NL2020483B1 - Method and apparatus for optical coherence projection tomography - Google Patents

Method and apparatus for optical coherence projection tomography Download PDF

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NL2020483B1
NL2020483B1 NL2020483A NL2020483A NL2020483B1 NL 2020483 B1 NL2020483 B1 NL 2020483B1 NL 2020483 A NL2020483 A NL 2020483A NL 2020483 A NL2020483 A NL 2020483A NL 2020483 B1 NL2020483 B1 NL 2020483B1
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path length
opl
distribution
obtaining
refractive index
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NL2020483A
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Kalkman Jeroen
Van Der Horst Jelle
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Univ Delft Tech
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
    • A61B5/0062—Arrangements for scanning
    • A61B5/0066—Optical coherence imaging
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
    • A61B3/102—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for optical coherence tomography [OCT]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/0209—Low-coherence interferometers
    • G01B9/02091—Tomographic interferometers, e.g. based on optical coherence
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes

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Abstract

The invention relates to a method for optical coherence projection tomography of an object comprising the steps of: obtaining optical coherence projection tomography spectroscopic data of the object; obtaining an optical path length, OPL, distribution using the spectroscopic data; selecting a region of interest in the OPL distribution corresponding to ballistic photons based on an estimated value of a size and a refractive index of the object; obtaining at least one of a path-length integrated attenuation coefficient and path-length integrated refractive index from the selected region in the OPL distribution; obtaining at least one sinogram for the obtained at least one of the path-length integrated attenuation coefficient and the obtained path-length integrated refraction index; and reconstructing an image of the object from the obtained at least one sinogram. The invention relates also to a device for performing the method.

Description

Field of the invention
The present invention relates to a method and apparatus for low coherence transmission optical tomography of an object.
Background art
Such a method and device is known from W02001/085022. In the known method photon migration methods are employed to image absorbing objects embedded in a turbid media such as tissue. According to the known method early arriving photons are detected to provide image using image reconstruction based on optical computed tomography. The CT method is generalized to take into account the distributions of photon paths. A point spread function (PSF) is expressed in terms of the Green's function for the transport equation. This PSF provides weighting functions for use in a generalized series expansion method. Measurements of turbid medium with scattering and absorption properties included coaxial transmission scans collected in two projections. Blurring associated with multiple scattering was removed and high-resolution images can be obtained.
There is a still existing demand for method and devices with increased resolution.
Summary of the invention
The present invention seeks to provide a method for transmission optical coherence projection tomography with quantitative 3D imaging having increased contrast and increased resolution.
According to a first aspect of the invention, this object is achieved by a method for optical coherence projection tomography of an object comprising the steps of: obtaining optical coherence projection tomography spectroscopic data of the object; obtaining an optical path length, OPL, distribution using the spectroscopic data; selecting a region of interest in the OPL distribution corresponding to ballistic photons based on an estimated value of a size and a refractive index of the object;
obtaining at least one of a path-length integrated attenuation coefficient and path-length integrated refractive index from the selected region in the OPL distribution;
obtaining a least one sinogram for the obtained at least one of the obtained path-length integrated attenuation coefficient and the obtained path-length integrated group refractive index; and reconstructing an image of the object from the obtained at least one sinogram. The object can be a translucent object. The OPL distribution can be calculated by obtaining corrected spectral data by subtraction of the background spectrum from the measured spectroscopic data and then obtaining the absolute value of inverse Fast Fourier transform of the resulting spectrum.
The insight of the invention is that ballistic photons or early arriving photons travel straight through the translucent object, accumulate the shortest optical path and create a sharp peak in the OPL distribution. Photons that have been scattered in the translucent object and are collected on the detector have travelled longer distances and result in a wide distribution behind the ballistic peak in the OPL distribution. By selecting a part of the OPL distribution of light with the shortest optical path length, only substantially ballistic photons are used for image reconstruction. In this way high resolution images can be obtained using known X-ray tomography reconstruction techniques. Given a reference measurement the height and location of the ballistic peak can be used to calculate the path length integrated attenuation coefficient and path length integrated refractive index. Optical coherence projection tomography is a point scanning technique wherein the measured optical properties are path-length integrated values. The spectroscopic data can be obtained by scanning of the object with an illumination beam or by translating and/ or rotating the object with respect to the illumination beam and detecting the light passing through the object. In this way a plurality of optical coherence spectroscopic data are obtained for different angles and lateral shifts. The path length integrated attenuation coefficient and path length integrated refractive index are placed in separate sinograms. Images can then be reconstructed from the sinograms in a similar way as in X-ray computed tomography (CT) for the path length integrated attenuation coefficient and the path length integrated refractive index.
In an embodiment the method comprises detecting a rising edge in the selected region of interest of the OPL distribution, fitting a Gaussian function around a predetermined window around the rising edge; and determining the at least one of the path-length integrated attenuation coefficient and the path-length integrated refractive index from the location and height of the Gaussian function. In this way an effective method to filter a region of non-scattered light from a region of scattered light in the OPL distribution is provided. The detection of the rising edge can be performed by a method for edge detection well-known to the skilled person in the field of signal processing.
In a further embodiment the rising edge in the selected region of interest of the OPL distribution is determined based on a first value above a predetermined threshold starting from the origin of the OPL distribution along an optical path length axis.
In a further embodiment the predetermined threshold is based on a noise level of the selected region of interest of the OPL distribution. For example, the value of the threshold is higher than three times the standard deviation of the noise floor level in the region selected region of interest. Thereafter, this location of the rising edge is used to the initialization of a fit of, for example, 10 surrounding pixel values with a Gaussian function. The location and height of the fitted Gaussian function contain information on the path length integrated refractive index and the path length integrated attenuation coefficient along the ballistic light path.
In a further embodiment the reconstruction is based on a filtered back projection, an algebraic reconstruction technique or a point spread function based reconstruction technique.
An advantage of the point spread function based reconstruction is that the technique can compensate for diffraction and focus position. In an embodiment the method comprises correcting the sinograms for centre of rotation off set. In this way artefacts in the reconstructed image can be further reduced.
In a further embodiment the method comprises obtaining the absolute value of the at least one of the refractive index and attenuation coefficient using a reference measurement.
In a further embodiment the method comprises a step of compensation for refraction artefacts based on ray tracing an initial reconstructed object. These steps can be repeated until the quality of the image remains substantially constant.
According to a second aspect of the invention this object is achieved by a device for optical coherence projection tomography of an object, the device comprising a light source arranged to generate an illumination light beam to the object;
a moveable stage arranged to move the object or the illumination beam relatively to each other, a detector arranged to detect a sample light beam from the object a controller arranged to control the light source, the moveable stage and the detector to obtain optical coherence projection tomography spectroscopic data of the object from the detected sample light beam; to obtain an OPL distribution using the spectroscopic data to select a region of interest in the OPL distribution corresponding to ballistic photons based on an estimated value of a size and a refractive index of the object; to obtain at least one of a path-length integrated attenuation coefficient and path-length integrated refraction index from the selected region in the OPL distribution; to obtain at least one sinogram for the obtained at least one of the obtained path-length attenuation coefficient and the pathlength integrated refraction index; and to reconstruct an image of the object from the obtained at least one sinogram. The light source can be a wide band light source or a light source with a variable wavelength.
In a further embodiment the device comprises a Mach-Zehnder interferometer provided with a reference branch arranged to generate a reference light beam and a sample branch arranged to generate the illumination light beam and to collect the light through the object in a sample beam;
and to combine the reference light beam and the sample light beam.
In a further embodiment the light source is a super-luminescent diode and the detector comprises a spectrometer. The super luminescent diode preferably having a central wavelength of 1300 nm and a bandwidth of 110 nm. In this arrangement a spectrogram can be obtained from the combined sample beam and the reference beam.
In a different embodiment the light source is a tuneable high coherence light source and the detector comprises a photodiode. In this arrangement a spectrogram can be obtained by adjusting the wavelength of the tuneable high coherence light source, obtained spectroscopic data from the photodiode and repeating these steps such that spectroscopic data can be obtained for a range of wavelengths. The tuneable high coherent light source can be a tuneable solid-state laser.
In a further embodiment the device comprises an optical amplifier arranged between the light source and the object to increase the optical power of the sample beam directed to object. In this arrangement the optical power of the sample beam is increased to obtain a higher intensity of the light travelling through the object.
In a further embodiment the device comprises a field extender arranged to extend a depth of field of the device based on non-diffracting optical beams such as a Bessel beam. The field extender extends the depth of field of the imaging capabilities of the device in a way that larger objects can be imaged.
In a further embodiment the moveable stage comprises a motor and an X, Y stage, and wherein the moveable stage is further arranged to translate or rotate the object with respect to the illumination beam.
In a further embodiment the device comprises a first galvanometer mirror arranged to scan the illumination beam with respect to the object and a second galvanometer mirror arranged to scan the sample beam from the object corresponding to the illumination beam from the first galvanometer mirror. In this arrangement a galvanometer scanning of the object can be performed.
Short description of drawings
The present invention will be discussed in more detail below, with reference to the attached drawings, in which
Fig. 1 shows diagrammatically a device for optical coherence projection tomography according to a first embodiment of the invention;
Fig. 2 shows diagrammatically a device for optical coherence projection tomography according to a second embodiment of the invention;
Fig. 3 shows a flow diagram of a method according to an embodiment of the invention.
Fig. 4 shows a graph of an optical path length distribution;
Fig. 5a and 5b shows sinograms of an integrated path length refractive index and an integrated path length attenuation coefficient; and
Fig. 6a and 6b show reconstructed images of the object from sinograms of an integrated path length refractive index and an integrated path length attenuation coefficient.
Description of embodiments
Certain exemplary embodiments will be described in greater detail, with reference to the accompanying drawings in figs 1 to 6.
The matters disclosed in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of the exemplary embodiments. Accordingly, it is apparent that the exemplary embodiments can be carried out without those specifically defined matters. Also, well-known operations or structures are not described in detail, since they would obscure the description with unnecessary detail.
Fig. 1 shows schematically a device for optical coherence projection tomography 1 according to a first embodiment. The device 1 comprises a light source 2, a MachZehnder interferometer and a detector. The light source 2 is coupled to the Mach-Zehnder interferometer via an optical fibre. In this embodiment the light source 2 can be a superluminescent diode, for example type D-1300-HP as provided by Superlum. The characteristics of this super-luminescent diode are: a central wavelength of 1300 nm and a bandwidth of 110 nm. Furthermore, in this embodiment the detector comprises a spectrometer. The spectrometer comprises a grating 16, lenses 14, 15, 17 and a line scan camera 18. In different embodiments the light source can be a broadband light source that can have a central wavelength in the range between 400 to 1800 nm.
In this embodiment the Mach-Zehnder interferometer comprises a sample branch 4 and a reference branch 5. The Mach-Zehnder interferometer further comprises a beam splitter 3 configured to split of a first part of light beam to the reference branch 5 arranged to provide a reference light beam and a second part to a sample branch 4 arranged to guide the second part of the light beam as the illumination light beam to an object 8 and to collect a sample light beam from light interacting with the object. In an embodiment the beam splitter comprises a single mode fibre beam splitter. In this description the object can be a translucent object or a biological sample.
The reference branch 5 may comprise an optical delay device 12 for matching the optical path length of the reference branch 5 to an optical path length of the sample branch 4. In an embodiment the reference branch 4 comprises a density filter for adjusting the power of the reference of the reference beam, not shown.
Furthermore, the sample branch 4 comprises an optical amplifier 6 for amplification of the light received from the beam splitter 3 to increase the power of the illumination beam to the object 8 to, for example, 100 mW. The optical amplifier can be a BOA 1132 S as manufactured by Thorlabs Inc., Newton, New Jersey, USA.
Furthermore, the sample branch 4 comprises a focussing lens 9 for focussing the illumination light beam received from the optical amplifier 6 to the object 8 or an object comprising a turbid media and a collimating lens 10 for collimating the light that interacted with the object into a sample light beam. The focussing lens 9 can have a focal distance of 100 mm. The collimating lens 10 can have a focal distance of 100 mm. Furthermore, the Mach-Zehnder interferometer comprises a beam combiner 13 for combining the reference beam and the sample light beam. The combined reference beam and sample beam is directed to the spectrometer arranged to detect the combined reference beam and sample beam.
Furthermore, the device comprises a moveable stage 7 provided with one or more motors and an X-Y stage. In this embodiment the one or more motors are arranged to drive the X-Y stage for translation of the object transvers or lateral to the illumination beam and a rotation stage for rotating the object with respect the illumination beam. The object can be hold for example in a transparent container fdled with a transparent fluid. The dimension of the container can be for example 10x50x50 mm. The object is immersed in the fluid. The fluid can be refractive index matching medium to reduce refraction effects.
Furthermore, the device 1 comprises a controller 19 connected to the light source 2, the moveable stage 7 and the line scan camera 18. In operation, the controller 19 is arranged to control the light source, the moveable stage and the line scan camera to obtain spectroscopic data from the object over a rotation angle from 0-180° with respect to the optical axis and a transverse scan along the width of the object transverse to the optical axis. The controller is further configured to perform the method according to the invention as will be described with reference to Fig. 3.
In another embodiment the device is provided with a first galvanometer mirror for scanning the illumination beam with respect to the object, wherein the object can be stationary or can be rotated about a single axis. Furthermore, the device comprises a second galvanometer mirror arranged to scan the sample beam from the object corresponding to the movement of the illumination beam from the first galvanometer mirror. This is preferred for imaging of biological samples. In this way a dataset can be obtained for a scan of a slice of the object over an angular range at a lateral position, where after the object is moved to a different lateral position for a next scan of the same slice.
Fig. 2 shows a device for optical coherence projection tomography 20 according to a second embodiment of the invention. In this embodiment, the light source comprises a tuneable coherent light source 21, for example a tuneable solid state laser, for generating a light beam with a selected wavelength. Furthermore, in this embodiment the detector comprises a photodiode 22. The arrangement of the device in this embodiment is further similar to the arrangement of the first embodiment, except that the super luminescent diode 1 is replaced by a tuneable coherent light source 21 and the spectrometer, comprising the grating 16, the lenses 14, 15, 17 and the line scan camera 18, is replaced by the photodiode 22. In this embodiment the controller 19 is arranged to obtain spectroscopic date by subsequently performing steps of selecting a distinct wavelength of the tuneable coherent light source from a range of wavelengths and detecting the combined light beam from the object, and repeating these steps for different wavelengths of the tuneable light source a number of times until the range of wavelengths is completed and the collecting of spectroscopic date is completed. The tuneable coherent light source can be a tuneable solid state laser having a centre wavelength adjustable in the range from 400 to 1800 nm.
Fig. 3 shows the steps of the method according to an embodiment of the invention. Step 301 comprises obtaining optical coherence projection tomography, spectroscopic data of the object. The spectroscopic data is measured for a slice or a plurality of slices of the object in a z-direction and wherein for the or each slice spectroscopic data is measured for a plurality of angles Θ in a range from 0 to 180° or 0 - 360°, wherein Θ represents a rotation angle of the object with respect to the illumination beam and a plurality of translations in a y-direction transverse or lateral to the illumination beam in a range from 0 to W, wherein W is the width of the object. The scanning may comprise 64 slices, spaced apart in first direction at a distance of 8 pm. Each slice is scanned in a lateral direction in 1000 steps of 8 pm and an angular direction in 180 steps of 1 degree.
In this description an imaginary coordinate system comprises an X, Y and Z- axis, wherein the X-axis corresponds to an optical path of the illumination beam, the Y axis corresponds in a lateral direction to the width of the object, and the Z-axis corresponds to the height of the object.
In a next step 302 for each measurement an OPL distribution is calculated from the measured spectroscopic data using inverse Fast Fourier Transform, as is well-known to the skilled person in the field of optical coherence tomography. In an embodiment the spectroscopic data can be corrected by subtracting the background spectrum of the reference arm from the measured spectroscopic data.
Fig. 4 shows an example of a graph 40 of an OPL distribution that can be calculated from the spectroscopic data using the inverse Fast Fourier transform. Furthermore, Fig. 4 shows a first peak 41 in the graph corresponding to the optical path length of substantially ballistic photons and a tail 42 corresponding to a range of optical path lengths of scattered photons.
In a next step 303 a region of interest is selected in the OPL distribution corresponding to ballistic or early arriving photons based on an estimated value of the size and refractive index of the object. A location of a first rising edge in the selected region of interest of the OPL distribution is detected by an edge detecting method well known to the skilled person in the field of signal processing. For example, by determining the first value higher than a threshold, for example, three times the standard deviations of the noise floor level in the region of interest, starting from the origin of the OPL distribution along an optical path length axis. The regions of interest is set a priori based on the size and refractive index of the translucent object. Fig. 4 shows the location of the detected first edge 41 in the OPL distribution by coordinates (a, b).
In a next step 304 a Gaussian function is fitted around a predetermined window around the location of the first rising edge. The width of this window can be for example 10 surrounding pixel values. The location and height of the fitted Gaussian function contains information on the path length integrated group refractive index and the path length integrated attenuation along the ballistic light path.
In the next steps 305 and 306 the path length integrated attenuation and the path length integrated refractive index along the ballistic light path are obtained from respectively the height of the peak of the Gaussian fit and the location of the peak of the Gaussian fit.
In a next step 307 the calculated path-length integrated attenuation coefficient and path length integrated refractive index are ordered in respectively a first sinogram ρμ(0, t) and a second sinogram ρη(θ, t) given by:
pg(0,t) = ƒ kp(s,t)ds = Ss^=1^Pj = 21n(-^-) (1) \asamp/ ƒ &n(s,t)ds Ss^j=ïdHj bsamp &ref (2) wherein Ss represents a voxel size in a direction s along the optical path, asamp represents the peak height determined from the Gaussian fit, bsamp represents the OPL location of the determined peak from the Gaussian fit; and and /ire/· represent respectively reference values obtained from a reference measurement of a reference object. The reference object can be, for example, a cuvette filled with an immersion fluid.
Fig. 5a and 5b shows respectively a sinogram of the integrated path length attenuation coefficient and a sinogram for the integrated path length refractive index of a scattering silicone phantom according to an embodiment of the method according to the invention.
Furthermore, these steps 301-307 are repeated for the complete set of spectroscopic data so to a set of sinograms is obtained for both the integrated path length attenuation coefficient and the integrated refractive index.
In a next step 308 a quantitative image of the refractive index the object can be calculated by a filtered back projection, FBP, or an algebraic reconstruction technique, ART, or a point spread function based reconstruction technique from the sinograms. These reconstruction techniques are well-known to the skilled person in the field of Xray tomography.
In an embodiment the first and second sinograms are corrected for centre of rotation off-sets. These corrections are well known for the skilled person in the field of X-ray tomography.
In a further embodiment the method comprises a step of compensating for diffraction and focus position based on a point spread function correction. This correction can be obtained using a measured or calculated point spread function and use the obtained point spread function in a step of filtering after reconstruction of the image or use the obtained point spread function in a model-based optimization.
In a further embodiment the method comprises a step of compensation for refraction artefacts based on ray tracing an initial reconstructed object. This step can be iterated a number of times until the quality of the image does not substantially improve anymore.
In a further embodiment images of the absolute values of the refractive index and attenuation coefficient can be obtained using a reference transmission optical coherence tomography measurement of the surrounding medium.
Fig. 6a and 6b respectively shows a reconstructed quantitative image of the attenuation coefficient of the phantom object and a reconstructed image of the refractive index of the phantom object.
The above described principles can be used to obtain a complete data set for obtaining 3D images. The 3D images can be obtained from the reconstructed images of multiple slices from the data set. In this description the object can be a translucent object or a biological sample.
The invention can be summarized as a method for optical coherence projection tomography of an object comprising the steps of: obtaining optical coherence projection tomography spectroscopic data of the object; obtaining an optical path length, OPL, distribution using the spectroscopic data;
selecting a region of interest in the OPL distribution corresponding to ballistic photons based on an estimated value of a size and a refractive index of the object; obtaining at least one of a path-length integrated attenuation coefficient and path-length integrated refractive index from the selected region in the OPL distribution; obtaining at least one sinogram for the at least one of the obtained path-length integrated attenuation coefficients and the obtained path-length integrated refractive indexes; and reconstructing an image of the object from the obtained at least one sinogram.
Some or all aspects of the invention may be suitable for being implemented in form of software, in particular a computer program product. The computer program product may comprise a computer program stored on a non-transitory computer-readable media. Also, the computer program may be represented by a signal, such as an optic signal or an electro-magnetic signal, carried by a transmission medium such as an optic fiber cable or the air. The computer program may partly or entirely have the form of source code, object code, or pseudo code, suitable for being executed by a computer system. For example, the code may be executable by one or more processors.
The examples and embodiments described herein serve to illustrate rather than limit the invention. The person skilled in the art will be able to design alternative embodiments without departing from the scope of the present disclosure, as defined by the appended claims and their equivalents. Reference signs placed in parentheses in the claims shall not be interpreted to limit the scope of the claims. Items described as separate entities in the claims or the description may be implemented as a single hardware or software item combining the features of the items described.

Claims (19)

ConclusiesConclusions 1. Werkwijze voor optisch coherente projectie tomografie van een voorwerp, die de stappen omvat van:A method for optically coherent projection tomography of an object, comprising the steps of: het verkrijgen van optisch coherente projectie tomografie spectroscopische data van het voorwerp;obtaining optically coherent projection tomography spectroscopic data from the object; het verkrijgen van een optische weglengte, OPL, verdeling door het gebruik van de spectroscopische data;obtaining an optical path length, OPL, distribution by using the spectroscopic data; het selecteren van een interessegebied in de OPL verdeling die correspondeert met ballistische fotonen gebaseerd op een geschatte waarde van een grootte en een brekingsindex van het voorwerp;selecting an area of interest in the OPL distribution that corresponds to ballistic photons based on an estimated value of a size and a refractive index of the object; het verkrijgen van ten minste één van een weglengte geïntegreerde verzwakkingscoëfficiënt en een weglengte geïntegreerde brekingsindex uit het geselecteerde gebied in de OPL verdeling;obtaining at least one attenuation coefficient integrated into a path length and a path length integrated refractive index from the selected area in the OPL distribution; het verkrijgen van ten minste één sinogram voor de ene van verkregen weglengte geïntegreerde verzwakkingscoëfficiënt en de verkregen weglengte geïntegreerde brekingsindex; en het opbouwen van een afbeelding van het object uit het verkregen ten minste ene sinogram.obtaining at least one sinogram for the one attenuation path length integrated attenuation coefficient and the obtained path length integrated refractive index; and constructing an image of the object from the obtained at least one sinogram. 2. Werkwijze volgens conclusie 1, waarbij de werkwijze omvat:The method of claim 1, wherein the method comprises: het detecteren van een stijgende helling in de geselecteerde interessegebied van de OPL verdeling;detecting a rising slope in the selected area of interest of the OPL distribution; het aanpassen van een Gaussfunctie om een vooraf bepaald venster rond de gedetecteerde helling; en het bepalen van ten minste één van de weglengte geïntegreerde verzwakkingscoëfficiënt en de weglengte geïntegreerde brekingsindex van de plaats en hoogte van de Gaussfunctie.adjusting a Gaussian function around a predetermined window around the detected slope; and determining at least one attenuation coefficient integrated into the path length and the path length integrated refractive index of the location and height of the Gaussian function. 3. Werkwijze volgens conclusie 2, waarbij de stijgende helling in het geselecteerde interessegebied van de OPL verdeling is bepaald door een eerste waarde van het OCT signaal boven een vooraf bepaalde drempel, beginnende van de oorsprong van de OPL verdeling langs een optische weglengte as.The method of claim 2, wherein the rising slope in the selected area of interest of the OPL distribution is determined by a first value of the OCT signal above a predetermined threshold, starting from the origin of the OPL distribution along an optical path-length axis. 4. Werkwijze volgens conclusie 3, waarbij de vooraf bepaalde drempel is gebaseerd op een ruisniveau van de spectroscopische data in het geselecteerde interessegebied.The method of claim 3, wherein the predetermined threshold is based on a noise level of the spectroscopic data in the selected area of interest. 5. Werkwijze volgens één van de voorgaande conclusies, waarbij het opbouwen van de afbeelding is gebaseerde op een gefilterde terug projectie, een algebraïsche reconstructie techniek of een puntspreidfunctie-reconstructie.The method of any one of the preceding claims, wherein the image building is based on a filtered back projection, an algebraic reconstruction technique or a point spread function reconstruction. 6. Werkwijze volgens een van de voorgaande conclusies omvattende het corrigeren van de sinograms voor een verschuiving van het centrum van rotatie van het voorwerp.A method according to any one of the preceding claims comprising correcting the sinograms for a shift of the center of rotation of the object. 7. Werkwijze volgens één van de voorgaande conclusies, waarbij omvattende het verkrijgen van een absolute waarde van de ten minste één van de brekingsindex en de verzwakkingscoëficiënt.A method according to any one of the preceding claims, wherein comprising obtaining an absolute value of the at least one of the refractive index and the attenuation coefficient. 8. Werkwijze volgens een van de voorgaande conclusies, waarbij omvattende een stap voor compensatie van buigingsafwijkingen gebaseerd op straalvolging van een initieel opgebouwd object.A method according to any one of the preceding claims, wherein comprising a step for compensating for flexural deviations based on beam tracking of an initially constructed object. 9. Werkwijze volgens conclusie 8, waarde de compensatiestap ten minste tweemaal wordt herhaald.The method of claim 8, wherein the compensation step is repeated at least twice. 10. Werkwijze volgens een van de voorgaande conclusies, waarbij het voorwerp een doorschijnend voorwerp is.The method of any one of the preceding claims, wherein the article is a transparent article. 11. Inrichting voor optische coherente projectie tomografie van een voorwerp, waarbij de inrichting omvat:An optical coherent projection tomography apparatus of an object, the apparatus comprising: een lichtbron ingericht voor het opwekken van een verlichtingslichtbundel;a light source adapted to generate an illumination light beam; een beweegbaar platform ingericht voor het bewegen van het object ten opzichte van de verlichtingslichtbundel;a movable platform adapted to move the object relative to the illumination light beam; een detector ingericht voor het detecteren van een bemonsterlichtbundel van het voorwerp; en een besturingsinrichting ingericht voor het besturen van de lichtbron, het beweegbare platform en de detector voor:a detector adapted to detect a sample light beam from the object; and a control device adapted to control the light source, the movable platform and the detector for: het verkrijgen van optisch coherente projectie tomografie spectroscopische data van het voorwerp;obtaining optically coherent projection tomography spectroscopic data from the object; het verkrijgen van een optische weglengte, OPL, -verdeling door het gebruik van de spectroscopische data;obtaining an optical path length, OPL, distribution by using the spectroscopic data; het selecteren van een interessegebied in de OPL-verdeling die correspondeert met ballistische fotonen gebaseerd op een geschatte waarde van de grootte en een brekingsindex van het voorwerp;selecting an area of interest in the OPL distribution that corresponds to ballistic photons based on an estimated magnitude value and an object refractive index; het verkrijgen van één van een weglengte geïntegreerde verzwakkingscoëfficiënt en een weglengte geïntegreerde brekingsindex uit het geselecteerde gebied in de OPL-verdeling;obtaining one attenuation coefficient integrated into a path length and a path length integrated refractive index from the selected area in the OPL distribution; het verkrijgen van ten minste één sinogram voor de ene van verkregen weglengte geïntegreerde verzwakkingscoëfficiënt en de verkregen weglengte geïntegreerde brekingsindex; en het opbouwen van een afbeelding van het object uit het verkregen ten minste ene sinogram.obtaining at least one sinogram for the attenuation coefficient of obtained path length integrated and the obtained path length integrated refractive index; and constructing an image of the object from the obtained at least one sinogram. 12. Inrichting volgens conclusie 11, waarbij de inrichting omvat:The device of claim 11, wherein the device comprises: een Mach-Zehnder interferometer gekoppeld met de lichtbron en voorzien van een referentietak ingericht voor het opwekken van een referentielichtbundel en een bemonstertak ingericht voor het opwekken van de verlichtingslichtbundel en het ontvangen van door het voorwerp komende licht; en het combineren van de referentielichtbundel en het licht in een bemonsterlichtbundel.a Mach-Zehnder interferometer coupled to the light source and provided with a reference branch adapted to generate a reference light beam and a sampling branch adapted to generate the illuminating light beam and receive light coming through the object; and combining the reference light beam and the light in a sample light beam. 13. Inrichting volgens conclusie 12, waarbij de lichtbron een super luminescente diode omvat, en de detector een spectrometer omvat.The device of claim 12, wherein the light source comprises a super luminescent diode, and the detector comprises a spectrometer. 14. Inrichting volgens conclusie 13, waarbij de lichtbron een afstembare coherente lichtbron omvat en de detector een fotodiode is.The device of claim 13, wherein the light source comprises a tunable coherent light source and the detector is a photodiode. 15. Inrichting volgens een van de conclusie 11 tot 14, waarbij de inrichting een optische versterker omvat, geplaatst tussen het voorwerp en de lichtbron om het optische vermogen van de verlichtingslichtbundel gericht naar het voorwerp te verhogen.The device of any one of claims 11 to 14, wherein the device comprises an optical amplifier disposed between the object and the light source to increase the optical power of the illumination light beam directed toward the object. 16. Inrichting volgens een van de conclusie 11 tot 15, omvattende een velduitbreidingsinrichting ingericht voor het uitbreiding van een velddiepte van de inrichting gebaseerd op niet-brekende optische bundels zoals een Bessel-bundel.An apparatus according to any of claims 11 to 15, comprising a field expansion apparatus adapted to expand a field depth of the apparatus based on non-refracting optical bundles such as a Bessel bundle. 17. Inrichting volgens een van de conclusies 11 tot 16, waarbij het beweegbare platform een motor en een X, Y-platform omvat, en waarbij het beweegbare platform verder is ingericht om het voorwerp te verschuiven of te draaien ten opzichte van de verlichtingsbundel.The device of any one of claims 11 to 16, wherein the movable platform comprises a motor and an X, Y platform, and wherein the movable platform is further adapted to shift or rotate the object relative to the lighting beam. 18. Inrichting volgens een van de conclusies 11 tot 17, waarbij de inrichting verder omvat een eerste galvanometerspiegel ingericht om het voorwerp ten opzichte van de verlichtingsbundel af te tasten en een tweede galvanometerspiegel ingericht om de bemonsterbundel ten opzichte van het voorwerp af te tasten overeenkomstig de verlichtingsbundel van de eerste galvanometerspiegel.The device of any one of claims 11 to 17, wherein the device further comprises a first galvanometer mirror adapted to scan the object relative to the illumination beam and a second galvanometer mirror adapted to scan the sample beam relative to the object corresponding to the lighting bundle of the first galvanometer mirror. 19. Inrichting volgens een van de conclusies 11 tot 18, waarbij de besturingsinrichting verder is ingericht voor het uitvoeren van een van de werkwijze volgens conclusie 2-10.Device according to one of claims 11 to 18, wherein the control device is further adapted to perform one of the method according to claims 2-10. LLLL
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