Apparatus and method for dating a body sample
A method and apparatus for dating a body sample, for example a sample of body fluid involves taking a series of spectroscopic measurements of the sample, each measurement in the series including at least two predetermined positions in the spectrum. The positions have spectral characteristics corresponding to two or more predetermined substances present in the sample that have a time varying relationship with each other. The measurements in the series are spaced in time. A concentration of each of the substances present in the sample is then determined from each of the spectroscopic measurements at each point in time. Next, a ratio of the concentrations of the two predetermined substances at each point in time is determined and then the ratios of the concentrations of the two predetermined substances over time are analyzed to estimate when the concentrations of the two substances were at a limit of their concentrations, thereby providing an indication of the age of the sample. The sample may be blood, which may be either within the body (e.g. as a bruise), or external to the body.
1. A method of dating a body sample comprising:
taking a spectroscopic measurement of a host material;
taking a series of spectroscopic measurements of the sample, each measurement in the series of spectroscopic measurements including at least two predetermined positions in a spectrum, the predetermined positions having spectral characteristics corresponding to two predetermined substances present in the sample that have a time varying relationship with each other, the measurements in the series of spectroscopic measurements being spaced in time;
determining a concentration of each of the two predetermined substances present in the sample from each measurement in the series of the spectroscopic measurements at each point in time;
determining a ratio of the concentrations of the two predetermined substances at each point in time;
analyzing the ratios of the concentrations of the two predetermined substances over time to estimate when the concentrations of the two predetermined substances were at a limit of their concentrations, thereby providing an indication of the age of the sample; and
wherein determining the concentrations of the two predetermined substances from the series of spectroscopic measurements comprises:
dividing a measured absorbance spectrum obtained from the series of spectroscopic measurements of the sample by an assumed optical path length to provide a corrected absorbance spectrum;
fitting measured spectra of the two predetermined substances to the corrected absorbance spectrum to obtain a residue, and
fitting the spectroscopic measurement of the host material to the residue to obtain relative concentrations of the two predetermined substances within the sample.
2. A method of dating a body sample according to claim 1 , wherein the sample is either inside or outside the body.
3. A method of dating a body sample according to claim 1 , wherein the sample is skin.
4. A method of dating a body sample according to claim 1 , wherein the sample is a body fluid.
5. A method of dating a body sample according to claim 4 , wherein the body fluid is blood.
6. A method of dating a body sample according to claim 5 , wherein one of the two predetermined substances is hemoglobin and the other substance is met-hemoglobin.
7. A method of dating a body sample according to claim 1 , wherein the series of spectroscopic measurements comprises reflectance, Raman or fluorescence spectroscopic measurements.
8. A method of dating a body sample according to claim 1 , wherein one of the two predetermined substances is hemoglobin and the other of the two predetermined substances is bilirubin.
9. A method of dating a body sample according claim 1 , wherein the series of spectroscopic measurements comprise interferometric spectroscopic measurements made at a series of depths in the body.
10. A method of dating a body sample according to claim 1 , wherein the series of spectroscopic measurements include measurements made at several different lateral positions on the body.
11. A method of dating a body sample according to claim 1 , wherein the series of spectroscopic measurements provide several series of measurements, for each of which an estimate of when the concentrations of the two predetermined substances were at a limit of their concentrations is determined, and the estimates for all the several series are analyzed to provide an indication of the age of the sample.