JPH03132748A - X-ray tomographic device - Google Patents

Abstract

PURPOSE:To decrease artifacts (flow images) by removing the section, such as bone part, where the coefft. of absorption is large from a tomographic image by energy subtraction. CONSTITUTION:Many accumulation type fluorescent material sheets are formed by alternately laminating 2a, 2b, 2c... types and 2a', 2b', 2c'... types of different X-ray absorption energy characteristics. After these sheets are subjected to tomography, the image signals obtd. from the accumulation type fluorescent material sheet 2a and the accumulation type fluorescent material 2b is interpolated to determine the image on the surface of the accumulation type fluorescent material sheet 2a'. The energy subtraction processing is executed by making subtraction processing between the image signal on the surface (position) of the accumulation type fluorescent material sheet 2a' determined in such a manner and the image signal actually read out of the accumulation type fluorescent material sheet 2a'. The exact subtraction is executed in this way and the tomographic image from which the artifacts are more exactly removed is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an X-ray tomography apparatus, and particularly to an X-ray tomography apparatus that uses energy subtraction to reduce flow images.

(Prior Art) An X-ray tomography method that obtains a tomographic image of a subject by blurring areas other than the focal plane is widely known.

This method involves placing an X-ray tube and an X-ray photographic film through the X-ray object, and when irradiating the X-ray, the X-ray tube and the X-ray photographic film are moved using the straight line rule (X The focal point of the ray tube, one point on the tomographic plane, and one point on the X-ray film form a straight line) and the geometric law (the ratio between the distance between the focal point and the tomographic plane and the distance between the tomographic plane and the film is constant) )
By moving the image relative to the X-ray film to satisfy An X-ray image can be obtained.

(Problem to be solved by the invention) In this method, areas other than the desired tomographic plane are blurred, but it is not possible to blur objects that have a large X-ray absorption coefficient, such as bones, so that they become completely invisible. Therefore, there is a problem in that this appears as a flow image superimposed on the tomographic image and becomes an artifact.

Therefore, it is desired to remove this artifact (flow image) and obtain an easily viewable tomographic image.

SUMMARY OF THE INVENTION In response to this demand, it is an object of the present invention to provide an X-ray tomography apparatus that removes flow images and obtains easy-to-see tomographic images.

(Means for Solving the Problems) The X-ray tomography apparatus according to the present invention is characterized by using energy subtraction to remove portions with high absorption coefficients, such as bones, from tomographic images, thereby reducing artifacts.

That is, in the X-ray tomography apparatus according to the present invention, a stimulable phosphor sheet and an X-ray tube are arranged through a subject, and the stimulable phosphor sheet and the X-ray tube are arranged so as to scan a desired tomographic plane of the subject. means for relatively moving the center so as to satisfy the linear law and the geometric law; means for irradiating the stimulable phosphor sheet with X-rays through the object at a plurality of relatively moved positions; irradiating excitation light onto the stimulable phosphor sheet on which an X-ray image of the subject has been accumulated and recorded, causing stimulated luminescence; and reading means photoelectrically reading the stimulated luminescent light to obtain an image signal. In a line tomography apparatus, two or more of the stimulable phosphor sheets are stacked and each of the stimulable phosphor sheets is irradiated with radiation having different energy that has passed through the subject, so that the stimulable phosphor sheets are exposed to the stimulable phosphor sheets. A recording means for accumulating and recording radiation images in which at least part of the image information of a subject differs from each other; and a recording means for photoelectrically reading out the amount of stimulated luminescence generated by scanning excitation light from these stimulable phosphor sheets. an energy subtraction calculation means for subtracting the obtained digital image signal between corresponding pixels of each image to obtain a difference signal to form a radiation image in which an image of a portion of the subject having a large radiation absorption coefficient is erased; The apparatus is characterized by comprising means for reproducing an image of the tomographic plane of the subject from the difference signal.

The energy subtraction used here takes advantage of the fact that a specific structure has unique radiation energy absorption characteristics by detecting the amount of transmission of different energy components when the same subject is irradiated with radiation. Then, an image with a different specific structure is created between two radiographic images, and then subtracting is performed with appropriate weighting between the image signals of these two radiographic images to create an image of the specific structure. It is something to extract.

This subtraction processing is an extremely effective method for diagnosis, especially in image processing of medical X-ray photographs.
It has received a lot of attention in recent years, and its research and development is actively progressing by making full use of electronic engineering technology.

More recently, as shown in Japanese Patent Application Laid-Open No. 58-183340, stimulable phosphor sheets with an extremely wide radiation exposure area have been used, and these phosphor sheets are exposed to the same conditions under different conditions as described above. Radiation that has passed through the object is irradiated to accumulate and record radiation images with different image information of specific structures on these phosphor sheets, and these accumulated images are read out by scanning with excitation light and converted into digital signals. It has also been proposed to perform the subtraction using digital signals. The above-mentioned stimulable phosphor sheet means that when irradiated with radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) as disclosed in JP-A No. 55-12429, When a part of the energy is accumulated in the phosphor and then irradiated with excitation light such as visible light, the phosphor exhibits stimulated luminescence depending on the amount of accumulated radiation energy, and has an extremely wide latitude (exposure range). ) and has extremely high resolving power. Therefore, if the above-mentioned subtraction is performed using the radiation image information accumulated and recorded on this phosphor sheet, sufficient image information can always be obtained even if the radiation dose fluctuates, and a radiation image with high diagnostic ability can be obtained. be able to.

Furthermore, the basic technology for energy subtraction using this type of stimulable phosphor sheet was published in Japanese Patent Application Laid-Open No. 59
It is disclosed in detail in No.-83486.

Note that in the present invention, the stimulable phosphor sheet does not necessarily have to be a separate sheet, and may be placed on the front and back sides of two supports (a filter layer may be sandwiched between them, or a stimulable phosphor sheet with energy absorption properties). The stimulable phosphor layer may have two different stimulable phosphor layers, or it may be a coated integral type.

Also, "by irradiating radiation with different energies" means:
Not only can a radiation absorbing filter be interposed between two or more stimulable phosphor sheets for irradiation, but also two or more stimulable phosphor sheets with different radiation energy absorption characteristics can be used as a result. This also includes cases in which cumulative recording is performed as if radiation with different energies were irradiated. Furthermore, even if similar stimulable phosphor sheets are stacked, the support of the upper sheet acts as a filter, and this includes cases in which the effect is substantially the same as when a filter is interposed.

(Operations and Effects) According to the X-ray tomography apparatus of the present invention, image signals of radiation images taken on two or more stimulable phosphor sheets during tomography are subtracted between corresponding pixels by means of energy subtraction. By doing so, it is possible to obtain a tomographic image in which images of structures with a large radiation absorption coefficient, such as bones, are removed.

Furthermore, if the apparatus of the present invention is used with a large number of stimulable phosphor sheets having different absorption energy characteristics stacked alternately, it is possible to perform multilayer tomography with fewer artifacts, as will be described in detail later.

Tomography is particularly performed on the chest, and is used to confirm the location of tumors, etc. However, the chest has many artifacts due to bones outside the focal plane, and the device of the present invention is particularly useful in this field.

Note that since quantitative shadows appear blurred, artifacts can be easily removed even if energy subtraction is performed using appropriate parameters.

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

FIG. 1 shows an example in which a horizontal linear movement method is adopted as the method of moving the X-ray tube and the stimulable phosphor sheet.

X-ray tube 1 and two stimulable phosphor sheets) 2A.

A sheet stack 2 formed by stacking 2B with an X-ray filter 3 interposed therebetween is arranged with an X-ray object 4 in between. The X-ray filter 3 is a thin metal plate such as Cu that partially absorbs X-ray energy, and the upper stimulable phosphor sheet 2A absorbs more X-rays than the lower stimulable phosphor sheet 2B.
It is designed to accumulate linear energy.

During imaging, the X-ray tube 1 irradiates the X-ray subject 4 with X-rays while moving the X-ray tube 1 and sheet stack 2 in the directions of arrows 5 and 6, respectively. As a result, the stimulable phosphor sheet 1-
The tomographic plane of the X-ray object imaged on 2A and 2B is always an intersection 8 formed by the X-rays 7a emitted from the X-ray tube 1 as the X-ray tube 1 moves. Since more accurate subtraction can be achieved when the two stimulable phosphor sheets 2A and 2B are placed as close together as possible, the filter 3 needs to be as thin as possible (thickness can be ignored). Instead of using the filter 3, if two stimulable phosphor sheets having different X-ray energy absorption characteristics are used, the two sheets can be placed closely together.

Next, an X-ray image is read from these two stimulable phosphor sheets 2A and 2B 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 2A in the direction of the arrow Y for sub-scanning, the laser beam 11 from the laser light source 10 is caused to main scan in the X direction by the scanning mirror 12, and the stimulable phosphor sheet 2A is moved in the direction of the arrow Y for sub-scanning. Accumulated X-ray energy,
It is emitted as stimulated luminescence light 13 according to the accumulated and recorded X-ray image. Stimulated luminescence light 13 is transmitted from one end surface of a light condensing plate 14 made by molding a transparent acrylic plate to this light condensing plate ■
The light enters the interior of the stimulated luminescent light 13 and reaches the photomultiplex 15 through repeated total reflection, and the amount of stimulated luminescent light 13 is output as an image signal S. This output image signal S is sent to an amplifier and A.
A logarithmic converter 1B including a /D converter converts the logarithmic value (1ag
S) digital image signal l.

converted to gSA. This digital image signal l.

The gSA is stored in a storage medium 17 such as a magnetic disk. Next, in exactly the same manner, the recorded image on another stimulable phosphor sheet 2B is read out, and its digital image signal logsB is similarly stored in the storage medium 17.

Next, the digital image signal 1o obtained as described above is
gSAs Subtraction processing is performed using IogSs. FIG. 3 shows the flow of energy subtraction processing used in one embodiment of the apparatus of the present invention. First, the digital image signal lo is obtained from the image file 17A and the image file 17B in the storage medium 17, respectively.
gsAS logSB is read out and input to the subtraction calculation circuit 18. The subtraction calculation circuit 18 receives the two digital image signals 10g5A and 10g5A.
ogS, is subtracted for each corresponding pixel with appropriate weighting, and digital difference signals 5Sub-a, 10g5A-b, 1agSR+C (aS
(b is a weighting coefficient, and C is a bias component that makes the density approximately constant). By appropriately determining this weighting coefficient, it is possible to eliminate images of objects such as bones, which have a large X-absorption coefficient (which is an artifact of the flow image). This difference signal 5sub is stored in the -tan image file 19, and then input to a display device such as a CRT, or a reproduction/recording device 20 such as a scanning recorder, and a subtraction image from which the above-mentioned artifacts have been removed is generated by the difference signal 5sub. is played back and recorded.

FIG. 4 shows an image scanning and recording apparatus as an example of a subtraction image reproduction and recording system. The photosensitive film 30 is moved in the sub-scanning direction of the arrow Y, and the laser beam 31 is main-scanned on the photosensitive film 30 in the X direction. The modulation forms a visible image on the photosensitive film 30. If the difference signal 5sub is used as the modulation image signal, a tomographic image from which artifacts due to digital subtraction processing have been removed can be reproduced and recorded on the photosensitive film 30.

The device of the present invention can also be applied to multilayer tomography. An embodiment applied to simultaneous multilayer tomography will be described with reference to FIGS. 5 and 6.

This replaces the sets of stimulable phosphor sheets in the embodiment of FIG. 1 with three sets, ie, 2a and 2a' in FIG.
Three sets of stimulable phosphor sheets, set 2b, set 2b', set 2c, 2c', are arranged in parallel.
Each set is a combination of two sheets having different X-ray absorption energy characteristics. These three sets of stimulable phosphor sheets are housed in one cassette 9.

During imaging, X-rays are irradiated from the X-ray tube 1 to the X-ray subject 4 while moving the X-ray tube 1 and the cassette 9 in the directions of arrows 5 and 6, respectively. In this way, for example, the stimulable phosphor sheet 2
The tomographic plane of the X-ray object imaged on the set of a and 2a' is
The intersection portion 8a is formed by the X-rays 7a, 7a' irradiated from the ray tube 1 as the X-ray tube 1 is transported, and the stimulable phosphor sheets 2b, 2b' and 2c, 2 are similarly formed.
The cross-sectional layer of the X-ray object imaged in the group c' is the X-ray 7c emitted from the X-ray tube 1.

Intersecting portion 8 formed by 7e' as the X-ray tube 1 is transferred
b and 8C.

This simultaneous multilayer tomography method can obtain images of multiple tomographic planes of an X-ray object in a single scan, so for example, for moving organs such as the heart and lungs, tomographic images with exactly the same motion phase can be obtained. In other parts of the body, images of multiple tomographic planes can be obtained without any movement of the subject, which is normally unavoidable between layered images. It is convenient for diagnosis because it reduces the burden on patients.

In the embodiment of the simultaneous multilayer tomography method shown in FIG. By performing the processing, it is possible to obtain a tomographic image in which artifacts (flow images) such as bones are reduced in each cross section.

This subtraction between a large number of stimulable phosphor sheets may also be performed as follows. As shown in FIG. 6, a large number of stimulable phosphor sheets 2a and 2b with different X-ray absorption energy characteristics are used.

2c... type and 2a', 2b', 2
c'...types are alternately stacked, tomographic imaging is performed on this in the same manner as described above, and image signals obtained from the stimulable phosphor sheet 2a and the stimulable phosphor sheet 2b are interpolated. , obtain an image on the surface of the stimulable phosphor sheet 2a'. The image thus obtained is closest to the image actually recorded on the stimulable phosphor sheet 2a' than the image recorded on the stimulable phosphor sheet 2a or 2b. A subtraction operation is performed between the image signal of the image on the surface (position) of the stimulable phosphor sheet 2a' obtained in this way and the image signal actually read out from the stimulable phosphor sheet 2a'. Then, perform energy subtraction processing. As a result, accurate subtraction can be performed, and a tomographic image in which artifacts are more accurately removed can be obtained.

Similarly, an image on the surface of the stimulable phosphor sheet 2b is obtained by interpolation from the stimulable phosphor sheets 2a' and 2b', and subtraction processing is performed between this and the image of the stimulable phosphor sheet 2b. A tomographic image on the surface of the stimulable phosphor sheet 2b is obtained.

Thereafter, the above processing is repeated for each cross section in the same manner to obtain a multilayer tomographic image with better image quality.

Note that the X-rays that have passed through the X-ray object are attenuated as they pass through multiple stimulable phosphor sheets, and the upper layer of the stimulable phosphor sheet has a higher concentration, while the lower layer has a lower concentration. It is necessary to correct variations in the concentration of each layer by adjusting the sensitivity of the stimulable phosphor sheet, but it is generally extremely difficult to achieve such sensitivity balance. There is also a limit to increasing the sensitivity of the body sheet. Therefore, by performing superposition processing at the same time, a high-quality multilayer tomographic image with less noise can be obtained.

(The superimposition process in multilayer tomography was developed in Japanese Patent Application Laid-open No. 58
The disclosure is in No.-86933. )

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the operation of the imaging section of a tomography apparatus according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing the image reading section thereof, and FIG. 3 is a schematic diagram showing the subtraction processing section and reproduction section thereof. A block diagram, FIG. 4 is a schematic diagram showing an example of the reproduction device, FIG. 5 is a schematic diagram showing the operation of the imaging unit of a multilayer tomography apparatus according to another embodiment of the present invention, and FIG. 6 is a further different embodiment. FIG. 2 is a partial side view showing an example of a laminate of stimulable phosphor sheets. 1... X-ray tubes 2A, 2B, 2a, 2a' - Storable phosphor sheet 3... Filter 4... Subject 8...
・Intersection part 11... Laser beam 13... Stimulated luminescence light 14... Condenser plate 15... Photomultiple 18... Subtraction calculation circuit 20... Reproduction/recording device Fig.

Claims (1)

[Scope of Claims] A stimulable phosphor sheet and an X-ray tube are arranged through a subject, and the stimulable phosphor sheet and the X-ray tube are arranged according to a straight line rule with a desired tomographic plane of the subject as the center. means for relatively moving the stimulable phosphor sheet so as to satisfy the law of proportions; means for irradiating the stimulable phosphor sheet with X-rays at a plurality of relatively moved positions through the object; An X-ray tomography apparatus comprising a reading means for irradiating excitation light onto the stimulable phosphor sheet on which an image has been stored and recorded to cause stimulated luminescence, and photoelectrically reading the stimulated luminescent light to obtain an image signal, Two or more of the stimulable phosphor sheets are piled up and the stimulable phosphor sheets are irradiated with radiation having different energies that have passed through the subject, so that at least a portion of the subject is irradiated onto these stimulable phosphor sheets. A recording means for accumulating and recording radiation images with different image information, and a digital image signal obtained by photoelectrically reading out the amount of stimulated luminescence generated by scanning excitation light from these stimulable phosphor sheets. , energy subtraction calculation means for obtaining a difference signal by subtracting between corresponding pixels of each image to form a radiation image in which the image of a portion of the subject with a large radiation absorption coefficient is erased; An X-ray tomography apparatus comprising means for reproducing an image of a tomographic plane.