Method for correcting a spectrum

Patent metadata

Field	Value
Publication number	US-2017103822-A1
Application number	US-201615288146-A
Country	US
Kind code	A1
Filing date	Oct 7, 2016
Priority date	Oct 9, 2015
Publication date	Apr 13, 2017
Grant date	—

Abstract

The invention relates to a method for processing energy spectra of a radiation transmitted by an object irradiated by a source of ionizing radiations, in particular an X radiation, for applications in medical imaging or non-destructive inspection. The method implements a detector comprising a plurality of pixels, each pixel being able to establish a spectrum of the radiation transmitted by the object. The method makes it possible, from a plurality of spectra detected, to establish so-called corrected spectra. Each corrected spectrum is an estimation of the spectrum of a radiation, called primary radiation, transmitted by the object. The invention makes it possible to reduce the influence of the scattering, by the object, of the spectrum emitted by the source.

First claim

1 . A Method for correcting a spectrum of an ionizing electromagnetic radiation transmitted by an object,
the object being arranged between an irradiation source and a detector, the irradiation source being configured to emit an ionizing electromagnetic radiation, called incident radiation, towards said object; the detector comprising pixels, each pixel being configured to detect a radiation transmitted by the object towards the detector, and to acquire a spectrum therefrom, the transmitted radiation comprising a scattering radiation, caused by the scattering of the incident radiation in the object, and a primary radiation;
the method comprising the steps of:
a) interposing a mask between the source and the object, and acquiring, by several pixels, a first spectrum of a first radiation transmitted by the object, the mask comprising attenuating elements, configured to attenuate a part of said incident radiation, and of which a projection on the detector defines a first group of pixels;
b) obtaining, for each pixel of the first group of pixels, a second spectrum of a second radiation transmitted by the object to the detector, in the absence of said mask;
c) comparing, for each pixel of said first group of pixels, the first spectrum and the second spectrum, so as to obtain a comparison spectrum;
d) at each pixel of the first group of pixels, applying a transition matrix, previously established, to said comparison spectrum, to obtain an estimation of a so-called primary spectrum representing the primary radiation transmitted by the object to said pixel, and estimating a scattering spectrum, representative of the scattering radiation transmitted by the object;
e) for all or some of the pixels of the detector, from each scattering spectrum estimated in the step d), correcting the second spectrum or the first spectrum, so as to obtain a corrected spectrum.

2 . The method according to claim 1 , in which the step e) comprises, prior to the correction, an estimation of a scattering spectrum for all of the pixels of the detector.

3 . The method according to claim 1 , in which the step e) comprises, for each pixel, a subtraction of the estimated scattering spectrum from the second spectrum or the first spectrum.

4 . The method according to claim 1 , in which, in the step b), for each pixel of the first group, the second spectrum is obtained:
either by an acquisition of the second spectrum by said pixel; or by an estimation on the basis of at least one first spectrum acquired by at least one pixel not belonging to the first group.

5 . The method according to claim 1 , in which:
the step a) is implemented in a plurality of configurations, each configuration being associated with a position of the detector and of the source relative to the object, so as to obtain, in each configuration and for each pixel, a first spectrum, each configuration also defining a first group of pixels; the step b) comprises, for all or some of the pixels of the first group defined by a configuration, a determination of a second spectrum from a first spectrum obtained according to another configuration.

6 . The method according to claim 5 , in which each configuration being associated with a parameter, such that at least one second spectrum according to a configuration associated with a first parameter is obtained from a first spectrum obtained according to another configuration, the latter being associated with a second parameter, different from the first parameter.

7 . The method according to claim 6 , in which said parameter is an angle of inclination of the source and/or of the detector relative to the object.

8 . The method according to claim 1 , in which, in the step d), the estimation of the primary spectrum comprises the matrix product of said transition matrix by each comparison spectrum.

9 . The method according to claim 1 , in which each attenuating element is configured to attenuate between 5% and 80% of the radiation to which it is exposed.

10 . The method according to claim 1 , in which, the mask extending along a surface, each attenuating element is distant from another attenuating element by a distance less than 1 cm.

11 . The method according to claim 1 , in which the steps a) to e) are implemented according to a plurality of configurations, each configuration having associated with it a position of the detector and of the source relative to the object, so as to obtain, in each configuration, for a plurality of pixels, a corrected spectrum, the corrected spectra of each configuration being used to produce a tomographic reconstruction of the object.

12 . The method according to claim 1 , in which the steps a) to e) are complemented by the steps of:
f) selecting at least one energy or an energy range; g) producing an image, of which each pixel comprises a data obtained from a corrected spectrum, associated with a pixel of the detector, within the selected energy or in the selected energy range.

13 . The method according to claim 12 , in which, in the step g), each pixel of the image comprises an information item relating to an integral or to a mean of said corrected spectrum in said selected energy range.

14 . The method according to claim 1 , in which the mask is interposed between the irradiation source and the object.

15 . The method according to claim 1 , in which the transition matrix is obtained by performing a plurality of so-called calibration measurements, each calibration measurement being performed by interposing a material of known nature and thickness between the irradiation source and the detector.

16 . An information storage medium, comprising instructions for the execution of steps c) to e) of the method according to claim 1 , these instructions being configured to be executed by a microprocessor.

17 . The Device for producing images of an object comprising:
an irradiation source, configured to emit an ionizing electromagnetic radiation, called incident radiation, towards said object; a detector comprising pixels, each pixel being configured to detect a radiation transmitted by the object towards the detector, and to acquire a spectrum therefrom; a mask, able to be interposed between the source and the object, the mask comprising attenuating elements, configured to attenuate a part of the incident radiation, and of which a projection onto the detector defines a first group of pixels; a) a processor, configured to to receive spectra detected by each pixel, and to implement steps c) to e) of the method of claim 1 .

Assignees

• Commissariat Energie Atomique

Inventors

• Sossin Artur
• Rebuffel Veronique
• Tabary Joachim

Classifications

• G21K1/10 Primary

  Scattering devices; Absorbing devices; Ionising radiation filters · CPC title

• G01N23/083

  the radiation being X-rays · CPC title

• G01T1/295 Primary

  using coded aperture devices, e.g. Fresnel zone plates (handling of radiation of particles, e.g. using diaphragms, collimators, diffraction G21K1/00) · CPC title

• A61B6/4035

  the source being combined with a filter or grating · CPC title