Enhancing selectivity and/or sensitivity of spectroscopic measurements in media
An apparatus for enhancing the selectivity for spectroscopic measurements of analytes in a turbid medium is described. In one example, spatial filters are used to select only certain radii from the medium to be imaged. This selection is accomplished by placing an optical obstruction on the surface of the medium or at an image plane of the surface later in the optical imaging system. In one implementation, this is achieved by placing a fiber bundle at an image plane of the collecting optical system and then using a spacer of appropriate size at the center of the fiber bundle to act as a central obstruction.
1. An apparatus for enhancing spectroscopic measurements of one or more analytes in a sample, the apparatus comprising:
optics that collect light scattered from a sample illuminated by a source of optical radiation, the sample containing one or more analytes;
a spatial filter positioned to reduce the strength of light scattered from or around a surface of the sample and collected by the optics;
a spectroscopic apparatus positioned to receive the scattered light collected by the optics, that divides the received light according to wavelength; and
one or more optical detectors that receive the wavelength-divided light from the spectroscopic apparatus.
2. The apparatus of claim 1 , wherein the spatial filter is a central obscuration located in an image plane of the optics.
3. The apparatus of claim 2 , wherein, at the surface of the sample, a diameter of the image of the source of optical radiation is less than a diameter of an image of the optical obscuration.
4. The apparatus of claim 2 , wherein the central obscuration is an annular obscuration.
5. The apparatus of claim 1 , wherein the sample is of biological origin.
6. The apparatus of claim 5 , wherein the sample is human tissue.
7. The apparatus of claim 5 , wherein the sample is human skin.
8. The apparatus of claim 1 , wherein a first analyte of the analytes is substantially absent from and around a surface of the sample, and the light collected by the optics includes light scattered by the first analyte.
9. The apparatus of claim 1 , further comprising the source of optical radiation, wherein a wavelength of the source is between 600 nm and 1300 nm.