WO2013038242A1

WO2013038242A1 - Method for spatially measuring tissue structures

Info

Publication number: WO2013038242A1
Application number: PCT/IB2012/001670
Authority: WO
Inventors: Zoran Djinovic; Milos Tomic; Marljana STOJKOVIC
Original assignee: Ima Integrated Microsystems Austria Gmbh
Priority date: 2011-09-12
Filing date: 2012-08-30
Publication date: 2013-03-21
Also published as: AT511935A2; AT511935A3; AT511935B1

Abstract

The invention relates to a method for spatially measuring a plurality of biological tissue structures that lie one behind the other in an organ, particularly in an eye (1), by evaluating interferograms that are obtained from reflected coherent light from a reference probe (6) directed at a reference reflector (3), and from at least one measurement probe (7). For a known spatial extension of a first tissue structure of the organ, both the reference probe and the at least one measurement probe are directed at said organ, wherein the path difference (ΔL) between these two probes is kept constant.

Description

Method for the spatial measurement of tissue structures

The invention relates to a method for spatially measuring a plurality of successive biological tissue structures in an organ, in particular in an eye obtained by evaluating interferograms, from reflected, low-coherent light from a reference probe directed to a reference probe and at least one measuring probe , The invention further relates to a device for carrying out this method.

In ophthalmology, for example, biometrical measurements on the eye are made for the early detection of glaucoma, from which conclusions about the intraocular pressure (IOP) can be obtained. State of the art here u.a. interferometric methods in which the spatial extent or thicknesses and spacings of reflective surfaces, e.g. the cornea and the lens are measured by means of an interferometer. In conventional interferometry, the eye to be examined is positioned at a defined distance from a measuring probe, generally a measuring light guide, and coherent light is transmitted through this measuring probe and through a reference probe or a reference light guide directed to a reference reflector in the interferometer. directed. The coherent light from the measuring probe or measuring light guide is reflected at the different structures and the superimposition of the reflected light leads to interference patterns due to the different path lengths which the coherently emerging light from the probes or light guides has to travel back to the respective reflecting structures. which can be evaluated with conventional mathematical algorithms to determine the distances of the reflective structures to each other.

CONFIRMATION COPY In the prior art, as already mentioned, the reference probe was directed to a reflector in the interferometer and the superimposition of the reflected light from the probe was via relatively complicated and large-scale devices with lenses and semi-transparent mirrors, which is why the corresponding devices in the practice were used stationary. However, it is known that the intraocular pressure and thus the spatial extent of the tissue structures to be examined, which allow a conclusion on the intraocular pressure vary so much in one and the same patient depending on the time of day and the physical activity that a single measurement of spatial Extension or the relative position of the relevant structures does not allow a satisfactory conclusion about the actual physiological conditions. Rather, it would be desirable to carry out a continuous spatial survey of the relevant biological tissue structures in an organ such as the eye over a longer period of time in order to obtain a more comprehensive picture of the physiological conditions. However, due to the fact that the corresponding measuring devices, namely the interferometers, had a considerable size, this was hitherto practically impracticable.

The invention is therefore based on the object of specifying a method with which a spatial measurement of a plurality of biological tissue structures in an organ by means of interferometry can be carried out continuously and over a longer period by means of mobile devices. According to the invention, therefore, the method of the type mentioned above is characterized in that, when the spatial extent of a first tissue structure of the organ is known, both the reference probe and the at least one measuring probe are directed onto the organ, the path difference between the two both probes is kept constant. In the method according to the invention, a first tissue structure of the organ is therefore measured and determined with respect to its spatial extent before the actual measurement. For example, the thickness of the cornea, which remains practically constant even with fluctuating intraocular pressure, is suitable for this purpose. By virtue of the fact that, according to the invention, a tissue structure on the organ to be measured itself is already known and can be assumed to be constant, it is no longer necessary to keep the at least one measuring probe at a constant distance from the organ, ie the tissue structures, if at the same time according to the present invention, both the reference probe and the probe are directed to the organ and the path difference between the two probes is kept constant. The path difference between see the two probes or optical fibers is always meant as a distance in the axial direction, ie in the direction of the path of the light or the electromagnetic reference and measurement signal. In the method according to the invention thus one of the biological tissue structures to be measured itself serves as a quasi reference reflector, so that a complex arrangement of lenses and semi-transparent mirrors in the interferometer is no longer necessary. Even a varying distance between the two probes and the tissue structures to be measured does not hinder a precise measurement of the respective spatial extent, so that no apparatus precautions must be taken to keep the eye at a suitable distance. Thus, with the surveying method according to the invention, the expenditure on equipment of an interferometer can be considerably reduced so that apart from the reference and measuring probes, only one arithmetic unit with a corresponding program logic is necessary in order to be able to process and store the measured data. According to a preferred embodiment of the present invention, the method is developed such that the path difference between the reference probe and the at least one measuring probe is adjusted and fixed to the organ to be measured such that the interference bands corresponding to the first tissue structure in a coupling curve, the known spatial extent of this structure specify, preferably in the interferogram associated with the other tissue structures to be measured interference bands and the actual distances of the other tissue structures are determined relative to the distance of the first tissue structure corresponding interference bands. A coupling curve is understood in the art of fiber optics that signal of a photodiode, in which the interference patterns are reflected in the AC component of the signal. This signal is obtained by varying the optical wavelength in a fiberoptic component Michelson interferometer (Fiber Optics Essentials, K. THYAGARAJAN, AJOY GHAKAK). In this way, the distances of the respective biological tissue structures from each other can be directly determined and recorded in order to subsequently be used for diagnosis. The interferograms obtained can have interference bands for different tissue structures. In particular, the method according to the invention has been used to measure, for example, the mean corneal thickness (CCT), the anterior chamber depth (ACD) and the length of the eyeball (axial length, AL). All of these values can be correlated with intraocular pressure and thus taken into account in the medical diagnosis.

The interference bands have the basic shape of a Gaussian bell curve and have a certain width, referred to as the "dynamic rank", depending on the coherence length of the light used. The invention is therefore preferred further developed that the exact positions of the interference bands are determined by distance determination of the maxima of the Gaussian envelopes of the interference bands. Preferably, the measured data determined over a certain period of time are used to calculate the relative movements of the plurality of tissue structures of the organ relative to one another. The treating physician can then determine the course of intraocular pressure over the period in question and receive appropriate information for the indicated treatment.

When using only two probes or light guides, the reference light guide and the measuring light guide only one-dimensional length information can be obtained. However, in order to obtain a three-dimensional image of the examined organ, the invention is developed to advantage in that a plurality of arranged in the form of an array probes are used and activated by an electronic circuit sequentially for the determination of measurement data. Due to the extremely short time required for a spatial measurement or length determination, a corresponding number of measurements can be made in a very short time, with appropriate wiring of the light guides or probes arranged next to each other on the array, so that practically a snapshot of the relevant Organ in the sense of a spatial, three-dimensional survey at a given time can be created.

The device for carrying out the method according to the invention is characterized in that reference and measuring probes of an interferometer are fixed to a holder that is portable by a patient and are connected to a portable computing unit. The patient thus carries the arithmetic unit and the holder with him, wherein the holder may be formed, for example in the form of glasses. The holder preferably has means for setting and fixing the path difference between the reference probe and the at least one measuring probe to the organ to be measured.

The invention will be explained in more detail with reference to an embodiment shown in the drawing. 1 shows the basic arrangement of the reference and measuring probes, FIG. 2 shows a coupling curve as obtained in the method according to the invention, FIG. 3 shows a curve indicating the changes of a measured value over time, and FIG. 4 shows a representation of an application example the invention.

In FIG. 1, 1 denotes an eye as an organ to be measured, the anterior chamber 4 being delimited by the lens 2 and the cornea 3. The spatial extent 5 of the anterior chamber 4, i. The distance between the lens 2 and the cornea 3 is subject to measurable fluctuations with changing intraocular pressure and can thus be used to determine the intraocular pressure, which is an important diagnostic indicator in connection with glaucoma.

In order to measure the spatial extent of the relevant tissue structures, according to the present invention, two light guides 6 and 7 are now fixed to a holder 8 (not shown) at a distance D to the organ to be examined which is adjustable and fixable. 9 with an unspecified light guide is referred to, which directs the reflected light from the optical fibers 6 and 7 to a computing unit, also not shown.

In FIG. 2 it can be seen that, depending on the distances of different structures in an eye model 10, which is formed by a glass plate 11 and a mirror 12 is in a coupling curve 13 interference bands 14 result, with a suitable setting of ÄL the distance X between the third and the fourth band regardless of the distance D corresponds to the average thickness of the cornea 3 and the Cornea representing glass plate 11. The distance Y between the fourth and the sixth interference band corresponds to the spatial extent 5 of the anterior chamber 4. If there are other structures which reflect light, such as a retina (not shown) in an eye, then further interference bands would be displayed which represent the distance specify the retina to the other structures.

FIG. 3 now shows a graph of the values for the spatial extent 5 of the anterior chamber 4 and it can be seen that it is subject to fluctuations over time.

In Fig. 4 it can be seen that the method according to the present invention can be applied to an interferometer in which a holder 8 carries the optical fibers 6 and 7, wherein the optical fibers 6 and 7 are fed to a computing unit 15 in which the evaluation the interference pattern takes place. Thus, a portable measuring device has been provided which allows continuous measurement of the spatial extent of biological tissue structures.

Claims

Claims:

1. A method for spatially measuring a plurality of successive biological tissue structures in an organ, in particular in an eye, by evaluating interferograms obtained from reflected, low-coherent light from a reference probe directed to a reference probe and at least one probe, characterized in that, given a known spatial extent of a first tissue structure of the organ, both the reference probe and the at least one measuring probe are directed onto the organ, the path difference between the two probes being kept constant.

2. Method according to claim 1, characterized in that the path difference between the reference probe and the at least one measuring probe is adjusted and fixed in such a way that the interference bands corresponding to the first tissue structure indicate the known spatial extent of this structure in a coupling curve.

3. The method according to claim 1 or 2, characterized in that in the interferogram associated with the other tissue structures to be measured interference bands and the actual distances of the other tissue structures are determined relative to the distance of the first tissue structure corresponding interference bands.

4. The method of claim 1, 2 or 3, marked thereby, that the exact positions of the interference bands by

Distance determination of the maxima of the Gaussian envelopes of the interference bands are determined.

5. The method according to any one of claims 1 to 4, characterized in that the determined over a certain period measurement data for calculating the relative movements of the plurality of tissue structures of the organ are used to each other.

6. The method according to any one of claims 1 to 5, characterized in that a plurality of arranged in the form of an array probes are used and activated by an electronic circuit sequentially for the determination of measurement data.

7. An apparatus for spatially surveying a plurality of successive biological tissue structures in an organ, in particular in an eye, according to one of claims 1 to 6, comprising an interferometer with a reference probe and a measuring probe, thus fixed to a portable support by a patient are that both the reference probe and the probe are directed to the organ, and further connected to a portable computing unit.

8. The device according to claim 7, characterized in that the holder comprises means for adjusting and fixing the path difference between the reference probe and the at least one measuring probe to be measured organ