WO2000048504A2

WO2000048504A2 - Medical instrument and method for its calibration

Info

Publication number: WO2000048504A2
Application number: PCT/US2000/003916
Authority: WO
Inventors: Lewis Levine; Eugene Gregerson; Teresa Seeley; Thomas Boyajian; Brian Conley
Original assignee: Visualization Technology, Inc.
Priority date: 1999-02-16
Filing date: 2000-02-16
Publication date: 2000-08-24
Also published as: WO2000048504A3; AU3492300A

Abstract

A system is disclosed for calibrating the position of a medical instrument (10) in a system for monitoring the medical instrument (10) in a surgical environment. The system includes a position detection unit (14), data representative of at least two points having a fixed spatial relationship with respect to the position detection unit (14), and an instrument tip (20) that may be positioned at a particular tip (20) location point to permit the system to define the plane described by the two points and said tip (20) location point.

Description

MEDICAL INSTRUMENT AND METHOD FOR ITS CALIBRATION

BACKGROUND OF THE INVENTION

The present application claims priority to United States Provisional Patent Application Ser. No. 60/120,183 filed on February 16, 1999.

The invention relates to the field of medical instruments that may be used in connection with a system for monitoring the position of the medical instrument and/or a patient during surgery as disclosed, for example, in United States Patent No. 5,873,822, the disclosure of which is hereby incorporated by reference. Such systems may include position monitoring systems such as electromagnetic position detection systems, as well as systems that rely on the speed of transmission of signals, e.g., light or sound, or systems that include cameras, charge couple devices (CCDs), and image processors to monitor the position of an instrument and/or a patient in a surgical environment, such as a hospital operating room. As shown in Figure 1 , such systems may include computer 3 that communicates with a display monitor 5, a medical instrument 7 and possibly a reference unit that is adapted to be attached to a patient 9.

In such position monitoring systems, it is generally desirable to continuously identify the position of the tip of a medical instrument as well as the orientation of the instrument itself in the surgical environment. It is not always possible to place a position detection unit (e.g., a transmitter, a sensor, a reflector, or other device that coacts with the position monitoring system) at the tip of the medical instrument. The position detection unit, therefore, must be placed on another portion of the medical instrument for some surgical applications. If the distance between the position detection unit and the tip of the instrument is known, then the position and orientation of the instrument tip may be monitored.

It is desirable that such medical instruments have replaceable tips that may be used for a variety of surgical applications. Such position monitoring systems must account for differences in the lengths of each of the variety of surgical instruments in order to know the distance between the position detection unit and the distal ends of each of the replaceable tips. The system, therefore, must know which tip is attached to the instrument during position monitoring.

The medical instrument and position detection unit must be calibrated prior to use to determine the position and orientation of the position detection unit with respect to the medical instrument housing to which it is attached or within which it is received. The position detection unit may be designed to be coupled to the medical instrument in a specific, possibly keyed, relationship which permits the system to know the general relative positions of the medical instrument and the position detection unit. Nonetheless, variations in manufacturing of the position detection units as well as the medical instruments may exist. Such variations may be particularly noticeable in highly accurate position detection systems. It is desirable, therefore, that each medical instrument having a position detection unit coupled to it, be calibrated prior to use. It is also desirable that the method for calibrating a medical instrument be as simple and fast as possible from a user's perspective.

There is a need, therefore, for an improved system and procedure for calibrating a medical instrument in a position detection system. There is further a need for such a system that requires a user to perform a minimum number of calibration steps, and that permits the medical instrument to be readily and easily calibrated for use with a variety of surgical tips.

SUMMARY OF THE INVENTION The invention provides a system and method for calibrating a medical instrument in a system for monitoring the position of the medical instrument in a surgical environment. The system includes a position detection unit, data representative of at least two points having a fixed spatial relationship with respect to the position detection unit; and an instrument tip that may be positioned at a particular tip location point to permit the system to define the plane described by the two points and the tip location point. In various embodiments, the set of points define a pointing vector that is unique to the medical instrument, and the data that is representative of the two points may be acquired prior to shipment of system to a customer, permitting the customer to be responsible for acquiring the tip location point only.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description of various embodiments of the invention may be further understood with reference to the drawings in which: FIG. 1 shows an illustrative view of a prior art system for monitoring the position of a medical instrument in a surgical environment;

FIG. 2 shows an illustrative view of a medical instrument in accordance with an embodiment of the invention; FIG. 3 shows an illustrative top view of the medical instrument shown in FIG. 1;

FIG. 4 shows an illustrative view of various components of a medical instrument calibration system of the invention;

FIG. 5 shows an illustrative side view of the medical instrument shown in FIG. 1 following initial calibration; and FIG. 6 shows an illustrative view of the medical instrument shown in FIG. 4 prior to use in a position monitoring system.

The drawings are included for illustrative purposes only, and are not to scale.

DETAILED DESCRIPTION OF THE INVENTION In accordance with an embodiment of the invention, position and orientation information for a position detection unit, such as a sensor, that is attached to a medical instrument, is determined in an initial calibration step that may be performed during manufacturing. The initial calibration data may be stored in non-volatile memory on the medical instrument itself or in any other part of the system with which it is provided. As shown in Figure 2, a medical instrument 10 in accordance with an embodiment of the invention includes an instrument housing 12 that includes a sensor 14 for use in a position detection system such as an electromagnetic position detection system. The instrument 10 also includes a rotatable handle 16, an attachment shaft 18, and an attached instrument tip 20. The rotatable handle 16 also includes a cap 22 that threads onto the top of the instrument housing 12. The instrument 10 also includes a communications cord 24 that is attached to an adapter plug 26 (which is shown enclosed by a protective cap) at one end. As shown in Figures 2 and 3, the instrument 10 further includes a calibration unit 28 that is coupled to the instrument 10 during calibration, and may then be removed during use in a surgical environment. Three points in space describe a plane, and by knowing the plane in which a medical instrument resides, its orientation may be determined. The position of the tip of the instrument may reside in the plane, thereby integrating the position and orientation information. The result is a direction vector describing the medical instrument. The plane as well as the vector may be used to direct the medical device to display image data of a patient's anatomy with respect to the plane and the vector. The result being oblique cut- planes through the patient's image data. Additionally, the plane and vector information may be used in other ways, such as to accurately project the vector onto any given plane, 5 determine when the plane or vector of the medical instrument intersects another plane or vector, and/or perform angular measurements with respect to another plane or vector.

As shown in Figure 4, during assembly of the instrument as shown in Figures 1 and 2, the attachment shaft 18 is passed through the calibration unit 28, and into the rotatable handle 16 which is received by the housing 12. Any of a variety of instrument tips 20a, 20b,

10 or 20c may then by attached to the instrument. Specifically, a threaded end 30a, 30b or 30c of each tip 20 is received within the distal end 32 of the attachment shaft 18. Stability of the tip 20 is further achieved by having the hex portion 34a, 34b or 34c (which has a hexagonally shaped cross section) be received within the distal end 36 of the rotatable handle 16 (which has a hexagonally shaped opening), and by having the circular sections

15 38a, 38b or 38c be received within distal portion of the interior of the housing 12 (which has a circularly shaped opening). The instrument tip 20 is then received within the housing against the biasing pin 40. Specifically, the distal end of the pin 40 includes retaining posts 42 that engage retaining grooves on the inside of the housing 12. An indicator 46 in the proximal portion of the pin 40 provides an indication of whether an instrument tip is

20 received within the housing 12.

One aspect of the invention relates to a two-step process for determining the position and orientation of a medical tool. An initial step determines the position of two points on the plane that are equidistant from the pointing vector of the medical instrument. These points may be ascertained by attaching calibration unit 28 to the medical instrument that results in

25 the measurement of two points (P,and P₂ as shown in Figure 2) that are equidistant from the pointing vector (generally indicated at V in Figure 1). The position of these points is collected by placing them in a known position with respect to the sensor in the medical instrument. The position of these points is then saved in the coordinate system of the sensor in the instrument, in the non- volatile storage of the medical device. The attached calibration

30 unit 28 is then removed and need not be re-applied. This ends step one which may typically be performed prior to customer shipment of the device. Step two completes the determination of the third point (P₃ as shown in Figure 2) which resides along the pointing vector of the medical instrument (and is therefore at the midpoint (M) between the two saved positions from step 1). This point is determined by touching the tip P_, of the instrument to a known location in space (L). The plane of the instrument may be calculated from the three positions (P,, P₂, P₃) now available, two from non-volatile storage and one from the current step. Additionally, the direction vector (and associated magnitude) may be determined from the midpoint of the two points saved in non-volatile storage from step 1 and the point acquired in step 2. The direction is predetermined to either emanate from the calculated midpoint through the new point, or in the reverse sense, which ever is desired. A single point only, therefore, needs to be determined at the time of final use, thereby saving time and making the final act of calibrating the plane and direction vector of the medical instrument easier. The system also permits the instrument tips to be readily replaced and easily recalibrated by repeating step 2, resulting in a new direction vector magnitude being calculated as defined by the distance from the midpoint (M) to P₃.

The housing 12 receives a position detection unit 14, e.g., a transmitter, a sensor, or a reflector, and further may include a button or switch for sending a communication signal to the system. The housing 12 may also include an attachment sensor to determine whether an instrument tip is received within the housing 12. In further embodiments of the invention, the identification of the instrument tip that is attached to the medical instrument may be automated. In addition to the two points taken in step 1, a third point along the direction vector is also saved. This becomes the ideal vector with its own ideal magnitude. During step 2, which takes place with an unknown tool having an unknown termination point along the ideal direction vector, the ideal direction vector as described by the three points in non- volatile storage (the mid-point (M) of two of the points as well as the third point) is used to determine when the ideal direction vector intersects the known point (L) to which the unknown third point P₃ is being determined. That is, when the tool is positioned at a particular point in space with a particular orientation, the sensor reports its position, which relates to the position of the ideal direction vector. When the motion of the ideal direction vector is brought to near zero, the device presumes that the user has placed the tip of the medical instrument at a known location (L). Given the ideal direction vector and a point in space, the device can determine if the vector passes through the location. From step 2, the known location (L) becomes the third point P₃. Therefore, when the tip of the instrument is brought to near zero speed to a location within a small radius of the known location (L), the system can automatically capture the new third point. Given this new third point, the system can complete the calibration by using the ideal direction vector and applying the newly calculated magnitude to arrive at the actual magnitude and direction vector.

Also, the system may automatically determine the type of instrument attached by using relative vector magnitudes. This is accomplished by retaining a set of direction vector magnitudes in the non-volatile data store, each corresponding to a unique type of instrument. When the device determines the vector magnitude, it uses this to look up in the table the type of instrument attached. In alternative embodiments, the table may include vector length measurements relative to a standard length. A match in length within a reasonable error bound allows the device to perform instrument-specific processing. The benefits include a) completion of the calibration step in an unattended manner (based on sensor speed and direction vs. a user menu, button press, etc.) b) medical instrument determination in an automated fashion based on a look-up table, allowing for instrument specific processing to take place.

As shown in Figure 5, the instrument tip 20 is retained within the housing 12. The biasing pin 40 includes a bias spring 44 and a retaining tab 46 which provides an indication of whether an instrument tip is attached. As shown in Figure 6, during use, the handle 16 may be rotated with respect to the housing 12, which causes the instrument tip 20 to rotate with respect to the housing. The instrument tip 20 may be easily replaced with a different instrument tip. Once in place, the instrument with the new tip is positioned at a known calibration location (L), and recalibrated. When a tip is attached, the tab 46 (which may include a small magnet) signals that a tip is in place, and the system will automatically wait r until the pointing vector intersects the known location (L) and the instrument stops moving. The system will then record the position of the tip of the instrument, which will permit the system to calculate the third point P₃. Those skilled in the art will appreciate that modifications and variations may be made to the above disclosed embodiments without departing from the spirit and scope of the invention.

What is claimed is:

Claims

1. A system for calibrating the position of a medical instrument in a system for monitoring the medical instrument in a surgical environment, said system comprising: a position detection unit; data representative of at least two points having a fixed spatial relationship with respect to the position detection unit; and an instrument tip that may be positioned at a particular tip location point to permit said system to define the plane described by said two points and said tip location point.

2. The system as claimed in claim 1, wherein said system further includes data representative of the midpoint between said at least two points.

3. The system as claimed in claim 1, wherein said system further includes a table of data representative of the lengths of a plurality of instrument tips that may be attached to the medical instrument.

4. The system as claimed in claim 1 , wherein said system further includes a removable calibration unit that may be removed from the medical instrument prior to use.

5. The system as claimed in claim 1 , wherein said system further includes a releasable attachment unit that facilitates attachment and release of an instrument tip to and from the medical instrument.

6. The system as claimed in claim 1, wherein said medical instrument includes a rotatable handle that is coupled to an instrument tip such that rotation of said handle causes the tip to rotate.

7. A method of calibrating the position of a medical instrument in a surgical environment, said method comprising the steps of: recording the positions of at least two points having a fixed spatial relationship with respect to a position detection unit that is secured to the medical instrument; and recording a tip location point to permit said system to define the plane described by said two points and said tip location point.

8. The method as defined in claim 7, wherein said method further comprises the step of determining a pointing vector that is characteristic of the medical instrument.

9. A system for calibrating the position of a medical instrument in a system for monitoring the medical instrument in a surgical environment, said system comprising: a position detection unit; data representative of at least two points having a fixed spatial relationship with respect to the position detection unit, and representative of a midpoint between said two points; and an instrument tip that may be positioned at a particular tip location point to permit said system to define the plane described by said two points and said tip location point, and to define a vector described by said midpoint and said tip location point.

10. A system for automatically calibrating the position of a medical instrument in a system for monitoring the medical instrument in a surgical environment, said system comprising: a position detection unit; data representative of at least two points having a fixed spatial relationship with respect to the position detection unit and data representative of a midpoint between said two points; an instrument tip that may be positioned at a particular tip location point to permit said system to define the plane described by said two points and said tip location point, and to define an instrument vector described by said midpoint and said tip location point; and vector data representative of a plurality of instrument tips that may be attached to the instrument, and a vector correlation unit for determining which of a plurality of instrument tips is attached to the instrument responsive to said instrument vector and said vector data.