JPS6285561A - Method for deciding reading condition of radiograph information - Google Patents

Abstract

PURPOSE:To avoid reading the noise component due to the scattered beams by applying the differential processing to the digital picture information at each position on a cumulative fluorescent sheet and detecting a prescribed section held between the positive and negative threshold values out of the differential pictures. CONSTITUTION:The pre-read exciting optical scan is applied to a cumulative fluorescent sheet 10 and the picture information recorded cumulatively on the sheet 10 are read out. Then the digital picture data are obtained at each position on the sheet 10 from said picture information. Then the differential processing is applied to the digital picture data for production of a differential picture consisting of the differential value. Then the prescribed threshold value Th is prepared to scan the processed differential picture in a single direction. Thus a prescribed section held between the differential value larger than +Th and that smaller than -Th is detected on each scan line. Then the existing pre-read picture information is extracted and the primary reading conditions are decide according to the extracted pre-read picture information. In such a way, the primary reading area is limited within an illumination field 12. Thus the noise components recorded on the area 14 outside the filed 12 can be deleted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a method for determining reading regulations for radiographic image information used in a radiographic image information recording and reproducing system using a stimulable phosphor used for medical diagnosis and the like.

<Technical background of the invention and prior art) Certain types of phosphors are exposed to radiation (X-rays, α-rays, β-rays.

When irradiated with γ-rays, electron beams, ultraviolet rays, etc., a part of this radiation energy is accumulated in the phosphor, and when this phosphor is irradiated with excitation light such as visible light, the phosphor changes depending on the accumulated energy. It is known that phosphors do not exhibit stimulated luminescence, and phosphors that exhibit this property are called stimulable phosphors (stimulable phosphors).

Using this stimulable phosphor, radiation image information of a subject such as a human body is partially recorded on a sheet of stimulable phosphor, and the stimulable phosphor sheet is scanned with excitation light such as a laser beam. This stimulated luminescence is read photoelectrically to obtain an image signal, and based on this image signal, a radiation image of the subject is recorded on a recording material such as a photographic light-sensitive material, or a CRT.
The edge of the radiation image to be output as a visible image on a display device such as
A Sae recording and reproducing system is already in use by the applicant. , (Unexamined Japanese Patent Publication No. 5:1-12429, 5G-11
395 etc. ) As a mode of the above-mentioned radiation image information recording and reproducing system, a stimulable phosphor sheet in which the radiation image information of the subject is stored and recorded using the radiation]-energy level as a medium is scanned with excitation light, and by this scanning, the radiation image information is extracted from the sheet. Prior to the "main reading" in which the emitted stimulated luminescence light is read by a charging reading means to reproduce a visual image for diagnosis, 1q of electrical image signals are generated. The sheet is scanned with excitation light at a certain level to read the outline of the image information accumulated and recorded on this sheet. The reading conditions are determined, the actual reading is performed according to the reading conditions, the image signal obtained from this actual reading is input to the image processing means, and the image processing means is used to determine the diagnostic purpose according to the image area and the image method, etc. A system is known in which an image signal is processed so as to obtain an output image suitable for the image, and this image signal is reproduced as a visible output image on a photographic light-sensitive material. Unexpectedly, the patent application was published in 1982.
It is disclosed in Japanese Patent No. 67240.

Here, the reading conditions refer to various conditions f1 that affect the relationship between the amount of stimulated luminescence light during reading and the output of reading aa.
For example, read gain (sensibility), scale shift factor (latitude), which determines the relationship between input and output.
Alternatively, it refers to the power of excitation light during reading.

Also, the fact that the excitation light used for pre-reading is at a lower level than the excitation light used for main reading means that P! 1
This means that the effective energy of the excitation light that the f11I phosphor sheet receives per unit area is smaller than that in the actual reading. As a method of making the pre-reading excitation light lower than the main reading excitation light, there is a method of reducing the output of an excitation light source such as a radar light source, a method of reducing the output of an excitation light source such as a radar light source, and a method of using an NO filter, There are two methods: attenuation by AOM, etc., and a method where a light source for pre-reading and a light source for main reading are provided separately so that the output of the lyI person is smaller than the output of the latter. Examples include a method of increasing the scanning speed of the excitation light, a method of increasing the scanning speed of the excitation light, and a method of increasing the transport speed of the stimulable phosphor sheet.

In this way, by grasping the outline of the image information stored in the IlO sheet before the actual reading and performing the actual reading in accordance with the reading regulations determined based on the outline of this image information, it is possible to identify the subject and the illuminated area. It is possible to eliminate inconveniences caused by fluctuations in the range of radiation energy levels stored and recorded on the sheet due to fluctuations or fluctuations during radiation exposure, etc., and to perform actual reading under desirable reading conditions at all times.

A specific method for determining the reading conditions for main reading based on the image information 1q obtained by such pre-reading is, for example, to obtain the histogram of the Koujin Shunkosha that is added to the pre-reading and to calculate this histogram from this histogram. Location l1ifij in the histogram & maximum stimulated luminescence light fi of the information range
l Swax and the maximum stimulated luminescence light maximum Sm1n are determined, and these 3 max and 3 min are determined by the maximum density Dmax and minimum density p min of the appropriate density range in the visible output image, respectively. The present applicant has filed an application for a method of determining reading conditions for main reading so as to correspond to the maximum signal level Q max and minimum signal level Q sin in the desired human power range of 0 (Japanese Patent Application No. 12658/1982).

On the other hand, in order to avoid irradiating radiation to areas that are not necessary for human diagnosis, or if radiation is applied to areas that are unnecessary for diagnosis, scattered radiation will enter the areas necessary for diagnosis from that area, reducing contrast resolution. Therefore, in order to prevent this, it is often preferable to narrow down the irradiation field for group 04 radiation when recording image information of radiation 131 radiation. However, when the radiation irradiation field is narrowed down in this way, the scattered radiation generated from the subject in the irradiation field usually enters the irradiation field on the stimulable phosphor sheet, and the stimulable phosphor sheet with a high tjlJ degree Since this scattered ray is also accumulated and recorded, the histogram of the amount of stimulated luminescence obtained by pre-reading also includes the amount of stimulated luminescence that is revealed by this scattered ray.

Based on these scattered rays, the photostimulated luminescence layer on the sheet and outside the irradiation area may be larger than the amount of stimulated luminescence within the irradiation field. It is difficult to distinguish between the inner and outer stimulated luminescent light 6. Therefore, as mentioned above, from the histogram, 3si
ax, 3m1n and determine the reading conditions from this, it is assumed that the minimum value of the stimulated luminescence light amount within the irradiation field is 3
A case may occur where the minimum value of the stimulated luminescent layer due to the scattered radiation outside the irradiation field is set to 3 gain, although it should be set to sin. In this way, when the minimum value of the amount of stimulated luminescent light in the irradiation field is set to 31 inches, that value is generally lower than the minimum value of the stimulated luminescent layer in the irradiated field, so J3 in the main reading is unnecessary for diagnosis. Scattered radiation will be recorded in the low concentration area,
Therefore, the density of the image in the portion necessary for diagnosis becomes too high, and as a result, the contrast decreases, making it difficult to make a satisfactory diagnosis.

In other words, when shooting with a narrowed irradiation field, scattered rays generated from the subject enter the irradiation field on the sheet,
The image information jqed by pre-reading will include information based on this scattered radiation, so even if the reading conditions are determined based on such pre-read image information, it is not possible to determine the optimal reading conditions. As a result, it is difficult to obtain visible images that are suitable for observation and interpretation.

(Object of the Invention) In view of the above-mentioned circumstances, the object of the present invention is to provide a method for determining the reading position during main reading based on image information obtained by pre-reading, which The object of the present invention is to provide a method that can eliminate the above-mentioned disadvantages caused by narrowing down the irradiation field and determine the optimal reading striae.

(Layering of the Invention) In order to achieve the object "-2," the method for determining reading conditions according to the present invention is to obtain digital image data at each position on the M-laminated phosphor sheet from the image information obtained by pre-reading. The digital image data is subjected to differential processing to determine the difference between the image data, for example, the difference between adjacent image data to create a difference image consisting of the difference values, a predetermined threshold value Th is prepared, and the A difference image or a processed difference image obtained by performing predetermined processing on the difference image is scanned in one direction, and a position on each scanning line where a difference value of +Th or more exists and a position where a difference molecule ti of -Th or less exists. Detecting a predetermined section interposed between the two, that is, a section within the irradiation field, and determining reading conditions for the main reading based on the image information obtained by the pre-reading of the section within the irradiation field on each scanning line. It is characterized by

<Embodiment B> Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The sharp IM mode described below is a method of determining reading conditions when reading a stimulable phosphor sheet 10 photographed with a rectangular irradiation field aperture, as shown in FIG. Note that the X axis and Y axis in FIG. Since the irradiation field is apertured so as to be parallel to each side of the sheet 10, the X-axis and Y-axis can be considered to be set along two adjacent sides of the sheet 10.

In this embodiment, first, the image information stored and recorded on the stimulable phosphor sheet 10 shown in FIG. 1 is read by pre-reading as described above.

Reading image information from the stimulable phosphor sheet 10 by pre-reading means reading the stimulated luminescence light emitted from the sheet 10 by scanning the sheet 10 with pre-read excitation light and reading the stimulated luminescence light emitted from the sheet 10 with a photoelectric conversion means. Each scanning point above (
In other words, this means obtaining information consisting of an electrical signal corresponding to the amount of stimulated luminescence light for each pixel.

Next, digital image data at each position on the sheet is obtained from the image information read as described above. In obtaining this digital image data, it may be obtained directly from the image information read by the above-mentioned pre-reading, or the image information may be subjected to spatial filter processing J11! It is also possible to perform pre-treatments such as the following.

If you want to obtain it directly, for example, you can set the position on the above sheet in pixel units, and digitize the above pre-read image information of the pixel corresponding to each position as the digital image data at that position. .

When calculating by performing preprocessing such as spatial filtering,
For example, multiple pixels that have a certain relationship are set together as one position, and based on the pre-read image information of the pixels included in this position, for example (adding and averaging them to calculate the digital image data of the position) Alternatively, the position r of sheet-L may be set in units of pixels, and the digital image data at this position is calculated based on the pre-read image information of a plurality of pixels corresponding to the position and surrounding positions of A. You can do it like this.

In this implementation B, the position on the sheet is set at the middle pixel,
The pre-read image information of pixels corresponding to each position is digitized and used as digital image data for that position.

Figure 2 is an enlarged view of part A of the stimulable phosphor sheet in Figure 1. Each square in the figure represents one pixel (position), and the f (1,
1), f (1, 2), ...... are each pixel (1,
1), '(1, 2), . . . show the digitized version of the above image information.

After obtaining digital image data at each position as described above, the image data is then subjected to differential processing to create a differential image consisting of differential values.

The above-mentioned difference processing refers to a process of calculating a difference value at a predetermined position based on the difference between digital image data that have a predetermined relationship, such as adjacent or nearby digital image data, and specifically, for example, Figure 3(a)
This refers to the process of finding a difference value using a difference operator as shown in ~(f).

Difference processing using an operator (not shown in FIG. 3(a)) involves subtracting digital image data at adjacent positions in the X-axis direction and using the result as a difference value. For example, in FIG. ! ! Digital image data r of t(3,4>
Subtract the digital image data f (3, 3) at position (3, 3) from (3, 4> and convert the result to position < 3.3
).

In addition, the difference processing using the dimensional operator shown in FIG. 3(b) extracts the digital image data at the positions on both sides of the predetermined position in the X-axis direction, and uses the result as the difference value for the predetermined position. For example, in Figure 2, position J3 (3,4
) digital image data f (3,4) to position (3
, 2>, the digital image data f (3, 2>) is subtracted and the result is used as the difference value at the position <3.3).

Difference processing using operators not shown in Figure 3 CC> is as follows:
The digital image data at adjacent positions in the Y-axis direction are extracted and the result is used as the difference value. For example, in FIG.
Subtract the digital image data f (3,3) at position (3,3) from (4,3) and use the result as position <3.3)
This is the difference value of .

Difference processing using four operators shown in FIG. 3(d) involves subtracting digital image data at positions on both sides of a predetermined position in the Y-axis direction and using the result as the difference value for the predetermined position, for example. In Fig. 2, the digital image data at position (4, 3) is “1ff from (4, 3) (2, 3)”.
The digital image data f (2, 3>) is subtracted and the result is used as the difference value at the position (3°3).

The difference processing using the operator shown in Figure 3(e) is as follows:
This process is performed by simultaneously using the operator in FIG. 3(a) and the operator in FIG. 3(C). For example, in FIG.
The result of subtracting the digital image data r (3, 3) of position ff1 (3, 3> from (3, 4) and the position (4, 3)
) digital image data f (4,3> to position (3
, 3) and the result of subtracting the digital image data f (3°3) are used as the difference value at the position (3, 3>).

The difference processing using the operator shown in FIG. 3(f) is
This process is performed using the operator shown in Figure 3(b) and the operator shown in Figure 3(d) at the same time.
Digital image data f of 3rd place 1fff (3, 4)
(3, 4> to !! (3, 2> digital m image data r (3, 2>) subtracted result and position (4, 3> digital image data f (4, 3> to !< 2.3
) is added to the result of subtracting the digital image data r (2°3), and the difference value at position (3, 3) is determined.

The above-mentioned difference value may be obtained for all of the above-mentioned positions, or may be obtained for some appropriately selected positions.

In this embodiment, the operator shown in FIG. 3(a) is used to obtain the difference values at all the positions, and a difference image is created from the difference values.

Next, a predetermined threshold value Th is prepared, and the differential image created as described above or the processed differential image obtained by performing appropriate processing on the differential image is scanned in one direction, and +Th on each scanning line is A predetermined interval between the above difference value and the difference value below Th is detected.

In this embodiment, a method is adopted in which a predetermined section is detected using the processed difference image.

That is, in this embodiment, the difference value obtained as described above is subjected to threshold processing using the predetermined threshold Th, and the difference value greater than or equal to -Th is reduced to +1, and the difference value less than or equal to -Th is reduced to +1. The difference value is -1, and the other difference values, i.e., the differences less than +Th and greater than -Th, are encoded with O as the difference (direction is O). The threshold-processed difference image is scanned in the X-axis direction, and if some combinations of 1 and -1 are found on each scanning line, the section sandwiched by 4.1 and -1 is scanned on that scanning line. Detected as a predetermined section.

Figure 4 does not show the digital image data on the arbitrary line correspondence in the The difference value obtained by the difference processing and the state in which the difference value is subjected to the ternarization threshold processing as described above are not shown. Figure 6 shows the detailed threshold processing performed on all lines in the X-axis direction. , the result (retarded threshold processed difference!a(
-1°0, +1> is a diagram showing a threshold-processed difference image. However, in Figure 6, the threshold-processed difference values +1 and -1 are simply displayed as ■ and O, and the parts where neither ■ nor O are displayed are the parts where the threshold-processed difference value is O. It is.

Since the digital image data at each position on the stimulable phosphor sheet corresponds to the energy level of the radiation incident on the sheet, the irradiation field slope 141 is as shown in Figure 4.
The image data in field 12 will generally have a low proton level, and the image data in field 12 will generally have a high proton level. Therefore, as shown in Fig. 5, the difference value between the image data in the part where the irradiation field contour is located is much larger or smaller than the difference value in other parts, and when this difference value is extremely large, it is extremely Threshold 1 with a small position set appropriately
By detecting using flTh, it is possible to detect the position of the irradiation field contour and, furthermore, the section within the irradiation field sandwiched between these two positions. Therefore, by scanning the difference image in the X-axis direction, each scanning line LXI, LXz is scanned as shown in FIG.
, LX3, -.=LXi.

...Detecting a predetermined section (shaded area in the figure) between a position on LXn where the difference value is above +Th and a position below -Th means that the difference value on each scanning line is This means detecting the distance within the irradiation field.

In addition, in FIG. 6, scanning lines LXI and LXz
Since the line is located in the outside irradiation area 14, naturally there is no line with a difference value of +Th or more or -Th or less on the line.・Also, like the line LXi in the figure, even if the line is located on the irradiation field 12, there may be cases where there is no combination of a position where the difference value is +Th or more and a position where the difference value is −Th or less. , in that case, it is treated as if the predetermined section was not detected from that scanning line.

Even when the same threshold processing as above is performed using the difference operator shown in FIG. 3(b), the difference image similar to the case of Hon*yats shown in FIG. 6 is 1! 'P'
As in the case of this embodiment, this differential image may be scanned to detect a predetermined section.

When using the difference operators shown in Fig. 3(C) and (d), v4! is shown in Fig. 7! In this case, the difference image is scanned in the Y-axis direction to detect a predetermined section (the section indicated by the double-headed arrow in the figure) in each scanning line.

If the difference operator is used in accordance with Figures 3(e) and (f), a difference image as shown in Figure 8 will be obtained, and in this case, scanning will be performed in one direction, either the X-axis direction or the Y-axis direction. Then, a predetermined section in each scanning line can be detected (in the figure, a double-headed arrow is shown indicating a predetermined section detected by scanning in the X-axis direction).

In short, the above-mentioned embodiment performs threshold value processing on the difference image to encode all the difference values such that difference values of +Th or more, difference values of -Th or less, and other difference values can be separated by p1, Threshold processed difference t created by this process
In(+1.0.-1>), the threshold-processed difference image was scanned to detect a predetermined section, but other processing, for example, the difference value between +Th and -Th, was Then, threshold processing is performed to encode only a part of the difference value, such as so-called half-threshold processing, which leaves other difference values as they are, and from the threshold-processed difference value obtained by this processing. The predetermined section may be detected by scanning the threshold-processed difference image.

Next, a predetermined section on each scanning line is detected as described above, and pre-read image information at a position corresponding to each predetermined section is extracted from among the pre-read image information that has already been obtained as described above. Then, reading conditions for main reading are determined based on the extracted pre-read image information.

As mentioned above, each predetermined section on each scanning line is an interval within the irradiation field on each scanning line, so the sum of the pre-read image information of the predetermined section on each scanning line extracted above is ultimately the area within the irradiation field. This means that it is pre-read image FIl information.

The determination of the reading line 1 during main reading based on the extracted pre-read image information, that is, the pre-read image information within the irradiation field, can be performed in various ways. From this histogram, a predetermined maximum stimulated luminescence light ffi S wax is created.
and the minimum stimulated luminescence light fi5min, and this Smax
, the reading conditions can be determined based on the Smi port.

Note that the determination of reading conditions is not limited to the case where the reading conditions are determined based only on the pre-read image information within the irradiation field.
The determination can also be made by taking into account the region to be imaged of the subject to be imaged, such as the chest, 11th part, and the imaging method, such as simple, contrast, tomography, and enlargement.

After determining the reading conditions as described above, main reading is performed according to the reading conditions, but this main reading is based on the reading conditions as disclosed in Japanese Patent Application Laid-open No. 120346/1983, which the applicant previously filed. Preferably, the area is limited to the irradiation field determined based on the above method.

By limiting the reading area for the main reading to within the irradiation field in this way, noise components due to scattered radiation recorded outside the irradiation field of the stimulable phosphor sheet are not read, making it possible to obtain an excellent final image. .

Furthermore, by narrowing down the reading area, it is possible to shorten the reading time or maximize the reading density.

Figure 9 is the actual fl! shown in Figure 3! ! FIG. 7 is a threshold-processed difference image created by a method similar to the embodiment, but does not show a case where the irradiation field is circular. As can be easily understood from this figure, the method according to the present invention is also applicable to cases where the irradiation field is not rectangular. Furthermore, even in the case of so-called divided photography in which one sheet is divided and each division is photographed, for example, by applying the present invention to each division, the reading conditions for each division of the sheet can be adjusted. can be determined optimally.

In the method according to the present invention, the difference image is scanned in one direction to detect a predetermined section, but the scanning direction is not necessarily arbitrary, and as understood from the above-mentioned actual aspects, the method of determining the difference value is It is decided according to.

Furthermore, the concept of difference value and difference processing in the method according to the present invention is applied to micromolecules Ii, which are substantially the same as these.
'IJ3 and the concept of differential processing are also included.

4γ113, it is also possible to determine the image processing conditions for performing the image based on the pre-read image information of a predetermined section on each scanning line detected by the method according to the present invention.

(Effect of R-light) As described above, the method for determining reading conditions for radiation image information according to the present invention performs differential processing on the digital image information (pre-read image information) at each position on the stimulable phosphor sheet. An image is created, and the difference image is scanned in one direction to detect a predetermined interval on each scanning line between a difference value greater than or equal to a predetermined threshold value +Th and a difference value less than or equal to -Th. However, the reading conditions are determined based on the pre-read 1IifJi information in each predetermined section.

However, as mentioned above, the predetermined sections on each scanning line are irradiation field-like sections on each scanning line, so determining the reading conditions based on the pre-read ii* information in each predetermined section means that This means that the reading conditions are determined based only on the pre-read image information within the irradiation field.

Therefore, according to the method for determining reading conditions according to the present invention, when dark shadowing is performed by applying the irradiation field aperture,
The reading conditions can be determined based only on the pre-read image information within the irradiation field, that is, the negative effects of scattered radiation incident on the sheet outside the irradiation field can be divided by 01, so the optimal reading conditions can always be determined. can.

[Brief explanation of drawings]

Figure 1 is a diagram showing the stimulable phosphor sheet photographed with the irradiation field aperture, Figure 2 is an enlarged view of section A in Figure 1 and is a diagram showing digital image data at each position, Figure 3 (a) to ([) are diagrams showing the difference operators, respectively, and FIG. 4 is the digital ii! on the line correspondence × in FIG. 1!
Figure 5 is a diagram showing i-image data; Figure 5 is a diagram showing difference values obtained by performing differential processing on the digital image data in Figure 4; t56, FIG. 7, and FIG. 8 are diagrams showing difference images created using different difference operators, and FIG. 9 is a diagram showing a difference image when the irradiation field is circular.

Claims (2)

[Claims] (1) By irradiating the excitation light onto the stimulable phosphor sheet on which the radiation image information is stored and recorded with an irradiation field aperture, the radiation image information stored on the stimulable phosphor sheet is radiated. Prior to main reading to emit luminescent light and photoelectrically read this stimulated luminescent light to obtain an electrical image signal for outputting a visible image, excitation with energy lower than the energy of the excitation light used in the main reading is performed. Reading the radiation image information by performing pre-reading of the radiation image information stored and recorded on the stimulable phosphor sheet using light, and determining reading conditions for the main reading based on the image information obtained by this pre-reading. In the condition determination method, digital image data at each position on the stimulable phosphor sheet is obtained from the image information obtained by the pre-reading, and this digital image data is subjected to differential processing to obtain a difference between the image data. A difference image consisting of values is created, a predetermined threshold value Th is prepared, and the difference image or a processed difference image obtained by performing a predetermined process on the difference image is scanned in one direction so that +Th or more on each scanning line Detecting a predetermined section sandwiched between a difference value of and a difference value of -Th or less, and determining reading conditions for the main reading based on image information obtained by the pre-reading within the predetermined section on each scanning line. A method for determining reading conditions for radiation image information, characterized in that: (2) A processed difference image obtained by performing predetermined processing on the difference image has a difference value of +Th or more and -Th with respect to the difference image.
The patent claim is characterized in that the image is a threshold-processed difference image that has been subjected to threshold processing to encode all or part of the difference values so that the following difference values can be distinguished from other difference values. A method for determining reading conditions for radiographic image information according to scope 1.