JPS60206392A - Auto density correction method and device of subtraction picture - Google Patents

Abstract

PURPOSE:To obtain a subtraction picture with constant background density by obtaining a histogram of a difference signal to derive its maximum frequency point signal, subtracting the maximum frequency point signal from a standard background density signal bearing a standard background density of a subtraction picture produced by a difference signal and correcting the density. CONSTITUTION:Assuming that a histogram with solid lines is of a difference signal where the density of a background BK of a reproduction picture attains to a favorable standard background density, first, a maximum frequency point signal X of anactual histogram is subtracted from a maximum frequency point signal X0, and its difference DELTAX is obtained. A signal correction circuit 24 adds uniformly the difference DELTAX to a difference signal Ssub introduced from a picture file 19. Accordingly, the difference signal Ssub is corrected so that the maximum frequency point signal of the histogram will be equal to the X0 without fail, and the background density goes to the standard background density in any case in the subtraction picture obtained from the corrected difference signal Ssub.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention uses a stimulable phosphor sheet to perform a radiographic image in detail using a stimulable phosphor sheet to perform a digital 1 knob 1 in a radiographic image to a constant appropriate level in luxation processing. A method and device for automatically correcting the density of a 1J btraction image so as to obtain 11ffl Iu.

(Technical Background of the Invention and Prior Art) Radiographic imaging has been known for some time. This digital subtraction of radiographic images involves photoelectrically reading out two radiographic images subtracted under different conditions to obtain digital image signals, and then using these digital image signals to correspond each pixel of both images. I! This is a method in which the difference signal is reduced by 1η to form an image of a specific structure in a radiographic image.
, Ushi U10 difference signals can be used to reproduce a radiographic image in which only specific structures are extracted.

There are basically the following 4-2 methods for this 1-nabtraction process. That is, the so-called time period in which a specific structure is extracted by subtracting (subtracting) the image signal of a radiographic image in which no contrast agent has been injected from the image signal of a radiographic image in which a specific structure has been emphasized by contrast agent injection. Subtraction processing involves irradiating the same subject with radiation having different energy distributions, then applying appropriate weighting to the image signals of these two radiation images and performing subtraction (subtraction) to identify specific structures. This is a so-called energy subtraction process that extracts images of objects.

This subtraction process is especially useful for medical X-rays.

Because it is an extremely effective diagnostic method for photographic image processing, it has attracted much attention in recent years, and its research and development are actively progressing by making full use of electronic engineering technology. This technology is
In particular, digital extraction processing (usually Digital
1 Radiography) and is abbreviated as DR.

Furthermore, recently, as shown in Japanese Patent Application Laid-Open No. 58-163340, for example, there is a radiation exposure area that is extremely wide. 1! Using two phosphor sheets 1 to 1, these phosphor sheets i are irradiated with radiation that has passed through the object 181- with different stripes 1 with and without contrast agent as described above. The image information +11 of the part where the contrast agent was injected into these phosphor sheets 1~ is the release! It has also been proposed to accumulate and record 8-line images, scan these images with excitation light, read them out, convert them into digital signals, and perform the digital reconstruction using these digital signals. -J2il!Storable phosphor C1~ refers to radiation (X-rays, α-rays, β-rays, γ-rays, ultraviolet rays, etc.) as disclosed in, for example, Japanese Patent Application Laid-Open No. 55-12429.
Shine! 1.l? 1", a part of the radiation energy is accumulated in the phosphor, and then exposed to excitation light such as visible light.
1. Depending on the accumulated energy, -C fluorophores exhibit no phosphorescent light, have a very wide latitude (exposure range), and have extremely high resolution. 6. If the above-mentioned digital rib 1 scanning is performed using the radiation image information accumulated and recorded in the phosphor sheets 1 to 1, it is possible to obtain 1 q radiation image with high diagnostic performance.
can be done.

When a subtraction image is formed on, for example, a photographic material using the difference signal obtained by the time rib 1~raction as explained above, the background, which is the part other than the specific structure injected with the contrast agent, is originally It should be possible to always output at a constant density (or brightness). However, during radiography, even if the radiation intensity is set constant, there are slight variations in the intensity of the actually irradiated radiation, and there are also variations in the sensitivity of the stimulable phosphor C. The density of the background often varies depending on each subtraction image. It has been pointed out that the variation in background density impedes proper diagnosis when making a diagnosis by comparing a plurality of sub-1 motion images.

(Object of the Invention) The present invention has been made in view of the above-mentioned circumstances, and provides an automatic subtraction image correction method and method that can always obtain a subtraction image with a constant background density. 7- For the purpose of providing equipment.

(Structure of the Invention) The automatic deepness compensation iF method of the rib 1 to 31 images of the present invention is performed using the stimulable phosphor sheets 1 to 31 as described above. When the tgIk difference signal is not subjected to gradation processing, the histogram of the difference signal is calculated to find the maximum frequency point signal, and a standard waveform that carries the standard background trend degree of the subtraction image by the difference signal is obtained. Calculate the difference Δχ obtained by subtracting the maximum frequency point signal from the head 81 electric signal, and then i) perform the gradation processing and correct by adding the difference Δχ to a part of the difference signal; 11) use it for the gradation processing; The gradation conversion table is set to the difference Δχ and the value -Δχ, which is equal to absolute 1 and has an opposite sign. 7.

Implement the above method/7 [! When performing the correction in i) above, the automatic atα correction apparatus of the present invention performs the above-mentioned excitation light scanning and photoelectric readout of stimulated luminescence light. An image reading means for obtaining a digital signal of a radiation image of a stimulable phosphor sheet, and a digital image signal read by the image reading means of a subject whose specific structure has been injected with a contrast agent, and a subject whose specific structure has not been injected with a contrast agent. a subtraction calculation means for obtaining a difference signal by subtracting a digital image signal between corresponding pixels to form an image of a specific structure; and image processing for performing gradation processing on this difference signal based on a gradation conversion table. means, a histogram calculation means for calculating the maximum frequency point signal of the difference signal [His] and Durham, and a storage means for storing a standard background density of a sub-1 motion image included in the difference signal; The maximum frequency point signal is subtracted from the standard background density signal carrying the standard background density read out from the storage means, and the difference Δ
and a signal correction circuit that adds χ to the difference signal before undergoing gradation processing.

Further, in place of the signal correction circuit, a gradation conversion table correction circuit that shifts the gradation conversion table in the direction of the ``ljj axis to the input Δχ which has the same absolute value and opposite sign as the difference Δχ; By setting [), the above-mentioned correction 11) can be performed.

In the histogram of the difference signal, [the maximum frequency point density of J is normal → J] - Back of the action image Ej411ifl
Since lσ, 1) or 11) as mentioned above
If this correction is performed, the degree of dorsal inclination will always be set to a constant, standard degree of dorsal inclination in the sub-1 helix image.

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

Figure 1 shows that X-rays 2 transmitted through the same subject 1 are applied to two stimulable phosphor sheets 1-A and B under different conditions. This shows the state of irradiation without any irradiation. That is, for example, in digital imaging (1) igitalanq iography, the first stimulable phosphor sheet 1 to
In A, the X-ray transmission images of the subject 1 are accumulated and recorded before the contrast medium is injected into the inner canal, and then the contrast medium is injected into the vein of the same subject 1. For example, in the case of the abdomen, after about 10 seconds have elapsed. Similarly, the x1fA transmission image of this subject 1 is accumulated and recorded. The tube voltage of the X-ray source 3 is the same, the positional relationship between the subject 1 and the phosphor sheets A and B is also the same, and two X-ray images with no difference other than the presence or absence of contrast agent are A. ,B.

In this way, two radiation images having different image information of the contrast agent injection part are accumulated and recorded on the two stimulable phosphor sheets 1 to A and [3. Next, these two stimulable phosphor sheets A
, B to X by an image reading means as shown in FIG.
The line image is read to obtain a digital image signal representing the image. First, while moving the stimulable phosphor sheet A in the direction of the arrow Y for sub-scanning, the laser beam 11 from the laser beam 110 is caused to main scan in the X direction by the scanning mirror 12, and the stimulable phosphor sheet A is moved in the direction of the arrow Y for sub-scanning. The linear energy is converted into an accumulated and recorded X-ray image and is therefore emitted as stimulated luminescence light 13. The stimulated luminescent light 13 enters the interior of the light condensing plate 14 from one end surface 11- of a light condensing plate 14 made by molding a transparent acrylic plate, and reaches A1 to circle 15 through repeated total reflection. , photostimulated light 13
The light emission ω is output as an image signal QS. This output image signal q3 is converted into a logarithmic value (t) by a logarithmic converter 16 including an amplifier and an AID converter.

qS) is converted into a digital image signal 10g5A. This digital image signal l OQ 3Δ is stored in a storage medium 17 such as a magnetic tape. Next, in exactly the same manner, the recorded image of another phosphor sheet 1-B of the storage 111 is read out, and its digital image signal 1oos is similarly stored in the storage medium 17.

Next, the digital image signal l obtained as described above is
Sub1 to luxion processing is performed using 0GSA 1 l ogSB. FIG. 3 shows the flow of subtraction processing performed while performing automatic density correction according to the first embodiment of the method of the present invention.

First, the digital image signal 1 is extracted from the image file 17A and the image file 17B in the storage medium 17, respectively.
0 (JSA-1ogsB) is read out and input to the subtraction calculation circuit 18. The subtraction calculation circuit 18 subtracts the two digital image signals 100SA and IooS for each corresponding pixel. , a digital difference signal 3sub is generated.This difference signal 5sub is stored in the -tan image file 19, and then,
The image is input to the image processing circuit 20, where it undergoes gradation processing based on the gradation conversion table 20a.

The difference signal 38ub' that has undergone gradation processing is input to a display device such as a CRT, or a reproducing/recording device 21 such as a scanning recorder, and a subtraction image is reproduced and recorded using the difference signal S S LJb'. FIG. 4 shows an image scanning and recording apparatus as an example of a subtraction image reproduction and recording system. While moving the photosensitive film 30 in the sub-scanning direction of arrow Y, the laser beam 3
1 on this photosensitive film 30 in the X direction, and the laser beam 31 is modulated by the image signal from the image signal supply device 33 by the A10 modulator 32.
A visible image is formed on the photosensitive film 30. If the difference signal Ssub' is used as the modulation image signal, images of only six desired specific structures can be reproduced and recorded on the photosensitive film 30 by digital subtraction processing.

FIG. 5 shows how an image of a desired specific structure is obtained by the above-described Jζ beat single translation. In the figure, 4AI is an X-ray image from the first stimulable phosphor sheet 1 to A that records an X-ray image before contrast medium was injected into the abdomen (images q), and 4B is an X-ray image of the same area after contrast medium was injected. An image obtained from the second stimulable phosphor sheet E3 on which the image was recorded, 4C represents the image of 4B, J represents the image of 4A from the digital image signal, 1 blood vessel obtained by reducing the digital image signal This is a 1J block image with only the 1J block visible.

In the subtraction image 4C, the portion of the back 113 around the extracted specific structure (blood vessel) should originally have the difference signal 3sublfiO (zero), and should always have a constant density (bright nail) on the reproduced image. It is. However, the above-mentioned J: Sea urchin photography http line strength variation,
Due to the variations in sensitivity of the stimulable phosphors C1 to △ and B,
The density of this background BK portion varies. Therefore, as shown in FIG. 3, the difference signal 5Sub is input to the histogram stop circuit 22, and the difference signal 35LJ
Find the hisi-gram of b. This histogram is the 6th
Although not shown in the figure, it usually has a large ridge M representing the area of the dorsal mBK and a small ridge representing the specific structure portion into which the contrast agent has been injected. Therefore, the big mountain M
If the position of elBK is always the same, the density of the back elBK will always be constant. However, for the reasons mentioned above, the -F histogram fluctuates as shown by the broken line in FIG. Therefore, if we assume that the solid line histogram in Fig. 6 is a difference signal in which the imi of the background BK of the reproduced image is a preferable standard density (standard background density), first of all, its maximum frequency point signal χ0 (standard background density signal),
The maximum frequency point signal χ of the actual histogram is subtracted, and the difference Δχ (−χ0−χ) is calculated. As shown in FIG. 3, this calculation is performed by storing the maximum frequency 15 one-point signal χ of the actual histogram produced by the histogram calculation circuit 22, and storing the standard background density 1! The standard background density signal χ0 read out from the storage means 23 is input to the signal correction circuit 24, and the signal correction circuit 24 performs the correction. This signal correction circuit 24 then processes the image file 19.
The difference Δχ is uniformly added to the difference signal 5sub. Therefore, in the difference signal 3 S IJ b, the maximum frequency point signal of its histogram is always the above-mentioned χ. The difference signal 3 S IJ after this correction is corrected so that
In the sub]heraction image obtained based on b,
In any case, the back degree is before the above standard [i! I yell a lot.

FIG. 7 shows the flow of subtraction processing for automatic density correction according to the second embodiment of the method of the present invention. In this case, the maximum frequency point signal χ from the histogram calculation circuit 22 and the standard Cao si signal χ0 from the storage means 23 are input to the gradation conversion table correction circuit 12/I. The tone conversion table 20a used in the image processing circuit 20 is of the type shown in FIG.
− After calculating Δχ−χ0−χ in the same way as in 24, the correction term - Δχ
is sent to the image processing circuit 20, and the original gradation conversion table 2 is
0a (solid line in FIG. 8) is shifted in the direction of the input signal axis by -Δχ (broken line in FIG. 8). When the gradation conversion table 20a is shifted in this way, the difference signal S, sub' after gradation processing is always a difference signal in which the maximum frequency point signal of the histogram is the standard background density signal χ0. 3 S LJ b takes the same value as when gradation processing is performed using the original gradation conversion table 20a.

Therefore, in the subtraction image obtained by the difference signal 3sub', the density of -C1 back IBK always becomes the standard background density.

As mentioned above, the standard background density signal χ0 is the difference signal 5 that forms a subtraction image with a preferable standard background density.
In addition to obtaining the maximum frequency point signal of the sub histogram,
In particular, without looking at the histogram of the difference signal 5sub, you can specify the image coordinate point and extract the forward-tilted density signal from the difference signal 5Sub that forms a subtraction image with a standard background density. J represents the standard dorsal abyss 1η
- It may be possible to generate a signal and use that signal.

(Efficacy of the invention Sung Dynasty) As explained in detail above, in this defense, it is necessary to use two sheets of stimulable phosphor sheet 1~, and to always keep the degree of back-order of the printed action image between the two stimulable phosphor sheets. Since it can be set to a constant value, it becomes possible to use sub-1 to traction images that are extremely excellent in diagnosis 1/1 and have high utility value in the medical field.

[Brief explanation of drawings]

Fig. 1 is a 31-picture diagram showing the step of accumulating and recording radiation images in the method of the present invention, and Fig. 2 is a schematic diagram illustrating the radiation image information + IJ reading from the nephrogenic phosphor sheet on which the accumulation and recording described above has been performed. 3 is a schematic diagram illustrating an overview of subtraction processing that performs automatic density correction according to the first embodiment of the method of the present invention; FIG. 4 is a schematic diagram illustrating an example of a subtraction image reproduction/recording system; The figure is a schematic diagram showing an example of a radiographic image with contrast medium injection, a IIi radiographic image without contrast medium injection, and a temporal subtraction image obtained from these radiographic images. A graph showing an example of a histogram, FIG. 7 is the second example of the method of the present invention. ! FIG. 8 is a schematic diagram illustrating the outline of sub-1-raction processing that performs automatic AI 1-degree correction depending on the embodiment, and FIG. 1... Subject 2... X-ray 3... X-ray source 4A, 4B... X-ray image 4C...
Vb1~Raction image 10... Radical light f, 11... Laser light] 2.
... Scanning mirror 13 ... Stimulated luminescence light 15 ... Photomultiple 16 ... Logarithmic converter 18 ... Subtraction calculation circuit 19 - 20 ... Image processing circuit 20a ... Gradation conversion table 22 ...Histogram calculation circuit 23...Storage means 24...Signal correction circuit 124.
... Gradation conversion table correction circuits A, B ... Stimulable phosphor sheet 1 oz, 1 ocks B ... Digital image signal △ 3 S LJ b ... Digital image signal difference signal 3
S LJ b'...Difference signal 20- subjected to gradation processing

Claims (1)

[Scope of Claims] 1) Irradiating each of the two storage 1/1 phosphor sheets with radiation that has passed through a subject in which a contrast agent has been injected into a specific structure and a subject in which no contrast agent has been injected; The image information of the specific structure is emitted in these phosphor sheets 1 to 1) Accumulating and recording tFAiii images, and excitation light is scanned over these phosphor sheets to convert the radiation image into stimulated luminescence light. The amount of stimulated luminescence light is read out photoelectrically and converted into a digital image signal, and this digital image signal is subtracted between corresponding pixels of both images to create an image of a specific structure in the radiation image. In time subtraction processing of radiographic images, which obtains a difference signal to be formed and then performs gradation processing on this difference signal based on a predetermined gradation conversion table, Next, calculate the maximum frequency point signal (a), calculate the difference Δχ obtained by subtracting the maximum frequency point signal from the standard background density signal carrying the standard background i1 degree of the subtraction image by the difference signal, and then 1) the gradation processing 11) A correction in which the difference Δχ is added to the difference signal before the gradation process is performed; 1. An automatic density correction method for a subtraction image, characterized in that one of the corrections for shifting the subtraction image is performed. 2) An image in which excitation light is scanned across a stimulable phosphor sheet on which a radiation image has been stored and recorded, and thereby stimulated luminescence light emitted from the stimulable phosphor sheet is read out photoelectrically and converted into a digital image signal. A reading means, and a digital image signal of a subject whose specific structure has been injected with a contrast agent, which is read by the image reading means, and a digital image signal of the object to which no contrast agent has been injected are subtracted between corresponding pixels. subtraction calculation means for obtaining a difference signal forming an image of the specific structure; image processing means for performing gradation processing on the difference signal based on a gradation conversion table; and a histogram of the difference signal. A histogram operation means for storing the maximum frequency point signal, a storage means for storing the standard background density of the one-nove traction image based on the difference signal, and the standard background density 1α read from the storage means. From the standard NV FA flifi degree signal carrying
and a signal correction circuit that adds to the difference signal before
Automatic 11i 1 degree correction device for Jb1~action images. 3) Storage f1 phosphor sheet 1 in which radiation images are stored and recorded
- an image reading means for scanning excitation light on the phosphor sheet, thereby photoelectrically reading out the stimulated luminescent light emitted from the storage v1 phosphor sheet and converting it into a digital image; 11 Contrast agents are present in specific structures.
A digital image signal of a human subject and a digital image signal of the subject injected with a contrast agent are set to correspond to η
Form an image of the specific 4M structure by subtracting it with the picture index.
a knob traction calculation means for processing the difference signal; an image processing means for performing gradation processing on the difference signal based on a gradation conversion table; and a histogram of the difference signal to find its maximum frequency point signal. a histogram calculation means, a storage means for storing standard background densities of sub-1 to traction images based on the difference signal, and a maximum frequency point signal from the standard background density signal carrying the standard background densities read from the storage means; and a gradation conversion table correction circuit that shifts the gradation conversion table in the direction of the input signal axis by -Δχ, which has an absolute value equal to and opposite in sign to the difference Δχ. Fuchi anti-correction device. -:3-