Abstract:
Systems and methods are described for determining an orientation and position of a capsule inserted into the body of a patient. A magnetic field is applied to an area of the patient where the capsule is located. Sensor data, including inertial data from an inertial sensor and magnetic field data indicative of the applied magnetic field as detected by at least one magnetic field sensor, is wirelessly received from the capsule. An orientation angle of the capsule is determined based at least in part on the inertial data. The magnetic field data is compared to known characteristics of the applied magnetic field and a location of the capsule is determined based on the comparison.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/753,755, filed Jan. 17, 2013, entitled “REAL-TIME POSE AND MAGNETIC FORCE DETECTION FOR WIRELESS MAGNETIC CAPSULE,” the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Magnetic coupling is one of the few physical phenomena capable of transmitting actuation forces across a physical barrier. In medicine, remote magnetic manipulation has the potential to make surgery less invasive by allowing untethered miniature devices to enter the body through natural orifices or tiny incisions and then maneuver with minimum disruption to healthy tissue. Magnetic coupling between a permanent magnet embed onboard the medical device and an external magnetic field source allows the medical device to be moved within the body of a patient. 
         [0003]    One type of insertable medical device that utilizes magnetic coupling for locomotion is a magnetic capsule used for controlled endoscopy or for site-specific drug delivery. These capsules are inserted into the body of a patient and an external magnetic field is applied to move the magnetic capsule through the body. 
       SUMMARY 
       [0004]    Knowing the pose (i.e., the position and orientation) of the insertable medical device helps the external magnetic field source control the position and movement of the medical device in the body of a patient. However, due to the strong magnetic link required for effective device manipulation, localization techniques based on electromagnetic fields are not adequate. The magnetic field that is applied to cause locomotion of the magnetic capsule prevents external systems from accurately determining in real-time the location and pose of the magnetic capsule inside the body of a patient. 
         [0005]    The system described herein determines the position, the orientation, and the pressure exerted on surrounding tissues by a magnetic capsule inside the body. A set of sensors (e.g., a magnetometer, inertial sensors, etc.) are placed inside the magnetic capsule. Information detected by these sensors is wirelessly transmitted to an external system in real-time. The external system then determines the location and pose of the magnetic capsule based on the received information from the capsule sensors. 
         [0006]    In one embodiment, the invention provides a method for determining an orientation and position of a capsule inserted into the body of a patient. A magnetic field is applied to an area of the patient where the capsule is located. Sensor data, including inertial data from an inertial sensor and magnetic field data indicative of the applied magnetic field as detected by at least one magnetic field sensor, is wirelessly received from the capsule. An orientation angle of the capsule is determined based at least in part on the inertial data. The magnetic field data is compared to known characteristics of the applied magnetic field and a location of the capsule is determined based on the comparison. 
         [0007]    In another embodiment, the invention provides a capsule position-determining system for determining an orientation and position of a capsule inserted into the body of a patient. The capsule position-determining system includes an inertial sensor mounted on the capsule, at least one magnetic field sensor mounted on the capsule, a wireless transmitter mounted inside the capsule, and a controller. The controller is configured to receive sensor data from the inertial sensor and the at least one magnetic field sensor and to transmit the sensor data to an external system through the wireless transmitter. 
         [0008]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings and appendices. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS AND APPENDICES 
         [0009]      FIG. 1A  is a perspective view of a robot arm for controlling the movement of the magnetic capsule externally. 
           [0010]      FIG. 1B  is a schematic diagram of an external magnet of  FIG. 1A  controlling the movement of the magnetic capsule through a body cavity. 
           [0011]      FIG. 1C  is a graph of a magnetic field generated by the external magnet of  FIG. 1A . 
           [0012]      FIG. 2A  is a perspective view of a magnetic capsule that can be moved by the robotic arm of  FIG. 1 . 
           [0013]      FIG. 2B  is a partial cutaway view of the magnetic capsule of  FIG. 2 . 
           [0014]      FIG. 3  is a partially transparent view of a capsule capable of detecting position with five degrees-of-freedom. 
           [0015]      FIG. 4  is a partially transparent view of a capsule capable of detecting position with six degrees-of-freedom. 
           [0016]      FIG. 5  is a partially transparent view of a capsule capable of detecting position with six degrees-of-freedom and of being moved by the robotic arm of  FIG. 1 . 
           [0017]      FIG. 6  is a partially transparent view of a capsule capable of being moved by the robotic arm of  FIG. 1  and detecting axial force acting on the capsule with one degree-of-freedom. 
           [0018]      FIG. 7  is a block diagram of a control system for a magnetic capsule with position detection functionality. 
           [0019]      FIG. 8  is a flow chart of a method of determining absolute position of a magnetic capsule. 
           [0020]      FIG. 9  is a flow chart of a method of determining the position of a magnetic capsule based on iterative changes in position and orientation. 
           [0021]      FIG. 10  is a flow chart of a method of operating the robotic arm of  FIG. 1  to control the movement of a magnetic capsule. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0023]      FIG. 1A  shows an industrial robotic arm  101 . A cylindrical driving magnet  103  is coupled to the distal end of the robotic arm  101 . A magnetic capsule  105  is shown proximate to the cylindrical driving magnet  103 . As described in further detail below, the magnetic capsule  105  can be inserted into the body of a patient  13  either surgically or through a natural orifice such as the mouth. In some constructions, the magnetic capsule naturally moves through the body of the patient until it reaches a target location (e.g., through the digestive tract) where, for example, an operation is performed or a medication is dispensed. In other constructions, the robotic arm  101  manipulates the cylindrical driving magnet  103 . By magnetic attraction, the cylindrical driving magnet  103  controllably causes the magnetic capsule to move within the body of the patient to the target location. 
         [0024]      FIG. 1B  shows the capsule  105  positioned within a body cavity  107  of a patient. The external cylindrical driving magnet  103  generates a magnetic field  109  that acts upon the capsule  105 .  FIG. 1C  shows a more detailed graph of the magnetic field created by the driving magnet  103  and how the capsule  105  sits within the magnetic field. 
         [0025]    As noted above, this magnetic field can be manipulated to cause a magnetic capsule  105  to move within the body cavity  107 . However, because the magnetic field created by the driving magnet  103  is predictable and controllable, magnetic field sensors integrated into the capsule  105  can be used to identify the orientation of the capsule  105  within the magnetic field. As such, the orientation, position, and location of the capsule  105  within the body cavity can be accurately determined. This information can then be used to safely control the movement and operation of the capsule  105  within the body. 
         [0026]      FIG. 2A  shows a perspective view of one example of a magnetic capsule  200 . The capsule  200  includes a triaxial accelerometer  201  positioned on one end of the capsule  200  and a number of magnetic field sensors  203  positioned around the capsule  200 . However, other constructions of the capsule  200  may use other types of inertial sensors such as, for example, a gyroscopic sensor or a combination IMU (inertial measurement unit) that includes both acceleration sensors and gyroscopic components. Although the sensors are shown at the surface of the capsule in the example of  FIGS. 2A , the arrangement and position of the sensors can be changed in other constructions of the magnetic capsule  200 . Furthermore, in some constructions, a protective casing is formed around the exterior of the capsule and the sensors are positioned below the protective casing. 
         [0027]      FIG. 2B  provides a partial cutaway view of the capsule  200  to better illustrate the different sensors and their locations. Again, the triaxial accelerometer  201  is positioned at the top of the magnetic capsule  200 . A series of uniaxial magnetic field sensors  203  are arranged in pairs around the magnetic capsule  200 . Each pair of magnetic field sensors  203  corresponding to one Cartesian of the directions—MFSx 1  and MFSx 2  for the x-axis, MFSy 1  and MFSy 2  for the y-axis, and MFSz 1  and MFSz 2  for the z-axis. Sensor MFSx 1  is positioned on one side of the magnetic capsule while sensor MFSx 2  is positioned on the opposite side of the capsule. Sensors MFSy 1  and MFSy 2  (not shown) are also positioned at opposite sides of the magnetic capsule and arranged perpendicular to the MFSx 1  and MFSx 2  sensor pair. Sensors MFSz 1  is positioned at the top of the capsule while corresponding sensor MFSz 2  is positioned at the bottom of the capsule. The various sensors are attached to or set within a housing  205 . As described in further detail below, a controller is positioned within the housing  205  that receives data from the various sensors and transmits that data to a processing or control system outside of the patient&#39;s body. 
         [0028]    Instead of utilizing multiple single-axis magnetic field sensors, the capsule can include one or more tri-axial magnetic field sensors. For example,  FIG. 3  illustrates a capsule  300  that includes a tri-axial accelerometer  301  and a tri-axial magnetic field sensor  303  both mounted on the same end of the capsule housing  305 . The magnetic field sensor  303  provides three orthogonal measurements of the magnetic field. The data provided by the accelerometer  301  and the magnetic field sensor  303  allow the system to determine the pose and orientation of the capsule with five degrees-of-freedom. 
         [0029]      FIG. 4  illustrates an example of a capsule  400  that again includes a tri-axial accelerometer  401  and a tri-axial magnetic field sensor  403  both positioned at the same end of a capsule housing  405 . However, the capsule  400  is equipped with a second tri-axial magnetic field sensor  409  positioned at the opposite end of the capsule housing  405 . The inclusion of a second tri-axial magnetic field sensor allows the data to better determine all three tilt angles (i.e., yaw, pitch, and roll) of the magnetic capsule based on the difference between the magnetic fields detected by the two sensor (e.g., the x-axis field detected by sensor  403  compared to the x-axis field detected by sensor  409 ). Without the benefit of the second tri-axial magnetic field sensor, the device is only capable of determining two of the tilt angles. 
         [0030]      FIG. 5  illustrates another example of a capsule  500 . This capsule  500  includes a tri-axial accelerometer  501  and a series of six single-axis magnetic field sensors  503  positioned around the capsule housing  505 . Like the example of  FIG. 2B , the single-axis magnetic field sensors are arranged in axis pairs around the capsule housing  505 . Sensors  503 x 1  and  503 x 2  are positioned on opposite sides of the housing  505  and monitor the x-axis magnetic field. Sensors  503 y 1  and  503 y 2  are positioned on opposite sides of the housing  505 —perpendicular to sensors  503 x 1  and  503 x 2 —and monitor the y-axis magnetic field. Sensors  503 z 1  and  503 z 2  are positioned on the top and bottom of the capsule housing  505 , respectively, and monitor the z-axis magnetic field. 
         [0031]    The capsule  500  of  FIG. 5  also includes a permanent magnet  507  positioned within the capsule housing  505 . The permanent magnet  507  allows the capsule to be controlled and moved by the external magnet on the robotic arm. In contrast, the capsules illustrated in  FIGS. 3 and 4  do not include internal permanent magnets. As such, an external driving magnet cannot be used to control the position of the capsules  300  and  400 . Instead, the magnetic field generated by the external magnetic can only be used to determine the location, position, and orientation of the capsule  300  and  400 . 
         [0032]    Because the internal permanent magnet  507  of capsule  500  is attracted to the external magnet, magnetic forces generated by the external magnet will act upon the capsule  500  and cause it to move within the body of the patient. In addition to detecting the position and orientation of the capsule, the sensor arrangement of capsule  500  allows the system to monitor the magnetic force. 
         [0033]      FIG. 6  shows an example of the capsule  600  with only four single-axis magnetic field sensors— 603 x 1 ,  603 x 2 ,  603 y 1 , and  603 y 2 —and an internal permanent magnet  607 . Each magnetic field sensor measures a single-axis magnetic field—B 1 , B 2 , B 3 , and B 4 —in real-time. These sensor measurements are used to calculate the magnetic force acting on the capsule in the z-axis (Fz 6 ) using the following equation: 
         [0000]        Fz 6 =B 1* Gk+B 2 *Gk−B 3 *Gk−B 4* Gk    (1)
 
         [0000]    where Gk is a calibration constant that is determined experimentally to account for the volume of the magnet  607  (pi/2*radius*height) and its magnetic properties such as Br0, vacuum magnetic constant, and calibration model coefficients. 
         [0034]    The capsule  600  can be implemented as a simplified magnetic force detection system and includes only the four magnetic field sensors as illustrated in  FIG. 6 . Alternatively, more advanced and complex capsule systems, such as the capsule  500  illustrated in  FIG. 5  can utilize the x-axis and y-axis magnetic field sensors to calculate magnetic force in the z-axis. Furthermore, systems such as capsule  500  can monitor the other components (x and y) of the magnetic force acting on the capsule  500 . 
         [0035]    In order to communicate the sensor readings to an external system where they can be processed, each capsule is equipped with an electronic control system  700 . The control system includes a controller  701  that receives magnetic field information from each of the magnetic field sensors  703  and the tri-axial accelerometer  705 . 
         [0036]    The controller  701  may include an internal memory for storing sensor data and program instructions. Alternatively, the controller  701  may include a processor that communicates with a non-transient memory module  707 . The memory module  707  stores computer-executable instructions that are executed by the control  701  to perform the various operations such as described herein. 
         [0037]    The controller  701  transmits the sensor data through a wireless transceiver  709  to an external system  711  where it is processed and analyzed. The memory  707  can be used to store the sensor data at least until a wireless communication link is established with the external system  711 . In some other constructions, the sensor data can be communicated to an external system  711  through a wired communication interface such as a “soft tether” with an electrical cable housed inside. Furthermore, in some embodiments, the controller  701  may also be configured to receive data from the external system  711  through the wireless transceiver  709 . Such received data can include, for example, instructions for controlling an operation of the capsule such as dispensing medication. 
         [0038]    Once the external system  711  receives the sensor data, the data is processed to determine the location, position, and orientation of the capsule within the body cavity.  FIGS. 8 and 9  illustrate two examples of method that use the magnetic field and accelerometer data gathered by the capsule sensors to determine localization of the capsule. 
         [0039]      FIG. 8  uses the data to determine an absolute position of the capsule with respect to an external fixed reference frame. The magnetic field data measurements B are received from the magnetic field sensors. If the capsule includes an internal permanent magnet, the magnetic field data measurements are offset (step  801 ) such that they represent only the magnetic field applied by the external driving magnet. The inertial measurements A from the tri-axial accelerometer are analyzed to determine the inclination/orientation of the capsule (step  803 ). A rigid transformation (i.e., rotations) of a pre-compiled magnetic field matrix is performed (step  805 ) to align a precompiled magnetic field matrix with the external magnet field source orientation and the measured capsule orientation. The external magnet field source orientation is determined based on a position of the external magnet as determined by the pose of the robotic arm and the orientation of the external magnet as determined by an inertial sensor coupled to the end effector of the robotic arm. The elaborated magnetic field (B̂) and the known capsule orientation are then used to compute an appropriate interpolation of the magnetic field MAP with the elaborated magnetic field (B̂) (step  807 ). The output of this interpolation is a capsule position X (including x, y, and z Cartesian coordinates) and the capsule orientation θ (including rotations around the three Cartesian axes). 
         [0040]      FIG. 9  illustrates an alternative method for determining the position and orientation of the capsule using an iterative approach. The magnetic field model MAP of the external driving magnet is calibrated and interpolated to reduce the matrix dimensions (step  901 ). The Jacobian of the magnetic MAP is also derived (step  903 ). The magnetic field sensor measurements B are offset to account for changes in the magnetic field caused by the permanent magnet installed within the capsule (step  905 ). The offset magnetic field sensor measurements are then compared to a previous set of magnetic field measurements to determine a change in the magnetic field (ΔB) (step  907 ). The inertial data from the tri-axial accelerometer A is again used to determine the capsule inclination θ (step  909 ). The relationship between the capsule orientation and the orientation of the applied magnetic field C is characterized based on the pose of the external magnet (as determined by the pose of the robotic arm and the orientation of the external magnetic as indicated by an inertial sensor coupled to the end effector of the robotic arm (step  911 ). The change in magnetic field (ΔB) and the capsule orientation θ are then used to generate a spatial transformation allying the capsule orientation with the magnetic field measured by the capsule itself (step  913 ). 
         [0041]    An iterative method is used to determine the capsule change in pose ΔX (tri-dimensional displacement) and Δθ(tri-dimensional rotation). This can be used to derive the absolute pose X (including Cartesian coordinates x, y, and z) and θ (including rotations around the three Cartesian axes) through iterative integration and inversion of the MAP image (which is given by the Jacobian J) (step  915 ). As a result, the capsule change in pose is determined based on changes in the measured magnetic field instead of an absolute analysis of the magnetic field thus reducing computational load. 
         [0042]    Localization algorithms utilizing this system have experimentally been able to provide an accuracy of 8 mm in position detection, one degree for roll and pitch detection, and 2.5 degrees for yaw detection within a spherical workspace of 15 cm in radius centered on the driving magnet. Computational time is 2 ms. 
         [0043]    Although, in the examples of  FIGS. 8-10 , the controller in the magnetic capsule only sends sensor readings to the external controller, in other constructions the controller in the magnetic capsule may be configured to analyze the sensor readings to determine the location and orientation of the capsule. The location and orientation information is then wireless transmitted from the capsule controller to an external controller. 
         [0044]    The determined orientation, position, and speed of the magnetic capsule through the body cavity can provide feedback to the control system (i.e., the robotic arm with the driving magnet) to safely maneuver the capsule through the body of the patient.  FIG. 10  provides an example of one such closed-loop robotic control mechanism. A movement command is generated (step  1001 ) either through user input or by an automated movement protocol. The system determines a robotic control maneuver necessary to achieve a desired position change (step  1003 ) and determines an appropriate speed control (step  1005 ). The robotic control system then activates the servo motor to move the robotic arm according to the position and speed controls (step  1007 ). The velocity V of the robotic arm end effector fed back to adjust the speed control (step  1005 ) and an inverse kinematic analysis (step  1009 ) of the position of the robotic arm is used to adjust the position control (step  1003 ). 
         [0045]    As magnetic field and inertial data are received from the capsule (step  1011 ), the control system analyzes the data to determine the position and orientation of the capsule (step  1013 )—for example, according to the absolute localization method of  FIG. 8  or the iterative localization method of  FIG. 9 . The location X of the capsule is used by the next iteration of the command generation to determine the next appropriate step to safely move the capsule to a target location. 
         [0046]    Thus, the invention provides, among other things, a systems and methods for determining the location and position of a capsule in the body of a patient based on information detected from a series of sensors coupled to the capsule and wireless communicated to an external controller. Various features and advantages of the invention are set forth in the following claims and the attached appendices.