Methods for three-dimensional (3-D) mapping of the endocardium (i.e., the inner surfaces of the heart) are known in the art. For example, U.S. Pat. No. 5,738,096, whose disclosure is incorporated herein by reference, describes a method for constructing a map of the heart. An invasive probe is brought into contact with multiple locations on the wall of the heart. The position of the invasive probe is determined for each location, and the positions are combined to form a structural map of at least a portion of the heart.
In some systems, such as the one described by U.S. Pat. No. 5,738,096 cited above, additional physiological properties, as well as local electrical activity on the surface of the heart, are also acquired by the catheter. A corresponding map incorporates the acquired local information.
Some systems use hybrid catheters that incorporate position sensing. For example, U.S. Pat. No. 6,690,963, whose disclosure is incorporated herein by reference, describes a locating system for determining the location and orientation of an invasive medical instrument.
A catheter with acoustic transducers may be used for non-contact imaging of the endocardium. For example, U.S. Pat. Nos. 6,716,166 and 6,773,402, whose disclosures are also incorporated herein by reference, describe a system for 3-D mapping and geometrical reconstruction of body cavities, particularly of the heart. The system uses a cardiac catheter comprising a plurality of acoustic transducers. The transducers emit ultrasonic waves that are reflected from the surface of the cavity and are received again by the transducers. The distance from each of the transducers to a point or area on the surface opposite the transducer is determined, and the distance measurements are combined to reconstruct the 3-D shape of the surface. The catheter also comprises position sensors, which are used to determine position and orientation coordinates of the catheter within the heart.
U.S. Pat. No. 5,846,205, whose disclosure is incorporated herein by reference, describes a phased-array ultrasonic transducer assembly that includes a catheter. An end portion is mounted to the catheter around a transducer array, and the end portion defines an acoustic window, which is essentially non-focusing to ultrasonic energy passing therethrough. Because the acoustic window is non-focusing, the inventors claim that a relatively small radius of curvature can be used on the radial outer surface of this window.
U.S. Pat. No. 6,066,096, whose disclosure is incorporated herein by reference, describes an imaging probe for volumetric intraluminal ultrasound imaging. The probe, configured to be placed inside a patient body, includes an elongated body having proximal and distal ends. An ultrasonic transducer phased array is connected to and positioned 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 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 electrode, or an ablation electrode.
U.S. Pat. No. 6,059,731, whose disclosure is incorporated herein by reference, describes a simultaneous side-and-end viewing ultrasound imaging catheter system. The system includes at least one side array and at least one end array. Each of the arrays has at least one row of ultrasonic transducer elements. The elements are operable as a single ultrasound transducer and are phased to produce different views.
U.S. Pat. No. 5,904,651, whose disclosure is incorporated herein by reference, describes a catheter tube that carries an imaging element for visualizing tissue. The catheter tube also carries a support structure, which extends 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 to contact surrounding tissue.
U.S. Pat. No. 5,876,345, whose disclosure is incorporated herein by reference, describes an ultrasonic catheter for two-dimensional (2-D) imaging or 3-D reconstruction. The ultrasonic catheter includes at least two ultrasonic arrays having good near and far field resolutions. The catheter 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, whose disclosure is incorporated herein by reference, describes a steering mechanism and steering line for a catheter-mounted phased linear array of ultrasonic transducer elements.
U.S. Pat. No. 6,226,546, whose disclosure is incorporated herein by reference, describes a catheter location system for generating a 3-D map of a part of a human body, from which a position of the catheter may be determined. A plurality of acoustic transducers is disposed about the catheter head at predetermined locations. Acoustic signals are generated by the acoustic transducers acting as sources. A signal processing unit generates the 3-D map responsive to signals received by the acoustic transducers acting as acoustic receivers.
U.S. Pat. No. 6,171,248, whose disclosure is incorporated herein by reference, describes an ultrasonic probe for 2-D imaging or 3-D reconstruction. The patent describes an ultrasonic probe that includes at least two ultrasonic arrays. The probe allows 3-D images to be constructed and examined.
Several methods are known in the art for non-contact reconstruction of the endocardial surface using intracardial ultrasonic imaging. 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. 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. PCT Patent Publications WO 99/05971 and WO 00/07501, whose disclosures 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.
Further examples of intracardial ultrasonic imaging are presented in U.S. Pat. No. 5,848,969, whose disclosure is incorporated herein by reference. This publication describes systems and methods for visualizing interior tissue regions using expandable imaging structures.
PCT Patent Publication WO 99/55233, whose disclosure is incorporated herein by reference, describes a method for delineating a 3-D surface of a patient's heart. A 3-D mesh model is developed using training data, to serve as an archetypal shape for a population of patient hearts. Multiple ultrasound images of the patient's heart are taken in different image planes. Anatomical locations are manually identified in each of the images. The mesh model is rigidly aligned with the images, in respect to the predefined anatomical locations.
Other methods of contour extraction and 3-D modeling using ultrasonic images are described in European Patent Application EP 0961135, whose disclosure is incorporated herein by reference. As another example, PCT Patent Publication WO 98/46139, whose disclosure is also 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.
U.S. Pat. No. 5,797,849, whose disclosure is incorporated herein by reference, describes a method for carrying out a medical procedure using a 3-D tracking and imaging system. A surgical instrument is inserted into a patient body. The position of the surgical instrument is tracked as it moves through a bodily structure. The location of the surgical instrument relative to its immediate surroundings is displayed to improve a physician's ability to precisely position the surgical instrument.
U.S. Pat. No. 5,391,199, whose disclosure is incorporated herein by reference, describes a method for ablating a portion of an organ or bodily structure of a patient. The method includes obtaining a perspective image of an organ or structure to be mapped, and advancing one or more catheters to sites adjacent to or within the organ or structure. The location of each catheter 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 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.
Some medical imaging systems apply methods for reconstructing 3-D models, based on acquired imaging information. For example, U.S. Pat. No. 5,568,384, whose disclosure is incorporated herein by reference, describes a method for synthesizing 3-D multimodality image sets into a single composite image. Surfaces are extracted from two or more different images and matched using semi-automatic segmentation techniques.
U.S. Pat. No. 6,226,542, whose disclosure is incorporated herein by reference, describes a method for 3-D reconstruction of intrabody organs. A processor reconstructs a 3-D map of a volume or cavity in a patient's body from a plurality of sampled points on the volume whose position coordinates have been determined. Reconstruction of a surface is based on a limited number of sampled points.
U.S. Pat. Nos. 4,751,643 and 4,791,567, whose disclosures are incorporated herein by reference, describe a method for determining connected substructures within a body. 3-D regions exhibiting the same tissue type are similarly labeled. Using the label information, all similarly labeled connected data points are determined. Some systems use image processing methods for analyzing and modeling body tissues and organs based on information acquired by imaging. One such technique is described by McInerney and Terzopoulos in “Deformable Models in Medical Image Analysis: A Survey,” Medical Image Analysis, (1:2), June 1996, pages 91-108, which is incorporated herein by reference. The authors describe a computer-assisted medical image analysis technique for segmenting, matching, and tracking anatomic structures by exploiting (bottom-up) constraints derived from the image data together with (top-down) a priori knowledge about the location, size, and shape of these structures.
Another analysis technique is described by Neubauer and Wegenkittl in “Analysis of Four-Dimensional Cardiac Data Sets Using Skeleton-Based Segmentation,” the 11th International Conference in Central Europe on Computer Graphics, Visualization and Computer Vision, University of West Bohemia, Plzen, Czech Republic, February 2003, which is incorporated herein by reference. The authors describe a computer-aided method for segmenting parts of the heart from a sequence of cardiac CT (Computerized Tomography) images, taken at a number of time points over the cardiac cycle.
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