Dental surface imaging using polarized fringe projection

Abstract

An intra-oral imaging apparatus having a fringe pattern generator energizable to emit a fringe pattern illumination having a predetermined spatial frequency, with light in the approximate 350-500 nm range. A polarizer in the path of the fringe pattern illumination has a first polarization transmission axis. A projection lens is disposed to direct the polarized fringe pattern illumination as incident illumination toward a tooth surface. An imaging lens is disposed to direct light reflected and scattered at the tooth surface along a detection path. An analyzer is disposed along the detection path, having a second polarization transmission axis. A detector disposed along the detection path obtains image data from the light provided through the analyzer. A control logic processor is responsive to programmed instructions and actuable to adjust the intensity over one or more portions of the fringe pattern illumination according to the image data obtained from the detector.

1 . An intra-oral imaging apparatus comprising:
 a fringe pattern generator energizable to emit a fringe pattern illumination having a predetermined spatial frequency, with light in the approximate 350-500 nm range;   a polarizer disposed in the path of the fringe pattern illumination emitted from the fringe pattern generator and having a first polarization transmission axis;   a projection lens disposed to direct the polarized fringe pattern illumination as incident illumination toward a tooth surface;   an imaging lens disposed to direct at least a portion of the light reflected and scattered from the incident illumination at the tooth surface along a detection path;   an analyzer disposed along the detection path and having a second polarization transmission axis;   a detector disposed along the detection path for obtaining image data from the light provided through the analyzer; and   a control logic processor responsive to programmed instructions and actuable to obtain image data from the detector and to adjust the intensity over one or more portions of the fringe pattern illumination that is emitted from the fringe pattern generator according to the obtained image data.   
     
     
         2 . The imaging apparatus of  claim 1  wherein the second polarization transmission axis is parallel to the first polarization transmission axis. 
     
     
         3 . The imaging apparatus of  claim 1  wherein the second polarization transmission axis is orthogonal to the first polarization transmission axis. 
     
     
         4 . The imaging apparatus of  claim 1  further comprising an actuator coupled to either the polarizer or the analyzer and energizable to rotate the coupled polarizer or analyzer to one of two positions, substantially 90 degrees apart. 
     
     
         5 . The imaging apparatus of  claim 1  wherein the analyzer is a polarization beam splitter and wherein the detector is a first detector disposed to receive light transmitted through the polarization beam splitter and further comprising a second detector disposed to receive light reflected from the polarization beam splitter. 
     
     
         6 . The imaging apparatus of  claim 1  wherein the fringe pattern generator comprises a grating. 
     
     
         7 . The imaging apparatus of  claim 1  wherein the fringe pattern generator comprises a spatial light modulator. 
     
     
         8 . The imaging apparatus of  claim 7  wherein the spatial light modulator is taken from the group consisting of a digital micromirror device and a liquid crystal device. 
     
     
         9 . The imaging apparatus of  claim 1  wherein the fringe pattern generator comprises an emissive device that forms and emits the fringe pattern. 
     
     
         10 . The imaging apparatus of  claim 1  further comprising a filter disposed along the detection path for transmitting light in the 350-500 nm range. 
     
     
         11 . A method for obtaining a surface image of a tooth comprising:
 obtaining a reference image of a portion of the tooth surface having at least a lighter area and a darker area;   generating and projecting one or more fringe patterns onto the portion of the tooth surface, wherein the intensity of the fringe pattern illumination that is directed toward the darker area exceeds the intensity of the fringe pattern illumination that is directed toward the lighter area and wherein the fringe pattern has the same spatial frequency for pattern features over the lighter and darker areas; and   obtaining one or more images from the one or more projected fringe patterns.   
     
     
         12 . The method of  claim 11  wherein obtaining the reference image further comprises directing a structured illumination onto the tooth surface. 
     
     
         13 . The method of  claim 11  wherein projecting the one or more fringe patterns comprises modulating light of a wavelength in the range from 350-500 nm. 
     
     
         14 . The method of  claim 11  wherein projecting the one or more fringe patterns comprises modulating polarized light. 
     
     
         15 . The method of  claim 11  wherein obtaining the reference image further comprises changing the transmission axis of an analyzer or a polarizer. 
     
     
         16 . The method of  claim 11  wherein generating the one or more fringe patterns comprises actuating a spatial light modulator. 
     
     
         17 . The method of  claim 11  wherein obtaining the reference image comprises obtaining light directed from a polarization beamsplitter. 
     
     
         18 . The method of  claim 11  wherein generating the one or more fringe patterns further comprises shifting the relative spatial position of two or more of the generated fringe patterns. 
     
     
         19 . The method of  claim 18  wherein shifting the relative spatial position of two or more of the generated fringe patterns comprises shifting by a fraction of the period of the fringe pattern. 
     
     
         20 . An intra-oral imaging apparatus comprising:
 a fringe pattern generator comprising a spatial light modulator and energizable to emit a fringe pattern illumination having a plurality of pattern features with a predetermined spatial frequency;   a polarizer disposed in the path of the fringe pattern illumination emitted from the fringe pattern generator and having a first polarization transmission axis;   a projection lens disposed to direct the polarized fringe pattern illumination as incident illumination toward a tooth surface;   an imaging lens disposed to direct at least a portion of the light reflected and scattered from the incident illumination at the tooth surface along a detection path;   an analyzer disposed along the detection path and having a second polarization transmission axis;   a detector disposed to form image data from light that is obtained from the tooth along the detection path;   a filter disposed along the detection path for transmitting light in a range from approximately 350-500 nm and attenuating light outside the range; and   a control logic processor responsive to programmed instructions and actuable to obtain image data from the detector and to adjust the intensity of light over one or more portions of the pattern features of the fringe pattern illumination that is emitted from the fringe pattern generator according to the obtained image data.