WO2002045578A1

WO2002045578A1 - Method and device for determining the topology of biological tissue

Info

Publication number: WO2002045578A1
Application number: PCT/EP2001/014501
Authority: WO
Inventors: Stephan SCHRÜNDER
Original assignee: Bioshape Ag
Priority date: 2000-12-08
Filing date: 2001-12-10
Publication date: 2002-06-13
Also published as: DE10061326A1; AU2002216092A1

Abstract

The invention relates to a method for determining the surface shape of biological tissue, characterized by irradiating the tissue (8a) with an irradiation pattern (26) produced by an excitation radiation (2). Said excitation radiation (2) comprises light of the wavelength ranges of the ultraviolet and/or infrared part of the spectrum. The scattered radiation pattern (27a) emitted by the irradiated tissue zones is detected at least in the wavelength ranges of the ultraviolet and/or infrared part of the spectrum and is evaluated to calculate the surface shape of the biological tissue (8a). The invention further relates to a method according to which a layer that contains molecules that can be induced to fluoresce and that adapts itself to the surface of the tissue is applied to the tissue (8a) and the layer (40) is irradiated with an irradiation pattern (26) produced by an excitation radiation (2). The fluorescence pattern emitted by the irradiated layer ranges (8a) is detected and evaluated to calculate the surface shape of the tissue (8a). The invention further relates to corresponding devices.

Description

Methods and devices for determining the topology of biological tissue

The invention relates to methods and devices for determining the topology of biological tissue.

In order, for example, to arrive at exact medical diagnoses, to be able to carry out operations precisely, or also to make clothing that is tailored to the body, it is necessary to know exactly the surface shape of the biological tissue in question. For this purpose, optical methods are known in which, for example, visible light is directed onto skin areas of the human body - such as the female breast or foot areas -, the scattered radiation is detected and evaluated to calculate the topometry of the corresponding shapes. In this way it is possible, for example, to produce items of clothing which are appropriately adapted to these parts of the body.

Other known methods are used for the surface measurement of the cornea of the human eye, since the cornea is transparent and visible light would not backscatter to any appreciable extent. With its refractive power of over 40 diopters, the cornea is a key factor in refraction of the light that enters the eye. The refractive power of the cornea depends primarily on the shape of the surface of the cornea and especially its curvature. Recently, methods have been developed in which tissue from the cornea is removed by means of a laser (so-called laser ablation) in order to prevent ametropia by changing the Correct corneal refractive power. The intervention is usually done on an outpatient basis. Depending on the procedure, the patients get a good one day (with the so-called laser in situ keratomileusis procedure, abbreviated LASIK) or 1-2 weeks (with the so-called photorefractive keratectomy procedure, abbreviated PRK) Eyesight without a visual aid. Since only a few ten micrometers of the cornea have to be removed, for example by means of a laser, an exact measurement of the surface is essential. This is currently being determined using optical methods before and several days after the ametropia correction.

A known method for measuring the cornea surface is the so-called slit-scan method, in which a light beam of visible light in the form of a straight, narrow slit is successively (scanned) projected onto adjacent areas of the cornea until the entire corneal section of interest is scanned. The light beam is divided into a reflected and a broken beam on the surface of the cornea. The latter penetrates the surface and is scattered in volume at internal scattering centers, ie omnidirectional. The clearest signals come from scattering centers near the surface of the cornea. It is therefore possible to calculate surface points independently of one another using the known so-called direct triangulation method. This method has the advantage that there is almost no scattering on the tear film in front of the cornea, so that the signals originating from the scattering centers are not influenced by the tear film. The disadvantage of this known method is the long measuring time, which is due to the scanning process. Spontaneous eye movements during this time make the measurement unusable. In addition, the intensity of the slit to be directed onto the cornea must be relatively high, since the intensity of the scattered, predominantly blue light is comparatively low. Therefore, this known method is not relatively uncomfortable for the patient. A long-known and predominantly used method for measuring the shape of the cornea uses so-called keratometers, in which concentric rings, the so-called placido rings, are projected onto the tear film in front of the cornea and the reflected signals are detected and evaluated with a camera , For this purpose, a disc with circular, concentric slots is arranged between the eye and the lighting device, in the center of which a camera is placed. Due to the curvature of the cornea, the reflected ring pattern detected by the camera is distorted. In order to obtain a determination of the curvature from these reflection signals, the distortions of the rings have to be compared with a known shape, which is usually chosen as a sphere with a radius of 7.8 mm. At the start of the measurement, a crosshair is first placed in the center of the cornea, in order to then usually project 20 rings onto the surface of the eye. Then 180 meridians are placed at 1 "intervals around the manually determined center of the cornea. Computer software then tries to determine the leading and trailing flanks of the reflected circles so that two intersection points per ring are obtained per meridian 7,200 data points (180 meridians x 20 rings x 2 intersection points), from which the curvature of the cornea can then be calculated.The disadvantage of this known method is that due to the camera being placed in the center of the ring arrangement on an area with a diameter of At least 1.5 mm in the center of the cornea, no data can be recorded, which would be particularly important. Furthermore, the manual placement of the crosshairs in the center of the cornea is susceptible to individual errors, since it is precisely in this area of the central cornea due to the arrangement the camera cannot be reliably checked The assumption of an ideal spherical surface of the skin of the skin also harbors sources of danger, since deviations from this standard eye that are more common than usual are not uncommon. The total number of 7,200 data points is also relatively small, especially since the distance between the data points increases with the distance from the center of the cornea decreases so that an inadequate determination of the surface is possible, particularly at the marginal areas of the cornea. Last but not least, deviations from the assumed slope of the ideal spherical surface along each measured meridian are determined using the placido method, so that the height of the cornea at each of these measuring points must be calculated in a further step from these slope points.

The so-called Fourier profilometry method is also known, in which two identical sine wave patterns are projected onto the surface of the eye. Here, filtered blue light is used for projection, which allows a liquid added to the tear film to fluoresce. The wave pattern of the fluorescent light is then recorded by a CCD camera and the phase shift is calculated using a two-dimensional Fourier transformation analysis, which is directly related to the homology topology. A disadvantage of this known method is that the data cannot be more precise than the thickness of the tear film (approx. 50-200 μm), which also varies depending on the time of day.

The so-called strip projection method is also known, which is mainly used in industry to measure surfaces of metals and other materials. This known method has the advantage that it can be carried out quickly and without contact, since only a single exposure is necessary. In this method, a suitable stripe pattern, which can be generated, for example, interferometrically or by imaging a suitable structure, is projected onto the surface to be measured and the light diffusely scattered from the surface is subsequently detected. If this method is used to measure an eye cornea, the detected stripe pattern is distorted due to the elevations of the cornea. A further distortion arises in that the detection camera is not in the beam path of the radiation pattern, but at an angle to the projection or radiation direction is arranged. By means of Fourier transformations, which can now be carried out very quickly with modern computers, the surface shapes can be determined from the distorted stripe patterns.

However, phase measurement errors can occur in this known method if the contrast of the detected stripe pattern is relatively weak. In order to avoid this, in known modifications of the method described, either the object to be measured is vaporized with a contrast-increasing, highly scattering layer or a fluorescent dye is applied in front of the surface to be measured. In Applied-Optics 34, 3644 ff., 1995 it has been proposed to add such a fluorescent dye to the tear film so that after irradiation of the tear film with blue light, it emits green light due to the fluorescence excitation, which can then be detected and evaluated. A similar method is described in US Pat. No. 5,406,342, in which two partial patterns are projected from different directions onto a tear film enriched with fluorescent dye, in order to subsequently record two emitted fields in succession with a camera. Due to the projection from different directions, the direct reflection of the radiation beam can be eliminated.

The described methods for determining the corneal topology are only used if there is a tear film in front of the cornea. If the cornea measurement is carried out indirectly by measuring the surface course of the tear film, measurement errors occur, however, in that the thickness of the tear film fluctuates temporally and locally. Furthermore, an added fluorescent medium is distributed over the entire tear film thickness, so that the measuring accuracy cannot be higher than the film thickness, ie up to 200 μm. Likewise, the epithelial layer of the cornea is always present when using the known methods described, but it is necessarily the outermost layer of the cornea during laser ablation be removed. If a fluorescent fluid were used with the epithelial layer removed, the fluid would penetrate the cornea and cause it to swell, thereby also reducing the depth resolution.

Methods are also known in which a thin, diffusely reflecting cover is applied to the cornea and a radiation pattern is projected onto the cover. No. 5,507,740 describes, for example, a method in which the pattern projected onto the cover consists of concentric circles and the distortions of the pattern due to the corneal elevations are examined. No. 5,116,115 likewise describes the projection of a structured pattern of visible light onto a layer covering the cornea, the phase of this light pattern being modulated. A computer calculates the phase of each reflecting point of the layer from the backscattered radiation, from which the relative height can then be deduced.

From DE 198 37 932.2 it is known to irradiate a tissue directly with an irradiation pattern generated with the aid of an excitation radiation, so that the irradiated tissue areas are excited to emit a fluorescence pattern consisting of fluorescent radiation, which is detected and evaluated to calculate the surface shape of the tissue.

It is an object of the present invention to provide methods or devices of the type mentioned at the outset in which the topology of a biological tissue and especially a cornea can be determined in a simple and yet very precise manner and the results, if applicable, in the surgical treatment can be used.

In a first aspect of the invention, this object is achieved by a method for determining the surface shape of biological tissue, in which the tissue is irradiated with an irradiation pattern generated with the aid of excitation radiation, the excitation radiation containing light of the wavelength ranges of the ultraviolet and / or infrared part of the spectrum, and in which the scattered radiation pattern emitted by the irradiated tissue regions at least in the wavelength ranges of the ultraviolet and / or infrared part of the spectrum is detected and evaluated to calculate the surface shape of the biological tissue.

In a second aspect of the invention, the object is achieved by a method for determining the surface shape of biological tissue, in which a layer adapting to the surface of the tissue is applied to the tissue, the layer is irradiated with an irradiation pattern generated with the aid of excitation radiation, and that of radiation patterns emitted in the irradiated layer regions are detected and evaluated to calculate the surface shape of the tissue, the layer containing molecules which are excited by the irradiation with the radiation pattern to emit a fluorescence pattern consisting of fluorescent radiation, which pattern is detected and used to calculate the surface shape of the layer and thus that of the tissue is evaluated.

With regard to the devices, the object is further achieved on the one hand by the features of independent claim 29 (corresponding to the invention according to its first aspect) and on the other hand by the features of independent claim 30 (corresponding to the invention according to its second aspect).

The advantages of the invention according to its first aspect are, in particular, that radiation with wavelength ranges is used which - depending on the type of tissue examined - can have an extremely small penetration depth. Characteristic cellular components of the tissue are responsible for the low penetration depth, which lead to an increased scattering of the light. Thus, especially from the outermost tissue backscattered light layers the tissue, which is recorded by a camera that is sensitive in the wavelength range of the scattered light - essentially the same range as that of the excitation radiation. A scattered light pattern can thus be detected, which essentially originates from the tissue areas that determine the surface shape. The light emitted by the tissue surface is scattered statistically in all directions, while the additional light that occurs directly reflected on the tissue surface is subject to the Snellius law of refraction.

In contrast to the method described in DE 198 37 932.3, the method according to the invention does not make use of a frequency shift due to a wavelength difference between the excitation radiation on the one hand and the fluorescence radiation on the other. Rather, the scattered radiation pattern that is not shifted in wavelength with respect to the excitation radiation or the excitation radiation is detected.

By means of the method according to the invention, areas located on the body surface and internal body sections can be measured topologically.

A preferred embodiment of the invention provides for a fluorescence pattern to be detected in addition to the scattered radiation pattern. The method according to the invention is accordingly combined with the method described in DE 198 37 932.3 mentioned above. If the wavelength for excitation of the fluorescence radiation is, for example, in the ultraviolet wavelength range, the same excitation radiation and the same radiation pattern can be used to generate the fluorescence pattern. In this additional method step, the biological tissue itself can advantageously be excited to emit fluorescent radiation. Here too, care must be taken that the intensity and in particular the wavelength of the excitation radiation is chosen such that its depth of penetration into the tissue is small and only the outermost weaving areas are stimulated to fluorescence. The thickness of these tissue areas is, for example, 2 to 3 μm. Measurement errors are minimal with this procedure, since there is no mixing of the fluorescent material with an upstream liquid - as is the case, for example, in the case of a tear film in front of the cornea. The tissue also does not swell due to the non-existent liquid film which penetrates into the tissue.

It is also possible to irradiate the tissue with at least two wavelengths or wavelength ranges, one wavelength or the one wavelength range causing the scattered radiation pattern and the other wavelength or the other wavelength range causing the fluorescence pattern.

If the corresponding measurement inaccuracies can (be) accepted, as an alternative to the intrinsic fluorescence of the tissue, a layer in front of the biological tissue enriched with a substance that can be excited by fluorescence can be used. The layer is preferably such that it does not or hardly penetrates the tissue. In this case the scattered light pattern would originate from the tissue and the fluorescence pattern from the upstream layer.

The absorption coefficient and the scattering coefficient are decisive for the low penetration depth of the excitation radiation during scattering. For the measurement of tissue surfaces, the wavelength of the excitation radiation is therefore advantageously less than 400 nm (UV light) or greater than 1.5 μm (IR light). UV light is particularly scattered on different components of cells and therefore does not penetrate the tissue beyond the first layers of tissue. IR light, on the other hand, is mainly scattered from the water molecules contained in all biological tissues. Since this is also contained in the top fabric layers, relatively intense IR light is emitted especially by these scattered weaving stories. Backscattered light from deeper tissue layers usually does not have sufficient intensity.

In addition to the scattered light, the direct reflection reflected on the surface of the tissue also reaches the detection unit and overlaps an area of the measuring field in which the scattered pattern can then no longer be distinguished from the direct reflection. To prevent this, linearly polarized light is preferably used to illuminate the tissue areas to be irradiated. For this purpose, a polarizer is preferably positioned in the beam path of the excitation radiation and an analyzer oriented perpendicular to the polarizer in the beam path of the radiation to be detected. In contrast to the scattered radiation, the polarization of the reflected radiation is retained during the reflection. Accordingly, only the scattered radiation and not the reflected radiation can pass the analyzer and reach the detector. This increases the contrast of the detected pattern and the accuracy of the evaluation.

The advantages of the invention according to its second aspect lie in particular in the fact that the surface to be measured is covered with an externally applied layer which lies against it and which reproduces the surface shape as precisely as possible. The contour of the artificially applied layer then essentially corresponds to the contour of the tissue surface. According to the invention, therefore, no additives are added to the tear film, but the layer is applied as a whole. The layer can be formed from an initially liquid substance or a solid layer, for example in the form of a flexible and possibly elastic mat - for example made of Teflon. The layer does not have to cover the fabric throughout, but can also be designed, for example, as a mesh with fine meshes. Both tissues that are external to the body and tissues that lie in the body can be considered as tissues, which can be achieved, for example, by means of invasive surgery. Since the layer contains molecules that can be excited by fluorescence, they can be illuminated to emit fluorescent molecules. stimulate the rescent light. Suitable filters can be placed in the beam path of the fluorescent light, with which the wavelengths of the excitation radiation are suppressed, so that only fluorescent light is received and not the direct reflection of the excitation radiation and, if this is not desired, scattered radiation. With this procedure, a high measuring accuracy can be obtained.

The layer thickness is preferably at most 10 μm. The layer thickness is advantageously in the range of 1-3 μm, but can also be selected to be even smaller, for example if the layer consists of only one molecular layer. The layer thickness should not be chosen too large because of the otherwise poorer depth resolution.

The layer can advantageously be dripped onto the previously largely liquid-free tissue surface and then lies evenly against the surface (a liquid layer that is still present would be between the tissue and the layer after application of the layer and falsify the measurements). In this way, an almost identical layer thickness can be achieved over the entire tissue surface. The layer thickness can also be set very small. The penetration depth of the excitation radiation no longer depends on the optical surface properties of the biological tissue, but only on those of the layer. If this is chosen so that the penetration depth is very small, the depth resolution is very good and is in the range of a few micrometers.

If the layer according to the invention is used, for example, for measuring the top layer of the skin, use with the epithelial layer removed is also possible if the layer is applied in liquid form. It is possible that liquid molecules actually penetrate tissue areas; the excitation radiation can, however, in this Case, for example, be chosen so that the absorption takes place essentially only in the layer itself.

If the layer hardens or is solid from the start, the aforementioned constellations do not occur from the outset.

A particularly thin but still tightly fitting layer of molecules can be achieved if the layer has electrostatically repelling molecules, so that a single to little layer is formed on the surface of the tissue. The charge of the electrostatically repelling molecules is advantageously chosen such that they themselves adhere electrostatically to the tissue surface. For example, layer molecules with a positive charge are selected if the tissue surface has essentially negatively charged molecules. In this way, the formation of many molecular layers on top of each other can be suppressed, which could represent a source of errors for the measurements due to non-ideal superimpositions.

A similar effect can be achieved if the molecules of the layer are polar.

The layer regions emitting the fluorescent radiation are preferably irradiated with an excitation radiation which has components in the ultraviolet wavelength range. The excitation radiation is preferably in the wavelength range from 150 nm to 400 nm. When using, for example, an ArF laser, the excitation radiation is 193 nm, while in the case of a frequency-quintupled Nd: YAG laser, for example, the excitation radiation has a wavelength of 213 nm. Wavelengths shorter than 150 nm can currently only be generated with sufficient energy and with great technical effort. In addition, the fluorescence radiation they generate is currently only insufficiently detectable using conventional technology. On the other side of the wavelength could be wavelengths more than 400 nm - depending on the material of the covering layer - have a penetration depth that is too great, so that the fluorescence radiation would also come from deeper layer layers or even from the tissue underneath and the depth resolution would thus be restricted.

In an alternative embodiment of the invention, it is provided that not only the fluorescent radiation emitted by the irradiated layer regions is detected and evaluated, but also - or alternatively - that the scatter radiation emanating from these regions is measured and used to calculate the surface shape of the tissue , This can either be done by measuring with the same detection device, or an additional detection device is used solely for the scattered radiation. When using two detection devices, at least one filter is advantageously arranged in front of each detection device, which filter is opaque to the radiation - scattered radiation or fluorescent radiation not to be detected by this detection device, but is permeable to the radiation to be detected - fluorescent radiation or scattered radiation.

With the methods presented, surfaces of biological tissues - be they external or internal body surfaces - can generally be measured, for example surface changes due to skin or other diseases or structural features to be used for individual identification, such as finger surfaces. In some cases, it may be necessary to remove interfering objects, such as hair, that are present in the light path.

A CCD camera or a CMOS camera is advantageously used to detect the radiation pattern - both the scattered radiation pattern and the fluorescence pattern, regardless of whether this originates from the biological tissue itself (self-fluorescence) or from a fluorescent layer applied thereon. Both allow one spatially resolved detection in the range of 5 to 10 μm with several 100,000 data points. While a CMOS camera has a lower sensitivity to light and a higher noise by a power of 10, its price is currently significantly lower than that of a CCD camera. However, both types of camera meet the requirements for an excellent topology determination. If a UV radiation source is used to generate the excitation radiation and the scattered radiation is detected, an ultraviolet sensitive camera must be used. On the other hand, if, alternatively or additionally, fluorescence radiation is to be measured, the detection camera must (also) operate in a longer-wave range due to the difference in wavelength to the excitation radiation. The detection of the direct reflection from the surface to be measured can be suppressed by placing a staining or polarization filter between the tissue and the detection device.

In an advantageous embodiment of the invention, the scattered and / or fluorescent radiation emitted by the biological tissue or by the layer is detected at an angle different from the direction of irradiation, which is, for example, 45 °. This makes it possible to measure the curvature of the tissue surface or the layer more precisely due to the perspective distortion of the scattered radiation or fluorescence pattern. The distortion ensures that the pattern appears more curved in the perspective than when viewed from the front, so that a more precise resolution with regard to the curvature course can be obtained.

The above-mentioned distortion effect can, however, also lead to the fact that lines in areas facing away from the detection device undesirably flow into one another and can therefore no longer be resolved precisely. In such a case, at least one further detection device can advantageously be used, which precisely measures the part of the pattern to be detected that the other detection device no longer precisely can dissolve enough. As an alternative to a second detection device, a mirror positioned in front of the biological tissue can be used, which mirror reflects the radiation to be detected from the side of the biological tissue remote from the detection device. With this arrangement, the spatial fields are recorded one after the other and used together for evaluation.

In the case of considerably curved surfaces to be measured, it is advantageously provided that the biological tissue or the layer is irradiated from at least two directions in order to achieve adequate illumination. With a cornea that is almost spherically symmetrical, it is advisable to implement a symmetrical structure of the two radiation sources with respect to the cornea. This means that the two projection or radiation directions enclose the same angles with a normal extending between them, which runs through the center of the visible corneal surface and on which, for example, a detection device is arranged. In addition to multiple radiation sources, multiple detection devices or multiple mirrors or other light deflection devices can also be provided.

Excimer lasers such as ArF lasers (λ = 193 nm), KrF lasers (λ = 248 nm), XeCI lasers (λ = 308 nm), XeF lasers (λ = 351 nm) and nitrogen can be used as the radiation source -Laser (λ = 337 nm) and frequency-multiplied solid-state lasers, such as, for example, a frequency tripled, quadrupled or quadrupled Nd: YAG laser with λ = 355 nm, 266 nm or 213 nm or pulsed by such solid-state lasers Dye lasers can be used. Care should be taken to ensure that the intensity of the scattered and / or fluorescent radiation is as high as possible (without the tissue or the layer being damaged by the excitation radiation) since the requirements on the detection device (s) are then lower. As a cost-effective alternative to a laser, flash lamps with gas mixtures containing xenon or deuterium, for example, whose wavelength ranges can be limited to the desired range by means of filters, can also be used. In order to obtain the same high sensitivity as when using lasers, more sensitive detection devices must be used due to the often lower intensity of the flash lamps.

The radiation pattern for projection onto the biological tissue or onto the layer preferably consists of parallel strips with a sinusoidal, cosineus ² or rectangular intensity curve. Using suitable computing algorithms, a resolution of a few micrometers can be achieved if, for example, a stripe width and a stripe spacing of 100 μm are selected. As an alternative to such a stripe projection method, a hole pattern or a ring pattern similar to the placido rings can be used. Likewise, a moire pattern consisting of two line patterns or also a grid can be used, the intersections of which can be found in the radiation pattern are evaluated. In general, any suitable geometric pattern can be used to create the radiation pattern on the biological tissue or layer.

A wide variety of devices can be used to generate the geometric radiation pattern. For example, a mask with parallel slits or regularly arranged holes is used. In some areas, structurally modified substrates, such as glasses, can also be used, in which, for example, areas of strong scattering or absorption alternate with unprepared areas of high transmission. Using commercially available microlenses on a transparent glass substrate, stripe patterns as well as other radiation and thus scattering or fluorescent patterns can also be obtained. The microlenses have that The advantage that, in contrast to a mask, almost all of the excitation radiation can fall on the biological tissue or the layer. In addition, there is a greater depth of field when using microlenses. A more precise sinusoidal intensity curve of the light and dark stripes is also available in a stripe pattern compared to a mask. Alternative exemplary embodiments for generating the radiation pattern include interference methods after, for example, expanding the beam from a monochromatic coherent laser by means of a beam splitter or generating an interference pattern on the tissue by means of two mutually coordinated radiation sources. Many closely spaced micromirrors that reflect the excitation radiation to the tissue can also be used. A combination of the above-mentioned possibilities of generating the radiation pattern is also possible.

The surface shape of the fabric is preferably calculated by an evaluation unit, ie a computer, and the result of the calculation can be used to control a laser. The laser can be the same as the laser used to determine the surface shape. In this way, a compact and inexpensive device for surface correction can advantageously be realized. Alternatively, a measuring laser can be mounted on an existing surgical laser or arranged in a defined manner in its vicinity in order to enable inexpensive retrofitting of this surgical laser. This eliminates the need to purchase an entire new system. If the biological tissue is the cornea of an eye, the control can be used to adjust the radiation duration and the intensity of the surgical laser in order to achieve the desired target thickness of the cornea by removing corneal layers. In order to achieve a controlled removal of the biological tissue, the surface shape is preferably determined before and during and possibly after the operation. If the topology of a cornea is to be measured, it must be taken into account that the eye moves spontaneously and independently of the will. On the one hand, lasers with very short pulse durations on the order of milliseconds, microseconds and nanoseconds can be used to circumvent these difficulties. As an alternative or in addition, so-called eye trackers can be used, by means of which longer exposure times can also be achieved. Such a device collects information about typical movements of the eye in order to use this information to track the excitation radiation to the corneal areas to be irradiated. Alternatively, the radiation or the detection can be stopped if the position of the eye changes. As an alternative or in addition, the position of the eye is determined with an eye tracker before each irradiation or after each detection and is taken into account when evaluating the scatter and / or fluorescence pattern. An eye tracker can be used in accordance with both aspects of the invention - for the invention in accordance with the second aspect in particular when a transparent layer is used which does not hinder the observation of eye movements.

In the case of a corneal topology determination, the method and the device according to the first aspect of the invention can also be used when there is no tear film and no epithelial layer. This makes it possible to determine the current tissue shape as often as required during an operation in order to carry out the next operation step on the basis of these results. This control option during the operation minimizes the errors and enables gradual, careful removal of corneal layers in order to correct the ametropia precisely. The surgeon no longer needs nomograms specially made for certain patient groups. If one and the same laser is used both for the application and for the measurement, there is a switch back and forth between the operation mode and the measurement mode during the operation in order to control or regulate the removal based on the measurement results. The method and the device according to the second aspect of the invention also allow the fluorescent excitable layer to be applied during an operation. In this case, the layer applied, for example, between the operation steps can be evaporated by increasing the incident radiation intensity and the operation can be continued.

It is particularly advantageous according to the invention that on the one hand the height - and not the slope - of the tissue surface can be measured directly. On the other hand, only a single recording of the scattered radiation and / or fluorescence pattern is necessary.

Advantageous developments of the invention are characterized by the features of the subclaims.

An exemplary embodiment of the invention is explained in more detail below with reference to the drawings. Show it:

1 shows a schematic structure of a device for projecting an irradiation pattern onto a cornea and for detecting the scattered radiation and possibly a fluorescence pattern generated according to the first aspect of the invention, the radiation source being used both for topology determination and for corneal ablation (one-piece system) ;

FIG. 2 shows a simplified schematic illustration essentially corresponding to the basic structure according to FIG. 1, but the radiation source for topology determination and the radiation source for corneal ablation are different; and 3 shows a detail from FIG. 1, but with a layer applied to the cornea.

The mode of operation of the invention according to its first aspect is first summarized on the basis of FIG. 1. From an excitation radiation 2 from a radiation source 1, an irradiation pattern 26 is generated from parallel strips and falls on a curved tissue 8a, in the illustrated embodiment the cornea 8a of a human eye 8b. Part of the scattered light 14a emanating from the cornea 8a is detected with a camera 12 which is placed in front of the cornea 8a at an angle α with respect to the direction of irradiation. Due to the surface curvature of the cornea 8a and the direction of observation rotated with respect to the direction of irradiation, the camera 12 records an image 27 of a stripe pattern 27a corresponding to the curved cornea 8a to be observed on a monitor 28.

1, the radiation source 1 generates an excitation radiation 2, preferably UV radiation or IR radiation. An optional first lens system 3 (indicated by a schematically illustrated converging lens) forms a parallel and homogeneous beam from this radiation, which then passes through means 4 for generating an irradiation pattern. In the embodiment shown, these means 4 are formed by a slit diaphragm or mask 4 set up perpendicular to the beam path with, for example, parallel strip-shaped openings with a width and a respective distance of 100 μm. The excitation radiation 2, of which only the center beam is shown in FIG. 1 as a solid line with an indication of the direction of radiation, and the envelopes or the marginal rays as dashed lines, is partially retained on this mask 4 and partially - let through - through the openings. In this way, the excitation radiation 2 is structured transversely to the radiation direction in the form of an irradiation pattern 26, which is deflected in the further beam path on a mirror 5 and by means of of a second lens system 6 (indicated by a schematically illustrated collecting lens) after passing through a first aperture diaphragm 7 on the surface of a biological tissue 8a (see reference number 26 assigned to the corneal surface). The tissue 8a in the selected embodiment is the cornea 8a of a human patient who is placed on the patient bed 13. For the sake of simplicity, only the patient's eye 8b is shown.

The excitation radiation 2 passing through the mask 4 is selected with regard to intensity and wavelength such that it penetrates only a few micrometers into the cornea 8a. This is the case if their wavelength is in the UV or IR range; the function of the cornea 8a is transparent in the visible region. Accordingly, the excitation radiation 2 is scattered essentially in all directions on the surface of the cornea 8a or in the tissue areas lying nearby, that is, scattered radiation 14a is produced in the form of a scattered radiation pattern 27a corresponding to the radiation pattern 26 and distorted by the curvature of the cornea the angle α is imaged on the sensor 11 of a detection device 12 with the aid of a third lens system 9 after passing through a second aperture diaphragm 10. The detection device 12 is, for example, a CCD or CMOS camera 12, which may be intensified by an image intensifier (not shown). In contrast to, for example, the slit-scan method, a single exposure with the detection device 12 is sufficient to obtain all the required information about the surface shape the cornea 8a. For this purpose, the detection device 12 - with the interposition of an analog-digital converter (not shown) when the detection device 12 outputs analog signals - is connected via a connecting line 29 to an evaluation unit 30, preferably formed by a computer, which uses evaluation programs to determine the topology of the cornea 8a calculated. The excitation radiation 2, at a suitable wavelength (for example UV light) and intensity, also excites the cornea 8a to emit fluorescent radiation 14b in the irradiated areas, while the non-irradiated areas of the cornea 8a cannot emit fluorescent radiation 14b. A fluorescence pattern 27b thus arises in addition to the scattered radiation pattern 27a. In the exemplary embodiment shown in FIG. 1, the scattered radiation 14a and the fluorescent radiation 14b are recorded by the same detection device 12. Because of the different wavelengths of the two radiations 14a, 14b - the fluorescent radiation 14b is longer-wave compared to the scattered radiation 14a - it is advantageous that two different detection devices that are sensitive to the respective radiation or can only be reached for a narrow wavelength range by appropriate filters 12 are used.

While the wavelength of the scattered radiation 14a essentially corresponds to that of the excitation radiation 2, the wavelength of the fluorescent radiation 14b - as mentioned - is shifted into a longer-wave range. When using an ArF laser as radiation source 1 (λ = 193 nm), the main maxima of the fluorescent radiation 14b emanating from the irradiated tissue areas of the cornea 8a are approximately 300 nm and 450 nm, which can be detected without great effort - such as by means of the CCD, Camera 12 - are accessible.

With the device according to FIG. 1, a reciprocal measurement of the cornea 8a and its operation by ablation on the tear-film-free eye 8b is possible, the same radiation source 1, usually a UV laser, being used for both purposes. This mutual process is preferably carried out automatically with the aid of a control device 32 connected downstream of the computer 30 via a data line 31 and which is connected to the laser 1 via a data line 33. During the measurement, there is neither a tear film nor an epithelial layer in front of the cornea 8a and the exposed top layers of the cornea 8a are directly excited in the areas irradiated with the radiation pattern 26 to emit scattered radiation 14a and possibly fluorescent radiation 14b with the aid of the excitation radiation 2. A removed epithelial layer grows back within a few days after an operation. Alternatively, if the epithelial layer has been folded away from the beam path of the excitation radiation with a part of the stroma underneath, it can be brought back into the original position after the operation.

If a single laser is used both for the measurement according to the invention and for - large-area - ablation, at least one intensity attenuator 15 (shown in dash-dot lines in FIG. 1) in the beam path of the excitation radiation 2 - that is, between the radiation source - is preferably used to protect the cornea 8a during the measurement phase 1 and the cornea 8a - which is removed from the beam path again during the operation phases. The insertion and removal of the intensity attenuator 15 in the beam path is preferably carried out under computer control (corresponding control not shown).

In a further embodiment, not shown, a laser beam with a relatively small diameter of, for example, 2 mm is used in order to remove the cornea 8a - in contrast to large-area radiation - in only small areas in each case. The laser beam is scanned over the cornea 8a. During the measurement of the corneal surface, it is therefore advisable to expand the laser beam to generate the radiation pattern 26, which is larger than the surgical beam, with at least one beam expander (not shown), which is introduced into the beam path between the radiation source 1 and the cornea 8a. During the operation phases, the at least one beam expander is removed again from the beam path of the excitation radiation 2. As an alternative to the embodiment of the combined radiation source shown in FIG. 1, both for measurement and for surgery, the radiation source 1 is placed on the surgical laser or is otherwise suitably arranged in a defined position relative to it. In this way, for example, existing surgical lasers can continue to be used. Such an arrangement is shown in simplified form in FIG. The radiation pattern 26 is projected onto the cornea 8a at an angle α with respect to the normal N by means of the radiation source 1 and the pattern of the scattered radiation 14a and that of the fluorescent radiation 14b is detected at an angle β with respect to the normal N with a detection device 12. The surgical laser 101 is arranged on the normal N. The means for generating the radiation pattern, mirrors, converging lenses, diaphragms, beam expanders and intensity attenuators are not shown for the sake of simplicity. The signals from the detection device 12 may be digitized by means of an AD converter 35 (if the detection device 12 is not already supplying digital signals) and forwarded to the computer 30, which performs the topology calculation using, for example, Fourier algorithms. The calculation results are then forwarded to the control / regulating unit 32 and there a decision is made as to whether and how, if necessary, a new measurement of the corneal topology is carried out by means of the radiation source 1 or the surgical laser 101 issues a command for emitting a pulse of certain energy and / or a certain pulse duration receives in order to remove a defined layer thickness of the cornea 8a.

In the combined system of FIG. 1 and the two-part system of FIG. 2, the results of the determination of the cornea shape can be used immediately in a subsequent operation step in order to control or regulate the corneal ablation by means of the corresponding radiation source 1, 101. During a measurement phase between two operational steps, the result of the previous operative can immediately be seen Steps are checked and the next step in the operation is coordinated accordingly.

In a further embodiment, not shown, in which the measuring and possibly the operating principle is basically the same as in FIGS. 1 to 2, two detection devices 12 are arranged opposite one another in front of the cornea 8a, the radiation source 1 being in the angular range between the two Detection devices 12 is arranged. The fluorescence pattern is detected on two sides in order to obtain a higher resolution, in particular in the case of a curved tissue surface. Alternatively or additionally, the tissue 8a can be irradiated from two directions. For example, a beam splitter splits the excitation radiation 2 from a radiation source 1 and directs it onto the tissue 8a with the aid of one or more light deflection devices, such as mirrors. Alternatively, several radiation sources 1 are used.

If necessary, digital subtraction of the images taken before and during the irradiation of the radiation pattern 26 can further increase the contrast and thus the precision of the method.

FIG. 3 shows a layer 40 applied to the cornea 8a. This layer contains molecules that fluoresce when irradiated with preferably UV radiation. Measured as in FIGS. 1 and 2, the radiation emanating from the tissue surface - in the illustrated case the surface of the cornea 8a - structured according to the radiation pattern 26, which here consists in particular of the fluorescent radiation 14b. Except for this difference, the above statements apply correspondingly to the scatter radiation emanating directly from the tissue according to FIGS. 1 and 2. 3, the fluorescent radiation is provided with the same reference number 14b as the intrinsic fluorescent radiation 14b of the cornea 8a according to FIGS. 1 and 2. In addition - or alternatively - to the fluorescent radiation 14b from the layer 40, the scattered radiation 14a measured by the layer 40 (here too, the same reference number 14a is used for the respective scattered radiation 14a in FIGS. 1 to 3).

A layer 40 applied to the cornea 8a before an operation (after removal or folding away of the epithelial layer) or during an interruption in the operation can be vaporized again using laser beams after the topology measurement and at the beginning of the next operation step, be it by increasing the intensity of the measurement and operation laser 1 (in the case of a one-part system according to FIG. 1) or by the measuring laser 1 or the operation laser 101 (in the case of a two-part system according to FIG. 2).

While the exemplary embodiments listed above were each explained with regard to the measurement of the surface shape of an eye cornea, the methods according to the invention and the devices according to the invention are likewise suitable without restriction for being used in a corresponding manner on other biological tissues. It does not matter whether these tissues are located on the body surface or inside the body.

Claims

Patent claims

1. Method for determining the surface shape of biological tissue, in which the tissue (8a) is irradiated with an irradiation pattern (26) generated with the aid of excitation radiation (2), the excitation radiation (2) being light of the wavelength ranges of the ultraviolet and / or contains an infrared part of the spectrum, and in which the scattered radiation pattern (27a) emitted by the irradiated tissue areas is detected at least in the wavelength ranges of the ultraviolet and / or infrared part of the spectrum and evaluated to calculate the surface shape of the biological tissue (8a).

2. The method according to claim 1, characterized in that in addition to the scattered radiation pattern (27a) a fluorescence pattern (27b) is detected, which is emitted by the irradiated tissue areas (8a) after excitation with the radiation pattern (26).

3. The method according to claim 1 or 2, characterized in that the wavelength of the excitation radiation (2) is chosen below 400 nm and / or above 1.5 microns.

4. The method according to at least one of the preceding claims, characterized in that a polarizer in the beam path of the

Excitation radiation (2) and an analyzer oriented perpendicular to the polarizer is positioned in the beam path of the radiation (14a) to be detected, so that the scattered radiation (14a) but not the reflected radiation can pass through the analyzer.

5 _.. Method for determining the surface shape of biological tissue, in which a layer adapting to the surface of the tissue is applied to the tissue (8a), the layer (40) is irradiated with an radiation pattern (26) generated with the aid of excitation radiation (2) and the Radiation patterns emitted by the irradiated layer regions (8a) are detected and evaluated to calculate the surface shape of the tissue (8a), the layer (40) containing molecules which are emitted by the irradiation with the radiation pattern (26) to emit fluorescent radiation

(14b) existing fluorescence pattern (27b) are excited, which is detected and evaluated to calculate the surface shape of the layer (40) and thus that of the tissue (8a).

6. The method according to claim 5, characterized in that the layer (40) is dripped onto the tissue surface and lies largely evenly against the tissue surface.

7. The method according to claim 5 or 6, characterized in that the layer thickness is not greater than 10 microns.

8. The method according to at least one of claims 5 to 7, characterized in that the layer consists of single-layer or few-layer molecular layers.

9. The method according to at least one of claims 5 to 8, characterized in that the layer (40) has electrostatically repelling molecules which adhere to the tissue surface due to their charge.

10. The method according to at least one of claims 5 to 9, characterized in that the fluorescent radiation (14b) emitting Layer areas are excited essentially with an excitation radiation (2) lying in the ultraviolet (UV) wavelength range.

11. The method according to at least one of claims 5 to 10, characterized in that the excitation radiation (2) is selected in the wavelength range from 150 nm to 400 nm.

12. The method according to at least one of claims 5 to 11, characterized in that a filter is positioned between the irradiated layer regions and a detection device (12) for detecting the emitted radiation pattern, which filter is at least partially opaque to the excitation radiation.

13. The method according to at least one of claims 5 to 12, characterized in that in addition to the emitted fluorescent radiation (14b) emitted scattered radiation (14a) from irradiated layer regions is detected and evaluated.

14. The method according to at least one of claims 5 to 13, characterized in that during an operation of the biological tissue (8a) a layer (40) which can be excited to fluoresce is repeatedly applied to the biological tissue (8a) and by means of a laser before the next operation step is evaporated again.

15. The method according to at least one of the preceding claims, characterized in that the tissue to be measured (8a) is the cornea (8a) of an eye (8b) or comprises other tissue areas of a human or animal body.

16. The method according to claim 15, characterized in that before the determination of the surface shape of the cornea (8a) the tear film on the cornea (8a) is removed.

17. The method according to claim 15 or 16, characterized in that before the determination of the surface shape of the cornea (8a), the epithelial layer of the cornea (8a) is at least temporarily removed from the beam path of the excitation radiation (2).

18. The method according to at least one of the preceding claims, characterized in that the scattered and / or fluorescent radiation (14a, 14b) with at least one detection device (12), preferably a CCD camera (12) or a CMOS camera, detected

19. The method according to at least one of the preceding claims, characterized in that the scattered and / or fluorescent radiation (14a, 14b) is detected at an angle (α) different from the direction of irradiation.

20. The method according to at least one of the preceding claims, characterized in that the biological tissue (8a) or the layer (40) is irradiated from at least two directions with the excitation radiation (2).

21. The method according to at least one of the preceding claims, characterized in that the scattered and / or fluorescent radiation (14a, 14b) is at least partially redirected from a light deflecting device to a detection device (12) and detected there.

22. The method according to at least one of claims 1 to 4 and 15 to 21, characterized in that an eye tracker records information about typical movements of the eye (8b) in order to use this information to excite the radiation (2) to the eye (8b) Realization of long irradiation times or in the event of changes tion of the eye (8b) to stop the radiation or the detection.

23. The method according to at least one of the preceding claims, characterized in that the excitation radiation (2) with an as

Laser (1) or flash lamp trained radiation source (1) is generated.

24. The method according to at least one of the preceding claims, characterized in that as the radiation pattern (26) a pattern of parallel strips, a right-angled grating, a hole pattern, a pattern of several concentric circular lines with radially starting from the center and arranged at the same angular distance or a moire pattern consisting of two line patterns is selected.

25. The method according to at least one of the preceding claims, characterized in that the surface shape of the fabric (8a) is calculated by an evaluation unit (30) which controls a laser (1) by means of the calculated surface shape.

26. The method according to at least one of the preceding claims, characterized in that the determination of the surface shape is carried out before, during and / or after an operation on the tissue area (8a) to be measured.

27. Method for supporting an operative intervention on a biological tissue, characterized in that the result of the evaluation of the method carried out according to at least one of the preceding claims before the current operative treatment of the biological tissue (8a), in particular into the current refractory ve surgery of a cornea (8a) of an eye (8b), regulating and / or controlling is included.

28. The method according to at least one of the preceding claims, characterized in that the excitation of the emission of

Scattered radiation (14a) and / or fluorescent radiation (14b) used

Radiation source (1) also for the surgical treatment of the tissue

(8a) is used.

29. The method according to at least one of claims 1 to 27, characterized in that different radiation sources (1) for excitation of the emission of scattered radiation (14a) and / or fluorescent radiation (14b) on the one hand and for the operative treatment of the tissue (8a) on the other hand are used ,

30. Device for determining the surface shape of biological tissue, in particular for performing the method according to at least one of claims 1 to 4 and 15 to 29, with at least one radiation source (1) for generating an excitation radiation (2), the wavelengths of which are essentially ultraviolet and / or infrared part of the spectrum, means (4) for generating an irradiation pattern from the excitation radiation (2) on the tissue (8a), at least one detection device (12) for detecting the scattered radiation pattern (27a) emitted by the tissue (8a) , and an evaluation unit (30) for calculating the surface shape of the fabric (8a) from this scattered radiation pattern (27a).

31. Device for determining the surface shape of biological tissue, in particular for carrying out the method according to at least one of claims 5 to 29, with at least one radiation source (1) for generating excitation radiation (2), means (4) for generating an irradiation pattern (26) from the radiation (2) on a layer (40) applied to the tissue (8a) and adapting to the tissue (8a) so that the irradiated layer regions are excited to emit a fluorescence pattern (27b) consisting of fluorescent radiation (14b), at least one detection device (12) for detecting the

Fluorescence pattern (27b), and an evaluation unit (30) for calculating the surface shape of the tissue (8a) from the detected fluorescence pattern (27b).

32. Device according to claim 30 or 31, characterized in that one or more detection devices (12) are provided so that both scatter radiation (14a) and fluorescent radiation (14b) from the irradiated tissue (8a) and / or layer areas (40 ) are detectable.

33. Device according to at least one of claims 30 to 32, characterized in that the at least one detection device (12) comprises a CCD camera (12) and / or a CMOS camera.

34. Device according to at least one of claims 30 to 33, characterized in that the radiation source (1) as a laser (1), preferably as a frequency-multiplied solid-state laser, excimer laser, gas laser or frequency / ielfacher dye laser, or as a flash lamp, preferably with a xenon or filled with a deuterium gas mixture.

35. Device according to at least one of claims 30 to 34, characterized by at least one further radiation source (1) and / or at least one device for splitting the excitation radiation (2) around the biological tissue (8a) from at least two

Irradiate directions with the excitation radiation (2).

36. Device according to at least one of claims 30 to 35, characterized by at least one light deflecting device for deflecting fluorescent radiation (14b) to a detection device (12).

37. Device according to at least one of claims 30 to 36, characterized in that the means (4) for generating the radiation pattern (26) a mask (4) with openings in the form of parallel slots or regularly arranged holes and / or a structured turized glass with areas that absorb and / or scatter the excitation radiation (2) and areas that are transparent to the excitation radiation (2) and / or a preferably regular arrangement of diffractive optical elements, preferably microlenses, and / or means arranged transversely to the beam path of the excitation radiation (2) to create an interference pattern on the biological

Include tissue (8a) and / or at least one field of micromirrors.

38. Device according to at least one of claims 30 to 37, characterized by an eye tracker for ascertaining information about typical eye movements in order to use this information to track the excitation radiation (2) to the eye (8b) in order to realize long irradiation times or when the Position of the eye to stop radiation or detection.

39. Device according to at least one of claims 30 to 38, characterized in that a computer (30) is provided which determines the surface shape of the fabric (8a), which is used to control a laser (1; 101).

40. Apparatus according to claim 39, characterized in that the laser (1) controlled by the computer (30) and which excite the Scattered radiation and / or fluorescence patterns (27a, 27b) of the biological tissue (8a) or the radiation source (1) used on the tissue (8a) layer (30) match.

41. Device according to at least one of claims 30 to 40, characterized in that the radiation source (1) with respect to intensity, pulse duration, repetition rate and wavelength of the excitation radiation (2) for the operative treatment of the biological tissue (8a), such as the area-wise removal of a cornea (8a).

42. Device according to at least one of claims 30 to 41, characterized by an intensity attenuator (15) or a beam expander between the at least one radiation source (1) and the biological tissue (8a) for insertion and removal from the beam path of the excitation radiation (2).