Patent Description:
Optical coherence tomography (in the following also called OCT, its typical abbreviation) is an imaging technique that uses low-coherence light to capture two- and three-dimensional images from within optical scattering media (e.g., biological tissue) with high resolution. It is, inter alia, used for medical imaging. Optical coherence tomography is based on low-coherence interferometry, typically employing near-infrared light. The use of relatively long wavelength light allows it to penetrate into the scattering medium.

A medical field of particular interest for OCT is ophthalmology, a branch of medicine related to (in particular human) eyes and its disorders and related surgeries. The ability to visualize the vitreous body of an eye (sometimes also just called "vitreous") during vitrectomy is critical to surgical success. The vitreous body is a transparent tissue and becomes slightly hazy with aging. Currently, the standard of care is to apply a white dye (typically triamcinolone) to stain the vitreous body. However, there is known toxicity related to the dye, and many surgeons prefer to use as little as possible or no dye at all when performing vitrectomy.

Document <CIT> relates to OCT for imaging subjects like eyes. Different amounts of conversion for converting an intensity distribution are used for different regions of the image like retina and vitreous body. Document <CIT> relates to OCT for imaging subjects like embryos.

According to the invention, a control system, an OCT imaging system and a method for imaging a subject with the features of the independent claims are proposed. Advantageous further developments form the subject matter of the dependent claims and of the subsequent description.

The present invention relates to a control system for an optical coherence tomography (OCT) imaging system for real-time imaging of a subject, the subject including a tissue material of interest. This subject, preferably, includes or is an eye, and the tissue material of interest, preferably, includes or is a vitreous body of the eye. The control system is configured to control the optical coherence tomography imaging system (the type of OCT to be used is, preferably, spectral domain OCT, as will also be described later) to scan the subject by means of optical coherence tomography for acquiring intensity scan data. Such scanning can include, in particular, performing a B-scan.

In OCT, areas of the sample or tissue that reflect back a lot of light will create greater interference than areas that do not. Any light that is outside the short coherence length will not interfere. This reflectivity profile is called an A-scan and contains information about the spatial dimensions and location of structures within the sample or tissue. A cross-sectional tomograph, called B-scan, may be achieved by laterally combining a series of these axial depth scans (A-scan).

In general, such intensity scan data is processed in order to provide image data than is to be or than can be visualized in display means, e.g., a display next to the OCT scanning system or the like. Due to the large range of intensity typically acquired during such scan, the image data is, up to now, determined based on a conversion scale that allows to condense the data such that all relevant intensity data can be visualized within a range of visible light. Typically, a conversion scale based on a logarithmic scale is used or such purposes.

A consequence of using such a conversion scale is that certain tissue material of interest like the vitreous body of an eye is not visible in image obtained for the image data. This is also the reason why staining the vitreous body was performed, as mentioned earlier.

It has now turned out that such tissue materials of interest (in a subject under imaging) like the vitreous body of an eye (and which is not visible without staining in OCT images up to now) can be made visible. In order to achieve this, within the present invention, when processing the intensity scan data (performed by the control system) to to provide the image data to be visualized on display means, for a selected range of intensity, correlated to the tissue material of interest, the image data is determined based on a selected conversion scale that is different from a conversion scale for intensity outside the selected range. While the conversion scale for intensity outside the selected range can, as previously, be based on a logarithmic scale, the conversion scale for the selected range is, preferably, based on a linear scale. Such different scale like or based in a linear scale allows much more of the intensity range of the scan data to be transferred into the image data than a conversion scale like a linear scale or the like does. In this regard, it is to be noted that image data that shall be used for displaying on a display means typically only comprises a certain range of gray scale depth (e.g., <NUM> different gray colors within a true depth color system of <NUM> bit).

While, in this example, the intensity range of relevance (for e.g., the vitreous body) is mapped to one or even no gray color when using the conventional conversion scale, this range of relevance can be mapped to, e.g., a plurality (e.g., three or four) gray colors. Since the remaining range of intensity (outside the selected range) is still converted using the conventional conversion range, the visibility of the remaining tissues of interest in the subject is affected only at a minimum.

The range of interest can be selected based on the tissue material of interest and its typical intensities in an OCT scan. This range can be obtained, e.g., by means of simulation and/or test measurements.

A main advantage of this different conversion scale for a selected range of intensity data is, besides allowing visualization on display means, an intraoperative use, i.e., the tissue material of interest like the vitreous body of an eye of a patient undergoing a surgery can be visualized on display means without any relevant time delay during the surgery. This allows very exact handling of a surgeon without (toxic) staining the vitreous bod of the eye of the patient.

The invention also relates to an optical coherence tomography (OCT) imaging system for real-time imaging of a subject, e.g. an eye, comprising the control system according to the invention and as described above, and optical coherence tomography imaging means in order to perform the OCT scan (for a more detailed description of such OCT imaging means it is referred to the drawings and the corresponding description). Preferably, the OCT imaging system is configured to visualize the image data on display means. Such display means can be part of the OCT imaging system.

It is of advantage if the OCT imaging system is configured to perform spectral domain optical coherence tomography (abbreviation: SD-OCT). Spectral domain OCT is a kind of frequency domain OCT (FD-OCT) in which broadband interference is acquired with spectrally separated detectors. Another, different kind of frequency domain OCT is swept source OCT (SS-OCT). Swept source OCT encodes the optical frequency in time with a spectrally scanning source. Spectral domain OCT, in contrast, uses a dispersive detector, like a grating and a linear detector array, to separate the different wavelengths. 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 imaging speed dramatically, while the reduced losses during a single scan improve the signal to noise ratio proportional to the number of detection elements.

Further, the OCT imaging system is, preferably, configured for use during a surgical procedure being performed on the subject like an eye of a patient. As mentioned before, the specific conversion scale used within the present invention allows an intraoperative use, i.e., the tissue material of interest like the vitreous body of the eye can be visualized on display means without any relevant time delay during the surgery.

The invention also relates to a method for imaging a subject like an eye in real-time, the subject including a tissue material of interest like a vitreous body of an eye, using optical coherence tomography (OCT), preferably, spectral domain OCT. The method comprises the following steps: the subject is scanned by means of OCT and intensity scan data is acquired, the intensity scan data is then processed to provide image data to be visualized on display means. Within these steps, a range of intensity, correlated to the tissue material of interest, is selected, wherein, in the selected range of intensity, the image data is determined based on a selected conversion scale, and wherein, outside the selected range, the image data is determined based on a conversion scale that is different from the selected conversion scale. In a further step, the image data can be visualized on display means.

With respect to further preferred details and advantages of the OCT imaging system and the method, it is also referred to the remarks for the control system above, which apply here correspondingly.

The invention also relates to a computer program with a program code for performing a method according to the invention when the computer program is run on a processor or on a control system according to the invention.

Further advantages and embodiments of the invention will become apparent from the description and the appended figures.

It should be noted that the previously mentioned features and the features to be further described in the following are usable not only in the respectively indicated combination, but also in further combinations or taken alone, without departing from the scope of the present invention.

In <FIG>, a schematic overview of an optical coherence tomography (OCT) imaging system <NUM> according to the invention in a preferred embodiment is shown. The OCT imaging system <NUM> comprises a light source <NUM> (e.g., a low coherence light source), a beam splitter <NUM>, a reference arm <NUM>, a sample arm <NUM>, a diffraction grating <NUM>, a detector <NUM> (e.g., a camera), a control system <NUM> and display means <NUM> (e.g., a display or monitor).

Light originating from the light source <NUM> is guide, e.g., via fiber optic cables <NUM>, to the beam splitter <NUM> and a first part of the light is transmitted through the beam splitter <NUM> and is then guided, via a lens <NUM> (which is only schematically shown and may represent also different, appropriate optics) in order to create a light beam <NUM> to a reference mirror <NUM>, wherein the lens <NUM> and the reference mirror <NUM> are part of the reference arm <NUM>.

Light reflected from the reference mirror <NUM> is guided back to the beam splitter <NUM> and is transmitted through the beam splitter <NUM> and is then guided, via a lens <NUM> (which is only schematically shown and may represent also different, appropriate optics) in order to create a light beam <NUM> to the diffraction grating <NUM>.

A second part of the light, originating from the light source <NUM> and transmitted through the beam splitter <NUM> and is guided, via a lens <NUM> (which is only schematically shown and may represent also different, appropriate optics) in order to create a light beam <NUM> (for scanning) to the subject <NUM> to be imaged and which comprises tissue material of interest <NUM>. The lens <NUM> is part of the sample arm <NUM>.

Light reflected from the subject <NUM> or the tissue material of interest <NUM> is guided back to the beam splitter <NUM> and is transmitted through the beam splitter <NUM> and is then guided, via lens <NUM> to the diffraction grating <NUM>. Thus, light reflected in the reference arm <NUM> and light reflected in the sample arm <NUM> are combined by means of the beam splitter <NUM> and are guided, e.g., via a fiber optic cable <NUM>, and in a combined light beam <NUM> to the diffraction grating <NUM>.

Light reaching the diffraction grating <NUM> is diffracted and captured by the detector <NUM>. In this way, the detector <NUM>, which acts as a spectrometer, creates or acquires intensity scan data <NUM> that are transmitted, e.g., via an electrical cable <NUM>, to the control system <NUM> comprising processing means (or a processor) <NUM>. The intensity scan data <NUM> is then processed to obtain image data <NUM> that are, e.g., via an electrical cable <NUM>, to the display means <NUM> and displayed as a real-time image <NUM>, i.e., an image that represents the currently scanned subject <NUM> in real-time.

The process in which the intensity scan data <NUM> is processed or converted to the image data <NUM> that allows displaying of the scanned subject <NUM> on the display means <NUM> will be described in more detail in the following.

In <FIG>, different conversion scales as used within the invention, are schematically shown in a diagram. In the diagram, a gray scale value G is shown versus an intensity or intensity value I. Note that while intensity I, typically, comprises continuous values, gray scale values are, typically discrete values or they are continuous and will be displayed in the display means with discrete values.

An exemplary (standard) conversion scale as typically used in OCT or SD-OCT imaging is denoted SO, starting at intensity I=<NUM>. This conversion scale SO is based on a logarithmic scale. For example, intensity values I=<NUM> to I=<NUM> are mapped to a gray scale value G=<NUM>, intensity values I=<NUM> to I=<NUM>^<NUM> are mapped to gray scale value G=<NUM>, intensity values I=<NUM>^<NUM> to I=<NUM>^<NUM> are mapped to gray scale value G=<NUM>, and so on.

Such a (standard) conversion scale as it is, up to now, used throughout all intensity values and indicated with dashed line in <FIG> results in that a certain range of intensity as, e.g., range RS being mapped to a single gray scale value or being part of a single gray scale value within an even much broader range (which may result in, effectively, no gray scale value).

Within the present invention, such (standard) conversion scale is not used throughout all intensity values but for a selected range of intensity, as indicated with RS in <FIG>, another and different conversion scale is used. In the example shown in <FIG>, a conversion scale SS based on a linear scale is used. This different conversion scale SS results in that the intensity values within selected range RS are mapped to a plurality of gray scale values or at least more than for the (standard) conversion scale SO.

For intensity values above the selected range RS the (standard) conversion scale SO is used again. As can be seen in <FIG>, it shifted with respect to the conversion scale indicated by the dashed line to higher gray scale values G. In other words, the (standard) conversion scale SO is used for the intensity (or all intensity values) outside the selected range RS.

The effect of this different conversion scale SS is that the intensity values within the selected range RS can be made visible in an image that is based on the gray scale values. Thus, the selected range RS can be selected with respect to a tissue material of interest like the vitreous body of an eye as described above. This selected range, i.e., its upper and lower limits, can be selected based upon simulations and/or test measurements.

For example, the intensities obtained from scanning a vitreous body (or any other tissue material of interest) can be measured. The selected range RS can then be adapted accordingly, such that when using the OCT imaging system the intensity values within the selected range RS are automatically processed with the different conversion scale SS and a corresponding real-time image is produced.

It is to be noted that also two or more of such selected ranges with conversion scales different from the (standard) conversion scale can be used if, e.g., to different tissue materials of interest shall be visualized. If necessary, different conversion scales for the different selected ranges can be used. Also, two or more of such selected ranges (with, e.g., the same conversion scale) can be used if the tissue material of interest provides intensities better divided into two or more ranges, wherein intensities between two of these ranges being used with the (standard) conversion scale.

In <FIG> a flow scheme describing a method according to the invention in a preferred embodiment using, e.g., the OCT imaging system shown in <FIG> is shown. In a first step <NUM>, the subject is scanned by means of OCT as described with respect to <FIG> and intensity scan data <NUM> is acquired and transmitted to the control system with its processing means.

In a next step <NUM>, the intensity scan data is processed by means of the processing means of the control system such that image data <NUM> is obtained. During this step, intensity values in the intensity scan data are converted into, e.g., grey scale values (as the image data) which can easily be visualized using the conversion scales as shown in and described with respect to <FIG>. This includes that a range of intensity, correlated to the tissue material of interest, is selected, wherein, in the selected range of intensity, the image data <NUM> is determined based on the selected conversion scale, and wherein, outside the selected range, the image data is determined based on a conversion scale that is different from the selected conversion scale, e.g., a standard conversion scale as described with respect to <FIG>.

In a next step <NUM>, the image data <NUM> is transmitted to and visualized by means of the display means as described with respect to <FIG>. The result is a real-time image <NUM> presented by the display means. These steps can be repeatedly or continuously performed such that the real-time image is repeatedly updated or is a live image of the subject showing any changes in the subject in real-time.

Some embodiments relate to an OCT imaging system comprising a control system as described in connection with one or more of the <FIG>. Alternatively, an OCT imaging system may be part of or connected to a system as described in connection with one or more of the <FIG>. <FIG> shows a schematic illustration of an OCT imaging system <NUM> configured to perform a method described herein. The OCT imaging system <NUM> comprises an OCT system and a computer or control system <NUM>. The OCT imaging system <NUM> is configured to take images and is connected to the computer system <NUM>. The computer system <NUM> is configured to execute at least a part of a method described herein. The computer system <NUM> may be configured to execute a machine learning algorithm. The computer system <NUM> and OCT imaging system <NUM> may be separate entities but can also be integrated together in one common housing. The computer system <NUM> may be part of a central processing system of the OCT imaging system <NUM> and/or the computer system <NUM> may be part of a subcomponent of the OCT imaging system <NUM>, such as a sensor, an actor, a camera or an illumination unit, etc. of the OCT imaging system <NUM>.

The computer system <NUM> may be a local computer device (e.g. personal computer, laptop, tablet computer or mobile phone) with one or more processors and one or more storage devices or may be a distributed computer system (e.g. a cloud computing system with one or more processors and one or more storage devices distributed at various locations, for example, at a local client and/or one or more remote server farms and/or data centers). The computer system <NUM> may comprise any circuit or combination of circuits. In one embodiment, the computer system <NUM> may include one or more processors which can be of any type. As used herein, processor may mean any type of computational circuit, such as but not limited to a microprocessor, a microcontroller, a complex instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a graphics processor, a digital signal processor (DSP), multiple core processor, a field programmable gate array (FPGA), for example, of a microscope or a microscope component (e.g. camera) or any other type of processor or processing circuit. Other types of circuits that may be included in the computer system <NUM> may be a custom circuit, an application-specific integrated circuit (ASIC), or the like, such as, for example, one or more circuits (such as a communication circuit) for use in wireless devices like mobile telephones, tablet computers, laptop computers, two-way radios, and similar electronic systems. The computer system <NUM> may include one or more storage devices, which may include one or more memory elements suitable to the particular application, such as a main memory in the form of random access memory (RAM), one or more hard drives, and/or one or more drives that handle removable media such as compact disks (CD), flash memory cards, digital video disk (DVD), and the like. The computer system <NUM> may also include a display device, one or more speakers, and a keyboard and/or controller, which can include a mouse, trackball, touch screen, voice-recognition device, or any other device that permits a system user to input information into and receive information from the computer system <NUM>.

Claim 1:
A control system (<NUM>) for an optical coherence tomography imaging system (<NUM>) for real-time imaging of a subject (<NUM>), the subject (<NUM>) including a tissue material of interest (<NUM>), the control system (<NUM>) being configured to:
control the optical coherence tomography imaging system (<NUM>) to scan the subject (<NUM>) by means of optical coherence tomography for acquiring intensity scan data (<NUM>), and
process the intensity scan data (<NUM>) to provide image data (<NUM>) to be visualized on display means (<NUM>), the control system being characterized in that for a selected range (RS) of intensity (I), correlated to the tissue material of interest (<NUM>), the image data (<NUM>) is determined based on a selected conversion scale (SS) that is different from a conversion scale (SO) for intensity outside the selected range (RS).