Calibration system for a pressure-sensitive catheter

ES 2 448 366 T3

DESCRIPTION

Calibration system for a pressure sensitive catheter

Field of the invention

The present invention relates generally to invasive probes, and specifically to calibrating pressure sensors on invasive probes.

Background

A wide variety of medical procedures involve the placement of objects, such as sensors, tubes, catheters, delivery devices, and implants, within the body. Position-determining systems have been developed to track the trajectory of such objects. In magnetic position sensing, magnetic field generators are typically placed in known positions external to the patient. A magnetic field sensor within the distal end of a probe generates electrical signals in response to those magnetic fields, which are processed in order to determine the positional coordinates of the distal end of the probe. These methods and systems are described in U.S. Patents 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612, and 6,332,089, in PCT International Publication WO 1996/005768 and Application Publications United States Patent 2002/0065455 A1,2003 / 0120150 A1 and 2004/0068178 A1.

When placing a probe within the body, it may be desirable to have the distal tip of the probe in direct contact with body tissue. Contact can be verified, for example, by measuring the contact pressure between the distal tip and the cluster tissue. US Patent Application Publications 2007/0100332 and 2009/0093806 describe methods of detecting contact pressure between the distal tip of a catheter and tissue in a body cavity using a force sensor incorporated in the catheter. The distal tip of the catheter is coupled to the distal tip of the catheter insertion tube by an elastic member, such as a spring, that deforms in response to the force exerted on the distal tip when it presses against endocardial tissue. A magnetic position sensor within the catheter detects the deviation (location or orientation) of the distal tip relative to the distal end of the insertion tube. Movement of the distal tip relative to the insertion tube is indicative of deformation of the elastic member, and thus gives an indication of pressure.

Summary of the invention

One embodiment of the present invention provides a calibration apparatus that includes a fixture, a sensing device, and a calibration processor. The fixture is coupled to accept a probe so that a distal tip of the probe presses against a point on the fixture and produces a first measurement indicative of a deformation of the distal tip relative to a distal end of the probe, in response to the pressure exerted on the distal tip. The sensing device is coupled to the fixture and is configured to produce a second measurement of a mechanical force exerted by the distal tip against the point. The calibration processor is configured to receive the first measurements from the probe, to receive the second measurements from the sensing device, and to calculate, based on the first and second measurements, one or more calibration coefficients to evaluate pressure as a function of the first measurements.

In some embodiments, the fixture is engaged to cause the probe to clamp against the point at one or more predefined angles, and the calibration processor is configured to calculate the calibration coefficients as a function of the predefined angles. The apparatus may include a dome covering the fixed element, the dome having a plurality of insertion holes that are configured to direct the probe to the point at predefined angles. Alternatively, the apparatus may include a socket configured to hold the distal end, a path coupled to the socket and configured to position the socket at multiple angles relative to the point, and a riser configured to raise the fixture to cause the bit distal tighten against the point. The apparatus may include an input device coupled to the calibration processor and configured to accept the predefined angles.

In another embodiment, the fixed element includes a cone-shaped cup. In yet another embodiment, the stationary element holds the probe in a temperature-controlled liquid. In yet another embodiment, the sensing device includes a load cell. In one embodiment, the calibration processor is configured to store the calibration coefficients in a memory that is coupled to the probe. The memory may include an Electronically Erasable Programmable Read Only Memory (MEBPSL).

Also provided, in accordance with one embodiment of the present invention, is a calibration method, which includes inserting a probe having a distal end into a fixture, pressing the distal tip against a point on the fixture to cause a deformation of the distal tip relative to a distal end of the probe in response to pressure exerted on the distal tip, with the probe receiving the first measurements indicative of strain, receiving from a sensing device coupled to the fixed element second measurements indicative of a mechanical force exerted by the distal tip against the point, and calculating,

ES 2 448 366 T3 based on the first and second measurements, one or more calibration coefficients to evaluate the pressure as a function of the first measurements.

Brief description of the drawings

The disclosure is described here, by way of example only, with reference to the accompanying drawings, where:

Figure 1 is a pictorial schematic illustration of a calibration system for a pressure sensitive catheter, in accordance with one embodiment of the present invention;

Figure 2 is a flow chart schematically illustrating a pressure sensitive catheter calibration method in accordance with one embodiment of the present invention;

Figure 3 is a pictorial schematic representation of a graphical user interface of a calibration system for a pressure sensitive catheter, in accordance with one embodiment of the present invention;

Figure 4 is a pictorial schematic illustration of a calibration system for a pressure sensitive catheter, in accordance with one embodiment of the present invention; Y

Figure 5 is a detailed schematic view showing the distal tip of a pressure sensitive catheter in contact with endocardial tissue, in accordance with one embodiment of the present invention.

Detailed description of realizations

Some invasive probes comprise pressure sensors to measure the contact pressure between the probe and intra-body tissue. For example, the distal tip of a cardiac catheter may comprise a pressure sensor, which deforms in response to the pressure exerted by the distal tip on endocardial tissue. A position sensor on the catheter measures the deflection of the distal tip, thus providing an indication of the contact pressure. In many practical cases, however, the relationship between the actual contact pressure and the position sensor reading varies from catheter to catheter.

In order to ensure accurate pressure measurements, embodiments of the present invention provide methods and systems for calibrating probes (eg, catheters) equipped with pressure sensors. In some embodiments, a calibration apparatus comprises a fixed element to accept a catheter at a certain angle, and a sensing device (eg, a load cell) to measure the mechanical force exerted by the catheter against a given point on the element. permanent. When the catheter is inserted into the fixture at a given angle and squeezed against the given point, the catheter produces measurements of deformation (eg, deflection) of its distal tip, and the sensing device produces force measurements.

In some embodiments, a calibration processor receives the catheter deflection measurements and the force measurements from the sensing device, and calculates the calibration coefficients to evaluate the pressure exerted by the catheter as a function of the deflection measurements.

In some embodiments, the calibration is performed for different engagement angles between the catheter and the point on the fixture. In some embodiments, the calibration coefficients are stored in a non-volatile memory that is coupled to the catheter. When the catheter is later used in a medical system, the actual pressure exerted by the distal tip of the catheter on the body tissue can be derived with high precision from the deviation measurements, using the calibration coefficients.

Figure 1 is an illustration of a calibration system 10 for a pressure sensitive catheter, in accordance with one embodiment of the present invention. System 10 comprises a calibration apparatus 12 coupled to a calibration unit 52. In the embodiment described here below, system 10 is used to calibrate a probe 42, in the example present a catheter for therapeutic and / or diagnostic purposes in a heart or other bodily organs.

Probe 42 comprises a distal end 14, with a distal tip 16 connected to the distal end by means of a joint 18. The distal end 14 and distal tip 16 are covered by a flexible, insulating material 22. The joint area 18 is also covered by a flexible and insulating material, which may be the same material 22 or it may be specially adapted to allow unhindered curvature and compression of the joint. (This material is cut in Figure 1 in order to expose the internal structure of the catheter). The distal tip 16 is typically relatively stiff, compared to the distal end 14.

The distal tip 16 is connected to the distal end 14 by an elastic member 20. In Figure 1, the elastic member is in the form of a coil spring, but other types of elastic components can be used.

ES 2 448 366 T3 alternatively for this purpose. The elastic member 20 allows a limited variety of relative movements between the tip 16 and the distal end 14 in response to forces exerted on the distal tip.

Distal tip 16 contains a magnetic position sensor 24. Sensor 24 may comprise two or more miniature coils, and typically comprises multiple coils oriented along different axes. The distal end 14 contains a miniature magnetic field generator 26 near the elastic member 20. Typically, the field generator 26 comprises a coil, which is driven by a current carried through the catheter from the calibration unit 52. Alternatively, the position sensor 24 may comprise another type of magnetic sensor, an electrode that serves as a position transducer, or position transducers of other types, such as ultrasonic or obstruction-based position sensors. Although Figure 1 shows a probe with a single position sensor, embodiments of the present invention may use probes with more than one position sensor.

The magnetic field created by field generator 26 causes the coils in sensor 26 to generate electrical signals at the pulse frequency of the field generator. The amplitudes of these signals will vary depending on the location and orientation of the distal tip 16 relative to the distal end 14. A calibration processor 46 in calibration unit 52 processes these signals in order to determine the axial displacement and the magnitude of the angular deviation of the distal tip relative to the distal end 14. (Due to the axial symmetry of the generated field For a coil, only the magnitude of the offset can be detected using a single coil in the field generator 26, and not the direction of the offset. Optionally, the field generator 26 may comprise two or more coils, in which case the direction of the deviation may also be determined). The magnitudes of displacement and deflection can be combined by adding a vector to give a total magnitude of movement of distal tip 16 relative to distal end 14.

The relative movement of the distal tip 16 relative to the distal end 14 gives a measurement of the deformation of the elastic member 20. Thus, the combination of the field generator 26 with the sensor 24 serves as a pressure sensing system. By virtue of the combined offset and deflection sensing, this pressure sensing system reads the pressure correctly regardless of whether the pressure is exerted on the distal tip 16 head-on or at the angle. More details of this type of probe and position sensor are described in US Patent Application Publications 2009/0093806 and 2009/0138007, cited above.

The probe 42 also comprises a non-volatile memory 44, such as an electronically erasable programmable read-only memory (MEBPSL), that stores the computational coefficients calculated during calibration. As discussed above, when the catheter is later used in a medical system, the actual pressure exerted by the distal tip of the catheter on body tissue can be accurately derived from the deviation measurements, using the calibration coefficients stored in memory 44.

Calibration apparatus 12 comprises a fixture 28 that is configured to accept a probe to be calibrated. In the embodiment of Figure 1, the fixed element 28 comprises a cup (eg, a cone-shaped cup) having a top 36 and a base 40. In the present example, the top 36 is wider than base 40. In alternative embodiments, fixtures having any other mechanical configuration may also be used.

Fixed element 28 may contain a temperature controlled liquid 34, which is maintained at a typical human body temperature (eg, using a thermostat and heating element). Using this technique, the probe 42 calibration procedure is performed at a temperature that closely resembles the operating temperature of the probe in the body. Temperature control can be important because the elasticity or other mechanical properties of probe elements can vary sharply with temperature. For example, gasket 18 may contain elements such as a nickel titanium alloy spring (also referred to as NiTi or Nitinol) or a plastic outer jacket (that is, insulating material 22), the elasticity of which may vary with temperature. liquid 34.

To control the angle of engagement between catheter 42 and fixture 28, an operator (not shown) inserts the catheter into one of multiple insertion holes 38 in a dome 30 that covers fixture 28. Each of the fixture elements insertion can accept the catheter in a different angular position. The insertion holes are configured to direct the distal tip 16 to press against a given point on the fixture 28. In the configuration shown in Figure 1, insertion holes 38 direct distal tip 16 to press against base 40.

In addition to the fixed element 28 and the dome 30, the calibration apparatus 12 comprises a load cell 32 coupled to the base 40. The load cell measures the downward mechanical force exerted by the distal tip on the base 40. Although the system shown in Figure 1 measures downward force using load cell 32, system 10 can use any other type of sensor to measure downward force, and such sensors are therefore considered to be within the spirit. and scope of this invention.

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Both the load cell 32 and the probe 42 are connected to the calibration unit 52 via suitable interfaces (eg, cables or connectors). The calibration unit 52 comprises a calibration processor 46, a memory 48, a monitor 54, and an input device 50, such as a keyboard. Processor 46 typically comprises a general purpose computer, with front end interface circuitry to receive signals from position sensor 24 and load cell 32, as well as to control other components of calibration unit 52. Processor 46 may be programmed in software to perform the functions described here. The software may be downloaded to processor 46 in electronic form, over a network, for example, or it may be provided on tangible media, such as optical, magnetic, or electronic memory media. Alternatively, some or all of the functions of the processor 46 may be performed by programmable or dedicated hardware digital components.

Figure 2 is a flow chart schematically illustrating a pressure sensitive catheter calibration method in accordance with one embodiment of the present invention. To calibrate the probe 42, the operator inserts the catheter into one of the insertion holes 38 (step 60) and presses the distal tip 16 against the base 40 (step 62). The configuration of fixture 28 and dome 30 helps ensure that distal tip 16 presses against base 40 (that is, the same point on fixture) regardless of which insert hole is used for calibration. Typically, each insertion hole defines a different angle of engagement of the catheter with respect to the base 40.

The action of pressing the distal tip 16 against the base 40 causes the catheter 42 to bend at the joint 18, thereby deflecting the distal tip. The position sensor 24 on the distal tip 16 produces a signal indicative of the deviation of the distal tip relative to the distal end 14. Simultaneously, the load cell 32 produces a measurement indicative of the mechanical downward force exerted by the tip. distal 16 on base 40. Both the deflection and downward force measurement are sent to calibration unit 52, where the operator enters the gear angle for this calibration stage via keyboard 50.

In some embodiments, the insertion holes 38 are labeled with respective identifiers. During the calibration process, the operator enters the identifier of the insertion hole being used into the calibration unit 52 via the input device 50. In an alternative embodiment, the dome 30 may comprise one or more proximity sensors, They automatically detect the insertion hole into which the catheter is inserted. When the operator inserts catheter 42 into one of the insertion holes, the proximity sensors will send electrical signals to the calibration unit 52, and the processor 46 will analyze the electrical signals to determine which insertion hole is being used. Any suitable type of proximity sensor can be used, such as optical sensors or Hall effect sensors.

Calibration unit 52 accepts the deflection measurements from sensor 24 at the probe (step 64), the downward force measurement from load cell 32 (step 66), and operator engagement angle. Based on these three inputs, processor 46 calculates calibration coefficients to calibrate the offset measurements from probe 42 (step 68). By mapping a position measurement from the position sensor 24 against a force vector from the load cell 32 at a given gear angle, the calibration coefficient determines the force on the distal tip 16 based on the sensor's measurements. position. In other words, a given calibration coefficient translates the tip 16 offset measurement to the actual pressure reading, for a given calibration angle.

If more calibration points are desired (step 70), then the method returns to step 60 above. Otherwise, the processor 46 stores the calibration matrix in memory 44 in the probe (step 72), and the method ends. In some embodiments, the operator can collect multiple data points for a given gear angle (a given insertion hole 38) by exerting different amounts of pressure on the probe.

To store the calibration matrix, processor 46 may store an analytical calculation in memory 44 based on the calculated coefficients. Alternatively, processor 46 may store a look-up table with intermeasurement interpolation in memory 44. In some embodiments, processor 46 may store a combination of the two (eg, coefficients chosen according to a region) in memory. 44.

Figure 3 is a schematic representation of a graphical user interface (GUI) 80 operative to direct the calibration of catheter 42, in accordance with one embodiment of the present invention. In this embodiment, monitor 54 presents GUI 80 to the operator. The operator enters the identity (eg, a serial number) of the catheter being calibrated into a text box 82 using an input device 50. IGU 80 displays a map 84 that comprises a diagrammatic representation of insertion holes 38. Each of the insertion holes in the map is color-coded to indicate its status during the calibration procedure. For example, in this embodiment, the insertion hole that the calibration procedure is currently using is black, previously used insert holes are gray, and insert holes that have not yet been used are white. Returning to step 70 in Figure 2, if additional calibration points are desired, the user presses a "Next" button 86 to identify the next insertion hole to be used in the calibration.

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The GUI 80 may comprise additional fields or features, such as text boxes 87 and 88 to display the actual or target pressure exerted on the catheter, respectively. A bar 89 on the left side of the screen indicates the actual pressure. The GUI shown in Fig. 3 is chosen purely by way of example, and any other suitable GUI can also be used.

Figure 4 is a pictorial illustration of a calibration system 90 for catheter 42, in accordance with an alternative embodiment of the present invention. In system 90, a socket 92 holds distal end 14, leaving distal tip 16 exposed at joint 18. Proximal end of socket 92 is coupled to path 94. Path 94 is arc-shaped and is coupled to a base 96 by means of gaskets 98. Joints 98 allow path 94 to rotate at the base. The positioning of the socket 92 along the path 94 and the rotation of the path allows the distal tip 16 to press against the cup 28 at a variety of engagement angles. To deflect distal tip 16 (that is, since path 90 has limited rotational movement, and the travel of socket 92 is limited to path), an elevator 100 raises cup 28 and load cell 32, squeezing the cup against distal tip 16. A load cell (not shown) is coupled to the riser and measures the pressure exerted on the catheter tip by the cup. When using the calibration system of Fig. 4, the calibration unit 52 operates in a similar manner to its operation in the system of Fig. 1 above.

Figure 5 is a schematic view showing distal tip 16 in contact with endocardial tissue 110 of heart 112, in accordance with one embodiment of the present invention. In the present example, tip 16 comprises an electrode 114. In some diagnostic or therapeutic electrophysiological procedures, such intracardiac electrical mapping is important to maintain the appropriate level of force between electrode 114 and tissue 110. When a medical professional (not shown) presses the distal tip 16 against the endocardial tissue 110, the catheter bends at the joint 18. Sufficient force is needed in order to ensure good electrode engagement between the distal tip and the tissue. Poor electrical contact can result in incorrect readings. On the other hand, excessive force can deform the fabric and thus distort the map.

When tip 16 presses against tissue 110, sensor 24 produces measurements that are indicative of the deflection of tip 16 from distal end 14. Medical imaging system (eg, mapping system, not shown) translate these measurements into accurate pressure readings using the calibration coefficients stored in probe memory 44. Thus, invasive probe calibration using embodiments of the present invention ensures that the medical professional can accurately control the force exerted by the probe on tissue.

The corresponding structures, materials, acts and equivalents of all means or steps in addition to the elements of function in the claims below are intended to include any structure, material or act to perform the function in combination with other elements claimed as specifically claimed. The description of the present disclosure has been presented for the purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure as disclosed. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and practical application, and to enable others skilled in the art to understand the disclosure for various embodiments with various modifications as suitable for use. particular suitable.

The appended claims are intended to cover all of these features and advantages of the disclosure. As numerous modifications and changes will be readily available to those skilled in the art, it is intended that the disclosure is not limited to the limited number of embodiments described herein.