JPH02275582A - Method and device for energy subtraction of radiation images - Google Patents

Abstract

PURPOSE:To reduce the generation of false images due to the displacement of images, to improve an SN ratio and to shorten a reading processing time by alternately recording the radiation images of respective parts of a subject obtained by plural radiant rays in a recording sheet like strips. CONSTITUTION:While relatively moving a radiant ray source 11, slits 12, 15, the subject 13, and the recording sheet 14, the radiation images of respective parts of the subject 13 due to plural radiant rays alternately generated from the radiant ray source 11 and having mutually different energy are alternately recorded on the sheet 14 like strips. Thereby, strip-like adjacent parts are continuously photographed within a short time. Consequently, false images due to the displacement of images are not almost generated. Since radiant rays having mutually different energy values are used with time division, energy transaction with a high S/N ratio can be executed. Since the radiation images obtained by using the radiant rays having mutually different energy values are alternately arranged like strips, images can be obtained only by one reading operation and the reading processing time can be shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method and apparatus for energy subtraction of radiographic images.

(Prior Art) It is practiced in various fields to read a recorded radiation image to obtain an image signal, perform appropriate image processing on the image signal, and then reproduce and record the image. For example, a low gamma X
An X-ray image is recorded using a ray film, the X-ray image is read from the film on which the X-ray image was recorded and converted into an electrical signal, and this electrical signal (image signal) is subjected to image processing and then a photocopy is made. By reproducing it as a visible image,
A system that can obtain reproduced images with good image quality performance such as contrast, sharpness, and graininess has been developed (see Japanese Patent Publication No. 81-5193).

The applicant has also discovered that when radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) is irradiated, part of this radiation energy is accumulated, and when excitation light such as visible light is irradiated, the energy is accumulated. Using a stimulable phosphor (stimulable phosphor) that emits stimulable luminescence light in an amount corresponding to the energy emitted, radiographic images of objects such as the human body are partially captured on a sheet of stimulable phosphor. The stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescent light, the resulting stimulated luminescent light is read photoelectrically to obtain an image signal, and based on this image signal, A radiation recording and reproducing system has already been proposed in which a radiation image of a subject is output as a visible image to a recording material such as a photographic light-sensitive material, a CRT, etc.
No. 429, No. 513-11395.

55-11340, 5G-104045, 5
5-110340 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, it is recognized that the amount of stimulated luminescence light emitted by excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range, and therefore the amount of radiation exposure varies considerably depending on various imaging conditions. Even if the stimulable luminescent light is emitted from the stimulable phosphor sheet, the reading gain is set to an appropriate value, the photoelectric conversion means reads it and converts it into an electrical signal (image signal), and this image signal is used to create a photograph. By outputting a radiation image as a visible image to a display device such as a photosensitive material or a CRT, a radiation image that is not affected by fluctuations in radiation exposure can be obtained.

In a system that uses a recording sheet such as an X-ray film or a stimulable phosphor sheet as described above, after obtaining an image signal by reading a plurality of radiation images recorded on the recording sheet, the radiation Image subtraction processing may be applied.

Here, radiographic image subtraction processing refers to processing to obtain an image corresponding to the difference between multiple radiographic images taken under different conditions, and specifically, these multiple radiographic images are collected at a predetermined sampling interval. Read and obtain multiple digital image signals corresponding to each radiographic image,
It is a process of obtaining a radiographic image in which only a specific subject part in the radiographic image is emphasized or extracted by performing subtraction processing on each corresponding sampling point of these plurality of digital image signals.

There are basically two types of subtraction processing: In other words, by subtracting a radiographic image in which no contrast medium has been injected from a radiographic image in which a specific part of the subject (for example, a blood vessel when the human subject is the subject) has been emphasized by injecting a contrast medium, the image of the subject can be visualized. Using so-called time difference subtraction to extract specific parts (such as blood vessels) and the fact that specific parts of the subject have different radiation absorption rates for radiation with different energies, A specific part of the subject is extracted by irradiating radiation with different energies to obtain multiple radiation images of each radiation having different energies, appropriately weighting these multiple radiation images, and calculating the difference. There is a so-called energy subtraction. The present applicant has also proposed energy subtraction using a stimulable phosphor sheet (Japanese Patent Laid-Open No. 59
(See Japanese Patent Laid-Open No. 60-225541).

(Problems to be Solved by the Invention) The method described in the above-mentioned Japanese Patent Application Laid-Open No. 00-225541 involves performing two radiographs using radiation having different energies, and then using two radiographs obtained as a result. An image is read to obtain two digital image signals, and subtraction is performed based on these image signals. However, with this method, there is a time difference between the two shots, so the subject moves during that time, resulting in discrepancies between multiple images due to this movement in the visible image reproduced based on the image signal after subtraction processing. Fake image by (
There is a problem in that motion artifacts) occur and the quality of this visible image is significantly degraded.

In addition, the above-mentioned Japanese Patent Application Laid-Open No. 59-83486 discloses that energy subtraction can be achieved in a single imaging by irradiating radiation that has passed through the subject onto two recording sheets sandwiching filters that have different absorption rates depending on the radiation energy. A method has been proposed that can perform this, but the problem is that the difference in radiation energy irradiated to the two recording sheets is small, and therefore only low-quality visible images with a low S/N ratio can be obtained. . Furthermore, although this method requires only one imaging, it is necessary to read two radiation images recorded on two recording sheets, and the reading processing time is not reduced compared to the above method.

In view of the above-mentioned problems, the present invention provides an energy subtraction method and method, which reduces the occurrence of false images due to image mismatch, has a high degree of separation of radiation energy, has a high S/N ratio, and shortens the reading processing time. The purpose of the present invention is to provide an apparatus for implementing the method.

(Means for Solving the Problems) The energy subtraction method for radiographic images of the present invention involves directing a plurality of rays having different energies alternately emitted from a radiation source to a subject through an open slit extending in a predetermined direction. irradiating the recording sheet with radiation that has passed through the subject, and moving the radiation source and the slit, the subject and the recording sheet relatively in a scanning direction substantially perpendicular to the predetermined direction. By doing so, the radiation images of each part of the subject by each of the plurality of radiations are alternately
ff shape on the recording sheet, obtain a plurality of image signals representing a plurality of radiation images of the subject by the plurality of radiations having mutually different energies from the recording sheet after recording, and based on the plurality of image signals. The method is characterized in that subtraction is performed on the radiographic image of the subject.

Here, in the energy subtraction method, the relative movement is performed as an intermittent movement so as to obtain a large number of sets of radiation images of the same part of the subject by a plurality of radiations having different energies on the recording sheet. , and the recording sheet may be moved back and forth in the scanning direction in synchronization with radiation irradiation.

Further, the energy subtraction device of the present invention includes: a radiation source that alternately emits a plurality of radiations having different energies; a subject placement section in which a subject is placed; and an energy subtraction device disposed between the subject placement section and the radiation source. Further, a slit extending and opening in a predetermined direction substantially perpendicular to the irradiation direction connecting the radiation source and the subject placement section, and a recording sheet capable of recording a radiation image of the subject caused by the radiation is held, the subject a sheet holding section provided at a position facing the radiation source sandwiching the placement section; the radiation source and the slit; the subject placement section and the sheet holding section; and a scanning means that moves relatively in a scanning direction substantially perpendicular to both, and alternately displays radiographic images of each part of the subject by each of the plurality of radiations on the recording sheet held in the sheet holding section. a recording unit that records in a short 111) shape; a reading unit that obtains an image signal by reading a plurality of radiation images of the subject recorded on the recording sheet in the recording unit and generated by the plurality of radiations having mutually different energies; and a processing unit that performs subtraction of a radiation image of the subject based on the image signal.

Here, the energy subtraction device is configured to obtain a large number of sets of a plurality of radiation images of the same portion of the subject by the plurality of radiations having mutually different energies on the recording sheet held by the sheet holding section. Preferably, the scanning means is configured to perform intermittent scanning, and may further include sheet moving means for reciprocating the recording sheet holding section in the scanning direction in synchronization with the irradiation of the radiation. .

(Function) The energy subtraction method of the present invention uses a plurality of radiations having different energies alternately emitted from a radiation source, and moves the radiation source and slit relative to the subject and the recording sheet. Since the radiographic images of each part of the object generated by multiple radiations are recorded alternately in strips on the recording sheet, the images of the strips adjacent to each other are taken continuously in a very short period of time. False images due to discrepancies rarely occur. In addition, since radiation with different energies is used in a time-sharing manner, the degree of separation of radiation energy is equivalent to when imaging is performed twice completely independently, and energy subtraction with a good S/N ratio can be performed. I can do it.

Furthermore, using radiation of different energies, iH7
The radiographic images obtained are arranged alternately in a short III) pattern, so reading only needs to be done once, and the reading processing time is shortened.

In addition, if the above-mentioned visual movement of the radiation source, etc. is a continuous movement and the recording sheet is fixed during imaging, mutually adjacent radiation images of the same type 111N are radiation images of the same part of the subject. Instead, they are radiation images of adjacent parts. Even in this case, subtraction processing can be performed by obtaining image signals of mutually identical parts of the subject using interpolation calculations, etc. However, in the energy subtraction method described above, the same part of the subject is synchronized with radiation irradiation during imaging. By obtaining a large number of sets of radiographic images of a portion, more accurate subtraction processing can be performed.

The energy subtraction device for radiographic images of the present invention is a device used for carrying out the energy subtraction method for radiographic images of the present invention, and has the above configuration, so that the generation of false images is small and the S/N ratio is It is possible to perform high energy subtraction, and furthermore, reading processing can be performed in a short time.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. An example using the above-mentioned stimulable phosphor sheet will be described below.

FIG. 1 is a schematic configuration diagram of an example of an X-ray image photographing device, which is an embodiment of a recording unit of a subtraction device of the present invention.

The X-ray image capturing apparatus 10 is equipped with an X-ray source 11 that can alternately apply different voltages.

Two types of X-rays with different energies are alternately emitted from this X-ray source 11, and these X-rays are converted into a fan beam ILa by a slit 12, and after passing through a subject 13, are irradiated onto a stimulable phosphor sheet 14. be done. A slit 15 is arranged on the front surface of the sheet 14, and is configured to prevent scattered X-rays from being irradiated to adjacent regions on both sides. During this imaging, the X-ray source 11. Slit 12. The slit 15 is moved in the direction of arrow A shown in the figure relative to the subject 13 and the sheet 14.

FIG. 2 is a diagram showing a pattern of an X-ray image photographed and recorded by the X-ray image photographing apparatus 10. As shown in FIG.

As shown in this figure, X-ray images 1 and 2 of two types of X-rays having different energies are alternately recorded in a strip shape. Here, mutually adjacent X-ray images 1a, 2a; lb,
2b; . . . are X-ray images of mutually adjacent portions of the subject 13.

FIG. 3 is a schematic diagram of an example of an X-ray image reading device, which is an embodiment of the reading unit of the subtraction device of the present invention.

The stimulable phosphor sheet 14 photographed by the X-ray photographing apparatus 10 shown in FIG. 1 is set at a predetermined position of the X-ray image reading apparatus.

The stimulable phosphor sheet 14 set at a predetermined position is conveyed (sub-scanned) in the direction of arrow Y by a sheet conveyance means 15 such as an endless belt driven by a drive means (not shown). On the other hand, the light beam 17 emitted from the laser light source 1B is reflected and deflected by the rotating polygon ff119 that is driven by the motor 18 and rotates at high speed in the direction of the arrow Z.
After passing through a focusing lens 20 such as a θ lens, a mirror 21
The light beam changes its optical path and enters the sheet 14, and main scans in the direction of arrow X, which is substantially perpendicular to the direction of sub-scanning (direction of arrow Y). Stimulated luminescent light 22 is emitted from the portion of the sheet 14 that is irradiated with the front beam 17, and the amount of stimulated luminescent light 22 corresponds to the radiographic image information that has been stored and recorded.
3 and photoelectrically detected by a photomultiplier (photomultiplier tube) 24. The light guide 23 is made by molding a light-guiding material such as an acrylic plate, and is arranged so that a linear entrance end surface 23a extends along the main scanning line on the stimulable phosphor sheet 14. , a photomultiplier 2 is provided on the injection end surface 23b formed in an annular shape.
The four light receiving surfaces are combined. The stimulated luminescent light 22 that has entered the light guide 23 from the incident end surface 23a is
The stimulated luminescent light 22 travels through the interior of the photomultiplier 3 through repeated total reflection, exits from the exit end face 23b, and is received by the photomultiplier 24, where the stimulated luminescence light 22 representing a radiation image is converted into an electrical signal by the photomultiplier 24.

The analog signal S output from the photomultiplier 24 is logarithmically amplified by the log amplifier 25, and then the A/D
The converter 26 samples and digitizes the image at predetermined sampling intervals to obtain a digital image signal SO. This image signal SO is once stored in the storage section 27 and then sent to the image processing device 30. In addition, the above sheet 14
There are two radiographs in the shape of a strip c? ! 1.2 is recorded, the above reading only needs to be done once.

Next, image processing performed by the image processing device 30 will be described. This image processing device 3o constitutes a processing unit of the subtraction device of the present invention.

The two X-ray images 1 and 2 (see FIG. 2) carried by the image signal SO are images of mutually adjacent parts of the subject,
In this state, subtraction processing cannot be performed. Therefore, first, an interpolation calculation is performed based on the image signal SO so as to obtain an X-ray image of the entire subject. Various known methods can be used for this interpolation calculation.

In this way, after the interpolation calculation is performed on the two X-ray images 1□2 based on the image signal SO, the images are imaged at each corresponding sampling point of the two X-ray images according to the following equation (1). Signal weighting is performed by subtraction, ie, subtraction processing, thereby generating an image signal S1 corresponding to a difference image between two X-ray images.

Wa+Wb However, SOa and SOb are two corresponding image signals after interpolation calculation, Wa and Wb are weighting coefficients, and C is a bias component.

This image signal S1 is stored in a storage unit (not shown) within the image processing device 30, and is sent to the image display device 40 as needed. The image display device 40 reproduces and displays a visible image (subtracisine image) based on the image signal S1.

The adjacent rectangular regions of the above two X-ray images 1.2 (see Figure 2) are images that were photographed and recorded at approximately the same time, although there is a slight time difference. Therefore, the subtraction images based on the image signal S1 Almost no false images occur due to differences between two X-ray images. Shigamo above 2
Since the two X-ray images are recorded in strips at different positions on the sheet 14 using different X-rays in a time-sharing manner, it is possible to obtain a subtraction image with a good S/N ratio. .

In the above embodiment, the mutually adjacent X-ray images la, 2
a; 1b, 2b; ... (see Fig. 2) are X-ray images of mutually adjacent parts of the subject 13, where X-rays are irradiated from the X-ray source 11. In synchronization with the timing, the sheet 14 is reciprocated in the direction of arrow B shown in FIG. 1 by the width of the fan beam lla, and the X-ray source 1
1. By intermittently moving the slit 12 etc. each time this reciprocation is made, the mutually adjacent X-ray images 1a shown in FIG.
, 2a; lb, 2b; . . . can be X-ray images of the same part of the subject 13. By obtaining X-ray images of the same portion of the subject 13 in this manner, the interpolation calculations in the above-described embodiments become unnecessary, and more accurate subtraction processing can be performed.

Further, in the above embodiments, a stimulable phosphor sheet is used, but in addition to the system using the stimulable phosphor sheet, the energy subtraction method and apparatus for radiographic images of the present invention also uses other recording sheets such as X-ray film. It can also be applied to the system used. Moreover, in the above embodiment,
This method can be widely applied to systems using landmine wires.

(Effects of the Invention) As explained in detail above, the energy subtraction method and apparatus for radiographic images of the present invention are such that a plurality of radiation beams having different energies are alternately irradiated onto a subject as a fan beam and transmitted through the subject. By irradiating radiation onto the recording sheet and moving a radiation source, etc. relatively in a predetermined direction, images of each part of the subject by each of the plurality of radiations are alternately recorded on the recording sheet in the form of strips. , it is possible to obtain an energy subtraction image with less generation of false images due to image mismatch and a high S/N ratio.

Since the present invention obtains an image signal from a recording sheet on which the radiographic images of the plurality of radiations are recorded alternately in a short+m shape, the reading required to obtain the image signal is one recording sheet, which is different from the conventional method of reading two recording sheets. The time required for reading is shorter than that required for reading.

Furthermore, in the present invention, if the strip-shaped radiation images adjacent to each other are configured to be radiation images of the same part of the object as described above, interpolation calculation processing is not necessary, and more accurate subtraction processing can be performed. be able to.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of an example of an X-ray imaging device, Figure m2 is a diagram showing an example of an X-ray image pattern accumulated and recorded on a stimulable phosphor sheet, and Figure 3 is an FIG. 1 is a schematic configuration diagram of an example of a line image reading device. 1.2...Radiation image 10...X-ray imaging device 11...X-ray source 11a...Fan beam 12.15...Slit 14...Stormative phosphor sheet 16...Laser light source 2
2... Stimulated luminescent light 23... Light guide 24
...Photo multiplier 30...Image processing device 4o...Image display device Display of incident 1999 patent application No. 097.808 Title of invention Energy subtraction method and device for radiographic images Relationship with the case of the person making the amendment Patent applicant

Claims (2)

[Claims] (1) A plurality of radiation beams having different energies alternately emitted from a radiation source are irradiated onto a subject through a slit that extends in a predetermined direction and is open, and the radiation that has passed through the subject is irradiated onto a recording sheet. , by relatively moving the radiation source and the slit, the object and the recording sheet in a scanning direction substantially perpendicular to the predetermined direction, each part of the object is affected by each of the plurality of radiations. Recording radiation images alternately in strips on the recording sheet, obtaining a plurality of image signals representing a plurality of radiation images of the subject by the plurality of radiations having different energies from each other from the recording sheet after recording, An energy subtraction method for a radiographic image, characterized in that subtraction is performed on a radiographic image of the subject based on an image signal. (2) a radiation source that alternately emits a plurality of radiations having different energies; a subject placement section in which a subject is placed; and the radiation source and the radiation source disposed between the subject placement section and the radiation source. a slit extending and opening in a predetermined direction substantially perpendicular to the irradiation direction connecting the subject placement section; and a slit sandwiching the subject placement section, which holds a recording sheet capable of recording a radiation image of the subject caused by the radiation. A sheet holding section provided at a position facing the radiation source, the radiation source and the slit, the subject placement section and the sheet holding section are scanned substantially perpendicular to both the irradiation direction and the predetermined direction. recording means for recording radiation images of each part of the subject by each of the plurality of radiations alternately in a strip shape on the recording sheet held by the sheet holding section; a reading unit that obtains an image signal by reading a plurality of radiation images of the subject recorded on the recording sheet in the recording unit by the plurality of radiations having different energies; 1. An energy subtraction device for radiographic images, comprising a processing unit that performs subtraction of a radiographic image of a subject.