Optical arm and microscope system comprising an optical arm for examining a freely moving experimental animal

Abstract

The invention relates to an optical arm comprising an output section for guiding an optical beam, a shoulder unit, an upper arm, an elbow unit, a forearm, and a wrist unit having an optical output, wherein the shoulder unit mechanically connects the output section and the upper arm so as to be rotatable relative to each other about at least a first and a second rotation axis perpendicular to each other, the elbow unit mechanically connects the upper arm and the forearm so as to be rotatable relative to each other about at least a third rotation axis, and the wrist unit mechanically connects the forearm and the optical output of the wrist unit so as to be rotatable relative to each other about at least one further rotation axis, wherein the output section, the upper arm, the forearm, and the optical output of the wrist unit are optically connected by mirrors arranged in the shoulder unit, the elbow unit, and the wrist unit, and wherein the optical arm comprises an afocal lens system in which the rear focal plane of each lens coincides with the front focal plane of the subsequent lens. The invention further relates to a microscope system comprising such an optical arm for examining a freely moving experimental animal.

Description

[0001] Optical arm and microscope system comprising an optical arm for examining a freely moving experimental animal

[0002] The present invention relates to an optical arm, preferably for a microscope or a laser scanner, and to a microscope system comprising such an optical arm, preferably a laser scanning microscope system, for examining a freely moving experimental animal.

[0003] In neurobiological research, brain electrophysiological (EEG, electrode) measurements and low-resolution microscopic measurements can readily be carried out on freely moving experimental animals (e.g. mice, rats). By contrast, high-resolution in vivo brain imaging, such as two-photon microscopy through a so- called craniotomy window, is performed with the head fixed. This fixed state, however, makes it difficult to conduct experiments in which the interaction of the animal with its environment, and the resulting brain activity, are to be studied.

[0004] Various approaches have been attempted to overcome the above- mentioned problem. One approach aims to create a virtual reality (VR) environment, enabling controlled animal experiments to be performed with a fixed head. One way of realising the virtual environment is to display the virtual visual content on the walls of a room surrounding the animal, using, for example, a projector or a screen. Hdlscher and co-workers (Rats are able to navigate in virtual reality. J Exp Biol (2005); 208(3): 561 -569) were the first to devise a construction that still forms the basis for most virtual environment designs for rodents. In this arrangement, the animal is surrounded by a torus-shaped dome with a diameter of 140 cm and a height of 80 cm, onto the inner surface of which the virtual visual content is projected by means of a projector. The animal stands inside the torus on a sphere with a diameter of 50 cm, the movement of which — detected via a sensor sensing the displacement of the driven surface — causes the projected virtual environment around the animal to change accordingly. Compared to this, European patent EP3996498B1 provides significantly better immersion, and thus faster learning, by attaching a virtual headset with two wings to the head-fixation mechanism of the experimental animal. The wings of the virtual headset are mechanically adjustable individually to the eyes of the experimental animal, and virtual visual content corresponding to the visual fields perceived by the animal’s eyes is projected onto the displays located in the wings. Despite the high degree of immersion, virtual reality still limits the possible observations, since the experimental animal is unable to physically interact with the virtual environment.

[0005] Another approach aims to enable the free movement of the experimental animal. Klioutchnikov, A., Wallace, D.J., Sawinski, J. et al., in “A three-photon headmounted microscope for imaging all layers of visual cortex in freely moving mice” (Nat Methods 20, 610-616 (2023) propose a solution in which a miniaturised laser scanning microscope is mounted on the head of the experimental animal (mouse), into which the laser light is delivered via an optical fibre from a remote laser light source. The drawback of this solution is, on the one hand, that this miniaturised microscope also disturbs the experimental animal, and, on the other hand, that the image quality is not sufficiently high for carrying out more sophisticated measurements.

[0006] The publication “Brain-wide neural recordings in mice navigating physical spaces enabled by a cranial exoskeleton” (James Hope, Travis Beckerle, Pin-Hao Cheng, Zoey Viavattine, Michael Feldkamp, Skylar Fausner, Kapil Saxena, Eunsong Ko, Ihor Hryb, Russell Carter, Timothy Ebner, Suhasa Kodandaramaiah; bioRxiv 2023.06.04.543578; doi: hitps: / / doj.orq / 10 1101 / 2823 06.04.543578) discloses a solution in which a microscope is mounted on an external robot arm. The robot arm, by means of a force and torque sensor, tracks the movement of the mouse’s head and keeps the microscope — which is of greater mass and correspondingly provides substantially higher resolution — in the correct position and orientation. The drawback of this solution is that the microscope remains mounted on the robot arm, which limits the mass of the microscope, so that only smaller microscopes with limited functionality can still be used.

[0007] It is an object of the present invention to provide an apparatus and a method which are free from the disadvantages of the the prior art solutions.

[0008] According to the present invention, the task is solved by means of an optical arm comprising, in succession, an output section, a shoulder unit, an upper arm, an elbow unit, a forearm, and a wrist joint unit with an optical output for guiding an optical beam, wherein the shoulder unit mechanically connects the output section and the upper arm to each other in a rotatable manner about at least a first and a second rotation axis perpendicular to each other, the elbow unit mechanically connects the upper arm and the forearm to each other in a rotatable manner about at least a third rotation axis, and the wrist joint unit mechanically connects the forearm and the optical output of the wrist joint unit to each other in a rotatable manner about at least one further rotation axis, wherein the output section, the upper arm, the forearm and the optical output of the wrist joint unit are optically connected to each other by mirrors arranged in the shoulder unit, the elbow unit and the wrist joint unit, and wherein the optical arm comprises an afocal lens system in which a rear focal plane of each lens coincides with a front focal plane of a subsequent lens.

[0009] According to the present invention, the task is further solved by means of a laser scanning microscope system comprising a microscope having an aperture stop and a focusing unit comprising an objective, wherein the aperture stop is optically connected to the focusing unit by the optical arm according to the invention in such a manner that the focusing unit is connected to the optical output of the wrist joint unit of the optical arm, and the aperture stop is imaged, through the optical arm, onto the entrance pupil of the objective.

[0010] Some preferred embodiments of the invention are defined in the dependent claims.

[0011] Further details of the invention will be described with reference to exemplary embodiments and with the aid of the drawings. In the drawings:

[0012] Figure 1 is a side view of a laser scanning microscope system according to the invention,

[0013] Figure 2 is a perspective view of the laser scanning microscope system,

[0014] Figure 3 is a perspective view of the optical arm and the robot arm of the laser scanning microscope system of Figure 1 ,

[0015] Figure 4 is an enlarged perspective view of the focusing unit of the laser scanning microscope system of Figure 1 ,

[0016] Figure 5 is a schematic view showing the optical beam path of the scanner and the optical arm of a laser scanning microscope system according to the invention, Figure 6A is an enlarged view of the part of the optical arm of Figure 5 containing the image rotation section,

[0017] Figure 6B is an enlarged view of the part of the optical arm of Figure 5 containing the shoulder unit,

[0018] Figure 6C is an enlarged view of the part of the optical arm of Figure 5 containing the elbow unit,

[0019] Figure 6D is an enlarged view of the part of the optical arm of Figure 5 containing the wrist joint unit,

[0020] Figure 7 is a schematic view showing the optical beam path of the scanner and the optical arm of another laser scanning microscope system according to the invention.

[0021] Definitions:

[0022] In the context of the present description, a lens (in the case of afocal relays, a lens element) is understood to mean any optical lens operating on a refractive, reflective and / or diffractive principle, for example a converging lens, a diverging lens, a compound lens, an objective lens, and the like.

[0023] In the context of the present description, for lenses (in the case of afocal relays, lens elements), a distinction is made between a front focal plane and a rear focal plane. The front focal plane, along the optical beam path in the direction towards the object under examination by the microscope, is the focal plane preceding the lens, whereas the rear focal plane is the focal plane following the lens.

[0024] In the context of the present description, the pupil of a lens or an imaging system is understood to mean the image of the aperture stop, as is well known to a person skilled in optical design.

[0025] In the context of the present description, a freely moving experimental animal is understood to mean a quasi-freely moving experimental animal whose movement is not significantly influenced by a focusing unit connected to the head of the experimental animal.

[0026] Figures 1 and 2 show an exemplary embodiment of a microscope system 10 according to the invention for examining a quasi-freely moving experimental animal. The microscope system 10 according to the invention will hereinafter be described by way of a laser scanning microscope system 10; however, the invention can similarly be implemented with other types of light microscope, for example a wide-field microscope.

[0027] The laser scanning microscope system 10 comprises a laser scanning microscope 11 having a laser scanner 100 and one or more laser sources 101 optically connected thereto. The laser scanning microscope 11 may, for example, be a confocal laser scanning microscope or a multiphoton laser scanning microscope, such as a two-photon laser scanning microscope.

[0028] The laser scanner 100 may be any known type of scanner, for example a scanner comprising acousto-optic deflectors or a scanner comprising movable (for example motorised) mirrors. The laser scanner 100 is associated with one or more laser sources 101 , which are shown schematically in Figures 1 and 2. The laser scanner 100 deflects and / or converges / diverges the beam from the laser source 101 in accordance with its control, thereby producing a scanned beam 105. In Figures 5 and 6A-6D, for illustrative purposes, three scanned beams 105 deflected to different extents are shown: a solid line for a scanned beam 105a deflected by 0° (see Figure 6A), a dashed line for a scanned beam 105b deflected to one edge of the field of view (see Figure 6A), and a dash-dotted line for a scanned beam 105c deflected to the opposite edge of the field of view (see Figure 6A), these corresponding to three different scanning settings of the laser scanner 100. The laser scanner 100 has an aperture stop 100A, which limits the size of the collimated beam (or the numerical aperture of the focusing beam) in a manner well known to a person skilled in optical design (see Figure 5). In scanners, the aperture stop is typically the optical element performing the deflection itself (mirror, acousto-optic deflector, etc.). The laser scanner 100 may also, in a known manner, comprise a built-in output lens 102 which focuses the scanned beam 105 onto a rear focal plane 102" (or, in the case of three-dimensional scanning, into the vicinity of this focal plane). Typically, the scanner field stop, which limits the scannable field of view, is arranged in this output image plane. The scanned beam 105a shown as a solid line is undeflected and is therefore focused onto the optical axis in the focal plane 102", whereas the deflected dashed and dash-dotted scanned beams 105b and 105c are focused to one side or the other at the edges of the field of view.

[0029] It is noted that if the microscope 11 is not a laser scanning microscope but another type of light microscope, then, instead of a laser source 101 , another type of light source may be used, and the laser scanner 100 may be entirely absent from the microscope 11 , for example in the case of a wide-field microscope. In the latter case, the present description can be applied with the modification that the aperture stop 100A is the aperture stop of the microscope 11 rather than that of the laser scanner 100, and the output lens 102 is the corresponding lens of the microscope 11 , which may, for example, be an eyepiece. The individual beams are then preferably identified by the object angle instead of the above-mentioned deflection or scanning angle.

[0030] The microscope system 10 further comprises an optical arm 200 according to the invention, which is connected to the optical output of the microscope 11 , and at the end opposite to the microscope 11 has a focusing unit 280. The objective 282 of the microscope system 10 is located here. For this reason, the microscope 11 forming part of the microscope system 10 preferably does not have its own objective (i.e. it is an objective-less microscope 11 ) but is complemented by the objective 282 located at the end of the optical arm 200.

[0031] In the optical arm 200, an optical beam path is formed by means of optical elements, which guides the laser beam arriving from the laser scanner 100 to the focusing unit 280.

[0032] In the present embodiment, the optical arm 200 according to the invention has, starting from the direction of the laser scanner 100, the following main units: image rotation section 210, output section 220, shoulder unit 230, upper arm 240, elbow unit 250, forearm 260, wrist joint unit 270, and focusing unit 280. The optical output of each main unit is optically connected to the optical input of the next unit, thereby jointly forming the optical beam path in the optical arm 200.

[0033] In other embodiments, the optical arm 200 does not comprise an image rotation section 210; instead, the image rotation is implemented in software.

[0034] It is also conceivable that the optical arm 200 does not comprise the focusing unit 280, but that the focusing unit 280 is connected as a separate unit to the optical output 270A of the wrist joint unit 270, which optical output 270A is indicated schematically in Figure 4.

[0035] In a preferred embodiment, the microscope system 10 comprises a robot arm 300 with at least three degrees of freedom, and the focusing unit 280 is mounted on the movable end of the robot arm 300, so that the focusing unit 280 is not held and moved by the optical arm 200 but by the robot arm 300, which in the present embodiment is suspended from a stand 400.

[0036] The optical arm 200 terminates at the objective 282 forming part of the focusing unit 280, and within the optical arm 200 an optical beam path is configured such that the aperture stop 100A of the laser scanner 100 is imaged onto the entrance pupil 282P of the objective 282.

[0037] The optical arm 200 is an opto-mechanical system by means of which the scanned beam 105 from the laser scanner 100 can be directed into the objective 282, the position of which can be varied dynamically, in such a manner that the aperture stop 100A of the laser scanner 100 is imaged onto the entrance pupil 282P of the objective 282. In this way, the arrangement functions as if the objective 282 were directly connected to the laser scanner 100 (optionally via a tube lens in the case of an infinity-corrected objective). The objective 282 focuses the scanned beams 105, entering through the pupil 282P as collimated beams, into the focal plane 282F. Thus, within the optical arm 200, in front of the objective 282, there are optical elements arranged for guiding the scanned beam 105, so that the properties of the scanned beam 105 travelling through the optical arm 200, such as deflection and divergence, are preserved (or, if required, rescaled by applying non-unity magnification relays), such that the scanned beam 105 enters the objective 282 with these properties. This is achieved by the optical elements arranged within the optical arm 200 appropriately tracking the mechanical movement of the optical arm 200. It is noted that the scanned beams 105 illustrated in the figures also represent the beam path defined by the optical elements, since by “beam path” is meant the path traversed by the scanned beams 105. In the case of a non-scanning microscope, the scanned beam 105 corresponds to the optical beam emerging from the aperture stop of the microscope 11 , and its optical path is defined by the optical elements of the optical arm 200.

[0038] As shown in Figure 3, the shoulder unit 230 mechanically connects the output section 220 and the upper arm 240 to each other in a rotatable manner about at least a first rotation axis A and a second rotation axis B perpendicular thereto. The elbow unit 250 mechanically connects the upper arm 240 and the forearm 260 to each other in a rotatable manner about at least a third rotation axis C. The wrist joint unit 270 mechanically connects the forearm 260 and the optical output 270A of the wrist joint unit 270, and the focusing unit 280 connected thereto, to each other in a rotatable manner about at least one, preferably two, rotation axes D and E indicated in the figure.

[0039] The output section 220, the upper arm 240, the forearm 260 and the focusing unit 280 are able to rotate relative to one another via bearing-mounted connections, the rotation preferably being effected by the robot arm 300 through the movement of the focusing unit 280. An embodiment is also conceivable in which there is no separate robot arm 300, and the optical arm 200 itself also functions as a robot arm. In this case, at the shoulder unit 230, the elbow unit 250 and the wrist joint unit 270, motorised bearing-mounted rotary drives of known type provide for the rotation of the output section 220, the upper arm 240, the forearm 260 and the focusing unit 280 relative to one another.

[0040] A preferred arrangement is to integrate, at or near the elbow unit 250 of the optical arm 200, a lifting cable (or another lifting device) operating with a quasiconstant force and not impeding the spatial movement of the elbow, which on the one hand provides appropriate load relief for the support zones of the optical arm, and on the other hand reduces the torques generated and minimises backlash. Similarly, a mechanical component providing a quasi-constant tensile force can preferably be incorporated between the shoulder unit 230 and the wrist joint unit 270, providing the same advantages as those listed above.

[0041] The output section 220, the upper arm 240 and the forearm 260 are preferably formed as rigid tubes, whether there is a separate robot arm 300 or the optical arm 200 itself functions as a robot arm.

[0042] At the ends of the output section 220, the upper arm 240 and the forearm 260, as well as on the side of the optical output 270A opposite to the focusing unit 280, mirrors 231 , 232, 251 , 252, 271 , 272 forming part of the shoulder unit 230, the elbow unit 250 and the wrist joint unit 270, respectively, are arranged at an angle of 45° to the longitudinal axis of the adjacent tube, and at an angle of 45° to the optical axis of the optical output 270A. Optically, these mirrors 231 , 232, 251 , 252, 271 , 272 connect the output section 220, the upper arm 240, the forearm 260 and the optical output 270A to each other. The mirrors 231 , 232, 252, 271 , 272 also form an angle of 45° with the respective rotation axes A, B, C, D, E passing through them. Thus, at the adjacent ends of the output section 220 and the upper arm 240, the mirrors 231 , 232 forming part of the shoulder unit 230 form angles of 45° with the rotation axes A and B, respectively. At one end of the forearm 260, the mirror 252 forming part of the elbow unit 250 forms an angle of 45° with the rotation axis C. At the other end of the output section 260 and beside the optical output 270A, the mirrors 271 , 272 forming part of the wrist joint unit 270 form angles of 45° with the rotation axes D and E, respectively.

[0043] The focusing unit 280, in addition to the objective 282, preferably comprises at least a first detector 284 and a beam-splitter unit 290 in which a main dichroic mirror 292 is arranged that optically connects the objective 282 to the second wrist joint mirror 272 and to the first detector 284. An alternative possibility is that the detector 284 forms part of the laser scanner 100, for example in the case of a confocal laser scanning microscope 11 where it forms part of the laser scanner 100. In this case, the focusing unit 280 collects the light to be detected that returns through the objective 282 and transmits it through the optical arm 200 to the laser scanner 100.

[0044] In the case of a non-laser-scanning microscope 11 , the detector may likewise be integrated with the microscope 11 , into which the light to be detected is returned via the optical arm 200. For example, in a wide-field microscope, the light returned through the optical arm 200 is detected by a camera, or passes through an eyepiece into the user’s eye.

[0045] The focusing unit 280 is connected to the optical output 270A in a rotatable manner about a rotation axis F coinciding with the optical axis of the optical output 270A, which forms an angle of 45° with both the second wrist joint mirror 272 and the main dichroic mirror 292.

[0046] In the present embodiment, the focusing unit 280 also comprises a second detector 285, and in the beam-splitter unit 290, a secondary dichroic mirror 293 is arranged between the main dichroic mirror 292 and the second detector 285. From the secondary dichroic mirror 293, a further mirror 294 directs the light from the objective 282 to the first detector 284.

[0047] Preferably, at the end of the objective 282, there is a head bearing 286 rotatable about the optical axis of the objective 282 and leaving the optical axis of the objective 282 unobstructed, to which a head connector fixed to the head of an experimental animal, typically a small experimental animal (such as a mouse), can be attached in a rotatable manner about the optical axis. The head connector is a plate which preferably - and in a customary manner - contains an observation aperture formed for the objective 282, through which craniotomy-based brain imaging in vivo on the experimental animal can be performed, as is known to the skilled person.

[0048] The head bearing 286 is preferably provided with a rotation sensor 287, which measures the rotation of the head bearing 286 and thereby of the head connector (not shown) affixed to the head of the experimental animal. The rotation sensor 287 may be any known type of rotation sensor, for example, an optical, magnetic, inductive, or other sensor. The signal from the rotation sensor 287 may be used to control the K-mirror 211 , which is arranged in an optional image rotator section 210 to be rotatable in a motorised manner about its optical axis, thereby ensuring that the microscope image remains stationary even when the head bearing 286 rotates. The K-mirror 211 comprises, in a known manner, a first mirror 211 a and a second mirror 211 b enclosing an obtuse angle with each other and facing towards the obtuse angle, and further comprises a third mirror 211c facing towards the two mirrors 211a, 211 b and parallel to the line of intersection of the planes of the two mirrors 211 a, 211 b. The K-mirror 211 is preferably provided with a control unit (which may coincide with the control unit of the entire microscope system 10) which controls the rotation of the K-mirror 211 in accordance with the signal of the rotation sensor 287. In a known manner, rotation of the K-mirror 211 by an angle alpha rotates the microscope image by twice the angle alpha about the optical axis. Accordingly, the K-mirror must be rotated by half of the rotation angle of the head bearing 286 in order to prevent the microscope image from rotating relative to the brain area of the experimental animal under examination.

[0049] As is known to the skilled person, image rotation can also be achieved using other optical elements or systems instead of a K-mirror, for example, a Dove prism, a Schmidt-Pechan prism or an Abbe-Koenig prism.

[0050] In the absence of the optional image rotator section 210, the control signal of the laser scanner 100 may be recalculated based on the signal of the rotation sensor 287, so that the scanned beam 105 follows the rotation of the head of the experimental animal, and the objective 282 continues to focus the scanned beam 105 on the point to be examined. The new position of the target point and the corresponding scanner control functions can be obtained by simple mathematical calculation.

[0051] The image-rotating optical system described above (or image rotation compensation by modifying the scanner control) may also be used to compensate for image rotation resulting from movements of the optical arm’s own rotational degrees of freedom. The angle of image rotation to be compensated can be expressed as a simple linear combination (algebraic sum) of the rotations of the individual degrees of freedom. The rotations of the degrees of freedom can be measured directly by encoders placed next to the bearings, or they can be calculated from the known (and queryable) position and orientation of the robot arm, which in this case means solving the inverse kinematic equation of the optical arm 200 (for which, as is known to the skilled person, commercially available and freely accessible software packages exist, for example, the MATLAB Robotics System Toolbox or the Robotics Toolbox for Python).

[0052] In the embodiment shown in Figure 5, a mirror 212 is arranged between the laser scanner 100 and the image rotator section 210, and a mirror 213 optically connects the image rotator section 210 to the output section 220; however, this may vary depending on the geometric arrangement, see for example the alternative embodiment shown in Figure 7.

[0053] It should be noted that among the rotation axes A, B, C, D, E, F, the rotation axis D may be omitted (fixed) without losing the free 3+3 dimensional (position and orientation) movement of the objective 282 (and thus of the experimental animal), since together with the head bearing 286, the rotation axes A, B, C, E, F are sufficient for this purpose. The significance of the D rotational degree of freedom is that it also provides the optical arm 200 with 3+3 dimensional freedom when rigidly coupled to the robot arm 300 (which is above the head bearing 286), so that the robot arm 300 can move completely freely along a continuous trajectory; its movement will be followed by the optical arm 200 without the occurrence of mechanical overconstraint (binding). As is known to the skilled person, mechanical overconstraint can also be avoided in alternative ways, for example by coupling the optical arm 200 and the robot arm 300 via a bearing coaxial with the objective 282 instead of rigidly fixing them together in 3+3 dimensions. In an embodiment without the robot arm 300, this extra rotational degree of freedom can be omitted.

[0054] The optical arm 200 contains an afocal lens system in which the rear focal plane of each lens coincides with the front focal plane of the next lens. The afocal lens system will be explained in more detail in connection with Figures 5 and 6A- 6D.

[0055] In the present embodiment, the afocal lens system comprises the following afocal relays and lenses.

[0056] The output section 220 and the upper arm 240 are optically connected by an afocal relay 234 around the shoulder, the lens element 234a before the shoulder unit 230 being arranged in the output section 220, and the lens element 234b after the shoulder unit 230 being arranged in the upper arm 240 in such a way that the rear focal plane 234a" of the lens element 234a before the shoulder unit 230 and the front focal plane 234b' of the lens element 234b after the shoulder unit 230 lie in a common plane between the first shoulder mirror 231 and the second shoulder mirror 232. The image of the aperture stop 100A lies in this plane. This is preferred because, along the optical path, the space occupied by the scanned beams 105 is minimal at the focal planes of the lenses, meaning they can pass through the smallest possible optics (e.g. the mirrors 231 , 232) at these points. The planes in which the scanned beam 105 is actually focused are less suitable for this purpose because at those points the small beam size results in increased intensity, which may burn the surfaces of the mirrors 231 , 232, and these planes are conjugate (object-image pairs) with the surface of the sample under examination, meaning that any contamination (or even damage, e.g. on the surface of a mirror) in these planes will be visible in the microscope image. Therefore, the optimal configuration is for the image of the aperture stop 100A to be in the vicinity of the mirrors 231 , 232, ideally falling between the mirrors 231 and 232.

[0057] The upper arm 240 and the forearm 260 are optically connected by an afocal relay 254 around the elbow, the lens element 254a before the elbow unit 250 being arranged in the upper arm 240, and the lens element 254b after the elbow unit 250 being arranged in the forearm 260 in such a way that the rear focal plane 254a" of the lens element 254a before the elbow unit 250 and the front focal plane 254b' of the lens element 254b after the elbow unit 250 lie in a common plane between the first elbow mirror 251 and the second elbow mirror 252. The image of the aperture stop 100A lies in this plane, for similar considerations as in the case of the mirrors 231 , 232.

[0058] The wrist joint unit 270 has a wrist joint section 273, which forms a 45- degree angle with each of the wrist mirrors 271 , 272 and in which a wrist joint lens 274, shown in Figure 6D, is arranged.

[0059] If there is no further lens between the lens element 234b after the shoulder unit 230 and the lens element 254a before the elbow unit 250, then the rear focal plane 234b" of the lens element 234b after the shoulder unit 230 coincides with the front focal plane 254a' of the lens element 254a before the elbow unit 250. Similarly, if there is no further lens, then the rear focal plane 254b" of the lens element 254b after the elbow unit 250 coincides with the front focal plane 274' of the wrist joint lens 274. The rear focal plane 274" of the wrist joint lens 274, if there is no further lens, coincides with the front focal plane of the objective 282, which, in the case of near-telecentric imaging, approximately coincides with the entrance pupil 282P of the objective 282, meaning that the wrist joint lens 274 images the aperture stop 100A onto the entrance pupil 282P of the objective 282. Ultimately, therefore, the aperture stop 100A is imaged at this location.

[0060] Preferably, the image rotator section 210 also contains an afocal relay 214, which, on its optical axis, consists of a lens element 214a before the K-mirror 211 and a lens element 214b after the K-mirror 211 . These are arranged such that the rear focal plane 214a" of the lens element 214a before the K-mirror 211 and the front focal plane 214b' of the lens element 214b after the K-mirror 211 coincide with the plane of the third mirror 211 c. The image of the aperture stop 100A is located here.

[0061] If there is no further lens, the front focal plane 214a' of the lens element 214a before the K-mirror 211 coincides with the rear focal plane 102" of the output lens 102 of the laser scanner 100.

[0062] If there is no further lens, the rear focal plane of the lens element 214b after the K-mirror 211 coincides with the front focal plane of the lens element 234a before the shoulder unit 230.

[0063] The microscope system 10 may optionally comprise an examination table 500 arranged beneath the suspension point of the robot arm 300, or, in the absence thereof, another surface on which the observed experimental animal may move. On the examination table, an arena or maze is preferably formed, which the experimental animal, such as a mouse, may explore in a quasi-free manner. The wall height of the maze is preferably selected so that the mouse cannot climb over the walls, while at the same time preventing the focusing unit 280 from colliding with them. The robot arm 300 is configured so as to be capable of tracking the movement of the head of the experimental animal and moving the objective 282 accordingly, while also providing the force required to support and appropriately move the optical arm 200. For this purpose, the robot arm 300 is preferably equipped with a force and torque sensor 302 for measuring the force and torque acting at the head bearing, and the microscope system 10 comprises a control unit which moves the robot arm 300 on the basis of the signals from the force and torque sensor 302 in such a way as to continuously predict the movement of the animal from the measured forces and torques, and to move the focusing unit 280 to the position and desired orientation intended to be assumed by the animal. To predict the desired position and orientation, a mechanical model having parameters characteristic of the animal (inertia, damping coefficient, stiffness) and equations of motion are used. The resulting motion is the combination of three translational and three rotational movements, carried out with controlled velocity and acceleration. An alternative possibility is that the displacement of the head of the experimental animal is detected optically or with a magnetic-based sensor, or with another type of sensor suitable for continuous 3D position measurement, and the movement of the robot arm 300 is controlled on that basis so that the robot arm 300 follows as precisely as possible the movement or intended movement of the animal. When such position and orientation sensors are used, it is not necessary to mechanically connect the head of the experimental animal to the robot arm 300 via the force and torque sensor 302, which may increase the freedom of movement; however, tracking the freer movement without substantial phase delays may become more difficult.

[0064] A suitable robot arm 300 is commercially available, for example the UR10e model manufactured by Universal Robots. A suitable force sensor is also commercially available, for example the NANO17-E model manufactured by ATI Industrial.

[0065] Microscopic movements of the animal (or, in general, the examined specimen) relative to the optical axis, as well as small displacements resulting from mechanical inaccuracies or uncertainties of the optical arm 200, and from residual errors in the optical alignment, can be eliminated in the image using motion correction methods - either in real time or post hoc - as known to the skilled person. The effects of mechanical uncertainties arising during movement of the optical arm 200 can also be minimized by using a beam stabilizer, motorizing certain mirrors, or incorporating beam position detectors (using a wavelength for the reference beam that does not interfere with imaging and can be filtered out, which is coupled into the arm bypassing the laser scanner 100 and independently thereof). A suitable motion correction method is disclosed, for example, in published application WO201 8042214A2, the contents of which are incorporated herein in their entirety by reference. A suitable beam stabilizer is disclosed, for example, in published application WO2024013529A2, the contents of which are incorporated herein in their entirety by reference.

[0066] In Figure 7, an alternative preferred embodiment is shown, illustrating how the optical arm 200 according to the invention can be coupled to a conventional base microscope containing a laser scanner 100. Similar elements are denoted with similar reference numerals. Compared to the previous embodiment, the difference is that the output lens 102 of the laser scanner 100 is followed by a tube lens 104a of the base microscope. In place of the objective of the base microscope, a mirror 106 is arranged, which is followed by a second tube lens 104b paired with the tube lens 104a, together also forming an afocal relay. In this embodiment, the image rotation section 210 and the output section 220 share a common axis, and only the mirror 212 is present before the image rotation section 210.

[0067] The optical arm 200 according to the invention is also suitable for connecting microscopes or laser scanning units to an endoscope, so that the former can be made flexibly usable in medical practice. In these cases, the aim is to connect the imaging system and the surgical or diagnostic area optically in a manner that is quasi freely movable according to the physician’s needs.

[0068] Various modifications and variations of the embodiments described herein will be apparent to those skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims

Claims1. An optical arm comprising, in succession, an output section, a shoulder unit, an upper arm, an elbow unit, a forearm, and a wrist joint unit with an optical output for guiding an optical beam, wherein the shoulder unit mechanically connects the output section and the upper arm to each other in a rotatable manner about at least a first and a second rotation axis perpendicular to each other, the elbow unit mechanically connects the upper arm and the forearm to each other in a rotatable manner about at least a third rotation axis, and the wrist joint unit mechanically connects the forearm and the optical output of the wrist joint unit to each other in a rotatable manner about at least one further rotation axis, wherein the output section, the upper arm, the forearm and the optical output of the wrist joint unit are optically connected to each other by mirrors arranged in the shoulder unit, the elbow unit and the wrist joint unit, and wherein the optical arm comprises an afocal lens system in which a rear focal plane of each lens coincides with a front focal plane of a subsequent lens.

2. The optical arm according to claim 1 , wherein each mirror forms an angle of 45° with the rotation axis passing therethrough, wherein in the shoulder unit there is a first shoulder mirror forming an angle of 45° with the output section and arranged rotatably relative to the output section, and a second shoulder mirror forming an angle of 45° with the upper arm and arranged rotatably relative to the first shoulder mirror, and wherein the output section and the upper arm are optically connected by a shoulder afocal relay, the lens element of which before the shoulder unit is arranged in the output section, and the lens element of which after the shoulder unit is arranged in the upper arm in such a way that a rear focal plane of the lens element before the shoulder unit and a front focal plane of the lens element after the shoulder unit are located in a common plane in the vicinity of the first shoulder mirror and the second shoulder mirror.

3. The optical arm according to claim 1 or 2, wherein in the elbow unit there is a first elbow mirror forming an angle of 45° with the upper arm and preferablyfixed relative to the upper arm, and a second elbow mirror forming an angle of 45° with the forearm and arranged rotatably relative to the first elbow mirror, and wherein the upper arm and the forearm are optically connected by an elbow afocal relay, the lens element of which before the elbow unit is arranged in the upper arm, and the lens element of which after the elbow unit is arranged in the forearm in such a way that a rear focal plane of the lens element before the elbow unit and a front focal plane of the lens element after the elbow unit are located in a common plane in the vicinity of the first elbow mirror and the second elbow mirror.

4. The optical arm according to any one of claims 1 to 3, wherein in the wrist joint unit there is a first wrist joint mirror forming an angle of 45° with the forearm and arranged rotatably relative to the forearm, and a second wrist joint mirror arranged rotatably relative to the first wrist joint mirror, the wrist joint unit having a wrist section connecting the first wrist joint mirror and the second wrist joint mirror and forming an angle of 45° with each of the first wrist joint mirror and the second wrist joint mirror, and wherein in the vicinity of said wrist section, preferably within said wrist section, there is arranged a wrist lens.

5. The optical arm according to any one of claims 2 to 4, wherein a rear focal plane of the lens element after the shoulder unit coincides with a front focal plane of the lens element before the elbow unit, and a rear focal plane of the lens element after the elbow unit coincides with a front focal plane of the wrist lens.

6. The optical arm according to any one of claims 1 to 5, comprising an image rotation section arranged optically before the output section, the image rotation section including an image rotation optic rotatable about an optical axis of the image rotation section, such as a K-mirror, the K-mirror comprising a first mirror and a second mirror enclosing an obtuse angle relative to each other and facing in the direction of the obtuse angle, and a third mirror facing the first and second mirrors and parallel to a line of intersection of planes of the first and second mirrors, and further comprising an afocal relay in the optical axis of the image rotation section including a lens element before the K-mirror and a lens element after the K-mirror arranged in such a way that a rear focal plane of the lens element before the K-mirror and a front focal plane of the lens element after the K-mirror substantially coincide with the plane of the third mirror.

7. The optical arm according to claim 6, wherein a rear focal plane of the lens element after the K-mirror coincides with a front focal plane of the lens element before the shoulder unit.

8. The optical arm according to any one of claims 1 to 7, comprising a focusing unit connected to the optical output of the wrist joint unit, the focusing unit comprising at least an objective.

9. The optical arm according to claim 8, wherein the focusing unit comprises at least a first detector and a beam-splitter unit having a main dichroic mirror optically connecting the objective to the second wrist joint mirror and to the first detector, and preferably wherein the focusing unit is rotatable about an optical axis of the optical output of the wrist joint unit, and the main dichroic mirror forms an angle of 45° with the optical axis of the optical output of the wrist joint unit.

10. The optical arm according to claim 8 or 9, wherein the focusing unit comprises a second detector, and wherein in the beam-splitter unit a secondary dichroic mirror is arranged between the main dichroic mirror and the second detector.11 . The optical arm according to any one of claims 8 to 10, wherein at the end of the objective there is a head bearing rotatable about the axis of the objective and leaving the axis of the objective unobstructed.

12. A microscope system for examining a freely moving experimental animal, comprising a microscope having an aperture stop and a focusing unit comprising an objective, wherein the aperture stop is optically connected to the focusing unit by an optical arm according to any one of claims 1 to 5 in such a way that the focusing unit is connected to the optical output of the wrist joint unit of the optical arm, and the aperture stop is imaged, through the optical arm, onto anentrance pupil of the objective.

13. The microscope system according to claim 12, wherein the focusing unit is connected to the optical output of the wrist joint unit in a rotatable manner about a connection axis of the focusing unit, and the main dichroic mirror forms an angle of 45° with the connection axis of the focusing unit.

14. The microscope system according to claim 12 or 13, wherein the focusing unit comprises at least a first detector and a beam-splitter unit having a main dichroic mirror optically connecting the objective to the second wrist joint mirror and to the first detector.

15. The microscope system according to claim 14, wherein the focusing unit comprises a second detector, and wherein in the beam-splitter unit a secondary dichroic mirror is arranged between the main dichroic mirror and the second detector.

16. The m icroscope system according to any one of claims 12 to 15, wherein at the end of the objective there is a head bearing rotatable about the axis of the objective and leaving the axis of the objective unobstructed.

17. The microscope system according to claim 16, wherein a rotation sensor is provided at the head bearing.

18. The microscope system according to claim 17, comprising an image rotation section arranged optically before the output section, the image rotation section including an image rotation optic, such as a K-mirror, rotatable in a motorised manner about the optical axis of the image rotation section.

19. The microscope system according to claim 18, wherein a rear focal plane of the lens element after the K-mirror coincides with a front focal plane of thelens element before the shoulder unit.

20. The microscope system according to claim 18 or 19, comprising a control unit configured to control the rotation of the K-mirror in accordance with a signal from the rotation sensor.

21. The microscope system according to any one of claims 12 to 20, comprising a robot arm having at least three degrees of freedom, wherein the focusing unit is mounted to the robot arm, and preferably comprising a stand for suspending the robot arm.

22. The microscope system according to any one of claims 12 to 21 , comprising an examination table arranged under the robot arm.

23. The m icroscope system according to any one of claims 16 to 20, wherein the robot arm is equipped with a force and torque sensor at the head bearing, and the system comprises a control unit configured to move the robot arm on the basis of signals from the force and torque sensor so as to continuously predict the movement of an experimental animal connected to the head bearing on the basis of the measured forces and torques, and to move the focusing unit to a desired position and desired orientation intended to be adopted by the animal.

24. The m icroscope system according to any one of claims 12 to 20, wherein in the optical arm, motorised bearing-mounted rotary drives in the shoulder unit, the elbow unit and the wrist joint unit rotatably connect, relative to each other, the output section and the upper arm, the upper arm and the forearm, and the forearm and the focusing unit.

25. The m icroscope system according to any one of claims 12 to 24, wherein in the optical arm the output section, the upper arm and the forearm are formed as rigid tubes.

26. The optical arm according to any one of claims 1 to 11 , wherein in theshoulder unit, the elbow unit and the wrist joint unit motorised bearing-mounted rotary drives rotatably connect, relative to each other, the output section and the upper arm, the upper arm and the forearm, and the forearm and the optical output of the wrist joint unit.

27. The optical arm according to any one of claims 1 to 11 , wherein the output section, the upper arm and the forearm are formed as rigid tubes.

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