WO2012150567A1

WO2012150567A1 - A catheter with electromagnetic position sensors and a location system catheters and guide wires

Info

Publication number: WO2012150567A1
Application number: PCT/IB2012/052219
Authority: WO
Inventors: Sara CONDINO; Vincenzo Ferrari; Aldo Alberti; Mauro Ferrari
Original assignee: Universita' Di Pisa
Priority date: 2011-05-05
Filing date: 2012-05-03
Publication date: 2012-11-08
Also published as: EP2704631A1; ITTO20110394A1; WO2012150567A8

Abstract

Catheter (1) comprising a tubular body (3) to be introduced into a body cavity, and a plurality of electromagnetic position sensors (17, 19), each of which is positioned on a respective one of said catheter segments (7, 9), and is designed to generate, in response to an externally generated magnetic field, an electrical signal representative of the position and orientation of the respective catheter segment. Each of said electromagnetic position sensors has a substantially needle-shaped body having a longitudinal axis placed parallel to the longitudinal axis of the respective catheter segment, and is located at the wall of the respective catheter segment, eccentrically with respect to the longitudinal axis thereof.

Description

A CATHETER WITH ELECTROMAGNETIC POSITION SENSORS AND A LOCATION SYSTEM FOR CATHETERS AND GUIDE WIRES

The present invention relates to a catheter comprising:

a tubular body to be introduced into a body cavity, said tubular body having a distal part including at least one curved or curvable portion, and corresponding catheter segments at the ends of said curved or curvable portion; and

a plurality of electromagnetic position sensors, each of which is positioned on a respective one of said catheter segments, and is designed to generate, in response to an externally generated magnetic field, an electrical signal representative of the position and orientation of the respective catheter segment.

Endovascular technology is a minimally invasive branch of vascular surgery which has also come to be adopted in other fields such as interventional radiology, cardiology, cardiac surgery, thoracic surgery, digestive surgery and neurosurgery.

The endovascular procedure is based on transarterial or transvenous catheterization, in which the devices are navigated along metal guides to reach the site of the vessel to be treated.

The most commonly used vascular access is a retrograde transfemoral access (via the common femoral artery), following local anaesthesia, with catheterization by the Seldinger technique. If this is impossible, due to occlusion of the common or iliac femoral artery, a brachial or radial access is formed. The guide is inserted into the needle, which is subsequently extracted, and a standard introducer is then inserted and a diagnostic arteriography is performed after a "pigtail" catheter has been positioned. The angiography reveals the anatomy of the vessel by the injection of a contrast medium (a radio-opaque dye) which is projected live on the angiograph monitor by means of X-rays. The development of endovascular technology has led to an improvement in the results in terms of morbidity and mortality, thus increasing the number of treatable patients. However, endovascular technology is not free of complications, and, although it is minimally invasive, this method has not yet been perfected, owing to the risks associated with injection of contrast medium (which is a nephrotoxic drug) [1] and the use of ionizing radiation (13.4 +/- 8.6 mSv for endovascular aneurysm repair (EVAR)) [2]. There are also numerous technical difficulties for the surgeon. Conventional fluoroscopes provide projected two-dimensional images which require the operator to perform a non- intuitive mental reconstruction of the three-dimensional structure of the vessels. In order to be performed correctly, this mental process requires considerable experience on the part of the operator, who must undergo a long period of training under the supervision of an expert surgeon before working independently. Navigation inside the vascular structures, based exclusively on sets of 2D projections of these structures, requires continual readjustment of the viewpoint of the fluoroscope and the acquisition of new sets of images. Incorrect positioning of the fluoroscope can also lead to problems such as the concealment of vessels of interest by overlying structures, or incorrect perception of the lengths of vessels.

Recent developments in computer graphics, virtual reality and image processing have opened the way to some initial projects for computerized assistance systems for endovascular surgery [3-10] and commercial solutions are now available for cardiac mapping and cardiac intervention [1 1-13].

The projects described in the literature include a system developed by S. Pujol [3, 10] for the treatment of abdominal aortic aneurysm (AAA), based on the electromagnetic location of the endoprosthesis and the recording of 3D models of the patient's anatomy acquired in the preoperative period by a computerized tomography (CT) scanning procedure.

The system proposed by S. Pujol is based on the use of a single electromagnetic sensor housed in a suitably modified endoprosthesis. The first validation tests of the system [3] were conducted by using a vascular catheter (diameter 3F, length 260 cm) fitted with an Aurora® electromagnetic sensor with five degrees of freedom (diameter 0.8 mm, length 10 mm), produced by Northern Digital Inc. S. Pujol has also described in [5] the use of an electromagnetic navigation system for neurological intervention. In this case also, a catheter fitted with a single Aurora® electromagnetic sensor was used. A catheter of the type defined in the introduction, provided with a plurality of electromagnetic position sensors, is described in EP 2 238 901. This known catheter has a plurality of sensors each composed of a single coil, distributed along the distal part of the catheter, and placed concentrically with the longitudinal axis of the catheter. As is known, the use of sensors may lead to problems due to the undesired creation of obstacles within the lumen of the catheter, the increase of the transverse dimensions of the instrument, and/or the reduction of its flexibility.

One object of the present invention is to provide a new arrangement of sensors which simplifies the sensor system fitted on the catheter, so as to reduce to a minimum any negative effect on the instrument, and which simultaneously makes it possible to obtain the necessary data to determine the position and path of the catheter and of its guide wire during use. This object is achieved according to the invention with a catheter of the type defined initially, wherein

each of said electromagnetic position sensors has a substantially needle-shaped body having a longitudinal axis placed parallel to the longitudinal axis of the respective catheter segment, and is located at the wall of the respective catheter segment, eccentrically with respect to the longitudinal axis thereof.

Preferred embodiments of the invention are defined in the dependent claims, which are to be considered as an integral part of the present description. A further object of the invention is a location system for catheters and guide wires, including

generating means for generating a magnetic field; a catheter comprising

- a tubular body to be introduced into a body cavity, said tubular body having a distal part including at least one curved or curvable portion, and corresponding catheter segments at the ends of said curved or curvable portion; and - a plurality of electromagnetic position sensors, each of which is positioned on a respective one of said catheter segments, and is designed to provide, in response to the generated magnetic field, an electrical signal representative of the position and orientation of the respective catheter segment;

processing means for processing the electric signals of said electromagnetic position sensors in order to provide data concerning the position and orientation of said distal part of the tubular body;

wherein each of said electromagnetic position sensors has a substantially needle- shaped body having a longitudinal axis placed parallel to the longitudinal axis of the respective catheter segment, and is located at the wall of the respective catheter segment, eccentrically with respect to the longitudinal axis thereof.

Further characteristics and advantages of the catheter according to the invention will be made clearer by the following detailed description of an embodiment of the invention, given with reference to the attached drawings which are provided purely as non-limiting illustrations, wherein:

- Figure 1 is a schematic perspective view of a catheter according to the invention;

- Figure 2 is a view in longitudinal section of the catheter of Figure 1;

- Figure 3 shows some examples of catheters of different shapes;

- Figure 4 is a schematic illustration of a steerable catheter according to the invention, in two different operating positions; and

- Figure_. 5 is a schematic perspective view of a guide wire according to the invention.

With reference to Figures 1 and 2, the number 1 indicates the whole of a catheter, or more precisely a distal part thereof.

The catheter 1 comprises a tubular body 3 to be introduced into a body cavity. This tubular body 3, or rather the distal part thereof, includes at least one curved or curvable portion 5 and respective catheter segments 7, 9 at the ends of the curved or curvable portion 5.

The catheter 1 further comprises a plurality of electromagnetic position sensors 17, 19. Each of these sensors is positioned on a respective one of said catheter segments 7, 9, and is designed to provide, in response to an externally generated magnetic field, an electrical signal representative of the position and orientation of the respective catheter segment.

This catheter can be used for endovascular surgery, which is a "minimally invasive" method used for the repair of vessels without surgical isolation of the artery concerned. This surgical procedure is performed endoluminally, using the lumen of the artery itself for access to the lesions, this lumen being reached by the cannulation of a peripheral artery (the femoral or axillary artery) which can be accessed in local anaesthesia by a transcutaneous puncture or mini-incision and through which are inserted the guide wires, catheters and prostheses (endoprostheses) which are guided under fluoroscopic control to reach the target lesion.

More precisely, the catheter according to the invention can be used for the provision of a computerized intraoperative assistance system for endovascular surgery, and in particular for the provision of a navigator based on the electromagnetic location of the surgical instruments.

The principle of electromagnetic location is based on the use of electromagnetic coils which, when connected to a field generator, supply information concerning their position and orientation in space.

Each of the electromagnetic position sensors 17, 19 of the catheter 1 is preferably a five- degrees-of-freedom sensor comprising a single solenoid coil. These sensors can be used to determine in a precise manner their position in space (more specifically, the position of the centre of each coil) and the direction of their longitudinal axis. Their orientation is therefore defined by means of the rotation about this axis. In an alternative embodiment, each of the electromagnetic position sensors of the catheters could be a six-degrees-of- freedom sensor, comprising two or more connected coils. These sensors supply all the information required to identify both their position and their orientation in space, namely three degrees of translation and three degrees of rotation. Each of the sensors 17, 19 of the catheter 1 has an body which is essentially needle-shaped, in other words straight and elongate in form, and has a longitudinal axis placed parallel to the longitudinal axis of the respective catheter segment.

An example of a commercial electromagnetic sensor which can be used in the present invention is the NDI Aurora® five-degrees-of-freedom sensor produced by Northern Digital Inc., which has extremely compact dimensions (0.5 mm in diameter x 8 mm in length). An NDI Aurora® sensor with six degrees of freedom has dimensions of 1.8 mm in diameter and 9 mm in length. The overall dimensions of the sensors can therefore be reduced by selecting coils with five degrees of freedom. These sensors have smaller dimensions than those of the six-degrees- of-freedom sensors, and are therefore preferable for use in the production of minimally invasive sensorized catheters and guide wires, within the size limits of standard endovascular instruments.

Each sensor 17, 19 is positioned at the wall of the corresponding catheter segment, eccentrically relative to the longitudinal axis of the segment. The sensor can be positioned on the radially outer surface of this wall, as in the illustrated example, or within the thickness of the wall.

Preferably, the electromagnetic position sensors 17, 19 are all positioned coplanarly with each other.

The specific arrangement of the sensors described above enables the overall dimensions to be reduced to a minimum, while also enabling the position and orientation of different "segments" of the catheter to be detected at the location of each sensor. For the purposes of the present invention, the term "segment" signifies any portion of a catheter in which there is an intrinsic direction of the tangent to the longitudinal axis of the catheter which differs or can be made to differ from that of another portion of the catheter.

The use of at least two five-degrees-of-freedom sensors is necessary in order to obtain the sixth degree of freedom and thus calibrate the catheter, and in order to reconstruct the curve and path of the curved portion 5 interposed between two catheter segments 7, 9.

The calibration procedure is used to calculate the position and orientation of the centre of the catheter lumen at the location of each sensor, when the positions of the sensors and the orientation of their longitudinal axis (supplied by the location system) are known.

More specifically, this procedure can be used to determine the translations which align the axes of the coil with the axis of the catheter at the location of each sensor. The aforesaid translations can be defined after the identification of the versors orthogonal to the axis of each coil and directed towards the centre of the catheter lumen (indicated by x and ½ in Figure 1 ). These versors can be identified by using at least a pair of coils, positioned as shown in Figure 2. The versors and ½ which lie on the plane of the two sensors, and which are, respectively, perpendicular to ½ and ¾ (the axes of the first and second coil), can be determined by simple geometrical operations, once the position and orientation of the axes of the two coils are known.

The curve of the curved portion 5 lying between the two sensors can finally be estimated by interpolation methods, and consequently the path of the whole distal portion of the catheter can then be determined.

It may be helpful to use more than two sensors in the case of a catheter having a complex shape. Figure 3 shows examples of catheters of different shapes. The first image on the left shows a vertebral catheter; only two sensors are required to reconstruct its curvature. The six central examples represent various types of Simmons catheters, while the last two on the right represent "shepherd's hook" catheters. In order to reconstruct the curvature of these catheters, at least three sensors are required (one for each catheter segment between one curved portion and the next).

Figure 4 shows the distal part of a catheter 1 of the type which can be steered by means of wires to vary the curvature of the aforesaid distal part. In this exemplary embodiment, the catheter segments 7, 9 on which the sensors 17, 19 are positioned are connected by a curvable part 5, the curvature of which is selectively modifiable (into the configuration shown in broken lines, for example) by actuating control means manoeuvred by an operator. Commercially available steerable catheters include designs having a double inner lumen. Advantageously, one of the two lumens can be used to house the electromagnetic sensors without the need for any particular design modifications to the existing steering system or changes in the dimensions of the catheter. Clearly, the present invention also relates to straight, non-steered catheters. These catheters are known to be flexible, and therefore curvable, so as to be able to adapt to the variations of the body cavity into which they are intended to be introduced.

With reference to Figure 5, the number 21 indicates the whole of the distal part of an example of a guide wire for guiding the catheter 1.

Guide wires are essential instruments for the performance of endovascular procedures: they provide a support for the insertion and manoeuvring of catheters, allow access and passage through lesions, and provide a support for catheters used for interventions.

A guide wire must have a flexible and non-injurious tip and a more rigid body which imparts manoeuvrability (or "pushability" of the guide wire) to the instrument.

The guide wire 21 shown in Figure 5 has a tubular body 23 of flexible material, such as Nitinol, within which is positioned a reinforcing tubular core 25, made of medical stainless steel for example. At its distal end, the guide wire 21 is free of the tubular core 25, in order to enable an electromagnetic position sensor 27 to be housed. The electrical output cable sensor to external processing means (not shown).

The sensor 27 is positioned on the tip of the guide wire 21, and is designed to provide, in response to an externally generated magnetic field, an electrical signal representative of the position and orientation of the tip of the guide wire.

In particular, the electromagnetic position sensor 27 of the guide wire 21 has a substantially needle-shaped body, in other words a body of straight and elongate shape, and has a longitudinal axis placed in alignment with the longitudinal axis of the guide wire. Preferably, the electromagnetic position sensor 27 of the guide wire 21 is a five-degrees- of-freedom sensor, comprising a single solenoid coil.

The sensorized guide wire, used in combination with the sensorized catheter described above during computer-assisted navigation, can provide all the functions required for the performance of complete endovascular procedures (identification of the distal portion of the catheter and of the distal portion of the guide wire).

The information supplied by a single five-degrees-of-freedom sensor, positioned on the axis of the guide wire as shown in Figure 5, is sufficient to describe the position and orientation of the distal end of the guide wire.

In order to determine the path of the whole distal portion of the guide wire, it is simply necessary to make use of the information on the position and orientation of the tip of the sensorized catheter (obtained as described above). This is because the guide wire is constrained to pass through the tip of the catheter.

With the solution described above it is possible to reduce the number of sensors and consequently the number of electrical wires to be housed in the guide wire: this arrangement optimizes the overall dimensions of the sensor system while keeping within the dimensional limits of standard endovascular instruments. Secondly, the mechanical characteristics of the guide wire are not compromised by any excessive stiffening of its structure due to multiple sensors and corresponding cables to be housed within it, arid finally the costs are also reduced.

References

[1] S. R. Walsh, et al, "Contrast-induced nephropathy," Journal of Endovascular Therapy, vol. 14, pp. 92-100, Feb 2007.

[2] C. Jones, et al, "The impact of radiation dose exposure during endovascular aneurysm repair on patient safety," Journal of vascular surgery: official publication, the Society for Vascular Surgery [and] International Society for Cardiovascular Surgery, North American Chapter, vol. 52, pp. 298-302, Aug 2010.

[3] S. Pujol, et al, "Minimally Invasive Navigation for the Endovascular Treatment of Abdominal Aortic Aneurysm: Preclinical Validation of the Endovax System," presented at the Proceedings of the 6th International Conference on Medical Image Computing and Computer Assisted Intervention., 2003.

[4] J. D. Lee, et al, "A Navigation System of Cerebral Endovascular Surgery Integrating Multiple Space-guiding Trackers," presented at the 30th Annual International IEEE EMBS Conference, Vancouver, British Columbia, Canada, 2008.

[5] S. Pujol, et al, "Preliminary results of nonfluoroscopy-based 3D navigation for neurointerventional procedures," J Vase Interv Radiol, vol. 18, pp. 289-98, Feb 2007.

[6] K. Dimitrov, "3-D Hall Sensor for use in Navigation Systems for Surgery Endovascular Interventions," presented at the IEEE International Workshop on Intelligent Data Acquisition and Advanced Computing Systems: Technology and Applications, Dortmund, Germany, 2007.

[7] M. Feuerstein, et al, "A novel segmentation and navigation tool for endovascular stenting of aortic aneurysms," presented at the Intl J CARS, 2006.

[8] O. Kuttera, et al, "Towards an integrated planning and navigation system for aortic stent-graft placement," presented at the Int J CARS, 2007.

[9] M. Castro, et al, "Estimation of 2d/3d Rigid Transformation of Computer- Assisted Endovascular Navigation," presented at the International Conference on Information and Communication Technologies: From Theory to Applications,

ICCTA Damascus, Syria, 2008.

[10] S. Pujol, et al, "A virtual reality based navigation system for endovascular surgery," Stud Health Technol Inform, vol. 98, pp. 310-2, 2004.

[1 1] CARTO® System, Biosense Webster® Available: http://www.biosensevvebster.com

[12] EP Navigator, Philips Electronics N. V. Available:

htt : //www .healthcare .phil ips . com

[13] EnSite System™, St. Jude Medical. Available: http : // ww . sj mpr ofessional .com

Claims

1. Catheter (1) comprising

a tubular body (3) to be introduced into a body cavity, said tubular body having a distal part including at least one curved or curvable portion (5), and corresponding catheter segments (7, 9) at the ends of said curved or curvable portion; and

a plurality of electromagnetic position sensors (17, 19), each of which is positioned on a respective one of said catheter segments, and is designed to generate, in response to an externally generated magnetic field, an electrical signal representative of the position and orientation of the respective catheter segment;

characterized in that

each . of said electromagnetic position sensors has a substantially needle-shaped body having a longitudinal axis placed parallel to the longitudinal axis of the respective catheter segment, and is located at the wall of the respective catheter segment, eccentrically with respect to the longitudinal axis thereof.

2. Catheter according to Claim 1, wherein each of said electromagnetic position sensors is a five-degrees-of-freedom sensor, comprising a single solenoid coil.

3. Catheter according to Claim 1 or 2, wherein said electromagnetic position sensors are placed coplanarly with respect to one another.

4. Catheter according to any of Claims 1 to 3, associated with a guide wire (21) comprising an electromagnetic position sensor (27) placed on a distal end of the guide wire (21) and designed to generate, in response to an externally generated magnetic field, an electrical signal representative of the position and orientation of the distal end of the guide wire (21);

wherein said electromagnetic position sensor (27) of the guide wire (21) has a substantially needle-shaped body having a longitudinal axis placed in alignment with the longitudinal axis of the guide wire.

5. Catheter according to Claim 4, wherein said electromagnetic position sensor (27) of the guide wire (21) is a five-degrees-of-freedom sensor, comprising a single solenoid coil.

6. Catheter according to Claim 4 or 5, wherein the guide wire (21) has a tubular body (23) of flexible material, within which a tubular strengthening core is placed (25); and wherein the distal end of the guide wire (21) is free of the tubular strengthening core (25), in order to allow the electromagnetic position sensor (27) to be housed, an electric output wire (29) of said sensor being passed through the tubular strengthening core (25) of the guide wire (21).

7. Location system for catheters and guide wires, including:

generating means for generating a magnetic field;

a catheter (1) comprising

- a tubular body (3) to be introduced into a body cavity, said tubular body having a distal part including at least one curved or curvable portion (5), and corresponding catheter segments (7, 9) at the ends of said curved or curvable portion; and

- a plurality of electromagnetic position sensors (17, 19), each of which is positioned on a respective one of said catheter segments, and is designed to provide, in response to the generated magnetic field, an electrical signal representative of the position and orientation of the respective catheter segment; processing means for processing the electric signals of said electromagnetic position sensors in order to provide data concerning the position and orientation of said distal part of the tubular body (3);

characterized in that

8. System according to Claim 7, wherein each of said electromagnetic position sensors is a five-degrees-of-freedom sensor, comprising a single solenoid coil.

9. System according to Claim 7 or 8, wherein said electromagnetic position sensors are placed coplanarly with respect to one another.

10. System according to any of Claims 7 to 9, wherein said processing means are programmed to determine the path of said curved or curvable portion (5) of the catheter on the basis of the electrical signals representative of the position and orientation of the catheter segments (7, 9).

11. System according to any of Claims 7 to 10, associated with a guide wire (21) comprising an electromagnetic position sensor (27) placed on a distal end of the guide wire

(21) and designed to generate, in response to the generated magnetic field, an electrical signal representative of the position and orientation of the distal end of the guide wire (21); wherein said electromagnetic position sensor of the guide wire has a substantially needle-shaped body having a longitudinal axis placed in alignment with the longitudinal axis of the guide wire (21).

12. System according to Claim 11, wherein said electromagnetic position sensor of the guide wire is a five-degrees-of- freedom sensor, comprising a single solenoid coil.

13. System according to Claim 11 or 12, wherein said processing means are also programmed for determining the path of a distal portion of the guide wire (21) on the basis of the electrical signal representative of the position and orientation of the distal end of the guide wire (21), and on the basis of the electric signals representative of the position and orientation of the catheter segments (7, 9).