U.S. patent application number 10/427472 was filed with the patent office on 2004-02-05 for system for monitoring the position of a medical instrument with respect to a patient's body.
Invention is credited to Ferre, Maurice R., Jakab, Peter D., Tieman, James S..
Application Number | 20040024309 10/427472 |
Document ID | / |
Family ID | 56289653 |
Filed Date | 2004-02-05 |
United States Patent
Application |
20040024309 |
Kind Code |
A1 |
Ferre, Maurice R. ; et
al. |
February 5, 2004 |
System for monitoring the position of a medical instrument with
respect to a patient's body
Abstract
A system is disclosed 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 said body
responsive to the position of said medical instrument. In one
embodiment the system includes a reference unit secured from
movement with respect to the patient's body such that said
reference unit is substantially immobile with respect to a target
operation site. The system also includes a remote unit for
attachment to the medical instrument. A field generator may be
associated with one of the units for generating a position
characteristic field in an area including the target operation
site. One or more field sensors may be associated with either of
the units responsive to the presence of the position characteristic
field for producing one or more sensor output signals
representative of said sensed field. A position detector in
communication with the sensor output signal produces position data
representative of the position of the remote unit with respect to
the reference unit. An output display in communication with the
position detector displays at least one of the prerecorded images
responsive to the position data.
Inventors: |
Ferre, Maurice R.; (North
Andover, MA) ; Jakab, Peter D.; (Canton, MA) ;
Tieman, James S.; (Watertown, MA) |
Correspondence
Address: |
Kirk A. Vander Leest
McAndrews, Held & Malloy, Ltd.
34th Floor
500 West Madison Street
Chicago
IL
60661
US
|
Family ID: |
56289653 |
Appl. No.: |
10/427472 |
Filed: |
April 30, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10427472 |
Apr 30, 2003 |
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09643608 |
Aug 22, 2000 |
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09643608 |
Aug 22, 2000 |
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09212024 |
Dec 15, 1998 |
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6175756 |
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09212024 |
Dec 15, 1998 |
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08637289 |
Apr 24, 1996 |
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5873822 |
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08637289 |
Apr 24, 1996 |
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08527517 |
Sep 13, 1995 |
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5803089 |
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08527517 |
Sep 13, 1995 |
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08306818 |
Sep 15, 1994 |
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5829444 |
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Current U.S.
Class: |
600/424 |
Current CPC
Class: |
A61B 6/037 20130101;
G06T 3/0068 20130101; A61B 6/032 20130101; A61B 2034/2051 20160201;
A61B 5/06 20130101; A61B 90/98 20160201; A61B 90/36 20160201; A61B
2090/3937 20160201; A61B 90/39 20160201; A61B 2017/00464 20130101;
A61B 2034/2068 20160201; A61B 90/10 20160201; A61B 2090/0818
20160201; A61B 5/062 20130101; A61B 5/064 20130101; A61B 2017/00482
20130101; A61B 2017/00477 20130101; G01B 7/004 20130101; A61B
90/361 20160201; A61B 34/20 20160201; A61B 2090/363 20160201; A61B
2034/2055 20160201; A61B 2090/3983 20160201; A61B 90/14 20160201;
A61B 2034/2072 20160201; A61B 2017/00022 20130101 |
Class at
Publication: |
600/424 |
International
Class: |
A61B 005/05 |
Claims
We claim:
1. Apparatus for securing a reference unit to a patient's head,
said apparatus comprising reference unit mounting means for
mounting said reference unit to said apparatus, said reference unit
for use in monitoring the position of a medical instrument with
respect to said patient's head, and a nose bridge mounting element
and two ear-mounting elements for attaching said reference unit to
said patient's head.
2. Apparatus as claimed in claim 1, wherein said reference unit
mounting means includes means for releasably attaching said
reference unit to said apparatus.
3. Apparatus as claimed in claim 1, wherein each of said nose and
ear mounting elements are disposed on a distal end of an elongated
mounting arm.
4. Apparatus as claimed in claim 1, wherein said apparatus further
includes an elongated center member and two side members, each of
said members being centrally attached to one another at first ends
thereof, and said nose bridge mounting element being attached to
said center member at a second end thereof and each of said ear
mounting elements being attached to a respective side member at
second ends thereof.
5. Apparatus as claimed in claim 3, wherein each of said center and
side members is made of a structurally resilient material and is
capable of accommodating a plurality of sizes of patient heads.
6. Apparatus as claimed in claim 5, wherein said structurally
resilient material is plastic.
7. Apparatus as claimed in claim 1, wherein said reference unit
includes a field generator for generating a three dimensional
position characteristic field.
8. Apparatus as claimed in claim 7, wherein said reference unit
further includes a reference sensor for generating a feedback
reference signal.
9. Apparatus as claimed in claim 1, wherein said reference unit
includes an electromagnetic field generator for generating an
electromagnetic field.
10. Apparatus as claimed in claim 1, wherein said reference unit
includes a field sensor for sensing a three dimensional position
characteristic field and for producing a sensor output responsive
to the presence of said sensed field.
11. Apparatus as claimed in claim 10, wherein said reference unit
further includes a reference sensor for generating an error
detection signal.
12. Apparatus as claimed in claim 1, wherein said reference unit
includes an electromagnetic field sensor responsive to the presence
of an electromagnetic field for producing a sensor output signal
representative of said sensed electromagnetic field.
13. Apparatus as claimed in claim 1, wherein said reference unit
includes a signal transmitter for transmitting a reference signal
to a signal receiver, said reference signal for use in detecting
the position of said reference unit with respect to said signal
receiver by comparing said signal to a second transmitted
signal.
14. Apparatus as claimed in claim 11, wherein said reference unit
further includes a second signal transmitter for transmitting said
second transmitted signal.
15. Apparatus as claimed in claim 1, wherein said reference unit
includes a signal receiver for receiving a reference signal from a
signal transmitter, said reference signal for use in detecting the
position of said reference unit with respect to said signal
transmitter by comparing said signal to a second transmitted
signal.
16. Apparatus as claimed in claim 15, wherein said reference unit
further includes a second signal receiver for receiving said second
transmitted signal.
17. Apparatus for monitoring the position of a medical instrument
with respect to a patient's body, said apparatus including a
reference unit removably attached to said medical instrument.
18. Apparatus as claimed in claim 17, wherein said reference unit
is removably insertable into said medical instrument.
19. Apparatus as claimed in claim 17, wherein said medical
instrument is an aspirating device.
20. Apparatus as claimed in claim 17, wherein said reference unit
includes a field generator for generating a three dimensional
position characteristic field.
21. Apparatus as claimed in claim 17, wherein said reference unit
further includes a reference sensor for generating a feedback
reference signal.
22. Apparatus as claimed in claim 17, wherein said reference unit
includes an electromagnetic field generator for generating an
electromagnetic field.
23. Apparatus as claimed in claim 17, wherein said reference unit
includes a field sensor for sensing a three dimensional position
characteristic field and for producing a sensor output responsive
to the presence of said sensed field.
24. Apparatus as claimed in claim 17, wherein said reference unit
further includes a reference sensor for generating an error
detection signal.
25. Apparatus as claimed in claim 17, wherein said reference unit
includes an electromagnetic field sensor responsive to the presence
of an electromagnetic field for producing a sensor output signal
representative of said sensed electromagnetic field.
26. Apparatus as claimed in claim 17, wherein said reference unit
includes a signal transmitter for transmitting a reference signal
to a signal receiver, said reference signal for use in detecting
the position of said reference unit with respect to said signal
receiver by comparing said signal to a second transmitted
signal.
27. Apparatus as claimed in claim 26, wherein said reference unit
further includes a second signal transmitter for transmitting said
second transmitted signal.
28. Apparatus as claimed in claim 17, wherein said reference unit
includes a signal receiver for receiving a reference signal from a
signal transmitter, said reference signal for use in detecting the
position of said reference unit with respect to said signal
transmitter by comparing said signal to a second transmitted
signal.
29. Apparatus as claimed in claim 28, wherein said reference unit
further includes a second signal receiver for receiving said second
transmitted signal.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to computer assisted medical surgery
and in particular relates to systems for displaying prerecorded
visual images during surgical operations.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
SUMMARY OF THE INVENTION
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The following detailed description of the invention may be
further understood with reference to the accompanying drawings in
which: FIG. 1 is a diagrammatic view of a system of an embodiment
of the invention;
[0015] FIG. 2 is a front view of the headset unit shown in FIG.
1;
[0016] FIG. 3 is a side view of the headset unit shown in FIG. 1
taken along line 3-3 of FIG. 2;
[0017] FIG. 4 is a rear view of a portion of the headset shown in
FIG. 1 taken along line 4-4 of FIG. 3;
[0018] FIG. 5 is an exploded side view of the surgical instrument
and remote sensor shown in FIG. 1;
[0019] FIG. 6 is an end view of the assembled surgical instrument
and sensor shown in FIG. 1 taken along line 6-6 of FIG. 5;
[0020] FIG. 7 is a side view of another embodiment of a surgical
instrument and sensor unit of the invention in accordance with an
alternative embodiment of the invention;
[0021] FIG. 8 is a side view of the surgical instrument shown in
FIG. 7;
[0022] FIG. 9 is an end view of the surgical instrument shown in
FIG. 7;
[0023] FIG. 10 is an elevational view of the surgical instrument
shown in FIG. 7;
[0024] FIG. 11 is a plan view of a remote sensor unit that is
adapted to be used with the surgical instrument shown in FIGS.
7-10;
[0025] FIG. 12 is a side view of another surgical instrument
together with the removable remote sensor unit shown in FIGS. 7 and
11;
[0026] FIG. 13 is a diagrammatic illustration of the system
employed to prerecord CT images for use with the system of the
invention;
[0027] FIG. 14 is diagrammatic illustration of a manual
registration process of the invention;
[0028] FIG. 15 is an elevational view of the components of a
fiducial marker system in accordance with an embodiment of the
invention;
[0029] FIG. 16 is a plan view of the components of the system of
FIG. 15 taken along line 16-16 thereof;
[0030] FIG. 17 is a flowchart-of the process of using the fiducial
marker system of FIG. 15;
[0031] FIG. 18 is a side view of a headset unit in accordance with
another embodiment of the invention;
[0032] FIG. 19 is an end view of the headset unit shown in FIG. 18
taken along line 19-19 thereof;
[0033] FIG. 20 is a plan view of a transmitter that is adapted to
be used with the headset unit shown in FIG. 18;
[0034] FIG. 21 is a partial view of a portion of the headset shown
in FIG. 16 taken along line 21-21 thereof;
[0035] FIG. 22 is a flow chart of an automatic registration process
of the invention;
[0036] FIG. 23 is a diagrammatic view of the position detection
components in accordance with a system of the invention;
[0037] FIGS. 24 and 25 are diagrammatic views of the principles of
an error detection calculation process in accordance with an
embodiment of the invention;
[0038] FIGS. 26 and 27 are diagrammatic views of the errors
detected by the process of FIGS. 24 an 25;
[0039] FIG. 28 is a diagrammatic view of another embodiment of the
invention; and
[0040] FIGS. 29-32 are diagrammatic views of further embodiments of
systems of the invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0041] As shown in FIG. 1, a system 10 of the invention includes a
headset 12 mounted on a patient 14, a medical instrument 16, a
control system 18 and a display 20. The control system 18 includes
a position-detection unit 22, a registration unit 24, and an image
storage unit 26.
[0042] 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 FIG. 1, the display 20 shows three images, a coronal image
21a, a sagittal image 21b, and an axial image 21c. Text information
may also be displayed as shown at 21d in FIG. 1.
[0043] As further shown in FIGS. 2-4, the headset 12 includes two
ear mounts 28 on side members 30, and a nose bridge mount 32 on a
center member 34. The headset 12 should be made of a resilient
plastic such that it may be snugly attached to a patient's head,
and may be provided in a variety of sizes. A primary objective of
the headset is to provide a reference unit that may be easily
attached to and removed from a patient's head wherein the headset
may be repeatedly reattached in exactly the same place with a high
degree of accuracy. In other embodiments, the side members 30 of
the headset 12 may be rotationally attached to one another and the
ear mounts 28 may be biased toward one another. Further, the center
member 34 may be rotatable with respect to the side members 30 and
biased toward the ear mounts 28 as well.
[0044] The headset 12 shown in FIGS. 1-4 also includes a reference
unit 36 connected to the position detection unit 22 via
communication lines 38. The reference unit 36 may be releasably
attached to the headset 12 by conventional clamp or fastening
means. In one embodiment the reference unit 36 may include a
position characteristic field generator capable of generating a
multidirectional field in three dimensions and may involve the use
of either electromagnetic or ultrasonic waves. The position
characteristic field differs from the transmit/receive
triangulation system, in part, because it does not rely on the
comparison of one transmitted signal with another as does
triangulation. This permits the path between the field generator
and the remote sensor to be obstructed by materials that do not
significantly alter the generated field. For example, the position
of the medical instrument could be identified even when the
instrument is within the patient's body when the generated field is
a magnetic field. Additionally, the reference unit may also include
a reference sensor 37 to provide verification of proper system
operation.
[0045] 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.
[0046] 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.
[0047] As shown in FIGS. 5 and 6 the medical instrument 16 may be
an aspirating device adapted to removably receive a remote sensor
40 for detecting, for example, the field generated by the position
characteristic field generator. The sensor 40 may be held inside
the instrument 16 by force fit sizing or through the use of a
resilient snap member in the wall opening 42. Since an aspirating
device is commonly used in most surgical operations, incorporating
the remote sensor into the aspirating device provides the surgeon
with a convenient position detection device that does not clutter
the operation site with unnecessary items. The instrument 16 may
further include a second backup field sensor 41 for system error
detection as discussed above with reference to the sensor 37.
[0048] 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.
[0049] 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 FIG. 1) is connected to a vacuum aspirating
unit (not shown).
[0050] 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 FIG. 1. In other
embodiments the orientation of the aspirating tube 46 may also be
identified on the displayed images. In further embodiments, a three
dimensional composite image may be displayed based on the
prerecorded images.
[0051] As shown in FIGS. 7-11 another embodiment of a removable
remote sensor unit 58 may be used with an aspirating device 60. The
sensor unit 58, including two sensors 62,64 may be removably
attached to the device 60 by first engaging recesses 66 on the unit
58 with fingers 68 on the device 60. A tounge 70 on the unit 58 is
then received between hinge posts 72 on the device 60, and finally
secured in place by rotating the lock 74 from an open position as
shown in FIG. 8 to a closed position as shown in FIG. 7. The lock
74 includes a recessed area at 76 adapted to frictionally engage
the tounge 70 on the sensor unit 58.
[0052] 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.
[0053] For example, if all of the transistors 78 sense the presence
of a magnet 80 then the instrument 60 shown in FIGS. 7-11 is known
to be attached to the sensor unit 58 since the instrument 60
includes three magnets. If only two magnets 82 are sensed then the
medical instrument attached to the sensor unit 58 is a different
instrument 84 as shown in FIG. 12. If no magnets are sensed then it
is known that the sensor unit 58 is not attached to any medical
instrument. Knowing the identity of the attached medical instrument
permits the system to automatically adjust the position detection
unit to compensate for the differences in instrument tip position
with respect to the position of the sensors 62,64 for a variety of
medical instruments. The removably engageable feature of the sensor
unit not only provides versatility, but also facilitates the use of
sterilized medical instruments.
[0054] As illustrated in FIGS. 13 and 14 the registration process
involves two fundamental steps: 1) recording the scan images of a
predetermined orientation and 2) mapping the special orientation of
the position detection system onto the recorded images. For
example, the orientations of the prerecorded images may be in the
sagittal (i-j plane), coronal (k-j plane) and/or axial (k-i plane)
as shown in FIG. 13. The images may be digitally stored and the
distance between each scanned image is recorded, as are the
relative orientations of each set of images. As those skilled in
the art will appreciate, in alternative embodiments certain of the
images may be created from other images without the need to
prerecord each of the sagittal, coronal and axial views. For
example, by multiplanar reformatting the sagittal and coronal
images may be created from the axial images.
[0055] 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 FIG. 14.
Specifically, when each marker 90 is sequentially located, for
example with the tip 48 of a medical instrument 16, the user
locates the same marker on the prerecorded images by using, for
example a computer mouse. The user then controls the entering of
the registration data through either a computer keyboard 94, a
mouse, or a foot switch. In alternative embodiments the
registration unit may scan each prerecorded digital image beginning
from one corner until it locates the identified marker.
[0056] 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 FIGS. 15 and 16.
[0057] 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 FIG. 17, the process of using the fiducial
markers 90' begins (step 1700) by first placing the strips 91 on
the patient's skin (step 1710). The fiducial markers 90' are then
placed on the strips 91 such that the radiopaque elements 95 align
with the markers 97 on the strips 91 (step 1704). The scan images
are then recorded (step 1706), and the fiducial markers 90' may
then be removed from the patient (step 1708). During manual
registration the surgeon or technician may locate the markers 97
with the tip of a pointer (step 1710) and thereby record the
positions of the fiducial marker radiopaque elements 95 with
respect to the transmitter. The use of the intermediate strips 91
not only provides increased comfort to the patient after the image
scanning and prior to surgery, but also facilitates accurate
registration. Since the radiopaque elements 95 were centered
directly on top of the markers 93, the accuracy of registration is
enhanced because the user may now locate the smaller sized markers
93 instead of more indefinitely locating a portion of the larger
sized radiopaque elements 95 with the pointer tip.
[0058] 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.
[0059] The images points are each processed as a matrix of the form
1 [ i r j r k r ] ( 1 )
[0060] and the collected sensor points are each processed as a
matrix of the form 2 [ x s y s z s ] ( 2 )
[0061] A computer processor then iteratively calculates the optimal
values for the transformation matrices 3 [ r 11 r 12 r 13 r 21 r 22
r 23 r 31 r 32 r 33 ] and [ t x t y t z ] ( 3 )
[0062] to solve the following equation: 4 [ i r j r k r ] = [ r 11
r 12 r 13 r 21 r 22 r 23 r 31 r 32 r 33 ] [ x s y s z s ] + [ t x t
y t z ] ( 4 )
[0063] such that
(i.sub.c-i.sub.i).sup.2+(j.sub.c-j.sub.i).sup.2+(k.sub.c--
k.sub.i).sup.2 is a minimum for the summation of all of the
collected image points. The optimization method employs distance
minimization, and at least three image points are required for this
method.
[0064] 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.
[0065] A further embodiment of the headset of the invention may be
employed in an automatic registration process. For example, as
shown in FIGS. 18 and 19 another embodiment of a headset 100 of the
invention includes two ear mounts 28, side members 30, and a nose
bridge mount 32 on center member 34 as discussed above with
reference to FIGS. 2-4. The headset 100 further includes a center
plate 102 on the center member 34. The center plate 102 is adapted
to receive a transmitter 104 as shown in phantom in FIG. 19 and
shown from the underside of the plate 102 in FIG. 21. The
transmitter 104 includes two posts 106 and a key 108 that is free
to rotate about a pin 110.
[0066] 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.
[0067] 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 FIG. 18. The automatic registration process locates
the balls 116 on the prerecorded scan images, and knowing the
spacial relationship between the balls 116 and the transmitter 104,
automatically generates the mapping function to translate from the
transmitter coordinate system to the image coordinate system.
[0068] Specifically and with reference to FIG. 22, the automatic
registration process begins (step 2200) by loading the prerecorded
images (step 2202) and then creating a three dimensional data set
(step 2204). Pixels having an intensity within a certain range are
then identified (step 2206), and groups of adjacent pixels are
located (step 2208) and classified together as a single group. The
volume of each group is calculated (step 2210) and groups not
within a predefined range of volumes are rejected (step 2212).
Groups not having at least one pixel with an intensity level of at
least a certain amount are rejected (step 2214). If the number of
groups remaining is less than the number of fiducial balls 116
(step 2216), e.g., 7, then the program ends having failed to
provide automatic registration (steps 2218 and 2220).
[0069] 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).
[0070] 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.
[0071] 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.
[0072] 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 Spaces Fastrak.TM. product
sold by Polhemus, Incorporated of Colchester, Vermont 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.
[0073] Specifically and with reference to FIG. 23, both the
magnetic field source 101 and the magnetic field sensor 103 include
three orthogonally disposed coils as shown. An alternating electric
current from an amplifier 105 is passed through each of the source
coils one at a time generating sequential magnetic fields. A
processing unit 107 generates the timing signals and controls a
digital-to-analog converter 109. The magnetic fields induce
voltages in the three coils of the sensor 103. The induced voltages
are amplified by an amplifier 111, digitized by an
analog-to-digital converter 113, and then processed by the
processing unit 107.
[0074] 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.
[0075] 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.RTM. Fastrak.TM. product at a given time as
a set of six values x.sub.s, y.sub.s, z.sub.s, .omega..sub.azs,
.omega..sub.els, and .omega..sub.ros. The values x.sub.s, y.sub.s,
and z.sub.s identify the position of the center of the sensor
within the X,Y,Z coordinate reference frame, and the angles
.omega..sub.azs, .omega..sub.els, and .omega..sub.ros identify the
orientation of the-sensor S with respect to the X,Y,Z coordinate
reference frame.
[0076] The value .omega..sub.azs 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 .omega..sub.els 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.
[0077] The value .omega..sub.ros 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
.omega..sub.azs, .omega..sub.els, and .omega..sub.ros.
[0078] 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.
[0079] 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 t.sub.1 and t.sub.2.
[0080] 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.
[0081] In a preferred embodiment involving field integrity
detection and with reference to FIGS. 1-3, a reference sensor 37
may be securely mounted on the transmitter assembly 12 at a fixed
distance from the center of the transmitter 36. The location and
orientation of this reference sensor should be determined through a
calibration process under controlled conditions, and thereafter
continuously calculated and verified. In certain embodiments a
weighted sum of all six sensor output parameters x.sub.s, y.sub.s,
Z.sub.s, .omega..sub.azs, .omega..sub.els, and .omega..sub.ros may
be continuously monitored as an indication of compromised field
integrity.
[0082] As also noted above and shown in FIGS. 7-12, the remote
sensor 58 may include a plurality of sensors (62,64) the outputs of
which are compared for error detection purposes. Potential error
conditions that would be detectable by such a system include sensor
failure where one sensor ceases to operate properly, as well as
uneven localized field distortions in the area of the medical
instrument.
[0083] 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.
[0084] 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.
[0085] 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 FIGS. 7-12 and by
monitoring the locations of two or more virtual points. As shown in
FIG. 25, the sensors S.sub.1 and S.sub.2 are separated from each
other by a distance 2d and for convenience defined to be positioned
along an axis such as the Y axis as shown. Sensor S.sub.1 uniquely
defines an X-Z plane in which it is located, and S.sub.2 uniquely
defines an X-Z plane in which it is located as shown. A first
virtual location v.sub.a is chosen to be between the X-Z planes
defined by the sensors, while a second virtual location v.sub.b is
chosen to be outside of the X-Z planes defined by the sensors as
shown in FIG. 11. The locations v.sub.a and v.sub.b are virtual
locations that are continuously calculated and compared with
factory defined positions.
[0086] In the embodiment diagrammatically shown in FIGS. 24 and 25
the virtual points v.sub.a (-d,-d,-d with respect to S.sub.2) and
v.sub.b (d,d,d with respect to S.sub.2) are equidistant from
S.sub.2. The sensor S.sub.2 is the protected sensor in this
embodiment, and the sensor S.sub.1 is used as a reference to
provide the error detection for S.sub.2 The magnitude of the
resultant vector from S.sub.2 to v.sub.a is the same as that from
S.sub.2 to V.sub.b but opposite in direction, and this magnitude is
approximately one half of the distance between S.sub.1 and
S.sub.2.
[0087] The locations of v.sub.a and V.sub.b in the reference
coordinate system (i.e., with respect to S.sub.1) must be
calculated and will be referred to as v.sub.a1 and V.sub.b1 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: 5 [ cos ? cos ? sin ? cos ? - sin ? cos ? - sin ?
- sin ? - sin ? cos ? cos ? - cos ? + sin ? - sin ? - sin ? cos ? -
sin ? cos ? - sin ? - cos ? + sin ? - sin ? sin ? - sin ? - cos ? -
cos ? - cos ? cos ? - sin ? ] ? indicates text missing or illegible
when filed ( 5 )
[0088] Then the locations of the virtual points are calculated
as:
v.sub.a1=A.multidot.v.sub.a2+PS
v.sub.b1=A.multidot.v.sub.b2+PS
[0089] 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 v.sub.ae and
V.sub.be . Throughout the use of the system, the actual measured
values of the virtual points (v.sub.am, v.sub.bm) are compared to
the stored reference values for the virtual points (v.sub.ae,
v.sub.be). If the distance between the established and measured
location (.DELTA.) for either virtual point is larger than a preset
value (.epsilon.), then a field integrity violation message is
displayed and normal operation of the system is suspended. In
particular and with reference to FIG. 26
.vertline.v.sub.alm-v.sub.alm.vertline.>.epsilon.or
.vertline.v.sub.blm-v.sub.ble>.epsilon.
[0090] 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:
.vertline.((A.sub.e+A.sub.m.DELTA.).multidot.v.sub.a2+PS.sub.e+PS.sub.m.DE-
LTA.)-(A.sub.e.multidot.v.sub.a2+PS.sub.e).vertline.>.epsilon.
or
.vertline.((A.sub.e+A.sub.m.DELTA.).multidot.v.sub.b2+PS.sub.e+PS.sub.m.DE-
LTA.)-(A.sub.e.multidot.v.sub.b2+PS.sub.e).vertline.>.epsilon.
[0091] which equals
.vertline.A.sub.m.DELTA..multidot.v.sub.a2+PS.sub.m.DELTA..vertline.>.e-
psilon.
or
.vertline.A.sub.m.DELTA..multidot.v.sub.b2+PS.sub.m.DELTA..vertline.>.e-
psilon.
[0092] Substituting
A.sub.m.DELTA..multidot.v.sub.a2=OPS.sub.am.DELTA.and
A.sub.m.DELTA.v.sub.b2=OPS.sub.bm.DELTA.
[0093] this relationship may be diagrammatically illustrated as
shown in FIG. 27. The tip location of the medical instrument should
be initially defined with respect to the protected sensor (S2), and
used in determining the position of the tip with respect to the
source.
[0094] 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.
[0095] As shown in FIG. 28 in alternative embodiments of the
invention a reference unit 120, including a field generator 122,
may be positioned a small distance away from the portion of the
patient's body (such as the head) 14 on an articulated arm 124. A
headset 12 including a reference sensor 126 may be attached to the
patient's body, and the medical instrument 16 may include a remote
sensor 40 as discussed above with reference to FIGS. 1-6. Once the
field generator 122 is positioned at a convenient location it may
be fixed in place by securing the joints of the articulated arm.
The position of the patient with respect to the field generator may
accordingly be monitored. The position of the instrument 16 with
respect to the patient may also be determined and the system may
then operate to display the appropriate prerecorded images as
discussed below.
[0096] 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.
[0097] 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 FIG. 29. If either the patient or the field generator is moved,
the image processor 130 will identify the amount of relative change
in location and advise the position detection unit 22 accordingly.
Additional cameras positioned to view the patient from a variety of
directions may be employed in further embodiments.
[0098] As shown in FIG. 30 in an alternate embodiment, the system
may include a flexible band 132 for secure attachment to a portion
of a patient's body 14 (e.g., a head or chest). The band 132
includes field generator 134 and a reference sensor 136 that
provides feedback to the signal generator in the position detection
unit 22. The position detection unit 22 is connected via
communication lines 138 to the flexible band 132, and is connected
via communication lines 140 to a flexible medical instrument 142
having a remote sensor at its tip 144. Because the medical
instrument 142 is not rigid, the sensor should be positioned
sufficiently close to the tip of the instrument 142 to provide
accurate position detection and monitoring within the patient's
body. The display 20 may indicate the relative orientation of the
instrument 142 on one or more images as shown.
[0099] As shown in FIGS. 31 and 32 a system of the invention may
include a flexible medical instrument 150 having a sensor 152 at
its distal tip 154, and a fiber optic endoscope 156 having a sensor
158 at it distal tip. 160. The fiber optic endoscope 156 is
connected at its proximal end to a camera 162 which is in
communication with an image processor 164. Because the field
generator 134 on the reference band 132 may move, for example as
the patient breaths, the location of the remote sensor 152 may
appear to move when in fact the medical instrument 150 has not
moved.
[0100] 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.
[0101] 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.
* * * * *