Camera Adapter Based Optical Imaging Apparatus

• US 20110043661A1
• Filed: 02/06/2009
• Published: 02/24/2011
• Est. Priority Date: 02/08/2008
• Status: Active Grant

• Current Assignee: University of Kent
• Original Assignee: University of Kent
• Inventors: Podoleanu, Adrian
• Granted Patent: US 8,619,184 B2
• Time in Patent Office: Days
• US Class Current: 348/239
• CPC Class Codes: A61B 3/102 for optical coherence tomography [OCT]
• CPC Class Codes: A61B 3/14 Arrangements specially adapted for eye photography apparatus or arrangements for taking photographs per se G03B
• CPC Class Codes: G01B 2290/35 Mechanical variable delay line
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02007 Two or more frequencies or sources used for interferometric measurement using only beat G01B9/02003
• CPC Class Codes: G01B 9/0203 With imaging systems
• CPC Class Codes: G01B 9/02049 characterised by particular mechanical design details
• CPC Class Codes: G01B 9/02069 Synchronization of light source or manipulator and detector
• CPC Class Codes: G01B 9/02079 Quadrature detection, i.e. detecting relatively phase-shifted signals
• CPC Class Codes: G01B 9/02091 Tomographic interferometers, e.g. based on optical coherence
• CPC Class Codes: G02B 21/0056 based on optical coherence, e.g. phase-contrast arrangements, interference arrangements
• CPC Class Codes: G02B 21/0064 multi-spectral or wavelength-selective arrangements, e.g. wavelength fan-out, chromatic profiling G02B21/0076 takes precedence
• CPC Class Codes: H04N 23/20 for generating image signals from infrared radiation only
• CPC Class Codes: H04N 23/51 Housings
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

The invention describes several embodiments of an adapter which can make use of the devices in any commercially available digital cameras to accomplish different functions, such as a fundus camera, as a microscope or as an en-face optical coherence tomography (OCT) to produce constant depth OCT images or as a Fourier domain (channelled spectrum) optical coherence tomography to produce a reflectivity profile in the depth of an object or cross section OCT images, or depth resolved volumes. The invention admits addition of confocal detection and provides simultaneous measurements or imaging in at least two channels, confocal and OCT, where the confocal channel provides an en-face image simultaneous with the acquisition of OCT cross sections, to guide the acquisition as well as to be used subsequently in the visualisation of OCT images. Different technical solutions are provided for the assembly of one or two digital cameras which together with such adapters lead to modular and portable high resolution imaging systems which can accomplish various functions with a minimum of extra components while adapting the elements in the digital camera. The cost of such adapters is comparable with that of commercial digital cameras, i.e. the total cost of such assemblies of commercially digital cameras and dedicated adapters to accomplish high resolution imaging are at a fraction of the cost of dedicated stand alone instruments. Embodiments and methods are presented to employ colour cameras and their associated optical sources to deliver simultaneous signals using their colour sensor parts to provide spectroscopic information, phase shifting inferometry in one step, depth range extension, polarisation, angular measurements and spectroscopic Fourier domain (channelled spectrum) optical coherence tomography in as many spectral bands simultaneously as the number of colour parts of the photodetector sensor in the digital camera. In conjunction with simultaneous acquistion of a confocal image, at least 4 channels can simultaneously be provided using the three color parts of conventional color cameras to deliver three OCT images in addition to the confocal image.

Claims

1. A camera adapter for imaging an object in cooperation with a digital camera with an optical illumination source, a camera sensor, and a shutter release, the camera adapter comprising:

a light input for accepting light from the optical illumination source;

a light output for directing light onto the camera sensor;

an object facing interface for directing light to the object and back from the object into the adapter;

means in the camera adapter for directing light from the optical illumination source received at the light input to illuminate the object via the object facing interface;

means in the camera adapter for directing light from the object received at the object facing interface onto the camera sensor via the light output; and

means for processing at least one image captured by the camera sensor to generate depth resolved information from the object.

2. A camera adapter according to claim 1 arranged to generate an OCT image, wherein the camera adapter further comprises:

an interferometer configuration using a main splitter, where light from the said optical source is delayed along a reference path within the adapter and the path length from the main splitter to the object and back defines an object path

and an optical path difference adjusting block to alter the optical path difference between the object path and the reference path;

wherein the light along the reference path and light along the object path define an object and a reference beam respectively, which after crossing the main splitter are incident on an optical dispersion element placed between the main splitter and the said light output to disperse light as a function of wavelength onto the camera sensor, where the two beams interfere.

3. A camera adapter according to claim 2 for implementing a combined optical coherence tomography/microscope imaging functionality, wherein the camera adaptor further comprises:

displacing means for laterally displacing the reference optical beam from the object beam in their path towards the optical dispersion element to produce a shifted reference beam; and

a confocal receiver which intercepts the intensity signal due to the object beam from the dispersing element;

wherein the displacing means are arranged to shift the shifted reference beam away from the entrance of the confocal receiver.

4. A camera adapter according to claim 3 where the said confocal receiver uses a point photodetector and the beam projected on the object is focused to a point.

5. A camera adapter according to claim 3 where the said confocal receiver uses a line camera and the interface optics illuminates the object using a line.

6. A camera adapter according to claim 2 further comprising

means for capturing three images of the object;

and

means for combining the three captured images to generate an OCT image.

7. A camera adapter according to claim 6 wherein

the optical path difference adjusting block includes at least one optical path phase modulator;

and

the camera adapter is arranged to capture at least three sequential images at different optical path difference values which are then used to generate a depth resolved image of the said object.

8. A camera adapter according to claim 6, where the camera sensor is a photodetector coloured array with three photodetector sensing arrays, one for each colour and the said three images of the object are images generated by each such said color photodetector sensing array.

9. A camera adapter according to claim 8, wherein

the optical path difference adjusting block includes three optical path phase modulators acting at three different respective wavelength bands;

the camera adapter is arranged to direct light in at least the three wavelength bands; and

the camera adapter is arranged to generate a depth resolved image of the object from the components of a single image in the three wavelength bands.

10. A camera adapter according to claim 9 further comprising a multiplexer for superposing light in the three wavelength bands onto the same pixels.

11. A camera adapter according to claim 1 for imaging an object in cooperation with digital cameras arranged at two positions;

wherein the camera adapter has;

two respective light outputs for directing light onto the camera sensor of respective camera positions;

a single object facing interface;

where the object beam is returned through the main splitter to one input of a 50/50 splitter and the reference beam is input to the second input of the 50/50 splitter;

and where an optical path difference adjusting block can be used to alter the path difference between the object path and the reference path;

means to laterally shift one of the two beams, object or reference before their incidence on the 50/50 splitter;

two optical dispersion elements dispersing light as a function of wavelength, each optical dispersion element arranged in the light path between one of the output of the 50/50 splitter and one of the said adapter output.

12. A camera adapter according to claim 11, further comprising:

two confocal receivers which intercept signals proportional to the intensity of the object beams incident on the two dispersing elements and wherein the displacing means are arranged to shift the shifted reference beams away from the entrances of the confocal receiver so that the confocal receivers receive signals proportional to the intensity of the object beams only.

13. A camera adapter according to claim 1 wherein the means for processing at least one image captured by the camera sensor to generate depth resolved information about the internal structure of the object is a computer programmed to carry out the processing.

14. A camera adapter according to claim 1 wherein the light input, the object facing interface, the means in the camera adapter for directing light to the object and the means in the camera adapter for directing light from the object, the splitter, dispersing elements and adjacent optics are mounted in a first housing and where the optical illumination source is in a 2nd housing mechanically attached to the first housing.

16. A kit comprising a camera adapter according to claim 1 and a digital camera having:

an optical illumination source in the form of a flash and/or infra-red output;

a camera sensor, and

a shutter release.

22. A method of high resolution imaging, comprising:

mounting a camera adapter according to claim 1 to a digital camera having a camera sensor;

connecting the digital camera to a computer arranged to receive the images recorded by the photodetector and process the images;

recording on the camera sensor at least one digital image of an object using the digital camera and adapter; and

processing the at least one digital image captured by the a camera sensor to generate depth resolved information from the object.

23. A method of high resolution imaging according to claim 22, wherein the method includes:

providing an object and a reference beam respectively, the object beam passing from a light source to the object to be imaged and the object beam and the reference beam passing through an optical dispersion element directing both dispersed beams to the camera sensor where they interfere to provide the depth resolved information.

24. A method of high resolution imaging according to claim 23 further comprising:

intercepting a signal proportional to the intensity of the object beam incident on the dispersion element, in a confocal receiver;

laterally displacing the reference optical beam from the object beam in their path towards the optical dispersion element to produce a shifted reference beam to shift the shifted reference beam away from the entrance of the confocal receiver.

25. A method of high resolution imaging according to claim 22, arranged to carry out OCT imaging system with demodulation based on phase shifting interferometry, comprising:

capturing three images sequentially with three different phase shifts; and

processing the three images to generate the depth resolved information.

26. A method of high resolution imaging according to claim 22, arranged to carry out OCT imaging system with demodulation based on phase shifting interferometry, comprising:

capturing three images at different wavelength bands with three different phase shifts in a single data acquisition step; and

processing the three images to generate the depth resolved information.

27. A method of high resolution imaging of an object according to claim 25, where the phase shifts are used in the processing step of the two interfering beams to generate full range depth resolved OCT images, with elimination of ghost terms.

15. A camera adapter for fundus imaging a retina in cooperation with a digital camera with an optical illumination source, a camera sensor, and a shutter release, the camera adapter comprising:

a light input for accepting light from the optical illumination source;

a light output for directing light onto the photodetector array;

an object facing interface for directing light to the retina and back from the retina into the adapter;

means in the camera adapter for directing light from the optical illumination source received at the light input to illuminate the retina via the object facing interface;

an wavelength filter and a spatial filter in the optical path from the optical illumination source to the object facing interface;

means in the camera adapter for directing light from the retina received at the object facing interface onto the camera sensor via the light output; and

means for processing at least one image captured by the camera sensor.

17. Apparatus for imaging an object providing simultaneous measurement in two channels, a confocal channel and an optical coherence tomography (OCT) channel, comprising:

an optical illumination source,

a camera sensor,

a main splitter and a 2^nd splitter

an optical dispersion element dispersing light as a function of wavelength, placed in the light path between one of the output of the 2nd splitter and the said adapter output

a confocal receiver which intercepts a signal proportional to the intensity of the object beam incident on the dispersing element;

where light from the said optical illumination source is split in a main splitter between an object beam and a reference beam, where the object beam is sent towards the object via the adapter input

where the path length from the main splitter along the object beam to the object and back to the main splitter and then along from one of the outputs of the main splitter to the 1^st input of a 2^nd splitter defines an object path and the path from the main splitter along the reference beam towards the 2^nd input of the 2^nd splitter defines a reference path

an optical path difference adjusting block between the path lengths of the object path and the reference path;

displacing means for laterally displacing the reference optical beam from the object beam in its path towards the optical dispersion element to shift the reference beam away from the entrance of the confocal receiver so that the confocal receiver receives a signal proportional to the intensity of the object beam only;

means for processing at least one image captured by the camera sensor to generate depth resolved information from the object as the OCT channel; and

means for producing an en-face image using the signal provided by the confocal receiver.

18. A camera adapter according to claim 17 where the said optical dispersion element is a diffraction grating and in addition to the diffracted output beam, an ‘

intensity’

signal proportional to the intensity of the incoming beam is produced in the zero order of diffraction.

19. A camera adapter according to claim 17 where the said optical dispersion element is a prism and in addition to the dispersed output beam, an ‘

intensity’

signal proportional to the intensity of the incoming beam is produced as a reflection on one of the prism facets.

20. A method of high resolution imaging, comprising collecting cross section OCT images to sample the volume of the object;

simultaneously collecting lines for an en-face image; and

generating and providing a complete en-face image by the time all cross section OCT images have been completed.

28. A method of high resolution imaging of an object according to claim 20, including frequency shifting to create a carrier to be subsequently used in the processing step of the two interfering beams to generate full range depth resolved OCT images. with elimination of ghost terms.

29. A method of high resolution imaging of an object according to claim 20, where three wavelength bands generated by the optical source are superposed onto the same pixels of a color camera sensor and where the camera outputs m depth resolved OCT images, one for each color sensor part out of the m color sensitive parts of the camera sensor.

21. A method of high resolution imaging of an object providing simultaneous measurement in two channels, a confocal channel and an optical coherence tomography (OCT) channel, the method comprising:

providing an object and a reference beam respectively, the object beam passing from a light source to the object to be imaged and the object beam and the reference beam passing through an optical dispersion element directing both dispersed beams to a camera sensor where they interfere to generate depth resolved image data of the OCT channel;

intercepting a signal proportional to the intensity of the object beam incident on the dispersion element in a confocal receiver;

laterally displacing the reference optical beam from the object beam in their path towards the optical dispersion element to produce a shifted reference beam to shift the shifted reference beam away from the entrance of the confocal receiver,

measuring the intensity of the object beam in the confocal detection of the object beam to provide the confocal channel; and

producing an A-scan OCT by evaluating the FFT of the signal delivered by reading the camera.