Test procedure for verifying a geometric calibration

Abstract

The present invention relates to a test method for verifying the geometric calibration of an image acquisition unit (64) using a calibration image (22) of an optical target (20), wherein the image acquisition unit (64) comprises a first image acquisition device (66) and a second image acquisition device (68), wherein the image acquisition unit (64) has the geometric calibration of the first image acquisition device (66) and the second image acquisition device (68) with respect to their imaging areas, wherein the image acquisition unit (64) is configured to receive calibration images (22) of the optical target (20), and wherein the geometric calibration of the image acquisition unit (64) can be verified using the calibration images (22).wherein the optical target (20) comprises at least one calibration pattern (54) and wherein the test procedure comprises a verification sequence with the steps of acquiring a first calibration image (180) using the first image acquisition device (66) and a second calibration image (182) using the second image acquisition device (68), such that these each depict the calibration pattern (54), creating a calibration representation (80) with a superimposed representation (82) based on the first calibration image (180) and the second calibration image (182), wherein the superimposed representation (82) includes at least a section of an image of the calibration pattern (54), and verifying the geometric calibration using the image of the calibration pattern (54) in the superimposed representation (82).

Description

The present application relates to a testing method for checking geometric calibration.Exoscopes are part of the prior art in medical imaging, by means of which spatial (magnification) representations of an examination region can be generated. For example, such exoscopes can be used to visualize microsurgical and / or open procedures to aid a surgeon. The spatial representation allows the surgeon to estimate and / or track his own actions more intuitively via a screen.In order to be able to generate the spatial representation, such exoscopes have at least two image capturing devices, which each record an image of the examination region. The image acquisition devices must have as exact a geometric calibration as possible, which can be particularly so that they are oriented relative to one another in such a way that images can be recorded in a common coordinate system. Otherwise, the spatial representation would be generated with errors and the observation of the representation, in particular over a longer period of time, would lead to a more severe cognitive burden on the surgeon, as far as headaches or other physical impairment thereof.Furthermore, the exoscopes can have image capturing devices which are at least additionally configured for capturing images in a wavelength range different from the wavelength range of visible light. For example, the different wavelength range can lie in the near-infrared range and luminescence imaging such as, for example, fluorescence imaging can be carried out by means of these image acquisition devices. Representations based on luminescent imaging may be overlaid on other representations to provide additional information about the examination area to the surgeon. It is therefore necessary for these image capturing devices to be matched to the remaining image capturing devices, i.e. to have a common geometric calibration therewith.The geometric calibration is usually carried out at the factory and an exoscope is supplied to a customer in a calibrated state. In this case, the factory calibration is checked before delivery. Bulky test equipment is used for the test. These test devices must have various illumination devices and / or light sources, each of which provides light in the wavelength range in which the image capturing devices operate. For example, it is customary for the test devices to have a (near) light source and a white light source.Proceeding from the prior art, the object of the invention is to easily and flexibly check the geometric calibration.This object is achieved according to the invention by a testing method for checking a geometric calibration, as described herein and defined in the claims.The present invention can provide a test method for checking a geometric calibration of an image acquisition unit on the basis of a calibration image of an optical target. This can be a development of the above-mentioned test method or a test method independent thereof. The image acquisition unit can comprise a first image acquisition device and a second image acquisition device, wherein the image acquisition unit has the geometric calibration of the first image acquisition device and the second image acquisition device with respect to their imaging regions. The image acquisition unit can be configured to record calibration images of the optical target, and the geometric calibration of the image acquisition unit can be checked on the basis of the calibration images. In addition, the optical target can comprise at least one calibration pattern. Furthermore, the test method can comprise a checking procedure with the steps of recording a first calibration image by means of the first image recording device and a second calibration image by means of the second image recording device, so that these respectively image the calibration pattern, creating a calibration representation with a superposition representation which is based on the first calibration image and the second calibration image, wherein the superposition representation comprises an image of the calibration pattern at least in sections, and checking the geometric calibration on the basis of the image of the calibration pattern in the superposition representation.According to one aspect, the present invention can provide an inspection apparatus comprising a light supply configured to guide first illumination light, a conversion element configured to convert light of the first illumination light having a first wavelength at least partially into second illumination light having a second wavelength different from the first wavelength, and an optical target arranged such that first illumination light and second illumination light for illuminating the target can be supplied thereto for capturing a calibration image of the optical target.According to this aspect, it can furthermore be provided to provide a system comprising an inspection device and a medical imaging device having an image acquisition unit. The image acquisition unit may include a first image acquisition device that is light-sensitive in a first spectral range that includes the first wavelength and a second image acquisition device that is light-sensitive in a second spectral range that is different from the first spectral range and includes the second wavelength. In this case, the image acquisition unit can have a geometric calibration of the first image acquisition device and the second image acquisition device with respect to their imaging regions and the image acquisition unit can be configured to record calibration images of the optical target. Furthermore, the geometric calibration of the image acquisition unit can be verified on the basis of the calibration images.Furthermore, according to this aspect, it can be provided to provide a test method. The test method can include the steps of generating first illumination light comprising light with a first wavelength, generating second illumination light comprising light with a second wavelength different from the first wavelength, supplying the first illumination light and the second illumination light to an optical target for illumination thereof, recording calibration images of the target by means of a medical imaging apparatus having an image recording unit, wherein the image recording unit comprises a first image recording device which is light-sensitive in a first spectral range and a second image recording device which is light-sensitive in a second spectral range different from the first spectral range and comprises the second wavelength, wherein the image recording unit has a geometric calibration of the first image recording device and the second image recording device with respect to their imaging ranges, and checking the geometric calibration of the image acquisition unit on the basis of the calibration images of the optical target. Generating the second illumination light may include converting light of the first illumination light having the first wavelength at least partially into second illumination light having the second wavelength different from the first wavelength.The test methods, systems and / or test devices may be independent of one another. Some embodiments may also use features of different test methods, systems, and / or test devices and / or partially or fully combine multiple test methods, systems, and / or test devices. Advantageously, the geometric calibration can be easily and flexibly checked. In particular, the geometric calibration can be verified after delivery of the exoscope to a customer and / or at regular verification intervals. It can consequently be easily and flexibly verified whether the customer has received and / or operates a sufficiently geometrically calibrated exoscope. Thus, with regard to the calibration, it can be ensured that the exoscope can operate within the scope of provided tolerance ranges and representations can be generated which are comfortable for an operator to view, in particular over a longer period of time. It is furthermore advantageous that no heavy and / or bulky test equipment has to be brought to the customer in order to be able to check the geometric calibration. In addition, the test method for checking the geometric calibration does not require a specially powerful arithmetic unit, but can be carried out using conventional arithmetic units. The test apparatus can be of compact design and can be provided for transport to the customer. Nevertheless, the test apparatus can be used to check image acquisition units for geometric calibration, which image acquisition units comprise image acquisition devices that are light-sensitive in different spectral ranges. This and / or the compactness can be achieved by the test apparatus comprising the conversion element. As a result, only first illumination light has to be guided by the light supply in order to provide the first and second illumination light. The simplicity of checking the geometric calibration can be achieved in particular by the calibration being able to be checked on the basis of the calibration images. Calibration images can be recorded, for example, in the same or at least similar manner as images would be recorded during normal operation. The image acquisition unit therefore does not have to be provided in a special manner for checking the optical calibration. This also makes it possible to achieve that the test apparatus can be used flexibly, in particular for different image acquisition devices. Furthermore, the use of the calibration pattern makes it possible to easily check the geometric calibration. The use of the optical target represents a convenient and fast way to check the calibration. By using the overlay display, the calibration can be checked efficiently on site.The test device can be, in particular, a calibration test device for checking the geometric calibration. The test apparatus can be configured in particular for checking the geometric calibration of medical imaging apparatuses, wherein the imaging apparatus comprises an image acquisition unit.The light supply can be configured to provide illumination light in such a way that the optical target can be illuminated and / or the conversion element can be at least partially illuminated. Guiding can mean that the light can be guided in a preferred direction. In general, guiding can mean that light from a location at which illumination light is coupled out from a light source is guided to the target by means of one or more optical elements. This can include both beam guidance and diffuse directional scattering. In particular, the light supply can be configured to guide light with a high efficiency, for example with a power loss of at most 50%, at most 40%, at most 30% or even at most 20%. Furthermore, light can be coupled into the light feed.Illumination light can generally comprise wavelengths that can be assigned to the wavelength range of visible light. Illumination light can be understood in principle as light provided for illuminating and / or illuminating a body and / or object. The first illumination light can be provided, for example, for illuminating the conversion element and / or for illuminating the optical target. For this purpose, light, in particular illumination light, can be guided in the test apparatus. The first illumination light can be, in particular, light which can be coupled into the light feed and / or can be generated therein. Furthermore, the first illumination light can be guidable to the conversion element in particular by means of the light feed.In principle, light in a specific range can mean that a part of the total spectral light intensity distribution of the light is located in this range. The spectral light intensity distribution can be defined as the distribution of the light intensity over the different light wavelengths of the entire spectrum. For example, the portion may be 10% to 100%, in particular 40% to 100% and preferably 80% to 100%. Particularly preferably, a part can mean that the light intensity is distributed in such a way that at least substantially the light intensity is in the said spectral range. If the spectral range is visible light, for example, the light intensity of the light is substantially divided over the spectral range of the visible light. This may be relevant in particular when features relate to the first illumination light and / or the first wavelength.The conversion element can be configured to convert light with the first wavelength, in particular light of the first illumination light, into light with the second wavelength, in particular light of the second illumination light. Furthermore, the conversion element can be partially transmissive for light having the first wavelength. For example, the conversion element can be configured to convert 10%-100%, in particular 30%-80%, preferably 40%-60%, of the amount of light and / or of the luminous flux of the light having the first wavelength into light having the second wavelength. In addition, the conversion element can be configured to convert light into narrow spectral bands according to the remaining features. Eng can mean that the converted spectral band is, for example, up to 200 nm, in particular 100 nm, preferably 50 nm, particularly preferably 20 nm wide. The conversion element can be configured in particular to emit light having the second wavelength. The emitted light can be used for illuminating the optical target. Alternatively or additionally, light with the first wavelength can be used to illuminate the optical target. For example, the conversion element can be configured to convert light and transmit light alternately in time.The conversion element can comprise filters configured for light conversion. The conversion element can be configured in particular to absorb light with the first wavelength and to emit light with the second wavelength. Further, in some embodiments, alternatively or additionally, the wavelength of the light with the first wavelength can be halved by means of the conversion, for example by second harmonic generation (SHG) and / or frequency multiplication by means of nonlinear optical processes. For example, the second wavelength can be a wavelength from the ultraviolet range. Furthermore, quantum dots can be provided for light conversion, or the conversion element can comprise quantum dots.The conversion element may comprise a transparent or a transparent plate. The conversion element may alternatively or additionally comprise a transluminescent plate. Furthermore, the conversion element can comprise a coating which acts in such a way that a greater amount of light and / or a greater luminous flux with the second wavelength can be emitted. Alternatively or additionally, the conversion element can comprise a film, in particular a matted film, and / or be laminated. The optional plate of the conversion element can be covered, for example, on one side and / or on both sides with the film. On one side and / or two sides, reference can be made in particular to the sides to which the light having the first wavelength can be guided or from which light having the second wavelength can be emitted.The optical target may serve as a target or target object to which an optical system, in particular the medical imaging system, may be aligned or calibrated. The optical target may comprise a structure which, when imaged, allows the calibration image to be acquired. This can mean that an optical calibration can be carried out on the basis of an imaging of the structure of the optical target. The optical target can be illuminatable with light having the first wavelength, in particular the first illumination light, and with light having the second wavelength, in particular the second illumination light, or can be supplied with this light. For example, the optical target can comprise sections of opaque regions and / or sections that can be used for optical calibration when they are imaged and / or are captured by means of the calibration image. For example, a target point can be defined by means of the optical target, and the geometric calibration can be checked with respect to the target point. Furthermore, a plurality of target points can also be provided. For example, the geometric calibration in a plurality of regions of the imaging regions of the image capturing devices can be checked by means of the optical target.The calibration image can be an image that can be recorded at least primarily for carrying out the checking of the geometric calibration. The calibration image can be detectable in particular with predefined and / or standardized image capture settings. This can mean that the image capturing devices, the image capturing unit and / or the medical system can have defined settings during the capturing of the calibration image. It can be provided that a temporal sequence of calibration images, in particular a calibration video, is / is detected. For example, calibration images can be detectable at least substantially in real time and / or can be transmitted to a display device, and / or a representation of the calibration images can be displayed at least substantially in real time on the display device. In particular, the calibration can be checked on the basis of a sequence of calibration images.The medical imaging device can preferably be an exoscope. Alternatively or additionally, the imaging device is an endoscope. The medical imaging device can be configured to record images of an examination region. In some embodiments, the imaging device may be configured to generate magnification representations of the examination region. The representation may be observed during the performance of a medical procedure and / or during a diagnostic action. The medical imaging device can be mobile and / or movable. It can be provided that the imaging device is movable, for example, in an operating room. If a user requires support by imaging, for example, the imaging device can be movable to the place of use, that is to say, for example, to a patient. The imaging device may also be movable in itself. The image acquisition unit can comprise a movable holding arm, for example, and / or the image acquisition unit can be arranged on the movable holding arm.The image acquisition unit can basically be configured to acquire images. Further, the image acquisition unit may include the imaging part of the imaging device. For example, the image acquisition unit can house components involved in this case together. The image capturing unit can in particular be selectively attachable to and / or detachable from the holding arm. This can mean that the image acquisition unit can be exchanged for another image acquisition unit. Furthermore, the image acquisition unit can comprise connections, by means of which image data, signals and / or electrical supply energy can be exchanged with the medical imaging device, in particular with a control unit of the imaging device, and / or transmitted between them.The image acquisition unit can comprise a plurality of, for example two, three, four, five and / or six image acquisition devices. Each image capturing device may include an image sensor. The image sensor can comprise, for example, a CCD sensor and / or a CMOS sensor. Furthermore, each image capturing device can comprise an optical device by means of which light can be guided onto the image sensor. The light can be coupled into the image capturing unit by means of an input optics. For example, each image capturing device can comprise its own input optics. Preferably, however, the image acquisition unit comprises an input optics, by means of which light can be coupled in for all image acquisition devices. The coupled-in light can then be divisible onto the image capturing devices, for example by means of a beam splitter. The input optics may comprise a converging lens. All image capturing devices can have a common image plane.The image capturing devices can be at least substantially identical in construction. Preferably, all image capturing devices can have at least substantially the same image capturing characteristics. For example, the light can be guided onto the image sensor in the same way and / or a distance to the input optics can be the same. The image capturing devices can furthermore be configured to image the same imaging region. This is particularly true if the image capturing devices have a good geometric calibration with respect to one another. The image capturing devices can image the imaging region from slightly different imaging angles. As a result, it is possible, for example, to produce a spatial representation of the imaging region. This can mean that the image acquisition unit can be at least partially a stereo image acquisition unit.Alternatively or additionally, the image acquisition unit can be configured to guide light in different spectral ranges and / or to image the imaging range in different spectral ranges. For this purpose, the first image capturing device can be light-sensitive in the first spectral range and the second image capturing device can be light-sensitive in the second spectral range. For example, the image sensor may be light-sensitive in the spectral range of visible light, in the spectral range of ultraviolet light and / or in the near-infrared spectral range. "Light-sensitive" can be understood in particular to mean that the respective image sensor is configured to capture light and / or to capture images in the specified range of the electromagnetic spectrum, or of the specified wavelength range. The image sensor can also be light-sensitive in the specified range and additionally in a wavelength range. For example, an image sensor may be light sensitive in the near infrared wavelength range and additionally in the visible light range.The wavelength range of visible light can be understood in principle as the wavelength range between approximately 380 nm and 780 nm, in particular between 400 nm and 700 nm.The geometric calibration of an image acquisition unit can be understood to mean that the image acquisition unit is oriented such that images can be acquired in a specific coordinate system. This can mean that the image capturing unit is aligned with a specific point and / or a specific pattern. The imaging range of an image acquisition unit having a geometric calibration is within a certain expectation range, within the limit of expectable and / or application-specific tolerances. The tolerances are determined, for example, from the need for exact geometric calibration. For some embodiments, a tolerance of, for example, 1 pixel to 100 pixels, in particular 3 pixels to 50 pixels, preferably 5 pixels to 25 pixels, may be sufficient. Two image acquisition units which have a common geometric calibration can be configured, for example, to image images of imaging regions in a common coordinate system. In particular, a spatial point imaged by one of the geometrically calibrated image acquisition units may be at a first location of the image of this image acquisition unit and the same spatial point imaged by the other geometrically calibrated image acquisition unit may be at at least a second location of the image of this image acquisition unit, wherein the first location corresponds at least substantially to the second location with respect to the image boundaries.In principle, the pixel size of different imaging devices may be different. An indication of a number of pixels is to be understood in connection with common pixel sizes. A pixel can be between 10 μm and 1 mm, for example.The geometric calibration can be checked on the basis of the calibration images of the image acquisition unit. This can mean that, for example, the relative position of an image of the optical target in two calibration images is comparable relative to one another in order to check the geometric calibration. A deviation of the relative position in two calibration images can indicate an inadequate geometric calibration. A deviation of the relative position can also indicate an adequate calibration, provided that the deviation lies in a tolerance range. The calibration images can each be detectable by means of one of the image capture devices.According to some embodiments, the second wavelength may comprise a wavelength from the infrared range, in particular from the near infrared range. This can mean that light with the first wavelength can be converted into light with the second wavelength by means of the conversion element, wherein the second wavelength can be assigned to the near infrared light. The conversion element can be configured in particular to emit and / or emit infrared, in particular near infrared, radiation. Near-infrared radiation may have a wavelength of approximately 780 nm to 3 μm, for example. Infrared radiation can generally have a wavelength of approximately 780 nm to 1000 μm. Furthermore, in this context, the imaging range of an image acquisition unit can be imageable in infrared, in particular near infrared, radiation. This may be the case for at least a portion of the infrared range and / or near infrared range. Depending on the sensor system used, infrared light in different spectral ranges can be detectable. Advantageously, this allows information to be obtained about an object which can go beyond the information obtainable from imaging with radiation of visible light. For example, molecules present in the imaging region may emit near infrared radiation. The presence of these molecules and / or an amount of these molecules can be checked by means of imaging by means of near-infrared radiation. For example, certain tissue types and / or structures can be selectively markable with these molecules. The molecules can be, in particular, dyes, in particular fluorescent dyes. In some embodiments, they can also be native molecules, for example proteins of their own body. The detection can then be directed to afluorescence. The tissue types may include, for example, cancer tissue. By labeling cancer tissue with molecules that emit light with near infrared radiation, it is possible to infer the presence of this tissue in the imaging area. For example, a representation based on the near infrared radiation may be producible and may be feasible available to the user. For example, the near-infrared radiation can be representable in a color-coded manner. Furthermore, a representation based at least partially on near infrared radiation can be present superimposed on a representation based at least partially on visible light. It is furthermore advantageous that the second wavelength comprises a wavelength from the infrared range, in particular from the near infrared range, since as a result, for checking the geometric calibration of an image acquisition device which is light-sensitive in the second spectral range, the checking device and / or the system does not have to comprise an illumination device by means of which light with the second wavelength can be generated. As a result, a particularly compact test apparatus can be provided. Furthermore, a cost-effective and / or less error-prone test apparatus can be provided. The test apparatus can advantageously be flexible and / or easily transportable to a customer in order to check the geometric calibration. It can be avoided in particular that a bulky, expensive, complex and / or heavy test device is necessary and / or has to be transported to a customer for checking the geometric calibration.In principle, "comprising, generating and / or converting" can mean "at least predominantly" comprising, generating and / or converting. "At least predominantly" comprising, generating and / or converting can relate in particular to the spectral light intensity distribution. "At least predominantly" can mean in the context that a main constituent of the spectral intensity distribution is located in the specified spectral range. For example, at least over 80%, in particular at least 90%, preferably at least 95%, of the light intensity can be located in the specified spectral range. If, for example, illumination light comprises at least predominantly light from the visible range, this can mean that at least 95% of the light intensity can be assigned to the spectral range of the visible light.Furthermore, the first illumination light can comprise at least predominantly light from the visible range. Such illumination light can be provided by available, conventional light sources, in particular simply and / or efficiently.In addition, the conversion element can be configured to convert light from the visible range at least partially into light from the infrared range. Light that can be easily provided can consequently be converted into light that can be less easily provided. Infrared light sources may be more expensive and / or less frequently available than white light sources. This is the case in particular, since a white light source is regularly present in the surgical room, but not an infrared light source. By the conversation element being configured in this way, a particularly simple, efficient, cost-effective and / or compact test apparatus can be provided.According to some embodiments, the conversion element can have luminescent properties, wherein the conversion element is configured to convert light of the first illumination light having the first wavelength at least partially into the second illumination light having the second wavelength different from the first wavelength by means of the luminescent properties. For example, the conversion element can have fluorescent and / or phosphorescent properties. The conversion element can have a coating, for example, be formed at least partially from a material alloy, comprise a material which is luminescent, in particular fluorescent and / or phosphorescent. The conversion element can be configured to absorb light having one wavelength, in particular the first wavelength, and to emit light having another wavelength, in particular the second wavelength. The conversion element can thus be produced in a favorable and / or compact manner. Furthermore, different second wavelengths can be provided flexibly and / or efficiently, in particular optionally. For this purpose, it is possible to provide, for example, different conversion elements having different optical properties, which conversion elements can be rapidly exchanged with one another.Furthermore, the test device can comprise a holder, wherein the holder is provided to make the test device couplable to a medical imaging device to be tested. By means of the holder, it can be achieved that the checking of the geometric calibration can be carried out reproducibly. Furthermore, the test apparatus can be operated easily, in particular by the test apparatus being able to be aligned efficiently, easily and / or easily with respect to the imaging apparatus.The fixture may also include a spacer that defines a distance between the medical imaging device under test and the target. The distance can correspond, for example, approximately to the distance that the imaging apparatus, in particular an image acquisition unit and / or input optics of the imaging device, can usually have during operation to an object to be examined. In addition, the distance may be specifically tunable with the optical target and / or with the imaging device. The distance can correspond at least substantially to a focal length of the first image capturing device and / or a focal length of the second image capturing device. In some embodiments, the distance may be at least 5 cm, at least 10 cm, or at least 20 cm and / or at most 100 cm, at most 80 cm, or at most 50 cm. Reproducibility of the inspection can be increased. Furthermore, the check can be standardizable.In addition, the holder can be configured to bear the dead weight of the test apparatus in a state coupled to the medical imaging apparatus to be tested. This can mean that the test device can be coupled to the imaging device in such a way that the test device is not standing on the ground. That is, the test device does not have to comprise a stand leg and / or the like. The system comprising the test device and the imaging device can thus be more dynamically couplable. Advantageously, fewer oscillations and / or a lower oscillation energy can be transmitted to the test device via the ground. Accuracy of the inspection can be improved. Furthermore, the test apparatus can be made more compact.The holder can also comprise a coupling section for coupling to the medical imaging device to be tested, wherein the coupling section comprises a protrusion which is configured to hold the test device by engaging behind it. The imaging device may also include a holding portion to which the holder is couplable. For example, the projection can at least partially engage behind the holding section. Furthermore, the projection can be configured to hold the test device during the coupling by engaging behind, in particular at least in sections, the holding section. The test device can be rotated about the projection, for example during the coupling, in particular while the latter partially engages behind the holding section. The protrusion may be rotatably supported in the holding portion. The test device, in particular the coupling section and / or the projection, and the imaging device, in particular the holding section, can together form a connection. The connection may comprise, for example, a dovetail connection. As a result, a compact and / or efficient test apparatus can be provided.The coupling section can further comprise a movable holding element which is configured to selectively fix the holder to the medical imaging device to be tested or to release it therefrom. For example, the holder can be clampable to the imaging device by means of the holding element. Alternatively or additionally, the movable holding element can be configured to engage behind the imaging device, in particular the holding section, in sections. The movable holding element can comprise, for example, a clampable holding element, in particular a clamping spring, an adjusting spring and / or the like, a screw and / or a latching nose. As a result, the test apparatus can be selectively fixable to and / or detachable from the imaging apparatus in a simple manner. Coupling can take place in a short time and / or flexibly.In addition, the light supply can comprise a reflective screen which is configured to guide the illumination light to the conversion element, wherein the screen has a cross-sectional area which increases in the direction of the conversion element. The screen can be funnel-shaped and / or conical, for example. Reflective may mean that a major part of the incident light is reflected back. Reflective may also comprise diffusely reflective. For example, the screen may include a reflective coating. The coating may be specular. Furthermore, the coating can comprise white color, which is configured to diffusely reflect light. "white" refers here in particular to the visible spectral range. Light can be guided onto the conversion element in an efficient manner and / or without large light losses.In addition, the test device can comprise an optical waveguide connection to which an optical waveguide can be connected in such a way that first illumination light guided in the optical waveguide can be coupled into the test device. Advantageously, the test device does not have to comprise its own light source. In some embodiments, the system and / or the medical imaging device may include a light source. A light guide of this light source can be connectable to the test device. The light guide connection can be any conventional light guide connection. If the geometric calibration of a medical imaging device is to be checked, consequently no light source has to be transported. It is sufficient to transport the test device to the customer. A light source present there can be connected to the test device. The light guide preferably guides first illumination light, which at least predominantly comprises white light and / or visible light.In addition, the light guide termination may be arranged at a proximal end of the reflective screen having a first cross-sectional area, and the conversion element may be arranged at a distal end of the reflective screen having a second cross-sectional area, the second cross-sectional area being larger than the first cross-sectional area. Consequently, an illuminatable imaginary cross-sectional area can be enlargeable with increasing distance from the light guide connection and / or an area of the conversion element large relative to the light guide connection can be illuminatable. The light can also be guided efficiently and / or with low light losses, in particular onto the conversion element.In addition, the light supply can comprise a diffusion element which is configured to diffuse and homogenize light of the first illumination light. The diffusion element may include a plate configured for diffusion. For this purpose, the plate can comprise a coating, for example. Alternatively or additionally, the plate may comprise a milk glass plate and / or a milky Plexiglass plate. The diffusion member may be disposed at the distal end of the reflective screen. The conversion element can be arranged distally of the diffusion element. In some embodiments, the conversion element can contact the diffusion element. For example, the conversion element can comprise a plate which is arranged lying on the diffusion element. The diffusion element and / or the conversion element can be fixed and / or fixable in this configuration. For example, the test device can comprise a receiving slot into which the diffusion element and / or the conversion element can be inserted. The receiving slot can be closable. By means of the diffusion element, a homogeneous illumination of the conversion element and / or of the optical target can be achieved. As a result, an accuracy of the check can increase.In addition, the optical target can be mounted movably. The test apparatus can comprise a storage device in which the optical target is movable. The target can be movable, for example, in a plane which corresponds to a main plane of the conversion element and / or of the diffusion element. In this case, it can be provided that the bearing device prevents movability of the target perpendicular to the plane, i.e. the movability is limited to the plane. The main plane can comprise the emission plane of the conversion element, from which the radiation plane is emitted in the direction of the optical target. Furthermore, the plane can be at least substantially parallel to the plane which can be imaged by the imaging unit, in particular in a coupled state, or in which the calibration image is intended to be detectable by means of the imaging unit. The optical target can thus be movably mounted in the image plane of the imaging unit. The optical target can further comprise at least one handle, by means of which the target is movable. The handle may be removable. The target can be insertable into the storage device, in particular in a state in which the handle is removed. Furthermore, the bearing device can be designed in such a way that mobility of the target is reduced. For example, the target can be mounted clamped. The test device, in particular the storage device, can comprise, for example, a rubber coating which is compressed by the target when the target is inserted into the test device. This can reduce a risk that the target will move unintentionally with respect to the imaging device. Operating safety is increased. Because the target is movable, the target can be alignable with respect to the imaging device.Furthermore, the optical target can comprise at least one calibration pattern and the calibration pattern can be imaged on the calibration image. The calibration pattern can be clearly recognizable in the calibration image and / or can be displayed and / or imaged, for example, with a sharp contrast and / or in a different color than the environment. The calibration pattern can be provided in such a way that the checking of the geometric calibration on the basis of the calibration pattern can be carried out easily and / or quickly. In some embodiments, the calibration pattern includes opaque, light reflective, and / or light absorbing portions. The calibration pattern can comprise, for example, a black print on a film. Furthermore, the calibration pattern can be formed as a relief in a plate, wherein the relief can be filled with a black and / or light-absorbing material. A film which comprises the calibration pattern can be arranged, or clamped and / or tensioned, between two transparent plates, in particular glass plates, for example. By means of the plates, a risk of damage to the calibration pattern can be reduced.The calibration pattern can further comprise at least one line and / or a cross. The line and / or the cross may also include isolated elements, such as dots, bars, or other objects, arranged on a line and / or a cross, in some embodiments, thereby forming the line and / or the cross. The line and / or the cross can be easily recognized in the calibration image. Furthermore, it is particularly well suited to checking the optical calibration. A cross may preferably be provided. The optical calibration can be checked in two spatial directions in a simple manner by means of the cross.In addition, the calibration pattern can comprise a central rectangular cross with elongate arms, the centre of which can be arranged in the centre of the calibration image, and which divides the calibration image into four quadrants, wherein in each of the four quadrants a respective further rectangular cross with elongate arms is arranged, the centre of which is arranged in a respective central region of the corresponding quadrant. Elongated arms may mean that the cross may comprise thin arms. When the cross is depicted, an arm can extend in width for example over 1 pixel to 20 pixels, in particular over 1 pixel to 10 pixels, preferably over 1 pixel to 5 pixels. The center of the central cross may be movable into the center of the calibration image by moving the optical target. As a result, the geometric calibration can be checked in the center. By means of the four further rectangular crosses in the central regions of the quadrants of the calibration image, the geometric calibration can be checked in edge regions of the calibration image. A central region may be understood to mean a region of the quadrant that includes the center of the quadrant. The center of the quadrant may at least substantially comprise the center of the central region. The central region can encompass, for example, up to 50%, in particular up to 30%, preferably up to 15%, of the area of the quadrant. The central region can be arranged in particular centrally in the quadrant. This can mean that, overall, the geometric calibration can be checked in a region of the calibration image which comprises at least substantially half of the lateral edge in each case from the center in both directions. Consequently, it can be ensured that the image acquisition unit has good geometric calibration over a large imaging range. This allows a particularly good imaging quality and particularly good spatial representation to be achieved.In addition, the optical target can be formed integrally with the conversion element. For example, the calibration pattern can be printed on the conversion element and / or a film comprising the optical target can be clamped on the conversion element. Advantageously, the test apparatus can be made more compact and / or lighter. Furthermore, the complexity of the test apparatus can be reduced.The system can further comprise a lighting device which is connected and / or connectable to the light supply. The illumination device can comprise a light source, in particular a white light source. Advantageously, light comprising the first wavelength, in particular the first illumination light, can be provided by means of the illumination device. The illumination device can be connected to the light supply in particular by means of a light guide.Furthermore, the illumination device can be connectable to the imaging device in an imaging operating mode for providing illumination light during an image acquisition. In a calibration operating mode, the illumination device can be connectable to the test device for the provision of illumination light. Advantageously, an illumination device for providing illumination light for the imaging device and the test device can be provided. Imaging devices regularly have an illumination device and / or an illumination device is provided in any case for the operation of the imaging device. That is, usually, an illumination device is provided when an imaging device is provided. The test apparatus can then be operable with this illumination apparatus. As a result, no separate illumination device needs to be provided in order to be able to check the geometric calibration.Furthermore, the system can comprise a display device which is configured to present a calibration representation based on the calibration images to a user. In the imaging operating mode, a representation of images of an object can be representable on the display device, wherein the images can be captured by means of the imaging device. The representation can comprise in particular the spatial representation and / or the superposition representation. Advantageously, a display device can thus be used for the checking, which is available in any case.The calibration images can comprise at least one first calibration image recorded by means of the first image recording device and at least one second calibration image recorded by means of the second image recording device, and the calibration representation can comprise a superposition representation which is based on the first calibration image and the second calibration image. "Superposition representation" can mean that the representation is based on both calibration images. For example, a superposition representation can be understood to mean a crossfade representation. The overlay display can comprise, for example, the first calibration image and the second calibration image, wherein at least one of the calibration images is shown in a partially transparent manner. In the overlay representation, image regions of the respective calibration images can be comparable and / or alignable with one another. For example, a spatial position of components of the calibration images can be compared. As a result, the geometric calibration can be checked.Furthermore, the superposition representation can comprise sections of the first calibration image and of the second calibration image that are arranged spatially next to one another. The sections of the calibration images can be about 5 pixels to 500 pixels, in particular 20 pixels to 250 pixels, preferably 30 pixels to 100 pixels in size, in particular with respect to at least one page length. In some cases, the portions may be square and / or rectangular. The pixel information can then relate to its length of a page, in particular a longer page. The size may refer to the extent in a spatial direction. As a result, the geometric calibration can be checked by a section-by-section comparison of the calibration images. It is thus possible to easily check whether the calibration images image an object, for example the optical target, identically, in particular locally, in the sections. An offset of these images indicates a quality of the geometric calibration. In addition, the superposition representation in two different spatial directions can comprise sections of the first calibration image and of the second calibration image arranged multiple times alternately next to one another. For example, the calibration representation may have a checkerboard pattern. The fields of the checkerboard may include portions of the first calibration image and the second calibration image arranged side by side. As a result, the geometric calibration can be checked in the two spatial directions.The optical target can comprise the calibration pattern and the sections of the respective calibration images used for the overlay display at least partially image the calibration pattern. It can thereby be possible to check whether an offset of the calibration pattern is present in the overlay representation. The offset is an indicator of the quality of the geometric calibration. The geometric calibration can be checked in a simple manner.The system can furthermore comprise an input device, by means of which control commands for checking the calibration of the image acquisition unit can be initiated by a user. The input device can comprise a laptop, a computer, a mobile terminal, for example a mobile telephone and / or a tablet, in particular a mouse and / or a keyboard. For example, arrow keys of the keyboard can be used to cause a control command to move a overlay. Furthermore, during the checking by means of the control commands, it can be switchable through a menu which can be provided to navigate through the checking of the geometric calibration.In addition, the display device can be configured to superimpose an alignment aid for the alignment of the optical target relative to the image capturing unit. The alignment aid can be provided for example in a supporting manner in that the calibration pattern, in particular the central cross, is movable into the center of the calibration image. For example, the alignment aid can mark the center and / or the center of the calibration image and / or the superposition representation, and the optical target can be aligned with the aid of the alignment aid. Advantageously, the optical target can be easily aligned within the test device. In particular, the optical target can be provided specifically for the imaging device. In some embodiments, the alignment aid comprises a central cross with elongate arms. The optical target can be moved in such a way to align it in such a way that the largest possible portion of the representation of the image of the target overlaps the alignment aid.According to some embodiments, the image capturing unit may include a third image capturing device that is photosensitive in the first spectral range and a fourth image capturing device that is photosensitive in the second spectral range. By means of the first image capturing device and the third image capturing device, stereo image capturing can be performable in the first spectral range, and by means of the second image capturing device and the fourth image capturing device, stereo image capturing can be performable in the second spectral range. For example, stereo image acquisition can be carried out in the spectral range of visible light and additionally in the near infrared and / or ultraviolet spectral range. A stereo representation, in particular a spatial representation, can be generated based on the stereo images in the two spectral ranges. The stereo representation based on the stereo images in a spectral range at least predominantly outside the visible light can be representable in a spectral range of the visible light. The geometric calibration can comprise an alignment of the imaging regions of all image capturing devices with respect to one another.Alternatively or additionally, stereo image acquisition can be carried out by means of the first image acquisition device and the second image acquisition device and / or by means of the third image acquisition device and / or the fourth image acquisition device. In general, image capturing devices can be usable for stereo image capturing in any combinations. For example, three, four, five and / or six image capturing devices can be used jointly for stereo image capturing. This can mean that stereo image acquisition does not necessarily have to be carried out in the first and / or the second spectral range. For example, stereo image acquisition can be carried out jointly in the first spectral range and the second spectral range.The test method may further comprise the step of coupling the test device to the medical imaging device. The coupling can in particular comprise a placement and / or a hooking of the projection of the test device on the imaging device and / or can further comprise an operation of the movable holding element. Furthermore, the inspection device can be applied to the imaging device at at least one point and pivoted about the point. After the coupling, the test device is in a coupled state. In this state, the image plane of the image acquisition unit or of the image acquisition devices can preferably lie at least substantially parallel to the plane in which the optical target, in particular the calibration pattern, extends.Furthermore, it may comprise the step of connecting an illumination device to the test device.In addition, the illumination device can be configured to be connected to the imaging device in an imaging operating mode for providing illumination light during an image acquisition.In addition, the superposition representation can comprise the sections of the first calibration image and of the second calibration image that are arranged spatially next to one another in such a way that the image of the calibration pattern is represented at least in sections in the sections of the first calibration image and of the second calibration image that are arranged spatially next to one another. As a result, the geometric calibration can be checked in a simple manner. Advantageously, the geometric calibration can be checked more independently of a resolution of the display device, for example. In particular, this applies in comparison, for example, with a crossfade display.The checking procedure can further comprise the steps of fading in a checking aid into the calibration representation, wherein the checking aid surrounds a checking region and thereby defines a tolerance range for the checking, moving the checking aid in the calibration representation such that a first portion of the image of the calibration pattern lies within the checking region, wherein the first portion originates from the first calibration image, and checking whether the checking aid is movable such that, in addition to the first portion, a second portion of the image of the calibration pattern lies within the checking region, wherein the second portion originates from the second calibration image.The checking aid can comprise a rectangular frame. "Rectangular" can thereby comprise the shape of a rectangle with rounded corners. The checking area can be definable by the section of the frame. The checking area can be viewable by a user. This can mean that a user views the examination region or the section of the frame in order to estimate the geometric calibration. The larger the tolerance range, the larger the section of the frame can be, or the larger the checking aid can be. Since an image of the calibration pattern can be partially represented in the calibration representation, a partial offset of the image of the calibration pattern between the calibration images can occur. This offset may be smaller the better the geometric calibration is. The offset can be so large that two sections of the image of the calibration pattern cannot be framed by the checking aid, wherein the image of the calibration pattern is imaged in different calibration images. For example, if the calibration pattern is a line, the line in the calibration plot may be shown as two parallel, offset, broken lines, with the lines running along the portions of the respective calibration image, respectively. In general, the image of the calibration pattern can be represented as if it were imaged in only one calibration image, in particular imaged at least substantially without offset, if the geometric calibration is ideal. By means of the checking aid, the geometric calibration can be checked in at least two spatial directions. In particular, if the checking aid comprises the rectangular frame, the geometric calibration can be checked in the direction of each direction of extension of the sides of the frame. In particular, the superposition display can be shown in a checkerboard pattern. This can mean that a periodic offset of the calibration pattern can occur between the individual fields of the checkerboard, in particular in two directions of the checkerboard. The calibration pattern may comprise a cross extending in the two directions. For checking, the checking aid can be movable by means of control commands. A user may cause the control commands. For checking the geometric calibration, the user can move or shift the checking aid pixel by pixel and / or two pixel by pixel in one of the directions, for example by means of a control command. The user can frequently initiate the control command until he, for example, either recognizes that the two sections of the image of the calibration pattern are located within the checking aid, in particular the tolerance range, and / or until he, for example, recognizes that the checking aid, in particular the tolerance range, cannot be moved such that the two sections of the image of the calibration pattern are located within the checking aid, in particular the tolerance range. This can be carried out by the user, for example, in all extension directions of the checking pattern or of the image of the checking pattern. According to one embodiment, the verification pattern comprises a rectangular cross with elongated arms. By checking along the arms and / or at at least one position of each arm, the geometric calibration can be checked in two spatial directions. Advantageously, this allows the geometric calibration to be very simple, rapid, efficient, cost-effective, reliable and / or effectively verified. In particular, this method of checking is suitable for checking the geometric calibration after delivery of the image acquisition unit, or of the imaging device, to a customer. For example, after delivery, geometric calibration may be quickly and / or efficiently checked to ensure that the customer has received a sufficiently calibrated image capture unit. For this purpose, in particular, no particularly heavy, bulky and / or difficult-to-transport test device is necessary. By creating the overlay display and checking the display of the image of the calibration pattern, a check of the calibration can be carried out in such a way that a particularly large computing power of a computing unit is not necessary, wherein the computing unit is involved, for example, in creating the overlay display.The checking of the geometric calibration can be evaluated as positive if the checking aid is movable in such a way that, in addition to the first section, a second section of the image of the calibration pattern lies within the checking range which originates from the second calibration image. Positive can mean that the image acquisition unit is geometrically calibrated in such a way that a sufficiently good spatial representation of an object can be produced for an application and / or a sufficiently good superimposed representation of images of the object can be produced, wherein the images have been acquired in different spectral ranges. In particular, the evaluation can result from the application. According to some applications, a particularly good presentation quality is necessary. In such cases, for example, a smaller checking aid or a smaller tolerance range can be used for checking.Furthermore, the inspection aid can extend in a spatial direction over at least 5, preferably at least 10 pixels and in a spatial direction perpendicular thereto over at least 5, preferably at least 18 pixels. In general, the number of pixels can be closely related to the pixel size, the resolution of the representation, the image sensor used and / or to the required size of the tolerance range and / or the checking aid.The test method can also comprise further test sequences for which the test aid is moved into different image regions of the calibration representation. Different image areas can be understood to mean areas between which a plurality of, for example at least two, three, four, five and / or six of the inspection aids would fit. The image areas may be spaced apart from each other. For example, the image areas can be moved into different edge regions of the calibration representation. This allows an assessment about the homogeneity of the geometric calibration over the entire imaging range of the image capturing devices. Furthermore, distortion of the images of the image capturing devices can be checked.In addition, at least one checking sequence can be carried out in a central region of the calibration representation and further checking sequences can be carried out in a central region of in each case one of the quadrants of the calibration representation. In principle, the calibration representation can be rectangular. At least one rectangular calibration representation can be divisible into four regions of at least substantially the same size, in particular rectangular regions. These regions may be the quadrants. This makes it possible to carry out a reproducible check of the geometric calibration in a plurality of regions of the calibration representation in a simple manner. The calibration pattern can be designed such that it comprises at least one sub-pattern which, when it is depicted, can be displayed in the central region of the calibration representation.Furthermore, the test method can comprise a step of generating a magnification representation of a section of the calibration representation, so that central regions of in each case one of the quadrants of the calibration representation are in each case represented in a region of a corner of the magnification representation. This can mean that the magnification representation can be generated by means of a two-fold magnification, or two-fold zoom, of the calibration representation. In the magnification representation, the geometric calibration in the center and / or in the corners of the magnification representation can be verified and / or checked. As a result, the center of the quadrants can be found in a simple and quick manner and / or the geometric calibration in the central regions of the quadrants of the calibration representation can be checked. The test method may be more efficient and reliable.The test method may further include a preparation procedure. The preparation process can include the steps of capturing an image of the optical target with one of the image capturing devices, generating a representation of the target from the captured image, blending in an alignment aid for the alignment of the optical target relative to the image capturing unit, and aligning the optical target on the alignment aid by moving the target. The preparation sequence can be performable and / or be performed before performing at least one checking sequence. Furthermore, the preparation procedure can be performable and / or be performed before at least substantially each execution of a checking procedure. By means of the alignment aid, the arrangement of the optical target can be simplified. For example, the optical target can be more easily arranged at a target location at which the target can be imaged in such a way that it can be displayed at a desired location in the calibration representation. The desired location can be, in particular, the center of the calibration representation. This can mean that the alignment aid can mark the center of the calibration representation and / or point to it. As a result, the test method can be quickly and / or easily applicable to different image capturing devices. Furthermore, for example, a movement of the target can be compensated during the execution of a checking procedure.In addition, the calibration pattern may comprise a central rectangular cross with elongated arms and the alignment aid may comprise a rectangular cross with elongated arms. Two patterns which are at least substantially identically shaped and / or formed can be comparable in a particularly simple manner. For example, a degree of overlap of representations of both patterns can be easily comparable and / or a quality of the alignment can be evaluated on the basis of the degree of overlap. A high degree of overlap can mean good alignment. According to other embodiments, the alignment aid can comprise, for example, a frame, in the section of which the image of the optical target is to be arranged at least substantially.The image acquisition unit can furthermore comprise at least one further image acquisition device and the image acquisition devices can have a common geometric calibration with respect to their imaging regions. The test method can furthermore comprise checking the calibration of the image capturing devices in pairs. By checking the image capturing devices in pairs, a high quality of the spatial representation and / or of the superimposed representation can be achieved. For example, a pair of image capturing devices can be configured for stereo image recording and / or a further pair can be configured for stereo image fluorescence recording in the near-infrared spectral range. The geometric calibration of all these image acquisition devices can be checked in pairs. The pairwise checking can take place successively. The geometric calibration of a plurality of image capturing devices can be checked in a simple and efficient manner.The present invention may further provide a system for performing a test method. In some embodiments, the checking can be carried out automatically and / or semi-automatically by means of the system.The present invention may further provide for providing program code comprising instructions which, when executed by a processor, cause a testing method according to the invention to be carried out.The present invention may further provide for a computer program product comprising a machine-readable medium on which program code according to the invention is stored.The invention is explained below by way of example with reference to figures. The drawings, specification and claims contain numerous features in combination. The person skilled in the art will also expediently consider the features individually and use them in combination within the scope of the claims.If more than one instance is present from a particular object, only one of them may be provided with a reference sign in the figures and in the description. The description of this instance can be transferred to the other instances from the object accordingly. If objects are designated in particular by means of numerical words, such as first, second, third objects, etc., these are used for designating and / or assigning objects. Accordingly, for example, a first object and a third object, but no second object, can be included. However, a number and / or an order of objects could also be derived additionally on the basis of numerical words.The following are shown: FIG. 1 is a schematic illustration of a system; FIG. 2A shows a schematic illustration of an image acquisition unit of the system in a side view; FIG. 2B shows a schematic illustration of the image acquisition unit in a plan view; FIG. 2C shows a schematic illustration of the image acquisition unit in a view onto the rear side of the image acquisition unit; FIG. 3 shows a perspective illustration of a checking device of the system and of the image acquisition unit; FIG. 4 is a perspective sectional view of a portion of the test apparatus; FIG. 5 shows a representation of a section of the test device at the distal end of a holder; FIG. 6 is a perspective view of a portion of the test device at the proximal end; FIG. 7 shows a schematic illustration of the functional principle of the test apparatus; FIG. 8 shows an exemplary schematic illustration of an intensity distribution; FIG. 9 is a schematic sectional view of an optical target; FIG. 10 shows an embodiment of a calibration pattern; FIG. 11 shows a calibration image comprising an image of a calibration pattern and an alignment aid; FIG. 12 shows a calibration representation based on a first calibration image and a second calibration image; FIG. 13 shows a checking aid; FIG. 14 shows a schematic illustration of a magnification representation of the calibration representation comprising a superimposition of the checking aid and of the image of the calibration pattern; FIG. 15 shows a section of the calibration representation, on the basis of which the geometric calibration is positively evaluated; FIG. 16 shows a section of the calibration representation, on the basis of which the geometric calibration is evaluated negatively; FIG. 17 shows a further exemplary embodiment of a superposition illustration; FIG. 18 shows a schematic flow diagram comprising a plurality of steps of a test method; FIG. 19 shows a schematic flow diagram comprising a plurality of steps of a checking procedure; and FIG. 20 shows a schematic flow diagram comprising a plurality of steps of a preparation sequence.FIG. 1 shows a schematic illustration of the system 100. The system 100 includes an image acquisition unit 64, a test apparatus 10, a lighting apparatus 74, a display apparatus 78, and an input apparatus 86. some of the components, in the illustrated case the lighting apparatus 74, the display apparatus 78, and the input apparatus 86, are disposed on a tool cart 124. The tool carriage 124 comprises rollers, so that it is movable in space. For example, a user may move the device cart 124 to a location of use of the image capturing unit 64.The image capturing unit 64 is detachably attached to a movable holding arm 122. The image acquisition unit 64 can be replaceable, for example, with another image acquisition unit, not shown. Furthermore, the image acquisition unit 64 can be positionable in space in all three spatial directions by means of the holding arm 122. The user can position the image acquisition unit 64, for example, in such a way that an image of an object, for example of an examination region for supporting an action, can be acquired by means of the image acquisition unit 64. Furthermore, a sequence of images can be detectable, for example a video. A representation of the image and / or video is displayable on the display device 78. Thus, the user may view the display of the image and / or video on the display device 78 while performing an action.Furthermore, the image acquisition unit 64 is configured for stereo imaging. For this purpose, the image acquisition unit 64 comprises a plurality of image acquisition devices 66, 68, 88, 90, 114. A more detailed schematic illustration of the image acquisition unit 64 is shown in FIGS. 2A and 2B. Stereo imaging can mean that a spatial representation can be generated. This is based on at least two images of two image capturing devices 66, 68, 88, 90, 114. The image acquisition unit 64 is basically configured to acquire images in a first spectral range 70 that is predominantly within the spectral range of visible light. In addition, the image acquisition unit 64 is configured to acquire images in a second spectral range 72, which is at least predominantly outside the spectral range of visible light. The image acquisition unit 64 is also configured for stereo imaging in the second spectral range 72. A spatial representation of the images of both spectral ranges 70, 72 can be shown together in a spatial superposition representation, not shown. In particular, the second spectral range 72 can comprise a second wavelength 18, wherein the second wavelength 18 comprises a wavelength from the infrared range, in particular from the near infrared range. As a result, for example, luminescence imaging, in particular fluorescence imaging and / or phosphorescence imaging, can be made possible. A structure to be examined within the examination region can be stained, for example, by means of a fluorescent dye which absorbs first light, in particular first illumination light comprising a first wavelength 16, and emits light comprising the second wavelength 18. The first wavelength 16 is to be assigned to the spectral range of the visible light, or the first light, in particular the first illumination light, comprises at least predominantly light from the visible range. Consequently, by means of the spatial superposition representation, the structure to be examined can be more accurately localized and / or made visible.The image capturing unit 64 further includes a light supply terminal 126. A light guide 44 of the lighting device 74 can be connectable to the light supply connection 126. The illumination device 74 is configured to generate and / or provide the first illumination light. That is, the lighting device 74 is configured to generate predominantly light of the visible range. In particular in an imaging operating mode, it is provided that the illumination device 74 is connected to the imaging device 26, in particular to the image acquisition unit 64, for the purpose of providing illumination light during an image acquisition. In a calibration mode, it is provided that the illumination device 74 is connected to the test device 10. In the calibration mode, a geometric calibration of the image acquisition unit 64 is checked. Clearly, only one illumination device 74 for operating the inspection device 10 and the imaging device 26 is provided. The imaging device 26 is typically operated with illumination devices such as the illumination device 74, so that such an illumination device is present anyway when the imaging device 26 is operated.The light guide 44 can be connectable to the test device 10, in particular to a light guide connection 42 of the test device 10. In the case shown, the light guide 44 is connected to the test apparatus 10, so that the first illumination light which is guided in the light guide 44 can be coupled into the test apparatus 10 and / or is coupled into it. The test apparatus 10 is coupled to the imaging apparatus 26, in particular the image acquisition unit 64, by means of a holder 24 of the test apparatus 10. In particular, the test apparatus 10 is coupled to an input optical unit (see FIGS. 2A and 2B ) of the image acquisition unit 64. As a result, at least one image of an object within the test apparatus 10 can be detected and / or detected by means of the image detection unit 64. According to the exemplary embodiment shown, at least one image of an optical target 20 is captured. The optical target 20 is illuminated at least partially by means of light provided by the illumination device 74.The image acquisition unit 64, in particular the image acquisition devices 66, 68, 88, 90, 114, has the geometric calibration with respect to their imaging regions. As will be described in more detail in the following figures, the image acquisition unit 64 is configured to record calibration images 22 of the optical target 20 and the geometric calibration of the image acquisition unit 64 can be checked on the basis of the calibration images 22. An exemplary embodiment of a test apparatus 10 is shown in more detail in the following figures. Furthermore, it can be seen from the following figures how the test apparatus can be operated, for example.Captured images, such as calibration images 22, are displayable on the display device 78. The representations are displayed on the display device 78. By way of example, in FIG. 1, the display device 78 displays the calibration representation 80 for a user, wherein the calibration representation 80 is based on the calibration images 22. The calibration representation 80 comprises a superposition representation 82 which comprises sections 84 of the calibration images 22 arranged spatially next to one another. The sections 84 originate in this case alternately from one of the calibration images 22 in each case. More precisely, the overlay representation 82 comprises sections of one of the calibration images 22 arranged in two different spatial directions in a plurality of mutually juxtaposed positions. the overlay representation 82 is shown in more detail at least in FIG. 11. In the imaging operating mode, for example, spatial representations, in particular spatial superposition representations, are displayed on the display device 78.By means of the input device 86, the user can, for example, prompt control commands for checking the calibration of the image acquisition unit 64. Furthermore, the input device 86 can be used, for example, to control the medical imaging device 26, in particular the image acquisition unit 64. The input device 86 may be connected to the imaging device 26, in particular the image acquisition 64, for example, as is illustrated in FIG. 1.FIGS. 2A, 2B and 2C show a schematic representation of the image acquisition unit 64 of the medical imaging device 26 of the system 100 in different views. FIG. 2A shows a schematic representation of the image acquisition unit in a side view, FIG. 2B shows a schematic representation of the image acquisition unit 64 in a plan view and FIG. 2C shows a schematic representation of the image acquisition unit 64 in a view onto the rear side of the image acquisition unit 64. The image capturing devices 66, 68, 88, 90, 114 are accommodated together by means of the housing 128. In addition, the image acquisition unit 64 comprises an input optical unit 130, by means of which light for the image acquisition devices 66, 68, 88, 90, 114 can be coupled into the image acquisition unit 64. The image capturing devices 66, 68, 88, 90, 114 have at least substantially the same optical properties. This means that they have, for example, at least substantially a common imaging region. The image acquisition unit 64 has the geometric calibration of the first image acquisition devices 66, 68, 88, 90, 114 with respect to their imaging regions. This means that the imaging ranges are at least substantially the same. Furthermore, the better the geometric calibration, the more congruent the imaging regions are. If, for example, an object is detected by means of images of different image detection devices 66, 68, 88, 90, 114, the object may have been detected at slightly different coordinates of the images as a function of the geometric calibration. That is, an offset may occur between images of the object captured by different image capture devices 66, 68, 88, 90, 114. The offset is smaller the better the geometric calibration is. This is of particular significance since spatial representations of an examination region are to be recorded by means of the image acquisition unit 64 and / or the medical imaging device 26. The smallest possible offset is desirable in this case so that the spatial representation has the highest possible quality. Furthermore, different spatial representations, wherein the spatial representations can be based on images of different spectral ranges, can also be displayed superimposed. The image capturing devices 66, 68, 88, 90, 114 are thus configured for stereo image capturing. In this case, pairs of image capturing devices 66, 68, 88, 90, 114 are formed.The image acquisition unit 64 comprises a first image acquisition device 66 and a second image acquisition device 88, which are each light-sensitive in the first spectral range 70. Furthermore, with acquisition unit 64, it comprised a second image acquisition device 68 and a fourth image acquisition device 90, which are each light-sensitive in the second spectral range 72. At least one of the third and fourth image capturing devices 88, 90 can also be referred to as a further image capturing device 114. By means of the first image capturing device 66 and the third image capturing device 88, stereo image capturing in the first spectral range 70 can be carried out. By means of the second image capturing device 68 and the fourth image capturing device 90, stereo image capturing in the second spectral range 72 can be carried out. In particular, the second spectral range 72 lies in the near infrared range. As a result, a fluorescence stereo image acquisition can be carried out by means of the second image acquisition device 68 and the fourth image acquisition device 90.The image capturing devices 66, 68, 88, 90, 114 each comprise an image sensor 132, 134 which are light-sensitive in different spectral ranges. The first image capturing device 66 and the second image capturing device 88 each comprise a first image sensor 132 which is at least predominantly light-sensitive in the first spectral range 70, wherein the first spectral range 70 is assigned to the spectral range of the visible light. That is, image acquisition in the visible light wavelength range is performable by the first image sensor 132. This corresponds approximately to the current image acquisition. By means of the second image sensor 134, image acquisition in the wavelength range of the near-infrared light can be carried out. This may allow fluorescence imaging. The second image capturing device 68 and the fourth image capturing device 90 each comprise a second image sensor 134. Since the second image sensor 134 is at least predominantly light-sensitive in the second spectral range 72 and is in particular light-insensitive relative thereto in the wavelength range of the visible light, light must be provided in both spectral ranges 70, 72 in order to be able to check the geometric calibration of the image acquisition unit 64. To check the geometric calibration, the image acquisition unit 64 records the calibration images 22 of the optical target 20. In particular, each of the image capturing devices 66, 68, 88, 90, 114 captures at least one calibration image 22 of the optical target 20 in each case. On the basis of the calibration images 22, the user can check the geometric calibration of the image acquisition unit 64, for example. In particular, it is provided that the geometric calibration of the image capturing devices 66, 68, 88, 90, 114 is checked in pairs. That is to say, it is provided in particular that the geometric calibration of an image acquisition unit 68, 90 which is light-sensitive in the second spectral range 72 (near infrared) and an image acquisition unit 66, 88 which is light-sensitive in the first spectral range 70 (visible light). For this purpose, it is necessary for near-infrared light, comprising the second wavelength 18, and visible light, in particular white light, comprising the first wavelength 16, to be provided and / or for the optical target 20 to be illuminated with this light. Calibration images 22 are thereby captured in both spectral ranges 70, 72 and superimposed display 82 can be generated, which are based on images captured in both spectral ranges 70, 72. Light in both spectral ranges 70, 72 can be provided by means of the conversion element 14, although the system comprises only one illumination device 74 which provides and / or generates light at least predominantly in the first spectral range 70 (visible light).The test apparatus 10 is shown in more detail in FIGS. 3 and 4. FIG. 3 shows a perspective illustration of the test apparatus 10 and of the image acquisition unit 64; FIG. 4 shows a perspective sectional view of a section of the test apparatus 10.The test apparatus 10 comprises the light guide connection 42, a light feed 12, the optical target 20, a conversion element 14 and the holder 24. the light guide 44 of the illumination apparatus 74 can be closed off to the light guide connection 42 in such a way that first illumination light guided in the light guide 44 can be coupled into the test apparatus 10, in particular into the light feed 12. The light guide connection 42 can be any conventional light guide connection. In particular, the light guide connection 42 can comprise a clamping device 156, by means of which the light guide 44 can be connected in a clampable manner. In this regard, see FIG. 6, FIG. 6 shows a perspective illustration of a section of the test device 10 at the proximal end 46 comprising the light guide connection 42, the clamping device 156, the light guide 44 and the screen 38. In particular, the first illumination light is guided onto the conversion element 14. The light supply 12 comprises a reflective screen 38 which is configured to guide light of the first illumination light to the conversion element 14. The screen 38 includes a specular coating on at least a major portion of its inner surface. In addition, the screen 38 has a cross-sectional area 40 which increases in the direction of the conversion element 14. The shield is hollow funnel-shaped and has openings at its proximal end 46 and at its distal end 49. The light guide connection 42 is arranged at the proximal end 46 and a diffusion element 52 and the conversion element 14 at the distal end 49, At the proximal end 46, the screen 38 has a first cross-sectional area 48 and at the distal end 49 a second cross-sectional area 50, wherein the second cross-sectional area 50 is larger than the first cross-sectional area 48, As a result, light, in particular the first illumination light which is coupled to the proximal end 46, is guided to a larger cross-sectional area 40. Planar elements can thereby be illuminated and / or illuminated. Light, in particular the first illumination light, impinges on the diffusion element 52 at the distal end 49, the light being homogenized and diffused by means of the diffusion element 52. As a result, a more uniform illumination of the conversion element 14 is achieved and, as a result, an image recording quality is improved. The diffusion member 52 is a milky plexiglass plate that is at least as large as the second cross-sectional area 50.The conversion element 14 is likewise of plate-shaped design and rests on the diffusion element 52. The function of the conversion element 14 is explained in more detail with reference to FIGS. 7 and 8. In principle, the conversion element 14 is configured to convert light, in particular the first illumination light, with the first wavelength 16 at least partially into light, in particular second illumination light, with the second wavelength 18, wherein the first wavelength 16 and the second wavelength 18 are different. The second wavelength 18 comprises a wavelength from the near infrared range. The first wavelength 16 comprises a wavelength from the visible range. The first illumination light comprises at least predominantly light from the visible range. The conversion element 14 is configured to convert light from the visible range at least partially into light from the infrared range. For this purpose, the conversion element 14 has fluorescent properties. The conversion element 14 is designed as a fluorescent plexiglass plate and is referred to with matt film on both main sides, i.e. sides which are illuminated and / or from which light is emitted at least with priority, in particular in the direction of the optical target 20. By means of the matt film, homogeneous radiation in the direction of the optical target 20 is made possible and the infrared radiation is coupled out more efficiently.The conversion element 14 is approximately as large as the diffusion element 52. Both elements 14, 52 are inserted together into a receiving slot 142 of the test apparatus 10, in particular into the light path of the light having the first wavelength 16, in particular of the first illumination light. If necessary, further elements can be inserted into the receiving slot 142 and / or at least one of the elements 14, 52 can be replaced. For this purpose, the test device 10 comprises a releasably fastenable closure plate 144 which can be fastened by means of screws. The closure plate 144 is arranged on a lateral side of the test device 10, in particular of the screen 38.The optical target 20 is arranged at a distance from the conversion element 14 and is likewise of plate-shaped design. The distance can be, for example, a 1 cm to 20 cm, in particular 2 cm to 10 cm, preferably 3 cm to 8 cm. In addition, the optical target 20 is movably mounted. For this purpose, the optical target 20 comprises two handles 138 on two opposite sides. The optical target 20 also has a smaller area than the conversion element 14, such that the main surface of the optical target 20, which is illuminated in particular by means of illumination light, is movable parallel to the main surface of the conversion element 14, from which light comprising the first wavelength 16 and the second wavelength 18 is emitted. As a result, the calibration pattern 54 of the optical target 20 can be aligned with respect to the image acquisition unit 64, in particular the image acquisition devices 66, 68, 88, 90, 114. The optical target 20 is mounted in a storage device 136. The bearing device 136 is a slide bearing device and is slot-shaped. A rubber coating 140 of the bearing device 136 is in contact with the optical target 20, and the rubber coating 140 is provided on all side walls 148, into which the bearing device 136 is let in slot-shaped fashion. The side walls 148 define a cavity 150 in which light of the first illumination light and of the second illumination light and / or light comprising the first wavelength 16 and / or the second wavelength 18 is guided. The handles 138 are removable such that when at least one of the handles 138 is removed, the optical target 20 is insertable into the storage device 136. The optical target 20 comprises two glass plates 152, in the center of which a film 154 is arranged, on which the calibration pattern 54 is provided and / or which comprises the calibration pattern 54. In this regard, see also FIG. 9, FIG. 9 shows a schematic sectional illustration of the optical target 20, the glass plates 152 serve to protect the film 154 from damage and / or for easier handling of the film 154, in particular of the calibration pattern 54. Alternatively or additionally, the calibration pattern 54 can be provided directly on the conversion element 14 and / or the optical target 20 can be provided integrated with the conversion element 14 (not illustrated).The holder 24 extends distally from the side walls 148. the holder 24 is in particular designed to be mass-reduced and / or mass-optimized. The holder 24 comprises a spacer 28 and a coupling section 32. The spacer 28, in particular the holder 24, extends only on two sides and / or has recesses 146. Weight can thereby be saved. The recesses 146 can be sawn out of aluminum plates and / or milled out. The coupling portion 32 is disposed at a distal end of the spacer 28. At the distal end, in particular by means of the coupling section 32, the test apparatus 10 is coupled to the image acquisition unit 64. The holder 24 is configured to bear the dead weight of the test apparatus 10 in the coupled state shown. This means that the test apparatus 10 is merely fastened to the image capturing unit 64 and is held and / or carried by the latter. The spacer 28 defines a distance 30 between the imaging device 26, in particular the image acquisition unit 64, and the optical target 20.The coupling section 32 is shown in more detail in FIG. 5. FIG. 5 shows an illustration of a section of the test apparatus 10 at the distal end of the holder 24. For coupling the test device 10, the test device 10 is fastened to the holding section 156 by means of the coupling section 32. The test device 10, in particular the coupling section 32, comprises a projection 34, which is configured to hold the test device 10 by engaging behind it. The protrusion 34 engages behind a portion of the holding portion 156 of the image capturing unit 64, and the holding portion 156 may include a circumferential groove 158 formed in a round shape. Furthermore, the test apparatus 10, in particular the coupling section 32, comprises a movable holding element 36 which is configured to fix the holder 24 selectively to the medical imaging apparatus 26 to be tested. The holding element 36 is in this case designed as a rotatable fixing screw which is rotatable in a thread provided on the coupling section 32. By rotating the screw, the inspection device 10 is fixed and / or clamped to the imaging device sixth 20. Specifically, the holding portion 156 is clamped between the protrusion 32 and the holding member 36. For coupling, the user may first insert the protrusion 32 into the circumferential groove 158 so that the protrusion 32 partially engages behind the holding portion, and then rotate the inspection device 10 around the protrusion 32 while the protrusion remains in contact with the holding portion. Thus, it can move the holding member 36 toward the holding portion 156. In the correct position, which is adjustable as required, the user can fix the test device by operating the movable holding element 36. The protrusion 32 and the retaining portion 156 may form a dovetail-like connection.Generally, the test apparatus 10 is of compact and manageable design. It weighs, for example, between 0.1 kg and 20 kg, in particular between 1 kg and 10 kg, preferably between 2 kg and 5 kg. Furthermore, it is between the light guide connection 42 and the coupling section 32 for example between 0.1 m and 2 m, in particular between 0.2 m and 1.3 m, preferably between 0.3 m and 0.8 m in length. In particular, the test apparatus 10 is shorter than the image acquisition unit 64. In particular, the material is easily cleanable, disinfectant and / or autoclavable.FIG. 7 shows a schematic illustration of the functional principle of the test apparatus 10. light in the first spectral range 70 comprising the first wavelength 16, in particular first illumination light, is provided and guided onto the conversion element 14. The conversion element 14 allows this light to pass through at least partially. In addition, the conversion element 14 converts light with the first wavelength 16, in particular the first illumination light, into light in the second spectral range 72 comprising the second wavelength 18, in particular the second illumination light. This is shown in more detail in FIG. 8 once again on the basis of an exemplary schematic illustration of an intensity distribution. This shows the intensity I plotted over the wavelength λ. It is understood that the intensity distribution shown is not based on an actual measurement of an emission spectrum of the illumination device 74 and / or the conversion element 14. The distribution is to be understood as an example and serves merely to explain the functional principle in more detail. Actual emission spectra can sometimes deviate significantly from the intensity distribution shown. FIG. 8 shows a diagram on whose abscissa 160 the wavelength is plotted and on whose ordinate 162 the light intensity is plotted. A first distribution 168 of the first illumination light is drawn in a solid line by way of example and a second distribution 170 of the second illumination light is drawn in a dashed line. The first distribution 168 is predominantly located within the first spectral range 70 and comprises the first wavelength 16, which is likewise located within the first spectral range 70. The second distribution 170 is predominantly located within the second spectral range 72 and comprises the second wavelength 18, which is likewise located within the second spectral range 72. The first spectral range 70 corresponds to the wavelength range of the visible light 164 approximately between 380 nm wavelength and 780 nm wavelength. The second spectral range 72 corresponds to the wavelength range of the near infrared light 166 between approximately 780 nm wavelength and 3000 nm wavelength. The conversion element 14 converts the light with the first wavelength 16 at least partially into light with the second wavelength 18 by fluorescence and / or phosphorescence, in particular luminescence, and consequently the conversion element 14 converts light of the visible region 164 into light of the near-infrared region 166. By providing the conversion element 14, therefore, no lighting device has to be provided which predominantly emits light in the wavelength range of the near-infrared light 166. The conversion element 14 can comprise a plurality of elements which convert light by means of luminescence. As a result, a broader second distribution 170 comprising a plurality of wavelength peaks can be provided.Returning to FIG. 7, it can thus be seen that, after the light in the first spectral range 70 has passed through the conversion element 14, light is present in the first spectral range 70 and in the second spectral range 72. This light is guided to the optical target 20, in particular for illuminating the latter. Consequently, at least one calibration image 22 can be captured by means of the image capturing unit 64. Preferably, at least one calibration image 22 is captured by means of each of the image capturing devices 66, 68, 88, 90. This means that calibration images 22 are acquired in the spectral range of visible light and near infrared light. The geometric calibration of the image acquisition unit 64 can be checked on the basis of the calibration images 22. In particular, the optical target 20 comprises the calibration pattern 54 and at least one image of the calibration pattern 54 is captured by means of the image capture unit 64. The image of the calibration pattern 54 can extend over different calibration images 22 approximately in sections, as will be shown below. The geometric calibration can be checked on the basis of the image of the calibration pattern 54 in the overlay representation 82.Figure 10 shows an embodiment of the calibration pattern 54. the calibration pattern 54 comprises a line 56 and / or a cross 58. the calibration pattern 54 comprises a central rectangular cross 59 having elongated arms 60 whose center is positionable at the center of the calibration image 22, and which divides the calibration image 22 into four quadrants 62. In this regard, see FIGS. 11 and 12, in each of the four quadrants 62, a respective further rectangular cross 58 is arranged with elongate arms 60, the centre of which is arranged in a central region of the corresponding quadrant 62. Although the calibration image 22 is divided into four quadrants 62, the calibration pattern 54 can also be divided into the four quadrants 62 for the sake of simplicity. The calibration pattern 54 is disposed in a central portion of the optical target 20. The calibration pattern 54 includes elongated pattern portions (e.g., the line 56 and / or the elongated arms 60). On the basis of this, an offset of the image of the calibration pattern 54 in the overlay representation 82 can be checked. If the offset is too large, the geometric calibration is not sufficient.Before carrying out the checking of the geometric calibration, the optical target 20, in particular the calibration pattern 54, can be aligned relative to the image acquisition unit 64, in particular the input optics 130. For this purpose, the optical target 20 is gripped by the user on the handles 138 and the calibration pattern 54 is aligned with the aid of an alignment aid 92. In this regard, see FIG. 11, a representation of a calibration image 22, comprising an image of the calibration pattern 172, and the alignment aid 92 is shown in FIG. 11. The display is displayed on the display 78 during alignment. That is, the display device 78 is configured to superimpose alignment aid 92. The calibration image 22 is captured by only one of the image capturing devices 66, 68, 88, 90. In particular, a sequence of calibration images 22, in particular a video, is displayed while being aligned. As the user moves the calibration pattern 54, he can view the display on the display 78. Thus, it recognizes how the calibration pattern 54 is arranged relative to the alignment aid 92. In a good alignment, the image of the central cross 59 and the alignment aid 92 are shown at least predominantly overlapping. In this orientation, the image of the calibration pattern 172, in particular of the central cross 59, is arranged at least substantially in the center of the calibration images 22. Thus, the image of the cross 59 also passes through the center of the superposition representation 82. In the example shown, the alignment aid 92 comprises a central cross with elongate arms.FIG. 12 shows the calibration representation 80 which is based on a first calibration image 180 and a second calibration image 182. The calibration representation 80 is divided into four quadrants 62. The display device 78 is configured to display the calibration representation 80 for the user based on the calibration images 22, 180, 182. The first calibration image 180 was captured by the first image capturing unit 66 and the second calibration image 182 was captured by the second image capturing unit 68. The calibration images 180, 182 have thus been recorded in different spectral ranges. The calibration representation 80 comprises the overlay representation 82. This means that the superposition representation 82 comprises sections 84 of the first calibration image 180 and of the second calibration image 182 arranged multiply alternately next to one another in two different spatial directions. The portions 84 of each of the first and second calibration images 180, 182 are each offset by an entire portion 84 in successive rows of the checkerboard 169. Overlay display 82 includes sections of image sections of various image capturing devices 66, 68, which were assembled to form overlay display 82. As can be seen in FIG. 14, an image of the calibration pattern 54 can also be composed of the sections 84. However, since the portions 84 originate from images of different image capturing devices 66, 68, which can image the optical target 20, in particular the calibration pattern 54, slightly differently, an offset 184 may occur between portions of the image of the calibration pattern 54. Offset 184 is a measure of a quality of the geometric calibration. The offset 184 is smaller as the geometric calibration is better.The calibration representation 80 comprises different image areas 106 in which the checking of the geometric calibration is carried out. For this purpose, a checking aid 94 (see FIGS. 13, 14, 15, 16 ) can be moved into the image regions 106. A checking procedure for checking the geometric calibration is then carried out in each of the image areas 106. First, a checking procedure is carried out in a central region 108 of the calibration representation 80. Subsequently, further examination sequences are carried out in a central region 110 of in each case one of the quadrants 62 of the calibration representation 80.In order to carry out a test method, in particular the test sequence, a magnified representation 112 (see FIG. 14 ) can be generated. The magnification representation 112 is based on a section 113 of the calibration representation 80. By means of the magnification representation 112, the user can more easily carry out the checking procedure, in particular better estimate the size of the offset 184. In the magnification representation 112, central regions 110 of the quadrants 62 of the calibration representation 80 are each shown in a region of a corner of the magnification representation 112. This means that the magnification representation 112 in the corner regions respectively comprises an image of the cross 58 of the calibration pattern 54. As a result, the geometric calibration can be checked in the magnification representation 112 in five regions.FIG. 13 shows the checking aid 94 by way of example. The checking aid 94 frames a checking region 94 and thereby defines a tolerance range 98 for checking the geometric calibration. The inspection aid 94 comprises an inspection frame 99 defining an edge region of the inspection aid 94. The cutout 101 of the frame 99 defines the tolerance range 98. tiles can be seen in FIG. 13. Each of the tiles corresponds to a pixel 174. The tiles are in particular not to be confused with the fields of the checkerboard 169. Each field of the check field 169 includes a plurality of pixels 174. The frame is 4 pixels wide. The width is changeable depending on the pixel size and / or resolution of the display device 78. The frame is intended to be easily recognizable to the user in a representation. The checking aid 94, in particular the tolerance range 98, extends in a spatial direction over at least 5, preferably at least 10 pixels and in a spatial direction perpendicular thereto over at least 5, preferably at least 18 pixels.FIG. 14 shows a schematic illustration of the magnification representation 112 of the calibration representation 80, in particular of the overlay representation 82 and / or of the checkerboard 169, comprising a overlay of the checking aid 94 and of the image of the calibration pattern 172. The sections 84 of the respective calibration images 22, in particular of the first calibration image 180 and of the second calibration image 182, used for the overlay display 82, at least partially image the calibration pattern 54. This may mean that the representation comprises the overlay representation 82 and the image 172 of the calibration pattern 54. The sections 84 of the first calibration image 180 and of the second calibration image 182 arranged spatially next to one another are included in such a way that the image 172 of the calibration pattern 54 is depicted in sections in the sections 84 of the first calibration image 180 and of the second calibration image 182 arranged spatially next to one another. This causes the offset 184 of the image 172 of the calibration pattern 54 between the portions 84. In a theoretical ideal geometric calibration, offset 184 is no longer detectable and / or at least substantially no offset 184 is present any longer. In the example shown, the calibration pattern 54 comprises the central cross 59 and the magnification representation 112 comprises an image of the cross 59 which is represented with a section-wise offset 184. Furthermore, offset images of the crosses 58 can be seen in the regions of the corners of the magnification representation 112. The geometric calibration can be checked wherever an offset 184 is visible in the representation 112.For this purpose, the checking aid 94 is blended into the calibration representation 80. The inspection aid 94 is then moved in the calibration representation 80 such that a first portion 102 of the image of the calibration pattern 54 lies within the inspection region 96, wherein the first portion 102 originates from the first calibration image 180. It is then checked whether the checking aid 94 is movable such that, in addition to the first section 102, a second section 104 of the image of the calibration pattern 54 lies within the checking region 96, wherein the second section 104 originates from the second calibration image 182. The checking of the geometric calibration is thereby evaluated as positive if the checking aid 94 is movable in such a way that, in addition to the first section 102, the second section 104 of the image of the calibration pattern 54 lies within the checking region 96 originating from the second calibration image 182. The user can perform the check by control commands that he initiates by means of the input device 86. It can move the checking aid approximately pixel by pixel to the right or left, top or bottom in order to carry out the checking. Alternatively or additionally, a system 120 can be provided (see FIG. 1 ), by means of which the checking and / or a checking method can be carried out in a partially automated and / or automated manner. A positive evaluation of the geometric calibration means that a spatial representation by means of the image capturing devices 66, 68, 88, 90 has a sufficiently good quality. In addition, a fluorescence image representation can be superimposed sufficiently well on the spatial representation.FIG. 15 shows an example in which the geometric calibration is positively evaluated on the basis of a section of the calibration representation 80. FIG. 16 shows an example in which the geometric calibration is evaluated negatively with reference to a section of the calibration representation 80.According to FIG. 15, the checking aid 94 can be moved in such a way that, in addition to the first section 102, the second section 104 of the image 172 of the calibration pattern 54 lies within the checking region 96, wherein the first section 102 originates from the first calibration image 180 and the second section 104 originates from the second calibration image 182. The sections 102, 104 are thus within the tolerance range 98.According to FIG. 16, the checking aid 94 cannot be moved in such a way that, in addition to the first section 102, the second section 104 of the image 172 of the calibration pattern 54 lies within the checking region 96, wherein the first section 102 originates from the first calibration image 180 and the second section 104 originates from the second calibration image 182. The sections 102, 104 are therefore outside the tolerance range 98.FIG. 17 shows a schematic representation of a further exemplary embodiment of a superposition representation 82' of a calibration representation 80'. A large part of the features corresponds to the explanations relating to the calibration representation 80. Overlay display 82' includes overlay display 225. The calibration representation 80', in particular the overlay representation 82' and / or the overlay representation 225, is based on the first calibration image 180 and the second calibration image ( 182). The first calibration image 180 and the second calibration image 182 each comprise an image 172 of the calibration pattern 54. The second calibration image 182 is shown partially transparent and superimposed on the first calibration image. An offset 184 can therefore be seen along a line of the images 172 of the calibration pattern 54. The geometric calibration can be checked on the basis of the offset 184. Furthermore, the superimposed checking aid 94 can be seen in the calibration representation 80'. The inspection aid 94 is movable in the calibration representation 80 in such a way that a first portion 102' of the image of the calibration pattern 54 lies within the inspection region 96, wherein the first portion 102' originates from the first calibration image 180. By means of the checking aid, it is possible to check whether, in addition to the first section 102', a second section 104' of the image 172 of the calibration pattern 54 can be arranged within the checking region 96, wherein the second section 104' originates from the second calibration image 182.FIG. 18 shows a schematic flow diagram comprising a plurality of steps of a test method. The test method can be carried out by means of the test apparatus 10 and / or by means of the system 100 and comprises the following steps:a step 201 of generating the first illumination light comprising light having the first wavelength 16;a step 202 of generating the second illumination light comprising light having the second wavelength 18 different from the first wavelength 16;a step 203 of supplying the first illumination light and the second illumination light to the optical target 20 for illumination thereof;a step 204 of recording the calibration images 22 of the target 20 by means of the medical imaging apparatus 26 with the image acquisition unit 64, wherein the image acquisition unit 64 comprises the first image acquisition device 66 which is photosensitive in the first spectral range 70 which comprises the first wavelength 16 and comprises the second image acquisition device 68 which is photosensitive in the second spectral range 72 which is different from the first spectral range 70 and comprises the second wavelength 18, wherein the image acquisition unit 64 has the geometric calibration of the first image acquisition device 66 and the second image acquisition device 68 with respect to their imaging ranges; anda step 205 of checking 205 the geometric calibration of the image acquisition unit 64 on the basis of the calibration images 22 of the optical target 20. generating 202 the second illumination light comprises converting light of the first illumination light having the first wavelength 16 at least partially into second illumination light having the second wavelength 18 different from the first wavelength 16.FIG. 19 shows a schematic flow diagram comprising a plurality of steps of a checking procedure. The verification procedure includes the following steps:a step 210 of recording the first calibration image 180 by means of the first image capturing device 66 and the second calibration image 182 by means of the second image capturing device 68, so that these respectively image the calibration pattern 54;a step of creating the calibration representation 80 with the overlay representation 82, which comprises the sections 84 of the first calibration image 180 and of the second calibration image 182 arranged spatially next to one another in such a way that the image of the calibration pattern 54 is represented in sections in the sections 84 of the first calibration image 180 and of the second calibration image 182 arranged spatially next to one another; anda step of checking the geometric calibration on the basis of the image of the calibration pattern 54 in the overlay representation 82.According to one exemplary embodiment, the checking procedure also comprises the following steps:a step 213 of blending the checking aid 94 into the calibration representation 80, wherein the checking aid 94 frames the checking region 96 and thereby defines the tolerance range 98 for the checking;a step 214 of moving the inspection aid 94 in the calibration representation 80 such that the first portion 102 of the image of the calibration pattern 54 lies within the inspection region 96, wherein the first portion 102 originates from the first calibration image 180; anda step 215 of checking whether the checking aid 94 is movable such that, in addition to the first section 102, the second section 104 of the image of the calibration pattern 54 lies within the checking region 96, wherein the second section 104 originates from the second calibration image 182. The checking procedure can comprise at least one further step 216.FIG. 20 shows a schematic flow diagram comprising a plurality of steps of a preparation sequence. The preparation procedure comprises the following steps:a step 220 of capturing the image of the optical target 20 with one of the image capturing devices 66, 68, 88, 90;a step 221 of generating the representation of the target 20 from the captured image;a step of fading in the alignment aid 92 for the alignment of the optical target 20 relative to the image acquisition unit 64; anda step of aligning the optical target 20 with the alignment aid 92 by moving the target 20.List of reference characters10 Test apparatus 12 Light supply 14 Conversion element 16 First wavelength 18 Second wavelength 20 Optical target 22 Calibration image 24 Holder 26 Medical imaging apparatus 28 Spacer 30 Distance 32 Coupling section 34 Projection 36 Holding element 38 Reflective screen 40 Cross-sectional area 42 Light guide connection 44 Light guide 46 Proximal end 48 First cross-sectional area 49 Distal end 50 Second cross-sectional area 52 Diffusion element 54 Calibration pattern 56 Line 58 Cross 59 Central cross 60 Arm 62 Quadrant 64 Image acquisition unit 66 First image acquisition device 68 Second image acquisition device 70 First spectral range 72 Second spectral range 74 Illumination apparatus 78 Display apparatus 80 Calibration representation 82 Superimposed representation 84 Section 86 Input apparatus 88 Third image acquisition device 90 Fourth image acquisition device 92 Alignment aid 94 Inspection aid 96 Inspection range 98 Tolerance range 99 Inspection frame 100 System 101 Section 102 First section 104 Second section 106 image area 108 central area 110 central area of a quadrant 112 magnification representation 113 section of the calibration representation 114 further image capturing device 120 system 122 holding arm 124 tool carriage 126 light supply connection 128 housing 130 input optics 132 first image sensor 134 second image sensor 136 storage device 138 handle 140 rubber coating 142 receiving slot 144 closure plate 146 recess 148 side wall 150 cavity 152 glass plates 154 film 156 holding section 158 circumferential groove 160 abscissa 162 ordinate 164 wavelength range of visible light 166 wavelength range of near infrared light 168 first distribution 169 checkerboard 170 second distribution 172 image of the calibration pattern 174 pixel 180 first calibration image 182 second calibration image 184 offset 201 step 202 step 203 step 204 step 205 step 206 further step 210 step 211 step 212 step 213 step 214 step 215 Step 216 Further step 220 Step 221 Step 222 Step 223 Step 224 Further step 225 Crossfade display

Claims

Test method for checking a geometric calibration of an image acquisition unit (64) on the basis of a calibration image (22) of an optical target (20), wherein the image acquisition unit (64) comprises: a first image acquisition device (66); and a second image acquisition device (68); wherein the image acquisition unit (64) has the geometric calibration of the first image acquisition device (66) and of the second image acquisition device (68) with respect to their imaging regions; wherein the image acquisition unit (64) is configured to record calibration images (22) of the optical target (20), and wherein the geometric calibration of the image acquisition unit (64) can be checked on the basis of the calibration images (22); wherein the optical target (20) comprises at least one calibration pattern (54); and wherein the test method comprises a checking procedure with the following steps: recording a first calibration image (180) by means of the first image capturing device (66) and a second calibration image (182) by means of the second image capturing device (68), such that these respectively image the calibration pattern (54); creating a calibration representation (80) with an overlay representation (82) which is based on the first calibration image (180) and the second calibration image (182), wherein the overlay representation (82) comprises an image of the calibration pattern (54) at least in sections; and checking the geometric calibration on the basis of the image of the calibration pattern (54) in the overlay representation (82).The test method according to claim 1, wherein the superposition representation (82) comprises sections (84) of the first calibration image (180) and of the second calibration image (182) arranged spatially next to one another in such a way that the image (172) of the calibration pattern (54) is represented at least in sections in sections (84) of the first calibration image (180) and of the second calibration image (182) arranged spatially next to one another.The test method according to claim 1 or 2, wherein the test procedure further comprises: inserting a test aid (94) into the calibration representation (80), wherein the test aid (94) frames a test area (96) and thereby defines a tolerance area (98) for the test; moving the test aid (94) in the calibration representation (80) such that a first portion (102) of the image of the calibration pattern (54) lies within the test area (96), wherein the first portion (102) originates from the first calibration image (180); checking whether the test aid (94) is movable such that, in addition to the first portion (102), a second portion (104) of the image of the calibration pattern (54) lies within the test area (96), wherein the second portion (104) originates from the second calibration image (182).The test method according to claim 3, wherein the geometric calibration check is evaluated as positive if the checking aid (94) is movable such that, in addition to the first portion (102), the second portion (104) of the image of the calibration pattern (54) lies within the checking range (96) originating from the second calibration image (182).The test method according to claim 3 or 4, wherein the inspection aid (94) extends in a spatial direction over at least 5, preferably at least 10 pixels and in a spatial direction perpendicular thereto over at least 5, preferably at least 18 pixels.The test method according to any one of claims 3 to 5, comprising further test sequences for which the test aid (94) is moved into different image regions (106) of the calibration representation (80).The test method according to claim 6, wherein at least one test sequence is carried out in a central region (108) of the calibration representation (80); and wherein further test sequences are carried out in a central region (110) of in each case one of the quadrants (62) of the calibration representation (80).The test method according to any one of the preceding claims, comprising: generating a magnified representation (112) of a section (113) of the calibration representation (80) such that central regions (110) of in each case one of the quadrants (62) of the calibration representation (80) are in each case represented in a region of a corner of the magnified representation (112).The test method according to any one of the preceding claims, further comprising a preparation procedure comprising: capturing an image of the optical target (20) with one of the image capturing devices; generating a representation of the target (20) on the basis of the captured image; inserting an alignment aid (92) for the alignment of the optical target (20) relative to the image capturing unit (64); and aligning the optical target (20) on the alignment aid (92) by moving the target (20).The test method of claim 9, wherein the calibration pattern (54) comprises a central rectangular cross (58) having elongated arms (60), and wherein the alignment aid (92) comprises a rectangular cross (58) having elongated arms (60).The test method according to any one of the preceding claims, wherein the image acquisition unit (64) further comprises at least one further image acquisition device (114); and wherein the image acquisition devices (66, 68, 114) have a common geometric calibration with respect to their imaging regions; further comprising: checking the calibration of the image acquisition devices (66, 68, 114) in pairs.A system (120) for performing a test method according to any one of claims 1 to 11.Program code comprising instructions which, when executed by a processor, cause a test method according to any one of claims 1 to 11 to be carried out.A computer program product comprising a machine readable medium having stored thereon the program code of claim 13.

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