X-ray imaging system allowing the correction of the scatter radiation and precise detection of the distance between the source and the detector

Patent metadata

Field	Value
Publication number	US-10175181-B2
Application number	US-201515326872-A
Country	US
Kind code	B2
Filing date	Jul 21, 2015
Priority date	Jul 22, 2014
Publication date	Jan 8, 2019
Grant date	Jan 8, 2019

Abstract

The invention relates to an X-ray imaging system wherein images are obtained using an X-ray blocking element, the system comprising means for determining a position of the detector ( 40 ) on the basis of coordinates of projected patterns of the blocker ( 20, 220 ) in an image in order to especially be able to perform a calibration and/or correct the contribution of the scatter radiation in a radiographic image obtained by the system.

First claim

What is claimed is:

1. An X-ray imaging system comprising:
an X-ray source,
an X-ray detector,
a blocker formed alternately by one or more opaque zones enabling X-rays to be blocked and one or more transparent zones enabling X-rays to pass therethrough,
blocker moving means configured to move the blocker between at least one first position and at least one second position, such that in the first position, an opaque zone fully occupies a first given location and a transparent zone fully occupies a second given location, in the second position, the first given location is fully occupied by a transparent zone, the second given location being fully occupied by an opaque zone,
image acquiring means configured to perform a first acquisition of a first image when the blocker is in the first position and to perform a second acquisition of a second image when the blocker is in the second position,
an image processing unit configured to determine a position of the detector from coordinates of one or more projected patterns of the blocker in the first image and/or in the second image.

2. The X-ray imaging system according to claim 1 , wherein the processing unit is further configured to:
deduce from a relative position of the detector with respect to the blocker that a given pixel of the detector belongs to a first pixel category or to a second pixel category,
estimate the primary radiation of the given pixel of the detector using a first estimator {circumflex over (P)} when the given pixel belongs to the first category or using a second estimator {circumflex over (P)}′ when the given pixel belongs to the second category.

3. The X-ray imaging system according to claim 2 , wherein the processing unit is further configured to estimate the primary radiation received by a given pixel n of the detector using an estimator {circumflex over (P)}, depending on a ratio between:
a difference I 1 (n)−I 2 (n) between a radiation intensity I 1 (n) detected by the given pixel n during the first acquisition and a radiation intensity I 2 (n) detected by the pixel n during the second acquisition,
a difference q 1 (n)−q 2 (n), with q 1 (n), q 2 (n) being predetermined parameters representative of primary radiation fractions received by the pixel n of the detector in the first position of the blocker and in the second position of the blocker without a target object.

4. The X-ray imaging system according to claim 1 , wherein the processing unit estimates the primary radiation received by a given pixel m of the detector using an estimator {circumflex over (P)}′, the estimation {circumflex over (P)}′(m) of the primary radiation received by a given pixel m, being a function of a primary radiation intensity I 1 (m) detected by the given pixel m during the first acquisition of an intensity I 2 (m) detected by the pixel m during the second acquisition, and of Ŝint(m) a value estimated by interpolating the scattered radiation of the pixel n from a scattered radiation value calculated for its neighbouring pixels.

5. The imaging system according to claim 1 , wherein the movement of the blocker is a translation of the blocker by a given pitch p and in a plane parallel to the detector.

6. The imaging system according to claim 1 , wherein the opaque zones and the transparent zones of the blocker have a width l, the translation pitch p being equal to k*l, with k being an integer.

7. The imaging system according to claim 1 , wherein the blocking element includes a front face on which the opaque zones and the transparent zones are distributed as parallel strips or in the form of a checkerboard arrangement.

8. The imaging system according to claim 1 , wherein the opaque zones ( 21 a ) are provided with longitudinal faces tilted with respect to each other and along directions that converge to the X-ray source.

9. The imaging system according to claim 1 , wherein the movement is a rotation of the blocker ( 220 ) about an axis passing through the X-ray source.

10. The imaging system according to claim 9 , wherein the opaque zones and the transparent zones of the blocker are distributed on a curved surface.

11. The imaging system according to claim 1 , wherein the image processing unit includes:
a memory for storing parameters of a first geometric transformation matrix relating coordinates of reference patterns with the coordinates of elements of the blocker respectively, each reference pattern corresponding to a projection of an element of the blocker in a reference radiographic image (Im_q i , Im_q 2 ) generated when the detector is located at a reference distance from the source without a target object between the blocker and the detector, the blocker being then in a given position from said first and second positions,
the image processing unit being further configured to:
identify projected patterns of elements of the blocker in another radiographic image called an alignment radiographic image generated when the blocker is in the given position with respect to the detector, and to match the projected patterns in the alignment image with respectively elements of the blocker, calculate parameters of a second geometric transformation matrix relating the coordinates of the patterns projected in the alignment radiographic image with the coordinates of the reference patterns, and calculate the position of the detector from the parameters of the first and second matrices.

12. A method for calibrating a radiographic imaging system according to claim 1 , comprising the following steps of:
disposing the blocker between the source and the detector,
acquiring by the detector at least one alignment radiographic image including one or more projected patterns of the blocker,
determining coordinates of the projected patterns of the blocker in the alignment image and
calculating a position of the detector from coordinates of the projected patterns in the alignment image.

Assignees

• Univ Grenoble Alpes
• Surgiqual Inst

Inventors

• Cinquin Philippe
• Desbat Laurent
• Grondin Yannick

Classifications

• G06T12/10

  Image preprocessing, e.g. calibration, positioning of sources or scatter correction · CPC title

• A61B6/4441

  the rigid structure being a C-arm or U-arm · CPC title

• G21K1/025

  using multiple collimators, e.g. Bucky screens; other devices for eliminating undesired or dispersed radiation · CPC title

• G01N2223/303

  calibrating, standardising · CPC title

• A61B6/06

  Diaphragms · CPC title