Head band for frameless stereotactic registration

A skin-based band is fixed to a patient's skin in a repeatable position and includes reference markers which, attached to the skin band, can be visualized in tomographic image scanning. The reference markers appear as reference marker images in the image scan data from the image scan and correspond to coordinate positions in the image scan coordinate system. The reference markers also provide corresponding reference marker positions in the physical space of the patient's anatomy, which may correspond to a stereotactic coordinate system associated with a digitized navigator or frameless stereotactic reference system near the patient. The band can also be placed on the patient again at the time of surgical intervention, and the reference markers can be touched or referenced by the surgical navigator in the stereotactic coordinate system. A computer system assimilates the image scan data and calibration data and enables a mapping from the image scan coordinate system to the stereotactic coordinate system so that surgical instruments can be tracked by a surgical navigator so that their position can be referenced to the image scan data.

BACKGROUND AND SUMMARY OF THE INVENTION 
The field of frameless stereotaxy is now a very active one. In the early 
works of Watanabe (1986) and Kosugi (1987), and other workers such as 
Guthrie and Adler in the same time frame, a digitized space pointer or 
stereotactic navigator was used which involved an encoded mechanical arm. 
This navigating arm was placed near the patient during surgery. Typically, 
reference points such as radiopaque skin markers or tattoos where 
radiopaque skin markers could be placed were located on the patient's 
skin. The skin markers were in place at the time the patient is scanned by 
an image scanner prior to surgery, and they appeared as reference marker 
images on the image scan data from for example a tomographic scan. The 
scan could be from CT, MRI, PET, or other modality, and appropriate 
markers visible on these scans could be used. One of the objectives was to 
transform from the image scan coordinate system to a reference frame 
associated with the stereotactic navigator, and in the case of Watanabe, 
Kosugi, Guthrie, and Adler, this was the reference frame of a digitized 
mechanical arm. Other types of reference frames and associated digitizers 
have been developed involving ultrasonic, optical, and magnetic coupling 
between a probe whose position is to be determined or tracked in space 
relative to the patient and a detector or sender system which represents 
the reference system for the space digitizer located near the patient's 
head. At the time of surgery, such a probe, whose position can be 
determined in the digitizer coordinate system, (herein referred to as the 
stereotactic coordinate system) could be used to touch each of the 
reference markers in sequence, thereby determining their positions 
relative to the stereotactic coordinate system of the digitizer. At this 
point, since the positions of the reference points are known with respect 
to their reference point images in the image scan coordinate system, and 
the physical reference points positions are known with respect to the 
coordinate system of the digitizer or the reference (stereotactic) 
coordinate system in space, then a mapping, transformation, or 
correspondence can be made between these two coordinate systems. 
Thereafter, the position of the surgical instrument which is being tracked 
by the digitizer system can be represented in the coordinate space of the 
image scan data. Thus, as the pointer or surgical instrument is moved in 
space near the patient's anatomy, a representation of where it will be 
relative to the inside of the patient's head, as represented by the image 
scan data, can be determined. All of this data: the image scan data, 
reference marker images, digitizing data from the reference frame of the 
digitizer, positions of the physical reference markers, can be loaded into 
a computer or computer graphic workstation and the transformations can be 
made by matrix transformations within the workstation, as explained in 
Kosugi's paper. Thereafter the position of the space probe can be 
represented in the image scan data as a representation of the slice 
containing the tip of the probe, or slice containing the probe itself (as 
in an oblique slice) or representation of the probe within the 3-D slices, 
or 3-D rendering of the image scan data itself. 
It would be convenient to be able to put the reference markers on the 
patient's body or head in a repeatable way and in a simple way for an 
operator. It would also be convenient to have a structure which can retain 
the reference markers so that they can be returned onto the patient's body 
repeatedly, as for example in the scan episode and in the surgical 
episode, so easy referencing of multiple markers can be done. It is also 
convenient if dynamic reference markers could be installed or coupled on 
the patient's body in a common structure with the reference markers, or 
convenient if the dynamic markers are the reference markers themselves 
which can be tracked by the space digitizer or its detection system in the 
coordinate reference frame of the space digitizer, so that the patient's 
movement can be tracked dynamically, and thereby corrections in the 
transformation between the image scan data coordinate system and the 
stereotactic coordinate system can be made. It would furthermore be 
convenient if the attachment means for the reference markers and the 
dynamic reference markers could also alternatively couple to a graphics 
reference means which can index all of the scan slices in a unified image 
scan coordinate system to eliminate errors due to patient's movement 
during the scanning or to correct for aberrations in the scan slice 
sequence itself. 
Thus, it is an objective of the present invention to provide an apparatus, 
a means, and associated technique, which can easily attach to and which 
may be repeatedly re-attached to the patient's anatomy if desired, in 
essentially the same location which contains a plurality or pattern of 
reference markers to be used for frameless stereotaxy. 
It is also an objective of the present invention that the patient 
attachment means can be placed on or connected to the patient's skin 
easily and that it can be quickly placed and re-placed at the time of 
scanning with minimal effort or technical knowledge. 
It is also an object of the present invention that the patient attachment 
device can include dynamic reference markers which can be detected rapidly 
by the space digitizer or the space digitizer detection or transmission 
means so that rapid corrections of patient movement, either in the scanner 
or in the operative setting, can be made so as to correct the 
transformation between the image scan coordinate system and the 
stereotactic coordinate system of the space digitizer. 
It is an objective of the present invention to provide a system which is 
non-invasive and would not necessarily require breaking of the patient's 
skin or any discomfort for the patient to have the patient attachment 
device installed on the patient. 
It is also an object of the present invention to provide a patient 
attachment device which can be cooperatively coupled to a graphic 
reference means with diagonal and parallel elements such that the image 
scan slice data or tomographic scan data can be indexed relative to the 
patient attachment device, and therefore to the patient's body, in a 
consistent image coordinate system.

DESCRIPTION OF THE FIGURES 
FIG. 1 shows a typical tomographic imaging machine coordinate system with 
schematic slices through a patient's anatomy. 
FIG. 2 shows an embodiment of the present invention involving a head band 
strapped around the patient's head with reference markers and dynamic 
reference markers in place and an optical digitizing system with the probe 
referencing to image scan data. 
FIG. 3 shows a schematic block diagram representing one example of how 
image scan data and physical data from the space navigator can be 
transformed from one to the other so as to transform the image scan 
coordinate system to the stereotactic coordinate system of the space 
digitizer and displays of probes and surgical instrument movement in the 
surgical field can be represented on image scan data via a computer 
graphic workstation. 
FIG. 4 shows an embodiment of the present invention which is a head band 
strapped around the patient's head with reference markers in place and a 
docking structure attached to it. 
FIG. 5 shows ink marker tattoos on the patient's skin which enable a head 
band to be repositioned on the patient's head repeatedly, or individual 
LED markers to be placed on the tattoo positions. 
FIG. 6A shows a graphic reference structure with parallel and diagonal 
elements that is coupled to the head band to provide image scan data as in 
FIG. 6B with varying index data so as to index the tomographic slices 
relative to the reference markers and the head band and/or for indexing of 
the image scan data with respect to the physical reference markers and/or 
the graphic reference structure. 
FIG. 7 shows the head band with dynamic reference markers installed on it; 
in this embodiment, the dynamic reference markers are LED lights which are 
detected by an optical tracking system, and in the same figure an ENT 
probe which is used for nasal surgery with optical tracking. 
DESCRIPTION OF THE INVENTION 
The embodiments below are meant as illustrations of the invention, and not 
to limit the scope of the invention. Those skilled in the art can think of 
other embodiments and variations which fall within the scope of the 
present claims. 
Referring to FIG. 1, the patient's anatomy 1, which in this case is his 
head and neck, is being scanned by tomographic slices illustrated by 
slices 2, 3, 4, and there could be many more slices in a typical scan 
sequence. These slices typically are taken from a CT scanner with X-rays 
or an MRI scanner, PET scanner, or other modalities. Although they are 
shown as slices, such scan data can be taken volumetrically or with a 
spiral scanner in modern scanners. The image scan data from the image 
scanning machine, such as a CT tomographic machine, usually can be 
referenced to its own coordinate system, the image scan coordinate system. 
In FIG. 1, this is illustrated by the X, Y, Z coordinate system 6 which 
has the X and Y axes related to the orthogonal axes of the two-dimensional 
scan slice, and the Z axis representing the scan number, scan depth, or 
scan position in space relative to the scanning machine, and this is 
typically orthogonal to the scan slice plane. Thus the image scan data can 
be referenced, in this example, relative to the three-dimensional 
coordinate system 6. The scan data usually is processed through an image 
scan computer and then can be sent to an off-line computer graphic 
workstation which can be used in conjunction with a stereotactic navigator 
or stereotactic space probe or digitizer. The data can be rendered in 
three dimensions or it can be left as two-dimensional slice data, and the 
position of the space probe can be indicated within that slice data or 
three-dimensional representation. Examples of this are given in the papers 
by Watanabe, et al and Kosugi, et al referenced above. As seen in FIG. 1, 
the intersection of each of the slices 2, 3, and 4 with the external 
anatomy or the skin of the patient are represented by the contour lines 
2A, 3A, and 4A respectively. In each of these slices, the patient's 
internal anatomy is represented. What has been described so far is prior 
art, and known in the image scan technology. 
FIG. 2 shows an embodiment of the present invention, which in this case is 
a skin band or head band 208, which is secured around the patient's 
anatomy, in this case the patient's head 201. This band could have been 
illustrated as being a stick-on, flexible plate, or other type structure 
which can be attached to the patient's skin, and the skin could be located 
on any part or any portion of the patient's anatomy throughout the body. 
In this example, reference markers 210, 211, 212, and 213 are positioned 
in some fixed relationship to the head band, and thus as the band is 
secured to the patient's head, the reference markers are essentially in a 
fixed relationship to the patient's head. These reference markers can be 
radiopaque dots, radiopaque rings, or other structures which are visible 
in an X-ray, CT, tomographic scan, or they may be MRI visible, or PET 
visible, or of other construction to be visible in other scanning 
modalities. As an example of a digitized navigator or space probe which 
can be used in a frameless stereotactic context, FIG. 2 shows two cameras 
230 and 231 which are mounted on a bar between them and fixed in the 
operating theater on some external apparatus. The camera system has an 
associated stereotactic coordinate system 232, which is represented by the 
axes X.sub.s, Y.sub.s, and Z.sub.s. The cameras in this case may be two 
two-dimensional cameras viewing the field near the patient. In the field 
is a surgical probe, or surgical instrument, or surgical apparatus, or 
other external apparatus, as the case may be, which is represented 
generically by the element 225. It has optically detectable elements 226 
and 227 on it, which might represent two light-emitting diodes (LEDs) 
which are visible and can be tracked in position by the cameras 230 and 
231. In this way, the position and orientation of the probe relative to 
the cameras can be determined, and that data can be assimilated in a 
processing element (designated as a camera system computer 235), which 
might be circuitry and a computer associated with it which can read out 
data from the camera system. This data, for example, might be the 
coordinate position data of the instrument 225 relative to the camera 
coordinate system, also referred to here as the stereotactic coordinate 
system. In a typical procedure (but not the only procedure for frameless 
stereotactic registration.) the point of the space probe or digital 
navigator might be touched to one of the reference markers 213, and 
thereby the coordinates of the reference marker with respect to the 
stereotactic coordinate system can be determined. The position of the 
other reference markers may also be determined in the same way. Thereby, 
the position of the reference markers and/or the reference structure 
attached to or associated with the head band can be determined with 
respect to the stereotactic coordinate system or the camera coordinate 
system. Similarly in FIG. 2, there is shown an image scan or image slice 
240, which in this case happens to have reference marker images 250, 251, 
252, and 253 corresponding to the reference markers 210, 211, 212, and 213 
in the physical space of the patient. Each of these reference marker 
images may have coordinates in the image scan coordinate system 6 of FIG. 
1. This coordinate system with respect to the scan 240 might be indicated 
by the coordinate axes 257, which are the orthogonal axes within the scan 
slice; and in addition, there is a Z coordinate which might be the slice 
number indexed by the appropriate slice spacing. By making a mapping, 
transformation, or other referencing of the coordinate data associated 
with the reference markers in the stereotactic coordinate space to the 
reference marker images in the image coordinate space, a transformation or 
mapping between the image scan coordinate system and the stereotactic 
coordinate system can be made. Such a transformation is described in the 
article of Kosugi, et al. It might also be added that schematically in 
FIG. 2 is shown the element 237 (designated as an image scanner computer), 
which might be the image scanner or the computer associated with the image 
scanner or a means for handling computationally the image scan data and 
the coordinates of the reference markers. This image scan data may be fed 
to the element 236 (designated as a computer graphic workstation), which 
may be a transformation means or maybe a computer graphic workstation or 
other computer means. Element 236 can process the data from the camera 
system 235 and the image scan data, and perform the transformations 
computer discussed above. Once these transformations are in hand, then the 
position of the probe 225 in real space can be mapped to its virtual 
position in the image space or scanner coordinate system of the image scan 
data. Thus, on a computer graphic display means such as a CRT screen 
associated with the computer graphic workstation 236, a position of the 
space probe can be displayed relative to the image scan data. The tip of 
the probe can be made to correspond to one or more image scan slice(s), 
the orientation of the probe can be shown in projection or in 
three-dimensional space relative to the image scan data, etc. These are 
standard manipulations now known in frameless stereotaxy. 
Also indicated in FIG. 2 as part of the head band are ancillary or 
additional reference markers indicated by the numbers 220, 221, and 222. 
They may be light-emitting diodes or other optically reflecting or 
optically visible objects which are in a fixed position or affixed to in a 
predetermined or non-predetermined position onto the head band 208, and 
are detected by the cameras 230 and 231 so that their position can be 
determined in the stereotactic coordinate space. These ancillary or 
dynamic reference markers may be in a pattern such that their orientation 
can be determined and therefore can be a representation of the position or 
movement of the patient's head with the head band in place. Such a 
movement of the patient's head will give rise to a change in the 
coordinate transformation between the image scan coordinate system, which 
is taken relative to the patient's head, and the stereotactic coordinate 
system of, in this case, the cameras, which may be fixed relative to the 
room or operating couch where the operation takes places. Thus, a 
modification of the transformation would be needed, and this can be 
corrected for by knowing the changes in the orientation of the dynamic 
reference markers. For example, in FIG. 2 there are three dynamic 
reference markers, and their positions can be detected in space by the 
cameras. If the patient's head moves, then a coordinate system which is 
affixed to the patient and therefore in a rigid body orientation relative 
to the head band, such as the dynamic reference markers, will also move. 
The movement of the patient's anatomy, in terms of a translation and 
rotation movement, can be taken into account by the movement in terms of 
translation and rotation of the head band dynamic reference markers. In 
this way, the camera system or navigator system can be continuously 
monitoring the position of the dynamic reference markers on the patient 
attachment device, in this case the head band, and a correction can be 
made to the coordinate transformation to take into account this 
rearrangement of the patient's head. Additionally, the cameras or other 
digitizer can be coupled to the patient's head by use of a fixation 
device. Indeed, any relative movement of the camera system and the 
patient's head can be so taken into account by the cameras monitoring 
these dynamic reference markers. The dynamic reference markers themselves 
could in fact be part of the reference markers on the head band shown in 
FIG. 2; that is to say, elements 210, 211, 212, and 213 themselves may be 
dynamic reference markers and can be identified or detected by the camera 
system for that purpose. On the other hand, the dynamic reference markers 
may be separable or distinct from the reference markers, as is illustrated 
in FIG. 2, and they can serve the separate functions described above or a 
unified function. The dynamic reference markers may have a predetermined 
pattern and can be affixed in a predetermined way to the head band so that 
their relationship with the reference markers may be know or 
predetermined. Alternatively, it is not necessary that they be in a 
predetermined relationship to the reference markers, since the correction 
to the coordinate transformation may be done without such a predetermined 
relationship. The dynamic reference markers, and indeed the reference 
markers, may have LEDs connected to them so that they become optically 
coupled to the camera system. They may be corner cube reflectors or other 
types of reflecting or light-gathering devices, or simply their pattern 
can be identified by the cameras so that their position can be determined 
and tracked, as described in the dynamic transformation correction. 
FIG. 3 shows one schematic example of the elements or steps in the process 
of using the skin band with dynamic reference markers and reference 
markers. Element 301 represents the image scan data plus the scan machine, 
and this gives rise to element 302, which are the images of the reference 
points or reference markers within the scan coordinate system as 
identified in the image scan data. This information can be determined 
automatically or by manual pick-off and be fed via line 330 into a 
computer 305, which may be part of the image scan computer or may be an 
off-line computer workstation, as the case may be. The image scan data has 
associated with it (as represented by line 324) an image scan coordinate 
system represented by the element 309, and this has been described in one 
embodiment as part of FIG. 1. The external reference system or 
stereotactic system can be represented by element 303, and in the example 
of FIG. 2, it is a camera system. Many other types of reference system or 
technique could be imagined, for example, a mechanical coupling system, 
ultrasonic coupling, electromagnetic coupling, radio frequency coupling, 
or other means so as to determine the position of physical objects in 
space in the stereotactic coordinate system. The coordinates of the 
reference points can be determined, as illustrated by the element 304, and 
an example is given associated with FIG. 2. This information about the 
coordinates of the reference points relative to the stereotactic 
coordinate system can be fed, as by line 331, into the same computer 
system 305 as the image scan data. Thereby, a transformation action 
(represented for illustration purposes as line 320) can be made between 
the image scan coordinate system 309 and the stereotactic coordinate 
system 308, illustrated here as the camera coordinate system. The camera 
coordinate system can be a coordinate system associated (as represented by 
line 322) with the structure holding the cameras or with one or more of 
the cameras which are observing the surgical field. One 
(position-sensitive) camera, two cameras, or a plurality of cameras can be 
used equivalently and can be implemented for the purpose described above. 
The dynamic reference system is illustrated by the element 306, and it is 
coupled (as represented by line 321), in the case of FIG. 2 optically 
coupled, to the stereotactic coordinate system. For example, the dynamic 
reference system may be tracked by the camera system in position and 
orientation. The position of the dynamic reference frame may be sent (as 
represented by line 335) to the same computer 305 as is the camera data, 
reference data, and image scan data. Thus, a correction to the 
transformation 320 involving, for example, a translation and rotation 
correction can be made to the coordinate transformation 320. In addition, 
surgical instruments or apparatus such as surgical tools, cutters, suction 
tubes, aspirators, bipolar forceps, endoscopes, etc. can be represented by 
the element 307. Element 307 could also include multiple instruments or 
instruments plus other surgical devices such as a microscope which is 
instrumented with lights and LEDs to be tracked (as represented by line 
323) by the camera system. These all can feed (as represented by line 334) 
their own position data into the same computer workstation -305, and the 
entire scene can be tracked by the computer so that one has an integrated 
view of the instruments, the microscope, the dynamic reference points, 
etc. This may be provided by the graphic display 310 which may be 
connected to the computer 305 via line 336. All of them can be set in the 
same coordinate reference frame as the camera system, and their relative 
positions can be determined so that the microscope, for example, can point 
in a direction which is determined relative to the image scan data. The 
surgical probe can also be determined relative to the image scan data, all 
of it corrected by the dynamic reference markers on the head band. 
Referring to FIG. 4, an embodiment of the present invention is shown which 
includes a head band 402 which is secured around the periphery of the 
patient's head 401 as in a conventional head band. It has a strap 417, 
which could be a Velcro strap or other tightening element so as to secure 
it with comfortable pressure around the patient's head. On the head band 
are reference markers 410, 411, 412, and 413. Any number of reference 
markers can be used, but it is convenient to have three or more so that 
one can more accurately reference the image slices as they pass through 
the reference markers. If there are three reference markers that are 
substantially non-colinear, then these reference markers can determine 
effectively a plane. Therefore such a pattern of reference markers can 
define the coordinate system of the image scan data coordinate system 
which can then be mapped to the coordinate system of the patient's anatomy 
or to the stereotactic coordinate system of the external reference 
apparatus associated with the stereotactic device or space digitizer. In 
FIG. 4, the reference markers such as 410 are annuli or rings which may be 
radiopaque or MRI visible or PET visible. They may have holes through them 
which enable visualization of the skin below, and indeed an ink mark can 
be made on the skin through each hole so as to reference where the head 
band was placed on the patient's head. For example, the head band could be 
put on the patient's head at the time of scanning and permanent or 
non-permanent ink marks can be put on the patient's forehead or scalp 
through these holes at the time the head band is put on. Then, at the time 
of surgery or repeat scanning or intervention, the head band could be 
replaced on the patient's head in substantially the same position by 
lining up the holes in the reference markers to the ink marks which are 
already on the patient's head, and then the head band can be secured in 
place by the straps or other means. In this way, a repeat reference frame 
is possible with such a head band. Other means of repositioning the head 
band are also possible such as lines, index spots, notches, or other means 
so as to reference it on the skin by means of ink markers or even 
anatomical or natural landmarks such as positions on the brow, over the 
ear, etc. Also shown in FIG. 4 is a docking platform 415. This can take 
many forms, means, and designs, but in this case it is a plate with, for 
example, index pin holes and a threaded hole to secure other devices to 
the head band such as dynamic reference markers or graphic reference 
structures to be described below. 
FIG. 5 shows the same patient's head with reference markers or ink markers 
510, 511, 512, and 513, which may correspond to the positions of the 
reference markers or hole positions 410, 411, 412, and 413 in FIG. 4. Such 
ink dots can then be used to secure either radiopaque reference markers 
later, or perhaps to secure a string of LED or optically effective objects 
which can be placed on the patient's head in essentially the same position 
as the reference markers of FIG. 4. These optically detected markers can 
then act as reference markers for a camera system which is viewing or 
monitoring the patient's anatomy, and thus the patient's anatomy can be 
tracked by these points such as 510, 511, 512, and 513 continuously during 
the time of intervention or surgery. For example, as shown in FIG. 5, a 
string of LEDs 520, 521, 522, and 523, with a common cable 527, can be in 
a bundle, and each of these stuck down over each spot, such as 510, 511, 
512, and 513, at the time of surgery, as indicated by the dashed lines, 
and the patient can immediately be mapped into the image scan coordinate 
system by the transformation referred to in association with FIG. 3. The 
cameras could be tracking the position of the LEDs in their position on 
the patient's skin continuously, and the movement of the patient can be 
corrected for by a correction in the transformation of mapping described 
above. Thus, these spots such as 510, 511, 512, 513, etc. can act as 
mapping elements or reference markers themselves; they can be radiopaque 
or MR compatible buttons, or dots, or rings, or other objects stuck onto 
the patient's skin directly, corresponding to the position of the head 
band markers; or they can be optically detectable reference points, for 
example LED's or light reflectors, or skin attachment points that can be 
tracked by, for example, a stereotactic camera system or stereoscopic 
cameras so as to reference the patient in the coordinate system of the 
camera system and/or track the patient's position dynamically during a 
surgery with respect to the camera system or with respect to other 
apparatus in the room such as a microscope whose position is known 
relative to the external coordinate system. 
FIG. 6A shows another embodiment of the present invention which involves a 
graphic reference means or graphic reference structure that is attached to 
the head band or skin band so as to index the tomographic slice data as it 
is taken. In this instance, a frame structure is attached by the docking 
mechanism 615 in a known, or a prescribed, or predetermined position 
relative to the head band 602. On the head band are shown also, for 
example, the reference markers 612, etc., which have been discussed 
previously. The graphic reference frame is rigidly or fixedly attached, 
and comprises vertical rod elements such as 650 and 653 together with 
diagonal elements such as 651, 654, 656, and 658, and there are others on 
the opposite side shown in dashed lines (not numbered), and there could be 
many more around the structure. In reference to FIG. 6A, the 
terms"vertical" and "horizontal" are defined relative to a view of the 
patient when the patient is in an upright position, not when the patient 
is in the supine position depicted in FIG. 6A. In addition, there are 
horizontal rods 652, 655, etc. (and others not numbered) for example, and 
others on the top as well as horizontal rods running from anterior to 
posterior relative to the anatomy such as 659, all of which can give rise 
to index markings when a tomographic slice passes through the anatomy and 
the graphic reference structure. Tomographic slices can be axial, 
sagittal, coronal, or oblique, and they will give rise to two-dimensional 
tomographic images such as that shown in FIG. 6B. In FIG. 6B, one sees two 
representative schematic image slices. The top slice 670 shows the 
patient's anatomy 685 and fiducial index marks such as 680, 681, and 683, 
which might correspond to the CT image slice intersection of the rods 650, 
651, and 653, respectively, on the graphic reference means of FIG. 6A. In 
the lower figure in FIG. 6B, another slice is shown, and one can see that 
the relative positions of the index marks 690 and 691 that correspond to 
rods 650 and 651 differ from the positions of marks 680 and 681. Such 
variation of image scan data can be used as a direct indexing, or mapping, 
or confirmation of the position of the scan slice. This is known from the 
work of Brown and the Radionics BRW and CRW Stereotactic Systems, in which 
case such a graphic reference means is used in conjunction with a 
stereotactic head ring for stereotactic indexing of tomographic slices. 
Other graphic reference structures or means could be devised by those 
skilled in the art and could be attached to the head band or skin band of 
the present invention. For example, the number of diagonals and rods could 
vary greatly. In fact, there could be only one vertical rod such as 650, 
and significant information on the indexing of the slice or the variation 
of head movement could be gained from that, such as head movement in the 
image scanner, etc. One of the advantages of such a graphic reference 
means attached to the patient is that if the patient moves from one slice 
to the next, then the index mark such as those shown in FIG. 6B can 
indicate the movement, and it is possible when assimilating the image scan 
data in a computer workstation to make corrections for this so that it can 
be placed in a consistent image scan coordinate system referenced, for 
example, to the patient's anatomy, or the head band, or the graphic 
reference means. For example, the image scan data can be referenced to a 
coordinate reference frame attached to the graphic reference structure, 
and all data from the image scanner can be transformed into that 
coordinate reference frame. The computer graphic workstation described in 
FIG. 3 can assimilate that image scan data, and it can be transformed 
directly from the coordinate system associated with the graphic reference 
means, as in FIG. 6A, rather than the coordinate system of the image scan 
machine as described in FIG. 1. Thus, this is an alternate possible 
mapping of the image scan data to the camera coordinate system. Should the 
patient move between slices or during the scanning or from one scanning 
episode to another, then the registration of any given slice or temporal 
collection of data can be referenced to this one common, patient-based or 
graphic-reference-structure-based coordinate system, and all of the data, 
therefore, can be in a consistent, unified data set. This data set can 
then be transformed to the stereotactic coordinate system of the camera or 
space navigator, and thereby errors can be corrected for and/or avoided. 
Another element which can help in this direction is a patient stabilizer 
such as that shown schematically as 660 in FIG. 6A. This may be a head 
clamp, or a head securing element, or an element that can be attached to 
the image scanner table, to the operating table, or to a treatment table 
such as for a LINAC in radiation therapy or stereotactic radiation 
delivery that can be secured to the head band 602, and thereby stabilize 
the position of the patient's head against movement. It can be a very 
secure or less secure clamp, and it can help the patient himself, if he is 
a cooperative patient, to resist movement during the scanning or during 
the operation. Thus the present invention comprises patient securing or 
fixation elements which can be attached to the skin band or head band. 
Such securing elements can be in turn fixed to the CT scanner couch or 
table or to any other couch or table associated with surgical intervention 
or radiation delivery. The graphic reference structure or means of FIG. 6A 
may include only one diagonal element, or one diagonal in conjugation with 
one parallel element, or a multiplicity of other elements whose geometry 
can enable referencing of the image scan data to the patient's anatomy so 
that movements in the patient's anatomy can be corrected for or taken into 
account. For instance, it may include a sequence, series, or pattern of 
radiopaque or MRI-visible dots, lines, rings, etc. so as to reference or 
index the image scan data. Furthermore, the data, when collected with such 
a graphic reference means, can correct for any aberrations in the scanning 
process itself. As is used in stereotaxy with stereotactic head frames, 
data can be collected and questions of alignment of the scanner to a base 
plane such as the head band or the base rod elements of the graphic 
reference means can be checked or confirmed, and full mathematical 
transformations of data can be made, if necessary, from images of the 
graphic reference means or structure to the base frame, in this case the 
head band or the element secured to the patient's body or skin. 
FIG. 7 shows a further embodiment of the present invention in which dynamic 
reference markers are attached as an independent element to the head band. 
The head band 702 is again secured around the patient's head, and it has 
the reference markers 710, 711, and 712, as described above (other markers 
could be present). In addition, there is the dynamic reference structure 
770, which can be secured to the head band by a securing element 788, and 
this may be secured to the patient before, during, or after scanning, or 
only during the surgical or interventive procedure. On the dynamic 
reference marker plate 770, there are the dynamic reference markers 
themselves 771, 772, and 773, which may be optically detectable structures 
or LED lights or other transmission or receiving elements for the spatial 
navigator reference system or external referencing apparatus, which in 
FIG. 7 is indicated by the optical cameras 730 and 731. These cameras are 
able to track the position of the dynamic reference markers, and thus 
track the orientation of the patient's head via the head band and correct 
for any head movement, as described above. Also shown in FIG. 7 is a 
surgical instrument 780, which has an offset handle 783 and LED or 
optically-detected index markers 781 and 782 which can be detected by the 
camera system 730 and 731. Thus, the orientation and position of the probe 
can be tracked in space, and, in particular, the position of the shaft of 
the probe 784 and its tip within the body can be tracked with respect to 
the camera system and therefore with respect to said patient's anatomy and 
with respect to the dynamic reference markers discussed above. The entire 
system can be an integrated system, where the relative positions of the 
probe and the patient's head can be tracked and differences can be 
determined. The reference markers 710, 711, etc., for example, on the head 
band could be used as dynamic reference markers as well, and the dynamic 
reference plate could be used as reference markers in the CT image scan 
also. Variations of this scheme can be devised by those skilled in the 
art. For example, the number of dynamic reference markers or reference 
markers can vary greatly, and their location and configuration can also 
vary to suit the situation. Discrete reference markers do not need to be 
used, but rather linear marks, or grid patterns, or other shapes that can 
be recognized by the camera system can be used. Intelligent software or 
artificial intelligence can be invoked so as to recognize patterns such as 
the head band, or the dynamic reference plate, or the reference markers 
and thereby the orientation of the patient's head, and other aspects of 
the scene can be determined and tracked. Similar remarks can be made about 
the probe 780. It can have a pattern of optically trackable markers or a 
shape of an optically detectable structure such that its position, 
orientation, and rotation can be determined in space. The scene in FIG. 7 
is a typical one in the case of ENT surgery. A second instrument could be 
used in the patient's other nostril for sinus surgery. For example, that 
other instrument could be an endoscope with light-emitting diodes on it so 
as to track its position. A multiplicity of cameras could be used, and 
even one position-sensitive camera can be used, if appropriately designed 
for range viewing to perform this function shown in FIG. 7. Typically, two 
or more cameras are useful to get a stereoscopic view or to have 
redundancy in the detection system, or to increase the range of angles of 
observation for a given surgical setting so as to eliminate line-of-sight 
problems. The dashed lines in FIG. 7 are meant schematically to illustrate 
the optical coupling between the cameras and the respective elements 
described here. 
Many variations of the invention described here can be thought of by those 
skilled in the art. For example, the head band might be adapted to be 
placed around the patient's torso, his limb, or some other portion of the 
anatomy. The head band need not be an entire encirclement of the body, but 
could be taped on or stuck down to the body. For instance, it could be a 
bandage-like structure that could be stuck to the forehead and it could 
have adhesive on its lower side to provide a secure sticking to the 
patient's skin. It could be a Velcro strap with an elastic band around the 
back, or it could be something akin to a pair of glasses which hook over 
the ear. Such "glasses" otherwise could be secured by straps over the head 
and perhaps around the back of the head near the neck. 
The skin band may take various forms and variations. It could be, in fact, 
a head band made of a thin plastic such as polyurethane, or polypropylene, 
or other thermal plastic; it could be a plate structure made out of 
plastic or other material such as carbon fiber or metal; it could be a 
strap such as a nylon strap or a Velcro strap; it could be something 
analogous to a surgical stick-on band-aid; it could be a stick-on band; it 
could be a head band or a cloth band that can wrap around the patient's 
head or the patient's anatomy and be bound to it by a strap, or clasp, or 
buckle system; it could have multiple bands, one going around the 
azimuthal circumferencial direction of the patient's head, for example, 
and another that goes over the top of the head in various directions such 
as sagittal, coronal, or other oblique paths; it could be similar multiple 
band structures wrapping around the patient's torso or the rest of his 
body, either in parallel bands or in random orientations; it could have 
attached to it or attachable to it a graphic reference device or graphic 
reference means which might be, for example, a hard hat, or a dome, or a 
helmet which has multiple, spatially-located reference markers that can be 
seen in the image scan and also located in the physical space. Also such 
variations are possible associated with the skin band. A very simple 
embodiment, as shown in the figures, is a simple belt which wraps around 
the patient's head or body that can be cinched and easily applied by a 
technician during scanning and re-applied in a replaceable or identical 
position at the time of surgery, such as for ENT surgery or even 
neurosurgical interventions. This would be a very convenient embodiment of 
the present invention. Such a belt-like structure or band-like structure 
could be disposable for essential single patient use. It could come 
sterile-packed or it could be autoclavable. For example, if it were made 
out of a high temperature thermoplastic, it could be easily molded and the 
reference markers or index hole positions could be molded into it so that 
each is exactly identical to another. The reference band could come in a 
kit form which includes a head band, an ink pen for skin marking, a 
dynamic reference marker system with LED lights and attachable cord, and a 
disposable graphic reference structure with diagonals or other points on 
it for the dynamic referencing of the patient's head. Such a kit could be 
disposable and intended for single patient use. 
There can be wide variations in the placement and configuration of 
reference markers and dynamic reference markers, as described above. The 
skin band may be more akin to a pattern of reference markers on a sheet 
structure which can be secured or stuck to the patient's skin. The skin 
band may be similar to a string of reference markers or LED lights that 
can be stuck down on a position or positions, as for example the ink mark 
positions that might be represented in FIG. 5 on a patient's forehead or 
in other locations on his skin. The skin band, reference markers, and 
dynamic reference frame could be used in conjunction with external 
apparatus for tracking the relationship of the apparatus to the patient's 
head. For example, cameras could be mounted on a microscope or on a linear 
accelerator (LINAC) for external beam irradiation of the patient so that 
the relative orientation of the patient on the linear accelerator's couch, 
or near the microscope, or relative to the beam delivery system of a 
radiation system could be used for the purpose of aligning the patient or 
tracking the position of the patient as he is moved into position for 
surgery or external treatment. Any such variations of the use of a skin 
band, or skin-fixed reference markers, or skin-fixed light systems are 
intended to be included within the scope of the present invention. 
A great variety and variation in the graphic reference means, as shown in 
the embodiment of FIG. 6, can be thought of and devised by those skilled 
in the art. The structure could be MRI and CT visible and thus be made of 
hollow tubes which can be water-filled. The structure can be made of 
diagonal plates or otherwise wire cage structures so as to provide the 
graphic reference means for the image scan data, as described above. The 
attachment to the skin fixation means might be done in a variety of ways 
other than the docking system described in FIG. 6. Such graphic reference 
means could be attached to the patient's torso or limbs so as to give 
local referencing to the anatomy within those parts of the body. The 
graphic reference means could be flexible or curvilinear in its structures 
and be attached in a molded fashion to the patient's body on or near the 
skin band structure, or it could be stuck down to the patient's body in 
conjugation with the skin band so as to achieve the kind of referencing of 
the image scan data as described above. All such variations are intended 
to be included within the scope of the present invention. 
It should be noted that the graphic reference structure may have a 
coordinate system of its own, which we might refer to as a graphic 
reference structure coordinate system, and this can be transformed or 
mapped into the image scan coordinate system, or data which is referenced 
with respect to said graphic reference means coordinate system can be 
mapped into or back from the image scan coordinate system. In this way, 
corrections associated with movement or change of position of the 
patient's anatomy in said image scanner as the scanning is being done can 
be made, and therefore corrections of such variations due to patient 
movement, or even aberrations of the image scan coordinate system, or 
slice indexing, or, for example, scanner couch tilt can be corrected for. 
Thus, the image scan coordinate system can be transformed into a graphic 
reference structure coordinate system, and the graphic reference structure 
coordinate system can be used as the basic image coordinate system that is 
mapped to the stereotactic coordinate system of the space navigator. As 
another example, the image scan data can be referenced, as it is being 
taken, to the graphic reference structure coordinate system, and that 
coordinate system can be used as a reference coordinate system analogous 
to the image scan coordinate system but, in this case, reference to the 
graphic referenced structure, which is in turn referenced to the patient's 
anatomy. It is that image scan data and that graphic reference structure 
coordinate system that can be used for the transformation to the 
stereotactic coordinate system associated with the space probe or 
navigator. All such variations in transformations and mapping of 
coordinate systems and corrections with respect to patient movement or 
aberrations in the image scan data can be taken into account and is 
claimed within the scope of this patent. 
It should be noted that the detection apparatus which tracks and/or 
determines the position of the reference frame markers for dynamic or 
real-time correction of the transformation between the image scan 
coordinate system and the stereotactic coordinate system, or corrects for 
patient's movement with respect to the external apparatus or space 
navigator system, can be separate from and different from the space 
navigator apparatus itself. For example, a mechanical arm could be used 
for the space navigator, and an optical system could be used to track the 
dynamic reference markers to make corrections for patient movement. On the 
other hand, these two elements, the apparatus to track the dynamic 
reference markers and the space navigator, could in fact be the same 
apparatus. For example, if the space navigator is an optical system or an 
ultrasonic system, then it could be the selfsame apparatus. 
Considering that those skilled in the art may make variations that are 
included within the present invention, what is claimed by U.S. Letters 
Patent herewith are the following claims.