JPH0782537B2 - Method and apparatus for energy subtraction of radiation image - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for energy subtraction of radiation images.

(Prior Art) In various fields, a recorded radiation image is read to obtain an image signal, the image signal is subjected to appropriate image processing, and then the image is reproduced and recorded. For example, an X with a low gamma value designed for later image processing.
An X-ray image is recorded using a line film, the X-ray image is read from the film on which the X-ray image is recorded, converted into an electric signal, and the electric signal (image signal) is subjected to image processing, and then a copy photograph By reproducing it as a visible image, etc.,
A system capable of obtaining a reproduced image with excellent image quality performance such as contrast, sharpness, and graininess has been developed (see Japanese Patent Publication No. 61-5193).

In addition, according to the applicant, radiation (X-ray, α-ray, β-ray, γ
Ray, electron beam, ultraviolet ray, etc.), a part of this radiation energy is accumulated, and then, when excitation light such as visible light is irradiated, a stimulable emission light of a light amount corresponding to the accumulated energy is accumulated. Utilizing the body (stimulable phosphor),
A radiation image of a subject such as a human body is once photographed and recorded on a sheet-shaped stimulable phosphor, and the stimulable phosphor sheet is scanned with excitation light such as laser light to generate stimulated emission light, and the resulting stimulated emission is obtained. A radiation recording / reproducing system that photoelectrically reads emitted light to obtain an image signal and outputs a radiation image of a subject as a visible image to a recording material such as a photographic photosensitive material or a CRT based on the image signal has already been proposed. (Japanese Patent Laid-Open No. 55-12429
No. 56, No. 56-11395, No. 55-0163472, No. 56-164645.
No. 55-116340).

This system has the practical advantage of being able to record images over a very wide radiation exposure area compared to conventional radiographic systems using silver halide photography. That is, it has been confirmed that the amount of stimulated emission light emitted by excitation after storage is proportional to the radiation exposure amount over a very wide range, and therefore the radiation exposure amount varies considerably depending on various imaging conditions. However, the stimulated emission light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means and read by photoelectric conversion means to be converted into an electric signal (image signal). By outputting a radiation image as a visible image on a display device such as a material or a CRT, it is possible to obtain a radiation image that is not affected by fluctuations in radiation exposure dose.

In a system using a recording sheet such as an X-ray film or a stimulable phosphor sheet as described above, a plurality of radiation images recorded on the recording sheet are read to obtain an image signal, and then the radiation is calculated based on the image signal. The image may be subjected to subtraction processing.

Here, the subtraction process of the radiographic image refers to a process of obtaining an image corresponding to a difference between a plurality of radiographic images captured under mutually different conditions, and specifically, the plurality of radiographic images at a predetermined sampling interval. Read to obtain multiple digital image signals corresponding to each radiation image,
This is a process of obtaining a radiation image in which only a specific subject portion in the radiation image is emphasized or extracted by performing a subtraction process for each corresponding sampling point of the plurality of digital image signals.

This subtraction process basically has the following two. That is, by subtracting (subtracting) the radiation image in which the contrast agent is not injected from the radiation image in which a specific portion of the object (for example, a blood vessel when the human body is the subject) is emphasized by injecting the contrast agent, Utilizing so-called time difference subtraction for extracting a specific part (for example, a blood vessel) and the fact that a specific part of a subject has different radiation absorption rates for radiations having different energies, the Radiation having different energies is applied to obtain a plurality of radiation images by the radiations having different energies, and the radiation images are appropriately weighted and the difference is also calculated to extract a specific portion of the subject. There is so-called energy subtraction. The present applicant has also proposed energy subtraction using a stimulable phosphor sheet (JP-A-59).
-83486, JP-A-60-225541).

(Problems to be Solved by the Invention) In the method described in Japanese Patent Laid-Open No. 60-225541, two radiation images obtained by performing radiation imaging twice using radiations having different energies from each other. The image is read to obtain two digital image signals, and subtraction is performed based on these image signals. However, in this method, since there is a time difference between the two shootings, the subject moves during that time, and the visible image reproduced based on the image signal after the subtraction processing does not match the plurality of images due to this movement. There is a problem that a false image (motion artifact) is generated due to, and the image quality of this visible image is significantly deteriorated.

Also, in the above-mentioned Japanese Patent Laid-Open No. 59-83486, energy subtraction is performed in a single photographing by irradiating radiation passing through an object on two recording sheets sandwiching a filter having different absorption rate depending on radiation energy. However, there is a problem in that the difference in radiation energy applied to the two recording sheets is small, and thus only a low-quality visible image with a low S / N ratio can be obtained. .

In view of the above problems, the present invention does not generate a false image due to image mismatch, and has a high radiation energy resolution.
It is intended to resist an energy subtraction method with a high S / N ratio and an apparatus implementing the method.

(Means for Solving the Problems) An energy subtraction method for a radiation image according to the present invention is performed by a plurality of radiation sources arranged apart from each other, which are responsible for irradiation of at least two types of radiation having different energies, and are emitted at substantially the same time. Irradiate the subject with
The radiation emitted from each of the plurality of radiation sources that has passed through the subject is irradiated to different areas on the recording sheet such as a stimulable phosphor sheet or an X-ray film, so that the recording sheet is exposed to the subject. A plurality of radiation images are recorded, and a plurality of image signals representing each of the plurality of radiation images are obtained from the recording sheet after recording, and the distortion of the radiation image is corrected based on these image signals. It is characterized in that the subtraction of the plurality of radiation images is performed based on the subsequent image signal.

Further, the energy subtraction device for a radiation image of the present invention comprises a plurality of radiation sources which are arranged apart from each other and which share the irradiation of at least two types of radiation having different energies, and a subject placement unit in which a subject is placed, And a sheet holding unit that holds a recording sheet capable of recording a radiation image of the subject due to the radiation, the sheet holding unit provided at a position facing the plurality of radiation sources across the subject placement unit. A recording unit for recording a plurality of radiation images of the subject by radiation emitted from each of the sources in different areas of the recording sheet held by the sheet holding unit, and recording the plurality of radiation images in the recording unit. A plurality of images representing each of the plurality of radiation images from the recording sheet From a processing unit that subtracts the plurality of radiation images based on the image signals after distortion correction, and a distortion correction unit that corrects distortion of the radiation images based on these image signals. It is characterized by being configured.

(Operation) An energy subtraction method for a radiation image according to the present invention irradiates a subject with radiations emitted from a plurality of radiation sources arranged apart from each other, which share the radiation of at least two types of radiations having different energies. Then, a plurality of radiation images of the subject are recorded on the recording sheet by irradiating different areas on the recording sheet with radiation emitted from each of the plurality of radiation sources that has passed through the subject. Therefore, you only have to shoot once.

However, the plurality of radiation images recorded on the recording sheet are distorted because they are captured and recorded by irradiating the subject with radiation from different directions. Therefore, in the present invention, after obtaining a plurality of image signals representing each of the plurality of radiation images from the recording sheet after recording, the distortion of the radiation image is corrected based on these image signals. The radiographic images are identical except that they are formed by the irradiation of radiation having different energies, and therefore false images due to image inconsistency do not occur.

Further, since a plurality of radiation sources are used, the resolution of radiation energy is equivalent to the method of twice imaging, and energy subtraction with a good S / N ratio can be performed.

The radiation image energy subtraction apparatus of the present invention is an apparatus used for carrying out the radiation image energy subtraction method of the present invention, and since it has the above-mentioned configuration, it does not generate a false image and has an S / N ratio. High energy subtraction can be performed.

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

FIG. 1 is a schematic configuration diagram of an example of an X-ray imaging apparatus, which is an example of a recording unit of a subtraction apparatus of the present invention.

The X-ray image capturing apparatus 10 is provided with two X-ray sources 11 and 12 to which different voltages are applied. X-rays 11 ', which have different energies from these two X-ray sources 11 and 12,
Two X-ray images by the X-rays 11 'and 12' are separately stored and recorded on the stimulable phosphor sheet 14 after 12 'are emitted almost at the same time and have passed through the subject 13 such as a human body.

FIG. 2 is a diagram showing an example of two X-ray images accumulated and recorded on the stimulable phosphor sheet.

In order to separate and record two X-ray images on the stimulable phosphor sheet 14, the two X-ray sources 11 and 12 shown in FIG. X-ray irradiation from different angles. Therefore, the two X-ray images 15a and 15b obtained by this imaging are slightly distorted from each other, except that the two X-ray images 15a and 15b are captured by X-rays having different energies.

FIG. 3 is a schematic view of an example of an X-ray image reading apparatus which is an example of a reading unit of the subtraction apparatus of the present invention.

The stimulable phosphor sheet 14 imaged by the X-ray imaging 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 in the direction of arrow Y by the sheet conveying means 15 such as an endless belt driven by a driving means (not shown) (sub scanning).
To be done. On the other hand, the light beam 17 emitted from the laser light source 16
Is driven by a motor 18 and is reflected and deflected by a rotary polygon mirror 19 that rotates at a high speed in the direction of arrow Z, passes through a focusing lens 20 such as an fθ lens, and then enters an optical path into a sheet 14 by a mirror 21 to make a sub scanning direction. The main scanning is performed in the direction of arrow X, which is substantially perpendicular to (the direction of arrow Y). From the portion of the sheet 14 irradiated with the light beam 17, a stimulated emission light 22 having a light amount according to the stored and recorded radiation image information is emitted, and this stimulated emission light 22 is guided by a light guide 23. , Photomultiplier (photomultiplier) 24 for photoelectric detection.
The light guide 23 is made by molding a light guide material such as an acrylic plate, and is arranged so that the linear incident end face 23a extends along the main scanning line on the stimulable phosphor sheet 14. The light receiving surface of the photomultiplier 24 is coupled to the exit end surface 23b formed in a ring shape. The stimulated emission light 22 that has entered the light guide 23 from the incident end face 23a is the light guide 23.
The photomultiplier 24 receives the photostimulated luminescent light 22 which is emitted from the exit end face 23b and is received by the photomultiplier 24, and is converted into an electric signal by the photomultiplier 24.

Analog signal S output from photomultiplier 24
Is logarithmically amplified by the log amp 25 and then the A / D converter 2
At 6, sampling is performed at a predetermined sampling interval and digitized to obtain a digital image signal S0. The image signal S0 is temporarily stored in the recording unit 27 and then sent to the image processing device 30.

Next, the image processing performed by the image processing device 30 will be described. The image processing device 30 constitutes a distortion correction unit and a processing unit of the subtraction device of the present invention.

The two X-ray images carried by the image signal S0 are mutually distorted as shown in FIG. 2, and the subtraction processing cannot be performed as they are. Therefore, first, a distortion correction calculation for correcting the distortion of the X-ray image is performed based on the image signal S0. Here, affine transformation is used as this distortion correction calculation.

The affine transformation is an operation that performs coordinate transformation on each coordinate point (i _I , j _I ) of the image and obtains the coordinate (i _J , j _J ) after the coordinate transformation. Specifically, for example, linear interpolation is performed. make use of, However, T _{l, m} (l = 1,2; m = 1,2,3) is for calculating the coefficient.

Since the arrangement positions of the X-ray sources 11 and 12, the subject 13 and the sheet 14 in the X-ray imaging apparatus 10 shown in FIG. 1 are known in advance, two X-ray images 15a and 15b (second
The distortion can be obtained by setting each coefficient T _{l, m} in the above equation (1) to a value corresponding to the distortion.

In this way, two X-ray images are obtained based on the image signal S0.
After distortion correction of 15a and 15b is performed, weighted subtraction of the image signal at each corresponding sampling point according to the following equation (2) at each corresponding sampling point of the two X-ray images, that is, subtraction The processing is performed, and as a result, the image signal S1 corresponding to the image of the difference between the two X-ray images is generated.

S1 = Wa.S0a-Wb.S0b + C (2) where S0a and S0b are image signals representing the two X-ray images 15a and 15b after distortion correction, Wa and Wb are weighting factors, and C
Is the bias.

The image signal S1 is stored in a storage unit (not shown) in 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 (subtraction image) based on the image signal S1.

The two X-ray images 15a and 15b are images that have been photographed and recorded almost at the same time, and since distortion correction has been performed according to the equation (1), two X-ray images 15a and 15b are included in the subtraction image based on the image signal S1. A false image due to the difference of does not occur. Moreover, since the two X-ray images are photographed and recorded at different positions on the sheet 14 using the independent X-ray sources 11 and 12 (see FIG. 1), the S / N ratio is good. A subtraction image can be obtained.

Although the stimulable phosphor sheet is used in the above-mentioned embodiment, the subtraction method and apparatus for radiation images of the present invention is not limited to the system using the stimulable phosphor sheet.
It can also be applied to a system using another recording sheet such as a line film. Further, although X-rays are used in each of the above-mentioned embodiments, the present invention can be widely applied to other systems using radiation such as electron microscopes using electron beams.

(Effects of the Invention) As described in detail above, the subtraction method and apparatus for radiation images of the present invention obtain a plurality of radiation images by radiation having different energies at the same time by using a plurality of radiation sources. Since the image signal obtained by reading the radiation image is subjected to the distortion correction calculation and then subjected to the subtraction process, it is possible to obtain a subtraction image having a good S / N ratio without any false image.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of an X-ray image capturing apparatus, FIG. 2 is a diagram showing an example of two X-ray images accumulated and recorded on a stimulable phosphor sheet, and FIG. It is a schematic block diagram of an example of an X-ray image reading apparatus. 10,10 '…… X-ray imaging device 11,12 …… X-ray source 13 …… Subject 14 …… Storable phosphor sheet, 16 …… Laser light source 22 …… Stimulated emission light, 23 …… Light guide 24 ...... Photo multiplier

Claims (2)

[Claims] 1. A subject is irradiated with radiation that is emitted at substantially the same time from a plurality of radiation sources that are arranged apart from each other and that share the radiation of at least two types of radiation having different energies from each other, and transmitted through the subject. A plurality of radiation images of the subject are recorded on the recording sheet by irradiating different areas on the recording sheet with radiation emitted from each of the plurality of radiation sources, and the plurality of radiation images are recorded from the recording sheet after recording. Obtaining a plurality of image signals representing each of the radiation images, correcting the distortion of the radiation image based on these image signals, and subtracting the plurality of radiation images based on the image signals after distortion correction Radiation image energy subtraction method characterized by: 2. A plurality of radiation sources, which are arranged apart from each other and which share the irradiation of at least two types of radiations having different energies, a subject placement section in which a subject is placed, and a radiation image of the subject by the radiation. A recording sheet capable of recording a sheet, a sheet holding section provided at a position facing the plurality of radiation sources across the subject placement section, and the radiation emitted from each of the plurality of radiation sources. A recording unit for recording a plurality of radiation images of the subject in different areas of the recording sheet held by the sheet holding unit, from the recording sheet on which the plurality of radiation images are recorded in the recording unit A reading unit for obtaining a plurality of image signals representing each of the plurality of radiological images, based on these image signals An energy subtraction of a radiation image, the distortion correction unit correcting a distortion of the radiation image, and a processing unit performing a subtraction of the plurality of radiation images based on the image signal after the distortion correction. apparatus.