Selective tissue targeting by difference frequency of two...

Details Selective tissue targeting by difference frequency of two... Selective tissue targeting by difference frequency of two...

1999-12-14

2002-08-06

Dvorak, Linda C. M. (Department: 3739)

Surgery

Instruments

Light application

C606S010000, C606S011000, C606S033000, C359S245000, C359S325000, C359S326000, C359S349000, C372S021000

Reexamination Certificate

active

06428532

ABSTRACT:

BACKGROUND OF THE INVENTION
Surgical instruments and surgical methods, methods of chemotherapy, radiation therapy and hyperthermic treatment can be utilized for the medical treatment of various proliferating diseases, e.g., tumors and cancer. Methods of acoustic surgery for similar applications have not presently been widely accepted in these areas of clinical practice.
Laser and improved acoustic techniques are under development for surgical techniques. Lasers are currently used for targeted energy delivery in a variety of medical procedures. The absorption of light is function of wavelength. The 600 nm to about the 1200 nm spectral band has been called a “window” region because there is deep penetration of photons into tissue due to low absorption (1). Measurement of the transmission of coherent photons using optical heterodyne detection has been performed for 2-7 mm thick tissue sections (2). The total extinction coefficient &mgr;, (790 nm) of skin, liver, and muscle is 0.96-1.75 mm
−1
. For targeted delivery the laser energy should be preferentially absorbed in the treatment site. One of the most successful medical uses of lasers occurs when endogenous chromophores are located in the treatment region. Unfortunately selective concentration of endogenous chromophores in the treatment location occurs rarely. Therefore exogenous chromophores that are preferentially delivered into the treatment site are currently under investigation (3).
For acoustic surgery, a mechanically oscillated hollow metal pin, for example, can be used as a therapeutic tool. High-power focused ultrasound acoustic fields are able to destroy human body tissue (see PCT published applications in the name of Fry WO 89/07907 and WO98/07909). Dunn and Fry have also described in “Ultrasonic threshold dosage for the mammalian central nervous system” IEEE transactions, volume BME 18, pages 253-256 how this destruction process involves two effects, more a specifically a thermal effect and a cavitation effect.
In general, the thermal effect predominates when the acoustic power at the point of focus is below the threshold of about 150 W/cm
2
at MHZ. Therefore, thermal effects are due to the acoustic absorption of the tissue which converts the mechanical energy of the acoustic wave into thermal energy.
More specifically, the cavitation effect becomes predominant when the acoustic power at the point of focus exceeds a threshold of 150 W/cm
2
. Cavitation is linked to the formation of microscopic bubbles of gas which implode when they reach a critical diameter with a local release of appreciable amounts of energy leading to destruction of neighboring tissue.
In order to obtain destruction of tissue exclusively by thermal effects, it has been necessary for the acoustic field to be able to reach a threshold of destruction referred to as the “thermal dose.” This threshold is a function of temperature reached and of the duration of application. Thus the presently known approaches have been to destroy tissue by application of a moderate temperature increase over a long duration of application or, through application of a significant temperature increase over a short period of application.
SUMMARY OF THE INVENTION
The present invention is based, at least in part, on the discovery that by directing two different wavelengths of energy (beams), simultaneously, at a focal point or region within tissue, an overlap region forms having an energy difference which causes selective cavitation and/or hyperthermia in tissue at the site of intersection of the two beams. This localized treatment does not effect tissue surrounding the area where the two beams do not overlap and is, therefore, an effective means to treat tissue, e.g., diseased tissue, without harming the surrounding tissue area about the site of selective cavitation.
The present invention pertains to apparati for treating tissue using two different wavelengths, e.g., energy beams. The apparati include a first energy emitter which produces a first wavelength of energy and a second energy emitter which produces a second wavelength of a second energy. The first and second wavelengths are focused onto a focal point or region of the tissue, so that the first and second wavelengths intersect and produce an overlap region having an energy difference. The energy difference causes cavitation and/or hyperthermia at the focal point or region within the tissue. The two different wavelengths are generated by energy emitters. Suitable energy emitters are lasers, e.g., ND:YAG lasers, or piezoelectric transducers. In a preferred embodiment, the acoustic energy difference between the two energy beams is about 200 kHz with a subharmonic frequency of about 100 kHz.
The present invention also pertains to apparati for treating tissue using two different wavelengths, energy beams, which include a first energy emitter, a second energy emitter and a control means. The first and second energy emitters produce two differing wavelengths. The control means facilitates transmission and focusing of the energy beams onto a focal point or region of the tissue. The energy beams intersect and produce an overlap region which has an energy difference which produces cavitation and/or hyperthermia at the focal point or region within the tissue. The control means causes transmission of cavitation waves, e.g., ultrasound, for a duration of between about 1 milliseconds and continuous. Alternatively, the control means causes hyperthermia when an energy pulse of between about 20 nanoseconds (10-
8
seconds) and 5 femtoseconds (10
−15
seconds). The controls means can also provide transmission of ultrasonic waves, light, coherent light, or energy waves which result in hyperthermia by successive pulses.
The present invention further pertains to methods for treating tissue using two different wavelengths simultaneously. The methods include directing a first wavelength of energy into a tissue and directing a second wavelength of a second energy into the tissue, such that the first and second wavelengths are focused onto a focal point or region of the tissue. The first and second wavelengths intersect to produce an overlap region which has an energy difference causing cavitation to occur at the focal point or region within the tissue, thereby treating the tissue. This localized treatment does not effect tissue surrounding the area where the two beams do not overlap and is, therefore, an effective means to treat tissue, e.g., diseased tissue, without harming the surrounding tissue area about the site of selective cavitation.


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