Surgery – Instruments – Light application
Reexamination Certificate
1998-01-23
2002-04-09
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Light application
C606S012000, C606S015000, C606S017000
Reexamination Certificate
active
06368318
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to the removal of blockages in tubular tissues and organs, and more specifically, it relates to the removal of intravascular occlusions such as atherosclerotic plaque or thrombus.
2. Description of Related Art
Ischemic strokes are caused by the formation or lodging of thrombus in the arterial network supplying the brain. Typically these occlusions are found in the carotid artery or even smaller vessels located still higher in the cranial cavity. Interventional cardiologists and vascular surgeons have devised minimally invasive procedures for treating these conditions in the vasculature elsewhere in the body. Among these treatments is ultrasound angioplasty whereby a microcatheter is directed to the site of an occlusion. An ultrasonic transducer is coupled to a transmission medium that passes within the catheter and transmits vibrations to a working tip at the distal end in dose proximity to the occlusion. Ultrasonic catheters for dissolving atherosclerotic plaque and for facilitating clot lysis have been described previously. Improvements on these inventions have concentrated on improving the operation or function of the same basic device (See Pflueger et al., U.S. Pat. No. 5,397,301). The vibrations coupled into the tissues help to dissolve or emulsify the clot through various ultrasonic mechanisms such as cavitation bubbles and microjets which expose the clot to strong localized shear and tensile stresses. These prior art devices are sometimes operated in conjunction with a thrombolytic drug. A radiographic contrast agent is often used to facilitate visualization.
The ultrasonic catheter devices all have a common configuration in which the source of the vibrations (the transducer) is external to the catheter. The vibrational energy is coupled into the proximal end of the catheter and transmitted down the length of the catheter through a wire that can transmit the sound waves. There are associated disadvantages with this configuration: loss of energy through bends and curves with concomitant heating of the tissues in proximity; the devices are not small enough to be used for treatment of stroke and are difficult to scale to smaller sizes; it is difficult to assess or control dosimetry because of the unknown and varying coupling efficiency between the ultrasound generator and the distal end of the catheter. Dubrul et al., U.S. Pat. No. 5,380,273, attempts to improve on the prior art devices by incorporating advanced materials into the transmission member. Placement of the ultrasonic transducer itself at the distal end of the catheter has been impractical for a number of reasons including size constraints and power requirements.
A related method for removing occlusions is laser angioplasty in which laser light is directed down an optical fiber to impinge directly on the occluding material. Laser angioplasty devices have been found to cause damage or destruction of the surrounding tissues. In some cases uncontrolled heating has lead to vessel perforation. The use of high energy laser pulses at a low or moderate repetition rate, e.g. around 1 Hz to 100 Hz, results in non-discriminatory stress waves that significantly damage healthy tissue or result in insufficient target-tissue removal when the laser parameters are adjusted such that healthy tissue is not affected. Use of pulses of high energy laser light to avoid thermal heating has been found to cause damage through mechanisms associated with large cavitation bubbles and shock waves that rupture or otherwise adversely affect the tissue.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide means for dissolution of vascular occlusions with low energy laser pulses at high repetition rates for generation of ultrasonic excitation in the fluids in close proximity to the occlusion.
It is another object of the present invention to provide techniques for removing clot material from the cerebrovasculature.
Another object of the invention is to provide techniques for removal of occlusions from the body.
Still another object of the present invention is to provide techniques for removing occlusions from the cerebrovasculature and the body without causing collateral damage to the vessel.
In the Opto-Acoustic Recanilization or Recanalization (OAR) device of the present invention, fiber delivered laser pulses emulsify thrombus by mechanical stresses that include a combination of pressure, tension and shear stress. High pressures primarily effect the small volume of material in which the laser light is absorbed, while the tensile and shear stresses effect a larger surrounding volume. The effectiveness of emulsification depends on the characteristics of the stresses-their magnitude, time-dependence and type (i.e. compressive, tensile or shear), and the response of the thrombus to such stresses. In general, the OAR device has been designed to maximize the mass of thrombus emulsified per unit laser energy. This is important for three reasons, (i) to minimize the required laser energy and thereby the laser cost, (ii) to minimize the time it takes to emulsify a given clot volume and (iii) to minimize the waste heat left in the tissue, which may lead to undesirable damage.
The present invention includes a laser coupled to an optical fiber delivery system and means for delivery of a cooling agent. The present design has evolved from a combination of experimental and theoretical modeling results. In concept, the laser radiation is delivered to the locality of a thrombus, the radiation is absorbed by blood, blood clot, or other present materials. The combination of a leading pressure wave and subsequent vapor bubble cause efficient emulsification of thrombus. The laser is operated in a low average power mode such that potential thermal complications are alleviated. The laser is operated in a high repetition rate mode to take advantage of ultrasound frequency effects of thrombus dissolution as well as to decrease the total procedure time. Specific parameter ranges for operation are described.
The delivery system for the OAR device of the present invention is intended to traverse through commercially available vascular catheters and must have the flexibility to traverse tortuous pathways and the diameter to pass smoothly through a small lumen. The device includes optical fibers surrounding a central lumen intended for flow of a cooling agent. The fibers may be arranged concentrically around the central lumen to deliver radiation and subsequent thermal energy over as large an area as possible. An alternative design approach incorporates the optical fibers into the wall of the guiding catheter and utilizes the catheter lumen as the cooling channel.
The distal tip firing pattern can be chosen to create a number of effects. A star pattern would serve to move the thermal energy in each consecutive pulse packet to a location far from the previous packet, and therefore never concentrate the heat. A circular pattern may be beneficial if there is a mechanical advantage to consecutively impacting adjacent areas. Additionally the fibers tips could be pointed towards or away from the central lumen to target specific areas.
Delivery of a pulse of laser radiation into an absorbing material can result in a significant movement of the fiber delivery system. This mechanical motion can be used to further disrupt thrombus. Fibers can be beveled or angled to aim the effect (primarily the shock wave) to produce a lateral deviation of the tip upon delivery of laser radiation, or promote a fluid jetting directional phenomenon. Fiber angling and/or particular firing patterns can be employed to produce agitation at the tip. In addition, the cooling agent can be employed to produce similar phenomena. The cooling tip can be made into a nozzle that would allow the coolant to jet in particular patterns or directions. In another configuration, a shrouded tip prevents the fibers from coming into contact with vessel wall yet enables interaction with blood or thrombus.
An ecce
Benett William
Broughton Kathryn
Celliers Peter M.
Da Silva Luiz B.
Esch Victor
Dvorak Linda C. M.
Ruddy David M.
The Regents of the University of California
Thompson Alan H.
Wooldridge John P.
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