# Patent

## Title
Locatable catheter

## Abstract

A catheter having a sensor at a distal end thereof, useable to detect and create signals from an electromagnetic field. The sensor is constructed and arranged to leave a lumen of the catheter open such that it may be used to pass instruments therethrough once a target location has been reached.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation application of U.S. patent Ser. No. 12/755,332 filed on Apr. 6, 2010 by Greenburg et al., now U.S. Pat. No. 8,611,984, which claims priority to U.S. Provisional Application Ser. No. 61/167,839 filed Apr. 8, 2009 entitled Locatable Catheter, which is hereby incorporated herein by reference in its entirety.


FIELD OF THE INVENTION
The field of the present invention pertains generally to the navigation of a device, such as a catheter, through a branched structure and the monitoring of a position of said device once a target location has been reached. More specifically, the present invention relates to a locatable catheter for navigating through body lumens and providing a delivery conduit for other devices.
BACKGROUND OF THE INVENTION
The most common interventional procedure in the field of Pulmonary Medicine (i.e., medicine pertaining to the respiratory system) is bronchoscopy, in which a bronchoscope is inserted into the airways through the patient's nose or mouth. The structure of a bronchoscope generally includes a long, thin, flexible tube that typically contains three elements: an illumination assembly for illuminating the region distal to the bronchoscope's tip via an optical fiber connected to an external light source, an imaging assembly for delivering back a video image from the bronchoscope's distal tip, and a lumen or working channel through which instruments may be inserted, including but not limited to diagnostic (e.g., biopsy tools) and therapeutic (e.g., laser, cryo or RF tissue elimination probes) instruments. The distal tip of a bronchoscope is steerable and therefore rotating a lever placed at the handle of the bronchoscope actuates the steering mechanism by deflecting the tip in two opposite directions.
Bronchoscopes are limited, however, in how far they may be advanced through the airways due to their size. Typically, a bronchoscope is much wider than other types of catheters, mainly due to the size constraints placed on their design by the camera. Unfortunately, the lesion or target of interest is often located deeper in the lungs than a bronchoscope can travel. Hence, three-dimensional location technology has been developed that allow the navigation of a steerable catheter deep into the lungs. The catheter includes a sensor that can be detected magnetically with great precision. Of particular relevance to the present invention are the devices and methods described in the following references: PCT Patent Publication No. WO 03/086498 entitled “Endoscope Structure and Techniques for Navigation in a Branched Structure” to Gilboa; U.S. Pat. No. 7,233,820 entitled “Endoscope Structures And Techniques For Navigating To A Target In Branched Structure” to Gilboa; U.S. Pat. No. 6,947,788 entitled “Navigable Catheter” to Gilboa; U.S. Pat. No. 6,833,814 entitled “Intrabody Navigation System For Medical Applications” to Gilboa et al.; U.S. Pat. No. 6,711,429 entitled “System And Method For Determining The Location Of A Catheter During An Intra-Body Medical Procedure” to Gilboa et al.; U.S. Pat. No. 6,615,155 entitled “Object Tracking Using A Single Sensor Or A Pair Of Sensors” to Gilboa; U.S. Pat. No. 6,593,884 entitled “Intrabody Navigation System For Medical Applications” to Gilboa et al.; U.S. Pat. No. 6,380,732 entitled “Six-Degree Of Freedom Tracking System Having A Passive Transponder On The Object Being Tracked” to Gilboa; U.S. Pat. No. 6,188,355 entitled “Wireless Six-Degree-Of-Freedom Locator” to Gilboa; each of which is hereby incorporated by reference in its entirety.
These references describe methods and devices in which locatable guides (“LGs”), enveloped by sheaths, are used to navigate to a location within the lung. The guide/sheath combination is inserted into the lung via the working channel of a bronchoscope. Once the tip of the guide is located at its target, a lock, which is placed at the orifice (“connection port”) of the bronchoscope's working channel, is operated to prevent the sheath from sliding in or out of the bronchoscope. The guide is then withdrawn from the sheath, leaving the sheath in place to guide a tool to the required target location.
Once the target has been reached with the LG, the LG is removed, leaving the sheath in place as a conduit to the target for other tools. However, the present design includes most or all of the location technology on the LG. Hence, once the LG is removed from the sheath, the physician is assuming that the sheath remains in close proximity to, and pointed at, the target.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention addresses the identified needs by providing a locatable sheath that can be used in conjunction with, or instead of, an LG. Adding a sensor to a sheath adds the complication of maintaining an open lumen through the sheath. As such, various sensor designs are provided that do not interfere with the sheath lumen.
One aspect of the present invention provides a catheter sheath with a sensor at the distal tip. The sensor is comprised of three coils of wire, each at an angle to the others but sharing a common center point, in order to reduce the overall longitudinal dimension of the sensor. By reducing the longitudinal dimension, the impact the sensor has on the flexibility of the distal tip is minimized.
Another aspect of the present invention provides a catheter sheath with a sensor incorporated into a side of the sheath, such that the sensor is off-center. This design allows the entire sensor to be manufactured separate from the catheter and attached later as a component.
Yet another aspect of the present invention provides a sheath with a sensor that comprises a single coil at the distal tip and surrounding the lumen. This design greatly reduces the impact the sensor has on the flexibility of the sheath. The single coil design does not provide the degrees of freedom that a triple-coil design does but would be used in conjunction with an LG and, after the LG is removed, provides enough information to notify the physician that the sheath has moved out of position and needs to be adjusted.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a preferred embodiment of the present invention; and,
FIG. 2 is a perspective view of a preferred embodiment of the present invention.



DESCRIPTION OF EMBODIMENTS
Specific embodiments of the invention will now be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements.
Turning now to the Figures and first to FIG. 1, there is shown a device 10 of the present invention. Device 10 generally comprises a locatable guide (“LG”) 12 and a locatable sheath 20. It is understood that locatable sheath 20 could be used with or without LG 12. The LG 12 includes a sensor 14 embedded in a distal tip 16 thereof. The distal tip 16 is shown with a cutout in order to view the embedded sensor 14. Examples of LG 12 embodiments are shown and described in PCT Patent Publication No. WO 03/086498 entitled “Endoscope Structure and Techniques for Navigation in Branched Structure” to Gilboa, which is hereby incorporated by reference in its entirety.
These LG 12 embodiments are steerable probes that incorporate six degree-of-freedom (“6 DOF”) sensors that operate by sensing externally-generated magnetic fields. For example, three magnetic fields may be generated, each using a separate frequency. The three magnetic fields vary in intensity throughout an operational area. Placing three orthogonally-oriented coils in the operational area results in signals generated by the coils that indicate three-dimensional location and three-dimensional orientation of the sensor 14.
The sheath 20 includes one or more coils 22 that are either embedded in its wall or are attached to an outside surface thereof. The sheath 20 also defines a central lumen 24 that is unobstructed by the coils 22. One embodiment of the sheath 20 includes only a single coil 22 proximate its distal tip 26. The coil 22 is used to generate signals indicating its location in a variety of ways.
For example, the single coil can generate signals using the same magnetic fields utilized by the LG 12. Hence, after the LG 12 is removed, the single coil 22 may be used to generate a signal indicating its three-dimensional location in the operational field.
Alternatively, a field may be generated on a fourth frequency such that the sensor 22 may be used concurrently with the sensor 14 of the LG 12. If the sensor 22 is dedicated to a single field on a fourth frequency, the sensor would not be useful for three-dimensional position data but could be used to generate a signal indicating that it has moved out of position after the LG 12 is withdrawn.
Another embodiment, shown in FIG. 1, utilizes multiple coils 22. The coils 22 are spaced apart along the length of the sheath 20. The coils 22 provide position data of various points along the length of the sheath 20, thereby “painting a picture” of the sheath. As such, even though the coils 22 are not providing 6 DOF data, when viewed together they provide an indication of the location and orientation of the sheath 20. Hence, this embodiment of sheath 20 may be used to both navigate to the target and provide a conduit for tools, possibly obviating the need for the LG 12.
Referring now to FIG. 2, there is shown an embodiment of a sheath 20 with a 6 DOF sensor 30 incorporated into its distal tip 26. The sheath 20 is shown as transparent such that the details of the sensor 30 may be more easily displayed. The sensor 30 includes three coils 32, 34 and 36. Coils 32 and 34 are angled, while coil 36 is relatively circumferential to the sheath 20. Preferably, coils 32 and 34 lie in planes that are relatively perpendicular to each other. More preferably, all three coils share a common center point 38. By sharing a common center point 38, the longitudinal dimension of the overall sensor is minimized, thereby reducing the impact of the sensor 30 on the flexibility of the sheath 20. This design represents an advantage over prior art designs, such as that shown and described in International Publication Number WO 97/29684, to Acker. Acker discloses several coil designs that leave a central lumen open but are longitudinally extended, resulting in a reduced flexibility of the catheter in order to maintain a constant spatial relationship between the coils.
Although the invention has been described in terms of particular embodiments and applications, it should be appreciated that other embodiments and applications also fall within the scope of the present invention. One of ordinary skill in the art, in light of the teaching, can generate embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention.
For example, each of the embodiments is described as having sensors incorporated into a sheath 20 that are passive. In other words, the described sensors generate signals when they pass through magnetic fields or reside within an electromagnetic field. However, one skilled in the art will understand that any or all of the coils of the sensors could be actively energized to generate magnetic fields. The generated magnetic fields could then be detected by external passive sensors and used to calculate a position and/or orientation of the coil(s). Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.

## Claims

1. A locatable medical instrument insertable through a working channel of a bronchoscope, comprising:
a sheath having at least three coils embedded therein, the at least three coils overlying one another and having a common center point, and each of the at least three coils is integrally formed within a wall defining a longitudinal lumen extending through the sheath,
wherein each of the at least three coils is configured to generate a signal when placed in an electromagnetic field, the signal indicative of a strength of the electromagnetic field and the position of the sheath; and
wherein two of the at least three coils are approximately perpendicular to each other.

2. The locatable medical instrument of claim 1, wherein the sheath includes a generally elongated configuration and is flexible.

3. The locatable medical instrument of claim 1, wherein the sheath includes a distal end configured to receive a probe therethrough for positioning the sheath adjacent target tissue.

4. The locatable medical instrument of claim 3, wherein the at least three coils are positioned proximate the distal end of the sheath.

5. A system for navigating through a branched structure, comprising:
a sheath having embedded therein a first electromagnetic field sensor configuration including at least three coils overlying one another and sharing a common center point, and each of the at least three coils is integrally formed within a wall defining a longitudinal lumen extending through the sheath;
a probe extendable through the lumen of the sheath and having a second electromagnetic field sensor embedded within a distal tip thereof;
an electromagnetic field generation device configured to create electromagnetic fields having a plurality of frequencies and configured to induce signals in the first and second electromagnetic field sensors,
wherein the first electromagnetic field sensor is configured to generate signals indicating its position relative to the branched structure; and
wherein two of the at least three coils are approximately perpendicular to each other.

6. The system of claim 5, wherein the first electromagnetic sensor is positioned proximate a distal end of the sheath.

7. The system of claim 5, wherein the first electromagnetic field sensor comprises a six degree-of-freedom sensor.

8. The system of claim 5, wherein the second electromagnetic field sensor comprises a six degree-of-freedom sensor.

9. The system of claim 5, wherein the electromagnetic field generation device creates electromagnetic fields of at least four frequencies, three of the at least four frequencies detected by the second electromagnetic field sensor, thereby allowing the second electromagnetic field sensor to generate six degree-of-freedom location information.

10. The system of claim 9 wherein one of the at least four frequencies is detected by the first electromagnetic field sensor, thereby allowing the first electromagnetic field sensor to generate a signal including location information.

11. A method for accessing a target in a branched structure, comprising:
providing an electromagnetic field generator defining a sensing volume containing the branched structure;
advancing a probe through the branched structure, the probe including a probe electromagnetic field sensor configured to sense electromagnetic fields generated by the electromagnetic field generator and creating probe location signals as a result to locate the target;
advancing a sheath over the probe to the target, the sheath at its distal end having at least three coils embedded therein and overlying one another so as to share a common center point, and each of the at least three coils is integrally formed within a wall defining a longitudinal lumen extending through the sheath, the at least three coils configured to sense electromagnetic fields generated by the electromagnetic field generator and creating sheath location signals as a result;
removing the probe proximally from the sheath;
monitoring a location of the sheath using the sheath location signals to ensure the distal end of the sheath remains at the target; and
accessing the target with one or more instruments by passing the one or more instruments through the sheath;
wherein two of the at least three coils are approximately perpendicular to each other.

12. The method of claim 11 wherein monitoring the location of the sheath further includes reading signals from the at least three coils on the sheath at a frequency that is independent of frequencies of signals from the electromagnetic field sensor on the probe.

13. The method of claim 11 wherein monitoring the location of the sheath further includes reading signals from the at least three coils on the sheath at a frequency that is the same as frequencies of signals from the electromagnetic field sensor on the probe.