JPH09166555A - Shading correcting method and device, for x-ray image recording and reproducing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method, by which total shading correction including the image pick-up process side in addition to the read process side can be performed. SOLUTION: An X-ray image related to a subject radiated with X-ray from an X-ray source 3 through the subject is picked up by an X-ray detector 2. Subsequently, in order to read the picked-up X-ray image, a solid X-ray source image without a subject is picked up by the X-ray detector 2 using an image pick-up device, and the solid X-ray image is read by a reader 9. According to the obtained solid X-ray image data, at the time of reading the X-ray image to an object, the read X-ray image data is corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses an X-ray source as a radiation source, a radiation image of a subject irradiated from the X-ray source through a subject is captured by a radiation detector, and the radiation image is captured by the radiation detector. The present invention relates to a shading correction device of an X-ray image recording / reproducing device for reading. Here, since X-rays are used as a radiation source, it is called an X-ray image recording / reproducing device.

[0002]

2. Description of the Related Art As an example of an X-ray image recording / reproducing apparatus as described above, for example, a printed circuit board is used to inspect whether or not a subject through which a part of the irradiated X-rays is transmitted, for example, the solderability of the printed circuit board. An image of a transmission amount distribution image of X-rays transmitted through the printed circuit board by irradiating X-rays is received by an imaging plate (IP) (here, synonymous with a stimulable photoreceptor sheet), and the imaging plate thus received is excited by excitation light. An X-ray inspection method for a printed circuit board, which scans and detects photostimulable light in proportion to the X-ray transmission amount distribution emitted from the imaging plate to create an X-ray transmission amount distribution image (Japanese Patent Laid-Open No. 6-3
17543) is known. In this X-ray inspection apparatus, in the X-ray image capturing step shown in FIG. 1A, the X-rays projected from the X-ray source 3 are partially transmitted through the printed board 1 and are received by the imaging plate 2. Is configured. Since the X-rays are transmitted according to the degree of X-ray shielding by the circuit patterns, components, soldering portions, etc. formed on the printed circuit board 1, the transmission amount distribution image is received by the imaging plate 2. The imaging plate 2 is arranged close to the printed circuit board 1 which is the subject, and an X-ray transmitted through the printed circuit board 1 forms a circuit image on the printed circuit board 1 at approximately the same size as the image on the imaging plate 2. . Therefore, a clear image with little blur can be obtained.

The imaging plate 2 is made of BaFB.
Microcrystals of a stimulable phosphor such as barium fluorobromide represented by r: Eu ²⁺ are uniformly applied to a polyester film or the like with a particle size of several μm to a thickness of 150 to 300 μm. In the stimulable phosphor, when information having a first wavelength is stored and recorded, it is excited by an electromagnetic wave having a second wavelength, so that the stored and recorded information is stored in a third state.
It has a photostimulated luminescence phenomenon that appears as a luminescence phenomenon having a wavelength of. Since the resolution of the imaging plate 2 is comparable to that of a photographic film, it has a much higher resolution than a conventional X-ray detector. On the imaging plate 2 which has received the X-ray transmission image, the image accumulated and recorded in the next X-ray transmission image reading step is taken out.

In the X-ray transmission image reading process shown in FIG. 1B, the imaging plate 2 on which the X-ray transmission image is received and the transmission amount distribution is accumulated and recorded is a HeNe laser source 5, a galvano mirror 6, When scanned by the laser beam from the excitation light source 4 including the fθ lens 7 and the reflection mirror 8, the photostimulable light is output in proportion to the X-ray transmission amount distribution stored and recorded at the spot diameter corresponding to the spot diameter of the laser beam. To do. This stimulating light is detected as an X-ray transmission amount distribution image by an image reading device equipped with a photomultiplier 9. The imaging plate 2 is two-dimensionally read by feeding the imaging plate 2 in the sub-scanning direction at a constant speed in the sub-scanning direction and performing main scanning by the excitation light source 4. The imaging plate 2 that has been scanned with the excitation light as described above is used for reuse after the residual image is erased in the erasing step 10 shown in FIG. In the erasing step 10, the remaining image is erased by irradiating visible light for a required time from an erasing light source that irradiates visible light, and the circulating step of the imaging plate 2 used in the X-ray irradiating step can be performed again. it can. As shown in FIG. 1, the X-ray inspection process for the printed circuit board configured as described above is performed by the steps (a), (b),
A series of inspection lines is formed by connecting between (c) with a conveyor belt or the like that conveys the imaging plate 2. Further, the printed circuit board 1 is successively transferred to the image pickup position by another transfer device, and continuous inspection can be performed.

In the X-ray image recording / reproducing apparatus as described above,
The step of capturing an X-ray transmission image of the subject (X-ray image capturing step (a)), and the capturing of the captured imaging plate 2 to X
At both the step of reading a line-transmissive image (X-ray transmissive image reading step (b)), various sensitivity unevenness (shading) due to the imaging principle, the individuality of the device or the reading principle occurs in the reading scanning direction or the sub-scanning direction. For example, in the actual imaging step (a) using an X-ray source, a planar imaging plate 2 is placed at a position separated by a distance L from the X-ray source 3 as shown in FIG. ) 1 to form a transmitted X-ray image on the imaging plate 2,
The X-ray intensity is reduced by the distance from the center, and the X-ray intensity reaching the imaging plate 2 is reduced by the distance from the center even when the subject 1 is not present. There is uneven sensitivity, which is moderate and weak at the edges. This transmitted X-ray distribution has individual differences for each X-ray source.

Also, the above-mentioned imaging plate IP cannot be said to have a uniform sensitivity over the entire surface, so that the sensitivity unevenness occurs for each type of imaging plate based on this. Also in the reading step (b) side, since the laser light scanned from one point is detected by the long photomultiplier 9, the sensitivity is the same in the central portion and the end portion as in the X-ray imaging. Differently, output unevenness of each pixel of the photomultiplier 9 also contributes as sensitivity unevenness. Further, in this method, since the principle of reading by the photomultiplier is used, sensitivity unevenness due to the offset caused by the characteristics of the photomultiplier that occurs regardless of the presence or absence of the subject or the presence or absence of the imaging plate 2 occurs in both processes, and this causes This is a cause of deteriorating the detection accuracy. Since such sensitivity unevenness (shading) is distributed in the scanning direction and the sub-scanning direction orthogonal thereto, it is necessary to detect this distribution in advance and perform an operation to remove the sensitivity unevenness from the detected value during actual recording. Thus, X-ray image data without unevenness in sensitivity can be obtained. As a device for correcting shading in the reading process described above, for example, a shading correction device described in Japanese Patent Laid-Open No. 5-15340 is known.

[0007]

However, the above-described known shading correction device is not limited to the correction of the sensitivity unevenness in the above-described reading process as described above, and the imaging process as described above. The correction of the sensitivity unevenness based on the sensitivity unevenness in 1 is not considered. Further, in the above-mentioned known apparatus, an X-ray film or an imaging plate having a uniform image density that serves as a reference is read in advance by a reading apparatus, and the difference between the image data and the actual detection data is obtained at the time of actual operation. The shading correction of the detection data is performed. The basis of this idea is that the read output D from the photomultiplier can be expressed as D = G × I (G is the gain of the photomultiplier, I is the output current from the photomultiplier), and this output is output via the logarithmic converter. LogD =
This is because the output represented by LogG + LogI can be obtained, that is, the gain can be corrected only by the addition operation. However, as described above, the read data is always accompanied by an offset associated with the personality of the device, etc., and the actual output D of the photomultiplier is represented by D = G × I + Lo (offset amount). Thus, if the logarithmic conversion is simply performed, a complicated calculation regarding the offset amount is required, and the shading correction cannot be performed only by a simple addition calculation. As described above, the known technique has a defect that the shading correction related to the offset is not performed.

Further, in the above conventional technique, as described above,
A uniform density X-ray film or an imaging plate is required, but a large imaging plate or the like is required if the distance L between the X-ray source and the imaging plate or the like is increased in order to improve the resolution. A device that provides uniform image density at a time can be very expensive or unavailable.
Therefore, it is a first object of the present invention to provide a method capable of performing overall shading correction including the reading process side and the imaging process side. A second object is to enable sensitivity unevenness based on offset to be excluded so that correction operation can be performed only by simple addition operation. Further, a third object of the present invention is to provide a practical shading correction method and apparatus that do not require an unrealistic uniform density imaging plate or the like.

[0009]

In order to achieve the above object, a first aspect of the present invention is an imaging for picking up a radiation image of an X-ray source and a subject irradiated from the X-ray source through the subject with a radiation detector. A shading correction method for an X-ray image recording / reproducing apparatus, comprising: an apparatus; and a reading apparatus for reading a radiation image picked up by the image pickup apparatus,
A solid exposure radiation image capturing step of capturing a solid exposure radiation image with the radiation detector using the image capturing apparatus, and a solid exposure radiation image obtained in the solid image capturing step is read by the reading device to obtain a solid exposure radiation image. Solid exposure radiation image reading step of obtaining image data, correction data storing step of storing in a correction data memory based on the solid exposure radiation image data obtained in the solid exposure radiation image reading step, and correction data stored in the memory And a shading correction step of correcting the read radiation image data when the X-ray image of the subject is read based on the above.

The second invention comprises a correction data calculation step for obtaining correction data for the difference between the solid exposure radiation image data obtained in the solid exposure radiation image reading step and the density level of a constant value. The radiation image data is corrected in the shading correction step based on the correction data obtained in the calculation step. A third aspect of the present invention comprises the offset correction step of removing the offset density data specific to the reading device from the solid exposure radiation image data obtained in the solid exposure radiation image reading step in the first aspect. The radiation image data is corrected in the shading correction process based on the data from which the density data has been removed. A fourth invention is the same as the second invention,
An offset correction step of removing offset density data unique to the reading device from the solid exposure radiation image data obtained in the solid exposure radiation image reading step is provided, and the data from which the offset density data is removed and a density level of a constant value are provided. It is configured as a shading correction method for an X-ray image recording / reproducing apparatus, which is characterized in that correction data for the difference between It is desirable to capture the radiation image for each radiation detector used.

The shading correction can be calculated using the average value of the solid exposure radiation image data for a plurality of pixels. The present invention is not limited to the case where a transmission X-ray is imaged on a stimulable phosphor sheet in the embodiment described later as the basic principle of the image pickup, and the absorption of the X-ray or the reflected X-ray as the relation between the front and the back is also used. It also includes the case of detecting diffracted X-rays. Furthermore, if a photosensitive film is used as a radiation detector (in this case, a developing process is required before the reading process), the radiation generated by the ionizing action by X-rays, the photoelectric effect, the Compton effect, the formation of electron pairs, etc. By taking an image, it is possible to perform physical properties of the subject, minute structure, defect evaluation, and the like. Therefore, a typical example of the radiation detector is a stimulable phosphor sheet that stores X-rays that have passed through an object. Further, a laser scanner using a photomultiplier is an example of the reading device. As a fifth invention, an X-ray source, an imaging device that captures a radiation image of a subject emitted from the X-ray source through the subject with a radiation detector, and a reading device that reads the radiation image captured by the imaging device. And a solid exposure radiation image capturing means for capturing a solid radiation source image by the radiation detector using the image capturing device, and a solid exposure radiation image capturing step in a shading correction device of an X-ray image recording and reproducing device including the device. Based on the solid exposure radiation image data obtained in the solid exposure radiation image reading step, the solid exposure radiation image obtained by reading the solid exposure radiation image with the reading device to obtain solid exposure radiation image data A shading correction hand that corrects the read radiation image data when reading an X-ray image of a subject. Shading correction apparatus and the like of the X-ray image recording and reproducing apparatus characterized by comprising comprises and.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments embodying the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention. The following embodiment is an example in which the present invention is applied to the case where a transmission X-ray is imaged by an imaging plate, and does not limit the technical scope of the present invention. Here, FIG. 1 is a conceptual diagram of an X-ray inspection apparatus including an imaging step (a), a reading step (b), and an erasing step (c) for use in one embodiment of the present invention, and FIG. 2 is the same apparatus. FIG. 3 is an X-ray transmission amount distribution chart according to the above-mentioned flow chart procedure, FIG. 4 is a density distribution chart of solid X-ray image data, and FIG. 5 is shading correction to solid X-ray image data. It is a concentration distribution map after applying. The specific contents of the imaging step (a), the reading step (b), and the erasing step (c) shown in FIG. 1 are as already described in the related art. This embodiment is different from the description of the conventional technique in that the analog X-ray image data read by the photomultiplier 9 is introduced as digital data into the arithmetic unit 13 by the A / D converter, and the correction arithmetic processing is performed. Is applied,
Points output as corrected data and the arithmetic unit 1
3, a memory 14 is connected to the memory 14. Shading correction data from solid X-ray image data etc. described later for each type of imaging plate is previously stored in the memory 14 and stored in the memory 14 during normal operation. The point is that the X-ray image data obtained by the photomultiplier 9 is corrected using the shading correction data.

The shading correction procedure will be described in more detail with reference to FIGS. 2 and 3. However, as a premise, it is assumed that the upper surface of the transport base 11 is colored with uniform brightness. [Step 1] First, under the imaging conditions (intensity of X-ray source, exposure time, distance L, type of imaging plate to be used, etc.) to be actually used, the imaging device ((a) in FIG. 1) is used. The subject 1 is removed, X-ray exposure is performed by the X-ray source 3, and the so-called solid X-ray is formed on the imaging plate 2.
This imaging plate 2 is used to capture line images.
Is transferred to the reading step (b) in the dark room state to read a solid X-ray image and obtain solid X-ray image data. This solid X-ray image data includes X-ray intensity distribution by the solid angle of the X-ray source, gain given by the applied voltage of a predetermined photomultiplier, shading characteristics by the surface distribution characteristics of the imaging plate, excluding the influence of the subject. It includes all the sensitivity unevenness (shading) elements that occur in the imaging process and the reading process, such as the effects of noise components and offsets, and as shown in FIG. 4, they appear unevenly in the main scanning direction. [Step 2] Since the solid X-ray image data is output data from all the pixels of the photomultiplier 9, there are many noise components, and if it is stored as it is, the storage capacity becomes too large. The pixels are averaged and smoothed. This data is the representative concentration data D
The outline of the distribution in the main scanning direction is shown in FIG. [Step 3] The representative density data D is D as described above.
Since the offset L0 is included in the form of = G × I + Lo, simple logarithmic conversion cannot be performed.

Then, in the state where the imaging plate 2 is not on the carrier base 11, the upper surface of the carrier base 11 is scanned with laser light to detect output data from the photomultiplier 9. As described above, the upper surface of the transport base 11 is colored with a uniform lightness, so that the detected data represents the offset data L0 of the photomultiplier 9. So various imaging plates like this
The offset data L0 for each 2 is subtracted from the representative density data D, and the representative peculiar data U (= DL) for the entire area of the imaging plate 2 in 32 × 32 pixel units.
(See FIG. 3C).

Further, the density level data A (= B-L0) of a constant value, which is replaced with the predetermined density level data B in consideration of the offset L0 (see FIG. 3 (d)),
A ratio with the representative unique data U is calculated to obtain a correction gain GI at which the solid X-ray image data actually measured in units of 32 × 32 pixels for the entire imaging region has a substantially constant value (FIG. 3).
(E)). [Step 4] The correction gain GI is stored in the memory 14 together with the offset value L0 for each of various imaging plates. The above steps are the procedure for creating the shading correction data (correction gain GI) in this embodiment. [Step 5] In the actual measurement stage, as described above, the X-ray image data from the photomultiplier 9 for the object to be measured (object) is converted into a digital signal by the A / D converter 12 and introduced into the arithmetic unit 13. Memory 1
The shading correction data corresponding to the used imaging plate is extracted from 4, the detection data is corrected with this shading correction data, and the value is subjected to logarithmic processing and output. As a result, the image density can be confirmed without being affected by offset or other shading that occurs in the imaging process and the reading process. FIG. 5 shows data obtained by performing shading correction on the solid X-ray image data. It can be seen that a flat image can be obtained by performing shading correction in this way.

If the representative correction positions of the imaging plate become inconsistent in the imaging process and the reading process, each region correction data will be displaced, so that the pixel unit of the correction region is to ensure the system position reproducibility. It should be determined in consideration of the number of pixels that can sufficiently perform the high-frequency noise averaging process and the amount of gain change in the entire imaging and reading area.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is not limited to the above-described case of imaging transmitted X-rays on a stimulable phosphor sheet as the basic principle of imaging, but also for absorbing X-rays or reflecting X-rays as a front-back relationship. It also includes the case of detecting diffracted X-rays. Furthermore, if a photosensitive film is used as a radiation detector (in this case, a developing process is required before the reading process), the radiation generated by the ionizing action by X-rays, the photoelectric effect, the Compton effect, the formation of electron pairs, etc. By taking an image, it is possible to perform physical properties of the subject, minute structure, defect evaluation, and the like.
In the above-described embodiment, the processing for removing the influence of the offset has been described. However, when the above-described offset is not present or is extremely small, this processing can be deleted. In this case, the density level data A having a constant value is directly subtracted from the representative density data D without measuring the offset data L0.
On the contrary, in some cases, the subtraction of the constant value may be omitted and only the offset may be removed. For example, when the obtained detection data has a value extremely close to the theoretical detection data, it may not be necessary to correct the data by subtracting the constant value.

[0018]

Since the shading correction method according to the present invention is configured as described above, there is provided a method capable of performing the overall shading correction not only on the reading process side but also on the imaging process side. . Further, sensitivity unevenness due to offset is also excluded, and correction calculation can be performed only by simple addition calculation. Furthermore, the present invention has succeeded in providing a practical shading correction method and apparatus that do not require the preparation of an imaging plate of uniform density in advance.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an X-ray image recording / reproducing apparatus used for implementing a shading correction method according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining a procedure of the method according to the above embodiment.

FIG. 3 is a diagram showing a distribution of data according to the procedure of the above embodiment.

FIG. 4 is a density distribution diagram of solid X-ray image data before correction.

FIG. 5 is a density distribution diagram of the corrected solid X-ray image data.

[Explanation of symbols]

 1 ... Printed circuit board (subject) 2 ... Imaging plate (X-ray detector) 3 ... X-ray source 4 ... Excitation light source 9 ... Photomultiplier (reader) 10 ... Erase process

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H04N 1/401 H04N 1/40 101A

Claims (11)

[Claims] 1. An X-ray source, an image pickup device for picking up a radiation image of a subject irradiated from the X-ray source through the subject with a radiation detector, and a reading device for reading the radiation image picked up by the image pickup device. In the shading correction method for an X-ray image recording apparatus, the solid exposure radiation image capturing step of capturing a solid exposure radiation image with the radiation detector using the image capturing apparatus, and the solid image obtained in the solid image capturing step. A solid exposure radiation image reading step of reading an exposure radiation image by the reading device to obtain solid exposure radiation image data, and correction data based on the solid exposure radiation image data obtained in the solid exposure radiation image reading step are stored in a memory. X-ray image of the subject based on the correction data storing step and the correction data stored in the memory. A shading correction method for an X-ray image recording / reproducing apparatus, comprising a shading correction step of correcting the read radiation image data at the time of reading. 2. A correction data calculating step for obtaining correction data of a ratio between the solid exposure radiation image data obtained in the solid exposure radiation image reading step and a density value of a constant value, the correction data calculating step being obtained. The shading correction method for an X-ray image recording / reproducing apparatus according to claim 1, wherein the radiation image data is corrected in the shading correction step based on the correction data. 3. An offset correction step for removing offset density data specific to the reading device from the solid exposure radiation image data obtained in the solid exposure radiation image reading step, and the data from which the offset density data is removed is provided. The shading correction method for an X-ray image recording / reproducing apparatus according to claim 1, wherein the radiation image data is corrected based on the shading correction step. 4. An offset correction step of removing offset density data unique to the reading device from the solid exposure radiation image data obtained in the solid exposure radiation image reading step, and the data from which the offset density data has been removed. The correction data of the ratio to a constant density level is obtained.
A shading correction method for the described X-ray image recording / reproducing apparatus. 5. A solid exposure radiation image is picked up for each radiation detector to be used, shading correction data is created from each solid exposure radiation image, and correction is performed. A shading correction method for an X-ray image recording / reproducing apparatus according to the item 1. 6. The method according to claim 1, wherein the shading correction is performed in a unit of a plurality of pixels, and the representative candidate data is calculated using an average value of the plurality of pixels. A shading correction method for the described X-ray image recording / reproducing apparatus. 7. The radiation detector is a stimulable phosphor sheet or an imaging plate for accumulating X-rays transmitted through an object, and the reader is a laser scanner using a photomultiplier. , 4,
5. A shading correction method for an X-ray image recording / reproducing apparatus according to 5 or 6. 8. The shading correction of the X-ray image recording / reproducing apparatus according to claim 7, wherein the solid exposure radiation image is a radiation image obtained by directly irradiating the stimulable phosphor sheet with X-rays in the absence of a subject. Method. 9. A shading correction method for an X-ray image recording / reproducing apparatus in which a subject is a printed circuit board. 10. An X-ray source, an image pickup device for picking up a radiation image of a subject irradiated from the X-ray source through the subject with a radiation detector, and a reading device for reading the radiation image picked up by the image pickup device. In a shading correction apparatus of an X-ray image recording apparatus comprising: a solid exposure radiation image capturing means for capturing a solid radiation source image with the radiation detector using the image capturing apparatus; and a solid exposure radiation image capturing step The solid exposure radiation image is read by the reading device to obtain solid exposure radiation image data, and the solid exposure radiation image data is corrected, and the correction data based on the solid exposure radiation image data obtained in the solid exposure radiation image reading step is stored in the memory. A correction data storage means to be stored in the memory, and to the subject based on the correction data stored in the memory. A shading correction apparatus for an X-ray image recording apparatus, comprising: a shading correction unit that corrects the read radiation image data when the X-ray image is read. 11. The subject is a printed circuit board, the radiation detector is a stimulable phosphor sheet for accumulating X-rays transmitted through the subject, and the reading device is a laser scanner using a photomultiplier. A shading correction device of the described X-ray image recording / reproducing device.