JPH0464226B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a method for determining reading conditions 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. is known to exhibit stimulated luminescence, and phosphors exhibiting this property are called stimulable phosphors (stimulable phosphors).

Using this stimulable phosphor, radiation image information of a subject such as a human body is recorded on a sheet of stimulable phosphor, and then the stimulable phosphor sheet is scanned with excitation light such as a laser beam. Generates stimulated luminescent light, reads this stimulated luminescent light photoelectrically to obtain an image signal, and based on this image signal, the radiation image of the subject is visible on recording materials such as photosensitive materials and display devices such as CRT. The applicant has already proposed a radiation image information recording and reproducing system that outputs the information as an image. (JP-A-55-12429, JP-A No. 56-11395, etc.) As one aspect of the radiation image information recording and reproducing system described above, the radiation image information of the subject is stored and recorded using the radiation energy level as a medium. "Book reading" in which a body sheet is scanned with excitation light, and stimulated luminescence light emitted from the sheet is read by a photoelectric reading means through this scanning to obtain an electrical image signal for reproducing a visible image for diagnosis.
Prior to this, "pre-reading" is performed in which the sheet is scanned with excitation light of a lower level than the excitation light used for this main reading to read the outline of the image information accumulated and recorded on this sheet, and the information obtained by this pre-reading is performed. The reading conditions for performing the main reading are determined based on the image information obtained, the main reading is performed according to the reading conditions, the image signal obtained by this main reading is input to an image processing means, and the image processing means performs the main reading. A system is known that processes an image signal so as to obtain an output image suitable for diagnostic purposes depending on the region to be imaged and the method of imaging, etc., and reproduces this image signal as a visible output image on a photographic light-sensitive material. This is disclosed in Japanese Patent Application Laid-Open No. 58-67240, which was previously filed by the present applicant and has already been published.

Here, reading conditions are a general term for various conditions that affect the relationship between the amount of stimulated luminescence light and the output of the reading device during reading, such as reading gain (sensitivity) that determines the relationship between input and output, It means the scale factor (latitude) or the power of excitation light during reading.

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. As a method to make the excitation light of the pre-reading at a lower level than the excitation light of the main reading, there is a method of reducing the output of the excitation light source such as a laser light source, and a method of passing the excitation light emitted from the light source to an ND filter, AOM, etc. in its optical path. There is a method in which the light source for pre-reading and a light source for main reading are provided separately and the output of the former is made smaller than the output of the latter.Furthermore, the beam diameter of the excitation light is increased. Examples include a method of increasing the scanning speed of excitation light, a method of increasing the transport speed of the stimulable phosphor sheet, and the like.

In this way, by grasping the outline of the image information stored on the sheet before the actual reading and performing the actual reading in accordance with 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 or fluctuations in the amount of radiation exposure, etc., and to always perform main reading under desirable reading conditions.

A specific method for determining the reading conditions for main reading based on the image information obtained by such pre-reading is, for example, to obtain a histogram of the amount of stimulated luminescence in pre-reading, and to obtain desired image information in this histogram from this histogram. Maximum stimulated light amount Smax and minimum stimulated light amount of the range
Find Smin, and these Smax and Smin are respectively
Maximum density of appropriate density range in visible output image
The applicant has filed an application for a method for determining reading conditions for main reading so as to correspond to the maximum signal level Qmax and minimum signal level Qmin of a desired input signal range in an image processing means determined by Dmax and minimum density Dmin. (Special application 1986-12658)
issue).

On the other hand, in order to avoid irradiating radiation to areas that are not necessary for humane 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. To prevent this, it is often preferable to narrow down the radiation irradiation field when recording radiation image information. 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 highly sensitive stimulable phosphor sheet Since these scattered rays are also accumulated and recorded, the histogram of the amount of stimulated luminescence obtained by pre-reading also includes the amount of stimulated luminescence based on these scattered rays. Since the amount of stimulated luminescence outside the irradiation field on the sheet based on this scattered radiation may be larger than the amount of stimulated luminescence inside the irradiation field, it is possible to distinguish between the amount of stimulated luminescence inside and outside the irradiation field from the obtained histogram. It is difficult to do so. Therefore, as mentioned above, find Smax and Smin from the histogram,
When determining the reading conditions from this, the minimum value of the stimulated luminescence light amount in the irradiation field should be Smin, but the minimum value of the stimulated luminescence light amount due to scattered radiation outside the irradiation field may be set as Smin. and,
In this way, the minimum value of the amount of stimulated luminescence outside the irradiation field is
When it is set as Smin, the value is generally lower than the minimum value of the amount of stimulated luminescence within the irradiation field, so in the main reading, scattered radiation unnecessary for diagnosis will be recorded in the low concentration area, and therefore the part necessary for diagnosis will be recorded. The image becomes too dense, resulting in reduced contrast and difficulty in making a satisfactory diagnosis.

In other words, when shooting with a narrowed irradiation field, scattered rays generated from the subject enter the irradiated field on the sheet, and the image information obtained by pre-reading includes information based on these scattered rays. Therefore, even if reading conditions are determined based on such pre-read image information, it is difficult to determine the optimal reading conditions, and as a result, it is difficult to obtain visible images that are suitable for observation and interpretation. becomes.

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

(Structure of the Invention) In order to achieve the above object, the reading condition determining method according to the present invention obtains digital image data at each position on the stimulable phosphor sheet from image information obtained by pre-reading, and obtains digital image data at each position on the stimulable phosphor sheet. A difference image consisting of difference values is created by performing difference processing on the data to find the difference between the image data, for example, a difference between adjacent image data, a predetermined threshold Th is prepared, and the difference image or the difference is A predetermined section sandwiched between a position where a difference value greater than or equal to +Th exists and a position where a difference value less than or equal to -Th exists on each scanning line by scanning a processed difference image obtained by performing predetermined processing on the image in one direction. ,
That is, the present invention is characterized in that the intra-irradiation field section is detected, and the reading conditions for the main reading are determined based on the image information obtained by the pre-reading of the intra-irradiation field section on each scanning line.

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

The embodiment 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 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 the pre-reading excitation light using a photoelectric conversion means. This means obtaining information consisting of electrical signals corresponding to the amount of stimulated luminescence light for each scanning point (that is, each pixel) on the top 10.

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 performing preprocessing such as spatial filter processing on the image information. .

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 filter processing, for example, multiple pixels in a certain relationship are set as one position, and based on the pre-read image information of the pixels included in this position, for example, they are The digital image data at the position may be calculated by averaging, or the position on the sheet may be set in units of pixels, and the digital image data at the position may be calculated by calculating the digital image data at the position and its surrounding positions. It may be calculated based on pre-read image information of pixels.

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 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), . . . indicate the digitized image information at each pixel (1, 1), (1, 2), .

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, This refers to the process of determining a difference value using a difference operator as shown in FIGS. 3a to 3f.

Difference processing using the operator shown in FIG. 3a is performed by subtracting digital image data at adjacent positions in the X-axis direction and using the result as a difference value. For example, in FIG. 2, positions (3, 4) digital image data f(3,4) to position (3,3)
The digital image data f (3, 3) is subtracted from the digital image data f (3, 3), and the result is used as the difference value at the position (3, 3).

In addition, the difference processing using the operator shown in FIG. Digital image data f at position (3, 4) in Figure 2
The digital image data f(3,2) at position (3,2) is subtracted from (3,4) and the result is subtracted from position (3,4).
3) is the difference value.

Difference processing using the operator shown in FIG. 3c subtracts digital image data at adjacent positions in the Y-axis direction and uses the result as a difference value. For example, in FIG. 2, position (4, 3) digital image data f(3,4) to position (3,3)
The digital image data f (3, 3) is subtracted from the digital image data f (3, 3), and the result is used as the difference value at the position (3, 3).

Difference processing using the operator shown in FIG. 3d 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, as shown in FIG. Digital image data f(4, 3) at position (4, 3) in
3) to position (2, 3) digital image data f
Subtract (2, 3) and put the result at position (3, 3)
This is the difference value of .

The differential processing using the operator shown in FIG. 3e is a process performed by simultaneously using the operator shown in FIG. 3a and the operator shown in FIG.
In the figure, the result of subtracting digital image data f(3,3) at position (3,3) from digital image data f(3,4) at position (3,4) and
The sum of the result of subtracting the digital image data f(3,3) at position (3,3) from the digital image data f(4,3) at position (6) is calculated as position (3,
3) is the difference value.

The differential processing using the operator shown in FIG. 3f is a process performed by simultaneously using the operator shown in FIG. 3b and the operator shown in FIG.
Digital image data f at position (3.4) in the figure
Result of subtracting digital image data f(3,2) at position (3,2) from (3,4) and position (4,3)
From digital image data f(4,3) of position (2,
The difference value of the position (3, 3) is obtained by adding the result of subtracting the digital image data f (2, 3) of 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 embodiment, the operator shown in FIG. 3a 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 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 set. A predetermined section sandwiched 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 predetermined threshold value Th is set for the difference value obtained as described above.
By performing threshold processing using Then, examine the thresholded difference image consisting of the thresholded difference values encoded in this way in the X-axis direction, and if a combination of +1 and -1 is found on each scan line, The section sandwiched between +1 and -1 is detected as a predetermined section on the scanning line.

Figure 4 is an arbitrary line in the X-axis direction in Figure 1.
FIG. 5 is a diagram showing the digital image data on lx, and FIG. 5 shows the difference value obtained by processing the digital image data in FIG. 4 using the difference operator shown in FIG. Figure 6 is a diagram showing how threshold processing is performed.
The thresholded difference values (-1, 0, +
1) is a diagram showing a threshold-processed difference image consisting of; However, in FIG. 6, the threshold-processed difference values +1 and -1 are simply displayed as and, and the portion where the peach is not displayed is a portion where the threshold-processed difference value is 0.

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 image data in the field irradiation area 14 generally has a low quantum level, as shown in FIG. , the image data within the radiation field 12 will generally be at a high quantum level. Therefore, as shown in Figure 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 there are positions where this difference value is extremely large and extremely small. By detecting the position using an appropriately set threshold value Th, it is possible to detect the position of the irradiation field contour, and furthermore, the section within the irradiation field sandwiched between the two positions. Therefore, by scanning the difference image in the X-axis direction, each scanning line LX ₁ , LX ₂ , LX ₃ , . . . LXi, . . . as shown in FIG.
The position on LXn where the difference value is +Th or more and -Th
Detecting a predetermined section (shaded area in the figure) sandwiched between the following positions means detecting a section within the irradiation field on each scanning line.

In addition, in FIG. 6, scanning lines LX ₁ and
Since LX ₂ is located in the outside irradiation area 14, naturally there is a difference value of +Th or more or -Th on this line.
None of the following exist. Also, the line in the diagram
Like Lxi, even for a line 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 less than -Th. It is treated as if the predetermined section was not detected from the scanning line.

Even if the same threshold processing as above is performed using the difference operator shown in Fig. 3b, the 6th
A difference image similar to that in the present embodiment shown in the figure is obtained, and a predetermined section may be detected by scanning this difference image in the same manner as in the present embodiment.

When the difference operators shown in FIGS. 3c and d are used, a difference image as shown in FIG. It is sufficient to detect the section indicated by the middle two-way arrow).

When using the difference operators shown in Fig. 3e and f, a difference image as shown in Fig. 8 is obtained, and in this case, each scan is performed by scanning in one direction, either the X-axis direction or the Y-axis direction. It is sufficient to detect a predetermined section in the line (in the figure, a double-headed arrow indicating a predetermined section detected by scanning in the X-axis direction is shown).

In short, the above embodiment performs threshold processing on the difference image to encode all of the difference values so that difference values of +Th or more, difference values of -Th or less, and other difference values can be distinguished, and The threshold-processed difference image consisting of the threshold-processed difference values (+1, 0, -1) created by the processing was scanned to detect a predetermined section, but other processing, For example, threshold processing is performed to encode only a part of the difference value, such as so-called half-threshold processing, in which the difference value between +Th and -Th is set to 0, and other difference values are left unchanged. A predetermined section may be detected by scanning a threshold-processed difference image made up of threshold-processed difference values obtained by.

Next, after detecting the predetermined sections on each scanning line as described above, the pre-read image information at the position corresponding to each predetermined section is extracted from 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 a section within the irradiation field on each scanning line, and therefore, the sum of the pre-read image information of the predetermined section on each scanning line extracted above is the area within the irradiation field. This means that this is pre-read image information.

The reading conditions for main reading based on the extracted pre-read image information, that is, the pre-read image information within the irradiation field, can be determined in various ways. , and from this histogram, calculate the large stimulated light amount Smax and the minimum stimulated light amount Smax.
Smin is determined, and reading conditions can be determined based on Smax and Smin.

Note that the determination of reading conditions is not limited to the case where the determination is made based only on the pre-read image information within the irradiation field. , a photographing method such as enlarged photographing, etc. can also be taken into account when determining the photographing method.

After determining the reading conditions as described above, the actual reading is performed according to the reading conditions, but this actual reading is as disclosed in Japanese Patent Application Laid-Open No. 120346/1989, which was previously filed by the applicant. Preferably, the reading area is limited to the irradiation field determined based on the above method. By limiting the reading area for the main reading 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. . In addition, by narrowing down the reading area,
It is possible to shorten reading time or maximize reading density.

FIG. 9 is a threshold-processed difference image created by the same method as the embodiment shown in FIG. 3, and shows 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 section can be optimally determined.

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 embodiments, it depends on how the difference value is calculated. It will be decided accordingly.

Further, the concept of a difference value and a difference process in the method according to the present invention also includes the concepts of a differential value and a differential process that are substantially the same.

Note that the image processing conditions for performing the image processing can also be determined based on pre-read image information of a predetermined section on each scanning line detected by the method according to the present invention.

(Effects of the Invention) As described above, the radiation image information reading condition determination method according to the present invention provides digital image information (pre-read image information) at each position on the stimulable phosphor sheet.
A difference image is created by performing differential processing, and the difference image is scanned in one direction to find a predetermined section sandwiched between a difference value greater than or equal to a predetermined threshold value +Th and a difference value less than -Th on each scanning line. The reading conditions are determined based on the pre-read image information in each predetermined section.

However, as mentioned above, the predetermined sections on each scanning line are sections within the irradiation field on each scanning line, so determining the reading conditions based on the pre-read image information in each of the predetermined sections ultimately means that the irradiation This means that the reading conditions are determined based only on Nouchi's pre-read image information.

Therefore, according to the reading condition determination method according to the present invention, when imaging is performed with the irradiation field apertured, it is possible to detect the scattering that has entered the irradiation field on the sheet based only on the pre-read image information within the irradiation field. Since the reading conditions can be determined while eliminating the adverse effects of the wire, the optimum reading conditions can always be determined.

[Brief explanation of drawings]

Figure 1 is a diagram showing the stimulable phosphor sheet photographed with the irradiation field apertured, Figure 2 is an enlarged view of section A in Figure 1, showing digital image data at each position, Figure 3 4 is a diagram showing the digital image data on the line lx in FIG. 1, and FIG. 5 is a difference value obtained by performing differential processing on the digital image data in FIG. 4. Figures 6, 7, and 8 are diagrams showing difference images created using different difference operators, and Figure 9 is a diagram showing difference images when the irradiation field is circular. be. 10... stimulable phosphor sheet, 12... irradiation field.

Claims (1)

[Scope of Claims] 1. Radiation images stored on a stimulable phosphor sheet by irradiating excitation light onto a stimulable phosphor sheet on which radiation image information is stored and recorded by applying an irradiation field aperture. Prior to main reading, in which information is emitted as stimulated luminescence light and this stimulated luminescence light is read photoelectrically to obtain an electrical image signal for outputting a visible image, the energy of the excitation light used in the main reading is Pre-reading is performed to read the radiation image information stored and recorded on the stimulable phosphor sheet using low-energy excitation light, and the reading conditions for the main reading are determined based on the image information obtained by this pre-reading. In the image information reading 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 a difference process is performed to obtain a difference between the image data. to create a difference image consisting of difference values, prepare a predetermined threshold value Th, scan the difference image or a processed difference image obtained by performing a predetermined process on the difference image in one direction, and perform each scan. Detecting a predetermined section sandwiched between a difference value of +Th or more and a difference value of -Th or less on the line, and reading in the main reading based on the image information obtained by the pre-reading within the predetermined section on each scanning line. A method for determining reading conditions for radiographic image information, the method comprising testing conditions. 2. A processed difference image obtained by performing predetermined processing on the difference image is such that the difference value of the difference value can be discriminated from the difference value of +Th or more, the difference value of -Th or less, and other difference values with respect to the difference image. 2. The method for determining reading conditions for radiation image information according to claim 1, wherein the threshold-processed difference image is a threshold-processed difference image that has been subjected to threshold processing to encode all or part of the image.