Operating pointer with interactive computergraphics

This invention relates to any operating pointer or arm apparatus whose position can be detected and read out on a computer and associated graphics display, and where the pointer can be changed from its pointer function to a "3D mouse" so as to alternately by use control the functionality of the computer as in calibration and display features. Specific embodiments of the invention are given, and one of them is a neurosurgical operating arm which has electronic readout for coupling to a computergraphic display which shows the position of the arm relative to patient anatomy. In one embodiment, the arm has five angular degrees of freedom to achieve a pointer position anywhere in space, at any angle. Electronic readout from the arm positions and joint angles are assimilated into a computegraphic display system. The display system displays anatomical image data taken from the patient with modern imaging techniques. Calibration steps are described to relate the initialization and the patient-related calibrations of the operating arm during surgery. A manual or footswitch control changes the operating arm from a space pointer to a "3D Mouse" that enables easy surgeon interaction with the computergraphics and control thereof. A unique arm geometry is described with specific joint and linkage configurations. In addition, a means for skin or skull-based fiducial system or a bite or dental impression-based frame with localizer rods for providing fiducial points is described for intraoperative calibration of the arm relative to the patient's anatomy. Other embodiments of pointers involving optical or ultrasonic detection are given as examples.

BACKGROUND TO THE INVENTION 
The field of human stereotactic neurosurgery is over 40 years old. 
Stereotactic neurosurgery has usually involved the attachment of a frame 
to the patient's skull. Various imaging method are used to relate the 
position of the frame to the patient's anatomy. Thereafter, that data is 
used to guide the operative approach to a desired target which is seen on 
the image data. The target, which represents a physical point in the 
patient's head, may be pre-calculated in a variety of ways depending on 
the image data. Its known three-dimensional coordinates relative to the 
stereotactic frame can be further determined, and typically a mechanical 
arc system fastened to the patient-attached frame is used to stabilize and 
guide a probe to a target. This technique is widely known in neurosurgery 
and represents one of the fundamental techniques in that field. 
More recently, attempts have been made to eliminate the need for a frame 
that is attached rigidly to the patient's skull. Thus, the field of 
"frameless stereotaxy" has become very active in the past year. Several 
investigators have made attempts at a frameless stereotactic mechanical 
arm as well as a frameless, non-mechanically coupled system to determine 
the position of a probe relative to the patient's anatomy without the need 
for a head frame. Most notable is the work by the present author, Dr. 
Barton Guthrie, who for many years has worked on an evolution of operating 
arms for the purpose. Other persons and organizations who have made 
similar operating arms following the lead of Dr. Guthrie are Dr. Maciunas, 
Dr. Watanabe, the ISG Company of Canada, and Dr. Reinhardt of Switzerland. 
In each of the latter four cases, the investigators have used an operating 
arm with six angular degrees of freedom. What is meant by this is an arm 
with articulating joints that gives rise to angular movements of arm 
linkages. One of the authors, Eric Cosman, has also investigated the use 
of optical coupling to determine a pointer's or probe's position, rather 
than mechanical coupling. 
Dr. Guthrie has evolved an operating arm over the past several years in 
experimental and pre-clinical release investigations. In some embodiments, 
he has used five articulating joints, although six or more could also be 
used. Mathematically, five articulating joints are sufficient to place a 
pointer at a give position in space from a arbitrary angular direction. 
This statement is moderated only by the fact that real mechanical 
operating arms have certain joint and linkage limits which in turn limit 
the positional and angular approach range of the device. However, within 
this operating range of the device, five degrees of freedom are 
sufficient. Thus, one of the embodiments of the development of Guthrie has 
involved one less degree of freedom than all other investigators have 
incorporated in their systems and separates the author's invention from 
all other such devices that have been conceived to date. The use of more 
degrees of freedom increases the overall flexibility of the operating arm. 
It also can increase in some situations the operating range, both in 
position and in angular orientation of a probe. This would be a further 
positive aspect of using six or more degrees of freedom. However, the more 
degrees of freedom one uses, the more complex the apparatus becomes and 
thus the more difficult it is to maintain accuracy. With the proper 
configuring of five degrees of freedom, the present invention enables wide 
flexibility of approach and position while maintaining an intrinsic 
simplicity that all other such devices do not have. The stability and 
accuracy of the present invention is reflected in this simpler 
construction with fewer degrees of freedom. Specific arrangements of the 
five degrees of freedom of the present invention make it practical and 
functionally easy to use. Avoidance of so-called "gimble-lock" is achieved 
only by proper configuration of the joints and the links in an operating 
arm. This has also been achieved in the present invention with a unique 
geometric configuration. We have also developed unique six degree of 
freedom arms, and they will be described below as part of this 
information. 
Other types of operating arms or pointers have been developed using 
ultrasonic and optical detection means to determine the pointers's 
position. These too may be considered "frameless" devices, although in all 
cases, they can be used with a stereotactic frame as well. What all other 
investigators have lacked in their devices is a simple way for the 
operator of the arm or pointer to convert it to a "3D mouse" so that the 
pointer itself can be used to change the functionality of the computer 
graphic system, that displays or reads out the pointer's position. 
Thus one main objective of the present invention is to have the operating 
pointer arm, no matter what is operating principle may be, serve 
alternatively as a space pointer and at another instance a "3-D mouse" for 
interactive graphic control of the arm itself. This was achieved by 
switching the operation of the arm from its primary use as a pointer to 
its secondary use as a mouse for the screen graphics. The switching can be 
done in a variety of ways: footswitch, hand switch, third-party-operated 
switch, or by the position itself of the pointer in space. This greatly 
increases the convenience of the system and the facility of its use in a 
practical setting. 
Yet a further objective of the present invention is to provide fiducial 
point means for calibrating the operating pointer or arm that involves a 
bite piece, or dental impression piece, that can be attached to the 
patient's dentition and which included localizer points, rods, or other 
structures to calibrate the position of the arm relative to the anatomy. 
In the operating setting, this will enable a skull-referenced fiducial 
marker system that can be accessed quickly and easily by the surgeon to 
recalibrate the position of his operating arm relative to the graphic 
anatomy which is displayed on the video monitor. 
Yet another objective of the present invention is to provide novel joint 
and link configurations, both five and six degrees of freedom, to achieve 
superior operating flexibility of the arm in use.

DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, one embodiment of the present invention is illustrated 
with a mechanical operating arm. The patient which is being operated on is 
shown together with the operating aram, a computer-graphic monitor screen, 
an interface box, and a footswitch system. The arm consists of a base 1 
which anchors the arm relative to the patient's head. The first rotation 
joint is comprised of a vertical element that has a rotating section 2 
that rotates about the axis 2A. This in turn attached to a structure which 
has a rotating element 3 that enables rotation about axis 3A. Axis 3A is 
perpendicular to axis 2A. Attached to element 3 is the first arm link 4 
which is connected to a third joint that has a rotation axis 5A and the 
rotating element 5 associated with it. Element 5 is connected further to 
the second arm link 6. This in turn attached to the fourth joint which is 
associated with axis 7A and rotating element 7. 7A is parallel to 5A, 
which is also parallel to axis 3A. Element 7 rotates around axis 7A, and 
it connects to a further joint element which has rotating piece 8 that 
rotates coaxially with axis 8A. This is the fifth and final axis and 
rotating joint. Attached to element 8 is the surgical point or operating 
point 9. This is indicated generically in this figure. It could be a 
detachable element and have a variety of functions as discussed below. The 
end point 10 of pointer 9 is designed to point at or touch various 
portions of the patient's anatomy. In this context, the operating arm is 
schematically shown relative to a patient's head 11. On the patient's head 
are index marks, one of which is indicated by point 12, which give 
fiducial positions that are known relative to an image scan. They can be 
located physically by the operating pointer 9 during the surgical 
procedure so as to relate the physical anatomy and the pointer to the 
patient's anatomy as visualized on the computer graphics. Other natural 
fiducial points, such as the tip of the noise 14 or structures around the 
ears and eyes, could obviously be used as natural anatomical landmarks 
that can be used to calibrate the operating arm relative to the anatomy in 
a similar way. Also shown is the computer system 16 with its graphic 
monitor. The computer may have stored in it previously gathered image data 
of the patient. This data can be brought up and visualized on the computer 
screen, and the screen may also show a representation of the graphic arm 
or of the arm pointer 9 as it approaches the physical anatomy of the 
patient. In this way the surgeon can visually determine where the pointer 
of the arm is relative to anatomy as represented by the image data. This 
can be made quantitative as well, showing measurements of distance, 
accurate relative positions to anatomy, etc. The computer and graphics 
display may be controlled by controller box 18 which, in turn, is attached 
to a switching means 22 by cable 21. The connection cable 17 links the 
controller and the computer. In addition, cable 20 indicates schematically 
the link from the operating arm to the controller box 18 and thus, in 
turn, to the computer 16. Controller box 18 may be integral with the 
computer 16. The electronic detection system in each of the articulating 
arm joints of arm 8 may be fed into the computer in this way giving a 
graphic electronic representation of the position of the operating arm on 
the screen of computer 16. These detectors may be encoders or other 
positional detection devices. 
The switch 22 is indicated as a foot switch, but it equally well could be 
integral with pointer 9 or a separate switch system altogether operated by 
a third person. The concept of including the switch 22 with the operating 
arm is to allow the surgeon himself, by pushing the footswitch, to change 
the mode of the operating arm from an operating pointer to a digital 3-D 
mouse or to "click onto" or activate menu functions on the graphics 
screen. This is described in detail below, but in brief, this enables that 
the arm itself can be manipulated by the surgeon in the 3-D mouse mode so 
that he can manipulate to objects, icons, or menus on a computer screen so 
as to change the function of the arm as in calibration, mode selection and 
so on. 
Referring to FIG. 2, this shows schematically the five-joint articulating 
operating arm, which is one of the novel embodiments of the present 
invention. The base element 201 may be attached via the clamp 232 to a 
solid platform in the room such as the operating table 230 with its side 
rail brackets 231. The position of base 201 may be reoriented or moved and 
reclamped onto the element 231 or any other such element. 201 may actually 
consist of a pole or bar which can be discretely reoriented in space or 
translated to discrete positions or moved continuously for the convenience 
of positioning by the surgeon. Once in position, 201 acts as a stable base 
for the rest of the operating arm. Element 202 represents the rotating 
element of the first joint. This rotates coaxially with axis 202A, which 
may be essentially vertical. The second joint consists of rotating element 
203 which rotates coaxially with the axis 203A. This axis is perpendicular 
to the first axis 202A and is represented here as a horizontal axis. The 
first arm link 204 connects to the third joint which has a movable piece 
205 that rotates coaxially with axis 205A. In this embodiment, axis 205A 
is parallel to the first axis 203A. Element 205 connects to the second arm 
link 206 which in turn connects to the fourth rotating joint having the 
rotating element 207. Element 207 rotates coaxially with the fourth axis 
207A. Axis 207A is parallel to axis 205A and axis 203A. The fifth joint 
contains rotating element 208 which rotates about axis 208A. Axis 208A is 
perpendicular to 207A. Element 208 is connected to an adaption means 
schematically indicated as 224. This does not need to be perpendicular to 
208, although is shown roughly so in this figure. Element 224 is adapted 
to join to a probe means 209. Probe means 209 may be a pointer, a 
stimulating probe, a lesion probe, an ultrasonic probe, or any other 
surgical apparatus which comes into proximity to the anatomical targets. 
Although the full scope of the present invention is not limited to a 
five-joint arm, the embodiment of FIG. 5 with five joints is novel and new 
and has certain advantages over other operating arms with more than 5 
joints. The joint sequences in FIG. 1 are: two joints at the base, 
followed by a link, followed by a single joint, followed by another link 
and followed by two perpendicular joints. This 2-1-2 geometry works very 
effectively. Having the second, third and fourth joints parallel, as 
shown, also works very well and may be considered as one of several 
preferred embodiments. Obviously, other choices of joint axes, 
configurations and orderings such as 2-2-1 configurations are possible and 
also practical. There are several other novel features of the device shown 
in FIG. 2. The clamping mechanism to the side of the operating table may 
be a standard clamp configuration used in the operating setting. In this 
way the arm can easily be attached to standard tables in a rigid fashion. 
That is a novel feature which is new with the present invention concepts. 
The removable tip 209 which can be fixed relative to element 224 is also a 
unique aspect of the present invention concepts. This could be a simple 
pointer as shown in FIG. 2, or it could be a suction device, a bipolar or 
monopolar forceps or tissue separating forceps, an electromagnetic tissue 
removal device, and ultrasonic probe, an electrode for stimulating or 
recording of the brain cortex, a laser light or laser delivery device, an 
endoscopic visualization device, and any of several other types of 
surgical probes. For each of these types of applicators, one can determine 
quantitatively where the tip of the instrument is relative to the anatomy 
shown on the imaging-based computer graphics, and thus relate the actual 
physical position of the said tip to physical anatomy at all times during 
the surgery. 
Another feature which we wish to claim in this patent is a locking or 
clamping mechanism for the articulated arm or similar operating arms of 
FIG. 1 and 2. The pointer 9 may be directed to a desired point in space, 
and a secondary physical clamp may be brought into position to hold it in 
that configuration. Alternatively, the joints themselves may have locking 
mechanisms so that the entire arm can be locked in a given position so 
that the surgeon does not need to hold the arm in that position while 
operating surgically. 
Referring to FIG. 3, the toggling or switching feature of the present 
invention is schematically illustrated. 309 represents the surgical probe 
or pointer of operating arm. Its position in space is electronically 
determined and carried by the information carrying element 340 to a switch 
system 322, in this figure illustrated as a foot switch. The switch could 
equally well be integrated into the pointer 9 or at some other physical 
location. The switch has another connection element 341 to the computer 
and computer graphic module 316. The graphics display of the computer is 
illustrated here as having various functionality or menu options: calib 
arm, calib head, localize, and exit. These are merely examples, and many 
others may be devised. By pressing the switch 322, the arm may be 
activated as a "3D-Mouse". This means that in the 3D-Mouse mode, the 
pointer 309 can be moved in space by the surgeon thus tracing out in an 
imaginary mathematical frame 316A its position as visualized by a cursor 
or crosshair 361 on the actual graphic screen 316. The dashed line 360 
represents this imaginary mathematical correspondence and the cross 361 
would indicate the corresponding position of the 3D-Mouse pointer on the 
actual menu screen 316. Thus by moving the pointer 309 manually, the 
cursor 361 can be moved around on the actual physical screen 316. It can 
be pointed to any of the various menu window positions. Pressing the 
footswitch again thereby activates that menu option. One similarly can 
switch the mode of the operating arm to the calib arm menu option, in 
which mode the arm is set into a holster or "home position" in which the 
relative orientation of the joint angles and links are predefined so as to 
initialize the geometry and configuration of the arm with respect to the 
computer. In the calib head mode, the probe 309 can be pointed to various 
index points on the head such as 12 in FIG. 1 so as to reference the arm 
in space relative to the physical anatomy. In the localizer mode, when the 
footswitch is pressed the instrument or pointer 309 becomes a physical 
pointer or localizer in space and its graphic representation can be seen 
on the computer screen. In the exit mode the face screen menu may 
disappear and only the graphics may show. Many other such menus can be 
thought of which can be toggled in or out by the 3D mouse. The utility of 
having the operating arm pointer act not only as a pointer, but also as a 
3D-mouse is very significant and one of the novel features of the present 
invention. It frees the surgeon from need for other assistance in the 
operating room and enables him to rapidly select different options for the 
arm or to move from calibration to localization quickly. The switch 322 
can be a footswitch, a hand or finger activated switch or the probe 309, 
or a remote switch. 
It is also anticipated that the switch may only act to click onto menu 
items and that the conversion of the operating arm probe 309 to a 3D mouse 
can be done in other ways. For example, when moving the arm out of the 
immediate operating field, the software may recognize that it is remote 
from the operating field and automatically turn it into a 3D mouse, 
whereby it becomes capable of pointing to icons such as in the Table 316 
in FIG. 3. Then pressing the footswitch 322 can click onto any given menu 
item, such as the 361. Thus, the presence of a switch in the system may 
have the functional objective of either converting the operating arm 
pointer to a 3D mouse or triggering on menu objects. 
It is also anticipated that the conversion and utilization of the operating 
arm pointer 309 from an anatomical pointer to a 3D mouse and for menu 
options may be done without the need for a physical switch altogether. 
This patent claims the generalized concept of an operating arm space 
pointer or any other type of space pointer or wand, whether mechanically 
or non-mechanically coupled to the computer system, converting to a 3D 
mouse in conjunction with computergraphics in general and does not 
necessarily need the intermediary of a mechanical switch. For instance, by 
bringing the pointer 309 out of a given physical region of interest near 
the patient, this may be detected by the computer, and the pointer may 
automatically convert itself to a 3D mouse. Thereafter, pointing to the 
screen when in 3D mouse mode can automatically activate a function on the 
screen by another physical manipulation of the probe 309, such as a rapid 
movement inward toward the direction of the screen or some other type of 
recognizable movement of the probe or simply a time delay. It may also be 
voice-activated or sound-activated and not require a mechanical switch in 
the usual sense. Thus, this invention generally seeks the application of 
an operating arm as either a space pointer or a 3D mouse in conjunction 
with computergraphics. 
Alternatively, the position of the probe or locating instrument may not be 
continuously monitored by the computer. The surgeon may initiate a request 
for information from the computer by depressing a foot pedal connected 
with the computer. Alternative to a foot pedal, a finger switch or other 
type of switch means can be used. Thus, the surgeon can get a rapid update 
of his location or orientation by depressing the foot pedal or alternate 
switch, causing the system to display instrument location on the 
computergraphic images of the cranium. 
The process by which the surgeon interacts with the computer may be called 
the interface. The interface for such a surgery and planning system is 
designed to minimize surgeon inconvenience. The entire program is menu 
driven. One of the unique features is that during the operation the 
localizer or probe itself can function as either a "mouse" to allow the 
surgeon to control program flow without contamination or stepping away 
from the operating field or as a localizer or pointer to inform the 
surgeon of his location with respect to the cranium. This feature is a 
novel aspect of the present invention and is not available, nor has it 
been suggested for use with any other surgical computer-based operating 
surgical system. 
Referring to FIG. 4, an example of a calibration procedure for the arm will 
be discussed. The index marks discussed above are shown on the patient's 
head 411. There are four index marks shown in FIG. 4, although there could 
be more. They are designated by 412A, 412B, and 412C. Three or more points 
may be used to calibrate the operating arm by putting its electronic 
readout into calibration with the actual patient anatomy and thus into 
calibration with the graphic image-based anatomy which is displayed on 
computer screen 16 in FIG. 1. This can be accomplished by toggling the 3D 
mouse into calib head mode illustrated in FIG. 3, and sequentially 
pointing to the three index points, pressing the footswitch each time the 
pointer of 309 is contacting index points in sequence. Each time the 
footswitch is pressed, the electronic information from the arm's joints 
will be passed to the computer and registered there. After indexing all of 
the three points in this way, the computer then has the mathematical 
transformation of the electronic joint readouts for three index points to 
the coordinates of these index points in the image-base data space stored 
in the computer 16. Presupposed here is that each index point is 
observable in the image-based data. This same transformation maps all of 
the other arm positions as it probes the physical anatomy to the 
image-based anatomy as seen on the computer, so the connection of the arm 
as a calibrated space pointer is now complete. 
Referring to FIG. 5, another method may be used to graphically map the 
calibration of the operating arm from the physical patient space to the 
image graphic space. This involves the use of a bite piece 550 which may 
have an impression of the patient's upper and/or lower teeth in it. The 
bite piece 550 is attached to a base plate 551 that in turn has a variety 
of vertical and diagonal rods or index points located on it. For example, 
the vertical rod 552 and 557 have between them a diagonal rod 554, forming 
an indexing "N-structure" (has the shape of an "N"). This is similar to 
that used for frame-based stereotactic surgery involving the BRW 
Stereotactic System of Radionics, Inc. Similar N-structures may be placed 
elsewhere around the head. In FIG. 5 three such N-structures are shown 
which are sufficient to determine mathematically the plane of an image 
slice when the slice plane cuts through these structures. Such imaging 
methodology is well known in the Radionics, Inc. literature. The point of 
FIG. 5 is to illustrate that a skull connection can be made via a bite 
piece, associated bridge, and localizer elements so that the localizer 
elements will stand at a given specific orientation relative to the 
patient's anatomy. If the patient image scans have been made with such a 
bite piece localizer in place, then all of the image data stored in 
computer 16 will be referenced relative to such index rod or points. This 
has a secondary advantage in accumulating the image data in that it 
confirms the accuracy of the slice to slice information, since this must 
give the integrity of the rod structure as straight line elements in the 
computer graphics if the scan planes have been all done in a parallel 
fashion. If they are not exactly parallel, the anatomical information can 
be transformed immediately to the index frame coordinate system and 
corrections for non parallelity can be made. 
In the context of the present operating arm, the fiducial point or fiducial 
structures shown in FIGS. 4 and 5 can be used to calibrate the arm. For 
example, in FIG. 5, the pointer 509 of the operating arm may be touched on 
the ends of the rod such as the end points 512A, 512B, 512C of the 
associated rods 555, 560, and 552. This will establish specific reference 
points on the structure and thus a reference point or plane relative to 
the patient anatomy for calibration purposes. Alternatively, there may be 
no rod or diagonal structures at all, but merely a base 551 attached to 
the bite piece 550 with index points such as 570 on it. The bite piece 550 
may in fact be integral with the base 551 making a very simple bite piece 
structure which can be removed with ease from the patient's mouth during 
operations, even if the patient is intubated or if he is sedated. The 
concept of using the secondary skull-based localizer in FIG. 5 as compared 
to the patient-based localizer points in FIG. 4 is novel to the present 
invention. It has the advantage that index points do not have to be put 
onto the patient's scalp or embedded into the patient's skull, as 
schematically indicated in FIG. 4. It also means that repeat scanning or 
repeat operations may be referenced to the same skull-based platform and 
coordinate system directly. The bite piece structure 550 and 551 may be 
securely anchored to the patient's upper teeth by means of straps over the 
patients head and securing mechanisms from the back of the patient's head 
analogous to the GTL-Gill-Thomas Localizer manufactured by Radionics, Inc. 
Alternatively, it may be put in and out of the patient's mouth during the 
course of the surgery if a calibration of the arm by the surgeon is 
required. Thus the novel feature of combining a non-invasive dental bite 
piece with localizer structures associated with it together with an 
operating arm and computer graphics is new to the field of stereotaxy and 
claimed in the present patent application. 
FIG. 6 shows a more generalized embodiment of the present invention where 
it is not restricted to a mechanically coupled articulating operating arm. 
The probe or pointer 609 is now in the form of a bipolar forceps, which is 
one particular embodiment of such a probe analogous to a standard surgical 
instrument. On it are index points, as an example 682 and 681, which may 
be optical or ultrasonic senders or receivers that can be interrogated by 
sensors or receivers 670 and 671. They in turn go to an interface box 618 
which can assimilate the signal and send it on to the computer and 
graphics display system 616. The exact nature of the interrogation between 
the points 681 and 682 and the elements 671 and 670 does not have to be 
specific here. As examples cited above, they could be optical, CCD, or 
camera sensors. They could be ultrasonic detectors and senders where 
triangulation of time delays or angular measurements could be present. 
There are a multiplicity of other types of schemes which can generically 
give a probe and cooperatively coupled detection or sensing elements 
analogous to this scheme that can tell the position of the probe relative 
to such sensing devices. There could be mechanical coupling as an 
operating arm, or electromagnetic coupling, or sonic coupling. In any 
case, the position of the probe 609 relative to the patient's anatomy 690 
is possible by a variety of physical principles, as illustrated in the 
FIGS. 1-6. The graphics representation in computer display 616, together 
with the graphics representation of both the anatomy and the probe 
position is as described above. A mechanical switch, such as 622, might be 
present or the switching may be done by software means and other 
principles as described previously. FIG. 6 thus illustrates the 
generalized concept of a probe, cooperative sensing means coupled to a 
computergraphics system, and a generic switching means so that the probe 
can be switched from being a space pointer or operating anatomical pointer 
to a 3D mouse or menu selector. The switch 622 is meant in a generic sense 
since it does not have to necessarily be physical, but rather could be a 
mode of phase transition. In any case, the probe can serve both as a 
pointer and as a function selector on the graphics display. This is 
important to free the operator from having to push footswitches or from 
having to have a second person involved in the surgery to change modes. 
Thus, a portion of this invention relates to the concept of the interface 
between the operating pointer and the computergraphic display related to 
switching the pointer from its pointer mode to the 3D mouse mode. In the 
3D mouse mode various functionalities can be controlled by the mouse 
itself on the computergraphic display. 
To give specific examples of the embodiment in FIG. 6 with regard to 
implementations other than the mechanical arm, the case of ultrasonic 
coupling and optical coupling will be briefly described. In the case of 
ultrasonic or sonic coupling, points 681 and 682 could be sources of sonic 
energy. Detectors 671 and 670 could be detectors of sonic energy. By the 
timing or the amplitude of the received signals by detectors 670 and 671, 
the processor 618 can determine the orientation of the overall probe 609 
by the relative positions of 681 and 682. Alternatively, 670 and 671 may 
be sources of sonic energy, and 681 and 682 may be receivers. The same 
statement about triangulation of time-of-light-of signals could apply to 
give sufficient information to determine the orientation of probe 609 in 
space, relative to the anatomy of the patient 690. There may be other 
calibration sources of sonic energy in the field of the patient, possibly 
either the index points schematically indicated as 612A, 612B, and 612C. 
In that case, the sonic detectors 670 and 671 could be continually 
calibrated relative to the field by these calibration or standard sources. 
An analogous situation could apply for optical coupling. Element 681 and 
682 could be points-like or nearly pointed sources of light and detectors 
670 and 671 could be CCD or optical detectors that can determine the 
position of sources 681 and 682 in their respective fields. These two view 
fields could thus be calibrated by means of standard or reference lights, 
such as 612A, 612B, and 612C, so that detectors 670 and 671 are 
continually calibrated. By this means, the position of the probe or 
pointer or locator 609 can be determined at all times by this optical 
detection system. The probe illustrated as a bayonet forceps may be 
connected by a table which can power the sources 681 and 682, or it can 
contain batteries which will give self power to these elements, thus 
becoming a totally mechanically decoupled and electrically decoupled 
device. 
Having described many of the features of the present invention, it is clear 
that those skilled in the art could make variations of the present 
described invention and such variations are also claimed in this patent 
application. The arm can be made of various materials or in various 
configurations different from those shown in FIG. 1 and 2. The number of 
joints may be greater than five, although as described above, five is a 
unique embodiment and has simplifying aspects. Variations on the switching 
mechanism to toggle the arm from a localizing pointer to a 3D-mouse or 
other graphic means can be devised. Switching mechanisms other than the 
foot switch or finger toggle switch may be used and may involve a switch 
done by a second party remote to the arm. Various configurations of joint 
geometry may be employed other than the ones shown specifically in the 
present figures. The localizer geometry and index point structure shown in 
FIG. 5 based on a dental tray can have wide variations but could serve the 
same purpose.