JPH02244881A - X-ray diagnostic device - Google Patents

Abstract

PURPOSE:To eliminate sufficiently a scattered X-ray signal component in a detected X-ray signal by subtracting a total scattered X-ray component signal obtained through the synthesis of the scattered X-ray component signals for each thickness from an X-ray signal data from an X-ray detection means. CONSTITUTION:An X-ray transmitted through an object 3 is detected by an X-ray detection means 4 and an X-ray signal corresponding to an incident X-ray is outputted. The X-ray signal data is compared respectively with comparison level signals S1-Sn corresponding to the thickness of the object depending on the diagnostic condition thereby classifying the data according to the thickness of the object. Filtering calculation is executed to the classified X-ray signal data with a relevant filter coefficient corresponding to the classified thickness independently respectively. Then a scattered X-ray signal component is calculated for each classified thickness of the object, the signals are synthesized to obtain the total scattered X-ray component signal. The signal is subtracted from each picture element from the X-ray signal data obtained by the detection means 4. Thus, the X-ray signal data of the direct X-ray component only whose scattered X-ray signal component is finally eliminated is obtained.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention is an X-ray system that creates a visible image based on transmitted X-ray information obtained by irradiating an object with X-rays and uses it for medical diagnosis. The present invention relates to a radiation diagnostic device.

(Prior Art) In general, in an X-ray diagnostic apparatus, not only direct X-rays but also scattered X-rays scattered by an object or the like are incident on a detector for detecting X-rays. Since this scattered X-ray is the main cause of deteriorating the contrast sharpness of an image, its removal is very important.

Therefore, various methods for removing such scattered X-rays have been proposed in the past. As an example, JP-A-59-1
No. 51940 discloses a correction means using a digital filter. The correction means includes an averaging calculation means for calculating an average value Irn obtained by averaging the X-ray data Im output from the detector of the X-ray diagnostic apparatus over the X-ray irradiation field; and 0.5 to 1.5. ), the average value 1rn output from the averaging calculation means is directly calculated as the average value I of the X-ray data.
1m-Ip conversion calculation means for converting into p, and the average value 1
An n-th power calculation means for calculating (Ip)n from p, and (ip)n! outputted from the n-th power calculation means. t) A (1-
n) (I p) A first multiplier that operates 11 on n, and from the X-ray data 21m output from the detector, the first
Output A (1-n) (I p) from the multiplication means of
Directly calculate X-ray data Ip (x, y) using a subtraction means for subtracting , and a filtering characteristic H defined by the subtraction result Tm outputted from the subtraction means, a system response function, and a scattered X-ray response function. and filtering calculation means.

The correction means using such a stationary filter is based on a function (P
o1nt 5pread Function:PS
F) A system in which the value does not change much depending on the thickness of the subject,
For example,
V) Effective for imaging or fluoroscopic equipment using a grid in a chain system.

(Problems to be Solved by the Invention) Computed radiography using an imaging plate other than the above-mentioned II-TV chain diagnostic equipment, for example,
: CR) and other shooting systems! Even if it is an I-TV chain type diagnostic device, in the case of an imaging device that does not use a grid, the PSF generally changes depending on the thickness of the subject. Therefore, with regard to the II-TV chain type diagnostic apparatus that does not use CR or grids as described herein, the scattered X-rays cannot be removed by the above-mentioned conventional correction means.

Although this is an extreme example, if there is a region of a bus (airbus) in the image that does not pass through the subject at all, it is clear that no scattered X-rays are generated from that region.

However, if an attempt is made to correct the scattered X-rays using a stationary filter as in the conventional method described above, the correction will be made even in the area where the above-mentioned scattered X-rays are not generated, resulting in artifacts and causing problems in diagnosis. It was also pointed out that.

This invention has been made in view of the above problems, and its purpose is to provide a II-TV chain-based diagnostic device that does not use a grid in a II-TV chain-based diagnostic device in which the PSF changes depending on the thickness of the subject; To provide an X-ray diagnostic device that can sufficiently remove scattered X-ray signal components in a detected X-ray signal even when using a device other than the X-ray diagnostic device, and can obtain a high-quality image with excellent contrast sharpness and no artifacts. It is in.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention detects the X-rays that pass through the object with an X-ray detection means, and detects the X-rays output from the detection means. Displays images based on line signal data
In the radiation diagnostic apparatus, there is a means for classifying the X-ray signal data according to data corresponding to the thickness of the object, and a filter operation is performed independently on the Xg signal data for each thickness classified by the classification means, and a filter operation is performed for each thickness. A filter calculating means for outputting a scattered X-ray component signal, a means for synthesizing the scattered X-ray component signals for each thickness obtained by the filter calculating means, and a total scattered X-ray component signal obtained by the combining means. The apparatus is characterized by comprising means for subtracting the X-ray signal data from the X-ray detection means.

(Function) The X-ray detection means detects the X-rays passing through the object and outputs X-ray signal data corresponding to the incident X-rays. This X-ray signal data is classified for each pixel according to the thickness of the subject by comparing it with a comparison level signal corresponding to the thickness of the subject determined according to the diagnostic conditions. The X-ray signal data classified in this way is subjected to filter calculations independently for each classification thickness based on the corresponding filter coefficients. As a result, scattered X-ray component signals are calculated for each classification thickness of the object, and these signals are combined to obtain a total scattered X-ray component signal.

By subtracting this signal from the X-ray signal data obtained by the detection means for each pixel, X-ray signal data containing only the direct X-ray component from which the scattered X-ray component has been removed is finally obtained.

As described above, the detected X-ray signal data is classified according to the thickness of the subject, and the data for each classified thickness is filtered to obtain the scattered X-ray components separately. Since it is subtracted from the data, it can also be used in systems where the PSF changes depending on the thickness of the subject, such as II-TV chain diagnostic equipment that does not use a grid or equipment other than XI-TV chain diagnostic equipment. Scattered radiation correction can be reliably performed.

(Embodiment) The configuration of an embodiment of the present invention will be explained with reference to FIG. The X-ray tube 1 has X-ray emission controlled by an X-ray controller 2. The X-rays emitted from the X-ray tube 1 and transmitted through the subject 3 are
Detected by line detector 4. After converting the analog detection signal for each pixel corresponding to the two-dimensional detection plane output from the detector 4 into a digital value by the A/D converter 5,
It is stored in the memory 6 as original image data. Meanwhile, various diagnostic conditions (imaging conditions), such as tube voltage, tube current, exposure pulse X-ray width, and distance between the X-ray tube and detector, are provided by the X-ray controller 2, and the thickness of the subject 3 is adjusted accordingly. A threshold level generator 1 is provided to generate a plurality of threshold levels Sl, . . . Sn.

The comparator 8 receives the original image data sequentially read out from the memory 6 pixel by pixel and the threshold level S1 . . . , Sn, and the plurality of memories 9-1 .・・・
・Distribute and store it in any of 9-n. That is, the signal level ■ of the original image is compared with the threshold level 51, Sn, and 1<St, Sl<I<S2.
, = -, Sn < 1, the original image is divided into n+1 areas according to the signal level. That is, in the memory 9-1, among the original image signals, only the signals at pixel positions having signal levels below the threshold level 81 are recorded as they are, and 0 is recorded at other pixel positions. Also, in the memory 9-2, only threshold levels falling within the range of s1<r<S2 are recorded in the same manner as above. Corresponding signals are recorded in the other memories 9-3[deg.], 9-n according to the threshold levels provided in the same manner as above. In this way, each memory 9-1. ..., 9-n, a partial area of the original image is recorded.

Each memory 9-1. ... 9-n, a filter function generator 10-1. ..., 10-n are provided. These filter function generators are given imaging condition data from the X-ray controller 2, and each generates a filter function based on a predetermined PSF. These filter functions are stored in each memory 9-1. ...9-n together with the corresponding data read from each filter operator 11-1. ..., 11
-n is used for filter calculation. When these filter operations are performed, a scattered X-ray component signal is calculated. Each filter calculator 11-1. . . , 11-n (scattered X-ray component signals) are all sent to the synthesizer 12, and the result of their addition is added to the memory 13. This memory 13
The total scattered X-ray component signal is stored for each pixel of the two-dimensional image. A subtracter 14 is provided for subtracting the data in the memory 13 from the original image data (2) stored in the memory 6. The subtracter 14 outputs image data containing only direct X-ray components, with all scattered X-ray components removed from the original image data.

Next, the operation of the embodiment having the above structure will be explained with further reference to FIGS. 2 and 3. First, the background of scattered X-ray generation will be explained with reference to FIG. Among the X-ray buses emitted from the X-ray tube 1, when considering bus A that does not pass through the subject 3 and bus B that passes through it, the direct transmitted X-ray intensity of each is shown by a solid line, and depending on the subject The generated scattered X-ray intensity distribution is shown by a broken line (hatched). Since the scattered X-rays are thus generated by the subject 3, it is clear that the scattered X-rays are not generated in the area of Airbus A.

FIG. 3 shows a relationship (P S F) in which the degree of spread of scattered X-rays differs depending on the thickness of the object 3. As shown in the figure, for example, assuming that the subject 3 is water and considering its thickness at three levels: 5 mark, 15 cm, and 25 gloss, the PSF curve shows a tendency to spread laterally as the thickness increases. . In the case of II-TV chain diagnostic equipment,
P due to the influence of Bering glare generated from II.
Although the difference in SF is not so remarkable, the PSF of scattered X-rays generally differs depending on the thickness of the subject in each diagnostic apparatus, as described above.

Therefore, in order to reliably perform scattered X-ray correction, it is necessary to roughly understand the thickness of the subject at the time of imaging. Such thickness data of the subject can be estimated from the pixel value data of the original image if the shooting conditions are given. For example, the imaging conditions are: tube voltage 70KVp, tube current 1mA, exposure X-ray pulse width lrnS, distance between X-ray tube and detector 100cm.
If the system is capable of detecting a signal with a magnitude of 1000 on the near bus A, then if there is an object with 5 cm of water, 1000Xe - μm°5 (where μW is the average absorption coefficient of water) , μW is 20, 25)
A direct X-ray signal of can be detected on bus B. Therefore, on the contrary,
If the threshold level of the threshold level generator 7 in FIG. It can be assumed that this is the case. However, since scattered X-rays are superimposed on the original image signal, the actual X-ray signal value detected after passing through the ice thickness of 5(7) is 1000Xe-μ7°5X (leα). (However, α indicates the content rate for scattered X-rays.) The value of α is often less than 1.0 in the case of an imaging system using a grid, and in this case, the estimation error of ice thickness due to α is 2~
It is about 3 cm. In addition, if α is large and causes a large error in ice thickness estimation in a photographing system that does not use a grid, α can be measured in advance by setting the tube voltage and ice thickness to predetermined values, and the ice thickness Set the threshold level to 5o- when extracting a signal area of 5cm or less.
It is sufficient to set the value to 1000Xe-μ7゛5×[1+a(5cm, 70KVI))]. (However, α5cm and 70KVp are values measured in advance under a tube voltage of 70KVp and an ice thickness of 5cm.) Similarly, 3l-1000Xe -μ7°10 is 1
Since the threshold level is for the ice thickness of 0cIIl, the image signal between So<I<SR is 5~10c8
The area of the object with + ice thickness will be displayed.

As described above, signals selected by each threshold level are stored in the corresponding memory 9-1. ..., 9-n
By storing it in memory 9-1, the ice thickness is 5cf.
A signal corresponding to a portion below fl, a signal corresponding to a portion of ice thickness 5 to 10 countries in memory 9-2, and so on, are stored in each memory 9-1. ....

Signals corresponding to the thickness of the subject are classified and sent to 9 to n.

By the way, the PSF of scattered X-rays with respect to the thickness of object 3 is
For example, it is measured in advance as shown in FIG. Furthermore, a technique for determining the content ratio of scattered X-rays to direct X-rays from ice thickness and imaging conditions is also generally known. Therefore, each memory 9-1
．． ..., the generated scattered X-ray distribution can be obtained independently for each ice thickness, that is, for each ice thickness. By adding these separate scattered X-ray distributions in the synthesizer 12, the total scattered X-ray distribution (total scattered X-ray distribution generated by the object including various thicknesses) is obtained, and this is stored in the memory 6. A scattered X-ray corrected image can be obtained by subtracting it from the stored original image signal by means of a subtractor 14.

[Effects of the Invention] As mentioned above, according to the X-ray diagnostic apparatus of the present invention,
The detected X-ray signal data is classified according to the thickness of the object, and the scattered X-ray components are separately obtained by filtering the data for each classified thickness and subtracted from the X-ray signal data from the X-ray detection means. Because it is RR-TV chain diagnostic equipment that does not use grid or II-
Scattered radiation correction can be reliably performed even in systems where the PSF changes with the thickness of the subject, such as in devices other than TV chain diagnostic devices.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing the scattered X-ray generation state, and FIG. 3 is a characteristic curve diagram showing the PSF of the scattered X-rays. 1...X-ray tube 2...X-ray controller 4...X
Line detector 6...Memory 7...Threshold level generator 8...Comparator 9-1. ...,
9-n...Memory 10-1. ..., 10-n...
Filter function generator 11-1. ..., 11-n...
Filter calculator 12...Synthesizer 13...Memory 14...Subtractor Agent Patent attorney Rule Kensuke Chika Agent Patent attorney Takeshi Kondo Il! 1

Claims (1)

[Claims] In an X-ray diagnostic apparatus that detects X-rays passing through an object using an X-ray detection means and displays an image based on the X-ray signal data output from the detection means, the X-ray signal data is used to determine the thickness of the object. means for classifying according to equivalent data; and filter calculation means for independently performing filter calculations on the X-ray signal data for each thickness classified by the classification means and outputting scattered X-ray component signals for each thickness. , a means for synthesizing the scattered X-ray component signals for each thickness obtained by the filter calculating means, and a total scattered X-ray component signal obtained by the synthesizing means from the X-ray signal data from the X-ray detecting means. An X-ray diagnostic apparatus comprising: means for subtracting.