WO2003065918A2 - Detector device for an object in a fluid and/or tissue and operational method - Google Patents

Abstract

The invention relates to a detector device and a method for detecting and processing an object, especially a stone, a clot, part of a tissue and/or a foreign substance in a fluid and/or tissue, especially human tissue, characterized by radiating means (20) for the production of at least one gaseous phase in the fluid and/or tissue, and a measuring means (23, 25) for the detection of reflections on a phase boundary between a gaseous phase and a liquid phase, thereby enabling low-cost recognition of an object, especially a stone without exposing the patient to any strain.

Description

Detector device for an object in a fluid and / or tissue, and method for detecting and processing the object.

The invention relates to a device according to the preamble of claim 1 and a method according to claims 17 and 18.

In medicine, the task is often to find an object, such as a gallstone, if it is embedded in a fluid and / or a tissue. This question is particularly important in laser lithotripsy, in which gallstones or kidney stones are destroyed by laser radiation.

The general problem with laser lithotripsy is that very high pulse energies are required for the laser to fragment a stone. Due to the high pulse energies, there is a risk that the tissue near the stone will be injured. Therefore a precise control of the position of the stone is necessary. X-ray control during the operation leads to an inappropriately high radiation exposure of the

Patients.

The present invention has for its object to provide a device and a method with which an inexpensive detection of an object, in particular a stone detection without stress on the patient is possible.

This object is achieved according to the invention by a device with the features of claim 1. According to the invention, a detector device has a radiation means for generating at least one gas phase in the fluid and / or in the tissue and a measuring means for detecting reflections between an optically transparent medium, in particular a glass fiber, and a gaseous and / or liquid phase. It is thus possible, for example, to measure a cavitation period after generation of a vapor phase in order to recognize the object in a simple manner. For this purpose, the device according to the invention evaluates different reflections in different phases (eg gas, liquid) by the measuring means. In principle, the partial reflections on the optically transparent medium (for example the end of a glass fiber) and a gas and / or liquid phase in the fluid are evaluated according to the invention. In particular, a change in density in a liquid phase before the end of a glass fiber can be detected and used for detection. However, it is also possible to evaluate changes in the reflection behavior in the optically transparent medium (for example as a result of changes in density).

It is particularly advantageous if the radiation means can generate a plasma pulse and subsequently a gas phase, in particular a cavitation bubble, in the fluid. The physical properties of the gas phase generated are recorded by the measuring device.

For an efficient detection of the object, it is advantageous if a by the radiation means

Plasma pulse with a pulse energy between 20 and 200 mJ can be generated.

Advantageously, a means is used for the targeted selection of different, predetermined levels of

Pulse energies to select certain energy levels. In particular, a low production level can be used a sample pulse to identify the object and a higher level to carry out processing of the object.

It is particularly advantageous if a first shock wave is generated by the expansion of the plasma in the fluid, and a second shock wave can be generated by the collapse of a cavitation bubble in the fluid.

The measuring device can advantageously measure the time between two shock waves in the fluid.

Furthermore, it is advantageous if the measuring means has a functional relationship between the energy of the cavitation bubble and the cavitation time

Object detection, especially stone detection used.

In an advantageous embodiment of the detector device, the radiation means is as

Measuring laser system trained. In particular, an embodiment which is advantageous for use in the human body has a radiation means which operates in a wavelength range between 350 and 800 nm, in particular 532 nm. The radiation means can also operate in a wavelength range from 700 to 1600 nm.

Because of the signal shape that occurs, it is advantageous to use at least one differentiator for measuring the cavitation period. It is also advantageous, or alternatively, to use at least one comparator circuit for measuring the cavitation period.

A particularly advantageous embodiment of the comparator circuit has two comparator circuits for detecting small signals, these being set to different threshold voltages. It is also advantageous to use an AD converter to evaluate the signal curve.

For noise reduction, it is advantageous to use a

Circuit for noise suppression, in particular to use an additional photodiode.

Optical interference is advantageously filtered out with at least one bandpass filter for the frequency of the measuring laser.

In a particularly advantageous embodiment, the detector device according to the invention is coupled to a working laser system (e.g. a laser lithropy system) for processing the object.

The object is also achieved by a method having the features of claim 17.

According to the invention, a phase change in a fluid and / or a tissue is initially generated by a radiation means, a measuring means being used to detect reflections at a phase boundary between an optically transparent medium and a gas phase and / or a liquid phase. It is also advantageous if an object is detected in this way and, depending on the detection result, processing, in particular destruction of the object, is carried out using a working laser system.

The invention is explained in more detail below with reference to the figures of the drawings using several exemplary embodiments. Show it: 1 shows a schematic representation of a laser lithotripsy system;

2 dependence of the radius of a cavitation bubble on time;

3 shock waves in laser lithotripsy;

4 shows a schematic representation of a cavitation implosion near a wall;

5 shows a schematic representation of the formation of a cavitation bubble;

Fig. 6 shows a schematic representation of the measurement signal

Photodiode, which receives the light returning via the laser fiber, for determining the cavitation period;

7 shows a schematic representation of the structure of an optical system for determining the cavitation period;

Fig. 8 graphical representation of the transmission of the beam splitter depending on the

Wavelength;

9 shows a schematic representation of a measurement setup for determining the cavitation period T _κ ;

10 shows a graphical representation of an ideal measurement signal when determining the cavitation period T _κ ;

Fig. 11 circuit diagram for a Dif erenzierglied;

12 graphical representation of the signal after the differentiator; Fig. 13 graphical representation of the signal after a comparative;

14 shows a schematic illustration of a comparator circuit;

15 measurement results of the DC voltage component of the

Measurement signal for air and water;

16 measurement results of the change in the reflectance as a function of the distance in the case of a red-brown gall stone;

Fig. 17 dependence of the cavitation period on the

Laser energy E _ou t with a dark brown stone;

18 measurement results of the change in the reflectance as a function of the distance in the case of kidney tissue;

19 measurement results of the change in the reflectance as a function of the distance in bile tissue;

20 measurement results of a bombardment of gallbladder tissue with 60 mJ;

21 Comparison of the cavitation time with living and dead tissue;

22 shows cavitation periods of different samples at low energy (E _out = 20-50 mJ);

23 cavitation periods of different samples at medium energy (E _out = 60-80 mJ);

24 cavitation periods of different samples at high energy (E _out = 90-120 mJ); 25 measurement signal after one, 50 and 100 laser pulses;

26 embodiment with an extended logic circuit for signal analysis;

27 embodiment with an extended circuit for noise suppression;

28 shows a circuit diagram for an amplifier circuit for a photodiode;

1 shows the basic components of a laser lithotripsy system for a gall stone 10. Even if the invention is explained here in connection with a gall stone 10, the detector device according to the invention can alternatively also be applied to other objects 10, such as e.g. Clots, foreign substances or kidney stones can be used. Non-medical applications are also part of the

Material processing possible.

According to the exemplary embodiment shown in FIG. 1, the laser radiation of a laser system 20 is directed onto the gall stone 10 via a glass fiber 21. The

Glass fiber 21 is guided through the bile duct 11. A radial and axial fixation of the glass fiber 21 in the bile duct 11 is achieved in the example shown via a balloon catheter 12.

The fragmentation of the gall stone 10 with laser lithotripsy is caused by different causes. Investigations of the physical mechanisms of action of laser lithotripsy with microsecond pulses of dye lasers have already been carried out

1992 by IHLER (Laser Lithropsie; investigation of in vitro fragmentation with microsecond pulses; Dissertation Universität Karlsruhe, 1992). The following was determined: The laser radiation emitted is absorbed or reflected by the surface of the gallstone 10.

The very rapid local temperature increase creates a plasma between the end of the glass fiber 21 and the gall stone 10. That with

Plasma which is expanding at supersonic speeds induces a local shock wave which is coupled into the gall stone 10 and is responsible there for fragmentation effects.

The local temperature increase also evaporates a small amount of the liquid that surrounds the gall stone 1. This creates a vapor bubble (pseudocavitation). The higher internal bladder pressure than the liquid pressure expands the bladder, which can reach a diameter of up to 10 mm and a lifespan of up to 0.8 ms.

The expansion of the bladder leads to a decrease in temperature and pressure inside the bladder until the static pressure of the surrounding liquid is greater than or equal to the bladder internal pressure. When this condition is reached, the cavitation bubble collapses and a second stronger shock wave is generated. This connection is in

Fig. 2 shown. The bubble radius (y-axis) increases very strongly with time (x-axis) at the beginning, then increases linearly. After the maximum, the radius decreases linearly, with an abrupt collapse of the cavitation bubble starting at a certain point (here radius 5 mm).

Due to the collapse of the cavitation bubble, the surrounding water flows into the cavity at high speed, creating a water jet that hits the stone surface with great pressure. These complex processes lead to local destruction and repeated repetition to complete fragmentation of the gallstone. Responsible for the destruction of the stone, but also for any damage to the tissue, are the expansion of the plasma and the resulting shock wave and the collapse of the cavitation bubble created by the plasma.

Both shock waves are shown in FIG. 3, approximately 0.8 ms lying between the first shock wave (plasma expansion) and the second shock wave (cavitation bubble collapse).

The following sections explain these two physical causes in more detail.

If a gas is heated to such an extent that its atoms are completely ionized, one speaks of a plasma, the so-called "fourth state of matter". Due to the high degree of ionization, a plasma can be strongly influenced by electrical and magnetic fields.

The presence of free electrons, which then multiply like an avalanche in the radiation field of the laser, is decisive for the formation of a plasma. If the surface of a solid is bombarded with a laser pulse, part of the laser light is absorbed and the rest is reflected. The following generally applies:

Absorption = 1 - reflection

How much energy is absorbed by the solid depends on its material parameters, such as color, density and the wavelength of the laser used. The Due to their dark color, most gallstones have good absorption properties, especially in the visible wavelength range (350-800nm). Water and tissue, on the other hand, only absorb about 5% of the incident light in the range of 500-900 nm. In the ultraviolet and infrared range, however, the absorption of water and tissue increases to over 50%.

By doubling the frequency of the laser system (e.g. according to EP 691 043 AI and US-A 5,963,575) this absorption behavior is used to achieve a low plasma ignition threshold for the gallstones on the one hand and to protect the tissue on the other hand. If the absorbed energy is sufficient, the solid structure of the stone is broken up and evaporated. If, in addition, enough energy is coupled in by the laser beam that atoms and molecules can be ionized, the plasma ignition threshold is exceeded and a plasma cloud is formed. The electrons it contains trigger further ionization processes, which leads to an exponential one

Leads to an increase in free charge carriers. The microplasma generated in this way behaves like a black absorber in relation to infrared radiation. This means that the infrared portion of the laser light is maximally absorbed by the plasma and the plasma is thus further heated ("pumped"). This process is also known as "plasma shielding".

The repulsive forces between the ionized gas atoms and the transition from the solid to the gaseous state cause a rapid expansion of the

Plasma. This rapid expansion creates a shock wave, which is responsible for the first fragmentation of the gall stone 10. In contrast to sound waves, shock waves are pressure amplitudes that move away from the point of origin at supersonic speed move away. Friction reduces the speed of the shock wave front until it reaches the speed of sound. The shock wave can therefore only be measured in the immediate vicinity of its point of origin. The strength of the shock wave depends on the energy content of the plasma and thus on the absorption properties of the stone and the energy of the laser pulse. The infrared portion of the laser pulse in particular has a major influence on the energy stored in the plasma.

In addition to the shock wave, the plasma expansion also creates a cavitation bubble.

In general, cavitation is the formation of "voids" (i.e. areas with much lower density than the surrounding liquid) in a liquid due to a rapid drop in pressure. In the case of the laser-induced cavitation that occurs here, the cavitation bubble is generated by the plasma expansion. In this steam cavitation or "hard" cavitation, the cavitation bubble essentially consists of gaseous water. After the water has evaporated, the cavitation bubble grows rapidly due to the higher internal pressure of the water vapor compared to the liquid pressure, until the maximum radius is reached with the same external and internal pressure. If the external pressure exceeds the internal pressure of the bladder, the bladder collapses slowly and then faster and faster.

This process, which is typical for "hard" cavitation, is called bladder implosion or bladder collapse. This collapse is accompanied by a shock wave with high intensity, which is also responsible for the typical cavitation noise. This second Shockwave is the primary fragmentation process in the crushing of gallstones.

If a cavitation bubble implodes close to a wall, the 5th one refers to the center of the bubble

Radial symmetry of the flow lost. As a result, the side of the bladder front facing away from the wall moves at a higher speed than the opposite side.

0 In addition to this shock wave, a "cavitation jet" is created during the bladder implosion.

As indicated in Fig. 4, one side of the bladder moves inward more and more rapidly and finally changes into a fine liquid jet which shoots out of the bladder at high speed. This

"Cavitation jet" also contributes to the fragmentation of the gallstone.

Due to their strong non-linearity, 0 cavitation processes are difficult to calculate and are often even regarded as a typical example of a physical chaos. However, with a few generalizations, the behavior of the cavitation bubbles can be described relatively precisely. 5 In Lord Rayleigh's model, water is considered an incompressible liquid, so this model is only valid for small amplitudes of bubble oscillation. However, the Rayleigh's bubble model is sufficient for an approximate determination of the first cavitation period T 0 relevant for stone detection. This model can also be used to estimate the energy of the cavitation bubble. The amplitude of the oscillation is defined as the ratio of the maximum bubble radius R _max to the equilibrium radius R _eq u-:

D

A _ymax

R equ

According to Rayleigh's model, a bubble with radius R shows the following equation of motion:

R _R + -R ² - ^

Here p _∞ stands for the pressure and p _∞ for the density of the liquid far from the bladder. P is the pressure in the liquid at the edge of the bubble. The collapse time T _c , which can be determined from the difference between T (R _max ) and T (R = 0), is given by the following expression:

where the saturation vapor pressure of water is jc = 2.6 * 10 ^"2 bar. Since the growth and collapse of the bubble are relatively symmetrical in water, the cavitation period T can be estimated as follows:

T _K = 2 * T _C

The total energy of the bladder can be determined from the work done at the turning point (R = R _m a _x ):

E = -π * R ³ _m * (p _∞ - _Pv ) It follows:

With this expression for T _c , the period of the

Cavitation bubble can be determined depending on the energy.

Similar to how the plasma energy depends on the different absorption behavior of stone and tissue, the plasma expansion determines the energy content and thus the period of the cavitation bubble.

The measurement of the cavitation period T _{κ will be} described later.

After describing the processes that occur when a stone or tissue is bombarded by a laser, the optical and acoustic signals that occur during the irradiation are examined in more detail in order to use them for stone detection.

Stimulated by the work pulse, a more or less strong plasma is generated when there is contact with stone, depending on the material. The higher the energy of the plasma, the greater the first shock wave caused by the plasma expansion. Since tissue generally only produces a very low-energy plasma, the first shock wave could be chosen as a distinguishing criterion between stone and tissue. However, as the measurements have shown, this method is not sufficiently precise, particularly when it comes to distinguishing between blood that occurs when tissue is damaged and light gallstones. The expansion of the plasma results in the described cavitation bubble, the size and thus the cavitation period T _κ of which depend on the plasma energy and on the relationship derived above

to be discribed. Since a second very high-energy shock wave is generated when the cavitation bubble collapses, the cavitation period can be determined by measuring the first and the second shock wave. Previous measuring methods used needle hydrophones or piezo sensors to detect the pressure waves, which are glued to the glass fiber directly in front of the catheter. The disadvantage here is that the glass fiber must also be used for sound transmission. Measurements have shown that clamping and bending the glass fiber result in a loss of 50% of the sound power, and that touching the bare fiber or a stone contact on the side can cause sound power losses of up to 90%. One solution would be to attach a pressure sensor directly to the tip of the fiber.

However, this sensor would have to be very small and, since the fiber is sterilized, it should also be designed to be very robust against heat, water vapor, etc.

If the glass fiber 21 has contact with the gall stone 10 or the tissue when a cavitation bubble 30 is formed, the resulting bubble encloses the fiber end until it collapses. This is shown schematically in FIG. 5.

During this time, the tip of the glass fiber 21 is in a cavity filled with water vapor with the refractive index n of air of approximately 1. When the cavitation bubble 30 implodes after the cavitation period T _κ the fiber end is again in water with the refractive index n of approximately 1.333.

An embodiment of the device according to the invention uses the different reflection during the transition from the glass fiber 21 in water or from the glass fiber 21 in air

The measurement signal obtained is shown schematically in FIG. 6. At the beginning of the signal there is a peak which is attributed to the plasma glow at 650 nm. The subsequent, essentially rectangular signal continues until the cavitation bubble collapses. The cavitation period T _κ here is approximately 0.8 ms.

FIG. 7 shows the schematic structure of an embodiment of a device for determining the cavitation period as a means for detecting an object. The gall stone 10 is there for the sake of

Vividness in a laboratory vessel with water as a fluid. A measuring laser beam is radiated onto the gall stone 10 by a measuring laser system 20 via a beam splitter 24, a deflecting mirror 22 and a glass fiber 21. A cavitation bubble 30 is generated by the plasma expansion 31. The change in the reflection factor R is measured

where n _{x stands} for the refractive index of the glass fiber 21, n ₂ for the refractive index of the water. The reflection of the

Measuring laser beam is guided via the semitransparent deflecting mirror 22 and the beam splitter 24 to a fast photodiode 23, the signal of which is transmitted to a measuring device 25 (signal processing, oscilloscope, computer etc.). The measuring means 25 registers the different reflection during the transition from glass fiber to water or glass fiber in the gas phase (air).

The measuring laser system 20 (as radiation means) and the measuring means 25 together form the components of the detector device according to the invention. The parts framed in dashed lines in FIG. 7 are also referred to as measuring branch 27 of the system.

The reflected signal is passed over the glass fiber 21, with which the high-energy laser pulse of a working laser 26 is transmitted to destroy the gallstone 10. This has the great advantage that no additional sensor has to be attached to the glass fiber 21. Since optical signals are transmitted, the transmitted measurement signal is relatively insensitive to mechanical stress and electromagnetic influences. The state of aggregation of the water in front of the glass fiber caused by the formation of the cavitation bubble 30 is registered. The difference between that

The reflection factor for the transition from glass fiber to water R _w and glass fiber to air R _L can be determined approximately using the formula given above. With the refractive index of the quartz glass fiber ni of approximately 1.46 and the refractive index n _w of water of approximately 1.333, an R _w of 0.0022 results. For air n _L of approximately 1, the reflection factor R _L = 0.035 and thus around 16 times higher than R _w for water.

This large difference in the reflected light output enables a relatively precise measurement of the

Cavitation period T _κ , which is used as a differentiating criterion for stone detection in this measurement method. Investigations with an acoustic stone detection system showed that a reliable distinction between dark gallstones and bile tissue is possible using T _κ . The pale stones cause problems because their absorption behavior is similar to that of bile tissue.

The determination of the cavitation period is described in more detail below.

Since the measurement of the cavitation period T _κ has to be measured over a period of up to 1000 μs, the detection of the change in reflectance described above becomes an additional one. Laser needed. The additional laser emits radiation that differs from the working radiation and can therefore be separated from the working beam (for processing the object 10) in a simple manner. Diode lasers are preferably used as an additional laser (measuring laser). The radiation is separated by dichroic mirrors.

For this, e.g. the deflecting mirror 22 (see FIG. 7) is chosen to be almost transparent for the wavelength range from 590 to 720 nm and a laser diode with a wavelength of 655 nm is used as the measuring laser. The mean laser energy of 20 mW in continuous wave mode ensures a sufficient signal-to-noise ratio during the measurement.

As with measuring the pulse duration, a fast sensor must be used to determine the cavitation period, which quickly subsides even in the event of a strong oversteer in order to be able to continue the measurement. This override can e.g. B. caused by plasma lights. A fast photodetector is therefore used as the sensor, For example, an Si PIN photodiode FDD-100 is used, which in addition to corresponding electrical properties also has a relatively large sensor area of A _s = 5.1 mm ² . This simplifies the focusing of the laser beam on the sensor surface by means of a biconvex lens and increases the mechanical tolerance range of the holder specially made for this sensor.

The measuring laser beam is coupled into the glass fiber via a suitable physical beam splitter, e.g. the deflecting mirror 22 of the working laser 26. Since both the laser and the mirror have a preferred direction, attention must be paid to this polarization direction when mounting the laser on the optical bench. This can be changed by rotating the laser diode until almost the entire light output can pass the deflecting mirror. A beam splitter 24 is attached between the deflecting mirror 26 and the measuring laser 20 and directs the measuring signal reflected at the end of the glass fiber to the photodiode. The beam price is designed so that for the

Wavelength range from 600 to 700 nm, a division ratio of 50:50 applies and the other wavelengths are transmitted almost unhindered.

This prevents the sensor from being overdriven by the reflected green and infrared components. As shown in Fig. 9, the sensor is mounted on an additional optical bench.

The focus of the reflected laser signal on the

The sensor surface is again made with a biconvex lens.

A cover of the sensor unit with a light-tight, absorbent cover, e.g. a black lacquered sheet prevents interference from interference, e.g.

Laser flash lamp light. The measurement is triggered as with the investigation of the plasma expansion with the sensor PEM 21, which is attached behind the deflecting mirror 1 (Fig. 9).

For the amplification of the diode current, an amplifier circuit with a photodiode in the

Resistance operation with preload used. The time characteristic is adjusted by the downstream amplifier stage and its wiring in the feedback branch. Such a circuit is shown in Fig. 28. In this circuit, the amplitude of the output voltage U _{out is determined} via the feedback resistor R _{F of} the circuit. The following applies:

Since the circuit shown in FIG. 28 tends to oscillate, the capacitance C _F = 1 pF is switched in parallel with one of the two resistors R _{F / 2} , which amplifies the high-frequency noise components of the signal. For additional noise reduction when powering the

Operational amplifiers provide two capacities, each with 47 / F. A bias voltage of U _D = 20 V reduces the

Rise time of the photodiode to 3.5 ns.

In the present example, the laser power is very weak (~ 50μW), so that the resistance R _F with 940 kΩ is selected for these measurements, resulting in a cut-off frequency F-3dB of 2.7 MHz. This is sufficient for the determination of the cavitation period, which can be up to 1000 μs. The measurement signal to be expected settles

The occurrence of a cavitation bubble theoretically consists of a 1 to 7 μs long pulse caused by the plasma lighting and a rectangular signal of the duration T _κ (Fig. 10).

Due to this initial voltage peak and the noisy square wave signal, an exact determination of the cavitation period by means of a counter is very difficult possible. The evaluation of a logic circuit is also not feasible because of the voltage level which is not firmly defined. The signal processing of the sensor signal is therefore necessary.

Since the rising and falling edges of the signal are very steep, they can be used to determine T _κ . A circuit which only amplifies a voltage change and thus the edges of a signal is referred to as a differentiator, and in the simple case is constructed like a first-order high-pass filter (FIG. 11).

The cut-off frequency f _{g of} the circuit is determined by the capacitance C _x and the feedback resistor R ₂ .

The differentiating element is therefore designed in such a way that it is also suitable for detecting even steep slopes, and nevertheless a good suppression of the DC component

To get tension. For this purpose, in the present example, a capacitance of 10 pF is chosen for the capacitor C and 18 kΩ for the resistor R ₂ . With these values, the cut-off frequency f _{g of} this circuit is 884 kHz. The resistance R ₂ is determined via the common mode gain A _{0 of} the circuit and the resistance R ₂ .

* - £

4

An operational amplifier becomes higher for amplification

Bandwidth, similar to that used in an amplifier circuit of the 0PA655.

By determining the time between the first and second negative spikes of that shown in FIG. 12 processed signal, the cavitation time can be determined exactly.

Another possibility of signal processing is the delivery of a fixed voltage level of e.g. 5 V at

Exceeding a predetermined voltage threshold U _s . For example, the voltage threshold U _s is selected so that it is on the one hand above the noise and on the other hand below the amplitude of the rectangular portion of the measurement signal. As a result, a rectangular pulse with an amplitude of 5 V and a pulse duration T _{κ is} generated, while the interference generated by the plasma lighting is suppressed (FIG. 13).

For this purpose, an operational amplifier (OPV) is operated without a feedback loop (comparator). A small voltage difference at the input immediately leads to maximum modulation of the OPV. The OPV TL 3116 used in this circuit sets the output to ground when the voltage threshold U _s is undershot and the output to + 5 V when U _{s is} exceeded

Threshold voltage U _s can be regulated between 0 and 5 V using a potentiometer (Fig. 14).

The square-wave signal generated in this way can be evaluated directly by means of suitable logic. In the present

An exemplary embodiment uses a digital counter (e.g. from HAMAG) to determine the pulse duration of the rectangle.

The laser of the measuring laser system 20 is operated in continuous wave mode, so that the reflection when the

Measuring laser beam only occurs in the form of a DC voltage. This DC voltage can either be suppressed directly by a capacitance connected in series, preferably 100 nF, or by an oscilloscope. This DC voltage also affects the gain range of the amplifier in the

Signal processing reduced by this voltage amount. This comes into play especially with the first pulse, since its high energy overrides the operational amplifier. However, since this pulse with 1.8 μs is very short compared to the cavitation period T _κ with 100 to 1000 μs, the effect for the actual measurement can be neglected.

In order to test the functionality of the measuring system for stone or tissue recognition, the following tests are described: • To substantiate the theoretical assumption that the transition of the glass fiber end from water to air is detected in the optical measuring method, the reflected laser power is measured in air and in Measure water. • The four different types of gallstones are bombarded with a pulse energy of 20 to 120 J, whereby the measurement is carried out at a distance of 5 mm, 2 mm from the glass fiber to the stone and with stone contact. These exemplary values can be applied analogously to comparable data and situations.

• As with gallstones, dead kidney and

Bile tissue and live bladder and bile tissue and blood are bombarded at a distance of 5 mm, 2 mm and contact with a pulse energy of 20 to 120 J.

In order to verify the hypothesis of a change in the state of matter, the reflected light output of the measuring laser system is measured once in air and once in water. For this purpose, the glass fiber is immersed in water and the direct voltage component U _{w is} measured. By repeating the measurement in air, the direct voltage component U _{L is obtained} . The

The difference between the two voltages gives U _D i _ff . This voltage value should coincide with the square wave signal that occurs during cavitation. This would confirm the assumption that the change in reflectance is associated with the change in the state of matter in the bladder. The measurement results are shown in Fig. 15. As can be seen from FIG. 15, the difference voltage U _D iff results in a value of 200 mV.

In the subsequent measurements, the signal coming from the amplifier is fed directly to a first channel of the oscilloscope, with a second channel the output of a comparator is shown and a third channel is used for triggering. The pulse duration is recorded with a counter. The comparator supplies the signal for the counter, since its output signal has only a low noise component.

In these measurements, the laser is operated at a pulse rate of one pulse per second. The output energy is increased from 20 to 120 mJ in steps of 10 mJ. 10 pulses are measured per step and the cavitation periods are noted, whereby a typical pulse is saved in each case. After every increase in energy, the glass fiber is examined for fiber burn-off and repaired if it is damaged by shortening.

In the following, the change in the reflected laser power is measured on four different gallstones. Dark and light stones are at a distance of 5 mm, 2 mm and 0 mm, i.e. direct contact with the

Glass fiber 21, shot at. Depending on the stone and the energy released, the voltage curve shown in FIG. 16 is shown (E _ou t = 60 mJ).

The cavitation time is determined via the rectangular pulse of the comparator. Since the cavitation time depends not only on the bombarded material, but also on the laser energy set, this relationship is shown separately in FIG. 17. When examining dead bile and kidney tissue, kidney and bile tissue is bombarded at a distance of 5 mm, 2 mm and in direct contact with the glass fiber and the resulting changes in the reflection behavior of the

Glass fiber 21 recorded. A 2 x 2 cm piece of tissue is cut out and fastened in a glass with wooden strips. In the case of dead kidney tissue, the signal curve shown in FIG. 18 is obtained, in which a very short cavitation period can be seen. The

Measurement results for dead bile tissue are shown in Fig. 19.

Since the properties of dead tissue to be lived differ greatly, were registered in the context of a

Animal experiment, the cavitation bubbles with laser bombardment of a gallbladder and a bladder examined in more detail. For this purpose, the tissue that was still supplied with blood was bombarded with different output energy E _ou t upon direct contact with the glass fiber and the reflected signal was recorded. Since the

Glass fiber could not be inserted directly into the bile duct, the tests were carried out on the open bile and urinary bladder.

The liquid required for the cavitation was supplied by means of a short catheter, which also serves as a holder for the glass fiber.

As in the previous measurements, the pulse energy E _ou was increased from 20 mJ in 20 mJ steps to 120 mJ. In order to get a meaningful result, 10 laser pulses were emitted per energy level and the different cavitation times were measured. The measurements were carried out with a laser diode with a power of 1.7 mW. Due to the correspondingly low signal-to-noise ratio, the measurement signal for the comparator was not can be clearly determined so that the cavitation time can be read directly on the oscilloscope. 20 shows the measurement signals during gallbladder bombardment.

The cavitation periods of dead and living tissue are compared in FIG. 21, the tissue of the bladder showing no difference from the kidney tissue. While cavitation can always be observed in the gallbladder, measurable cavitation effects only occur in light kidney and bladder tissue from an energy of 100 mJ.

The investigations have further shown that the cavitation times are much higher with living bile tissue than with dead tissue. One reason for this is the blood flow to the living tissue.

To confirm this assumption, the cavitation time of blood is examined in more detail. For this purpose, as with the tissue test, 10 laser pulses per energy level are emitted into the blood and the cavitation times are noted. The results are shown in Figs. 22 to 24.

Each of FIGS. 22 to 24 contains the measured cavitation times of the four types of gallstones used, of the dead and living bile and kidney tissue and of blood, each of these three diagrams being associated with a specific energy range of the laser pulse emitted. 22 shows the results of the time measurements at an energy E _ou of 20 to 50 mJ. 23 shows the cavitation times of different samples with an energy of 60 to 80 mJ. 24 shows the results for high-energy pulses in the range from 90 to 120 mJ. Before the measurement results achieved with the device according to the invention are explained, a technical peculiarity will be discussed here.

Since high pulse energies of 120 mJ are used for the fragmentation of the gallstones, the end of the glass fiber is heavily stressed, so that fiber burn-off can occur. In order to investigate the influence of fiber burnup, a stone with a very dark stone is shot several times with a laser pulse with an energy of 120 mJ and the measurement signal is recorded. The measurement signal is stored after the first, the 50th and the 100th pulse, with a plasma ignition occurring with each pulse. The result of this investigation is shown in FIG. 25.

Now the results achieved are to be discussed.

The strength of the shock wave generated by the plasma expansion depends on the energy stored in the plasma and thus on the absorption behavior of the bombarded surface. The more laser energy from the gallstone or

Tissue is absorbed, the stronger the radiated shock wave.

In addition to the shock wave, the plasma expansion 31 also forms a cavitation bubble 30 and light quanta are emitted. The radiated shock wave leads to an increase in the water pressure in front of the glass fiber and a decrease in the reflected laser energy.

Since the shock wave is still generated during the laser pulse duration of 1.7 μs, a change in the reflection behavior of the glass fiber can be measured with the portion of the laser pulse emitted reflected at the glass fiber end.

When measuring the cavitation period T, the cavitation bubble that arises during the plasma expansion is shown as Differentiation criterion between stone and fabric used. As described, the radius of the cavitation bubble and thus the cavitation period depends on the plasma energy. The more laser energy is absorbed by the bombarded test specimen, the larger the cavitation bubble and the longer the cavitation period T _κ .

The cavitation bubble grows from its center of origin up to a maximum radius R _max and then collapses with increasing speed until it collapses completely, whereby a second shock wave is emitted. The period between the first shock wave and the second shock wave is called the cavitation period. If the glass fiber is at a distance of less than 2 mm in front of the test specimen when the laser pulse is emitted, the cavitation bubble forms around the glass fiber end and the glass fiber tip is located inside the gas bubble.

The measurement of the cavitation time is caused by the transition of the glass fiber from water to air

Increase in reflectance measured. This increase remains until the glass fiber end is wetted again with water. Theoretically, the measurement signal should show the same voltage difference of 200 mV when measuring within the cavitation bubble as when measuring the reflected light output of the glass fiber in air and in water (see Fig. 15).

Depending on the type of stone and pulse energy, there are differences in the signal curve of the measurement signal (see Fig. 18). Is at low pulse energies up to 50 mJ

Voltage difference below 200 mV usually has a value of up to 300 mV for pulse energies above 90 mJ. The lower voltage can be explained by the not exactly defined physical states in the cavitation bubble. This means that the fiber can still be partially wetted with water. Damage too the fiber tip can lead to a reduction in the tension difference. The higher voltage difference than the 200 mV caused by the different refractive index of water and air was not further investigated because it is not a disadvantage for the measurement. In addition to the higher voltage difference mentioned above, the measuring signal increasingly takes the form of an ideal rectangular pulse with increasing pulse energy, which simplifies the determination of the cavitation period for high pulse energies. For low pulse energies in the range of 20 to 50 mJ, depending on the gallstone used, the edges of the measurement signal are less pronounced than for medium and high pulse energies. This effect is particularly evident when measuring the red-brown gallstone (see Fig. 19). By using the 20 mW photodiode as a measuring laser, the signal-to-noise ratio is high enough for these measurements, too, to be able to measure a clear difference in voltage levels. Here, however, the threshold voltage of the comparator would have to be reset depending on the level of the pulse energy. Due to the not exactly predictable behavior of the

Cavitation bubbles during and after the implosion can lead to different signal patterns after the first transition from air to water. Ideally, the measured voltage level drops after the implosion to the value U ₀ , which is also displayed in water, and remains constant. The

However, the voltage of the signal can also rise to the value before the implosion after a short negative voltage peak or show other signal curves. Since after the collapse of the bladder the voltage drops to the value U ₀ at least for a short time, detection of the

Cavitation period T _κ possible with this measuring system.

As described above, the cavitation period depends on the absorption behavior of the test specimen. A longer cavitation period should therefore be measured for gallstones than for tissue and blood. According to the measurement results shown in FIGS. 21 to 24, this prediction agrees except for the difference between light gallstones and living gallbladder tissue and blood. Especially with a high pulse energy between 90 and 120 mJ there is an overlap of the cavitation period of blood and light gallstone. The reason for this is the similar absorption behavior of light gallstones and blood. The blood is also responsible for a longer period of cavitation in the living and thus perfused soft tissue of the gallbladder compared to the dead and therefore no longer perfused gallbladder tissue (see Fig. 21). Since the cavitation period also increases with an increase in the pulse energy of the laser (see FIG. 17), the difference between the cavitation period of the gallstones and the soft tissue is greatest at a pulse energy of 90 to 120 mJ (see FIG. 24). But even with a low laser energy of 20 to 50 mJ, a good distinction between dark gallstones and soft tissue and blood is possible (see Fig. 24). Only the very bright and rarely occurring cholesterol stone cannot be detected with any pulse energy. Its very bright surface does not absorb enough laser energy at 532 nm to achieve plasma ignition. Cavitation bubble formation is therefore rarely the case.

The optical stone recognition method presented is able to distinguish between dark gallstones and soft tissue and blood by determining the cavitation period. In the case of light-colored stones, this is sometimes only possible with a low pulse energy after the delivery of more than two pulses. However, there is good detection for high energies. The great advantage of the optical method compared to the acoustic method is that the glass fiber can be used as an optical sensor without the measurement signal being disturbed by contact or mechanical stress. With the acoustic measuring system, on the other hand, even light touches with the hand lead to losses of measurement signals up to 90%. The integration of the stone detection system in the laser system and the use of glass fiber as a sensor make the system very robust in the clinical area against external influences. Since no 5 sensors have to be attached to the glass fiber, the system is also easy to use.

In the optical measuring system, the signal quality is dependent on the condition of the glass fiber tip. With up to 50 L0 pulses, which are emitted on a very dark stone with an energy of 120 J, stone detection is still possible.

Through the use of more robust glass fibers, which are very low even with L5 high mechanical stress

If there are deformations at the end of the glass fiber, improvements can be achieved.

Since the fiber fragmentation also causes the 20 fragmentation properties to deteriorate, the optical measuring system can be used to detect the fiber erosion. However, special signal processing is necessary for this.

25 An improvement in measurement accuracy can be achieved above all with an extended analysis of the measurement signal, since the signal curves can vary depending on the color of the stone. Especially a reddish-brown gallstone produces a low energy compared to a dark brown and light stone

30 relatively "dirty" signal. From a pulse energy of 90 mJ, the transition from glass fiber in air to glass fiber in water is very clearly defined.

An inexpensive solution to signal processing is the use of several, different ones

Threshold voltages of comparators that are set can still detect small signals. The result can then be evaluated using a corresponding logic circuit (see FIG. 26).

Alternatively, an analog-digital converter can be used with which the entire signal curve can be evaluated.

In addition to the better signal analysis, a clearer signal can also be registered by improving the noise characteristics of the measuring circuit. The thermal noise of the photodiode and the diode laser is critical here. The light fluctuations of the diode laser can be minimized by installing a second photodiode, which measures the signal emitted by the laser before it enters the glass fiber. This is shown in Fig. 27.

The interference caused by the high-voltage power supply unit of the laser can be avoided by means of an adequate ground connection and shielding of the sensor and the evaluation electronics.

A bandpass filter with the frequency of the measuring laser can also filter out optical interference pulses, such as the reflected green component. This could avoid the signal increase caused by the reflected green portion of the laser pulse at the start of the measurement.

The embodiment of the invention is not limited to the preferred exemplary embodiments specified above. Rather, a number of variants are conceivable which make use of the device according to the invention and the method according to the invention even in the case of fundamentally different types. LIST OF REFERENCE NUMBERS

10 gallstone

11 bile duct

5 12 balloon catheters

13 photodiode for measuring the light passing through the laser fiber

20 measuring laser system

0 21 glass fiber

22 Deflecting mirror as beam splitter, working laser / measuring branch

23 photodiode

24 Beam splitter measuring laser / photodiode .5 25 signal processing means

26 working laser system

27 measuring branch of the system

30 cavitation bladder

! 0 31 Plasma expansion

32 wall

Claims

Patent claims 1. Detector device for an object (10), in particular for a stone, for a clot, for a part of tissue and / or for a foreign substance in a liquid and / or a tissue, in particular in human body tissue, marked by a radiation means (20) for generating at least one gas phase in the fluid and/or in the tissue and a measuring means (23, 25) for detecting reflections at a phase boundary between an optically transparent medium, in particular a glass fiber, and a gaseous and/or liquid phase . 2. Detector device according to claim 1, characterized in that a plasma pulse and subsequently a gas phase, in particular a cavitation bubble (30), can be generated in the fluid by the radiation means (20), the properties of the gas phase being usable for detection. 3. Detector device according to claim 2, characterized in that a plasma pulse with a pulse energy between 20 and 200 mJ can be generated by the radiation means (20). 4. Detector device according to at least one of the preceding claims, characterized by a means for the targeted selection of different, predetermined levels of pulse energies, in particular a low level for generating a test pulse and a higher level for carrying out processing of the object (10). 5. Detector device according to at least one of the preceding claims, characterized in that a first shock wave is generated by the expansion of the plasma in the fluid, a second shock wave can be generated by the collapse of a cavitation bubble (30) in the fluid. 6. Detector device according to claim 5, characterized in that the time between two shock waves in the fluid can be measured with the measuring means (23, 25), 7. Detector device according to at least one of the preceding claims, characterized in that the measuring means (23, 25) uses a functional relationship between the energy of the cavitation bubble and the cavitation time for detecting the object (10), in particular for stone detection. 8. Detector device according to at least one of the preceding claims, characterized in that the radiation means is designed as a measuring laser system (20). 9. Detector device according to at least one of the preceding claims, characterized in that the radiation means (20) operates in a wavelength range between 350 and 800 nm and / or in a wavelength range from 700 to 1600 nm. 10. Detector device according to claim 9, characterized in that the radiation means (20) operates at a wavelength of 532 n. 11. Detector device according to at least one of the preceding claims, characterized by at least one differentiating element for measuring the cavitation period. 12. Detector device according to at least one of the preceding claims, characterized by at least one comparator circuit for measuring the cavitation period. 13. Detector device according to claim 12, characterized in that at least two comparator circuits for detecting small signals are set to different threshold voltages. 1 . Detector device according to at least one of the preceding claims, characterized by an AD converter for evaluating the signal curve. 15. Detector device according to at least one of the preceding claims, characterized by a noise suppression circuit, an additional photodiode. 16. Detector device according to at least one of the preceding claims, characterized by at least one bandpass filter for the frequency of the measuring laser for filtering optical interference. 17. Detector device according to at least one of the preceding claims, characterized by a working laser system (26) for processing the object (10). 18. Method for detecting an object (10) in a fluid, in particular a stone, a clot, a piece of tissue and / or foreign substances in the body human body, marked by a) Generation of a phase change in the fluid and / or in the tissue by a radiation agent (20), b) Detecting reflections at a phase boundary between an optically transparent medium, in particular a glass fiber, and a gas phase and / or a liquid phase by a measuring device (23, 25). 19. Method for processing an object (10) in a fluid, in particular a stone, a clot, a piece of tissue and / or foreign substances in the human body, marked by a) a detection of the object according to the method according to claim 17, b) processing, in particular destruction, of the object (10) with a working laser system (26) depending on the result of the detection.