Three-dimensional contents determination method using transmitted x-ray

• US 7,813,470 B2
• Filed: 12/04/2006
• Issued: 10/12/2010
• Est. Priority Date: 04/13/2006
• Status: Active Grant

• Current Assignee: Shimadzu Corporation
• Original Assignee: Shimadzu Corporation
• Inventors: Kuwabara, Shoji
• Primary Examiner(s): Glick; Edward J
• Assistant Examiner(s): Taningco; Alexander H
• Application Number:
  US12/297,142
• Publication Number:
  US 20100172470A1
• Time in Patent Office: 1,408 Days
• Field of Search: 378/4, 378/53, 378/54, 378/57
• US Class Current: 378/4
• CPC Class Codes: G01N 23/087 using polyenergetic X-rays

Abstract

An X-ray that has passed through a target object 13 is detected by a two-dimensional X-ray detector 14 capable of energy discrimination, to determine an actual X-ray strength at a specific energy level. The target object 13 is rotationally scanned in predetermined angular steps around an axis perpendicular to the X-ray. The target object 13 is imaginarily divided into a large number of micro-sized unitary cubic cells, and each detection element 14a is considered to be receiving an X-ray that has passed through a plurality of unitary cubic cells. A data processor 6 creates a system of equations including a measured intensity ratio between the transmitted and direct X-rays and a theoretical X-ray intensity ratio calculated from the mass absorption coefficients, unknown weight ratios and density of the elements contained in each unitary cubic cell. The number of equations is equal to or larger than the total number of the elements having unknown weight ratios and the density. In this manner, one can measure the three-dimensional distribution of the weight ratio of each element and/or compound and the density in the target object containing a plurality of known kinds of elements and/or compounds.

Claims

1. A three-dimensional contents determination method using a transmitted X-ray, for determining a three-dimensional distribution of weight ratios and density of elements and/or compounds contained in a target object by means of an X-ray measurement system including:

an X-ray irradiator for irradiating the target object with a divergent X-ray or parallel pencils of X-rays having a predetermined energy range;

an X-ray detector with a two-dimensional array of micro-sized X-ray detection elements capable of energy discrimination for detecting a transmitted X-ray that has passed through the target object or a direct X-ray that has not passed through the target object;

a signal processor for obtaining X-ray intensity data of the transmitted or direct X-ray for each of the micro-sized X-ray detection elements on a basis of a detection signal produced by the X-ray detector; and

a rotational scanner for rotating either the target object or the X-ray irradiator and the X-ray detector in steps of a predetermined rotation angle so that a relative position of the target object, the X-ray irradiator and the X-ray detector changes around an axis perpendicularly or obliquely intersecting with an incident X-ray impinging on the target object, the contents determination method comprising steps of;

imaginarily dividing the target object into a large number of three-dimensionally arranged unitary cubic cells, a size of the unitary cubic cell being determined by taking into account a difference between an incident area and exit area of the X-ray passing through the target object, a size of a detection surface of the micro-sized X-ray detection element, and a scan angle of the rotational scanner;

creating, for each rotational scan operation and each micro-sized X-ray detection element, a system of equations whose number is equal to or greater than a total number of elements and/or compounds having unknown weight ratios and the density in each of the aforementioned one or more unitary cubic cells including

an equation including a measured intensity ratio between an intensity of the transmitted X-ray that has passed through the target object and an intensity of the direct X-ray that has not passed through the target object at a same energy level and a theoretical X-ray intensity ratio expressed using the mass absorption coefficients, the weight ratios and the density of all the elements and/or compounds contained in one or more unitary cubic cells located within a range where the X-ray passes through the target object, and

an equation expressing that a sum of the weight ratios of the elements and/or compounds contained in one or more unitary cubic cells located within a range where the X-ray passes through the target object equals one; and

detecting the transmitted X-ray that has passed through the target object and the direct X-ray that has not passed therethrough by means of the X-ray detector, calculating the measured intensity ratio from the X-ray intensity data thereby obtained, applying the measured intensity ratio to the system of equations, and solving the system of equations for the weight ratio of each element and/or compound and the density in each unitary cubic cell, thereby determining the three-dimensional distribution of the elements and/or compounds contained in the target object.

4. The three-dimensional contents determination method according to claim 1, wherein:

parallel pencils of X-rays are used as the X-ray; and

if a parallel pencil of incident X-rays is directly impinging on some of the micro-sized X-ray detection elements of the X-ray detection detector without being blocked by the target object, the intensity of the direct X-ray is measured by a micro-sized X-ray detection element located at any position where the X-ray is directly coming.

2. A three-dimensional contents determination method using a transmitted X-ray, for determining a three-dimensional distribution of weight ratios and density of elements and/or compounds contained in a target object by means of an X-ray measurement system including:

an X-ray irradiator for irradiating the target object with a divergent X-ray or parallel pencils of X-rays having a predetermined energy range;

an X-ray detector with a two-dimensional array of micro-sized X-ray detection elements capable of energy discrimination for detecting a transmitted X-ray that has passed through the target object;

a signal processor for obtaining X-ray intensity data of the transmitted X-ray for each of the micro-sized X-ray detection elements on a basis of a detection signal produced by the X-ray detector; and

a rotational scanner for rotating either the target object or the X-ray irradiator and the X-ray detector in steps of a predetermined rotation angle so that a relative position of the target object, the X-ray irradiator and the X-ray detector changes around an axis perpendicularly or obliquely intersecting with an incident X-ray impinging on the target object,

the contents determination method comprising steps of;

imaginarily dividing the target object into a large number of three-dimensionally arranged unitary cubic cells, a size of the unitary cubic cell being determined by taking into account a difference between an incident area and exit area of the X-ray passing through the target object, a size of a detection surface of the micro-sized X-ray detection element, and a scan angle of the rotational scanner;

in a case where all of the elements and/or the constituent elements of all of the compounds contained in the target object have absorption edges within an energy range that is measurable for a combination of the X-ray irradiator and the X-ray detector, creating, for each rotational scan operation and each micro-sized X-ray detection element, a system of equations whose number is equal to or greater than a total number of elements and/or compounds having unknown weight ratios and the density in each of the aforementioned one or more unitary cubic cells including

an equation including a transmitted X-ray intensity ratio measured on both sides of the absorption edge of each element and a theoretical X-ray intensity ratio expressed using the mass absorption coefficients, the weight ratios and the density of all the elements and/or compounds contained in one or more unitary cubic cells located within a range where the X-ray passes through the target object, and

an equation expressing that a sum of the weight ratios of the elements and/or compounds contained in one or more unitary cubic cells located within a range where the X-ray passes through the target object equals one; and

detecting the transmitted X-ray that has passed through the target object by means of the X-ray detector, calculating the transmitted X-ray intensity ratio from the X-ray intensity data thereby obtained, applying the transmitted X-ray intensity ratio to the system of equations, and solving the system of equations for the weight ratio of each element and/or compound and the density in each unitary cubic cell, thereby determining the three-dimensional distribution of the elements and/or compounds contained in the target object.

3. A three-dimensional contents determination method using a transmitted X-ray, for determining a three-dimensional distribution of weight ratios and density of elements and/or compounds contained in a target object by means of an X-ray measurement system including:

an X-ray irradiator for irradiating the target object with a divergent X-ray or parallel pencils of X-rays having a predetermined energy range;

an X-ray detector with a two-dimensional array of micro-sized X-ray detection elements capable of energy discrimination for detecting a transmitted X-ray that has passed through the target object or a direct X-ray that has not passed through the target object;

a signal processor for obtaining X-ray intensity data of the transmitted or direct X-ray for each of the micro-sized X-ray detection elements on a basis of a detection signal produced by the X-ray detector; and

a rotational scanner for rotating either the target object or the X-ray irradiator and the X-ray detector in steps of a predetermined rotation angle so that a relative position of the target object, the X-ray irradiator and the X-ray detector changes around an axis perpendicularly or obliquely intersecting with an incident X-ray impinging on the target object,

the contents determination method comprising steps of;

imaginarily dividing the target object into a large number of three-dimensionally arranged unitary cubic cells, a size of the unitary cubic cell being determined by taking into account a difference between an incident area and exit area of the X-ray passing through the target object, a size of a detection surface of the micro-sized X-ray detection element, and a scan angle of the rotational scanner;

for each of the elements and/or compounds contained in the target object,

if the element has an absorption edge within an energy range that is measurable for a combination of the X-ray irradiator and the X-ray detector, then, creating, for each rotational scan operation and each micro-sized X-ray detection element, a system of equations whose number is equal to or greater than a total number of elements and/or compounds having unknown weight ratios and the density in each of the aforementioned one or more unitary cubic cells including

an equation including a transmitted X-ray intensity ratio measured on both sides of the absorption edge of each element and a theoretical X-ray intensity ratio expressed using the mass absorption coefficients, the weight ratios and the density of all the elements contained in one or more unitary cubic cells located within a range where the X-ray passes through the target object, and

an equation expressing that a sum of the weight ratios of the elements and/or compounds contained in one or more unitary cubic cells located within a range where the X-ray passes through the target object equals one;

if the each element has no absorption edge within the measurable energy range, then, creating a system of equations whose number is equal to or greater than a total number of elements and/or compounds having unknown weight ratios and the density in each of the aforementioned one or more unitary cubic cells including

an equation including a measured intensity ratio between an intensity of the transmitted X-ray that has passed through the target object and an intensity of the direct X-ray that has not passed through the target object at the same energy level, and a theoretical X-ray intensity ratio expressed using the mass absorption coefficients, the weight ratios and the density of all the elements contained in one or more unitary cubic cells located within a range where the X-ray passes through the target object, and

an equation expressing that a sum of the weight ratios of the elements and/or compounds contained in one or more unitary cubic cells located within a range where the X-ray passes through the target object equals one; and

detecting the transmitted X-ray that has passed through the target object by means of the X-ray detector, and also detecting the direct X-ray that has not passed through the target object by means of the X-ray detector, and calculating the transmitted X-ray intensity ratio or measured intensity ratio from the X-ray intensity data thereby obtained, applying the transmitted X-ray intensity ratio or measured intensity ratio to the system of equations, and solving the system of equations for the weight ratio of each element and/or compound and the density in each unitary cubic cell, thereby determining the three-dimensional distribution of the elements and/or compounds contained in the target object.

5. The three-dimensional contents determination method according to claim 3, wherein:

parallel pencils of X-rays are used as the X-ray; and

if a parallel pencil of incident X-rays is directly impinging on some of the micro-sized X-ray detection elements of the X-ray detection detector without being blocked by the target object, the intensity of the direct X-ray is measured by a micro-sized X-ray detection element located at any position where the X-ray is directly coming.