Multi-frequency mapping catheter and mapping method

Abstract

To provide systems, apparatuses and methods for mapping intra-body cavities.SOLUTION: The present disclosure provides systems, apparatuses and methods that include a catheter configured to be inserted into an intra-body cavity of a patient. An ultrasonic transducer array including a plurality of multi-frequency ultrasonic transducers may be arranged on the catheter. Each of the multi-frequency ultrasonic transducers may be configured to transmit a wide beam ultrasonic signal and a narrow beam ultrasonic signal, and may further be configured to receive a wide beam echo signal and a narrow beam echo signal. A processor may be configured to detect free space of the intra-body cavity by processing the wide beam echo signals and the narrow beam echo signals.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] (Incorporated by reference) This application claims the benefit of U.S. Provisional Patent Application No. 62 / 908,204, filed Sep. 30, 2019, which is incorporated by reference herein as if set forth in its entirety.

[0002] FIELD OF THEINVENTION The present application provides systems, devices, and methods for mapping inter-body cavities. [Background technology]

[0003] Medical conditions such as cardiac arrhythmias (e.g., atrial fibrillation (AF)) are often treated with internal procedures. For example, electrical pulmonary vein isolation (PVI) from the left atrial (LA) body is performed using ablation to treat AF. PVI, and many other minimally invasive catheterization procedures, require real-time visualization and tracking of internal body surfaces.

[0004] Visualization and tracking of the body's surfaces can be performed by mapping propagation of activation waves, fluoroscopy, computerized tomography (CT), and magnetic resonance imaging (MRI), as well as other techniques that may require large amounts of time or resources to provide the visualization and tracking. Summary of the Invention [Means for solving the problem]

[0005] The present disclosure provides systems, devices, and methods including a catheter configured to be inserted into a body lumen of a patient. An ultrasound transducer array including a plurality of multi-frequency ultrasound transducers may be disposed on the catheter. Each of the plurality of multi-frequency ultrasound transducers may be configured to transmit a wide beam ultrasound signal and a narrow beam ultrasound signal, and each of the plurality of multi-frequency ultrasound transducers may be further configured to receive a wide beam echo signal and a narrow beam echo signal in response to the wide beam ultrasound signal and the narrow beam ultrasound signal, respectively.

[0006] In one aspect, the processor is configured to identify free space within the body lumen by processing the broad beam echo signals and the narrow beam echo signals. [Brief description of the drawings]

[0007] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings, in which: [Figure 1] 1 is an exemplary diagram of a catheter-based cardiac mapping system. [Diagram 2] FIG. 1 is an exemplary diagram of a basket-type catheter having an ultrasound transducer. [Diagram 3] 1 is an exemplary diagram of a projection mapping technique. [Figure 4A] 1 is a graph of an exemplary narrow beam pattern. [Figure 4B] 1 is a graph of an exemplary wide beam pattern. [Diagram 5] 1 is a flow chart for mapping an intra-body chamber. [Figure 6A] 1 is a graph of an exemplary wide beam 1.6 MHz simulated signal template. [Figure 6B] 1 is an exemplary graph illustrating the distance between a detected boundary and a simulated reflector. [Figure 7]FIG. 1 shows an example of a left atrial silicon phantom. [Figure 8A] FIG. 1 shows an exemplary slice of a recorded volume with contrast-to-noise ratio (CNR). [Figure 8B] FIG. 13 illustrates an example of fitting an ellipsoid to detected boundary data. [Figure 9] FIG. 13 shows reconstruction data for phantom modeling of the left atrium. [Figure 10A] FIG. 1 illustrates a model created by free space mapping using a single reflector. [Figure 10B] FIG. 1 shows a model created by free space mapping using a dual reflector. [Figure 10C] FIG. 1 shows the average absolute summary mapping using a single reflector. [Figure 10D] FIG. 1 shows average absolute summary mapping using dual reflectors. [Figure 10E] FIG. 1 illustrates coherent sum mapping using a single reflector. [Figure 10F] FIG. 1 illustrates coherent sum mapping using a dual reflector. [Figure 11A] FIG. 2 illustrates a narrow beam pattern according to one embodiment. [Figure 11B] FIG. 2 illustrates a wide beam pattern according to one embodiment. [Figure 11C] FIG. 1 shows the amplitude of the template signal and the envelope signal over time. [Figure 12A] FIG. 1 illustrates multiple arrays, an elliptical obstacle, and free space with one imaging technique. [Figure 12B] FIG. 13 shows the mean, RMS and maximum elliptical distances for various element and acceptance angle pairs. [Figure 13A] FIG. 13 illustrates pixel intensity around the boundary in a given slice for three different imaging methods. [Figure 13B] 13B shows the respective distributions for the imaging method of FIG. 13A. FIG. [Figure 14A] FIG. 13 is a diagram showing a reconstruction result by a first simulation. [Figure 14B] FIG. 13 is a diagram showing a reconstruction result by a second simulation. [Figure 15A] FIG. 1 illustrates an ellipsoid phantom according to one embodiment. [Figure 15B] FIG. 1 illustrates a left atrial silicon phantom according to one embodiment. [Figure 16A] FIG. 13 shows various slices through the detected boundary calculated by the free space algorithm in different regions along different axes. [Figure 16B] FIG. 13 shows various slices through the detected boundary calculated by the free space algorithm in different regions along different axes. [Figure 16C] FIG. 13 shows various slices through the detected boundary calculated by the free space algorithm in different regions along different axes. [Figure 17A] FIG. 1 shows reconstruction results and errors according to various techniques. [Figure 17B] FIG. 1 shows reconstruction results and errors according to various techniques. [Figure 18A] FIG. 2 shows the response to a high frequency signal from a transducer. [Figure 18B] FIG. 2 shows the response to a high frequency signal from a transducer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] As disclosed herein, systems, devices, and methods provide instantaneous localization of large numbers (e.g., thousands) of points on a surface, such as an endocardial surface. The disclosed subject matter provides images and reconstructions comparable in detail to that provided by MRI.

[0009] In accordance with embodiments of the disclosed subject matter, systems and methods are provided for generating contrast-enhanced spatial maps of body cavities, such as cardiac chambers, employing rapid acquisition and reconstruction schemes.

[0010] An array of ultrasound transducers (e.g., 64 transducers) is provided that is configured to transmit both broad and narrow beams and receive corresponding scattered broad and narrow beams. The broad beams are used to map broad portions of body chambers, such as the surface of a heart chamber. The narrow beams are used to map narrow portions of body chambers, such as veins that communicate with the heart chamber.

[0011] As used herein, the term "broad" as used with respect to the term "broad beam" or "broad beam ultrasound signal" may have a frequency in the range of 1 MHz to 3 MHz. In one embodiment, the term wide beam refers to a signal having a frequency within + / - 50% of 1.4 MHz. As used herein, the term "narrow" as used with respect to the term "narrow beam" or "narrow beam ultrasound signal" may have a frequency in the range of 5 MHz to 9 MHz, or 12 MHz to 16 MHz. In one embodiment, the term "narrow beam" refers to a signal having a frequency within + / - 50% of 7.4 MHz.

[0012] The wide beam or wide beam ultrasound signal may include a beam width ranging from 100 degrees to 150 degrees. In one embodiment, the wide beam has a width of at least 40 degrees or more. The narrow beam or narrow beam ultrasound signal may include a beam width ranging from 4 degrees to 12 degrees. Those skilled in the art will appreciate that the exact values ​​of the wide beam and narrow beam may vary depending on the particular medium through which the beam is transmitted or the geometry being mapped.

[0013] Although a 64-element transducer array is described herein, one of ordinary skill in the art will appreciate that the number of transducers may vary and may include less than 64 transducers or more than 64 transducers.

[0014] The embodiments disclosed herein include an ultrasound mapping system with algorithms that accurately map the entire surface of an endocardial chamber in a single glance (e.g., a single heartbeat). Such mapping, along with simultaneous mapping of electrical activity at all points on the chamber surface, results in a significant reduction in overall procedure time in all scenarios, including complex arrhythmias. The disclosed subject matter provides the ability to reconstruct anatomy within a few scans by scanning the entire volume of space with beams in various patterns and quickly composing this information to find the boundaries of the ventricles.

[0015] An array of multi-frequency ultrasound transducers mounted on a geometrically shaped catheter (e.g., a basket-shaped spherical catheter) is disclosed. The array allows for geometric mapping of the entire endocardial surface, including the ostia of the pulmonary veins, as well as other veins and small components associated with the endocardial surface. The endocardial surface may be mapped using a non-rectilinear, elliptical, expanded Radon backprojection, as further disclosed herein.

[0016] In some embodiments, a basket catheter for ultrasound spatial mapping is provided. The ultrasound basket catheter may be capable of acquiring data to map the entire surface of a ventricle from a single location within the ventricle, for example, without the need to rotate or move the entire ventricle during the process. Improved reconstruction methods for use with the ultrasound basket catheter are also provided, which allow for the reconstruction and presentation of spatial maps that visualize enhanced contrast within the chamber, including the main myocardial surface, as well as smaller surfaces such as veins (e.g., pulmonary veins).

[0017] In some embodiments, an ultrasonic basket catheter may be equipped with multiple multi-frequency ultrasonic transducers that are coupled to splines that form a basket shape. The transducers are sparsely distributed on the splines and work in amplitude mode (A-mode) to generate and acquire echo signals. These echo signals are then processed by a processor and used to prepare the mapping of the heart. In one aspect, the processor uses a free-space method. In another embodiment, the processor uses an elliptical backprojection method to rapidly generate a spatial map. In general, an elliptical backprojection method is essentially the same as synthetic aperture beamforming, which is the same as delay-and-sum beamforming. This type of projection works on the following principle: When an array is used to examine a point in space, it is possible to transmit with a time delay from all transducers of the array so that all waves hit this point at the same time. This concept involves sending a focus to the point. The same concept can be used to receive beams or echoes. Since sound waves are linear in nature, instead of physically transmitting and receiving beams, these events can be performed by software. Thus, transmitting from a first transducer, receiving echo or response signals at all of the other transducers in the array, and then doing the same for the second transducer, the third transducer, etc. Data is collected from all of the transducers. When focusing on a point, a time shift is performed so that all signals hit the point at the same time or at the same time. The reflectance value of this point is the sum of these signals time shifted by the appropriate time value. This concept is incorporated into the Boundary Reflectance Value (BRV) which is described in more detail herein.

[0018] In one aspect, the free space mapping method disclosed herein is a variation or modification of the elliptical backprojection method, which uses a synthetic aperture to align a beam in time to focus it using calculations to find the reflectance of a small region in space. The disclosed subject matter finds an upper limit on the reflectance providing a more robust imaging technique.

[0019] A wide beam echo signal is used to map the main myocardial surface, and a narrow beam signal is used to map narrow surfaces such as veins. The term "multi-frequency transducer" is used herein to refer to a transducer configured to emit more than one frequency. In one embodiment, the multi-frequency transducer is a dual frequency transducer, i.e., a two or dual frequency transducer. In other embodiments, the multi-frequency transducer emits three or more frequencies.

[0020] The disclosed elliptical backprojection method assumes a finite number of transmit / receive ultrasound transducers, each transmitting one echo signal at a time while all transducers receive scattered echo signals. In one aspect, these signals are transmitted within a few microseconds. The acquisition time is determined by how large an area is being imaged. In one embodiment, the parameter setting period is about 70 microseconds with a range of about 4 cm per transmit / receive event. The location of scatterers within the volume and the reflection amplitude from the scatterers are calculated based on an elliptical calculation.

[0021] The accuracy of the spatial map of the ventricles benefits from faster acquisition and reconstruction times. In one embodiment, the disclosed method reduces computation time by generating a composite spatial map, which is based on analyzing one-dimensional A-mode signals, rather than attempting to reconstruct the complete image, which is unnecessary and computationally intensive. The disclosed system and method, which combines (i) a basket-type ultrasound array that instantly acquires multiple ultrasound measurements, and (ii) an improved reconstruction scheme that includes wide and narrow beam signals, may be advantageous to physicians who can receive more accurate spatial and functional maps of body cavities such as the ventricles. Thus, the disclosed system and method may enable physicians to perform efficient invasive diagnostics and possibly subsequent treatment sessions.

[0022] FIG. 1 is a diagram of a catheter-based cardiac mapping system 20 including an ultrasound basket catheter 40, according to one embodiment. Although a basket shape is disclosed throughout, it will be understood that any shape catheter with multiple transducers may be used to practice the embodiments disclosed herein. The system 20 includes a catheter 21 having a shaft 22 that may be navigated by a physician 30 into a heart 26 of a patient 28 lying on a table 29. As shown in FIG. 1, the physician 30 may insert the shaft 22 through the sheath 23 while manipulating the distal end of the shaft 22 using a manipulator 32 near the proximal end of the catheter and / or a deflector from the sheath 23. As shown in inset 25, a basket catheter 40 may be attached to the distal end of the shaft 22. The basket catheter 40 may be inserted through the sheath 23 in a collapsed state and then expanded within the heart 26.

[0023] In one embodiment, the basket catheter 40 may be configured to perform spatial mapping of a ventricle of the heart 26 by transmitting wide and narrow echo signals and receiving wide and narrow echo signals reflected from a ventricle surface 50. Inset 45 shows a close-up view of the basket catheter 40 inside a ventricle of the heart 26. As shown, the basket catheter 40 may include an array of ultrasound transducers 48 coupled on splines that form a basket shape.

[0024] The proximal end of the catheter 21 may be connected to a console 24. The console 24 may include a processor 41, such as a general-purpose computer with suitable front-end and interface circuitry 38 for transmitting and receiving signals to and from the catheter 21 and for controlling other components of the system 20. In some embodiments, the processor 41 may be further configured to receive multi-frequency (e.g., wide and narrow) echo signals and calculate a map of the ventricular surface from the echo signals. In one aspect, the processor 41 is configured to identify a first region of the body lumen by processing the wide beam echo signals and to identify a second region of the body lumen by processing the narrow beam echo signals. In other words, the wide beam echo signals are configured to specifically map only certain portions of the lumen and the narrow beam echo signals are configured to specifically map only other portions of the lumen. When used in combination, both sets of echo signals provide a complete mapping of the lumen.

[0025] In one embodiment, on the display 27 the surface of the surrounding anatomical structures may be presented to the physician 30 in graphical form, for example in a mesh diagram 35 .

[0026] As noted above, the processor 41 includes a general-purpose computer that may be programmed in software to perform the functions described herein. The software may be downloaded in electronic form to the computer, for example over a network, or alternatively or additionally may be provided and / or stored on a non-transitory tangible medium, such as a magnetic, optical, or electronic memory. The exemplary configuration shown in FIG. 1 has been selected for conceptual clarity purposes. The subject matter disclosed herein may be used in a variety of applications, including but not limited to mapping a patient's heart, and not limited to mapping anatomical objects. The techniques of the present disclosure may be similarly applied using other system components and configurations. Furthermore, the system 20 may include additional components, such as those for electrophysiological mapping and / or ablation. Although the illustrated embodiment is specifically directed to the use of an ultrasonic basket catheter for cardiac mapping, the elements of the system 20 and the methods described herein may alternatively be applied to ultrasonic mapping using catheters having other multi-arm geometries.

[0027] 2 is an exemplary diagram of a basket-type catheter 40 with attached ultrasound transducers 48, according to an embodiment of the present invention. As shown, the transducers 48 may be coupled to splines 49 and may form a shape such as a basket. The transducers 48 may be distributed in a sparse manner (e.g., in this case, there may be a large gap between each of two adjacent transducers such that most of the surface area of ​​the basket surface defined by the splines 49 is free of transducers). The transducers 48 may be distributed in a generally spherical pattern beyond the distal end of the shaft 22. As further disclosed herein, each transducer 48 may have a sufficiently large transmit and receive acceptance angle, and calculations performed based on signals between the transducers 48 may be optimized to take advantage of the sparse array, so that the array of transducers 48 can still obtain the required range and detail of ventricular features.

[0028] The catheter 40 shown in Figure 2 is merely an example. The number of transducers 48 and their arrangement may vary. Additional elements such as electrodes may be disposed on the splines 49. In one embodiment, there are 60 transducers and the splines are formed as flex PCB splines bonded onto a nylon balloon. Other catheter geometries (e.g., spiral arms, balloons, etc.) may be provided.

[0029] In one aspect, a device is provided that includes a catheter 40 configured to be inserted into a body lumen of a patient and an ultrasound transducer array including a plurality of multi-frequency ultrasound transducers 48 disposed on the catheter 40. Each transducer 48 is configured to transmit a wide beam ultrasound signal and a narrow beam ultrasound signal, and each transducer 48 is configured to receive a wide beam echo signal and a narrow beam echo signal in response to the wide beam ultrasound signal and the narrow beam ultrasound signal. A processor 41 is configured to detect free space in the body lumen by processing the wide beam echo signal and the narrow beam echo signal. In one aspect, the processor 41 is configured to detect free space by determining a boundary reflection value (BRV), the BRV being indicative of whether a particular point in the space in the body lumen is in free space. The processor 41 is configured to identify the free space based on at least one of signal directivity or signal strength as described in more detail herein. A monitor or display 27 is configured to indicate the free space.

[0030] In one embodiment, the narrow beam ultrasound signal has a frequency in the range of 12 MHz to 16 MHz and the wide beam ultrasound signal has a frequency in the range of 1 MHz to 3 MHz. In one embodiment, the wide beam ultrasound signal has a beamwidth of at least 40 degrees and the narrow beam ultrasound signal has a beamwidth in the range of 4 degrees to 12 degrees.

[0031] Also disclosed herein is a method that includes inserting a catheter 40 into a body lumen of a patient. The catheter 40 includes an ultrasound transducer array that includes a plurality of multi-frequency ultrasound transducers 48. The method includes transmitting a wide beam ultrasound signal and a narrow beam ultrasound signal from each of the multi-frequency ultrasound transducers 48, and receiving a wide beam echo signal in response to the wide beam ultrasound signal and a narrow beam echo signal in response to the narrow beam ultrasound signal. The method includes identifying free space in the body lumen by processing the wide beam echo signals and the narrow beam echo signals.

[0032] According to one embodiment, a two-dimensional intra-atrial ultrasound array (e.g., a basket-mounted array) may include an ensemble Ω of N transmit / receive elements, as shown in FIG. 2 via transducer 48. The array may be operated in a synthetic aperture-like mode involving N transmit-receive events, where a single element transmits, followed by all elements jointly receiving the transmission from the single element. As disclosed further herein, application of such an implementation may result in identification of the location and reflection coefficients of scatterers at the endocardium surface, where the scatterers may occur at points on the endocardium surface.

[0033] Each transmitter s has x s ∈ R 3 and may be located at the position of Px s (r,t)=p 0 (t) may be a source of a spherical pressure wave of 1 / 4Πrδ(r-ct), where r is the distance from the transmitter, c is the speed of sound in the medium, R is a set of real numbers, and p0(t) is the signal waveform. As used herein, the terms "transmitter", "transmitter-receiver", or "transmitter-receiver pair" are all used generically to refer to a transducer.

[0034] Wave is x sc may be scattered (also called echo) from a point scatterer sc at x reThe signal may be received by the transducer element re at point x. The angle θ(el,X) may be the angle between the normal to the surface of the element el ∈ Ω and the vector from the center of the element to point X. Dir(θ,ka) may be a directivity factor that attenuates the signal as a function of θ, wavenumber k, and element radius a. The signal strength is sc may be the measured response received at the receiver in the presence of scatterers at x as a function of time t. re The signal strength measured at is:

[0035]

number

[0036] In the above formula, P 0 (s) is the peak envelope (absolute value of the complex envelope) of the signal transmitted from s, P1 is the scattering coefficient of the scatterer at sc, c is the speed of sound in the medium, and D(x,y)=||xy|| means the Euclidean distance between two points x and y.

[0037] For a transmitter-receiver pair s, x s ∈ R 3 and x re ∈ R 3 In each of these, re ∈ Ω and the formula ct s,sc,re =D(x s ,x sc )+D(x sc ,x re ) for all points x that satisfy sc ∈ R 3 The two foci s and re have a length of ct s,sc,re Let E ∈ R lie on its principal axis. 3 Define.

[0038] Based on experiments, and as further disclosed herein, x s The total signal transmitted from and scattered from all scatterers sc ∈ E(s,re,sc) is x reIt has been shown that the received signals are simultaneously and coherently received at

[0039] Furthermore, a signal is sent from s, scattered from all reflectors sc ∈ E(s,re,sc), and t s,re,sc The maximum signal envelope S(s,re,sc) received at time re after seconds is given by the integral:

[0040]

number

[0041] In the above formula, P 0 (s) is the maximum value of the envelope of the signal transmitted from s, which is assumed to be positive and independent of s, and P 1 (X) is the reflection coefficient at X. Equation 2 provides the signal strength based on all scatterers above a given ellipsoid, so the signal strength value provided by Equation 2 may correspond to the signal strength actually measured at the receiver at a given time.

[0042] According to the embodiments disclosed herein, the free space is P 1 The ensemble F of all points X for which (X)=0. Any region containing blood pool exhibits a minimum reflectance such that after boundary reflectance values ​​are calculated, segmentation methods can be applied to exclude such blood pool regions from the surface calculation, as described further herein. Segmentation methods can be applied on the BRV to detect free space (e.g., blood pool regions) from the surface calculation, as described further herein.

[0043] With regard to BRV, the disclosed subject matter provides imaging and detection of openings or holes (i.e., pulmonary veins) by using narrow beams, as well as the ability to integrate various beam patterns (i.e., directivity) to achieve better viewing of shapes using beams of various widths. Certain aspects of the imaging techniques are generally disclosed in U.S. Patent Application Publication No. 2019 / 0209089, which is incorporated by reference as if fully set forth herein. In general, BRV examines a set of time-shifted signals, but instead of calculating the sum used in elliptical backprojection, it focuses on the minimum of the envelope (i.e., energy) of all signals at the appropriate time. The principle of BRV is based on the concept that all points with a corresponding time of flight (i.e., from the transducer to a point in space and back to the receiver) are in free space, even if one transducer / transmitter-receiver pair does not receive an echo (i.e., a noise-level signal) at a particular time.

[0044] The segmentation method may be any applicable technique, such as a region growing method, that distinguishes the blood pool with low signal intensity values ​​from the surface with high signal intensity values. Given that the entire group of transducer elements Ω is in free space, and because the acoustic impedance of the myocardial tissue is greater than that of blood, all scatterers P 1 It follows that (X) ≥ 0. The triplet (s,re,sc), sc ∈ E(s,re,sc), and s,re ∈ Ω define all ellipsoids that pass through the point sc, whose foci are all the transducer elements in Ω. Considering the above, the integrand in Eq. 1 is non-negative, so if S(s,re,sc) = 0, then P1(x sc ) = 0, so that sc ∈ F, where the point sc is in free space.

[0045] 3 shows an example diagram of an elliptical Radon-like projection, where point sc 350 is the actual scattering element and sc′ 351 is in free space. The two ellipses 310 and 320 induced by the pairs (s301, re302), (s301, re′ 303) intersect at sc′ 351 but not at sc350.

[0046] Equation 3 below describes the distance and directivity at a particular point.

[0047]

number

[0048] In Equation 3, if s,re ∈ Ω, then for all X,s,re

[0049]

number

[0050] The BRV may be defined for all points X as follows:

[0051]

number

[0052] As defined above, the BRV is measured in A / D voltage units proportional to the received acoustic wave pressure. The BRV may be calculated by a segment of a volume, such as detected free space. For example, the BRV may be calculated by a volume (10 cm) centered on the center of the catheter (e.g., a basket catheter) and sampled using a three-dimensional 2 mm grid. 3 The volume can be segmented into connected free spaces by using a region growing algorithm (e.g., Equation 2) with a seed at the volume center. The voxels at the periphery of the resulting free space can also be referred to as detected boundary points.

[0053] In other words, the BRV is calculated in a voxel grid in space to generate a 3D image similar to CT or MRI. This image is used to segment the object space into free space and tissue, which gives a set of points on the boundary that represent the chamber surface. These can then be processed using additional advanced algorithms such as model-based fast anatomical mapping (mFAM) or smoothing methods or neural networks to generate a realistic looking surface image.

[0054] The BRV gives low values ​​(i.e., noise values) for locations in the blood pool that are always free, and higher values ​​for locations that are potentially occupied (i.e., the presence of at least a single scatterer P 1 ) These values ​​vary with relative distance, directivity, etc. The values ​​also depend on system parameters that affect the signal to noise ratio (i.e., frequency voltage, amount of averaging, filtering, etc.) and the reflecting tissue itself. In a particular application, the signal to noise ratio (SNR) may be 10, i.e., the signal is roughly 500-1000 and the noise level is less than 100.

[0055] The left atrial border is a 10x10x10cm area centered on the center of the catheter. 3 It is determined by starting with a volume of 2 x 2 x 2 mm 3 The volume is sampled using a 3D grid with a voxel resolution of 1000 MHz. In one embodiment, the BRV is first calculated for all voxels in the volume. Then, in one embodiment, the volume is segmented into connected free spaces using a region growing algorithm with a seed at the volume center. A growing zone algorithm is used to define a locally adaptive threshold for the BRV. A particular region is considered to be free space if it falls below a predefined threshold. The voxels at the periphery of the resulting free space are referred to as detected border points.

[0056] The disclosed subject matter embodiments may utilize both wide and narrow beams to map the body chamber. Each element may be configured to transmit both wide and narrow beams and receive corresponding wide and narrow beams. The wide beam may have a first directivity or may be within a first directivity, and the narrow beam may have a second directivity or may be within a second directivity. A narrow beam may be used in addition to the wide beam because the wide beam may be too wide to distinguish between a hole (e.g., PV) and a body chamber surface (e.g., endocardial surface), such as when there is no ellipsoid that exists entirely in free space that intersects with the interior of a pulmonary vein (PV).

[0057] At a general level, the free space method essentially involves using a very sparse array of ultrasound elements, i.e., catheter 40 and transducer 48, to transmit a signal and then, based on the echo or reflected signal, determine whether the transducer is in free space (i.e., in blood or not touching a cardiac structure) or in occupied space (i.e., touching a cardiac structure). A wide beam echo signal will have one set of characteristics and a narrow beam echo signal will have another set of characteristics.

[0058] The free-space method combines magnified nonlinear beamforming with surface rendering. An analytical scheme is provided to determine the number of array elements and frequencies required to achieve a desired segmentation accuracy. The catheter 40 disclosed herein captures hundreds of surface points or scans simultaneously. Each scan takes less than 16 ms when using three frequencies that provide real-time tracking of the endocardium surface. A boundary representing the chamber surface is determined by segmenting the sampled BRV in a voxel grid using a region growing algorithm. This boundary can be tracked in time to provide real-time motion imaging.

[0059] Additional information about free space may be obtained using the dependence of the emitter directivity pattern as a function of wavelength. Based on this configuration, it is possible to use both narrow and wide beams to map or identify regions of the cavity that may be smaller than the main chamber. The directivity of the piston model is proportional to:

[0060]

number

[0061] In Equation 5, J 1 is the first order Bessel function. Directivity can produce either a wide beam, suitable for elliptical backprojection, or a narrow beam that provides laser-like scanning of a narrow portion of a body lumen (e.g., PV). Beams with intermediate widths can add information to the elliptical backprojection.

[0062] FIG. 4A shows an example of a narrow beam (at 13 MHz) pattern with a directivity ka of 26.5. FIG. 4B shows an example of a wide beam (at 1.8 MHz) pattern with a directivity ka of 3.67. Normalized intensity values ​​are shown on the right hand side of these figures. The narrow beam may be used in a first echo detection mode such that a given volume is free until the first echo is hit. The response information from the transmission and reception of such a narrow beam is added to the wide beam scan to obtain mapping information of a narrow portion of an intra-cardiac chamber such as a vein (e.g., PV).

[0063] In one embodiment, the narrow beam is used in the first echo mode. The system then checks for the first time that the signal exceeds the noise level threshold and sets this instance or time as a hit. The time corresponds to the distance. The location of the transducer, the orientation, and the beam shape are all known variables. In terms of the beam shape, the beam is assumed to be a narrow cone with a known angle calculated using the directivity (i.e., the angle is defined to be 6 DB down from the center, which is about 10 degrees for 13 MHz). Until a hit occurs, all the space within the cone from the transducer is considered free, while the area around the hit is occupied. This information is added to a segmentation map, where the free space detected by the narrow beam is given a higher priority than the wide beam. In other words, the space that is occupied by the wide beam and is considered not to contain the narrow beam is ultimately determined to be free. This allows the mapping of various smaller passages or veins that lead to the chamber.

[0064] The directivity of the beam depends on the wavelength. Shorter wavelengths emit narrower beams, while longer wavelengths emit wider beams. Based on this configuration, additional information is obtained or determined, since the wide beam, which requires the ellipsoid to be completely contained in free space, is generally insufficient to detect holes (i.e., pulmonary vein ostia) in the endocardial surface. Using the techniques disclosed herein, points in space where the directivity falls off more than 6 DB for either the transmitter or receiver are ignored, so there is a negligible contribution to the signal. Improved images are provided by continuously varying the beam width between a beam targeting the ellipsoid and a narrow beam providing a laser-like scan into the pulmonary vein. A beam with intermediate or interim width compared to the wide and narrow beams can also be used to provide additional information.

[0065] 5 shows a flow chart 500 for mapping a body chamber according to an embodiment disclosed herein. As shown, in step 510, a catheter including an ultrasound transducer array (e.g., basket catheter 40 of FIG. 2) is inserted into a patient's body. The ultrasound transducer array is inserted into a body chamber, such as a cardiac chamber. In step 520, transducers in the ultrasound transducer array transmit echo signals of wide and narrow beams. In step 530, the echo signals are received at one or more transducers in the ultrasound transducer array after being reflected from free space scatterers and actual scatterers, including the main myocardial surface, as well as narrower surfaces such as veins (e.g., pulmonary veins).

[0066] In step 540 of the flowchart 500, the processor calculates the reflection amplitude to segment the body chamber (e.g., endocardium) boundary based on the techniques disclosed herein. In one aspect, the processor is configured to combine multiple scans during catheter movement. These scans can be used to create a model-based fast anatomical mapping (mFAM) by matching a statistical model to the data collected by the catheter. In one aspect, a combination of imaging techniques is used in which free space is prioritized over occupied space. In one aspect, a minimum operator is used across the BRV values ​​from all scans for all points in the sampled grid space. A region growing algorithm is used to provide boundary voxels between the free space and the chamber tissue. To further improve this imaging technique, an anatomically aware algorithm such as mFam or a neural network imaging tool can be used.

[0067] At step 550, the segmented body chambers are rendered via a display. A display, monitor, or other type of output device may be configured to receive and display the segmented body chamber data.

[0068] According to the in silico experiments, a 64-element transducer with a radius of 30 mm was inserted into the left atrium model and placed in the center of a cube with 10 cm sides. A 2 mm three-dimensional grid was used to divide the cube into 503 voxels. Reflectors were assigned to all grid points inside a 6 mm thick shell around the atrial border of the ventricle. As seen in chart 610 of FIG. 6A, several cycles of 1.6 MHz and 7.4 MHz sinusoidal signals 611 with Gaussian envelopes were assumed. For each transducer element pair, the responses of each reflector were appropriately time shifted and summed to generate a simulated signal according to Equation 1. The simulated signals were used to reconstruct the wide and narrow response volumes according to embodiments disclosed herein. The distance between the detected border and the simulated reflector is shown in graph 620 of FIG. 6B, which illustrates the probability of normalized distances on both sides. The asymmetric distribution results in median and median absolute deviation (MAD) of the distance (in mm) of 1.99 and 0.983, respectively, from the detected boundary to the reflector 621, and 3.377 and 1.26, respectively, from the reflector to the boundary 622. The distances from the detected boundary to the reflector and from the reflector to the boundary estimate the error from the model surface.

[0069] According to the in vitro experiments, a 64-element piezoelectric transducer array mounted on a 12-printed circuit board (PCB) spline basket was tested. Each transducer element contained two resonant frequencies, approximately 1.6 MHz and 7.4 MHz, respectively. The elements were connected to an acquisition system that allowed for generating pulses and recording sequential transmission sweeps for all elements in real time. The catheter was placed in a phantom chamber containing a water bath to simulate blood and enclosed in an elliptical plastic housing simulating the wall of the ventricle. To simulate natural heart wall motion, the walls of the phantom chamber were continuously moved by pumping water in and out. A long-term average was then subtracted from all time signals to eliminate constant signals caused by reflections from the splines themselves. In all simulations, the location of the transducer was assumed to be known. FIG. 7 shows an exemplary left atrial silicon phantom that can be used to test the embodiments disclosed herein.

[0070] According to the elliptical phantom experiment, the basket catheter was placed in an elliptical phantom made of silicon water with radii of 35 mm, 32.5 mm, and 22.5 mm. Acquisition was performed using a wide beam as described herein. The volumes were subjected to dynamic range reduction using a square root function such that each acquired voxel in a given volume was square rooted. An ellipsoid was fitted to the boundary detected by an algorithm. Figure 8A shows a slice of the recorded volume with the contrast-to-noise ratio (CNR) calculated for a pixel population at 6 mm around the boundary. Element 810 shows a CNR of 1.88 with a Z value of 15 (slice along the height axis), element 820 shows a CNR of 1.62 with a Z value of 25, and element 830 shows a CNR of 1.82 with a Z value of 35. The values ​​on the right hand side of Figure 8A are intensity values.

[0071] FIG. 8B shows the fit and deviation of the detected boundaries. Distance values ​​in mm are shown on the right hand side of FIG. 8B. As shown, an ellipsoid 850 is fitted to the detected boundary data. Only the first half of the volume is shown in FIG. 8B. The bottom of the fit and deviation shown in the ellipsoid 850 in FIG. 8B is an outlier because the phantom used in this experiment was not a perfect ellipsoid. The bottom therefore makes the error distribution, median and MAD asymmetric (this estimates the standard deviation in a Gaussian distribution by a factor of about 1.5). The radii obtained based on this experiment were 36, 33.4 and 25.5, while the ellipsoid median deviation value from the data was 1.4 mm and the MAD was 0.6283 mm.

[0072] According to the left atrial phantom experiment, a silicon left atrial phantom shown in FIG. 7 was scanned using narrow and wide beams. The detected boundary points along with six manually tagged anatomical interest points were used as input to an anatomy-aware model-based reconstruction algorithm. The reconstructed anatomical structure was aligned with a ground truth CAD mesh, and the difference between each vertex of the reconstruction and the ground truth mesh was calculated. The resulting mean, standard deviation, median, MAD, and RMS were 4.2 mm, 4.4 mm, 2.6 mm, 1.77 mm, and 6.1 mm, respectively. The reconstruction results and errors are shown in FIG. 9. As shown in FIG. 9, the right hand side shows the distance in mm. Element 910 in FIG. 9 shows a plan view of the distance in mm from the detected boundary-based model to the atrial phantom. Element 920 in FIG. 9 shows a side view of the distance in mm from the detected boundary-based model to the atrial phantom. Element 930 in FIG. 9 shows a left PV view of the distance in mm from the detected boundary-based model to the atrial phantom. As shown, the resulting model is visually close to the phantom, while the detected PVs are consistent with the CAD. In a left atrial shaped silicon phantom, image accuracy is at least within 4.0 mm using the systems, devices, and methods disclosed herein.

[0073] In one aspect, the array is operated in a synthetic aperture mode that includes a number (N) of transmit and receive events. In this mode, each element in the array transmits once sequentially, but all elements receive. An ensemble is generated that includes (N(N+1)) / 2 distinct RF signals. According to embodiments disclosed herein, the scatterers x sc Location and reflection coefficient P1(x sc ) is located and found at the endocardial surface boundary using this ensemble of signals. In one aspect, all of the signals in the ensemble are sampled and used to define a particular location in space. In other words, if one of the signals does not receive an echo from a particular location, it is determined or assumed that there is free space in that region. If a low value signal is produced, it is determined or assumed that the catheter is positioned in blood.

[0074] A chart is generated with signal amplitude versus distance. The RF response to a high frequency signal from a transducer is measured as shown in Figures 18A and 18B. Figure 18A shows the RF response after applying a median filter to 15 signals. The arrow in Figure 18A shows the excitation signal. Figure 18B shows the absolute value of the amplitude where the excitation signal is removed. The circled area in Figure 18B shows the first hit and the arrow shows the dead zone.

[0075] Reflection coefficient P1(x sc ) with X sc Reflected from a point reflector at x s The signal emitted from the transducer element at time t is defined by the following equation 6: d After x re is received.

[0076]

number

[0077] In Equation 6, c = 1.54 mm / μs, which is the speed of sound in blood, and t dIt is a copy of the following equation delayed by (s,re,sc).

[0078]

number

[0079] In Equation 7, P 0 are the transmit / receive peak amplitudes corrected by the transmit and receive directivities defined by Equation 8 below:

[0080]

number

[0081] Equation 8 corresponds to the directivity factor that attenuates the signal as a function of the angle of incidence with the transducer surface θ. In Equation 8, the wave number k=(2πf / c) and J 1 is the first order Bessel function, with element size = 0.5 mm. According to Equation 8, these values ​​are divided by the transmitter scatterer and receiver distances to obtain the scattering coefficient P 1 (x sc ).

[0082] Imaging system quality is generally measured by the response to a single point reflector. In one aspect, the response to the reflector is the point spread function (PSF). In one experiment, a point spherical reflector was placed in front of a planar rectangular array with nine elements. The distance from the array to the reflector was 4-5 times the distance between the individual array elements. Figures 10A-10F compare the PSF and two reflector responses for the free space (FS) method, the envelope method and the coherent sum (DAS) method. The values ​​on the right hand side of Figures 10A-10F show the intensity values.

[0083] 10A and 10B correspond to free space mapping, 10C and 10D correspond to average absolute summary mapping, and 10E and 10F correspond to coherent sum mapping. 10A, 10C, and 10E correspond to a single reflector configuration, and 10B, 10D, and 10F correspond to a dual reflector configuration. As shown in 10A and 10B, the free space method has a PSF with minimal array processing artifacts and distinguishes between the two reflectors. As shown in 10C-10F, the DAS experiences up to 33% of the reflector signal across the space, and the DAS also experiences up to 40% blurring between the two reflectors. When the positional accuracy of the elements is less than sub-wavelength for a non-rigid catheter, only absolute sum is feasible, resulting in relatively large artifacts. In other words, the left atrium and other chambers are assumed to be bodies that can be closely approximated as ellipsoids, and this assumption therefore provides a relatively accurate approximation of actual system requirements and performance.

[0084] In terms of the analytical framework, the embodiments disclosed herein calculate the free space based on a circular array in a plane within the obstacle ellipse center and measure the boundary distance error. For cavities with low curvature, the cross section of a uniformly distributed array can be approximated according to the following process. For other types of cavities, a synthesis of several viewpoints may be used.

[0085] The transmitter-receiver pair defines a reception area, where a particular echo can be detected based on the directivity and relative positioning, while other echoes are considered noise for the particular transmitter-receiver pair. Free space is generally identified or detected via the transmitter-receiver pair by determining the time of the first echo from an obstacle reflected either at the reception area boundary or within it. For a very narrow reception angle, the transmitter-receiver pair denigrates into two narrow beams, resulting in as many intersections with obstacles as there are elements, i.e., transducers. For a very wide reception angle, the number of ellipses associated with an element pair is approximately proportional to the square of the number of elements or transducers.

[0086] In terms of a 2D mathematical framework, the embodiments disclosed herein rely on a 2D array of n elements uniformly spaced around a circle with radius r. In one embodiment, the radius is 15 mm. Those skilled in the art will appreciate that the radius may vary according to various parameters and circumstances. The acceptance angle of each element is φ. Points outside the circle are truncated. The array is defined as an ellipse E with major axes a, b. 0 The process calculates the free space detected by the array as a union of geometric objects based on the following values ​​and parameters: i is a slice s in the plane defined by the acceptance angle of the element that is essentially perpendicular to the surface of the element i,Φ For each pair of elements p i,j generates a wedge from which the pair receives reflections. A wedge is made up of two slices, namely s i、φ , and s j,φ , and the intersection of the following equation:

[0087]

number

[0088] In the situation where i=j, the pair is the element itself and the wedge is the slice s j,Φ A sector of the pair p i,j To determine the free space detected by i,j The time of the first echo detected by the pair must be determined. The time and pair are combined to form an ellipse E P The free space of this pair is defined as a wedge W i,j and ellipse E P is the intersection of

[0089] The following observation (Observation 1) is provided based on the process disclosed herein. The first echo has two possible cases: P Located in E PE 0 , or ∂W i,j ∩E P The received message may be received from any one of the endpoints.

[0090] Observation 1 is p i,j This is solved using the following set of equations:

[0091]

number

[0092] Equation 10 requires that the intersection point belongs to an ellipse defined by the transmitter-receiver pair and the obstacle ellipse.

[0093] Equation 11 below shows that the obstacle ellipse and the transmitter-receiver pair are tangent.

[0094]

number

[0095] In formulas 10 and 11, p 1 , p 2 is the location of the transmitter-receiver pair, and (u,v) is the mean or center of the ellipse. Elements a, b are the major axes of the obstacle ellipse. θ , b θ are the major and minor axes of the ellipse defined by the transmitter-receiver pair and the first echo point. The angle θ=∠(p 1 -p 2 ) and the angle θ is the rotation angle of the transmitter-receiver ellipse from the positive x-axis.

[0096] Element x 0 , α, and a θ There are three equations for , which are solved numerically. The signs (i.e., the positive and negative square root solutions of the fundamental elliptic equations) are i,jThe free space is calculated using observation 1. If the first echo is inside the wedge, this is the tangent to the obstacle ellipse, E P where the normals are equal at the tangent points and the curvature of the obstacle ellipse is E P This relation applies to any smooth reflecting surface. Based on the above relation, the following theorem is provided: Let x be the point of the first echo of the pair Pi,j, and x ∈ W i,j and

[0097]

number

[0098] In one aspect, the disclosed subject matter is configured to identify free intervals based on at least one of spherical pressure waves, directivity, or signal strength. Generally, free space is the level of system noise, and the actual echo is at least 5 times larger. This relationship and calculation is determined by the system SNR. All of the transducers emit spherical pressure waves. This wave is attenuated in a particular direction due to directivity. Along a line that starts at the transducer center and is tangent to its normal (i.e., the transducer axis), there is no attenuation at all. If this line is rotated, points in space along this rotation line will feel less pressure from the wave compared to points on the axis. This change is a result of directivity. Signal strength as used in this aspect is defined as the measured signal in the receiving transducer. Signal strength is a direct result of the pressure wave reflecting from one or more reflectors in the space, which in this application are typically tissues.

[0099] The complete form of the signal is P 1 (x sc ) in which

[0100]

number

[0101] The signal transmitted from s and received by re is calculated based on the sum of the magnetic reluctances from all the scatterers, as shown by the following equation:

[0102]

number

[0103] Classical delay (i.e., normal DAS beamformer) and sum (DAS) beamformer P 1 (x sc is estimated by summing ψ(s,re,t) over all (N(N+1)) / 2 transducer element pair (s,re) signals at point sc to obtain

[0104]

number

[0105] Equation 14 represents the sum of all contributions from transmission and receiver pairs to a particular point in space over a given time period. The peak envelope of a signal s operator is denoted as ε(s). The envelope is calculated using the absolute value of the signal and taking the maximum value within a relatively reduced time window ΔW (wavelength wide). The transducer / receiver element pair (s,re) and scatterers (sc) are expressed as x s and x re The focus is on point x sc Since the acoustic impedance of blood is lower than that of the myocardium, we define an ellipsoid E(sc,s,re) that passes through the blood pool for all points sc ∈ V BP or P at the blood pool / myocardium interface 1 (x sc) ≧0. All reflectors are assumed to be specular (i.e., speckles are ignored or not taken into account). Thus, if there is no signal received (i.e., below the noise level) at a particular time T for a given pair (s,re), then for all points T, the signal is defined by Equation 15 as shown below:

[0106]

number

[0107] In Equation 15, T is the reflectance of an ellipsoid with zero reflectance or in free space.

[0108]

number

[0109]

number

[0110] For all points sc ∈ V BP and for a transmitter-receiver pair (s,re), the signal is defined by:

[0111]

number

[0112] Since ε(S) is positive by definition, and part of equation 14 is a result of ignoring or not taking speckles into account, the following is also true:

[0113]

number

[0114] BRV is all points

[0115]

number

[0116]

number

[0117] FIG. 11A shows a narrow beam pattern with a frequency of 7.4 Mhz, and FIG. 11B shows a wide beam pattern with a frequency of 1.4 Mhz. The values ​​on the right hand side of FIG. 11A and FIG. 11B show normalized intensity. Narrow beams are generally used in the first echo detection mode. In other words, the navigated space is free until the beam hits the first echo. This information is added to the information about the wide beam scan. The narrow beam provides better definition and analysis in the pulmonary veins. FIG. 11C shows the amplitude of the template signal and the envelope signal over time. In FIG. 11C, the signal bandwidth is 77%.

[0118] FIG. 12A shows multiple arrays, elliptical obstacles (shown as outer elliptical rings), and free space (shown by shading). The arrays are bounded by the free space and at the innermost point shown by a dot. Each subset of the images in FIG. 12A shows the number of elements as the first value in the brackets and the acceptance angle as the second or subsequent value in the brackets. FIG. 12B shows the mean, RMS, and maximum ellipse distances for each element and acceptance angle pair. For FIGS. 12A and 12B, simulations were performed with arrays having a radius of 15 mm for 8, 10, and 12 elements operating at acceptance angles of π / 3, π / 4, and π / 6. The obstacle ellipse has a major axis x with a range of 50 mm and a major axis y with a range of 25 mm. This ratio of major axes is larger than a typical left atrium, but illustrates the capabilities of the disclosed subject matter. A distance called the ellipse distance is measured from the found free space to a sampling point along the obstacle ellipse, each of which is less than 0.25 mm apart. The value of 0.25 mm is a sampling option that limits the error measurement. Those skilled in the art will appreciate that this value may be smaller or larger. FIG. 12A shows the resulting free space area detected within the shaded area by each array and acceptance angle pair, and also shows the union of all three acceptance angles for the 10 element array. This configuration shows an example of multi-frequency operation. In FIG. 12B, the horizontal line corresponds to approximately 3.5 mm, indicating the accuracy of these configurations.

[0119] In simulation experiments, the free-space method was compared to the DAS method in silicon. To provide a coherent sum, the location of the elements is assumed to be precisely known. A spherical array of 15 mm radius with 64 elements in the left atrium was segmented from a computed tomography (CT). The volume was divided into 50 regions using a 2 mm 3D grid. 3The 10 cm cube is divided into 10 voxels. The reflectors are sampled in a grid inside a 6 mm thick shell around the atrial border. A template hydrophone recorded signal (i.e., 1.4 MHz, 77% bandwidth) is used for the simulation, which also includes a time-scaled version at a higher frequency (7.4 MHz). This corresponds to the values ​​in FIG. 11C. No additional noise is used to evaluate optimal algorithm performance. According to Equation 12 below, the template signal is delayed and summed for each transmitter-receiver pair and reflector. These generated RF signals are used to calculate the BRV for the wide beam and the first echo for the narrow beam. The imaging volume is also calculated using the DAS and envelope DAS. The envelope is calculated as the maximum absolute value within a window corresponding to the cycle length. Pixel intensities of 4 mm were collected around the border in a given slice for the three methods (for the free space method) shown in FIG. 13A, and the respective distributions were compared as shown in FIG. 13B. As shown in Figure 13A, the closed loop forms the boundary of each slice. The free space boundary suffers less from array processing artifacts and has a much higher contrast-to-noise ratio (CNR) compared to the DAS and DAS envelope methods. The values ​​at the bottom of Figure 13A are intensity values.

[0120] 14A and 14B show the reconstruction results of two simulations using the free space method. The reconstruction is close to the left atrial body, while the location of the pulmonary veins is detectable given the valves obtained from the narrow beam. The mesh reconstruction is modeled according to the distance to the reflector. The outer mesh is illustrated, which shows the different patches at different distances to the reconstruction. All of the distances were clipped at 15 mm. The median distance (in mm) and the median absolute deviation (MAD) are provided. In simulation 1, the median distance from the detected boundary to the reflector was 2.27 mm, with a MAD of 1.3 mm. In simulation 2, the median distance from the detected boundary to the reflector was 2.78 mm, with a MAD of 1.8 mm. From the reflector to the boundary, simulation 1 resulted in a median distance of 3.78 mm and a MAD of 1.68 mm, and simulation 2 resulted in a median distance of 3.54 mm and 1.53 mm. The distance from the reflector to the border was calculated from the center of the outer atrial wall shell 2 mm away from the endocardium.

[0121] In another embodiment, additional in vitro experiments were performed using a distributed 64-element piezoelectric (PZT-5H) transducer array. In these experiments, each element has a size of 1×1×0.3 mm and is mounted on the splines of a spherical basket as shown in FIG. 2. Each transducer element has two resonant frequencies, a first of about 1.4 MHz and a second of about 7.4 MHz. The location of the elements in the array is measured by an optical system with an accuracy of about 1.0 mm. The array is configured to generate an arbitrary pulsed excitation and is operated using a National Instruments (NI) acquisition system that simultaneously receives echoes from all elements in the array. The catheter is placed in a water bath designed to simulate a blood pool and then enclosed in an elliptical plastic housing designed to simulate the walls of a cardiac chamber. FIG. 15A shows an ellipsoid phantom and FIG. 15B shows a left atrial silicon phantom. Heart-like wall motion is generated by continuously pumping water in and out of the chamber. Direct transmit and receive signals that did not experience reflections from moving walls are removed by subtracted long-term signal averaging. Signals are averaged over multiple acquisitions. In one embodiment, about 15 acquisitions are made at low frequency and 3 at high frequency. This produces at least 4 SNR values.

[0122] In another embodiment, additional elliptical phantom experiments were performed using the disclosed subject matter. In this experiment, the catheter is placed inside a water-filled silicone elliptical phantom. The phantom has radii of 35 mm, 32.5 mm, and 22.5 mm. In one embodiment, acquisitions were performed using a 1.4 MHz wide beam (i.e., 2.5 cycles). As used herein, the term "cycle" refers to a transmit signal made up of a number of sine wave cycles. The signal dynamic range was adjusted using square root signal compression. An ellipsoid was then fitted to the algorithm detection boundary. Figures 16A-16C include multiple slices through the detected boundary calculated by the free space algorithm at various points along various axes. These Figures 16A-16C show the results of the BRV operator. In each of Figures 16A-16C, the detected boundary is shown as a closed loop that generally surrounds the central shaded mass. 16A-C show a series of slices through the recorded volume perpendicular to the x-, y-, and z-axes at 15 mm, 25 mm, and 35 mm, respectively. The CNR is calculated for a subvolume of 6 mm around the boundary. The error distribution is asymmetric because the phantom is not a perfect ellipsoid. The median and MAD were calculated. The MAD estimates the standard deviation of a Gaussian distribution with a factor of about 1.5. The measured radii were 36 mm in FIG. 16A, 33.4 mm in FIG. 16B, and 25.5 mm in FIG. 16C. The ellipsoid median deviation was 1.4 mm and the MAD was 0.6283 mm.

[0123] In another embodiment, additional left atrial shaped silicon phantom experiments were performed, as shown in Figure 15B. In these experiments, scans were acquired using narrow and wide beams, and a free space algorithm detected the boundary points of the phantom. These points were used as input for the model-based fast anatomical mapping smoothing algorithm (mFam).

[0124] The reconstructed anatomical structures were manually aligned with the ground truth CAD mesh. The distance of each vertex of the smoothed surface to the corresponding ground truth mesh was calculated. The resulting mean was 4.2 ± 4.4 mm (compared to 3.5 for FAM), the median was 2.6 mm, the MAD was 1.77 mm, and the RMS was 6.1 mm.

[0125] The reconstruction results and errors are shown in Figures 17A and 17B. Figures 17A and 17B show the BRV, segmentation over the BRV, and model-based smoothing with the segmentation boundary as input to the mFam algorithm. The left hand images in Figures 17A and 17B are the distances between the detected boundary-based model and the CAD in mm. The right hand images in Figures 17A and 17B are CAD ground truth images with distances to the reconstruction. The resulting model is close to the phantom, while the detected pulmonary veins match the CAD mesh, but the size estimation is poor, resulting in large errors in these regions. This problem can be addressed by performing additional acquisitions. Some errors experienced in the reconstruction of the left atrium were caused by the inter-sensor distance not being fixed in place, which can cause errors in the sensor position of up to several millimeters, which then translates into reconstruction errors. The disclosed subject matter improves the calibration of these distances with sub-millimeter accuracy.

[0126] In summary, elements in a sparse array do not meet the Nyquist criterion because they are not separated by sub-wavelength distances. It is difficult to determine the location of elements with sub-wavelength accuracy, which introduces additional errors, especially in the coherent summation. The differences between the disclosed processes, systems, apparatus, and methods and DAS have been discussed above with reference to experiments such as in silico experiments, and by array processing related artifacts that are evident in the PSF and to distinguish nearby reflectors. This is illustrated in Figures 10A-10F.

[0127] The subject matter disclosed herein and the envelope signal significantly improves detection results, as shown at least by Figures 13A and 13B. In one aspect, to match clinical system performance, at least 10 elements operating at a wide angle of π / 3 are required to be present at any given 2D slice. Unlike other systems that use only narrow beams and linearly sample the endocardium surface, the system disclosed herein samples at a quadratic rate when examining echoes received by pairs of transducers while gaining additional normal and curvature information by the theorem disclosed herein. Compared to existing systems that require 1 minute per region for 3 mm accuracy, the disclosed subject matter accurately maps the entire endocardium with fewer acquisitions performed in real time. In one embodiment, the scan described herein is less than 16 ms.

[0128] The disclosed subject matter is not limited to the left atrium or any ventricle. The disclosed subject matter can be used in a variety of applications, including applications that utilize an array of elements to analyze features of an object, such as a chamber.

[0129] In summary, in one aspect, a catheter is provided that allows for detection of electrical activity using real-time imaging and tracking of cardiac wave propagation, thereby enabling mapping of complex arrhythmias and reducing the time required to provide reliable images and data.

[0130] In general, a particular time in the signal corresponds to the time of flight of the catheter within the cavity, which defines an entire ellipsoid in space. Due to the inherent structure of the heart, narrow cavities such as pulmonary veins are not contained within the ellipsoid and are therefore difficult to detect by known mapping methods. The use of narrow beam radiation overcomes this problem due to its size, which easily fits inside the narrow parts of the heart structure. Additional beams with different directivity patterns rely on the same ellipsoid concept, with slices of acceptance angles defined by the beam directivity. Thus, the combination of beams provides additional information about the boundary shape with a relatively small tendency to decrease the acquisition time. For example, an additional acquisition time of 70 microseconds per element may be required.

[0131] Any of the functions and methods described herein may be implemented in a general purpose computer, processor, or processor core. Suitable processors include, by way of example, general purpose processors, special purpose processors, conventional processors, digital signal processors (DSPs), multiple microprocessors, one or more microprocessors associated with a DSP core, controllers, microcontrollers, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Array (FPGA) circuits, any other type of integrated circuit (IC), and / or state machines. Such processors may be manufactured by configuring a manufacturing process using the results of processed hardware description language (HDL) instructions and other intermediate data such as netlists (such instructions may be stored in a computer readable medium). The result of such processing may be a mask work that is then used in a semiconductor manufacturing process to manufacture a processor embodying the features of the present disclosure.

[0132] Any of the functions and methods described herein can be implemented in a computer program, software, or firmware embodied in a non-transitory computer-readable storage medium and executed by a general-purpose computer or processor. Examples of non-transitory computer-readable storage media include read only memory (ROM), random access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks and digital versatile disks (DVDs).

[0133] It should be understood that many variations are possible based on the disclosure herein, and although features and elements have been described above in specific combinations, each feature or element may be used alone without the other features and elements, or in various combinations with other features and elements, with or without the other features and elements.

[0134] [Embodiment] (1) A device comprising: a catheter configured to be inserted into a body lumen of a patient; an ultrasound transducer array including a plurality of multi-frequency ultrasound transducers disposed on the catheter, each transducer of the plurality of multi-frequency ultrasonic transducers is configured to transmit a broad beam ultrasonic signal and a narrow beam ultrasonic signal; an ultrasonic transducer array, each transducer of the plurality of multi-frequency ultrasonic transducers configured to receive a wide beam echo signal and a narrow beam echo signal in response to the wide beam ultrasonic signal and the narrow beam ultrasonic signal; a processor configured to detect free space in the body lumen by processing the wide beam echo signals and the narrow beam echo signals. (2) The device of embodiment 1, wherein the processor is configured to detect the free space by determining a bounding reflection value (BRV), the BRV indicating whether a particular point in a space within the body lumen is within the free space. (3) The device of embodiment 1, wherein the ultrasonic transducer array comprises at least 64 transducers. (4) The device of embodiment 1, wherein the narrow beam ultrasound signal has a frequency in the range of 12 MHz to 16 MHz. (5) The device of embodiment 1, wherein the wide beam ultrasound signal has a frequency in the range of 1 MHz to 3 MHz.

[0135] (6) The device of embodiment 1, wherein the wide beam ultrasound signal has a beam width of at least 40 degrees. (7) The device of embodiment 1, wherein the narrow beam ultrasound signal has a beam width in the range of 4 degrees to 12 degrees. (8) The device of embodiment 1, wherein the body cavity includes a vein. (9) The device described in embodiment 1, further comprising a monitor configured to display the free space. (10) The device of embodiment 1, wherein the body cavity is a cardiac ventricle.

[0136] (11) The device of embodiment 1, wherein the processor is configured to identify the free space based on at least one of signal directivity or signal strength. (12) A method comprising the steps of: inserting a catheter into a body lumen of a patient, the catheter comprising an ultrasound transducer array including a plurality of multi-frequency ultrasound transducers; transmitting a wide beam ultrasonic signal and a narrow beam ultrasonic signal from each of the plurality of multi-frequency ultrasonic transducers; receiving wide beam echo signals in response to the wide beam ultrasound signal and receiving narrow beam echo signals in response to the narrow beam ultrasound signal; and identifying free space in the body lumen by processing the wide beam echo signals and the narrow beam echo signals. (13) The method of claim 12, wherein the ultrasound transducer array comprises at least 64 transducers. (14) The method of claim 12, wherein the narrow beam ultrasound signal has a frequency in the range of 12 MHz to 16 MHz. (15) The method of claim 12, wherein the wide beam ultrasound signal has a frequency in the range of 1 MHz to 3 MHz.

[0137] (16) The method of claim 12, wherein the wide beam ultrasound signal has a beam width of at least 40 degrees. (17) The method of claim 12, wherein the narrow beam ultrasound signal has a beam width in the range of 4 degrees to 12 degrees. (18) The method of claim 12, wherein the body cavity comprises a vein. (19) The method of embodiment 12, further comprising providing information regarding the free space to a display. (20) The method of embodiment 12, wherein the processor is configured to detect the free space by determining a boundary reflectance value (BRV), the BRV indicating whether a particular point within a space in the body lumen is within the free space.

Claims

1. A device, comprising: a catheter configured to be inserted into a body lumen of a patient; an ultrasound transducer array including a plurality of multi-frequency ultrasound transducers disposed on the catheter, each transducer of the plurality of multi-frequency ultrasonic transducers is configured to transmit a broad beam ultrasonic signal and a narrow beam ultrasonic signal; an ultrasound transducer array, each transducer of the plurality of multi-frequency ultrasound transducers configured to receive broad beam echo signals and narrow beam echo signals in response to the broad beam ultrasound signals and the narrow beam ultrasound signals; and a processor; the ultrasonic transducer array comprises a plurality of transmit / receive elements; The processor, detecting free space in the body lumen by processing a combination of the wide beam echo signals and the narrow beam echo signals; A device configured such that a single transmit element transmits, followed by all of the receive elements operating in concert to receive the transmission from the single transmit element, thereby aligning the narrow beam ultrasound signal and the wide beam ultrasound signal in time.

2. 2. The device of claim 1, wherein the processor is configured to detect the free space by determining a boundary reflectance value (BRV), the BRV indicating whether a particular point within a space in the body lumen is within the free space.

3. The device of claim 1 , wherein the ultrasound transducer array comprises at least 64 transducers.

4. The device of claim 1 , wherein the narrow beam ultrasound signal has a frequency in the range of 12 MHz to 16 MHz.

5. The device of claim 1 , wherein the broad beam ultrasound signal has a frequency in the range of 1 MHz to 3 MHz.

6. The device of claim 1 , wherein the wide beam ultrasound signal has a beamwidth of at least 40 degrees.

7. The device of claim 1 , wherein the narrow beam ultrasound signal has a beamwidth in the range of 4 degrees to 12 degrees.

8. The device of claim 1 , wherein the body lumen comprises a vein.

9. The device of claim 1 , further comprising a monitor configured to display the free space.

10. The device of claim 1 , wherein the body cavity is a cardiac ventricle.

11. The device of claim 1 , wherein the processor is configured to identify the free space based on at least one of signal directivity or signal strength.

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