JP2869975B2 - Radiation image receiving device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an apparatus for obtaining an image of an object using radiation such as X-rays used for observing a human body tissue in a medical field, for example. About.

<Prior Art> The most widely used technology for obtaining an image of an object using radiation is a medical X-ray photograph. The general principle is that X-rays emitted from the focus of the X-ray tube and traveling straight,
In the process of transmitting through the target part of the subject, part of the transmitted part is absorbed by physical interaction such as photoelectric effect or Compton effect due to differences in density, elemental composition, thickness, etc.
Due to the attenuating effect of scattering, as a result, a difference in intensity occurs in the distribution of X-rays after transmission, and this is reproduced on a film as a density distribution of photographic density.

In addition to expressing such a grayscale distribution on a film, there is also a technique of expressing the grayscale distribution on a CRT using an image intensifier, an imaging plate, a semiconductor imaging device, or the like.

<Problems to be Solved by the Invention> In order to obtain an X-ray image suitable for the purpose of diagnosis using each of the above-described techniques, X-ray imaging conditions must be determined according to the target or site. However, since the X-rays generated from the X-ray tube are not monochromatic but have a continuous distribution and the composition of the object is extremely complicated, the tube voltage, the tube current, the imaging time, the imaging distance, the scattering grid It is actually very difficult to combine various factors, such as the availability of, with optimal conditions, and experience and multiple shootings were indispensable.

The radiation image receiving method proposed by Japanese Patent Application Laid-Open No. 60-80746 is designed to effectively utilize not only the X-ray density distribution information but also the energy information, so that each pulse wave height of the X-ray transmitted through the subject can be obtained. It is characterized by obtaining a density distribution for each image, but there is no consideration to obtain an image more suitable for the purpose of diagnosis, such as having a characteristic for each wave height. In addition, according to this method, information relating to pulses other than the pulse height of interest is substantially excluded, and as the number of pulse height groups to be discriminated increases, the information amount of each of them decreases, and image quality is reduced. Drops. Therefore, in order to obtain a high-quality image for each wave height using this method, it is necessary to multiply the photographing time, which causes a problem of an increase in the dose.

An object of the present invention is to provide a radiographic image as rough as possible under rough imaging conditions, that is, even under less than optimal imaging conditions, or without lengthening the imaging time.
It is an object of the present invention to provide a radiation image receiving apparatus that can be obtained while freely correcting after imaging.

<Means for Solving the Problems> A configuration for achieving the above object will be described with reference to FIGS. 1 and 2 corresponding to the embodiment.
One pulse amplifier 1 is provided for each radiation detection element S forming the one-dimensional or two-dimensional radiation detection element array A.
And a plurality of peak-height discriminating circuits for inputting output pulses of the pulse amplifier 1 and discriminating which of a plurality of peak-height ranges can be set arbitrarily.
2a, 2b ‥‥, a plurality of counting circuits 3a, 3b ‥‥ for counting the outputs of the respective peak height discriminating circuits 2a, 2b ‥‥, and the outputs of the respective counting circuits 3a, 3b ‥‥. A plurality of weighting circuits 4a, 4b} for adding the weights to be obtained, and an adding circuit 5 for adding the outputs of the respective weighting circuits 4a, 4b #.
It is characterized in that each of the 5,5 ° outputs is used as a pixel grayscale signal.

<Operation> The radiation incident on the radiation detecting element S is subjected to a wave height discrimination circuit.
2a, 2b}, they are discriminated into a plurality of groups according to the magnitude of the energy. The output of each counting circuit 3a, 3b # therefore represents the dose of the radiation incident on its element S by energy group. This counting circuit 3
a, 3b ‥‥ are added to the output after weighting them with a certain weight. Take a value.

By performing the above calculation for all the radiation detection elements S ‥‥ S and forming an image as the density signal of the pixel corresponding to each element S ‥‥ S, the energy information can be obtained in the spatial distribution of the transmitted radiation. A superimposed image with an arbitrary weight is obtained.

<Example> An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a signal processing circuit according to an embodiment of the present invention for one radiation detecting element S, and FIG. 2 is a conceptual diagram showing the overall configuration of the embodiment of the present invention.

In this example, an X-ray tube 10 is used as a radiation source, and a compound semiconductor having a high atomic number such as CdTe or HgI ₂ is used as a radiation detecting element S.

As shown in FIG. 2, the X-ray tube 10 includes a controller 11
Thus, the voltage and current according to the set values are supplied from the high-voltage power supply 12 for the set time, and the X-rays according to the set conditions are applied to the subject 13.
Irradiated toward Behind the subject 13, an X-ray detection element array A in which X-ray detection elements S ‥‥ S are arranged on a two-dimensional plane, and a signal processing circuit group corresponding to each element S ‥‥ S are provided. The circuit unit 14 is provided. The circuit unit 14 converts an X-ray distribution including transmission information of the subject 13 into a density distribution of electric pulses as described later, and expresses the image on the display unit 15 with each detection element S ‥‥ S as a pixel. Configuration.

Now, as shown in FIG. 1, each detecting element S ‥‥ S has one pulse amplifier circuit 1 and a plurality of pulse height discriminating circuits.
2a, 2b}, the same number of pulse counting circuits 3a, 3b # and weighting circuits 4a, 4b #, and one addition circuit 5
Is connected.

The pulse height discrimination level of each of the pulse height discrimination circuits 2a and 2b # is configured to be arbitrarily set by a discrimination level setting device 6 common to the signal processing circuits of the respective detection elements S # S.

Each of the weighting circuits 4a and 4b} is configured such that the weighting factor can be arbitrarily set by a weighting factor setting circuit 7 common to the signal processing circuits of the detection elements S 検 出 S. A reverse bias is applied to each of the radiation detection elements S に よ り S by a bias power supply 16, and the X-rays incident on the depletion layer generated in the semiconductor due to the reverse power are subjected to various physical processes so that the wave height corresponding to the energy is increased. Generates an electric pulse.

The electric pulse from the detection element S is amplified and shaped by the pulse amplifier circuit 1, and the peak value of the electric pulse is a next-stage pulse height discrimination circuit group.
In 2a, 2b}, the signal is compared with a preset discrimination level, and is input to one of the pulse counting circuit groups 3a, 3b corresponding to the peak value, and the count value is increased by one. That is, the number of X-rays transmitted through the subject 13 and incident on the detection element S is divided into a plurality of groups based on the energy, and is counted for each group.

Then, the count values for each group are weighted by the weighting circuit groups 4a, 4b # at the next stage according to the respective settings, and then added up by the addition circuit 5.

The above circuit is provided for each detection element S ‥‥ S, and the output of each addition circuit 5 is output as a pixel density value on the display unit 15.

Next, the operation and usage will be described with reference to an example in which a human body is used as a subject using the embodiments of the present invention.

In general, soft tissues such as breasts have a relatively low tube voltage (60 KV) because their X-ray attenuation coefficient is smaller than that of muscles and bones.
In the following, shooting is performed. In this case, most of the X-ray attenuation is due to the photoelectric effect, and the influence of the scattering can be considered to be negligible. However, for example, as shown in FIG. 3 which shows an example of a radiation X-ray spectrum at a tube voltage of 90 KV, the energy distribution of the X-rays generated from the X-ray tube 10 is not monochromatic but changes with the tube voltage. It has a wide spread. This is why it is difficult to set the optimum tube voltage for the purpose of diagnosis as described above.

Now, FIGS. 4 (a) and (b) show the same X
4 is a graph showing transmission spectra in a low-density portion and a high-density portion when a line is irradiated on soft tissue. As is clear when comparing FIGS. 4 (a) and 4 (b),
Since the lower energy X-rays have a greater degree of attenuation by the substance, the difference in the count of transmitted X-rays between the low-density portion and the high-density portion becomes larger on the low energy side.

Therefore, when observing such soft tissue, the discrimination level setting unit 6 sets the discrimination level of one peak discrimination circuit 2a in the processing circuits of all the detection elements S ‥‥ S from A shown in FIG. At B, the discrimination level of another wave height discrimination circuit 2b is set to B or higher, and an image is taken. Here, A is a value slightly larger than the noise level, and B is near the peak value of the spectrum of the irradiated X-ray. Thereby, the pulse counting circuit 3a _calculates n _{aL in the} low density part, n _aH in the high density part, and
Pulse counting circuit 3b low density part n _bL, high density part n _bH
Will be counted. At this time, since the shape of the X-ray spectrum is generally almost bilaterally symmetric, (n _aL −n _aH )> (n _bL −n _bH ) (1) according to the above-described principle.

Next, the weighting factor of the weighting circuit 4a is And the weighting factor of the weighting circuit 4b And display images. Where a and b
Is a numerical value of 0 or more and 2 or less.

Accordingly, the output of the adder circuit 5 is such that if the X-ray transmitted through the low-density portion is incident on the corresponding detection element S, And if X-rays transmitted through the high-density part are incident, Becomes In other words, the pixel density signal for the detection element S is n ' _{L for} a low density part and n' _{H for} a high density part, and the density difference n ' _LH is Becomes

Incidentally, when no weight is assigned (a = b), in other words, when the outputs of the pulse counting circuits 3a and 3b are directly input to the adding circuit 5, the density difference n _LH is n _LH = (n _aL −n _aH ). + (n _bL -n _bH) becomes a ...... (5), n _'LH compared to the n _LH is, the following (6)
It increases by Δn shown in the equation.

This is because, in the case of soft tissue, the equation (1) is satisfied. Therefore, by setting a> b, the maximum (when a = 2, b = 0) is obtained, and (n _aL −n _aH ) − (n _bL −n _bH ) has been proved to be capable of increasing the contrast.

Next, on the contrary, when a thick portion such as the chest, abdomen, or thigh, or a high-density portion such as a bone or an organ is included, a relatively high tube voltage ( It is necessary to shoot at 60KV or more). In such a case, X-rays of relatively high energy are generated, and the effect of the Compton effect cannot be ignored. The scattered X-rays pass a part of the energy to the electrons in the substance, so that the scattered X-rays are incident on the detection element S ‥‥ S with lower energy than the energy originally possessed. However, the one whose energy is too low is absorbed inside the substance and does not reach the detection element S ‥‥ S, so that its spectrum is apparently as shown in FIG.

When observing such a part, the wave height discrimination circuit 2a
The discrimination level of A to B shown in FIG. 5 and the wave height discrimination circuit 2b
The photographing is performed by setting the discrimination level of B to C and the discrimination level of the wave height discrimination circuit 2c to C or higher. Here, A is a value slightly larger than the noise level, B is near the energy at which the effect of Compton scattering appears, and C is a value near the peak value of the spectrum of the irradiated X-ray.

Accordingly, the pulse counting circuit 3a, 3b and 3c as is shown in FIG. 5, respectively N _a, so that counting the N _b and N _c.

In the image display, the largest value is assigned to the count value Na of the region from A to B having a large difference in attenuation, similarly to the case of the soft tissue, and the region from B to C where the influence of the scattering is greatest. the count value N _b give the smallest weight. Thus, the addition circuit 5 outputs a weighted pixel density N 'expressed by the following equation (7) in which the influence of scattering is reduced and the difference in absorption based on the difference in tissue density is emphasized.

Thus, even in the case of a high tube voltage, the effect of scattered radiation is small and an image with good contrast can be obtained.

In the above-described embodiment of the present invention, the weighting factor can be set while viewing the obtained image after simple imaging in a state where each wave height discrimination level is set. Obtainable.

Note that the present invention can be variously modified with respect to the types and arrangement methods of the detection elements.

That is, the detection element only needs to be capable of measuring energy, and can be replaced with, for example, a scintillator, MWPC, or the like.

As an arrangement method, as a two-dimensional arrangement other than the planar arrangement as shown in FIG. 2, for example, as shown in FIG. It is possible to adopt a method in which the elements S ‥‥ S are arranged in a stepwise manner as a whole. Alternatively, as shown in FIG. 7, the elements S ‥‥ S are arranged in a straight line or an arc to form a so-called one-dimensional array 71, and this one-dimensional array 71 is interposed between the X-ray tube 72 and the subject 73. A method of obtaining a two-dimensional image by moving the element S ス リ ッ ト S at regular intervals in a direction perpendicular to the arrangement direction of the elements S ‥‥ S in conjunction with the slit 74 and repeating measurement and data transmission for a fixed time each time. Can be adopted.

Further, it goes without saying that the concept of the image receiving apparatus of the present invention can be applied to X-ray CT and the like, and is also effective for γ-rays and the like other than X-rays.

<Effects of the Invention> As described above, according to the present invention, it is possible to obtain an image in which energy information is superimposed with an arbitrary weight on the spatial distribution of transmitted radiation, and the image is obtained under conditions that are not optimal imaging conditions. After the simple imaging, it is possible to arbitrarily correct as necessary, such as enhancing the contrast of the tissue of interest and removing scattered radiation, thereby dramatically improving the diagnosis based on the radiographic image. At the same time, this also leads to a reduction in the exposure dose of the subject, and the effect in this respect is great.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of a signal processing circuit according to an embodiment of the present invention for one radiation detecting element S, and FIG. 2 is a conceptual diagram showing the overall configuration. FIG. 3 is a graph showing an example of a radiation X-ray spectrum, FIG. 4 is a graph showing a difference in transmission spectrum due to a difference in density in soft tissue, and FIG. 5 is a graph showing a transmission spectrum in a case where the Compton effect is affected. It is. 6 and 7 are explanatory views of another embodiment of the present invention. 1 pulse amplifying circuit 2a, 2b pulse height discriminating circuit 3a, 3b pulse counting circuit 4a, 4b weighting circuit 5 addition circuit 6 discrimination level setting device 7 weighting coefficient setting device 10 ... X-ray tube 13 ... subject 14 ... circuit unit 15 ... display unit A ... X-ray detection element array S ... X-ray detection element

Claims (1)

(57) [Claims] 1. A radiation beam including transmission information of a subject from a radiation source is incident on a detection element array in which a plurality of radiation detection elements capable of measuring energy of incident radiation are arranged one-dimensionally or two-dimensionally. In the apparatus for obtaining a radiation image of a subject, 1
A plurality of pulse amplifiers, each of which receives an output pulse of the pulse amplifier, and a plurality of pulse height discriminating circuits for discriminating which of a plurality of pulse height ranges whose pulse peak value can be arbitrarily set, A plurality of counting circuits for counting the outputs of each wave height discrimination circuit, a plurality of weighting circuits for arbitrarily setting the weights of the outputs of the respective counting circuits, and an adding circuit for adding the outputs of the respective weighting circuits. A radiation image receiving apparatus, wherein an output of each addition circuit corresponding to each radiation detection element is provided as a pixel grayscale signal.