U.S. patent application number 17/535182 was filed with the patent office on 2022-05-26 for apparatus and method for enhancing laser beam efficacy in a liquid medium.
The applicant listed for this patent is LUMENIS LTD.. Invention is credited to Hernan Altman.
Application Number | 20220166178 17/535182 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-26 |
United States Patent
Application |
20220166178 |
Kind Code |
A1 |
Altman; Hernan |
May 26, 2022 |
APPARATUS AND METHOD FOR ENHANCING LASER BEAM EFFICACY IN A LIQUID
MEDIUM
Abstract
The present disclosure generally relates to the field of laser
based medical devices. Particularly, but not exclusively, the
present disclosure relates to an apparatus and method for enhancing
laser beam efficacy in a liquid medium. In many embodiments, laser
pulses are modulated based on bubble dynamics to improve energy
delivery to a target. A variety of exemplary pulse modulation
scheme are described including modulating pulse power down during
expansion of an index bubble and modulating pulse power up during
collapse of the index bubble.
Inventors: |
Altman; Hernan; (Kyriat
Tivon, IL) |
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Applicant: |
Name |
City |
State |
Country |
Type |
LUMENIS LTD. |
Yokneam |
|
IL |
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|
Appl. No.: |
17/535182 |
Filed: |
November 24, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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63118117 |
Nov 25, 2020 |
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63118857 |
Nov 27, 2020 |
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63252830 |
Oct 6, 2021 |
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International
Class: |
H01S 3/067 20060101
H01S003/067; H01S 3/02 20060101 H01S003/02 |
Claims
1. A system, comprising: a fiber laser; and a controller comprising
a processor and memory, the memory comprising instructions that
when executed by the processor cause the processor to: determine a
pulse energy for the fiber laser; identify a distance between a tip
of the fiber laser and a target, wherein a liquid is located
between the tip of the fiber laser and the target; determine a
modulation scheme based on the distance; set an initial pulse power
for the modulation scheme to generate an index bubble in the liquid
based on the distance; and initiate a pulse according to the
modulation scheme via the fiber laser, wherein the modulation
scheme reduces power of the pulse after initiation of the pulse at
the initial pulse power.
2. The system of claim 1, wherein the modulation scheme increases
power of the pulse to a maximal system power level at a time
estimated for the index bubble to reach maximal size.
3. The system of claim 2, wherein the instructions, when executed
by the processor, further cause the processor to estimate the time
the index bubble takes to reach maximal size based on the initial
pulse power and an absorption coefficient of the liquid at a
wavelength of the fiber laser.
4. The system of claim 1, wherein the instructions, when executed
by the processor, further cause the processor to: identify an
updated distance between the tip of the fiber laser and the target;
and determine an updated modulation scheme based on the updated
distance.
5. The system of claim 1, wherein the modulation scheme is
configured to modulate pulse power down during expansion of the
index bubble and modulate pulse power up during collapse of the
index bubble.
6. The system of claim 1, wherein the modulation scheme comprises
an initial modulation frequency and the instructions, when executed
by the processor, further cause the processor to determine the
initial modulation frequency based on a time to collapse of the
index bubble, a time for the index bubble to reach maximum size,
and a time from lasing initiation to start of bubble formation.
7. The system of claim 1, wherein the instructions, when executed
by the processor, further cause the processor to set the initial
pulse power for the modulation scheme to generate the index bubble
in the liquid based on the distance and the pulse energy.
8. The system of claim 1, wherein the instructions, when executed
by the processor, further cause the processor to integrate the
power of the pulse with respect to time and terminate the pulse
when the integral of the power of the pulse with respect to time
equals the pulse energy.
9. The system of claim 1, wherein the instructions, when executed
by the processor, further cause the processor to classify the
target as distant target based on the distance and set the initial
pulse power to a maximal system power level based on classification
of the target as distant.
10. The system of claim 9, wherein the modulation scheme is
configured obtain a resonant effect by cycling at periods between
0.7 and 1.3 times a time from start to collapse of the index
bubble.
11. At least one non-transitory computer-readable medium comprising
a set of instructions that, in response to being executed by a
processor circuit, cause the processor circuit to: determine a
pulse energy for a fiber laser; identify a distance between a tip
of the fiber laser and a target, wherein a liquid is located
between the tip of the fiber laser and the target; determine a
modulation scheme based on the distance; set an initial pulse power
for the modulation scheme to generate an index bubble in the liquid
based on the distance; and initiate a pulse according to the
modulation scheme via the fiber laser, wherein the modulation
scheme reduces power of the pulse after initiation of the pulse at
the initial pulse power.
12. The at least one non-transitory computer-readable medium of
claim 11, wherein the modulation scheme increases power of the
pulse to a maximal system power level at a time estimated for the
index bubble to reach maximal size.
13. The at least one non-transitory computer-readable medium of
claim 12, wherein the set of instructions, in response to execution
by the processor circuit, further cause the processor circuit to
estimate the time the index bubble takes to reach maximal size
based on the initial pulse power and an absorption coefficient of
the liquid at a wavelength of the fiber laser.
14. The at least one non-transitory computer-readable medium of
claim 11, wherein the set of instructions, in response to execution
by the processor circuit, further cause the processor circuit to:
identify an updated distance between the tip of the fiber laser and
the target; and determine an updated modulation scheme based on the
updated distance.
15. The at least one non-transitory computer-readable medium of
claim 11, wherein the set of instructions, in response to execution
by the processor circuit, further cause the processor circuit to
set the initial pulse power for the modulation scheme to generate
the index bubble in the liquid based on the distance and the pulse
energy.
16. The at least one non-transitory computer-readable medium of
claim 11, wherein the set of instructions, in response to execution
by the processor circuit, further cause the processor circuit to
integrate the power of the pulse with respect to time and terminate
the pulse when the integral of the power of the pulse with respect
to time equals the pulse energy.
17. A method, comprising: determining a pulse energy for a fiber
laser; identifying a distance between a tip of the fiber laser and
a target, wherein a liquid is located between the tip of the fiber
laser and the target; determining a modulation scheme based on the
distance; setting an initial pulse power for the modulation scheme
to generate an index bubble in the liquid based on the distance;
and initiating a pulse according to the modulation scheme via the
fiber laser, wherein the modulation scheme reduces power of the
pulse after initiation of the pulse at the initial pulse power.
18. The method of claim 17, comprising modulating pulse power down
during expansion of the index bubble and modulating pulse power up
during collapse of the index bubble.
19. The method of claim 17, comprising classifying the target as
distant target based on the distance and set the initial pulse
power to a maximal system power level based on classification of
the target as distant.
20. The method of claim 19, comprising cycling at periods between
0.7 and 1.3 times a time from start to collapse of the index
bubble.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn. 119 to U.S. Provisional Patent Application No.
63/118,117, titled "Apparatus and Method for Enhancing Laser Beam
Efficacy in a Liquid Medium", filed on Nov. 25, 2020, the entirety
of which is incorporated herein by reference.
[0002] This application claims the benefit of priority under 35
U.S.C. .sctn. 119 to U.S. Provisional Application No. 63/118,857,
titled "Method and System for Estimating Distance Between a Fiber
End and a Target", filed on Nov. 27, 2020, the entirety of which is
incorporated herein by reference.
[0003] This application claims the benefit of priority under 35
U.S.C. .sctn. 119 to U.S. Provisional Patent Application No.
63/252,830, titled "Method and System for Estimating Distance
Between a Fiber End and a Target", filed on Oct. 6, 2021, the
entirety of which is incorporated herein by reference.
TECHNICAL FIELD
[0004] The present disclosure generally relates to the field of
laser based medical devices. Particularly, but not exclusively, the
present disclosure relates to an apparatus and method for enhancing
laser beam efficacy in a liquid medium.
BACKGROUND
[0005] Lasers are widely used for performing various medical
treatments such as tissue coagulation, ablation, cutting,
fragmenting, dusting and enucleation. Laser treatments are
conducted through and within various mediums and environments such
as gases, solids, and liquids. During laser treatments, the
interaction between the laser radiation and a target object (e.g.,
body tissue such as prostate, kidney, or urinary stones), depends
on the laser used and, among other things, on the absorption,
reflection, and dispersion of the environment and the target
object. Ureteral stones, kidney stones, or prostate are only three
examples of common targets which may be treated by a laser.
Typically, the treatment environment may be saline or other similar
liquids. The efficiency of laser treatment may be a function of the
interaction between the laser energy and target. The portion of the
laser energy that reaches and is absorbed by the target contributes
to the required surgical effect. However, the laser energy absorbed
by the environment medium can be considered lost energy, which is
no longer available for target treatment. Oftentimes, laser
parameters, such as wavelength, may be selected based on the
desired clinical effect and the characteristics of the target. For
example, infrared (IR) lasers, such as Holmium or Thulium, may be
used for laser lithotripsy to treat ureteral stones, renal colic
and for prostate ablation or enucleation.
BRIEF SUMMARY
[0006] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to
necessarily identify key features or essential features of the
claimed subject matter, nor is it intended as an aid in determining
the scope of the claimed subject matter.
[0007] In one aspect, the present disclosure relates to a system,
comprising a fiber laser and a controller. The controller may
include a processor and memory. The memory may include instructions
that when executed by the processor cause the processor to perform
one or more of: determine a pulse energy for the fiber laser;
identify a distance between a tip of the fiber laser and a target,
wherein a liquid is located between the tip of the fiber laser and
the target; determine a modulation scheme based on the distance;
set an initial pulse power for the modulation scheme to generate an
index bubble in the liquid based on the distance; and initiate a
pulse according to the modulation scheme via the fiber laser,
wherein the modulation scheme reduces power of the pulse after
initiation of the pulse at the initial pulse power.
[0008] In some embodiments, the modulation scheme increases power
of the pulse to a maximal system power level at a time estimated
for the index bubble to reach maximal size. In some such
embodiments, the instructions, when executed by the processor,
further cause the processor to estimate the time the index bubble
takes to reach maximal size based on the initial pulse power and an
absorption coefficient of the liquid at a wavelength of the fiber
laser.
[0009] In various embodiments, the instructions, when executed by
the processor, further cause the processor to identify an updated
distance between the tip of the fiber laser and the target; and
determine an updated modulation scheme based on the updated
distance.
[0010] In several embodiments, the modulation scheme is configured
to modulate pulse power down during expansion of the index bubble
and modulate pulse power up during collapse of the index
bubble.
[0011] In many embodiments, the modulation scheme comprises an
initial modulation frequency and the instructions, when executed by
the processor, further cause the processor to determine the initial
modulation frequency based on a time to collapse of the index
bubble, a time for the index bubble to reach maximum size, and a
time from lasing initiation to start of bubble formation.
[0012] In some embodiments, the instructions, when executed by the
processor, further cause the processor to set the initial pulse
power for the modulation scheme to generate the index bubble in the
liquid based on the distance and the pulse energy.
[0013] In various embodiments, the instructions, when executed by
the processor, further cause the processor to integrate the power
of the pulse with respect to time and terminate the pulse when the
integral of the power of the pulse with respect to time equals the
pulse energy.
[0014] In several embodiments, the instructions, when executed by
the processor, further cause the processor to classify the target
as distant target based on the distance and set the initial pulse
power to a maximal system power level based on classification of
the target as distant. In several such embodiments, the modulation
scheme is configured obtain a resonant effect by cycling at periods
between 0.7 and 1.3 times a time from start to collapse of the
index bubble.
[0015] In another aspect, the present disclosure relates to at
least one non-transitory computer-readable medium comprising a set
of instructions that, in response to being executed by a processor
circuit, cause the processor circuit to perform one or more of:
determine a pulse energy for a fiber laser; identify a distance
between a tip of the fiber laser and a target, wherein a liquid is
located between the tip of the fiber laser and the target;
determine a modulation scheme based on the distance; set an initial
pulse power for the modulation scheme to generate an index bubble
in the liquid based on the distance; and initiate a pulse according
to the modulation scheme via the fiber laser, wherein the
modulation scheme reduces power of the pulse after initiation of
the pulse at the initial pulse power.
[0016] In some embodiments, the modulation scheme increases power
of the pulse to a maximal system power level at a time estimated
for the index bubble to reach maximal size. In some such
embodiments, the set of instructions, in response to execution by
the processor circuit, further cause the processor circuit to
estimate the time the index bubble takes to reach maximal size
based on the initial pulse power and an absorption coefficient of
the liquid at a wavelength of the fiber laser.
[0017] In various embodiments, the set of instructions, in response
to execution by the processor circuit, further cause the processor
circuit to: identify an updated distance between the tip of the
fiber laser and the target; and determine an updated modulation
scheme based on the updated distance.
[0018] In several embodiments, the set of instructions, in response
to execution by the processor circuit, further cause the processor
circuit to set the initial pulse power for the modulation scheme to
generate the index bubble in the liquid based on the distance and
the pulse energy.
[0019] In many embodiments, the set of instructions, in response to
execution by the processor circuit, further cause the processor
circuit to integrate the power of the pulse with respect to time
and terminate the pulse when the integral of the power of the pulse
with respect to time equals the pulse energy.
[0020] In yet another aspect, the present disclosure may include a
method comprising one or more of determining a pulse energy for a
fiber laser; identifying a distance between a tip of the fiber
laser and a target, wherein a liquid is located between the tip of
the fiber laser and the target; determining a modulation scheme
based on the distance; setting an initial pulse power for the
modulation scheme to generate an index bubble in the liquid based
on the distance; and initiating a pulse according to the modulation
scheme via the fiber laser, wherein the modulation scheme reduces
power of the pulse after initiation of the pulse at the initial
pulse power.
[0021] In some embodiments, the method includes modulating pulse
power down during expansion of the index bubble and modulating
pulse power up during collapse of the index bubble.
[0022] In various embodiments, the method includes classifying the
target as distant target based on the distance and set the initial
pulse power to a maximal system power level based on classification
of the target as distant. In various such embodiments, the method
includes cycling at periods between 0.7 and 1.3 times a time from
start to collapse of the index bubble.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Non-limiting embodiments of the present disclosure are
described by way of example with reference to the accompanying
figures, which are schematic and not intended to be drawn to scale.
In the figures, each identical or nearly identical component
illustrated is typically represented by a single numeral. In will
be appreciated that various figures included in this disclosure may
omit some components, illustrate portions of some components,
and/or present some components as transparent to facilitate
illustration and description of components that may otherwise
appear hidden. For purposes of clarity, not every component is
labeled in every figure, nor is every component of each embodiment
shown where illustration is not necessary to allow those of
ordinary skill in the art to understand the disclosure. In the
figures:
[0024] FIG. 1 illustrates an exemplary diagram of pulses of a
Holmium laser and a Thulium laser according to one or more
embodiments described herein.
[0025] FIGS. 2A and 2B illustrate various aspects of Holmium laser
short pulses in different mediums according to one or more
embodiments described herein.
[0026] FIGS. 3A and 3B illustrate various aspects of Thulium laser
long pulses in different mediums according to one or more
embodiments described herein.
[0027] FIG. 4A illustrates an exemplary diagram of a Thulium laser
long pulse in an air medium according to one or more embodiments
described herein.
[0028] FIG. 4B illustrates an exemplary diagram of a Thulium laser
long pulse in a liquid medium according to one or more embodiments
described herein.
[0029] FIG. 5 illustrates an exemplary time series of images of
bubble dynamics according to one or more embodiments described
herein.
[0030] FIG. 6 illustrates an exemplary diagram of laser power
modulated in relation to bubble size according to one or more
embodiments described herein.
[0031] FIG. 7 illustrates an exemplary diagram of modulated and
unmodulated laser pulses in conjunction with associated bubble
dynamics according to one or more embodiments described herein.
[0032] FIG. 8 illustrates an exemplary diagram of a modulated laser
pulse in conjunction with associated bubble dynamics according to
one or more embodiments described herein.
[0033] FIG. 9 illustrates an exemplary laser system according to
one or more embodiments described herein
[0034] FIG. 10 illustrates an exemplary process flow according to
one or more embodiments described herein.
[0035] FIG. 11 illustrates a block diagram of a method for
implementing embodiments consistent with the present
disclosure.
[0036] FIG. 12 illustrates a block diagram of an exemplary computer
system for implementing embodiments consistent with the present
disclosure.
DETAILED DESCRIPTION
[0037] The present disclosure provides medical devices and
techniques for enhancing laser beam efficacy in a liquid medium,
such as for a desired surgical effect on a target. The liquid
environment of many treatment environments tends to absorb a
significant portion of laser energy. For example, the liquid medium
can absorb and attenuate the laser energy, leaving less energy
available for the desired surgical effect on the target.
Additionally, energy absorbed by the liquid medium can heat
surrounding tissue, leading to unwanted safety issues and the need
to irrigate the areas with cooling fluids.
[0038] One laser treatment technique, referred herein as the bubble
path effect, utilizes one or more bubbles to serve as a gaseous
pathway for laser energy to pass from a laser fiber tip to the
target. The resulting gaseous pathway has an absorption coefficient
that is smaller than a liquid pathway. The bubble path effect is
described in more detail in U.S. patent application Ser. Nos.
15/927,143, 16/177,800, 15/861,905, which are incorporated herein
by reference. However, as will be described in more detail below,
bubble dynamics introduce many challenges in establishing and
maintaining a gaseous pathway between a laser fiber tip and a
target to improve laser beam efficacy.
[0039] Accordingly, it is one aspect of the present disclosure to
optimize the available laser energy to treat a target based on an
enhanced bubble path effect for targets which will be discussed in
more detail below. The amount of energy needed to create a bubble
path effect, that is, the creation of an air tunnel between a tip
of an optical (or laser) fiber and a target, is also a function of
the distance between the tip of the fiber and target. Therefore, it
is another aspect of the present disclosure, to reduce the amount
of laser energy which may be wasted to create the bubble path
effect for a specific distance to a tissue target, and thus to
increase the amount of laser energy available to treat the target.
It is yet another aspect of the present disclosure to increase the
distance of the bubble path effect and to reach targets further
away from the laser fiber tip for a specific laser energy.
Utilizing the present disclosure can result in less wasted energy
when treating a tissue at a given distance or allow treating tissue
further distances away from the laser fiber tip for a given level
of energy.
[0040] In some bubble path effect technologies, a first laser pulse
may be provided to create a first bubble through which a second
laser pulse is provided through the bubble after a predefined time
delay. The second laser pulse is transferred with reduced
absorption due to the first bubble (and the relative absence of
fluid) and reaches the tissue with higher energy as compared to
that of a single laser pulse traveling through a liquid medium
only. Furthermore, the energies of the first and second pulse, as
well as the time delay between the two pulses, may be varied to
achieve a higher energy delivery to the tissue, which is present at
various distances from a tip of the laser fiber.
[0041] Infrared lasers, such as Holmium (Ho) lasers, having a
wavelength of 2100 nm and Thulium (Tm) lasers, having a wavelength
in the range of 1940 nm to 1970 nm, are strongly absorbed in a
liquid environment. For example, the photons at 1940 nm wavelength
have an absorption coefficient of 110 [1/cm] and the photons at
2100 nm wavelength have the absorption coefficient of 25 [1/cm].
Typically, in a liquid environment, many of the photons produced by
the Holmium laser are absorbed before the laser pulse travels a
distance of 0.5 mm from where it exits the optical fiber while the
photons produced by the Thulium lasers are absorbed before the
laser pulse travels a distance of 0.1 mm from where it exits the
optical fiber. In comparison, a solid-state Holmium laser is
characterized by high peak power and relatively short pulses, while
a Thulium fiber laser (TFL) is characterized by a lower peak power.
Therefore, it takes a longer time for a TFL, compared to a
solid-state Holmium laser, to generate an equal amount of energy.
For example, a TFL will generate an energy of 0.5 Jules in a pulse
duration of about 1 milliseconds (ms) while it takes about 0.2 ms
for a solid-state Holmium laser to generate the same amount of
energy. As will be further discussed below, it has been observed
that the life cycle of a single bubble lasts about 0.2-0.3 ms.
Moreover, it has been observed that the bubble, once initiated, has
its own dynamic characteristics which is in many aspects unrelated
to the laser pulse (except for the pulse's initial characteristics
at a very short time frame of a few tens of microseconds). Based on
the above, a short solid-state Holmium laser pulse may end before
the bubble will reach its maximum size while a longer TFL pulse
will last 3-4 bubble life cycles. The incorporated references
mentioned above describe how to optimize the timing and the
distribution of energies among the first and subsequent laser
pulses to minimize the energy invested in bubble creation and
maximize the amount of energy that reaches the target. Further, a
Holmium laser with a reduced peak power may be used to extend the
usual short pulse duration.
[0042] However, spreading a Holmium laser pulse energy over a
longer pulse duration, like that in the above-mentioned Thulium
pulse, may result in a pulse duration which is longer than the life
cycle of a single bubble. As in the case with Thulium, a laser
pulse which is longer than the life cycle of a single bubble
results in the creation of a cascade of multiple bubbles. A cascade
of multiple bubbles may create a gaseous pathway to the target.
However, such a bubble cascade is characterized by sequence of
independent bubbles, which expand and collapse at different times
and at different locations along the pathway. As a result, the
effective length of the gaseous pathway changes over time. Gaseous
discontinuations along the pathway, at different times and
locations, are filled with energy absorbing liquid and this will
again increase attenuation of the pulse produced by the laser.
Thus, the energy delivered to the target is frequently interrupted
during these bubble collapses in an unpredictable fashion,
resulting in multiple sub-pulses during the pulse duration and a
significant waste of energy.
[0043] Accordingly, one or more embodiments described herein
provide for effectively and efficiently manage the level of the
laser energy along long laser pulses. In various embodiments,
effective and efficient management of laser energy during long
laser pulses can provide one or more of the following advantages:
(i) laser energy delivered to the target at a given distance is
increased, (ii) laser energy losses while the gaseous pathway to
the target is being built are decreased, and (iii) stabilization of
the pathway over the course of the pulse, as opposed to being
subjected to stochastic collapses with unpredictable energy deliver
results. Many embodiments optimize the energy distribution along
long laser pulses.
[0044] Several embodiments described herein provide to reduce, or
prevent, heat buildup in the surrounding tissues by more
effectively delivering laser energy to a target at lower energy
levels to achieve the same level of treatment. For example, laser
energy may be delivered to a target at 30 W instead of 40 W while
achieving the same level of treatment. Many embodiments may
generate pulses that optimize the delivery of energy through a
water environment. In many such embodiments, when formed, the
optimized pulse may be used to obtain one of the following
benefits: (1) using the same pulse energy to deliver more energy to
the target at a given distance resulting in faster/stronger
intended effect on tissue, such as fragmentation, dusting,
pop-corning, etcetera (improved efficiency/efficacy); (2) using the
same pulse energy to deliver energy to the target at a longer
distance (better action at distance/action at longer distances);
and (3) using a lower pulse energy to obtain the same intended
effect as with a higher pulse energy, thus reducing unintended side
effects and adverse outcomes, such as over-heating of surrounding
tissue (improved safety profile).
[0045] In some embodiments, a laser with low peak-power and long
pulses, such as a TFL, may be utilized so that the total size and
stability of the bubble cascade generated is much longer (along the
fiber axis from the laser fiber tip to the target) than the single
bubble of a typical short pulse laser. Therefore, and unexpectedly,
even though Tm photons have much stronger absorption in water than
Ho, when comparing short pulse Ho to long pulse Tm, the latter
travels further, as it travels through the longer train of bubbles
produced by the TFL. Further, a longer pulse duration takes better
advantage of the cascade of bubbles as the pulse persists while the
bubbles reach the target. However, while it has been observed that
the TFL pulses are severed into several sub-pulses due to the
multiple bubble collapses, resulting in a widely variable energy
delivery during the pulse duration, the Ho laser energy may produce
similar energy delivery.
[0046] As mentioned above, the bubble has its own dynamics, and
once initiated, in many aspects it is no longer related to the
characteristics of the laser pulse. An initial bubble formed by
firing the laser first grows to a maximum size (dependent on the
initial peak power of the pulse), and then collapses. The typical
bubble duration for a Holmium laser is -200-300[.mu.s]. Laser
pulses which are longer than the life cycle of the bubble, create
several bubbles, in a series, emanating from the laser fiber tip
towards the target.
[0047] FIG. 1 illustrates an exemplary diagram 100 of pulses of a
Holmium laser and a Thulium laser according to one or more
embodiments described herein. In the illustrated embodiment, the
Holmium and Thulium lasers have an equal energy of 0.2 Joules.
Diagram 100 illustrates a typical high peak-power Holmium laser
short pulse versus low peak-power quasi-continuous Thulium long
pulse. The diagram 100 includes bubble size on the positive y-axis
102 (with a potential target position at line 112), pulse power on
the negative y-axis 104, and time on the x-axis 106. With respect
to the high peak-power Holmium laser short pulse, area 118
corresponds to the pulse power, curve 108 corresponds to the bubble
created, and line 114 corresponds to the effective distance the
laser pulse travels through liquid. With respect to the low
peak-power quasi-continuous Thulium long pulse, area 120
corresponds to the pulse power, curve 110 corresponds to the bubble
created, and line 116 corresponds to the effective distance the
laser pulse travels through liquid.
[0048] In both cases, after a short delay, on the order of a few
tens of microseconds (.mu.s), following the laser pulse initiation,
a bubble is created and starts to expand. In both cases, the life
cycle of the bubble, once created, appears to have its own internal
dynamics which are not solely related to the laser pulse, and
includes the internal vapor pressure generated in the bubble
enucleation site, which in turn can depend on absorption,
instantaneous peak power, laser beam quality, and/or the presence
and amount of air pockets inside the liquid.
[0049] It takes time for the bubble to expand. In the case of the
Holmium pulse, the bubble reaches its maximum size well after the
highest power peak of the laser and in the case of the Thulium
laser, the bubble reaches its maximum size during the laser pulse.
Also shown in FIG. 1 is that for an exemplary target distance 112
(positioned at a distance of about 3 mm), the effective distance
the Thulium laser pulse can travel through liquid 114 is much
longer than the effective distance the Holmium laser pulse can
travel through liquid 116. Several embodiments described herein
take advantage of the independent dynamics of the bubbles in order
to optimize the energy distribution using a long pulse.
[0050] FIGS. 2A and 2B illustrate exemplary diagrams 200A, 200B of
Holmium laser short pulses in different mediums according to one or
more embodiments described herein. FIG. 2A corresponds to an air
medium and includes diagram 200A of pulse power over time 202 as
measured in the air medium from a distance of 3 mm. FIG. 2B
corresponds to a liquid medium and includes diagram 200B of pulse
power over time 206 as measured in the liquid medium from a
distance of 3 mm. Additionally, FIG. 2B includes a time series of
images of bubble dynamics 204 corresponding to, and shown in
synchrony with, the diagram 200B. In each case a sensor placed
within an air or water pathway can be utilized to sense and record
pulse power over time.
[0051] In the illustrated embodiment, the times series of images of
bubble dynamics 204 were taken using a high-speed camera. As shown
in the times series of images of bubble dynamics 204, a single
index bubble was initiated after a short delay following the
beginning of the laser pulse. Also shown in FIG. 2B is that the
bigger the bubble, the higher amount of laser power reaches the
target, which was a sensor in this exemplary lab setting. The
maximum energy is experienced by the target while the bubble size
(or bubble tunnel size) meets or exceeds the distance to the
target, resulting in only air between the fiber tip and the target.
Once the bubble starts to collapse, less laser power can reach the
target. Also shown in FIG. 2B is that the bubble life cycle is
longer than the laser pulse duration.
[0052] FIGS. 3A and 3B illustrates exemplary diagrams 300A, 300B of
Thulium laser long pulses in different mediums according to one or
more embodiments described herein. FIG. 3A corresponds to an air
medium and includes diagram 300A of pulse power over time 302 as
measured in the air medium from a distance of 2 mm. FIG. 3B
corresponds to a liquid medium and includes diagram 300B of pulse
power over time 306 as measured in the liquid medium from a
distance of 2 mm. Additionally, FIG. 3B includes a time series of
images of bubble dynamics 304 corresponding to, and shown in
synchrony with, the diagram 300B. In FIGS. 3A and 3B, the pulse
powers over time 302, 306 may correspond to an exemplary long pulse
of Thulium laser of 0.2 Joule. In each case a sensor placed within
an air or water pathway is utilized to sense and record pulse power
over time.
[0053] FIGS. 3A and 3B show the very different behavior of a long
laser pulse in contrast to the short laser pulse of FIGS. 2A and
2B. Surprisingly, as shown in diagram 300B, the target in this case
experiences two separate effective laser pulses 308a and 308b,
although only a single long laser pulse was generated. The dynamics
of the cascade of bubbles can provide the explanation. It is only
after the gaseous pathway gets close enough to the target that some
energy reaches the target (in the case of Tm, most energy is
absorbed in water within 0.1 mm). Further, it takes time for the
gaseous pathway to come close enough to the target, and during this
time, no laser power reaches the target. Instead, the laser power
is mainly absorbed by the liquid in the way to the target. As
previously mentioned, energy absorbed by the liquid is not
available to treat the target and may turn into unwanted heating of
surrounding tissues.
[0054] Due to the lower peak power, in comparison to FIGS. 2A and
2B, it takes more time for the gaseous pathway to expand close
enough to the target and for energy to reach the target. Moreover,
in the case of the Thulium laser, which is more absorbed by water
than Holmium, the rising profile of the laser (as well as the
falling time) as experienced by the target is much steeper than it
is in the Holmium case, as can be appreciated by a comparison of
the diagrams 200B and 300B. Many embodiments described herein may
utilize a predetermined pulse energy and a distance to the target
to control and optimize the power modulation along the pulse so
that more laser power is available during an effective pulse
experienced by a target, and less laser power is lost between
effective pulses. In many such embodiments, a user may select the
pulse energy.
[0055] Referring now to the time series of images of bubble
dynamics 304 of FIG. 3B, several of the images (or frames) of the
time series are numbered, 1-23 from left to right. More
specifically, frame #1 shows the tip of the fiber before the
initiation of the laser pulse. Once the laser pulse starts, an
index bubble, shown in frame 2, starts to grow relatively
spherically at the tip of the fiber. As this index bubble continues
to grow, it can be seen in frame 3 and 4 that at its front edge, a
second bubble starts to grow in a forward direction. Moreover,
since this second bubble is an extension of the index bubble, the
high pressure inside the index bubble shapes the second bubble to a
more cylindrical shape. In addition, as pressure is drained from
the index bubble into the second bubble, the index bubble expansion
decreases. The result of these two processes is that most of the
inside pressure in these two bubbles expands mainly forwardly
toward the target as can be seen in frames 5-7.
[0056] At this stage, according to the example, the gaseous pathway
has reached close enough to the target so that the target
experiences the laser power. It is another aspect of the disclosure
to generate an index bubble, to generate a second bubble at the
front edge of the index bubble and to let the index bubble to
inflate and shape the second bubble spontaneously while modulating
down the laser pulse power during that time to a lower level than
the level which is required to initiate the index bubble.
Furthermore, the index bubble at the tip of the fiber tends to
collapse on tip of the fiber itself and may degrade it. As a
result, the laser beam quality may be reduced as well as the
treatment efficiency. The higher the laser power during the
initiation of the index bubble, the higher the internal pressure
inside the index bubble and the stronger the cavitation effect on
the tip of the fiber once the index bubble collapses. Therefore, in
an embodiment of the present disclosure a minimum laser power
needed to initiate an index bubble is used, followed by a decreased
laser power during the expansion of the index bubble while the
laser power is increased again only after the index bubble starts
to collapse to further build additional bubbles and a gaseous
pathway to the target. Reducing the cavitation effect on the tip of
the fiber may delay its degradation.
[0057] Referring now to frame 9, it can be seen that the index
bubble starts to collapse, and the second bubble breaks off and
away from the collapsed index bubble. As seen in next frame 10,
fluid fills up the gap between the separated bubbles, and also
collapsing second bubble, and the collapsing index bubble. As a
result, the target starts to experience a decreased power of laser
until no energy reaches the target around frame 11. Also, in frame
10 and more clearly in frame 11, it can be seen that another index
bubble is initiated and starts to expand at the tip of the fiber.
At this stage, a similar process which was described above
regarding fames 1-5 takes place where the gaseous pathway has to be
rebuilt, and it is only until the pathway reaches close enough to
the target before it starts to experience again an exposure to
laser power in around frame 16.
[0058] Accordingly, many embodiments described herein may modulate
down the laser power once an index bubble has been initiated and
during the buildup of the gaseous pathway to the target. Many such
embodiments thereby optimize the energy distribution along long
pulses to make the bubble path effect more efficient in light of
the independent life cycles of the bubbles.
[0059] FIGS. 4A-4B and FIG. 5 illustrate various aspects of Thulium
long laser pulses according to one or more embodiments described
herein. More specifically, FIG. 4A illustrates an exemplary diagram
400A of a Thulium laser long pulse in an air medium with pulse
power over time 402; FIG. 4B illustrates an exemplary diagram 400B
of a Thulium laser long pulse in a liquid medium with pulse power
over time 404; and FIG. 5 illustrates an exemplary time series of
images of bubble dynamics 500 corresponding to diagram 400B.
[0060] Referring to FIG. 4A, the pulse power over time 402 of a
long Thulium laser pulse, in an air medium, of about 1 ms in
duration and which generates 0.5 Joule as measured from a distance
of 2.5 mm is shown in diagram 400A. The corresponding measurement
in a liquid medium is shown in FIG. 4B. The pulse of FIGS. 4A and
4B are longer than the pulse shown in FIGS. 3A and 3B. As such, the
target experiences 4 effective laser "sub-pulses" 406a, 406b, 406c,
406d, as shown in FIG. 4B, as opposed to the two effective laser
"sub-pulses" 308a, 308b discussed in relation to FIG. 3B. As
previously mentioned, and shown in FIG. 4A, the laser is
quasi-continuously on for about 1 ms. However, effectively, a
target in this example, experiences four separated laser sub-pulses
406a, 406b, 406c, 406d. These four separated effective laser pulses
406a, 406b, 406c, 406d are the result of the creation and
destruction of the gaseous pathways during the time that the laser
is on. Several embodiments described herein may modulate the power
of the laser down during the time that the gaseous pathways are
built, thereby allowing the spontaneous expansion of the bubbles,
and saving laser energy until the gaseous pathway is close enough
to the targe tissue. Further, when a gaseous pathway is close
enough to a target, embodiments may modulate the laser power up and
the utilize the gaseous pathway to bring higher amounts of laser
power to the target.
[0061] Providing further laser energy during bubble expansion may
waste energy because the bubble will not grow further in size
during the initial pulse energy applied, since that would mean
"pushing against air" within the bubble. In other words, there may
be no further absorption within the bubble after it starts
expanding. To increase the size of the bubble until the target is
reached, laser energy may be expended only while there is liquid in
the path from the laser fiber tip to the target so that the
resulting absorption is translated into pressure which in
re-expands the bubble. Then, when the gaseous pathway starts to
break down and develop liquid bridges between separated gaseous
pockets, to modulate the laser power down again until the next
opportunity to deliver higher laser power to the target through
another effective gaseous pathway. FIG. 5 shows the images of the
bubbles cascade dynamics discussed above in relation to the FIG.
4B.
[0062] A Thulium Fiber Laser (TFL) is typically pumped by a diode
laser to create long pulses. Further, a TFL produces a long pulse
regime. Accordingly, one or more embodiments described herein may
leverage the fact that the time constants associated with bubble
formation, initiation, expansion, and collapse are shorter than the
laser pulse lengths to modify the pulse power during long laser
pulses. In contrast, short pulse lasers are usually pumped by flash
lamps, which themselves operate in very short pulse regimes. Short
pulse lasers operate in a domain in which the bubble life cycle is
longer than the laser pulse length. However, embodiments described
herein provide a variety of lasers arranged to emit light having a
high absorption coefficient in the relevant liquid and which may
generate pulses that are longer than the life cycle of the bubble,
and further which may be modulated up and down. For example, one or
more of Yttrium Aluminum Garnet (YAG), Erbium, Holmium, and other
IR diode or solid state lasers may be modulated up and down
according to the present disclosure without departing from the
scope.
[0063] Various embodiments described herein may utilize a distance
between the tip of the optical fiber and the target to determine a
mode of operation. For example, there could be two (or more)
different scenarios or settings, which might be selected (often
automatically by the laser system) based on the distance from the
tip of the optical fiber and the target. In a first example
scenario, the index bubble expands to a large enough distance and
gets close enough to the target for delivery of laser energy. In a
second example scenario, the expansion of the index bubble alone is
not enough to get close enough to the target and at least a second
bubble is required to further expand the gaseous pathway before the
target may be treated. In the first scenario, and in accordance
with the present disclosure (e.g., see various V-shape techniques
described below), once the index bubble is created, the power of
the laser is modulated down until the index bubble gets close
enough to the target. Once the index bubble gets close enough to
the target, the power of the laser is modulated up to treat the
target. In the second scenario, and in accordance with the present
disclosure (e.g., see various resonant modulation techniques
described below), once the index bubble is generated the laser
power is modulated down and it is modulated up again to treat the
target once the second or third bubble reaches the target and when
the gaseous pathway starts to break the laser power is modulated
back down.
[0064] As discussed above, different wavelength and types of laser
emissions have different absorption coefficients in a liquid
working environment. Therefore, to be "close enough" to a target is
a function of the laser and may represent different distances for
different lasers. As discussed above in relation to FIGS. 3B and
4B, the slope of the rising profile of an effective laser pulse a
target experiences, is also a reflection of this distance. For
example, a Thulium laser is absorbed more strongly in the liquid
than a Holmium laser. Accordingly, only when the gaseous pathway
reaches a distance to the target in a magnitude close to that a
Thulium laser photons can travel in the liquid, the target may
start to experience some laser power impact. However, since Holmium
laser photons may travel in the liquid environment a longer
distance than Thulium, the slope of the rising effective laser
pulse is less steep. It follows that a close enough distance to a
target for a Thulium laser is a shorter distance than it is for a
Holmium laser. Since this disclosure may be realized and practiced
by different lasers, it will be appreciated that the notion of
being close enough is a function of the laser used and the distance
its photons can travel in the liquid environment.
[0065] Bubble dynamics generally have two phases, expansion
followed by collapse. Further, this dynamic has its own time
constants. During this bubble expansion, in which the bubble
expands, further delivery of laser pulse power (power=rate of
energy) appears not to effectively act on the bubble itself, as
there is nothing inside the bubble to push against (i.e. there is
no or very few absorption media inside the bubble).
[0066] Thinking of the harmonics of the operation of a
playground-type swing as an analogy, in order to effectively
increase the swing's amplitude, the "pushing" frequency should be
matched to the swing's natural frequency. In other words, a pulse
will be most effective at increasing bubble size if it is
"resonant" with the bubble natural frequency (f.about.1/200[us]
.about.5000 [Hz]). Accordingly, various embodiments described
herein may modulate laser pulses based on the natural frequency of
a bubble.
[0067] In various embodiments, laser pulses may be modulated based
on the natural frequency of a bubble as follows. A quasi-continuous
wave (QCW) laser that is suitable to also being powered up and down
during a long quasi-continuous pulse may be used, such as a TFL. In
many embodiments, powering up and down during quasi-continuous
pulses may be accomplished by generating fluctuating power. Further
the fluctuating power may be generated by driving the pumping laser
sources at variable currents while integrating over time to deliver
a requested pulse energy (PE). In various embodiments, the overall
integral of the modulated power over time equals the requested PE
as defined by the user. According to some embodiments, power may be
at its highest at the start of the pulse, for example, at the
maximum power deliverable by the system.
[0068] Once an index bubble is initiated, the power may preferably
then be reduced until the bubble is at its max size, thus providing
a "reserve" of laser energy that may be better utilized to impact
the target once the gaseous pathway gets close enough to the
target. At the time the bubble starts to collapse, power may
preferably be fluctuated back to its maximum level. This should be
repeated in cycles, with a period approximately or substantially
equal to the bubble lifetime.
[0069] Since in some cases the target may move (in the case of a
kidney stone for example) or, even if the target is more or less
stationary with respect to the laser fiber tip, the distance
between the laser fiber tip and the target may differ depending on
the anatomy of the person or the practical access to the target by
the laser fiber tip, or destruction of the target during a
procedure. Accordingly, the power fluctuation technique may be
varied based on the distance between the laser fiber tip and the
target. For example, when the distance to a target is changed
(e.g., due to a movement of the target and/or the optical fiber,
due to patient anatomy or target changes, or the like) such a
distance change may be measured, monitored, or estimated so that
the power of the laser may be adjusted accordingly on the fly.
Accordingly, when the distance increases/decreases, the system may
recalculate the length of the pulse required to create enough
effective pulses and/or to expose the target to enough laser energy
in order to meet the clinical effect required. For example, with
distant targets, the number of cycles may be increased in order to
provide a clear, stable, liquid free path from the laser fiber tip
to the target.
[0070] FIG. 6 illustrates an exemplary diagram 600 of laser pulse
power modulation 604 in relation to bubble size 602 according to
one or more embodiments described herein. In various embodiments,
diagram 600 includes an exemplary pulse power modulation scheme. A
pulse modulation scheme may include one or more settings, modes,
parameters, characteristics, features, and the like of the pulse,
the environment (e.g., liquid medium, distance), and/or various
components utilized to implement the pulse (see e.g., laser system
900). The pulse power modulation 604 is shown by a sinusoidal-type
pattern shown in the slanted hatched area. In this case, power is
modulated from a high level of 500 W to a low level of 300 W.
According to this aspect of the disclosure, the laser power over
long pulses is modulated in an opposite direction to the bubble
dynamics described above so that when the bubble expands the laser
is modulated down and when the bubble collapses the laser is
modulated up. Embodiments are not limited in this context.
[0071] FIG. 7 illustrates an exemplary diagram 700 of modulated and
unmodulated laser pulses in conjunction with associated bubble
dynamics according to one or more embodiments described herein.
Diagram 700 shows an exemplary comparison between an unmodulated
long laser pulse scheme 704a and its associated bubble dynamics
704b and a modulated long pulse scheme 702a according to the
present disclosure and its associated bubble dynamics 702b. The
diagram 700 includes pulse power on a first y-axis 706, bubble size
on a second y-axis 708, and time on the x-axis 710. In various
embodiments, FIG. 7 may correspond to bubble path resonant
modulation techniques. For instance, the laser pulse may be fit to
bubble dynamics to cause bubble size resonation, leading to
increased energy delivery to a target.
[0072] The flat, unmodulated, long pulse 704a shown in FIG. 7 may
cause a cascade of bubbles which expand and collapse in a
sinusoidal pattern (corresponding to bubble dynamics 704b).
Moreover, the bubbles from the unmodulated pulse 704a grow to about
the same size and collapse to about zero size repeatedly in an
uncontrolled way. In other words, since there is no mechanism to
control or synch the timing and/or location of the bubble collapse
and the laser power pulses there is only random constructive and
destructive interactions. As will be appreciated, the amount of
energy invested in the process is equal to the area below the pulse
power line 704a (the integral of the power over time). However,
when the laser power is modulated in an opposite direction to the
bubble dynamics (see 702a, 702b), energy is saved during the
expansion of the bubble. Further, the higher energy modulation
during bubble collapsing, reduces the pace of collapse, and
accelerates the formation of the next bubble. The accelerated
creation of the second bubble takes place before the previous
bubble collapses to a zero size and vanishes. Therefore, the second
bubble starts from the "shoulders" of the first bubble and reaches
further distance. Accordingly, many embodiments described herein
may utilize a pulse modulation scheme (e.g., 702a) whereby the same
distance reached by the unmodulated pulse 704a is reached while
using less laser energy.
[0073] FIG. 8 illustrates an exemplary diagram 800 according to one
or more embodiments described herein. Diagram 800 shows an
exemplary pulse modulation scheme 810 in conjunction with its
associated bubble dynamics 812. The diagram 800 includes pulse
power on a first y-axis 802, bubble size on a second y-axis 804
(with a target position line 808 at 2 mm), and time on the x-axis
806. In various embodiments, FIG. 8 may correspond to bubble path
resonant modulation techniques. For instance, a target distance may
be utilized to create a correspondingly sized bubble prior to
delivering a pulse burst.
[0074] The pulse modulation 810 illustrated in diagram 800 works in
a counter direction to the bubble size dynamics 812. In this
example, the target is located at a distance of 2 mm from the tip
of an optical fiber (see line 808). As shown in the illustrated
embodiment, since the power of the laser is modulated up when the
bubble size starts to shrink, the bubbles do not collapse to a zero
size, or the collapse is at least reduced. Every successive bubble
is built on the "shoulders" of its previous bubble, creating a step
wise pattern until the gaseous pathway reaches close to the target.
As used herein, close to the target can be taken to mean less than
or equal to a threshold distance. In many embodiments, the
threshold distance may be determined based on one or more of the
wavelength of the laser beam, its associated water absorption
coefficient, and the maximum available power of the laser beam. For
example, the threshold distance may be approximately 0.1 mm when
using a Thulium laser and approximately 0.5 when using a Holmium
laser.
[0075] Once the gaseous pathway is built, the laser power is
switched (or ramped up) to its maximum power (or the power setting
associated with the desired treatment) so that most of the pulse
energy may be delivered to the target. In various embodiments, the
laser energy transfer in a liquid medium may be a function of the
laser pulse shape in the air, the dynamic of the bubble front over
time, and the delay between the initiation of the laser pulse and
the initiation of the bubble.
[0076] While the above discussion has generally been directed to
treating targets at a distance, an alternative pulse modulation
profile to improve energy delivery at relatively nearby target
distances may be the termed as a "V-shape". In various embodiments,
nearby targets may be defined as those located at distances that
can be bridged by the index bubble alone, and distant targets may
be defined as those located at distances which are 2 to 4 times the
size of the index bubble, requiring a "train of bubbles" to deliver
sufficient energy to the target. Different lasers may result in
different index bubble sizes. For example, an index bubble for a
Holmium laser may be approximately between 1 mm and 2 mm and an
index bubble for a Thulium laser may be approximately between 0.5
mm and 1 mm.
[0077] In various embodiments, a V-shape pulse modulation may have
one or more of the following profile characteristics: (a) start
with maximal power to create initial bubble; (b) drop power while
bubble expands; and (c) increase power back to maximum while bubble
is at its maximal size or when the bubble is expected to reach the
target (whichever is shortest). In various embodiments, this
V-shape pulse modulation would result in more efficient energy
delivery than a Holmium laser short mode (which resembles a
downward slope triangle) because it delivers more of the pulse
energy during the expanded phase of the bubble, thus encountering
less water absorption.
[0078] In various embodiments, the laser power and a distance
between the fiber tip and the target may be provided as input for
optimizing the pulse modulation. The index bubble maximal size may
be a function of the instantaneous pulse power during the first few
10 s of microseconds as well as of the wavelength absorption in
water, beam quality, and delivery fiber geometry. Accordingly, for
a given laser and delivery fiber, the bubble dynamics for various
peak powers can be measured, such as in a bench setup. A lookup
table may be created to tabulate the relationship between {peak
power and/or initial power, fiber size, and wavelength} vs. {max
bubble size, time from lasing initiation to start of bubble
formation (t0), time to reach bubble maximum size (tmax), and time
to collapse (tc)}. From this information, the initial modulation
frequency may be obtained as roughly 1/(tc-tmax-t0). Further
insight into modulation frequency dynamic adjustment may be derived
by experimental observation in the bench setup of modulation
frequency change effects on vapor tunnel stability and energy
delivery distance without departing from the scope of this
disclosure. The index bubble size as a function of time may be
strongly dependent on pulse (peak) power and the absorption
coefficient of the liquid at the laser wavelength. Accordingly the
pulse (peak) power and the absorption coefficient of the liquid at
the laser wavelength may be utilized to estimate the time an index
bubble reaches its maximal size and starts to collapse.
[0079] FIG. 9 illustrates an exemplary laser system 900 according
to one or more embodiments described herein. In various
embodiments, laser system 900, or one or more components thereof,
may be utilized to implement one or more of the techniques
described herein, such as one or more of the pulse modulation
schemes. In many embodiments, laser system 900 may be, or include,
a fiber laser. In the illustrated embodiment, laser system 900
includes a laser source 921 capable of producing a laser beam 923,
a controller 922, laser fiber 924 (or optical fiber 924), connector
925, a partially transparent mirror 926A, a partially transferred
mirror 926B, a photodetector 927, and a distance measurement module
929 that utilizes reflected light 928 to dynamically measure the
distance between the tip of the laser fiber 924 a target (not
shown). In various embodiments, a known apparatus (e.g., an
endoscope) may be utilized to introduce the laser fiber 924 into a
body cavity for positioning the tip of the laser fiber 924
proximate to a target, such as a kidney or other urinary tract
stone or a prostate that is to be treated by ablation or
enucleation. One or more components of FIG. 9, or aspects thereof,
may be incorporated into other embodiments of the present
disclosure, or excluded from the described embodiments, without
departing from the scope of this disclosure. For example, distance
measurement module 929 and/or photo detector 927 may be excluded
from laser system 900 without departing from the scope of this
disclosure. Embodiments are not limited in this context.
[0080] The laser source 921 of system 900 may produce the laser
beam 923 which is transmitted through the connector 925 to the
laser fiber 924 and thence to the target. The system also includes
a controller 922. FIG. 9 illustrates schematically one embodiment
of the present invention. Laser system 900 consists of a laser
module 921 and a control unit 922. A laser beam 923 exiting laser
source 921 is configured to reach an optical fiber 924 through
connector 925. Partially transparent mirror 926A located along the
optical path of beam 923 and is configured to reflect, at least a
portion of beam 923 into photodetector module 927. Some of the
backscattered light from a target enters optical fiber 924, passes
through connector 925, and is configured to target partially
transferred mirror 926B and enter into distance measurement module
929. Module 929 is configured to measure the distance between the
tip of optical fiber 924 and a target. Modules 927 and 929 are also
controlled by programmable controller 922. In some embodiments,
during operation, programmable controller unit 922 may receive a
first electrical signal from module 927 indicative of the energy
level of the laser pulse and/or a second electrical signal from
distance measurement module 929 indicative to a distance change
between the tip of optical fiber 924 and a target. In various
embodiments, laser system 900, based on at least one of the first
and second indicative signals, may be configured to adjust one or
more operating parameters, such as the amount of the current
supplied to the laser pumping element to keep energy levels within
target parameters and in accordance with any dynamic change in the
laser performance or the distance to a target. Some aspects of the
system 900 are described in more detail in U.S. Pat. No.
10,231,781, (the '781 patent), the entire disclosure of which is
herein incorporated by reference.
[0081] It will be appreciated that one or more embodiments
described hereby may be implemented without one or more of photo
detector 927 and distance measurement module 929. In some
embodiments, a distance between a fiber tip and a target may be an
expected or predetermined distance. For example, the predetermined
distance may be based on a mode of the laser system. In another
example, the predetermined distance may be based on user input.
Further, in some embodiments, modulation schemes may be selected
based on a mode of operation and/or user input.
[0082] In various embodiments, the controller 922 may include a
processor and memory comprising instructions that when executed by
the processor cause the processor to perform one or more techniques
or aspects described herein. In many embodiments, the controller
922 may initiate and regulate the power emanating from the laser
source 21. In some embodiments, the controller 922 may measuring
the distance from the tip of the laser fiber to the target. In
other embodiments, the distance may be provided as input to the
controller 922. For example, distance measurement module 929 may
provide the distance as input to controller 922. Techniques for
determining distance between the tip of the laser fiber and the
target are described in more detail in U.S. Pat. No. 9,017,316 and
U.S. Provisional Patent Application No. 63/118,857, the entire
disclosures of which are herein incorporated by reference.
Depending on the distance measured, the controller 922 may initiate
and regulate the amount of power which is provided to the laser
fiber, and in the context of the present disclosure, the varying
power configurations (modulation schemes) described herein.
[0083] In many embodiments, the laser system 900 may operate in
different modes for nearby targets and distant targets. As
previously mentioned, for example, V-shape optimization may be
utilized to determine pulse modulation schemes for nearby targets
and resonant modulation optimization may be utilized to determine
pulse modulation schemes for distant targets. In various
embodiments, the controller 922 may determine which optimization
and/or modulation scheme to use based, at least in part, on the
distance to the target.
[0084] For V-shape optimization on nearby targets, the inputs may
include pulse energy and a target at close proximity
("contact"/"close"). As described above, the term "close proximity"
can mean that the target is within a distance from the tip of the
laser fiber 924 that can be bridged by the index bubble alone. In
such a scenario, the initial pulse power may be determined to
deliver a bubble of size approximately (or substantially) 1 to 2
times the distance to the target. Max energy delivery may occur
while the bubble is equal to and larger than the distance to the
target. Accordingly, in some embodiments, bubble size may be
utilized to control an amount of time maximal energy is delivered
to a target. For example, a bubble size approximately two times the
distance to the target may be utilized to deliver maximal energy
for a relatively long period of time and a bubble size
approximately equal to the distance to the target may be utilized
to deliver maximal energy for a relatively short period of time. In
some embodiments, the controller 922 may determine the initial
pulse power. The laser may be fired at the initial pulse power and
then modulated down until the time the bubble is near maximal size.
Then the pulse power may be raised to maximum. In some embodiments,
when the initial pulse power is equal to the max power the system
may start at max power, reduce power during bubble expansion, and
raise to max power again when the bubble is at maximal size.
Finally, the pulse may be terminated when the integral
(power.times.time) is equal to the requested pulse energy. As used
herein, "max power" may not mean the maximum power with which the
laser source can deliver, but instead can mean the power level for
the desired therapy or treatment.
[0085] For resonant modulation optimization on distant targets, the
inputs may include pulse energy and a target at distance
("distance" mode). The initial pulse power may be set at the
maximal system power. For example, controller 922 may set the
initial pulse power to the max level based on classification of a
target as distant based on a distance estimation. The laser may be
fired at the maximal power level and then modulated down during
bubble expansion. The power may be modulated up to max again when
the bubble reaches maximal size. Then the modulation may be cycled
at periods in the range of 0.5 to 1.5 times the bubble
expansion/collapse dynamics (e.g., .times.0.7-.times.1.3 of the
time from start to collapse) to achieve a resonant effect. In
various embodiments, the period may be adjusted for each sequential
bubble in the bubble train, such as due to changes in the distance
to the target. When the train of bubbles is expected to bridge the
distance to the target, the pulse power may be raised to max to
take advantage of minimal liquid being located along the pathway of
the laser between the fiber tip and the target. Finally, the pulse
may be terminated when the integral (power.times.time) is equal to
the requested pulse energy.
[0086] In one embodiment, a method of operating the laser system
900 may include one or more of the following exemplary operational
steps of the laser system 900, which is configured to implement one
or more pulse modulation schemes described herein. Step one, a user
selects the type of fiber in use. According to one embodiment, a
user may select manually a type of fiber to be used in the
treatment. According to another embodiment, an automatic fiber
recognition system may be implemented. Step two, a user may select
the required treatment energy level. The pulse energy defined by
the user for the treatment may be the overall energy expected to be
emitted by the laser system in a modulated pulse. In other words,
and as will be discussed below, the system may be programmed and
configured, using a suitable programmable controller, to set up a
pulse modulation scheme in a way transparent to the user. For
example, the user in this embodiment may not be required to set up
the values for various parameters.
[0087] Step three, a user may select the modulation scheme
repetition rate (e.g., the time between modulated pulses). Step
four, a user may select a desired (average) working distance
between the tip of the fiber and the target tissue. According to
another embodiment, the working distance may be detected by the
system automatically, for example, by using a distance evaluation
technology as described in the U.S. patent application Ser. No.
13/811,926, the entirety of which is incorporated herein by
reference. Step five, based on previously manually loaded or
automatically detected parameters, the system may define
automatically, from a lookup table operatively associated with the
programmable controller or calculates the working values for one or
more of peak power, initial power, fiber size, wavelength, max
bubble size, time from lasing initiation to start of bubble
formation (t0), time to reach bubble maximum size (tmax), and time
to collapse (tc).
[0088] Step six, a pulse may be fired according to the modulation
scheme. In various embodiments, the system may be configured to
measure actual values of each pulse/modulation scheme. In step
seven and eight, the system may be configured to compare the
measured values to the predefined values on step five. Should the
measured parameters deviate from the predefined parameter, the
system automatically corrects such deviation in step nine, and a
new set of working parameters are sent to the programmable
controller which for implementation in the next modulation scheme
by repeating at step six. In this way, the system may maintain the
actual working values within the predefined range. It should be
understood that during step seven, the system may be configured to
measure different parameters which may be related to actual laser
pulse energy.
[0089] For example, according to one embodiment, the system may use
photodetector 927 to measure optical energy output of the
modulation scheme. According to another embodiment, for example,
the system may be configured to measure current or voltage pulses
which are sent to the laser pumping energy source. Therefore, the
feedback loop may be configured to feedback, based on each measured
parameter, whether this is a measured optical value, a measured
current value, a measured voltage value, or any other measured
parameter which is related to a pulse modulation scheme.
[0090] In some embodiments, a method of operating the laser system
900 may be loosely based on FIGS. 3A and 3B of the '781 patent,
accounting, of course, for any differences in the laser source, and
the sequence of laser firings described herein, as illustrated in
the flowchart of FIG. 10.
[0091] FIG. 10 illustrates an exemplary process flow 1000 (or
method 1000) according to one or more embodiments described herein.
In process flow 1000, a subset of operation steps may include
measuring the distance from the laser fiber tip to the target at
block 1002. For example, controller unit 922 can determine a
distance between the tip of the laser fiber 924 and a target. More
specifically, circuitry of controller unit 922 and/or distance
measurement module 929 can execute instructions and/or receive
signals to determine a distance between the tip of the laser fiber
924 and the target. At decision block 1004, if the distance
measured is less than or less than or equal to a distance (D) X,
then the method 1000 can proceed to a V-shape mode; if, however,
the distance D is greater than or greater than or equal to the
distance X, the method can proceed to a modulation mode of
operation. In various embodiments, the distance X may be determined
experimentally and the results recorded in a lookup table which
includes distances as well as other parameters such as the number
of pulses and the power applied to the pulses. It should also be
mentioned that since the target may be mobile in its environment,
such as a kidney stone, the controller may be dynamic in nature and
able to adjust parameters for the laser, including changing from a
V-shape mode to a resonant modulation mode, and vice versa, based
on repeatedly determining the distance D and repeatedly determining
whether the distance D is greater than or less than X. Embodiments
are not limited in this context.
[0092] After the mode is selected (e.g., at block 1006 or block
1020), method 1000 include selecting parameters for the selected
mode. For example, the controller 924 can select the number of
pulses and the energy level to be applied to the target (block
1008, 1022). More specifically, where the V mode is selected at
block 1006, controller 924 can select an energy level of the
pulses; and where the resonant mode is selected at block 1020, the
controller 924 can select an energy level of the pulses and a
modulation frequency for the pulses.
[0093] Continuing to block 1010 and 1024, method 1000 can include
sending control signals to the laser source 921 to cause the laser
source to activate to fire the laser beam (block 1010, 1024),
whereupon the method 1000 includes operations for the controller
924 to calculate the pulse energy delivered to the target (block
1012, 1026). For example, controller 924 can determine (or receive
signals from sensors comprising indications of) pulse energy
delivered to the target. In addition, at blocks 1012 or 1026) the
controller 924 may estimate one or more of the number of effective
pulses to be experienced by a target, the effective energy per
every single effective pulse to be delivered to the target, and the
accumulated effective energy to be delivered to the target by the
number of effective pulses. Moreover, for a selected energy level
as may be selected by a user, the controller 924 can select the
power modulation and bubble path modulation resonant frequency so
that the selected energy is actually delivered to the target in one
of more effective pulses.
[0094] If the controller selections were sufficient (block 1014,
1028) to achieve the desired effect (stone breakup, dusting, etc.),
the operator observing the extent of treatment may stop the system
(block 1016, 1032) and vice versa if the effects are not achieved
(block 1018, 1030). Accordingly, method 1000 can include receiving
an indication from an operator (e.g., physician, or the like) that
the treatment is sufficient or not. Based on the received
indication, method 1000 can either end (block 1016, 1032) or can
repeat (block 1018, 1030) or said differently, return to block
1002. In this manner, the operator may provide an indication to the
system (e.g., system 900) and the system 900 can receive the
indication and further or additional treatments carrier out to
reach the desired effects. The steps may be adjusted dynamically
using a closed feedback circuit connected to the controller. Thus,
by way of example, if the distance to the target changes during the
procedure, the closed feedback loop may provide that information to
the controller which then may cause the controller to change the
parameters of treatment.
[0095] FIG. 11 illustrates a flowchart showing a method 1100 of
implementing a modulation scheme in accordance with some
embodiments of the present disclosure. The method 1100 is described
with reference to the system 900 and to the various configurations
and embodiments described above. It is to be appreciated however,
that the method 1100 could be implemented using a system different
than that described herein. Embodiments are not limited in this
context.
[0096] At block 1102, the method 1100 includes determining a pulse
energy for a fiber laser. For example, controller 922 may determine
a pulse energy for laser source 921. In some embodiments,
controller 922 may determine the pulse energy based on input
received via a user interface. In other embodiments, controller 922
may determine the pulse energy based on one or more settings of the
laser system 900. At block 1104, the method 1100 includes
identifying a distance between a tip of the fiber laser and a
target, wherein a liquid is located between the tip of the fiber
laser and the target. For example, controller 922 may identify
determine a distance between the tip of laser fiber 924 and a
treatment target based input from distance measurement module 924.
At block 1106, the method 1100 includes determining a modulation
scheme based on the distance. For example, controller 922 may
select between V-shape modulation schemes and resonant modulation
schemes based on the distance between the tip of laser fiber 924
and a target.
[0097] At block 1108, the method 1100 includes setting an initial
pulse power for the modulation scheme to generate an index bubble
in the liquid based on the distance. For example, when the distance
is over a threshold distance, the initial pulse power may be set to
a maximal system power. In another example, when the distance is
under a threshold distance, the initial pulse power may be set to
deliver a bubble with a size that is 1 to 2 times the distance to
the target. In some such examples, a lookup table may be used to
determine the initial pulse power that will deliver the bubble with
a size that is 1 to 2 times the distance to the target. At block
1110, the method 1100 includes initiating a pulse according to the
modulation scheme via the fiber laser, wherein the modulation
scheme reduces power of the pulse after initiation of the pulse at
the initial pulse power. For example, controller 922 may initiate a
pulse according to modulation scheme 702a, or modulation scheme
810, via laser source 921 and laser fiber 924.
[0098] FIG. 12 is a block diagram of an exemplary computer system
for implementing embodiments consistent with the present
disclosure. In some embodiments, FIG. 12 illustrates a block
diagram of an exemplary computer system 1200 for implementing
embodiments consistent with the present disclosure. In some
embodiments, the computer system 1200, or one or more portions
thereof, may comprise controller 922. In some such embodiments, the
computer system 1200 may be utilized to control operation of laser
system 900 with respect to a target. Embodiments are not limited in
this context.
[0099] The computer system 1200 may include a central processing
unit ("CPU" or "processor") 1202. The processor 1202 may include at
least one data processor for executing program components for
executing user or system-generated business processes. A user may
include a person, a person using a device such as those included in
this disclosure, or such a device itself. The processor 1202 may
include specialized processing units such as integrated system
(bus) controllers, memory management control units, floating point
units, graphics processing units, digital signal processing units,
etc. The processor 1202 may be disposed in communication with input
devices 1211 and output devices 1212 via I/O interface 1201. The
I/O interface 1201 may employ communication protocols/methods such
as, without limitation, audio, analog, digital, stereo, IEEE-1394,
serial bus, Universal Serial Bus (USB), infrared, PS/2, BNC,
coaxial, component, composite, Digital Visual Interface (DVI),
high-definition multimedia interface (HDMI), Radio Frequency (RF)
antennas, S-Video, Video Graphics Array (VGA), IEEE 802.n/b/g/n/x,
Bluetooth, cellular (e.g., Code-Division Multiple Access (CDMA),
High-Speed Packet Access (HSPA+), Global System For Mobile
Communications (GSM), Long-Term Evolution (LTE), WiMax, or the
like), etc.
[0100] Using the I/O interface 1201, computer system 1200 may
communicate with input devices 1211 and output devices 1212. In
some embodiments, the processor 1202 may be disposed in
communication with a communication network 1209 via a network
interface 1203. In various embodiments, the communication network
1209 may be utilized to communicate with a remote device 1220, such
as for accesses look-up tables or utilizing external resources. The
network interface 1203 may communicate with the communication
network 1209. The network interface 1203 may employ connection
protocols including, without limitation, direct connect, Ethernet
(e.g., twisted pair 10/100/1000 Base T), Transmission Control
Protocol/Internet Protocol (TCP/IP), token ring, IEEE
802.11a/b/g/n/x, etc. In some embodiments, one or more portions of
the computer system 1200 may be integrated into the laser system
900. In some such embodiments, one or more components of the laser
system 900 may comprise an input device 1211 and/or an output
device 1212 (e.g., distance measurement module 929, laser source
921, photodetector 927, etcetera).
[0101] The communication network 1209 can be implemented as one of
the different types of networks, such as intranet or Local Area
Network (LAN), Closed Area Network (CAN) and such. The
communication network 1209 may either be a dedicated network or a
shared network, which represents an association of the different
types of networks that use a variety of protocols, for example,
Hypertext Transfer Protocol (HTTP), CAN Protocol, Transmission
Control Protocol/Internet Protocol (TCP/IP), Wireless Application
Protocol (WAP), etc., to communicate with each other. Further, the
communication network 1209 may include a variety of network
devices, including routers, bridges, servers, computing devices,
storage devices, etc. In some embodiments, the processor 1202 may
be disposed in communication with a memory 1205 (e.g., RAM, ROM,
etc. not shown in FIG. 12) via a storage interface 1204. The
storage interface 1204 may connect to memory 1205 including,
without limitation, memory drives, removable disc drives, etc.,
employing connection protocols such as Serial Advanced Technology
Attachment (SATA), Integrated Drive Electronics (IDE), IEEE-1394,
Universal Serial Bus (USB), fiber channel, Small Computer Systems
Interface (SCSI), etc. The memory drives may further include a
drum, magnetic disc drive, magneto-optical drive, optical drive,
Redundant Array of Independent Discs (RAID), solid-state memory
devices, solid-state drives, etc.
[0102] The memory 1205 may store a collection of program or
database components, including, without limitation, a user
interface 1206, an operating system 1207, a web browser 1208, and
instructions 1215, etcetera. In various embodiments, instructions
1215 may include instructions that when executed by the processor
1202 cause the processor 1202 to perform one or more techniques,
steps, procedures, and/or methods described herein, such to
estimate a distance or perform a calibration. For example,
instructions to perform method 380 may be stored in memory 1205. In
many embodiments, memory 1205 includes at least one non-transitory
computer-readable medium. In some embodiments, the computer system
1200 may store user/application data, such as the data, variables,
records, etc. as described in this disclosure. Such databases may
be implemented as fault-tolerant, relational, scalable, secure
databases such as Oracle or Sybase.
[0103] The operating system 1207 may facilitate resource management
and operation of the computer system 1200. Examples of operating
systems include, without limitation, APPLE.RTM. MACINTOSH.RTM. OS
X.RTM., UNIX.RTM., UNIX-like system distributions (E.G., BERKELEY
SOFTWARE DISTRIBUTION.RTM. (BSD), FREEBSD.RTM., NETBSD.RTM.,
OPENBSD, etc.), LINUX.RTM. DISTRIBUTIONS (E.G., RED HAT.RTM.,
UBUNTU.RTM., KUBUNTU.RTM., etc.), IBM.RTM.OS/2.RTM., MICROSOFT.RTM.
WINDOWS.RTM. (XP.RTM., VISTA.RTM./7/8, 10 etc.), APPLE.RTM.
IOS.RTM., GOOGLE.TM. ANDROID.TM., BLACKBERRY.RTM. OS, or the like.
The User interface 1206 may facilitate display, execution,
interaction, manipulation, or operation of program components
through textual or graphical facilities. For example, user
interfaces may provide computer interaction interface elements on a
display system operatively connected to the computer system 1200,
such as cursors, icons, checkboxes, menus, scrollers, windows,
widgets, etc. Graphical User Interfaces (GUIs) may be employed,
including, without limitation, Apple.RTM. Macintosh.RTM. operating
systems' Aqua.RTM., IBM.RTM. OS/2.RTM., Microsoft.RTM. Windows.RTM.
(e.g., Aero, Metro, etc.), web interface libraries (e.g.,
ActiveX.RTM., Java.RTM., JavaScript.RTM., AJAX, HTML, Adobe.RTM.
Flash.RTM., etc.), or the like.
[0104] In some embodiments, the computer system 1200 may implement
the web browser 1208 stored program components. The web browser
1208 may be a hypertext viewing application, such as MICROSOFT.RTM.
INTERNET EXPLORER.RTM., GOOGLE.TM. CHROME.TM., MOZILLA.RTM.
FIREFOX.RTM., APPLE.RTM. SAFARI.RTM., etc. Secure web browsing may
be provided using Secure Hypertext Transport Protocol (HTTPS),
Secure Sockets Layer (SSL), Transport Layer Security (TLS), etc.
Web browsers 1208 may utilize facilities such as AJAX, DHTML,
ADOBE.RTM. FLASH.RTM., JAVASCRIPT.RTM., JAVA.RTM., Application
Programming Interfaces (APIs), etc. In some embodiments, the
computer system 1200 may implement a mail server stored program
component. The mail server may be an Internet mail server such as
Microsoft Exchange, or the like. The mail server may utilize
facilities such as Active Server Pages (ASP), ACTIVEX.RTM.,
ANSI.RTM. C++/C#, MICROSOFT.RTM., .NET, CGI SCRIPTS, JAVA.RTM.,
JAVASCRIPT.RTM., PERL.RTM., PHP, PYTHON.RTM., WEBOBJECTS.RTM., etc.
The mail server may utilize communication protocols such as
Internet Message Access Protocol (IMAP), Messaging Application
Programming Interface (MAPI), MICROSOFT.RTM. exchange, Post Office
Protocol (POP), Simple Mail Transfer Protocol (SMTP), or the like.
In some embodiments, the computer system 1200 may implement a mail
client stored program component. The mail client may be a mail
viewing application, such as APPLE.RTM. MAIL, MICROSOFT.RTM.
ENTOURAGE.RTM., MICROSOFT.RTM. OUTLOOK.RTM., MOZILLA.RTM.
THUNDERBIRD.RTM., etc.
[0105] Furthermore, one or more computer-readable storage media may
be utilized in implementing embodiments consistent with the present
disclosure. A computer-readable storage medium refers to any type
of physical memory on which information or data readable by a
processor may be stored. Thus, a computer-readable storage medium
may store instructions for execution by one or more processors,
including instructions for causing the processor(s) to perform
steps or stages consistent with the embodiments described herein.
The term "computer-readable medium" should be understood to include
tangible items and exclude carrier waves and transient signals,
i.e., non-transitory. Examples include Random Access Memory (RAM),
Read-Only Memory (ROM), volatile memory, non-volatile memory, hard
drives, Compact Disc (CD) ROMs, Digital Video Disc (DVDs), flash
drives, disks, and any other known physical storage media.
[0106] It will be understood by those within the art that, in
general, terms used herein, and are generally intended as "open"
terms (e.g., the term "including" should be interpreted as
"including but not limited to," the term "having" should be
interpreted as "having at least," the term "includes" should be
interpreted as "includes but is not limited to," etc.). It will be
further understood by those within the art that if a specific
number of an introduced claim recitation is intended. For example,
as an aid to understanding, the detail description may contain
usage of the introductory phrases "at least one" and "one or more"
to introduce claim recitations. However, the use of such phrases
should not be construed to imply that the introduction of a claim
recitation by the indefinite articles "a" or "an" limits any
particular claim containing such introduced claim recitation to
disclosures containing only one such recitation, even when the same
claim includes the introductory phrases "one or more" or "at least
one" and indefinite articles such as "a" or "an" (e.g., "a" and/or
"an" should typically be interpreted to mean "at least one" or "one
or more"); the same holds true for the use of definite articles
used to introduce claim recitations. In addition, even if a
specific number of an introduced claim recitation is explicitly
recited, those skilled in the art will recognize that such
recitation should typically be interpreted to mean at least the
recited number (e.g., the bare recitation of "two recitations,"
without other modifiers, typically means at least two recitations,
or two or more recitations).
[0107] All of the devices and/or methods disclosed and claimed
herein can be made and executed without undue experimentation in
light of the present disclosure. While the devices and methods of
this disclosure have been described in terms of preferred
embodiments, it may be apparent to those of skill in the art that
variations can be applied to the devices and/or methods and in the
steps or in the sequence of steps of the method described herein
without departing from the concept, spirit, and scope of the
disclosure. All such similar substitutes and modifications apparent
to those skilled in the art are deemed to be within the spirit,
scope and concept of the disclosure as defined by the appended
claims.
* * * * *