Patent Description:
Schlieren techniques are used for imaging in various applications, such as in some medical imaging.

For example, <CIT> describes a frame ensures that the alignment between a high intensity focused ultrasound (HIFU) transducer designed for vaginal use and a commercially available ultrasound image probe is maintained, so that the HIFU focus remains in the image plane during HIFU therapy. A water-filled membrane placed between the HIFU transducer and the treatment site provides acoustic coupling. The coupling is evaluated to determine whether any air bubbles exist at the coupling interface, which might degrade the therapy provided by the HIFU transducer.

<CIT> describes a device for perforating tissue, especially for transmyocardial revascularisation, the device comprising an ultrasonic generator coupled to an attachable solid needle.

As shown in Figs. 1a-1i of the publication "SCHLIEREN IMAGING: A POWERFUL TOOL FOR ATMOSPHERIC PLASMA DIAGNOSTIC" by Enrico Traldi, Marco Boselli, Emanuele Simoncelli, Augusto Stancampiano, Matteo Gherardi, Vittorio Colombo and Gary S. Settles, published by EPJ Techniques and Instrumentation (<NUM>) eight different arrangements (shown in this publication as Figures 1b, 1c, 1d, 1e, 1f, <NUM>, <NUM> and 1i) of the Schlieren imaging technique can be utilized from the Schlieren technique first invented by August Toepler in <NUM> (shown in Fig. 1a of this publication).

Marijn Groen, "Feasibility of irreversible electroporation for pulmonary vein isolation", April <NUM>, describes using Schlieren imaging for qualitative temperature measurements during catheter IRE-ablation in a transparent medium. In this work, a parallel light beam is send by means of a converging lens through a transparent medium and focused using an imaging lens on a high speed camera. The degree of light deflected due to changes in optical density of the transparent medium are color coded by a rainbow filter. The center of the filter is black and therefore nondeflected rays are blocked. Because the background light is blocked, the contrast of the images is enhanced. The circles around the center of the filter are gradually shifting from blue to red, corresponding with a shift from colder to warmer temperatures. The Schlieren images obtained by the set-up described in this work also visualize bubbles generated in the transparent medium during catheter IRE-ablation.

An embodiment of the present invention that is described herein provides a system according to claim <NUM> for visualizing one or more bubbles formed by a catheter, the system includes a fluid container, a pulse generator, a schlieren imaging assembly, and a processor. The fluid container is configured to: (i) contain a fluid, and (ii) receive into the fluid the catheter having one or more electrodes. The pulse generator is configured to apply one or more pulses to at least one of the electrodes. The schlieren imaging assembly is configured to acquire schlieren images of the bubbles occurring in the fluid when applying the one or more pulses, and the processor is configured to visualize the bubbles using the schlieren images.

In accordance with the invention, the fluid is at least partially transparent, and the schlieren imaging assembly is configured to acquire two-dimensional (2D) schlieren images of the fluid. The schlieren imaging assembly includes: (i) a first lens, positioned at a first side of the fluid container, and configured to direct a collimated light beam through the fluid, and (ii) a second lens, positioned at a second side of the fluid container, opposite the first side, and configured to produce, based on the collimated light beam, a focused light beam for visualizing the bubbles.

In accordance with the invention, the schlieren imaging assembly includes: (i) a knife-edge, which is configured to partially block the focused light beam, and (ii) a camera, which is configured to produce, based on the partially-blocked focused light beam, an image indicative of the bubbles. In another embodiment, at least one of the pulses applied by the pulse generator includes an ablation pulse, and at least one of the electrodes includes an ablation electrode, which is configured to apply at least the ablation pulse to tissue of a patient organ.

There is additionally provided a method for visualizing one or more bubbles formed by a catheter according to claim <NUM>.

In a catheterization procedure, such as in radiofrequency (RF) ablation and irreversible electroporation (IRE) carried out in a patient heart, it is important to prevent formation of bubbles that may occur, e.g., in the blood, when ablating tissue of the heart. For example, micro bubbles having a sub-millimeter diameter, which may undesirably occur during a cardiac ablation procedure, may be transferred with the blood stream to the brain, and may cause, for example, an ischemic stroke in the brain. Thus, it is important to test ablation catheters, so as to prevent or minimize the formation of such bubbles or micro bubbles in the blood during the catheterization procedure.

Embodiments of the present invention that are described hereinbelow provide methods and systems for testing a catheter, so as to detect and visualize one or more bubbles or micro bubbles that may occur during catheterization, such as an RF ablation procedure.

According to the present invention, a system for visualizing one or more bubbles formed by a catheter comprises:.

Note that the system is typically positioned in a laboratory or in a quality assurance section of a catheter production facility. The system is configured to serve for improving and/or testing the RF ablation catheter (also referred to herein as a catheter, for brevity) by detecting and/or visualizing bubbles that may occur when applying ablation pulses to ablation electrodes of the catheter, as described in detail below.

In some embodiments, the fluid container is transparent to light and is configured to contain a fluid, which is typically transparent. The fluid container is further configured to receive into the fluid a catheter having one or more ablation electrodes, which are configured for applying ablation pulses to the fluid within the container. In the present configuration, the bubbles are formed within the fluid (e.g., water, or any other fluid that resembles the blood) placed within the fluid container and surrounding the catheter. Subsequently, the bubbles move toward the surface of the water.

In some embodiments, the pulse generator is configured to apply the RF ablation pulses to one or more ablation electrodes of the ablation catheter. In such embodiments, in case bubbles are formed in the water in response to the applied ablation pulses, the system is configured to detect and/or visualize the bubbles formation.

In some embodiments, the schlieren imaging assembly comprises an illumination source, configured to emit any suitable light beam (e.g., visible light), and a schlieren camera. The schlieren camera is configured to acquire schlieren images of the water, so as to detect bubbles occurring in the water when applying the ablation pulses, through the ablation electrodes, to the water.

According to the invention, the schlieren imaging assembly comprises: (i) a first lens, which is positioned at a first side of the fluid container, and is configured to direct a collimated light beam through the water, and (ii) a second lens, which is positioned at a second side of the water container, opposite the first side, and is configured to produce, based on the collimated light beam passed through the water, a focused light beam for visualizing the bubbles.

According to the invention, the schlieren imaging assembly comprises: (i) a knife-edge, which is configured to partially block the focused light beam, and (ii) a camera, which is configured to produce, based on the partially-blocked focused light beam, an image indicative of the bubbles. Note that in the presence of bubbles, at least a portion of the collimated light beam is deflected, and therefore, is not reaching the camera. In such embodiments, the image produced by the camera may comprise a contour or any other indication of a shadow figure caused by the bubbles.

In some embodiments, the processor is configured to visualize and display the bubbles using the schlieren images. In the present example, the camera is configured to produce two-dimensional (2D) schlieren images.

In other embodiments, the system may comprise multiple schlieren imaging assemblies positioned at different orientations relative to the catheter for producing multiple 2D images, and the processor is configured to produce, based on the multiple 2D images, a three-dimensional (3D) schlieren image.

The disclosed techniques improve the quality of catheters, and in particular the quality of RF ablation catheters and the electrodes thereof. Moreover, the disclosed techniques improve the patient safety in catheterization procedures, such as in RF ablation, by testing and preventing the formation of bubbles, before the catheters are being used during RF ablation or during any other catheterization procedure.

<FIG> is a schematic, pictorial illustration of a system <NUM> for detecting and visualizing bubbles that may occur during an ablation procedure.

The system <NUM> may be used for characterizing catheters during product development, and/or for testing catheters during production.

The system <NUM> comprises a fluid container <NUM>, a schlieren imaging assembly <NUM>, a pulse generator <NUM>, and a control console <NUM>. In the present example, pulse generator <NUM> is assembled within console <NUM>, and is configured to apply radiofrequency (RF) ablation pulses (or irreversible electroporation (IRE) pulses) to ablation electrodes <NUM> described in detail below. In other embodiments, pulse generator <NUM> may be assembled in system <NUM> using any other suitable configuration (e.g., external to console <NUM>).

In some examples, schlieren imaging assembly <NUM> comprises a schlieren camera <NUM> described below, and an illumination source <NUM>, which is configured to direct light beams having any suitable wavelength or range of wavelengths. In the present example, illumination source <NUM> is configured to direct a green light beam having a wavelength of about <NUM>, but in other examples, illumination source <NUM> may direct one or more light beams having any other suitable wavelength or range of wavelengths. For example, a visible light having a wavelength between about <NUM> and <NUM>.

In some examples, illumination source <NUM> may comprise any suitable type of light source, such as but not limited to a white light emitting diode (LED) light source or a light source configured to emit a light beam having any visible light.

In some examples, illumination source <NUM> comprises a coherent light source, which is configured to emit light beams having zero or constant phase difference and same frequency. Moreover, schlieren imaging assembly <NUM> is configured to emit collimated light beams, which may be produced by illumination source <NUM>, or by optics (not shown) of schlieren imaging assembly <NUM>.

In the context of the present disclosure and in the claims, the terms "about" or "approximately" for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein.

In some examples, fluid container <NUM> is typically made from glass or plastic or any other suitable material, which is transparent at least to the light beam directed by illumination source <NUM>. Fluid container <NUM> is configured to contain a liquid, which is at least partially transparent to the light beam directed by illumination source <NUM>, and to any other selected wavelength or range of wavelengths. In the present example, the liquid comprises water <NUM> having minerals and other features for resembling the patient blood. For example, water <NUM> may comprise one or more minerals selected from a list of eight essential minerals of the human blood (e.g., sodium (Na), calcium (Ca), magnesium (Mg), potassium (K), iron (Fe), zinc (Zn), copper (Cu), and selenium (Se)), and maintained at a temperature between about <NUM> and <NUM>. In other embodiments, fluid container <NUM> may contain water without additives, or may contain any other substance, and/or be maintained at any other suitable temperature.

In some examples, fluid container <NUM> is configured to receive into water <NUM>, one or more catheters <NUM>, in the present example a single lasso-type ablation catheter, but in other embodiments, catheter <NUM> may comprise any other suitable type of probe, or several catheters tested in fluid container <NUM> at the same time.

In an example, catheter <NUM> has one or more ablation electrodes <NUM>, which are configured to apply the aforementioned RF ablation pulses to water <NUM> contained within container <NUM>.

During an RF ablation procedure, it is important to prevent formation of bubbles that may occur, e.g., in the blood, when ablating tissue of the patient heart. For example, during a cardiac ablation procedure, one or more ablation electrodes <NUM> may be placed in contact with the patient blood, and bubbles may be formed in the blood when applying the ablation pulses to the tissue. In some cases, the bubbles may comprise micro bubbles having a diameter smaller than about <NUM> millimeter. Such micro bubbles may be transferred with the blood stream into the brain, and may cause severe damage in the brain, such as an ischemic stroke. Thus, it is important to characterize and test ablation catheters, so as to prevent or minimize the formation of such bubbles or micro bubbles in the patient body during the RF ablation procedure.

In some examples, schlieren camera <NUM> of schlieren imaging assembly <NUM>, is configured to acquire two-dimensional (2D) schlieren images of water <NUM> when applying the RF ablation pulses to electrodes <NUM>. In the present example, schlieren camera <NUM> comprises an Alpha A7 III camera, produced by Sony Corporation (Tokyo, Japan), or any other suitable type of camera. Schlieren imaging assembly <NUM> and the formation of the schlieren images are described in detail in <FIG> below.

In some examples, schlieren camera <NUM> is configured to sense an indication of the presence of bubbles or micro bubbles at respective locations within the field of view (FOV) of schlieren camera <NUM>.

In some examples, control console <NUM> comprises a processor <NUM>, typically a general-purpose computer, with suitable front end and interface circuits for receiving signals from schlieren camera <NUM> and for controlling (by sending control signals, via electrical cables <NUM> to) several components of system <NUM>, such as but not limited to pulse generator <NUM>, schlieren camera <NUM> and illumination source <NUM> of schlieren imaging assembly <NUM>.

In some examples, processor <NUM> may be programmed in software to carry out the functions that are used by the system, and the processor stores data for the software in a memory <NUM> of console <NUM>. The software may be downloaded to console <NUM> in electronic form, over a network, for example, or it may be provided on non-transitory tangible media, such as optical, magnetic or electronic memory media. Alternatively, some or all of the functions of processor <NUM> may be carried out by dedicated or programmable digital hardware components.

In some examples, control console <NUM> comprises a display <NUM> for displaying information and images described below, and input devices <NUM>.

In some examples, processor <NUM> is configured to receive from schlieren camera <NUM>, via electrical cable <NUM>, signals indicative of the one or more schlieren images acquired when applying the ablation pulses from pulse generator <NUM>, via electrodes <NUM>, to water <NUM>.

In some examples, processor <NUM> is configured to visualize water <NUM> using the schlieren images received from schlieren camera <NUM>. Based on the schlieren image acquired in a field-of-view (FOV) of schlieren camera <NUM>, processor <NUM> is configured to display, on display <NUM> of control console <NUM>, an image <NUM>, which is a visualization of water <NUM> and an indication of bubbles that may be formed when applying the ablation pulses by electrodes <NUM>, as described above. In the present example, image <NUM> shows bubbles <NUM> occurring in water <NUM> when applying the RF ablation pulses to electrodes <NUM>.

In some examples, schlieren imaging assembly <NUM> may comprise multiple illumination sources (not shown) such as illumination source <NUM>, each of which configured to direct a light beam having one or more predefined wavelengths, and one or more schlieren cameras <NUM>, configured to acquire the schlieren images. For example, schlieren imaging assembly <NUM> may comprise (i) a first schlieren camera <NUM>, which is configured to acquire a first schlieren image at a first viewing angle relative to the orientation of catheter <NUM>, and (ii) a second schlieren camera (not shown) which is configured to acquire a second schlieren image at a second viewing angle, different from the first viewing angle.

In some examples, at least one of, and typically all of, the schlieren images comprise two-dimensional (2D) schlieren images, acquired from different viewing angles. In an embodiment, processor <NUM> is configured to visualize bubbles that may be undesirably formed between water <NUM> and electrodes <NUM> of catheter <NUM> by producing, based on the 2D schlieren images acquired from two or more different viewing angles, one or more three-dimensional (3D) schlieren images.

In some examples, processor <NUM> is configured to display a time-series of 3D schlieren images shown in video (e.g., a video clip produced using the thirty frames of schlieren images per second, as described above).

This method of using schlieren imaging for testing functionality of catheters is described in detail, for example, in <CIT> (published as <CIT>) and <CIT> (published as <CIT>).

This particular configuration of system <NUM> is shown by way of example, in order to illustrate certain problems that are addressed by embodiments of the present invention, which are defined in the appended claims, and to demonstrate the application of these embodiments in enhancing the performance of such a visualization and/or testing system.

The present invention, however, is by no means limited to this specific sort of example system, and the principles described herein may similarly be applied to other sorts of visualizing and/or testing system, without departing from the scope of the invention defined in the appended claims.

<FIG> is a schematic side view of an apparatus <NUM> used for detecting and visualizing bubbles that may occur in an ablation procedure. Apparatus <NUM> may replace, for example, at least part of schlieren imaging assembly <NUM> of <FIG> above.

The apparatus <NUM> comprises a bright monochromatic light source, such as a light emitting diode (LED) <NUM> that is thermally coupled to a heat sink <NUM>. LED <NUM> may replace, for example, illumination source <NUM> of <FIG> above. In some examples, LED <NUM> together with a pinhole <NUM> and a lens <NUM> (comprising a lens assembly of one or more lenses), which is positioned at a focal length f from pinhole <NUM>, form a source of a plane wave of collimated light beam <NUM>, incident through the optical path of apparatus <NUM>.

The plane wave of collimated light beam <NUM> is transmitted to incident water <NUM> contained in fluid container <NUM> and positioned between lenses <NUM> and <NUM> of apparatus <NUM>. In the present example, a bubble <NUM> is undesirably formed in water <NUM>, when applying the RF ablation pulses to electrodes <NUM> of catheter <NUM>, and bubble <NUM> moves within water <NUM>, so as to reach the surface of water <NUM> in fluid container <NUM>. Bubble <NUM> may comprise a micro bubble having a diameter smaller than about <NUM>, as described in <FIG> above, or a larger bubble. The plane wave of collimated light beam <NUM> passes into a field-of-view (FOV) <NUM> of a video camera <NUM> described below, and produces a plane wave <NUM>, which contains information of water <NUM>.

The apparatus <NUM> comprises a lens <NUM> comprising an assembly of one or more lenses, which is configured to focus the collimated light of plane wave <NUM> onto a knife-edge <NUM>. The knife-edge <NUM> is configured to partially block the focused light beam. Note that lens <NUM> is positioned at a first side of fluid container <NUM>, whereas lens <NUM> is positioned at a second side of fluid container <NUM>, opposite the first side. For example, in the configuration of <FIG> above, lens <NUM> is positioned between illumination source <NUM> and the first side of fluid container <NUM>, and lens <NUM> is positioned between the second side of fluid container <NUM>, and schlieren camera <NUM>.

The apparatus <NUM> may further comprise video camera <NUM> having suitable optics configured for acquiring the focused beam passing through knife-edge <NUM>, and producing a 2D schlieren images of the focused light beam captured within FOV <NUM>. Video camera <NUM> may replace, for example, camera <NUM> of <FIG> above.

The components of apparatus <NUM> may be controlled by a processor <NUM>, using electrical leads (not shown) and/or one or more wireless communication devices (WCDs) <NUM>, depending on the system design. Processor <NUM> may replace, for example, processor <NUM> of <FIG> above.

In the present example, light beam <NUM> is deflected by bubble <NUM> to produce one or more deflected light beam(s) <NUM>. Since bubble <NUM> blocks at least part of light beam <NUM>, a shadow figure <NUM> of the bubble is formed on lens <NUM>, and is imaged in the 2D schlieren image by video camera <NUM>.

The apparatus <NUM> may be configured to produce a time-series of 2D schlieren images corresponding to respective time instances of bubbles <NUM> occurring in water <NUM> when applying one or more RF ablation pulses to one or more electrodes <NUM>.

The apparatus <NUM> may comprise one or more additional detectors (not shown), which are configured to detect one or more deflected light beam(s) <NUM>, and to produce a signal indicative of deflected light beam(s) <NUM>. In such embodiments, processor <NUM> is configured to display (i) shadow figure <NUM> on the 2D schlieren image produced by video camera <NUM>, which is indicative of bubble <NUM>, and (ii) the signal produced in response to detecting deflected light beam(s) <NUM>, which is also indicative of the presence of bubble <NUM>. Note that each of the two indications of bubble <NUM> have improved contrast relative to 2D images acquired using other imaging techniques, such as any sort of regular optical microscopy based on visible light. It will be understood that detection of bubbles, and particularly of micro bubbles is essential for patient safety in ablation procedures, therefore, improving the contrast can make the difference between designing a safe catheter, as well as releasing or disqualifying a faulty catheter.

The system <NUM> of <FIG> above may comprise multiple schlieren imaging assemblies (such as apparatus <NUM>), positioned at different orientations relative to catheter <NUM> for producing multiple 2D images. In such embodiments, processor <NUM> (or processor <NUM>) is configured to produce, based on the multiple 2D images, a three-dimensional (3D) schlieren image.

The configuration of apparatus <NUM> is simplified for the sake of conceptual clarity and is provided by way of example. In other embodiments, processor <NUM> of system <NUM> (shown in <FIG> above) may be used in addition to or instead of processor <NUM>, and additional components of the optical path may be added.

<FIG> is a flow chart that schematically illustrates a method for detecting and visualizing bubbles <NUM> that may occur during a catheterization procedure, such as an RF ablation procedure.

The method begins at an ablation pulse application step <NUM>, with receiving into water <NUM> contained in fluid container <NUM>, catheter <NUM> having one or more ablation electrodes <NUM>, and applying one or more RF ablation pulses (e.g., by pulse generator <NUM>, which is controlled by processor <NUM> or <NUM>) to at least one of ablation electrodes <NUM>.

At a schlieren images acquisition step <NUM>, when applying the RF ablation pulses, collimated light beam <NUM> is applied through water <NUM> positioned between lenses <NUM> and <NUM>, which constitutes a section of the optical path of apparatus <NUM> shown in <FIG> above. Note that water <NUM> is surrounding catheter <NUM> (as shown in <FIG> above) and in case one or more bubbles <NUM> are formed between electrodes <NUM> and water <NUM>, apparatus <NUM> is configured to detect bubble <NUM> as described in detail in <FIG> above.

At a bubble visualization step <NUM> that concludes the method, processor <NUM> and/or <NUM> produces image <NUM> for visualizing one or more bubbles <NUM> using the schlieren images acquired by schlieren camera <NUM> and/or by video camera <NUM> of apparatus <NUM>. As described in <FIG> and <FIG> above, the visualization of one or more bubbles <NUM> may comprise: (i) one or more 2D schlieren images and/or a video clip for visualizing bubbles <NUM>, and/or (ii) one or more 3D schlieren images produced based on the aforementioned two or more 2D schlieren images acquired from by two or more cameras positioned in two or more different viewing angles, respectively.

Claim 1:
A system (<NUM>) for visualizing one or more bubbles (<NUM>) formed by a catheter (<NUM>), the system comprising:
a fluid container (<NUM>), configured to: (i) contain an at least partially transparent fluid (<NUM>), and (ii) receive into the fluid the catheter having one or more electrodes (<NUM>) ;
a pulse generator (<NUM>), configured to apply one or more pulses to at least one of the electrodes (<NUM>); a schlieren imaging assembly (<NUM>), configured to acquire two-dimensional schlieren images of the bubbles (<NUM>) occurring in the fluid when applying the one or more pulses, wherein the schlieren imaging assembly comprises:
(i) a first lens (<NUM>), positioned at a first side of the fluid container, and configured to direct a collimated light beam (<NUM>) through the fluid,
(ii) a second lens (<NUM>), positioned at a second side of the fluid container, opposite the first side, and configured to produce, based on the collimated light beam, a focused light beam for visualizing the bubbles (<NUM>),
(iii) a knife-edge (<NUM>), which is configured to partially block the focused light beam, and
(iv) a camera (<NUM>), which is configured to produce, based on the partially-blocked focused light beam, an image indicative of the bubbles (<NUM>); and
a processor (<NUM>), which is configured to visualize the bubbles (<NUM>) using the schlieren images.