Surgery – Instruments – Light application
Reexamination Certificate
1999-11-15
2002-05-14
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Light application
C606S010000, C606S011000, C606S013000, C606S014000, C606S041000, C607S098000, C128S898000
Reexamination Certificate
active
06387088
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is conceptually related to co-pending Ser. No. 09/049,711 (Ionothermal Delivery System and Technique for Medical Procedures) in which an initial photonic-media interaction is used to create a photoconductive effect in media (e.g., tissue) to thereafter enable, enhance or focus the application of electrical energy to structure within a patient's body. More particularly, this invention relates to a novel method for non-contact application of intense electrical energy to a tissue surface for selectively removing thin surface layers without collateral thermal damage. The instrument of the invention utilizes (i) a UV light source to irradiate and thereby photoionize a path through a selected gas environment overlying the targeted tissue, and (ii) a high-energy electrical source for creating an electrical field in the ionized gas to thereby apply an intense electrical energy pulse to volatilize macrmolecules of the surface to cause a plasma-mediated removal of thin layers without transfer of thermal energy.
2. Description of the Related Art
Various energy delivery sources have been investigated for surgical tissue ablation or removal, including radiofrequency (Rf) current flow within tissue, high intensity focused ultrasound (HIFU) interactions in tissue and microwave energy absorption in tissue. In general, at high intensities, the above listed energy sources generate thermal effects that can vaporize tissue as the means of tissue ablation or removal. In other words, the energy sources elevate the temperature of water in intra -and extracellular spaces to above 100° C. thereby explosively vaporizing water to damage or destroy the tissue The drawback to such purely thermally-mediated ablations is significant collateral damage to tissue volumes adjacent to the targeted site. While in many surgical fields, the above-described collateral thermal damage may be acceptable, in fields such as neurology, interventional cardiology and ophthalmology, there is a need to prevent, or limit, any such collateral damage. These energy sources also have the disadvantage of typically requiring contact between the working end of the instrument and the tissue targeted for ablation.
Various laser systems also have been developed for tissue ablation or removal. The conventional long-pulse laser systems outside the UV range, wherein long-pulse is defined as a system operating in a range of 10's of nanoseconds to microseconds in pulse duration, have been found to be inefficient in volumetric tissue removal without causing extensive collateral damage. In a the conventional long-pulse laser system (e.g., Nd:YAG, Er:YAG, IR lasers), the photonic energy delivered to a targeted site does not directly disrupt the molecular integrity of surface layers of the site, but rather the energy is transferred into surrounding tissue volumes as photothermal energy, or photomechanical energy. These collateral effects propagate through surrounding tissues as heat, and perhaps mechanical shock waves, which manifest themselves as undesirable collateral damage. More specifically, the generally accepted model of volumetric ablation or removal with lasers having a pulse longer than tens or hundreds of picoseconds is described as follows: The energy absorption is chromophore dependent (and/or scattering dependent), and the energy transfer involves the heating of conduction band electrons by the incident beam of coherent photons which is followed by transfer of thermal energy to the structure's lattice. Ablation or damage occurs by conventional heat disposition resulting in vaporization, melting, or fracture of the structure. The rate of volumetric structure removal depends on thermal conduction through the structure lattice and its thermodynamic properties (heat capacity, heat of vaporization, heat of fusion, etc.). Thus, the minimum energy requirements to cause an ablation effect in the structure's properties may be defined by a threshold of incident laser energy per unit of structure volume at the target site, which threshold is directly dependent on pulse duration. It has been found that ablation thresholds generally require relatively long pulse durations, which in turn are the source of undesirable collateral photothermal or photomechanical damage.
In certain tissue ablation fields (e.g., thrombus ablation in cardiology; corneal ablation in ophthalmology), excimer lasers have been developed that emit high intensity pulses of ultraviolet (UV) light, typically with pulse duration in the 1 ns to 100 ns range. The short wavelengths, as well as sequenced nanosecond pulse regimes, define a substantially non-thermal form of tissue ablation sometimes termed photodecomposition. Such ablation with UV irradiation occurs since biological tissues exhibit strong absorption characteristics in the UV region of the electromagnetic spectrum (e.g., at c. 1.93 &mgr;m). Short wavelength UV photons are highly energetic and when radiated onto biological tissue can break the chemical bonds in molecules of the surface layer. Thus, a UV excimer laser can vaporize a surface tissue layer with minimal thermal energy being transferred to underlying tissue volumes. Tissue ablation with UV irradiation can be controlled depth-wise by varying the number of pulses of ns energy delivery, since each pulse only penetrates to a depth of about 0.25 &mgr;m to 1.0 &mgr;m per pulse. The objectives of UV laser-tissue ablation include the uniform application of energy to a tissue surface as shown in FIG.
1
A. Such an even energy application, if applied in a series pulses, could result in the hypothetical ablation shown in FIG.
1
B. In fact, the idealized ablation characteristics shown in
FIGS. 1A-1B
may not achievable with a UV laser.
FIGS. 2A-2B
represent uneven energy densities over a surface layer (see
FIG. 2A
) and the resultant uneven ablation (see
FIG. 2B
) that may be characteristic of certain UV laser ablations. A potentially significant disadvantage of UV laser ablation is the type of uneven ablation surfaces (as hypothetically represented in FIGS.
2
A-
2
B). Such uneven ablations are highly undesirable for some biomedical applications (e.g., corneal shaping in ophthalmology).
A primary objective underlying the present invention is the development of technology for creating smooth ablations at a microscopic level, while at the same time providing for bulk removal. For this reason, it is useful to explain why, it is believed, that UV ablations may result non-smooth ablation surfaces as represented in the hypothetical ablations of
FIGS. 2A-2B
.
FIGS. 3A-3F
are graphic representations of a prior art UV ablation event in an extended sequence, although the ablation event or events actually occur within a period of 10's to 100's of ns (nanoseconds).
FIG. 3A
is an illustration of a targeted tissue surface with a UV laser above the tissue.
FIG. 3B
is a sectional view showing the surface layer within an initial ns interval of UV laser irradiation of the tissue surface. Next,
FIG. 3C
depicts the surface layer several ns or 10's of ns later when an ablation plume or ejecta E (plasma) has been ejected from the tissue surface. It is believed that this ejecta E or plasma absorbs substantially all UV laser energy thereafter still radiating. In other words, the beam's energy will be substantially blocked from reaching the tissue surface and the actual UV ablation will be terminated or will be randomly spotty.
FIG. 3D
thus depicts the ablation created after termination of UV energy delivery in this hypothetical situation. The resultant uneven energy application is potentially further aggravated by secondary effects of the ablation plume (ejecta) which secondarily transfer heat randomly to regions indicated at R outside the exact targeted site. Finally,
FIGS. 3E-3F
show the effects that may occur from multiple additional pulses of energy delivery making the ablation yet more uneven. It is an objective of the present invention to deliver energy to a ti
Shattuck John H.
Strul Bruno
Dvorak Linda C. M.
Hann James F.
Haynes Beffel & Wolfeld LLP
Kearney R.
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