Device and method for imaging scattering objects - Patents.com

Abstract

The present invention comprises a linear illumination module (2) that generates a line of light on an object (20); The present invention relates to an imaging device (1) comprising: a scanning means for moving a line of light over an object; a two-dimensional sensor (14) with a rolling shutter; a synchronization module having a first mode in which the sensor (14) senses a bright-field signal with a zero time offset between the rolling shutter and the scanning means, and a second mode in which the sensor senses a dark-field signal with a non-zero time offset between the shutter and the scanning means; and an image processing module for generating a bright-field image from the bright-field signal and a dark-field image from the dark-field signal. The present invention further relates to a method of imaging.

Description

[Technical Field]

[0001] The present invention relates to a device for imaging scattering objects. The present invention further relates to a method for imaging such objects. The field of the invention is that of imaging scattering media or objects such as, but not limited to, biological tissue. [Background technology]

[0002] [Prior art] Numerous imaging techniques are used in all fields of science, particularly in medicine. With regard to imaging complex biological tissues in vivo, particularly the eye, it is possible to distinguish between incoherent and coherent techniques. Incoherent techniques can be based on direct reflectance imaging, or phase and absorption imaging. Reflectance imaging is any type of imaging that relies on intensity contrast, based on the amount of light reflected or backscattered by one or more structures in a sample. Coherent techniques are based on interferometric measurements. Incoherent imaging techniques are generally based on direct measurement of reflectivity.

[0003] For full-field measurements, the photons backscattered by the eye are counted by a camera. This is a fast technique for recording all photons in parallel. In fact, the entire field can be illuminated in parallel and the photons from this field can be recorded in parallel or by a rolling shutter of the camera. In both cases, the contrast of the resulting image is the same and the measurement is not as sensitive. In either case, and more commonly, for full-field measurements, the photons are recorded by a 2D camera.

[0004] However, image processing is difficult, if not impossible, because not only do they capture photons backscattered by the layer of interest, but they also capture photons scattered by other layers and multiply scattered photons, which reduces image contrast and adds noise, thus reducing the signal-to-noise ratio.

[0005] In confocal imaging, measurements are taken one by one using a scanning system to obtain a two-dimensional image. Confocal filtering is used to remove photons originating from depths other than the object being measured, as well as to increase scattered photons, allowing for better contrast and signal-to-noise ratios.

[0006] By offsetting the confocal detection filters relative to the illumination, dark-field imaging can also be performed, in which case photons from unilluminated areas are detected. Absorption and phase contrast can be determined from the dark-field image.

[0007] However, single-point scanning techniques suffer from the slow acquisition speed of the scan, which can result in distortion artifacts being present in such scanning systems, especially when the imaged object is in motion, such as the retina being imaged in vivo. The axial resolution of these techniques depends on the numerical aperture of the measurement system.

[0008] Coherent imaging techniques are generally based on interferometric measurements of backscattered light. An important coherent technique is optical coherence tomography (OCT). OCT can be used to image complex, scattering biological tissues, especially by using low-coherence interferometry to select the imaging depth. In this case, the axial resolution is determined by the spectral width and is independent of the numerical aperture. Summary of the Invention

[0009] [DISCLOSURE OF THE INVENTION] The present invention aims to overcome the drawbacks of the prior art mentioned above. In particular, it is a goal of the present invention to provide a device and method for imaging scattering objects that allows full field of view imaging at high speed, high contrast and high signal-to-noise ratio. It is a further goal of the present invention to provide a device and method for imaging scattering objects that allows for both bright field and dark field imaging. It is a further object of the present invention to provide a device for imaging scattered objects that is simple and compact in construction.

[0010] At least one of the targets is a device for imaging scattering objects comprising: - a linear illumination module configured to generate illumination in the form of a line of light on an object within the field of view; - scanning means configured to move a line of light over an object in the field of view; - 2D sensor with rolling shutter; a synchronization module configured to operate in a first synchronization mode in which the time offset between the rolling shutter and the scanning means is zero and the sensor is configured to sense bright-field signals, and in a second synchronization mode in which the time offset between the rolling shutter and the scanning means is a determined offset other than zero and the sensor is configured to sense dark-field signals; and an image processing module configured to generate a bright-field image from the bright-field signal and a dark-field image from the dark-field signal; This is achieved using a device comprising: The imaging device according to the invention combines the advantages of bright-field and dark-field configurations of imaging devices.

[0011] The device according to the invention allows for both bright field and dark field imaging, and the two configurations are independent of each other: the device according to the invention can generate images in bright field only, dark field only, or both.

[0012] In bright-field imaging, the sequential exposure of lines of sensor pixels by the sensor's rolling shutter acts as a real-time spatial filter, limiting the rate at which multiply scattered photons spread across the field of view and, as a result, increasing the contrast of structures imaged in an illuminated region relative to the contrast achieved in the same region when the entire field of view is illuminated. By filtering out photons from non-illuminated regions within each region and sequentially illuminating different parts of the field of view, images of the field of view with improved contrast can be reconstructed. This reduction in background noise significantly increases detection sensitivity compared to unfiltered full-field configurations. No additional digital filtering is required during image processing. Images with high contrast and high signal-to-noise ratios can therefore be displayed in real time.

[0013] For a given exposure time, only a portion of the field of view is detected, while the other pixels of the sensor are rendered insensitive to light by a rolling shutter. To form an image of the entire field of view, lines of light are sequentially illuminated across the field of view, and the completed image is formed from all captured and filtered lines. To achieve the best compromise between contrast and acquisition speed, the device according to the present invention has an illumination line thickness that takes into account the scattering properties of the object and the time constraints of acquisition (e.g., eye movement). This can either cover only the illuminated area to detect photons backscattered by the object (bright-field detection), or cover an area adjacent to the illuminated area to detect multiply scattered photons refracted by weakly reflective structures (dark-field detection).

[0014] The device according to the present invention allows bright-field imaging. In a first synchronous mode configuration, the illumination is synchronized with a rolling shutter (or variable numerical aperture), so that only the exposed pixels at each time step receive light backscattered by the object, i.e., only pixels corresponding to the illuminated area are actually read. It is possible to image scattering objects and obtain reflection contrast images. In particular, bright-field imaging provides images of scattering structures with very good contrast. The imaging speed in this configuration is the same as in the full-field configuration, while spatial filtering increases the detection sensitivity. In the first synchronous mode, reflection contrast images can be obtained.

[0015] The device according to the present invention also allows imaging in dark field. In a second synchronous mode configuration, the illumination is synchronized with the rolling shutter so that the pixel exposed at each time step receives multiply scattered light rather than light backscattered by the object. The pixel actually read at each time step therefore corresponds to the non-illuminated area. In this way, the sensor captures only light that has been scattered several times. This configuration makes it possible to detect phase gradients and, as a result, to observe semi-transparent structures that are not visible in direct imaging (bright field). In this second synchronous mode, absorption and / or phase contrast images can be obtained.

[0016] According to an important aspect of the present invention, the device is configured to image an object or sample in both bright field and dark field and to utilize measurements obtained by the two synchronized modes. Switching from one synchronized mode to the other is achieved simply by adjusting the time offset between the sensor's rolling shutter and the scanning means, without requiring any mechanical manipulation by the operator. In this way, different types of full-field images of the same object or region of interest can be obtained from the same device, which can operate in different bright field and dark field configurations.

[0017] By synchronizing the sequential illumination of the object with the sensor's rolling shutter, selective line-by-line detection of the sensor is possible without loss of progress.

[0018] The device according to the invention allows easy switching from a bright-field configuration, which allows measurements of the reflection contrast of high-contrast structures, to a dark-field configuration, which allows measurements of the phase contrast and / or absorption using offset detection.

[0019] By projecting a line of light that scans the object to be imaged (e.g., the retina) at the same speed as the rolling shutter, and acquiring it with a fixed time offset between the shutter position and the illumination line, high-resolution images can be obtained even in the presence of aberrations. Adjusting the rolling shutter offset and exposure time allows for the phase gradient angle and signal-to-noise ratio to be changed. When switching from the first to the second mode, the sensor exposure time is ideally increased. For example, in bright field, the offset can be 0 and the exposure time can be 50 μs. To switch to dark field, the offset can be increased, for example, to 100 μs, and the exposure time can be increased to 200 μs.

[0020] Relative to state-of-the-art systems, the device according to the invention maintains the imaging speed of full-field systems without spatial filtering, while increasing detection sensitivity.

[0021] In the device according to the invention, illumination and detection are decoupled, i.e., independent of each other. Due to the presence of a two-dimensional sensor with a rolling shutter, the sensing line on the sensor is not fixed in the same position, and it is not necessary to "unscan" the sensing line, i.e., to move the scanning means in the opposite direction to nullify the set angle, as is the case with one-dimensional sensors. By simply delaying the time, it is easy to detect signals outside the illuminated area of ​​the object and obtain phase and absorption contrasts. This allows for fast switching from one synchronization mode to another.

[0022] The presence of a two-dimensional optical sensor (and the absence of a one-dimensional sensor) makes the device of the present invention robust with respect to nonlinearities of the scanning means, which may result from mechanical limitations of the scanning means, and optical aberrations introduced by the scanning means, which may cause artifacts and reduced spatial resolution, respectively. As a result of decoupling illumination and detection, nonlinearities of the light beam scanning means may cause a time delay between illumination and detection, resulting in loss of signal. In the absence of a signal, it is possible to directly determine the nonlinearities of the scanning system, which is not possible with confocal or line imaging. In confocal and line systems, illumination and detection are coupled, and nonlinearities of the scanning system result in artifacts that distort the structure of the imaged object. The time delay to switch from one mode to the other is typically a few microseconds. When imaging the eye, high speed imaging is particularly important to avoid distortion artifacts caused by eye movement. High sensitivity allows detection of less reflective structures such as individual cells and their organelles. The two-dimensional sensor may be, for example, a complementary metal oxide semiconductor (CMOS) camera. According to one embodiment, the synchronization module may be configured to operate in a first synchronization mode and a second synchronization mode for the entire field of view. Advantageously, the image processing module may be configured to generate a phase contrast image from the at least two dark field images.

[0023] In practice, it is possible to obtain an image with enhanced phase contrast by subtracting two dark-field images and then expressing a phase-contrast image using a positive or negative time offset between the shutter and the scanning means, respectively. Alternatively or additionally, the image processing module may be configured to generate an absorption contrast image from at least two dark field images.

[0024] In practice, it is possible to obtain an absorption contrast image by combining two dark field images using a positive or negative time offset between the shutter and the scanning means, respectively.

[0025] According to one embodiment, the device according to the invention may further comprise an adaptive optics module configured to correct static and / or dynamic imperfections incurred by the wavefront of the illumination passing through the object.

[0026] The adaptive optics module effectively corrects static and / or dynamic imperfections imparted to the wavefront by the object or sample and / or the optical surfaces of the device. This correction is particularly important when the object being imaged is moving and the wavefront is prone to rapidly evolving aberrations, as is the case with the human eye. This correction maintains the high resolution of the device even in the presence of imperfections or disturbances. The adaptive optics system also ensures that the illumination maintains its line shape and does not broaden, so that the direct signal of a broadened line does not obscure the phase signal and thereby limit the contrast obtainable with the device. The adaptive optics system also ensures optimal overlap between the size of the line of light and the rolling shutter. The adaptive optics module thus ensures both the correct size of the line of light on the imaged object and the image quality of the structure of interest. Advantageously, the illumination module may comprise a point light source combined with a line generator lens.

[0027] Alternatively, the illumination module may comprise a bulk light source combined with a line-shaped spatial filter or with a digital micromirror device (DMD). The light source may be an infrared source. Infrared wavelengths are particularly well suited to imaging biological tissue as they are only poorly absorbed by such tissue.

[0028] According to one embodiment, the light source may be a superluminescent diode (SLD). SLDs have the advantage of being relatively powerful (a few milliwatts) and highly directional. Furthermore, the short temporal coherence length of SLDs helps to reduce "spotting," i.e., granular intensity distribution. The line generator lens may be, for example, a cylindrical lens or a Powell lens. The Powell lens ensures an even intensity distribution along the line of generated light.

[0029] According to another aspect of the invention, a method for imaging a scattering object is proposed, which is realized by an imaging device comprising an illumination module, a scanning means, a two-dimensional sensor with a rolling shutter, a synchronization module and an image processing module, in particular by an imaging device according to the invention. The method comprises the following steps: - illuminating the object with a line of light within the field of view by a linear illumination module; - scanning a line of light over an object in the field of view by a scanning means;

[0030] - synchronizing the scanning means and the rolling shutter by a synchronization module with a time offset of zero in a first synchronization mode in which the sensor is configured to sense bright field signals, and with a determined non-zero time offset in a second synchronization mode in which the sensor is configured to sense dark field signals; - detecting bright field and / or dark field signals by a sensor; and generating a bright-field image from the bright-field signal and a dark-field image from the dark-field signal by an image processing module; Includes: Advantageously, the synchronization and detection steps can be performed alternately to generate a bright field image and successively a dark field image.

[0031] In fact, it is easy to switch from the first synchronous mode to the second synchronous mode by adjusting the time offset between the rolling shutter of the sensor and the scanning means. In this way, bright-field and dark-field images of the same object or the same part of the object can be obtained, combining the advantages of both modes to obtain more information from the imaged object. According to an advantageous embodiment, the method according to the invention may further comprise the step of generating a phase contrast image from the at least two dark field images. Alternatively or additionally, the method according to the present invention may further comprise the step of generating an absorption contrast image from the at least two dark field images. The method according to the invention may further comprise a step for correcting static and / or dynamic imperfections of the illumination wavefront passing through the object. To this end, an adaptive optics module can be implemented as described above.

[0032] The devices and methods according to the present invention can be used in many applications requiring imaging of scattering structures, objects or samples, such as biological or medical imaging, underwater imaging, imaging in haze or fog, imaging against a cloud background, or non-destructive testing of materials (e.g., glass fiber).

[0033] More specifically, for retinal imaging, the device and method according to the present invention allow for the observation of most structures of interest in the retina, whether they are strongly backscattering, such as cones and rods, or weakly scattering, such as ganglion cells and capillaries. The fast acquisition speeds achievable and the large imaged field of view satisfy the medical need to scan as wide an area as possible while limiting imaging time for the patient. The fast acquisition speeds also allow for the imaging of blood flow in the capillaries present in the retina. [Description of drawings and embodiments] Other advantages and features will become apparent upon examination of the detailed description of the entirely non-limiting embodiments and from the accompanying drawings. [Brief explanation of the drawings]

[0034] [Figure 1] 1A and 1B schematically illustrate non-limiting exemplary embodiments of an imaging device according to the present invention; [Figure 2] 1 shows a schematic diagram of an example of an illumination module of a device according to the invention; [Figure 3] 2 shows a schematic diagram of a first synchronization mode performed by a device according to the invention; [Figure 4] 3A and 3B illustrate a schematic representation of a second synchronization mode performed by a device according to the invention; [Figure 5] 1 shows an example of an image acquired with a device according to the invention; [Figure 6] 1A and 1B show examples of phase contrast images obtained with a method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0035] It is clearly understood that the embodiments described below are in no way limiting. In particular, all of the described variations and embodiments can be combined with each other if there are no technical obstacles to the combination. In the drawings, the same reference numbers may be used for features that are common to several drawings. FIG. 1 shows a schematic representation of a non-limiting embodiment of an imaging device according to the invention.

[0036] A device 1 can be implemented to perform the steps of the imaging method according to the present invention, as shown in Figure 1. Example embodiments of the device and method described in the present invention are described below. The device 1 comprises a linear illumination module 2, a scanning means 12 and a two-dimensional image sensor 14. The linear illumination module 2 generates a line-shaped illumination for the object 20 or sample to be imaged. An example of such an illumination module is shown in FIG.

[0037] The illumination module 2, as shown in Figure 2, comprises a collimated point light source 3 and a line generator lens 5. The line generator lens 5 is preferably a Powell lens. The lens 5 may also be a cylindrical lens. The light source 3 is a two-dimensional light source. Preferably, the light source has broadband emission and a short temporal coherence length. For example, the light source may emit light at a wavelength of 850 nm with a spectral bandwidth of 55 nm.

[0038] The output of the light source 3 can be fiberized and connected to a collimator (not shown). The output of the light source 3 can also be non-fiberized, in which case a collimator is not required. The light source 3 may be, for example, a superluminescent diode (SLD).

[0039] The beam 7 from the light source 3 passes through a Powell lens 5, which converts the parallel beam into a diverging beam with a linear cross section, which has an aperture angle in one direction but remains parallel in the orthogonal direction.

[0040] FIG. 1 shows the shape of the beam 7 emerging from the lighting module 2 in the two planes (x,z) and (y,z) and the linear cross section 21 in the plane (x,y).

[0041] 1, an achromatic doublet 6 placed at the output of the illumination module 2 limits the illumination field in the direction of divergence of the beam 7 to minimize power loss. The overlapping focal planes of the Powell lens 5 and the doublet 6 form a line of light at the image focal plane of the lens.

[0042] To ensure homogeneous illumination at the edge of the line of light, and as shown in Figure 1, a slit 13 can be placed in the image focal plane of the achromatic doublet 6, which focal plane is conjugate to the plane of the object or sample being imaged.

[0043] An illumination beam 7 emitted from illumination module 2 is directed towards object 20 using semi-transparent mirror 8, so that the object is illuminated with the resulting line of light. Illumination beam 7 is focused by lens 16 into or onto object 20 in the direction of the width of the line of light. Light 11 scattered by object 20 returns via semi-transparent mirror 8 and is detected by sensor 14. When implementing the device 1 for imaging the retina, the eye acts as the lens 16 .

[0044] The line of light is scanned within the field of view about the object 20 to be imaged using a scanning means. For this purpose, the illumination beam 7 is directed towards a galvanometer mirror 12, which directs the light beam 7 towards the object 20 at different angles (indicated by the double arrows in FIG. 1 ) to enable the line of light formed by the illumination module 2 to scan the entire field of view.

[0045] The scanning amplitude can be adjusted to provide a specific field of view. The scanning frequency of the galvo mirror is the same as the frequency of full-field image acquisition over the field of view. For example, images over the full field of view can be acquired at a frequency of 200 Hz for a typical 1000 pixel row.

[0046] The illumination of object 20 must be in the form of a line at the image focal plane, and galvanometer mirror 12 must be at the pupil plane so that the line of light can be repositioned only on the object by the angle of mirror 12. Two lenses 17, 18 arranged on either side of galvanometer mirror 12 allow the transition from the image plane to the pupil plane.

[0047] The two-dimensional sensor 14 of the device 1 according to the invention is configured to detect light 11 scattered by an object 20. The sensor 14 comprises a rolling shutter. This shutter is an electronically controllable shutter. In particular, the shutter width can be adjusted to define the number of rows or lines of pixels of the sensor 14 that are exposed. The exposure time per pixel row of the sensor 14 is constant. The speed of the rolling shutter is determined in particular by the frame rate of the sensor 14. The sensor 14 is, for example, a CMOS camera. The device 1 according to the invention comprises a synchronization module (not shown) for managing the synchronization mode between the scanning means and the rolling shutter of the sensor 14 .

[0048] The first and second synchronization modes are shown schematically in Figures 3 and 4, respectively. In Figures 3 and 4, the field of view of the sensor is shown by a matrix of 15 x 9 pixels 31. A line 32 of backscattered light on the sensor is shown with a grey background. A rolling shutter exposing three pixel rows is shown with a bold rectangle 33.

[0049] In the first synchronous mode, the time offset between the scanning means and the rolling shutter is zero. In this case, the sensor captures the area of ​​the object illuminated by the line of light and detects the light backscattered by the object. This is bright-field detection. The operating principle of the first synchronous mode is shown in FIG.

[0050] In a first synchronization mode, light in the form of a line directly backscattered from the object is detected by a row of pixels 31 of the sensor exposed by the rolling shutter. In order to synchronize the rolling shutter with the scanning means, and in particular with the galvanometer mirror, the generation and transmission of an electronic trigger signal of the transistor-transistor logic (TTL) type to the sensor can be synchronized with the generation and transmission of a linear voltage signal of the sawtooth wave type to the galvanometer mirror, for example by means of an analog output card.

[0051] In order to filter out multiply scattered and / or unfocused light and capture backscattered light, the shutter must have a width corresponding to the width of the line of light, and the center of this line must coincide with the center of the pixel row exposed by the shutter.

[0052] In the example shown in Figure 3, a line 32 of backscattered light illuminates three rows of pixels 31 on the sensor. The rolling shutter speed is t i The exposure of the first pixel row begins at time t0, which coincides with the occurrence of, for example, a trigger signal. The exposure of the next pixel row begins at time t i The same is repeated until the last pixel row in the image.

[0053] The exposure time is, for example, 50 μs for an acquisition frequency of 200 Hz. This corresponds to exposing each line for a time corresponding to 10 pixel rows. For an illumination line width of 10 pixel rows on the sensor 14, an exposure time of 50 μs is optimal. For a field of view of 1000 pixel rows, this corresponds to an acquisition time of 5.05 ms per image. A complete image is obtained when all pixels corresponding to the field of view, i.e., all 1000 rows, have been exposed, i.e., in 5.05 ms.

[0054] The galvanometer mirror returns to its initial position before a new image is acquired, or to a position that allows a given lead or delay to be applied between the line of light and the rolling shutter. The image obtained using this first synchronization mode is a reflection contrast image. An example of a reflectance contrast image is shown in Figure 5(a) ("bright field").

[0055] In the second synchronous mode, the time offset between the scanning means and the rolling shutter is non-zero. In this case, the sensor senses light signals from unilluminated areas of the object. This is light that is multiply scattered by the object, hence dark field detection. The operating principle of the second synchronous mode is shown in FIG. In the second synchronous mode, line-shaped light directly backscattered from the object is not detected by the sensor.

[0056] Here, the sensor's rolling shutter rotates relative to the galvanometer mirror (and thus the line of light 32 on the sensor) for a time 3t i 4, the rolling shutter 33 is in front of the illumination: in the plane of the drawing, the exposed pixels are below the pixels that are then illuminated.

[0057] A line 34 of backscattered light illuminates two rows 32 of pixels 31 on the sensor, with a rolling shutter speed of ti per row. Exposure of the first pixel row begins at time t0, which coincides, for example, with the occurrence of a trigger signal. Exposure of the next pixel row begins ti later, and so on until the last pixel row in the image. The rolling shutter also exposes two rows of pixels 35 that are offset by three rows from the illuminated row 32. Of course, it is also possible to delay the rolling shutter relative to the illumination. The image obtained by this second synchronous mode is a dark-field image, from which phase contrast and absorption images can be generated.

[0058] Two example dark-field images are shown in Figures 5(b) and 5(c). The two images correspond to two different temporal offsets between detection and illumination ("Offset 1" and "Offset 2"). Specifically, these are opposite temporal offsets.

[0059] In a device according to the present invention, the synchronization module is configured to operate in first and second synchronization modes while combining bright-field and dark-field imaging to improve the imaging quality of the device.

[0060] To obtain an enhanced phase-contrast image, two dark-field images, which are also phase-contrast images, can be subtracted. One of the two original images is captured with a positive time offset between the shutter and the scanning means, and the other original image is captured with a negative time offset. These time offsets preferably have the same value, only the sign changes.

[0061] To obtain an absorption contrast image, two dark-field images can be summed: one of the two original images is captured with a positive time offset between the shutter and the scanning means, and the other original image is captured with a negative time offset. Two examples of images obtained by combining two phase contrast images respectively are shown in Figures 5(d) and 5(e).

[0062] Figure 5(d) ("Phase contrast") shows the phase contrast image corresponding to the two subtracted phase contrast images. Specifically, image 5(d) corresponds to image 5(c) minus image 5(b).

[0063] Figure 5(e) ("Absorption Contrast") shows the absorption contrast image corresponding to the two phase contrast images summed together. Specifically, image 5(e) corresponds to the addition of images 5(b) and 5(c).

[0064] Scanning and synchronization parameters, such as the electronic trigger signal, the width and speed of the rolling shutter, or the various temporal offsets implemented, can be controlled via a user interface.

[0065] 1, the device 1 according to the invention further comprises an adaptive optics module 15. The illumination beam 7 passes through the adaptive optics module 15 before reaching the object 20.

[0066] Adaptive optics module 15 can improve image resolution by measuring and correcting aberrated wavefronts, for example due to wavefront deformations caused by the object being observed.

[0067] The adaptive optics module 15 includes a light source (known as an analytical light source), such as a fiberized superluminescent diode, a wavefront sensor, e.g., a Shack-Hartmann type, and a deformable mirror. The wavelength or spectral band of the analytical light source is preferably different from that of the light source 3 used for imaging; alternatively, a spectral filter may be used to separate the light sources. The light source beam is illuminated onto the object. The deformed wavefront of the light backscattered by the object is directed toward the deformable mirror and reflected back to the wavefront sensor, which measures the wavefront perturbations. The deformable mirror, acting as a wavefront corrector, is controlled in real time to correct the wavefront detected by the wavefront sensor. The wavefront is corrected for both the illumination beam heading towards the object and the beam scattered from the object, and the wavefront corrector is placed in the common illumination and imaging path. The imaging device according to the present invention further comprises an image processing module. The image processing module generates a bright field image from the images captured by the camera, i.e., from the lines captured over the entire field of view. The image processing module further generates a dark-field image from the multiply scattered photon signals for the entire field of view. In these two cases, the image processing module effectively corresponds to the read mode of the image sensor. Finally, the image processing module calculates or acquires an enhanced phase contrast or absorption contrast image as described above.

[0068] The image processing module comprises at least one computer, central processing unit or computing unit, microprocessor, and / or suitable software means.

[0069] An example of a method for imaging scattering objects is described below, which can be implemented, for example, by an imaging device according to the embodiment described with reference to FIGS. The method according to this embodiment comprises the following steps: - illuminating the object with a line of light within the field of view by a linear illumination module; - scanning a line of light over an object in the field of view by a scanning means;

[0070] - synchronizing the scanning means and the rolling shutter in a first synchronization mode with a zero time offset by a synchronization module in order to detect a bright field signal using the sensor and to obtain a bright field image using an image processing module. Includes: The acquired bright field image can then be optimized in terms of image quality to find the correct temporal offset between the line scan and the rolling shutter.

[0071] If the object being imaged is the retina, this step is important to ensure that the imaging parameters are correct, especially that the photoreceptors can be imaged in the correct plane, which also allows for setting the optimal temporal offset for dark-field imaging.

[0072] In particular, in bright-field mode, this optimization step ensures that the rolling shutter is always centered on the line of light and that the width of the rolling shutter is the same as the width of the line. This condition is met when the signal in the resulting bright-field image is uniform and maximal across the entire image. The time delay is zero in this case.

[0073] Optimal settings in the bright-field imaging mode allow for the introduction of a controlled temporal offset for the phase-contrast imaging obtained from the dark-field imaging mode.

[0074] Thus, if the bright-field mode is set up correctly, applying the same temporal offset value early or late effectively results in a rolling shutter offset forward (early) or backward (late) with the same spatial offset at each instant, symmetrical about the center of the line of light. Without this symmetry, the symmetry in dark-field mode between the image obtained with the early rolling shutter and the image obtained with the late rolling shutter would be lost. This optimization or adjustment step can be performed during the calibration stage of the device.

[0075] Optionally, an adaptive optics module can be implemented as described above to correct for static and / or dynamic imperfections in the illumination wavefront passing through the object or sample and to ensure a well-defined line of light on the object and high imaging resolution.

[0076] In a subsequent step, a synchronization module can be used to apply a positive time offset to the scan by synchronizing the scanning means and the rolling shutter with a positive time offset in a second synchronization mode in order to detect dark field signals using a sensor and generate a dark field image using an image processing module. The acquired dark field image can be optimized in terms of image quality to find the correct temporal offset.

[0077] In practice, in dark-field mode, the offset required to obtain optimal contrast will depend on the structure being observed. To observe the change in contrast and sharpness of the imaged structure based on the temporal offset, a parameter study can be performed by acquiring a series of images of the same area with the same exposure time while varying the temporal offset between the illumination line and the rolling shutter. From this data, the optimal temporal offset that maximizes the contrast of the structure of interest can be determined. The same steps can be performed to obtain one or more dark field images with a positive temporal offset and a negative temporal offset of the same value. Between steps to acquire a dark-field or bright-field image, it may be useful to switch back to bright-field or dark-field mode, respectively.

[0078] For example, when acquiring an eye, the eye is prone to gaze at a target and involuntary movements that cause a relative offset between the acquired images. Therefore, the images must be recalibrated in post-processing. In that case, it may be easier to estimate the relative offset between images from bright-field images than from dark-field images. The estimated offset for each bright-field image can also be used to extrapolate the offset for the dark-field image that follows the offset just estimated for the bright-field image.

[0079] In another example, it may be useful to acquire images with absorption contrast and phase contrast for certain retinal structures, such as photoreceptors. In this case, it is possible to sequence image acquisitions in bright field (e.g., 100 times) followed by image acquisitions in dark field. Alternatively, image acquisitions may alternate between bright field and dark field. The advantage of this alternative is that the same structures are imaged very close together in time, making it possible to study the dynamics of retinal cells.

[0080] According to one embodiment, the method further comprises generating a phase contrast image from the at least two dark field images by subtracting an image acquired at a positive temporal offset and an image acquired at a negative temporal offset from each other. By way of example, Figure 6 shows a phase contrast image obtained with a method according to the above embodiment, which shows blood vessels, capillaries and fibres.

[0081] When alternating between dark-field modes corresponding to positive and negative time offsets, two successive acquisitions can be subtracted to obtain a "split detection" image sequence with maximum phase contrast. If the initial sequence of alternating dark-field modes with positive and negative time offsets is, say, 800 fps, the effective rate of the "split detection" image sequence obtained from two successive images from the initial sequence is half that, or 400 fps.

[0082] If the method according to the invention is used for retinal imaging, it is important to ensure that the light source of the illumination module, and possibly the light source of the adaptive optics module, is eye-safe when switched on.

[0083] Naturally, the invention is not limited to the examples described above, and many adjustments can be made to these examples without departing from the scope of the invention.

Claims

1. A device (1) for imaging a scattering object (20), comprising: a linear illumination module (2) configured to generate illumination in the form of a line of light on an object (20) in the field of view; - scanning means (12) configured to move a line of light over an object (20) in the field of view; - a two-dimensional sensor with a rolling shutter (14); a synchronization module configured to operate in a first synchronization mode in which the sensor (14) is configured to sense bright field signals and the time offset between the rolling shutter and the scanning means is zero, and in a second synchronization mode in which the sensor (14) is configured to sense dark field signals and the time offset between the shutter and the scanning means is a determined offset other than zero; and an image processing module configured to generate a bright-field image from the bright-field signal and a dark-field image from the dark-field signal; A device comprising:

2. 2. The device (1) according to claim 1, characterized in that the image processing module is configured to generate a phase contrast image from at least two dark field images.

3. The device (1) according to any one of claims 1 to 2, characterized in that the image processing module is configured to generate an absorption contrast image from at least two dark field images.

4. The device (1) according to any one of claims 1 to 3, characterized in that it further comprises a adaptive optics module (15) configured to correct static and / or dynamic defects incurred by the wavefront of the illumination passing through the object (20).

5. The device (1) according to any one of claims 1 to 4, characterized in that the lighting module (2) comprises an infrared light source (3).

6. The device (1) according to any one of claims 1 to 5, characterized in that the lighting module (2) comprises a point light source (3) combined with a line generator lens (5).

7. The device (1) according to any one of claims 1 to 6, characterized in that the sensor (14) is a complementary metal oxide semiconductor sensor.

8. A method for imaging a scattering object (20) realized by an imaging device comprising a linear illumination module (2), a scanning means, a two-dimensional sensor (14) with a rolling shutter, a synchronization module, and an image processing module, comprising the following steps: - illuminating the object (20) with a line of light in the field of view by the illumination module (2); - scanning a line of light over an object (20) in the field of view by a scanning means; - synchronizing the scanning means and the rolling shutter by means of a synchronization module with a time offset of zero in a first synchronization mode in which the sensor (14) is configured to sense bright field signals, and with a determined non-zero time offset in a second synchronization mode in which the sensor (14) is configured to sense dark field signals; - detecting bright field and / or dark field signals by a sensor (14); and generating a bright-field image from the bright-field signal and a dark-field image from the dark-field signal by an image processing module; A method comprising:

9. 9. The method of claim 8, wherein the synchronization and detection steps are performed alternately to generate a bright-field image and successively generate a dark-field image.

10. 10. The method of claim 8 or 9, further comprising the step of generating a phase contrast image from at least two dark field images.

11. The method according to any one of claims 8 to 10, further comprising the step of generating an absorption contrast image from at least two dark field images.

12. Method according to any one of claims 8 to 11, characterized in that it further comprises the step of correcting static and / or dynamic imperfections of the illumination wavefront passing through the object (20).

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