JPS6185928A - Method and apparatus for improving quality of energy subtraction image - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to subtraction processing of radiographic images, specifically, in digital subtraction processing of radiographic images performed using a stimulable phosphor sheet, the image quality of subtraction images is improved. The present invention relates to a method and an apparatus for doing so.

(Technical Background of the Invention and Prior Art) Digital subtraction of radiographic images has been known for some time. This digital subtraction of radiographic images is to photoelectrically read out two radiographic images recorded under different conditions, to create a digital image (after setting n to 19), and to convert these digital image signals into corresponding pixels of both images. This is a method in which a difference signal is extracted to form an image of a specific structure in the radiographic image Q by subtraction processing, and only the specific structure is extracted using the difference signal obtained in this way. The radiographic image 1ψ can be reproduced.

There are two basic methods for this 4J attraction process: In other words, the radiographic color emphasizes the J-stiff specific structure due to contrast agent injection! So-called temporal subtraction processing extracts specific structures by subtracting (subtracting) the image signals of radiographic images in which no contrast agent has been injected from image 41:3@, and extraction of different energies for the same subject. By irradiating radiation with a distribution, and thereby making use of the fact that 1η constant structures have unique radiation energy absorption characteristics, images with different specific 11'4 structures exist between two radiation images, and one of them These two radiation images "9 images l!jl signals are appropriately weighted and subtraction is performed to extract an image of a specific structure. be.

This subtraction processing is an extremely effective method for diagnosis, especially in image processing of X-ray photographs for medical F/I, so in recent years it has been attracting attention to the hole, and its research and development is being carried out by making full use of electronic engineering technology. /ν is being advanced.

More recently, as shown in Machima Sho 58-163340, for example, stimulable phosphor sheets having a sharp and wide exposed area of the radiant rays have been used, and these phosphor sheets are coated with the above-mentioned methods. By irradiating the phosphor sheets with radiation that has passed through the same YIQ body under different conditions, the image information of the specific structure is different on these phosphor sheets, so the Q dimension is 2! Accumulate and record images,
J! Two proposals have been proposed. , the phosphor sheet is a phosphor sheet as disclosed in JP-A-55-12429, for example.
; J-rays (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.)
When irradiated with radiation, part of the radiation energy is accumulated in the phosphor, and when excitation light such as visible light is irradiated, the phosphor emits stimulated luminescence depending on the accumulated radiation energy, which is extremely Has a wide radius (exposure range),
It also has extremely high resolution. Therefore, if the digital subtraction is performed using the radiographic image information accumulated and recorded on this phosphor sheet, sufficient image information can always be obtained even if the radiation dose fluctuates, and radiographic images with high diagnostic ability can be obtained. 1! can do.

However, when two accumulative images as described above (1'i are stored and recorded on a photoreceptor sheet of a subject including bone and soft tissue, and bones are removed by performing energy rib I/rough contrast), The image signal of the extracted soft tissue is the difference signal generated by the sub 1 to radial calculation processing. Therefore, there is a problem that the S/N is low, and the image quality of the soft silk texture extraction image is therefore poor.

(Objective of the Invention) Therefore, the present invention provides a method for improving energy subtraction images that can sufficiently improve the image quality of 4'i-soft tissue extraction images as described in above. The purpose is to use the equipment.

(Structure of the Invention) The method for improving the image quality of energy subtraction images of the present invention uses two or more stimulable photoreceptor sheets to form an image in which bones are removed from a radiographic image of a subject that includes bone and soft tissues. In energy subtraction to obtain a difference signal, the incoming signal subtracted by subtraction is used for the pixels in the area where the meter exists, and the original image signal read out from the stimulable phosphor sheet is used for the pixels in other areas. The system is characterized in that a radiographic image of the subject is reproduced using the .

The above original 1i1ii9 signal may be the digital image signal itself read out from one stimulable phosphor sheet, or the signal obtained by adding and averaging the digital image signals read out from each of multiple stimulable phosphor sheets. etc. can be used.

The above method scans excitation light onto a stimulable phosphor sheet on which an emission IA image has been stored and recorded, and thereby photoelectrically reads out the stimulated luminescent light emitted from the stimulable phosphor sheet. An image reading means for converting into a digital image signal, and 51i! When the subject is irradiated with rays of light, at least some image information of the subject becomes insignificant.
The image reading means reads one image from each of the two or more stimulable phosphor sheets on which Ml iji images have been accumulated and recorded.
η is 11 times the subtraction between the corresponding images M of each digital image signal.
1, thereby forming a difference signal forming an image in which the bone is removed W'J and a difference signal forming an image in which the soft tissue phase is removed! ?・Lapthicone a stop means and a means to form an image in which the soft tissue has been erased. an identification means for outputting a circle, the original image I8 read from the above-mentioned shi~1-, and fli
Differences that form an image in which bones have been erased 1. ;8 is input, and the position 18 is input from the +iff identification means.
A signal is input, and by referring to this position signal, it is determined whether the bone in the radiographic image exists ("has the bone been erased as a pixel image 3 in the blank area?"). , and signal selection means for outputting the original image signals as pixels (38) of other parts.

N a3 As mentioned above, in the method of the present invention (Y), one radiographic image is formed by the difference signal obtained by subtraction and the original image signal g. At least one of the two signals is adjusted to match the other's 1g degree range, contrast range, or edge Iff range and contrast range so that the two signals are combined without any discomfort. It is preferable to perform contrast correction or density J3 and contrast correction.

(Embodiments) Hereinafter, the present invention will be described in detail based on embodiments not shown in the drawings.

Figure 1 shows two stimulable phosphor sheets A and B with lung fields and I.
11' Identical subject 1 having soft tissues such as canals and bones
) shows the state in which the X-rays 2 that pass through the tongue are irradiated with different energies. That is, the order of X-ray transmission of the subject 1 is stored and recorded on the first stimulable phosphor sheet △, and then, within a short period of time, the X By changing the tube voltage of the radiation source 3, the X-ray image of the subject 1 where the L energy of transmitted X-rays is 5
℃ body sea 1-131. : ,'? Record the product. At this time, it is assumed that the positional relationship of the subject 1 between the stimulable phosphor sheets 8 and 8 is the same.

In this way, two radiographic images having at least six different image information tR are stored on two stimulable 97 light sheets A and B.
Accumulate and record. Next, both xI2 images are read from these two stimulable phosphor sheets Δ and B by an image reading means as shown in FIG. 2 to obtain a digital image signal representing the image. First, while moving the stimulable phosphor sheet 8 in the direction of the arrow Y for sub-scanning, the laser beam 11 from the laser light source AO is caused to main scan in the X direction by the scanning mirror 12, and from the phosphor sheet △. Accumulated X-ray 1 energy,
It is emitted as stimulated luminescence light 13 according to the accumulated and recorded X-ray image. Stimulated luminescence light +3LJi is a product of the light condensing plate 14 made by molding a bright acrylic plate; it enters the inside of this condensing plate 14 from the surface, and repeats total reflection inside the light A.
Tomaru 15 is reached, and the amount of luminescence of stimulated luminescence light 13 is
It is output as a signal S. This output ii! ii The image signal S is a logarithm 'Ej 1 including an amplifier and an A/[) converter.
It is converted into a digital image signal MIOgS of 1fI (IOQs). This digital image f3 No. 10GsA is stored on a storage medium 1 such as a magnetic disk.
7 is stored. Next, in exactly the same manner, the recorded image on another stimulable phosphor sheet B is read out, and its digital image signal 10QSB is similarly stored in the storage medium 17.

Next, the digital image H bow 1 created as described above is
ooS8, 11 Navtraxicon processing using 1OQsB. FIG. 3 shows a subtraction process 11t! performed by applying a method for improving the image quality of an energy subtraction image according to an embodiment of the method of the present invention. It shows the flow. First, the digital image signals ilog38 and logSB are read out from the image file 17Δ and the image file 17B in the storage medium 17, respectively, and input into the subtraction performance circuit 18. The subtraction performance Q circuit 18 receives the two digital image signals ";"31.
0 '1 SQ and IQ (jsB is suitably reduced and then reduced for each corresponding pixel, the digital difference is 1.18S
sub=a-+0QsA-b-10Q S3 +C
(a, b are weighted 1p coefficients, C is a bias component that makes a straight path constant cJ). This difference signal Ss
ub is stored in the image 7/il 19A, and transmitted through the IR circuit 20 (to be described later) to a display device such as a CRT; a'2+, and the difference signal 3 S L
The subtracticon image is reproduced and recorded by Jb. FIG. 4 shows an example of a sub-action image reproducing and recording system shown in No. 6 of the image running system 11 but not shown. When the photosensitive film 30 is moved in the sub-scanning direction of arrow Y, the ray beam 31 is moved to the photosensitive film 30'7.
is main-scanned in the X direction, and the radome 31 is modulated by the image signal from the image signal supply device 33I) by the Δ10 modulator 32, thereby forming a visible image on the photosensitive film 30 in the form 1+Q7r. Ru. As this image signal for modulation,
By using the Difference No. 13 5sub, it is possible to reproduce and record on the photosensitive film 30 an image of only a desired specific groove structure by digital subtraction processing.

Here, the image based on the difference signal 3 SLJ b is the X-ray image of the subject 1 stored in the image file 17A or the image file 17B, for example, as shown in (△) in FIG.
As shown in FIG. ), the bone 6 is erased and only the soft tissue 5 is extracted. The above difference IStan3sub is stored in -tan'#1@file 19A.

Next, the above-mentioned subtraction calculation circuit 18 performs the same calculation as above S S U b'-a' ・l OQ S p,
b'·l OQ S B + C'(a' and b' are smoke coefficients, and C' is a bias component that is approximately constant: 9 degrees). Here, the above coefficients a', b'
, c' are appropriately selected IR, the difference 3 S LJ b' can be reproduced by the reproducing/recording device 21 as described above.
The image (06) in which the soft tissue 5 is erased and the two X-ray images are reproduced (as shown in FIG. 5(C))
Only the following will be extracted. However, this l4rs No. 3 Sub' is not inputted to the record 1)2 position 21 again, but is stored in the image-77 file 19B.

As mentioned above, by performing the calculation 3sub-a・l0g5A-b・toO8B10 and reproducing the X-ray image using this difference signal 5sub, the bones 6 are erased and only the soft tissue 5 is extracted, making the diagnosis possible. However, the image quality of the soft part 1fI tissue 5 of this bone-erased image is determined by the original image signal, that is, the digital image signal l0QSA or the digital both BI
The quality of the soft tissue in the image formed from the QIO QSB is 6 inferior. In other words, image No. 15 (i.e., difference signal n S S LJ b ) forming the above-mentioned bone-erased image is
It is obtained by applying the above-mentioned "Una operation (sub 1 to raction)" to the digital image signal 10GSA and the digital image (No. 3 logSB), and of course it is a digital image signal (No. 10QS4 or digital image Signal 1゜g
This is because the S/N is lower than that of SB.

Therefore, as shown in Fig. 3, the digital image signal qlo
QsA and digital image signal log3 Addition and averaging circuit 2
2, 7S, 8, and 10Qss are inputted to both signals to, and are averaged after being appropriately weighted, and the averaged signal is then added to an appropriate density and J in a degree and/or contrast correction circuit 23. : and/or contrast correction is performed and then stored in the -/v image file 24. This averaged signal indicates the original image and is input to the signal selection circuit 20 as the original image No. 13 10QSo. This signal selection circuit 20 also includes an image file 193.
Receives the difference signal qSsub' (which carries the image from which only bones are extracted as described above) stored in the
A position signal 8Sp of the bone 6 outputted from an identification circuit 25 that identifies the position of the portion where the detection 6 of J5 is present in the X-ray image is input. This identification circuit 251j, for example, converts the image signal 5sub' of all pixels to a predetermined threshold I17'i.
If the value of a certain pixel exceeds the threshold 1+?i, that pixel is formed to be identified as a pixel in the part 6. The selection circuit 20 receives the above-mentioned positional signal Sp, and selects the difference signal S s u b for the pixels in the portion where the detection 6 is (r rr ) out of all the pixels of the reproduced X-ray images, and the other pixels. For the pixels in the portion, the original image signal 10g5o from the image file 24 is selected and output.

In this way, the difference (g'74
3sub or original image f, i p log So
The X-ray image ff was reproduced using the
Q becomes a bone-erased image as shown in ([3)] in Figure 5 of l'IQ. Zunawa I) The t2 difference signal SS IJ b is used as the image signal of both sides of the part where the bone 6 is present, while the original image No. 43 1ogso without subtraction is used as the pixel image 15 of the other part. Since the reconstructed X-ray image (t1! is the one in which the bone 6 has been deleted and only the soft tissue silk!:&5 has been extracted), the original image (ij ``y l OQ S o H2 The original image of (,i′;″,1OaS8,10QsB?y
Since the S/N is naturally higher than the difference signal S S LJ b processed by i, this reproduced X-ray image has a In other words, in this reconstructed X-ray image, the image quality deterioration due to the subtraction FQn principle is suppressed to only the areas where bones are present. become.

Note that the above-mentioned J: sea urchin original image signal logso is the density OJ,
The density (6) and/or contrast are corrected by the contrast correction circuit 23, but this correction is applied to the area other than the area where the bone 6 is present based on the original image signal 1ogso, and the difference signal 8S. This is done in such a way that the part where the bone 6 is present due to the and/or contrast correction may be performed manually based on experience and the original image signal 10c.
] so and the difference P 'r S S LJ b
It may also be done manually while being displayed on RT or the like. Furthermore, the difference No. 18 S S LJ b between the two systems at a predetermined specific point of the soft tissue is input to the concentration and 1.' or the correction circuit 23, and the difference (is 4: Original image signal 10S. The original image signal +008o can be corrected to the same value as white.
The original image is 15 January 1.
0QsO to SJL, then use V instead, difference signal 3 S IJ
It may be applied to b, or depending on 1gJO, it may be applied to both the original image (3910g5oJ and difference IM sub). Such degree and/or contrast 1- correction is not necessarily Although it is not necessary, if it is implemented, a natural-looking reproduced image in which the two parts of the illegal signals are combined without any discomfort can be obtained.

Further, the identification circuit 25 automatically identifies the position of the bone 6 by comparing the predetermined threshold value and the image signal 361J b ′ as described above, and also automatically identifies the position of the bone 6 in the image a! Wet'；3S S u b
The image may be displayed on a CRT or the like, and the operator may manually input the IM 'It information of the bone 6 while viewing the display.

In the above embodiment, the digital image signal log SA obtained from each of the two stimulable phosphor sheets and the summed average signal of 109SB are used as the original image signal log8, but the log SA is used as the log3o.
It goes without saying that either J'j or IQ (IsB) may be used.

Implementation using the above two stimulable phosphor sheets A and B!
As explained above, three or more stimulable phosphor sheets are emitted with different energies, and digital images are folded from these sheets (by subtracting the brush signal, a difference signal of 10g5o is obtained (q RukoC→-d, where a, b
, c is a weighting coefficient, and d is a bias component that makes the difference r51og3o approximately constant density).Therefore, the present invention also applies when three or more such stimulable phosphor sheets are used. Applicable.

Furthermore, in the embodiment described above, two sheets A, [
Is it possible to accumulate and record the line images on the 3 sheets by separately irradiating each sheet with 1 line of radiation with different energies? However, the method of rapidly accumulating and recording late rA line drawings on multiple sheets is not limited to this, and
i 59-8348 [; stimulable phosphor sheet laminate or stimulable phosphor sheet-
It may be carried out in a single radiation irradiation using a filter ra FZ body. That is, I5, multiple accumulative 9? As long as each light sheet is irradiated with 04 rays because the energy transmitted through the same object is different from each other, 2. II There is no 11.

Although the present invention has been described above using the terms "bone" and "soft tissue,"
For example, energy sub 1 to laxation is an image obtained by erasing the metal fittings from a line image of a human body in which a therapeutic metal fitting etc. has been implanted. It can also be applied to erase the image of the bone. It also includes metals, contrast agents, etc. that can be regarded as soft tissue, and "soft tissue" includes anything that has radiation absorption properties similar to the above "related" and can be extracted on a radiographic image by energy subtraction.

<Effects of the Invention> As explained in detail above, according to the present invention, it is possible to reliably improve the image quality of extracted soft tissues in f) erased images in which kidney parts are erased by energy subtraction. , energy +) The diagnostic ability of rupture images will be improved to a greater extent than ever before.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the step of accumulating and recording yl ray images in the method of the present invention, and Fig. 2 is the above? A schematic diagram illustrating the reading of radiographic image information from a stimulable phosphor sheet on which 8-product recording has been performed. 4 is a schematic diagram showing an example of a reproducing/recording system for rib 1 to traction images. FIG. 5 is an explanatory diagram illustrating the energy rib 1 to traction according to the present invention. 1. ...Subject 2...X-ray 3...X-ray source 5...Soft tissue 6...Bone
10... Laser light source 11... Laser light 1
2... Scanning mirror 13... Stimulated luminescence light 15.
... Photomaru 18 ... Subtraction control circuit 20 ... Signal selection circuit 21 ... Reproduction recording device 2
5...Identification circuit A, B...Storage t11 Fluorescent sheet 10QSA, l 0QSB...Digital image signal 3
sub...Digital image signal g sub signal 910QsO...
・Original image signal g Sp...Position signal Fig. 1 Fig. 3

Claims (4)

[Claims] (1) Two or more stimulable phosphor sheets are each irradiated with radiation having different energies that have passed through an object including bones and soft tissue, and these phosphor sheets are exposed to at least a portion of the object. Radiation images with different image information are stored and recorded, and excitation light is scanned across these phosphor sheets to convert the radiation images into stimulated luminescence light, and the amount of luminescence of this stimulated luminescence light is measured photoelectrically. In energy subtraction, the bone is read out and converted into a digital image signal, and a subtraction of this digital image signal is performed between corresponding pixels of each image to obtain a difference signal forming an image in which the bone of the radiographic image is erased. The radiation image of the subject is reproduced by using the difference signal for pixels in a portion where the image is present and using the original image signal read from the sheet for pixels in other portions. How to improve the image quality of subtraction images. (2) Energy subtraction according to claim 1, wherein at least one of the difference signal and the original image signal is subjected to density and/or contrast correction in accordance with the density range and/or contrast range of the other. How to improve image quality. (3) The energy according to claim 1 or 2, wherein an average signal of the digital image signals read from the two sheets is used as the original image signal. How to improve the image quality of traction images. (4) Excitation light is scanned across the stimulable phosphor sheet on which the radiation image has been stored and recorded, and the stimulated luminescent light emitted from the stimulable phosphor sheet is thereby photoelectrically read out and converted into a digital image signal. two or more radiographic images in which at least part of the image information of the subject differs from each other by irradiation with radiation of different energy transmitted through the same subject including bones and southern tissues; subtraction is performed between corresponding pixels of each digital image signal obtained by the image reading means from each of the stimulable phosphor sheets, whereby the difference signal forming an image in which the bone is erased and the soft tissue is a subtraction calculation means for obtaining a difference signal forming an image in which the soft tissue has been erased; and a subtraction calculation means for identifying a portion where a bone exists in the radiographic image based on the difference signal forming an image in which the soft tissue has been erased, and generating a position signal thereof. an identification means that outputs an original image signal read from the sheet and a difference signal forming an image in which the bone has been deleted, and the position signal is inputted from the identification means; With reference to the position signal, a difference signal forming an image in which the bone has been deleted is output as a pixel signal of a portion of the radiographic image where bone and soft tissue overlap, while a difference signal forming an image in which the bone has been deleted is output as a pixel signal of the original image as a pixel signal of other portions. An image quality improvement device for energy subtraction images, comprising a signal selection means for outputting a signal.