US 20060036151 A1
A system for monitoring a position of a medical instrument with respect to a patient's body, including a medical instrument, a reference mount attachable to the patient's body for movement with the patient's body, and an electromagnetic unit for association with the reference mount and the medical instrument for monitoring movement of the medical instrument relative to the reference mount. The electromagnetic unit includes a first member attachable to the patient's body and a second member attachable to the medical instrument. The first and second members communicate by electromagnetic radiation.
30. A system for monitoring a position of a medical instrument with respect to a patient's body, comprising:
a medical instrument;
a reference mount attachable to the patient's body, and
an electromagnetic unit for monitoring movement of the medical instrument relative to the reference mount, the electromagnetic unit including a first member attachable to the patient's body and a second member attachable to the medical instrument, the first and second members communicating by electromagnetic radiation.
31. The system of
32. The system of
33. The system of
34. The system of
35. The system of
36. The system of
37. The system of
38. The system of
39. The system of
40. The system of
41. The system of
42. The system of
43. A system for monitoring a position of an instrument with respect to an object, comprising:
a reference mount attachable to the object; and
an electromagnetic unit for monitoring movement of the instrument relative to the reference mount, the electromagnetic unit including a first member attachable to the object and a second member attachable to the instrument, the first and second members communicating by electromagnetic radiation.
44. The system of
45. The system of
46. The system of
47. The system of
48. The system of
49. The system of
50. The system of
51. The system of
52. The system of
53. The system of
54. The system of
55. The system of
This application is a continuation of pending U.S. Ser. No. 10/427,472, filed Apr. 30, 2003, which is a continuation of U.S. Ser. No. 09/643,608, filed Aug. 22, 2000, now U.S. Pat. No. 6,694,167, which is a continuation of U.S. Ser. No. 09/212,024, filed Dec. 15, 1998, now U.S. Pat. No. 6,175,756, which is a continuation of U.S. Ser. No. 08/637,289, filed Apr. 24, 1996, now U.S. Pat. No. 5,873,822, which is a divisional of U.S. Ser. No. 08/527,517, filed Sep. 13, 1995, now U.S. Pat. No. 5,803,089, which is a continuation-in-part of U.S. Ser. No. 08/306,818, filed Sep. 15, 1994, now U.S. Pat. No. 5,829,444, all of which are hereby incorporated by reference in their entireties.
The invention relates to computer assisted medical surgery and in particular relates to systems for displaying prerecorded visual images during surgical operations.
Presently available medical imaging techniques such as CAT (Computerized Axial Tomography), MRI (Magnetic Resonance Imaging), and PET (Position Emission Tomography), are known to be helpful not only for diagnostic purposes, but also for providing assistance during surgery. Prerecorded images may be displayed during surgical operations to provide the surgeon with illustrative reference mappings of pertinent portions of a patient's body.
Tracking systems for monitoring the position of a medical instrument have also been developed for use with image display systems. Generally, as the surgeon moves the medical instrument with respect to the patient's body, associated prerecorded images are displayed responsive to the movement of the instrument. Such tracking systems typically involve either the use of a passive articulated arm attached to the medical instrument, optical detection or ultrasonic detection.
Tracking systems using a passive articulated mechanical arm attached to a medical instrument are disclosed in U.S. Pat. Nos. 5,186,174 and 5,230,623. Generally, as the surgeon moves the surgical instrument with respect to the patient's body, micro recorders at the joints of the articulated arm record the respective amounts of movement of each arm member. The outputs of the micro recorders are processed and the position of the medical instrument with respect to the base of the articulated arm is thereby monitored. One or more prerecorded images are then displayed responsive to the movement of the surgical instrument. Such articulated arm tracking systems, however, require that the instrument be attached to a cumbersome mechanical arm. Also, although free movement of the tip of the arm in three dimensional space may be theoretically possible, the surgeon might experience difficulty positioning the instrument at certain locations and in desired orientations within the body.
Tracking systems using optical detection (video cameras and/or CCDs (Charge Coupled Devices)) have been proposed for monitoring the position of a medical instrument with respect to a reference unit as mentioned in U.S. Pat. No. 5,230,623. Such systems, however, require that the reference unit and the instrument both be within the view of the camera. This not only limits the movement of the surgical staff, but also requires that at least a portion of the medical instrument remain outside the patient's body.
Tracking systems using ultrasonic detection are generally disclosed in U.S. Pat. No. 5,230,623. Such systems, however, are disclosed to be used in a fashion similar to optical detection, i.e., triangulation of transmitted signals. The transmitted signals are sent from one or more senders to associated receiver(s), and the distances travelled by the signals are determined from either timing or amplitude changes. Again, the transmission path must remain unobstructed.
A further shortcoming common to each of the above tracking systems is that the patient must not move during the operation. Although the patient is likely to be generally anesthetized, the patient's body may be inadvertently moved by the surgical staff, or the surgeon may want to move the body for better positioning. If the body is moved after the tracking system has been initialized, then the tracking will be misaligned.
There is a need therefore for a system for monitoring the position of a medical instrument with respect to a patient's body that avoids these and other shortcomings of present devices.
The invention relates to a system for monitoring the position of a medical instrument with respect to a patient's body and for displaying at least one of a plurality of prerecorded images of the body responsive to the position of the medical instrument. The system includes a reference unit, a remote unit, a position characteristic field generator, a field sensor, a position detection unit and an output display.
In one embodiment, the reference unit is secured from movement with respect to at least a portion of the patient's body such that the reference unit is substantially immobile with respect to a target operation site. The remote unit is attached to the medical instrument. The field generator is associated with one of the reference or remote units and generates a position characteristic field, such as a multiplexed magnetic field, in an area including the target operation site. The field sensor is associated with the other of the reference or remote units and is responsive to the presence of the field for producing a sensor output signal representative of the sensed field.
The position detection unit is in communication with the sensor output signal and produces position data representative of the position of the remote unit with respect to the reference unit. The output display unit is in communication with the position detection unit for displaying at least one of the prerecorded images responsive to the position data.
The system further may include a registration unit in communication with a storage unit and the position data. The storage unit stores the plurality of prerecorded images of the body. Each prerecorded image is representative of a planar region within the body such that the plurality of planar regions represented by the prerecorded images define a first coordinate system. The registration unit correlates the position data of a second coordinate system (as defined by the position detection unit) with the plurality of prerecorded images of the first coordinate system, and identifies a desired prerecorded image associated with the position of the remote unit with respect to the patient's body.
The invention also relates to a reference unit that is attachable to a patient's head, and a medical instrument, such as an aspirating device, that is adapted to removably receive a position detection unit.
The following detailed description of the invention may be further understood with reference to the accompanying drawings in which:
As shown in
The image storage unit 26 stores sets of prerecorded images such as CAT, MRI or PET scan images. Each set of images may be taken along, for example, coronal, sagittal or axial directions. AS shown in
As further shown in
The headset 12 shown in
In the present embodiment the field generator includes three orthogonally disposed magnetic dipoles (e.g., current loops or electromagnets), and the orthogonally disposed magnetic fields generated by each of the three dipoles are mutually distinguishable from one another (e.g., via either phase, frequency, or time division multiplexing). The near-field characteristics of the multiplexed magnetic fields may be relied upon for position detection, for example as generally described in U.S. Pat. No. 4,054,881. In alternate embodiments the field generator may be located somewhere other than on the headset and the headset may include two field sensors 36,37. When the distance between the sensors 36,37 is known, the second sensor may be used to act as a backup or reference check for monitoring the proper operation of the system. If the sensed fields are inconsistent then an error signal is displayed and/or sounded.
In other embodiments the headset 12 may be employed in systems based on the triangulation of signals where the reference unit 36 includes one or more signal transmitters and/or one or more signal receivers. In such a triangulation system, position detection is achieved by comparing certain characteristics of one transmitted signal with those of a second transmitted signal to determine the relative distances travelled. The transmitted signals may be electromagnetic (e.g., radio, laser light or light emitting diodes) or may be ultrasonic. The position of the patient's head with respect to the surgical instrument may thereby be monitored.
As shown in
The remote sensors 40,41 are removable from the aspirating device and may be interchangeably inserted into any of a variety of specially adapted surgical instruments. In the illustrated embodiment, the remote sensors 40,41 are received through an opening 42 in the proximal end of the instrument 16, and are connected to the position detection unit 22 via communication lines 44. The sensors 40,41 may also each include three orthogonally disposed dipole sensing elements for detecting the presence of the field generated by the field generator. For example, in one embodiment, the field generator and the sensors each include three orthogonally disposed electrical wire loops. The generator produces an alternating current through one generator loop at a time thus generating a time division multiplexed alternating electromagnetic field. The sensor loop signals are each processed in synchronous timing with the generator loops to produce outputs responsive to each respective alternating electromagnetic field.
The distal end of the instrument 16 includes a rigid aspirating tube 46 having a flared tip 48. The position of the tip 48 with respect to the center of the remote sensor 40 is a known constant and may be easily seen by the surgeon during surgery. The aspirating tube 46 is in fluid communication with an aspirating catheter 50 through the proximal end of the instrument 16 via internal channel 52 and a connector element 54. The aspirating catheter 50 (shown in
In operation, the position detection unit monitors the position of the medical instrument 16 with respect to the reference unit 36. The registration unit 24 correlates the changes in position of the instrument 16 with the spacial orientation of the stored images. As the surgeon moves the medical instrument 16, images appear on the display 20 responsive to the position of the medical instrument 16. This permits the surgeon to always have available the coronal, sagittal, and axial views associated with the precise location of the tip 48 of the instrument 16 regardless of whether the tip 48 is inside of the patient 14. Moreover, since the field generator is attached to the patient's head, the patient is free to be moved without loss of the tracking capabilities. The display 20 may further identify the location of the tip 48 on each of the displayed images as shown at 56 in
As shown in
The sensor unit 58 further includes the ability to identify which of a plurality of medical instruments is attached to the sensor unit 58 at any time. Specifically, the unit 58 includes a plurality of Hall effect transistors 78, and the medical instrument 60 includes one or more tiny permanent magnets 80. By the number and/or positioning of the magnets 80, the transistors 78 identify which of the medical instruments is attached to the sensor unit 58.
For example, if all of the transistors 78 sense the presence of a magnet 80 then the instrument 60 shown in
As illustrated in
In one embodiment, fiducial markers 90 are placed on the patient's head 14 prior to scanning with the scanner 92. The markers then appear on certain of the scanned images, and may be located by the position detection system as shown in
In further embodiments involving the use of fiducial markers that are placed on the patient's body (e.g., face) prior to recording the scan images, fiducial markers 90′ may be adhered to intermediate adhesive strips 91 which are directly adhered to the patient's skin 93 as shown in
The fiducial markers 90′ include a radiopaque element 95 and the strips 91 include a small puncture hole or other marker 97. With reference to
Once each of the markers has been located using the position detection unit, the registration unit generates a mapping function to translate the position detection data (in x-y-z coordinates) to the stored image orientation data (in i-j-k coordinates). In particular, the mapping equation is determined by using Powell's method as follows. The images points are each processed as a matrix of the form
A computer processor then iteratively calculates the optimal values for the transformation matrices
The optimal values for the transformation matrices comprise the transformation equation and may now be used to translate the position of the medical instrument with respect to the transmitter in the x-y-z coordinate system, to the appropriate orientation of the prerecorded images in the i-j-k coordinate system.
A further embodiment of the headset of the invention may be employed in an automatic registration process. For example, as shown in
To install the transmitter 104 on the center plate 102, the key is passed through a longitudinal opening 112 in the plate 102, and the posts 106 are each received by post openings 114. One of the post openings 114 is preferably formed as a slot to provide a snug fit for the transmitter yet still accommodate variations between headsets due to manufacturing tolerances. The key 108 may then be rotated to lock the transmitter onto the outer facing surface of the plate 102. The transmitter 104 may then be removed from and reattached to identical headsets in the same location and orientation with a high degree of accuracy.
The headset 100 further includes very small (e.g., about 2 mm dia.) metal fiducial balls 116 secured within the center plate 102 as shown in
Specifically and with reference to
The center of each group is then located and the distances between each group's center and the other centers are calculated and recorded in a matrix of at least 7 by 7 (step 2222). The known distances between the fiducial balls comprise a predefined 7 by 7 matrix. The program then compares each of the known distances with the various predefined distances between the fiducial balls, then generates a best fit approximation of the correlation between the sets of distances (step 2224). If the distance correlation provides an approximation outside of a preset tolerance (step 2226) then the program ends (steps 2218 and 2220) having failed to automatically generate the transformation matrices. If the correlation of distances is within tolerance and there are seven groups (step 2228) then the image data is recorded in the image matrix (step 2230). If the number of groups is above seven, then a geometry correlation is performed comparing the geometry of the groups to the known geometry of the fiducial balls (step 2232). If the geometry correlation is successful (step 2234) then the transformation matrices are recorded (step 2230), and if not the program reports the error condition (step 2218).
Having successfully generated the image point matrix (step 2230), and since the sensor point matrix is based on the known layout of the fiducial markers with respect to the transmitter, the mapping equation may now be automatically generated as discussed above with reference to Powell's method.
In other embodiments wherein the patient is wearing a reference unit when the scan images are prerecorded the registration program may automatically locate portions of the reference unit itself on the scanned images, thereby identifying the orientation of the reference unit with respect to the scanned images. Again, since the relative orientation of the field generator with respect to the reference unit is known, the registration unit may then generate the appropriate mapping function. In further embodiments the surfaces of the patient's skin may be tracked such as by a laser light pointer or a movable tip pointer that is biased in a forward direction. The tracked surfaces may then be located on the stored images. In still further embodiments, the registration unit could be programmed to identify characteristic structures or features of the patient's body and thereby provide fully automatic registration. For example, the system might, knowing the size and shape of a headset, identify where the headset would be placed on the patient's head, even though it does not appear on the prerecorded images.
The position detection system may operate by any desired principle suitable for generating a field in which position detection may be achieved at any location within the field. For example, it has been found that the 3 Space. RTM. Fastrak. TM. product sold by Polhemus, Incorporated of Colchester, Vt. operates via principles suitable for use in the present invention. This product uses three orthogonally disposed magnetic dipoles for both the transmitter and the sensor, and produces alternating electromagnetic fields of 8-14 kHz that are time division multiplexed.
Specifically and with reference to
The time division multiplexed excitation of the three coils of the source creates a unique magnetic field sequence throughout the field of the source. For every location in the field of the source, the six degree of freedom data can be calculated from the data present on the three coils of the sensor. The six degree of freedom information is then sent to a host computer 115.
The position of a sensor S with respect to the field generator defining a reference coordinate frame (X,Y,Z) may be produced by the 3 Space.® Fastrak.™. product at a given time as a set of six values xs, ys, zs, ωazs, ωels, and ωros. The values xs, ys and zs identify the position of the center of the sensor within the X,Y,Z coordinate reference frame, and the angles ωazs, ωels, and ωros identify the orientation of the sensor S with respect to the X,Y,Z coordinate reference frame.
The value ωazs is the azimuth angle of the sensor. The azimuth angle identifies the amount of rotation of the X and Y reference axes together about the Z axis to a new position in which the X axis is aligned with the center of the sensor in the Z direction. The new positions of the X and Y axes are defined as X′ and Y′ respectively.
The value ωels is the elevation angle of the sensor. The elevation angle identifies the amount of rotation of the X′ and Z axes together about the Y′ axis to a new position in which the X′ axis is aligned with the center of the sensor S. The new positions of the X′ and Z axes are defined as X″ and Z′ respectively.
The value cros is the roll angle of the sensor. The roll angle identifies the amount of rotation of the Y′ and Z′ axes together about the X″ axis to a new position defining new axes Y″ and Z″ respectively. The sensor is oriented in the X″, Y″, Z″ reference frame, and this orientation is defined by the values ωazs, ωels, and ωros.
The combined power of all the sensor data is inversely proportional to the distance of the sensor from the source. The ratio between the sensor data components, created by the individual source coils, will determine the x, y, z position coordinate of the sensor. The ratio between the individual sensor coil data will determine the orientation of the sensor.
Because the medical instrument is free to move with respect to the transmitter at speeds that may be faster than the rate at which the electronics can process the information, the speed of the instrument should be monitored. If the speed of movement of the instrument is above a defined threshold, then inconsistent sensor readings should be ignored until the speed falls below the threshold. The speed may be monitored by calculating a weighted sum of the differences between each of the x, y, and z coordinates at successive time intervals t1 and t2.
The presence of a signal from another source, or the magnetic field of the eddy current in a conductive object, or the field distorting effect of a ferro-magnetic object will change the magnitude/direction of the original magnetic field of the source. This will result in an error in the sensor position/orientation.
In a preferred embodiment involving field integrity detection and with reference to
As also noted above and shown in
It has further been found that simply comparing the sensor outputs may not sufficiently identify all types of error conditions that can occur, even if the distance between the sensors is taken into account. Such a potentially undetectable error condition may exist when a foreign ferromagnetic object enters the electromagnetic field and produces identical distortions at each of the sensors. This may be the case, for example if the foreign object has uniform ferromagnetic properties, if the foreign object approaches the two sensors from the same distance and at the same rate, and if the sensors are equidistant from the generator.
In this situation the outputs of the sensors would produce identical outputs and an error detection signal might therefore not be produced even though a foreign object would be in the electromagnetic field altering the electromagnetic field as well as the sensed position data. Although the use of additional sensors may reduce the risk of this occurring, it does not eliminate the possibility of an error condition being undetected.
It has been discovered that an error detection system sufficient to identify localized uniform distortions in the area of the medical instrument or headset may be designed using two sensors separated by a fixed distance as shown in
In the embodiment diagrammatically shown in
The locations of va and vb in the reference coordinate system (i.e., with respect to S1) must be calculated and will be referred to as va1 and vb1. The location (PS) and the orientation of the protected sensor (S1) with respect to the reference sensor must be determined. The attitude matrix (A) is calculated from the orientation values of the protected sensor:
Then the locations of the virtual points are calculated as:
To establish a reference value for the virtual point location in the reference sensor coordinate system, a measurement is taken in a distortion free environment during factory calibration. These stored reference values are called vae and vbe. Throughout the use of the system, the actual measured values of the virtual points (vam, vbe) are compared to the stored reference values for the virtual points (vae, vbe). If the distance between the established and measured location (Δ) for either virtual point is larger than a preset value (ε), then a field integrity violation message is displayed and normal operation of the system is suspended. In particular and with reference to
The operation is based in part on the principle that if the position error is being reduced by the orientation error at one virtual point, then the error will be increased at the other virtual point causing a field integrity violation signal to be generated. If for example, there is an error in the measured position and orientation of the protected sensor, then the measured value will have an error added to the established value. The field integrity checking is performed in this case as follows:
The integrity of the field generated by the field generator may be monitored as discussed above by positioning a reference sensor a fixed distance from the generator, and continuously monitoring its position for any changes. The calculations involved in the above field integrity detection analysis regarding the two sensors S. sub. 1 and S. sub. 2, may be performed for a transmitter and single sensor field integrity detection system. Specifically, the calculations may be performed by substituting the field transmitter for the protected sensor (S. sub. 2), and by substituting the single sensor for the reference sensor (S. sub. 1). These field integrity analyses may also be used to identify the half field of the operation environment.
As shown in
In various embodiments, the position of the field generator 88 may be adjusted during the surgical operation by moving the articulated joints. If neither the remote sensor 40 nor the reference sensor 126 are moved with respect to one another, then moving the field generator 122 should not affect the position detection system. If the accuracy of the system depends at all on the relative positions of the field generators 122 and the sensors 40, 126, then it may be desirable to move the field generator 122 during the surgical operation. This may be the case, for example, if the system relies on the near-field characteristics of a multiplexed magnetic field wherein it might be desirable to keep the sensors 40, 126 generally equidistant from the generator 122. In still further embodiments, the system may periodically prompt the user to reposition the generator 122 such as through visual cues on the display. Those skilled in the art will appreciate that the relative positioning of the field generator and the one or more field sensors is in no way limited to those shown.
The monitoring of the position of the patient may be accomplished by means other than using a headset and reference sensor. For example, a camera 128 connected to an image processor 130 may be positioned to record the location of the field generator with respect to the target operation site of the patient as shown in
As shown in
As shown in
To correct for this problem, the fiber optic endoscope 156 can be used to monitor the position of the tip 154 of the instrument 150 with respect to the inside of the patient's body as shown. Any sensed movement of the sensor 152 with respect to the field generator 134 can be evaluated with reference to whether the tip 154 has moved with respect to the interior of the patient's body. If the camera observes that the tip 154 has not moved, but the sensor 152 indicates that it has moved, then the system can identify that such movement was due to the movement of the field generator and not the sensor 152. The system may then automatically correct for such variation. Further, the fiber optic endoscope 156 itself may include a sensor 158 for detecting whether the tip 160 of the fiber optic has moved. This should further enhance the accuracy of the correction system. Also, the camera 162 may provide continuous registration of the prerecorded images based on the internal structure of the patient's body.
It will be understood by those skilled in the art that numerous variations and modifications may be made to the above described embodiments without departing from the spirit and scope of the present invention.