Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Light application
Reexamination Certificate
2000-03-21
2002-12-10
Dvorak, Linda C. M. (Department: 3739)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Light application
C607S088000, C606S003000, C606S007000, C606S010000, C606S011000, C606S012000, C128S898000, C604S021000, C604S027000, C604S048000
Reexamination Certificate
active
06491715
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Description
The invention relates to a device for treating growing, dilated or malformed blood vessels with a laser which emits radiation in a wavelength range from 750 nm to 850 nm.
2. Description of the Related Art
WO 97/31582 has already disclosed the treatment of, for example, tumors by administering to the patient a dye or chromophore having an absorption maximum in a wavelength range from 770 nm to 840 nm, and treating the diseased area of the body with light having a wavelength in the stated range. Indocyanine green is proposed as dye or chromophore. A diode laser is a preferred light source.
U.S. Pat. No. 5,394,199 discloses the production of angiographic images of the capillary network of the eye (choriocapillaris) using indocyanine green in order to use them for precise adjustment of the therapeutic laser.
“Ophthalmic Surgery”, March 1994, Vol. 25, No. 3, pages 195-201 discloses the selective removal of choroidal neovascular membranes with administration of ICG and treatment with a diode laser having an emission wavelength of 805 nm.
U.S. Pat. No. 5,304,170 discloses the destruction of carotene-containing body tissue with a laser with an emission wavelength of 504 nm. It is provided for this purpose to increase the carotene content by administering carotene.
U.S. Pat. No. 5,071,417 discloses an apparatus for fusion of biological material using a laser. Since the progress of such a fusion is often difficult to observe with the naked eye, the apparatus is equipped with a reflectance monitor which establishes the change in the reflectance characteristics of the tissue material caused by the fusion and thus indicates the success of the fusion to the therapist.
WO 91/18646 discloses a device for laser photothermotherapy. In the disclosed device, tissue which contains endogenous or exogenous chromophore is irradiated with a laser. The temperature of the treated tissue is measured, and the measured signal is used to control the pulse energy and the rate of repetition of the laser pulses.
WO 93/03793 discloses a medical light treatment apparatus, in particular for acupuncture. With the apparatus, the light reflected by the biological tissue is detected and, on the basis of this detection, the energy of the light directed into the tissue is controlled.
In summary, concerning the prior art discussed above it can be stated that most known devices are not intended and not suitable for treating blood vessels, in particular for treating small blood vessels (spider veins). The known devices chiefly make use of endogenous chromophores such as, for example, hemoglobin for absorbing the laser light. The problem which therefore arises on treatment of blood vessels is that vessels which are too small contain too little hemoglobin whereas blood vessels which are too large cannot, because of the poor absorption properties of hemoglobin and the increased heat convection, be heated sufficiently and thus in both cases a sufficient thermal effect with subsequent coagulation of the vessel is not achieved.
SUMMARY OF THE INVENTION
The invention is by contrast based on the object of providing a device for treating growing, dilated or malformed blood vessels with a laser, which is distinguished in that the blood vessels are effectively coagulated and adverse effects on the surrounding tissue are minimal. It is further object of this invention to provide a method for treating biological material with a light beam.
These objects are achieved according to the invention with a device and a method for treating growing, dilated or malformed blood vessels with a laser which emits radiation in a wavelength range from 750 nm to 850 nm and which has a measuring unit which measures the concentration of an exogenous chromophore which absorbs the laser beam in a blood vessel to be treated, and which also has a control unit which controls the power of the laser in a contrary sense to the measured concentration. The measurement according to the invention of the concentration of an exogenous chromophore, i.e. chromophone which has been administered to the patient, and the corresponding control of the laser power makes it possible to meter the laser power optimally. As long as the concentration of the exogenous chromophore in the blood vessel to be treated is high, a lower laser power is sufficient. If over the course of time, as a consequence of the breakdown or excretion of the exogenous chromophore from the blood circulation, the concentration thereof falls, in the device according to the invention the power of the laser is controlled in the contrary sense, i.e. increased. It may be pointed out in this connection that power means the energy per unit time (with watt as unit of measurement) introduced into the vessel by the treatment.
The concentration of the exogenous chromophore in the blood vessel can be measured in a variety of ways, for example also by taking a blood sample.
However, a particularly advantageous measuring unit is designed as a reflection measuring unit because this operates non-invasively and is accordingly associated with less stress for the patient. A certain fraction of the laser light which impinges on the surface of the skin is, owing to the different refractive indices of air and skin, reflected (reflection coefficient R).
P
1
is
P
0
−RP
0
=P
0
(1−
R
)
where P
1
is the reflected and P
0
is the originally emitted power. The fraction P
2
of the original power P
0
which arrives, after passing through the epidermis and part of the dermis, at the blood vessel emerges from the following formula:
P
2
=P
1
exp(−&agr;
mel
(&lgr;)
z
)−
P
1
R
H
=P
1
[exp(−&agr;
Mel
(&lgr;)
z
)−
R
H
]
P
2
=P
0
(1−
R
)[exp(−&agr;
MEL
(&lgr;)
z
)−
R
H
}].
In this, the factor &agr;
H
(&lgr;)z describes the attenuation of the laser light in the direction of propagation z from the surface of the skin until the particular blood vessel is reached. The factor &agr;
Mel
(&lgr;)z depends on the melanin content of the particular section of skin. The absorption, mediated by the chromophore concentration, of the laser light of power P is thus
P=P
2
(1−
T
)
P=P
0
(1−
R
)[exp(−&agr;
Mel
(&lgr;)
z
)−
R
H
][1−exp(−&agr;
CH
((&lgr;,
t
)
z
)]
The attenuation of the laser light by the reflection R, the internal reflection
RH
and by the factor exp(−&agr;
Mel
(&lgr;)z) does not, in contrast to the chromophore concentration &agr;
CH
(&lgr;,t), vary with time. It is possible by measuring the reflected proportion of the incident light to determine, by the above calculation, the changing chromophore concentration in the blood vessel (&agr;
CH
((&lgr;,t)). The control unit controls, on the basis of the measured chromophore concentration, the power of the laser in the contrary sense to the measured concentration, i.e. the power of the laser is set at a comparatively low level when the concentration is high, whereas a comparatively high laser power is applied when the concentration is relatively low.
Another advantageous embodiment of the invention provides for the control unit, in order to measure the concentration of the chromophore, to cause a pilot light pulse to be emitted, the power of which is so small that it causes no permanent changes in the blood vessel or the tissue surrounding the latter. There is merely determination of the chromophore concentration on the basis of the pilot light pulse, so that this concentration can be set appropriately beforehand, i.e before starting the treatment. The control unit can moreover be programed so that such a pilot light pulse can be emitted at regular intervals or, for example, before emitting each therapeutic pulse, in order to detect changes in the chromophore concentration in good time.
A computer unit then determines the chromophore concentration from a power of the pilot light pulse and the reflected light power, measured by the measuring unit, usi
Abels Christoph
Szeimies Rolf-Markus
Dvorak Linda C. M.
Farah Ahmed
Pulsion Medical Systems AG
Squire Sanders & Dempsey L.L.P.
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