U.S. patent application number 09/171148 was filed with the patent office on 2001-11-22 for x-ray guided surgical location system with extended mapping volume.
Invention is credited to BEN-HAIM, SHLOMO, GOVARI, ASSAF, WEINFELD, ZEEV.
Application Number | 20010044578 09/171148 |
Document ID | / |
Family ID | 26719714 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010044578 |
Kind Code |
A1 |
BEN-HAIM, SHLOMO ; et
al. |
November 22, 2001 |
X-RAY GUIDED SURGICAL LOCATION SYSTEM WITH EXTENDED MAPPING
VOLUME
Abstract
Apparatus for X-ray guided surgery, including a reference
element (20), which is placed in contact with the body (32) of a
subject. The element includes a plurality of fiducial marks (22a,
22b, 22c) and a first coordinate sensing device (24), in
predetermined, fixed positions in the element (20). A surgical tool
(36), having a distal end for insertion into the body (32),
includes a second coordinate sensing device (40) fixed thereto. A
fluoroscope (54) forms an X-ray image of the body, including the
fiducial marks. A computer analyzes the image to determine the
position of the reference element in the image, so as to find
coordinates of the first coordinate sensing device relative to the
image, and registers the position of the tool with the X-ray image
by referring coordinates of the second coordinate sensing device to
the known coordinates of the first position sensor.
Inventors: |
BEN-HAIM, SHLOMO; (HAIFA,
IL) ; WEINFELD, ZEEV; (HERZLIYA, IL) ; GOVARI,
ASSAF; (KIRIAT HAIM, IL) |
Correspondence
Address: |
AUDLEY A CIAMPORCERO JR
ONE JOHNSON & JOHNSON PLAZA
NEW BRUNSWICK
NJ
089337003
|
Family ID: |
26719714 |
Appl. No.: |
09/171148 |
Filed: |
January 28, 1999 |
PCT Filed: |
January 22, 1998 |
PCT NO: |
PCT/IL98/00034 |
Current U.S.
Class: |
600/424 ;
606/130 |
Current CPC
Class: |
A61B 2034/207 20160201;
A61B 90/36 20160201; A61B 2034/107 20160201; A61B 2090/363
20160201; A61B 34/20 20160201; A61B 2034/2051 20160201; A61B
2034/2072 20160201; A61B 34/25 20160201; A61B 2034/2063
20160201 |
Class at
Publication: |
600/424 ;
606/130 |
International
Class: |
A61B 006/00 |
Claims
1. A method for X-ray guided surgery, comprising: placing a
reference element, to which a reference coordinate sensing device
is fixed, on the body of a patient; acquiring an X-ray image of the
body, including the element, during the surgery; processing the
image to determine image-based coordinates of the reference
coordinate sensing device; receiving and processing signals from
the reference coordinate sensing device to determine signal-based
coordinates thereof, and registering the image-based and
signal-based coordinates to determine a coordinate transformation
therebetween.
2. A method according to claim 1, wherein registering the
coordinates to determine a coordinate transformation comprises
determining an image scale factor.
3. A method according to claim 2, and comprising determining
coordinates of an X-ray camera used to acquire the X-ray image,
wherein determining the image scale factor comprises comparing the
camera coordinates to the coordinates of the reference coordinate
sensing device.
4. A method according to claim 1, and comprising: bringing a
surgical tool, to which a tool coordinate sensing device is fixed,
into proximity with the body of the patient; receiving and
processing signals from the tool coordinate sensing device to
determine signal-based coordinates thereof, and determining
image-based coordinates of the tool by applying the coordinate
transformation to the signal-based coordinates of the tool
coordinate sensing device.
5. A method according to claim 4, and comprising displaying the
image and registering a representation of the tool thereon using
the image-based coordinates of the tool.
6. A method according to claim 5, wherein acquiring the X-ray image
comprises acquiring a plurality of images from different view
angles with respect to the body, and wherein displaying the image
and registering the representation of the tool therein comprises
registering a suitably-oriented representation of the tool in at
least two of the plurality of images.
7. A method according to claim 5, and comprising designating
image-based coordinates of a target point within the body, and
determining and displaying a linear course along which the tool is
to be advanced so as to reach the target point.
8. A method according to claim 7, and comprising advancing the tool
into the body and comparing coordinates of the tool to the linear
course so as to detect a deviation of the tool from the course.
9. A method according to any of claims 1-8, wherein acquiring the
X-ray image comprises acquiring a sequence of images during the
surgery, and wherein processing the image to determine image-based
coordinates comprises processing at least two images in the
sequence to determine respective image-based coordinates based on
each of the at least two images.
10. A method of tracking an object within a body, comprising:
attaching a plurality of reference coordinate sensing devices to
the body and at least one object coordinate sensing device to the
object; registering the positions of the plurality of reference
coordinate sensing devices in a frame of reference fixed to the
body; selecting at least one of the plurality of reference
coordinate sensing devices in proximity to the object; and
receiving and processing signals from the at least one selected
reference coordinate sensing device and the object coordinate
sensing device to determine signal-based coordinates of the object
and of the selected reference device so as to register the object
coordinates relative to the body.
11. The method of claim 10, wherein attaching the plurality of
reference devices comprises attaching devices such that at
substantially every point in an area of interest in or on the body,
at least one device is within a predetermined range of the
point.
12. The method of claim 11, wherein receiving the signals comprises
receiving signals responsive to the strength of a field transmitted
by or incident on at least one field transducer in proximity to the
body, and wherein the predetermined range is determined in
accordance with a detection volume of the field transducer.
13. The method of claim 12, wherein the detection volume has a
substantially smaller extent than the area of interest.
14. The method of claim 10, wherein attaching the plurality of
reference devices comprises attaching at least one strap comprising
the plurality of sensing devices.
15. The method of claim 10, wherein selecting at least one of the
reference devices comprises determining which of the reference
devices provides registration of the coordinates of the object to a
desired degree of accuracy.
16. The method of claim 15, wherein receiving the signals comprises
receiving signals responsive to the strength of a field transmitted
by or incident on a field transducer, and wherein determining which
of the reference devices provides the registration to the desired
degree of accuracy comprises measuring the strength of the signals
received from the at least one of the reference devices.
17. The method of claim 10, wherein selecting the at least one of
the reference devices comprises periodically repeating the step of
selecting at least one of the reference devices.
18. The method of any of claims 10-17, wherein registering the
positions of the plurality of reference devices comprises acquiring
an image of the body including two or more of the plurality of
reference coordinate sensing devices.
19. The method of claim 12, and comprising displaying a map of
areas which are included in the detection volume of the at least
one field transducer.
20. A method of tracking an object within a body comprising:
placing at least one field transducer, having a detection volume,
in a vicinity of the body; determining the position of the at least
one field transducer; displaying a map showing the detection volume
of the at least one field transducer relative to the body; and
controlling the tracking of the object responsive to the map.
21. A method according to claim 20, wherein controlling the
tracking comprises moving the at least one field transducer
responsive to the map so as to optimize tracking of the object.
22. A method according to claim 21, wherein determining the
position of the at least one field transducer comprises determining
the position of the at least one field transducer relative to a
reference device attached to the body.
23. A method according to claim 21, wherein moving the at least one
field transducer comprises moving the field transducer such that
the object is within the detection volume.
24. A method according to any of claims 19-23, and comprising
producing an image of a portion of the body and wherein displaying
the map comprises superimposing the map on the image.
25. A method according to any of claims 19-23, wherein placing the
at least one field transducer comprises placing a plurality of
field transducers, and wherein displaying the map comprises
associating each field transducer with an area on the map included
in its respective detection volume.
26. A reference sensor strap for registering position information,
comprising: a band attachable to a patient's body; and a plurality
of reference sensors mounted on the band.
27. The strap of claim 26, and comprising a plurality of fiducial
marks at fixed positions relative to the reference sensors.
28. A system for determining the disposition of an object within a
body of a patient, comprising: a position sensor, which is coupled
to the object; a plurality of reference sensors, which are attached
to the body; a movable field transducer, which transmits fields to
or receives fields from the position sensor and reference sensors;
and a processor, which selects at least one of the reference
sensors in proximity to the object and determines coordinates of
the position sensor relative to the selected reference sensor,
irrespective of movement of the field transducer relative to the
patient.
29. A system according to claim 28, wherein the processor
periodically selects the at least one reference sensor so as to
allow accurate determination of the position of the object relative
to the selected reference sensor.
30. A system according to claim 29, wherein the processor selects
the at least one reference sensor by transmitting fields which
generate signals in the sensors, and comparing the strengths of the
signals in the sensors.
31. A system according to any of claims 28-30, and comprising an
imaging device for producing an image on which the determined
coordinates are registered.
32. A system according to claim 31, wherein the processor indicates
a detection volume of the field transducer on the image.
33. A system for determining the disposition of an object within a
body of a patient, comprising: a position sensor for coupling to
the object; at least one reference sensor for attaching to the
body; one or more field transducers having respective detection
volumes for transmitting fields to or receiving fields from the
position sensor and reference sensor; and a processor, which
determines the disposition of the object and the positions of the
field transducers responsive to the transmitted fields and
indicates the detection volumes of the field transducers responsive
to the positions.
34. A system as in claim 33, wherein the processor displays a map
of the detection volumes.
35. Apparatus for X-ray guided surgery, comprising: a reference
element, which is placed in contact with the body of a subject,
said element comprising a reference coordinate sensing device, in a
predetermined, fixed position thereon; a fluoroscope, for forming
at least one X-ray image of the body, including the reference
element; and a computer, which receives signals from the reference
coordinate sensing devices and processes the signals to determine
signal-based coordinates thereof, and which analyzes the image to
derive an image-based coordinate system and to find a
transformation to register the signal-based coordinates and the
image-based coordinate system.
36. Apparatus according to claim 35, wherein the reference element
comprises a plurality of fiducial marks in predetermined, fixed
positions thereon, and wherein the computer analyzes the image to
find image-based coordinates of the marks, so as to derive the
image-based coordinate system.
37. Apparatus according to claim 35, and comprising a surgical
tool, having a distal end for insertion into the body, and
including a tool coordinate sensing device fixed to the tool,
wherein the computer receives signals from the tool coordinate
sensing device and applies the transformation to the signals to
determine image-based coordinates of the surgical tool.
38. Apparatus according to claim 37, and comprising a display,
driven by the computer, on which display the at least one X-ray
image is shown with a representation of the tool superimposed
thereupon, wherein the representation is registered with the image
based on the image-based coordinates of the tool.
39. Apparatus according to claim 37, and comprising a frame, which
guides the tool along a predetermined path into the body, wherein
the frame is adjusted in response to variations in the image-based
coordinates of the tool.
40. Apparatus according to any of claims 35-39, wherein the at
least one X-ray image comprises a plurality of X-ray images, formed
by the fluoroscope from at least two different angles with respect
to the body.
41. Apparatus according to claim 35, and comprising a coordinate
sensing device fixed to the fluoroscope, for determining the
position of the fluoroscope relative to the body.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of co-pending PCT
Patent Application PCT/US97/02440 and claims the benefit of U.S.
Provisional Patent Application No. 60/042,873. These applications
are assigned to the assignee of the present patent application, and
their disclosures are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to non-contact
object location systems, and specifically to position tracking of
medical probes.
BACKGROUND OF THE INVENTION
[0003] In recent years, minimally-invasive surgical techniques have
become the preferred methods of performing many procedures that
were previously carried out through an open incision. The adoption
of these minimally-invasive techniques has gone hand-in-hand with
the development of methods of visualizing the position of a
surgical tool being manipulated inside the body. Although
endoscopes offer a preferred mode of visualization in some areas of
surgery, they are unsuitable for use in many procedures, such as
neurosurgical and orthopedic procedures, in which tools must be
inserted and manipulated very delicately in narrow spaces with poor
optical visibility. In spinal surgery, for example, and in
particular, in treatments of the intervertebral discs, a thin,
hollow needle must be inserted near the center of the
intervertebral space, in such a manner as to aspirate the fluid
disc matter without touching the spinal cord, spinal nerves and
blood vessels nearby.
[0004] In neurosurgery, before performing surgery, a
three-dimensional image of the patient's head is formed, preferably
using a CT imaging system. The image is used by the surgeon, as is
known in the art, in planning the procedure and, preferably, in
establishing a three-dimensional frame of reference for the
operation, fixed with respect to the patient's anatomy. During the
surgery itself, as the surgeon inserts and manipulates a surgical
tool, its position is tracked in relation to the frame of
reference. A stereotactic frame may be fastened to the patient's
skin or bones, to be used in tracking and guiding the position of
the needle.
[0005] Various methods are known in the art for tracking the
position of a surgical tool with respect to the anatomy of a
patient. For example, Medivision Advanced Support Systems, of
Oberdorf, Switzerland, offers a system for spinal surgery that
includes an optical position sensor fixed to a surgical tool and a
reference element having three optical fiducial marks, in a fixed,
predetermined spatial relationship. The reference element is fixed
to the patient's back in a known position, and a camera is used to
track the movement of the tool, relative to the reference
element.
[0006] PCT patent publication WO 96/08209, whose disclosure is
incorporated herein by reference, describes a combined position
tracking and imaging system for use in medical applications, using
a reference frame secured to a patient's head. The system monitors
the position of a surgical instrument relative to the reference
frame, using a mobile sensor, such as electromagnetic field sensor,
as is known in the art, fixed to the instrument. Prerecorded images
of the patient's body, generally CT images of the patient's head,
are displayed responsive to the monitored position of the
instrument relative to the body. The position of the instrument is
registered on the prerecorded images.
[0007] Preferably, before the surgery, the frame is fixed to the
patient's head, and a set of CT images is acquired. These images
are used to register the position coordinates of the frame,
including the coordinates of a reference position sensor therein,
in relation to the patient's anatomy. Subsequently, during the
surgery, signals output by the reference and mobile position
sensors are monitored so as to track the coordinates of the
sensors. The coordinates of the mobile sensor relative to the
reference are used to register the position of the instrument with
respect to the patient's anatomy, for example using the
previously-acquired CT images.
[0008] Similarly, U.S. Pat. No. 5,383,454, whose disclosure is
incorporated herein by reference, describes a position tracking and
imaging system for use in neurosurgery. Before surgery, ultrasonic
emitters are fixed to a number of reference points on the patient's
head, and a set of CT images of the head are produced showing the
positions of the reference points. Similar emitters are fixed to a
surgical probe for insertion into the head. During surgery, an
array of microphones in the operating room receive ultrasound
signals emitted by the emitters on the patient's head and on the
probe. These signals are used to determine the position and
orientation of the probe relative to the reference points. The
position and orientation information is used to display an image of
the probe superimposed on the prerecorded CT images.
[0009] Position determination procedures are also described, for
example, in U.S. Pat. Nos. 5,558,091, 5,391,199, 5,443,489 and
5,377,678, all of which are incorporated herein by reference.
Position determining systems generally use extrabody apparatus to
locate a sensor attached to the surgical tool. The extrabody
apparatus-includes one or more field transducers, generally
radiators or receivers, positioned above and/or around the patient,
which transmit fields to and/or receive fields from the sensor.
Each radiator or receiver has a characteristic "detection volume"
in which the fields have sufficient strength in order to generate a
strong enough signal in conjunction with the sensor, such that the
location of the surgical tool can be determined to a desired level
of accuracy.
[0010] The size of the detection volume is generally dependent on
the size of the radiators or receivers. In some types of surgery,
such as back surgery, the size of the detection volume may cause
limitations on the surgery. If large radiators are used, they may
interfere with the movements of a physician or other medical-staff
member. Small radiators, which do not occupy much space, may not
have a large enough detection volume and/or may have low
resolution.
[0011] Although the position sensing system may be used to register
the position of the tool with previously--acquired CT or MRI
images, as described above, surgeons are generally unwilling to
rely only on prerecorded images. In addition to the use of a
reference frame or reference points and position sensors to track a
surgical tool, as described in the abovementioned PCT publication
and in U.S. Pat. No. 5,383,454, for example, fluoroscopic X-ray
imaging is generally also used to verify that the tool is indeed at
the position indicated by the position sensors. This verification
is needed, inter alia, to ensure that the frame has not shifted
relative to the patient's anatomy, and that the position readings
from the position sensors have not drifted. An error in the angle
and depth of penetration of the tool can, clearly, have devastating
consequences.
[0012] Typically, two-plane fluoroscopic X-ray imaging is used,
wherein two perpendicular X-ray images are formed simultaneously,
one an anterior-posterior image (top to bottom) and the other a
lateral image (side to side). The two-plane fluoroscope is costly,
however, and must be operated substantially continuously to monitor
the position of the surgical tool resulting in undesirably high
radiation dosages to the patient, as well as to the operating room
staff Furthermore, the fluoroscopic images acquired during surgery
are not registered with the previously-acquired CT images or with
the coordinates of the reference position sensor, so that there is
no convenient way to re-calibrate the readings of the position
sensors if they are found to be erroneous.
[0013] U.S. Pat. Nos. 5,265,610 and 5,577,502 suggest performing
invasive medical procedures during which multiple X-ray images are
periodically acquired, to give the operator information on the
three-dimensional location of an invasive tool. In order to
minimize the X-ray dosage to the patient, RF transmitters and
receivers are used to receive positional information on the
invasive tool. The positional information from the RF transmitters
is used to superimpose the position of the tool on the X-ray
images. The patient's motion may also be tracked, and the image
display adjusted accordingly. Thus, it is maintained that the X-ray
images may be updated less frequently than in conventional X-ray
tracking systems.
SUMMARY OF THE INVENTION
[0014] It is an object of some aspects of the present invention to
provide devices and methods for use in performing X-ray guided
surgery with improved accuracy and convenience.
[0015] It is a further object of some aspects of the present
invention to provide devices and methods useful in reducing
radiation dosage to a patient during such surgery.
[0016] It is an additional object of some aspects of the present
invention to provide devices and methods for registering coordinate
readings received from a coordinate sensing device with an X-ray
image during the course of a surgical procedure.
[0017] It is another object of some aspects of the present
invention to provide apparatus and methods for tracking a medical
probe within a patient using small field transducers, such as
magnetic field radiators, which do not substantially obstruct
access to the patient.
[0018] It is a further object of some aspects of the present
invention to provide apparatus and methods for tracking a medical
probe within a patient using small field transducers while
maintaining a high signal-to-noise ratio.
[0019] It is another object of some aspects of the present
invention to allow object tracking within a patient over an
extended area, while maintaining high tracking accuracy.
[0020] In one aspect of the present invention, the surgery is
guided using a single-plane X-ray image, without loss of
three-dimensional position information.
[0021] In a further aspect of the present invention, the devices
and methods are provided for use in spinal surgery, and in
particular, for guiding a needle in the intervertebral space.
[0022] In accordance with these aspects of the present invention, a
surgeon guides a surgical tool within the body of a patient by
viewing an image indicating the position and orientation of the
tool, superimposed on and registered with one or more fluoroscopic
images of the body.
[0023] The fluoroscopic images are captured as required during the
surgery, preferably using a low cost, single-plane fluoroscope. The
fluoroscope is preferably rotated around the patient to capture and
display multiple images from different angles, on which images the
position and orientation of the tool are simultaneously registered.
A costly two-plane fluoroscope, with its attendant high radiation
dosage, is not required. The fluoroscopic images are captured and
updated in real time, in the operating room, unlike CT images,
which must typically be captured in advance, as described in the
above-mentioned PCT publication WO 96/08209 and U.S. Pat. No.
5,383,454.
[0024] In some preferred embodiments of the present invention, a
surgery system comprises a rigid, elongate tool, such as a needle,
having a sharp distal end for insertion into the body of a patient,
and a reference element, to be placed in contact with the body. The
tool includes a coordinate sensing device, preferably adjacent the
tool'proximal end. The reference element likewise includes a
coordinate sensing device, preferably similar to that of the tool,
and at least three X-ray fiducial marks, in known positions
relative to the sensing device on the element. The fiducial marks
are placed so as to filly define the position and orientation of
the element, and thus of the sensing device thereon, in X-ray
images thereof.
[0025] Preferably, each of the coordinate sensing devices on the
tools and within the reference element comprises one or more coils,
which generate electrical signals in response to an
externally-applied magnetic field generated by one or more
radiators, for example, as described in U.S. Pat. No. 5,391,199,
whose disclosure is incorporated herein by reference. More
preferably, each of the sensing devices comprises a plurality of
magnetic field-responsive coils, as described in PCT patent
publication number WO96/05768, which is also incorporated herein by
reference. A biopsy needle to which such a position sensing device
is attached is described in PCT patent application PCT/IL97/00058,
which is incorporated herein by reference. The signals generated by
the coils are processed, preferably, to determine six-dimensional
position and orientation coordinates of both the tool and the
reference element relative to a reference frame based on a common
set of magnetic field radiators, preferably coils, positioned in
proximity to the patient's body.
[0026] Alternatively, any other suitable type of coordinate sensing
device may be used for this purpose, including sensors, known in
the art, based on mechanical, electromagnetic, ultrasonic, and
optical principles. In particular, sensors responsive to a DC
magnetic field may be used, as described in U.S. Pat. No.
5,558,091, which is incorporated herein by reference.
[0027] In the context of the present patent application and in the
claims, the term "coordinate sensing device" will be understood to
refer to any suitable sensor that generates signals responsive to
position and/or orientation thereof, which signals are processed to
determined coordinates of an object to which the sensor is fixed.
It will further be understood that although preferred embodiments
are described herein with reference to coordinate sensing devices
that provide both position and orientation information, the
principles of the present invention may similarly be applied using
suitable combinations of sensing devices that provide only position
information or only orientation information. Furthermore, while
preferred embodiments are described herein with reference to
sensors on the tool and fixed to the patient, which measure fields
from radiators adjacent to the body, the principles of the present
invention may also be applied by placing field emitters on the tool
and patient and using receivers adjacent to the body to receive the
emitted fields.
[0028] In preferred embodiments of the present invention, the
reference element is placed in contact with the patient's skin,
adjacent to the area of the body into which the tool is to be
inserted, and is preferably clamped or glued firmly in place. The
position and orientation of the element, relative to anatomical
features of interest in the patient's body, are ascertained by
acquiring one or more X-ray images in one or more planes, and then
determining the coordinates of the fiducial marks on the element in
the one or more images. It will be appreciated that since the
relative positions of the fiducial marks on the element are
predetermined and known, the coordinates of the marks in even a
single one of the images are sufficient to determine the scale of
the X-ray image and the six-dimensions of position and orientation
of the element relative to the patient's body.
[0029] Preferably, the images are input to an image processing
computer, of any suitable type known in the art, which analyzes the
images to identify and determine the positions of the marks. The
computer then finds the scale of the image and the position and
orientation of the element.
[0030] Further preferably, two fluoroscopic images are acquired in
two respective, generally perpendicular planes, so as to verify the
coordinate determination. Alternatively or additionally, a CT image
or image set may be acquired for this purpose.
[0031] The coordinates of the fiducial marks thus determined are
used to find image-based six-dimensional position and orientation
coordinates of the sensing device on the element, based on the
known position of the sensing device relative to the marks. These
image-based coordinates of the sensing device are compared with the
six-dimensional signal-based coordinates, determined from the
signals that are generated by the sensing device itself, as
described above, so as to register a signal-based coordinate
system, associated with the coordinate sensing device, with an
image-based coordinate system, associated with the X-ray images.
Preferably, the computer displays the position of the element and
the device thereon in one or more of the images.
[0032] Further preferably, the computer compares the distances
between the positions of the fiducial marks in the X-ray images to
the actual, known distances between the marks, and determines an
image scaling factor based on the comparison.
[0033] Alternatively or additionally, a coordinate sensing device
may also be provided on a fluoroscopic camera that is used to
acquire the X-ray images, in addition to the coordinate sensing
devices on the reference element and the surgical tool, as
described above. Signals from the sensing device on the camera may
be used in determining the image scaling factor, as well as in
identifying the image view angle. The additional coordinate sensing
device on the camera may obviate the need for the coordinate
sensing devices on the reference element and the surgical tool to
provide both position and orientation coordinates thereof.
[0034] When the tool is brought into the surgical field, its
position and orientation coordinates are determined using the
signals generated by the sensing device thereon. Preferably,
three-dimensional position coordinates and two-dimensional angular
azimuth and elevation coordinates of the tool are determined.
(Generally, it is not necessary to known the tool's angle of roll,
i.e., rotation about its own axis.) Alternatively,
three-dimensional position coordinates of sensors at two points
along the length of the tool may be determined and used to
determine the tool's position and orientation.
[0035] The coordinates of the tool, determined in this manner, are
registered with the X-ray images by reference to the calibrated
coordinate readings generated by the sensing device on the
reference element. The coordinates of the tool are then used to
determine the position of the distal tip of the tool relative to
the patient's anatomy based on the X-ray images. Preferably, the
known coordinates and dimensions of the tool are also used by the
computer to generate a properly scaled and oriented image of the
tool, superimposed on one or more of the X-ray images.
[0036] During the surgery, as the tool is advanced into the
patient's body, signals generated by the sensing device on the tool
are used to track the tool's coordinates and, preferably, to update
accordingly the display showing the image of the tool. Preferably,
a new X-ray image is acquired from time to time, and the image is
processed to find the coordinates of the fiducial marks on the
reference element in the new image. More preferably, such a new
image should be acquired and processed when the sensor-derived
position or orientation coordinates of the element are observed to
change, or at any other suitable time determined by a user of the
system. The coordinates of the marks in the new image are compared
with the previously8 determined coordinates. If the coordinates of
the marks are found to have changed, the sensor-derived position
and orientation coordinates of the element and the tool are
re-registered with the new image, using the method described above.
This procedure is used to correct for any translational or
rotational motion within the surgical system, as well as for any
changes of scale of the X-ray image that is acquired and
displayed.
[0037] In some preferred embodiments of the present invention, the
X-ray images acquired immediately before and/or during a surgical
procedure are registered with previously-acquired CT images of the
patient's body. Before acquiring the CT images, the reference
element is fixed to the patient's body in a desired position, as
described above, so that the fiducial marks on the element appear
in the CT images. The reference element remains fixed to the body
in this position during the surgical procedure. The image-derived
coordinates of the fiducial marks in the X-ray images are compared
with corresponding image-derived coordinates in the CT images, in
order to register the X-ray and CT images.
[0038] Preferably, based on this image registration, the CT images
are rotated and/or scaled, as is known in the art, so as to align
the CT images with the X-ray images. Furthermore, three-dimensional
CT image information, rotated and/or scaled in this manner, may be
projected onto the plane of the X-ray image and superimposed on the
X-ray image or displayed alongside it. Additionally or
alternatively, the coordinates of the tool and/or an image of the
tool may be displayed on an appropriate CT image.
[0039] In some preferred embodiments of the present invention, the
tool is held in an adjustable guide, which aligns the long axis of
the tool with a desired, linear course of penetration into the
patient's body, for example, in one of the intervertebral spaces.
The guide, as is known in the art, allows the tool to be advanced
only along this linear course, although the course may be adjusted
if necessary. The methods described above for determining and
registering the position and orientation coordinates of the tool
are used in adjusting the guide with respect to the desired
course.
[0040] In other preferred embodiments of the present invention, the
desired, linear course of penetration is marked by the user with
reference to one or more of the X-ray images, for example, by
entering into the computer coordinates of points along the course.
Preferably, the computer marks the course on the image, and
displays the position of the tool relative to the course. Further
preferably, the computer sounds an alarm if the tool deviates from
the course by more than a predetermined tolerance and/or presents a
visual cue to indicate the correct direction in which the tool
should be moved.
[0041] It will be appreciated that the above-described preferred
embodiments of the present invention enable a surgeon to insert and
manipulate a tool in a patient's body under the visual guidance of
an X-ray image of the body that includes an accurate,
continuously-updated representation of the tool. The X-ray image is
acquired during the surgical procedure and may be updated as
desired. In methods known in the art, by contrast, visual guidance
is provided, if at all, using previously-acquired X-ray or CT
images. Such images cannot show changes occurring within the
patient's body. Furthermore, if registration or proper scaling of
the previously-acquired images is disturbed, for example, by
mechanical disalignment of elements of the system, the procedure
must generally be interrupted in order to recalibrate.
[0042] Furthermore, the present invention may be practiced using
ordinary fluoroscopy equipment that is already present in many
operating rooms. The image and the coordinates of the tool are
updated, as described above, with minimal interference with the
surgical procedure and with other equipment present in the
operating room, and with minimal radiation dosage to the patient.
The present invention also allows the surgeon to view images of the
patient's anatomy and the tool being inserted in two
mutually-perpendicular image planes. Under methods known in the
art, special dual-plane fluoroscopes, which are bulky, costly and
expose the patient to greater radiation dosage, must normally be
used for this purpose.
[0043] In accordance with another aspect of the present invention,
surgery is performed using one or more miniature magnetic field
transducers, preferably radiators, which are moveable with respect
to the patient. Such miniature radiators generally do not interfere
with the actions of the surgeon, and may be moved during surgery
out of positions which interfere with the surgeon, without
disrupting position determination.
[0044] In PCT patent application PCT/US97/02440, which is assigned
to the assignee of the present application and whose disclosure is
incorporated herein by reference, a radiator including one or more
miniature field transducers is placed in proximity to a patient.
The radiator is small and does not substantially obstruct access of
a physician to the patient's body. However, the radiator has a
small detection volume due to the miniature size of the
transducers. Therefore, PCT/US97/02440 suggests using a moveable
radiator which can be repositioned during surgery. One or more
reference elements are attached to the patient's body. The
reference elements are generally used to register the position of a
surgical tool or probe with the body. In addition, when the
radiator is moved, the reference elements are necessary in order to
establish the position of the radiator with respect to the frame of
reference of the patient's body.
[0045] In some preferred embodiments of the present invention, the
method of the above-mentioned PCT application PCT/US97/02440 is
improved to allow more accurate, quick and flexible use of the
transducer radiators. A plurality of reference elements, preferably
coupled with fiducial marks, are placed on the patient's body. The
reference elements include miniature coordinate sensing devices, as
described above. The fiducial marks allow the positions of the
reference elements to be visualized in images taken of the body, as
described above, including both CT images acquired before the
surgical procedure and fluoroscopic X-ray images acquired during
the procedure. The reference elements are placed on the body in a
sufficient density such that for every desired position of the
radiator relative to the body, at least one of the reference
elements is situated within the detection volume of the
radiator.
[0046] Preferably, the reference elements and fiducial marks are
placed on a strap, which is laid along the patient's body.
Preferably, the fiducial marks are mounted on the reference
elements or are positioned at fixed points relative to the
reference elements, so that it is easy to register the positions of
the reference elements on images of the body.
[0047] Alternatively or additionally, the strap has sufficient
rigidity to maintain a substantially fixed shape when placed on the
body, and the reference elements are attached at fixed points
relative to the strap. Three or more fiducial marks are attached to
the strap at positions suitable to register the reference elements
on an image taken of the body and reference elements.
[0048] During surgery, the radiators and/or the patient are moved
as needed. Each time the position of the surgical tool is
determined, the position of at least one of the reference elements
is also determined, so as to register the position of the tool in a
reference frame fixed to the body, by comparing the tool position
determination to that of the reference elements. Due to the quick
rate of position determination, the position tracking continues
substantially uninterrupted even when the radiator is in
movement.
[0049] Preferably, each time the radiators or patient are moved,
and/or periodically, independent of the movements of the radiator,
the signals from all the reference elements are compared to find
the element which offers the strongest signal. The position of this
reference element is determined and is used to register the
position of the tool during position tracking. Preferably, the
position of the tool derived in this manner is used to register an
image of the tool, either on a fluoroscopic X-ray image, as
described above, or on a previously-acquired image, such as from a
CT or MRI scan.
[0050] In some preferred embodiments of the present invention, the
detection volumes of the radiators are indicated on the images of
the body, or in any other suitable manner. Preferably, the
detection volume of each radiator is indicated separately. For
example, each detection volume may be indicated by a different
color, which is preferably also marked on the respective radiator
itself. Preferably, the indication of the detection volume of each
radiator is updated each time the radiator is moved. Further
preferably, the surgeon may set a desired resolution level, and the
detection volume is determined accordingly and indicated on the
images.
[0051] Preferably, before surgery the position determining system
is calibrated by sequentially determining the positions of the
reference elements relative to the body. Preferably, an image of
the body is produced which includes the reference elements attached
to the body, for example, by CT, MRI or X-ray imaging, and the
positions of the reference elements are registered on the
image.
[0052] It will be appreciated that although preferred embodiments
are described herein with reference to certain types of surgical
procedures, for example, treatment of the intervertebral discs, the
principles of the present invention may similarly be applied to
procedures of other types, such as other orthopedic and
neurosurgical procedures.
[0053] There is therefore provided in accordance with a preferred
embodiment of the present invention a method for X-ray guided
surgery, including: placing a reference element, to which a
reference coordinate sensing device is fixed, on the body of a
patient, acquiring an X-ray image of the body, including the
element, during the surgery, processing the image to determine
image-based coordinates of the reference coordinate sensing device,
receiving and processing signals from the reference coordinate
sensing device to determine signal-based coordinates thereof, and
registering the image-based and signal-based coordinates to
determine a coordinate transformation therebetween.
[0054] Preferably, registering the coordinates to determine a
coordinate transformation includes determining an image scale
factor.
[0055] Preferably, the method includes determining coordinates of
an X-ray camera used to acquire the X-ray image, wherein
determining the image scale factor includes comparing the camera
coordinates to the coordinates of the reference coordinate sensing
device.
[0056] Preferably, the method includes determining a view angle of
the camera relative to the body, based on the coordinates of the
camera.
[0057] Preferably, receiving and processing the signals from the
reference coordinate sensing device to determine signal-based
coordinates thereof includes determining six-dimensional position
and orientation coordinates.
[0058] Preferably, the method includes bringing a surgical tool, to
which a tool coordinate sensing device is fixed, into proximity
with the body of the patient, receiving and processing signals from
the tool coordinate sensing device to determine signal-based
coordinates thereof, and determining image-based coordinates of the
tool by applying the coordinate transformation to the signal-based
coordinates of the tool coordinate sensing device.
[0059] Preferably, the method includes displaying the image and
registering a representation of the tool thereon using the
image-based coordinates of the tool.
[0060] Preferably, acquiring the X-ray image includes acquiring a
plurality of images from different view angles with respect to the
body, and wherein displaying the image and registering the
representation of the tool therein includes registering a
suitably-oriented representation of the tool in at least two of the
plurality of images.
[0061] Preferably, the method includes designating image-based
coordinates of a target point within the body, and determining and
displaying a linear course along which the tool is to be advanced
so as to reach the target point.
[0062] Preferably, the method includes designating image-based
coordinates of a target point within the body and determining a
linear course along which the tool is to be advanced to the target
point.
[0063] Preferably, the method includes advancing the tool into the
body and comparing coordinates of the tool to the linear course so
as to detect a deviation of the tool from the course.
[0064] Preferably, the method includes providing an indication to a
user of the tool when the deviation detected exceeds a
predetermined tolerance.
[0065] Preferably, providing the indication to the user includes
issuing an alarm.
[0066] Preferably, the method includes correcting the linear course
responsive to the deviation.
[0067] Preferably, receiving and processing signals from the
reference and tool coordinate sensing devices includes receiving
and processing signals generated by the devices in response to a
common magnetic field.
[0068] Preferably, processing the image to determine image-based
coordinates of the reference position sensor includes finding the
locations in the image of fiducial marks on the reference
element.
[0069] Preferably, acquiring the X-ray image includes acquiring a
sequence of images during the surgery, and wherein processing the
image to determine image-based coordinates includes processing at
least two images in the sequence to determine respective
image-based coordinates based on each of the at least two
images.
[0070] Preferably, the method includes acquiring a CT image of the
body after placing the reference element on the body, and
registering the CT image with the X-ray image by finding
coordinates of the element in the CT and X-ray images.
[0071] There is further provided in accordance with a preferred
embodiment of the present invention, a method of tracking an object
within a body, including attaching a plurality of reference
coordinate sensing devices to the body and at least one object
coordinate sensing device to the object, registering the positions
of the plurality of reference coordinate sensing devices in a frame
of reference fixed to the body, selecting at least one of the
plurality of reference coordinate sensing devices in proximity to
the object, and receiving and processing signals from the at least
one selected reference coordinate sensing device and the object
coordinate sensing device to determine signal-based coordinates of
the object and of the selected reference device so as to register
the object coordinates relative to the body.
[0072] Preferably, attaching the plurality of reference devices
includes attaching devices such that at substantially every point
in an area of interest in or on the body, at least one device is
within a predetermined range of the point.
[0073] Preferably, receiving the signals includes receiving signals
responsive to the strength of a field transmitted by or incident on
at least one field transducer in proximity to the body, and wherein
the predetermined range is determined in accordance with a
detection volume of the field transducer, within which volume the
coordinates of the coordinate sensing devices can be determined to
a desired degree of accuracy.
[0074] Preferably, the detection volume has a substantially smaller
extent than the area of interest.
[0075] Preferably, attaching the plurality of reference devices
includes attaching at least one strap comprising the plurality of
sensing devices.
[0076] Preferably, attaching the at least one strap includes
attaching a substantially rigid strap.
[0077] Preferably, selecting at least one of the reference devices
includes determining which of the reference devices provides
registration of the coordinates of the object to a desired degree
of accuracy.
[0078] Preferably, receiving the signals includes receiving signals
responsive to the strength of a field transmitted by or incident on
a field transducer, and wherein determining which of the reference
devices provides the registration to the desired degree of accuracy
includes measuring the strength of the signals received from the at
least one of the reference devices.
[0079] Preferably, selecting the at least one of the reference
devices includes comparing the strengths of the signals received
from two or more of the plurality of reference devices.
[0080] Preferably, selecting the at least one of the reference
devices includes periodically repeating the step of selecting at
least one of the reference devices.
[0081] Preferably, receiving the signals includes transmitting and
receiving energy fields between at least one of the devices and a
field transducer situated in proximity to the body.
[0082] Preferably, the method includes changing a relative
disposition between the field transducer and the body, wherein
selecting the at least one of the reference devices includes
selecting responsive to changes in the relative disposition between
the field transducer and the body.
[0083] Preferably, the object includes a surgical tool.
[0084] Preferably, registering the positions of the plurality of
reference devices includes acquiring an image of the body including
two or more of the plurality of reference coordinate sensing
devices.
[0085] Preferably, registering the positions includes processing
the image to determine image-based coordinates of the two or more
of the devices.
[0086] Preferably, the method includes attaching a plurality of
fiducial marks to the body at fixed points relative to the
reference devices.
[0087] Preferably, determining the image-based coordinates of the
reference devices includes registering the positions of the devices
relative to image-based coordinates of the fiducial marks.
[0088] Preferably, receiving signals includes transmitting and
receiving non-ionizing fields.
[0089] Preferably, the method includes displaying a map of areas
which are included in the detection volume of the at least one
field transducer.
[0090] Preferably, the method includes producing an image of the
body and wherein displaying the map includes superimposing the map
on the image. There is further provided in accordance with a
preferred embodiment of the present invention, a method of tracking
an object within a body including placing at least one field
transducer, having a detection volume, in a vicinity of the body,
determining the position of the at least one field transducer,
displaying a map showing the detection volume of the at least one
field transducer relative to the body, and controlling the tracking
of the object responsive to the map.
[0091] Preferably, controlling the tracking includes moving the at
least one field transducer responsive to the map so as to optimize
tracking of the object.
[0092] Preferably, determining the position of the at least one
field transducer includes determining the position of the at least
one field transducer relative to a reference device attached to the
body.
[0093] Preferably, the method includes producing an image of the
body, wherein displaying the map includes superimposing the map on
the image.
[0094] Preferably, moving the at least one field transducer
includes moving the field transducer such that the object is within
the detection volume.
[0095] Preferably, placing the at least one field transducer
includes placing a plurality of field transducers, and wherein
displaying the map includes associating each field transducer with
an area on the map included in its respective detection volume.
[0096] There is further provided in accordance with a preferred
embodiment of the present invention, a reference sensor strap for
registering position information, including a band attachable to a
patient's body and a plurality of reference sensors mounted on the
band.
[0097] Preferably, the strap includes a plurality of fiducial marks
at fixed positions relative to the reference sensors.
[0098] There is further provided in accordance with a preferred
embodiment of the present invention, a system for determining the
disposition of an object within a body of a patient, including a
position sensor, which is coupled to the object, a plurality of
reference sensors, which are attached to the body, a movable field
transducer, which transmits fields to or receives fields from the
position sensor and reference sensors; and a processor, which
selects at least one of the reference sensors in proximity to the
object and determines coordinates of the position sensor relative
to the selected reference sensor, irrespective of movement of the
field transducer relative to the patient.
[0099] Preferably, the field transducer includes a radiator.
[0100] Preferably, the field transducer includes a small transducer
which does not substantially obstruct movements of a surgeon.
[0101] Preferably, the position sensor and reference sensors
include magnetic field sensors.
[0102] Preferably, the system includes a strap which includes the
reference sensors.
[0103] Preferably, the processor periodically selects the at least
one reference sensor so as to allow accurate determination of the
position of the object relative to the selected reference
sensor.
[0104] Preferably, the processor selects the at least one reference
sensor by transmitting fields which generate signals in the
sensors, and comparing the strengths of the signals in the
sensors.
[0105] Preferably, the system includes an imaging device for
producing an image on which the determined coordinates are
registered.
[0106] Preferably, the processor indicates a detection volume of
the field transducer on the image.
[0107] Preferably, the object includes a surgical tool.
[0108] There is further provided in accordance with a preferred
embodiment of the present invention, a system for determining the
disposition of an object within a body of a patient, including a
position sensor for coupling to the object, at least one reference
sensor for attaching to the body, one or more field transducers
having respective detection volumes for transmitting fields to or
receiving fields from the position sensor and reference sensor, and
a processor, which determines the disposition of the object and the
positions of the field transducers responsive to the transmitted
fields and indicates the detection volumes of the field transducers
responsive to the positions.
[0109] Preferably, the processor displays a map of the detection
volumes.
[0110] Preferably, the map is superimposed on an image of the
body.
[0111] There is further provided in accordance with a preferred
embodiment of the present invention, apparatus for X-ray guided
surgery, including a reference element, which is placed in contact
with the body of a subject, said element comprising a reference
coordinate sensing device, in a predetermined, fixed position
thereon, a fluoroscope, for forming at least one X-ray image of the
body, including the reference element, and a computer, which
receives signals from the reference coordinate sensing devices and
processes the signals to determine signal-based coordinates
thereof, and which analyzes the image to derive an image-based
coordinate system and to find a transformation to register the
signal-based coordinates and the image-based coordinate system.
[0112] Preferably, the reference element includes a plurality of
fiducial marks in predetermined, fixed positions thereon, and
wherein the computer analyzes the image to find image-based
coordinates of the marks, so as to derive the image-based
coordinate system.
[0113] Preferably, the apparatus includes a surgical tool, having a
distal end for insertion into the body, and including a tool
coordinate sensing device fixed to the tool, wherein the computer
receives signals from the tool coordinate sensing device and
applies the transformation to the signals to determine image-based
coordinates of the surgical tool.
[0114] Preferably, the apparatus includes a display, driven by the
computer, on which display the at least one X-ray image is shown
with a representation of the tool superimposed thereupon, wherein
the representation is registered with the image based on the
image-based coordinates of the tool.
[0115] Preferably, the apparatus includes a frame, which guides the
tool along a predetermined path into the body, wherein the frame is
adjusted in response to variations in the image-based coordinates
of the tool.
[0116] Preferably, the at least one X-ray image includes a
plurality of X-ray images, formed by the fluoroscope from at least
two different angles with respect to the body.
[0117] Preferably, the apparatus includes a coordinate sensing
device fixed to the fluoroscope, for determining the position of
the fluoroscope relative to the body.
[0118] Preferably, at least one of the coordinate sensing devices
includes a coil, which generates signals responsive to an
externally applied magnetic field.
[0119] Preferably, the at least one coordinate sensing device
includes a plurality of non-concentric coils.
[0120] Preferably, the apparatus includes one or more magnetic
field generators, which apply magnetic fields to the coils.
[0121] The present invention will be more fully understood from the
following detailed description of the preferred embodiments
thereof, taken together with the drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0122] FIG. 1A is a schematic side view of a surgical reference
element, including fiducial marks and a sensing device, in
accordance with a preferred embodiment of the present
invention;
[0123] FIG. 1B is a schematic top view of the element shown in FIG.
1A;
[0124] FIG. 2 is a schematic illustration of a surgical system,
including the element of FIG. 1, in accordance with a preferred
embodiment of the present invention;
[0125] FIG. 3 is a schematic representation of a lateral X-ray
image, including elements of the system of FIG. 2, in accordance
with a preferred embodiment of the present invention;
[0126] FIG. 4 is a schematic representation of an
anterior-posterior X-ray image, similarly including elements of the
system of FIG. 2, in accordance with a preferred embodiment of the
present invention; and
[0127] FIG. 5 is a schematic representation of a split-screen
fluoroscopic video image, illustrating simultaneous dual-plane
imaging, in accordance with a preferred embodiment of the present
invention;
[0128] FIG. 6 is a schematic illustration of a surgical system, in
accordance with another preferred embodiment of the present
invention;
[0129] FIG. 7 is a perspective view of a reference sensor strap, in
accordance with a preferred embodiment of the present
invention;
[0130] FIG. 8 is a schematic illustration of a surgical system, in
accordance with still another preferred embodiment of the present
invention; and
[0131] FIG. 9 is a schematic representation of an X-ray image,
including elements of the system of FIG. 8, in accordance with a
preferred embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0132] Reference is now made to FIGS. 1A and 1B, which
schematically illustrate a reference element 20, in top and side
views, respectively, in accordance with a preferred embodiment of
the present invention. Element 20 preferably comprises a disc of
plastic material 26, which is most preferably transparent to both
visible light and X-rays. A plurality of metal fiducial marks 22a,
22b and 22c, as are known in the art, are embedded in disc 26. A
position and orientation sensing device 24, with an additional
fiducial mark 23 on or adjacent to the sensing device, is similarly
embedded in or fastened to element 20. Preferably, device 24 is
fabricated so that a portion of the device, for example, a coil as
will be described below, can itself serve as mark 23. The positions
of fiducial marks 22a, 22b, 22c and 23 and of device 24 on element
20, and thus the distances between each pair of marks and between
each mark and device 24, are predetermined and known.
[0133] Preferably, device 24 comprises a plurality of
non-concentric sensor coils, as described in PCT patent publication
number WO96/05768, and incorporated herein by reference. The coils
generate signals in response to an externally-applied magnetic
field, as will be described below. These signals are processed to
determine six-dimensional position and orientation coordinates of
device 24 and hence of element 20 to which the device is fixed.
[0134] Alternatively, device 24 may comprise any suitable type of
position sensor known in the art, so long as it can be used to
determine the six-dimensional coordinates of element 20 with
sufficient accuracy for use in surgery, as will be described
below.
[0135] As shown in FIGS. 1A and 1B, element 20 includes three
fiducial marks 22a, 22b, and 22c, along with additional mark 23,
although any suitable number of marks may be used. The fiducial
marks have individual shapes or other features, differing one from
another, so that each of the marks may be easily individually
identified. Preferably, element 20 includes at least three marks,
so as to fully define a coordinate system wherein, for example, the
marks define the X-Y plane and an origin and distance scale
therein. Further preferably, element 20 has indentations 27
adjacent each of marks 22 and 23. Indentations 27 are sized to
receive the end of a tool having a position sensor thereon, for
example, needle 36, as will be described below, so that the
position sensor on the tool can be calibrated with respect to the
positions of marks 22 and 23.
[0136] Although element 20 is conveniently made in a disc shape as
shown in FIGS. 1A and 1B, any suitably-shaped element may be used.
Preferably element 20 should conform to and/or be easily fixed to a
part of the body of a patient against which it is to be placed.
[0137] Reference is now made to FIG. 2, which illustrates the use
of element 20 as part of a system 30 for spinal surgery, in
accordance with a preferred embodiment of the present invention.
Element 20 is fixed to the back of a patient 32, preferably by
gluing the element to the patient's skin. The element is placed
adjacent to an intervertebral space 34 in the patient's back into
which a needle 36 is to be inserted, for example, for the purpose
of aspirating a ruptured disc, but not in such a position as to
interfere with access of the needle to the space. Preferably needle
36 is held by a needle guide 38, known in the art, which enables
the point at which the distal end of needle 36 is to penetrate the
skin and the angle of its penetration to be precisely set and
maintained.
[0138] A position and orientation sensing device 40, similar to
device 24 on element 20, is fixed to the proximal end of needle 36.
Magnetic field generator coils 42 are placed on or adjacent to a
bed 44 on which patient 32 is lying. Field generator coils 42
generate time-varying magnetic fields at different frequencies,
under the control of driver circuitry 46, as described in the
above-mentioned PCT publication. These fields cause the sensor
coils in devices 24 and 40 to generate electrical signals,
responsive to the devices' respective positions and orientations
relative to coils 42. These signals are received by a computer 48,
which analyzes them to determine relative six-dimensional position
and orientation coordinates of devices 24 and 40, with respect to a
common frame of reference, defined by field generator coils 42.
[0139] Alternatively, needle 36 may include one or more sensor
coils, preferably of the type described in the above-mentioned U.S.
Pat. No. 5,391,199, fixed along the length of the needle. For
example, the needle may have two such coils at predetermined,
mutually-spaced locations. Signals generated by these sensor coils
in response to the magnetic field are analyzed by the computer to
determine three-dimensional position coordinates of each of the
sensor coils. The position coordinates of the two sensor coils are
taken together to determine three-dimensional position and
two-dimensional angular azimuth and elevation coordinates of needle
36 with respect to the frame of reference defined by field
generator coils 42. It is generally not necessary to know the
needle's roll angle (rotation about its own axis).
[0140] Preferably, computer 48 controls multiple aspects of system
30, including driver circuitry 46, and performs image processing
functions, as will be described below. The computer preferably also
receives input from user interface controls 50 and a drives a
display 52, and may be coupled to a printer, disk drive and other
suitable peripheral devices known in the art.
[0141] System 30 further includes a fluoroscope 54, as is known in
the art, comprising an X-ray tube, which irradiates patient 32 from
one side of his body, and an image intensifier/camera 56 on the
opposite side. Any of a wide variety of existing fluoroscopes may
be used for this purpose. Fluoroscope 54 need not be specially
adapted for use in the framework of system 30, except that a video
signal or other suitable image signal output is connected to
computer 48. The X-ray tube is not shown in FIG. 2, since it is
forward of the plane of the picture. Preferably, the tube and
intensifier 56 may be placed at any convenient positions relative
to patient 32, for example, with the tube below and the screen
above the patient, so as to capture fluoroscopic images from any
desired angle. These images are displayed by display 52 either one
at a time or in split-screen or multi-screen combination, as will
be described below. Optionally, an additional coordinate sensing
device 55 is fixed to fluoroscope 54 and is coupled to computer 48,
for determining the distance and/or view angle of the fluoroscope
relative to reference element 20 and patient 32.
[0142] FIG. 3 is a schematic illustration of a lateral fluoroscopic
image 60, as displayed by display 52 following processing by
computer 48. Image 60 includes vertebrae 64, along with reference
points 62a, 62b, 62c and 63, corresponding respectively to fiducial
marks 22a, 22b, 22c and 23 on element 20, whose general position is
indicated by the dashed line connecting points 62a, 62b and 62c.
Two-dimensional coordinates of points 62a, 62b, 62c and 63 in image
60 are determined, using image processing methods known in the art,
and are used to determine the location and angular orientation of
element 20. The relative coordinates of these points are compared
with the known positions of marks 22 on element 20 to find a
scaling factor for image 60 and to locate the six-dimensional
image-based coordinates of device 24. Device 24 is not itself shown
in FIG. 3, but its coordinates are indicated by
pseudo-three-dimensional axes 66.
[0143] The image-based coordinates of device 24 are compared with
the six-dimensional coordinates of the device as determined by
computer 48 based on the magnetic-field-responsive signals
generated by the device. A coordinate transformation, for example,
a transformation matrix, is determined so as to register the
signal-based coordinates with the image-based coordinates and to
transform the coordinates from one coordinate system to the other.
Normally, element 20 does not move during a surgical procedure, so
that the signal- and image-based coordinates will remain in
registration. The transformation is applied to transform the
signal-based coordinates of device 40 on needle 36 (shown in FIG.
2) with image 60. The coordinates of device 40 are indicated by
axes 68 in image 60, as shown in FIG. 3. If desired, an additional
position sensor can be fixed directly to patient 32, to verify, if
necessary, that the registration of the coordinates has not
changed.
[0144] Preferably, computer 48 superimposes on image 60 a
computer-generated representation 70 of needle 36 or,
alternatively, a representation or cursor mark indicative only of
the tip of the needle. Representation 70 will accurately portray
needle 36 within image 60, since the representation is positioned,
oriented and scaled in the image in accordance with the known
coordinate transformation, determined as described above. As needle
36 is advanced into intervertebral space 34, computer 48
continually receives signals from device 40 and updates its
determination of the signal-based coordinates of the device. This
determination is used to update representation 70 within image 60,
to show its true position, without the necessity of actually
acquiring additional X-ray images. Nonetheless, a surgeon using
system 30 will generally operate fluoroscope 54 from time to time
to acquire additional images as the needle is being inserted, and
particularly when the tip of the needle is approaching a potential
danger zone, such as the spinal column.
[0145] Further preferably, controls 50 may be used to program a
desired course 72, marked by a dash-dot line in FIG. 3, that needle
36 is to follow into intervertebral space 34. Course 72 is
programmed, for example, by indicating to computer 48 an entry
point 74 and a terminal point 76 for insertion of the needle. These
data are then displayed on image 60 to aid in alignment of guide 38
with course 72, and to track the progress of needle 36 along the
course. Preferably, computer 48 issues an audible alarm if needle
36 deviates from course 72 by more than a predetermined tolerance
and/or cues the surgeon as to the required course correction.
Additionally or alternatively, if guide 38 is suitably automated
and connected to computer 48, the computer may automatically
control and adjust the guide to position needle 36 at an
appropriate angle.
[0146] Image 60 may be renewed as desired, by acquisition of new
images by fluoroscope 54. Preferably, after each such acquisition,
computer 48 repeats the image processing steps described above, in
order to re-register the image-based and signal-based coordinates
of element 20 and needle 36. Image 60 should be renewed, in
particular, if the signal-based coordinates of device 24 change,
for example due to movement of patient 32. Similarly, if a new
image is acquired from a different view angle or having a different
scale from the previous image, the coordinates are preferably
re-registered and transformed.
[0147] FIG. 4 illustrates schematically an anterior--posterior
image 80 acquired by fluoroscope 54, after suitably rotating the
tube and screen 56 by approximately 90.degree. around patient 32
from the position shown in FIG. 2. The image is processed to locate
points 62a, 62b, 62c and 63 and to display respective position and
orientation axes 66 and 68 of devices 24 and 40, along with
representation 70 of needle 36, as described above. As needle 36 is
viewed along a generally longitudinal direction in image 80,
representation 70 is foreshortened. The surgeon operating system 30
may, however, choose any convenient view angles, including oblique
views.
[0148] FIG. 5 illustrates schematically a split-screen display 90
showing the data generated by system 30, in accordance with a
preferred embodiment of the present invention. Preferably, image 80
is displayed alongside image 60 within display 90, and the position
of representation 70 in both images is updated, as described above,
so that the progress of needle 36 entering space 34 can be
visualized in both lateral and anterior-posterior views
simultaneously. It will be appreciated that the present invention
makes it possible to observe such dual-plane, dynamic images,
without the need for repeatedly acquiring new images in both or
even one of the planes. New images in either of the planes or in
another, different plane may be acquired as often as desired,
however, and display 90 will be updated accordingly.
[0149] In some preferred embodiments of the present invention,
X-ray images 60 and/or 80 are registered with previously-acquired
CT images of the body of patient 32. Before acquiring the CT
images, reference element 20 is fixed to the body in a desired
position, as shown in FIG. 2, for example, so that fiducial marks
22 and 23 on the element appear in the CT images. Element 20
remains fixed to the body in this position during the surgical
procedure. The image-derived coordinates of the fiducial marks in
the X-ray images are compared with corresponding image-derived
coordinates in the CT images, in order to register the X-ray and CT
images.
[0150] Preferably, based on this image registration, the CT images
are rotated and/or scaled, as is known in the art, so as to align
the CT images with one or both of X-ray images 60 and 80.
Furthermore, three-dimensional CT image information, rotated and/or
scaled in this manner, may be projected onto the plane of one or
both X-ray images and superimposed on the X-ray images or displayed
alongside them. Additionally or alternatively, the coordinates of
tool 36 and/or an image of the tool may be displayed on an
appropriate CT image.
[0151] Although the above preferred embodiments have been described
generally with reference to certain types of position and
orientation sensing devices 24 and 40, it will be appreciated that
the principles of the present invention may be applied using any
other suitable types of position and orientation sensors, as are
known in the art.
[0152] FIG. 6 is a schematic view of a system 120 for spinal
surgery, in accordance with another preferred embodiment of the
present invention. As in FIG. 2, patient 32 is lying on a bed 44 in
preparation for back surgery. A plurality of reference sensors 126
are attached to the back 128 of patient 32, preferably using a
suitable medical adhesive. Each sensor 126 preferably comprises a
fiducial mark 130, allowing easy recognition of sensors 126 in
images of back 128. Preferably, fiducial marks 130 are embedded
within, or placed on sensors 126. In order to register the position
of a sensor 126 on an image of back 128, at least three marks 130
are used, preferably those marks associated with sensors
neighboring the registered sensor. Alternatively, each sensor 126
is fixedly coupled to three fiducial marks attached to patient 32,
such that there is a known relation between sensors 126 and marks
130. Further alternatively, a plurality of marks 130 are attached
to back 128 at a sufficient density such that each sensor 126 has
at least three marks 130 in its proximity, so as to allow
registration of the position of sensor 126 relative to the
image.
[0153] A surgical needle 36, with a sensor 142 mounted at a fixed
position relative its tip, is inserted into back 128, for example,
to aspirate a ruptured disc. A radiator 132, coupled to a position
determining system 150, is maneuverably positioned in the vicinity
of back 128, in order to transmit and/or receive magnetic fields to
and/or from sensor 142 and determine the position of the tip of
needle 36. Position determining system 150 is preferably as
described above with reference to FIG. 2, and/or as described in
U.S. Pat. Nos. 5,558,091, 5,391,199 or 5,443,489, or in
International Patent Publications WO 94/04938 or WO 96/05768, which
are incorporated herein by reference.
[0154] Preferably, position determining system 150 is coupled with
an imaging device 156, such as fluoroscope 54 described above, in
order to register the positions of sensors 142 and 126 on an image
visualized by the surgeon. It will be understood, however, that
system 150, as described herein, may also be used together with
other imaging devices, including MRI and CT, and/or other coupling
methods may be used, for example, as described in PCT publication
WO/08209 or in U.S. Pat. No. 5,383,454, which are incorporated
herein by reference.
[0155] Preferably, radiator 132 comprises one or more field
transducers, preferably field transmitting coils of a small size.
Preferably, radiator 132 comprises three coils, which are most
preferably mutually substantially orthogonal. Alternatively or
additionally, a plurality of radiators are used, as shown in FIG.
8, below. Preferably, a ferrite core is incorporated within each
coil. The coils are preferably mounted on radiator 132 in a manner
described in PCT/US97/02440, although any other suitable mounting
setup may be used. Preferably, the coils of radiator 132 are driven
at different frequencies or alternatively are time multiplexed or
otherwise driven differently, so that the respective field
generated by each of the coils can be distinguished from the fields
of the other coils.
[0156] Preferably, radiator 132 is mounted on a goose neck 148
which is attached to bed 44 by a clamp 149. Alternatively, goose
neck 148 may slide along a railing of bed 44. Further
alternatively, radiator 132 may be mounted on any suitable mounting
device allowing easy movement into and out of the vicinity of
needle 36.
[0157] Sensors 126 are preferably placed near the vertebrae 34 of
patient 32 at a suitable density. Preferably, for substantially
every point in which sensor 142 may be positioned, at least one
sensor 126 will be within a detection volume of radiator 132 which
encompasses both sensor 126 and the point. The detection volume of
radiator 132 is defined as the volume in which sensors 126 and 142
may be placed such that signals passed between radiator 132 and the
sensors are strong enough to allow the location of the sensor to be
determined to a predetermined accuracy and/or with a predetermined
signal/noise ratio.
[0158] FIG. 7 schematically shows a strap 160 holding reference
sensors 126, in accordance with a preferred embodiment of the
present invention. Strap 160 comprises a long strip of a cloth or
other suitable material for fixed attachment to patient 32. Sensors
126 are embedded within strap 160 or are attached on an outer
surface 166 of the strap. Fiducial marks. 130 are fixedly
positioned on strap 160 relative to sensors 126. Preferably, marks
130 are attached to sensors 126. A wire bus 162 connects sensors
126 along strap 160 to a standard plug connection 164 at an end of
strap 160.
[0159] Preferably, strap 160 is produced in standard sizes and is
supplied wound in a small bundle. In preparation for surgery, strap
160 is unwound onto patient 32. Preferably, an inner surface 168 of
strap 160 has a medical adhesive which attaches strap 160 to
patient 32. Alternatively, the adhesive is placed by a surgeon when
strap 160 is unwound onto the patient.
[0160] In some medical procedures, more than one strap 160 may be
used for position reference. Specifically, two straps 160 may be
placed adjacent to an area which is to be operated on, at opposite
sides of the area.
[0161] Preferably, reference sensors 126 comprise three-axis
miniature coils such as described, for example in the
above-mentioned PCT publication WO96/05768, or in PCT publications
PCT/GB93/01736, WO97/24983 or WO94/04938, or in U.S. Pat. No.
5,391,199, all of which are incorporated herein by reference.
[0162] Before the surgery, position determining system 150 is
calibrated, so that the determined positions of sensors 126 are
registered on an image of patient 32 which includes images of
fiducial marks 130. The determined positions of sensors 126 are
registered on the image according to the image of their
corresponding marks 130. Preferably, marks 130 are automatically
identified on the image according to their shape or computed
density. Alternatively or additionally, the surgeon indicates the
locations of marks 130 on the image. Consequently, the positions of
sensors 126 on the image are determined according to their known
relation to marks 130.
[0163] Preferably, calibration also includes determining the
positions of sensors 126 relative to one another. Preferably a
large, long-range radiator is used to determine the relative
positions of reference sensors 126. Alternatively, radiator 132 is
used for calibration which is performed relative to one of
reference sensors 126', which is chosen arbitrarily. Radiator 132
is positioned at an arbitrary point near reference sensor 126', and
the positions of the adjacent sensors 126" are determined. Radiator
132 is then moved to determine the positions of another group of
sensors 126 relative to those sensors whose positions were already
determined. This procedure is repeated until substantially all the
positions of sensors 126 are determined. Further alternatively,
sensors 126 are at fixed positions relative to each other, and
these positions are pre-stored in position determining system 150.
During calibration it is only necessary to determine the position
of one of sensors 126 and the positions of the rest of sensors 126
are calculated accordingly.
[0164] During surgery, radiator 132 is maneuvered as necessary into
the proximity of needle 36 to provide accurate tracking, without
interfering with the actions of medical staff performing the
surgery. Radiator 132 continues to transmit magnetic fields,
regardless of its position. Position determining system 150
measures the signals received at sensor 142 on needle 36, and in
one or more of reference sensors 126 near the needle, and
accordingly determines the needle's position and orientation.
Position determining system 150 thus registers the position of
needle 36 in a reference frame fixed to back 128, irrespective of
the movement of radiator 132 or of patient 32, and displays an
image or cursor corresponding to the needle position on
fluoroscopic and/or CT or MRI images of the back, as described
above.
[0165] Preferably, periodically at a suitable rate, such as every
few seconds and/or every time radiator 132 is moved, position
determining system 150 performs a procedure of assigning a current
reference sensor 126, with respect to which the position of sensor
142 on needle 36 is determined. Radiator 132 transmits a test
signal, which is preferably the same signal used for position
determination. System 150 measures the signals received by each of
reference sensors 126 responsive to the test signal. The sensor
having the strongest received signal is defined as the currently
assigned reference sensor. Alternatively, the currently assigned
reference sensor is chosen to be the reference sensor 126 closest
to radiator 132, based on a real-time image of patient 32.
[0166] FIG. 8 is a schematic illustration of a surgical system 200,
in accordance with another preferred embodiment of the present
invention. System 200 includes a plurality of radiators 132, which
are used to determine the positions of sensors 126. Use of multiple
sensors 126 allows use of small radiators 132, which do not require
much space. Also, use of multiple radiators allows the detection
volume of each radiator 132 to be decreased, and consequently
increases the resolution of position determination performed using
the radiators.
[0167] Preferably, radiators 132 are operated sequentially, so that
fields transmitted by one radiator do not interfere with position
determination using the other radiators. Alternatively, only one
radiator is operated continuously at any given time. This radiator
is chosen to be the radiator closest to needle 36. Further
alternatively, the radiators generate fields of different
frequencies which substantially do not interfere with each other.
Preferably, assigning the current reference sensor 126 is performed
independently for each radiator 132, i.e., each radiator has its
own current reference sensor.
[0168] Preferably, system 200 includes a fluoroscope 256 which
acquires images of patient 32 and fiducial marks 130. A computer
248 processes the resulting images and displays them on a display
252. Preferably, the images are processed according to positions
determined using radiators 132.
[0169] FIG. 9 is a schematic illustration of a fluoroscopic image
260, as displayed by display 252 following processing by computer
248, in accordance with a preferred embodiment of the present
invention. Preferably, areas 262 included in the detection volume
of radiators 132 are indicated on image 260. Preferably, the
detection volume of each radiator 132 is indicated differently, so
as to associate indicated areas 262 with respective radiators 132.
For example, each radiator 132 may be painted a different color,
and that color is used on image 260 to indicate the detection
volume of the respective radiator. Preferably, areas included in
two detection volumes, for example area 264, are marked
accordingly.
[0170] During surgery the surgeon or an assistant preferably makes
sure that desired areas are included within the detection volume of
at least one radiator. When a desired area is not in the detection
volume of any of radiators 132, the surgeon or assistant may move
one of the radiators to a position in which it includes the desired
area in its detection volume.
[0171] Preferably, the span of the detection volume of each
radiator 132 is known by computer 248 before surgery, possibly as a
function of a predetermined, maximum coordinate resolution, and
according to the position of the radiator, its detection volume is
indicated. Alternatively or additionally, the radiator transmits
fields to reference sensors 126 and according to those which
respond with a strong enough signal, the radiator position and/or
detection volume is determined.
[0172] It will be appreciated that although preferred embodiments
are described herein with reference to certain types of surgical
procedures, for example, treatment of the intervertebral discs, the
principles of the present invention may similarly be applied to
procedures of other types, including head surgery, biopsies, and
tube insertion.
[0173] Furthermore, although in the preferred embodiments described
hereinabove, the radiators are described as transmitting magnetic
fields, which are received by the position sensors, the principles
of the present invention can similarly be applied in position
determining systems in which the sensors transmit fields, and the
radiators are replaced by receivers, as are known in the art. It
will also be understood that other types of energy fields may be
used in the position determination, as is known in the art, such as
ultrasonic energy.
[0174] It will further be understood that the preferred embodiments
described above are cited by way of example, and the full scope of
the invention is limited only by the claims.
* * * * *