Method and system for scanning a laser beam for controlled distribution of laser dosage

A system and method for distributing an output beam from a laser system on a body which provides for a uniform fluence level throughout an entire treatment region. A first structure receives the laser beam and aims it along a propagation axis. A scanner scans the propagation axis of the laser beam at a controlled scan velocity, so that the laser beam essentially continuously scans a treatment pattern on the body. The treatment pattern can consist of an essentially straight line, or a ring, or other pattern which can be easily fitted together with other patterns to fill in a treatment area. The method includes the steps of: PA1 supplying a laser beam, PA1 directing a laser beam along a propagation axis to the body, and PA1 scanning the propagation axis of the laser beam at a controlled scanned velocity, so that the laser beam essentially continuously scans the treatment pattern on the body.

FIELD OF THE INVENTION 
The present invention relates to an instrument for distributing laser 
dosage in a treatment pattern, such as used in dermatology for the 
treatment of angiomas and the like. 
DESCRIPTION OF RELATED ART 
A condition known as the planar angioma occurs due to hypervasculation of 
the skin. This hypervasculation causes the skin to appear discolored. This 
discoloration is commonly known as a "port wine stain". 
Current treatments for the planar angioma comprise closing off the blood 
vessels in the affected zone. This stops blood flow and the resultant 
discoloration in the hypervascularized area. 
The techniques used for closing off the blood vessels involve application 
of laser beams to the treatment zone. This effects closing off the blood 
vessels by photocoagulation, when the laser beam is generated at preferred 
wavelengths, as commonly known in the art. 
The photocoagulation occurs due to thermal effects of the impact of the 
laser beam. In treating angiomas, the thermal effects desired occur in a 
specific temperature range. This elevated temperature range must be 
limited to the microvessels in the dermis in order to avoid any tissue 
damage and scar formation as a result of the procedure. 
This laser treatment can be applied manually by a practitioner, or by means 
of an instrument such as disclosed in International Publication No. WO 
87/06478 of International Patent Application No. PCT/FR87/00139, entitled 
SYSTEMATIZED TREATMENT INSTRUMENT, USING TICULARLY LASER ENERGY, USEFUL 
FOR EXAMPLE IN DERMATOLOGY. 
The problems with the manual treatment are explained in the International 
Publication No. WO 87/06478, and include problems with regulating the 
distribution of the dosage of radiation and the like in a manner which 
avoids overexposing certain areas and underexposing other areas. Thus, the 
skill of the practitioner in applying the treatment is of utmost 
importance for the manually administered technique. 
The International Publication No. WO 87/06478 provides a mechanized 
instrument for distributing the laser energy. This mechanized instrument 
involves delivering the laser beam in an optical fiber to a treatment 
head. In the treatment head, the end of the optical fiber is positioned to 
expose elementary spots using stepper motors in a sequential scan pattern. 
A shutter in the treatment head is used to control the duration of pulses 
at each position in the scan pattern. While this technique has proved to 
provide great advances over the manual technique, it still suffers certain 
problems. 
In particular, in this prior art system, the dosages of laser radiation are 
delivered to the treatment area in discreet elementary spots. One spot is 
irradiated, and then a shutter is closed and the beam delivery apparatus 
repositioned to a second spot. Then the second spot is illuminated and so 
on until the entire treatment area is scanned. The shape of the spot is 
basically circular. Because of the circular shape, it is difficult to 
position successive elementary spots across the treatment area in a way 
that provides for a uniform distribution of dosage across the treatment 
area. Some areas get greater amounts of radiation while others get lesser 
amounts. This effect can be understood by considering positioning three 
pennies adjacent to one another. Unless the pennies overlap one another, 
there must be an open region between the pennies. There are similar open 
regions which will receive no direct radiation between the spots of the 
prior art treatment system. This inability to provide a uniform dosage 
across the entire treatment area has resulted in stipple patterns in the 
planar angioma regions being treated. To remove the stipple pattern, the 
angioma must be re-treated to compensate for the underexposed portions. 
Obviously, re-treatment is costly, and subjects the patient to an 
increased risk of scarring or other problems that may occur during the 
procedure. 
Furthermore, the very high repetition rates in which the shutter must be 
opened and closed to illuminate each spot, has resulted in high failure 
rates in the shutter mechanism. It is difficult to provide a shutter which 
is durable enough and operates quickly enough, in the portable treatment 
head which is utilized with such systems. 
Accordingly, it is desirable to provide a system and method for treating 
planar angiomas, and other medical conditions, with a controlled 
distribution of laser radiation which is more uniform, reliable, and 
easier to apply than the prior art. 
SUMMARY OF THE INVENTION 
The present invention provides an apparatus and method for distributing an 
output beam from a laser system on a body which provides for a uniform 
fluence level throughout an entire treatment region. Furthermore, it 
eliminates the need for very high repetition rates of the shutter in the 
treatment head. Accordingly, the present invention provides a safer and 
more reliable system for distributing a laser beam across a treatment area 
in medical applications. 
In one aspect, the present invention provides an apparatus for distributing 
an output beam from a laser. The apparatus includes the first structure 
which receives the laser beam and directs it along a propagation axis. 
This structure directing the laser beam is then coupled with a scanner, 
that scans the propagation axis of the laser beam at a controlled scan 
velocity, so that the laser beam essentially continuously scans a 
treatment pattern on the body. Thus, the laser beam is moved across a 
treatment pattern on the body, rather than held stationary to illuminate 
an elementary spot as suggested in the prior art. 
The treatment pattern can consist of an essentially straight line, or a 
ring, or other pattern which can be easily fitted together with other 
patterns to fill in a treatment area. Alternatively, the treatment pattern 
can be a spiral or raster scan pattern which completely fills a treatment 
area. 
The structure which directs the laser beam in one aspect of the invention 
includes an optically transmissive fiber which supplies the laser beam, 
and means for securing the fiber so that the laser beam propagates along a 
propagation axis transverse to and having a position in a scanning plane. 
The scanner controls the position of the propagation axis in the scanning 
plane in order to scan the treatment region. Other mechanisms, such as 
galvanometer mounted mirrors and the like, may be used for scanning the 
laser beam. 
According to another aspect of the present invention, a method for 
distributing an output beam from a laser is provided. The method includes 
the steps of: 
supplying a laser beam, 
directing a laser beam along a propagation axis to the body, and 
scanning the propagation axis of the laser beam at a controlled scanned 
velocity, so that the laser beam essentially continuously scans the 
treatment pattern on the body. 
The step of scanning, according to one aspect of the invention, is 
successively repeated so that the laser beam scans a plurality of 
essentially continuously scanned treatment patterns, wherein the 
successive treatment patterns fill a treatment region on the body. The 
successive treatment patterns can be positioned so that a first sequential 
treatment pattern is non-adjacent to a next sequential treatment pattern. 
According to yet another aspect, the method includes providing a template 
having an opening defining an outside dimension of the treatment region. 
With the template, the step of scanning includes turning on the laser beam 
while the propagation axis directs the laser beam outside of the opening 
of the template. Next, the propagation axis is scanned at a constant 
velocity across the opening while the laser beam is on until the laser 
beam is directed outside the opening. While the laser beam is directed 
outside the opening, the propagation axis is repositioned, with laser beam 
either on or off, for a successive treatment pattern. 
As can be seen, the system and method according to the present invention 
allows for completely filling a treatment region with a constant fluence 
level. This minimizes the possibility of stipple patterns and the like 
being left after a first treatment. Further, the present system includes 
much lower repetition rates on the shutter mechanism in the treatment 
head, which improves the reliability of the treatment system. 
Other aspects and advantages of the present invention can be seen on review 
of the figures, the detailed description and the claims which follow.

DETAILED DESCRIPTION 
A detailed description of an embodiment of the present invention is 
provided with reference to the figures. FIG. 1 illustrates the system for 
delivering the laser output beam. FIG. 2 illustrates one construction for 
the treatment head for distributing the beam. FIGS. 3, 4, and 5 illustrate 
the operation of the beam distribution technique. FIGS. 6 and 7 illustrate 
alternative treatment patterns which can be used according to the present 
invention. 
As shown in FIG. 1, the laser system according to the present invention 
includes a laser 10 which generates an output beam along path 11. The 
output beam is supplied through external beam path components 12 such as a 
shutter 13 and an attenuator 14. From the external beam path components 
12, the beam is delivered through a lens 15 into a fiber-optic coupler 16. 
The beam is then delivered through an optical fiber 17 to a treatment head 
18, which distributes the laser beam output on a body 19. A data processor 
20 is coupled with the laser 10, the external beam path components 12, and 
the treatment head 18 for controlling operation of the system. User 
interface 21 is coupled to the data processor 20, for providing user input 
utilized in controlling the system during treatment. 
Intense light sources other than lasers, such as arc lamps, LEDs, etc., can 
be used as well according to the present invention. 
FIG. 2 provides a schematic illustration of a treatment head 18 which can 
be used in the present invention. This treatment head is similar to that 
described and disclosed in the above-referenced International Publication 
No. WO 87/06478. As can be seen, the fiber 17 enters the treatment head 18 
and is supplied to an aiming bracket 30. The aiming bracket 30 establishes 
a propagation axis along which the laser output 31 from the fiber 17 
proceeds. This aiming bracket 30 is mounted on a mechanism, such as a 
plurality of stepper motors (of which motor 32 is representative), which 
are operative to scan the propagation axis defined by the bracket 30 
through a scan plane transverse to the propagation axis. In the preferred 
system, this plane will be orthogonal to the propagation axis by the 
bracket 30. 
The output 31 from the fiber 17 is supplied through a lens 33 past shutter 
34, beam splitter 35, and through a template 36 to the treatment area. A 
photo detector 37 is coupled with the beam splitter 35 for indicating the 
intensity of the output light. 
The template 36 is mounted on stand-off posts 38, 39 which place the 
template 36 adjacent to the focal plane of the lens 33. 
The lens 33 can be an adjustable lens by which the spot size of the laser 
beam at the template 36 can be adjusted. 
Alternative systems for scanning the propagation axis of the laser beam 
could include galvanometer-mounted mirrors and the like and a wide range 
of other equivalent mechanisms known in the art. 
FIG. 3 illustrates one embodiment of the template 36 according to the 
present invention, and a plurality of treatment patterns numbered 
sequentially 1 through 12. 
As can be seen, the template 36 has a rectangular opening 45 which allows 
passage of a laser beam into a treatment area. The treatment area has been 
for this example divided into twelve lines, where each line is a treatment 
pattern to be scanned by the laser beam. 
In operation, the laser beam is positioned at point 46 on the template body 
36 to begin a treatment. A first treatment pattern is exposed by scanning 
the laser beam at essentially constant velocity along line 47 across the 
opening in the template 36 until the laser beam falls outside the opening. 
Next, the laser beam is positioned for a second treatment pattern at point 
48. From point 48 the beam is scanned at an essentially constant velocity 
across the opening until the propagation axis directs the beam outside the 
opening 45. These line-shaped treatment patterns are successively scanned 
in the order illustrated, where each sequential treatment pattern is 
non-adjacent to the next treatment pattern in the sequence. Thus, as can 
be seen, treatment patterns 1, 2, 3, 4, 5, and 6 are spaced apart from one 
another. Treatment pattern 7 is between patterns 1 and 2. Treatment 
pattern 8 is between patterns 2 and 3. Treatment pattern 9 is between 
patterns 3 and 4. Treatment pattern 10 is between pattern 4 and 5. 
Treatment pattern 11 is between patterns 5 and 6. Finally, treatment 
pattern 12 is between the pattern 6 and the edge of the template 36. 
By controlling the intensity of the laser beam and the velocity of scanning 
of the beam across the treatment patterns, the fluence level throughout 
the entire treatment area can be precisely controlled, and a uniform 
distribution of laser energy can be produced. The laser beam can be left 
on while it is irradiating the template area during repositioning, or it 
can be turned off using the shutter 34, or the shutter 13 in the external 
beam path 12. Also, the beam can be turned off using a Q-switch within the 
laser system itself 10, or other apparatus known in the art. Further, the 
effect of the template can be achieved by proper timing of the shutter. 
The precise control of the fluence level is illustrated with reference to 
FIGS. 4 and 5. FIG. 4 is a graph of the temperature (trace 100) and 
fluence (trace 101) level versus scan direction for a particular treatment 
pattern, e.g. pattern 1, which correlates with the coordinate axes 
illustrated in FIG. 3. As can be seen, the fluence for a beam which is 
scanned at an essentially constant velocity with constant intensity across 
the treatment pattern begins centered at approximately -1 beam diameters 
at the beginning of the treatment pattern, rises to a constant level 
F.sub.T approximately one half beam diameter before getting into the 
treatment pattern, and continues at the constant value F.sub.T until 
approximately one half beam diameter after the end of the treatment 
pattern. This insures a constant fluence level. At the end of the 
treatment pattern on the edge of the template, the transmitted fluence 
level drops to 0. The treatment temperature T.sub.T induced by this 
constant fluence level rises rapidly after the edge 102 of the template to 
the preferred level and remains constant to the opposite edge 103 of the 
template. 
As can be seen, a scan of an essentially constant velocity allows for very 
even distribution of fluence through a treatment pattern. So long as all 
of the changes in velocity of the scan, such as occur at turns or when the 
scan is stopped, occur outside the treatment area on the template or after 
the shutter is closed, the fluence level in a treatment pattern can be 
very precisely, and evenly distributed. 
For temperature sensitive treatments, such as the treatment of planar 
angiomas, is desirable to insure that the temperature reached by the 
entire treatment area is essentially constant, and does not exceed levels 
which would cause scarring or other damage to the tissue. Therefore, the 
treatment patterns used to fill the treatment area, are scanned in a 
manner so that each successive treatment pattern is not adjacent to a next 
treatment pattern. The thermal effect of this spacing of treatment 
patterns is illustrated in FIG. 5, where a cross-section of the 
temperature caused by successive scans is illustrated heuristically. The 
graph of FIG. 5 includes a first temperature axis which shows the 
temperature profiles of the scans 1, 2, 3 and so on, and a second 
temperature axis which shows the temperature profiles of the scans 7, 8, 
and 9. It can be seen that for scan number 1, the temperature begins at a 
constant value and rises to the temperature of treatment T.sub.T very 
quickly within the width of the treatment pattern. At the edge of the 
treatment pattern, it falls off back to the body temperature. The next 
treatment pattern, number 2, causes an elevated temperature which does not 
overlap with the elevation in temperature caused by treatment pattern 
number 1. A similar effect occurs with treatment pattern number 3. As can 
be seen, elevated temperature is reached in areas outside the directly 
exposed scan pattern, due to heat conduction and scattering of the beam. 
However, treatment pattern number 7 on the second pass through the 
treatment area, fills the area which was left untreated between treatment 
pattern numbers 1 and 2. A similar effect occurs with patterns 8 and 9 and 
so on. 
These patterns 7, 8, and 9 are scanned after the temperature in the edges 
of the regions reached during the previous scans 1, 2, 3, has relaxed 
substantially. This effect allows the entire treatment area to be brought 
to the preferred treatment temperature T.sub.T, and insures that no area 
reaches a temperature which is too high due to elevated temperature 
generated in a previous treatment pattern. 
Because the treatment patterns illustrated in FIG. 3 are essentially 
straight lines having a finite width, they can be easily fitted together 
in a way which avoids leaving areas underexposed or overexposed. 
The treatment pattern illustrated with respect to FIG. 3 provides that the 
scan direction for each treatment pattern will alternate, such that 
treatment pattern number 1 is scanned from left to right, while treatment 
pattern number 2 is scanned from right to left and so on. If the effects 
of the reduced temperatures at the beginning of a treatment pattern are 
critical, the treatment patterns can all be scanned in the same direction, 
so that the boundary of the uniform fluence level is more continuous. 
The template 36 illustrated with respect to FIGS. 3 and 4 is rectangular in 
shape. However, these templates can be designed in a variety of shapes to 
meet the needs of a particular laser treatment. Furthermore, the intensity 
of the laser beam, the rate of scanning and the positioning of the various 
treatment patterns within the template can be precisely controlled with 
the data processing system. 
Thus, one method of the present invention for distributing a constant 
fluence level of laser radiation in a treatment includes: 
(1) providing a template having an opening defining an outside dimension of 
a treatment region; 
(2) directing a laser beam along a propagation axis through the template; 
and 
(3) scanning the propagation axis of the laser beam at a controlled scan 
velocity so that the laser beam essentially continuously scans a treatment 
pattern within the template. 
The treatment pattern can either completely fill the template, or the step 
of scanning can be successively repeated so that the laser beam scans a 
plurality of essentially continuously scanned treatment patterns to fill 
the treatment region. The distribution of temperature caused by the laser 
scanning can be controlled further by positioning successively scanned 
treatment patterns so that a first sequential treatment pattern is 
positioned non-adjacent to a next sequential treatment pattern. 
The step of scanning can be computer controlled so that it includes turning 
on the laser beam while the propagation axis directs the laser beam 
outside of the opening of the template, scanning the propagation axis at a 
constant velocity across the opening while the laser beam is on until the 
laser beam is directed outside of the opening, and while the laser beam is 
directed outside of the opening, repositioning the propagation axis of the 
laser beam for a successive treatment pattern. 
Another method of the present invention for distributing a constant fluence 
level include: 
(1) directing a laser beam aiming device to direct a laser beam along a 
propagation axis toward a treatment region; 
(2) beginning to scan the propagation axis and then enabling the laser beam 
by opening a shutter or other technique, at a controlled position in the 
treatment region while the propagation axis is being scanned; and 
(3) continuously scanning the propagation axis of the laser beam at a 
controlled scan velocity so that the laser beam essentially continuously 
scans a treatment pattern within the treatment region, and then closing 
the shutter or disabling the laser beam while the propagation axis is 
being scanned. 
This process can be successively repeated until the laser beam scans a 
plurality of essentially continuously scanned treatment patterns to fill 
the treatment region. The treatment pattern will have a width of at least 
one beam diameter, and a length of more than one, and preferably many, 
beam diameters. Further, the treatment patterns used to fill a treatment 
region can take a variety of shapes as suits the needs of a particular 
situation. 
According to this technique, the need for a template is minimized, and the 
shape of the outside dimensions of the treatment region can be precisely 
controlled using a computer. It is desirable to have the propagation axis 
being scanned when the laser beam is enabled so that the beam does not 
overexpose or underexpose the starting point of the scan. 
FIGS. 6 and 7 illustrate alternative treatment patterns which can be 
utilized according to the present invention. 
In FIG. 6, the treatment pattern is essentially a spiral. By shutter 
control or Q-switch control of the laser light the spiral provides for 
placing sequential scans 1-5 of the beam non-adjacent previous scans. The 
spiral can be effectively used to provide a constant fluence level within 
a treatment area. 
FIG. 7 illustrates a treatment pattern consisting of concentric rings 
having respective radii and radial width. The concentric rings could be 
scanned such that rings 1, 3 and 5 are scanned in a first pass, and rings 
2 and 4 are scanned in a second pass to insure that sequential treatment 
patterns are non-adjacent. 
This computer controlled scanning technique for treatment of 
dermatology-related disorders with a consistent fluence level throughout 
the treatment area provides significant advantages over the prior art. It 
allows for the shape of the treatment area to be precisely controlled, 
while insuring a constant fluence level which entirely fills the treatment 
area. With computer control, the intensity and scan velocity can be 
precisely controlled so that the fluence level actually distributed 
throughout the treatment area can be selected over a wide range with high 
accuracy and uniformly distributed. 
The preferred laser 10 for dermatological applications such as the 
treatment of planar angiomas is a Nd:YAG laser providing a 
frequency-doubled output of 532 nanometers or 659 nanometers, such as is 
commercially available from Laserscope Corp. in San Jose, Calif. Also, 
other laser systems such as argon ion lasers, dye lasers, or copper vapor 
lasers commonly used in dermatology applications can be utilized. 
The foregoing description of preferred embodiments of the present invention 
has been provided for the purposes of illustration and description. It is 
not intended to be exhaustive or to limit the invention to the precise 
forms disclosed. Obviously, many modifications and variations will be 
apparent to practitioners skilled in this art. The embodiments were chosen 
and described in order to best explain the principles of the invention and 
its practical application, thereby enabling others skilled in the art to 
understand the invention for various embodiments and with various 
modifications as are suited to the particular use contemplated. It is 
intended that the scope of the invention be defined by the following 
claims and their equivalents.