Patent Publication Number: US-2023157889-A1

Title: Treating eye conditions with subthreshold femtosecond laser pulses

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to ophthalmic laser surgical systems, and more particularly to treating eye conditions with subthreshold femtosecond laser pulses. 
     BACKGROUND 
     In ophthalmic laser surgery, a surgeon may direct a laser beam into the eye to treat the eye. For example, a laser beam may be directed into the vitreous to treat eye floaters. Eye floaters are clumps of collagen proteins that form in the vitreous. These clumps can disturb vision with moving shadows and distortions. The laser beam may be used to fragment the floaters to improve vision. 
     BRIEF SUMMARY 
     In certain embodiments, an ophthalmic laser surgical system for treating a target tissue in an eye includes a target detection system and a laser device. The target tissue has an optical breakdown threshold. The target detection system directs detection beams along a detection beam path towards the target tissue in a vitreous of the eye, and determines a location of the target tissue within the vitreous. The laser device includes a femtosecond laser that generates subthreshold laser pulses that have a pulse energy below the optical breakdown threshold of the tissue. The laser device directs a laser beam comprising the subthreshold laser pulses along a laser beam path towards the target tissue. 
     Embodiments may include none, one, some, or all of the following features:
         The ophthalmic laser surgical system further comprises an xy-scanner. The xy-scanner: receives the detection beams from the target detection system and directs the detection beams along the detection beam path towards an xy-location of a target shadow cast by the target tissue onto the retina of the eye, the xy-location relative to an xy-scanner; and receives the laser beam from the laser device and directs the laser beam along the laser beam path aligned with the detection beam path towards the xy-location of the target shadow.   The pulse energy is 1 to 100 nanojoules (nJ).   The subthreshold laser pulses have a duration of 10 to 500 femtoseconds (fs).   The subthreshold laser pulses have a repetition rate of 1 to 100 megahertz (MHz).   The laser device configured to direct the laser beam comprising the plurality of subthreshold laser pulses by directing 10 to 100 subthreshold laser pulses towards the same spot of the target tissue. The number N of subthreshold laser pulses at the same target spot may be controlled by a repetition rate f of the laser device, an xy-scanning speed v of a laser spot of the laser beam, and a target spot diameter d according to N=(d*f)/v.   The laser device comprises a z-focusing component that receives a z-location of the target tissue relative to the retina, and directs a focal point of the laser beam towards the z-location of the target tissue.   The target detection system comprises an xy-location device that provides an xy-location of a target shadow of the target tissue relative to an xy-scanner, and a z-location device that provides a z-location of the target tissue relative to the retina.   The xy-location device comprises a scanning laser ophthalmoscopy (SLO) device.   The z-location device comprises an interferometer device.   The target tissue comprises a vitreous-retinal traction fiber.   The target tissue comprises a vitreous floater.   The laser forms a cloud of low-density free electrons using the subthreshold laser pulses to trigger a chemical reaction that locally disintegrates a portion of the target tissue.   The laser forms singlet oxygen molecules using the subthreshold laser pulses to cause a chemically reaction within a portion of the target tissue.   The laser causes a multiphoton chemical reaction using the subthreshold laser pulses to locally disintegrate a portion of the target tissue.   The laser cause a supersonic thermoelastic wave using the subthreshold laser pulses to locally disintegrate a portion of the target tissue.       

     In certain embodiments, an ophthalmic laser surgical system for treating a target tissue in an eye comprises a target detection system and a laser device. The target detection system directs detection beams along a detection beam path towards the target tissue in the vitreous of the eye and determines the location of the target tissue. The laser device comprises a femtosecond laser that generates subthreshold laser pulses. The subthreshold laser pulses have a pulse energy below the optical breakdown threshold of the target tissue, e.g., 1 to 100 nanojoules (nJ), a duration of 10 to 500 femtoseconds (fs), and a repetition rate of 1 to 100 megahertz (MHz). The laser device directs a laser beam comprising the subthreshold laser pulses along a laser beam path towards the target tissue by directing 10 to 100 subthreshold laser pulses towards the same target spot of the target tissue. 
     Embodiments may include none, one, some, or all of the following features:
         The ophthalmic laser surgical system comprises an xy-scanner that: receives the detection beams from the target detection system and directs the detection beams along the detection beam path towards the xy-location of a target shadow cast by the target tissue onto the retina of the eye, the xy-location relative to an xy-scanner; and receives the laser beam from the laser device and directs the laser beam along the laser beam path aligned with the detection beam path towards the xy-location of the target shadow.   The target detection system comprises: an xy-location device that provides the xy-location of a target shadow of the target tissue, the xy-location related to an xy-scanner; and a z-location device that provides the z-location of the target tissue relative to the retina of the eye.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an example of an ophthalmic laser surgical system that may be used to treat an eye, according to certain embodiments; 
         FIG.  2    illustrates an example of a retinal image that may be generated by the system of  FIG.  1   ; and 
         FIG.  3    illustrates an example of a method for treating a target tissue in an eye that may be performed by the system of  FIG.  1   , according to certain embodiments. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Referring now to the description and drawings, example embodiments of the disclosed apparatuses, systems, and methods are shown in detail. The description and drawings are not intended to be exhaustive or otherwise limit the claims to the specific embodiments shown in the drawings and disclosed in the description. Although the drawings represent possible embodiments, the drawings are not necessarily to scale and certain features may be simplified, exaggerated, removed, or partially sectioned to better illustrate the embodiments. 
     Known ophthalmic laser surgical systems include a YAG or femtosecond laser (“femto laser”) that generates laser pulses to photodisrupt eye tissue. For example, YAG laser pulses with a 5 millijoule (mJ) pulse energy, 4 nanosecond (ns) pulse duration, and 1.064 micrometer (um) wavelength or femtosecond laser pulses with a 15 to 20 microjoule (uJ) pulse energy and 500 femtosecond (fs) pulse duration can photodisrupt tissue to create cavitation bubbles in the tissue. 
     However, YAG laser pulses cannot treat floaters closer than 10 millimeters (mm) to the retina without exceeding standard radiation exposure limits. Moreover, Chirped Pulse Amplification with Master Oscillator Power Amplifier (CPA MOPA) femto lasers are needed to produce the pulses that can photodisrupt tissue, and these lasers are prohibitively expensive for certain applications. 
     Accordingly, the surgical systems described herein include a femtosecond laser that produces subthreshold laser pulses. Subthreshold laser pulses have a pulse energy below the breakdown threshold of the tissue, i.e., the pulse energy at which optical breakdown occurs in the tissue. The pulses do not cause optical breakdown (photodisruption) or form cavitation bubbles. The lower pulse energy allows for destruction of floaters in more situations without overexposing the retina. Moreover, a femtosecond laser is much more affordable and reliable than a CPA MOPA femto laser. 
       FIG.  1    illustrates an example of an ophthalmic laser surgical system  10  that may be used to treat an eye, according to certain embodiments. Surgical system  10  may provide any suitable treatment where laser pulses are directed to a target tissue (e.g., vitreous floaters or vitreous-retinal traction fibers) in an eye. Examples of treatments include laser vitreolysis, traction fiber removal, and retinal microsurgery. 
     As an overview, system  10  includes a target detection system  20 , a laser device  22 , one or more shared components  24 , and a computer  26 , coupled as shown. Laser device  22  includes a laser  30  and a z-focusing component  32 , coupled as shown. Shared components  24  include an xy-scanner  40 , an xy-encoder  41 , and optical elements (such as a mirror  42  and lenses  44  and  46 ), coupled as shown. Computer  26  includes logic  50 , a memory  52  (which stores a computer program  54 ), and a display  56 , coupled as shown. In certain embodiments, target detection system  20  and laser device  22  share xy-scanner  40 , which allows target detection system  20  and laser device  22  to be co-registered. For ease of explanation, an axis (e.g., optical or visual axis) of the eye approximates a z-axis, which in turn defines enface planes (e.g., xy-planes) substantially orthogonal to the z-axis. 
     As an overview of operation of system  10 , target detection system  20  directs detection beams along a detection beam path towards the target tissue in a vitreous of the eye, and determines the location of the target tissue within the vitreous. Laser device  22  comprises a femtosecond laser that generates subthreshold laser pulses with a pulse energy of 1 to 100 nanojoules (nJ). Laser device  22  directs a laser beam comprising the laser pulses along a laser beam path towards the target tissue. 
     Turning to the parts of the system, target detection system  20  includes one or more detection devices that detect, locate, and/or image a target tissue and/or a target shadow cast by the target tissue on the retina. To detect, locate, and/or image a target tissue and/or a target shadow, a detection device directs a detection beam along a detection beam path towards the interior of the eye. The interior reflects the detection beam, and the device detects the reflected light and detects, locates, and/or images a target tissue and/or a target shadow. In addition, the detection devices may provide the x, y, and/or z locations of the target tissue and/or a target shadow to another component. For example, an xy-location device provides the xy-location of the target shadow, and a z-location device provides the z-location of the target tissue. 
     The devices may utilize the same or different technologies (e.g., scanning laser ophthalmoscopy (SLO) and/or interferometry). In certain embodiments, a detection device is an SLO device that provides the xy-location of a target shadow. In certain embodiments, a detection device is an interferometer device with any suitable interferometer, e.g., a Fourier domain type (such as a swept source or a spectral domain type) that utilizes a fast Fourier transform (FFT). Examples of interferometer devices include an optical coherence tomography (OCT) device (such as a swept-source OCT device) and a swept source A-scan interferometer (SSASI) device. A SASSI device performs only A-scans. 
     Turning to laser device  22 , laser  30  includes a femtosecond laser that produces subthreshold laser pulses to perform subthreshold laser surgery (SLS). In contrast, most femtosecond lasers used in ophthalmic surgery cut tissue with above-threshold pulses that cause photodisruption (or plasma mediated ablation). As an example of photodisruption, 3 microjoule (uJ), 500 femtosecond (fs) laser pulses are focused down to about 2 micrometer (um) spots. The peak intensity of the laser pulses at the focus is about 50 TW/cm 2  (50*10 12  W/cm 2 ) where W represents watt, TW represents terawatt, and cm represents centimeter. 
     At such extremely high laser intensities, multiphoton absorption can occur. The intensity removes electrons from atoms and molecules and creates a cloud of free electrons. The electric field of the laser pulses accelerate the free electrons by a process called inverse bremsstrahlung, and the accelerated free electrons ionize neutral atoms of the tissue in process called avalanche ionization. As a result of these processes, a high-density, high-temperature (e.g., approximately 5000K°) plasma is formed at the focus. The high-temperature plasma burns and evaporates a small (e.g., approximately 4 um×4 um×50 um) volume of tissue. The cascade of processes is known as breakdown. Breakdown threshold energy is the minimal laser pulse energy that can cause breakdown. 
     The high-temperature, high pressure vapors rapidly expand and form a cavitation bubble having a diameter of, e.g., about 200 um. The acceleration of the wall of a cavitation bubble (i.e., the vapor-tissue interface) can achieve an acceleration of 10 7  m/s 2 , i.e., approximately 1 million times free fall acceleration. The acceleration of bubble walls can also form shock waves in the tissue. The forces of acceleration and the shock waves tear apart a spherical volume of tissue having a diameter of approximately 100 to 200 um, which can be used to disintegrate tissue. 
     The high-temperature plasma, the rapidly expanding cavitation bubbles, and the shock wave may damage the retina if the focus is near the retina. For this reason, surgery with above-threshold laser pulses is not allowed to be performed very near to or at the surface of the retina. For example, surgery with above-threshold laser pulses is not allowed on the internal limiting membrane, epiretinal membrane, traction fibers connecting the hyaloid membrane and the retina, or retinal drusens. 
     Accordingly, the femtosecond laser of system  10  produces subthreshold laser pulses for subthreshold laser surgery (SLS), which may be performed closer to the retina as well as farther away. Subthreshold laser pulses have a pulse energy below the breakdown threshold of the tissue, e.g., a pulse energy of 1 to 100 nanojoules (nJ), such as a 50 nJ 500 fs laser pulse energy. The pulses do not cause an optical breakdown, form a high-density, high-temperature plasma, yield a cavitation bubble, or produce shock waves. However, subthreshold laser pulses can yield other effects that can disintegrate tissue. Moreover, several (e.g., greater than 5, e.g., 10) laser pulses may be spatially superimposed on top of each other at the same place at repetition rate of a few MHz to increase disintegration. Subthreshold laser pulses, even when superimposed, disintegrate the tissue locally, only substantially at the focus, so can be used for surgery near the retina. 
     Subthreshold laser pulses can cause the following effects that disintegrate tissue. Spatial superposition of laser pulses at the same spot can increase effects (1), (2), and (3) that can locally disintegrate tissue at the spot. 
     (1) Low-density free electrons. Subthreshold laser pulses can form a cloud of low-density free electrons that can trigger a chemical reaction that locally disintegrates tissue. 
     (2) Singlet oxygen molecules. Subthreshold laser pulses can form singlet oxygen molecules that are extremely chemically reactive. 
     (3) Multiphoton chemical reaction. Subthreshold laser pulses can cause a multiphoton chemical reaction that disintegrates tissue. 
     (4) Disruptive local thermoelastic strain. In an example, multiphoton absorption of a laser pulse can increase the temperature of tissue at the focus from, e.g., 37 to 47 centigrade. According to the temperature coefficient of the expansion of water, a focal volume of 2 um diameter may expand by 0.13%, i.e., by 0.0026 um. At a 500 fs rate, the expansion speed may be 0.0026 um/500 fs=5200 m/s. The speed of sound in the ophthalmic tissue is about 1500 m/s, so the expansion waves are supersonic. Accordingly, subthreshold laser pulses can cause supersonic, explosion-like transient thermoelastic waves that can tear ophthalmic tissue and cause local tissue disintegration of tissue. 
     Laser  30  generates a laser beam with any suitable wavelength, e.g., in an ultraviolet or infrared range. In certain embodiments, the pulses have a duration of 10 to 500 fs (e.g., 10 to 100, 100 to 200, 200 to 300, 300 to 400, and/or 400 to 500 fs), a pulse energy of 1 to 100 nanojoules (nJ) (e.g., 1 to 5, 5 to 25, 25 to 50, 50 to 75, and/or 75 to 100 nJ), and a repetition rate of 1 to 100 megahertz (MHz) (e.g., 1 to 40, 40 to 60, and/or 60 to 100 MHz). The same spot of the tissue may be exposed to a number N of laser pulses, where N is 10 to 100 (e.g., 10 to 40, 40 to 60, and/or 60 to 100) laser pulses. The number N of pulses at the same target spot may controlled by the repetition rate f of the laser, the xy-scanning speed v of the laser spot of the laser beam, and the target spot diameter d as N=(d*f)/v. 
     Z-focusing component  32  longitudinally directs the focal point of the laser beam to a specific location in the z-direction. Examples of z-focusing component  32  include a longitudinally adjustable lens, a lens of variable refractive power, an electrically or mechanically tunable lens (e.g., Optotune lens), an electrically or mechanically tunable telescope, or a deformable mirror that can control the z-location of the focal point. Z-focusing component  32  may direct the focal point in any suitable manner. In certain embodiments, z-focusing component  32  receives the z-location of the target tissue from target detection system  20  (and may receive it via computer  26 ), and directs the laser beam towards the z-location of the target tissue. 
     Shared components  24  direct detection and laser beams from target detection system  20  and laser device  22 , respectively, towards the eye. Because detection and laser beams both use shared components  24 , both beams are affected by the same optical distortions (e.g., fan distortion of scanners, barrel or pillow distortions of the scanner lens, refractive distortions from the inner eye surfaces, and other distortions). The distortions affect both beams in the same way, so the distortions are compensated for. This allows for aiming the laser beam using images generated by the detection beam with improved accuracy. 
     As an example of aiming the laser beam, an image of the eye may include a reticle, which is a graphical overlay (e.g., crosshairs) that indicates where the beam is currently aimed in an enface plane. The user or computer  26  may place the reticle over the target tissue in the image to aim the beam at the target tissue. Target detection system  20  provides the xy-location to xy-scanner  40 . Xy-encoder  41  detects the position of xy-scanner  40  to determine the xy-location of the reticle (in encoder units) centered at the target tissue. 
     As an overview of operation of shared components  24 , mirror  42  directs a beam (detection and/or laser beam) towards xy-scanner  40 , which transversely directs the beam towards lens  44 . Lenses  44  and  46  direct the beam towards eye. Shared components  24  may also provide spectral and polarization coupling and decoupling of detection and laser beams to allow the beams to share the same path. 
     Turning to the details of shared components  24 , xy-scanner  40  transversely directs the focal point of the beam in the x- and y-directions. Xy-scanner  40  changes the angle of incidence of the beam into the pupil, allowing for the beam to cover a wider range within the eye. Xy-scanner  40  may transversely direct the beam in any suitable manner. For example, xy-scanner  40  may include a pair of galvanometrically-actuated scanner mirrors that can be tilted about mutually perpendicular axes. As another example, xy-scanner  40  may include an electro-optical crystal that can electro-optically steer the beam or an acousto-optical crystal that can acousto-optically steer the beam. As another example, xy-scanner  40  may include a fast scanner that can create, e.g., a 3D matrix of laser pulses. Examples of such scanners include a galvo scanner, resonant scanner, or acousto optical scanner. In certain embodiments, xy-scanner  40  receives the xy-location of the target shadow from target detection system  20 , and directs the detection and/or laser beam towards the xy-location. 
     Xy-encoder  41  detects the position of xy-scanner  40  and reports the position as the xy-location. For example, xy-encoder  41  detects the angular orientations of the galvanometer mirrors of xy-scanner  40  in encoder units. Xy-encoder  41  may report the position in encoder units to target detection system  20 , laser device  22 , and/or computer  26 . Since target detection system  20  and laser device  22  share xy-scanner  40 , computer  26  can use the encoder units to instruct system  20  and device  22  where to aim their beams, making it unnecessary to perform the computer-intensive conversion from encoder units to a length unit such as millimeters. Xy-encoder  41  may report the positions at any suitable rate, e.g., once every 5 to 50 milliseconds (ms), such as every 10 to 30 or approximately every 20 ms. 
     Shared components  24  also include optical elements. In general, an optical element can act on (e.g., transmit, reflect, refract, diffract, collimate, condition, shape, focus, modulate, and/or otherwise act on) a laser beam. Examples of optical elements include a lens, prism, mirror, diffractive optical element (DOE), holographic optical element (HOE), and spatial light modulator (SLM). In the example, optical elements include mirror  42  and lenses  44  and  46 . Mirror  42  may be a trichroic mirror. Lenses  44  and  46  may be scanning optics of an SLO device. 
     Computer  26  controls components of system  10  (e.g., target detection system  20 , laser device  24 , and/or shared components  24 ) in accordance with a computer program  54 . Computer  26  may be separated from components or may be distributed among system  10  in any suitable manner, e.g., within target detection system  20 , laser device  24 , and/or shared components  24 . In certain embodiments, portions of computer  26  that control target detection system  20 , laser device  24 , and/or shared components  24  may be part of target detection system  20 , laser device  24 , and/or shared components  24 , respectively. 
     Computer  26  controls the components of system  10  in accordance with a computer program  54 . Examples of computer programs  54  include target imaging, target tracking, image processing, target evaluation, retinal exposure calculation, patient education, and insurance authorization programs. For example, computer  26  may use a computer program  54  to instruct target detection system  20 , laser device  24 , and/or shared components  24  to image a target tissue and focus a laser beam at the target tissue. 
     In certain embodiments, computer  26  uses an image processing program  54  to perform image processing on an image, e.g., analyze the digital information of the image to extract information from the image. In certain embodiments, image processing program  54  analyzes an image of a target tissue or a target shadow to obtain information about the target tissue. For example, program  54  may detect a target shadow by detecting a darker shape in an image (using, e.g., edge detection or pixel analysis). As another example, program  54  may detect the shape and size of a target shadow, which indicate the size and shape of the target tissue. As another example, program  54  may detect the tone or luminescence of the target shadow, which indicates the density of the target tissue. 
     In certain embodiments, computer  26  uses a target evaluation and diagnosis program  54  to evaluate a target tissue, such as a floater, to determine if the target tissue is clinically significant, i.e., affects vision. In certain embodiments, display  56  of computer  26  displays images (such as a video) of a target shadow so a user can evaluate the target tissue. In other embodiments, computer  26  uses image processing to evaluate the target tissue. Target evaluation and diagnosis are as described in more detail with reference to  FIG.  2   . 
       FIG.  2    illustrates an example of a retinal image  60  that may be generated by system  10  of  FIG.  1   . Image  60  shows the retina  62  of an eye, with a foveal region (or fovea)  64  and a parafoveal region (or parafovea)  66 . Generally, fovea  64  has a visual angle of approximately +/−one degree, and parafovea  66  has a visual angle of approximately +/−seven degrees. Image  60  also shows floater shadows  68  ( 68   a ,  68   b ,  68   c ) that floaters cast on retina  62 . In general, non-moving shadows are not caused by floaters, and may be caused by, e.g., corneal or lens opacities or anatomical changes of the retina, so floater treatment is not concerned with non-moving shadows. 
     A floater may be regarded as clinically significant if it can cause a visual disturbance, which can be determined from any suitable features of the floater shadow, e.g., the size and/or density of the shadow, proximity of the shadow to the fovea and/or parafovea, and/or the track of the shadow relative to the fovea and/or parafovea. As an example, a floater can cause a visual disturbance if it permanently or transiently casts a shadow  68  on fovea  64  or can cause distraction or annoyance if it permanently or transiently casts a shadow  68  on parafovea  66 . 
     Accordingly, if a floater shadow falls within or is predicted to move within fovea  64  and/or parafovea  66 , the floater may be designated as clinically significant. As another example, floater shadow  68  can be used to estimate the size and density of the floater. Larger, denser floaters are more likely to cause a visual disturbance. Thus, a shadow  68  larger than a critical shadow size can indicate a clinically significant floater. A shadow  68  with a higher contrast relative to the background may indicate a clinically significant floater. 
       FIG.  3    illustrates an example of a method for treating a target tissue in an eye that may be performed by system  10  of  FIG.  1   , according to certain embodiments. The method starts at step  110 , where the target detection system directs a detection beam towards the target tissue shadow to generate an image of the target shadow. 
     The target tissue is evaluated as to whether it should be treated at step  112 . The evaluation may evaluate the target shadow to determine the location, size, shape, and/or density of the target tissue. The target tissue may be treated at step  114 . If the target tissue is not to be treated, the method returns to step  110  to continue generating images of the target tissue. If the target tissue is to be treated, the method proceeds to step  116 , where the target detection system is used to determine the location of the target shadow. 
     Subthreshold laser pulses are directed at the target tissue at step  120  to treat (e.g., fragment) the target tissue. Subthreshold laser pulses have a pulse energy below the breakdown threshold of the tissue, so do not cause photodisruption. The pulses treat the target tissue by exposing the same spot to a number N of laser pulses, where N is 10 to 100, to fragment and remove the target tissue. 
     A component (such as the control computer) of the systems and apparatuses disclosed herein may include an interface, logic, and/or memory, any of which may include computer hardware and/or software. An interface can receive input to the component and/or send output from the component, and is typically used to exchange information between, e.g., software, hardware, peripheral devices, users, and combinations of these. A user interface is a type of interface that a user can utilize to communicate with (e.g., send input to and/or receive output from) a computer. Examples of user interfaces include a display, Graphical User Interface (GUI), touchscreen, keyboard, mouse, gesture sensor, microphone, and speakers. 
     Logic can perform operations of the component. Logic may include one or more electronic devices that process data, e.g., execute instructions to generate output from input. Examples of such an electronic device include a computer, processor, microprocessor (e.g., a Central Processing Unit (CPU)), and computer chip. Logic may include computer software that encodes instructions capable of being executed by an electronic device to perform operations. Examples of computer software include a computer program, application, and operating system. 
     A memory can store information and may comprise tangible, computer-readable, and/or computer-executable storage medium. Examples of memory include computer memory (e.g., Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (e.g., a hard disk), removable storage media (e.g., a Compact Disk (CD) or Digital Video or Versatile Disk (DVD)), database, network storage (e.g., a server), and/or other computer-readable media. Particular embodiments may be directed to memory encoded with computer software. 
     Although this disclosure has been described in terms of certain embodiments, modifications (such as changes, substitutions, additions, omissions, and/or other modifications) of the embodiments will be apparent to those skilled in the art. Accordingly, modifications may be made to the embodiments without departing from the scope of the invention. For example, modifications may be made to the systems and apparatuses disclosed herein. The components of the systems and apparatuses may be integrated or separated, or the operations of the systems and apparatuses may be performed by more, fewer, or other components, as apparent to those skilled in the art. As another example, modifications may be made to the methods disclosed herein. The methods may include more, fewer, or other steps, and the steps may be performed in any suitable order, as apparent to those skilled in the art. 
     To aid the Patent Office and readers in interpreting the claims, Applicants note that they do not intend any of the claims or claim elements to invoke 35 U.S.C. § 112(f), unless the words “means for” or “step for” are explicitly used in the particular claim. Use of any other term (e.g., “mechanism,” “module,” “device,” “unit,” “component,” “element,” “member,” “apparatus,” “machine,” “system,” “processor,” or “controller”) within a claim is understood by the applicants to refer to structures known to those skilled in the relevant art and is not intended to invoke 35 U.S.C. § 112(f).