Method and apparatus for imaging tissue topography

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.

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;   means for controlling said illumination sources and said optical system enabling changing the illumination directions and capturing said plurality of images with different spatial properties;   means for eliminating specular reflection from said captured images, wherein said means comprises at least two polarisers, a first polariser positioned between the illumination sources and the surface, and a second polariser between the surface and the optical imaging system; and   means 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.   
     
     
         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 1  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 two or more illumination sources are illuminated simultaneously during the acquisition of a single image and a linear combination of representative illumination vectors is used as a virtual source, wherein the two or more sources illuminate the surface at a time to increase the illumination intensity and reduce the number of individual images acquired to produce said three dimensional image. 
     
     
         5 . 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. 
     
     
         6 . The image capture device according to  claim 1  wherein at least one of the illumination sources operate within the visible range of electromagnetic spectrum. 
     
     
         7 . 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. 
     
     
         8 . 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. 
     
     
         9 . The image capture device according to  claim 1  comprising an interchangeable imaging lens system and/or wherein the interchangeable imaging lens system is integrated with an attachment enabling to maintain the optimal working distance between the imaging system and the inspected object. 
     
     
         10 . (canceled) 
     
     
         11 . The image capture device according to  claim 1  comprising means for the automatic recognition of an imaging lens and removable attachment used. 
     
     
         12 . The image capture device according to  claim 1  comprising an interchangeable imaging lens system wherein within the field of view specific patterns; such as a bar code patterns, colour-coded patterns specific for each of the imaging lens and removable attachment and used for their automatic recognition. 
     
     
         13 . 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. 
     
     
         14 . The image capture device according to  claim 1  wherein said illumination sources comprises non-identical spectral characteristics to measure the spectral characteristics of the surface and/or wherein the measured spectral characteristics is used for colorimetry analysis of the skin tissue surface and/or wherein the spectral characteristics is 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. 
     
     
         15 - 16 . (canceled) 
     
     
         17 . The image capture device according to  claim 1  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 and/or 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 optionally 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. 
     
     
         18 - 19 . (canceled) 
     
     
         20 . The image capture device according to  claim 1  wherein the surface image captured is human skin tissue and/or 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 and/or wherein said constituents represent levels of haemoglobin, oxyhaemoglobin, deoxyhaemoglobin, melanin or collagen. 
     
     
         21 - 22 . (canceled) 
     
     
         23 . Device, according to  claim 1 , for use in dermatology and/or skin care applications for human skin tissue. 
     
     
         24 . Device, according to  claim 1 , for use in aesthetic medicine, cosmetics or wound management applications such as the assessment of skin surface structure, and/or wrinkles analysis, and/or skin micro-relief and/or the examination of skin lesions and wounds for human skin tissue. 
     
     
         25 . An image capture device for the acquisition of the topography of a skin tissue surface, comprising:
 three or more illumination sources for illuminating said surface;   an optical system adapted for the capture of a plurality of images of said surface;   means for controlling said illumination sources and said optical system enabling changing spatial properties of the illumination and capturing said plurality of images with different spatial properties;   wherein two or more illumination sources are used simultaneously during the acquisition of a single image and a linear combination of representative illumination vectors is used for description of combined virtual source, such that the two or more sources illuminate the surface at a time increases the illumination intensity and reduce the number of individual images acquired; and   means 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.   
     
     
         26 . 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;   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.   
     
     
         27 . An optical apparatus for the image 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;   means for controlling said illumination sources and said optical system enabling changing the illumination directions and capturing said plurality of images with different spatial properties;   means for eliminating specular reflection from said captured images, wherein said means comprises at least two polarisers, a first polariser positioned between the illumination sources and the surface, and a second polariser between the surface and the optical imaging system; and   means 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.