Patent ID: 8077827

Claim:
A method for calibrating an transmissive energy imaging system for quantitatively determining the thickness of a first absorbing material in the presence of a second absorbing material where an incident transmissive energy having an incident intensity is transmitted through the first and second absorbing materials, wherein the method comprises the steps of: fixing the thickness (t S ) of the first absorbing material and varying the thickness of the second absorbing material to obtain a calibration standard having a multiple combinations of thicknesses of the first and the second absorbing material; exposing the calibration standard to the incident transmissive energy; detecting the intensity of the incident transmissive energy which passes through the calibration standard by acquiring multiple pairs of image data which are representative of a portion of the transmissive energy which is measured after transmission through the first and the second absorbing materials, where a logarithm form of a foreground value (log n (I c+s )) in each pair of image data corresponds to a portion of the incident intensity which is transmitted through the known thickness of the first absorbing material in combination with one of the multiple thicknesses of the second absorbing material, and the logarithm form of a background value (log n (I c ) in each pair of transmitted intensities corresponds to a portion of the incident intensity which is transmitted through only the corresponding thickness of the second absorbing material which was in combination with the first absorbing material when the foreground value was acquired; changing the thickness (t Si ) of the first absorbing material to other fixed thicknesses and repeating the above steps to obtain a plurality sets of intensity data, wherein each set of the intensity data corresponds to a fixed thickness of the first absorbing material; determining a fitting constant I d such that a plurality of intercept values ( μ s α ⁢ t Si ) are each described by a line as a function of one of the set of the intensity data, wherein the line has the general form of: μ s α ⁢ t S = log n ⁡ ( I c + I d ) - log n ⁡ ( I c + s + I d ) where ⁢ ⁢ μ s α is related to the characteristic of the first absorbing material and the generation process of the image data; and determining a best fit of the proportional constant μ s α to accomplish the calibration.