WO2015071343A1

WO2015071343A1 - Detection of rotational angle of an interventional device

Info

Publication number: WO2015071343A1
Application number: PCT/EP2014/074441
Authority: WO
Inventors: Melike BOZKAYA; Ahmet Ekin
Original assignee: Koninklijke Philips N.V.
Priority date: 2013-11-13
Filing date: 2014-11-13
Publication date: 2015-05-21

Abstract

An interventional device, e.g. an intravascular catheter such as IVUS or OCT, by using an optical shape sensor (OSS)-based mechanism at the time of the intravascular image acquisition. An OSS fiber with a predetermined shape is merged with the intravascular catheter and the predetermined shape of OSS fiber has OSS identifiable features positioned to allow optical determination of orientation (rotational angle relative to a longitudinal axis of the catheter) at the longitudinal position of the catheter where the imaging sensor resides. The predetermined shape of the OSS-device indicates an angle of rotation of a predetermined reference orientation of the catheter relative to an OSS sensor during navigation/pullback of the intravascular catheter through a vessel. Alternatively, or additionally, a multi-core OSS cable can be used, which allows calculation of twist angle between two nodes of the OSS cable, and thus a measure of rotational angle. With such a system, it is possible to get rotational angle (orientation) information gathered for each intravascular image. Such orientation information can be used to visualize one single image with correct angular alignment. Further, by calibrating individual images of a pull-back sequence with respect to the gathered rotational angle and position information, it is possible to orient the cross- sectional intravascular data on an X-ray image with improved accuracy that may have better diagnostic value.

Description

Detection of rotational angle of an interventional device

FIELD OF THE INVENTION

The present invention relates to the field of medical devices, more specifically interventional devices with image capabilities, such as intravascular catheters with an image sensor.

BACKGROUND OF THE INVENTION

For the evaluation and intervention of Coronary Artery Disease (CAD), intravascular technologies like Intra Vascular Ultra Sound (IVUS), Optical Coherence Tomography (OCT), Near-InfraRed Spectroscopy (NIRS), Fractional Flow Reserve (FFR), etc. can be used to gather information about the internal structure and function of the vessel and the plaque/tissue characteristics.

While intravascular imaging technologies provide high resolution assessment of the plaque and vessel walls, the generated images do not allow determination of the location and the orientation of a specific intravascular image frame in 3D space. In order to solve the localization problem, different co-registration techniques have been proposed. These techniques link the intravascular data with the global vessel geometry in different ways, such as recording X-ray fluoroscopy images during the pullback of the intravascular image sensor. By this, the location of the intravascular sensor at the time of the acquisition can be shown on the vessel geometry on X-ray.

However, use of X-ray for solving the localization problem introduces additional radiation. Furthermore, even though the correct location is known for each intravascular image frame, X-ray does not provide a measure of orientation of the image sensor for each frame. Thus, the orientation of the image sensor that is used to provide image data from the vessel wall at a given longitudinal position is not known. This may be important for a physician to be able to provide a correct anatomical interpretation of an image, e.g. by comparing the image with another image captured at another longitudinal position in the vessel. The orientation is important both in case of images of a limited angular portion of the vascular cross section, or in case the image sensor is capable of providing a 360° cross sectional image. Intravascular image frames captured at different longitudinal positions of a blood vessel may also be used to provide a longitudinal view of a vessel wall, e.g. by providing a combined longitudinal image by stacking the individual image frames each obtained at one longitudinal position. Also in this case, information about orientation of the individual image frames is important to be able to correctly rotationally align the images, since in curved vessels, the image sensor will in general be oriented differently at different longitudinal positions. None or incorrect orientation information may provide a resulting constructed longitudinal view with a poor image information of the vessel wall, thus offering a limited value for a physician to diagnose a patient based thereon. SUMMARY OF THE INVENTION

It would be advantageous to be able to detect rotational orientation of an intravascular catheter during an intravascular imaging procedure, e.g. so as to allow correct orientational alignment of cross- sectional intravascular images with improved accuracy.

In a first aspect, the invention provides an interventional device comprising: - an elongated device arranged for interventional application,

a sensor positioned on a distal portion of the elongated device, wherein the sensor is arranged to sense characteristics of material present perpendicular to a longitudinal axis of the elongated device, and

an optical fiber with optical shape sensing properties along at least a part of its longitudinal extension, wherein the optical fiber is attached to at least a part of the elongated device and a portion of the optical fiber is positioned with a non-zero angle relative to a longitudinal axis of the elongated device, at or near a longitudinal position of the elongated device where the sensor is positioned, so as to allow optical tracking of rotational angle orientation of the sensor.

By the use of optical shape sensing (OSS) technique, e.g. built into an IVUS catheter or the like, it is possible to provide knowledge of an orientation (rotational angle) of the sensor, e.g. an ultrasound image sensor, during an intravascular pull back procedure. Thus, it is possible to obtain, for each captured image during pull back, a measure of rotation angle of the sensor, e.g. referred to a reference position. Hereby, a more meaningful interpretation of an image is possible, and a more meaningful comparison between two images captured at different positions is possible, since it is possible to rotationally align the images even though they may be captured with different orientations of the sensor.

Furthermore, the individual images captured at respective longitudinal positions, e.g. during pull back procedure, can be combined into a combined image by aligning the plurality of images with respect to said data indicative of orientation of the sensor. Hereby, it is possible to provide a combined image which takes into account the different rotational orientation of the sensor during the pull back procedure, and therefore rotational mis-alignment between subsequent images in the combined image can be eliminated or at least reduced. Hereby, it is possible to provide a longitudinal view, i.e. an image of the interior of a blood vessel wall, with an improved quality without distortion caused by rotational misalignment, thereby providing a physician with an image with an improved diagnostic value. The device is advantageous for use in various types of devices with different types of sensors, e.g. in IVUS catheters. By use of OSS technique, the location (position) of the sensor, e.g. referring to a reference position, can also be determined, thus eliminating the need for X-ray for determination the location of the sensor during capturing of each image.

The invention is based on the insight, that in addition to a 3D shape, it is possible to provide optical information from an OSS fiber to allow determination of an orientation (i.e. twist or rotational angle) of the elongated device at the longitudional position where the sensor is positioned. This can be done in several ways by selecting a suitable position of the OSS fiber in or on the elongated device relative to the sensor position, and by selection of a proper calculation algorithms, as will be further explained below.

OSS is known to be able to reconstruct a 3D shape of an elongated object by integration of an optical fiber with optical shape sensing elements in such a device. This is possible by optical interrogating the optical fiber e.g. with optical shape sensing elements by means of Fiber Bragg Gratings or Rayleigh based elements. This can be done in real time which may be useful for visualization of the reconstructed 3D shape e.g. within medical applications as navigational guidance for elongated interventional medical devices. Thus, in this case, the optical fiber can be utilized in addition for navigational guidance during insertion of the elongated interventional, e.g. into a blood vessel to be examined.

It is to be understood the OSS properties of the optical fiber can be obtained in various ways, as known by the skilled persons. E.g. the optical interrogation may use Rayleigh scattering, or make use of Fiber Bragg Gratings written into the fiber. The method for optical interrogation of the optical shape sensing properties may be performed in several ways, such as also known by the skilled person. In some embodiments, the optical fiber only has optical shape sensing properties in a part of its length. Especially, the optical fiber only has shape sensing properties along a distal part of its longitudinal extension. Thus, a low cost optical fiber can be used, which only has optical shape sensing properties in a limited part of its length, where it is necessary in a given application. Especially, only a distal portion of the optical fiber length may be important to be shape sensed, e.g. to identify an orientation of a tip position of the longitudinal device, or at least to precisely identify a distal position of the optical fiber which may be used for estimating the tip position of the longitudinal device.

By 'an optical fiber with optical shape sensing properties' is understood to cover an OSS fiber consisting of a single optical fiber with OSS properties, as well as it covers variants in the form of a multi-core cable comprising several optical fiber cores each with OSS properties, e.g. multi-core variants comprising two, three, or more single optical fiber cores.

By 'material present perpendicular to a longitudinal axis of the elongated device' it so be understood that at least the sensor is capable of providing information regarding characteristics of material, e.g. a vessel wall, to the side of the elongated device. It is to be understood that the sensor may further be capable of providing more information than this. The sensor may cover only a limited angular window, or the sensor (or a plurality of individual sensors) may be arranged to cover a full cross sectional image, i.e. a 360° image.

In the following, a number of embodiments will be defined.

A portion of the optical fiber may be positioned with a non-zero angle relative to a longitudinal axis of the elongated device, at a longitudinal position near or at the longitudinal position where the sensor is positioned. This will allow an optical feature which by means of optical interrogation can be used to identify a deviation from the longitudinal axis of the elongated device which is caused by a rotation (twist). Especially, a portion of the optical fiber may be positioned perpendicular to a longitudinal axis of the elongated device, at a longitudinal position near or at the longitudinal position where the sensor is positioned. With a suitable portion, e.g. between 0.5 mm and 1.5 mm, of the optical fiber positioned perpendicular to the longitudinal axis of the elongated device, a clear indication of orientation of this part of the optical fiber is detectable, since this part will be point away from the longitudinal axis of the elongated device. Still, perpendicular optical fiber will allow for a total thickness of the device to be acceptable for intervascular use. More specifically, the tip portion of the optical fiber may be positioned perpendicular to a longitudinal axis of the elongated device, at a longitudinal position near or at the longitudinal position where the sensor is positioned. The tip portion may especially be "hook" shaped and placed at the tip or even slightly in front of a tip of the elongated device, just ahead of where the sensor is positioned.

In some embodiments, a portion of the optical fiber is positioned parallel to a longitudinal axis of the longitudinal device. Especially, its tip portion may end at a longitudinal position near or at the longitudinal position where the sensor is positioned. The twist angle at the tip portion, and thus the orientation of the sensor, can thus be determined by optical interrogation.

The orientation may be determined as a rotational angle relative to an orientation determined for a reference position defining also a reference orientation in 3D space.

A portion of the optical fiber may be attached to a portion of the elongated device, so as to allow tracking of a three-dimensional shape of said portion of the elongated device. Especially, the optical fiber may be arranged to optically shape sense a predetermined distal portion of a catheter, e.g. by the optical fiber being arranged along the center of the elongated device, or at least following the longitudinal axis of the elongated device. This allows navigational guidance in 3D space during insertion of the interventional device, and further it allows longitudinal tracking when capturing intravascular images.

The sensor can be many different types of sensors arranged for providing different types of images of material present to a side of the elongated device where the sensor is positioned. Especially, the sensor may comprise at least one of: an ultrasound sensor (UV), an optical coherence tomography (OCT) sensor, a near-infrared spectroscopy (NIRS) sensor, and a fractional flow reserve (FFR) sensor. Especially, the sensor may be arranged to capture at least a two-dimensional image covering at least an angular window perpendicular to the longitudinal axis of the elongated device. E.g. the sensor may be able to cover an entire cross-sectional view, i.e. a 360° angular window. However, other sensors may be able to provide a smaller angular window, e.g. between 90° or 180°. In all cases, to provide a longitudinal view, the orientational alignment of a stack of images is important to be able to provide a combined image of a longitudinal portion of e.g. a blood vessel wall without severe distortion due to different (unknown) orientations of the individual images captured at different longitudinal positions inside the blood vessel, e.g. during a pull back procedure.

The optical fiber may comprise at least one optical fiber core arranged so as to allow determination of a twist for the optical fiber. Especially, the optical fiber may comprise a plurality of single optical fiber cores arranged so as to allow determination of a twist for the optical fiber. E.g. the optical fiber may comprise a cable incorporating three optical fiber cores spatially arranged within the cable to allow computation of twist, i.e. rotational angle of the cable between nodes at different longitudinal positions of the cable.

It is to be understood that the optical fiber may be attached to the elongated device in various ways, e.g. the optical fiber may be attached to an outside part of the elongated device, however it may be preferred that the optical fiber is arranged within the elongated device, e.g. except for the tip portion of the optical fiber. The elongated device may be formed by a structural element, such as made of a material known in the art of interventional devices.

In a special embodiment, the interventional device is an intravascular catheter, e.g. arranged for intravascular imaging, e.g. an IVUS catheter. Especially, the interventional device may be an intravascular catheter arranged for imaging of human blood vessels.

In a second aspect, the invention provides an interventional imaging system comprising:

- an interventional device comprising

an elongated device arranged for interventional application,

- an optical fiber with optical shape sensing properties along at least a part of its longitudinal extension, wherein the optical fiber is attached to at least a part of the elongated device and a portion of the optical fiber is positioned with a non-zero angle relative to a longitudinal axis of the elongated device, at or near a longitudinal position of the elongated device where the sensor is positioned, so as to allow optical tracking of rotational angle orientation of the sensor, and

an optical console system arranged for:

optically interrogating the optical shape sensing properties of the optical fiber, and

determining an orientation of the sensor in response to said optical

interrogation.

Such system allows viewing of e.g. cross sectional images obtained with the sensor inside a human blood vessel. With the known orientation of the sensor, it is possible to visualize the image to the user with a correct orientation, thereby providing a more meaningful information to the user. This may be even more pronounced if two images captured at different longitudinal positions in the vessel should be compared, since here the orientation information allows correct rotational alignment of the two images, thus allowing a more meaningful comparison of the two images.

Preferred embodiments of the system enables determining a reference orientation. Thus, preferably an orientation of the sensor is measured this reference orientation. The reference orientation can be chosen by registering a coordinate system of the OSS fiber and the interventional device technology prior to using the interventional device, i.e. prior to the data acquisition using the sensor. Alternatively or additionally, a reference orientation can be chosen by a user input, and/or by selecting the first obtained image frame as having a reference orientation, and the subsequently obtained image frames are the referred to this reference orientation.

In one embodiment, after a single image has been obtained with the sensor, e.g. an intravascular image, a reference orientation is selected for the image, e.g. selected by the user. Such single image may be aligned and overlaid on an image obtained with another modality, e.g. an X-ray image. This may provide additional information to a physician.

In one embodiment, the system further comprises:

an imaging system arranged for:

collecting a plurality of images from the sensor at respective points in time, and storing for each image data indicative of orientation of the sensor in response to optical interrogation of the optical fiber, and

generating a combined image in response to said plurality of images by aligning the plurality of images with respect to said data indicative of orientation of the sensor.

In one embodiment, the system is used to generate a so-called L-view based on a plurality of images from the sensor, and the orientational information for all images used in this L-view allows a correct orientational alignment of the images. The user can additionally select a new L-view referring to a different orientational angle, and this is provided by rotating/shifting all the stacked images forming the L-view. This may provide additional anatomical information to a physician, since in case of intravascular image data, this will allow the physician to rotate the cross-sectional view of the blood vessel wall.

Such system embodiment allows generation of a longitudinal view of a vessel wall without disturbing effects caused by different orientations of the sensor when capturing the individual image frames. The orientation information for each individual image allows correct rotational alignment of the images to produce a longitudinal view with improved image quality.

Still further, the optical console system may be arranged to determine a measure of three-dimensional location of the sensor in response to said optical interrogation of the optical fiber, and wherein the imaging system may be arranged for generating said combined image in accordance with said measure of three-dimensional location of the sensor for each of the plurality of images. In such embodiment, both orientation and position are provided by means of OSS technique, thus eliminating the need for X-ray images.

In a third aspect, the invention provides a method for interventional imaging, the method comprising:

- a) providing an elongated device arranged for interventional application with a sensor positioned on a distal portion of the elongated device, wherein the sensor is arranged to sense characteristics of material present perpendicular to a longitudinal axis of the elongated device, and wherein an optical fiber with optical shape sensing properties along at least a part of its longitudinal extension is attached to at least a part of the elongated device and a portion of the optical fiber is positioned with a non-zero angle relative to a longitudinal axis of the elongated device, at or near a longitudinal position of the elongated device where the sensor is positioned,

b) capturing an image with the sensor,

c) optically interrogating the optical fiber, and

- d) calculating a measure of rotational angle orientation of the sensor in response to the optical interrogation of the optical fiber.

In one embodiment, the method further comprises

e) repeating steps b), c) and d) to arrive at a plurality of images and a corresponding plurality of measures of orientation of the sensor, and

- f) combining the plurality of images into a combined image by aligning the plurality of images with respect to said measures of orientation of the sensor.

In a fourth aspect, the invention provides a computer executable program code adapted to control an optical console system forming part of an interventional imaging system comprising a sensor positioned on a distal portion of an interventional longitudinal device, wherein the program code is adapted to:

capture an image with the sensor representative of characteristics of material present perpendicular to a longitudinal axis of the longitudinal device,

optically interrogate optical shape sensing properties of an optical fiber connected to the optical console system and attached to the longitudinal device, and

- calculate an orientation of the sensor in response to said optical interrogation in accordance with a predetermined algorithm.

Such computer executable program code is thus capable of performing the steps of the method according to the third aspect which can be implemented in software, e.g. as an add-on or modification of the existing OSS software. The program code may be further arranged to generate a combined image being combined from a plurality of captured images aligned in accordance with correspondingly calculated orientations of the sensor.

The computer executable program code may especially be present on a non- transitory computer readable storage medium, or it may be loaded into memory of a processor system arranged to execute the program code.

It is appreciated that the same advantages and embodiments of the first aspect apply as well for the second, third, and fourth aspects. In general the first, second, third, and fourth aspects may be combined and coupled in any way possible within the scope of the invention. These and other aspects, features and/or advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

Fig. 1A illustrates a tip of an interventional device embodiment where an OSS fiber is provided near a longitudinal position of the elongated device where the sensor is positioned,

Fig. IB illustrates a tip of an interventional device embodiment where an OSS fiber is provided with a hook-shaped tip portion to identify a rotational angle at the position of a catheter where the image sensor resides,

Fig. 2 illustrates a cross sectional sketch of a three-core OSS fiber which can be used for determination of twist,

Fig. 3 illustrates an intravascular catheter positioned in a curved blood vessel,

Fig. 4A illustrates an X-ray image of a blood vessel, and corresponding grayscale IVUS data sets are shown: cross-sectional IVUS image is given in FIG. 4C, while longitudinal view (L-view), which is constructed by stacking up the cross-sectional images in single axis, is given in FIG. 4B,

Fig. 5 illustrates a block diagram of an imaging system embodiment with a catheter with optical shape sensing properties according to the invention, and

Fig. 6 illustrates a diagram of steps of an imaging method embodiment. DESCRIPTION OF EMBODIMENTS

Figs. 1A and IB illustrate sketches of a distal portion of interventional device embodiments in the form of a catheter C with different configurations of optical shape sensing fiber OSF to provide orientational information of the image sensor I_S.

Both of Figs. 1 A and IB illustrate an interventional device in the form of a catheter C, e.g. an IVUS catheter. An image sensor I_S in the form of an ultrasonic sensor, is arranged on a distal portion of the flexible elongated structural element SE forming the core of the catheter C. The image sensor I_S has a reference direction perpendicular to the longitudinal axis of the elongated device SE, since it is arranged to provide ultrasonic images of a cross section of a blood vessel. When inserted into a curved blood vessel, the flexible catheter C bends to follow the curve of the blood vessel, and further the catheter C will twist, thus changing the orientation or rotational angle of the image sensor I_S relative to proximal end of the catheter C (not shown). Thus, in general the orientation of the image sensor I_S is unknown, e.g. if the location of the tip of the catheter C is tracked by means of an X-ray image.

In the embodiment of Fig. 1A, an OSS fiber OSF is arranged along the longitudinal extension of the structural element SE with its fiber tip FT positioned near the longitudinal position of the structural element SE where the image sensor I_S is located. At least the optical fiber OSF should be attached to the structural element SE to follow its bending and twisting in the area wherein the image sensor I_S is positioned. In principle a single core OSS fiber OSF may be used in this embodiment, however it is also possible to use a multi-core OSS fiber, e.g. a 3-core OSS fiber. Hereby, it is possible by means of optical interrogation techniques to derive a measure of orientation of the fiber tip FT, and thus the image sensor I_S, e.g. relative to a proximal end of the catheter C. Calculation techniques to derive the orientation (rotational angle) will be explained below. An advantage of this embodiment is that it is easy to provide an interventional device C with a small overall cross sectional area, thus allowing the catheter C to be used also in rather narrow human blood vessels.

In the embodiment of Fig. IB, the tip portion FT of the OSS fiber OSF before is bent to provide a tip portion FT which is perpendicular to the longitudinal axis of the elongated structural element SE of the catheter C. Hereby, it is possible to use OSS technique to track both the location and the orientation of the point of the catheter C where the image sensor I_S is positioned, since the hook shaped tip portion FT provides a distinct feature to allow both tracking of location and orientation of the tip of the optical fiber OSF. Hereby, a measure of orientation of the image sensor I_S is obtained. At least the optical fiber OSF should be attached to the structural element SE of the catheter C to follow its bending and twisting in the area wherein the image sensor I_S is positioned. In principle a single core OSS fiber OSF may be used in this embodiment, however it is also possible to use a multi- core OSS fiber.

The embodiment of Fig. IB is based on detection of a known shape or curvature of the fiber tip FT of the OSS fiber OSF. It is to be understood that it may be curved in other distinct and predetermined ways than the shown perpendicularly bent shaped tip portion FT. An alternative way of forming the identifiable feature FT of the optical fiber OSF can be a semi circular shape that surrounds the sensor I_S and has the sensor I_S in its center. More alternatively, the optical fiber OSF can be placed at the distal end of the elongated structural element SE of the catheter C in order not to affect the signals of the imaging sensor I_S, e.g. in the form of an ultrasonic transducer.

The crucial point is to provide an identifiable shape of the optical fiber OSF that can be identified by optical interrogation, and thus allow determination of location as well as orientation (rotational angle) of the elongated structural element SE, and thus the interventional device C, at the longitudinal position where the sensor I_S is positioned. In the example shown in FIG. IB, the tip part FT of the optical fiber OSF serves to provide the optically identifiable feature, it may be other parts of the optical fiber OSF that provide this identifiable feature that serves to provide information regarding position and orientation of the sensor I_S. In the example in FIG. IB, the tip part FT of the optical fiber OSF points in the direction perpendicular to the longitudinal axis of the elongated structural element SE of the catheter C, where the image sensor I_S is positioned. However, the tip part FT may point in other directions different from where the sensor I_S is positioned, since the crucial point regarding proper angular alignment of images from the sensor I_S is to provide a known angular position of each image frame in relation to a known reference.

In the embodiment of Fig. IB, the total thickness of the interventional device C puts a limit to the maximum size allowed for the optically identifiable feature FT of the optical fiber OSF, e.g. an IVUS device arranged for narrow blood vessels. Large features are easier to optically identify, but it has been found in tests that it is possible to identify features FT having a curvature below 10 mm, such as features FT having a size of 5-10 mm, such as features FT having a size of 1-5 mm, and even features FT below 1 mm. Thus, the principle behind the embodiment of FIG. 1 can be applied in thin interventional devices C suitable for use in blood vessels, even for use in a variety of human blood vessels. The smaller the feature FT, the more sensitive the optical identification is to noise, and thus proper filtering techniques are preferably applied in the signal processing of the optical interrogation of the optical fiber OSF.

Using very small optical features FT, the rotational angle may be possible to detect only with a limited precision, however still with an angular precision of such as 10°- 20°, or even poorer, a valuable orientational information may be obtained that allows improved quality in the following alignment and combination of image frames obtained with the sensor I_S, e.g. obtained in a pull back procedure. Applying filtering steps, which will be explained more below, it is possible to detect bending, twist, curvature values that allow computation of rotation angle for each node along the catheter C. Because of noise and other constraints, these parameters may be noisy and may not be accurate. However, if the optical feature FT, i.e. the shape and/or curvature of the optical fiber OSF to detect, is known beforehand, reliable measurements can be obtained that enable the use of the fixed shape information of the FT to compute the rotation angle more accurately, and thus knowledge of orientation of the sensor I_S is provided.

The signal processing may comprise a filtering step that utilizes rotation information from previous time instant(s). As smooth changes can be expected in the values of these parameters, temporal filtering can be used to get better estimates of the rotation angles.

In other embodiments, it is possible to determine orientation, i.e. rotation angle, by means of optical interrogation of an optical fiber arranged along the longitudinal axis of the elongated device, i.e. without the need for a portion of the optical fiber being perpendicular to the longitudinal axis of the elongated device. This can be done with an optical fiber having multiple cores, e.g. 3 cores. Such further embodiments will be explained in the following. It is to be understood, that these embodiments can be combined, if desired, with the principle embodiment explained in connection with both of Figs. 1 A and IB, in case even further orientational precision is required. E.g. the optical fiber OSF of FIG. 1 A may be a single core or a multi-core optical fiber OSF.

Fig. 2 shows a cross-section of an optical fiber in the form of a multi-core OSS cable comprising 3 optical fiber cores CRl, CR2, CR3 along an x-axis, and arranged mutually displaced in the yz -plane. In FIG. 2, the optical fiber cores CRl, CR2, CR3 are shown an arbitrary bending direction 0_b. OSS technology uses strain measurements at individual nodes along each optical fiber core CRl, CR2, CR3 to compute shape. This allows to compensate for the effects of temperature-induced changes and to resolve multiple angles in 3D.

In each node, it is possible to relate the bending, twisting, and curvature of the physical fiber with the strain by using the geometrical configuration already known and by using the Frenet-Serret formulas, as known by the skilled person. See e.g. "Shape sensing using multi-fiber optic cable and parametric curve solutions ", J. P. Moore & M.D. Rogge, Optics Express, 30 January 2012, Vol. 20, No. 3, pp. 2967-2973, as well as "Spatially continuous six degree of freedom position and orientation sensor", L. Danisch, K. Englehart & A. Trivett, Sensor Review, Vol. 19 Iss: 2, pp.106 - 112. These values are initially only computed at the nodes of the fiber. To calculate the values of these parameters between the nodes, interpolation methods, such as splines, are used. Having all these parameters, it is possible to compute the rotation angle around the x-, y-, and z-axes, see e.g. the above- mentioned papers. Because the position of the sensor, e.g. ultrasonic transducer, it is known which nodes correspond to the sensor location. In order to remove noise in measurements, data can be filtered, and estimate the rotation angle by using combination of filtered measurements. It can be considered to use median filtering or averaging of the bending, twist, and curvature values. In a possible further filtering step, it is possible to use the rotation information from the previous time instant(s). As smooth changes in the values of these parameters is expected, temporal filtering can be used to get even better estimates of the rotation angles.

Using a plurality of OSS sensors, e.g. in the form of two or three, or even more separate OSS fibers, may be used to improve rotational tracking accuracy. This principle can be used both for the embodiments in Figs. 1A and IB, and the embodiment in Fig. 2. In the embodiment of FIG. IB, a plurality of OSS fibers may be placed adjacent to each other in or on the catheter C, and each having respective curvature or bend features FT to allow improved accuracy in the determination of orientation angle. Thus, even though the size of the feature FT for each single optical fiber is small, the OSS results can be used in the signal processing to improve rotational tracking accuracy by utilizing the spatial redundancy obtained by using several separate OSS fibers.

The signal processing for rotation angle can use the combination of estimates from the plurality of separate OSS fibers or sensors, and different methods. E.g. angle estimations can be averaged to find the final rotation angle estimate.

In addition to OSS-based estimation of orientation (rotation angle), image- based refinement of rotation angle can be considered for improvement of the orientational precision that can be obtained from the OSS system. For example, a first estimated rotation angle may be obtained from the OSS system, e.g. an OSS system as one of or a combination of the embodiments described above. Then, image data from the sensor I_S, e.g. from an IVUS device, is used to find the best rotation angle within the estimate coming from the OSS system. Thus, image features are used as matching metrics to evaluate the quality of the match.

Fig. 3 illustrates to the left a catheter C arranged insides a curved blood vessel VS, and to the right cross sectional views are seen at two longitudinal positions xl and x2. Intravascular technologies that provide information about the internal structure of the vessels are evolved as a complementary method to the standard coronary angiography. Angiography images depict the lumen whereas intravascular imaging techniques, e.g. IVUS, allows analyzing vessel VS wall and plaque. However, IVUS provides localized information and lacks the global information. For the global information, co-registration techniques are in use.

Moreover, IVUS does not provide a geometrically correct 3D representation of the vessel VS as the catheter C also moves with a rotational angle during the pullback. This is illustrated in FIG. 3, since at position xl, the catheter C is positioned close to one angular part of the vessel VS wall, whereas at position x2, the catheter C is positioned close to another angular part of the vessel VS wall. Different effects cause rotational movement of the catheter C such as bending of the catheter C due to vessel VS curvature, heart motion, etc. Thus, the orientation of the sensor during capturing of image frames is different, resulting in generated images that are not centered and aligned as will be shown.

Figs. 4A, 4B, and 4C illustrate an example of co-registered X-ray image of a human blood vessel VS and IVUS data sets. The IVUS catheter has been used in a pull-back procedure to examine the vessel VS wall, and markers xl and x2 indicated two different longitudinal positions. A cross-sectional IVUS image within this segment is shown in FIG. 4C. Fig. 4B illustrates the longitudinal view (L-view) of this defined segment with the corresponding markers xl and x2. The L-view gives an oversimplification of the defined vessel segment since it is constructed by stacking up the cross- sectional IVUS images on a single axis. Due to the simplified view of the vessel structure, curvature info of the vessel is missing. Moreover, this view lacks axial twisting of the catheter during the pullback and therefore, orientation of the cross-sectional images is unknown, and this may provide difficulties in medically interpreting the combined image.

Solutions to this problem, such as post-processing and back-projecting each IVUS frame cross-sections into the X-ray angio image, have been proposed. However, these solutions are prone to erroneous results in the local orientation. Moreover, these solutions cannot provide the global (axial) orientation of the resulting frame set. Additionally, prior art 3D/longitudinal reconstruction systems are based on automatic pull-back with a certain speed and single direction in order to have constructions close to real vessel VS structure.

With the interventional device and the method according to the present invention, manual pull-back is possible as well, and still the OSS technique can provide orientational information of the image sensor at each captured image frame, thus allowing a calibration or alignment of the image frames, so as to provide a clearer combined image of a curved vessel VS wall. This allows better possibilities for physicians in providing a meaningful medical interpretation of such images.

Fig. 5 shows an interventional imaging system embodiment. An elongated interventional device C_OSF comprising an elongated device arranged for interventional application, e.g. an IVUS catheter, having a sensor I_S positioned on a distal portion of the elongated device. The sensor I_S may be an ultrasonic transducer arranged to sense characteristics of a blood vessel wall present to the side of the catheter C_OSF. An optical fiber with OSS properties, is integrated to follow the catheter C_OSF. This optical fiber is attached to at least a part of the catheter C_OSF at or near a longitudinal position of the catheter C_OSF where the sensor I_S is positioned, so as to allow optical tracking of an orientation of the sensor I_S, i.e. a rotational angle relative to a longitudinal axis of the catheter C_OSF.

The OSS fiber is connected to an optical console system OSS_C arranged for optically interrogating the OSS properties of the optical fiber, and for determining an orientation 0_D of the sensor I_S in response to said optical interrogation.

The system further comprises a unit CS_I arranged to collect a plurality of cross sectional images from the sensor I_S at respective points in time, and a processor P which receives these images, and stores for each image, data 0_D indicative of orientation of the sensor I_S, received from the optical console OSS_C. Finally, the processor generates a combined image S_CS_I in response to said plurality of images by aligning the plurality of images with respect to said data 0_D indicative of orientation of the sensor I_S. However, it is to be understood that the system may further use single images and still utilize the orientation data 0_D to provide a visualization of one single cross-sectional image which is correct with respect to a reference orientation.

The optical console system OSS_C may further be arranged to determine a measure of three-dimensional location, or longitudinal position in a blood vessel, of the sensor I_S by means of optical interrogation of the optical fiber, and wherein the processor is then arranged for generating said combined image in accordance with said measure of three- dimensional location of the sensor I_S for each of the plurality of images.

Fig. 6 illustrates steps of a method embodiment in the form of a specific interventional imaging method, namely an intravascular imaging method, e.g. based on data from an catheter C. First step is to provide (P_IV_OSF) an elongated device arranged for interventional application, e.g. an IVUS catheter, with a sensor (e.g. ultrasonic transducer) positioned on a distal portion of the elongated device, wherein the sensor is arranged to sense characteristics of material present perpendicular to a longitudinal axis of the elongated device, and wherein an optical fiber with optical shape sensing properties along at least a part of its longitudinal extension is attached to at least a part of the elongated device at or near a longitudinal position of the elongated device where the sensor is positioned. Next step is to capture C_I an image with the sensor, and to optically interrogate I_OSF the optical fiber, and calculate a measure of orientation C_0_L of the sensor in response to the optical interrogation of the optical fiber. The sub steps C_I, I_OSF, C_0_L are then repeated N times, e.g. during a pull-back procedure, to obtain a set of data with a plurality of images (obtained at respective longitudinal position in a blood vessel), and a corresponding plurality of measures of orientation of the sensor. Then the plurality of images are combined CM_I, e.g. stacked, into a combined image by aligning the plurality of images with respect to said measures of orientation of the sensor. Hereby, a combined longitudinal image of the interior of a blood vessel can be obtained without distortion due to rotational misalignment of the sensor at the catheter, due to curvature of the blood vessel. Still further, optical interrogation of the optical fiber is further used to provide precise and corresponding 3D position information of the sensor for each image frame.

Thus, after a pull-back procedure, a post-processing uses the stored orientation and position information to align e.g. IVUS image frames with respect to the previous frame and/or a reference orientation, which can be a specified angle or which can be the angle at a certain anatomical location. Accurate alignment of IVUS frames with respect to each other provides an accurate local orientation, and this data can be used to stack the IVUS frames on a single-axis to construct a so-called L-view. The same orientation information of each IVUS image can also be used in relation to the X-ray image in order to display the cross-sectional images in the accurate x-y alignment on the X-ray image. By this, more accurate vessel morphology and lesion location information can be displayed to the physicians in a co- registration system. Especially, the invention is suitable for IVUS longitudinal construction, i.e. stacking of a plurality of images, for X-ray IVUS Co-registration (x-y axis alignment information), i.e. orientation alignment for visualization of single cross sectional images, and for 3D reconstruction of coronary arteries from fusion of IVUS/OCT and X-ray angiography images. However, it is to be understood that the interventional device, the imaging system, and the method according to the invention has a number of applications within medical or within non-medical applications.

To sum up, the invention provides an interventional device, e.g. an intravascular catheter such as IVUS or OCT, by using an optical shape sensor (OSS)-based mechanism at the time of the intravascular image acquisition. An OSS fiber with a predetermined shape is merged with the intravascular catheter and the predetermined shape of OSS fiber has OSS identifiable features positioned to allow optical determination of orientation (rotational angle relative to a longitudinal axis of the catheter) at the longitudinal position of the catheter where the imaging sensor resides. The predetermined shape of the OSS-device indicates an angle of rotation of a predetermined reference orientation of the catheter relative to an OSS sensor during navigation/pullback of the intravascular catheter through a vessel. Alternatively, or additionally, a multi-core OSS cable can be used, which allows calculation of twist angle between two nodes of the OSS cable, and thus a measure of rotational angle. With such a system, it is possible to get rotational angle (orientation) information gathered for each intravascular image. Such orientation information can be used to visualize one single image with correct angular alignment. Further, by calibrating individual images of a pull-back sequence with respect to the gathered rotational angle and position information, it is possible to orient the cross-sectional intravascular data on an X-ray image with improved accuracy that may have better diagnostic value.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. 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. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless

telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. An interventional device (C) comprising:

an elongated device (SE) arranged for interventional application, a sensor (I_S) positioned on a distal portion of the elongated device (SE), wherein the sensor (I_S) is arranged to sense characteristics of material present perpendicular to a longitudinal axis of the elongated device (SE), and

an optical fiber (OSF) with optical shape sensing properties along at least a part of its longitudinal extension, wherein the optical fiber (OSF) is attached to at least a part of the elongated device (SE) and a portion of the optical fiber is positioned with a non-zero angle relative to a longitudinal axis of the elongated device, at or near a longitudinal position of the elongated device (SE) where the sensor (I_S) is positioned, so as to allow optical tracking of rotational angle orientation of the sensor (I_S).

2. Interventional device (C) according to claim 1, wherein a portion of the optical fiber (OSF) is positioned parallel to a longitudinal axis of the elongated device (SE), at a longitudinal position near or at the longitudinal position where the sensor (I_S) is positioned.

3. Interventional device (C) according to claim 1, wherein a portion (FT) of the optical fiber (OSF) is positioned perpendicular to a longitudinal axis of the elongated device (SE), at a longitudinal position near or at the longitudinal position where the sensor (I_S) is positioned.

4. Interventional device (C) according to claim 1, wherein a portion (FT) of the optical fiber (OSF) is shaped and positioned at a longitudinal position near or at the longitudinal position where the sensor (I_S) is positioned, so as to provide an optically recognizable feature by an optical interrogation of the optical fiber (OSF).

5. Interventional device (C) according to claim 1, wherein a portion of the optical fiber (OSF) is attached to a portion of the elongated device (SE), so as to allow tracking of a three-dimensional shape of said portion of the elongated device (SE).

6. Interventional device (C) according to claim 1, wherein the sensor (I_S) comprises at least one of: an ultrasound sensor, an optical coherence tomography sensor, a near-infrared spectroscopy sensor, and a fractional flow reserve sensor.

7. Interventional device (C) according to claim 1, wherein the optical fiber (OSF) comprises at least one optical fiber core arranged so as to allow determination of a twist for the optical fiber (OSF).

8. Interventional device (C) according to claim 7, wherein the optical fiber (OSF) comprises a plurality of optical fiber cores (CR1, CR2, CR3) arranged so as to allow determination of a twist for the optical fiber (OSF).

9. Interventional device (C) according to claim 1, wherein the interventional device is an intravascular catheter (C).

10. Interventional imaging system comprising:

an interventional device (C_OSF) comprising:

an elongated device arranged for interventional application,

- a sensor (I_S) positioned on a distal portion of the elongated device, wherein the sensor (I_S) is arranged to sense characteristics of material present perpendicular to a longitudinal axis of the elongated device, and

an optical fiber with optical shape sensing properties along at least a part of its longitudinal extension, wherein the optical fiber is attached to at least a part of the elongated device and a portion of the optical fiber is positioned with a non-zero angle relative to a longitudinal axis of the elongated device, at or near a longitudinal position of the elongated device where the sensor (I_S) is positioned, so as to allow optical tracking of rotational angle orientation of the sensor, and

an optical console system (OSS_C) arranged for:

- optically interrogating the optical shape sensing properties of the optical fiber, and

determining an orientation (0_D) of the sensor (I_S) in response to said optical interrogation.

11. Interventional imaging system according to claim 10, comprising:

an imaging system (CS_I, P) arranged for:

collecting a plurality of images from the sensor (I_S) at respective points in time, and storing for each image data indicative of orientation (0_D) of the sensor in response to optical interrogation of the optical fiber, and

generating a combined image (S_CS_I) in response to said plurality of images by aligning the plurality of images with respect to said data indicative of orientation (0_D) of the sensor (I_S).

12. Interventional imaging system according to claim 11, wherein the optical console system (OSS_C) is arranged to determine a measure of three-dimensional location of the sensor (I_S) in response to said optical interrogation of the optical fiber, and wherein the imaging system (CS_I, P) is arranged for generating said combined image (S_CS_I) in accordance with said measure of three-dimensional location of the sensor (I_S) for each of the plurality of images.

13. A method for interventional imaging, the method comprising:

a) providing (P_IV_OSF) an elongated device arranged for interventional application with a sensor positioned on a distal portion of the elongated device, wherein the sensor is arranged to sense characteristics of material present perpendicular to a longitudinal axis of the elongated device, and wherein an optical fiber with optical shape sensing properties along at least a part of its longitudinal extension is attached to at least a part of the elongated device and a portion of the optical fiber is positioned with a non-zero angle relative to a longitudinal axis of the elongated device, at or near a longitudinal position of the elongated device where the sensor is positioned,

b) capturing (C_I) an image with the sensor,

c) optically interrogating (I_OSF) the optical fiber, and

d) calculating a measure of rotational angle orientation (C_0) of the sensor in response to the optical interrogation of the optical fiber.

14. Method according to claim 13, comprising:

e) repeating steps b), c) and d) to arrive at a plurality of images and a corresponding plurality of measures of orientation of the sensor, and f) combining the plurality of images (CM_I) into a combined image by aligning the plurality of images with respect to said measures of orientation of the sensor.

15. A computer executable program code adapted to control an optical console system (P, OSS_C, CS_I) forming part of an interventional imaging system comprising a sensor (I_S) positioned on a distal portion of an interventional elongated device (C_OSF), wherein the program code is adapted to:

capture an image with the sensor I_S) representative of characteristics of material present perpendicular to a longitudinal axis of the elongated device (C_OSF), optically interrogate optical shape sensing properties of an optical fiber connected to the optical console system (OSS_C) and attached to the elongated device (C_OSF), and

calculate an orientation (0_D) of the sensor (I_S) in response to said optical interrogation in accordance with a predetermined algorithm.