Catheter with optical sensing

Abstract

A catheter (12) has an image sensing system (S1-S5) for imaging the interior wall of a passageway in which the catheter is to be located. The catheter has a radial imaging system comprising a light source arrangement for generating a light output radially around the catheter and an image sensor for receiving the generally radial light after the light has been scattered back by the interior wall. The catheter is positioned within the passageway with a known position and orientation, for example a known angle with respect to the anterior-posterior plane along the length of the catheter, so that it is known where along the catheter length, and at which angular position around the catheter, it is close to the passageway wall. The light output has a different intensity at different radial directions and/or the catheter comprises a light transmission arrangement which gives rise to different transmission of the light output at different radial directions. These provide alternative measures to reduce the light received by the image sensor, thereby to prevent blooming in the captured image.

Claims

1. A catheter having an image sensing system for imaging the interior wall of a passageway in which the catheter is to be located, comprising: a radial imaging system comprising a light source arrangement for generating a light output radially around the catheter and an image sensor for receiving the radial light output after reflection by the interior wall, wherein the catheter is adapted to be positioned within the passageway with predetermined position and orientation within the passageway along its length, and wherein the light output has a different intensity at different radial directions and/or the catheter comprises a light transmission arrangement which gives rise to different transmission of the light output to the image sensor for different radial directions, such that an envelope shape of the light output intensity distribution around the catheter or a light transmission function of the light transmission arrangement around the catheter is non-circular, wherein the catheter has a noncircular outer shape in cross section across the catheter length that influences bending of the catheter in a known manner such that the catheter adopts a particular known path of position and orientation within the passageway due to the noncircular outer shape.

2. The catheter of claim 1, wherein the radius of curvature of the catheter outer shape, in cross section across the catheter length, is greater at one angular position around the catheter compared to an opposite angular position around the catheter.

3. The catheter of claim 2, wherein the catheter has a flat edge in its outer shape, in cross section across the catheter length, where the catheter is to be in contact or in close proximity with the passageway wall.

4. The catheter of claim 2, wherein the outer shape or angular orientation of the outer shape varies along the catheter length.

5. The catheter of claim 1, wherein the bending properties of the catheter vary along the length of the catheter.

6. The catheter of claim 5, wherein the catheter stiffness to bending in particular directions varies along the length of the catheter.

7. The catheter of claim 1, wherein the light output intensity is least where the catheter is to be closest to the passageway wall.

8. The catheter of claim 1, wherein the light transmission arrangement comprises electrical cables or optical fibers which provide attenuation.

9. The catheter of claim 1, wherein the light source arrangement comprises: a light source inside the catheter and optionally a collimator for collimating the light source output.

10. The catheter of claim 1, wherein the light source arrangement comprises: a light source outside the catheter; an optical fiber which is adapted to transmit the light output from the light source from outside the catheter to inside the catheter and to emit the light in a direction centered parallel to the catheter elongate axis; optionally a collimator for collimating the light from the optical fiber; and a reflector for redirecting the emitted light to form a ring of generally radially directed light around the catheter length.

11. The catheter of claim 10, wherein the reflector is non-axisymmetric thereby creating a non-uniform light intensity with respect to radial direction.

12. The catheter of claim 9, further comprising a second reflector for redirecting the radial light after reflection by the interior wall toward the image sensor.

13. The catheter of claim 12, wherein the second reflector is non-axisymmetric thereby creating a non-axisymmetric field-of view of the sensor with respect to radial direction.

14. The catheter of claim 1 for use in determining the presence and location of obstructions in an upper airway, wherein the catheter comprises a plurality of radial imaging systems along the length of the catheter.

15. The catheter of claim 1, wherein the intensity of the light at different radial directions is fixed.

16. A catheter having an image sensing system for imaging the interior wall of a passageway in which the catheter is to be located, comprising: a radial imaging system comprising a light source arrangement for generating a light output radially around the catheter and an image sensor for receiving the radial light output after reflection by the interior wall, wherein the catheter is adapted to be positioned within the passageway with predetermined position and orientation within the passageway along its length, and wherein the light output has a different intensity at different radial directions and/or the catheter comprises a light transmission arrangement which gives rise to different transmission of the light output to the image sensor for different radial directions, such that an envelope shape of the light output intensity distribution around the catheter or a light transmission function of the light transmission arrangement around the catheter is non-circular, wherein the catheter has bending properties that vary along the length of the catheter in a manner that influences bending of the catheter in a known manner such that the catheter adopts a particular known path of position and orientation within the passageway.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a schematic illustration of a length section of an example catheter disposed inside an airway;

(3) FIG. 2 shows a schematic illustration of an example catheter inserted into a patient's nasal cavity and upper airway;

(4) FIG. 3 shows a problem which arises due to non-central catheter positioning;

(5) FIG. 4 shows how the catheter shape can influence the bending performance;

(6) FIG. 5 shows a catheter with non-circular outer shape within a passageway;

(7) FIG. 6 shows how attenuation may be used to alter a radial light pattern;

(8) FIG. 7 shows how different orientations may be appropriate at different positions along the length of the catheter; and

(9) FIG. 8 shows a catheter design.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(10) The invention provides a catheter having an image sensing system for imaging the interior wall of a passageway in which the catheter is to be located. The catheter has a radial imaging system comprising a light source arrangement for generating a light output radially around the catheter and an image sensor for receiving the generally radial light after the light has been scattered back by the interior wall. The catheter is positioned within the passageway with a known position and orientation, for example a known angle with respect to the anterior-posterior plane along the length of the catheter, so that it is known where along the catheter length, and at which angular position around the catheter, it will be closest to the passageway wall. The light output has a different intensity at different radial directions and/or the catheter comprises a light attenuation arrangement which gives rise to different attenuation of the light output at different radial directions. These provide alternative measures to reduce the light received by the image sensor, thereby to prevent blooming in the captured image.

(11) The invention may for example be used for imaging with a conduit. This may have non-medical applications for imaging non-living objects such as pipes, channels and tunnels as well as for medical imaging applications such as for imaging airway passages, intestinal passageway or capillaries or arteries.

(12) By way of illustration, FIG. 1 schematically depicts an example catheter 12 of known basic configuration, arranged within a stretch of an upper airway 14. Along the length of the airway are indicated four anatomical regions or features, labeled 18, 20, 22, and 24, these, by way of non-limiting example, representing the soft palate (velum), the oropharynx, the tongue base and the epiglottis respectively. Disposed within the airway 14 is the catheter 12, which comprises a series of optical sensors S1 to S5. They each comprise a laser light source for generating light generally axially, a first reflector for redirecting the light to include at least a component in the radial direction, a second reflector for redirecting reflected light from the side wall of the duct being investigated towards an image sensor for capturing an image of side wall of the duct being investigated. FIG. 1 shows schematically a space and therefore a radial distance between the catheter and the airway 14.

(13) The optical arrangement is represented schematically in FIG. 1 as a single triangle.

(14) For illustration, FIG. 2 schematically shows the catheter 12 disposed in the upper airway of a patient 34, having been inserted via the nostril 36 of the patient. The distal end of the sensor is anchored in the esophagus. The approximate positions of the four anatomical regions of FIG. 1 (velum 18, oropharynx 20, tongue base 22, and epiglottis 24) are indicated along the airway 14 of the patient 34.

(15) This invention relates in particular to the issue of a non-central position of the catheter within the passageway and the effect this has on the radial light intensity captured by the imaging sensor.

(16) The light source arrangement generates a radial ring of light emitting radially outwardly from the catheter to illuminate a ring shaped section of the wall of the upper airway 14. The ring may be continuous, but it may instead be formed as a set of discrete points generally following an annular path.

(17) The radial projection may be entirely radial, i.e. at 90 degrees to the catheter axis, but it may be inclined at an acute angle to this perfectly radial direction. For compactness, for example to fit the optical system within a catheter, the light is routed axially along the catheter, and a reflection arrangement redirects the light to form the radial pattern.

(18) As explained above, the distance between the catheter and airway wall influences the light intensity of the received light.

(19) A first aspect of the invention involves ensuring the catheter has a known position within the passageway being imaged. One way to control this is to have control over the path followed by the catheter when it is inserted into the passageway.

(20) FIG. 4 shows how the catheter shape can influence the bending performance, which can then be used to control the shape and position adopted by the catheter. A circular cross section is shown as 50, and a cross section which is fattened is shown as 52. The outer shape 52 is non-circular in cross section across the catheter length. This non circular shape means the catheter will have a preference to bending in certain directions. In particular, it will preferentially bend around an axis 54 parallel to the width direction. In this way, the inserted catheter can be designed to follow a particular path to match the shape of a passageway which is itself of known general shape.

(21) The radius of curvature of the catheter outer shape at the bottom is greater (i.e. there is a more gentle curve) than at the sides. This flatter bottom is where the catheter is to be in contact with the passageway wall. The outer shape is thus generally squashed. It may be an asymmetrical shape (i.e. with rotational order of symmetry equal to 1) but it may still have some symmetry, for example an ellipse which has a rotational order of symmetry of 2. The flatter bottom may be a completely flat edge

(22) The catheter thus has a smaller diameter in the height direction than in the width direction.

(23) The most flattened side (the bottom in the example shown) is also particularly optimized to stick to the passageway wall.

(24) When the catheter bends or flexes around the axis 54 the flat region will preferably orient itself towards the passageway wall. The catheter is entered into the passageway to support the correct alignment. In this way it is possible to predict the part of the sensor that will be closest to a passageway wall with a high degree of confidence.

(25) It is also possible to obtain a similar behavior, without changing the geometric cross section of the catheter, but by adapting the mechanical properties for different orientations. This could be done for example by including stiff fibers in the catheter. In this way, the bending properties of the catheter vary along the length of the catheter. This provides another way to control the way the catheter is steered into a known shape and location within the passageway. The catheter stiffness to bending in particular directions may for example vary along the length of the catheter.

(26) These two approaches may be combined so that both shape and stiffness parameters are variables which together enable the catheter to adopt a desired shape when guided by the passageway.

(27) The approximate shape of the passageway, for example the upper airway, at a given depth is known. By controlling which side of the catheter is close to the airway, the light intensity can then be shaped according to the expected distance to the airway.

(28) The light intensity can then be increased in directions where a large distance is expected to the airway wall, and the intensity can be decreased in directions where a small distance is expected.

(29) Thus, in a second aspect, once the catheter position is known, there is control of the light pattern and/or the sensing optics to provide a non-rotationally symmetric function. In particular, when the light output intensity is controlled, the envelope shape of the light output intensity distribution around the catheter is non-circular. When the light intensity received by the image sensor is controlled by varying the light transmission with angle, the light transmission function is non-circular. The light dose and optical field of view around the sensor can then be optimized taking account of the known positioning.

(30) FIG. 5 shows a catheter 52 with non-circular outer shape within a passageway 42. The intensity of the illumination pattern depends on the expected distance from the catheter. The light intensity is thus controlled to depend on the angular radial position around the catheter. For example, the intensity is highest in general region 60, lower in general region 62 and lowest in general region 64. The light intensity is not uniform in these regions, and they are only shown as three distinct regions for the purposes of explanation. In practice, there will be a function which relates the intensity to the angle around the catheter.

(31) An asymmetric light pattern can be easily realized for example by adding different concentration of absorbers, or purposely misaligning the deflection cone which generates the radial light pattern from the center of the beam. In this way, the light pattern may be created by manipulating the output of the light source or the way it is reflected.

(32) An alternative is to provide selective absorption of the light after it has been reflected for redirection radially. A dedicated light attenuation arrangement may be used for this purpose, but it may make use of existing parts of the device.

(33) FIG. 6 shows a non-circular catheter outer shape 52 (in cross section across the catheter length) with a flat edge 70 to be closest to the passageway wall. The catheter contains a camera and optical components 72 generally aligned along its central axis. There are various electrical cables or optical fibers 74 forming part of the device, and these are arranged at the flat side 70 to provide deliberate attenuation of the light from that area of the catheter outer wall. In this way, existing components of the overall system may be used to provide a desired light blocking function, by suitable selection of their locations. This avoids the need for additional components.

(34) The various measures explained above for creating asymmetry may be oriented differently at different locations along the catheter length.

(35) Like FIG. 2, FIG. 7 shows the catheter in use in the upper airway of a patient. In the manner explained above, the catheter is adapted along its length to match the orientation of the catheter to the airway wall.

(36) For example, in FIG. 7 the catheter might prefer to stick close to the posterior walls at the level of the oropharynx until the epiglottis (location 80a) and stick close to the anterior airway wall at the velum level (location 80b). Therefore the catheter has the orientations of the flatter side change accordingly. Of course the other parameters could be adapted along the length of the catheter accordingly, such as the ring intensity, the orientation of cables or the catheter stiffness.

(37) To provide an image sensor sensitivity which is dependent on radial direction, it is not only possible to adapt the intensity of the ring pattern according to the expected distance to the airway wall (as explained above), but it is also possible to adapt the distance range of the sensor. This can for example be implemented by using a non-rotational symmetric light collection cone in front of the camera, or by purposely misaligning the camera and the cone.

(38) The resolution of such a sensor is typically limited by the number of pixels available in a small camera and by the field-of-view of the camera together with the light reflection cone. By using non-symmetric optics in front of the camera, the field of view of the camera changes depending on the radial direction. That means also that the pixels of the camera chip will be mapped differently depending on the radial direction. The asymmetry may be before the radial illumination pattern is formed (e.g. by design of the first reflector) or after it is formed but before it reaches the image sensor (e.g. by design of the second reflector) or both.

(39) The invention may be applied to the catheter shown in FIG. 1.

(40) The light source arrangement may comprise a light source such as a laser, an optical fiber which transmits the light output and emits the light in a direction centered parallel to the catheter elongate axis, and a first reflector for redirecting the emitted light to form a ring of generally radially directed light around the catheter length. It might also comprise a collimating element, which collimates the light from the fiber. This collimating element may be combined with the first reflector. This reflector may be designed to provide the asymmetric ring by its alignment or shape. For example, the reflector may be non-axisymmetric thereby creating a non-uniform light intensity with respect to radial direction. In this way, a non-uniform radial light pattern is implemented by the reflector without requiring complex optical alterations to the light output.

(41) As mentioned above, an alternative is to implement the asymmetry using a second reflector which is for directing the light received from the passageway wall to the image sensor.

(42) To illustrate the components mentioned above more clearly, FIG. 8 shows an illustrative example of a catheter 91 incorporating a radial illumination system as described above. The catheter 91 is encapsulated within a transparent capillary, and received a light output from a laser 92 which is outside the catheter, arranged to propagate generated laser light in an axial direction along an optical fiber 94. The laser is mounted at the end of the optical fiber. The optical fiber has a collimator and conical reflector 96 at its end 97.

(43) The reflector 96 may in some examples be designed to provide the required non-uniform light output intensity with respect to the radial direction as explained above.

(44) The cross sectional shape of the catheter cannot be seen in FIG. 8. It may be non-circular as explained above.

(45) The radial illumination system generates the radial light output, and after reflection by the channel in which the catheter is mounted (for example a patient airway 98), it is reflected by a cone reflector 100 towards an image sensor 102.

(46) The catheter may comprise multiple imaging systems in series, whereas FIG. 8 shows only one such imaging system.

(47) FIG. 8 also shows an external light source, whereas the light source may be inside the catheter. It may also for example comprise a ring of lighting elements which face outwardly (rather than axially), so that the reflector 96 is not needed. In this case, different lighting elements may have different intensity in order to vary the intensity with angular position around the catheter.

(48) The catheter may be for use in determining the presence and location of obstructions in an upper airway, the catheter comprising a plurality of radial imaging systems along the length of the catheter. In this way, each radial imaging system is for a particular one of the locations at which airway obstructions can be ascertained.

(49) As mentioned above, one application of particular interest is to improve the performance of an optical catheter sensor for measuring the upper airway patency in OSA patients during natural (or sedated) sleep; in this application a laser plane is created in the sensor module that is approximately perpendicular to the image sensor and cone axis and in the associated cross section in the upper airway a contour lights up. The sensor elements are contained in a capillary.

(50) Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.