Apparatus for laser treatment of body lumens

Abstract: A laser microsurgical method and apparatus are dis­ closed for safely treating occluded body lumens with laser energy. The disclosed method involves the use of pulsed laser energy from an argon-ion laser (62) to destroy the tissue of luminal occlusions, such as atheromatous plaque and the like, with substantially no thermal necrosis of the surrounding tissue. A flexible catheter and associated laser microsurgical system is also disclosed which provides for aiming of the fibers (18a-18d) to transmit the laser beam at the distal end of the catheter and rotational positioning of the catheter to permit coverage of virtually the entire cross-sectional area of the lumen. A lens system (46-48) at the distal end of each laser fiber minimizes beam divergence and directs the beam to­ ward the central axis of the catheter. A further embodiment of the catheter of the invention provides an array of laser fibers (118) which are optically scanned (66) with laser energy to cover the cross-sectional area of the lumen. The system is designed to minimize the possibility of damage to or perfora­ tion of the surrounding tissue of the lumen.

Description: BACKGROUND OF THE INVENTION The present invention relates to performing surgery in a body lumen having an obstruction therein, comprising the features of the preamble of claim 1, and more particularly to the intraluminal use of laser energy to perforate and/or remove luminal occlusions, such as thrombi and/or atherosclerotic plaques in the cardiovascular system. Cardiovascular disease is a major cause of death and morbidity and manifests a grave concern to both the scientific community andthe lay public. Arteriosclerotic cardiovascular pathophysiology is a complex of diseases which affects many blood vessels in the body, the decreased lumen diameter causing tissue ischemia. Other very common diseases, such as diabetes mellitus, enhance the occlusion of important blood vessels and ischemia of the organs they supply. Those diseases, aggravated by such other common abnormalities as hypertension, and other vascular diseases and cardiovascular diseases, account for cerebrovascular accidents, myocardial infarctions, and other devastating illnesses, including loss of life and limb. Unfortunate individuals affected with arteriosclerotic cardiovascular diseases and the related vasculopathies often manifest disease in coronary, carotid and cerebral arteries, in popliteal, tibial and dorsalis pedis arteries of the lower extremeties and in other vessels. Those individuals, apart from having a shortened life expectancy, and suffering from sudden death, frequently also suffer from other debilitating problems including angina, shortness of breath and restricted activity, claudication or restricted use of the lower extremities, sometimes with loss of those extremities from disease, and loss of functions of movement, speech, cerebral interpretation and cognitive abilities. Historically, there are few effective means for preventing some of the foregoing disastrous medical problems. Patients with certain types of coronary insufficiencies documented by certain coronary angiographic findings may be helped symptomatically by coronary artery bypass operations. Other patients sometimes may be benefited by other types of arterial surgery, for example, various bypass operations, or endarterectomies, which surgically attempt recanalization of certain occluded blood vessels or other operations. Those are generally patients with severe disease, but yet who meet certain diagnostic criteria and who are healthy enough to undergo what amounts to major surgery with relatively high morbidity and mortality rates. The cost is immense for many of these operations and incumbent hospitalization, including expensive special equipment which is required, and special training which is necessary for a team to operate the special surgical equipment. For example, it is estimated that a single coronary bypass operation may cost a patient over $50,000 including the hospitalization fees, and surgical fees. Availability of this special type of surgery for vascular problems is limited. Long term efficacy of coronary bypass surgery is as yet unknown, and the appropriate diagnostic and surgical criteria remain controversial. Because of the severity of the morphology and nature of the disease, for many patients treatment has been unavailable and has been beyond the current scope of surgical intervention. For example, many patients lose extremities or their lives by virtue of having these inoperable conditions. In a different context, problems of lumens of the body, particularly small lumens, are complicated by occlusive diseases of other types. As an example in the nervous system, the Aqueduct of Sylvius, in the ventricular system of the brain, may be blocked in a child born with congenital hydrocephalus. This condition necessitates a complicated and often unsuccessful corrective neurosurgical procedure known as shunting. Considering the genito-urinary system, for example, fallopian tubes may become occluded by inflammatory or other disease processes. This may cause infertility and is a common problem. There is no effective treatment for this problem at this point in time, and this has stimulated interest in the "test tube baby" controversy. One suggested solution to the problem of atherosclerotic obstructions is a non-operative technique to improve coronary blood flow known as percutaneous transluminal coronary angioplasty (PTCA). Generally, PTCA involves introducing a balloon catheter into the femoral artery or by brachial cutdown and fluorscopic positioning at the appropriate coronary ostium. Pressure monitoring is also used to aid in positioning the balloon tip of the catheter at the stenosis. The ballooon is inflated for 3-5 seconds to mechanically enlarge the stenosis and is then deflated for measurement of distal coronary pressure. The cycle may be repeated several times until a satisfactory decrease in pressure gradient is achieved. Although the PTCA technique is sometimes effective to improve coronary blood flow, there are complications which must be weighed before undertaking the procedure. Such complications which may occur include arterial spasms, myocardial infarction, thrombotic occlusion, embolization and dissection, or frank perforation of the vessel wall. It has also been suggested that cardiovascular occlusions, as well as occlusions in other body lumens, might be vaporized by means of continuous wave (CW) laser energy. U.S. Patent No. 4,207,874 to Choy, for example, discloses a flexible conduit which accommodates a fiberoptic bundle divided into light source, viewing and laser bundle portions. The flexible conduit is introduced into a vein or other body lumen and advanced until it contacts an obstruction such as a thrombus. A laser apparatus optically associated with the laser fiber bundle is then activated so that the laser energy vaporizes the obstruction, the remaining particles of which are then removed by suction. Other flexible laser endoscopes for use in the therapeutic laser treatment of body lumens are disclosed in U.S. Patent No. 4,072,147; 4,146,019; 4,170,997; and German Offenlegungsschrift No. 2,640,406. Such intraluminal laser devices typically are said to function by thermal vaporization and/or coagulation of the luminal obstruction mass. One of the most serious risks inherent in the intraluminal use of laser radiation, especially in coronary or cerebral blood vessels, is the possibility of perforation of or thermal damage to the vessel walls and surrounding tissue. Accordingly, intravascular recanalization of occluded blood vessels is still an experimental procedure. Recently, investigators have reported the use of continuous wave (CW) argon, neodymium-YAG and carbon dioxide laser sources to successfully vaporizes, coagulate and penetrate atherosclerotic placque in animals and in sections of coronary arteries taken from human cadavers. However, the investigators also report perforation of the vessel walls in many cases, particularly at laser energy levels which have been increased to a level sufficient to effect vaporization of the placque. Such laser energy levels are appropriately characterized as the "thermal" mode of laser operation which involves causing damage to tissue by virtue of heat accumulation in the tissue impinged by the laser radiation. Excessive heat accumulation causes thermal degradation or thermal necrosis. In other words, the temperature of the tissue rises, tissue proteins are denatured and ultimately the tissue is coagulated and "evaporated" or "vaporized." While the laser thermal energy mode is effective in coagulating and vaporizing many tissues, including the tissues forming atherosclerotic placques and stenoses, its use heretofore in occluded coronary and cerebral blood vessels, for example, is not sufficiently safe and controllable. Consequently, the problem of inadvertent damage to or destruction of surrounding vessel tissue has been a major obstacle in the development of an acceptable microsurgical technique for laser angioplasty in the human vascular system. Apart from the risk of using continuous wave (CW) laser energy in the human vascular system, the prior art intraluminal laser devices lack effective mechanisms for "aiming" the laser beam to minimize the possibility of inadvertent damage to the vessel walls and to maximize the exposure of a large area of the occlusion, e.g., the artherosclerotic placque, to the laser energy. An apparatus as described in the preamble of claim 1 is disclosed in EP-A-0 144 764. This document discloses an apparatus for performing laser surgery in a body lumen having an obstruction therein. The apparatus comprises a catheter for insertion into said body lumen, said catheter having a longitudinal axis, proximal and distal ends, and a plurality of optical fibers, each with proximal and distal ends, disposed within said catheter for transmitting a laser beam from said proximal end to said distal end of the catheter to impinge on said obstruction. The apparatus further comprises a laser source arranged adjacent the proximal end of said catheter for generating a non-continuous wave, pulsed laser beam. Laser energy can be delivered in the visible wavelength range such as 500 nm through the optical fibres. Steering means can be included at the tip of the catheter of a type currently used in gastrointestinal fibreoptic endoscopy and focusing means at the tip which would provide radiation over a well-delineated area or linear region of atheromatous plaque. "Multispot laser photocoagulation system using a fiber bundle scanner" by H. Fujii et al., Applied Optics, Vol.21, No.19, 1 October 1982, pages 3437 to 3442 describes to cover an increased area of the skin to be laser-treated by equipping a photo-coagulation system with a fibre bundle scanner. US-A-3 858 577 relates to a flexible endoscope with a surgical laser connected thereto for simultaneous viewing and performance of surgery on the interior stomach wall. In a first embodiment described in this document, the distal end of the laser fibre is provided with a bend. This bend is required by the fact that the laser fibre is carried on the side of the endoscope and that, therefore, bending of the fibre is necessary in order to converge the lines of sight of the endoscope and the laser fibre. In a second embodiment the fibre is positioned within the endoscope; it therefore does not include a fibre having a bend. The technical problems underlying the present invention are complete coverage of the cross-sectional area of the body lumen confronting the distal end of the catheter with the laser beam, and aiming of the laser beam to minimise the risk of perforation of the luminal wall, or, alternatively, achieving overlapping of laser impingement or aiming at areas not impinged by the laser beam or blind spots caused by the positioning of other elements in the catheter. Briefly described, the aforementioned problems underlying the invention are solved by an apparatus according to claim 1. Preferred embodiments of this apparatus are characterized in claims 2-5. In one embodiment of the invention, the optical fibers include a bundle of laser transmitting fibers eccentrically arranged relative to the catheter axis and radially movable toward that axis by means of a balloon positioned within the catheter sheath. Each laser fiber has a distal lens system which converges and cants the radiation beam away from the circumference of the catheter and toward the axis thereof. Alternate embodiments of the catheter include distal lens systems for the laser fibers which may comprise one or more diverging lenses for special applications or techniques to be hereinafter described. A flexible optical fiber viewing element with a distal lens system is provided within the catheter sheath which comprises a plurality of individual fibers having a glass cladding and extending over a substantial part of the cross-sectional area of the catheter, for instance, 50% or more. An illuminating system comprising several individual plastic clad quartz glass fibers cooperates with the optical viewing element and is arranged adjacent thereto for delivering white light from a conventional light source. Fluid systems within the catheter include an outflow or suction channel for removal of fluids and debris and two or more inflow channels for injection of saline, pharmacologic agents, radiopaque positioning dyes, immuno-specific antibodies and the like. Carbon dioxide gas channels are also provided for inflation/deflation of both the laser aiming balloon and a balloon circumferentially disposed about the catheter adjacent the distal end thereof for occluding the vascular lumen and for establishing stabilization of the catheter distal end relative to said lumen. A laser microsurgical system is operatively connected to the proximal end of the flexible angiographic catheter and comprises a proximal optical and fluid coupler for interconnecting the optical fibers and fluid channels of the catheter to the various system components, such as the laser apparatus and control, laser fiber optical scanner, illumination and visualization systems, positioning systems and fluid systems. The invention uses visible light laser energy in the wavelength range of 351 to 515 nanometers, and, preferably, the blue-green emission lines at wavelengths of 488 and 514 nanometers from an argon-ion laser with a peak power output of about 20 watts, such as a Spectra-Physics 171 Laser. The argon laser apparatus is operated in the pulsed or non-conducting mode using a pulse width or duration in the range of from 5 to 200 milliseconds and a pulse repetition rate of 1 to 50 pulses per second with a duty cycle of between 5 and 50%. The preferred pulse energy is in the range of from 150 to 500 millijoules. Spot size for each fiber in the laser fiber bundle may be from 100 to 500 microns, preferably, the largest possible spot size in that range compatible with energy density requirements. The above parameters of the pulsed laser energy are selected to effect damage to a luminal obstruction with substantially no thermal necrosis of the surrounding tissue. A hole is drilled in the obstruction by heating a given volume of the tissue thereof to its boiling point and then supplying the heat of vaporization to that volume to convert it to vapor. Ideally, the total laser energy needed to vaporize the given volume of the tissue of the obstruction is delivered in such a short period of time that heat conduction to the surrounding tissue is negligible. That time period is defined as the "thermal time constant" or "thermal relaxation time" for the given volume of tissue. According to the invention, the pulse characteristics, e.g., pulse width, pulse repetition rate and energy, are selected to operate in the conduction-free mode, that is, the laser energy is preferably delivered just at the threshold of the thermal relaxation time of the illuminated volume of the obstruction tissue. Experimental results have indicated that over the range of laser focal diameters of 50 to 100 microns for an argon-ion laser, the diameter of the laser drilled hole in arterial placque is approximately 500 microns, i.e., 5 to 10 times greater than the laser focal diameter. That phenomenon is believed to be the result of a combination of strong, small angle scattering and weak absorption of the placque tissue. The larger area, and consequent larger volume, of illuminated tissue results in a greater energy threshold for drilling the placque, that is, a greater thermal input is necessary because of the scattering of the laser light and the absorption characteristics of the placque. For the argon-ion laser, the energy threshold is about 200 millijoules per pulse over a pulse width of 200 milliseconds or less. An alternate embodiment of the invention takes advantage of the foregoing experimental results by locating a plurality of laser fibers in a flexible catheter in an array with the laser fibers appropriately spaced to provide substantially complete coverage of the cross-sectional area of a body lumen or vessel with little or no overlapping of the drilled laser hole. Thus, "aiming" may be accomplished by optically scanning the plurality of laser fibers to impinge laser energy on selected target areas, e.g., a plurality of target areas, each having a 500 micron diameter, over the entire cross-sectional area confronting the distal end of the catheter. Optical scanning of the laser fibers in a predetermined sequence also permits a greater number of pulses or "shots" to be made in a given time period without exceeding the energy threshold and causing thermal necrosis of the surrounding tissue. The laser fibers disposed adjacent the outermost periphery of the catheter may also be "skewed" toward the center of the catheter to minimize the possibility of perforation of the luminal wall. With the foregoing and other objects, advantages and features of the invention that will become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims, and to the several views illustrated in the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic block diagram showing the laser microsurgical system of the present invention; Figure 2 is a transverse cross-sectional view of the distal end of an alternate embodiment of the flexible catheter of the present invention, taken along line 3-3 of Figure 2; and Figure 3 is a longitudinal cross-sectional view of the catheter of Figure 6 taken along line 7-7 showing skewing of the outermost laser fibers. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now in detail to the drawings wherein the same parts are designated by the same reference numerals throughout, there is illustrated details of the distal end of the inventive flexible catheter which is designated generally by reference numeral 110. The laser microsurgical system 60 of the invention is shown schematically in Figure 1. The system 60 includes a laser source 62 which is preferably an argon-ion laser, such as a Spectra-Physics 171 Laser for generating a pulsed laser beam. The output of laser source 62 is a pulsed laser beam 64 which is inputted to a multi-fiber optical scanner 66 of a known type, for example, of the type described by Fujii et al in Applied Optics, Vol. 21, No. 19, pp. 3437-3442, October 1, 1982. Scanner 66 is used to scan the four laser fibers 18a-18d of the laser fiber bundle 16 with pulsed laser beam 64. Control of pulse width or duration, pulse repetition rate, wavelength, length of exposure, intensity and firing is provided by a laser control 68 associated with the laser source 62. Firing of the laser 62 is accomplished by closing a firing switch 69 which may be, for example, a foot pedal switch. The proximal end of the optical visualization element 24 supplies an optical image to a viewing microscope 70 which has a built-in eyepiece shutter mechanism 72. The shutter 72 is responsive to activation of the laser source 62 to prevent back-scatter of laser energy which could damage the surgeon's eyes. The optical image from optical element 24 is also supplied to an image analyzer 74 controlled by microprocessor 76 both of which are used to analyze the visual images transmitted from the intraluminal region at the distal end of the catheter and to aid in longitudinal positioning of the catheter distal end, "aiming" of the laser fiber or fibers at the appropriate target in the intraluminal region and timing of the laser firing signal in relation to the cardiac cycle. A suitable microprocessor and image analyzer is a Videoplan Computerized Image Analyzer available from Carl Zeiss, Inc., 444 Fifth Avenue, New York, New York 10018. A conventional cathode ray tube video display 78 and video recorder 80 are connected to the image analyzer for real time observation and recording, if desired, of the microsurgical procedure. An illumination source 82 is connected to the proximal ends of optical fibers 132, 134, 136 for delivery of white light thereto. The light is provided by mercury or xenon high pressure arc lamps within quartz enclosures; however, other types of light sources may be used. A vacuum unit 84 and fluids input unit 86 are connected to the suction channel 140 and fluid inflow lines 142, 144, respectively. The proximal end of the catheter 110 is mounted in an axial and rotational drive mechanism 98 which rotates the catheter about its axis and moves the same axially in response to mechanical or electrical signals from a micromanipulator 100 which, in turn, receives command signals from the microprocessor 76. Suitable micropositioners are well-known in the art and are available from numerous sources, such as Klinger Scientific Corporation, 110-120 Jamaica Avenue, Richmond Hill, New York 11148. See also related application, Serial No. 329,978. An embodiment of the catheter of the invention is shown in Figure 2 and identified with reference numeral 110. The catheter 110 comprises a plastic sheath 112, the outside diameter of which is preferably from about 1.2 to about 5.0 millimeters for use in the described laser coronary angioplasty techniques. The Figure 2 embodiment illustrates a catheter having an outside diameter of about 1.5 millimeters which diameter is essentially defined by the arrangement of the laser fiber array disposed within the sheath 112 as explained in greater detail hereinafter. A plurality of elements similar are arranged to extend longitudinally within the sheath 112 about the longitudinal axis 114 thereof and are somewhat loosely disposed in relation to one another, although in actual practice the elements are packed in closer proximity, preferably in a fixed relationship to one another and to the sheath 112. The catheter 110 has an optical viewing element 124, illumination fibers 132, 134, 136, suction channel 140 and inflow channels 142, 144. Individually clad laser fibers 118 are disposed about the catheter axis 114 in a predetermined, parallel array designed to provide impingement of laser energy on substantially the entire cross-sectional area of an obstruction confronted by the catheter 110 with little or no overlapping of laser impingement. Inasmuch as experiments have indicated that drilled holes with an argon-ion laser have a diameter of about 500 microns regardless of laser focal diameter, an array of seven (7) 50 to 200 micron diameter fibers 118 in the arrangement shown in Figure 2 will provide laser energy coverage of virtually the entire cross-sectional area of a luminal obstruction confronting the catheter 110, particularly in the central region thereof as shown by the dashed line areas 116 of laser impingement. Advantageously, the largest areas 120 not included in the total laser impingement area are located at the outermost periphery of the catheter adjacent the vessel walls where laser energy impingement is least desirable, and, in fact, may be detrimental. In view of the above teachings, various arrangements of laser fibers for different diameter catheters will be apparent to those skilled in the art. For example, the same seven (7) fiber array may be used for a 1.2 millimeter diameter catheter by arranging the centers of the laser fibers at a 400 micron spacing rather than the 500 micron spacing shown in Figure 2. While a certain amount of laser impingement overlap will result from that arrangement, by appropriate scanning of the laser fibers with laser energy any overheating of the tissue can be avoided. Generally speaking, a laser fiber disposed on the axis 114 of the catheter is preferred, but is not essential. Thus, although a 1.2 millimeter diameter catheter is preferably provided with an array of 5 to 7 laser fibers, an array of four (4) laser fibers equiangularly spaced may be provided with their impingement areas in tangential relationship. While such an arrangement would not provide laser impingement in the central region of an obstruction confronting the catheter, destruction of the obstruction surrounding the central region will eliminate support of such central region and ultimately cause it to gravitate to a laser impingement area where it will be destroyed. In larger diameter catheters, a larger number of laser fibers are preferably employed. For instance, a 5.0 millimeter diameter catheter encompasses an area 100 times greater than the 500 micron diameter area impinged by a single laser fiber. Therefore, an array of 80 to 100 laser fibers would be required to cover the entire area confronted by a 5.0 millimeter diameter catheter. The laser microsurgical system 60 shown schematically in Figure 1 may be used with the second embodiment of the catheter 110 of the invention shown in Figure 2. Advantageously, the multi-fiber optical scanner 66 may be programmed to scan each of the laser fibers 118 with pulsed laser energy in a preselected sequence. The scanning sequence is preferably selected to operate in the conduction-free or non-heat conducting mode. In that way, the possibility of overheating and the consequent thermal necrosis of a given impingement area is avoided, while at the same time the number of pulses of laser energy that can be delivered to the impingement area in a given time period is maximized. Although the laser fibers 118 are described above as extending parallel to the catheter axis 114, as shown in Figure 3, the distal ends of the outermost laser fibers may also be inclined or skewed inwardly toward the catheter axis by an angular amount identified by reference numeral 122. The amount of skewing may amount to between 5° and 45°. Preferably, the distal ends of the laser fibers 118 are inserted or molded into an end plate 126 fixed to the sheath 112. The end plate 126 may also receive the other longitudinally extending elements of the catheter, such as the viewing element 124, illumination fibers 132, 134, 136 and fluid channels 140, 142, 144. The above-described skewing of the peripheral laser fibers advantageously causes the outermost laser energy beams to converge toward the axis of the body lumen or vessel and thereby provide further protection against the possibility of perforation of the luminal wall. Such skewing, however, reduces the total area of laser illumination of a given diameter of catheter and arrangement of laser fibers and results in varying degrees of laser beam overlap depending on the distance between the obstruction and the distal end of the catheter. It would be possible to skew the distal ends of some of the interiorly disposed laser fibers of an array having fiber groups disposed at varying radial distances from the axis of the catheter. Such skewing may cause the axes of the fibers to diverge or converge with the catheter axis so as to achieve overlapping of laser impingement if desired or to "aim" at areas not impinged by the laser beam or blind spots caused by the positioning of other elements in the catheter, such as the elements 124, 132, 134, 136, 142, 144, etc. According to the method of the present invention, laser energy is not supplied as continuous wave (CW) laser energy in the thermal mode to vaporize atheromatous occlusions as in the prior art, but rather as pulses of 5-200 millisecond duration at a pulse repetition rate of 1-50 pulses per second and a duty cycle of between 5 and 50%. The pulse energy is from 150 to 500 millijoules. The laser source 62 is an argonion laser delivering 20 watts peak power at wavelengths of about 488 and 514 nanometers and a preferred spot size of about 100-500 microns diameter. Pulsing of the laser source in the ranges described above has been advantageously found to be both safe and effective; safe from the standpoint that the vessel walls will neither be perforated nor subjected to thermal necrosis, and effective from the standpoint that the laser energy is sufficiently great to effect vaporization of the occlusion. The selection of specific values for the pulse duration, pulse repetition rate, pulse energy parameters within the aforesaid ranges to effect destruction of an occlusion without thermal necrosis is dependent to a large extent on the thermal time constant and absorption characteristics of particular type or material of the occlusion, e.g., fibrin, cholesterol, calcium, collagen, low-density lipoproteins and the like. Based on the teachings herein, however, one skilled in the art can readily select a suitable value for each pulse parameter to effect conduction-free operation, i.e., destruction of the tissue of the occlusion with substantially no thermal necrosis of the surrounding tissue.

Claims: Apparatus for performing laser surgery in a body lumen (L) having an obstruction (X) therein, said apparatus comprising a) a catheter (110) for insertion into said body lumen (L), said catheter having a longitudinal axis (114), proximal and distal ends, and a plurality of optical fibers (118), each with proximal and distal ends, said optical fibers (118) being disposed within said catheter (110) and arranged in a predetermined array about said longitudinal axis (114) for transmitting a laser beam from said proximal end to said distal end of the catheter (110) to impinge on said obstruction (X); and b) a laser source (62) arranged adjacent the proximal end of said catheter (10, 110) for generating a non-continuous wave, pulsed laser beam (64) having a predetermined pulse duration, pulse repetition rate, and pulse energy; characterized by c) a multi-fiber optical scanner (16) arranged between said laser source (62) and said catheter (110) for optically scanning the proximal ends of said optical fibers (118) with said pulsed laser beam (64) for sequentially directing said pulsed laser beam through preselected ones of said optical fibers (118) at different areas of said obstruction (X); and d) the distal ends of some of said optical fibers (118)are converged radially inwardly or diverged radially outwardly at an angle towards or away from said longitudinal axis (114). Apparatus according to claim 1, whereby the non-continuous wave, pulsed laser beam (64) is an argon-ion laser beam having a pulse duration in the range of from 5 to 200 milliseconds, a pulse repetition rate from about 1 to 50 pulses per second and a pulse energy in the range from 150 to 500 millijoules. Apparatus according to claim 2, whereby the laser beam (64) has a wavelength in the range of about 351 to 515 nanometers, and a spot size of 500 microns or less. Apparatus according to any of claims 1 to 3, whereby the laser source (62) produces a laser beam (64) having a duty cycle selected to operate substantially at the threshold of the thermal relaxation time of the illuminated volume of the obstruction (X). Apparatus according to claims 1 to 4, whereby the sequence of the scanning of the optical fibers (118) and the predetermined pulse duration, pulse repetition rate and pulse energy of said laser beam (64) being selected such that the pulsed laser beam vaporizes the obstruction (X) with substantially no thermal necrosis of the surrounding tissue of the body lumen (L).

Inventors: COSTER A ARTHUR, FOX KENNETH R, COSTER, A. ARTHUR, FOX, KENNETH R.
Applicants: PILLCO LIMITED PARTNERSHIP
Application year: 1986
Main classification: A61B17
IPC codes: A61B18, A61B19, A61B17