MXPA00003120A - Bubble detection - Google Patents

Abstract

The present invention is intended as a means of diagnosing the presence of a gas bubble and incorporating the information into a feedback system for opto-acoustic thrombolysis. In opto-acoustic thrombolysis, pulsed laser radiation at ultrasonic frequencies is delivered intraluminally down an optical fiber and directed toward a thrombus or otherwise occluded vessel. Dissolution of the occlusion is therefore mediated through ultrasonic action of propagating pressure or shock waves. A vapor bubble in the fluid surrounding the occlusion may form as a result of laser irradiation. This vapor bubble may be used to directly disrupt the occlusion or as a means of producing a pressure wave. It is desirable to detect the formation and follow the lifetime of the vapor bubble. Knowledge of the bubble formation and lifetime yields critical information as to the maximum size of the bubble, density of the absorbed radiation, and properties of the absorbing material. This information can then be used in a feedback system to alter the irradiation conditions.

Description

DETECTION E? RBUBBUJAS BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to the use of lasers to produce acoustic signals in liquid media, and more specifically, it relates to systems for diagnosing the presence of a gas bubble in liquid medium. Description of the Related Art In the patent of US Pat. No. 4,986,659, entitled "Method for Measuring the Size and Velocity of Spherical Particles Using the Phase and Intensity of Scattered Light", an improved apparatus and method is disclosed for determine the change in effective cross section of a volume sample defined by two crossed laser beams. A laser generating means is provided to generate a pair of coherent laser beams and means are provided to change the spacing, angle of intersection and focused diameter of the beams. These rays are directed along an axis, and causes them to cross the axis at a given angle to define an interference pattern that constitutes a sample volume. A collection apparatus is provided to capture the sweep of light caused by particles, droplets, and bubbles, or the like, within the sample volume. In the currently preferred embodiment, the collection apparatus is arranged at off-axis angles including rear sweeps with the predetermined angle, and the angle defined by the ray propagation direction. The collected scanning light is directed on the photo-detectors, which are coupled to a signal phase determination means, to measure the relative phase between the signals produced by each photo-detector and a means of determining the signal amplitude to measure the relative amplitude of the signals produced as the particle, drop, bubble, or the like, passes through the test volume. The sizing means are coupled to the signal phase and the amplitude determining means determine the size of the particle, drop, bubble or the like of the phase and amplitude changes in the received signals. The methods and apparatus are described to determine the change in the effective cross section of the test volume due to the variations in particle size that pass through the interference pattern. The velocity of the particle, drop, bubble, or the like, is determined using well-known laser Doppler anemometry techniques. U.S. Patent No. 5, 263,361, entitled "Apparatus For Leak Testing A Fluid Containing Chamber Utilizing A Laser Beam" is directed to a method and apparatus for leak testing a chamber containing a fluid, wherein the chamber is pressurized with a gas and immersed in a liquid. Gas bubbles emerging from the submerged chamber are directed beyond a plurality of predetermined locations each being in optical communication with a photoelectric detector. The signals of the detectors are counted and when the number of bubbles exceeds a predetermined number, a signal is activated indicating that the container is leaking. By grouping a number of adjacent photoelectric detectors in a predetermined set, the apparatus can discriminate between random bubbles that leave the surface of the chamber as it submerges and a number of bubbles originating from a given location indicating a leak. The photoelectric detectors can be placed in the liquid adjacent to the predetermined locations or placed outside the liquid and coupled to the predetermined places by fiber optic cables. Alternatively, a laser beam can be directed through the predetermined site and received by a detector on the opposite side of the laser source. When a bubble interrupts the laser beam, a signal is generated. U.S. Patent No. 4,662,749, entitled "Fiber Optic Probé And System For Particle Size And Velocity Measurement" describes a system for the simultaneous measurement of the size and velocities of droplet bubbles in a multi-phase process environment wherein the Light passes through a Ronchi grid, is projected onto a measurement volume within the multiple process stream by means of a coherent optical fiber beam and gradient index imaging lenses. Droplets or bubbles passing through the measurement volume reflect or refract light, which is captured by fiber optic bundles that pick up speed and size arranged opposite the imaging lenses and the captured signal is coupled to the media of signal processing which convert the light signal to electrical signals. Appropriate size velocity measurements are made using one or more of the visibility techniques, delaying techniques of technical phases of transit time control. U.S. Patent No. 5,473,136, entitled "Method And Apparatus For The Machining Of Material By Means Of A Laser "describes a method to treat the material using a laser with detection of the material to be treated, where the laser light is directed to the material via the laser optical system and the light emitted by the material is guided to a first disposition detector which measures the intensity of the light and behind which an evaluation circuit is connected to control the laser power or energy.The power supply to the material via the laser optical system is It measures, and the detector's arrangement supplies a display signal to the evaluation circuit, which indicates the beginning of the dielectric alteration.The evaluation circuit reduces the power of the laser and / or interrupts the laser pulse if it has not yet been presented a display signal at a predetermined time at which predetermined energy was fed to the material.DECENDER OF THE INVENTION It is a goal of The present invention provides an optical based method for detecting the presence of a vapor bubble. It is another object of the invention to produce a signal which indicates the presence of a vapor bubble.

Still another object of the invention is to provide a feedback system for laser pulse control used for bubble formation. A light source, such as a laser, is coupled to an optical fiber and transmitted to the desired origin of bubble formation. The light reflected back at the tip of the distal fiber is monitored as it returns and is emitted outside the proximal end of the fiber. While a bubble is formed at the distal end, the amount of reflected light increases while the decoupled refractive index (nf¡bra-na¡re> nf¡bra-npquido) increases - This signal can give information about the bubble and irradiated material such as formation time and bubble collapsing, bubble size, material absorption characteristics, and mechanical characteristics of the material. This data can be used in a feedback control system to optimize the irradiation conditions. The invention can be used in a variety of applications including remote detection of a cavity or vaporization of white material, as a result of laser irradiation. It can be used in hospitals together with laser-based methods for stroke treatment and can be used for remote bubble detection in a variety of experiments where bubbles are formed, particularly at the end of an optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows an embodiment of the present invention.

Figure 2A shows the usual output of the detector of Figure 1 during bubble formation and collapse. Figures 2B-E show the growth and collapse of the bubble at times of 5 μs, 55 μs, 85 μs, and 100 μs respectively. Figure 3 shows a flow chart of the logical control elements of a modality of the feedback system of the invention. Figure 4 shows data on the life time of the bubble. Figure 5 shows data of the diameter of the bubble against the impulse / energy. Figure 6A shows a representation of an application of the present invention in an opto-acoustic thrombotic catheter based on optical fiber. Figure 6B represents the ultrasonic dissolution of a block using an attached fluid. Figures 7A-C, represent the thermo-elastic operation as a method of bubble formation. Figures 8A-C, represent the mode of expansion of steam over heated as a method of bubble formation. DETAILED DESCRIPTION OF THE INVENTION Although this invention can be used for a variety of bubble detection applications, it is discussed in view of medical applications, where a bubble forms at a remote site within the body. There are many methods of detecting bubbles but they are not practical for this application. Optical methods have been used to detect bubbles, often collecting light from the opposite side of the broadcast signal. In the present invention, light can be supplied and collected from the same optical fiber, eliminating the need to cross an occlusion and allowing remote and minimally invasive access. In addition, the same optical fiber used to deliver therapeutic radiation can be used by the bubble detection mechanism. This invention incorporates a beam of a light source, such as a HeNe laser beam or laser beam diode, which is coupled to an optical fiber via a lens and directed to the bubble formation site. This diagnostic beam can use the same optical fiber used by a second laser beam for the generation of bubbles. Some of the diagnostic light that emerges from the distal end of the fiber will couple back into the fiber through reflection and sweep. The light reflected directly back into the fiber depends on the load on the refractive index between the fiber, n 1, and the material at the distal end, n2, where the fraction of reflected light R = | (n2-n1 ) / (n2 + n1) | 2. In addition, some Juz is swept back into the fiber, depending on the optical properties (sweep coefficient, absorption coefficient, and anisotropy) of the material at the distal end. This reflected and sweeping feedback light is measured at the proximal end of the same fiber, allowing remote access to the treated area. As one develops bubble, change the intensity of the feedback light. The CD level of the measured signal depends on the material at the fiber output. The AC component of the signal corresponds to the dynamics of the bubbles. The time of growth and collapse, and the size of the bubble or bubbles generated, can be determined. Because the feedback signal depends on the optical properties of the material, feedback signals at multiple wavelengths can be used as a method to identify different types of tissues. This information can be incorporated into a system of feedback, as discussed above, this controls and adjusts the irradiation parameters of the treatment laser. One embodiment of the present invention is shown in Figure 1. A laser system provides a laser beam 10 for generating bubbles. This ray is reflected from a mirror dichroic or ray separator 12, passes through a ray separator 14 (or a mirror 14 with a hole), and is focused by the lenses 16 at the proximal end of optical fiber 18. The distal end of this fiber is placed for the delivery of laser light in a medium, such as near a thrombus within the vascuJatura. One second laser system provides a laser beam 20 for the detection of bubbles. The laser beam 20 passes through the ray separators 12 and 14 and is focused by the lenses 16 on the optical fiber 18. As a laser beam 10 bubbles in the liquid medium, the laser beam 20 reflects variably (Fresnel reflection) by the fiber bubble interface at the distal end of the fiber - "• • • optical 18, to exit and be collected by the lenses 16. A portion of this collected ray is reflected by the ray separator 14, and is passed through a polarizer 28, is focused by the lenses 22, and it is passed through the filter 24 on the grid 26. other surfaces 5 within this system also generate the reflected light back, v. gr. , the dominant cause of the unwanted back reflected light is the focusing lens 16 and the proximal surface of the optical fiber 18. A properly orientated linear pointer 28 rejects the linearly polarized reflected laser light from these surfaces while which transmits the randomly polarized light emerging from the optical fiber 18. A component of the laser beam 10 also propagates back the ray separators 14, to focus by the lens 22 and pass through the polarized J / 28. The fi xer 24 eliminates a portion of this bubble generation light. The grid 26 separates spatially the two wavelengths produced on each by the laser beam 10 and the laser beam 20. The detector 30 is generally positioned to receive light only from the laser beam 20. Figure 2A shows the signal emitted by the detector 30. This signal is supplied to the logic control electronics 50 which provide feedback information, as shown in Figure 3. The magnitude and temporal history of the Juz that reaches the detector, and therefore the output signal of the detector, produces important information about the state of bubble formation and properties. of the material at the far end of the fiber. An exit Of the detector during the formation and collapse of bubbles is aassSfe ^ «^^ ^^ a? ^^^ t ^? ^ a ^ ÁtMji? ^ AU ^^ shown in Figure 2A. Once a bubble forms at the tip of the fiber, the detector signal increases in magnitude as more light reflects on the fiber. Figure 2B shows the formation of a bubble 40 at the tip of the fiber 18 at 5 μs. A simple bubble or non-bubble determination can be made by purchasing the signal before the therapeutic laser is turned on and shortly thereafter, for example, 10 μs. A synchronization signal 52, as shown in Figure 3, to the therapeutic laser 54 (and its associated power supply 56) can also be provided to the logic control electronics 50 of the feedback device. This signal can synchronize the feedback system to obtain a sample 58 from the output detector 30 immediately before the laser 54 is driven. A second sample 62 is taken with a predetermined delay 60 and compared with the first, as shown in block 64. If a pre-set threshold is exceeded, as shown in block 66, it can be assumed that a bubble formed. If a bubble was not formed, either insufficient laser energy was provided or insufficient absorption due to, for example, a diluted sample or improper placement of the fiber tip. This information could be used to temporarily shut down the laser, as shown in block 68, preventing the supply of high energy usage. As shown in block 70, the laser synchronization and the laser opening signal from the laser computation control 72 and the logic control signal must - ^^ *. * * i ^^^^^^^^ 3 to be present before the light generating laser 54 can be turned on. It can be seen from the sample traces (Fig. 2A) that the life time of the bubble can be determined from the duration of the increased detector signal. The detector signal can sample at multiple times to determine when the signal returns to the baseline. Figures 2C-E show the growth and collapse of bubble 40 at times of 55 μs, 85 μs and 100 μs, respectively. Alternatively a regulation circuit can be synchronized to the overpumping a positive edge entry and terminated to a negative edge. This will produce data on the life time of a bubble which correlates directly to the maximum bubble diameter (Fig. 4). Referring to Figure 5, the size of the bubble is a function of the energy density (laser energy, input size, and depth of penetration) in the material properties. As the intensity of the reflected light depends on the refractive difference index between the fiber and the surrounding medium, tissue discrimination can be carried out by analyzing the detector signal. The biological tissues have refractive indices that vary between approximately 1.33 to 1.5. depending on the option of fiber optic material N = 1.4-1.5), the percentage of reflected light due only to the Fresnel reflection at the tip of the fiber can be made to vary between 0 and 0.3%. Monitoring the detector signal, which has a previous calibration curve (for index of JS & amp; s refractivity), and prior knowledge of potential tissues found, a user can distinguish which material is immediately next to the tip of the fiber. The use of additional test wavelengths will make tissue discrimination easier since different wavelengths can have dramatically different optical properties in tissues (refractive index, absorption, sweep, anisotropy). The returned and detected signals of two or more test wavelengths can be related to give an indication of the type of material. For example, to discriminate if a test is immersed in blood or near an artery wall, a wavelength strongly absorbed by blood (blue wavelength) and a wavelength poorly absorbed by both (red) can be used. When the fiber is immersed in blood, the ratio of red light to strongly absorbed and less blue light sweep should be greater than when the fiber is in contact with the container. In this way, intelligent options can be made for laser wavelengths with respect to the likely target tissues and calibration curves could be generated. An "intelligent" laser system could provide this data to determine which tissues will be irradiated and alter the irradiation parameters (wavelength, pulse duration, energy / pulse, power, etc.) to carry out a desired effect or prevent undesirable consequences. A laser could be tuned to match the stronger absorption of the white material or it could be disabled when an inappropriate target is present. A computer could be used to interpret this data and control the laser or these tasks could be performed by synchronizing level detection and logic circuits. In one embodiment of the invention, a feedback system can be included in the laser-based method to alter the thrombus as a stroke treatment. The laser treatment may consist of a pulse laser. Since the minimum thermal energy could initiate additional complications and damage, irradiation should be limited to the possible extent. If the laser treatment is not producing the desired effect, continuous operation should be avoided. The present feedback system, which incorporates a low-power continuous wave laser, monitors the state at the distal end of the fiber optic supply system. If there is no significant change in the detector signal observed immediately before, and several microseconds denuded, the treatment pulse, then the blocks of the feedback system supply the treatment laser. After a certain duration, another treatment impulse is given and the bubble monitor proves a positive indication of a bubble. When a bubble is detected, it is assumed that the laser is interacting appropriately with the target medium and the treatment is allowed to continue. In this way, waste deposition and potential heat damage are avoided. The applications visualized for this invention include any method or method where it is convenient to detect vapor or bubbles in the cavity. Applications may include bubble diagnosis and / or feedback mechanism during: • Laser-based treatment (eg, acoustic thrombolysis optics) of vascular occlusions that lead to ischemic stroke. This technology can lyse the thrombus and allow reperfusion of the affected brain tissue. • Laser-based treatment (eg, acoustic thrombolysis optics), cerebral vasospasm. This technology can relax vaso-constriction allowing the restoration of normal perfusion and therefore avoid additional temporary ischemic attacks or other situations of abnormal perfusion. • Laser-based treatment (eg, acoustic thrombolysis optics) of cardiovascular occlusions. This technology can lyse the thrombus or remove atherosclerotic plaques from the arteries. • Laser-based treatment (eg, acoustic thrombolysis optics) of carotid artery stenosis. • The general restoration of patency in any of the luminal passages of the body where access can be facilitated via percutaneous insertion of optical fibers and managed ablation of subsequent vaporization. • Any vaporization or cavity based on the procedure using laser or other means of generation of vapor bubbles. One embodiment of the invention incorporates a catheter containing an optical fiber, the optical fiber is coupled at the proximal end to a laser system of high repetition regime which injects pulses of light along the beam path of laser beam 110 as described in Figure 1. The light emerging from the fiber at the distal end is absorbed by the fluid surrounding the catheter. This fluid can be blood, a biological saline solution containing an absorption dye, a pharmaceutical thrombolytic or the thrombus by itself. The optical fiber functions as a means of transmitting energy in such a way that the optical energy produced by the laser is supplied to the end of the fiber. The high-repetition regimen laser light emerging from the distal end of the optical fiber has a pulse frequency within the range of 10Hz to 100 kHz, a wavelength within the range of 200 nm to 5000 nm and a density of energy within the range of 0.01 J / cm2 to 4 J / cm2, or up to 50 J / cm2, if dictated by a small fiber optic diameter; the applied energy is kept below 5 milli-Joules, and preferably less than one milli-Joule. In one embodiment, the pulse frequency is within the range of 5 kHz to 25 kHz. Alternatively, a lower end of the pulse frequency can be 100 Hz, an upper end of the scale being 100 kHz. Lysis of the thrombus, atherosclerosis plaque or any other that occludes the material in the tubular tissue is facilitated by an ultrasonic radiation field created in the fluids near the occlusion. As an adjunct treatment, a working channel which surrounds or operates parallel to the optical fiber can be used to dispense small amounts of thrombotic drugs to facilitate the additional leakage of any significantly coupled debris (> 5 μ day. in the process of acoustic thrombolysis. The conversion of acoustic optical energy can proceed through several mechanisms that can be thermoelastic, thermodynamic or a combination of these. Figure 6A shows an optical fiber 110 with a parallel working channel 112, where the fiber 110 and the working channel 112 are located within a catheter 114 which has been inserted into a blood vessel 116. The distal fiber end 110 is located near thrombus 118 and / or stenoic plate 120 within blood vessel 116. In Figure 6B, fiber 110 supplies laser light to produce a bubble of collapsing cavity 11 and the resulting acoustic wave of expansion. A parallel working channel 112 in the catheter 114 supplies an attached fluid 115 to assist in the removal of occlusion 117 from the internal blood vessel 116. As shown in Figures 7A-C, in the thermoelastic mode, through the fiber optic 121, each laser pulse 122 provides a controlled level of energy in fluid 1.24 which creates a large thermoelastic tension in a small volume of fluid. The direction of expansion of this tension is indicated by arrows 125 in Figure 7A. The volume of the fluid 124 which is heated by the laser pulse 122 is determined by the depth of absorption of the laser light in the fluid 124. and must be controlled to produce a desired size. For example, an appropriate size ^ A = *; i ^^ ~ ¥ ^^ can be the fiber diameter, or a distance comparable to some fraction of the vessel containing the occlusion. This can be adjusted by controlling the laser wavelength or the composition of the fluid such that most of the laser energy is deposited at a depth of fluid of the desired size. The laser pulse duration is ideally short and sufficient to deposit all the laser energy in the absorption fluid on a shorter time scale than the acoustic transit time crosses the smaller dimension of the absorption region. This is an isochoric heating process (constant volume). For an absorption volume of approximately 100 μm in diameter the acoustic transit time is approximately 70 ns, since the deposit time must be significantly shorter than the same, v. gr. , around 10 ns. The absorption fluid responds thermoelastically to the energy reservoir in such a way that a high pressure region is created in the fluid in the heated volume. The boundary of the high pressure zone decays into a pattern of acoustic waves: a compression wave propagates from the region of energy deposition X that diverge from the wave front) and a rarefaction wave propagates towards the center of the region of energy deposition (which converges from the wavefront). When the wave rarefaction converges on the center of the initial deposition region, this creates a voltage region 126 that promotes the formation of a cloud of cavity bubbles which collide to form a large bubble 130.

Eventually, the bubble cavities collapse (132), resulting in an acoustic expansion wave 133. The collapse and subsequent bounce of the cavity bubble will generate acoustic pulses in the fluid surrounding it, which will carry a portion of the bubble. energy of the cavity. The collapse and rebound process take place on a time scale regulated mainly by the density of the fluid and the maximum size of the initial cavity. The first collapse and rebound will be followed by a collapse and subsequent rebound events of decreased intensity until the energy of the cavity dissipates in the fluid. The consequent laser pulses are supplied to repeat or continue this cycle and generate a field of ultrasonic radiation at a frequency or frequencies determined by the laser pulse frequency. In summary, an operating device through the first mode produces a field of ultrasonic radiation in the fluid by: (i) depositing laser energy in a volume or fluid comparable to the fiber dimension in a time scale of less duration that the acoustic transit time through this dimension (controlled by the choice of the laser wavelength and absorption fluid as the case may be); (ii) controlling the energy of the laser in such a way that the maximum size of the bubble cavity is approximately the same as the diameter of the fiber; and (iii) driving the laser in a repetition regime of such form that multiple cycles of this process generate a field of acoustic radiation in the surrounding fluid; the resonant operation can The laser pulse repetition rate with the life time of the cavity is synchronized to be effected. The usual operation leads to a transducer based on a fluid that circulates at 1-100 kHz with a reciprocal displacement of 100-200 μm (for usual optical fiber dimensions). This displacement is very similar to that found in mechanically activated ultrasound angioplasty devices. In the overheated steam expansion mode, as shown in Figures 8A-C in optical fiber 141, each laser pulse 140 supplies a controlled level of energy in the fluid within an absorption depth which is very small compared to the size characteristics of the vessel containing the catheter, even lower compared to the fiber diameter. The depth of absorption can also be small compared to the distance at which a sound wave travels at the duration of the laser pulse: the laser energy deposits a sufficient level of energy to heat most of the fluid at an ambient pressure. In the process of depositing laser energy, an acoustic wave generated thermoelastically is thrown into the fluid, which propagates outside the heated region. On longer time scales of 1 μs, the overheated fluid 142 undergoes vaporization, which creates a vapor bubble. While the fluid vaporizes, its volume 144 increases by a large factor. The laser pulse duration need not be restricted to such short times as in the thermoelastic mode since the expansion of a bubble is closely an isobaric process; however, the laser pulse duration must be shorter than the bubble expansion time, and this must be much shorter than a usual relaxation time for the overheated region. (According to Rayleigh's bubble collapse theory, the life time of the bubble in water is about 25 μs for a bubble diameter of 50 μm, thermal relaxation occurs on a time scale of a few hundred microseconds , so that the laser pulse must to be several microseconds or less in duration). The vapor bubble expands to a maximum radius which depends on the vapor pressure initially created in the fluid and the properties of the fluid. At the maximum bubble radius, the vapor pressure in the expanded bubble has dripped for good after the room temperature and the bubble 146 suffers samienlo tail, which results in an acoustic wave of expansion 148. The events of rebound and subsequent collapse may take place following the first collapse. The expansion of the bubble and collapse couples acoustic energy in the fluid. Subsequent laser pulses will provide to repeat or continue this cycle and generate an ultrasonic radiation field at a frequency or frequencies determined by the laser pulse frequency. Similar to the first mode, a resonant operation can be carried out by machining the laser pulse period to the life time of the vapor bubble.

^^ ^ MñA t ^^^^^ í ^^^! I ^^^^ .aatejA 2.1 & In summary, a device operating through the second mode produces a field of ultrasonic radiation in the fluid by: (i) reservoir of laser energy in a small volume of fluid (as controlled by choice of laser wavelength) and that absorbs the fluid as may be the case); (ii) control the energy of the laser in such a way that the maximum size of the vapor bubble is such that the bubble does not damage the surrounding tissues; and (iii) pressing the energy of the laser in a repetition rate in such a manner of multiple cycles of the generation of bubbles and collapse processes generates a field of acoustic radiation in the fluid that surrounds it. Unlike the first mode, the delivery time is not a significant emission, very long pulse lasers (up to several μs) can be useful. For any mode of operation of the laser wavelength, the duration of the laser pulse and the depth of laser absorption must be controlled precisely in such a way that an adequate acoustic response is obtained with a minimum of laser pulse energy. For the first mode this links the absorption volume coupling to a characteristic dimension of the system such that the diameter of the fiber or some fraction of the diameter of the vessel, and using a short laser pulse (less than 20 ns). For the second mode this links the deposit of the laser energy at a very small depth of absorption to carry out a sufficient level of superheat in a small mass of fluid as can be accommodated by an apequeña J? G ^^^ accumulation of energy and without creating a vapor bubble so long as to damage the tissues that surround it. These opto-acoustic modes of laser energy coupling in acoustic excitations in tissues include a number of aspects. Low to moderate laser pulse energy combined with a high repetition regimen prevents excessive tissue heating or intense shock generation. Localized absorption of laser energy occurs. The laser energy can interact thermoelastically or thermodynamically with the fluids of the environment. An acoustic radiation field is generated by repeated expansion and collapse of a bubble at the tip of the fiber. The resonant operation can be carried out by coupling the period of the laser pulse of the lifetime of the generated bubble. Soft fibrous occlusions (thrombus) can be interrupted by generating bubbles directly within the thrombus. The control and / or manipulation of the temporal and spatial distribution of the energy deposited in the fluid at the tip of the fiber, as shown in Figure 1 and Figure 3, can be used to modify the near-field acoustic radiation pattern , for example, to concentrate acoustic energy on an object in proximity to the fiber, or to distribute the acoustic radiation more uniformly. The techniques based on this strategy will be more successful for a special case of thermoelastic response (first mode) when the duration of the laser pulse is short and the fluid absorption is also relatively strong, so that the 2% »v energy of the laser is deposited in a thin layer adjacent to the surface of the tip of the fiber. For example, by forming a concave surface on the tip of the fiber, the optical energy is deposited in the fluid in a similar distribution. The acoustic waves emitted from this concave distribution will tend to focus at a point at a distance R from the tip of the fiber, where R is the radius of curvature of the concave surface. A flat fiber tip will initially generate a flat acoustic wave front in proximity to the tip of the fiber. A convex fiber tip will produce a divergent spherical wave front which will scatter acoustic energy over a longer solid angle. Another means of modifying the near-field radiation pattern can use a fiber bundle through which the laser energy is supplied, and control the temporal distribution of deposited laser energy. The laser energy can be arranged to arrive at individual fiber strands at the tip of the catheter at different times, which, in combination with the different spatial positions of these individual strands, can be adjusted to control the direction and shape of the radiation pattern. acoustic, similar to the techniques disposed of phase used in the radar. Commercial fibers are usually covered to protect them from the environment. "Uncovered" or uncovered fibers are available. It is useful to use coatings on the fibers to make the slides more easily through the catheter. An optical fiber of variable diameter allows for greater physical resistance in tSj & Ži the proximal end and greater access at the distal end. This can be completed through the existing modification fibers (by detaching the protective cover around the center) or by making the usual fibers. The manufacture of customary fibers can be completed by varying the extrusion or stretching regime for the fiber. The glass or plastic composition can be changed as a function of stretching the fiber such that there is more control of the fiber from a distal end without sacrificing optical quality. A particular instance of this is to treat the tip in such a way that it is "soft", so the end will not tighten the catheter cover. Also, the size of the memory at the tip allows the direction of the fiber when it protrudes from the distal end of the catheter cover. The laser-driven power source used by this invention may be based on a gaseous, liquid or solid state medium. The posterior-ground-altered solid-state lasers, ruby laser, alexandrite laser, Nd: YAG laser and Ho: YLF laser are examples of lasers that can operate in a pulse mode at a high repetition rate and it is used in the present invention. Either of these solid state lasers can incorporate double-frequency or triple-frequency non-linear crystals for the harmonic production of the fundamental laser wavelength. A solid state laser that produces a coherent beam of ultraviolet radiation can be used directly with the invention or used together with a dye laser to produce an output ray which rotates over a wide portion of the ultraviolet and visible spectrum. The ability to rotate over a broad spectrum provides a wide range of flexibility to couple the wavelength to the absorption characteristics of the fluids located at the distal end of the catheter. The output beam is coupled by means of an optical fiber to the surgical site through, for example, a percutaneous catheter. In operation, the pulsed ray of light drives the ultrasonic excitation which removes and / or emulsifies the thrombus or atherosclerotic plaque with less damage to the underlying tissue and less change of perforation of the wall of blood cases than the devices of the prior art. Several used lasers can be substituted for the laser sources described. Similarly, various colorant materials and configurations can be used in the coloring laser. The different configurations of a free-flowing dye, such as plastic films impregnated with dye or dyes enclosed in a specimen, can be replaced in the dye laser. The dye laser can also store a plurality of different dyes and substitute one for another automatically in response to control signals initiated by the user or conditions encountered during use (eg, when exchanging a filling field of blood to a saline field or in response to deposits of calcification). Colorants suitable for use in the dye laser components of the invention include, for example, P-terphenyl (peak wavelength 339); BiBuQ ifeaataaia (peak wavelength; 385); DPS (peak wavelength; 405); and Coumarin 2 (peak wavelength: 448) In yet another embodiment, the pulsed light source may be an oscillated optical parametric (OPO) pumped by a dual-frequency or triple-frequency solid-state laser. The OPO systems allow for a wide range of wavelength modulation in the compact system comprised entirely of solid state optical elements. The wavelength of the laser in OPO systems can also be varied automatically in response to control signals initiated by the user or conditions encountered during its use. Catheters, useful in the practice of the present invention, can take various forms. For example, one embodiment may consist of a catheter having an external diameter of 3.5 millimeters or less, preferably 2.5 millimeters or less. Arranged within the catheter is the optical fiber which may be a diameter of 400 microns or smaller silicon fiber (fused quartz) such as the model SG 800 fiber manufactured by Spectran, I nc. From Sturbridge, Mass. The catheter can be multi lumens to provide emptying and suction ports. In one embodiment, the tip of the catheter can be constructed of radio-opaque and heat-resistant material. The radio-opaque tip can be used to locate the catheter under fluoroscopy. Changes and modifications to the modalities described specifically can be carried out without departing from the framework of the invention which is intended to be limited by the scope of the appended claims.

Claims (12)

1. CLAIMS 1. Apparatus for detecting the presence of a bubble (40, 111, 130, 144, 146), comprising - means (12, 14, 16) for the combination of a first laser beam (10,122,140) and a second ray of laser (20) to make them coiineal; an optical fiber (18, 110, 121, 141) comprising a proximal end and a distal end; means (16) for focusing said first (10, 121, 140) and said second (20) laser beams at the proximal end of the optical fiber (18, 11, 121, 141); a detector (30) means (14, 16, 22, 24, 26, 28) for directing reflected light from the distal end of the optical fiber (18, 110, 121, 141) to the detector; and a logic control system (50,58,60,62,64,66,68) comprising means for analyzing a signal produced by the detector (30) to detect the presence of a bubble (40, 111, 130, 144 , 146). Apparatus according to claim 1, including means for analyzing a signal produced by the detector (30) to control a laser that generates the first laser beam (10, 122, 140). Apparatus according to claim 1 or 2, wherein said second laser beam (20) is produced by a laser selected from the group consisting of a diode laser, a dye laser and a He-Ne laser. An apparatus according to any of the preceding claims, wherein the means for combining said first (10, 121, 140) and second (20) laser beams comprises one of a dichroic mirror and a ray separator (14) . Apparatus according to any preceding claim, wherein the means for directing light reflected from said distal end of the optical fiber (18, 110, 121, 141) to the detector (30) comprises one of: a ray separator ( 14); a mirror with a hole (14); a polarizer (28) for extracting light from said first laser beam (10, 121, 140) and primary surface reflections from said second laser beam (20); a filter (24) for removing light from said first laser beam 810, 121, 140); and a grid (26) to draw light from said first laser beam (10, 121, 140). Apparatus according to any preceding claim including means for storing a first sample (58) of said signal detector before a first firing of the first laser beam (10, 121, 140); means for storing a second sample (62) of said signal detector a predetermined delay (60) after the first firing of the first laser beam (10, 121, 140); means (64) to subtract the second sample from the first sample to obtain a sample difference; and half (66, 68, 70) to control the firing of the first laser beam based on said sample difference. Apparatus according to claim 6, wherein the means for controlling comprises means (52, 70) for continuing the firing of the first laser beam (10, 121, 140) if said sample difference is greater than a predetermined input level. (66); and means (68) for discontinuing the firing of the first laser beam if said sample difference is less than said predetermined input level (66). Apparatus according to claim 7, wherein the control means includes means for any (i) of ignition discontinuance said first laser beam (10, 121, 140) from said transmission means for at least one period of time or (ii) increasing the power of said first laser beam, above a predetermined power, until said bubble (40, 11, 130, 144, 146) forms, if said sample difference is less than said predetermined level ( 66). Apparatus according to any preceding claim, wherein the optical fiber (18, 110, 121, 141) is of a sufficient construction for insertion into a liquid environment medium (124, 142), and the first laser beam ( 10, 121, 140) is supplied to the liquid environment medium (124, 142). 10. An optical fiber device for treating a body lumen having occlusive materials herein, comprising: an optical fiber (18, 110, 121, 141) having a proximal end and a distal end, said optical fiber (18, 11, 121, 141) of a construction sufficient for the insertion of the distal end in a fluid medium (124, 142) within the lumen of the body (116), means (12, 14, 16) for coupling a first ray of light (10, 122, 140) and a second beam of light (20) at the proximal end to supply the distal end, wherein the first beam (10, 122, 140) is capable of interacting with the fluid medium (124, 142) for interrupting the occlusion material (117, 118, 120); means (14, 16, 22, 24, 26, 28) to monitor a reflection of the second ray (20) at the distal end to obtain information selected from a group consisting of the first information related to any bubble (40, 11, 130, 144, 146) at the distal end, second information related to any material (117, 118, 120) at the distal end, and any combination thereof, the first information selects from a group consisting of an absence or presence of the bubble (40, 11, 130,144,146), a duration of the bubble (40, 111, 130, 144, 146), a bubble size (40, 11, 130, 144, 146), and any combination thereof, and the second information selects from a group consisting of one type of material (117, 118, 120), a material absorption feature (117, 118, 120), a mechanical property of the material (117, 118, 120) and any combination thereof; and means for controlling the first beam (10, 122, 140) based on the information 11. A device according to claim 10, including a working channel (112) which surrounds or operates parallel to the optical fiber (18). , 11, 121, 141). A device according to claim 11, including a catheter (114) which contains the optical fiber (18, 110, 121, 140) and working channel (112), and is of sufficient construction for insertion of a distal end thereof within the lumen of the body (116) 13 A device according to any of claims 10 to 12, wherein at least one of the first (10, 122, 140) and second (20) rays of Light is generated by means of a laser (54). 14. A device according to claim 13, wherein the first beam (10, 122, 140) is generated by one of a pulsed laser and an optical paramétpco oscillator. 15. A device according to claim 13 or claim 14, wherein the second beam (20) is generated by means of a continuous wave laser. 16. A device according to any of claims 10 to 15, wherein the means for monitoring comprises means for monitoring a reflection of the second beam. as represented by a signal having a CD component and a CA component, the CA component that provides the first information. A device according to any of claims 10 to 16, wherein the means for controlling is adapted to discontinue, at least temporarily, the supply of the first beam (10, 122, 140), continuous supply of the first beam ( 10, 122, 140) or control of an irradiation parameter of the first beam (10, 122, 140).