Characterizing a sample by material basis decomposition

Patent metadata

Field	Value
Publication number	US-10969220-B2
Application number	US-201615181882-A
Country	US
Kind code	B2
Filing date	Jun 14, 2016
Priority date	Jun 15, 2015
Publication date	Apr 6, 2021
Grant date	Apr 6, 2021

Abstract

A method for characterizing a sample, by estimating a plurality of characteristic thicknesses, each being associated with a calibration material, including acquiring an energy spectrum (Sech) transmitted through this sample, located in an X and/or gamma spectral band; for each spectrum of a plurality of calibration spectra (sbase(Lk; Lt)) calculating a likelihood from said calibration spectrum (Sbase(Lk; Lt)), and from the spectrum transmitted through the sample (Sech), each calibration spectrum (Sbase(Lk; Lt)) corresponding to the energy spectrum transmitted through a stack of gauge blocks, each formed of a known thickness of a calibration material; estimating the characteristic thicknesses (L1, L2) associated with the sample according to the criterion of maximum likelihood.

First claim

The invention claimed is:

1. A method for characterization of a sample, the method comprising:
acquiring, by circuitry comprising a memory and a detector connected to a processor, a spectrum transmitted through the sample, said spectrum being an energy spectrum defined by a number of photons transmitted through the sample in each channel of a plurality of energy channels located in an X spectral band and/or a gamma spectral band;
acquiring, by said memory, calibration spectra, wherein each of the calibration spectra corresponds to a calibration spectrum transmitted through a stack of gauge blocks, each gauge block of said stack consisting of a different calibration material, and said stack consisting of a different set of thicknesses for each of the gauge blocks;
calculating, by said circuitry, values of a likelihood function from said acquired calibration spectra and from the spectrum transmitted through the sample;
determining, by said circuitry, a maximum likelihood value from among the calculated values of the likelihood function, the determined maximum likelihood value corresponding to an acquired calibration spectrum corresponding to a stack of gauge blocks, each gauge block of the stack consisting of a different calibration material, the acquired calibration spectrum being most similar to the acquired spectrum transmitted through the sample; and
outputting, from the circuitry, a plurality of estimated characteristic thicknesses, each of the outputted estimated characteristic thicknesses being associated with a different calibration material, wherein each different calibration material making up a gauge block from the stack of gauge blocks of the acquired calibration spectrum corresponding to said determined maximum likelihood value, the method further comprising:
interpolating the calculated values of the likelihood function by a likelihood interpolation function, said interpolated calculated values being associated with combinations of predetermined thicknesses of respective calibration materials, such that for each respective calibration material a corresponding set of thicknesses is located within a first interval associated with the respective calibration material;
searching for a maximum among calculated values of said likelihood interpolation function, thicknesses associated with said maximum among the calculated values of the likelihood interpolation function forming approximate values of the plurality of estimated characteristic thicknesses of the respective calibration materials;
interpolating the calibration spectrum by a spectrum interpolation function depending on at least one variable, said at least one variable corresponding to a thickness of said each calibration material, and taking values located within a second respective interval, narrower than the first interval associated with the respective calibration material and centred on an approximate value of said approximate values; and
for each value of said spectrum interpolation function, calculating a value of the likelihood function and searching for a maximum among said calculated values of the likelihood function, thicknesses associated with the maximum among the calculated values of the likelihood function for each value of the spectrum interpolation function forming the plurality of estimated characteristic thicknesses of the respective calibration materials.

2. The method according to claim 1 , wherein said outputting the plurality of estimated characteristic thicknesses comprises searching for the maximum likelihood value from among the calculated values of the likelihood function, the thicknesses associated with the maximum likelihood value from among the calculated values of the likelihood function forming the plurality of estimated characteristic thicknesses.

3. The method according to claim 1 , wherein at least one of the interpolating the calculated values of the likelihood function and the interpolating the calibration spectrum implements a non-linear interpolation function.

4. The method according to claim 1 , wherein the likelihood function is determined from a statistical modelling of the spectrum transmitted through the sample, according to a Poisson distribution.

5. The method according to claim 1 , wherein the likelihood function calculated from said calibration spectrum and from the spectrum transmitted through the sample, is defined by:

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Assignees

• Commissariat Energie Atomique

Inventors

• Brambilla Andrea
• Gorecki Alexia
• POTOP Alexandra

Classifications

• G01N23/087 Primary

  using polyenergetic X-rays · CPC title

• G01N2223/423

  multispectral imaging-multiple energy imaging · CPC title

• G01N2223/401

  image processing · CPC title

• G01N2223/03

  by transmission · CPC title

• G01N2223/50

  Detectors · CPC title