Device for performing optical coherence tomography

Abstract

A device for performing optical coherence tomography (OCT), comprising an interferometer (1) with a sample arm (2) through which light can be directed to a sample (3) to be detected, a reference arm (4) through which light can be directed on a reference path, and a detector (5) through which signals of interfering light from the two arms (2, 4) can be detected, is characterized in view of the task of detecting and compensating the Z-drift of OCT signals caused by temperature changes in a device for performing optical coherence tomography, wherein the detection and compensation are preferably to be automated, in that an internal and / or sample-invariant calibration target (6) is provided to which light can be directed on a control path (7).

Description

[0001] The invention relates to a device according to the preamble of claim 1.

[0002] Optical coherence tomography (OCT) is an imaging technique that can be used to create two- and three-dimensional images of light-scattering structures. This method typically involves splitting light with a specific bandwidth into two beams using a beam splitter. The first beam falls on the sample or object to be examined, while the second beam travels through a reference path. The light reflected by the sample or object interferes with the reference beam. Using interference signals, the sample can be examined with depth resolution, i.e., at the depth of the optical axis of the first beam, using A-scans.

[0003] Typically, axial shift of an OCT image due to changing temperature differences between the sample and reference arms is not compensated.

[0004] The disadvantage here is that the absolute Z position of the OCT image varies with temperature differences. Any calibration of the device that is dependent on the Z position is therefore faulty or potentially faulty. Even with devices that are not dependent on calibration, readjustments of the Z position may be necessary.

[0005] The invention is therefore based on the object of detecting and compensating for the Z-drift of OCT signals caused by temperature changes in a device for performing optical coherence tomography. Preferably, the detection and compensation should be automated.

[0006] The present invention solves the above-mentioned problem by the features of claim 1.

[0007] According to the invention, it was first recognized that a device-internal and / or sample-invariant calibration target must be provided, to which light can be guided on a control path.

[0008] It has also been recognized that this allows a Z-calibration scan to be performed very quickly during the actual imaging process to the fixed, internal calibration target. The Z-calibration scan can preferably be performed using a scanner.

[0009] Against this background, it has been recognized that the calibration target appears at different image depths when reference and sample signals come from components that are subject to different temperatures or when a reference section is subject to a different temperature than the sample section.

[0010] Furthermore, it has been recognized that a suitable additional reference path can be introduced into the interferometer, provided that the path lengths between the additional calibration target and the actual sample position differ beyond the OCT image depth.

[0011] It has also been discovered that an OCT signal from the calibration target appears at a specific image depth, which is preferably detected automatically. The determined differences in the respective image depths also correspond to the shift in the actual imaging, since both reference and sample sections are exposed to the same temperature changes.

[0012] Finally, it has been recognized that additional changes in the path length difference between the reference and sample signal must be taken into account or calibrated in order to distinguish these changes from changes due to temperature drifts.

[0013] The control section could correspond entirely or partially to the sample arm or sample section. This allows for particularly reliable automatic compensation of temperature drifts. The calibration target can be located in the sample arm.

[0014] The device could include a control unit that detects an OCT signal from the calibration target at a specific depth of an OCT scan or OCT image as a displacement relative to a reference point and, under user control, preferably by manually starting a measurement, or automatically, i.e., without operator intervention, changes the optical path length of the sample arm and / or the reference arm such that the OCT scan or OCT image does not experience the displacement of the OCT signal from the calibration target. Alternatively, the representation of the sample in a display unit could be adjusted accordingly. This ensures that OCT scans always remain at the desired position, even in the Z direction. The determination of quantitative measurement data from the OCT data and the registration of different imaging modalities are also possible. Manual tracking is no longer necessary.

[0015] A path length change unit could be assigned to the sample arm and / or the reference arm to change the optical path length of the light guided in the respective arm. The path length adjustment can be achieved using an optical path length change unit, a so-called delay line, located in the sample and / or reference arm. To compensate for temperature drift, the length difference between the sample and reference arms is adjusted. Z-drift of the OCT signal is automatically compensated by the device.

[0016] The optical path lengths of the sample arm and the control path can be the same or differ by no more than the image depth. This allows for particularly reliable compensation of temperature drifts with a simple optical setup.

[0017] The optical path lengths of the sample arm and the control section could be different, and therefore two reference sections could be provided. This makes it possible to expose both reference sections and the sample sections—namely, the sample section of the sample under investigation and the sample section of the calibration target, i.e., the control section—to the same temperature changes.

[0018] The calibration target could be light-scattering, allowing it to be easily detected optically when illuminated by a light source.

[0019] The calibration target could be designed as a retroreflector. The device's internal calibration target must be sufficiently scattering. If designed as a retroreflector, it is designed to contribute to an improvement in the signal-to-noise ratio (SNR).

[0020] The calibration target can be brought into focus using an additional lens.

[0021] The sample arm and the reference arm could be spatially separated from each other, at least in sections. The device comprises an optical block in which the calibration target is arranged, the sample arm and the control section being arranged at least partially or completely within the optical block, and the reference arm being arranged at least partially or completely outside the optical block. Thus, the sample arm and the control section can be exposed essentially jointly or entirely jointly to a first temperature, whereas the reference arm can be exposed essentially completely or entirely to a second temperature. The optical block can be designed as a structural unit, which is preferably movable.

[0022] Using a control device, light could be directed alternately or simultaneously onto the calibration target and the sample, or into a section of the sample arm that can be turned toward the sample. This allows a Z-calibration scan to be performed.

[0023] A control device could decouple a portion of the sample arm's light shortly before the end of a fiber-guided sample arm and direct it onto a fiber-coupled calibration target. This allows the calibration scan to be performed fiber-assisted. Fibers are particularly good at maintaining or suppressing polarizations of light. The interferometer can be constructed as a free-space optical system or in fiber optics, with the fiber-based system being advantageous.

[0024] The control system could include at least one scanner, an optical switcher, or a coupler. A scanner can perform a Z-calibration scan. Reference arms can be activated via switches or couplers, if needed.

[0025] Light emitted by a light source could be guided to both the sample arm and the reference arm via a splitter, with light reflected from the sample being guided back from an optical block via the sample arm to a combining device for interference with light from the reference arm. This allows a sample arm and a reference arm to be at least partially spatially separated from each other.

[0026] Against this background, the sample arm could be divided into a first sample arm section and a second sample arm section, with a path length change unit arranged between the sample arm sections, and with the path length change unit arranged between the splitting device and the combining device. Thus, the path length change unit can be arranged in a spatial region where a different temperature prevails than the spatial region in which the optics block is arranged.

[0027] Two reference arm sections could be connected to the reference arm via a coupler or optical switcher, allowing each reference arm section to become part of the reference arm. The reference arm can thus be single or double, depending on the position of the calibration target.

[0028] A path length change unit could be arranged in the reference arm between the splitting device and the combining device. This allows the path length change unit to be located in a spatial area where a different temperature prevails than the spatial area in which the optics block is located.

[0029] Alternatively or additionally, a path length change unit could be arranged in the reference arm between the splitting device and a coupler or optical switcher. The reference arm can thus be single or double, depending on the position of the calibration target.

[0030] The sample arm could be divided into a first sample arm section and a second sample arm section, with a path length change unit arranged between the sample arm sections, and the path length change unit arranged between the splitting device and the optics block. Thus, the path length change unit can be arranged in a spatial region where a different temperature prevails than the spatial region in which the reference arm is arranged. The path length change unit can be placed toward the sample.

[0031] An arrangement could comprise a device of the type described here and a first spatial region in which a first temperature prevails, and a second spatial region in which a second temperature prevails, with an optical block arranged in the second spatial region for spatially facing the sample to be detected. This enables mobile separation of optical components, so that some of the optical components are subjected to a first temperature and another part of the optical components to a second temperature.

[0032] In the drawing show Fig. 1 is a schematic view of a prior art interferometer in which the sample arm is exposed to a lower temperature, namely cold, and the reference arm is exposed to a higher temperature, namely heat, Fig. 2 a graphical representation of the dependence of a Z-shift of an OCT signal on the temperature difference between the sample arm and the reference arm, Fig. 3 a schematic view of an optical block extended by a calibration target, Fig. 4 is a schematic view of an interferometer in which a path length change unit is arranged in both the sample arm and the reference arm, Fig. 5 is a schematic view of a device in which the path length change unit in the sample arm is arranged optically after the sample, Fig. 6 a further schematic view of a device in which the path length changing unit is arranged in the sample arm after the sample, wherein the reference arm can be designed in duplicate, Fig. 7 is a schematic view of a device in which the path length changing unit is arranged in the reference arm, Fig. 8 shows a further schematic view of a device in which the path length changing unit is arranged in the reference arm, wherein the reference arm can be designed in duplicate, Fig. 9 a schematic view of a device in which the path length changing unit is arranged in the sample arm to the sample, and Fig. 10 a schematic view of a device in which the path length changing unit is arranged in the sample arm to the sample, wherein the reference arm can be designed in duplicate.

[0033] Fig. Figure 1 shows a schematic view of a prior art device for performing optical coherence tomography (OCT), comprising an interferometer 1 with a sample arm 2, through which light can be guided to a sample 3 to be detected, a reference arm 4, through which light can be guided along a reference path, and a detector 5, through which signals of interfering light from the two arms 2, 4 can be detected. Furthermore, a light source 11 is provided.

[0034] Fig. Figure 1 shows a prior art arrangement comprising a device, a first spatial region W in which a first temperature prevails, and a second spatial region K in which a second temperature prevails. If the reference arm 4 and the sample arm 2 in an interferometer are spatially separated from each other, temperature differences can occur between these two units.

[0035] Fig. Figure 2 shows the effects of heating the reference arm 4 while keeping the sample arm 2 at room temperature. Measurements show that a temperature difference between the sample arm 2 and the reference arm 4 of the interferometer leads to a Z-drift, or Z-shift, of the OCT signal.

[0036] Fig. Figure 2 shows a graphical representation that the Z-drift during heating is 4 mm when the sample arm length is 6 m and the heating is about 20°C. On the x-axis of the diagram the Fig. 2 shows the temperature in °C, and the y-axis shows a peak position of the OCT signal in mm.

[0037] To compensate for the above-mentioned effect, the device is Fig. 1 is extended by a device-internal and / or sample-invariant calibration target 6, to which light can be guided on a control path 7.

[0038] Fig. Figure 3 shows the calibration target 6, which is assigned to an optical block 9, in which the sample arm 2 also runs. Light is guided to the calibration target 6 along a control path 7. The control path 7 can correspond entirely or partially to the sample arm 2 or the sample path.

[0039] Against this background, Fig. 4 shows a schematic view of a device for carrying out optical coherence tomography (OCT), comprising an interferometer 1 with a sample arm 2, through which light can be guided to a sample 3 to be detected, a reference arm 4, through which light can be guided on a reference path, and a detector 5, by which signals of interfering light from the two arms 2, 4 can be detected.

[0040] In this device, a device-internal and / or sample-invariant calibration target 6 is provided, to which light can be guided on a control path 7, as shown in Fig. 3 is shown schematically.

[0041] The optical path lengths of the sample arm 2 and the control path 7 can be the same or not differ by more than the image depth.

[0042] Calibration target 6 is light-scattering. Calibration target 6 is designed as a retroreflector.

[0043] Fig. 4 further shows schematically that a control device 8 is provided which detects an OCT signal of the calibration target 6 at a specific depth of an OCT scan or OCT image as a displacement relative to a reference point.

[0044] The control device 8 can change the optical path length of the sample arm 2 and / or the reference arm 4 in a user-controlled manner, preferably by manually starting a measurement, or automatically, i.e. without the influence of an operator, such that the OCT scan or the OCT image does not experience the shift of the OCT signal of the calibration target 6.

[0045] The control device 8 can alternatively change the optical path length of the sample arm 2 and / or the reference arm 4 such that the representation of the sample 3 in a display unit is adjusted accordingly and does not undergo any Z-shift.

[0046] Fig. 4 shows in addition to Fig. 3 further states that, in order to compensate for the above-mentioned thermal effect, a path length change unit 4a, 2a or delay line is inserted into the reference arm 4 and / or the sample arm 2 and the optics block 9 is extended by the calibration target 6.

[0047] The sample arm 2 and / or the reference arm 4 are each assigned a path length changing unit 2a, 4a for changing the optical path length of the light guided in the respective arm 2, 4.

[0048] A path length change unit 2a of the sample arm 2 can be assigned to the sample arm 2, or a path length change unit 4a of the reference arm 4 can be assigned to the reference arm 4. It is also conceivable that each of the arms 2, 4 is assigned a path length change unit, if this makes sense.

[0049] By means of the control device 8, light can be directed alternately or simultaneously onto the calibration target 6 and onto the sample 3 or into a section of the sample arm 2 which can be turned towards the sample 3.

[0050] The control device 8 could decouple a portion of the light from the sample arm 2 shortly before the end of a fiber-guided sample arm and direct it onto a fiber-coupled calibration target 6. This makes it possible to implement a device with a fiber structure.

[0051] Fig. 3 further shows that the control device 8 according to Fig. 4 has at least one scanner 10 to perform a Z-calibration scan.

[0052] The Fig. 5 to 10 each schematically show arrangements comprising a device, a first spatial region W in which a first temperature prevails, and a second spatial region K in which a second temperature prevails, wherein an optical block 9 for spatially facing the sample 3 to be detected is arranged in the second spatial region K.

[0053] Fig. 5 to 10 show, based on various embodiments of the device, that the sample arm 2 and the reference arm 4 are spatially separated from one another at least in sections, wherein the device has an optical block 9 in which the calibration target 6 is arranged, wherein the sample arm 2 and the control section 7 are arranged at least partially or completely in the optical block 9 and wherein the reference arm 4 is arranged at least partially or completely outside the optical block 9.

[0054] Fig. 5 to 10 show that light emitted by a light source 11 can be guided to a splitter 12 both into the sample arm 2 and into the reference arm 4, wherein light reflected from the sample 3 coming from an optical block 9 can be fed back via the sample arm 2 to a combining device 13 for interference with light from the reference arm 4.

[0055] In Fig. 5 and Fig. 6, the sample arm 2 is divided into a first sample arm section 2.1 and a second sample arm section 2.2, wherein a path length changing unit 2a is arranged between the sample arm sections 2.1, 2.2 and wherein the path length changing unit 2a is arranged between the dividing device 12 and the combining device 13.

[0056] In Fig. 6, two reference arm sections 4.1, 4.2 can be connected to the reference arm 4 by a coupler 14 or optical switcher in order to allow the respective reference arm section 4.1, 4.2 to become part of the reference arm 4.

[0057] Fig. 5 and Fig. 6 specifically show that the path length change unit 2a is placed in the sample arm 2 after the sample 3. The reference arm 4 must be single or double depending on the position of the calibration target 6, whereby a second reference arm can be realized or implemented either by a coupler 14 or switch.

[0058] In Fig. 7 and Fig. 8, a path length changing unit 4a is arranged in the reference arm 4 between the dividing device 12 and the combining device 13.

[0059] In Fig. 8, a path length changing unit 4a is arranged in the reference arm 4 between the splitting device 12 and a coupler 14 or optical switcher.

[0060] Fig. 7 and Fig. 8 shows that the path length change unit 4a can be placed in the reference arm 4. The reference arm 4 must be single or double depending on the position of the calibration target 6.

[0061] With two reference arm sections 4.1, 4.2, the path length change unit 4a must be located in the common path of the reference arm sections 4.1, 4.2, whereby the second reference arm 4.2 can be implemented or designed either as a coupler 14 or a switch. The path length change unit 4a is therefore optically arranged in front of the splitting point, specifically in front of the coupler 14, in the reference arm 4.

[0062] In Fig. 9 and Fig. 10, the sample arm 2 is divided into a first sample arm section 2.1 and a second sample arm section 2.2, wherein a path length changing unit 2a is arranged between the sample arm sections 2.1, 2.2 and wherein the path length changing unit 2a is arranged between the dividing device 12 and the optical block 9.

[0063] Fig. 9 and Fig. 10 show that the path length change unit 2a is placed in the sample arm section 2.1 towards the sample 3. It should be noted that the path length change unit 2a deploys double stroke.

[0064] Depending on the position of the calibration target 6, the reference arm must be single or double, whereby the second reference arm section 4.2 can be realized or implemented either by a coupler 14 or switch.

[0065] The optical path lengths of sample arm 2 and control section 7 can be different, so two reference sections can be provided. Advantageously, the optical path length to calibration target 6 is the same as to sample 3, eliminating the need for a second reference. To avoid significantly increasing noise and minimizing the signal-to-noise ratio of the actual sample signal, the second reference arm section should have as little power as possible or be implemented using a switcher.

[0066] The interferometer can be constructed as a free-space optic or in fiber optics, with the fiber optic configuration being advantageous. Furthermore, it is advantageous to position the calibration target 6 internally within the device. List of reference symbols: 1 interferometer 2 sample arms 2.1 first sample arm section 2.2 second sample arm section 2a Path length change unit of the sample arm 3 Sample 4 Reference arm 4.1 first reference arm section 4.2 second reference arm section 4a Path length change unit of the reference arm 5 Detector 6 Calibration target 7 Control section 8 Control unit 9 Optics block 9a Collimator 10 scanners 11 Light source 12 Distribution device 13 Association facility 14 couplers

Claims

[1] Device for carrying out optical coherence tomography (OCT), comprising an interferometer (1) with a sample arm (2) through which light can be guided to a sample (3) to be detected, a reference arm (4) through which light can be guided on a reference path, and a detector (5) through which signals of interfering light from the two arms (2, 4) can be detected, characterized by that a device-internal and / or sample-invariant calibration target (6) is provided, to which light can be guided on a control path (7). [2] Device according to claim 1, characterized by that the control section (7) corresponds completely or partially to the sample arm (2) or the sample section. [3] Device according to one of the preceding claims, characterized bythat a control device (8) is provided which detects an OCT signal of the calibration target (6) at a specific depth of an OCT scan or OCT image as a displacement relative to a reference point and, in a user-controlled manner, preferably by manually starting a measurement, or automatically, i.e. without the influence of an operator, changes the optical path length of the sample arm (2) and / or the reference arm (4) in such a way that the OCT scan or the OCT image does not experience the displacement of the OCT signal of the calibration target (6), or that the representation of the sample in a display unit is adapted accordingly. [4] Device according to one of the preceding claims, characterized by that the sample arm (2) and / or the reference arm (4) is assigned a path length changing unit (2a, 4a) for changing the optical path length of the light guided in the respective arm (2, 4). [5] Device according to one of the preceding claims, characterized bythat the optical path lengths of the sample arm (2) and the control section (7) are the same or do not differ by more than the image depth. [6] Device according to one of the preceding claims, characterized by that the optical path lengths of the sample arm (2) and the control path (7) are different and therefore two reference paths are provided. [7] Device according to one of the preceding claims, characterized by that the calibration target (6) is light-scattering. [8] Device according to one of the preceding claims, characterized by that the calibration target (6) is designed as a retroreflector. [9] Device according to one of the preceding claims, characterized byin that the sample arm (2) and the reference arm (4) are spatially separated from one another at least in sections, wherein the device has an optical block (9) in which the calibration target (6) is arranged, wherein the sample arm (2) and the control section (7) are arranged at least partially or completely in the optical block (9) and wherein the reference arm (4) is arranged at least partially or completely outside the optical block (9). [10] Device according to one of the preceding claims, characterized by that by means of a control device (8) light can be directed alternately or simultaneously onto the calibration target (6) and onto the sample (3) or into a section of the sample arm (2) which can be turned towards the sample (3). [11] Device according to one of the preceding claims, characterized bythat a control device (8) decouples part of the light of the sample arm (2) shortly before the end of a fiber-guided sample arm and directs it onto a fiber-coupled calibration target (6). [12] Device according to one of the preceding claims, characterized by that the control device (8) has at least one scanner (10), an optical switcher or a coupler (14). [13] Device according to one of the preceding claims, characterized by in that light emitted by a light source (11) can be guided at a dividing device (12) both into the sample arm (2) and into the reference arm (4), wherein light reflected from the sample (3) coming from an optical block (9) can be fed back via the sample arm (2) to a combining device (13) for interference with light from the reference arm (4). [14] Device according to claim 13, characterized byin that the sample arm (2) is divided into a first sample arm section (2.1) and a second sample arm section (2.2), wherein a path length changing unit (2a) is arranged between the sample arm sections (2.1, 2.2) and wherein the path length changing unit (2a) is arranged between the dividing device (12) and the combining device (13). [15] Device according to one of the preceding claims, characterized by that two reference arm sections (4.1, 4.2) can be connected to the reference arm (4) by means of a coupler (14) or optical switcher in order to allow the respective reference arm section (4.1, 4.2) to become part of the reference arm (4). [16] Device according to one of claims 13 to 15, characterized bythat a path length changing unit (4a) is arranged in the reference arm (4) between the splitting device (12) and the combining device (13) and / or that a path length changing unit (4a) is arranged in the reference arm (4) between the splitting device (12) and a coupler (14) or optical switcher. [17] Device according to one of claims 13 to 16, characterized by in that the sample arm (2) is divided into a first sample arm section (2.1) and a second sample arm section (2.2), wherein a path length changing unit (2a) is arranged between the sample arm sections (2.1, 2.2) and wherein the path length changing unit (2a) is arranged between the dividing device (12) and the optical block (9). [18] Arrangement comprising a device according to one of the preceding claims, a first spatial region (W) in which a first temperature prevails, and a second spatial region (K) in which a second temperature prevails, wherein an optical block (9) for spatially facing the sample (3) to be detected is arranged in the second spatial region (K).

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