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LOCATION SENSING WITH REAL-TIME
ULTRASOUND IMAGING
CROSS-REFERENCES TO RELATED
APPLICATIONS
This application is a continuation-in-part of U.S. patent application Ser. No. 09/902,087, filed Jul. 10, 2001, entitled, "Three-dimensional reconstruction using ultrasound," which is assigned to the assignee of the present patent application and is incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates generally to systems and methods for three-dimensional mapping and reconstruction, and specifically to mapping and reconstruction of the interior of body organs, such as the heart.
BACKGROUND OF THE INVENTION
Methods for three-dimensional geometrical mapping and reconstruction of the endocardial surface are known in the art. For example, U.S. Pat. No. 5,738,096, whose disclosure is incorporated herein by reference, describes methods for mapping the endocardium based on bringing a probe into contact with multiple locations on a wall of the heart, and determining position coordinates of the probe at each of the locations. The position coordinates are combined to form a map of at least a portion of the heart. These methods are effective and accurate, but they require substantial time and skill to carry them out.
PCT Patent Publications WO 99/05971 and WO 00/07501 to Willis et al., which are incorporated herein by reference, describe the use of ultrasound transducers on a reference catheter to locate ultrasound transducers on other catheters (e.g., mapping or ablation catheters) which are brought into contact with the endocardium.
A variety of methods have been developed for noncontact reconstruction of the endocardial surface using intracardial ultrasonic imaging. These methods typically use a catheter with a built-in, miniaturized ultrasonic imaging array or scanner. For example, PCT Patent Publication WO 00/19908, whose disclosure is incorporated herein by reference, describes a steerable transducer array for intracardial ultrasonic imaging. The array forms an ultrasonic beam, which is steered in a desired direction by an active aperture. Similarly, U.S. Pat. No. 6,004,269, whose disclosure is also incorporated herein by reference, describes an acoustic imaging system based on an ultrasound device that is incorporated into a catheter. The ultrasound device directs ultrasonic signals toward an internal structure in the heart to create an ultrasonic image.
Further examples of intracardial ultrasonic imaging are presented in U.S. Pat. No. 5,848,969 and in PCT Patent Publication WO 98/18388, whose disclosures are incorporated herein by reference. These publications describe systems and methods for visualizing interior tissue regions using expandable imaging structures. The structures assume an expanded geometry once inside the heart, which stabilizes an associated imaging probe or array.
U.S. Pat. No. 5,797,849 and PCT Patent Publication WO 99/58055, whose disclosures are also incorporated herein by reference, describe methods for carrying out medical procedures using a three-dimensional tracking and imaging system. The position of a catheter or other probe inside the body is tracked, and its location relative to its immediate surroundings is displayed to improve a physician's ability to
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precisely position it. Various procedures using such a probe are described in these publications. One such procedure is ultrasonic imaging, using an ultrasound imaging head with transducers held outside the body to image an area inside the
5 body in which a probe with a position sensor is located. Various methods are known in the art for enhancing ultrasonic images and for extracting information, such as three-dimensional contours, from such images. These methods typically combine information from multiple two
1° dimensional images to define three-dimensional features. For example, PCT Patent Publication WO 99/55233, whose disclosure is incorporated herein by reference, describes a method for defining a three-dimensional surface of at least a portion of a patient's heart using a plurality of images in
15 different planes. The images are made using an ultrasound transducer at known positions and orientations outside the patient's body. Anatomical landmarks are manually identified in the plurality of images.
Other methods of contour extraction and three
20 dimensional modeling using ultrasonic images are described in European Patent Application EP 0 961 135 and in Japanese Patent Application JP 9-285465, whose disclosures are also incorporated herein by reference. As another example, PCT Patent Publication WO 98/46139, whose
25 disclosure is incorporated herein by reference, describes a method for combining Doppler and B-mode ultrasonic image signals into a single image using a modulated nonlinear mapping function.
3Q U.S. Pat. No. 5,846,205 to Curley et al, which is incorporated herein by reference, describes a phased-array ultrasonic transducer assembly mounted on a catheter. An end portion is attached to the catheter around a transducer array, and the end portion defines an acoustic window which is
35 essentially non-focusing to ultrasonic energy passing therethrough. Because the acoustic window is non-focusing, a relatively small radius of curvature can be used on the radially outer surface of this window.
U.S. Pat. No. 6,066,096 to Smith et al., which is incor
4q porated herein by reference, describes imaging probes and catheters for volumetric intraluminal ultrasound imaging. Apparatus configured to be placed inside a patient includes an elongated body having proximal and distal ends, with an ultrasonic transducer phased array connected to and posi
45 tioned on the distal end of the elongated body. The ultrasonic transducer phased array is positioned to emit and receive ultrasonic energy for volumetric forward scanning from the distal end of the elongated body. The ultrasonic transducer phased array includes a plurality of sites occupied by
50 ultrasonic transducer elements. At least one ultrasonic transducer element is absent from at least one of the sites, thereby defining an interstitial site. A tool is positioned at the interstitial site. In particular, the tool can be a fiber optic lead, a suction tool, a guide wire, an electrophysiological
55 electrode, or an ablation electrode.
U.S. Pat. No. 6,059,731 to Seward et al., which is incorporated herein by reference, describes a simultaneous sideand-end viewing ultrasound imaging catheter system which includes at least one side array and at least one end array.
go Each of the arrays has at least one row of ultrasonic transducer elements. The elements are operable as a single ultrasound transducer which are phased to produce different views.
U.S. Pat. No. 5,904,651 to Swanson et al, which is 65 incorporated herein by reference, describes a catheter tube which carries an imaging element for visualizing tissue. The catheter tube also carries a support structure, which extends
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beyond the imaging element for contacting surrounding tissue away from the imaging element. The support element stabilizes the imaging element, while the imaging element visualizes tissue in the interior body region. The support structure also carries a diagnostic or therapeutic component 5 to contact surrounding tissue.
U.S. Pat. No. 5,876,345 to Eaton et al., which is incorporated herein by reference, describes an ultrasonic catheter for two dimensional imaging or three-dimensional reconstruction. An ultrasonic catheter including at least two 1° ultrasonic arrays having good near and far field resolution provides an outline of a heart chamber, in order to assist in interpreting images obtained by the catheter.
U.S. Pat. No. 6,228,032 to Eaton et al., which is incorporated herein by reference, describes a steering mechanism 15 and steering line for a catheter-mounted phased linear array of ultrasonic transducer elements.
U.S. Pat. No. 6,226,546 to Evans, which is incorporated herein by reference, describes a catheter location system for generating a three dimensional map of a part of a human 20 body, from which three dimensional map a position of the catheter may be determined. A plurality of acoustic transducers are disposed about the catheter head at predetermined locations. A signal processing unit generates the three dimensional map responsive to signals received by a plurality of acoustic transducers acting as acoustic receivers, which acoustic signals were generated by at least one of said plurality of acoustic transducers acting as an acoustic source.
U.S. Pat. No. 6,226,542 to Reisfeld, which is assigned to 3Q the assignee of the present patent application and incorporated herein by reference, describes a method for threedimensional reconstruction of intrabody organs. A processor reconstructs a 3D map of a volume or cavity in a patient's body from a plurality of sampled points on the volume 3J whose position coordinates have been determined. Reconstruction of a surface is based on a limited number of sampled points. The number of sampled points is generally less than 200 points and may be less than 50 points. Preferably, ten to twenty sampled points are sufficient in 4Q order to perform a preliminary reconstruction of the surface to a satisfactory quality.
U.S. Pat. No. 6,171,248 to Hossack et al, which is incorporated herein by reference, describes an ultrasonic probe for two-dimensional imaging or three-dimensional 45 reconstruction. The patent describes an ultrasonic probe that includes at least two ultrasonic arrays, and allows three dimensional images to be constructed of the region examined by the probe.
PCT Patent Publication WO 96/05768 to Ben-Haim et al., 50 which is incorporated herein by reference, describes a system for determining the location and orientation of an invasive medical instrument such as a catheter or endoscope. A plurality of field generators typically outside a patient's body generate known, distinguishable fields, preferably con- 55 tinuous AC magnetic fields, in response to drive signals. A plurality of sensors situated in the invasive medical instrument proximate the distal end thereof generate sensor signals in response to the fields. A signal processor receiving the sensor and drive signals processes the information to 60 determine three location coordinates and three orientation coordinates (i.e., 6 dimensions of information) relating to a point on the medical instrument.
U.S. Pat. No. 5,391,199 to Ben-Haim, which is incorporated herein by reference, describes a method for the treat- 65 ment of cardiac arrhythmias, particularly, a method for ablating a portion of an organ or bodily structure of a patient.
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The method includes obtaining a perspective image of an organ or structure to be mapped and advancing one or more catheters having distal tips to sites adjacent to or within the organ or structure, at least one of the catheters having ablation ability. The location of each catheter's distal tip is sensed using a non-ionizing field. At the distal tip of one or more catheters, local information of the organ or structure is sensed, and the sensed information is processed to create one or more data points. The one or more data points are superimposed on a perspective image of the organ or structure, to facilitate the ablating of a portion of the organ or structure.
SUMMARY OF THE INVENTION
It is an object of some aspects of the present invention to provide improved methods and apparatus for threedimensional mapping and geometrical reconstruction of body cavities, and particularly of chambers of the heart.
In preferred embodiments of the present invention, a cardiac catheter comprises a primary acoustic transducer and a plurality of secondary acoustic transducers distributed longitudinally along a distal portion of the catheter. The primary acoustic transducer is actuated to emit acoustic waves, preferably ultrasonic waves, while the catheter is inside a chamber of the heart. The acoustic waves are reflected from the endocardial surface of the cavity, and are received by the secondary acoustic transducers and also, typically, the primary acoustic transducer. Processing circuitry, coupled to the transducers, determines the times of flight of the received acoustic waves, thus providing a measurement of the distance from each of the transducers to a point or area on the endocardial surface. Subsequently, the primary acoustic transducer is actuated to emit acoustic waves towards other sites on the endocardium, to enable determinations of the distances from these sites to the various transducers. The distance measurements are then combined to reconstruct the three-dimensional shape of the surface, which is preferably displayed in the form of a geometrical map.
In order to direct the ultrasound from the primary acoustic transducer to the various sites on the endocardium, the catheter is preferably physically moved by the user within the chamber of the heart. Alternatively or additionally, a phased array ultrasound transducer incorporated into the primary acoustic transducer directs the ultrasound pulses to a range of sites on the endocardium. Reflected pulses from these sites are detected by the secondary acoustic transducers to enable the time of flight calculations used in the generation of the geometrical map.
For some applications, the secondary acoustic transducers are actuated individually, in sequence, to emit acoustic waves, preferably ultrasonic waves, while the catheter is inside the heart chamber.
In accordance with a preferred embodiment of the present invention, a significant portion of the endocardial surface may be mapped rapidly, typically within a single heart beat. This rapid mapping can be achieved because the acoustic waves are used to measure three-dimensional distances directly, rather than by attempting to image the heart and then extract geometrical information from the images as in methods known in the art. The distance measurements are facilitated by the unique design of the catheter, wherein the secondary acoustic transducers are distributed longitudinally along the catheter, instead of being concentrated in a phased array or other imaging configuration. In this manner, a greater range of times of flight are attained, allowing a
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highly-accurate assessment of the locations of the various sites on the endocardium with respect to the catheter or with respect to an absolute reference system. Preferred embodiments of the present invention also avoid the need for physical contact between the catheter and the endocardial 5 surface during measurement.
In some preferred embodiments of the present invention, the catheter comprises one or more position sensors, which are used to determine position and orientation coordinates of the catheter within the heart. For some applications, each 1° position sensor is associated with a particular one or set of the secondary acoustic transducers. Alternatively, one or several position sensors are placed at discrete locations on the catheter. Using the position sensors in conjunction with the acoustic measurements allows the reconstructed three- :5 dimensional shape of the surface to be located and oriented in space. It also enables multiple measurements to be taken at different positions within the heart, during movement of the catheter, in order to enhance the accuracy of the reconstruction. 20
Preferably, the position sensors comprise one or more miniature coils, which are used to determine position and orientation coordinates by transmitting or receiving electromagnetic waves, as described, for example, in the abovecited PCT Patent Publication WO 96/05768 or U.S. Pat. No. 25 5,391,199, which are incorporated herein by reference. Alternatively, the acoustic transducers on the catheter also serve as position sensors, by receiving acoustic waves transmitted from a plurality of acoustic transducers at fixed positions outside the body, or by transmitting acoustic waves 30 to these external transducers. The times of flight of these waves are used to determine the position and orientation of the catheter. Further alternatively, other types of position sensing systems, as are known in the art, may be used.
In further preferred embodiments of the present invention, the catheter comprises a plurality of electrodes in addition to the acoustic transducers, and is used for electrical, as well as geometrical, mapping of the heart. Preferably, the electrical mapping is performed rapidly using an array of non-contact 4Q electrodes, most preferably as described in U.S. patent application Ser. No. 09/598,862 entitled "Rapid Mapping of Electrical Activity in the Heart," filed Jun. 21, 2000 (applicant's docket no. BIO 97 US), which is assigned to the assignee of the present patent application and is incorporated 4J herein by reference. The electrical and geometrical maps are registered to provide an integrated view of mechanical and electrical properties of the heart.
In some preferred embodiments of the present invention, other features of the acoustic waves received by the trans- 50 ducers on the catheter are analyzed to provide further geometrical and diagnostic information. For example, in one such embodiment, the processing circuitry analyzes the reflected waves to find reflections from both the endocardial and the epicardial surfaces. In this manner, both of the 55 surfaces can be reconstructed simultaneously, and the thickness of the heart wall can be mapped.
In another embodiment, the processing circuitry analyzes the frequency, as well as the time of flight, of the reflected waves in order to detect a Doppler shift. The Doppler 60 measurement is used to determine and map the heart wall velocity. This method thus enables the relative speeds of opposing or mutually-perpendicular segments of the heart wall to be measured simultaneously. By contrast, methods of echo Doppler measurement known in the art use a probe 65 outside the body and therefore can measure wall velocity of only one side of the heart at any given time.
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Although preferred embodiments are described herein with reference to cardiac catheters for mapping chambers of the heart, other applications of the present invention will be apparent to those skilled in the art. These applications include, but are not limited to, mapping and geometrical reconstruction of other body cavities, such as the coronary arteries or the gastrointestinal system.
There is therefore provided, in accordance with a preferred embodiment of the present invention, apparatus for mapping a surface of a cavity within a body of a subject, including:
an elongate probe, having a longitudinal axis and including a distal portion adapted for insertion into the cavity;
a primary acoustic transducer on the distal portion of the probe, adapted to emit acoustic waves while the probe is in the cavity; and
a plurality of secondary acoustic transducers, distributed along the longitudinal axis over the distal portion of the probe, which are adapted to receive the acoustic waves after reflection of the waves from the surface of the cavity and to generate, responsive to the received waves, electrical signals indicative of times of flight of the waves.
Preferably, the apparatus includes apparatus for mapping a chamber of the heart of the subject, and the probe includes an intracardiac catheter.
In a preferred embodiment, the primary acoustic transducer includes a phased array ultrasound transducer. Alternatively, the primary acoustic transducer includes an ultrasound transducer configured only for non-phased array operation. Further alternatively or additionally, the secondary acoustic transducers include ultrasound transducers configured only for non-phased array operation.
Preferably, the probe includes at least one position sensor, which is adapted to generate a position signal indicative of position coordinates of the probe within the body. Preferably, the apparatus further includes control circuitry, adapted to process the electrical signals generated by the secondary acoustic transducers responsive to the position signal, so as to reconstruct a three-dimensional shape of the surface of the cavity based on the times of flight and the position signal. Typically, the position sensor includes a coil, and the position signal includes an electrical current induced in the coil by an externally-applied magnetic field.
Additionally or alternatively, the at least one position sensor includes a plurality of position sensors. Preferably, one of the plurality of position sensors is disposed on the probe near a first subset of the secondary acoustic transducers, and another one of the plurality of position sensors is disposed on the probe near a second subset of the secondary acoustic transducers, and the apparatus includes control circuitry, adapted to process the electrical signals generated by the secondary acoustic transducers responsive to position signals generated by the first and second position sensors, so as to reconstruct a three-dimensional shape of the surface of the cavity based on the times of flight and the position signals.
Preferably, the apparatus includes control circuitry, adapted to receive and to process the electrical signals generated by the secondary acoustic transducers so as to reconstruct a three-dimensional shape of the surface of the cavity based on the times of flight. Most preferably, responsive to the times of flight, the circuitry is adapted to determine distances from the secondary acoustic transducers to respective points on the surface of the cavity, and to combine the determined distances so as to reconstruct the shape. Additionally or alternatively, the circuitry is operative
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