of heart activity HA, i.e. a heart beat of the heart H.The intravascular ECG lead E is detected for at least one cycle of heart activity HA in the embodiment shown.The calculation device 3 serves for calculating a virtual intravascular ECG lead. The calculation is carried out in a manner described in more detail below with computer assistance and on the basis of a simulation model M. The position P is determined on the basis of the measured ECG lead E and the computer-assisted calculation.Computer-assisted calculation takes place, as is made clear with reference to FIG. 3, between a virtual catheter tip 5' and at least one virtual surface electrode 7'. The calculation is carried out on the basis of the numerical simulation model M. The numerical simulation model M is executed on a processor unit 31 of the calculation device 3 in the embodiment shown. The numerical simulation model M depicts physical properties A 1, A 2 to A n of the body K, the surface position Q of the at least one surface electrode 7, said electrical cardiac activity HA and the electrical field F resulting from the electrical cardiac activity HA in a model-like manner. These modeled quantities / characteristics are shown in FIG. 3 using the same reference numerals and reference letters, each with an apostrophe. Thus, a virtual electric field F', a virtual electric heart activity HA', a virtual body K' and virtual field lines L' can also be referred to. Here, "virtual" means modeled and / or calculated.The calculation is carried out not only for a single virtual position but for a plurality of virtual positions P1' to P6' of the virtual catheter tip 5'. The virtual position of the virtual catheter tip 5' is changed during the calculation, in particular stepwise and / or iteratively. In the present case, only six virtual positions are schematically illustrated with reference to FIG. 3. It is understood that clearly more than the six positions shown here can be used as the basis for the calculation.A catheter lead E1' to E6' is calculated for each of the plurality of virtual positions P1' to P6' on the basis of the numerical simulation model M. In this case, for example, the virtual position P1' is assigned to the catheter lead E1' and vice versa. For the remaining virtual positions P2' to P6', a corresponding assignment to the remaining calculated catheter derivatives E2' to E6' applies. As further illustrated in Figure 3, the measured catheter lead E is compared to each of the calculated catheter leads E1' to E6'. This comparison is effected in the present case in a separate determination unit 32 of the calculation device 3. The determination device 32 can, however, also be formed by the already mentioned processor unit 31 or be assigned to it. Comparing the measured catheter lead E with the calculated catheter leads E1' to E6' preferably comprises calculating a comparison value. This comparison value can be a difference value, which is formed, for example, by a subtraction between the measured catheter lead E and the calculated catheter leads E1' to E6'.The position P is determined as a function of said comparison (see FIG. 3 ). The virtual position P1' to P6' for which said difference value becomes minimum represents the actual position P of the catheter tip 5.Furthermore, it is provided that the virtual / modelling heart activity HA' is matched to the actual, real heart activity HA. For this purpose, the measured catheter lead E is used in the present case as an input variable for the numerical simulation model M. This adaptation or correction can be carried out in particular as explained below: a phase of the measured ECG vector is calculated for each time of the (time-discrete) measured ECG vector. For each of these calculated phases, the amplitude of the simulated ECG signal for a particular position of the surface electrode as well as the intravascular electrode is looked up (or calculated) in a table. This amplitude is corrected by the amplitude of the measured ECG vector at exactly this point in time. This is repeated for all discrete-time measured positions of the ECG vector. From the results, the virtual ECG signal is thus formed at the intravascular position determined above as a function of the measured ECG signal and the skin electrode position.Furthermore, in the present case, the aforementioned physical properties A 1, A 2 to A n are also supplied to the numerical simulation model M as input variables. The physical properties in the present case are a body dimension A 1, for example the body length, a mass of the body K, i.e. the body weight, and a body fat fraction A n. The said physical properties of the body K influence the properties of the electric field F resulting from the electrical cardiac activity HA. By taking into account the said properties, the calculation of the virtual catheter lead or catheter leads E1' to E6' can be carried out with improved accuracy.Furthermore, it is provided in the present case that the measurement-technology detection and the computer-assisted calculation are not carried out only using the surface electrode 7 already mentioned and its position Q. Rather, in the present case, a further surface electrode 8 and its position R are also taken into account both during the measurement and during the calculation. The further surface electrode 8 is connected to the measuring device 2 via a further signal line 81. The surface electrodes 7, 8 can also be referred to as first surface electrode 7 and second surface electrode 8. This also allows an improved accuracy to be achieved. It is understood that more than the two surface electrodes shown here can also be used, for example three, four, five, six or even more than six surface electrodes. It may be expedient for at least one or more of the surface electrodes to be placed along an (expected) feed path of the catheter tip.With reference to FIG. 4, the method already explained with reference to FIGS. 1 to 3 is again schematically illustrated. Thus, method 1000 basically provides for a measurement process 1100, a computer-assisted calculation 1200, a comparison 1300 and a determination 1400.In the measurement process 1100, the intravascular ECG lead E is measured between the catheter tip 5, in the present case the catheter electrode 6, and at least the first surface electrode 7. For this purpose, the measuring device 2 is present.The computer-assisted calculation 1200 takes place on the basis of the numerical simulation model M already explained and using the calculation device 3.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Cited Non-Patent LiteratureW. Schummer et al.: "Optimized positioning of central venous catheters by a modified application of intravascular electrocardiography", Anesthesist 54 (2005), pp. 983-990

[0005]

Claims

Method (1000) for determining a position (P) of a catheter tip (5) in the interior of a body (K), comprising the steps of: metrological detection (1100) of an intravascular ECG lead (E) between the catheter tip (5) and a surface electrode (7, 8), wherein the surface electrode (7, 8) is arranged at a defined surface position (Q, R) of the body (K); computer-assisted calculation (1200) of a virtual intravascular ECG lead (E1' to E6') between a virtual catheter tip (5') and a virtual surface electrode (7', 8'), wherein the calculation (1200) is carried out using a numerical simulation model (M) which calculates physical properties (A1, A2 to A n) of the body (K), the surface position (Q, R) of the surface electrode (7, 8), an electrical cardiac activity (HA) and an electrical field (F) resulting from the electrical cardiac activity (HA) are mapped in a model-like manner, wherein a modeled electrical cardiac activity (HA') on which the numerical simulation model (M) is based is modeled and / or corrected as a function of the ECG derivation (E) acquired in a metrology manner, wherein the modeled electrical cardiac activity (HA') is matched to the actual electrical cardiac activity (HA) which is causative of the ECG derivation (E) acquired in a metrology manner, and wherein the calculation (1200) takes place for a plurality of different virtual positions (P1' to P6') of the virtual catheter tip (5'); comparison (1300) of the ECG derivative (E) acquired by measurement technology with the calculated virtual ECG derivative (E1' to E6'), wherein the comparison takes place for the plurality of virtual positions (P1' to P6') of the virtual catheter tip (5'); determination (1400) of the position (P) of the catheter tip (5) as a function of the comparison (1300).Method (1000) according to claim 1, characterised in that the metrological detection (1100) and the computer-assisted calculation (1200) are carried out for different surface positions of a single surface electrode and / or for a plurality of differently positioned surface electrodes (7, 8), and that the comparison (1300) of the metrologically detected ECG lead (E) and the calculated virtual ECG lead (E1' to E6') is carried out for the different surface positions of the surface electrode and / or for the plurality of differently positioned surface electrodes (7, 8).Method (1000) according to one of the preceding claims, characterized in that the physical properties (A1, A2 to A n) of the body (K) on which the numerical simulation model (M) is based comprise at least one body dimension (A1), a mass (A2) of the body (K) and / or a body fat fraction (A n).Medical system (1) for determining a position (P) of a catheter tip (5) in the interior of a body (K), comprising a measuring device (2) which is configured to record (1100) by measurement an intravascular ECG lead (E) between the catheter tip (5) and a surface electrode (7, 8), wherein the surface electrode (7, 8) is configured to be arranged at a defined surface position (Q, R) of the body (K), and a calculating device (3) which is configured to calculate (1200) a virtual intravascular ECG lead (E1' to E6') between a virtual catheter tip (5') and a virtual surface electrode (7', 8'), wherein the calculating (1200) is carried out using a numerical simulation model (M), the physical properties (A 1, A 2 to A n) of the body (K), the surface position (Q, R) of the surface electrode (7, 8), an electrical heart activity (HA) and an electrical field (F) resulting from the electrical heart activity (HA) are mapped in a model-like manner, wherein a modeled electrical heart activity (HA') on which the numerical simulation model (M) is based is modeled and / or corrected as a function of the ECG derivation (E) recorded in a metrology manner, wherein the modeled electrical heart activity (HA') is matched to the actual electrical heart activity (HA) which is causative of the ECG derivation (E) recorded in a metrology manner, and wherein the calculation (1200) is provided for a plurality of different virtual positions (P1' to P6') of the virtual catheter tip (5'), and for comparing (1300) the ECG derivative (E) acquired by measurement with the calculated virtual ECG derivative (E1' to E6'), wherein the comparison is provided for the plurality of virtual positions (P1' to P6') of the virtual catheter tip (5'), and for determining (1400) the position (P) of the catheter tip (5) as a function of the comparison (1300).

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