JPS63133762A - Irradiation field recognizing method and image processing condition deciding method - Google Patents

Abstract

PURPOSE:To decide an area decided with a differential value and a threshold value as an irradiation field, by finding the differential value between adjacent picture data from read picture information, comparing the differential value with the threshold value, and scanning it in two directions. CONSTITUTION:Firstly, a cumulative phosphor sheet 10 is scanned by prereading excitation light, and a stimulated excitation beam of light generated from the sheet 10 is read by a photoelectric means. The differential value between a digital picture data obtained in such way and the adjacent picture data is found, and the differential value is compared with the prescribed threshold value Th. Then, as for a a direction of X-axis, change points are generated at the point where it changes from out of the irradiation field to the irradiation field (over +Th), and the point where it changes from the irradiation field to the out of the irradiation field(less than -Th). By deciding the point at every scanning line, two vertical lines are expressed, and the area sandwiched with the two vertical lines is decided as the irradiation field in the direction of X-axis. As for a direction of Y-axis, it is possible to decide the irradiation field by comparing the differential value with the threshold value Th similarly.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention recognizes the irradiation field when radiation image information is recorded on a recording medium such as a stimulable phosphor sheet by aperture irradiation field. The present invention relates to a method and a method of determining image processing conditions when processing image information read from the recording medium, using the irradiation field recognition method.

(Conventional Technique I) When a certain type of phosphor is irradiated with radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a part of this radiation energy is accumulated in the phosphor. It is known that when this phosphor is irradiated with excitation light such as visible light, the phosphor exhibits stimulated luminescence depending on the accumulated energy, and phosphors that exhibit this property are called stimulable phosphors. Called.

Using this stimulable phosphor, radiation image information of a subject such as a human body is recorded on a -H sheet of stimulable phosphor, and then the stimulable phosphor sheet is scanned with excitation light such as a laser beam. generates stimulated luminescence light, photoelectrically reads this stimulated luminescence light to obtain an image signal, performs image processing on this image signal, and creates a radiation image of the subject based on the image signal subjected to image processing. The applicant has already proposed an IR image information recording and reproducing system that outputs visible images to recording materials such as photographic light-sensitive materials and display devices such as CRTs.
TeIll'le. (* till Showa 55-1242
No. 9, No. 56-11395, etc. ) In addition, in the above system, in order to improve the suitability for II observation and interpretation of visible images, when reading the stimulated luminescence light photoelectrically, the system uses optimal reading conditions determined according to each photographed image. It is desirable to read the information, and from this point of view, as one aspect of the above system, a stimulable phosphor sheet on which radiation image information of a subject is stored and recorded is scanned with excitation light, and this scanning causes the radiation emitted from the sheet to be scanned. Prior to the "main reading" in which the stimulated luminescence light is read by a photoelectric reading means to obtain an electrical image signal for reproducing a visible image for diagnosis, excitation light of a lower level than the excitation light used for this main reading is used in advance. scan the sheet and read the outline of the image information accumulated and recorded on this sheet.
Based on the image information obtained by this pre-reading, the reading conditions for performing the main reading are determined, the music book reading is performed according to the reading conditions, and the image signal obtained by this main reading is processed by an image processing means. This image processing means processes the image signal so as to obtain an output image suitable for diagnostic purposes according to the imaging site and imaging method, etc., and reproduces this image signal as a visible output image on a photosensitive material, etc. A system for doing this is known, and is disclosed, for example, in Japanese Patent Laid-Open No. 58-67240, which was previously filed by the present applicant and has already been published.

Here, the reading conditions refer to the relationship between the input and output of the reading means, for example, in the above example, the relationship between the input ("i" of the emitted light m) and the output (electrical image signal level) of the photoelectric reading means. It is a general term for various conditions that give
, scale factor (latitude), power of excitation light in reading, etc.

In addition, 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 the effective energy of the excitation light that the stimulable phosphor sheet receives per unit area during pre-reading is equal to that during main reading. means smaller than.

In this way, by grasping the outline of the image information stored on the sheet before the actual reading and performing the actual reading according to the reading conditions determined based on the outline of this image information, it is possible to It is possible to eliminate inconveniences caused by fluctuations in the range of radiation energy levels accumulated and recorded on the sheet due to fluctuations in radiation exposure, etc., and to always obtain visible images with excellent suitability for observation and interpretation.

(Problem to be solved by the invention) However, in the above system, in order to avoid irradiating radiation to areas that are not necessary for humane diagnosis, or to prevent radiation from being irradiated to areas that are unnecessary for diagnosis, diagnosis may be performed from that area. Scattered rays enter necessary areas and the contrast resolution deteriorates, so in order to prevent this, the radiation field may be narrowed down when recording the 9A-line image information (during imaging).

When imaging is performed with the irradiation field narrowed down in this way, there will be a part within the irradiation field and a part outside the irradiation field within the stimulable phosphor sheet. In other words, it is convenient if it is possible to know where the irradiation field contour line is.

This is because, for example, when reading the above-mentioned stimulable phosphor sheet in advance and determining the reading conditions for main reading based on the image information determined by this pre-reading, the stimulable phosphor sheet is This is because it is preferable to determine the reading conditions based only on the pre-read image information within the irradiation field range.

This point will be explained in more detail below. That is, as a specific method of determining the reading conditions for main reading based on the image information obtained by the pre-reading,
For example, a histogram of the image information (image signal level) that has been cleared by pre-reading is obtained, and from this histogram, the maximum image signal level p n+ax and the minimum image signal level P of the desired image information range in this histogram are obtained.
1n is calculated, and PIlax and Plin are the maximum density [) 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 Qiax and minimum signal level Qmin of a desired input signal range in an image processing means determined by laX and minimum density QIlin. (Japanese Unexamined Patent Publication No. 156055/1983).

However, when imaging is performed by narrowing down the radiation irradiation field as described above, scattered radiation generated from the subject in the irradiation field usually enters the irradiation field on the stimulable phosphor sheet, resulting in a highly sensitive stimulant. Since the phosphor sheet also accumulates and records these scattered rays, the histogram of image information (image signal level) obtained by pre-reading also includes the image signal level based on these scattered rays. Since the image signal level outside the irradiation field on the sheet based on this scattered radiation may be higher than the image signal level within the irradiation field, it is necessary to distinguish between the image signal levels inside and outside the irradiation field from the obtained histogram. It is difficult. Therefore, pIlax, pn from the histogram as mentioned above
When calculating in and determining reading conditions from this, the minimum value of the image signal level within the irradiation field should be Plin, but the minimum value of the image signal level due to scattered radiation outside the irradiation field may be determined to be Pm1n. obtain. In this way, when the minimum value of the image signal level outside the irradiation field is set to Pln, that value is generally lower than the minimum value of the image signal level within the irradiation field, so d5 is used in the main reading to eliminate scattered radiation unnecessary for diagnosis. Since the image is recorded in a low density area, the density of the image in the portion necessary for diagnosis becomes too high, resulting in a decrease in contrast and making it difficult to perform a satisfactory diagnosis.

In other words, when shadowing is performed by narrowing down the irradiation field, scattered rays generated from the subject enter the irradiation field on the sheet,
Since the pre-read image information includes information based on this scattered radiation, it is difficult to determine the optimal reading conditions even if the reading conditions are determined based on such pre-read image information. As a result, it is difficult to obtain visible images that are suitable for observation and interpretation.

Therefore, when trying to determine reading conditions based on pre-read image information using the above method, when the irradiation field is narrowed down, the irradiation field is accurately recognized and the pre-read image information within that irradiation field is used. It is desirable to determine it based on the above and eliminate the adverse effects caused by the scattered radiation outside the irradiation field.

The above is an explanation of the necessity of irradiation field recognition when determining the reading conditions for imaging using a stimulable phosphor sheet. This may become necessary due to various circumstances when radiation image information is recorded using field aperture.

On the other hand, in the above system, image processing is performed on the read image signal as described above.

This image processing is generally performed on each individual image based on image processing conditions determined based on the imaging area and shadowing method so that an output image suitable for diagnostic purposes can be obtained. However, for example, the above-mentioned image gripping site and I! It is also conceivable that the determination may be made based on the image information obtained by the above-mentioned pre-reading or main-reading, or based on both of the above-mentioned image information and the above-mentioned imaging site/imaging method, rather than the shadow method.

However, when imaging is performed with the irradiation field apertured, even if the image processing conditions are determined based on the pre-read or main-read image information, as mentioned above, the image information contains information due to scattered radiation outside the irradiation field. (noise), it is difficult to obtain image processing conditions that are as favorable as one would have expected if they were initially determined based on image information.

Therefore, when determining the image processing conditions based on the image information as described above, if the image is being photographed with an irradiation field aperture, it is not determined simply based on the read image@information itself, but the scattering conditions are determined in some way. It is desirable to make a decision based on image information with less noise, excluding line information.

Problems in determining such image processing conditions occur not only in the case of illumination using the above-mentioned stimulable phosphor sheet, but also in cases where radiation image information is generally recorded by applying an irradiation field aperture to the recording medium. This can occur in

Note that the above-mentioned image processing conditions are a general term for various conditions that affect the relationship between input and output in the image processing means, and include, for example, gradation processing conditions and spatial frequency processing conditions.

In view of the above circumstances, a first object of the present invention is to provide a method for recognizing an irradiation field when radiation image information is recorded on a recording medium such as a stimulable phosphor sheet by restricting the irradiation field. It's about doing.

In view of the above circumstances, a second object of the present invention is to eliminate scattered radiation information in the field of irradiation when radiation image information is recorded on a recording medium such as a stimulable phosphor sheet by applying irradiation field aperture. An object of the present invention is to provide a method for determining image processing conditions based on image information with less noise.

(Means for Solving the Problems) In order to achieve the above object, the irradiation field recognition method according to the first aspect of the present invention provides a stimulable phosphor sheet on which radiation image information is photographed with the irradiation field apertured. The image information is read from a recording medium such as, image data at each position on the recording medium is obtained from the read image information, and this image data is subjected to differential processing to calculate the difference between the image data, and the difference value is obtained. Create a difference image consisting of a predetermined threshold ■
h, scan the difference fraction or a processed difference image obtained by processing the difference image in a predetermined method in at least two directions, and calculate a difference of +Th or more on each scanning line in that direction for each scanning direction. A predetermined range formed by a set of predetermined sections sandwiched between the value and the difference value less than or equal to -Th is detected, and a predetermined area determined based on each predetermined range detected for each scanning direction is defined as an irradiation field. Characterized by recognition.

In order to achieve the above object, the method for determining image processing conditions according to the second aspect of the present invention provides a method for determining radiation image information from a storage medium such as a stimulable phosphor sheet on which radiation image information has been captured by applying irradiation field aperture. Reading image information, determining image data at each position on the recording medium from the read image information, and performing differential processing on this image data to determine differences between the image data to create a difference image consisting of difference values. A predetermined threshold value Th is prepared, and the difference image or a processed difference image obtained by processing the difference image by a predetermined method is divided into at least two
scan in the direction, and for each scanning direction, detect a predetermined range formed by a set of predetermined sections sandwiched between a difference value of +Th or more and a difference value of -Th or less on each scanning line in that direction, A predetermined area determined based on each predetermined range detected for each scanning direction is recognized as an irradiation field, and the image is processed based on image information within the recognized irradiation field among the image information read from the recording medium. It is characterized by determining processing conditions.

Note that the above-mentioned recording medium J refers to a medium capable of recording radiation image information, and a specific example thereof includes the above-mentioned stimulable phosphor sheet, but is not necessarily limited thereto.

In addition, the term "image information read from a recording medium" as used above means that the image information recorded on the recording medium is read by some method, such as the pre-reading in the NV4 phosphor sheet mentioned above. This refers to image information obtained through book reading, but is not necessarily limited thereto.

Of course, the method of using the irradiation field recognized by the above method is not limited to any particular method.

In addition, in the method for determining both edge processing conditions described above, image information and images for recognizing the irradiation field! It does not matter whether the image information for determining the processing conditions is the same or not. For example, the irradiation field may be recognized from the main reading image information and image processing conditions may be determined based on the main reading image @ information within the irradiation field, or the irradiation field may be recognized from the pre-read image information and the pre-read or main reading within the irradiation field may be determined. Image processing conditions may be determined based on image information.

In addition, the above-mentioned "determine image processing conditions based on image information within the irradiation field" refers to cases where the image processing conditions are determined based only on such image information, as well as cases where such image information and other things, such as the above-mentioned This meaning also includes cases where the decision is made based on the part to be photographed, the method of photographing, etc.

Further, the above-mentioned image processing conditions may be determined in any manner as long as it is based on image information within the irradiation field, that is, by using the image information, and the specific method is not limited in any way. .

Furthermore, the image processing conditions determined are also gradation processing.

Although the conditions are listed as typical, they are not necessarily limited thereto.

<Effects of the Invention> As described above, the irradiation field recognition method according to the first invention creates a difference image by performing differential processing on image data at each position on a recording medium, and processes this difference image (or a predetermined method). (processed difference image processed in ) in at least two directions, and for each scanning direction, the difference value on each scanning line in that direction is separated by a difference value greater than or equal to a predetermined threshold value +Th and a difference value less than or equal to -7h. A predetermined range consisting of a set of predetermined sections is detected, and a predetermined area determined based on these predetermined ranges is recognized as an irradiation field.

Since the image data at each position on the recording medium corresponds to the energy level of the radiation incident on the recording medium, image data in the field outside the irradiation field will generally have a low quantum level, and image data within the irradiation field will generally have a high quantum level. At the quantum level. Therefore, 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 the position where the difference value is extremely large and the position where the difference value is extremely small are set as appropriate thresholds. By detecting using the value Th, it is possible to detect the position β of the irradiation field contour, and furthermore, the irradiation field-like section sandwiched between these two positions.

Therefore, the predetermined sections on each scanning line are irradiation field sections on each scanning line, and therefore, for example, a predetermined range that is a set of predetermined sections on each scanning line in one direction is originally a true irradiation field. However, in reality, they do not necessarily match exactly for various reasons.

The method according to the present invention uses predetermined ranges obtained by scanning in at least two different directions as described above, and appropriately combines them to determine a predetermined area to be recognized as an irradiation field, so that a more true irradiation field can be obtained. A nearby area can be recognized as the irradiation field.

As described above, the method for determining image processing conditions according to the second invention recognizes an irradiation field by the irradiation field recognition method according to the first invention, and performs image processing based on image information within the recognized irradiation field. It determines the conditions.

If you find the irradiation field and extract only the image information within that irradiation field, the extracted image information will be the image information read from the entire recording medium excluding the image information due to scattered radiation outside the irradiation field. It can be said that this is true image information that does not include line noise.

Therefore, according to the present invention, image processing conditions can be determined based on true image information that does not include such scattered radiation noise, and as a result, more appropriate image processing conditions can be determined. I can do it.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First, an embodiment of the irradiation field recognition method according to the first invention will be described.

In the example described below, as shown in FIG. 1, a stimulable phosphor sheet 1 is photographed with a rectangular irradiation field
The present invention is applied to the case where the irradiation field 12 is recognized from pre-read image information in No. 0. Note that the X axis and Y axis in FIG. is the above sheet 1
Since the irradiation field is apertured so that it is parallel to each side of the sheet 10, the X-axis and Y-axis are
You can think of it as being set along the edges.

In this embodiment, first, the above-mentioned pre-reading is performed from the stimulable phosphor sheet 10 shown in FIG. 1 to read the information stored and recorded on the stimulable phosphor sheet 10.

Reading image information from the stimulable phosphor sheet 10 by pre-reading means reading the stimulated luminescence light emitted from the sheet 10 by subjecting the sheet 10 to constant distortion with pre-reading excitation light, using a light source reading means. Each scanning point above (
In other words, this means obtaining information consisting of electrical signals corresponding to the exhaustion of light emitted by 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 it may be obtained by subjecting the image information to preprocessing such as spatial filter processing.

In the case of direct determination, for example, the position on the sheet may be set in units of pixels, and the pre-read image information of the pixels corresponding to each position may be digitized and used as digital image data at that position.

When calculating by performing preprocessing such as spatial filtering,
For example, multiple pixels in a certain relationship may be set together as one position, and based on the pre-read image information of the pixels included in this position, for example, they may be averaged to highlight the digital image data at that position. Alternatively, the position on the sheet may be set in units of pixels, and the digital image data at the position may be calculated based on pre-read image information of multiple pixels corresponding to the position and surrounding positions. good.

In this embodiment, positions on the sheet are set pixel by pixel, and pre-read image information of pixels corresponding to each position is digitized and used as digital image data at 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), ...... is each pixel (1,
1>, <1.2>, . . . , the above image information is digitized.

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 is a one-way difference process. (This is a process for finding a difference value between image data in only one direction, for example, a process for finding a difference value using a difference operator as shown in FIGS. 3(a) to (d) described below). and differential processing in two or more directions (
This process calculates the difference value between image data in two or more directions, for example, as shown in FIGS. 3(e) and (f) described below.
) may be used to obtain a difference value using a difference operator as shown in (). Further, the difference image created by performing difference processing in multiple directions is not necessarily one, but may be composed of a plurality of difference images. For example, when creating a difference image by performing difference processing in two directions, use the difference operator as shown in Figure 3(e) or (f) to create a difference image.
It is also possible to create two differential images, as shown in Figure 3.
The difference image obtained by the difference operator shown in a) and the difference image shown in Fig. 3 (C
), two difference images may be created using a difference operator.

The difference processing by the difference operator shown in FIGS. 3(a) to 3(f) above is as follows.

The differential processing using the operator shown in FIG. 3(a) is
The digital image data at adjacent positions in the X-axis direction are subtracted and the result is used as a difference value. For example, in FIG.
, 4) to position (3, 3) digital image data f
<3.3> is subtracted and the result is used as the difference value at position (3, g).

Further, the difference processing using the operator shown in FIG. 3(b) subtracts 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, the position (3, 4>
Digital image data f (3,4) from position <3.
The digital image data f (3, 2) at position (3, 2) is subtracted and the result is used as the difference value at position (3, 3).

Difference processing using the operator shown in FIG. 3(C) is
The digital image data at adjacent positions in the Y-axis direction are extracted and the result is used as a difference value. For example, in FIG. 2, the digital image data f (
4,3) to the digital image data f at position <3.3>
(3, 3> is subtracted and the result is the difference value of the order @(3, 3).

Difference processing using the operator 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. In Figure 2, the digital image data f (2, 3) at position (2, 3) is subtracted from the digital image data f (4, 3,) at position <4.3) and the result is calculated at position (3°3). This is the difference value of .

The differential processing using the operator shown in FIG. 3(e) is a process performed by simultaneously using the operator shown in FIG. 3 <a> and the operator shown in FIG. 3(C). For example, in FIG. 3, 4> digital image data f (3
, 4) to position (3, 3>) digital image data f
Add the result of subtracting (3, 3) and the result of subtracting the digital image data f (3°3) of position <3.3> from the digital image data f <4.3) of position <4.3>. The combined value is the difference value for the position (3, 3>).

Difference processing using the operator shown in FIG. 3(f) is a process performed by simultaneously using the operator shown in FIG. 3(b) and the operator shown in FIG. 3<d). For example, in FIG. 3, 4> digital image data f (
3, 4) to position (3, 2>) digital image data f
The result of subtracting (3,2) and the result of subtracting the digital image data f (2°3) of position @ (2,3) from the digital image data f (4,3) of position <4.3) The sum is used as the difference value for the position <3.3).

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 practical example, a difference value image is created by performing difference processing in two directions, and in creating the difference image, the operator shown in FIG. 3(a) is used to calculate the difference values at all the positions. Using the operator shown in FIG. 3(C), a difference image (Y-axis difference image) consisting of the integral values at all the positions is created.

Next, a predetermined threshold Th is prepared, and the difference image created as described above or the processed difference image obtained by performing appropriate processing on the difference image is displayed in at least two directions (each direction is not parallel to each other, +Th on each scanning line in that direction for each scanning direction.
A predetermined range formed by a set of predetermined sections sandwiched between the above difference value and the difference value less than or equal to -Th is detected.

In this embodiment, the predetermined range is detected using the processed difference image. That is, the X-axis direction difference image and the Y-axis direction difference image obtained as described above are subjected to threshold processing using the above-mentioned predetermined threshold Th, respectively, and +
The inspection value of Th or more is +1. −1 for the difference value less than or equal to Th,
The other difference values, that is, the difference values smaller than +Th<−Th, are encoded as O, and the thresholded X is made up of the thresholded difference values encoded in this way
The axial and Y-axis difference images are scanned in the X-axis direction and the Y-axis direction, respectively, and a set of predetermined sections sandwiched between +1 and -1 on each scanning line in the X-axis direction is defined as a predetermined range in the X-axis direction. A set of sections sandwiched between +1 and -1 on each scanning line in the Y-axis direction is detected as a predetermined range in the Y-axis direction.

FIG. 4 is a diagram showing digital image data on an arbitrary line 9Jx in the X-axis direction in FIG. 1, and FIG. 5 is a diagram showing the digital image data in FIG. FIG. 6 is a diagram illustrating a ladder in which the left-hand value and the difference value obtained are subjected to ternarization threshold processing as described above, and such threshold processing is performed for all lines in the X-axis direction.

The resulting threshold-processed difference value (-1°0, +
1> in the present actual m aspect consisting of
A diagram showing an axial difference image. FIG. 7 is a diagram showing a threshold-processed Y-axis difference image in the present embodiment created in the same manner using the difference operator in FIG. 3(C). . However, in FIGS. 6 and 7, +1 and -1 of the threshold-processed cavity values are simply displayed as ■ and e, and the parts where neither ■ nor e are displayed are threshold-processed g! The completed difference value is O.

Since the digital image data at each position on the stimulable phosphor sheet corresponds to the energy level of the rays incident on the sheet, for example, as shown in FIG. The image data within the irradiation field 12 generally has a high Φ value.

Therefore, for example, as shown in Fig. 5, if the irradiation field contour is
The difference value between the image data in the part where the difference value occurs is much larger or smaller than the difference value in other parts, and the positions where the difference value is extremely large and the positions where it is extremely small are detected using an appropriately set threshold value Th. By doing this, it is possible to detect the position of the irradiation field contour and, furthermore, the irradiation field section sandwiched between these two positions. Therefore, by scanning the X-axis direction difference image in the X-axis direction, each scanning line L is scanned as shown in FIG.
Xi, LXz, LX3.・・・・・・L X i
r...Difference value on LXn - is +T
Detecting a predetermined range consisting of a set of predetermined sections (shaded areas in the figure) sandwiched between a position above i1 and a position below -Th means ultimately detecting a range corresponding to the irradiation field. It means that. Further, the Y-axis direction difference image is scanned in the Y-axis direction, and each scanning line is Yl as shown in FIG.

LYz, LY3, ”-, LY!
The same goes for detecting a predetermined range consisting of a set of predetermined intervals on , --, LYn.

Note that in FIGS. 6 and 7, the scanning line LXt
, LXz +1'j (FLYx , LYz , LY
3 is located in the outside irradiation area 14, so naturally there is no difference value greater than +Th or -Th on this line. Furthermore, even for lines located on the irradiation field 12, such as the line Lxi in FIG. 6, in some cases there may not be a combination of a position with a difference value of +11 or more and a position with a difference value of -Th or less. In that case, it is treated as if the designated section was not detected from that scanning line.

In the above embodiment, two difference images are created using the difference operators shown in FIG. 3(a) and FIG. 3(C), and each difference image is scanned in one direction. It scans and detects two predetermined ranges.

The creation of two differential images in this case is, for example, shown in Figure 3 (b
) and the difference operator shown in FIG. 3(d) may be used. 6 and 7, respectively, when a difference value is obtained using the difference operator shown in FIGS. A difference image similar to the above is obtained, and therefore, a predetermined range can be detected by scanning both difference image edges in the X-axis direction and the Y-axis direction, respectively, as in the case of the above embodiment.

Alternatively, only one difference image may be created, and the difference image may be scanned in two directions to detect two predetermined ranges. for example,
When a difference image is created using the difference operator shown in FIG. 3(e) or (f) above, and the difference image is subjected to threshold processing using the method described above, threshold processing as shown in FIG. 8 is obtained. Since a completed difference image is obtained, this difference image is
It is sufficient to scan in two directions of the axis to detect two predetermined ranges.

Note that the arrows in the X-axis and Y-axis directions in FIG. 8 are predetermined sections on each scanning line when scanning in the X-axis and Y-axis directions, respectively. The set is a predetermined range detected by scanning in the X-axis direction, and the set of predetermined sections indicated by arrows in the Y-axis direction is a predetermined range detected by scanning in the Y-axis direction.

In short, the above embodiment performs threshold processing on the difference image to encode all the difference values so that difference values of +11 or more, difference values of -Th or less, and other difference values can be distinguished. The thresholded difference value (+
1.0. -1) to detect a predetermined range by scanning the threshold-processed difference image consisting of -1), but other processing, such as setting the difference value between +Th and -Th to 0,
Threshold processing is performed to encode only a part of the difference value, such as so-called half-threshold processing, while leaving other difference values as they are. A predetermined range may be detected by scanning the value-processed difference image.

Next, after detecting the predetermined ranges in each scanning direction as described above, the predetermined area determined based on each of the predetermined ranges is recognized as an irradiation field. A predetermined area to be recognized as this irradiation field (
As a method for determining the irradiation field area, the following two methods can be considered, for example.

One method is to determine the sum of the predetermined ranges as the irradiation field area, and the other method is to determine the common part of the predetermined ranges as the irradiation field area.

The summation part of each predetermined range means a part formed by putting together each predetermined range, and a part that corresponds only to any of the predetermined ranges is also treated as an irradiation field area. Specifically, for example, in this embodiment, a predetermined range in the X-axis direction indicated by diagonal lines in FIG. 6 and a predetermined range in the Y-axis direction indicated by diagonal lines in FIG. 7 are detected. , the range consisting of both predetermined ranges (the shaded area in Figure 9)
is determined as the irradiation field area. If the irradiation field area is determined only from a predetermined range detected by unidirectional scanning, if there is a line in which a predetermined section is not detected, such as line LXi in FIG. 6 or line LYi in FIG. A problem arises in that the section is not recognized as an irradiation field area even though it should originally be recognized as an irradiation field area.However, as in this method, the sum of the predetermined ranges detected by scanning in two directions is used as an irradiation field area. If it is determined that It can be determined as a region.

On the other hand, the common part of each predetermined range means a part that corresponds to all of the predetermined ranges, and a part that only applies to any one of the predetermined ranges is not treated as an irradiation field area. This method can be suitably used, for example, in the case of so-called divided imaging, in which the stimulable phosphor sheet 10 is divided into two parts and the irradiation field is apertured for each division, as shown in FIG. 10. It's a method. That is,
In the case of such divisional imaging, for example, the threshold-processed difference image created in the same manner as in the case of FIG. 8 may have an incomplete shape as shown in FIG. 1ffD may not be e1■, and in this case, the predetermined section (predetermined range) obtained by scanning this differential image in the X-axis direction will be as shown by the double-headed arrow in the X-axis direction. Scan from the left to the right in the axial direction, and extract only the ■→O section as a predetermined section, ○→e
The predetermined section (predetermined range) obtained by scanning in the Y-axis direction is as shown by the double-headed arrow in the Y-axis direction, and if the sum of both predetermined ranges is determined as the irradiation field area as described above. The part that is not originally the irradiation field area (the above surface position fl
However, if only the common part of a predetermined range in both scanning directions is determined as the irradiation field area as in this method, such non-irradiation field area are excluded, and only the portion that is originally the irradiation field can be determined as the irradiation field area.

FIGS. 12(a) and 12(b) are diagrams of threshold processing and difference images created in the same manner as FIGS. 6 and 7, respectively, and show the case where the irradiation field is circular. . As can be easily understood from this figure, the present invention is also applicable to cases where the irradiation field is other than rectangular.

FIG. 13(a) is a diagram showing a stimulable phosphor sheet 10 that has been approved using a diagonal aperture of a rectangular irradiation field. In this case, for example, the differential plate of FIG. 3(a) is used. By calculating the difference in the X-axis direction and creating a difference image, and applying the same threshold processing as in Fig. 6, a threshold-processed difference image as shown in Fig. 13(b) is created. By scanning this differential image in the X'-axis and Y'-axis directions in the figure, a predetermined range in each axis direction can be determined.

In the case of the divided photographing, the present invention can also be applied to each section on the sheet by obtaining information in advance that the photographing is divided.

The concept of a difference value and a difference process in the present invention also includes the concepts of a differential value and a differential process that are substantially the same.

The irradiation field recognized as described above can be used for various purposes. For example, it can of course be used to extract only the image information within the irradiation field from the pre-read image information as mentioned above and determine the reading conditions based on that, but it can also be used to extract only the image information within the irradiation field from the main reading image information as described below. In addition to extracting only image gA information and determining image processing conditions based on it, it can also be used to extract only image information within the irradiation field from the pre-read image information and determining image processing conditions based on it. It is possible, and furthermore, for other purposes, such as recognizing the irradiation field from pre-read image information and at the time of actual reading, it is possible to use Japanese Patent Laid-Open No. 60-12 filed earlier by the present applicant.
As disclosed in No. 0346, it can also be used to limit the reading area within the irradiation field. By thus limiting the reading area for the main reading within the irradiation field, noise components due to scattered radiation recorded outside the irradiation field of the stimulable phosphor sheet are not read, and an excellent final image can be obtained. Furthermore, by narrowing down the reading area, it is possible to shorten the reading time or increase the reading density.

Of course, the recognition of the irradiation field in the present invention is not limited to the pre-read image information as in the above embodiments, but can also be performed based on other image information, for example, main-read image information.

Next, an embodiment of the image processing condition determining method according to the second invention will be described.

In the embodiment described below, the irradiation field is recognized from the main reading image information in a stimulable phosphor sheet that has been patterned by performing irradiation field aperture, and the image processing conditions are set based on the main reading image information within the recognized irradiation field. This is an application of Mokubomei when setting Ivi treatment conditions, which is one of the methods.

In this embodiment, first, the stimulable phosphor sheet is read to obtain image information.

Reading the image information blue refers to scanning a stimulable phosphor sheet with pre-read excitation light, and reading the stimulated luminescence light emitted from the sheet by the scanning, using a photoelectric reading means. The obtained image information is information consisting of electrical signals corresponding to the amount of stimulated luminescence light for each scanning point (that is, each pixel) on the sheet.

Next, digital image data at each position on the sheet is obtained from the image information obtained in this way, and a difference process is performed on this digital image data to obtain a difference between the image data, resulting in a difference image consisting of the difference values. , prepare a predetermined threshold value '1'-h, scan the difference image or a processed difference image obtained by processing the difference image in a predetermined method in at least two directions, and for each scanning direction, A predetermined range formed by a set of predetermined sections sandwiched between a difference value of +Th or more and a difference value of -Th or less on each scanning line in that direction is detected, and each predetermined range detected for each scanning direction is detected. The predetermined area determined based on the above is recognized as the irradiation field.

Since this irradiation field recognition method is the same as the irradiation field recognition method of the first aspect of the present invention described above, a detailed detailed explanation thereof will be omitted.

Next, gradation processing conditions are determined based on the image information within the recognized irradiation field among the main reading image information read from the recording medium. Although any method may be used for this determination, for example, the following method may be used.

In this method, a histogram of main reading image information (image signal level) within the irradiation field is obtained, and from this histogram, the maximum image signal level pnax and the minimum image signal level p of the desired image signal range in this histogram are determined.
nin is determined, and p n+ax and ptarn are the maximum signal level R1lax and minimum signal level of the desired input signal range in the image reproduction means determined by the maximum density Q nax and n Kofuchi degree Dnin of the appropriate density range in the visible output image, respectively. The gradation processing conditions are determined to correspond to RIlin.

This method will be described in detail below with reference to FIG. In addition, in FIG. 14, the histogram of the stimulated luminescent light before being photoelectrically read is not the histogram of the electrical image signal obtained by photoelectrically reading the stimulated luminescent light by the photoelectric reading means. However, since this stimulated luminescence light is converted into an electrical image signal according to the fixed and linear reading conditions shown in the figure, the stimulated luminescence light amount and image signal level are fixed. Therefore, the histogram of the stimulated luminescent light is substantially the same as the histogram of the image signal. Therefore, in the following explanation, the first
The explanation will be given by regarding the stimulated luminescence light histogram in FIG. 4 as an image signal histogram.

In addition, the image information used for creating the histogram in this example is not necessarily limited to that read based on the linear reading conditions as described above, but in short, the image information used to create the histogram is not necessarily limited to that read based on the linear reading conditions as described above. For example, it may be image information read under non-linear reading conditions.

First, a histogram of main reading image information (image signal) within the irradiation field is obtained, and a desired range of image signals (range of stimulated luminescence light amount) is obtained from this histogram. The desired image signal range is determined from the histogram with reference to the region to be imaged and the copying method, since the histogram pattern varies to some extent depending on the region to be imaged and the imaging method. For example, in the case of chest imaging, the histogram has a pattern like this in Figure 14, where J is the mediastinal region, K is the heart region,
From this histogram, we can determine the maximum image signal level PIIax, which is the range of the desired image signal, from this histogram.
(maximum photostimulation light intensity 3max) and minimum image signal level pIlin (a small photostimulation light intensity 3nin) can be determined. For example, in the case of FIG. 14, if information on the skin and soft parts M and the outside of the subject N is unnecessary, then the desired image signal range J, including L as shown in the figure, is
The range is from lax to p min. This Pra
As a method for determining ay and Pnin, for example, it is fixed depending on the desired image signal range (7) L key rriT
1. One possible method is to determine T 2 and calculate from Tt and Tz, but any other method may be used to calculate from the histogram.

On the other hand, in a radiographic image information recording and reproducing system, as mentioned above, a photoelectric reading means usually generates an electrical image signal from stimulated luminescence light, and an image processing means performs various signal processing, especially gradation processing, on this signal. This signal is reproduced and recorded as a visible output image on a photographic light-sensitive material or the like by an image reproduction means. In this output image, there is a density range suitable for observation and interpretation, and generally this appropriate density range (Dnax
-Dmin) is predetermined, and the reproduction conditions for the image reproduction means (conditions that determine the relationship between the input to the reproduction means and the output from the reproduction means) are also predetermined, so that the appropriate density Range (DInaX -Ql
The input signal level range (Rn+ax-RIIin) to the image reproducing means corresponding to lin) is uniquely determined according to this image reproducing condition.

Therefore, p max and Pm1n obtained as above
is R max and R++ determined by the above equation
The gradation processing conditions in the gradation processing are determined so as to correspond to +in.

Gradation office 51! is a process in which each image signal input to an image processing means (gradation processing means) is output after converting its level according to certain conditions.The certain conditions are called gradation processing conditions, and usually It is represented by a nonlinear gradation curve.

The purpose of such gradation processing is to obtain a preferable visible output image suitable for diagnostic purposes depending on the imaging conditions such as the imaging region such as the head or chest and the imaging method such as simple or contrast imaging. In general, a basic form of non-linear gradation processing conditions that has the most preferable pattern for each shooting condition is determined in advance, and when gradation processing is performed for each image, it is determined appropriately according to the shooting conditions of that image. It is preferable to select a basic form of gradation processing conditions and perform Ivi gradation processing using that basic form (1).

In this embodiment as well, in this way, an appropriate one is selected from among the basic forms of gradation processing conditions predetermined according to the image shooting conditions, and it is modified based on the in-field image information. In other words, by shifting its basic shape vertically into the sphere shown in the second quadrant of FIG. 14 or rotating it around a predetermined center point O,
The 1viW4 processing conditions to be used are determined so that pnin etc. correspond to R+nax and Rn1n.

Note that the gradation processing conditions are not limited to the nonlinear ones determined by the shooting conditions as described above, but may also be linear ones. In that case, one predetermined straight line may be used as the above case. The gradation processing conditions to be used are determined by similarly rotating or shifting and positioning so that Pmax, Plin, etc. correspond to RIaX, Rmin.

The determination of gradation processing conditions by this method is not based on the imaging site or imaging method as in the former method, but is performed based only on image information within the irradiation field.

As mentioned above, if the gradation processing of radiation images and other information is performed according to the gradation processing conditions set for each individual irradiation image (image information), for example, when taking individual images, it is possible to The site or radiation dose changes,
As a result, even if the range of radiation energy levels accumulated and recorded on each patterned sheet changes, the necessary subject image information is always within the appropriate density range for observation and interpretation in any visible output image regardless of the fluctuations. This is convenient because it can be displayed on the screen.

Further, in this case, according to the present invention, since the determination can be made based on image information that does not include scattered radiation information noise, the desired image information range can be determined more accurately from the image information histogram, and as a result, the above-mentioned necessary subject image The effect of displaying information within the appropriate concentration range is more pronounced.

Ill like this! The method for determining iw4 processing conditions is particularly useful when processing image information read based on reading conditions determined without considering fluctuations in the radiation energy level range recorded in individual imaging as described above. is beneficial.

Note that the first and second inventions described above may be modified in various ways without departing from the gist thereof, and are not limited to the embodiments described above.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a stimulable phosphor sheet subjected to distance imaging with the irradiation field apertured; Figure 2 is an enlarged view of section A in Figure 1, showing digital image data at each position; Figures (a) to (f') are diagrams showing the difference operators, respectively. Figure 4 is a diagram showing digital image data on the line x in Figure 1. Figure 5 is a diagram showing the digital image data in Figure 4. Figures 6, 7, and 8 are diagrams showing the difference values obtained through processing, respectively.
A diagram showing a thresholded difference image obtained by thresholding the difference both created using the difference operator shown in (C) and (e). Figure R9 is a diagram showing the irradiation field area, Figure 10 is a diagram showing a stimulable phosphor sheet that has been cut and repelled, and Figure 11 is a diagram showing a threshold-processed difference image of the sheet shown in Figure 10. , Figures 12(a) and (b) do not show threshold-processed cavity images when the 14th field is circular, and Figure 13(a)
) is a diagram showing a stimulable phosphor sheet imaged with a diagonal aperture of a rectangular irradiation field, and FIG.
FIG. 14 is a diagram showing an example of a method for determining gradation processing conditions from a desired image information range. 10... Recording medium (stimulable phosphor sheet) 12...
Irradiation field 〇−〇〇″.

Claims (5)

[Claims] (1) A method for recognizing the irradiation field when the irradiation field is recorded from radiation image information by applying an irradiation field aperture on the recording medium, the method comprising: determining each position on the recording medium from image information read from the recording medium; Find the image data in , perform a difference process on this image data to find the difference between the image data to create a difference image consisting of the difference values, prepare a predetermined threshold Th, and use the difference image or the difference image. A processed difference image processed by a predetermined method is scanned in at least two directions, and for each scanning direction, the difference value is sandwiched between a difference value of +Th or more and a difference value of -Th or less on each scanning line in that direction. An irradiation field recognition method characterized by detecting a predetermined range formed by a set of predetermined sections, and recognizing a predetermined area determined based on each predetermined range detected for each scanning direction as an irradiation field. . (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.
A threshold-processed difference image is a threshold-processed difference image that has been subjected to threshold processing to encode all or a part of the difference values so that the following difference values can be distinguished from other difference values. The irradiation field recognition method described in Scope 1. (3) The irradiation field recognition method according to claim 1 or 2, characterized in that the sum of the predetermined ranges detected in each scanning direction is determined as the predetermined region. (4) The irradiation field recognition method according to claim 1 or 2, characterized in that a common portion of each predetermined range detected in each scanning direction is determined as the predetermined region. (5) A method for determining image processing conditions for processing image information read from a recording medium on which radiation image information is recorded by applying irradiation field aperture, the method comprising: Image data at each position on the recording medium is obtained, and this image data is subjected to differential processing to determine the difference between the image data to create a differential image consisting of differential values, a predetermined threshold Th is prepared, and the A difference image or a processed difference image obtained by processing the difference image in a predetermined method is scanned in at least two directions, and for each scanning direction, a difference value of +Th or more and a difference of -Th or less on each scanning line in that direction is determined. detecting a predetermined range formed by a set of predetermined sections sandwiched between the values, and recognizing a predetermined area determined based on each predetermined range detected for each scanning direction as an irradiation field, from the recording medium. A method for determining image processing conditions, characterized in that the image processing conditions are determined based on image information within the recognized irradiation field among the read image information.