JPS631054B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for automatic recognition of the thermal effect of a laser beam in biological tissues.

In recent years, high power lasers working continuously or in long pulses have been increasingly used in general and endoscopic surgery for tissue cutting and coagulation and hemostasis. In this case, the irradiation time is 0.1-10 seconds per pulse, using special argon-laser, Nd:YAG-laser and _CO2-
laser is used.

In the medical use of lasers, in addition to the desired therapeutic effect, concerns especially regarding patient and operator safety are important. Various safety measures have already been proposed for this purpose, such as, for example, laser safety glasses and protective filters. German Published Patent Application No. 2323137, which represents a significant step forward in improving safety during surgical procedures with laser beams, provides a specially designed focusing means as follows. That is, the irradiation part of the working laser is only connected when this focus adjustment means is located directly in front of the surgical position with an exact, constant distance, and is automatically switched off again when the focal position leaves this surgical position again. is configured to be This prevents accidental laser irradiation from causing damage to the patient and to those cooperating with him at the operating table, especially visual impairment.

Here, it is clear that too little attention has been paid to the issue of patient safety with respect to the dosage of the laser beam energy applied and the side effects of the emitted radiation on extraneous organs.
Criteria for this determination are conventionally determined by the physician performing the procedure from optically visible tissue destruction, reference values described in the literature, or previous experience.

However, reactions vary greatly depending on the type of tissue, and therefore extensive experience is required to perform the work with the necessary safety for the patient.

The object of the present invention is to provide a medical laser coagulation device which allows direct monitoring of the degree of destruction of the tissue being treated during coagulation, and in which the laser is automatically switched off in the event of a dangerous situation. The purpose of the present invention is to create a device for automatically recognizing the thermal effects of a laser beam in biological tissues. The aim is to determine and display the degree of tissue change using a measuring technique and to automatically switch off the laser irradiation before undesired damage occurs.

A feature of the device according to the invention is that the infrared-sensitive detector, thermistor or thermopile is arranged close to the optical axis in the focusing means of the laser and is provided with side filters.

In this case, the measuring signal produces an acoustic indication when a certain limit value is reached and, if this limit value is exceeded, triggers the shut-off electronics for the working laser.

With this configuration, any tissue changes are immediately and automatically displayed, and laser irradiation is automatically shut off if certain limits are exceeded. Of course, the critical value is below a value that would lead to undesired tissue destruction.

The invention will be explained in more detail below with reference to embodiments illustrated in the accompanying drawings.

The problem of the present invention is solved by a device as described above, which can be applied to incisional surgical operations, but in the actual operation of this device, the thermal return from the laser-irradiated tissue is Either the changes in the irradiation are recorded by a detector and converted into a temperature value by an evaluation electronic device, or the changes in the laser beam that diffuse back from the irradiated tissue are recorded in the center of the impact surface of the laser beam and outside this impact surface. A mode of operation is adopted in which the ratio of return diffusion from the surface area to internal diffusion, which is a direct measure of thermal destruction of the tissue, is measured, recorded and evaluated. In the case of endoscopic surgery, this device is operated in the latter manner of operation described above. However, in both cases, the measurement signal becomes an acoustic representation as shown in FIGS. 5a, 5b and 8. These acoustic signals indicate to the operator the extent to which the tissue has been thermally destroyed. In both of the above-mentioned operating methods of the device according to the invention, the measurement signal serves to control the electronics to automatically switch off the laser if a certain limit value is exceeded at which damage to the patient begins.

Thermal effects seen when a laser is irradiated into organic tissue are often difficult for the operator to notice when observed only with the eyes.

In the case of _CO2 lasers used, for example, as cutting tools, scalpels, etc., the laser beam is almost completely absorbed by the tissue surface. However, in this case the thermal effects - evaporation and combustion at the beam impingement surface - can be easily adjusted by visual observation. However, in the case of, for example, argon laser and Nd: Yag laser, which serve exclusively for tissue coagulation or hemostasis, the degree of tissue destruction is difficult to visually discern. This is because this use requires a large penetration depth. That is, if the laser beam is highly diffused at the same time, only little absorption is required. In this case a significant volume of tissue is captured by the radiation and heated almost uniformly. However, tissue destruction or coagulation, vascular cell occlusion, etc. already occur at a temperature of 60°C. Any increase in temperature above this level is medically undesirable. This is because at temperatures above 60°C and below 100°C, cell fluid evaporates, and at 100°C it violently boils. If the irradiation continues longer than that, the organic material will carbonize, evaporate and burn.

For most medical prescriptions, a temperature of 60-70°C is sufficient to reduce gangrene within the tissue by approximately 2-3 mm. However, if the site is irradiated further, there is a risk, especially in the case of membranous tissues such as the stomach and bladder walls, that gangrene will break through these walls and this will lead to some degree of perforation of the tissue.

Another risk is damage to organs located behind the surgical target location. Since it is difficult to visually recognize changes in the irradiated tissue surface during coagulation and at a temperature of 70 to 100°C, the present invention proposes a method for controlling laser irradiation using electro-optical means. A solution for measuring and displaying the change in the degree of coagulation during the process is presented (see FIGS. 1-3).

FIG. 1 shows a temporal diagram at the center of the impingement surface of the laser beam. Since medical applications during coagulation have to be carried out in a temperature range of 60° C. to 70° C., in order to avoid tissue destruction and evaporation of cell water, this curve in FIG. The time range at 65° C. is relatively wide, indicating that this allows a quiet and unhurried treatment.

FIG. 2 shows the geometrical evolution of the return diffusion of the laser beam over a certain time course. That is, during irradiation the geometry of the scattering garden of the laser beam within the tissue changes and this change in total return irradiation is measured and evaluated. The length of surface irradiation is a clear measure of the course of tissue destruction. The smaller the scattering, the greater the tissue destruction;
And the laser beam penetrates deeper and deeper into this tissue.

FIG. 3 diagrammatically shows the parameters of this total return diffusion of the laser beam. From this figure, it can be seen that the total return diffusion is highest in the temperature range of 65°C and remains constant within a certain irradiation time.

In the device according to the invention, on the one hand, changes in temperature and the associated changes in the thermal return radiation are evaluated, and on the other hand, the geometry of the scattering field of the laser radiation in the tissue is evaluated. The changes in the total return radiation are measured, recorded and evaluated under consideration of the changes in the total return radiation.

FIG. 4 shows one embodiment of the device according to the invention. The total luminous flux density S of the heat rays of the tissue irradiated by the laser is S=ε·σ·T ₄ . where σ is the Steffen-Boltzmann constant, ε is the tissue emittance rate equal to 1 in the infrared region, and T is the absolute temperature of the tissue.

In this case, an infrared sensitive detector 12, thermistor or thermopile is provided. This is provided near the optical axis 11 within the laser focusing means 10. A so-called edge filter 13 is provided in front of the detector 12 and serves to suppress the laser beam returning and diffusing. In FIG. 4, the comparison measurement position is indicated by reference numeral 14. The coaxiality of the light emitting and receiving axes is achieved by incorporating an annular detector 12 surrounding the aperture 17 of the focusing means 10 or a 90° turning mirror that transmits the laser beam and reflects the heat source. Either arrangement can be used alternatively.

The signal voltage of the detector 12 when the hot wire collides is V _Det =Mσ(T _T ⁴ −T _R ⁴ )·R. In the formula, T _T is the temperature at the heated place,
T _R is the comparison or reference temperature of the tissue before the start of irradiation, R is the detector sensitivity and M is a geometric factor of the device. In this case, M=1/π・A _T A _D /π ² . In the formula, A _T is the size of the irradiation surface, A _D is the size of the detector surface, and r is the distance from the irradiation point of the detector.

This optical arrangement must be made in such a way that the value of M remains as constant as possible even if the working distance changes, ie the distance of the detector 12 from the laser irradiation point 19 changes. In the drawings, the tissue is designated by the reference numeral 16. This constant maintenance is achieved by placing the detector 12 as close as possible to the focal point 18 of the focusing means 10. If the beam is not focused, the detector position is not a reference.

5a and 5 to evaluate the measurement signal.
Two circuits as shown in Figure b are arranged. In the arrangement according to FIG. 5a, the variation of the detector voltage proportional to T ⁴ is used to control a frequency-voltage controlled oscillator. Subsequently, the temperature rise can be heard through the speakers. In order to carry out measurements independent of external disturbance elements and deviations of the electrical construction elements, the temperature value is stored at the start of the laser irradiation, in particular just before the firing of the direct laser beam 15, and the next temperature value is stored at this initial stage. Values and evaluations of - divided among electronic devices.

Parallel to this display, in the exemplary embodiment shown, a limit value switching amplifier for automatic switching off of the laser can be controlled.

The block diagram according to FIG. 5b is constructed in such a way that only the inflection points of the temperature curve are acoustically indicated by a differential element or used for switching off the laser.

As illustrated in FIG.
The surface diffusion extension of 5 is a sensitive measure for the course of tissue destruction. This effect is used in opto-electronic displays. The configuration for this is shown in Figures 7 and 8.
Schematically illustrated in the figure. It shows how the total diffusion point 19 of the laser beam 15 in the tissue 16 is mapped onto the bifurcated surface detector 20 and
Moreover, this mapping is carried out in such a way that the point diameter of the total diffusion point or focal point 19 is independent of the working distance - this is achieved by a suitable adaptation of the focal length of the mapping lens (focal point 18) to the aperture angle of the treatment beam. - is shown. In the case of an endoscope, this is the divergence of the emitted laser beam and, in the case of focusing means 10, the focal length of the focusing lens.

In other embodiments, the mapping of the diffuse points is such that the point of impact 19 of the laser beam 15 is completely by the inner detector 20 and the outer diffuse area is completely by the outer detector 20, or It is designed to be partially captured. Light receiving optical system and irradiating optical system 24, 25
If the detectors 20 are constructed coaxially, the detector 20 consists of an annular inner surface and an outer annular surface. In the case of endoscopic instruments, it is advantageous to use a common viewing path with the safety device according to the invention, as shown in FIG.

The distance between the axis lines between the observation optical systems 23, 24 - in this case reference numeral 23 indicates the observation path, and reference numeral 24 indicates the optical elements in this observation path - and the laser optical systems 21, 22 allows the bladder shown to be Parallel axes occur within the field of view of the mirror. That is, the laser point moves across the field of view in a certain direction depending on the distance from the tissue wall 19 of the cystoscope. However, this movement does not have any disturbing effect on the detector. This is because the aspect of sensitivity is formed as a condition.

In order to avoid disturbances due to changes in the total intensity of the returning laser beam or changes in optical properties from one tissue to another, values are calculated by electronic addition and division from the detector voltage. U ₁ −U ₂ /U ₁ +U ₂ (where U ₁ means the signal at the inner detector and U ₂ means the signal at the outer detector) is obtained. This value is then used analogous to the previously described block diagram to control a threshold amplifier for a signal generator or laser circuit. Details regarding this can be seen from FIGS. 8 and 9.

[Brief explanation of the drawing]

Figure 1 is a diagram of the temperature change over time at the center of the laser beam collision surface, Figure 2 is a diagram of the geometric changes in the return diffusion of the laser beam, and Figure 3 is a diagram of the geometric return of the laser beam. Diffusion diagram, FIG. 4 is an embodiment of the device according to the invention, FIG. 5a is a control circuit diagram of a frequency-voltage controlled oscillator, and FIG. 5b is for the acoustic representation of the reversal point of the temperature curve. 6 is a pulse diagram for the circuit arrangement according to FIG. 5b, FIG. 7 is a schematic diagram of a laser cystoscope with monitoring detector, and FIG. 8 is a diagram of the measured values and evaluation values of the electronic equipment. Circuit diagram, FIG. 9 is a diagram of pulses for the circuit arrangement according to FIG. The symbols in the figure are 10... focus adjustment means, 11...
Optical axis, 12...detector, 13...edge filter.

Claims (1)

Claims: 1. A device for automatically detecting the thermal effect of a laser beam in biological tissue, in which an infrared sensitive detector 12, a thermistor or a thermopile is placed within the focusing means 10 of the laser and aligned with the optical axis 11. 1. A device for automatically detecting the thermal effect of a laser beam in the biological tissue, characterized in that the edge filter 13 is provided in the vicinity of the biological tissue. 2. Device according to claim 1, characterized in that a detector 12 is provided which annularly surrounds the aperture 17 of the focusing means 10. 3. The device according to claim 1, wherein the detector 12 is arranged in the vicinity of the focal point 18 of the focusing means 10. 4 Diffusion point 1 of laser beam 15 in tissue 16
Surface detector 2 divided into two for mapping 9
4. Device according to any one of the claims 1 to 3, characterized in that 0 is provided. 5. The device according to claim 4, wherein the detector 20 comprises a combination of a toric inner surface and an outer toric surface.