WO2007066096A2

WO2007066096A2 - Interventional device location method and apparatus

Info

Publication number: WO2007066096A2
Application number: PCT/GB2006/004543
Authority: WO
Inventors: Derek Hill; Raza Razavi; Kawal Rhode
Original assignee: King's College London; University College London
Priority date: 2005-12-07
Filing date: 2006-12-05
Publication date: 2007-06-14
Also published as: GB0524974D0; WO2007066096A3

Abstract

The position of an interventional device, such as a catheter, introduced into a human body is determined by producing an image of a region of the body into which the device is to be introduced, using 3-dimensional imaging apparatus; displaying the 3-dimensional image on a two-dimensional display screen; detecting the device in the body using a single-plane detecting apparatus, thereby to determine the position of the device substantially in two dimensions; superimposing the image of the region of the body onto an image of the detected device on the display screen in registration therewith; detecting the movement of the device in response to internal movement of the body, thereby to determine the position of the device in said two dimensions; and displaying the position of the device on the image on the display screen.

Description

INTERVENTIONALDEVICELOCATIONMETHODANDAPPARATUS

The present invention relates to a method of and apparatus for determining the position of an interventional device introduced into a body of a human or other animal, and finds application in particular, though not exclusively, in the field of cardiovascular catheterisation.

Cardiovascular catheterisation procedures are traditionally carried out under X-ray fluoroscopic guidance. The catheters, guidewires and other endo-vascular instruments employed are designed to be X-ray visible and can be seen throughout the part of their length that lies in the field of view, since X-ray imaging is a projecting imaging modality. Also, since images can be acquired relatively rapidly, typically at 25 frames per second, cardiac motion does not cause significant motion artifacts. However, there are disadvantages associated with this approach to determining the location of the catheters. Since X-ray imaging is a projection imaging modality, more than one view is necessary to gain an appreciation of the three-dimensional location and path of the catheter. This results in the requirement either for moving the so-called C-arm of the X-ray apparatus to obtain different, usually orthogonal, projections or, where available, using a biplane X-ray system for the same purpose. Biplane X-ray systems are comparatively expensive, and thus are not commonplace. Furthermore, since soft tissue, such as heart and blood vessels, are not visible during X-ray exposure, the images acquired by the apparatus can be difficult to interpret. Additionally, it is to be noted that it is desired to minimize the dose of X-rays that any patient receives, and the dose can be significant for prolonged procedures, and particularly disadvantageous in paediatric cases. Imaging modalities such as magnetic resonance imaging (MRI) and computed tomography (CT) imaging have been shown to generate excellent three-dimensional images of cardiovascular anatomy. It is possible to align or register the 3D anatomical information obtained in this way with real-time X-ray imaging during cardiovascular interventions in order to provide anatomical guidance during deployment of a catheter by producing a fused image such as an anatomical overlay of the 3D image with the X- ray image, see, for example, IEEE Transactions on Medical Imaging, Volume 22 No. 11, November 2003, page 1369 et seq, Rhode et. al, and IEEE Transactions on Medical Imaging, Volume 24, No. 11, November 2005, page 1428 et seq, Rhode et. al, the entire disclosure of each of which is included herein by this reference. Such techniques allow the precise positioning of an ablation catheter on the endocardial surface during electrophysiology studies, for example. However, these techniques require comparatively expensive biplane X-ray equipment, or the moving of a single

/ plane X-ray apparatus, with the disadvantage of a comparatively high X-ray dose and the difficulties in synchonising the two separate views to the cardiac and respiratory cycles.

Since anatomical correspondence between the tip of the catheter and structures of interest in the heart is difficult to derive from X-rays alone, it has been proposed to use an electroanatomical mapping system, whereby catheters are tracked in three dimensions using electromagnetic tracking technology with internal or external antennae. Such systems can be used to provide an approximate localization of the endocardial surface using the tracked catheters and to align pre-treatment CT or MRI scans with a catheter coordinate system. However, such systems are expensive to purchase, and require the use of single use (disposable) trackable catheters, which are between 10 and 100 times more expensive than standard catheters.

It is an object of the present invention to provide tracking of a catheter, or other invasive medical instrument or device, that requires a reduced level of X-ray dosage and that does not require the use of specialised interventional devices.

In accordance with one aspect of the present invention, there is provided a method of determining the position of an interventional device introduced into a body of a human or other animal, comprising the steps of producing an image of a region of the body into which the device is to be introduced, using 3 -dimensional imaging apparatus; displaying the 3 -dimensional image on a two-dimensional display screen; detecting the device in the body using single-plane detecting apparatus, thereby to determine the position of the device substantially in two dimensions; superimposing the image of the region of the body onto an image of the detected device on the display screen in registration therewith; detecting the movement of the device in response to internal movement of the body, thereby to determine the position of the device in three dimensions relative to the 3 -dimensional image; and displaying the position of the interventional device on the image on the display screen.

In accordance with a further aspect of the present invention, there is provided apparatus for determining the position of an interventional device introduced into a body of a human or other animal, comprising imaging apparatus for producing a 3-dimensional image representative of a region of the body into which the device is to be introduced; a display device for displaying the 3-dimensional image on a two-dimensional screen; . single-plane detecting apparatus for detecting the position of the device in the body in substantially two dimensions, and producing an image in accordance therewith; means for registering the images of the region of the body produced by the 3-dimensional imaging apparatus and the single-plane detecting apparatus and superimposing the two images, showing the two-dimensional position of the device, on the display device; means for detecting movement of the device in response to internal movement of the body; and means for determining from said movement of the device the position of the device on said screen.

Preferably the three dimensional imaging apparatus comprises magnetic resonance imaging (MRI) apparatus, or computed tomography (CT) scanning apparatus, or ultrasound imaging apparatus.

Preferably, the single plane detecting apparatus comprises X-ray apparatus.

/ ^• /

In many applications, it is envisaged that the interventional device will be a catheter, or a flexible wire acting as a guide therefor, but it is also envisaged that the device could be a needle, or a stent being inserted..

The internal movement of the body that produces the movement of the device that is to be detected, will typically comprise respiratory and/or cardiac cycle movement. The motion of the organs in the body with the cardiac or respiratory cycle may be estimated from independent measurements made on the body, e.g: using X-ray visible markers or ultrasound, and used to improve the accuracy of the tracking of the device. Whilst typically it would be the tip of the device whose position is required to be determined, it is envisaged that two or more portions, such as points or locations along the length of the device, may be detectable by the single plane detecting apparatus. Typically, when a medical practitioner introduces an interventional device into the body, for example a catheter into the heart, the practitioner will be able to determine when the device abuts a wall of that region of the body either from the force feedback or from a sensor, e.g: an electrical recording electrode, at the tip. However, from a single plane detection apparatus, for example X-ray apparatus, it will not be possible to determine whether the wall, for example a cardiovascular wall, is the one closer to or further away from the detecting device of the single-plane detecting apparatus. By detecting how the device, in contact with the wall, moves in response to the internal movement of the body, with a knowledge of the geometry of the single plane detecting apparatus, of the 3D anatomy of the anatomical structure in which the device is placed, and of the registration between this 3D anatomy and the 2D view, it then becomes possible to resolve this ambiguity in the position of the device.

The three dimensional imaging apparatus may be arranged to produce an image of the region of the body into which the device is to be inserted by deriving the image remote from the actual body that is subject to X-ray investigation, by operation on a corresponding region of a reference body, for example a standard heart. If necessary, particular variable features of the actual heart may be noted in real time so that the image derived from the reference body may be appropriately modified, thereby to enhance the accuracy of the measurement, when the reference body image is superimposed upon the X-ray image of the device. However, it is also envisaged that the three dimensional image may be derived in situ and in real time from the same body into which the device is introduced.

Advantageously, the accuracy of the determined position of the device is evaluated, and an indication may be provided to the practitioner should the determined accuracy fall below a predetermined level.

Conventional computational segmentation techniques may be applied to the output of the three dimensional apparatus to remove extraneous detail from the image when displayed. It is known that various algorithms are available to effect this, for example by selecting structures of the image that exceed a predetermined brightness level. Alternatively, the segmentation may be carried out manually.

As well as determining the instantaneous position of the device, for example the tip of a catheter, the method may be arranged to store successive position determinations so that a history of the route taken by the device is retained and is displayed.

The necessary registration of the images obtained by the three dimensional apparatus and the single plane detecting apparatus may be achieved by the application of a marker or markers physically applied on the outer surface of the body. It will be appreciated, that the marker(s) would be such as to be detectable by each of these pieces of apparatus. Alternatively, or additionally, the registration of the two images may be achieved by noting at least one anatomical landmark identified on both images, and such a landmark advantageously comprises a bony structure of the body, for example the spine, or a vascular structure, such as a blood vessel. As well as determining the static position of the device within the body, it is envisaged that the position of the device may be monitored as it is moved through the body, either on a continuous basis or from one region to another. In this case, the size of the region of the. body displayed on the display screen is advantageously varied in dependence on the speed of the movement of the device, such that a larger region would be displayed the higher the speed of movement of the device.

It is envisaged that the position of the device may be determined only in accordance with cardiac movement of the body, with the heart typically beating at 70 times per minute, but also beating at up to 100 or even 300 times per minute, whilst the respiratory movement of the body is arrested, for example by requiring the patient to hold his breath. Alternatively, the position of the device may be monitored only at substantially the same point in successive cardiac cycles, thereby removing the effect of cardiac movement, so that the position of the device is determined only in accordance with the internal respiratory movement of the body, which is typically at the rate of 10 cycles per minute. Clearly, by using appropriate electronic filtering, advantage can be taken of the significantly different frequencies of these two kinds of movement such that the position of the device is determined even when both cardiac and respiratory cyclical movements are occurring.

In a preferred embodiment, the single plane detecting apparatus comprises a substantially point source of radiation that is located at one side of the body so as to direct radiation therethrough, and a planar detector, such as image intensifier or flat panel, that is located at an opposing side of the body so as to receive radiation passing therethrough; wherein the radiation is arranged to pass through a region of the body that is subject to internal movement; wherein the device is introduced into the said region such that a portion of the device, preferably its tip, is in contact with an inner surface of a chamber of the body; and wherein the extent of the detector that receives radiation varies in accordance with the internal movement of the body, and a determination is made as to whether the device is in contact with a surface of the chamber that is closer to or further away from the detector.

It will be appreciated that having positioned the interventional device precisely where required using the present invention, the medical practitioner is then able to perform the required treatment on the body. Such treatment may comprise cardiac treatment, for example a cardiac electrophysiology procedure, or a radio-frequency (RF) ablation procedure. Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic representation of the determination of the position of the tip of a catheter located in a patient's heart unambiguously when moving in accordance with respiratory motion of the patient, using a single plane X-ray detecting apparatus;

Figure 2 is an X-ray image showing four electrophysiology catheters placed in the right ventricle of a patient's heart. One of the catheters is provided with an electrode at its tip and is shown in contact with the inner ventricular surface as it has been moved therealong;

Figure 3 shows a 3D anatomical model of the heart derived from magnetic resonance imaging of that region of- the patient, overlaid onto the X-ray image. The arrow indicates a tracked electrode of the catheter so that the tracked tip of the catheter is in contact with the inner ventricular surface; and

Figure 4 shows the position of the tracked tip of a catheter and the path of the catheter on which it lies displayed on the 3D anatomical model of the heart.

Referring to Figure 1 a human heart is shown schematically at H at one extreme of the respiratory motion of the patient, and at H' at the other extreme of the respiratory motion. Ei and E₂ are points on opposed positions of the inner surface of the heart H, and moved by the same amount to points E₁' and E₂' of the heart H' as a result of the respiratory motion. Four lines of radiation are shown emanating from an X-ray source X₈, passing through each of the four points, terminating in respective positions P₁, P₂, P₂' and Pi' on a linear X-ray detector X_D. Points Pi and P₁' are separated by the distance dγ and points P₂ and P₂' by the distance d₂. Thus, the apparent motion on the imaging plane of the detector XD of the point E₁ is thus di, and that of E₂ is d₂. It will be appreciated that di exceeds d₂ due to the projection geometry of the imaging system.

In practice, the cardiologist will introduce an electrophysiology catheter into the heart for carrying out an endovascular cardiovascular intervention, the progress of the catheter being monitored on a display screen upon which the image from the X-ray apparatus is projected. Referring to Figure 2, the X-ray image shows four electrophysiology catheters located in the right ventricle of the heart, each of which is provided with an X-ray opaque electrode at its tip. The position of catheter Ci has been tracked, with the current position CN of its electrode tip indicated in the position in which the catheter C₁ is in contact with the inner ventricular surface. It will be appreciated that from the image of Figure 2, it is not possible to tell whether the inner ventricular surface that is contacted is that which is nearer to or further away from the detector.

Magnetic resonance imaging apparatus, for example, has been used to derive a 3D anatomical model of the heart in a known manner, and, provided the heart of the patient under investigation is not significantly abnormal, the heart model used for the magnetic resonance imaging can be that of a standard heart, and thus can be stored in a computer associated with the X-ray equipment. As described in the IEEE papers referred to above, the X-ray and MRI images are then overlaid, with the result as shown in Figure 3. The arrow indicates the tracked electrode catheter tip C_N in contact with the inner ventricular surface.

Following segmentation, a view such as that of Figure 4 is obtained which shows the position of the tracked catheter tip CN and the path of the catheter displayed in the 3D anatomical model of the heart. It will be appreciated that although a single view is shown in Figure 4, the model may be manipulated so as to show any required view of the heart and catheter on the display screen. By noting the apparent motion, d] or d₂ (Figure 1) of the detected tip of the catheter during respiratory motion of the patient's heart, it can thus be determined whether the catheter is at the lower position E₁ or the upper position E₂ of the ventricle, which positions would otherwise be indistinguishable from the X-ray image. Although Figure 1 indicates that the motion of the heart is purely due to the respiratory cycle, the discrepancy between di and d₂, and thus the determination of the catheter position, could result also from cardiac motion alone or more likely a combination of respiratory and cardiac motion.

Thus the cardiologist is now presented with an accurate determination of the position of the tip of the catheter.

Should the positions E₁ and E₂ for any reason not be sufficiently distinguished by the apparatus, then it may be arranged for that fact to be indicated to the cardiologist, for example by providing a suitable indication on the display screen, so that he will be warned that the location of the catheter tip has not been sufficiently accurately determined.

It will be appreciated, that the present invention thus requires only a single plane X-ray set, and that for many cases there will be no need to take an MRI (or CT) scan of the particular patient, since the model of a standard heart may be employed. In the event that the patient's heart is damaged or is in some other way abnormal such as would affect the determination of the position of the catheter using a standard model, then the 3D dimensional scan can be obtained directly from the patient being treated in realtime, along with the provision of the X-ray data.

It is also envisaged that, referring to Figure 4, for example, the historical position of the catheter, that is the path that it has already followed, may be presented in a different colour to the colour representing the current position of the tip, so that the movement of the catheter to and fro within the body can be distinguished. In some instances it may be desirable, or even essential, to enhance the accuracy of the tracking of the interventional device by determining an initial position of the device within the body prior to the positional tracking described above. For example, a determination of the initial position of the device in three dimensions may be obtained by synchronising two views of the device moving under cardiac and/or respiratory motion provided by a single plane detection apparatus, such as X-ray apparatus. These views may be provided by rotating the single plane detection apparatus about the patient through a known angle whilst the patient holds his or her breath. It will be appreciated that the present invention does not require the use of any special catheter, but typically would employ a standard catheter of plastics material, with one or more X-ray opaque, typically steel or platinum, markers, or electrodes, therealong which can be tracked. In practice, a fine metallic wire will initially be inserted into the patient to act as a guide, with the catheter subsequently passed thereover. If desired, tracking of the guide wire may be carried out as described above.

Claims

1. A method of determining the position of an interventional device introduced into a body of a human or other animal, comprising the steps of:

(a) producing an image of a region of the body into which the device is to be introduced, using 3 -dimensional imaging apparatus;

(b) displaying the 3-dimensional image on a two-dimensional display screen;

(c) detecting the device in the body using a single-plane detecting apparatus, thereby to determine the position of the device substantially in two dimensions;

(d) superimposing the image of the region of the body onto an image of the detected device on the display screen in registration therewith;

(e) detecting the movement of the device in response to internal movement of the body, thereby to determine the position of the device in said two dimensions; and

(f) displaying the position of the device on the image on the display screen.

2. A method according to claim 1, wherein the 3-dimensional imaging apparatus comprises magnetic resonance imaging (MRI) apparatus, or computed tomography (CT) scanning apparatus, or ultrasound imaging apparatus.

3. A method according to claim 1 or claim 2, wherein the single-plane detecting apparatus comprises X-ray apparatus.

4. A method according to any one of the preceding claims, wherein the interventional device comprises a catheter or a guide therefor, or a needle, or a stent.

5. A method according to any of the preceding claims, wherein the internal movement of the body comprises respiratory and/or cardiac cycle movement.

6. A method according to claim 5, wherein me respiratory movement of the body is arrested, whereby the position of the interventional device is determined in accordance with cardiac movement only.

7. A method according to claim 5, wherein the position of the inventional device is monitored only at substantially the same point in successive cardiac cycles, whereby the position of the interventional device is determined in accordance only with respiratory movement of the body.

8. A method according to any one of the preceding claims, wherein a portion of the interventional device whose position is to be monitored is initially brought into engagement with an internal surface of the body and the movement of that surface is used to determine the position of that portion of the device.

9. A method according to claim 8, where the said portion of the device comprises its tip.

10. A method according to any one of the preceding claims, wherein the device is introduced into the cardiac region of the body.

11. A method according to any one of the preceding claims, wherein the 3- dimensional imaging apparatus produces an image of the region of the same body into which the interventional device is introduced.

12. A method according to any one of claims 1 to 10, wherein the 3-dimensional imaging apparatus produces an image of the region of a reference body that is superimposed onto the image of the device when introduced into an actual body.

13. A method according to claim 12, wherein the image of the region of the reference body is modified by data relating to the region of the actual body, thereby to produce a more accurate image of the region on the display screen.

14. A method according to claim 13, comprising the step of using ultrasound apparatus to obtain the modifying data.

15. A method according to claim 13 or 14, wherein the modifying data relates to the age and/or size of the actual body.

16. A method according to any one of the preceding claims, comprising providing an indication of the accuracy of the determined position of the interventional device.

17. A method according to any one of the preceding claims, comprising the step of applying a computational segmentation technique to the output of the 3-dimensional imaging apparatus to derive the image of the region that is to be stored in the memory of a computer, thereby to remove extraneous detail from the image when displayed.

18. A method according to any one of the preceding claims, wherein a history of the position of the device is retained and displayed.

19. A method according to any one of the preceding claims, wherein the image derived by the 3-dimensional imaging apparatus is a static image of the region of the body at one stage in the cyclic internal movement thereof.

20. A method according to any one of the preceding claims, wherein the registration of the images is achieved by the application of at least one marker to an outer surface of the body, the or each marker being detectable by the 3-dimensional imaging apparatus and the single-plane detecting apparatus.

21. A method according to any one of the preceding claims, wherein the registration of the images is achieved by noting at least one anatomical landmark identified on both images.

22. A method according to claim 21, wherein the anatomical landmark comprises a bony structure of the body, for example the spine, or a vascular structure, for example a blood vessel.

23. A method according to any one of the preceding claims, wherein the interventional device comprises a catheter that has at least one portion that is detectable by the single-plane detecting apparatus and at least one portion that is not detectable by the said apparatus.

24. A method according to any one of the preceding claims, wherein the position of the device is monitored as it is moved through the body, and wherein the size of the region of the body displayed on the display screen is varied in dependence on the speed of said movement of the device.

25. A method according to any one of the preceding claims; wherein the single- plane detecting apparatus comprises a substantially point source of radiation that is located at one side of the body so as to direct radiation therethrough, and an area detector that is located at an opposing side of the body so as to receive radiation passing therethrough;

wherein the radiation is arranged to pass through a region of the body that is subject to internal movement;

wherein the interventional device is introduced into the said region such that a portion of the device is in contact with an inner surface of a chamber of the body; and wherein the extent of the detector that receives radiation varies in accordance with the internal movement of the body, and a determination is made as to whether the device is in contact with a surface of the chamber that is closer to or further away from the detector.

26. Apparatus for determining the position of an interventional device introduced into a body of a human or other animal, comprising:

(a) imaging apparatus for producing a 3 -dimensional image representative of a region of the body into which the device is to be introduced; (b) a display device for displaying the 3 -dimensional image on a two-dimensional screen;

(c) single-plane detecting apparatus for detecting the position of the device in the body in substantially two dimensions, and producing an image in accordance therewith; (d) means for registering the images of the region of the body produced by the 3- dimensional imaging apparatus and the single-plane detecting apparatus and superimposing the two images, showing the two-dimensional position of the device, on the display device;

(e) means for detecting movement of the device in response to internal movement of the body; and

(f) means for determining from said movement of the device the position of the device on said screen.

27. Apparatus according to claim 26 for carrying out the method of any one of claims 1 to 25.

28. Apparatus according to claim 26 or 27, wherein the 3 -dimensional imaging apparatus and the single-plane detecting apparatus are substantially fixed with respect to the body.

29. A method of and apparatus for determining the position of an interventional device in a body of a human or other animal, substantially as hereinbefore described with reference to the accompanying drawings and specific embodiments.

30. A method in accordance with any one of claims 1 to 25, wherein, subsequent to the determination of the position of the device, the device is used to administer treatment to the body.

31. A method according to claim 30, wherein the treatment comprises cardiac treatment.

32. A method according to claim 31, wherein the treatment comprises a cardiac electrophysiology procedure.

33. A method according to any one of claims 30 to 32 , wherein the treatment comprises radio-frequency (RF) ablation.