Abstract:
Apparatus for performing a medical procedure includes an invasive probe having opposite distal and proximal ends. The probe includes a transmitter, which is arranged to transmit an energy field, and a receiver, which is arranged to receive the energy field, wherein the transmitter and the receiver are disposed at the opposite ends of the probe. A control unit is adapted to determine an orientation of the distal end relative to the proximal end responsively to the energy field received by the receiver.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Patent Application 60/605,233, filed Aug. 26, 2004, whose disclosure is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   During endoscopic procedure using a flexible endoscope, the shape of the endoscope is typically deformed due to constraints of the body passages through which the endoscope must pass, as well as to steering of the endoscope by the operator. As a result, the operator may have difficulty in determining the actual orientation of the distal end of the endoscope, and may therefore be unable to correctly associate the positions of objects seen in endoscopic images with the actual locations of the objects in the patient&#39;s body. 
   In response to these problems, methods have been proposed for measuring the orientation of the endoscope, and then rotating the endoscopic image optically, mechanically or electronically to compensate for the orientation. Exemplary methods for such purposes are described in U.S. Pat. Nos. 6,478,743, 5,545,120, 6,471,637, 6,097,423, U.S. Patent Application Publication 2002/0161280, and U.S. Pat. No. 6,663,559, whose disclosures are incorporated herein by reference. Measurements of the orientation of an invasive probe, such as an endoscope or catheter, may also be used in controlling other types of procedures carried out inside the body using the probe. 
   SUMMARY OF THE INVENTION 
   In methods known in the art for determining orientation of an invasive probe, the orientation (and location) of the distal end of the probe is generally measured relative to an external frame of reference, which is separate from the probe itself. For example, a magnetic sensor in the probe may be used to determine the probe orientation relative to a set of magnetic field generators placed in known locations outside the patient&#39;s body. 
   By contrast, in some embodiments of the present invention, the orientation of the distal end of a probe is measured relative to the proximal end of the probe itself, by wireless transmission of an energy field between the distal and proximal ends. Measuring the orientation of the distal end of the probe relative to the proximal end, rather than relative to an external frame of reference, obviates the need for external measurement appliances in order to define the frame of reference. The measured, relative orientation of the distal end of the probe is then used in controlling an aspect of an endoscopic procedure. For example, endoscopic images captured by the probe may be rotated to compensate for the orientation. Since the proximal end of the probe is located outside the body, the operator knows the orientation of the proximal end, so that the relative orientation of the distal end is sufficient for some purposes. Alternatively, the absolute orientation of the proximal end of the probe may be measured relative to an external frame of reference, and the orientation of the distal end in the external frame may then be calculated by combining the relative and absolute measurements. 
   In some embodiments of the present invention, the measured orientation of the distal end of the probe is used in tracking an imaging scan of the inner surface of a body cavity. A system controller tracks and maps the areas of the surface that have been imaged by the endoscope. The map is presented graphically to the operator of the endoscope, and thus enables the operator to see which areas have not yet been imaged and to steer the endoscope accordingly. Alternatively, the controller may automatically steer the endoscope so as to image the entire surface or a desired area of the surface. The orientation of the distal end maybe measured for this purpose using the relative measurement technique described above or, alternatively, using any other suitable method of orientation tracking. 
   There is therefore provided, in accordance with an embodiment of the present invention, a method for performing a medical procedure using an invasive probe having distal and proximal ends, the method including: 
   determining an orientation of the distal end relative to the proximal end by wireless transmission of an energy field between the distal and proximal ends; and 
   controlling an aspect of the procedure responsively to the orientation. 
   Determining the orientation may include transmitting the energy field from a transmitter in the proximal end and sensing the energy field using a receiver in the distal end, or transmitting the energy field from a transmitter in the distal end and sensing the energy field using a receiver in the proximal end. In a disclosed embodiment, the energy field includes an electromagnetic field. 
   In some embodiments, the method includes inserting the distal end of the probe into a body of a patient, and capturing an image of an area inside the body in proximity to the distal end, wherein controlling the aspect includes rotating the image responsively to the orientation. In one embodiment, determining the orientation of the distal end relative to the proximal end includes finding a first orientation, and rotating the image includes finding a second orientation of the proximal end of the probe relative to a predefined frame of reference, and rotating the image responsively to the first and second orientations so as to orient the image relative to the predefined frame of reference. 
   In some embodiments, the probe includes a handle at the proximal end thereof, and determining the orientation includes finding the orientation of the distal end relative to the handle. 
   There is also provided, in accordance with an embodiment of the present invention, apparatus for performing a medical procedure, including: 
   an invasive probe having opposite distal and proximal ends, the probe including a transmitter, which is arranged to transmit an energy field, and a receiver, which is arranged to receive the energy field, wherein the transmitter and the receiver are disposed at the opposite ends of the probe; and 
   a control unit, which is adapted to determine an orientation of the distal end relative to the proximal end responsively to the energy field received by the receiver. 
   There is additionally provided, in accordance with an embodiment of the present invention, apparatus for endoscopy, including: 
   an endoscope, which includes:
         an insertion tube, having distal and proximal ends;   an imaging assembly within the distal end of the insertion tube, for capturing images of objects in proximity to the distal end;   a handle, fixed to the proximal end of the insertion tube; and   a field transmitter and a field receiver, one disposed within the handle and the other disposed within the distal end of the insertion tube;       

   a display, for displaying the images captured by the imaging assembly; and 
   a control unit, which is coupled to drive the field transmitter to transmit an energy field, and is coupled to receive signals from the field receiver responsively to the energy field transmitted by the field transmitter, and which is adapted to determine an orientation of the distal end of the insertion tube relative to the handle based on the signals and to rotate the images responsively to the orientation. 
   There is further provided, in accordance with an embodiment of the present invention, a method for imaging a cavity using an endoscope having a distal end, the method including: 
   inserting the distal end of the endoscope into the cavity; 
   manipulating the distal end of the endoscope within the cavity so as to capture images of areas of an inner surface of the cavity at multiple, respective viewing angles; 
   measuring an orientation of the viewing angle while capturing the images; and 
   mapping the areas of the inner surface that have been imaged by the endoscope responsively to the measured orientation. 
   There is moreover provided, in accordance with an embodiment of the present invention, an endoscopic imaging system, including: 
   an endoscope which includes:
         an insertion tube, having a distal end, which is adapted to be inserted into a cavity;   an imaging assembly within the distal end of the insertion tube, for capturing images of areas of an inner surface of the cavity at multiple, respective viewing angles;   an orientation sensor, which is arranged to generate a signal indicative of an orientation of the viewing angles of the images; and       

   a control unit, which is coupled to receive the images and the signal, and to map the areas of the inner surface by combining the images responsively to the respective viewing angles. 
   The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic, pictorial illustration of a system for endoscopy, in accordance with an embodiment of the present invention; 
       FIG. 2  is a schematic, sectional view of an endoscope, in accordance with an embodiment of the present invention; 
       FIG. 3  is a flow chart that schematically illustrates a method for rotating an image based on the measured orientation of the distal end of an endoscope, in accordance with an embodiment of the present invention; and 
       FIG. 4  is a schematic representation of a graphical map shown on a display, in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
     FIG. 1  is a schematic, pictorial illustration of a system  20  for endoscopy, in accordance with an embodiment of the present invention. In this example, system  20  is used for bronchoscopic inspection of a lung  26  of a patient  27 . In other embodiments, similar systems may be used in other fields of endoscopy, particularly cystoscopy, renoscopy and gastro-intestinal endoscopy, as well as in minimally-invasive surgery. System  20  comprises an endoscope  22 , which comprises an insertion tube  24 . An operator  36 , typically a physician, manipulates the insertion tube using controls (not shown) on a handle  34  at the proximal end of endoscope  22 . The operator thus advances a distal end  28  of the insertion tube into a body cavity, such as a bronchial passage in lung  26 , and maneuvers the distal end within the lung. 
     FIG. 2  is a schematic, sectional view of endoscope  22 , in accordance with an embodiment of the present invention. Distal end  28  of insertion tube  24  comprises an imaging assembly  30 , for capturing images in the area of the distal end, inside lung  26 . The imaging assembly typically comprises an image sensor, with objective optics that form an image of the region outside distal end  28  on the sensor. Typically, endoscope  22  also comprises a light source, for illuminating the region outside the distal end, as well as other functional elements. The image sensor and other imaging-related elements of endoscope  22  are omitted from the figures for the sake of simplicity, but such elements are well known in the art. Endoscopic imaging elements of this sort are described, for example, in PCT publication WO 03/098913, whose disclosure is incorporated herein by reference. Alternatively, optical images may be conveyed from distal end  28  via relay optics, such as a fiberoptic bundle, to an image sensor at the proximal end of the endoscope. 
   Video signals generated by imaging assembly  30  are conveyed via a cable  40  to a console  42 , which processes the signals to generate an image  46  on a display  44  ( FIG. 1 ). The console may rotate image  46  depending on the orientation angle of distal end  28 , as described hereinbelow. 
   As shown in  FIG. 2 , endoscope  22  comprises a distal field transducer  32  in distal end  28  and a proximal field transducer  38  at the proximal end of insertion tube  24 , inside handle  34 . In this embodiment, transducers  32  and  38  are assumed to be magnetic field transducers, which are produced by winding an electrical coil on a suitable core. Typically, transducer  38  serves as the field transmitter, while transducer  32  serves as the field receiver. In other words, console  42  drives a current through transducer  38  via cable  40  in order to generate a magnetic field, which causes a current to flow in transducer  32 . Alternatively, transducer  32  may serve as the transmitter, and transducer  38  as the receiver. In either case, the current flowing in the receiver is proportional to the distance between transducers  32  and  38  and to the relative orientations of the transducers. 
   Console  42  measures the current flowing in the receiving transducer and uses the current value to determine the orientation angle of transducer  32  relative to transducer  38 , and thus to determine the orientation of distal end  28  relative to handle  34 . In order to measure the orientation unambiguously, it is desirable that transducer  38  comprises multiple coils, which generate spatially-distinct magnetic fields. For example, transducer  38  may comprise three coils wound on orthogonal axes, as shown in  FIG. 2 . Assuming that transducer  38  serves as the transmitter, console  42  typically drives the coils with waveforms selected so that the currents generated in transducer  32  due to the magnetic fields of the different transmitter coils are distinguishable by the console on the basis of time-, frequency- or phase-domain multiplexing. A position sensing system of this sort is described, for example, in U.S. Pat. No. 6,484,118, whose disclosure is incorporated herein by reference. 
   Typically, transducer  32  comprises only a single coil, so as to minimize the space required by the transducer within distal end  28  and hence to minimize the diameter of insertion tube  24 . Alternatively, for enhanced accuracy, transducer  32  may comprise multiple coils. For example, transducer  32  may comprise three mutually-orthogonal coils, as described in U.S. Patent Application Publication US 2002/0065455 A1, whose disclosure is incorporated herein by reference. Further alternatively, the receiving transducer may comprise a Hall effect transducer or another sort of antenna. Other sorts of magnetic field transmitters and receivers, as are known in the art, may also be used. 
   In other embodiments, transducers  32  and  38  transmit and receive energy fields of other sorts. For example, the transducers may transmit and receive ultrasonic fields. In this case, console  42  may use the strength and/or phase of the received ultrasonic signals in order to determine the orientation of distal end  28  relative to handle  34 . 
   Optionally, endoscope  22  also comprises an orientation sensor  50  in handle  34 . Sensor  50  generates signals that are indicative of the orientation of handle  34  in an external frame of reference. For example, sensor  50  may comprise an inertial sensor, such as an accelerometer or gyroscope. The output of this sensor may be used by console  42  to determine the orientation of handle  34  relative to the earth&#39;s gravitational field, as well as sensing movement of the handle relative to its initial position and orientation at the beginning of the endoscopic procedure. Alternatively, sensor  50  may be used to determine the orientation of handle  34  relative to one or more reference transducers (not shown), which are fixed in an external frame of reference outside the body of patient  27 . For example, sensor  50  may receive magnetic, optical or ultrasonic energy from the reference transducers, or it may transmit such energy to the reference transducers. The reference transducers may be fixed to objects in the room in which the endoscopic procedure is taking place, such as the walls, ceiling or table on which patient  27  is lying. Alternatively, the reference transducers may be fixed to patient  27  or to operator  36 , so that the handle orientation is determined relative to the patient or operator. In any case, console  42  processes the received energy signals from sensor  50  or from the reference transducers (if sensor  50  is configured as a transmitter) in order to determine the orientation of handle  34 . 
     FIG. 3  is a flow chart that schematically illustrates a method for rotating image  46  based on the measured orientation of distal end  28  of endoscope  22 , in accordance with an embodiment of the present invention. To determine the actual orientation angle of distal end  28  relative to an external frame of reference, the absolute orientation angle of handle  34  relative to this external frame is first measured, at a handle orientation measurement step  60 . Typically, the handle orientation is measured using sensor  50 , as described above. The orientation of distal end  28  is measured relative to handle  34  using transducers  32  and  38 , at a tip orientation measurement step  62 . Step  62  may occur before, after or simultaneously with step  60 , and these steps are typically repeated continually in the course of a given endoscopic procedure. 
   Based on the orientation angles measured at steps  60  and  62 , console  42  calculates the orientation of distal end  28  in the external frame of reference, at an orientation computation step  64 . Typically, the orientation of the distal end is determined by vector addition of the handle and distal end orientations determined at steps  60  and  62 . Alternatively, steps  60  and  64  may be eliminated, and the relative orientation found at step  62  may be used in the step that follows. 
   Console  42  rotates image  46  to compensate for the orientation of distal end  28 , at an image rotation step  66 . It is generally sufficient for this purpose that the orientation angle of distal end  28  be measured to an accuracy of a few degrees. Typically, the console rotates the image so that it is oriented in the same direction as patient  27 , i.e., so that the right and left directions in the image correspond correctly to the right and left directions within the patient&#39;s body. Since it is generally the left/right orientation that is of greatest concern to the operator, the three-dimensional vector that represents the spatial orientation of the endoscope may simply be projected onto the frontal plane of the patient, and the image rotated accordingly. Alternatively or additionally, the image may be transformed to correct for distortion (such as foreshortening) of the image when the image plane of the endoscope is not parallel to the frontal plane. Further alternatively or additionally, other image rotation methods and criteria may be applied, as are known in the art. 
     FIG. 4  is a schematic representation of a graphical map  70  shown on display  44 , in accordance with an embodiment of the present invention. This embodiment is useful particularly in imaging the inner surface of a body cavity, such as the bladder, for example. In such applications, operator  36  typically inserts distal end  28  of endoscope  22  into the cavity, and then deflects the distal end over a range of angles in order to image different areas of the surface. It is difficult under such circumstances for the operator to know exactly what areas of the surface he has scanned and whether there are areas that he has missed. 
   Map  70  assists operator  36  in visualizing the areas that have and have not been scanned by endoscope  22 . In this example, the inner surface of the body cavity is represented as the interior of a sphere, which is divided into a posterior hemisphere  72  and an anterior hemisphere  74 . Typically, operator  36  presses a button or gives some other input to console  42  to indicate that the imaging scan is to begin. Console  42  then tracks the orientation of distal end  28  within the cavity and accordingly adds a mark  76  to map  70  to represent each area of the surface that has been imaged. A cursor  78  may be used to indicate the current orientation of the distal end of the endoscope on map  70 . Using this map, the operator steers the distal end of endoscope  22  so as to image all areas of interest on the inner surface and to identify areas that have not yet been covered. 
   Console  42  may track distal end  28  and produce map  70  using the relative orientation sensing method described above. Alternatively, other methods of orientation sensing may be used to track the distal end of the endoscope and produce the map. For example, the console may determine the orientation of distal end  28  by sensing the rotation of control knobs or pulleys (not shown) within handle  34  of endoscope  22  that are used in deflecting the distal end. Other methods of orientation sensing that are known in the art, such as magnetic and ultrasonic measurement relative to an external frame of reference, may similarly be used. Furthermore, console  42  may be programmed to control the orientation of distal end  28  automatically, based on the information in map  70 , so as to scan the entire inner surface of the body cavity, or to scan a predetermined region of interest within the body cavity. 
   The method exemplified by  FIG. 4  may also be used with endoscopes of other types, including rigid endoscopes. In this latter case, of course, the distal end of the endoscope is not deflected, but it may be rotated, and the endoscope viewing angle may be varied using methods known in the art, such as those described in some of the patents cited in the Background section above. Any suitable method, such as the inertial measurement methods mentioned earlier, for example, may be used to measure the orientation of the endoscope and the viewing angle. 
   Although the embodiments described above relate to certain particular applications of the present invention in endoscopic imaging, the principles of the present invention may also be used in measuring the orientation of other types of flexible probes, such as catheters. The orientation measurements may be used not only in correcting the orientation of endoscopic images, but also in controlling other types of diagnostic and therapeutic procedures that use flexible invasive probes. It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.