Patent Application
20100191101
The present invention relates generally to invasive medical devices, and specifically to invasive probes that combine imaging and position sensing functions.
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 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 location and orientation coordinates of the catheter within the heart.
U.S. Patent Application Publication 2006/0241445, whose disclosure is incorporated herein by reference, describes a method and apparatus for modeling an anatomical structure, such as a chamber of the heart. A probe that comprises an array of ultrasound transducers and a position sensor is used to image a target organ or structure in the patient's body. In one embodiment, the probe comprises a catheter, which is inserted into the patient's heart. The probe acquires multiple 2-D ultrasound images of the target organ and sends them to an image processor. For each image, location and orientation coordinates of the probe are measured using the position sensor. A three-dimensional (3-D) model of the anatomical structure is constructed, based on the ultrasound images and on the measured location and orientation coordinates.
Combining position sensing and ultrasonic imaging functions in a single probe, such as a cardiac catheter, may give rise to safety concerns. The ultrasonic subsystem, including an ultrasonic transducer contained in the probe and external processing circuitry, may generate relatively high voltages and is typically held at ground potential and electrically isolated from the patient. On the other hand, the position sensing subsystem, including a position transducer in the probe and external position tracking circuitry, may be held at the “applied part” potential of the patient's body, which should be kept isolated from the ground for safety reasons. The position transducer and ultrasonic transducer, however, are typically located in close proximity to one another in the probe. A short circuit between these components or their associated wiring could violate the desired isolation and endanger the patient.
Embodiments of the present invention that are described hereinbelow provide secure electrical isolation between position sensing and ultrasonic subsystems in an invasive imaging system. The isolation may be achieved by using isolation circuitry to convey signals between the position sensor in the probe and the external position tracking circuitry without creating a conductive path between the position sensor and the position tracking circuitry.
There is therefore provided, in accordance with an embodiment of the present invention, medical apparatus, including:
an invasive probe, for insertion into a body of a living subject;
an ultrasonic subsystem, including an ultrasonic transducer contained in the probe and image processing circuitry, which is located outside the probe and is coupled to communicate with the ultrasonic transducer in the probe; and
a position sensing subsystem, including a position transducer contained in the probe and position tracking circuitry, which is located outside the probe and is coupled to communicate with the position transducer so as to determine position coordinates of the ultrasonic transducer in the body,
wherein the position sensing subsystem is electrically isolated from the ultrasonic subsystem.
In some embodiments, the invasive probe includes a catheter for insertion into a heart of the subject. In one embodiment, the ultrasonic transducer is configured to capture a plurality of ultrasonic input images of an organ at different, respective positions of the probe within the body, and the image processing circuitry is configured to combine the input images, using the position coordinates, to generate a three-dimensional image of the organ. Additionally or alternatively, the position sensing subsystem includes one or more magnetic field generators, which are configured to generate a magnetic field within the body, and the position transducer includes a magnetic field sensor, which is configured to output position signals to the position tracking circuitry responsively to the magnetic field.
Typically, the ultrasonic transducer is held at a ground potential by the ultrasonic subsystem, while the position sensing subsystem is at a non-ground potential.
In a disclosed embodiment, the apparatus includes isolation circuitry, which is interposed between the position transducer and the position tracking circuitry so as to convey position signals between the position transducer and the position tracking circuitry without creating a conductive path between the position transducer and the position tracking circuitry. Typically, the isolation circuitry includes one or more isolation transformers.
There is also provided, in accordance with an embodiment of the present invention, a method for producing an invasive medical system, including:
providing an invasive probe, for insertion into a body of a living subject;
assembling an ultrasonic subsystem by installing an ultrasonic transducer in the probe and coupling the ultrasonic transducer to communicate with image processing circuitry outside the probe;
assembling a position sensing subsystem by installing a position transducer in the probe and coupling the position transducer to communicate with position tracking circuitry outside the probe so as to determine position coordinates of the ultrasonic transducer in the body; and
electrically isolating the position sensing subsystem from the ultrasonic subsystem.
The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:
Position sensor 32 is one type of position transducer. In an alternative embodiment, the position transducer in the distal end of catheter 28 may be configured as a radiator, which generates magnetic fields. In this case, coils 30 may sense these fields. Further alternatively, other types of position transducers may be used in the catheter, such as electrical impedance-based transducers (transmitters or sensors), as are known in the art.
The position tracking subsystem in system 20 may operate on the principles of magnetic position tracking systems that are known in the art. Systems of this sort are described, for example, in U.S. Pat. Nos. 6,690,963, 6,618,612 and 6,332,089, and U.S. Patent Application Publications 2002/0065455 A1, 2004/0147920 A1 and 2004/0068178 A1, whose disclosures are all incorporated herein by reference. A tracking system of this type is used in the CARTO™ system, which is produced by Biosense Webster Inc. (Diamond Bar, Calif.). Alternatively, as noted above, the principles of the present invention may be implemented, mutatis mutandis, using any other suitable positioning subsystem.
Catheter 28 also comprises an ultrasonic transducer 34 at its distal end, for use in creating images of heart 24. Typically, transducer 34 captures multiple intracardiac ultrasound images (which may be two-dimensional or three-dimensional images). The coordinate readings provided by position sensor 32 are used in registering the ultrasound images captured at different positions of the catheter in order to reconstruct a full 3D image. This image may comprise one or more chambers of the heart, as well as nearby structures outside the heart, such as blood vessels. A catheter and system with such capabilities (and also including an electrode for electro-anatomical sensing) are described in the above-mentioned U.S. Patent Application Publication 2006/0241445.
Further additionally or alternatively, catheter 28 and system 20 may be adapted to create images of other types, such as maps showing mechanical activity or other types of physiological activity within the heart. Furthermore, although the embodiments described herein relate specifically to cardiac imaging, the principles of the present invention may similarly be applied in imaging of other organs of the body.
A console 42 drives and controls the elements of system 20. Console 42 comprises position tracking circuitry 46, which generates signals to drive radiator coils 30 and processes the position signals that are output by position sensor 32 in catheter 28. The signals from the position sensor are conveyed from the catheter via a cable 40 to isolation circuitry 48, which couples the position sensor to position tracking circuitry 46 without creating a conductive path between the sensor and the position tracking circuitry. Thus, catheter 28 itself is isolated from the position tracking circuitry. Details of the isolation circuitry are shown in the figures that follow.
Image signals output by ultrasonic transducer 34 are conveyed from catheter 28 via a cable 38 to image processing circuitry 44. This circuitry processes the image signals in order to generate a 3D ultrasound image of heart 24, as noted above. The image is presented on an output device, such as a display 50. Typically, circuitry 44 comprises a general-purpose computer, with suitable interface circuits and possibly hardware acceleration circuits. The computer is programmed in software to combine the individual images into the 3D image. This process, using the position coordinates computed by position tracking circuitry 46, is described in greater detail in the patents and patent applications cited above.
Isolation barrier 90 may also comprise ancillary components, such as an isolated DC/DC converter 98 for providing operating voltage to front end circuitry 54 in handle 36, as well as opto-couplers 100 for transferring digital control and data signals. In the embodiment shown in
Thus, patient 22 is protected from leakage currents and high-voltage transients that might otherwise penetrate through to heart 24 via catheter 28. Although
