JP2006105786A - X-ray inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray inspection device constituted so as to inspect an inspection target from the X-ray transmission data of the inspection target, obtained by moving the inspection target so as to traverse the space between an X-ray source and an X-ray detector to continuously irradiate the same with X rays and capable of eliminating the occurrence of wrong decisions caused by the dynamic characteristics, based on the afterglow characteristics of a scintillator sheet used in the X-ray detector. <P>SOLUTION: The effect of the afterglow of the scintillator sheet contained in each of the pixel outputs of the X-ray detector 2 is removed by Formula (1) by using a preliminarily stored coefficient h[m] (m=1, 2, ..) and the inspection target is inspected to eliminate the occurrence of misdecision caused by the dynamic characteristics of the X-ray detector 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an X-ray inspection apparatus for inspecting the internal state of various products including pharmaceuticals and foods in a non-destructive manner.

  Conventionally, an X-ray source and X-ray detection are used as an X-ray inspection apparatus for inspecting whether or not a foreign object is mixed in an object from X-ray transmission data obtained by irradiating the inspection object with X-rays. An apparatus is known in which an X-ray fluoroscopic image of an object to be inspected is obtained by determining the presence or absence of a foreign object by conveying the object to be inspected so as to cross between them. (For example, refer to Patent Document 1).

  Further, as an X-ray detector in this type of X-ray inspection apparatus, a scintillator sheet and a photosensor array such as a photodiode array are combined, X-rays are converted into an optical signal by the scintillator sheet, and the optical signal is converted into an optical sensor array. A method of converting into an electric signal by using the method is often used.

  By the way, it is known that the scintillator sheet has a so-called afterglow characteristic in which a light conversion output remains when irradiation is stopped from an X-ray irradiation state. That is, when the scintillator sheet is irradiated with X-rays as shown in FIG. 2A, for example, a photodiode or the like due to the afterglow characteristics of the scintillator sheet as shown in FIG. The output of the photosensor array does not accurately represent the amount of incident X-rays as shown in FIG.

  Based on such poor dynamic characteristics of the X-ray detector, in particular, in the X-ray inspection apparatus of the type that passes the inspection object across the X-ray source and the X-ray detector, the inspection object The X-ray fluoroscopic image may become unclear and cause erroneous determination.

Here, as a technique for removing the influence of the afterglow of the scintillator sheet in the X-ray detector combining the scintillator sheet and the photodiode array, conventionally, when X-rays are repeatedly irradiated in a pulse shape, the X-ray non-interval between pulses It is known to detect the output of the photodiode in the irradiation state, grasp the afterglow component of the scintillator sheet based on the detection result, and subtract the afterglow component from the output of the photodiode in the irradiation state of the X-ray pulse. (For example, refer to Patent Document 2).
JP 2001-281173 A JP-A-10-85207

  By the way, the above-mentioned conventional afterglow removal technique is limited to the case of irradiating pulsed X-rays, and is a type of X that moves an object to be inspected across an X-ray source and an X-ray detector. It cannot be applied when X-rays are continuously irradiated as in a line inspection apparatus.

  The present invention has been made in view of such circumstances, and an X-ray detector is arranged opposite to the X-ray source, and the X-ray from the X-ray source is continuously irradiated while crossing between them. In the X-ray inspection apparatus of the type that moves the inspection object as described above, the influence of the afterglow of the scintillator sheet can be removed, and the X-ray transmitted through the inspection object can be accurately measured and used for determination. An object of the present invention is to provide an X-ray inspection apparatus that can eliminate erroneous determination caused by afterglow.

  In order to solve the above-described problems, the X-ray inspection apparatus of the present invention comprises a scintillator sheet and an optical sensor array that continuously irradiates X-rays while moving the inspection object, and transmits X-rays transmitted through the inspection object. In an X-ray inspection apparatus that inspects an inspection object by image processing using an X-ray transmission image of the inspection object based on the detection output detected by the X-ray detector, each pixel output of the X-ray detector The effect of the afterglow of the scintillator sheet included in the difference equation represented by the following equation (1) using the coefficient h [m] (m = 1, 2,...) Obtained and stored in advance It is characterized by having an afterglow removal calculating means for removing and applying it to image processing.

Here, in the present invention, the afterglow characteristic of the scintillator sheet is approximated to I = I ₀ · exp (−t / τ), and the difference equation used by the afterglow removal calculating means is expressed by the following (2) A configuration (claim 2) can be adopted.

  According to the present invention, if the afterglow characteristic of the scintillator sheet is known in advance, the afterglow component of the scintillator sheet can be removed from the output of the X-ray detector, that is, the output of the optical sensor array, using a difference equation. It is used. The principle will be described below.

In an X-ray detector comprising a scintillator sheet and an optical sensor array such as a photodiode array, when attention is paid to that one pixel, the X-ray dose actually incident on that pixel is exemplified in FIG. X (t), as a result of being affected by the afterglow characteristic e (t) of the scintillator sheet as illustrated in FIG. 5B, the output of the pixel is y (t) as shown in FIG. And between these,
y (t) = ∫e (u) · x (tu) du (3)
There is a relationship.

When the equation (3) is Fourier transformed,
Y (ω) = E (ω) · X (ω) (4)
So that
X (ω) = {1 / E (ω)} · Y (ω) (5)
Thus, the observed signal (actual detector output) is Fourier-transformed, multiplied by 1 / E (ω) obtained in advance, and then inversely transformed again to obtain a signal x (t having no influence of afterglow. ) Can be obtained.

In practice, 1 / E (ω) is expanded into a series,
1 / E (ω) = h [0] + h [1] · exp (−jωt) + h [2] · exp (−jω2t) +... + H [k] · exp (−jωkt) (6)
The coefficients h [0], h [1], h [2]... H [k] are obtained from the above, and the detector output y [n] discretely sampled (sampling period 2π / ω) is obtained.
x [n] = h [0] .y [n] + h [1] .y [n-2] + h [2] .y [n-3] +... h [k] y [n-k] (7)
X [n] representing the X-ray dose incident on the actual detector can be obtained based on the difference equation (the same as the above-described equation (1)).

Here, as in the invention according to claim 2, the afterglow characteristics of the scintillator sheet,
e (t) = exp (−t / τ) (t ≧ 0),
e (t) = 0 (t <0) (8)
(7) becomes as simple as the above-mentioned (2), and the arithmetic processing becomes extremely easy. This approximation is an approximation that has no problem at all compared to the actual situation. For example, in Gd ₂ O ₂ S that is commonly used as a scintillator sheet, τ has a value of about 0.026.

  According to the present invention, in the X-ray detector in which the scintillator sheet and the optical sensor array are combined, the bad dynamic characteristics due to the afterglow characteristics of the scintillator sheet are corrected by a difference equation using coefficients obtained in advance. Since the corrected value is used as an X-ray transmission data of the inspection object for inspection, the inspection object is inspected in an X-ray inspection apparatus of a type in which the inspection object passes between the X-ray source and the X-ray detector. An error included in the X-ray transmission data of an object is eliminated, and accurate determination can always be performed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram illustrating a schematic diagram showing a mechanical configuration and a block diagram showing an electrical configuration.

  The X-ray source 1 emits X-rays through a slit (not shown) provided in the X-ray emission port to form fan beam-like X-rays, which are output vertically downward. A one-dimensional X-ray detector 2 is disposed below the X-ray source 1. The one-dimensional X-ray detector 2 has a known structure in which a scintillator sheet is arranged so as to cover a sensitive surface of a photodiode array composed of a plurality of elements, and the arrangement direction of each element of the photodiode array is a fan. It arrange | positions along the spreading direction of a beam-like X-ray.

  A belt conveyor 3 is provided between the X-ray source 1 and the one-dimensional X-ray detector 2, and the belt conveyor 3 is mounted with the inspection object W and spreads in the fan beam-shaped X-ray direction. It is conveyed in the direction orthogonal to

  With the above configuration, the output of each pixel of the one-dimensional X-ray detector 2 from the time when the inspection object W reaches the position where the X-ray source 1 and the one-dimensional X-ray detector 2 face each other until the inspection object W finishes passing therethrough. Thus, X-ray transmission data of the entire inspection object W can be obtained. Each pixel output of the one-dimensional X-ray detector 2 is taken into the image processing apparatus 10 and used for determination of the presence or absence of a foreign substance by known image processing. In this embodiment, the one-dimensional X-ray detector 2 is used. Each pixel output from the line detector 2 is subjected to afterglow removal processing by the afterglow removal processing calculation unit 11 and then subjected to determination by the image processing apparatus 10. If the result of the determination is, for example, that there is a foreign object, for example, an exclusion device provided on the downstream side of the belt conveyor 3 is driven to exclude the corresponding inspection object from the line into a specified box or the like. To do.

  The afterglow removal processing calculation unit 11 is constituted by, for example, a personal computer and its peripheral devices. The afterglow removal processing calculation unit 11 includes τ corresponding to the coefficient in the difference equation shown in the above equation (2), and each The sampling interval ts of pixel output is set and stored in advance, and the sampling value y [n], y [n−1], y [n−2] is calculated for each pixel output using the coefficient. ,... Are corrected to x [n] by equation (2).

  As described above, x [n] obtained by the equation (2) is a value that accurately represents the X-ray dose at each time point after removing the afterglow component of the scintillator sheet. Thus, the X-ray transmission data of the inspection object W that is not affected by the afterglow of the scintillator sheet is used, and the erroneous determination caused by the dynamic characteristics of the conventional X-ray detector can be eliminated. .

  Here, in the above embodiment, the example in which the one-dimensional X-ray detector 2 is arranged corresponding to the fan beam-shaped X-ray irradiation region is shown, but the present invention is not limited to this. In short, if the X-ray inspection apparatus is such that the object to be inspected relatively moves within the field of view of the X-ray detector, the dynamic characteristics of the X-ray detector based on the afterglow of the scintillator sheet becomes a problem. Of course, the present invention can be equally applied to other configurations of X-ray inspection apparatuses that perform inspection using the X-ray transmission data of the inspection object while performing such relative movement.

  Further, the difference equation used for afterglow removal by the afterglow removal processing calculation unit 11 can be easily calculated by using equation (2) as in the above-described embodiment. It goes without saying that the formula may be used.

In the block diagram of embodiment of this invention, it is the figure which writes together and shows the schematic diagram showing a mechanical structure, and the block diagram showing an electric structure. It is explanatory drawing of the dynamic characteristic of the X-ray detector using a scintillator sheet | seat and an optical sensor array, (A) is a graph showing the time change of the X-ray dose which injects into an X-ray detector, (B) is X A graph showing an example of afterglow characteristics of a scintillator sheet in a line detector, (C) is an X-ray detector using the scintillator sheet having the afterglow characteristics shown in (B), and the X-rays shown in (A) are It is a graph showing the time change of the output when it injects.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray source 2 One-dimensional X-ray detector 3 Belt conveyor 10 Image processing apparatus 11 Afterglow removal process calculating part W Inspected object

Claims (2)

X-rays are continuously irradiated while moving the inspection object, X-rays transmitted through the inspection object are detected by an X-ray detector comprising a scintillator sheet and an optical sensor array, and the inspection object is based on the detection output In an X-ray inspection apparatus that inspects an inspection object by image processing using an X-ray transmission image of
A coefficient h [m] (m = m = m = m) obtained in advance and storing the influence of the afterglow of the scintillator included in each pixel output y [n] (n = 1, 2,...) Of the X-ray detector. (1), and the afterglow removal calculating means for removing the value x [n] after the removal by the difference equation expressed by the following equation (1) and using it for image processing. X-ray inspection equipment.

The afterglow characteristic of the scintillator sheet is approximated to I = I ₀ · exp (−t / τ), and the difference equation used by the afterglow removal calculating means is expressed by the following equation (2): The X-ray inspection apparatus according to claim 1.

Images