FIELD OF THE INVENTION

The invention relates to a sensing apparatus, a sensing method and a sensing computer program for sensing an object. BACKGROUND OF THE INVENTION

The article "Acoustic radiation force impulse imaging of myocardial radiofrequency ablation: initial in vivo results" by B.J. Fahey et al., IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, volume 52, pages 631 to 641 (2005) discloses an ultrasound sensing apparatus for generating ultrasound images of cardiac tissue, while the cardiac tissue is compressed using acoustic radiation forces in a temporally modulated way. The ultrasound images are used to determine a stiffness measure of the cardiac tissue, wherein a property of the cardiac tissue, for instance, whether the cardiac tissue is healthy tissue or ablated tissue, is determined based on the stiffness measure. The compression of the cardiac tissue is provided by using an ultrasound pulse.

The level of compression generated by the ultrasound pulse is relatively low, which leads to a relatively low quality of determining local tissue displacements and, thus, of determining the stiffness measure. Since the property of the cardiac tissue is determined based on the stiffness measure, the low quality of determining the stiffness measure leads in turn also to a low quality determination of the property of the cardiac tissue.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a sensing apparatus, a sensing method and a sensing computer program for sensing an object by using ultrasound, wherein the quality of sensing the object can be improved.

In a first aspect of the present invention a sensing apparatus for sensing an object is presented, wherein the sensing apparatus comprises:

a fluid stream providing unit for providing a modulated fluid stream for compressing the object, an ultrasound unit for sending ultrasound into the compressed object, receiving ultrasound from the compressed object and generating an ultrasound signal based on the received ultrasound, and

a property determination unit for determining a property of the object based on the generated ultrasound signal.

Since a modulated fluid stream is used for compressing the object, the object can be compressed accurately as desired and with a relatively large level of compression, in particular, in comparison with the level of compression that can be generated by acoustic radiation forces. The generated ultrasound signal is therefore indicative of an object, which has been compressed relatively accurately in accordance with a desired compression and with a relatively large level of compression. Thus, the generated ultrasound signal can be used by the property determination unit for determining compression related information about the object like the stiffness of the object and for determining the property of the object based on the determined compression related information with improved quality.

The fluid stream providing unit can be adapted to compress the object directly by the modulated fluid stream, i.e. by directing the fluid stream directly onto the object to be compressed, and/or to compress the object indirectly by the modulated fluid stream, i.e. by abutting at least a part of the fluid stream providing unit against the object and by directing the fluid stream to a relatively fixed element like a relatively fixed wall such that the fluid stream providing unit is modulately pressed against the object by counterforces.

In an embodiment the property determination unit is adapted to determine a strain image from the ultrasound signal and to determine the property of the object from the strain image. The property determination unit can be adapted to determine the strain image in a known way. For instance, the property determination unit can be adapted to determine the strain image as disclosed in the article "A quantitative method for imaging the elasticity of biological tissues" by J. Ophir et al., Ultrasonic Imaging, volume 13, pages 111 to 134 (1991), which is herewith incorporated by reference.

It is preferred that the sensing apparatus further comprises an energy application unit for applying energy to the object, wherein the fluid stream providing unit is adapted to provide a cooling fluid stream as the fluid stream for cooling at least one of the energy application unit and the object. The fluid stream can therefore fulfill two functions, compressing the object in a modulated way and cooling at least one of the energy application unit and the object. This allows providing a relatively compact sensing apparatus, which does not necessarily need a first fluid stream for compressing the object and a second fluid stream for cooling the energy application unit and/or the object.

The ultrasound unit is preferentially adapted to send ultrasound into the compressed object, receive ultrasound from the compressed object and generate an ultrasound signal based on the received ultrasound, while the energy application unit applies energy to the object. Moreover, the energy application unit is preferentially an ablation unit for ablating tissue. In particular, the energy application unit is preferentially a radio frequency (RF) ablation electrode. However, the energy application unit can also be adapted to apply energy in another way. For instance, the energy application unit can be an optical or acoustical unit for applying optical or acoustic energy, in particular, high intensity focused ultrasound, to the object.

In a preferred embodiment the sensing apparatus is adapted to sense tissue during an ablation procedure for ablating the tissue, wherein the property determination unit is adapted to determine a dimension of ablated tissue as the property depending on the generated ultrasound signal. In particular, the property determination unit can be adapted to determine an ablation depth being the depth to which the tissue has been ablated, i.e. the depth of the created necrotic lesion. Thus, the property determination unit can be adapted to monitor the formation and progression of a necrotic area in the tissue due to ablation, especially in realtime. The tissue is preferentially cardiac tissue such that the sensing apparatus is preferentially adapted to sense cardiac tissue during an ablation procedure.

The property determination unit can also be used to determine gaps between consecutive ablation lesions created by applying the energy to cardiac tissue. If a gap has been identified, the gap can be closed by applying the energy to the cardiac tissue at the gap, thereby creating a non-conductive barrier in the cardiac tissue generated by a sequence of neighboring ablation lesions. The resulting electrical isolation of a part of the heart can stop cardiac arrhythmias.

In an embodiment the property determination unit is adapted to determine a spatial distribution of a stiffness measure from the strain image and to determine the property of the object, for instance, an ablation depth, based on the determined spatial distribution of the stiffness measure. For example, the property determination unit can comprise predefined assignments between stiffness measure value ranges and properties, wherein the property determination unit can be adapted to determine the property based on the determined stiffness measure and the predefined assignments, i.e. for instance predefined assignments between stiffness measure value ranges and necrotic tissue can be provided, wherein the distribution of the necrotic tissue and, thus, the ablation depth can be determined based on the actual spatial distribution of the stiffness measure obtained from the strain image and the predefined assignments. For the determination of a strain image from the generated ultrasound signal and for the determination of the spatial distribution of the stiffness measure based on the strain image known techniques can be used like the technique disclosed in the above mentioned article by J. Ophir et al.

It is further preferred that the ultrasound unit and the energy application unit are integrated into the fluid stream providing unit. The integrated ultrasound unit, energy application unit and fluid stream providing unit form preferentially a single sensing probe, thereby providing a relatively compact sensing probe.

It is also preferred that the fluid stream providing unit is configured for being inserted into a subject in which the object is present and for being forwarded to the object. In particular, the fluid stream providing unit preferentially comprises a catheter or a needle, wherein at the tip of the catheter or the needle fluid stream locations are present, from which one or several fluid streams emanate. For instance, the fluid stream providing unit can be adapted to be inserted into the heart of a person for compressing cardiac tissue. In a preferred embodiment also the ultrasound unit and the energy application unit are integrated in the catheter or needle such that they form a single sensing probe, wherein by inserting the sensing probe simultaneously the fluid stream providing unit, the ultrasound unit and the energy application unit can be inserted into the heart for ablating and simultaneously sensing cardiac tissue by the sensing probe.

If the fluid stream providing unit comprises a catheter or needle, for instance, if the fluid streams are provided by irrigation fluid streams leaving a catheter through irrigation openings, the catheter tip may be relatively heavy and/or rigid by locking a steering mechanism of the catheter. For example, pull wires inside the catheter can be fixed. The resulting inertia and/or rigidness of the catheter can ensure that the catheter tip does substantially not move, if the fluid streams are directed to the part of the object to be sensed.

In a further embodiment the fluid stream providing unit is adapted to provide one or several modulated fluid streams such that, if the one or several modulated fluid streams are provided in a homogeneous environment, counterforces caused by the one or several fluid streams meeting the homogeneous environment lead to a zero net force acting on the fluid stream providing unit. The counterforces can be generated, when the one or several fluid streams traverse or are blocked by the homogeneous environment. The fluid stream providing unit can be adapted to provide the spatial distribution of fluid stream locations on the sensing probe, from which fluid streams may emanate, the fluid stream direction of the respective fluid stream at the respective fluid stream location and the intensity of the fluid streams such that the net force acting on the fluid stream providing unit would be zero in a homogeneous environment. In particular, the fluid stream providing unit can be adapted to provide several modulated fluid streams emanating from several fluid stream locations, wherein the fluid stream locations are homogeneously distributed along a circumference of the fluid stream providing unit, for instance, along a circumference of a catheter tip of the fluid stream providing unit. This can lead to a reduced axial net force applied to the sensing probe in a substantially homogeneous environment, which can allow for a more facilitated holding of the sensing probe at a fixed position with respect to the object, thereby allowing the sensing apparatus to compress the object more accurately.

In a further preferred embodiment the fluid stream providing unit is adapted to provide one or several modulated fluid streams such that, if the one or several modulated fluid streams are provided in a homogeneous environment, counterforces caused by the one or several fluid streams meeting the homogeneous environment lead to a non-zero net force acting on the fluid stream providing unit. The counterforces can be generated, when the one or several fluid streams traverse or are blocked by the homogeneous environment. The fluid stream providing unit can be adapted to provide the spatial distribution of fluid stream locations on the sensing probe, from which fluid streams may emanate, the fluid stream direction of the respective fluid stream at the respective fluid stream location and the intensity of the fluid streams such that the net force acting on the fluid stream providing unit would be non-zero in a homogeneous environment. In particular, the fluid stream providing unit can be adapted to provide several modulated fluid streams emanating from several fluid stream locations, wherein the fluid stream locations are inhomogeneously distributed along a circumference of the fluid stream providing unit, for instance, along a circumference of a catheter tip of the fluid stream providing unit. The non-zero net force acting on the sensing probe presses the sensing probe against the object, thereby compressing the same in a modulated way.

The sensing apparatus can comprise a fluid stream controller for controlling the fluid stream. Moreover, the sensing apparatus can comprise a net force providing unit for providing a desired net force acting on the fluid stream providing unit, wherein the fluid stream controller can be adapted to control the fluid stream such that the desired net force acts on the fluid stream providing unit. In a preferred embodiment the fluid stream providing unit is adapted to provide several groups of fluid streams emanating from several fluid stream locations on the sensing probe, which are separately controllable. A group can comprise one or several fluid streams. Thus, for instance, different fluid stream locations can be connected by different fluid conduits like different tubes within the fluid stream providing unit to allow a separate control of the different fluid streams. In particular, single fluid stream locations or groups of fluid stream locations may be connected to the same conduit, in order to control the corresponding one or several fluid streams independently from other fluid streams. This control can be used to compress the object as desired by directly pointing the one or several fluid streams to the object in a desired controlled away or by indirectly compressing the object by controlling the fluid streams such that a desired net force acts on the fluid stream providing unit that abuts against the object for compressing the same.

The fluid stream providing unit can comprise a fluid stream location from which the fluid stream emanates, wherein the sensing apparatus can further comprises a modulating pump for pumping fluid to the fluid stream location in a modulated way and a conduit for guiding the fluid from the modulating pump to the fluid stream location.

Alternatively, the fluid stream providing unit can comprise a fluid stream location from which the fluid stream emanates, wherein the sensing apparatus can comprise a constant pump for pumping fluid to the fluid stream location in a non-modulated way, a conduit for guiding the fluid from the constant pump to the fluid stream location and a flow modulator for modulating the flow from the constant pump to the fluid stream location. The flow modulator is preferentially arranged between the constant pump and the fluid stream location. This allows providing a modulated fluid stream just by adding a flow modulator to a non- modulated fluid stream providing unit. Thus, for instance, the system can be provided, without exchanging a constant pump, which may already be present, by a modulating pump. An update of an existing fluid stream providing unit to one or several of the above mentioned fluid providing units may therefore be simplified.

In a further aspect of the present invention a sensing method for sensing an object is presented, wherein the sensing method comprises:

- providing a modulated fluid stream for compressing the object by a fluid stream providing unit,

sending ultrasound into the compressed object, receiving ultrasound from the compressed object and generating an ultrasound signal based on the received ultrasound by an ultrasound unit, and determining a property of the object based on the generated ultrasound signal by a property determination unit.

In a further aspect of the present invention a sensing computer program for sensing an object is presented, wherein the sensing computer program comprises program code means for causing a sensing apparatus as defined in claim 1 to carry out the steps of the sensing method as defined in claim 13, when the sensing computer program is run on a computer controlling the sensing apparatus.

It shall be understood that the sensing apparatus system of claim 1, the sensing method of claim 13 and the sensing computer program of claim 14 have similar and/or identical preferred embodiments as defined in the dependent claims.

It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims with the respective independent claim.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following drawings:

Fig. 1 shows schematically and exemplarily an embodiment of a sensing apparatus for sensing an object,

Figs. 2 and 3 show schematically and exemplarily an embodiment of a tip of a catheter of the sensing apparatus, and

Fig. 4 shows a flowchart exemplarily illustrating an embodiment of a sensing method for sensing an object. DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows schematically and exemplarily a sensing apparatus for sensing an object. The sensing apparatus 1 comprises a fluid stream providing unit 40 for providing a modulated fluid stream for compressing the object. The fluid stream providing unit 40 comprises a catheter 5 having a tip 6, which can be introduced into the heart 3 of a person 2, wherein in this embodiment the person 2 is lying on a table 4.

The tip 6 of the catheter 5 is shown in more detail in Fig. 2, wherein the upper part of Fig. 2 shows the tip 6 of the catheter 5 pressed against cardiac tissue 13 of the heart 3 and more of the environment and wherein the lower part of Fig. 2 shows an enlarged view of the tip 6 of the catheter 5 and less of the environment. In this embodiment the cardiac tissue 13 is the object to be sensed.

The tip 6 of the catheter 5 comprises several ultrasound units 7, i.e. several ultrasound transducers, for sending the ultrasound into the cardiac tissue 13, for receiving ultrasound from the compressed cardiac tissue 13 and for generating the ultrasound signal based on the received ultrasound. The catheter tip 6 further comprises an energy application unit 9 for applying energy to the cardiac tissue 13. The energy application unit 9 is an RF ablation electrode for applying RF energy to the cardiac tissue 13, in order to ablate the cardiac tissue 13. The catheter tip 6 also comprises several fluid stream locations 8, from which several modulated fluid streams can emanate. The fluid streams are preferentially used for cooling the RF ablation electrode 9 and/or the cardiac tissue 13 and for compressing the cardiac tissue.

The ultrasound units 7 preferentially send ultrasound into the compressed cardiac tissue 13, receive ultrasound from the compressed cardiac tissue 13 and generate an ultrasound signal based on the received ultrasound, while the RF ablation electrode 9 applies energy to the cardiac tissue 13. Thus, the sensing apparatus 1 is preferentially adapted to sense the cardiac tissue 13 during an ablation procedure, wherein a property determination unit 15 is adapted to determine a dimension of ablated tissue as the property depending on the generated ultrasound signal. In particular, the property determination unit 15 is adapted to determine an ablation depth being the depth to which the tissue has been ablated, i.e. the depth of the created necrotic lesion. The property determination unit 15 is therefore adapted to monitor the formation and progression of a necrotic area in the cardiac tissue 13 due to ablation, especially in realtime.

The property determination unit 15 is adapted to determine, i.e. to calculate, a strain image from the ultrasound signal and to determine the property of the object from the strain image. In particular, the property determination unit 15 is adapted to determine, especially to estimate, a spatial distribution of a stiffness measure based on the strain image and to determine the property of the object, i.e. in this embodiment the ablation depth, based on the determined spatial distribution of the stiffness measure. The property determination unit 15 comprises predefined assignments between stiffness measure value ranges and properties, wherein the property determination unit 15 is adapted to determine the property based on the determined stiffness measure and the predefined assignments. In this embodiment the property determination unit 15 comprises predefined assignments between stiffness measure value ranges and necrotic tissue, wherein the distribution of the necrotic tissue and, thus, the ablation depths can be determined based on the actual spatial distribution of the stiffness measure obtained from the strain image and the predefined assignments. The predefined assignments can be determined by a training procedure, wherein stiffness measure values are determined for cardiac tissue, of which it is known whether the cardiac tissue is healthy tissue or necrotic tissue, and wherein the assignments are predefined such that the resulting determined tissue property corresponds to the known tissue property.

The ultrasound units 7 and the RF ablation electrode 9 are integrated into the fluid stream providing unit 40, i.e. into the catheter 5. Thus, the integrated ultrasound units 7, the RF ablation electrode 9 and the fluid stream providing unit 40 form a single sensing probe being relatively compact, wherein the sensing probe is adapted to be inserted into the heart 3 of the person 2 and wherein by inserting the sensing probe simultaneously the fluid stream providing unit 40, the ultrasound units 7 and the energy application unit 9 are inserted for ablating, cooling and sensing the cardiac tissue 13 by the single sensing probe.

The fluid streams emanating from the fluid stream locations 8 can be used to compress the cardiac tissue 13 directly by directing the fluid streams directly onto the cardiac tissue 13 and/or to compress the cardiac tissue 13 indirectly by abutting the tip 6 of the catheter 5 against the cardiac tissue 13 and by directing the fluid streams to an opposite inner wall of the person 2, in particular, against an opposite cardiac wall of the person 2, such that the tip 6 of the catheter 5 is modulately pressed against the cardiac tissue 13 by

counterforces.

In this embodiment the fluid stream providing unit 40 is adapted to provide several modulated fluid streams such that, if the several modulated fluid streams are provided in a homogeneous environment, counterforces caused by the several fluid streams meeting the homogeneous environment lead to a non-zero net force acting on the fluid stream providing unit 40. Generally, the fluid stream providing unit can be adapted to provide the spatial distribution of fluid stream locations on the sensing probe, from which the fluid streams emanate, the fluid stream direction of the respective fluid stream at the respective fluid stream location and the intensity of the fluid streams such that the net force acting on the fluid stream providing unit would be non-zero in a homogeneous environment. In this embodiment the several fluid stream locations 8 are homogeneously distributed along a circumference of the tip 6 of the catheter 5. The catheter tip 6 can be brought into contact with the cardiac tissue such that at least one fluid stream is directed to the cardiac tissue for allowing the at least one fluid stream to periodically compress the cardiac tissue. During this compression the catheter is preferentially relatively rigid by locking, for instance, a steering mechanism of the catheter, for example, by fixing pull wires inside the catheter. Since the fluid streams are provided in a modulated way, the cardiac tissue 13 is also compressed in a modulated way.

Fig. 3 shows schematically and exemplarily further details of the tip 6 of the catheter 5 shown in Fig. 2. As can be seen in Fig. 3, the fluid stream locations 8 within the RF ablation electrode 9 are openings, which are connected with tubes 27 for guiding the fluid to the openings 8. The ultrasound units 7 are arranged in further openings 23 in the RF ablation electrode 9, wherein the ultrasound units 7 are electrically connected with an ultrasound control unit 14 by electrical connections 26 like insulated wires, and the RF ablation electrode 9 is electrically connected by an electrical connection 25, which may also be an insulated wire, with an RF source 16. Reference number 24 indicates an electrical insulator in Fig. 3.

The tubes 27 connect the fluid stream locations 8 with a constant pump 18 for pumping the fluid to the fluid stream locations 8, wherein between the constant pump 18 and the fluid stream locations 8 a flow modulator 17 is arranged for modulating the flow from the constant pump 18 to the fluid stream locations 8. In another embodiment the pump 18 can be a modulating pump for pumping the fluid to the fluid stream locations 8 in a modulated way, wherein in this case the flow modulator 17 is not needed. Due to the modulation the compression of the cardiac tissue is dynamically amended. The modulation can be provided, for instance, by switching the one or several fluid streams compressing the cardiac tissue periodically on and off.

The sensing apparatus 1 further comprises a fluid stream controller 19 for controlling the fluid stream and a net force providing unit 22 for providing a desired net force acting on the tip 6 of the catheter 5, wherein the fluid stream controller 19 is adapted to control the fluid streams emanating from the fluid stream locations 8 such that the desired net force acts on the tip 6 of the catheter 5. In this embodiment the net force providing unit 22 is an input unit allowing a user to input a value being indicative of the desired net force. For instance, the input unit 22 can be adapted to allow a user to input the frequency and/or the pumping pressure applied to the different tubes 27, wherein the fluid stream controller 19 can be adapted to control the pump 18 and the optional flow modulator 17 such that the desired modulation frequency and the desired pump pressure are obtained. Since in this embodiment each opening 8 is separately connected with the pump 18, the corresponding fluid streams are separately controllable. Thus, the fluid streams can be controlled such that a desired force compresses the cardiac tissue 13. The pump can comprise several sub pumps, wherein each sub pump is connected to a respective opening by a separate fluid conduit, in order to control the fluid streams emanating from the different openings independently from each other. Alternatively, all openings may be connected to the same pump, wherein the catheter tip can comprise a mechanism for closing and opening the fluid stream openings individually or simultaneously. For instance, a cylinder with holes may be rotatable arranged within the catheter tip such that the positions of the holes of the cylinder can be modified relative to the positions of the fluid stream openings in the catheter tip, in order to modify the fluid streams. In a further embodiment, the fluid stream openings are just connected to the same pump, which may be switched on and off periodically, in order to provide the modulated fluid streams.

A position detection system 30 can be used to detect the position of the tip 6 of the catheter 5 within the person 2. In this embodiment the position detection system is an x- ray fluoroscopy system, in particular, an x-ray C-arm system. The x-ray fluoroscopy system comprises an x-ray source 31 for generating x-rays 32 which traverse the person 2 on the table 4, wherein the x-rays 32, which have traversed the person 2, are detected by an x-ray detector 33. The x-ray fluoroscopy system 30 further comprises a fluoroscopy control unit 34 for controlling the x-ray source 31 and the x-ray detector 35. The x-ray detector 35 generates x-ray images of the person 2, which can be shown on a display unit 21. On the generated x- ray images the catheter tip 6 is visible within the person 2 such that the x-ray images show the position of the catheter tip 6 within the person 2.

On the display unit 21 also a generated ultrasound image, a strain image and/or a determined property of the cardiac tissue, in particular, the ablation depth, can be shown.

Referring again to Fig. 2, the catheter further comprises ring electrodes 10, 11, 12 for measuring electrical signals being indicative of the activity of the heart, in particular, for measuring electrocardiography signals. The ring electrodes 10, 11, 12 are electrically connected to an electrical sensing control unit 29 for controlling the electrical sensing via the ring electrodes 10, 11, 12. Also the measured electrical signals, in particular, measured electrocardiograms, can be shown on the display unit 21.

The sensing apparatus 1 further comprises a catheter navigation unit 20 for allowing the catheter 5, in particular, the catheter tip 6, to be navigated to a desired location within the person 2. The navigation unit 20 can be adapted to allow a user to navigate the catheter 5 completely by hand or semi-automatically. The catheter 5 comprises built-in guiding means (not shown in Fig. 1), which can be controlled by the catheter navigation unit 20. The catheter 5 can, for example, be steered and navigated by the use of steering wires, in order to guide the catheter tip 6 to a desired location within the person 2.

In the following an embodiment of a sensing method for sensing an object will exemplarily be described with reference to a flowchart shown in Fig. 4.

In step 101 a modulated fluid stream is provided by the fluid stream providing unit, in order to compress the object in a modulated way. For instance, a pulsed fluid stream can be provided for compressing cardiac tissue in a modulated way. In step 102 ultrasound is sent into the compressed object, ultrasound is received from the compressed object and an ultrasound signal is generated based on the received ultrasound by the ultrasound units. Steps 101 and 102 are performed simultaneously. In step 103 a property of the object is determined based on the generated ultrasound signal by the property determination unit. In particular, a strain image is determined from the ultrasound image, a stiffness measure is determined from the strain image and a property like an ablation depth is determined based on the determined stiffness measure. In step 104 at least the determined property is shown on the display unit. Steps 101 to 104 can be performed repeatedly during an ablation procedure such that during the ablation procedure the ablated tissue can be continuously monitored, in particular, in realtime.

Although in the above described embodiments the sensing apparatus is adapted to determine the ablation depth of cardiac tissue, the sensing apparatus can also be adapted to determine properties of other objects like a property of tissue of other parts of the person or like a property of a technical object.

Although in the embodiment described above with reference to Fig. 3 several tubes connect the openings in the ablation electrode with the pump, in other embodiments several openings can be connected via a single fluid conduit with the pump. Moreover, although in above described embodiments the ablation electrode comprises a certain number of homogeneously distributed openings along a circumference of the ablation electrode, in other embodiments the ablation electrode can also comprise another number of openings for allowing the fluid to leave the ablation electrode, which may be arranged differently. For instance, the ablation electrode may only comprise a single opening for allowing the fluid to leave the ablation electrode.

The fluid is preferentially water, in particular, saline. Moreover, the sensing apparatus is preferentially adapted to compress tissue due to a modulated water outlet of an open irrigation system in a cardiac ablation catheter. The irrigation fulfills two functions, cooling the tip of the catheter and compressing the tissue with the force of the jetting cooling water leaving the irrigation holes, i.e., for instance, the openings in the ablation electrode, in the catheter and generating strain in the cardiac tissue being preferentially myocardial tissue. This tissue strain is visualized preferentially by using known image processing tools.

The sensing apparatus is preferentially adapted to be used during a cardiac ablation, in particular, in order to prevent atrium fibrillation, wherein the catheter is inserted into cardiac spaces like the atrium and the ventricle. The tip of the catheter is equipped with an RF ablation electrode by which heat induced necrosis can be generated inside the myocardial wall. The RF ablation catheter has a fluid cooled tip, in particular, a water cooled tip. The cooling is done with a fluid, in particular, a liquid, via an open irrigation system connected to an external pump, wherein the cooling fluid leaves the catheter with high velocity and power such that it forms "jetting" streams of fluid.

The sensing apparatus preferentially uses the force of cooling water which is pushed out through irrigation channels of an ablation catheter against a cardiac wall.

Modulating, in particular switching on and off with a fixed or changing frequency, the cooling water jets results in a compressing force against the cardiac wall. This, in turn, results in an internal tissue strain which can be visualized with ultrasound.

The irrigation holes at the fluid stream locations can be placed in a regular spatial pattern. In a homogeneous medium this can result in no or only an axial net force that the outflow of the cooling fluid exerts on the catheter. However, if the catheter tip is in proximity of or in contact with the tissue to be ablated, this inhomogeneous environment may of course cause a net force. In another embodiment the design and placement of the irrigation holes can be such that the flow of the irrigation fluids through the irrigation holes can result in a net force on the tip even in a homogeneous medium, for instance, by placing most or all irrigation holes at one side of the tip and/or by directing the streams into specific directions. The catheter can comprise multiple irrigation channels that each service specific single or groups of irrigation holes, allowing a control over the direction of the net force that the outflow of cooling liquid exerts on the catheter. Preferentially, the fluid stream providing unit and the ultrasound unit are adapted such that a compression direction, in which the object is compressed, and an ultrasound sensing direction, in which the object is acoustically sensed, are substantially the same.

Although in the embodiment described above is reference to Figs. 2 and 3 the catheter tip comprises two ultrasound units, the sensing apparatus can comprise only one or more than two ultrasound units for generating an ultrasound signal, while the object to be monitored is compressed in a modulated way. 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 unit or device may fulfill 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 measures cannot be used to advantage.

Determinations like the determination of the property of the object performed by one or several units or devices can be performed by any other number of units or devices. The determinations and/or the control of the sensing apparatus in accordance with the sensing method can be implemented as program code means of a computer program and/or as dedicated hardware.

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.

The invention relates to a sensing apparatus for sensing an object, in particular, for sensing cardiac tissue during an ablation procedure. A fluid stream providing unit provides a modulated fluid stream for compressing the object, wherein an ultrasound unit sends ultrasound into the compressed object, receives ultrasound from the compressed object and generates an ultrasound signal based on the received ultrasound. A property

determination unit determines a property of the object based on the generated ultrasound signal. The modulated fluid stream can compress the object in a modulated way accurately as desired and with a relatively large level of compression, in particular, in comparison with the level of compression which could be generated by acoustic radiation forces. The generated ultrasound signal contains therefore accurate and significant compression related information about the object which can be used for determining reliably a property of the object like an ablation depth.