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Description  |
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TECHNICAL FIELD
The present invention relates to an apparatus for delivering laser energy
in the form of a laser beam to tissues for the purpose of medical
intervention in a number of clinical applications and particularly to a
micromanipulator for precision control of the direction of the laser beam.
BACKGROUND ART
The development of the laser in 1960 opened the possibility of the
application of this form of energy in a number of medical disciplines.
Lasers offer the advantages of high power, narrow spectral widths, small
focused spot sizes, and good absorption of the energy by the target
tissues. Since then, numerous lasers of different wavelengths and modes of
operation have been developed, and many of these have been used in
specific medical applications. For example, the argon laser, with emission
in the blue-green part of the visible portion of the electromagnetic
spectrum, has found extensive use in ophthalmology because of its good
transmission by the ocular media and good absorption by the target tissues
in the retina and choroid.
Among the many lasers that have been developed, however, the carbon dioxide
laser, with its emission wavelength of 10.6 microns, offers the most
extensive range of applications in medicine because it is highly absorbed
by all tissues of the body. For this reason, by focusing the carbon
dioxide laser on tissues, it is possible to photocoagulate, to cut, or to
vaporize almost any tissue of the body. The carbon dioxide laser has been
applied to a number of medical problems in various disciplines--including
otolaryngology, gynecology, neurology, dermatology, and in plastic and
general surgery.
In the field of gynecology, the carbon dioxide laser has been used almost
exclusively for medical intervention in a number of disorders. The laser
is used for making incisions, to coagulate small arteries and veins, and
to vaporize tumors and other abnormal tissues.
A number of instruments have been developed for use in the field of
gynecology. These devices typically comprise a console that contains the
power supplies, vacuum pump, gas tanks, and water pump and heat exchanger,
for operating the laser. An umbilical cord is typically used to connect
the console with a laser head that is directly coupled to a colposcope or
an operating microscope, supported by a stand that is free standing or is
connected to the console. The operating microscope is typically mounted on
an optical head assembly which may be provided with a
micromanipulator--more popularly, a joy-stick--to permit the operating
physician free control of the locus of impact of the beam on the target
site.
In such laser systems, the laser energy is produced in a laser head and is
transmitted to the target site by a series of redirecting mirrors. The
last mirror in the path is linked mechanically to the joy-stick to permit
the desired manipulation. To permit the desired movement of the beam on a
target plane separated a specified distance such as, for example, a foot
from the viewing optics of the operating microscope, the mechanical
linkage between the micromanipulator and the last mirror must provide for
two degrees of freedom, conveniently referred to as the x and y axis. A
problem arises, however, in linking the micromanipulator to the last
mirror. If the axis of rotation of the mirror is normal to the plane of
the incident and reflected laser beam, then each degree of rotation of the
mirror results in a two degree change in the direction of the deflected
beam (y axis); however, if the rotation of the mirror is about an axis
lying within the plane of travel of the beam, then each degree of mirror
rotation is matched by one degree of beam deflection (x axis). Thus,
direct linkage of the micromanipulator to this last mirror without
compensation results in a distortion in one dimension so that if the
micromanipulator were to trace a circle, the deflection of the laser beam
by the mirror would trace an ellipse whose minor axis corresponded to the
radius of the circle.
SUMMARY OF THE INVENTION
I have invented a precision beam directing micromanipulator for a surgical
laser system in which the operator's manual movement is reproduced exactly
by a like amount of displacement by the laser beam in either the x or y
axis on the target plane, and I have done this without using any springs
or complex linkages.
In a preferred mode, my micromanipulator comprises a manipulator handle
connected to a universal pivot assembly by a first sphere which serves as
the reference point for the movement of the handle. Attached to the first
sphere on the side opposite the exposed handle is a smaller sphere whose
movement is always opposite that of the manipulator handle. The smaller
sphere is coupled to an angled brass manipulator arm which is provided
with a slanted cylindrical opening at one end portion thereof. The other
end of the manipulator arm is connected to a mirror mount housing a beam
redirecting mirror. The mount permits the mirror the necessary two degrees
of freedom to deflect the exiting laser beam a prescribed amount in the x
and y directions. The brass manipulator arm is free-floating and is
designed to precisely compensate for the above-noted y axis distortion
while at the same time yielding the one-to-one relationship in x axis
movement. In the preferred embodiment, the slant of the cylindrical
opening in the manipulator arm is 13 degrees relative to the horizontal,
but it will be appreciated that this angle is a function of the dimensions
of a specific system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing a laser delivery system including a
beam directing manipulator handle in accordance with the present
invention;
FIG. 2 is an elevational view of the optical head assembly of FIG. 1 shown
on an enlarged scale;
FIG. 3 is an elevational view, partially in section, of the
micromanipulator assembly and illustrating also several of the beam
redirecting mirrors of the laser delivery system;
FIG. 3A is a view taken along line 3A--3A of FIG. 3;
FIG. 4 is a perspective view of the micromanipulator assembly illustrating
the permitted degrees of freedom;
FIG. 5A is a schematic elevational view showing the manipulator handle
deflected in the vertical orientation;
FIG. 5B is a schematic view of a section of the target plane showing the
incidence of the laser beam on the target plane corresponding to the
position of the manipulator handle in FIG. 5A;
FIG. 6A is a schematic top plan view showing the manipulator handle
deflected in the horizontal orientation;
FIG. 6B is a schematic view of a section of the target plane showing the
incidence of the laser beam on the target plane corresponding to the
position of the manipulator handle in FIG. 6A;
FIG. 7 is a schematic view of the target plane showing the incidence of the
laser beam when movement of the manipulator handle has both a horizontal
and vertical component;
FIG. 8 is a schematic side view of a beam deflecting mirror illustrating
the optical principle that the angle of incidence equals the angle of
reflection and its effect when the mirror is rotated about an axis
perpendicular to the plane of the beam's path;
FIG. 9 is a schematic rotated side view of the mirror illustrated in FIG.
8; and
FIG. 10 is a schematic view of a section of the target plane illustrating
the distortion that would be caused by the optical effect shown in FIG. 8
of a laser beam striking the target plane as the manipulator handle is
rotated to circumscribe a circle.
DETAILED DESCRIPTION
In FIG. 1 there is shown in perspective a surgical laser device referred to
generally as 10 including a cabinet 12 that houses the necessary power
supplies and required electronics and which doubles as a seat for the
operating physician. A generally vertical tiltable laser head housing 14
is connected to the cabinet 12. Laser head housing 14 supports a removable
colposcope or operating microscope delivery system referred to generally
as 16.
The laser head housing 14 contains a carbon dioxide laser that is used for
treatment, such as a Laakmann ElectroOptics, Inc. rf excited waveguide
laser, and a helium-neon laser used for aiming purposes since the beam of
the carbon dioxide laser is invisible to the human eye. The beams of the
two lasers are combined by a method well known to those familiar with the
art, and are directed upward to the colposcope 16 through its support stem
18 which is axially hollow so that the beams can propagate along its
central or longitudinal axis. The laser head housing 14 is designed to
pivot and can be tilted in any direction about the vertical; thus,
allowing for the approximate aiming of the delivery system 16 onto a
prescribed target plane 20, such as shown in FIG. 2.
The operating microscope delivery system 16 is shown on an enlarged scale
in greater detail in FIG. 2. In normal operation, the laser beam is
directed upward through the stem 18 and then by a series of beam
deflecting mirrors 22, 24, 26, and 28. The first three of these
mirrors--22, 24, and 26--are precision mounted in fixed orientation so
that each reflects the oncoming beam 90 degrees along an axis orthogonal
to the previous path of the beam. The last mirror 28 is the mirror which
controls the site at which the laser beam strikes the target plane 20. A
diverging lense 30 and a converging lense 32 are provided along the path
of the laser beam to provide for the desired focusing of the laser beam by
the operating physician. The last mirror 28 is controlled by a
micromanipulator assembly which includes a manipulator handle or a
joy-stick 34 as will be described in greater detail below. When the
manipulator handle 34 is in its horizontal orientation, as shown in FIG.
2, the last mirror 28 is arranged to deflect the laser beam an angle
.alpha. relative to the horizontal so that the beam strikes the target
plane 20 at a point coincident with the center line of sight of the
viewing optics. In the preferred embodiment, the target plane 20 is
separated from the viewing optics by one foot and the angle .alpha. is
seven degrees.
As illustrated in greater detail in FIG. 3, the beam deflection is
accomplished by the handle 34 which includes a first large spherical
member 36 which serves as a fulcrum and represents a fixed point. The
sphere 36 is retained in pivot assembly 38 which permits the manipulator
handle 34 to be pivoted universally as shown by the arrows in FIG. 4.
Pivot assembly 38 is provided with a generally cylindrical retaining
member 40 as well as a rotatable insert 42 which provides for tension
adjustment of the manipulator handle. Connected to the first large sphere
36 is a second smaller sphere or movable member 44, preferably made of
stainless steel. Since the first sphere 36 acts as a fulcrum, movement of
the manipulator handle 34 in any direction will result in movement of the
second sphere 44 in the opposite direction. The internal end of the
manipulator handle 34 is coupled to an angled manipulator arm 46 which is
provided with a slanted cylindrical opening 48 that surrounds the
spherical member 44. At least a portion of the manipulator arm 46 is made
of brass to minimize wear between the steel sphere 44 and its points of
contact. The angled manipulator arm is, in turn, connected to a mirror
mount 50 which retains the last mirror 28.
As shown with greater clarity in FIG. 4, the mirror mount 50 includes a
mirror yoke 52 which defines an axis X--X about which the mirror is
pivotable whenever the handle 34 is deflected along the vertical (y) axis.
The mirror yoke 52 is in turn rotatable about an axis Y--Y orthogonal to
the axis X--X, such rotation being exhibited whenever the manipulator
handle is deflected along the horizontal (x) axis. 46 is connected to the
mirror mount 50 by a pair of fastening means such as screws 54 and 56.
Mirror mount 50 is separated from manipulator arm 46 by a dowel 58 which
permits fine adjustment of the orientation of the mirror mount by applying
independent tension on screws 54 and 56. Thus, as the manipulator handle
34 is moved to the right as designated by the +X direction, the small
sphere 44 will force the manipulator arm 46 to move to the left (+X
direction) which rotates the mirror mount 50 about the Y--Y axis in the
direction designated by +X. The reverse is true when the manipulator
handle is moved to the left or -X direction. Likewise, when the
manipulator arm is moved upward in the direction designated +Y, the small
sphere 44 will move downward in the + Y direction causing the mirror to be
pivoted about axis X--X in the +Y direction or counterclockwise. The
opposite is true when the manipulator handle is deflected downward (-Y).
As is well known in optics, in the ray model of light propagation, as
illustrated in FIG. 8, the angles of incidence and reflection are measured
with respect to the normal N to the reflecting surface, the mirror and the
point where the light strikes it. The normal is a line drawn perpendicular
to the surface at that point. In the representation of FIG. 8, the angles
of incidence (i) and reflection (r) are equal. The incident ray, the
reflected ray and the normal all lie in the same plane. As the mirror is
rotated an angle theta (.theta.) about an axis perpendicular to the paper
and intersecting the point where the light strikes the mirror, the angle
of reflection, assuming the path of the incident light beam I is fixed,
will be two theta (2.theta.). Since rotation of the mirror about this axis
also rotates the normal through an angle theta, the new angle of incidence
is i' which equals i plus .theta.. Thus, the new angle of reflection is
equal to the new angle of incidence and is r' which equals r plus theta.
Hence, the total angle through which the light beam is deflected is now i'
plus r' which equals i plus r plus 2 .theta. which exceeds i plus r by
twice the angle theta through which the mirror was turned.
This phenomena, however, does not occur when the mirror is rotated about an
axis orthogonal to the axis of rotation of FIG. 8, such as shown in FIG.
9. In the rotation of the mirror mount 50 of FIG. 9, about axis Y--Y, the
change in the angle of reflection equals the angle of rotation of the
mirror. Thus, there is an optical distortion whenever the beam is
deflected in the vertical axis, though none exists when the beam is
deflected in the horizontal axis. The result of this selective distortion
is that, uncorrected, a combination of the two degrees of rotation of the
mirror mount defining a circle, as shown in FIG. 10, would yield an
elliptical beam path.
The inventive mechanism described herein compensates for this distortion
problem and does so without the need for springs or complex mechanical
linkages. For example, as shown in FIG. 5A, a movement in the handle 34 in
the direction +Y results in a counterclockwise pivot of the mirror mount
50 an amount (R to Ry) that results in the incidence of the target beam on
the plane 20 to be moved in the vertical direction a like distance +Y, as
shown in FIG. 5B. Likewise, as shown in FIG. 6A, a horizontal deflection
of the manipulator arm 34 a distance +X results in a corresponding
movement of the manipulator arm 46 and hence, in the rotatable mirror
mount 50 about axis Y--Y (R to Rx) an amount which results in the laser
beam striking the target plane a corresponding distance +X from the center
point. In the preferred embodiment illustrated in FIG. 3, the slant of the
cylindrical opening 48 is 13 degrees relative to the horizontal. It will
be appreciated that this slant is a function of the specific geometry and
dimensions of the described system, wherein the distance d.sub.1 between
the center points of the two spheres 36 and 44 is 0.25 inches, the
vertical distance h.sub.1 between the center point of large sphere 36 and
the axis X--X about which the mirror mount rotates is 2.4 inches, and the
horizontal distance d.sub.2 between the center point of sphere 36 and axis
X--X is 2.6 inches.
When the manipulator handle 34 is moved to a point where it has both a
horizontal and a vertical component, the mirror mount 50 will be pivoted
about axis X--X as well as rotated about axis Y--Y resulting in the
incidence of the laser beam on the target plane at a vector from the
center point of the plane corresponding to the X,Y position of the
manipulator handle relative to the center point of sphere 36. Thus, if the
manipulator handle 34 were to circumscribe a circle, the impact on the
target plane by the laser beam would also yield a circle of equal radius.
Thus, if the surgeon is operating on a region of the patient, his movement
of the manipulator handle 34 requires no compensation since its motion in
all directions and in a consistent fashion will be faithfully reproduced
on the target plane.
* * * * *
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