JPH02248889A - X-ray receiver - Google Patents

Abstract

PURPOSE:To obtain an apparatus free from a deterioration in quality of picture due to a change in intensity of X rays by monitoring a hourly change in irradiat ing X rays from an X-ray generator by the optimum value to correct a pixel signal of each line based on a signal thereof. CONSTITUTION:A radiation detector 1 for correcting X-ray intensity converts incident X rays into an electrical signal to be preserved into a memory as X-ray intensity change data 5 through an integrator, an automatic gain adjustment circuit 3 and an A/D converter 4. A CPU 6 calculates an X-ray intensity correction data 14 from the data 5 by a specified computation while determining the optimum gain to generate a gain control signal 16 so that a gain of the circuit 3 is switched. An image data 15 is corrected by the optimum data thus obtained thereby enabling the obtaining of an apparatus with no deterioration in quality of picture regardless of hourly change in the intensity of X rays.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an X-ray image receiving apparatus that uses X-rays in the medical and industrial fields, and particularly relates to a configuration for correcting its uniformity.

Conventional technology In recent years, devices using stimulable phosphors have been introduced in place of X-ray receivers that use silver halide photographic films to obtain X-ray transmission planar images.
One using an X-ray sensitive solid state device array has been developed.

In the former method, a method is known in which a stimulable fluorescent plate is used instead of an X-ray film, an X-ray latent image is created, and pixel signals are extracted by sequential stimulation with a laser (Japanese Patent Laid-Open No. 15025/1982).

The latter method uses a silicon element combined with a fluorescent material as an X-ray sensitive solid state element to measure the amount of current generated in the photoelectric groove (Japanese Unexamined Patent Publication No. 53-105179 1
．． JP-A-53-98787) and one using a radiation semiconductor detector array (JP-A-59-94046) are known.

Problems to be Solved by the Invention However, although the former conventional method using a stimulable phosphor can obtain image quality comparable to that of X-ray photography, it has had the problem of a large amount of X-ray exposure. Furthermore, in the latter conventional example using an X-ray sensitive solid state element array, the surface resolution is poor due to the material.

On the other hand, conventional examples using radiation semiconductor detector arrays have high radiation sensitivity and surface resolution, but the radiation semiconductor detector array is arranged in a straight line or curved arc with respect to the human body. Since it is a line-sequential method in which pixel signals are obtained by scanning in a curved arc, the image quality has been somewhat unsatisfactory.

This is because the X-ray exposure time is extremely short in the X-ray photography method or methods using stimulable phosphors to obtain two X-ray transmission plane images, whereas the radiation semiconductor detection This is because when an array of X-rays is used, an X-ray exposure time of one second or more is required to obtain pixel signals for each line. Therefore, temporal fluctuations in the X-rays emitted from the X-ray generator cannot be ignored, and a fluctuation component of the X-ray intensity appears in the pixel signal for each line, leading to a reduction in image quality.

In view of this, the present invention monitors the temporal fluctuations of the X-rays emitted from the X-ray generator at an optimal value, and corrects the pixel signal of each line based on this signal.
It is an object of the present invention to provide an X-ray image receiving device that does not deteriorate image quality due to fluctuations in X-ray intensity.

Means for Solving the Problems The present invention irradiates a subject with a fan-shaped beam from an X-ray generator, makes the transmitted beam incident on a radiation semiconductor detector array arranged on a straight or curved dish, and and the radiation semiconductor detector array are driven in a straight line or on a curved plate relative to the object to obtain line-sequential X-ray pixel signals to obtain an X-ray transmission plane image, wherein the radiation semiconductor detector A correction radiation semiconductor detector or a group of detectors is provided separately from the array, and means for integrating and outputting the X-ray dose of the fan-shaped beam incident on each of them at fixed time intervals, and gain adjustment means for changing the amplification degree. , A/D conversion means for A/D converting the integrated X-ray dose, storage means for storing the A/D converted data signal, calculation means for determining an optimal gain from the data signal, and this calculation. an X-ray device comprising: a control means for controlling the gain adjustment means based on a result of the gain adjustment means; and a means for calculating a correction coefficient for X-ray intensity fluctuation from the data signal and correcting an X-ray pixel signal in a corresponding time period. It is an image receiving device.

According to the above-described configuration, the present invention calculates the optimum gain for performing A/D conversion based on the X-ray intensity fluctuation data obtained by the correction radiation semiconductor detector or the detector group, and the gain adjustment means calculates the optimum gain for performing A/D conversion. Gain is set. After setting the gain, imaging is performed, and the radiation semiconductor detector array stores an X-ray transmission plane image as image data, and at the same time, the correction radiation detector stores X-ray intensity fluctuation data.

From this X-ray intensity fluctuation data, X-ray intensity correction data is determined, and image data for the corresponding time period is corrected to obtain a uniform image.

Embodiment FIG. 1 shows a block diagram of an X-ray image receiving apparatus in a first embodiment of the present invention.

In the figure, reference numeral 1 denotes a radiation detector for X-ray intensity correction, which is sensitive to incident X-rays and converts them into electrical signals. 2 is an integrator that integrates the output signal from the radiation detector 1 for X-ray intensity correction. 3 is an automatic gain adjustment circuit, which switches the gain based on the gain control signal 16. The output signal of the automatic gain adjustment circuit 3 is digitized by an A/D converter 4 and stored in a memory (not shown) as X-ray intensity fluctuation data 5. Reference numeral 10 denotes a radiation semiconductor detector array arranged in a straight line or a curved arc with respect to the human body as an object, and by scanning this in a straight line or curved arc with respect to the human body, an X-ray transmission plane image can be obtained. It will be done.

The output pulses from the radiation semiconductor detector array 10 are generated for each photon of the incident radiation and therefore have the highest theoretical sensitivity. 11 is a pulse amplification circuit.

Reference numeral 12 denotes a pulse height discrimination circuit for discriminating the energy of pulses, and outputs a pulse when there is a pulse input having a preset peak value or higher. A pulse counting circuit 13 continuously counts the output pulses from the pulse height discrimination circuit 12 line by line. 6 is the CPU, and the X-ray intensity fluctuation data 5
calculates the X-ray intensity correction data 14 from the X-ray intensity correction data 14, determines the optimum gain and generates the gain control signal 16, generates a reset signal 17 for each line when scanning the radiation semiconductor detector array 10, The integrator 2 and pulse counting circuit 13 are reset. Furthermore, the count value counted by the pulse counting circuit 13 is saved as image data 15.

For example, the calculation of the X-ray intensity correction data 14 is performed as follows. m pieces of X-ray intensity fluctuation data 5 are obtained at regular intervals in the scan direction, and this i-th data 5 is
, the average value is X, 0. shall be. All image data 1 corresponding to the time period in which the i-th X-ray intensity fluctuation data 5 was obtained
The image data 15 is corrected by multiplying 5 by X, . . . n/X.

Next, the gain is determined, for example, as follows.

Note that the current gain is assumed to be Aa.

If the number of bits of the A/D converter 4 is n bits, the maximum number A D represented is: AD□8=20-1, .
,,, (1).

Also, m pieces of X obtained by one scan
Average value of line strength fluctuation data 5 X10. is, by dividing the i-th data by X+, X @ @ l n ” (ΣX+)/m
, , , , (2) Represented by Ill.

Here, the variation in the number of photons of X-rays is considered to have a Poisson distribution, and this N standard deviation σ is expressed as σ= n , , , , (3
) is known to be expressed as Therefore, σ”Y
Let it be sssl.

In this case, if n≧5, it can be approximated to a normal distribution, so
When converting approximately 99.7% into a digital signal with the A/D converter 4 without overflowing, the gain is (AD, , -3σ)/X, , , , , , , ,
(4) Just multiply it.

Therefore, if the gain to be sought is A, then A, = (
CAD,,,-3σ”)/X,,,,) ・As,,,
, , (5) becomes. -In the membrane, Ak= ((AD, , -δ)/X, ,,,) ・
It is expressed as Ag, , , , (6), and the margin until overflow is determined by δ. Here, δ=3 a , , , , (
7), but other suitable values may be used.

2 and 3 are circuit diagrams of the basic automatic gain adjustment circuit 3. FIG. In FIG. 2, 20 is an operational amplifier, 21a is a group of resistors connected in series, and 22a is a group of switches connected in parallel between each resistor and the output terminal. By selecting one, the value of the feedback resistor can be changed. 23 is an input resistance.

In the example shown in FIG. 3, +1 resistor groups 21b are connected in series to serve as feedback resistors. 22b is a switch connected in parallel to both ends of each resistor, and by closing this switch, the corresponding resistance value is set to zero. Here, resistance group 2
1b is R, 2R, 4R.

..., 2kR, and by closing an arbitrary number of switches 22b at the same time, from zero to (2 to ◆1-1
) R can be obtained in R intervals.

Further, as shown in FIG. 4, the automatic switching circuit 32 can be configured to set an arbitrary resistance value. 30a, 30b, and 30c are resistor groups, and resistors lk, 8k, and 64 are inserted in series between the respective terminals. 31 is a selector capable of switching eight terminals. With this configuration, one 8-terminal selector 31 can be controlled by a 3-bit control signal 16. Also,
Since it has 8 terminals, the resistance value is expressed as an octal number, that is, N 8
By multiplying 8' by 182, the resistance value between terminals X and Y can be set from O to 511k in 1k increments. are connected in cascade in three stages, but those with p terminals may be connected in cascade in nine stages (p and q are arbitrary natural numbers).In this case, the resistance value at each selector 31 is multiplied by a p-adic number,
That is, pg+ T"l p21... p a
Needless to say, it is 41 times more. Further, in this embodiment, A/D conversion is performed only once during one line scan, but it can be averaged by performing it multiple times.

As described above, according to this embodiment, the X-ray intensity correction radiation detector 1 is provided, and the integrated output is performed for each line.
When performing D conversion, by providing the automatic gain adjustment circuit 3, it is possible to set the optimal gain for the intensity of the irradiated X-rays, so accurate X-ray intensity fluctuation data 5 can be obtained. This makes it possible to obtain optimal X-ray intensity correction data 14 and eliminate disturbances in the image due to X-ray intensity fluctuations.

FIG. 5 is a block diagram of an X-ray image receiving apparatus according to a second embodiment of the present invention.

In the figure, 10 is a radiation semiconductor detector array; 11 is a radiation semiconductor detector array;
12 is a pulse amplification circuit, 12 is a pulse height discrimination circuit, 13 is a pulse counting circuit, 14 is X-ray intensity correction data, and 15 is image data, which are similar to the first embodiment (see FIG. 1). . The difference from the first embodiment is that an optimal correction radiation semiconductor detector 80 that outputs a pulse for each photon of radiation is used, and a separate pulse counting circuit is used to measure the X-ray intensity correction data 14. 13 was provided.

The operation will be explained below. X-ray photons transmitted through the object are incident on the radiation semiconductor detector array 10, absorbed, and output as pulses. This pulse is transmitted to the pulse amplification circuit 11
The pulse height discriminator circuit 12 selects only those having a pulse height higher than a preset value and outputs a pulse.

The output pulses are counted by a pulse counting circuit 13 and recorded as image data 15. On the other hand, the X-ray intensity correction data 14 is obtained by counting pulses generated for each line in a correction radiation semiconductor detector 80 provided at a position where the X-ray photons generated by the X-ray source are directly incident. .

FIG. 6 is an explanatory diagram of the spread of X-rays and the number of photons when the X-ray source is considered as a point light source. 50 is a plane with area S1 located at distance r+, and 51 is a plane with area S2 located at distance r2. Here, the relationship between both areas S1 and S2 is Fz /82 = r+ 2/r22 , , , ,
(8), and assume that the normal line from the center of both planes 50 and 51 lies on the X-ray source.

Furthermore, the areas S1 and S9 are assumed to be sufficiently small compared to the square of the distances r+ and r2. The X-rays generated in the X-ray source spread radially. Therefore, although both areas S1182 are different from each other, the number of X-ray photons passing through per unit time is equal. In other words, when both areas S4 and S2 are equal, the number of photons incident on the plane 50 closer to the X-ray source is equal to the number of photons incident on the plane 51 farther from the X-ray source (ra ”
/r+ 2) Double. Therefore, when the same radiation semiconductor detector is used, pile-up occurs more often on the plane 50 side that is closer.

FIG. 7 is a configuration diagram showing the relationship between a radiation semiconductor detector 60 for X-ray intensity correction and a radiation semiconductor detector array 61 for obtaining an X-ray transmission plane image in a second embodiment of the present invention.

The radiation semiconductor detector 60 for X-ray intensity correction has a distance r+ from the X-ray source, a thickness X@, an area S1 of a portion where radiation actually enters within the radiation-sensitive portion, and a radiation semiconductor detector array. 61 is the distance r2 from the X-ray source and the thickness X8N
This is the area S2 of the portion where radiation actually enters within the radiation-sensitive portion per element. When the radiation semiconductor detector 60 for X-ray intensity correction and the radiation semiconductor detector array 61 are made of the same material, the relationship between the areas S1 and S2 is Fz /Sa = r+ 2/r22.
,,(8)'. With this configuration, the counting rate of the number of X-ray photons counted by the rain detector per unit time can be made to be approximately the same.

FIG. 8 shows a third embodiment of the present invention, in which a radiation semiconductor detector 70 for X-ray intensity correction has a distance r+ from the X-ray source 100, a thickness Xl, and an actual radiation-sensitive portion within the radiation-sensitive portion. is the area S11 of the portion on which the radiation is incident. The radiation semiconductor detector array 7D has a distance r2 from the X-ray source 100 and a thickness x2.
．． This is the area S@ of the portion where radiation actually enters within the radiation-sensitive portion per element. Below, both thicknesses XI,
The relationship of X2 will be explained.

The rate at which incident radiation is absorbed within a semiconductor detector has the following relationship.

ICE) = I@(E) (1-e xp(-μ(E
)x) ),,,,,, (9) However, I(E) is the number of absorbed radiation photons, l5(E)
is the number of incident radiation photons, μ(E) is the attenuation coefficient, and X is the thickness of the semiconductor detector. Therefore, in order to equalize the counting rate per unit time of the rain detector 70171 shown in FIG. 8, the following relational expression is satisfied.

I 5(E) (1-e X p(-μ1(E)x+)
) = (r1/r2)2Ig(E) {1-eXp (
-tt2(E)X2) )
......(10) From this relational expression, both thicknesses Xl,
The relationship of X2 is as shown in the following equation.

X+=-in [1(r1/ra)2(L-exp
(-μ2(E)X2)) 7μm(E
), (11) where μI(E) is the attenuation coefficient of the radiation semiconductor detector 70 for X-ray intensity correction, and μ2(E) is the attenuation coefficient of the radiation semiconductor detector array 71. That is, the thickness X11 X2 of the rain detector 70171 is calculated so as to satisfy the relational expression (11).
By setting , the counting rate can be made the same even with detectors 70171 having the same incident area, despite the difference in the number of incident photons.

The incident area of photons can be easily adjusted by providing a grid that blocks radiation. For example, an explanation will be given by taking Si+CdTe as an example of a semiconductor detector. Radiation semiconductor detector 70 for X-ray intensity correction Both the radiation semiconductor detector array 71 are made of Si, the thickness of the radiation semiconductor detector array 71 is 0.1 cm, and the attenuation coefficient at 60 keV is 0.
．． 3cm-' Distance ratio r1/r2=0. 2, the thickness of the radiation semiconductor detector 70 for X-ray intensity correction is approximately 0.0039 cm. Next, rain detector 70.71
The radiation semiconductor detector array 71 is both made of CdTe.
The thickness is 0.1cm and the attenuation coefficient at 160keV is 33c.
m” distance ratio r1/r2=0.2, the thickness of the radiation semiconductor detector 70 for X-ray intensity correction is approximately 0.00.
It will be L2cm. Moreover, when St is used for the radiation semiconductor detector 70 for X-ray intensity correction and CdTe is used for the radiation semiconductor detector array 71 under the above conditions, the thickness of the radiation semiconductor detector 70 for X-ray intensity correction is approximately 0. It will be 1310cm.

FIG. 9 shows an example of the overall configuration of an X-ray image receiving device equipped with the semiconductor detector 70 for X-ray intensity correction.
101 is a fan-shaped beam X-ray slit, and 103 is a top plate for protecting the radiation semiconductor detector array 71.

In the above configuration, the fan beam X-ray slit 101
By driving the radiation semiconductor detector array 71 and the radiation semiconductor detector array 71 in synchronization in the direction of the arrow, an X-ray transmission planar image can be obtained. In addition, the semiconductor detector 70 for X-ray intensity correction is provided at a position where X-rays are directly incident, and obtains X-ray intensity fluctuation data.

As described above, according to this embodiment, even if the radiation semiconductor detector 70 for X-ray intensity correction is installed near the X-ray source 100,
The counting rate can be made comparable to that of the radiation semiconductor detector array 71. Therefore, in the radiation semiconductor detector 70 for X-ray intensity correction, there is no possibility that the pile-up phenomenon increases and the value becomes smaller than the actual count value, making it impossible to obtain a correct correction value. Moreover, since the X-ray intensity correction data is obtained by directly counting the number of X-ray photons, it is possible to construct an X-ray image receiving apparatus with extremely high sensitivity.

In this embodiment, the relationship between the radiation semiconductor detector 70 for X-ray intensity correction and the radiation semiconductor detector array 71 is determined based on either the incident area or the thickness of the detector in order to make the number of absorbed photons approximately equal. Although this was determined by making one of them equal and calculating the other, it is also possible to determine either the incident area or the thickness of the detector to an arbitrary value. In this case, it goes without saying that the other value can be easily calculated using the following equation, which is obtained by multiplying the right side of equation (10) by the area ratio term.

l1I(E)(1-exp(-μ1(E)Xl))”
(S2/81) (r1/rt) 2Ig(E) {1-e
x 1) (-μ2(E)X2) ) ,,-,,,
, (12) Furthermore, in this embodiment, the relationship between the radiation semiconductor detector 70 for X-ray intensity correction and the radiation semiconductor detector array 71 is such that the number of absorbed photons is approximately equal; however, the X-ray intensity The number of photons absorbed by the radiation semiconductor detector 70 for correction may be set within a range that does not exceed the number of photons absorbed by the radiation semiconductor detector array 71.

As described in detail, according to the present invention, it is possible to configure an X-ray image receiving device with good image quality even if the X-ray intensity of the X-rays generated by the X-ray generating device fluctuates over time. And its practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an X-ray image receiving device according to a first embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams of a basic automatic gain adjustment circuit in the same device, and FIG. A circuit diagram of an automatic gain adjustment circuit equipped with an automatic switching circuit for setting an arbitrary resistance value, FIG. 5 is a block diagram of an X-ray image receiving apparatus in the second embodiment of the present invention, and FIG. 6 shows the spread of X-rays. FIG. 7 is a configuration diagram of both detectors in the third embodiment of the present invention, FIG. 8 is a configuration diagram of both detectors in the fourth embodiment of the present invention, and FIG. It is a schematic perspective view of the X-ray image receiving apparatus in the same Example. 1.60.70.80... Radiation detector for X-ray intensity correction, 2... Integrator, 3... Automatic gain adjustment circuit, 4
...A/D converter, 5...X-ray intensity fluctuation data, 6
...CPU110.61.71...Radiation semiconductor detector array, 11...Pulse amplification circuit, 13...Pulse counting circuit, 14...X-ray intensity correction data, 15.
...Image data, 16...Gain control signal,
50...Plane with area Sr located at distance 1lIir +, 5
1... Plane with area S2 located at distance r2, 100...
X-ray source, 101...X-ray slit for fan-shaped beam. Name of agent Patent attorney Shigetaka Awano Figure 18 Figure 2 Funeral diagram Figure Figure Figure Illustration

Claims (10)

[Claims] (1) A fan-shaped beam from an X-ray generator is irradiated onto a subject, the transmitted beam is made incident on a radiation semiconductor detector array arranged on a straight line or a curved arc, and the fan-shaped beam and the radiation semiconductor detector array are In an X-ray image receiving apparatus that obtains line-sequential X-ray pixel signals by driving a pixel on a straight line or a curved arc with respect to a subject to obtain an X-ray transmission plane image, a radiation semiconductor for correction is provided separately from the radiation semiconductor detector array. means for providing a detector or a group of detectors and integrating and outputting the X-ray dose of the fan-shaped beam incident on each of them at fixed time intervals;
Gain adjustment means for changing the degree of amplification and integrated X
A/D conversion means for A/D converting the dose, storage means for storing the A/D converted data signal, calculation means for determining an optimal gain from the data signal, and based on the result of the calculation means. An X-ray image receiver comprising: a control means for controlling the gain adjustment means; and a means for calculating a correction coefficient for X-ray intensity fluctuations from the data signal and correcting an X-ray pixel signal in a corresponding time period. Device. (2) The X-ray image receiving apparatus according to claim 1, wherein the correction radiation semiconductor detector is provided at a position where it directly receives the X-rays irradiated from the X-ray source. (3) The correction radiation detector is a scintillator, Si, G
2. The X-ray image receiving apparatus according to claim 1, wherein the X-ray image receiving apparatus is made of one of e, GaAs, and CdTe. (4) The X-ray image receiving apparatus according to claim 1, wherein the A/D conversion means is configured to perform A/D conversion multiple times during one line scan. (5) A fan-shaped beam from an X-ray generator is irradiated onto a subject, the transmitted beam is made incident on a radiation semiconductor detector array arranged on a straight line or a curved arc, and the fan-shaped beam and the radiation semiconductor detector array are In an X-ray image receiving apparatus that obtains line-sequential X-ray pixel signals by driving a pixel on a straight line or a curved arc with respect to a subject to obtain an X-ray transmission plane image, a radiation semiconductor for correction is provided separately from the radiation semiconductor detector array. A detector or a group of detectors is provided, an amplifying means for amplifying the pulse output from the correction radiation semiconductor detector or the group of detectors, a counting means for counting the pulse output from the amplifying means at regular intervals; An X-ray device characterized by having a storage means for storing data counted by the counting means, and a means for calculating a correction coefficient for X-ray intensity fluctuation from the data signal and correcting an X-ray pixel signal in a corresponding time period. line image receptor. (6) The correction radiation semiconductor detector and the radiation semiconductor detector array have the following relational expression, I_g(E) {1-exp(-μ_1(E)x_1)}
≦(S_2/S_1)(r_1/r_2)^2I_g(
E) {1-exp(-μ_2(E)x_2)} However, I_g(E): Number of radiation photons incident on the radiation semiconductor detector for correction μ_1(E): Attenuation coefficient μ of the radiation semiconductor detector for correction
_2(E): Attenuation coefficient x of the radiation semiconductor detector array
1: Thickness of the radiation semiconductor detector for correction x_2: Thickness of the radiation semiconductor detector array r_1: Distance from the X-ray source to the radiation semiconductor detector for correction r_2: Distance from the X-ray source to the radiation semiconductor detector array S_1: Opening area of radiation semiconductor detector for correction S_2:
6. The X-ray image receiving apparatus according to claim 5, wherein the X-ray image receiving apparatus is configured to be expressed by the aperture area of the radiation semiconductor detector array. (7) The X-ray image receiving apparatus according to claim 8, wherein the molecular weight of the radiation semiconductor detector for correction is less than or equal to the molecular weight of the radiation semiconductor detector array. (8) The radiation semiconductor detector for correction or the radiation semiconductor detector array is made of Si, Ge, GaAs, CdTe, Hg
The X-ray image receiving apparatus according to claim 6, characterized in that it is constructed from one of I_2. (9) The X-ray image receiving apparatus according to claim 6, wherein the radiation semiconductor detector for correction and the radiation semiconductor detector array are constructed of the same element. (10) The X-ray image receiving apparatus according to claim 5, 6, 7, 8 or 9, characterized in that the correction radiation semiconductor detector is provided at a position where it directly receives the X-rays irradiated from the X-ray source.