Characterizing a sample by material basis decomposition

Patent metadata

Field	Value
Publication number	US-2016363442-A1
Application number	US-201615181882-A
Country	US
Kind code	A1
Filing date	Jun 14, 2016
Priority date	Jun 15, 2015
Publication date	Dec 15, 2016
Grant date	—

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 (S ech ) transmitted through this sample, located in an X and/or gamma spectral band, naled spectrum transmitted through the sample; for each spectrum of a plurality of calibration spectra (S base (L k ; L l )), calculating a likelihood from said calibration spectrum (S base (L k ; L l )), and from the spectrum transmitted through the sample (S ech ), each calibration spectrum (S base (L k ; L l )) 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 (L 1 , L 2 ) associated with the sample according to the criterion of maximum likelihood.

First claim

1 . A method for characterizing a sample, by estimating a plurality of thicknesses, named characteristic thicknesses, each being associated with a material named calibration material, wherein said method comprises the following steps:
acquiring an energy spectrum, named spectrum transmitted through the sample (S ech ), said spectrum being defined by a number of photons transmitted through the sample in each channel of a plurality of energy channels located in an X and/or gamma spectral band; for each spectrum of a plurality of energy spectra named calibration spectra (S base (L 1 ; L 2 )), calculating the value of a likelihood function from said calibration spectrum (S base (L 1 ; L 2 )) and from the spectrum transmitted through the sample (S ech ), each calibration spectrum (S base (L 1 ; L 2 )) corresponding to the spectrum transmitted through a stack of gauge blocks, each gauge block being formed of a known thickness of a calibration material; determining the estimations of the characteristic thicknesses ({circumflex over (L)} 1 ech ; {circumflex over (L)} 2 ech ) associated with the sample, from said values of a likelihood function and according to the criterion of maximum likelihood.

2 . The method according to claim 1 , wherein determining the estimations of the characteristic thicknesses (L 1 ech ; L 2 ech ) associated with the sample, comprises searching for a maximum of the values of the likelihood function, the thicknesses associated with this maximum forming the estimations ({circumflex over (L)} 1 ech ; {circumflex over (L)} 2 ech ) of the characteristic thicknesses (L 1 ech ; L 2 ech ).

3 . The method according to claim 1 , wherein said method comprises at least one step of interpolating the values of the likelihood function or of interpolating the calibration spectra.

4 . The method according to claim 3 , wherein at least one step of interpolating implements a non-linear interpolation function.

5 . The method according to claim 3 , wherein said method comprises the following steps:
interpolating values of the likelihood function by a likelihood interpolation function depending on at least one variable, each variable corresponding to the thickness of a calibrating material; and searching for a maximum of the values of said likelihood interpolation function, the thicknesses associated with this maximum forming the estimations of the characteristic thicknesses.

6 . The method according to claim 3 , wherein it comprises the following steps:
Interpolating the calibration spectra by a spectrum interpolation function depending on at least one variable, each variable corresponding to the thickness of a calibration material; and searching for a maximum of the values of said spectrum interpolation function, the thicknesses associated with this maximum forming the estimations of the characteristic thicknesses.

7 . The method according to claim 3 , wherein the following steps are implemented:
interpolating the values of the likelihood function by a likelihood interpolation function, said values being associated with combinations of known thicknesses of calibration materials such that for each calibration material, the associated thicknesses are located within a first respective interval; searching for a maximum of the values of said likelihood interpolation function, the thicknesses associated with this maximum forming approximate values ({circumflex over (L)}′ 1 , {circumflex over (L)}′ 2 ) of the estimations of the characteristic thicknesses; interpolating the calibration spectra by a spectrum interpolation function depending on at least one variable, each variable corresponding to the thickness of a calibration material and taking values located within a second respective interval ([L′ 11 , L′ 12 ]; [L′ 21 , L′ 22 ]) narrower than the first interval associated with the same calibration material and centred on the approximate value ({circumflex over (L)}′ 1 , {circumflex over (L)} 2 ) associated with the same calibration material; for each of the values of said spectrum interpolation function, calculating the value of the likelihood function and searching for a maximum of said values of the likelihood function, the thicknesses associated with this maximum forming consolidated estimations ({circumflex over (L)} 1 ech ; {circumflex over (L)} 2 ech ) of the characteristic thicknesses.

8 . The method according to claim 3 , wherein the following steps are implemented:
interpolating calibration spectra by a spectrum interpolation function, said calibration spectra being associated with combinations of known thicknesses of calibration materials such that for each calibration material, the associated thicknesses are located within a first respective interval; for each of the values of said spectrum interpolation function, calculating the value of the likelihood function and searching for a maximum of said values of the likelihood function, the thicknesses associated with this maximum forming approximate values ({circumflex over (L)} 1 (2) , {circumflex over (L)} 2 (2) ) of the estimations of the characteristic thicknesses; interpolating the values of the likelihood function by a likelihood interpolation function depending on at least one variable, each variable corresponding to the thickness of a calibration material and taking values located within a second respective interval ([L 11 (2) ; L 12 (2) ]; [L 21 (2) ; L 22 (2) ]) narrower than the first interval associated with the same calibration material and centred on the approximate value ({circumflex over (L)} 1 (2) , {circumflex over (L)} 2 (2) ) associated with the same calibration material; and searching for a maximum of the values of said likelihood interpolation function, the thicknesses associated with this maximum forming consolidated estimations ({circumflex over (L)} 1 ech ; {circumflex over (L)} 2 ech ) of the characteristic thicknesses.

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

10 . 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

• G01N2223/304

  electric circuits, signal processing · CPC title

• G01N2223/401

  image processing · CPC title

• G01N2223/423

  multispectral imaging-multiple energy imaging · CPC title

• G01N2223/50

  Detectors · CPC title

• G01N2223/03

  by transmission · CPC title