JPH0453541A - Reproducing device for radiographic image - Google Patents

Abstract

PURPOSE:To reproduce and output a visible image of constantly proper density so as to detect even changes in the amount of air in the lung of a human body by finding according to image data indicating radiographic images of the lung a characteristic amount which is characteristic of the amount of air in the lung, and reproducing the characteristic amount together with or before or after a visible image of a radiograph. CONSTITUTION:A characteristic amount which is characteristic of the amount of air in a lung serving as a subject to be photographed is found in a computer system 40 according to an initially read image signal input to the system. An image signal obtained by digitization by an A/D converter 17' is input to the computer system 40 and subjected to proper image processing. The image signal subjected to this image processing is transmitted to a CRT display 44 and a radiographic image based on the image signal is reproduced and displayed as a visible image. The characteristic amount is also displayed in the CRT display 44 together with the visible image by a numerical value or sign indicating the characteristic amount.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a radiation image reproducing device that reproduces and outputs a radiation image, and more particularly to a radiation image reproducing device that reproduces and outputs a radiation image of the lungs of a human body as a visible image. It is.

(Prior Art) It is practiced in various fields to read a recorded radiation image to obtain image data, perform appropriate image processing on this image data, and then reproduce and record the image. For example, an X-ray image is recorded using an X-ray film with a low gamma value designed to be compatible with later image processing, and the X-ray image is read from the film on which it is recorded and converted into an electrical signal. By performing image processing on this electrical signal (image data) and then reproducing it as a visible image in a copy photograph, etc., it is possible to obtain a reproduced image with good image quality performance such as contrast, sharpness, and graininess. (Refer to Japanese Patent Publication No. 5193/1983).

In addition, the applicant has proposed radiation (X-rays, α-rays).

When irradiated with β rays, γ rays, electron beams, ultraviolet rays, etc., a part of this radiation energy is accumulated, and then when irradiated with excitation light such as visible light, stimulable fluorescence exhibits stimulated luminescence depending on the accumulated energy. Radiographic image information of a subject such as a human body is partially recorded on a sheet of stimulable phosphor using a stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam. The resulting stimulated luminescent light is read photoelectrically to obtain image data, and based on this image data, a radiation image of the subject can be recorded on recording materials such as photographic materials, CRTs, etc. Radiation image recording and reproducing systems that output visual images have already been proposed (Japanese Patent Application Laid-Open No. 12429/1983, No. 5B-11395, Japanese Patent Application Laid-open No. 55-1139).
No. 163472, No. 5B-104645, No. 55-1
No. 16340, etc.).

This system has the practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, in a stimulable phosphor, it is recognized that the amount of emitted light that is stimulated to emit light due to excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range.
Therefore, even if the amount of radiation exposure varies considerably due to various imaging conditions, the amount of stimulated luminescence emitted from the stimulable phosphor sheet can be read by the photoelectric conversion means by setting the reading gain to an appropriate value. Convert it into an electrical signal and use this electrical signal (image data) to record materials such as photographic materials,
By outputting a radiation image as a visible image on a display device such as a CRT, it is possible to obtain a radiation image that is not affected by fluctuations in radiation exposure.

In the above system, the stimulable phosphor sheet is scanned in advance with a low-level light beam before obtaining image data by reading it under optimal reading conditions depending on the dose of radiation irradiated on the stimulable phosphor sheet. Pre-reading is performed to read the outline of the radiation image recorded on this sheet, the pre-read image data obtained by this pre-reading is analyzed, and then the sheet is irradiated with a high-level light beam and scanned, and this radiation image is There is also a system configured to perform main reading in which image data is obtained by reading under optimal reading conditions.

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, scale factor, or , the power of excitation light during reading, etc.

Also, the high level and low level of the light beam are, respectively.
If the energy of the light beam irradiated per unit area of the sheet or the energy of stimulated luminescence light emitted from the sheet depends on the wavelength of the light beam (has a wavelength sensitivity distribution), It refers to the weighting energy after weighting the energy of the light beam irradiated per unit area of the sheet with the wavelength sensitivity.As a method of changing the level of the light beam, light beams of different wavelengths are used. methods used, methods that change the intensity of the light beam itself emitted from a laser light source, methods that change the intensity of the light beam by inserting or removing an ND filter, etc. on the optical path of the forward beam, and methods that change the beam diameter of the forward beam. Various known methods can be used, such as a method of changing the scanning density and a method of changing the scanning speed.

In addition, regardless of whether the system performs this prefetching or the system that does not, the obtained image data (including prefetched image data) is analyzed to determine the optimal image processing conditions when performing image processing on the image data. Some systems let you decide. The method of determining the optimal image processing conditions based on this image signal is not limited to systems using stimulable phosphor sheets, and for example, image signals are obtained from radiation images recorded on recording sheets such as conventional X-ray films. It is also applied to the system.

One of the conditions to consider when determining the reading conditions and/or image processing conditions mentioned above is the unnecessary parts recorded on the recording sheet during imaging, such as parts of only scattered radiation, ), and when the visible output image is finally reproduced and recorded on a photographic material, etc., only the part that is desired to be observed is reproduced and recorded at the appropriate image density. The first step is to determine the reading conditions and/or image processing conditions.

FIG. 4 is a diagram showing an example of a histogram of the pre-read image signal Sp. An example of a method for determining the above-mentioned reading conditions etc. will be explained with reference to this figure.

This method is an example of a method used in a system that performs pre-reading using the stimulable phosphor sheet described above.

The horizontal axis (logarithmic axis) is the pre-read image signal Sp which is proportional to the amount of stimulated luminescence light obtained by reading the stimulated luminescence light emitted from the stimulable phosphor sheet during pre-reading,
The appearance frequency of the pre-read image signal Sp of that value is plotted on the vertical axis (upper side), and the image signal S0 in the main reading is plotted further below the vertical axis (logarithmic axis). Assume that the histogram obtained at this time consists of two peaks A and B as shown in the figure, and that the part that is ultimately necessary as a visible output image is the peak A part. At this time, in order to find the mountain A, for example, search should be performed in the direction in which the value of the pre-read image signal Sp increases from the position of the minimum value SL of the pre-read image signal Sp using the threshold value Th (corresponding to the dashed line in the figure), Find the first intersection point a and the next intersection point s. These two points a.

Let the range between b be the image information range that needs to be reproduced and recorded as a visible output image. The above-mentioned reading condition determination method is based on Sa
(corresponding to point a) and Sb (corresponding to point S), Sa and sb are, in this reading, photographic materials, etc. that reproduce and record visible output images, or CRT display devices, etc. that reproduce and display visible output images. (hereinafter represented by the reproduction recording sheet), the minimum density DIin and the maximum density DxaX of the appropriate image density range (hereinafter, the minimum density Dsin of the reproduction recording sheet, respectively).

This is called the maximum density Dmax. ), the reading conditions for the main reading are determined so that the minimum image signal S.sub.in and the maximum image signal 5IaX, respectively, are obtained, that is, along the straight line G in FIG. 4. In addition, in 22, "concentration"
Here, the term includes the brightness of a visible image displayed on a CRT display device or the like.

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, scale factor, or , the power of excitation light during reading, etc.

By determining the reading conditions for main reading as described above, only necessary image information can be read with maximum resolution.

Furthermore, in systems that do not perform pre-reading, the same thing as above is performed during image processing. That is, when considering the pre-read image signal Sp shown in FIG.
S shown in the figure.

It is necessary to obtain the entire range of image signals sandwiched between
Image processing is performed so that the range between Sa and sb in FIG. 4 corresponds to the range between the minimum density I)+in and the maximum density DIaX of the reproduced recording sheet.

As mentioned above, the minimum value of the image signal required as a visible output image (Sa in pre-reading in Figure 4, S in main reading
The reading conditions and/or image processing are set so that the range between the minimum density Dgain and the maximum density Dwax of the reproduction recording sheet is utilized to the maximum extent. After determining the conditions,
By making full use of the performance of the reproduction recording sheet, it is possible to obtain a visible reproduction image with maximum density resolution.

Here, in radiographic images of human lungs, cell infiltration, cell proliferation, and fluid exudation within the lung field due to pneumonia, etc.

When air production occurs, the amount of air (air content) in the lung field decreases. When this air content decreases, the radiation penetration throughout the lung field decreases, and as shown in the peak A' in Figure 4, a portion with a large value of the image signal Sp is missing compared to the peak A, which corresponds to a normal lung. This becomes a mountain A'.

In this case, for example, the entire lung field appears as a whitish image on a conventionally used X-ray photosensitive film, and the degree of whitishness can be used to determine the approximate degree of decrease in air content.

(Problem to be Solved by the Invention) However, when the reading conditions, etc. are determined by the above method using a histogram, two points Sa and Sc are determined for images with reduced air content, and the reading conditions, etc. are determined along the straight line G'. As a result, the final visible output image is corrected for changes in air content and always has a nearly constant density, and a visible output image suitable for observation is always reproduced. This results in the problem that the change in air content becomes unclear.

In view of the above circumstances, it is an object of the present invention to provide a radiographic image reproducing device that is capable of always reproducing and outputting visible images with an appropriate density, and also capable of detecting changes in air content within the lung fields. This is the purpose.

(Means for Solving the Problems) The radiographic image reproducing device of the present invention includes a feature calculating means for calculating a feature that indicates the air content in the lung based on image data representing a radiographic image of the lung of a human body. , a reproduction means for reproducing the feature amount together with the visible image of the radiation image or in succession with the visible image.

Here, the method for obtaining the above-mentioned "feature amount" and the feature amount are not limited to specific ones, but for example, the maximum value SM of the image signal sb or Sc and the image signal Sp obtained by the above-mentioned histogram analysis. , or the average value of the image signal corresponding to the lung field (mountain A or mountain A' shown in FIG. 4), and these differences or average values can be used as feature quantities.

Further, the above-mentioned "reproducing means" may be a CRT display device or the like that displays a visible image of a radiation image, or may be a laser printer or the like that obtains a hard copy of a radiation image.

(Function) The radiographic image reproducing device of the present invention obtains a feature quantity that indicates the air content in the lungs based on image data, and uses the feature quantity together with a visible image of a radiographic image or in comparison with this visible image. Because it is reproduced back and forth, for example, as mentioned above, in order to obtain a visible image with the optimum density, changes due to air content are also corrected, and it is difficult to determine the degree of decrease in air content from the visible image itself. Even in cases where it is impossible to know, the air content can be known from this feature amount.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. Here, a system for performing pre-reading using the above-mentioned stimulable phosphor sheet will be described.

FIG. 1 is a schematic diagram of an example of an X-ray imaging apparatus.

X-rays 12 are irradiated from the X-ray source 11 of this X-ray imaging device 10 toward the chest 13a of the human body 13, and the X-rays 12a that have passed through the human body 13 are irradiated onto the stimulable phosphor sheet 1, thereby causing the human body to An X-ray image of the chest 13a is accumulated and recorded on the stimulable phosphor sheet l.

FIG. 2 is a diagram showing an example of a chest X-ray image accumulated and recorded on the stimulable phosphor sheet 1 as described above.

In this X-ray image, shadows of bone parts such as ribs and shadows of soft parts such as lung fields are superimposed.

FIG. 3 is a schematic perspective view showing a computer system which is an embodiment of an X-ray image reading device and a radiation image reproducing device of the present invention.

A stimulable phosphor sheet 1 on which an X-ray image has been recorded as shown in FIG. 2 is first scanned with a weak light beam.
The XIIA energy is set at a predetermined position in the pre-reading section 3° which performs pre-reading by releasing only a part of the XIIA energy stored in the XIIA energy. The stimulable phosphor sheet 1 set at a predetermined position is transported in the direction of arrow Y (sub-scanning) by a sheet transport means 3 such as an endless belt driven by a motor 2.
be done.

On the other hand, a weak light beam 5 emitted from a laser light source 4 is reflected and deflected by a rotating polygon mirror 6 that is driven by a motor 13 and rotates at high speed in the direction of the arrow, passes through a focusing lens 7 such as an fθ lens, and then passes through a mirror 8 to The light beam enters the sheet 1 while changing the direction of the light beam and performs main scanning in the direction of arrow X, which is substantially perpendicular to the direction of sub-scanning (direction of arrow Y). Stimulated luminescent light 9 is emitted from the portion of the sheet 1 irradiated with the excitation light 5 in an amount corresponding to the radiographic image information stored and recorded, and this stimulated luminescent light 9 is focused by the light guide 10. and a photomultiplier (photomultiplier tube) 11 as a photodetector.
is detected photoelectrically by The light guide 10 is made by molding a light guiding material such as an acrylic plate,
A linear input end surface 10a is arranged to extend along the main scanning line on the stimulable phosphor sheet 1, and the photomultiplier 11 is arranged on an annular output end surface 10b.
The light-receiving surfaces of the two are combined. The stimulated luminescent light 9 that has entered the light guide IO from the incident end surface 10a is transmitted through the light guide 1
The stimulated luminescence light 9 travels through the interior of the 0 through repeated total reflection, is emitted from the output end face 10b and is received by the photomultiplier 11, and the amount of stimulated luminescence light 9 carrying the radiation image information is converted into an electrical signal by the photomultiplier 11. be done.

The analog output signal SA output from the photomultiplier 11 is amplified by the amplifier 1B and digitized by the A/D converter 17, and in the above pre-reading in which the pre-read image signal Sp is obtained, the analog output signal SA is applied to the stimulable phosphor sheet 1. Reading conditions such as the voltage value applied to the photomultiplier 11 and the amplification factor of the amplifier 16 are fixed so that the accumulated radiation energy can be read over a wide area.

The obtained pre-read image signal Sp is sent to the computer system 40.
is input.

This computer system 40 includes an example of the radiation image reproducing apparatus of the present invention, and includes a main body 41 containing a CPU, an internal memory, etc., and a drive into which a floppy disk as an auxiliary storage medium is inserted and driven. 42, a keyboard 43 for inputting information, commands, etc. necessary for this system, and a CRT display 4 for displaying visible images and other necessary information based on image signals.
It consists of 4.

Here, in this computer system 40, reading conditions for actual reading are determined based on the input pre-read image signal Sp, and based on these reading conditions, the voltage to be applied to the photomultiplier 11' during actual reading is determined. The amplification factor of amplifier IB' and the like are controlled. Incidentally, an example of how to obtain this reading condition has been described above with reference to FIG. 4, so the explanation will be omitted here.

Furthermore, within the computer system 40, a feature quantity that indicates the air content inside the lung, which is the object, is determined based on the input pre-read image signal Sp.

An example of a feature value that indicates the air content and how to obtain the feature value will be explained with reference to FIG. 4.

First, the maximum value SM of this pre-read image signal Sp is determined, and the image signal sb or Sc corresponding to the dot or point C is determined by searching using the threshold value Th as described above. As mentioned above, when the air content decreases, the peak A', which corresponds to a normal lung, becomes a peak A' in which the side with the larger value of the pre-read image signal Sp is missing, so that the maximum value SM and the image signal sb Alternatively, by determining the difference Δ1 from Sc, the larger the value of this difference Δ1, the lower the air content is, and therefore, this difference Δ1 can be used as an example of the feature quantity referred to in the present invention.

Note that for different people, depending on whether the person is fat or thin, even if the person has normal lungs, the pre-read image signal Sp corresponding to the lungs may have a mountain, such as a mountain A' shown by a dashed line in FIG. may appear at different positions on the left and right sides of the figure. Therefore, if the person is different, the difference Δ1 may not necessarily be a feature that correctly represents the air content. Therefore, more preferably, when performing follow-up observation on the same person, the difference Δ2 between the above-mentioned difference Δ1 when the image was taken in a normal state or in a state with mild symptoms and the above-mentioned difference Δ1 when the current image was taken (in FIG. , Δ2−
8b-8c) and use this difference Δ2 as a feature quantity.

Note that the feature amount may be anything that indicates the air content, and is not limited to the above-mentioned difference Δl or Δ2. An area may be extracted, the average value of the pre-read image signal Sp corresponding to this area may be determined, and this average value may be employed as a feature quantity that indicates the air content.

The stimulable phosphor sheet 1' whose pre-reading has been completed is set at a predetermined position in the main reading section 30', and the stimulable phosphor sheet 1' is scanned by a light beam 5' which is stronger than the light beam used for the pre-reading. , an image signal is obtained according to the reading conditions determined based on the pre-read image signal Sp, but since the configuration of the main reading section 30' is different from the structure of the above-mentioned pre-read reading section 30, the pre-read reading Components corresponding to the respective components of the section 30 are indicated by adding a dash to the numbers used in the prefetch reading section 30, and detailed explanations thereof will be omitted.

The image signal S0 obtained by being digitized by the A/D converter 17' is input to the computer system 40, and within the computer system 40 it is converted into an image signal SQ.
Appropriate image processing is applied to the images. The image signal subjected to this image processing is sent to a CRT display 44, and a radiation image based on this image signal is reproduced and displayed as a visible image. In addition, the feature amount obtained as described above is also displayed on the CRT together with the visible image as a numerical value or symbol representing the feature amount.
displayed on the display 44. This visible image is based on the image signal SQ obtained as a result of the actual reading based on the reading conditions G and G' as explained using FIG. Changes in air volume are also absorbed and simply reproduced as an image with a density suitable for observation.
Therefore, even if this visible image is compared with, for example, a visible image of a lung X-ray image of the same person obtained in the same manner as before, it is not possible to detect changes in air content. However, since the visible image and the feature amount are displayed here, it is possible to know how the air content has changed from the displayed feature amount. Note that the visible image and the feature values do not necessarily need to be displayed at the same time; for example, after observing the visible image, if it is necessary to know the change in air content, the visible image may be displayed instead of the visible image. Feature amounts may also be displayed.

In the above embodiment, the visible image and the feature amount are displayed on the CRT display 44, but a hard copy of the visible image and the feature amount may be obtained using, for example, a laser printer.

Further, in the above embodiment, the prefetch reading unit 30 and the main reading reading unit 30
' are configured separately, but as mentioned above, the configuration of the prefetch reading section 30 and the main reading reading section 30' is between the two, so the prefetching reading section 30 and the main reading reading section 30' may be combined and used for both purposes. In this case, after performing pre-reading by scanning with a weak light beam, part of the stimulable phosphor sheet 1 may be moved back, and main reading may be performed by scanning again with a strong light beam.

When the pre-reading section and the main reading section are used together, it is necessary to switch the intensity of the light beam for pre-reading and main reading. A method of switching the light intensity by inserting or removing an ND filter or the like on the optical path of the light beam, a method of changing the beam diameter of the light beam, a method of switching the speed of the main scanning and the speed of the sub-scanning, etc. Various known methods can be used.

Further, in the above embodiment, the reading conditions for the main reading are determined by the computer system 40, but the reading conditions for the main reading are predetermined reading conditions regardless of the shape of the histogram of the pre-read image signal Dp, and the reading conditions for the main reading are set as predetermined reading conditions, The image processing conditions when image processing is performed on the image signal SQ by the computer system 40 may be determined, or both the reading conditions and the image processing conditions may be determined. In this case, the feature value indicating the air content may be obtained based on the pre-read image signal Sp, or may be obtained based on the image signal S0 obtained in the actual reading.

Furthermore, although the above embodiment has been described with respect to a system that performs pre-reading, the present invention can also be applied to a system that immediately performs reading corresponding to the main reading in the above system without performing pre-reading. In this case, the reading conditions for reading are such that an image signal is obtained by reading under predetermined reading conditions, and image processing conditions and features that indicate the air content when image processing is applied to the image signal based on this image signal. quantity is required.

It goes without saying that the present invention can be used not only for systems using stimulable phosphor sheets but also for systems using conventional X-ray films.

(Effects of the Invention) As described in detail above, the radiation image reproducing apparatus of the present invention obtains a feature amount that indicates the air content in the lungs, and uses this feature amount together with the visible image of the radiation image or as a corresponding amount. Since the image is reproduced at the same time as the visual image, the visible image can be reproduced at the optimum density suitable for observation, and the air content can also be determined.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an example of an X-ray imaging device, FIG. 2 is a diagram showing an example of a chest X-ray image, and FIG. 3 is a diagram showing an example of an X-ray image reading device and a radiation image reproducing device of the present invention. FIG. 4 is a schematic perspective view showing a computer system according to an embodiment. FIG. 4 is a diagram showing an example of a histogram of a pre-read image signal. 1.1'...Stormable phosphor sheet 2, 2', 13.13'...Motor 3.3'
...Sheet transport means 4.4' ...Laser 6.6'...Rotating polygon mirror 9.9'...Stimulated luminescence light 10, 10'...Light guide 1i, ii'...・Photo multiplier te, i
e'...Amplifiers 17, 17'...A/D converter 30...Pre-read reading unit 30'...Main reading reading unit 40...Computer system Fig. 1 Fig. 2

Claims (1)

[Scope of Claims] Feature calculation means for calculating a feature amount that indicates air content in the lung based on image data representing a radiographic image of the lungs of a human body; A radiation image reproducing device characterized by comprising a reproducing means for reproducing the visible image together with or in succession with the visible image.