JPH08280658A - X-ray photographing apparatus - Google Patents

Abstract

PURPOSE: To set an optimum X-ray exposing condition without giving unnecessary X-ray exposure to an subject to be examined by obtaining parameters for determining a direct line level or a scattering line level from image data on X-ray images obtd. by exposing phantoms with different thicknesses with X-rays under different exposing conditions. CONSTITUTION: A measuring part 1 performs to set the photographing condition of an X-ray tube and to control the distance between an image intensifier and the X-ray tube in accordance with inputting from a console 1a. In addition, it performs operations for obtaining parameters for determining a scattering line glare level and a direct line level and an X-ray condition from image data of the image processed by means of an image processing apparatus 10. Then, between the X-ray tube 3 and the image intensifier 7, a lead piece 4 as an X-ray shielding body, a grid 6 for removing scattered X-ray and a phantom 5 are arranged according to the display 1b of the measuring part 1 and the parameter is obtd. automatically by photographing an X-ray image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray imaging apparatus for exposing a subject to X-rays, collecting the X-rays transmitted through the subject, and taking a fluoroscopic image. X-ray exposure conditions,
The present invention relates to a shooting condition calculation method for appropriately setting image processing conditions.

[0002]

2. Description of the Related Art In recent years, X-ray diagnostic apparatuses have been widely used as medical diagnostic apparatuses have been developed. The X-ray diagnostic apparatus arranges an X-ray tube and an image intensifier so as to face each other with a subject placed on a medical bed interposed therebetween, and emits X-rays from the X-ray tube toward the subject. Then, the X-rays that have passed through the subject are collected by an image intensifier, and this is image-processed to create an X-ray image.

In such an X-ray photographing apparatus, it is necessary to suitably control photographing conditions such as image contrast. Usually, when determining such imaging conditions, the tube voltage, the tube current, and the pulse width of the X-ray tube are arbitrarily controlled.

However, in reality, the imaging conditions are different each time depending on the imaging region of the subject and the size of the subject, so that even if the above tube voltage, tube current and pulse width are fixed, the same contrast is always obtained. Not always available. Therefore,
Conventionally, when performing X-ray photography, a method of simulating X-ray exposure before performing actual photography and adjusting the tube voltage, tube current, and pulse width while observing the imaging conditions has been adopted. Was there.

[0005]

However, in such a conventional method, a method of deciding the imaging condition while simulating X-ray exposure to the subject is adopted, so that the subject needs more than necessary. It has the drawback of being exposed to radiation.
In reality, the brightness of the image is adjusted by simulating X-ray exposure. Since an X-ray image is obtained by conversion by an X-ray tube, an image intensifier, a television camera, etc., it is difficult to optimally adjust the contrast.

The present invention has been made in order to solve such a conventional problem, and an object of the present invention is to optimize the X-ray exposure condition without giving unnecessary X-ray exposure to a subject. An object of the present invention is to provide an imaging condition calculation method for an X-ray imaging apparatus capable of setting the.

[0007]

In order to achieve the above object, an X-ray imaging apparatus of the invention according to claim 1 of the present invention is an X-ray detector for an object placed between an X-ray tube and an X-ray camera unit. In an X-ray imaging apparatus that exposes an X-ray image of a subject by irradiating X-rays from a tube, regarding phantoms having different thicknesses while arranging an X-ray shield in an X-ray passage from the X-ray tube. ,
It is characterized by having a means for obtaining a parameter for determining a direct ray level or a scattered ray level from image data of X-ray images obtained by X-ray exposure under different exposure conditions.

The X-ray imaging apparatus of the invention according to claim 2 of the present application is, in addition to the structure of claim 1, further provides a direct radiation level, a scattered radiation level, and an image level of an X-ray image for a given exposure condition. Is further provided.

In addition to the structure of claim 1, the X-ray imaging apparatus of the invention according to claim 2 of the present application is such that the means for obtaining the parameters is in the state without the phantom and with the grid of the X-ray camera unit. The grid transmittance Tp, which is one of the parameters, is obtained from the obtained X-ray image and the X-ray image obtained in the absence thereof, and the average attenuation coefficient μ of the phantom for each exposure condition is obtained from this transmittance Tp and the image data. (kv) and the constants a and b necessary to obtain the average attenuation coefficient μ under arbitrary exposure conditions, and X without the phantom.
The Behring glare ratio V is obtained from the X-ray image obtained with the grid of the line camera unit, and the scattered ray gain factor GTs (kv) of the phantom for each exposure condition is obtained from the Behring glare ratio V and the image data. The coefficients a ₁ and a ₂ necessary to obtain the scattered radiation gain factor GTs for any exposure condition are obtained, and from the transmittance Tp, the constants a and b, the Bering glare ratio V, and the coefficients a ₁ and a ₂ , It is characterized in that the average attenuation coefficient μ and the scattered radiation gain factor GTs are calculated under arbitrary exposure conditions.

[0010]

According to the present invention constructed as described above, a phantom (for example, an acrylic phantom) close to a human body is placed between the X-ray tube and the image intensifier tube, and the lead piece is placed in the passage of the X-ray. X-ray imaging is performed by arranging such X-ray shields, changing the thickness of the phantom in two or more types, and changing the X-ray exposure conditions two or more times to perform pseudo-exposure. The image level of the X-ray image obtained by this varies depending on the thickness of the phantom and the X-ray exposure conditions, and differs depending on the portion with and without the X-ray shield.

The above parameters are obtained from such differences in image levels, and by using these parameters, image levels such as direct ray levels and scattered ray levels according to arbitrary exposure conditions can be calculated. Therefore, it becomes possible to obtain the optimum X-ray imaging conditions without giving unnecessary exposure to the subject.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of an X-ray imaging apparatus according to the present invention.

The image intensifier (image intensifier) 7 collects the X-ray image transmitted through the subject and converts it into a light image. The X-ray incident on the surface of the image intensifier 7 is collected. A grid 6 for limiting the direction of the X is attached so that an optical image can be obtained from X-rays in a certain direction. The optical image from the image intensifier 7 is supplied to the television camera 9 via the aperture adjusting device 8 and converted into an electric signal. The aperture adjusting device 8 has an iris (aperture) 8a and a filter 8b for adjusting the amount of light incident on the television camera 9, and these allow the photographing of the television camera 9 to be optically adjusted. There is.

These reference numerals 7, 8 and 9 form an X-ray camera unit.

The image processing apparatus 10 stores an X-ray image from the output signal of the television camera 9 and also adds a plurality of stored images, subtracts between the plurality of images, contour processing, image enhancement, feature extraction, etc. Image processing is performed.

The X-ray tube 3 is arranged opposite to the image intensifier 7, and the X-ray tube 3 is controlled by the X-ray controller 2.
Output a line. The X-ray controller 2 controls the tube voltage (k
V), tube current (mA), pulse width (msec), and other imaging conditions are controlled by the measuring unit 1.

The measuring section 1 is for controlling X-ray imaging such as control of the above-mentioned imaging conditions and control of the aperture adjusting device 8, and is constructed by using a computer device having a display 1b and measurement software. To be done. Then, in accordance with the input from the console 1a, the imaging condition of the X-ray tube is set and the distance SID between the image intensifier and the X-ray tube is controlled. The measurement unit 1 performs the processing for capturing such an X-ray image and, in order to capture the favorable X-ray image, the scattered radiation glare level I _sv from the image data of the image processed by the image processing apparatus 10. And the direct line level I _p ,
A calculation for obtaining a parameter (described later) for determining the X-ray condition is performed. Between the X-ray tube 3 and the image intensifier 7, a lead piece 4 as an X-ray shield, a grid 6 for removing scattered X-rays, and a phantom 5 are arranged according to the display on the display 1b of the measuring unit 1. Then, the above parameters can be automatically obtained by photographing an X-ray image, and the photographing level under any X-ray condition can be known by using the obtained parameter, and thus the optimum X-ray condition can be known. You can do it.

A parameter for the measuring unit 1 to determine a direct ray level or a scattered ray level from collected data of X-ray fluoroscopic images obtained by X-ray exposure under different exposure conditions with respect to phantoms having different thicknesses. Form a means of seeking. Further, the measuring unit 1 is configured to obtain the variance of the image data of the image obtained by subtracting the two X-ray images by the image processing device 10.

Table 1 shows an example of the grid 6 and the phantom 5 for obtaining the above parameters. Shows that the grid 6 is not present and the phantom 5 is not present. Indicates that there is no phantom 5 and that there is a grid, and phantoms 6 of 10 cm and 20 cm are arranged, respectively. The lead piece 4 is attached to the front surface of the grid 6 (the front surface of the image intensifier when there is no grid) during the measurement.

[0020]

[Table 1] The display of Table 1 is displayed on the display in order from the top,
X-ray imaging is performed only at a tube voltage of 70 kV, and at 70 kV in order to change the tube voltage as an exposure condition.
X-ray imaging is performed for both exposure conditions of 90 kV and 90 kV. FIG. 2 shows the processing of the measuring unit 1 at that time.

First, the measuring unit 1 displays the display from Table 1 and instructs the operator to bring the grid 6 and the phantom 5 into the displayed state (reference numeral 2 in FIG. 2).
10). When the operator finishes the arrangement and inputs that to the console 1a, the measuring unit 1 starts the measurement. First, the measurement unit 1 controls the aperture adjustment device 8 to set the opening of the iris 8a and the filter 8b, and prepares for the X-ray image capturing of the phantom 5. Then, the X-ray control device 2 is controlled so that the tube voltage is set to 70 kV, and the X-ray is irradiated from the X-ray tube 3 a plurality of times, and the phantom 5
A plurality of X-ray images of the above are photographed (reference numeral 220 in the figure).

This X-ray image is converted into an electric signal by the television camera 9 and added / subtracted by the image processing device 10. The noise components are averaged in the added X-ray images, and the added and averaged image of the X-ray images is given to the measurement unit 1 as image data. In the X-ray image averaging image at this time, as shown in FIG. 3, the image value of the portion where the lead piece 4 is present is low and the image value of only the phantom 5 where the lead piece 4 is absent is high.

The measuring unit 1 uses the image data of the arithmetic mean image to obtain an image value (scattered ray glare level) corresponding to the lead piece 4.
I _sv and the image value I _sv + I _p (I _p (I _p
Is the direct ray level) and the scattered ray glare level I _sv and the direct ray level I _p are obtained and stored in the memory (reference numeral 230 in the figure). In the measurement of Table 1, the thickness of the phantom is 1
Since it is not 0 or 20 cm, an X-ray image is not taken at 90 kV (reference numeral 230 in the figure), but an X-ray image is similarly taken at a tube voltage of 90 kV (reference numeral 220 in the figure).
Then, the scattered ray glare level I _sv and the direct ray level I _p are obtained and stored in the memory (reference numeral 230 in the figure). In this way, the measurements of Tables 1 to 1 are sequentially carried out (reference numeral 2
70).

Since the scattered ray glare level I _sv and the direct ray level I _p obtained by the measurement in Tables 1 are different measurement values, they are distinguished by adding subscripts as shown in Table 2 here. .

[0025]

[Table 2] It is known that the output I _o of the X-ray when there is no phantom 5 is obtained by the following equation (1). Where Φ is
It is a function of the tube voltage, the tube current, and the pulse width, and is previously obtained by experiment for each combination of conditions. The distance SID between the image intensifier and the X-ray tube is determined by the control of the measuring unit 1, and the 1 pixel area, the light amount attenuation rate, etc. can be obtained from the measurement. The correction coefficient is an empirical constant. In the equation (1), the system gain ζ is
Calculated from measured data with a value that is unique to each device.

[0026]

[Equation 1] The measurement unit 1 uses these scattered ray glare level I _sv and direct ray level I _p to find a parameter for obtaining an X-ray condition by the following procedure, and uses the parameter to determine an optimum X-ray condition.
Determine line conditions.

First, the measuring unit 1 uses the direct line level when the phantom 5 is not present, "{I _{p2 1} / light quantity transmittance)} / {I _p10 / light quantity transmittance)}". Is calculated to obtain the direct line transmittance T _p of the grid. The direct line level I _p is given by the following equation (2
Since it can be expressed by a) and when it is not expressed by the following equation (2b), the direct line transmittance T of the grid is calculated from the ratio of I _p10 and I _p21.
It is possible to find _p .

[0028]

[Equation 2] The average attenuation coefficient μ of the phantom is shown as a function of the tube voltage (kV), and is approximately represented by equation (3).

[0029]

(Equation 3) Using this, the measuring unit 1 uses the direct line levels I _p31 and I _p41 of the tube voltage 70 kV to average the attenuation coefficient μ (70 kV) of the tube voltage 70 kV and the direct line level I _{p3 2} , I of the tube voltage 90 kV.
The average attenuation coefficient μ (90 kV) of the tube voltage of 90 kV is calculated using _p42 (equations (4a) and (4b)).

[0030]

[Equation 4] Then, the measuring unit 1 obtains the obtained average attenuation coefficient μ (70 kV)
And μ (90 kV), the constants a and b of the equation (3) are obtained using the equations (5) and (6).

[0031]

(Equation 5)

(Equation 6) In this way, concrete values of the constants a and b are obtained, and the equation (3)
Can be specifically defined. The measuring unit 1 uses the calculated constant a,
From b and equation (3), the average attenuation coefficient μ is calculated for a given arbitrary tube voltage.

On the other hand, the scattered radiation gain factor GTs is a value that changes depending on the tube voltage, but the scattered radiation glare level I _sv
And the direct line level I _p can be used to _express as in equation (7). Where V (Bering glare ratio)
Is I using the scattered ray glare level I _sv and the direct ray level I _p with the grid 6 and without the phantom 5.
_{It is calculated by sv} / I _p . Further, g is a parameter peculiar to the phantom 5 and is obtained from an experiment.

[0033]

(Equation 7) Using this fact, first, the measurement unit 1 uses the scattered ray glare level I _sv21 and the direct ray level I _p21 obtained by the measurement in Table 2.
_Is used to determine the Bering glare ratio V from I _sv21 / I _p21 . Then, the measuring unit 1 uses the thus obtained Behring glare ratio V and the direct line transmittance T _p previously obtained, and determines the tube voltage.
Scattered-ray gain factor GTs (70 kV) at a tube voltage of 70 kV from the average of equations (8a) and (8b) in which the measured values I _sv31 , I _p31 , I _{sv 41} , and I _p41 at _{70 kV} are substituted into equation (7). )
(G is a constant). Similarly, the measuring unit 1 measures values I _sv32 , I _p32 , I _sv42 , and I _p42 when the tube voltage is 90 kV.
Scattered-ray gain factor GTs when the tube voltage is 90 kV from the average of simultaneous equations (8c) and (8d)
Calculate (90kV).

[0034]

(Equation 8) The scattered radiation gain factor GTs can be expressed by Expression (9) which is a linear function of the tube voltage (kV). The measuring unit 1
Obtained scattered radiation gain factors GTs (70 kV) and GT
Simultaneous equations (9a) (9b) obtained by substituting s (90kV)
The coefficients a ₁ and a ₂ are obtained from Specifically, equation (10)
It can be obtained by the calculation of (11).

[0035]

[Equation 9]

[Equation 10]

[Equation 11] The specific values of the coefficients a ₁ and a ₂ thus obtained are obtained,
Formula (9) can be specifically defined. The measurement unit 1 calculates the scattered radiation gain factor GTs of the given arbitrary tube voltage from the obtained coefficients a ₁ and a ₂ and the equation (9).

As described above, the measuring unit 1 uses the direct ray transmittance T _p of the grid, the Behring glare ratio V, the average attenuation coefficient μ of the phantom, and the scattered radiation gain factor GT as parameters for obtaining the X-ray condition. It becomes possible to obtain _s (reference numeral 280 in FIG. 2). The direct ray transmittance T _{p of the} grid, the Behring glare ratio V, the constants a and b of the equation (2) for obtaining the average attenuation coefficient μ of the phantom, and the coefficient of the equation (8) for obtaining the scattered ray gain factor GT _s. The a ₁ and a ₂ are stored in a storage device such as a magnetic disk device built in the measuring unit 1. Then, the value of each of the above parameters is obtained for any given tube voltage that is read out when necessary.

Further, the measuring section 1 uses the obtained parameters described above to calculate the scattered ray glare level I for an arbitrary tube voltage (kv) given by using the following equations (12) and (13). _The calculation for _{obtaining sv} and the direct line level I _p is performed, and the image level is obtained for an arbitrary tube voltage given by using the equation (14) (reference numeral 290 in FIG. 2).

[0038]

(Equation 12)

(Equation 13)

[Equation 14] In this way, it is possible to estimate the image level when a subject having a certain thickness is photographed under an arbitrary X-ray photographing condition from the measurement using the phantom. Normally, the light intensity of the Aliis and the filter was adjusted by simulating X-ray exposure, but since the image level can be estimated in advance, the light intensity can be adjusted in advance, resulting in a simulated X-ray. You can shoot without spraying.

Further, assuming the attenuation coefficient of a contrast agent, which indicates the characteristics of a substance such as a contrast agent often used for examination, the contrast can be estimated from the attenuation coefficient of the phantom, the attenuation coefficient of the substance, and the image level. . It is possible to estimate the contrast for arbitrary X-ray imaging conditions. Generally, the contrast increases as the tube voltage decreases. It is possible to determine the contrast standard and determine the shooting conditions such as the tube voltage that meet the standard.

As described above, by obtaining the parameters capable of estimating the image level, it is possible to perform photographing without unnecessary exposure. Also, since only two types of phantoms are required and it is not necessary to measure at all tube voltages (kV), the burden of obtaining parameters is small and quick.

[0041]

As described above, according to the present invention,
The X-ray imaging conditions can be obtained without actually exposing the subject to X-rays. Therefore, it becomes possible to perform imaging without giving unnecessary X-ray exposure to the subject.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an X-ray imaging apparatus according to the present invention.

FIG. 2 is a diagram showing an outline of processing of the measuring unit 1.

FIG. 3 is an explanatory diagram showing the sizes of a scattered radiation level and a direct radiation level.

[Explanation of symbols]

1 measuring unit, 2 X-ray control device, 3 X-ray tube, 4
Lead pieces, 5 phantoms, 6 grids, 7 image intensifiers, 8 aperture adjustment devices, 9 television cameras, 10 image processing devices

Claims (3)

[Claims] 1. An X-ray imaging apparatus for irradiating an object placed between an X-ray tube and an X-ray camera unit with X-rays from the X-ray tube to take an X-ray image of the object. While arranging an X-ray shield in the passage of X-rays from the X-ray tube, from phantoms having different thicknesses, from image data of X-ray images obtained by X-ray exposure under different exposure conditions, An X-ray imaging apparatus having means for determining a parameter for determining a direct ray level or a scattered ray level. 2. The X-ray imaging apparatus according to claim 1, further comprising means for obtaining a direct ray level, a scattered ray level, and an image level of an X-ray image from the parameters under a given exposure condition. . 3. The means for obtaining the parameter is the parameter obtained from an X-ray image obtained in the absence of a phantom and with the grid of the X-ray camera unit, and an X-ray image obtained in the absence thereof. Obtaining the transparency Tp of the grid, which is one of the above, and determining the average attenuation coefficient μ (kv) of the phantom for each exposure condition from this transparency Tp and the image data, and for any exposure condition The constants a and b necessary for obtaining the average attenuation coefficient μ are obtained, and the Bering glare ratio V is obtained from the X-ray image obtained with the grid of the X-ray camera unit without the phantom.
And the scattered radiation gain factor GT of the phantom for each of the exposure conditions based on the Bering glare ratio V and the image data.
In addition to obtaining s (kv), the coefficients a ₁ and a ₂ necessary to obtain the scattered radiation gain factor GTs for any exposure condition are obtained, and the transparency Tp, the constants a and b, the Behring glare are obtained. The X-ray imaging apparatus according to claim 1, wherein an average attenuation coefficient μ and a scattered radiation gain factor GTs are calculated for an arbitrary exposure condition from the ratio V and the coefficients a ₁ and a ₂ .