JPH0715498B2 - X-ray receiver - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray image receiving apparatus using X-rays in the medical field and industrial field, and more particularly to a structure for correcting the uniformity thereof.

2. Description of the Related Art In recent years, those using a stimulable phosphor instead of an X-ray image receiving device for obtaining an X-ray transmission plane image using a silver salt photographic film,
A device using an X-ray sensitive solid-state element array has been developed.

The former is known in which a stimulable fluorescent plate is used instead of an X-ray film, an X-ray latent image is formed, and pixel signals are taken out by sequential stimulation with a laser (JP-A-55-15025).

In the latter case, a silicon element combined with a fluorescent material is used as the X-ray sensitive solid element to measure the amount of current generated by photoconduction (Japanese Patent Laid-Open No. 53-105179 and Japanese Patent Laid-Open No. 53-105179).
96787) and those using a radiation semiconductor detector array (Japanese Patent Laid-Open No. 59-94046).

Problems to be Solved by the Invention However, the former conventional example using the stimulable phosphor has an image quality comparable to that of X-ray photography, but has a problem of high X-ray exposure. Further, the latter conventional example using the X-ray sensitive solid-state element array has a poor surface resolution in terms of material.

On the other hand, in the conventional example using the radiation semiconductor detector array, although the sensitivity to radiation and the surface resolution are high, the radiation semiconductor detector array arranged in a straight line or a curved arc with respect to the human body is linear or curved with respect to the human body. Since it is a line-sequential system in which pixel signals are obtained by scanning in a curved arc shape, there is a problem that the image quality is slightly insufficient.

This is because the X-ray exposure time is extremely short in the method using X-ray photography or the stimulable phosphor to obtain one X-ray transmission plane image, while the radiation semiconductor detection is performed. This is because the X-ray exposure time of 1 second or more is required to obtain the pixel signals line by line when the detector array is used. Therefore, the temporal fluctuation of 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, which leads to deterioration in image quality.

In view of such a point, the present invention monitors the time variation of X-rays emitted from the X-ray generator at an optimum 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 apparatus in which the image quality is not deteriorated due to the fluctuation of X-ray intensity.

Means for Solving the Problems According to the present invention, a fan-shaped beam from an X-ray generator is applied to a subject, and the transmitted beam is incident on a radiation semiconductor detector array arranged on a straight or curved arc. And a radiation semiconductor detector array for driving a subject on a straight or curved arc to obtain line-sequential X-ray pixel signals to obtain an X-ray transmission plane image. Correction radiation semiconductor detectors or detector groups are provided separately from the array, and means for integrating and outputting the X-ray dose of the fan-shaped beam that is 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 optimum gain from the data signal, and this calculation means Control means for controlling the gain adjusting means based on the result of
An X-ray image receiving apparatus comprising means for calculating a correction coefficient for X-ray intensity fluctuation from the data signal and correcting the X-ray pixel signal in a corresponding time zone.

The present invention has the above-described configuration, the optimum gain for A / D conversion is calculated based on the X-ray intensity fluctuation data obtained by the correction radiation semiconductor detector or the detector group, and the gain is set by the gain adjusting means. To be done. After setting the gain, imaging is performed, and the radiation semiconductor detector array stores the X-ray transmission plane image as image data, and at the same time, the correction radiation detector stores the X-ray intensity fluctuation data. From this X-ray intensity fluctuation data, X-ray intensity correction data is obtained, and the image data in the corresponding time zone is corrected to obtain a uniform image.

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

In the figure, 1 is a radiation detector for X-ray intensity correction, which is sensitive to the incidence of X-rays and converts it into an electric signal. An integrator 2 integrates the output signal from the X-ray intensity correction radiation detector 1. Reference numeral 3 denotes 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 the A / D converter 4 and stored as X-ray intensity fluctuation data 5 in a memory (not shown). Further, 10 is a radiation semiconductor detector array arranged in a straight line or a curved arc with respect to a human body as an object, and by scanning this with a straight line or a curved arc, the X-ray transmission plane image can be obtained. To be

The output pulse from the radiation semiconductor detector array 10 is theoretically the most sensitive because it is generated for each photon of the incident radiation. Reference numeral 11 is a pulse amplifier circuit. Reference numeral 12 is a wave height discriminating circuit for discriminating the energy of the pulses, and outputs the pulse when a pulse input having a preset wave height value or more is received. Reference numeral 13 is a pulse counting circuit, which continuously counts the output pulses from the pulse height discrimination circuit 12 line by line. Reference numeral 6 denotes a CPU for calculating the X-ray intensity correction data 14 from the X-ray intensity fluctuation data 5, generating the gain control signal 16 by determining the optimum gain, and causing the radiation semiconductor detector array 10 to scan. Reset signal 17 is generated for each line, and integrator 2 and pulse counting circuit
13 and reset. The count value counted by the pulse counting circuit 13 is stored as the image data 15.

The calculation of the X-ray intensity correction data 14 is performed as follows, for example. M pieces of X-ray intensity variation data 5 are obtained at regular intervals in the scanning direction, and the i-th data 5 is Xi, and the average value is Xmean. Xm for all image data 15 corresponding to the time period when the i-th X-ray intensity fluctuation data 5 was obtained
The image data 15 is corrected by multiplying by ean / Xi.

Next, the gain is determined as follows, for example.
The current gain is A ₀ .

When the number of bits of the A / D converter 4 is n bits, the maximum number ADmax represented is ADmax = 2n-1 (1).

In addition, m Xs obtained by scanning once
The average value Xmean of the line strength variation data 5 is the i-th data set to Xi, It is represented by.

Here, it is considered that the variation in the number of X-ray photons has a Poisson distribution, and this standard deviation σ is known to be expressed as σ = ... (3), where n is the average number of photons. Therefore, σ = mean.

At this time, if n ≧ 5, it can be approximated to a normal distribution.
To convert about 99.7% into a digital signal by the A / D converter 4 without overflowing, the gain should be multiplied by (ADmax-3σ) / Xmean (4).

Therefore, if the gain to be obtained is Ag, then Ag = {(ADmax-3σ) / Xmean} · A ₀ (5). Generally, it is expressed as A _K = {(ADmax−δ) / Xmean} · A ₀ (6), and δ determines the margin until overflow. Here, δ = 3σ (7), but other appropriate values may be used.

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

In the example shown in FIG. 3, k + 1 resistor groups 21b are connected in series to form a feedback resistor. 22b is a switch connected in parallel to both ends of each resistor, and by closing the switch, the corresponding resistance value becomes zero. Where resistor group 21b
Is R, 2R, 4R, ..., 2kR, and by closing any number of switches in the switch 22b at the same time, from zero to (2k ⁺ 1-1) R
It is possible to obtain any resistance value up to R intervals.

Further, as shown in FIG. 4, the automatic switching circuit 32 can be configured to set an arbitrary resistance value. Reference numerals 30a, 30b and 30c are resistance groups, and resistors 1k, 8k and 64k are inserted in series between the respective terminals. Reference numeral 31 is a selector capable of switching 8 terminals. With this configuration, one 8-terminal selector 31 can be controlled by the 3-bit control signal 16. Also, since it has 8 terminals, the resistance value is expressed in octal, that is,
By multiplying 8 ⁰ , 8 ¹ , 8 ² times, the resistance value between terminals XY can be set from 0 to 511 k in 1 k units.
In the present embodiment, the select 31 having eight terminals is connected in three stages, but the one having P terminals is connected in q stages (p, q).
May be any natural number). In this case, each select 31
It is needless to say that the resistance value at is a p-adic multiple, that is, p ⁰ , p ¹ , p ² , ..., Pq ⁺¹ times. Further, in the present embodiment, the A / D conversion is performed only once during one line scan, but the averaging can be performed by performing the A / D conversion a plurality of times.

As described above, according to the present embodiment, the radiation detector 1 for X-ray intensity correction is provided, and this is integrated and output for each line and the A / D
In the case of conversion, by providing the automatic gain adjusting circuit 3, the optimum gain can be set for the irradiated X-ray intensity, so that accurate X-ray intensity fluctuation data 5 can be obtained. Thereby, the optimum X-ray intensity correction data 14 can be obtained, and the disturbance due to the X-ray intensity fluctuation of the image can be eliminated.

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

In the figure, 10 is a radiation semiconductor detector array, 11 is a pulse amplifier 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. It is similar to the example (see FIG. 1). The difference from the first embodiment is that the optimum radiation semiconductor detector for correction 80 outputs a pulse for each photon of radiation.
Is used, and another pulse counting circuit 13 is provided for measuring the X-ray intensity correction data 14.

The operation will be described below. X-ray photons that have passed through the subject are incident on the radiation semiconductor detector array 10, are absorbed, and are output as pulses. This pulse is amplified by the pulse amplifier circuit 11, and only those having a peak value higher than a preset peak value are selected by the pulse height discrimination circuit 12 and output as a pulse. The output pulses are counted by the pulse counting circuit 13 and the image data 15
Is recorded as. On the other hand, the X-ray intensity correction data 14
It is obtained by counting, for each line, the pulse generated by the correction radiation semiconductor detector 80 provided at the position where the X-ray photons generated by the radiation 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 plan of the area S ₁ at a distance r _1, 51 is a plan of the area S ₂ at a distance r _2. Here, the relationship between both areas S ₁ and S ₂ is S ₁ / S ₂ = r ₁ ² / r ₂ ² (8), and the normal line from the center of both planes 50 and 51 is X.
It shall be on the radiation source.

Further, the areas S ₁ and S ₂ are sufficiently smaller than the square of the distances r ₁ and r ₂ . The X-rays generated in the X-ray source spread radially. Therefore, both areas S ₁ and S ₂ are different from each other, but the number of X-ray photons passing through per unit time is the same. In other words, when both areas S ₁ and S ₂ are equal, the number of photons incident on the plane 50 closer to the X-ray source is (r ₂ ² / r ₁ ² ) times. Therefore, when the same radiation semiconductor detector is used, pile-up often occurs on the plane 50 side which is closer.

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

The radiation semiconductor detector 60 for X-ray intensity correction is the distance r ₁ from the X-ray source, the thickness x ₀ , and the area S ₁ of the portion where the radiation is actually incident in the radiation sensitive portion. The device array 61 is a distance r ₂ from the X-ray source, a thickness x ₀ , and the area of the part where the radiation is actually incident within the part sensitive to the radiation.
It is S ₂ . 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 S ₁ and S ₂ is S ₁ / S ₂ = r ₁ ² / r ₂ ² …… (8) ′. With this configuration, the count rates of the X-ray photons counted by both detectors per unit time can be made similar.

FIG. 8 shows a third embodiment of the present invention, in which the radiation semiconductor detector 70 for X-ray intensity correction has a distance r ₁ from the X-ray source 100,
The thickness x ₁ is the area S ₀ of the part where the radiation is actually incident in the part sensitive to the radiation. The radiation semiconductor detector array 71 has a distance r ₂ from the X-ray source 100, a thickness x ₂ , and an area S _{0 of} a portion where radiation is actually incident within a portion sensitive to radiation per element.
Is. The relationship between the thicknesses x ₁ and x ₂ will be described below.

The ratio of the incident radiation absorbed in the semiconductor detector has the following relationship.

I (E) = I ₀ (E) {1-exp (-μ (E) x)}
(9) where I (E) is the number of absorbed radiation photons, I ₀ (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 make the count rates per unit time of both detectors 70 and 71 shown in FIG. 8 equal, the following relational expression is satisfied.

I (E) {1-exp (-μ ₁ (E) x ₁ )} = (r ₁ / r ₂ ) ² I
₀ (E) {1-exp (-μ ₂ (E) x ₂ )} (10) From this relational expression, the relationship between both thicknesses x ₁ and x ₂ is as follows. x ₁ = over _{{1n [1- (r 1 /} r 2) 2 {1 -exp (-μ 2 (E) x 2)}]} / μ 1 (E) ...... (1
1) where μ ₁ (E) is a radiation semiconductor detector for X-ray intensity correction
Attenuation coefficient of 70, μ ₂ (E) is radiation semiconductor detector array
The damping factor is 71. That is, by setting the thicknesses x ₁ and x ₂ of both the detectors 70 and 71 so as to satisfy the relational expression (11), the detectors 70 having the same incident area even though the number of incident photons is different, Even with 71, the counting rate can be the same.

The incident area of photons can be easily adjusted by providing a grid that blocks radiation. For example, Si and CdTe will be described as an example of the semiconductor detector. Both the radiation semiconductor detector 70 for X-ray intensity correction and the radiation semiconductor detector array 71 are made of Si.
Is the material, and the thickness of the radiation semiconductor detector array 71 is 0.1c.
Attenuation coefficient at m, 60keV is 0.3cm ^-1 , distance ratio r ₁ / r ₂ = 0.2
In that case, the thickness of the radiation semiconductor detector 70 for X-ray intensity correction is about 0.0039 cm. Next, both detectors 70 and 71 are CdTe.
The radiation semiconductor detector array 71 has a thickness of 0.1c
When the attenuation coefficient at m and 60 keV is 33 cm ⁻¹ and the distance ratio r ₁ / r ₂ = 0.2, the thickness of the X-ray intensity correction radiation semiconductor detector 70 is about 0.0012 cm. When Si 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 about 0.1310 cm. Becomes

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

In the above structure, the X-ray transmission plane image can be obtained by driving the fan beam X-ray slit 101 and the radiation semiconductor detector array 71 synchronously in the arrow direction. At this time, the X-ray intensity correction semiconductor detector 70 is provided at a position where X-rays directly enter, and obtains X-ray intensity fluctuation data.

As described above, according to the present embodiment, the X
Even if the radiation intensity detecting radiation semiconductor detector 70 is installed, the counting rate can be made approximately the same as that of the radiation semiconductor detector array 71. Therefore, in the radiation semiconductor detector 70 for X-ray intensity correction, the pile-up phenomenon does not increase and the value becomes smaller than the actual count value, so that a correct correction value cannot be obtained. 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 device 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 by either the incident area or the thickness of the detector in order to make the number of absorbed photons substantially equal. Although it 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 from the following equation in which the right side of equation (10) is multiplied by the area ratio term.

I ₀ (E) {1-exp (-μ ₁ (E) x ₁ )} = (S ₂ / S ₁ )
^{_{(R 1 / r 2) 2}} I 0 (E) {1-exp ( over _{μ 2 (E) x 2)} } ...
(12) Further, in the present embodiment, the relationship between the radiation semiconductor detector 70 for X-ray intensity correction and the radiation semiconductor detector array 71 is set so that the number of photons absorbed is almost equal. The number of photons absorbed by the correction radiation semiconductor detector 70 may be set within a range not exceeding the number of photons absorbed by the radiation semiconductor detector array 71.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to configure an X-ray image receiving device having good image quality even if the X-ray intensity of X-rays generated by the X-ray generator fluctuates with time. , Its practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of an X-ray image receiving apparatus according to the first embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams of a basic automatic gain adjusting circuit in the apparatus, and FIG. FIG. 5 is a circuit diagram of an automatic gain adjustment circuit having 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 is spread of X-rays. 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 embodiment. 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 …… CPU, 10, 61, 7
1 ... 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 ... Distance r the plane of the area S ₁ in the _1, 51 ...... distance r ₂ the plane of the area S ₂ in the, 100 ...... X-ray source, 101 ...... fan beam X-ray slit for.

Claims (10)

[Claims] 1. A fan-shaped beam from an X-ray generator is irradiated onto a subject, and the transmitted beam is made incident on a radiation semiconductor detector array arranged on a straight or curved arc, and the fan-shaped beam and the radiation semiconductor detector. In an X-ray image receiving device for obtaining an X-ray transmission plane image by driving an array and a subject on a straight or curved arc to obtain line-sequential X-ray pixel signals,
A radiation semiconductor detector or a detector group for correction is provided separately from the radiation semiconductor detector 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 for changing the amplification degree. Gain adjusting means, A / D converting means for A / D converting the integrated X-ray dose, storing means for storing the A / D converted data signal, and calculation for determining an optimum gain from the data signal. Means, control means for controlling the gain adjusting means based on the result of the computing means, means for calculating a correction coefficient for X-ray intensity fluctuation from the data signal, and means for correcting the X-ray pixel signal in a corresponding time zone. An X-ray image receiving apparatus comprising: 2. The X-ray image receiving apparatus according to claim 1, wherein the correcting radiation semiconductor detector is provided at a position for directly receiving the X-ray emitted from the X-ray source. 3. A radiation detector for correction is a scintillator, Si,
The X-ray image receiving apparatus according to claim 1, wherein the X-ray image receiving apparatus is composed of any one of Ge, 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 a plurality of times during one line scan. 5. A fan-shaped beam from an X-ray generator is applied to a subject, and the transmitted beam is made incident on a radiation semiconductor detector array arranged on a straight or curved arc, and the fan-shaped beam and the radiation semiconductor detector. In an X-ray image receiving device for obtaining an X-ray transmission plane image by driving an array and a subject on a straight or curved arc to obtain line-sequential X-ray pixel signals,
A correction radiation semiconductor detector or a detector group is provided separately from the radiation semiconductor detector array, and amplification means for amplifying a pulse output from the correction radiation semiconductor detector or the detection group, and a pulse from the amplification means Counting means for counting the output at constant time intervals, storage means for storing the data counted by this counting means, and a correction coefficient for the X-ray intensity fluctuation calculated from the data signal, and an X-ray pixel signal in a corresponding time zone. And means for correcting X
Ray receiver. 6. A radiation semiconductor detector for correction and a radiation semiconductor detector array have the following relational expression: I ₀ (E) {1-exp (−μ ₁ (E) x ₁ )} ≦ (S ₂ / S ₁ )
(R ₁ / r ₂ ) ² I ₀ (E) {1-exp (−μ ₂ (E) x ₂ )} where I ₀ (E): Number of radiation photons incident on the correcting radiation semiconductor detector μ ₁ (E): Attenuation coefficient of radiation semiconductor detector for correction μ ₂ (E): Attenuation coefficient of radiation semiconductor detector array x ₁ : Thickness of radiation semiconductor detector for correction x ₂ : Thickness of radiation semiconductor detector array r ₁ : Distance from X-ray source to radiation semiconductor detector for correction r ₂ : Distance from X-ray source to radiation semiconductor detector array s ₁ : Area of aperture of radiation semiconductor detector for correction s ₂ : Radiation semiconductor detector The X-ray image receiving apparatus according to claim 5, wherein the X-ray image receiving apparatus is configured to be represented by an opening area of the array. 7. The X-ray image receiving apparatus according to claim 6, wherein the molecular weight of the correcting radiation semiconductor detector is not more than the molecular weight of the radiation semiconductor detector array. 8. The X-ray image receiving apparatus according to claim 6, wherein the radiation semiconductor detector for correction or the radiation semiconductor detector array is made of any one of Si, Ge, GaAs, CdTe, and HgI _2. . 9. The X-ray image receiving apparatus according to claim 6, wherein the correcting radiation semiconductor detector and the radiation semiconductor detector array are formed of the same element. 10. The X-ray image receiving apparatus according to claim 5, wherein the correcting radiation semiconductor detector is provided at a position for directly receiving the X-ray emitted from the X-ray source. apparatus.