Treatment of pigmented tissues using optical energy

Abstract

A method and apparatus for selectively photobleaching or killing pigmented tissues by photochemically converting pigments in the tissues using light and specifically two-photon excitation. Phototoxic products thereby produced then kill pigmented cells. Hyperthermia or an exogenous agent can also be added to augment efficacy. The present invention is also directed to selective thermal destruction of pigmented tissues using related optical means.

Description

[0001] This application is a continuation-in-part of U.S. patent application Ser. No. 09 / 130,213 filed Aug. 6, 1998 which is a continuation-in-part of U.S. patent application Ser. No. 08 / 739,801, filed on Oct. 30, 1996.BACKGROUND OF THE INVENTION [0002] The present invention is directed to a method and apparatus for treating pigmented tissues by selective photoactivation of pigments in such tissues using optical energy and more specifically two-photon excitation. This selective photoactivation may be used to effect photobleaching of such pigments or to effect photochemical conversion of such pigments into phototoxic products. Photobleaching reduces or eliminates undesirable pigmentation, for example that caused by pigments present in moles, freckles, hair follicles and tattoos. Photochemical conversion produces phototoxic products that destroy pigmented tissues, such as those pigmented tissues in pigmented tumors. The present invention is also directed to selective thermal destructi...

AI Technical Summary

Benefits of technology

[0021] In an alternative embodiment, an exogenous photodynamic agent can be added to the particular volume of tissue. The exogenous agent can be photoactivated by the simultaneous two-photon excitation. Activation of the exogenous photodynamic agent augments the effectiveness of the endogenous pigment.

[0022] In a further alternate embodiment of the invention, the effectiveness of such photoactivation is augmented through the localized application of hyperthermia in the pigmented tissues.

Problems solved by technology

However, previous methods for photobleaching tissues using visible or ultraviolet light have produced undesirable collateral effects, including irritation of surrounding tissues and possible scarring at the treatment site.

More specifically, an important subset of pigmented tissues are pigmented tumors, such as melanomas, which are life threatening and highly difficult to treat.

While melanomas can be treated if detected early using standard surgical, radiation or chemotherapeutic methods, these methods still do not have acceptable levels of effectiveness and produce high levels of collateral damage to normal tissue.

Hence, even if detected relatively early, the prognosis is usually poor.

Further, if a melanoma has metastasized beyond the primary tumor site, less than 20% of patients will survive beyond five years.

For such melanomas, there are no effective therapies.

Further exacerbating the difficulties in treating melanomas is the fact that the incidence of melanoma in Caucasians is increasing at a rate of 6% per year.

However, utilization of such phototoxic reactions by illumination of melanin, melanin precursors, or other endogenous pigments has not previously been possible.

More specifically, the poor penetration of such light has produced little effect on patients whose skin tumors are larger than or at a depth greater than 3 mm.

Previous photodynamic methods using UV / Near UV light also produced undesirable collateral effects that not only prohibited the photoconversion of melanin and prevented it from killing pigmented tissues but also was potentially dangerous to the patient.

For example, UV light can create thymidine dimers which damage genetic material.

DNA damage is a major and possibly the sole cause of skin cancers like melanomas.

As a result, tumor cells when treated with UV light will have a greater mutation and error rate because the UV light can inactivate mechanisms designed to identify and correct genetic errors (in addition to creating new errors).

Therefore, prior techniques were not only unable to effectively kill pigmented tissues by accessing endogenous pigments but also created side effects that could be lethal.

Such heating alone, however, has not been shown to produce a significant therapeutic effect.

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