Surgical needle abstract
The head of a patient is held in place horizontally on the indexable
sliding cradle of an X-ray scanner by a vertical ring encircling
the head having radiolucent rests supporting the head behind the
ears at the mastoid processes and beneath the eyes at the cheekbone
area. Adjustable horizontally-projecting instrument support structure
is carriage-mounted on an arcuate track in the ring between the
forward rests and has a horizontally-bored instrument guide-holder
of such density as to appear on an X-ray scan and positionable adjacent
to the head with its horizontal bore in the plane of any indexable
scanning section of the X-ray scanner. By scanning the head and
adjacent guide holder, the holder may be positioned with its bore
in the same plane as and on a line directed to a point of interest
in the brain. Thereafter, the holder may be utilized to guide a
surgical needle to the point of interest.
Surgical needle claims
We claim:
1. A method of performing brain surgical procedures through the
skull to a point of procedure by utilizing a computer-assisted tomography
scanner of the type which develops indexed parallel planar sectional
representations of the head, comprising the steps of
securing a patient's head, below the level at which such sectional
representations are to be developed, in fixed position relative
to the movable, indexable cradle of the scanner,
preliminarily scanning the head and selecting from the sectional
representations so developed an indexed plane of interest at which
a chosen point of procedure is located,
positioning an instrument holder having a density substantially
of the order of that of soft human tissue and having a bore for
guiding a surgical instrument with the axis of the bore in the plane
of interest,
further positioning the instrument holder angularly in the plane
of interest with the axis of its bore along a straight line directed
to the point of procedure through a point of entrance into the skull,
scanning at the plane of interest to confirm that the bore of the
instrument holder is positioned for guidance of the instrument along
the selected line to the point of procedure,
drilling through the skull at the point of entrance guided by the
bore of the instrument holder, and
inserting the surgical instrument through the guide-holder bore
and the skull point of entrance and guiding same by the instrument
holder bore to the point of procedure.
2. The method defined in claim 1 wherein the step of inserting
the surgical instrument is accompanied by the step of
scanning at the plane of interest with the surgical instrument
so inserted to confirm that the instrument is inserted to the point
of procedure.
3. The method defined in claim 1 wherein the step of securing
a patient's head to the scanner includes
supporting the rear of the head behind the ears at the mastoid
processes, and
supporting the front of the head beneath the eyes at the zygomatic
arches.
4. The method defined in claim 1 wherein the step of securing
a patient's head to the scanner includes
supporting the rear of the head beneath the ears at the mastoid
processes, and
supporting the front of the head beneath the eyes at the maxilla.
Surgical needle description
BACKGROUND OF THE INVENTION
The present invention relates to surgical procedures in which small
medical instruments, generally needles, are inserted through bone
or other tissue to a particular point of interest, with a minimum
of disturbance. More specifically, the invention may relate to insertion
of a needle through the skull to a point of interest within the
brain, such as a lesion or tumor, for aspiration biopsy or decompression.
Representations of parallel planar sections of human tissue, such
as horizontal sections taken through the brain, may be made by a
computed-tomography X-ray scanner. Various tomographic techniques
make possible study of tumors, lesions, or other points of interest.
Surgical procedures performed on the brain at such points of interest
may be done by insertion of needles or other slender instruments
through a bore in the skull, but these procedures heretofore have
been difficult because the surgeon had no simple and direct way
to insert the instrument directly to the point of interest. This
limitation often dictated use of the alternative technique of a
craniotomy, to permit visual inspection of the point of interest.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a simple and
direct way by which a medical instrument may be precisely guided
to a point of interest within the brain, or other portion of the
body, by utilizing a computer-assisted tomography scanner.
Briefly summarized, a patient is horizontally supported on the
cradle of such a scanner with his head secured within a ring vertically
mounted to the cradle, whose precise horizontal positioning makes
possible representations of an indexable plurality of parallel vertical
sections through the upper part of the head. The head is held in
place relative to the ring by a pair of radiolucent rests behind
the ear at the mastoid processes and another pair beneath the eyes
at the maxilla or zygomatic arches, leaving the entire upper portion
of the head unobstructed for purposes of the X-ray scanner. Adjustable
instrument support structure is carriage-mounted on an arcuate track
between the rests at the front of the head, projecting perpendicularly
from the plane of the ring toward the top of the head. The support
structure includes a horizontally bored guide-holder preferably
of a plastic whose density as hereafter described, is substantially
of the order of that of soft body tissue, positionable with the
bore in the plane of any vertical scanning section.
After preliminarily scanning to determine the index of the scanning
plane in which the point of interest is found, the support structure
is adjusted to position the axis of the guide-holder bore in the
plane of interest and also locate it angularly along the ring and
direct its bore through a desired point of entry into the skull
along a line leading to the point of interest. Another scan confirms
the position of the guide-holder bore relative to the point of interest.
After incision of the skin at the point of passage through the skull,
the guide-holder bore provides a guide for drilling through the
skull. Then a needle or other surgical instrument may be inserted
in the plane of interest through the aligned guide-holder bore and
skull bore, with its depth determined by repeated scanning and adjustment
until it is properly positioned to the point of interest. The desired
surgical procedure may then be performed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric projection of a preferred embodiment of
the apparatus of the present invention.
FIG. 2 is a schematic isometric view of a typical X-ray scanner
and being of the type with which the apparatus of FIG. 1 is adapted
to be used, having a horizontally-movable and indexable cradle.
FIG. 3 is a side view of the apparatus of FIG. 1 mounted to the
cradle of the FIG. 2 X-ray scanner, shown in dashed lines, and supporting
the head of a patient, shown in phantom lines, in position for scanning.
For clarity, the instrument holding provision is shown rotated 90.degree.
from its FIG. 1 position.
FIG. 4 is a schematic representation of a typical X-ray scan when
utilizing the present invention, showing a section of the head and
the guide-holder of the present invention positioned with its bore
in the plane of the scan and directed to a lesion or other point
of interest within the skull.
FIG. 5 is a view similar to FIG. 4 with a needle inserted through
the bore of the guide-holder and through the skull into the brain
to the point of interest.
BESCRIPTION OF THE PREFERRED EMBODIMENT
In the present invention, scanning X-ray equipment utilizing computerized
tomography aids in directing a surgical needle to a point of interest
within the body of a patient. In the preferred embodiment, the insertion
is of a needle through the skull to a point of interest within the
brain, though the invention may be applicable to uses within the
neck, the chest cavity, the long bones of the body, or to other
points of interest, expecially those not easily accessible because
of overlying bones or delicate organs.
In the present invention, the X-ray scanner, generally designated
a, is of the type shown in FIG. 2 having a table b, including a
patient-supporting movable cradle c forming a support with a longitudinal
axis. The cradle c has a transverse vertically-bored concave-downward
head restraint mount d at one of its ends, as shown in FIGS. 2 and
3. At one end of the table b the scanner a has an X-ray scanning
mechanism f having a horizontally-extending circular throat g, sufficiently
large to receive the head of a reclining patient. The vertical scanner
throat g is at such a level that the head restraint end of the movable
cradle c may be slided axially therein, so that the patient's head
may be moved horizontally to an indexed position within the scanner
throat g when the patient is reclined on the table b. The scanner
f is of the type having an X-ray tube, not shown, and corresponding
opposing receptors revolving about the scanner throat g in a scanning
plane h, shown by the dashed lines in FIG. 3. Digital information
processing equipment, along with a cathode ray tube display, not
shown, utilize the X-ray projections to produce representations
of the parallel planes transverse to the head by tomographic techniques.
In developing an X-ray scan, the X-ray tube and corresponding receptors,
as they revolve about the scanner throat g, obtain a great quantity
of density information. The raw data received from the receptors
is received and compiled by the computer to produce attenuation
coefficients for a matrix of points in the scanning plane h, including
a patient's head positioned within the scanner throat g. Typically,
these attenuation coefficients may be arranged on a scale from negative
to positive 1000 known as the Hounsfield scale, for which -1000
is the attenuation coefficient for air, zero is the attenuation
coefficient for water, and +1000 is the attenuation coefficient
for dense bone. For purposes of reference, the Hounsfield number
for brain tissue, which is considered a soft tissue, is approximately
30. Since the densities of points of interest within the brain may
be only slightly different than that of normal brain tissue, for
example, an increase from 30 to 33 on the Hounsfield scale, only
a portion of the scale can be utilized to achieve the required contrast.
Accordingly, the information processing equipment is utilized to
assign the gray scale of the CRT display to a desired range within
the Hounsfield scale. For example, to study brain tissue, it may
be appropriate to select a "window" of 100 about a center
"level" of 30 on the Hounsfield scale. In such a representation,
all tissue denser than Hounsfield number +80 appears as solid white,
and all material less dense than Hounsfield number -20 appears as
black. Materials with densities between appear as varying shades
on the grey scale. The "level" and/or the "window"
may be changed instantly by adjusting the equipment, permitting
the surgeon to search for those density differences which appear
only with greater or lesser sensitivities or at different "levels".
In the preferred embodiment of the present inventive apparatus,
a patient's head may be supported within the scanner throat g, as
shown in FIG. 3 by head-holding apparatus comprising a ring-like
member or ring 30 encircling the head, forming frame-like patient
restraint means, securable to the movable cradle c on the X-ray
scanner table b. A ring mount, generally designated 20 clamps the
lower end of the ring 30 and an adaptor 10 pin-mounts the ring mount
20 to the head restraint mount d of the cradle c.
The adaptor 10 shown in FIGS. 1 and 3 has a concave-downward
lower side, matable with the head restraint mount d of the movable
cradle c of the X-ray scanner a; a plurality of downward-extending
pins 11 on the adaptor lower side are matable with corresponding
bores in the head restraint mount d. The upper side of the adaptor
10 presents an upward arcuate concave edge in a plane perpendicular
to the longitudinal axis of the needle c. A plurality of horizontal
threaded bores 12 are provided in the side of the adaptor 10 for
mounting the ring mount 20 to the adaptor 10. The construction of
the head restraint mount d may vary with different scanner models;
thus, a suitable adaptor may be used for each.
The ring mount 20 shown in FIGS. 1 and 3 is made up of an arcuate
front plate 21 a similar arcuate back plate 27 and an intermediate
arcuate spacer 25 of lesser depth sandwiched between the front and
rear plates 21 27 at their lower sides, the spacer thickness being
substantially the same as or somewhat less than the ring 30. The
arcuate front plate 21 has a plurality of adaptor mounting bores
alignable with the threaded bores 12 of the adaptor 10 to receive
stud bolts for mounting the adaptor 10 to the front plate 21. The
back plate 27 and spacer 25 have a plurality of aligned bores, aligned
with a plurality of threaded bores in the front plate 21. Thumbscrews
28 extend through the bores in the back plate 27 and spacer 25 to
the front plate threaded bores, to mount these three parts together
to form an adjustable width arcuate concave upward-opening slot
with which to clamp the ring 30 upright in a chosen angular position
between the front plate 21 and back plate 27 upward of the spacer
25.
The ring 30 is, in the preferred embodiment, constructed of one-fourth
inch thick aluminum plate having approximately a fourteen inch diameter
circular outer edge, smaller than the scanning throat; the outer
edge of at least its lower portion is interengageable with the slot
in the ring mount 20. The upper portion of the planar ring 30 has
an arcuate slot or track 33 through it extending approximately 55
degrees to each side of center. The arcuate track 33 provides angular
range of positions at which to affix a carriage-mounted instrument
support structure, described below. The interior dimensions of the
ring 30 are sufficient to accommodate a patient's head.
At about 18 degrees upward of the level of its center, as shown
in FIG. 1 the ring 30 has a pair of mounting bores for the upper
head rests, one bore at each side of the ring 30 spaced downward
of the end of the slot 33. Correspondingly, the ring 30 has three
mounting bores for the lower rests, one on its vertical centerline,
and the other two about 45 degrees upward therefrom.
The three identical lower adjustable head supports or rests, each
on the same side of the ring 30 are hereafter generally designated
as the left lower support 41 the right lower support 42 and the
center lower support 43. Each is made up of a standard 45 having
a flared end with a threaded concentric bore by which the standard
45 is mounted to the lower rest mounting bores by a mounting bolt
46. The opposite end of the standard 45 has a threaded bore, perpendicular
to the axis of the standard 45 which receives a threaded shaft
48 having a flattened finger grip portion 49 at one end and a ball
and socket joint 50 at its opposite end. The ball and socket joint
50 mounts to a thin, circular acrylic plastic plate 51 which carries
a substantially radiolucent foam rubber donut-shaped cushion 52.
Two identical adjustable upper head supports or rests are utilized,
the left rest generally designated 61 and the right rest generally
designated 62 both on the same side of the ring 30 as the lower
supports 41 42 43. Each has a standard 64 with a reduced diameter
threaded end extending through one of the upper rest mounting bores
to a thumbnut 66. At its opposite end, the standard 64 has a bore,
perpendicular to its axis, receiving a shaft 70 which has a ball
and socket 71 at one of its ends, mounted to a similar thin circular
acrylic plastic plate 72 carrying similar foam rubber cushions 73.
A tubular spacer 68 on the standard 45 between the bore and the
ring 30 clamps the shaft 70 when the thumbnut 66 is tightened.
The preferred embodiment is further comprised of a carriage 80
preferably of cast aluminum, slidably mounted to the arcuate track
33. The carriage 80 is formed of a substantially triangular plate
portion 81 parallel to the ring 30 at whose apex is a perpendicular
tubular portion 82 on the inner side of the ring 30. The triangular
plate portion 81 has a pair of threaded bores 83 which receive thumbscrews
84 which extend through the slot or track 33 and provide for both
sliding within and clamping to the slot 33. Perpendicular to its
axis, the tubular portion 82 has a threaded bore carrying a thumbscrew
85.
A cylindrical arm 90 is received by the tubular portion 82 thereby
extending perpendicular to the plane of the ring 30 and is slidably
adjustable by loosening the thumbscrew 85. That end of the arm 90
which extends to the same side of the ring 30 as the bottom and
top head supports 40 60 has a large bore perpendicular to its axis,
and a smaller threaded bore with a thumbscrew 92 perpendicular to
and extending into the large bore. The larger bore accepts a circular
riser post 94 having at its end a perpendicular instrument guide-holder
95 preferably made of a three-eighths inch thick plastic plate
which extends from the riser post 94 to an opposite end having a
threaded bore 97 parallel to the axis of the riser post 94. The
threaded bore 97 accepts an exteriorly-threaded instrument guide
98 having a small concentric bore 99 which will accept a surgical
instrument such as a needle or drill bit. Several replaceable instrument
guides having various internal bore diameters may be provided, to
accept needles of different sizes, as well as a twist drill bit
for boring through the skull. An instrument guide 98 utilized to
guide a twist drill is provided with an outer lip at one end, to
prevent the drill bit from turning the guide 98 from its position
within the guide-holder bore 97.
The drill guide 98 and guide-holder 95 are made of material having
such a density as to be visible on a scan by the X-ray scanner.
Therefore it may thus be of a density in the range at which the
X-ray scanner utilized operates, for example, one which falls on
the Hounsfield scale between the density of air and dense bone.
For greater convenience, the drill guide 98 and guide-holder 95
of the preferred embodiment are made of material having a density
substantially on the order of magnitude of the density of soft body
tissue but slightly greater than that of the brain tissue under
study, preferably such as in the range of 50 to 200 on the Hounsfield
scale, though materials having Hounsfield numbers as high as 400-500
may be utilized, depending upon the relative dimensions of the material.
In the preferred embodiment, an acrylic plastic, specifically polymethylmethacrylate,
manufactured and sold under the trademark PLEXIGLASS and having
a Hounsfield number believed to be approximately 100-150 is utilized,
though other arcylic plastics or other materials could be substituted.
Since this plastic has a density greater than that of brain tissue
(which has a Hounsfield number of approximately 30), it appears
on a typical scan of the brain as solid white on scan representations
having a small grey scale "window", such as 50 or 100
and having a "level" of near 30 while causing substantially
no artifacts. To avoid severe artifacts in the scan, other parts
of the apparatus, such as the arm 90 and riser post 94 may be of
the same material, or of a material of lesser density, such as that
of the radiolucent cushions 52 73.
In use of the apparatus of the preferred embodiment, the specific
adaptor 10 for the make and model of X-ray scanner to be utilized
is mounted to the ring mount 20. Then the downward pins 11 of the
adaptor 10 are fitted into the head restraint mount d of the removable
cradle c, and the ring 30 is mounted and clamped to the ring mount
20 by tightening the thumbscrews 28. A patient j then reclines on
the cradle c with his head encircled by the ring 30 as shown in
FIG. 3. The lower rests 41 42 43 are adjusted by turning the threaded
shaft 48 until the head is approximately centered within the ring
30 with the left and right rests 41 42 supporting the head behind
the ears substantially at the mastoid processes, and the center
rest 43 supporting the back of the neck. Next the thumbnuts 66 for
the top support rests 60 are loosened and the shafts 70 are pushed
inward to press the foam rubber cushions 73 against the cheekbone
areas of the head beneath the eyes, either at the maxilla or the
zygomatic arches, and the thumbnut 66 is tightened, clamping the
shaft 70 in place. The head is thus fixedly supported on the cradle
c of the X-ray scanner a by the opposed rests, at a chosen angular
position determined by the angular setting of the ring 30 in the
clamping slot of the ring mount 20. By the reproduceable positioning
of the cradle c, the patient's head is indexable to any position
within the X-ray scanner throat g. Preliminary scans of the head
may be performed at successive sections, and the index number for
the position of the cradle at which the point of interest within
the brain is in the scanning plane noted.
Next, the surgeon will determine the best straight-line path for
the needle through the skull and brain to the point of interest
and its point of entrance through the skull is marked on the skin
of the head. Often the path chosen will simply be the shortest possible
one, but a different angular path may be chosen to avoid certain
portions of the brain, at the judgment of the surgeon. The patient
is indexed into the scanner throat g so that its scanning plane
h is at the point of interest, with the carriage 80 slided to an
estimated proper position, the arm 90 extended, and the guide-holder
95 in place. Preferably, an insturment guide 98 is screwed into
the guide-holder 95; its decreased bore size provides increased
accuracy. The positions of the carriage 80 arm 90 and guide-holder
95 are adjusted until the guide bore 99 is approximately at the
plane of interest and the desired point of entrance through the
skull for the chosen path. Then a scan may be made to determine
whether the guide bore 99 is in the scanning plane of interest and
whether it is directed along the desired path, as shown in FIG.
4 which is a scanner representation of the skull k with an interior
brain lesion m and the guide-holder 95 with the instrument guide
98 in place. Repeated scanning and readjustment may be required
until exact positioning is achieved. In the preferred embodiment,
where the guide-holder provided has a density of the order of and
slightly greater than that of the brain tissue, the guide-holder,
including its path-directing bore, may be seen on the same grey
scale scanner representation (substantially the same "level"
and "window") as the brain lesion or other abnormality,
the guide-holder appearing as solid white and its bore as black.
But, where the density of the guide-holder substantially differs
from that of body tissue, such as having a density substantially
grater than the brain or other body tissue under study, it may be
necessary to temporarily mark the position of either the point of
interest or the guide-holder on the exterior of the CRT screen,
such as by utilizing a grease pencil, and then change the grey scale
by adjusting the "level" and/or the window to clearly
show the other. This may be necessary due to artifacts caused by
a high density guide-holder which interferes with the grey scale
representation of the brain; changing the grey scale may avoid the
artifacts. Though good results may be available utilizing such a
relatively dense material for the guide-holder, it clearly will
be more convenient to avoid the necessity of such an adjustment
of the grey scale.
Next, the scanner cradle c may be moved out of the throat g and
the point of entrance marked on the patient's head at the location
of the guide bore 99. Afterward, by loosening the thumbscrew 92
in the outer end of the arm 90 the riser post 94 may be rotated
to swivel the guide-holder 95 away from the marked point of entrance,
to permit an incision to be made in the skin at that point. The
guide-holder 95 may then be rotated back to the incised point, and
a drill guide 98 threaded into the guide-holder bore 97; then a
twist drill is inserted through the drill guide 98 and a bore is
made in the patient's skull at the point of entrance. A scan preliminary
to drilling may be desirable to recheck the orientation of the guide
bore 99 for most accurate results.
Finally, a needle guide 98 is threaded into the guide-holder bore
97 replacing the drill guide. At this point, a scan may be performed
at the plane of interest to assure that the guide-holder 95 is properly
positioned with the needle guide bore 99 in the plane of interest
on a line directed to the point of interest, as shown in FIG. 4.
When exact placement is achieved, a needle n of the type suitable
for performing the surgical procedure, is inserted, through the
needle guide 98 and skull bore, into the brain tissue. The insertion
distance required may be determined by consulting the cathode ray
tube display and utilizing the known ratio of scanner image to real
image size to calculate the linear distance; or for greater accuracy,
the needle may be inserted into the brain approximately to the required
depth and one or more scans performed in the plane of interest to
determine whether the needle is to the correct depth, as well as
along the desired path, as shown in FIG. 5. Once it has been determined
that the needle is at the correct depth and position, the desired
surgical procedure is performed.
Summarizing, the method of carrying out the present invention may
be described as a method for performing surgical procedures on the
brain through a bore in the skull to a point of procedure or interest
in the interior of the brain by utilizing an X-ray scanner of the
type which utilizes computer-assisted tomography to develop indexed
parallel planar sectional representations of the head. The steps
in the method include first securing the patient's head in a fixed
position relative to the indexable cradle of the scanner and preliminarily
scanning the head to develop as many sectional representations as
may be necessary to select an indexed plane of interest at which
a chosen point of procedure is located. Then the guide-path-establishing
instrument holder is positioned outward of the skull in the plane
of interest so that its guide path may become visible on a developed
sectional representation of the head. Scanning at the plane of interest
and further adjustment of the instrument holder confirms its position
for such guidance of the instrument or needle along the selected
straight-line path to the point of procedure. Finally, a bore is
drilled through the skull at the point of interest, preferably guided
by the bore of the instrument holder, and the surgical needle is
inserted through the instrument holder bore and skull bore to be
guided by the holder to the point of procedure.
Where the exact depth of the surgical instrument is critical, the
needle or other instrument may be inserted to a proposed depth and
then a scan performed at the plane of interest with the instrument
so inserted to confirm that it is inserted to the point of procedure.
It has been found to be most desirable in securing the patient's
head in fixed position relative to the scanner cradle to support
the rear of the head behind the ears substantially at the mastoid
processes, and to support the front of the head beneath the eyes
at the cheekbone area, either at the zygomatic arches or at the
maxilla. This low position of mounting on the head leaves the entire
upper portion of the head free of any obstruction which might cause
artifacts on the X-ray scans. As will be obvious, such combination
of a ring-like member with first adjustable rest means to conform
to and support the head at the mastoid processes and second adjustable
rest means to conform to and support the head at the cheekbone area
may be utilized as head-holding apparatus for restraint to any adjacent
support fixed relative to the patient's body during any surgical
procedure performed on the upper portion of the head.
Other advantages of the present invention will be apparent to persons
familiar with the problems of cranial surgery. Fixing the guide-holder
to the head-holding ring establishes an accurate guide path to the
point of interest. By providing the track and carriage mechanism
at the upper end of the ring, the guide-holder may be moved to either
side of the head or to its center so that the selected straight-line
path to the point of interest may be the most direct path possible;
or where the brain tissue along a direct path is thought to be too
delicate to attempt insertion of a needle through it, the carriage
80 may be slided around the head and fixed at a different position,
to permit operation along a different angular path. Mounting the
ring at the location beneath the eyes and ears assures that as much
of the upper portion of the head as possible is unobstructed by
metal or other dense objects which may cause artifacts on the X-ray
scan; they are further avoided by use of the radiolucent foam and
the polymethylmethacrylate plastic for the head rests and low density
material such as the polymethylmethacrylate for the arm 90. The
slide clamping-type mount of the ring 30 to the ring mount 20 permits
the patient's head to be rotated to a desired angular position,
for example, with the patient lying on his side. In such case, the
rests may nevertheless comfortably and securely support the head
at the mastoid process, behind the ear, and beneath the eyes, substantially
at the cheekbone area.
Modifications of the present invention will be apparent to persons
skilled in the art. For example, another type of adjustable rest
means to conform to and support the head behind the ears substantially
at the mastoid processes and beneath the eyes at substantially the
cheekbone area may be utilized. Likewise, other means mounted to
the ring-like member and angularly adjustable relative thereto may
be utilized to support an instrument utilized for the surgical procedure
on the head. From these examples, other modifications will suggest
themselves.
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