JP2824878B2 - Radiation image energy subtraction imaging processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention records radiographic image information on a recording medium, and then obtains radiographic image information from the recording medium. The present invention relates to a radiation image energy subtraction method as described above.

[0002]

2. Description of the Related Art A recorded radiographic image is read to obtain an image signal, and the image signal is subjected to appropriate image processing.
2. Description of the Related Art Reproduction and recording of images are performed in various fields.
For example, recording an x-ray image using a low gamma x-ray film designed to be compatible with subsequent image processing;
The X-ray image is read from the film on which the X-ray image is recorded, converted into an electric signal, the electric signal (image signal) is subjected to image processing, and then reproduced as a visible image in a copy photograph or the like, thereby obtaining a contrast. A system capable of obtaining a reproduced image with good image quality such as image quality, sharpness, and graininess has been developed (see Japanese Patent Publication No. Sho 61-5193).

[0003] Further, according to the present applicant, radiation (X-ray, α
Radiation, 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, the amount of stimulated emission light corresponding to the accumulated energy is increased. Phosphor that emits light (stimulable phosphor)
Utilizing, a radiographic 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,
A radiation recording / reproducing system that photoelectrically reads the obtained stimulated emission 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. Have already been proposed (JP-A-55-12429, JP-A-56-11395, JP-A-55-0163472,
Nos. 56-164645 and 55-116340).

This system has the practical advantage of being able to record images over a very wide radiation exposure area as compared to conventional radiographic systems using silver halide photography. That is, it has been recognized that the amount of stimulating light emitted by excitation after accumulation with respect to the amount of radiation exposure is proportional over a very wide range, and thus the amount of radiation exposure varies considerably depending on various imaging conditions. Also, the stimulable light emitted from the stimulable phosphor sheet is read, the gain is set to an appropriate value, read by photoelectric conversion means, converted into an electric signal (image signal), and a photograph is taken using this image signal. By outputting a radiation image as a visible image to a display device such as a photosensitive material or a CRT, a radiation image which is not affected by a change in radiation exposure amount can be obtained.

In a system using an X-ray film or a stimulable phosphor sheet as described above, a plurality of recorded radiographic images are read to obtain a plurality of image signals, and then the radiographic image is obtained based on these image signals. Image subtraction processing may be performed.

Here, the subtraction processing of the radiation images refers to processing for obtaining an image corresponding to the difference between a plurality of radiation images taken under different conditions. By reading at a sampling interval, obtaining a plurality of digital image signals corresponding to each radiation image, and performing a subtraction process for each corresponding sampling point of the plurality of digital image signals,
It refers to a process of obtaining a radiation image in which only a specific subject portion in the radiation image is emphasized or extracted.

There are basically the following two methods for this subtraction processing. That is, a so-called time period in which a specific structure is extracted by subtracting (subtracting) an image signal of a radiation image in which a contrast agent is not injected from an image signal of a radiation image in which a specific structure is enhanced by injection of a contrast agent. Subtraction processing, irradiating the same subject with radiation having different energy distributions, or irradiating the radiation after passing through the subject to two radiation detecting means with changing energy distribution state, thereby a specific structure Is a method of extracting an image of a specific structure by subtracting an image between the two radiographic images by performing appropriate subtraction after appropriately weighting the image signals of the two radiographic images. This is energy subtraction processing.

Since this subtraction processing is a particularly effective method for medical diagnosis, it has attracted much attention in recent years, and its research and development have been actively promoted by making full use of radiation physics / digital image processing technology.

For example, in the radiation image information recording / reproducing system using the stimulable phosphor sheet described above,
Since the radiation image information recorded on the sheet is directly read in the form of an electrical image signal, this system makes it possible to easily perform the above-described subtraction processing. In order to perform energy subtraction processing using this stimulable phosphor sheet, image recording (photographing) is performed on two stimulable phosphor sheets such that image information of a portion corresponding to a specific structure is different. More specifically, 1) imaging is performed twice using two types of radiation having different energy distributions, 2) a metal that absorbs a low energy component of the radiation between two stimulable phosphor sheets. There is known a method of simultaneously irradiating two stimulable phosphor sheets with radiation transmitted through a subject through a filter such as described above. However, in the above-described method, in addition to having to perform imaging twice, the radiation irradiating means must be adjusted for each imaging, so that workability is poor, and in the latter method, a filter is formed of a stimulable phosphor sheet. Since it is necessary to interpose the stimulable phosphor sheet between them, there arises a problem that handling of the stimulable phosphor sheet at the time of photographing and reading is troublesome.

Therefore, conventionally, two stimulable phosphors each having a phosphor layer composed of phosphors of different types so that a required image can be recorded in one shot without using a filter. A sheet having a stimulable phosphor layer having a higher absorption characteristic of a low-energy component of radiation among these stimulable phosphor sheets is disposed on the object side (radiation source side), and these two sheets are accumulated. There has been proposed a method of simultaneously irradiating the luminescent phosphor sheet with radiation (JP-A-59-83486, etc.).

In addition, two X-ray films are used, and of these X-ray films, the X-ray film on the subject side (radiation source side) includes the X-ray of the subject related to the low energy component of X-rays.
A method of obtaining an energy subtraction image by recording a line image has also been proposed (JP-A-59-83147).

[0012]

However, in the above-described method using the stimulable phosphor sheet, since two types of stimulable phosphors are used, both stimulable phosphors have a high radiation energy accumulating property. In addition, there is a problem that it is difficult to select one having a sufficiently high emission level of stimulated emission light upon irradiation with excitation light.

Further, in the method using the stimulable phosphor sheet and the X-ray film, since two recording media are used, it is difficult to perform positioning when performing the energy subtraction process, and furthermore, the two recording media are used. To capture the subject with overlapping, radiation energy separation is poor,
Further, there is a problem that a radiation dose reaching a recording medium placed farther from the subject is reduced.

Further, in the above-mentioned method, since a phosphor layer or a filter is interposed between the two recording media, a certain distance is required between the recording media, and this distance causes a greater distance from the subject. Since the recording medium placed at the position is irradiated with a wider radiation than the recording medium placed closer to the subject, it is difficult to obtain an energy subtraction image with a good S / N ratio. Was.

The present invention has been made in view of the above circumstances, and provides an energy subtraction photographing processing method for a radiation image capable of obtaining an energy subtraction image with no need for alignment, good separation of radiation energy, and improved S / N ratio. It is intended to do so.

[0016]

According to the present invention, there is provided a method for processing an energy subtraction radiograph of a radiation image by irradiating an object including a specific structure having a radiation energy absorption characteristic different from that of another object, and applying the radiation transmitted through the object. ,
A filter formed by alternately combining two types of filter elements having different absorption bands of radiation energy on the surface receiving the radiation at a uniform fine pitch throughout the filter, and transmitting the radiation transmitted through the filter to a recording medium. To record the radiation image information of the subject on the recording medium, and then obtain an image signal carrying the radiation image information from the recording medium, and apply the image signal to each of the two types of filter elements. Separating each image signal obtained by the transmitted radiation to obtain first and second image signals having missing portions that complement each other at a pitch twice the fine pitch of the filter element. The missing portion of the second image signal is complemented based on a signal value of a peripheral portion of the missing portion, and a pixel corresponding to the complemented first and second image signals is extracted. Performing operation between Te signal, it is characterized in that extracting a difference signal representing an image of the specific structure.

Here, there is a filter in which two kinds of filter elements are alternately combined. One of the two kinds of filter elements of this filter is transparent, that is, one that does not absorb radiation and transmits radiation as it is. This includes the case where one filter element is not provided, that is, the case where the part of one filter element is a space.

Further, the complement is based on the signal value of the peripheral portion of the missing portion. This peripheral portion is the periphery of the region to be complemented, and the complement is performed by a method of combining filter elements. May be appropriately determined based on the pattern and the size of the pitch of the filter element.

[0019]

According to the present invention, there is provided a method for processing an energy subtraction radiograph of a radiographic image, in which two types of filter elements having different absorption bands of radiation energy are alternately combined at a uniform fine pitch over a radiation receiving surface. And a radiographic image of the subject is recorded on one recording medium through this filter. Thereafter, an image signal carrying radiation image information is obtained from the recording medium, the image signal is separated for each of the above-described filter elements, and a missing portion of the separated image signal is complemented based on a signal value of a peripheral portion thereof. In this case, energy subtraction processing is performed.

Therefore, it is not necessary to perform the necessary alignment when two sheets are used, the radiation energy is well separated, and the difference in distance from the subject between the two separated image signals is small. Therefore, an energy subtraction image with an improved S / N ratio can be obtained.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows image recording (photographing) in an energy subtraction photographing method according to an embodiment of the present invention.
FIG.

In this embodiment, a stimulable phosphor sheet is used as a recording medium.

In this imaging apparatus, two radiation images for subtraction processing having different degrees of absorption of the energy component of the radiation 3 emitted from the radiation source 2 can be obtained in a portion corresponding to a specific structure of the subject 1. To
Specifically, two types of filter elements having different absorption bands of radiation energy are applied to a stimulable phosphor sheet 6 through a filter 5 which is alternately combined on a surface receiving the radiation 3. The radiation image of the subject 1 is stored and recorded.

As shown in FIG. 2, the filter 5 used in this embodiment is formed by alternately combining copper 7 (hatched portion in FIG. 2) and aluminum 8 in a grid pattern. Since the copper 7 has a high absorptivity of a low energy component of the radiation energy, the radiation transmitted through the copper 7 becomes high-energy radiation, and the radiation transmitted through the aluminum 8 becomes low-energy radiation.

The size of each of the grids of copper 7 and aluminum in the filter 5 is desirably equal to the size of the pixel of the energy subtraction image obtained by the present embodiment, but the size of the pixel is usually 0.1 to 0.2 mm. Therefore, in consideration of processing accuracy and the like, the length of one side of each lattice is desirably about 0.3 to 0.7 mm. Further, as a processing method of the filter 5, a method using laser processing or etching can be considered.

An object 1 is placed on a support 4 having radiation transparency, and a filter 5 and a stimulable phosphor sheet 6 are provided below the support 4 at a position facing the radiation source 2 via the object 1. Is disposed, the radiation 3 is emitted from the radiation source 2.

When the radiation 3 is emitted from the radiation source 2,
The radiation 3 passes through the subject 1 including a specific structure whose radiation energy is different from the others, and then passes through the filter 5. The radiation 3 transmitted through the filter 5 reaches the stimulable phosphor sheet 6. Here, the transmitted radiation image of the subject 1 is recorded on the stimulable phosphor sheet 6,
The radiation 3 transmitted through the lattice of copper 7 among the radiations 3 transmitted through is in a state where the low energy component is absorbed by the copper 7 and the high energy component is emphasized. The low energy component is emphasized. Therefore, on the stimulable phosphor sheet 6, the radiation image information on the low energy component and the radiation image information on the high energy component of the radiation 3 transmitted through the subject 1 are accumulated and recorded in a grid pattern.

When the photographing of the stimulable phosphor sheet 6 is completed in this manner, the radiation image information stored and recorded on the stimulable phosphor sheet 6 is read by the radiation image information reader shown in FIG.

First, while the stimulable phosphor sheet 6 is moved in the direction of arrow Y for sub-scanning, the laser beam 11 from the laser light source 10 is scanned in the X direction by the scanning mirror 12 in the main direction. From stored radiation energy,
The light is emitted as stimulating light 13 according to the radiation image stored and recorded. The stimulating light 13 enters the inside of the light collector 14 from one end surface of the light collector 14 formed by molding a transparent acrylic plate, and reaches the photomultiplier 15 while repeating total reflection inside, thereby stimulating light emission. The light emission amount of the light 13 is output as an image signal S. The output image signal S is converted into a logarithmic digital image signal lo by a logarithmic converter 16 including an amplifier and an A / D converter.
converted to gS.

Next, the digital image signal log S is input to the subtraction operation circuit 17. In the subtraction operation circuit 17, the digital image signal log S is separated into an image signal obtained by the radiation transmitted through the copper 7 of the filter 5 and an image signal obtained by the radiation transmitted through the aluminum 8. Here, since the aluminum 8 has good radiation transmittance, the amount of radiation energy applied to the stimulable phosphor sheet 6 is large, and the level of the obtained image signal is also large. On the other hand, since the copper 7 absorbs a low energy component of the irradiated radiation energy, the amount of the radiation energy applied to the stimulable phosphor sheet 6 is small, and the level of the obtained image signal is small. Become. Therefore, when the digital image signal log S is filtered to extract the maximum value of a certain neighboring area, an image signal obtained by the radiation transmitted through the aluminum 8, that is, an image signal log S _A representing a low-energy radiation image is obtained. Can be In addition, the digital image signal lo
For g S, the filtering for extracting a minimum value of a neighboring region, the image signal obtained by radiation transmitted through the copper 7, that is, the image signal log S _B representing a high energy radiation image is obtained.

When two images log S _A and log S _B are obtained, the missing portions of the respective image signals are complemented. This complementation is, for example, given the image signal log S _A ,
Since the image signal log S _A is obtained by the radiation transmitted through the aluminum 8 portion of the filter 5 in FIG. 2, the entire image is obtained by the radiation transmitted through the copper 7 portion of the filter 5. image signal log S _B
Is missing. Therefore, the image signal lo
Among g S _A, part image signal log S _B are missing by the separation, is complemented on the basis of the image signal log S _A of the peripheral portion of the missing part, low no missing portion as a whole as a result Image signal lo representing the energy radiation image
g S _A ′ is obtained. Similarly, the image signal log S _B representing a high energy radiation image is also missing portion is complemented, the missing section is not an image signal log S _B 'is obtained.

This complementing method can be appropriately determined according to the size of the filter pattern and the pitch of the filter element.
Of g S _B , aluminum 8a of filter 5 shown in FIG.
If you want to complement the corresponding part, copper 7a above and below it
And the image signals corresponding to the portions 7c and 7c, or the image signals corresponding to the portions of copper 7b and 7d before and after it. Further, the complement may be performed based on the image signal corresponding to the copper 7a, 7b, 7c and 7d, and further, the copper portion outside the copper 7a, 7b, 7c and 7d (the thick line in the figure) May be complemented based on the image signal corresponding to the portion surrounded by.

Further, when a plurality of pixels are included in one grid as in this embodiment, the image corresponding to all the pixels included in the grid portion around the missing portion to be complemented is obtained. The complement may be performed based on the signal, or the complement may be performed based only on the image signals of some pixels adjacent to the missing portion.

In addition, as the complement, an average value, a maximum value, a minimum value, and the like can be appropriately used based on the image signal of the peripheral portion.

[0036] When the image signal log S _A 'and log S _B' is obtained, the two image signals log S _A 'and log S _B'
Suitable weighting is made, is subtracted for each corresponding pixel, digital difference signal _{Ssub = a · log S A '} -b · log S B' -c (a, b are weighting factors, c is a bias component) Is obtained. The difference signal Ssub is subjected to image processing such as gradation processing and frequency processing in an image processing circuit 18, and then sent to an image reproducing apparatus 19 outside the recording / reading apparatus to be used for reproducing a radiation image. The reproducing apparatus 19 may be a display means such as a CRT, a recording apparatus for performing optical scanning recording on a photosensitive film, or temporarily store an image signal in an image file such as an optical disk or a magnetic disk. It may be replaced by a device.

The reason why the digital image signal is treated as a logarithmic value is that band compression of image data is performed and unnecessary image information can be completely removed. The same can be performed by the image signal.

If the coefficients a and b are appropriately determined when performing the above-described subtraction operation, the obtained difference signal S
In sub, the signal component of the portion other than the specific structure is eliminated. Therefore, if an image is reproduced based on the difference signal Ssub, a radiation image in which only the specific structure is extracted can be obtained.

In the above embodiment, a filter in which copper and aluminum are combined in a grid pattern is used. However, there is no particular need to combine them in a grid pattern. For example, as shown in a filter 30 in FIG. May be combined.

In this case, the missing portion may be complemented, for example, based on the image signals of the portions before and after the portion to be complemented. Furthermore, it is not always based on the image signal of the adjacent part, and may be complemented based on the image signals of the part before and after the adjacent part. Further, as shown in the filter 31 of FIG. 5, the filter may be one in which a plurality of minute holes 33 are formed in a copper plate 32.

Further, in the above embodiment, copper and aluminum are used as filter elements, but the present invention is not limited to this. For example, a combination of copper and acrylic, or a combination of copper and gadmium is used. Any material may be used.

Further, in the above embodiment, when separating the digital image signal, the filter for extracting the maximum value and the minimum value of the image signal is used. However, the present invention is not limited to this, and any method may be used. May be used for separation. For example, when a marker is affixed to a filter and the image signal is obtained by reading the stimulating light from the stimulable phosphor sheet, the position of the marker is detected, and based on the information on the position, the position of each marker is determined. The image signal may be sampled to separate the image signal representing the low energy radiation image from the image signal representing the high energy radiation image.

Although the above embodiment is directed to a system for reading a radiation image recorded on a stimulable phosphor sheet to obtain an image signal, the present invention is not limited to a system using a stimulable phosphor sheet. The present invention can be widely applied to a system for obtaining an image signal from an X-ray image recorded on an X-ray film, a radiation image obtained from an image intensifier, or a general image recorded on another recording medium.

[0044]

As described in detail above, the energy subtraction radiographing method for a radiographic image according to the present invention can obtain an energy subtraction image with one recording medium, so that the alignment at the time of the energy subtraction processing becomes unnecessary. In addition, an energy subtraction image with good energy separation and an improved S / N ratio can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an image recording apparatus for implementing an energy subtraction photographing processing method according to the present invention.

FIG. 2 is a diagram showing a filter for implementing the energy subtraction imaging processing method of the present invention.

FIG. 3 is a schematic diagram showing an example of a radiation image information reading apparatus for implementing the energy subtraction imaging processing method of the present invention.

FIG. 4 is a diagram showing another filter for implementing the energy subtraction imaging processing method of the present invention.

FIG. 5 is a diagram showing still another filter for implementing the energy subtraction imaging processing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Subject 2 Radiation source 3 Radiation 5, 30, 31 Filter 6 Storage phosphor sheet 7, 7a, 7b, 7c, 7d Copper 8, 8a Aluminum 10 Laser light source 11 Laser light 12 Scanning mirror 13 Stimulated emission light 15 Photomulti Pliers

Claims (1)

(57) [Claims] An object including a specific structure having radiation energy absorption characteristics different from that of another object is irradiated with radiation, and the radiation transmitted through the object is passed through two types of filter elements having different radiation energy absorption bands. On the receiving surface, the light is transmitted through a filter that is alternately combined at a uniform fine pitch throughout, and the radiation transmitted through the filter is irradiated on the recording medium,
Recording the radiation image information of the subject on the recording medium; obtaining an image signal carrying the radiation image information from the recording medium; and obtaining the image signal by the radiation transmitted through each of the two types of filter elements. A first image signal and a second image signal having missing portions that complement each other at a pitch twice the fine pitch of the filter element. The missing portion is complemented based on the signal value of the peripheral portion of the missing portion, and the complemented first and second image signals are calculated between signals of pixels corresponding to each other, Extracting a difference signal representing an image of the specific structure.