Method and apparatus for imaging tissue topography

• US 9,706,929 B2
• Filed: 03/23/2016
• Issued: 07/18/2017
• Est. Priority Date: 02/25/2009
• Status: Active Grant

• Current Assignee: The Provost Fellows and Scholars of the College of the Holy and Undivided Trinity of Queen Elizabeth, near Dublin
• Original Assignee: The Provost Fellows and Scholars of the College of the Holy and Undivided Trinity of Queen Elizabeth, near Dublin
• Inventors: Kantor, Roman, Mariotto, Guido, Shvets, Igor
• Primary Examiner(s): Rahman, Mohammad J
• Application Number:
  US15/078,714
• Publication Number:
  US 20160270665A1
• Time in Patent Office: 482 Days
• Field of Search: None
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 2562/08 Sensors provided with means for identification, e.g. barcodes or memory chips
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/0075 by spectroscopy, i.e. measuring spectra, e.g. Raman spectroscopy, infrared absorption spectroscopy A61B5/0071 takes precedence
• CPC Class Codes: A61B 5/0077 Devices for viewing the surface of the body, e.g. camera, magnifying lens
• CPC Class Codes: A61B 5/14546 for measuring analytes not otherwise provided for, e.g. ions, cytochromes
• CPC Class Codes: A61B 5/442 Evaluating skin mechanical properties, e.g. elasticity, hardness, texture, wrinkle assessment
• CPC Class Codes: A61B 5/443 Evaluating skin constituents, e.g. elastin, melanin, water
• CPC Class Codes: A61B 5/444 Evaluating skin marks, e.g. mole, nevi, tumour, scar
• CPC Class Codes: A61B 5/445 Evaluating skin irritation or skin trauma, e.g. rash, eczema, wound, bed sore
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: G06F 18/22 Matching criteria, e.g. proximity measures
• CPC Class Codes: G06T 2207/10152 Varying illumination
• CPC Class Codes: G06T 2207/30024 Cell structures in vitro; Tissue sections in vitro
• CPC Class Codes: G06T 2207/30088 Skin; Dermal
• CPC Class Codes: G06T 7/0012 Biomedical image inspection
• CPC Class Codes: G06T 7/586 from multiple light sources, e.g. photometric stereo

Abstract

The present invention relates to an optical device for imaging and measuring characteristics of an objects surface shape, surface spectral reflectance and structure of sub-surface layers. In particular, the invention relates to imaging of topography of human skin and skin sub-surface layers and determination of concentration of skin constituents. The present invention has applications in areas such as skin care, dermatology, cosmetics, wound management and tricology. The imaging device of the invention significantly improves photometric stereo measurements by suppressing specular reflection and allows accurate determination of the surface shape. Consequently the device allows elimination of the influence of the shape and illumination conditions on spectral measurements and allows accurate measurement of skin constituents.

Claims

1. An image capture device for the acquisition of the topography of a skin tissue surface, comprising:

a plurality of illumination sources for illuminating said surface;

an optical imaging system adapted for the capture of a plurality of images of said surface;

a controller for controlling said illumination sources and said optical system enabling changing the illumination directions and capturing said plurality of images with different spatial properties,

wherein during the acquisition of at least one image the plurality of individual illumination sources illuminate the surface simultaneously,

wherein properties of the plurality of simultaneously illuminating sources are characterised to a single virtual source based on a calibration obtained from the illumination properties measured individually for each position and each illumination source previously,

at least two polarisers for eliminating specular reflection from said captured images, a first polariser positioned between the illumination sources and the surface, and a second polariser between the surface and the optical imaging system; and

a processor for analysing the differences between images captured with different illumination properties to reconstruct the topography of said surface based on a diffusive reflection model to produce a three dimensional image of said skin tissue surface,

wherein the variation in illumination properties for different points within the imaged area are taken into account to specify the surface properties for subsequent processing,

wherein data for each image and position are adjusted according to prior calibration data to compensate for the errors due to variations in the illumination intensity or in the illumination direction,

wherein said calibration data characterize the effective intensities and directions of the illumination sources for each image and position within the viewing area, and

wherein said prior calibration data were obtained from calibration images using a reference surface with known shape and optical properties, and such calibration data is used during subsequent measurements.

2. The image capture device according to claim 1 wherein the first and second polarisers are linear light polarisers and aligned in a cross-polarised relationship with each other.

3. The image capture device according to claim 2 wherein the plurality of captured images are of substantially the same area with varying illumination conditions all under the same polarisation direction of the incident light and substantially cross-polarised direction of detected reflected and scattered light.

4. The image capture device according to claim 1 wherein the means for analysing comprises processing said plurality of captured images to calculate the tilt of the surface at each point of the area from the difference between images taken under different illumination conditions and recover the topography of the surface.

5. The image capture device according to claim 1 wherein at least one of the illumination sources operates within the visible range of electromagnetic spectrum.

6. The image capture device according to claim 1 wherein at least one of the illumination sources emits radiation outside the visible range of the electromagnetic spectrum.

7. The image capture device according to claim 1 wherein the illumination sources contain elements for further light conditioning utilising refractive or reflective or dispersive optics such as lenses, beam splitters, planar or curved mirrors, filters, reflective or transmissive diffusers.

8. The image capture device according to claim 1 comprising an interchangeable imaging lens system.

9. The image capture device according to claim 8 wherein the interchangeable imaging lens system is integrated with an attachment to maintain the optimal working distance between the imaging system and the inspected object.

10. The image capture device according to claim 8 comprising means for the automatic recognition of the imaging lens and removable attachment used.

11. The skin tissue image capture device according to claim 8 comprising within the field of view specific patterns such as bar code patterns and colour-coded patterns specific for each of the imaging lens and removable attachment, and used for their automatic recognition.

12. The image capture device according to claim 1 wherein the optical system comprises one or more reflection pads for measuring variation of the intensities of illumination sources for further calibration.

13. The image capture device according to claim 1 wherein said illumination sources comprise non-identical spectral characteristics to measure the spectral characteristics of the surface.

14. The image capture device according to claim 13 wherein the measured spectral characteristics are used for colorimetry analysis of the skin tissue surface.

15. The image capture device according to claim 13 wherein the spectral characteristics are measured using light sources of different wavelengths propagating to different depths below the surface and the spectral differences are used for the sub-surface characterisation of the surface.

16. The image capture device according to claim 1 wherein the surface image captured is human skin tissue.

17. The image capture device according to claim 16 wherein data collected is used for the characterisation of human skin and the assessment of skin condition and health and/or for the identification of skin constituents present.

18. The image capture device according to claim 17 wherein said constituents represent levels of haemoglobin, oxyhaemoglobin, deoxyhaemoglobin, melanin or collagen.

19. The image capture device according to claim 1 wherein the image is human skin tissue.

20. The image capture device according to claim 1 wherein the image is related to skin lesions and wounds of human skin tissue.

22. The image capture device according to claim 1, further comprising means for calibrating each individual source based on a measurement of light intensity for each individual pixel within a device field of view and measured upon response over a well-defined target reference surface, and the property of the characterized virtual source is determined as a sum of vectors of individual sources, and wherein a magnitude of each individual source is proportional to its illumination intensity, and the direction of each individual source is determined as normalised positional difference between pixel coordinates and the source coordinates.

21. A method of capturing images for the acquisition of the topography of a skin tissue surface, comprising the steps of:

illuminating said surface using a plurality of illumination sources;

capturing a plurality of images of said illuminated surface using an optical system;

controlling said illumination sources and said optical system enabling changing spatial properties of the illumination and capturing said plurality of images with different illumination directions, wherein during the acquisition of at least one image the plurality of individual illumination sources illuminate the surface simultaneously, wherein properties of the plurality of simultaneously illuminating sources are characterised to a single virtual source based on a calibration obtained from the illumination properties measured individually for each position and each illumination source previously, wherein the intensities of the illumination sources are calibrated using a reference surface with known shape and optical properties, and such calibration data is used during subsequent measurements to compensate for the variations of illumination intensities;

eliminating specular reflection from said captured images; and

analysing the differences between images captured with different illumination properties to reconstruct the topography of said surface based on a diffusive reflection model,

wherein the variation in illumination properties for different points within the imaged area are taken into account to specify the surface properties for subsequent processing, and

wherein calibration data is acquired for each position within the viewing area and each illumination source to compensate for the errors due to variations in the illumination intensity or in the illumination direction.