System for tissue ablation using pulsed laser

Abstract

Systems for enabling delivery of very high peak power laser pulses through optical fibers for use in ablation procedures preferably in contact mode. Such lasers advantageously emit at 355 nm wavelength. Other systems enable selective removal of undesired tissue within a blood vessel, while minimizing the risk of damaging the blood vessel itself, based on the use of the ablative properties of short laser pulses of 320 to 400 nm laser wavelength, with selected parameters of the mechanical walls of the tubes constituting the catheter, of the laser fluence and of the force that is applied by the catheter on the tissues. Additionally, a novel method of calibrating such catheters is disclosed, which also enables real time monitoring of the ablation process. Additionally, novel methods of protecting the fibers exit facets are disclosed.

Description

FIELD OF THE INVENTION[0001]The present invention relates to the field of pulsed high power lasers and the problem of delivering their output through optical fibers and especially for use in tissue ablation with the energy transmitted through those fibers.BACKGROUND OF THE INVENTION[0002]Delivery of high pulsed laser power through optical fibers is widely used for ablation of tissue or other targets. For such ablation procedures, ultra-violet (UV) light has many advantages, as it is well absorbed by biological matter and organic compounds. Rather than burning or cutting material, the UV laser adds enough energy to disrupt the molecular bonds of the surface tissue, which effectively disintegrates into the air in a tightly controlled manner through ablation rather than burning. The laser energy is also strongly absorbed and leads to sharp local elevation of temperature and results in generation of strong mechanical forces leading to photo-acoustic and photo-thermal ablation. Thus lase...

AI Technical Summary

Benefits of technology

This patent describes a system that uses a laser with multiple modes to create a highly multimode output. The laser is a stable resonator cavity, which reduces the likelihood of fiber damage from interference. The laser also produces a more uniform beam profile, which improves the immunity from fiber damage. The use of a bundle of fibers also increases the energy density of the laser pulses before fiber damage occurs. The diamond coated catheter has several advantages, including protecting the fiber tips from damage, reducing friction for improved material removal, and distributing heat from absorption of the laser pulses.

Problems solved by technology

The laser energy is also strongly absorbed and leads to sharp local elevation of temperature and results in generation of strong mechanical forces leading to photo-acoustic and photo-thermal ablation.

However, such lasers are bulky, require careful maintenance and frequent calibration, and the beam quality is poor and may not be stable.

The delivery of such fluences is very challenging for the optical fibers, and can lead to damage at the entrance or exit facets of the fiber, or in the bulk of the fiber by selective heating, plasma generation, self-focussing or the generation of cracks at the exit facet.

However, all of the above mentioned methods have disadvantages, particularly in terms of the limited improvement in energy density carrying capacity that can be achieved for the optical fiber setup used, and / or the system energy throughput, and / or damage to the fiber tip when in contact with tissue.

In addition to the need for new systems for enabling the ablation process, there is a growing need for the specific procedure of removing pacemaker and defibrillator leads in patients, due to such reasons as lead fracture or abrasion of the insulation causing shorting and infections.

When the electrode separation procedure is performed, there is a risk of perforation of the vein by the catheter, and in severe cases, this can even result in death of the patient.

However, since use of the 420-530 nm range, with its advantageous ablation selectivity, has an inherent disadvantage in the potential thermal damage caused by the larger energies needed for efficient ablation and deeper penetration, it is preferable to use a method for selective ablation which uses laser radiation within the UV region.

The problem with such methods for use in clinical treatments is that tetracycline is an antibiotic, and needs additional regulation and tests to ensure absence of side effects.

Since the catheters are sterilized before use, this method can involve risk of moving the distal tip of the catheter out of the sterilized area in the operation room.

However, the system design used in the present application, uses the fact that it is precisely because of the high quality mode structure of such lasers that the serious problems of coupling and transmission through the optical fiber arise, even when dealing with fibers with small diameter such as 100 micron core fibers.

The transmission of such pulses down the fibers results in a higher damage threshold than when using high quality laser pulses, and it has been found possible to transmit pulses having higher energy density, than those of prior art systems, before fiber damage sets in.

It is believed that this phenomenon is related to the absence of meaningful interaction between discrete parts of the beam across its profile, which could generate hot spots or interference.

First, the coating hardness may protect the fiber tips from damage due to contact with hard biological media and from the resulting shockwaves from laser ablation.

DLC's are generally not thought suitable for visible wavelengths due to their high absorption.

Another limitation of use of CLD is the high index of refraction which leads to very high “Fresnel Loses”.

A potential way to deal with those loses is to add an AR coating, but this is problematic in the current embodiment due to a number of reasons:

The AR coating can't withstand very high power at the fiber tip.

Furthermore, the AR coating is subject to mechanical abrasion when in contact with tissue.

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