Intravascular device and system with energy wave detection function

Abstract

The method may include the steps of inflating a balloon to an inflated state in a conductive medium, generating a high-voltage pulse in a high-voltage pulse generator to generate an energy wave in the conductive medium, wherein, at least during the generation of the energy wave, light of a desired wavelength is emitted into the balloon from a laser source along a first optical guide, the light emitted into the balloon is reflected by the acousto-optic effect of the energy wave, and the reflected light is detected by a photodetector via a second optical guide to determine energy wave data from the reflected light. The system may include a high-voltage pulse generator, a laser source for generating light of a desired wavelength along a first optical guide to be emitted into the balloon, and a photodetector positioned along a second optical guide for detecting reflected light from inside the balloon as a result of the generation of an energy wave by a high-voltage pulse based on the acousto-optic effect of the energy wave.

Description

Technical Field

[0001] Cross - reference to related applications This application claims priority and the benefit thereof to U.S. Provisional Patent Application No. 63 / 458,728, filed on April 12, 2023, the entire content of which is incorporated herein by reference in its entirety.

[0002] The present invention is directed to a catheter system for treating vascular thrombi or calcified lesions, etc., by utilizing energy waves generated by electrodes within a conductive fluid medium.

Background Art

[0003] [[ID=十七]] Catheter systems having angioplasty balloons are generally used to apply a physical force by inflating the balloon against calcified lesions in the vascular system to push the calcification back against the vessel wall and press against the vessel wall. Certain such calcified lesions and thrombi are not effectively destroyed by the use of angioplasty balloons.

[0004] More recently, catheter systems have been developed that include a balloon similar to an angioplasty balloon filled with a conductive liquid medium, such as physiological saline solution, to inflate the balloon at a predetermined position within a lesion or thrombus. The catheter system includes one or more pairs of electrodes operably disposed within the conductive liquid medium.The electrodes are pulsed with a high - voltage direct - current to generate a spark across the gap between the two electrodes for each pulse. The spark within the conductive medium generates an energy wave that propagates through the liquid medium and causes the balloon to physically force against the lesion or thrombus. The propagation of energy also includes the generation of microbubbles that facilitate a physical force. Such devices are known to impart energy waves acting on lesions or thrombi for the purpose of destroying calcification and coagulation.

[0005] Current catheter systems include a treatment sequence that includes the maximum number of consecutive pulses, the subsequent minimum delay time, and the exact maximum total pulse count associated with a particular catheter. One such product specifies the following:

[0006] [Table 1]

[0007] If treatment is not completed after the maximum total pulses per catheter, the doctor must replace the catheter, which involves undesirable costs, delays, and distractions.

[0008] Intravascular lithotripsy (IVL) devices are available for several calcification patterns. Disposable IVL balloon devices are offered in different designs and dimensions for peripheral vascular or coronary artery applications. All designs utilize reusable power sources such as IVL generators. One reusable DC generator has the following specifications:

[0009] [Table 2]

[0010] One such disposable device consists of a fluid-filled balloon angioplasty catheter fitted to a 0.014-inch guidewire, which has two lithotomy dischargers incorporated into a 12 mm long balloon compartment shaft. The fluid-filled balloon (e.g., 50 / 50 saline contrast agent) is inflated to approximately 4 atmospheres, and then an electrical pulse is applied to the dischargers, which generate high-voltage sparks to perform the treatment. Acoustic waves are generated, and calcium is broken down. [Overview of the project]

[0011] A method for determining energy wave characteristics in an intravascular lithotripsy apparatus, according to one aspect of the present invention, comprising at least one radiator disposed within an inflatable balloon and electrically connected to a high-voltage pulse generator. The method may include the steps of: inflating the balloon to an inflated state with a conductive medium; generating a high-voltage pulse with a high-voltage pulse generator to generate an energy wave within the conductive medium; radiating light from a laser source within the balloon at a desired wavelength along a first optical guide, at least during the generation of the energy wave; reflecting the light radiated within the balloon by the acousto-optic effect of the energy wave; and sensing the reflected light with a photodetector via a second optical guide and determining energy wave data from the reflected light.

[0012] Preferably, a high-voltage pulse, if generated, creates an electrical spark between the electrodes of the radiator, which generates acoustic energy in the conductive medium in the form of a sound wave, and the sound wave acts as a reflector of light of a specific wavelength. The energy wave generated by the spark or laser discharge can cause a change (e.g., with respect to the local refractive index) in the conductive medium, thereby reflecting light of the emission wavelength of light from a first optical light guide, which can be detected by a photodetector through a second light guide. In particular, the energy wave can cause a discontinuity in the refractive index of the conductive medium as it moves through the conductive medium with the energy wave. For comparison, a standing wave requires a continuous energy source at a specific frequency in a vessel designed with a shape based on a multiple of the wave's wavelength. Such results are inconsistent with energy impulses from a spark or laser discharge, as in the case of the present invention. According to the present invention, a moving wavefront is generated.

[0013] The method may also include a step of determining energy wave data from reflected light over a series of high-energy pulses applied over time. The reflected light detected by the photodetector may have a different wavelength than the synchrotron radiation.

[0014] In another embodiment, the method can determine energy wave velocity data in the direction moving away from the distal tip of the optical fiber provided as part of a second conduit, based on the phase change of reflected light as a function of time.

[0015] According to another aspect of the present invention, a system for determining energy wave characteristics within an intravascular lithotripsy device may include: an inflatable balloon distally separated along the catheter of the intravascular lithotripsy device; at least one radiator positioned within the inflatable balloon and electrically connected to a high-voltage pulse generator for generating energy waves in a conductive medium as a result of high-voltage pulses from the high-voltage pulse generator; a laser source for generating light of a desired wavelength along a first optical guide radiated within the balloon; and a photodetector positioned along a second optical guide for sensing reflected light from within the balloon as a result of the generation of energy waves by high-voltage pulses based on the acousto-optical effect of the energy waves. [Brief explanation of the drawing]

[0016] [Figure 1] This figure illustrates a system for performing endovascular lithotripsy according to an aspect of the present invention. [Figure 2] This figure illustrates an inflated balloon in a blood vessel for performing endovascular lithotripsy according to an aspect of the present invention. [Figure 3] This figure schematically illustrates an energy wave sensing system for an IVL apparatus according to an embodiment of the present invention, which includes a first optical fiber from a laser source for emitting light within the balloon of the IVL apparatus, and a second optical fiber for transmitting reflected light from within the balloon to a photodetector. [Figure 4] This figure is similar to Figure 3 and illustrates another energy wave sensing system for an IVL device, having a shared optical fiber provided from the optical circulator to the distal end of the shared optical fiber inside the balloon. [Figure 5] This graph compares energy waves of different intensities, such as those that affect the amount of reflected light. [Figure 6]This is a graphical representation of the method used to determine the energy wave velocity. [Modes for carrying out the invention]

[0017] The present invention relates to an IVL device of the type that includes an electrode or lithography radiator that generates acoustic waves by arc discharge between electrode components, but may also include a device that generates acoustic energy in a balloon via a laser energy source. Examples of such laser systems are described in U.S. Patent No. 11,058,492 and U.S. Patent No. 11,246,569 (their entire contents incorporated by reference). Examples of electric arc or spark systems are described in U.S. Patent No. 8,728,091, U.S. Patent No. 9,642,673 and U.S. Patent No. 10,850,078 and U.S. Patent Application Publication No. 2022-0054194.

[0018] Referring to the figures, FIGS. 1 and 2 show a system 10 according to the present invention, which includes a console or power source 12 (in the form of a generator or alternatively in the form of a laser system), a handle 14 having a treatment delivery control unit 15, and a catheter 20 having two lithotripter emitters 22 (shown in the form of a pair of arc electrodes, but alternatively they may comprise light or laser emitters), as well as a fluid-filled balloon 24. An optional marker band B may be provided. The catheter 20 preferably includes a central tube 26 that defines a guide wire lumen 27 through which a guide wire G passes to deliver the balloon 24 to a desired position along the guide wire G. A sheath 28 surrounds the central tube 26 and includes a delivery lumen 29 through which saline can be controllably delivered for inflation of the balloon 24. The lumen 29 provides a concentric space around the central tube 26 within which electrode wires (not shown) can extend from the control unit 15 to the emitter 22, among several components according to the present invention and discussed below. The sheath 28 is connected to a hub 17 at its proximal end, and the hub 17 may include any number of ports that allow electrode wires to pass through the lumen 29, along with saline for inflation, the guide wire G, and any number of other components as desired.

[0019] The balloon 24 can be placed in a deflated configuration to more easily pass through the patient's vasculature and reach the site of calcification. In use, the balloon 24 is inflated to a pressure common in angioplasty (e.g., 4 atm), and treatment is initiated via the treatment delivery control unit 15.

[0020] FIG. 2 shows the balloon 24 inflated to a treatment delivery state in which the lithotripter emitter 22 can be "fired" to break up vascular calcification C. An optional indicator band B may be provided to allow visualization and proper placement by use of known imaging techniques. The balloon 24 can be inflated to the pressure of angioplasty (e.g., 4 atm), and treatment can then be delivered. The balloon 24 can expand naturally during or immediately after treatment is delivered to clear the vessel for blood passage.

[0021] The control unit 15 is used to generate one or a series of voltage pulses according to a treatment scheme. The high-voltage pulses are continuously applied to one of the emitters 22 having a pair of spaced electrodes, and according to the illustrated embodiment, then to a second emitter 22 also having a pair of spaced electrodes. The high-voltage pulses sequentially cause sparks across the first electrode pair and then across the second electrode pair within the balloon 24. Some conductive saline solution within the balloon 24 enables high-voltage sparks across each electrode pair, thus generating an energy wave that propagates within the balloon towards vascular calcification.

[0022] The sparks generated within the balloon 24 disposed within the patient's vasculature also generate a visible or detectable light event. Such light events can be detected at wavelengths other than those of visible light. Further, it is understood that a visible or detectable light reader can emit from the grounded electrode of any electrode pair when the high-voltage pulse is initiated at the hot electrode pair prior to the actual spark event. Such a reader is similar to what can be detected from a conductive object prior to a lightning strike. Monitoring of detectable light for visualizing the timing of the spark is the subject of co-owned pending U.S. Provisional Patent Application No. 63 / 434912, filed December 22, 2,022, the entire content of which is incorporated herein by reference.

[0023] It is also intended that catheters without balloons may be used in the present invention. Such catheters preferably include a lumen 29 for delivering saline solution to a controlled volume containing one or more radiators 22. Such a controlled volume may be created by the structure of the patient's vascular system, along with the distal end of the catheter in the region of the radiators. Saline solution may be supplied to fill such a controlled volume, or may flow in and out of such a controlled volume at a controlled flow rate. Partial balloons are also intended, from which a fluid flow of saline solution may flow out from the open distal end of the partial balloon. Such partial or open balloon designs may be useful in forward-facing electrode systems, such as those disclosed in pending U.S. Provisional Patent Application No. 63 / 416,231, filed October 14, 2022, the entire contents of which are incorporated herein by reference. In the case of a catheter 20 having a balloon 24, the controlled volume is provided within the volume of the balloon 24.

[0024] Similarly, as shown in Figure 2, the first optical fiber 30 may be extended within the lumen 29 to a desired location within the balloon 24 for the purpose of emitting light of a desired wavelength within the balloon 24. The second optical fiber 32 may also be extended within the lumen 29 to another desired location within the balloon 24, preferably to sense reflected light emitted from the first optical fiber 30. The distal ends of the first and second fibers 30, 32 are preferably located within the balloon 24 to sense the characteristics of energy waves, such as those generated by the generation of high-voltage sparks in one or more radiators 22, as described above.

[0025] A schematic diagram of the system according to the present invention is shown in Figure 3. Specifically, a catheter 120 extends into an inflatable balloon 124, as described above. Within the lumen 129, a first optical fiber 130 is extended to a selected location within the balloon 124, and a second optical fiber 132 is extended to another selected location within the balloon 124. An electrical wire is also preferably extended from a high-voltage (e.g., between 100V and 10,000V) pulse generator 154 through the lumen 129 to a radiator 122 in order to generate a controlled high-voltage spark and, as described above, to generate an energy wave W in a bolus or a volume of conductive solution within the balloon 124. The distal ends of the first and second optical fibers 130 and 132 are positioned within the balloon 124 to detect the characteristics of such generated energy wave W.

[0026] The proximal end of the first optical fiber 130 is preferably optically connected to a laser source 150. While other light sources may be used, lasers are preferred in that the light source is provided at a known frequency. The laser source 150 may be a low-power laser diode that travels along the optical fiber 130 and generates light of a specific wavelength emitted from the distal end of the first optical fiber 130. The light may be continuous or pulsed, such as being tuned to a high-voltage pulse for spark generation in the radiator 122. The advantage of pulsed light source 150 is that the specific timing of the pulse is known, since it can be controlled relative to the high-voltage pulse. The timing of the light may be controlled, for example, to observe different points in time of the high-voltage pulse. A continuous light source allows for time-series observation in response to changes in other operating conditions of the system of the present invention.

[0027] The proximal end of the second optical fiber 132 is preferably optically connected to a photodetector 152 to detect light of a specific wavelength, such as light radiated from the first optical fiber 130 and reflected within the balloon 124, as described below. The proximal end of the second optical fiber 132 may also be optically connected to an optical detector that preferably provides an amplified signal of the detected light. Optical fibers are well known to have an optical core through which light can propagate, surrounded by a cladding layer. The cladding layer may be further surrounded by a protective layer. In this embodiment of the present invention, the first optical path is defined by the optical fiber 130, and the second optical path is defined by the optical fiber 132.

[0028] Light emitted from the first optical fiber 130 may be reflected based on the acousto-optical effect caused by the generation of energy waves W. The acousto-optical effect can act as a wavelength-specific reflector, similar to a fiber Bragg grating. A fiber Bragg grating can be provided within the optical fiber core by causing a periodic change in the refractive index of the fiber core. Fiber Bragg gratings and the like reflect light of specific wavelengths and transmit all others. A fiber Bragg grating can be used as an in-line optical filter to block certain wavelengths, or it can be used as a wavelength-specific reflector.

[0029] When acoustic energy is applied to a medium such as a saline solution inside balloon 124, sound waves are formed within the medium. In this invention, an energy wave W generated by a high-voltage spark or laser discharge causes a change in the medium, thereby reflecting light of the emission wavelength from the first optical fiber 130, which is then detected by a photodetector 152 via a second optical fiber 132. The energy wave W causes a discontinuity in the refractive index of the conductive medium as it travels with the wave W. In this way, when wave W is present, a portion of the light emitted from the light source 150 is reflected back to the detector. In either case, a few percent of the light from the light source is reflected back and can be detected as an observed value of the energy wave W. The data determined by the photodetector 152 may include the reflected signal over time, such as the intensity or amplitude of the light, and the velocity of the energy wave W. From this data, certain characteristics of the energy wave can be empirically determined over time.

[0030] For example, an energy wave W has an amplitude or intensity based on the strength of the spark in any radiator. The higher the intensity of the energy wave W, the greater the impact on the lesion. Figure 5 shows a comparison of two different energy waves W1 and W2, each having intensities (shown as wave amplitudes) P1 and P2, respectively. The amplitudes of each exemplified wave W1 and W2 are shown over time as the peaks P1 and P2 of each wave. For illustrative purposes, wave W1 in the upper graph has a lower intensity or lower pressure than wave W2 in the lower graph. Arrow A1 represents the intensity of the light source radiated toward the energy wave W1. Arrow B1 represents the amount of radiated light passing through wave W1, and arrow C1 represents the amplitude of the reflected light reflected back from wave W1. The lower graph illustrates wave W2 with a greater intensity than W1 (the amplitude P2 of wave W2 is greater than the amplitude P1 of wave W1). As shown, arrow A2 represents the intensity of the light source radiated toward the energy wave W2. As shown similarly, arrow A2 can be the same as arrow A1. Arrow B2 represents the amount of light passing through wave W2, and arrow B2 represents less light passing through than arrow B1. Arrow C2 represents the amount of reflected light returning from wave W2, and arrow C2 represents a greater amount of reflected light than arrow C1.

[0031] Waves of greater intensity or pressure will cause a greater change in the refractive index of the fluid through which the wave passes, which in turn means a higher reflectivity in the change of rate. In this way, more reflected light suggests that the energy wave W is stronger. Figure 5 shows such a comparison of two waves W1 and W2 of different intensities, and the increase in reflected light from the stronger energy wave W.

[0032] Another wave characteristic that can be monitored by this invention and which can provide useful information is the wave velocity. Figure 6 shows a method for optically determining the velocity of wave W, due to the fact that the phase (phi) of the reflected light (arrows R1 and R2) changes as a function of time (t1~t2) as the wave moves away from the distal tip of the optical fiber receiving the reflected light. This technique is based on the Doppler effect and optical heterodyne detection (as a well-known technique), but essentially, the light is reflected as an energy wave moving away from the distal tip of the optical fiber receiving the reflected light, and therefore the reflected light appears to have a lower frequency than the emitted laser light. The difference in frequency serves as an indicator of the wave velocity.

[0033] In the photodetector 152, light can be filtered for the wavelength of the light source 152. It is also intended that other light may be detected at other wavelengths by the use of additional photodetectors and filters. For example, light from the spark itself may also be detected to provide data related to the spark, in addition to data specific to the energy wave W. In this regard, Provisional Application No. 63 / 434,912 filed on 22 December 2022 and PCT / US No. 23 / 85515 filed on 21 December 2023 are incorporated herein by reference in their entirety.

[0034] Referring next to Figure 4, another preferred embodiment of the IVL system of the present invention is schematically illustrated. Instead of having two separate optical fibers such as optical fibers 130 and 132 described above, an optical circulator 256 may be provided as part of a first optical guide from the light source 250 to the balloon 224 and as part of a second optical guide from the balloon 224 to the photodetector 252. In this embodiment, the first optical fiber 230 extends from the light source 250 to a first port of the optical circulator 256, and the second optical fiber 232 extends from a third port of the optical circulator to the photodetector. The third optical fiber 233 may then extend from the second port of the optical circulator 256 to a location within the balloon 224. In this way, both portions of the first and second optical guides can be shared within the third optical fiber 233 from the circulator 256 into the balloon 224. Such an optical circulator 256 can be configured as a three-port circulator, where light from the light source 250 enters the first port of the circulator and passes through the second port of the circulator to the balloon 224. The reflected light can pass from the balloon 224 through the second port of the circulator 256 and through the third port of the circulator to the photodetector 252. In this system, the circulator 256 separates the light from the light source from the reflected light and controls the first and second light guide paths as described above.

[0035] It is also intended to provide such acousto-optical determination of energy wave characteristics in a forward electrode system, such as those disclosed in jointly owned pending U.S. Provisional Patent Application No. 63 / 416,231 filed October 14, 2022, and PCT / US No. 23 / 35025 filed October 12, 2023, the entire contents of which are incorporated herein by reference. Using forward or axial emission IVLs, phase changes in the synchrotron radiation can be detected in the reflected light. For example, synchrotron radiation traveling axially directly away from the first optical fiber 130 may change wavelength, as in the Doppler effect and as discussed above, when reflected in either direction by energy waves also traveling axially. [Explanation of Symbols]

[0036] 10 Systems 12 consoles or power sources 14 handles 15 Treatment Delivery Control Unit 17 Hubs 20 Catheters 22. Stone crushing sprayer 24 Fluid-filled balloons 26 Central tube 28 Sheath 29 delivery lumens 30. The first optical fiber 32. The second optical fiber 120 catheters 122 Radiators 124 Balloons 129 lumens 130 The first optical fiber 132 The second optical fiber 150 Laser source, light source 152 Photodetectors, light sources 154 High-voltage pulse generator 224 Balloons 233 The third optical fiber 250 light source 252 Photodetectors 256 Light Circulator A1 Arrow A2 Arrow B Marker band, indicator band B1 Arrow B2 Arrow C Vascular calcification C1 Arrow C2 Arrow G guidewire P1: Intensity, peak, amplitude P2 Intensity, Peak, Amplitude R1 Reflected light R2 reflected light W energy wave W1 energy wave W2 energy wave

Claims

1. A method for determining energy wave characteristics in an intravascular lithotripsy apparatus comprising at least one radiator placed inside an inflatable balloon and electrically connected to a high-voltage pulse generator, A step of inflating a balloon to an inflated state using a conductive medium, The steps of generating a high-voltage pulse with the high-voltage pulse generator and generating an energy wave in the conductive medium, The steps include, at least during the generation of the energy wave, emitting light from a laser source along a first optical guide path at a desired wavelength within the balloon, The steps of reflecting light emitted within the balloon due to the acoustic-optical effect of the energy wave, and The step of sensing reflected light with a photodetector via a second light guide path and determining energy wave data from the reflected light. Methods that include...

2. The method according to claim 1, wherein when the high-voltage pulse is generated, an electrical spark is generated between the electrodes of the radiator, the spark generates acoustic energy in the conductive medium in the form of sound waves, and the sound waves act as a reflector of light of a specific wavelength.

3. The method according to claim 1 or 2, wherein the acoustic energy is provided as an energy pulse that generates a moving wavefront.

4. The method according to any one of claims 1 to 3, wherein the energy wave generated by the spark causes a change in the conductive medium, thereby reflecting light of the emission wavelength of light from the first optical light guide, which is detected by the photodetector via the second light guide, and as a result, a moving discontinuity is generated.

5. The method according to any one of claims 1 to 4, wherein the energy wave causes a discontinuity in the refractive index of the conductive medium.

6. The method according to any one of claims 1 to 5, further comprising the step of determining energy wave data from reflected light over a plurality of high-energy pulses applied over time.

7. The method according to any one of claims 1 to 6, wherein the reflected light detected by the photodetector has a different wavelength from the synchrotron radiation.

8. The method according to any one of claims 1 to 7, wherein the energy wave velocity in the direction moving away from the distal tip of the optical fiber provided as part of the second conduit is determined based on the phase change of the reflected light as a function of time.

9. A method for determining the energy wave velocity in a selected direction as a characteristic in an intravascular lithotripsy apparatus comprising at least one radiator placed inside an inflatable balloon and electrically connected to a high-voltage pulse generator, A step of inflating a balloon to an inflated state using a conductive medium, The steps of generating a high-voltage pulse with the high-voltage pulse generator and generating an energy wave in the conductive medium, The steps include, at least during the generation of the energy wave, emitting light from a laser source along a first optical guide path at a desired wavelength within the balloon, The steps of reflecting light emitted within the balloon due to the acoustic-optical effect of the energy wave, and The step of sensing reflected light with a photodetector via a second light guide path and determining energy wave velocity data in the selected direction based on the reflected light. Methods that include...

10. The method according to claim 9, wherein the energy wave velocity data is determined in a direction moving away from the distal tip of the optical fiber provided as part of the second optical guide, based on the phase change of the reflected light as a function of time.

11. A system for determining the energy wave characteristics within an intravascular lithotripsy device, An inflatable balloon, positioned distal to the proximal end of the catheter of the intravascular lithotripsy device, wherein the catheter has a lumen for delivering a conductive medium to the balloon, and At least one radiator, disposed within the inflatable balloon and electrically connected to a high-voltage pulse generator provided at the proximal end of the catheter, for generating energy waves in the conductive medium as a result of high-voltage pulses from the high-voltage pulse generator. Equipped with, A laser source for generating light of a desired wavelength along a first optical guide path that is emitted within the balloon, A photodetector positioned along a second light guide path for sensing reflected light from within the balloon, which is reflected as a result of the generation of the energy wave by a high-voltage pulse based on the acoustic-optical effect of the energy wave. A system that further enhances this feature.

12. The system according to claim 11, wherein during the generation of the energy wave, the laser source is controlled to emit light at the desired wavelength.

13. The system according to claim 11 or 12, wherein the photodetector determines energy wave data from the reflected light.

14. The system according to any one of claims 11 to 13, wherein the radiator comprises a pair of electrodes, and as a result, the high-voltage pulse generates an electrical spark between the electrodes, the spark generates acoustic energy in the conductive medium in the form of sound waves, and the sound waves act as a reflector of light of a specific wavelength.

15. The system according to any one of claims 11 to 14, wherein the acoustic energy is applied as an energy pulse that generates a moving wavefront.

16. The system according to any one of claims 11 to 15, wherein the energy wave generated by the spark causes a change in the conductive medium, thereby reflecting light of the emission wavelength from the first optical light guide, which is detected by the photodetector via the second light guide, and as a result, a moving discontinuity is generated.

17. The system according to any one of claims 11 to 16, wherein the energy wave can generate a discontinuity in the refractive index of the conductive medium.

18. The system according to any one of claims 11 to 17, further comprising a sensor for determining energy wave data from reflected light over a series of high-energy pulses applied over time.

19. The system according to any one of claims 11 to 17, wherein the reflected light detected by the photodetector may have a different wavelength from the synchrotron radiation.

20. The system according to any one of claims 11 to 17, wherein the energy wave velocity in the direction moving away from the distal tip of the optical fiber provided as part of the second conduit can be determined based on the phase change of the reflected light as a function of time.

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