Three-dimensional imaging using a fluorescent medium
The attenuation and other optical properties of a medium are exploited to measure a thickness of the medium between a sensor and a target surface. Disclosed herein are various mediums, arrangements of hardware, and processing techniques that can be used to capture these thickness measurements and obtain three-dimensional images of the target surface in a variety of imaging contexts. This includes general techniques for imaging interior/concave surfaces as well as exterior/convex surfaces, as well as specific adaptations of these techniques to imaging ear canals, human dentition, and so forth.
1. A method for obtaining three-dimensional data comprising:
distributing a medium between a target surface and a sensor, the medium including a single fluorescent substance having a fluorescence emission spectrum that overlaps in wavelength with a non-zero absorption spectrum of the medium, wherein the single fluorescent substance is the only fluorescent substance in the medium and consists of a single fluorescent dye;
exciting the single fluorescent substance to provide a fluorescent emission;
measuring the fluorescent emission with the sensor in a direction of a location on the target surface, including measuring an intensity at a first wavelength and an intensity at a second wavelength, wherein the medium has a different coefficient of attenuation for the first wavelength and the second wavelength; and
determining a thickness of the medium in the direction of the location based upon a function of the intensity of the first wavelength and the intensity of the second wavelength.
2. The method of claim 1 wherein the medium has zero absorption at the second wavelength.
3. The method of claim 1 wherein the single fluorescent substance is fluorescein sodium.
4. The method of claim 3 wherein the first wavelength is about 510 nanometers and the second wavelength is about 540 nanometers.
5. The method of claim 1 wherein the medium includes at least one of a liquid, a gas, a solid, and a gel.
6. The method of claim 1 wherein the medium is a gas, the method further comprising providing a transparent barrier between the target surface and the sensor to retain the gas against the target surface.
7. The method of claim 1 wherein the medium is a liquid, the method further comprising: immersing the target surface in the liquid; and positioning the sensor above a top surface of the liquid.
8. The method of claim 1 wherein determining the thickness includes calculating a ratio of the intensity of the first wavelength to the intensity of the second wavelength.
9. The method of claim 1 wherein the sensor measures the intensity of the first wavelength and the intensity of the second wavelength from a plurality of locations on the target surface at a corresponding plurality of pixel locations within the sensor, thereby providing a two-dimensional array of thickness measurements.
10. The method of claim 1 further comprising constructing a three-dimensional image of a region of interest with a plurality of measurements from the sensor.
11. The method of claim 9 further comprising constructing a three-dimensional image of the target surface from a plurality of three-dimensional images of a plurality of regions of interest.
12. The method of claim 1 wherein exciting the single fluorescent substance includes directing a broadband light source toward the single fluorescent substance.
13. The method of claim 1 wherein exciting the single fluorescent substance includes directing a light emitting diode toward the single fluorescent substance.
14. A device comprising:
a target surface having a region of interest; a sensor positioned to measure an intensity at a first wavelength and an intensity at a second wavelength in a direction of a location in the region of interest;
a medium distributed between the target surface and the sensor, the medium including a single fluorescent substance having a fluorescence emission spectrum that overlaps in wavelength with a non-zero absorption spectrum, wherein the medium has a different coefficient of attenuation for the first wavelength and the second wavelength, wherein the single fluorescent substance is the only fluorescent substance in the medium and consists of a single fluorescent dye;
a light source positioned to excite the single fluorescent substance to provide a fluorescent emission; and
a processor programmed to calculate a thickness of the medium in the direction of the location based upon a function of the intensity of the first wavelength and the intensity of the second wavelength.
15. The device of claim 14 wherein the single fluorescent substance is fluorescein sodium.
16. A system comprising:
a distributing means for distributing a medium between a target surface and a sensor, the medium including a single fluorescent substance having a fluorescence emission spectrum that overlaps in wavelength with a non-zero absorption spectrum, wherein the single fluorescent substance is the only fluorescent substance in the medium and consists of a single fluorescent dye;
an illuminating means for exciting the single fluorescent substance to provide a fluorescent emission;
a sensor means for measuring the fluorescent emission with the sensor in a direction of a location on the target surface, including measuring an intensity at a first wavelength and an intensity at a second wavelength, wherein the medium has a different coefficient of attenuation for the first wavelength and the second wavelength; and
a processing means for calculating a thickness of the medium in the direction of the location based upon a function of the intensity of the first wavelength and the intensity of the second wavelength.
17. The system of claim 16 wherein the single fluorescent substance is fluorescein sodium.