WO2014193310A1

WO2014193310A1 - Optical imaging device and method of controlling the same

Info

Publication number: WO2014193310A1
Application number: PCT/SG2014/000249
Authority: WO
Inventors: Nanguang Chen
Original assignee: National University Of Singapore
Priority date: 2013-05-31
Filing date: 2014-05-30
Publication date: 2014-12-04

Abstract

According to embodiments of the present invention, an optical imaging device is provided. The optical imaging device includes an optics arrangement configured to generate an illumination pattern that is elongate to illuminate a section of a sample to be imaged along a plurality of axial-lines within the section of the sample, wherein the optics arrangement is further configured to form an interference signal from each return light of respective return lights from respective axial-lines of the section of the sample illuminated by the illumination pattern, and a reference light, and an area detector configured to receive the interference signals for generating an image corresponding to the section of the sample, wherein a respective interference signal is received by a respective portion of the area detector. According to further embodiments of the present invention, a method of controlling an optical imaging device is also provided.

Description

OPTICAL IMAGING DEVICE AND METHOD OF CONTROLLING THE SAME

Cross-Reference To Related Application

[0001] This application claims the benefit of priority of US provisional application No. 61/829,411, filed 31 May 2013, the content of it being hereby incorporated by reference in its entirety for all purposes.

Technical Field

[0002] Various embodiments relate to an optical imaging device and a method of controlling an optical imaging device.

Background

[0003] Optical coherence tomography (OCT) is an optical signal acquisition and processing method. It captures micrometer-resolution, two-dimensional or three- dimensional images from within optical scattering media (e.g. biological tissue).

[0004] Optical coherence tomography is an interferometric technique, typically employing near-infrared light. The use of relatively long wavelength light allows it to penetrate into the scattering medium. Confocal microscopy, another similar technique, typically penetrates less deeply into the sample. Commercially available optical coherence tomography systems are employed in diverse applications, including diagnostic medicine, notably in ophthalmology where it can be used to obtain detailed structural information from within the retina. Recently, it has also begun to be used in interventional cardiology to help diagnose coronary artery disease.

[0005] Typical OCT implementations include time-domain OCT and spectral-domain (frequency-domain) OCT. In time-domain OCT, the path length of the reference arm is translated longitudinally in time. A property of low coherence interferometry is that interference, i.e. the series of dark and bright fringes, is only achieved when the path difference lies within the coherence length of the light source. This interference is called auto correlation in a symmetric interferometer (both arms have the same reflectivity), or cross-correlation in the common case. The envelope of this modulation is related to the depth resolved reflectivity. In spectral-domain OCT, the broadband interference is acquired with spectrally separated detectors (either by encoding the optical frequency in time with a spectrally scanning source or with a dispersive detector, like a grating and a linear detector array). Due to the Fourier relation the depth scan can be immediately calculated by a Fourier-transform from the acquired spectra, without movement of the reference arm. This feature improves the imaging speed compared to the time-domain method, while the reduced losses during a single scan improve the signal to noise proportional to the number of detection elements.

[0006] Both time-domain and spectral-domain OCT need lateral scanning of the sample beam. Focusing the sample beam to a point on the surface of the sample under test, and recombining the reflected light with the reference will yield an interferogram with sample information corresponding to a single A-scan (along Z-axis). Scanning of the sample is generally accomplished by scanning the light on the sample. A linear scan will yield a two-dimensional data set corresponding to a cross-sectional image (X-Z axes scan).

Summary [0007] According to an embodiment, an optical imaging device is provided. The optical imaging device may include an optics arrangement configured to generate an illumination pattern that is elongate to illuminate a section of a sample to be imaged along a plurality of axial-lines within the section of the sample, wherein the optics arrangement is further configured to form an interference signal from each return light of respective return lights from respective axial-lines of the section of the sample illuminated by the illumination pattern, and a reference light, and an area detector configured to receive the interference signals for generating an image corresponding to the section of the sample, wherein a respective interference signal is received by a respective portion of the area detector.

[0008] According to an embodiment, a method of controlling an optical imaging device is provided. The method may include generating an illumination pattern that is elongate, illuminating, with the illumination pattern, a section of a sample to be imaged along a plurality of axial-lines within the section of the sample, forming an interference signal from each return light of respective return lights from respective axial-lines of the section of the sample illuminated by the illumination pattern, and a reference light, and receiving the interference signals for generating an image corresponding to the section of the sample, wherein a respective interference signal is received by a respective portion of an area detector of the optical imaging device.

Brief Description of the Drawings [0009] In the drawings, like reference characters generally refer to like parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which:

[0010] FIG. 1A shows a schematic cross-sectional view of an optical imaging device, according to various embodiments.

[0011] FIG. IB shows a flow chart illustrating a method of controlling an optical imaging device, according to various embodiments.

[0012] FIG. 2A shows a schematic view of an optical imaging device, according to various embodiments.

[0013] FIG. 2B shows a prototype set-up of a scan-free optical coherence tomography (OCT) system, according to various embodiments.

[0014] FIG. 3 shows a schematic diagram illustrating a process of obtaining a raw image and a reconstructed optical coherence tomography (OCT) image of a sample imaged by the optical imaging device of various embodiments.

[0015] FIG. 4A shows a raw image of a sample obtained by the optical coherence tomography (OCT) system of various embodiments.

[0016] FIG. 4B shows an intensity profile measured along the dashed horizontal line indicated in FIG. 4A.

[0017] FIG. 5 shows a reconstructed optical coherence tomography (OCT) of the sample corresponding to the raw image of FIG. 4A. The scale bar represents 200 microns (μηι). [0018] FIG. 6 shows a cross-sectional image of an Oyster Plant leaf obtained using the optical coherence tomography (OCT) system of various embodiments. The scale bar represents 200 microns (μπι). Detailed Description

[0019] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0020] Embodiments described in the context of one of the methods or devices are analogously valid for the other methods or devices. Similarly, embodiments described in the context of a method are analogously valid for a device, and vice versa.

[0021] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and/or combinations and/or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0022] In the context of various embodiments, the articles "a", "an" and "the" as used with regard to a feature or element include a reference to one or more of the features or elements.

[0023] In the context of various embodiments, the phrase "at least substantially" may include "exactly" and a reasonable variance.

[0024] In the context of various embodiments, the term "about" as applied to a numeric value encompasses the exact value and a reasonable variance. [0025] As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

[0026] As used herein, the phrase of the form of "at least one of A or B" may include A or B or both A and B. Correspondingly, the phrase of the form of "at least one of A or B or C", or including further listed items, may include any and all combinations of one or more of the associated listed items.

[0027] Various embodiments may relate to non-invasive optical imaging of biological tissues.

[0028] Various embodiments may relate to optical coherence tomography (OCT), for example scan-free optical coherence tomography. For example, various embodiments may provide an OCT implementation that does not need a scanning device to acquire 2D (two-dimensional) cross-sectional images.

[0029] Optical coherence tomography (OCT) is a coherence-gating based imaging technique that may provide a penetration depth of up to about 3 mm in biological tissues. Conventional OCT systems use a scanning device to shift the sample beam laterally so as to obtain cross-sectional images. However, lateral scanning ultimately limits the imaging speed of OCT. It is also challenging to include a scanner in an endoscopic OCT. As compared to conventional OCT systems, various embodiments enable an implementation of OCT which may capture a cross-sectional image with an area camera in a single exposure. As beam scanning is not needed, the acquisition time for one image frame may be reduced to as little as a few nanoseconds, which may be desirable for in vivo imaging applications where motion artifact may be a big concern. In addition, the approach of various embodiments may greatly simplify the design of endoscopic OCT and may enable miniaturization of the imaging catheter.

[0030] The optical imaging device (e.g. optical coherence tomography (OCT) device or system) of various embodiments may provide the following features as compared to existing OCT techniques.

[0031] (1) Imaging speed : Most OCT systems need lateral scanning of the sample beam to obtain cross-sectional images. The scanner resonance frequency is typically smaller than a few kilohertz, which set the ultimate limit of frame rate to around 1000 frames per second. In contrast, various embodiments may enable 2D (two-dimensional) cross- sectional image acquisition in a single snap shot. In embodiments where a pulsed light source is combined with a high-speed camera (ns (nanosecond) electronic shutter), an OCT image may be captured within a few nanoseconds. Such an ultra-high speed opens doors to many new applications.

[0032] (2) Miniaturization : Endoscopic OCT requires an imaging catheter small enough to be inserted into hollow human organs such as blood vessels and the gastrointestinal tract (GI tract). A usual problem in catheter design is that a scanning device has to be included, making it difficult to minimize the overall size of the catheter. In contrast, various embodiments may eliminate the need for a scanner and may be immune to motion artifacts due to its high speed. As a result, it is highly competitive to be employed in endoscopic OCT.

[0033] (3) Cost : Popular swept-source and spectrum domain OCT systems cost more than USD 100k due to the expensive light source, special detectors, and scanning devices. The optical imaging device of various embodiments is much simplified and does not require a scanner. There are also a wide range of low cost light sources and image sensors that may be suitably employed in various embodiments, making it possible to build a very low cost imaging device or system.

[0034] The optical imaging device (e.g. optical coherence tomography (OCT) device or system) of various embodiments may be employed in a wide range of applications including but not limited to ophthalmology imaging, skin imaging, gastrointestinal tract (GI tract) imaging and blood vessel imaging.

[0035] FIG. 1A shows a schematic cross-sectional view of an optical imaging device 100, according to various embodiments. The optical imaging device 100 includes an optics arrangement 101 configured to generate an illumination pattern 130 that is elongate to illuminate a section 121 of a sample 120 to be imaged along a plurality of axial-lines (e.g. three axial-lines 123a, 123b, 123c are shown) within the section 121 of the sample 120, wherein the optics arrangement 101 is further configured to form an interference signal 140 from each return light 131 of respective return lights 131 from respective axial-lines 123a, 123b, 123c of the section 121 of the sample 120 illuminated by the illumination pattern 130, and a reference light, and an area detector 129 configured to receive the interference signals 140 for generating an image corresponding to the section 121 of the sample 120, wherein a respective interference signal 140 is received by a respective portion of the area detector 129.

[0036] In other words, an optical imaging device 100 may be provided. The optical imaging device 100 may include an optics arrangement 101, which may for example include an assembly of optical components or elements. The optics arrangement 101 may generate an illumination pattern 130 that is elongate, or in other words, an elongate illumination pattern, which may be employed to illuminate a section (e.g. a cross- section) 121 of a sample 120 to be imaged. The illumination pattern 130 may illuminate the section 121 along a plurality of axial-lines 123a, 123b, 123c, along a direction into or through the sample 120, as represented by the double-headed arrow 160. An enlarged view of some axial-lines 123a, 123b, 123c within the section 121 illuminated by the illumination pattern 130 are illustrated in FIG. 1A. Therefore, the illumination pattern 130 may illuminate sub-surface portions or interior portions of the sample 120, along axial-lines 123a, 123b, 123c.

[0037] The illumination pattern 130, being elongate, may mean a pattern extended in at least one dimension, for example a height of the illumination pattern 130 and/or a width of the illumination pattern 130. One dimension of the illumination pattern 130 may be larger than another dimension of the illumination pattern 130, for example the illumination pattern 130 may have a height that is larger compared to its width.

[0038] In the context of various embodiments, the illumination pattern 130 may include a plurality of beamlets, where a respective beamlet may be associated with a respective axial-line 123a, 123b, 123c, for example a respective beamlet may illuminate the sample along a respective axial-line 123a, 123b, 123c within the section 121.

[0039] In the context of various embodiments, a width of the illumination pattern 130 may be in a range of between about 4 μιη and about 20 μπι, for example, between about 4 μηι and about 10 μιη, between about 4 μπι and about 6 μηα, or between about 10 μπι and about 20 μιη, while a height (or length) of the illumination pattern 130 may be between 500 and 2000 times larger than the width of the illumination pattern 130, for example between 500 and 1500 times larger, between 500 and 1000 times larger, or between 1000 and 2000 times larger. This may mean that the illumination pattern 130 may include between 500 and 2000 beamlets combined as a linear array. [0040] In the context of various embodiments, the term "axial-line", also known as a-line or A-line, and their corresponding plural forms, may be defined in a direction from a surface of a sample through which an illumination pattern is incident on the sample, into the sample. This may mean that axial-line(s) may be defined along a direction of incidence of the illumination pattern on the sample. As a non-limiting example, an axial- line may be defined as a line along a depth direction of the sample.

[0041] In various embodiments, the illumination pattern 130 may provide a sheet illumination of the section 121 of the sample 120. For example, the illumination pattern 130 may illuminate a cross-section 121 of the sample 120.

[0042] In various embodiments, the illumination pattern 130 may illuminate the section 121 of the sample 120 in one or single exposure. This may mean that the plurality of axial-lines 123a, 123b, 123c may be illuminated by the illumination pattern 130 during or within one or single illumination or exposure. Further, this may mean that the plurality of axial-lines 123a, 123b, 123c may be simultaneously illuminated by the illumination pattern 130.

[0043] In various embodiments, the optics arrangement 101 may be further configured to form an interference signal (or spectrum) 140 from each return light 131 of respective return lights 131 from respective axial-lines 123a, 123b, 123c of the section 121 of the sample 120 illuminated by the illumination pattern 130, and a reference light (not shown).

[0044] In various embodiments, a respective return light 131 may originate from the section 121 along a respective axial-line 123a, 123b, 123c. Each respective return light 131 may include light reflected and/or backscattered from the section 121 along a corresponding axial-line 123a, 123b, 123c. Therefore, a respective return light 131 may include information of the section 121 corresponding to a respective axial-line 123a, 123b, 123c.

[0045] In various embodiments, a light may be reflected from a reference point or plane (e.g. by means of a reflector or a mirror) to form the reference light.

[0046] In various embodiments, the illumination pattern 130 and the return lights 131 may propagate along an optical path defined in a sample arm or sample path of the optical imaging device 100 while the reference light may propagate along an optical path defined in a reference arm or reference path of the optical imaging device 100, where the sample arm and the reference arm may define an interferometer or an interferometric arrangement. An interference signal 140 may be formed by means of interference between each return light 131 and the reference light. The interference signals 140 may be formed during or within one or single illumination or exposure.

[0047] The optical imaging device 100 may further include an area detector 129 configured to receive the interference signals 140, formed between the respective return lights 131 and the reference light, for generating an image (e.g. a cross-sectional image) corresponding to the section 121 of the sample 120, wherein a respective interference signal 140 may be received by a respective portion of the area detector 129. Each respective portion of the area detector 129 may include a set of detecting elements (e.g. pixels) such that a respective interference signal 140 may be received or captured by a plurality of detecting elements. The respective portion of the area detector 129 may correspond to a respective axial-line of the plurality of axial-lines 123a, 123b, 123c within the section 121 of the sample 120. Respective portions of the area detector 129 may be different portions of the area detector 129.

[0048] In various embodiments, the interference signals 140 may be received simultaneously by the area detector 129. The area detector 129 may capture the interference signals 140 during or within one or single illumination or exposure. In this way, a two-dimensional (2D) image of the section 121 of the sample 120 may be generated in one or single exposure.

[0049] The area detector 129 may be a two-dimensional detector or a detector capable of generating a two-dimensional image. The area detector 129 may be capable of receiving the respective interference signals 140 on respective portions of the area detector 129 for generating a two-dimensional image of the section 121 of the sample 120.

[0050] The area detector 129 may be composed of detecting elements, for example arranged in rows and columns. In various embodiments, a respective portion of the area detector 129 may include a respective set of detecting elements, e.g. a row of detecting elements or a column of detecting elements.

[0051] In the context of various embodiments, the optical imaging device 100 may enable a two-dimensional (2D) cross-sectional image acquisition of a sample 120 in a single snap shot or exposure. This may mean that the optical imaging device 100 may enable generation of an image (e.g. a cross-sectional image) corresponding to a section 121 of the sample 120 from one or single exposure of the section 121 of the sample 120 by an illumination pattern 130.

[0052] In various embodiments, the illumination pattern 130 may be or may include a linear (or line) illumination pattern.

[0053] In various embodiments, the optics arrangement 101 may include a grating arranged to spectrally disperse each interference signal 140 to be received by the area detector 129. The respective spectrally dispersed interference signals may be received by respective portions of the area detector 129.

[0054] In various embodiments, the optics arrangement 101 may include an imaging lens (e.g. an objective lens or a focusing lens) arranged to focus the interference signals 140 onto the area detector 129. The imaging lens may be arranged between the grating and the area detector 129.

[0055] In various embodiments, the area detector 129 may include or may be a camera (e.g. an area camera) capable of receiving the respective interference signals 140 on respective portions of the camera for generating a two-dimensional image of the section 121 of the sample 120.

[0056] In various embodiments, the optics arrangement 101 may include a beam splitter arranged to receive and split a light into a first light portion (e.g. a sample beam) to define the illumination pattern 130 for illuminating the section 121 of the sample 120, and a second light portion (e.g. a reference beam) from which the reference light may be derived. The beam splitter may be a polarization independent beam splitter. In various embodiments, each return light 131 of the respective return lights 131 and the reference light may interfere with each other at the beam splitter to form an interference signal 140.

[0057] In various embodiments, the optics arrangement 101 may include focusing optics (e.g. at least one objective lens) for focusing or forming the illumination pattern 130 onto the sample 120 for illuminating the section 121 of the sample 120. The focusing optics may also receive the respective return lights 131.

[0058] In various embodiments, the optics arrangement 101 may include a collimation lens configured to generate a collimated light from which the illumination pattern 130 may be formed or derived. The optics arrangement 101 may further include a condenser arranged to receive and concentrate light to be received by the collimation lens. In various embodiments, the condenser may be defined by an arrangement of lenses. The condenser may include at least one of a spherical lens or a cylindrical lens.

[0059] In various embodiments, the optics arrangement 101 may further include a slit arranged between the collimation lens and the condenser. The slit may be arranged at a position corresponding to a focal length of the condenser.

[0060] In various embodiments, the optics arrangement 101 may include a spatial filter arranged to reject at least some lights originating from parts of the sample 120 not covered by the illumination pattern 130. In this way, the spatial filter may reject out-of- focus light from the sample 120. In various embodiments, the spatial filter may spatially filter the interference signals 140 to reject at least some lights originating from parts of the sample 120 not covered by the illumination pattern 130. This may mean that out-of- focus lights from the sample 120 may be removed from the interference signals 140. In various embodiments, the spatial filter may include a lens and a slit. Nevertheless, such parts of the sample not covered by the illumination pattern 130 may be illuminated by scattered light.

[0061] In various embodiments, the optical imaging device 100 may further include a light source, wherein the optics arrangement 101 may be configured to generate the illumination pattern 130 based on a light produced by the light source.

[0062] In various embodiments, the light source may include or may be a pulsed light source.

[0063] In various embodiments, the light source may include or may be a broadband light source. The broadband light source may include a short arc lamp or an array of light emitting diodes (LEDs).

[0064] In various embodiments, an array of optical fibers may be optically coupled to the light source (e.g. a broadband light source). Light from each optical fiber may provide or define a point source. This may generate an illumination pattern 130 having or defined by an array of point sources (e.g. a linear array of point source).

[0065] In various embodiments, the light source may include or may be an array of light emitting diodes (LEDs). Each LED may provide or define a point source. This may generate an illumination pattern 130 having or defined by an array of point sources (e.g. a linear array of point source).

[0066] In various embodiments, the optical imaging device 100 may further include a processor (or a processing circuit) configured to obtain information (e.g. spectral information) corresponding to the section 121 of the sample 120 from the interference signals 140 for generating the image corresponding to the section 121 of the sample 120. The processor may be configured to perform inverse Fourier transform on the interference signals 140. The processor may be configured to perform inverse Fourier transform on each interference signal 140.

[0067] In the context of various embodiments, the illumination pattern 130 may define an array of independent point sources (e.g. a linear array of independent point sources).

[0068] In the context of various embodiments, the illumination pattern 130 may include a plurality of beamlets, a respective beamlet of the plurality of beamlets illuminating the section 121 of the sample 120 along a respective axial-line 123a, 123b, 123c of the plurality of axial-lines 123a, 123b, 123c. The beamlets may be aligned parallel to each other. The beamlets may be incident at least substantially perpendicularly to the section 121 of the sample 120.

[0069] In the context of various embodiments, the optical imaging device 100 may be an optical coherence tomography (OCT) device or system.

[0070] In the context of various embodiments, the optical imaging device 100 may be an endoscopic OCT device.

[0071] In the context of various embodiments, the optical imaging device 100 may be free of any scanning device. Therefore, the optical imaging device 100 may be a scan- free optical coherence tomography (OCT) device or system.

[0072] In the context of various embodiments, the optical imaging device 100 may be free of a scanning device in an optical path of the illumination pattern 130. For example, the optical imaging device 100 may be free of a scanning device that may effect lateral scanning of the illumination pattern 130 across the sample 120. This may mean that the optical imaging device 100 may be free of a scanning device in a sample arm of the optical imaging device 100. Therefore, the optical imaging device 100 may be a scan- free optical coherence tomography (OCT) device or system. [0073] FIG. IB shows a flow chart 150 illustrating a method of controlling an optical imaging device, according to various embodiments.

[0074] At 152, an illumination pattern that is elongate is generated.

[0075] At 154, a section of a sample to be imaged is illuminated with the illumination pattern along a plurality of axial-lines within the section of the sample.

[0076] At 156, an interference signal is formed from each return light of respective return lights from respective axial-lines of the section of the sample illuminated by the illumination pattern, and a reference light.

[0077] At 158, the interference signals are received for generating an image corresponding to the section of the sample, wherein a respective interference signal is received by a respective portion of an area detector of the optical imaging device.

[0078] In various embodiments, at 152, a linear illumination pattern may be generated.

[0079] In various embodiments, each interference signal to be received by the area detector may be spectrally dispersed.

[0080] In various embodiments, the interference signals may be focused onto the area detector.

[0081] In various embodiments, the area detector may include a camera capable of receiving the respective interference signals on respective portions of the camera for generating a two-dimensional image of the section of the sample.

[0082] In various embodiments, the method may include receiving a light, for example from a light source, and splitting the light into a first light portion to define the illumination pattern for illuminating the section of the sample, and a second light portion from which the reference light may be derived.

[0083] In various embodiments, the illumination pattern may be focused onto the sample for illuminating the section of the sample.

[0084] In various embodiments, a collimated light may be generated, wherein the illumination pattern may be generated from the collimated light. Light may be received and concentrated from which the collimated light may be generated. The concentrated light may be filtered.

[0085] In various embodiments, the method may further include spatially filtering (or rejecting) at least some lights (e.g. out-of-focus lights) originating from parts of the sample not covered by the illumination pattern. For example, the method may include spatially filtering the interference signals to reject at least some lights originating from parts of the sample not covered by the illumination pattern. Such parts of the sample nevertheless may be illuminated by scattered light.

[0086] In various embodiments, the method may further include obtaining information (e.g. spectral information) corresponding to the section of the sample from the interference signals for generating the image corresponding to the section of the sample. For example, inverse Fourier transform may be performed on the interference signals to obtain the information.

[0087] In various embodiments, the method may be free of scanning the illumination pattern across the sample. This may mean that the method may be free of lateral scanning of the illumination pattern across the sample.

[0088] In various embodiments, the illumination pattern may include a plurality of beamlets, a respective beamlet of the plurality of beamlets illuminating the section of the sample along a respective axial-line of the plurality of axial-lines.

[0089] While the method described above is illustrated and described as a series of steps or events, it will be appreciated that any ordering of such steps or events are not to be interpreted in a limiting sense. For example, some steps may occur in different orders and/or concurrently with other steps or events apart from those illustrated and/or described herein. In addition, not all illustrated steps may be required to implement one or more aspects or embodiments described herein. Also, one or more of the steps depicted herein may be carried out in one or more separate acts and/or phases.

[0090] FIG. 2A shows a schematic view of an optical imaging device 200a, according to various embodiments, illustrating a non-limiting example of a scan-free optical coherence tomography (OCT) device or system.

[0091] The principle of the scan-free optical coherence tomography system of various embodiments will now be described with reference to the optical imaging device 200a of FIG. 2A. The optical imaging device 200a includes a light source 202 which may generate a source beam or light 204. The light source 202 may be a broadband light source, for example a short arc lamp or LED (light emitting diode). The optical imaging device 200a may include a condenser (CD) 206 arranged to receive the source beam 204. The condenser 206 may be a spherical lens, or a cylindrical lens or a combination of lenses (e.g. one or more spherical lenses and/or one or more cylindrical lenses). The optical imaging device 200a may further include a first slit (SL1) 208. The slit 208 may be arranged adjacent to the condenser 206 such that the condenser 206 may be used to maximise or optimise the light power, corresponding to the beam source 204, squeezing or passing through the slit 208. The source beam 204 passing through the slit 208 may be spatially incoherent and may be considered as a linear array of independent point sources. The source beam 204 may then be collimated by a lens (LI) (e.g. a collimation lens) 210 and directed towards a beam splitter (BS) 212. The beam splitter 212 may be a polarization independent beam splitter.

[0092] The source beam 204 may be split by the beam splitter 212 into a sample beam 230 and a reference beam 236. The sample beam 230 may define an illumination pattern for illuminating a sample to be imaged. The sample beam 230 may be provided to and through a sample arm 232 of the optical imaging device 200a, while the reference beam 236 may be provided to and through a reference arm 238 of the optical imaging device 200a. The sample arm 232 and the reference arm 238 may define an interferometer or an interferometric arrangement.

[0093] The reference beam 236 may be focused by a lens (e.g. an objective lens) (L3) 214 onto a mirror (M) 216, which may reflect the reference beam 236 to provide a reflected reference beam (or a reference light) 237 back to the beam splitter 212. The reference light 237 may propagate through the lens 214 towards the beam splitter 212. The reference beam 236, split from the source beam 204 by the beam splitter 212, and the reference light 237, being the reference beam 236 reflected by the mirror 216, may propagate through an at least substantially or identical optical path, but in opposite directions.

[0094] The sample beam 230 may be focused by a lens (e.g. an objective lens) (L2) 218 so as to generate a sheet illumination onto a sample (e.g. a tissue sample) 220 to be imaged. The sample beam 230 may be employed to illuminate a section of the sample 220 along a plurality of axial-lines, along a direction represented by the double- headed arrow 260, within the section of the sample 220. [0095] Interaction between the sample beam 230 and the section of the sample 220 being illuminated may result in backscattered and/or reflected light being generated. This may mean that return lights 231 , which may include light reflected and/or light scattered from the sample section along a plurality of axial-lines under illumination by the sample beam 230, may be generated. A respective return light 231 may be associated with the sample section along a respective axial-line. The return lights 231 may be collected by the lens 218 and directed towards the beam splitter 212. The sample beam 230, split from the source beam 204 by the beam splitter 212, and the return lights 231, may propagate through an at least substantially or identical optical path, but in opposite directions.

[0096] The return lights 231 may be combined with the reference light 237 at the beam splitter 212 to form a combined beam 240. The combined beam 240 includes a plurality of interference signals, where a respective interference signal is formed from a respective return light 231 and the reference light 237. For example, at the beam splitter 212, the respective return lights 231 and the reference light 237 may interfere with each other or may be combined to form the combined beam 240. The combined beam 240 may be directed towards a spatial filter 222 which may include a lens (e.g. an objective lens) (L4) 224 and a second slit (SL2) 225. The spatial filter 222 may be used to reject out-of- focus light originating from the sample 220, in a similar manner as the confocal pinhole in a confocal microscope. The out-of-focus light may be present as part of the return lights 231 originating from the sample 220, for example originating from parts of the sample 220 not covered by illumination by the sample beam 230.

[0097] The spatially filtered beam or light 241, based on the combined beam 240, may then be collimated by a lens (e.g. an objective lens) (L5) 226, which may then pass through a grating (e.g. a diffraction grating) (GR) 227 where various wavelength components of the spatially filtered light 241 may be dispersed angularly.

[0098] An image lens (L6) 228 in combination with a 2D (two-dimensional) image sensor (e.g. a CCD (charge-coupled device) or a cmos (complementary metal-oxide- semiconductor) sensor) 229 may be employed to capture the 2D spectra 244 generated, which may be a function of lateral position (the point where the sample beam 230 enters the sample 220) and wavelength. For clarity and ease of understanding, only two respective separate lights 246a, 246b of respective wavelenghts making up the spectra 244 are shown in FIG. 2A. Accordingly, the optical imaging device 200a may include the grating 227 to spectrally disperse the combined beam 240, where respective separate lights of respective wavelengths may be focused by the lens (L6) 228 and directed towards an image sensor 229 acting as a detector to detect or capture the 2D spectra 244.

[0099] Processing may then be carried out to obtain spectral information from the 2D spectra 244 corresponding to the section of the sample 220 illuminated by the sample beam 230. An OCT image of the sample 220 may be obtained or reconstructed from the information obtained from the processing carried out.

[0100] It should be appreciated that in various embodiments, the linear array of point sources defining the source beam 204 may also be implemented by the use of a light emitting diode (LED) array or an array of optical fibers coupled to a broadband source (e.g. 202).

[0101] FIG. 2B shows a prototype set-up of a scan-free OCT system 200b, according to various embodiments. The structure or configuration of the scan-free OCT system setup 200b is similar to the OCT system 200a illustrated in FIG. 2A, except that the spatial filter 222, made up of the lens, L4 224 and the slit, SL2 225, is not included in the OCT system 200b. Nevertheless, it should be appreciated that the lens L4 224 and the slit SL2 225 may be incorporated into the OCT system 200b. The OCT system 200b may include a light source 202, a linear fiber bundle (including a holder) 203 optically coupled to the light source 202 to supply light, a lens (e.g. a condenser) 206a, a slit 208, a lens (e.g. a collimation lens) 210a, an aperture 270, a beam splitter 212, a lens (e.g. an objective lens) 214a, a mirror 216, a lens (e.g. an objective lens) 218a, a grating (e.g. a diffraction grating) 227, a lens (e.g. an image lens) 228a, and a camera (e.g. an area camera) 229a. Also shown in FIG. 2B is a sample 220a, which is a cover slip. The OCT system 200b, including the different components, may be as described in the context of the OCT system 200a, and therefore the corresponding descriptions relating to the OCT system 200b are omitted here.

[0102] FIG. 3 shows a schematic diagram illustrating a process 300 of obtaining a raw image and a reconstructed optical coherence tomography (OCT) image of a sample imaged by the optical imaging device of various embodiments. FIG. 3 shows the relationship between the sample beam 230 which may define an illumination pattern, the raw image 302 of a spectrum array, which may define interference signals, from an image sensor (e.g. 229, FIG. 2A), and a reconstructed OCT image 304 of the sample 220.

[0103] As a non-limiting example, an array 301 of point sources, which may define a linear source array, may generate a sample beam 230 including a large number of beamlets which may enter the sample 220 at least substantially perpendicularly and at least substantially in parallel. Each point source corresponds to a beamlet which may probe or illuminate the sample 220 along one a-line (axial-line) 323 within a sample section. The return light from each a-line 323 may interfere with a reference light (e.g. 237, FIG. 2A), resulting in a spectrum or interference signal 340 that may be detected by a row of pixels in an image sensor (e.g. 229, FIG. 2A). The raw image 302 from the sensor is generally an array 302 of spectra, defined by a plurality of interference signals 340, obtained after spectral dispersion by a grating. The array 302 may have a spectrum ranging from blue to red along each line defined by a respective interference signal 340 corresponding to a respective a-line 323. Further, the intensity may vary along each line defined by a respective interference signal 340 corresponding to a respective a- line 323. Different rows of pixels in the image sensor may correspond to different a-lines 323 and different point sources.

[0104] Processing may be performed on each spectrum 340. For example, inverse Fourier transform of each spectrum 340 may lead to a reflectivity profile along the corresponding a-line 323. A cross-sectional image of the section of the sample 220 may be obtained by performing a one-dimensional inverse Fourier transform of the raw image 302 along the spectral dispersion direction (or horizontal direction), e.g. as indicated in relation to FIG. 4A which will be described below.

[0105] FIG. 4A shows a raw image 400 obtained by the OCT system of various embodiments, illustrating the interference spectra of a sample being imaged. The exposure time was about 40 milliseconds (ms). As may be seen in the raw image 400 as captured by the camera (or detector) of the OCT system, interference fringes (which appear as alternating dark bands (e.g. 450a) and bright bands (e.g. 450b)) are visible in the image 400. As indicated in FIG. 4A as an example, the fringes 450a, 450b have alternating intensities along the horizontal direction, e.g. a line along the horizontal direction is represented by the dashed line 452. FIG. 4B shows an intensity profile (a single spectrum) 460 measured along the dashed horizontal line 452 indicated in FIG. 4A.

[0106] Inverse Fourier transform performed based on the raw image 400 obtained may lead to an OCT image 500 (FIG. 5) of the sample imaged, which is a cover slip (about 100 micron (μιη) in thickness). Two surfaces (which appear as bright lines), e.g. a top surface 552a and a bottom surface 552b, of the cover slip may be clearly seen with high resolution.

[0107] FIG. 6 shows a cross-sectional image 600 of an Oyster Plant leaf obtained using the optical coherence tomography (OCT) system of various embodiments, illustrating another example of an OCT image that may be obtained.

[0108] While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.

Claims

1. An optical imaging device comprising:

an optics arrangement configured to generate an illumination pattern that is elongate to illuminate a section of a sample to be imaged along a plurality of axial-lines within the section of the sample,

wherein the optics arrangement is further configured to form an interference signal from each return light of respective return lights from respective axial-lines of the section of the sample illuminated by the illumination pattern, and a reference light; and an area detector configured to receive the interference signals for generating an image corresponding to the section of the sample, wherein a respective interference signal is received by a respective portion of the area detector.

2. The optical imaging device as claimed in claim 1, wherein the illumination pattern comprises a linear illumination pattern.

3. The optical imaging device as claimed in 1 or 2, wherein the optics arrangement comprises a grating arranged to spectrally disperse each interference signal to be received by the area detector.

4. The optical imaging device as claimed in any one of claims 1 to 3, wherein the optics arrangement comprises an imaging lens arranged to focus the interference signals onto the area detector.

5. The optical imaging device as claimed in any one of claims 1 to 4, wherein the area detector comprises a camera capable of receiving the respective interference signals on respective portions of the camera for generating a two-dimensional image of the section of the sample.

6. The optical imaging device as claimed in any one of claims 1 to 5, wherein the optics arrangement comprises a beam splitter arranged to receive and split a light into a first light portion to define the illumination pattern for illuminating the section of the sample, and a second light portion from which the reference light is derived.

7. The optical imaging device as claimed in any one of claims 1 to 6, wherein the optics arrangement comprises focusing optics for focusing the illumination pattern onto the sample for illuminating the section of the sample.

8. The optical imaging device as claimed in any one of claims 1 to 7, wherein the optics arrangement comprises a collimation lens configured to generate a collimated light from which the illumination pattern is formed.

9. The optical imaging device as claimed in claim 8, wherein the optics arrangement further comprises a condenser arranged to receive and concentrate light to be received by the collimation lens.

10. The optical imaging device as claimed in 9, wherein the optics arrangement further comprises a slit arranged between the collimation lens and the condenser.

11. The optical imaging device as claimed in any one of claims 1 to 10, wherein the optics arrangement comprises a spatial filter arranged to reject at least some lights originating from parts of the sample not covered by the illumination pattern.

12. The optical imaging device as claimed in any one of claims 1 to 1 1, further comprising a light source, wherein the optics arrangement is configured to generate the illumination pattern based on a light produced by the light source.

13. The optical imaging device as claimed in 12, wherein the light source comprises a broadband light source.

14. The optical imaging device as claimed in 12 or 13, further comprising an array of optical fibers optically coupled to the light source.

15. The optical imaging device as claimed in 12 or 13, wherein the light source comprises an array of light emitting diodes.

16. The optical imaging device as claimed in any one of claims 1 to 15, further comprising a processor configured to obtain information corresponding to the section of the sample from the interference signals for generating the image corresponding to the section of the sample.

17. The optical imaging device as claimed in 16, wherein the processor is configured to perform inverse Fourier transform on the interference signals.

18. The optical imaging device as claimed in any one of claims 1 to 17, wherein the optical imaging device is free of a scanning device in an optical path of the illumination pattern.

19. The optical imaging device as claimed in any one of claims 1 to 18, wherein the illumination pattern comprises a plurality of beamlets, a respective beamlet of the plurality of beamlets illuminating the section of the sample along a respective axial-line of the plurality of axial-lines.

20. A method of controlling an optical imaging device, the method comprising:

generating an illumination pattern that is elongate;

illuminating, with the illumination pattern, a section of a sample to be imaged along a plurality of axial-lines within the section of the sample;

forming an interference signal from each return light of respective return lights from respective axial-lines of the section of the sample illuminated by the illumination pattern, and a reference light; and

receiving the interference signals for generating an image corresponding to the section of the sample, wherein a respective interference signal is received by a respective portion of an area detector of the optical imaging device.

21. The method as claimed in claim 20, wherein generating the illumination pattern comprises generating a linear illumination pattern.

22. The method as claimed in 20 or 21, further comprising spectrally dispersing each interference signal to be received by the area detector.

23. The method as claimed in any one of claims 20 to 22, further comprising focusing the interference signals onto the area detector.

24. The method as claimed in any one of claims 20 to 23, wherein the area detector comprises a camera capable of receiving the respective interference signals on respective portions of the camera for generating a two-dimensional image of the section of the sample.

25. The method as claimed in any one of claims 20 to 24, further comprising:

receiving a light; and

splitting the light into a first light portion to define the illumination pattern for illuminating the section of the sample, and a second light portion from which the reference light is derived.

26. The method as claimed in any one of claims 20 to 25, further comprising focusing the illumination pattern onto the sample for illuminating the section of the sample.

27. The method as claimed in any one of claims 20 to 26, further comprising generating a collimated light,

wherein generating an illumination pattern comprises generating the illumination pattern from the collimated light.

28. The method as claimed in claim 27, further comprising receiving and concentrating light from which the collimated light is generated.

29. The method as claimed in 28, further comprising filtering the concentrated light.

30. The method as claimed in any one of claims 20 to 29, further comprising spatially filtering at least some lights originating from parts of the sample not covered by the illumination pattern.

31. The method as claimed in any one of claims 20 to 30, further comprising obtaining information corresponding to the section of the sample from the interference signals for generating the image corresponding to the section of the sample.

32. The method as claimed in 31, wherein obtaining information comprises performing inverse Fourier transform on the interference signals.

33. The method as claimed in any one of claims 20 to 32, wherein the method is free of scanning the illumination pattern across the sample.

34. The method as claimed in any one of claims 20 to 33, wherein the illumination pattern comprises a plurality of beamlets, a respective beamlet of the plurality of beamlets illuminating the section of the sample along a respective axial-line of the plurality of axial-lines.