JP7531337B2 - Radiography system, control device, control method, and program - Google Patents

Description

The present invention relates to a radiation imaging system, a control device , a control method, and a program.

Conventionally, it is known to measure the quantity of bone mineral in bones for the diagnosis of osteoporosis, etc. One method for measuring bone mineral quantity is, for example, the DXA (Dual-energy X-ray Absorptiometry) method, which uses two X-rays with different energy distributions to measure bone density based on the difference in the X-ray absorption coefficients of soft tissue and bone tissue.

In dedicated bone density measurement devices using DXA, the problem occurs that the detection value of low-energy X-rays is significantly reduced due to the measurement being dependent on the physique of the subject, while the high-energy X-rays can be too strong and cause blackouts. In response to this problem, Patent Document 1 proposes a measure to control the ratio of the generation time of high-energy X-rays and low-energy X-rays for each line in a fan beam that is irradiated alternately at a constant cycle according to the physique of the subject, as a measure to reduce the detection value of low-energy X-rays in the case of a thick subject compared to a subject of normal physique.

JP 2009-131564 A

Meanwhile, attempts are being made to make it possible to measure bone density using DXA with radiography systems for general radiography. In this case, it is difficult for a general X-ray system to control the ratio of the time that high-energy X-rays and low-energy X-rays are emitted alternately at a fixed interval according to the subject's build, as can be done with devices dedicated to bone density measurement, and exposure-controlled radiography is required to prevent radiography due to insufficient or excessive doses. In addition, for the X-ray beam emitted by a general radiography system, a cone beam is used, rather than a fan beam, and a method is required to simultaneously image a plane at once.

In view of the above-mentioned conventional techniques, the present invention aims to provide a radiography technique that can obtain the quantity of a substance that constitutes a subject using multiple radiography images acquired based on exposure-controlled radiation in a general radiography system.

In order to achieve the above object, a radiation imaging system according to one aspect of the present invention comprises:
a radiation generating means for generating radiation having different energies in response to different tube voltages set as imaging conditions;
a radiation detection means for detecting radiation of different energies ;
an exposure control means for controlling generation of the radiation by the radiation generating means based on a comparison between an irradiation amount of the radiation and a target exposure value of the radiation calculated according to the imaging conditions;
A radiation imaging system comprising:
If the radiation exposure is stopped by releasing the exposure switch before the radiation exposure amount from the previous radiography reaches the exposure target value,
The exposure control means sets an exposure target value for the other radiography to be performed later, which is different from the exposure target value for the previously performed radiography, based on the radiography time from the start of the previously performed radiography to the stop of radiation irradiation by releasing the irradiation switch, and on the other tube voltage information .

The present invention provides a radiography technique that can obtain the quantity of material constituting a subject using multiple radiography images acquired based on exposure-controlled radiation in a general radiography system.

According to the present invention, even when obtaining the quantity of material constituting a subject (e.g., when performing bone density measurement) using multiple radiation images obtained by a general radiation imaging system, it is possible to prevent radiation imaging due to insufficient or excessive dose.

1 is a diagram showing a schematic configuration of a radiation imaging system according to a first embodiment. FIG. 4 is a diagram for explaining processing of processing flow 1 according to the first embodiment. FIG. 4 is a diagram for explaining processing of a processing flow 2 according to the first embodiment. FIG. 13 is a diagram showing a schematic configuration of a radiation imaging system according to a second embodiment. FIG. 13 is a diagram for explaining processing in a processing flow 3 according to the second embodiment. FIG. 13 is a diagram showing a schematic configuration of a radiation imaging system according to a third embodiment. 13A to 13C are diagrams for explaining a radiation energy generating method according to a third embodiment. 5A to 5C are diagrams showing an example of an automatic exposure calculation method according to the first embodiment.

The following embodiments are described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe multiple features, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicate explanations are omitted.

[First embodiment]
(Outline of the radiography system)
1 is a diagram showing a schematic configuration of a radiation imaging system 10 according to a first embodiment of the present invention. The radiation imaging system 10 includes a radiation generation unit 101, a control device 11, and a radiation detector 12.

The radiation generating unit 101 is equipped with a radiation tube that generates radiation, and irradiates a patient, who is a subject, with radiation 100. The radiation generating unit 101 irradiates cone beam radiation 100 toward the radiation detector 12.

The radiation detector 12 is configured as a flat panel detector (FPD) and has an exposure dose detection unit 105 that detects the exposure dose of radiation 100 emitted from the radiation generation unit 101, and a radiography unit 102 that acquires radiation distribution information (radiation image data) based on the radiation 100.

The radiography unit 102 detects the cone beam radiation 100 emitted from the radiation generation unit 101 all at once, and has pixels arranged in an array (two-dimensional area) that output signals according to the incident light. The photoelectric conversion element of each pixel converts the light converted by the phosphor into an image signal, which is an electrical signal, and outputs the image signal. In this way, the radiography unit 102 is configured to detect the radiation that has passed through the subject and obtain an image signal (radiation image data).

The irradiation amount detection unit 105 has multiple detection elements for detecting the irradiation amount in a specific area within the imaging area of the radiation imaging unit 102, separate from the pixels for imaging, and detects (monitors) the cumulative irradiation amount in the specific area. The irradiation amount detection unit 105 transmits the detected irradiation amount to the control device 11 (exposure control unit 106).

The radiography unit 102 acquires radiation distribution information (X _L ) due to low-energy radiation and radiation distribution information (X _H ) due to high-energy radiation based on radiation of different energies (low-energy radiation, high-energy radiation) irradiated from the radiation generation unit 101. Here, the low-energy radiation distribution information (X _L ) becomes a low-energy radiation image. Also, the high-energy radiation distribution information (X _H ) becomes a high-energy radiation image. The radiography unit 102 transmits the acquired radiation distribution information (low-energy radiation image, high-energy radiation image) to the control device 11 (measurement quantity calculation unit 103).

The control device 11 controls the operation of the radiation generating unit 101 based on calculation processing based on the radiation distribution information acquired by the radiography unit 102 and the dose detected by the dose detection unit 105.

The hardware configuration of the control device 11 includes a CPU that controls the overall operation of the control device 11, a storage unit realized by a hard disk drive, RAM, ROM, etc., and a communication I/F (interface) unit that manages communication with the outside world, and the control device 11 is communicatively connected to the radiation generation unit 101 and the radiation detector 12 via the communication I/F unit. The communication I/F (interface) unit is also connected to the RIS (radiology department information system), PACS (image server), and HIS (hospital information system) via a network, and can send and receive radiation image data, patient information on the subject, etc.

The storage unit stores, for example, various data and various information required when the CPU performs processing using a computer program, etc. The storage unit also stores, for example, various data and various information obtained when the CPU performs processing using a computer program, etc.

The RAM (writable memory) of the storage unit functions as the CPU's main memory, work area, etc. When executing processing, the CPU loads the necessary computer programs, basic data, etc. from the hard disk device or ROM into the RAM, and executes the computer programs, etc., thereby realizing various functional operations of the control device 11.

The control device 11 has, as its functional components, a measurement amount calculation unit 103, a shooting condition acquisition unit 104, and an exposure control unit 106. Each functional component is realized by the CPU expanding a computer program into the RAM and executing it. Each functional block of the control device 11 is merely an example, and the control device 11 may be configured to include further functional blocks.

Furthermore, the functional configuration of the control device 11 (measurement quantity calculation unit 103, shooting condition acquisition unit 104, exposure control unit 106) may be provided inside the radiation detector 12.

(Processing flow 1 of the radiation imaging system 10)
2 is a flowchart illustrating a process flow in which the control device 11 controls the operation of the radiation imaging system 10. Each step in FIG. 2 is executed by the CPU of the control device 11 controlling the radiation imaging system 10 based on a computer program.

The radiography system 10 according to this embodiment uses multiple radiation image data acquired with different radiation energies to acquire material images (e.g., soft tissue images and bone tissue images) separated into multiple materials (e.g., soft tissue and bone tissue) that make up the subject, and is capable of acquiring bone density (bone mineral quantification value) as the amount of material in the bone tissue by performing image processing based on the acquired material images.

The radiation generating unit 101 generates two types of radiation 100, high energy radiation and low energy radiation, depending on the imaging conditions. The radiation generating unit 101 can generate two types of radiation 100 and irradiate the subject with the radiation 100, for example, by switching the tube voltage and by placing a filter in front of the radiation tube to switch the energy.

As the imaging conditions, for example, E1 (kV) is set as the tube voltage (tube voltage information) that generates high-energy radiation, and E2 (kV) lower than E1 is set as the tube voltage (tube voltage information) that generates low-energy radiation. The imaging conditions are not limited to the tube voltage, and may be the tube current. The tube voltage and tube current may be set in advance according to the subject's physique, age, sex, imaging site, and the type of material to be separated by energy subtraction. In the following embodiment, an example of generating radiation of different energies based on the tube voltage will be described as an example of the imaging conditions. The radiation generating unit 101 generates low-energy radiation and high-energy radiation having a higher energy level than the low-energy radiation according to the different tube voltages set as the imaging conditions.

In S101, the imaging condition acquisition unit 104 acquires, as imaging conditions, multiple tube voltages (tube voltage information: E1, E2) for generating high-energy radiation and low-energy radiation in the radiation generation unit 101, and transmits the acquired multiple tube voltages (tube voltage information) to the exposure control unit 106.

In S102, the exposure control unit 106 calculates an automatic exposure target value for each of radiography based on low-energy radiation and radiography based on high-energy radiation, based on the multiple tube voltages (tube voltage information: E1, E2) acquired from the imaging condition acquisition unit 104.

Next, in S103, the control device 11 performs low-energy imaging. First, the exposure control unit 106 of the control device 11 sets multiple pieces of tube voltage information in the radiation generation unit 101 by communication via the communication I/F (interface) unit, and controls the radiation generation unit 101 to generate low-energy radiation. The radiation generation unit 101 generates radiation 100 based on tube voltage information (E2) for generating low-energy radiation, and irradiates the radiation 100 to a patient, who is the subject.

In low-energy imaging, the exposure detection unit 105 detects the exposure dose of radiation 100 irradiated from the radiation generation unit 101, and the radiation imaging unit 102 acquires radiation distribution information (X _L ) based on the low-energy radiation 100 and samples and holds it in the radiation detector 12.

In S104, the irradiation amount detection unit 105 detects (monitors) the irradiation amount of radiation 100 irradiated from the radiation generation unit 101 during low-energy imaging, and transmits cumulative information on the detected irradiation amount of radiation 100 to the exposure control unit 106.

The exposure control unit 106 controls the generation of radiation by the radiation generation unit 101 based on a comparison between the radiation dose and the automatic exposure target value of radiation calculated according to the imaging conditions. Specifically, the exposure control unit 106 acquires cumulative information on the dose of low-energy radiation 100 transmitted from the dose detection unit 105, and determines whether the dose has reached the automatic exposure target value for low-energy radiation imaging (automatic exposure target value for low-energy imaging) calculated in S102. If the dose has reached the automatic exposure target value for low-energy imaging, the exposure control unit 106 instructs the radiation generation unit 101 to stop irradiating radiation 100. On the other hand, if the dose has not reached the automatic exposure target value, the exposure control unit 106 instructs the radiation generation unit 101 to continue irradiation.

When the irradiation of the radiation 100 is stopped, the radiation distribution information (X _L ) sampled and held in the radiation detector 12 becomes readable, and the radiography unit 102 transmits the radiation distribution information (X _L ) acquired based on the low-energy radiation 100 to the measurement quantity calculation unit 103.

The detection area in which the dose detection unit 105 detects (monitors) the dose of radiation 100 is set to correspond to the object of interest (e.g., bone tissue), and the same detection area is set for irradiation with high-energy radiation and irradiation with low-energy radiation.

Next, in S105, the control device 11 performs high-energy imaging. The control device 11 sets tube voltage information in the radiation generation unit 101 by communication via a communication I/F (interface) unit, and controls the radiation generation unit 101 to generate high-energy radiation. The radiation generation unit 101 generates radiation 100 based on tube voltage information (E1) for generating high-energy radiation, and irradiates the radiation 100 to a patient, who is the subject.

The dose detection unit 105 detects the dose of radiation 100 irradiated from the radiation generation unit 101 , and the radiography unit 102 acquires radiation distribution information (X _H ) based on the high-energy radiation 100 and samples and holds it in the radiation detector 12 .

In S106, the irradiation amount detection unit 105 detects (monitors) the irradiation amount of the radiation 100 irradiated from the radiation generation unit 101 in high-energy imaging, and transmits cumulative information on the detected irradiation amount of the radiation 100 to the exposure control unit 106. The exposure control unit 106 acquires the cumulative information on the irradiation amount of the high-energy radiation 100 transmitted from the irradiation amount detection unit 105, and determines whether the irradiation amount has reached the automatic exposure target value (high-energy automatic exposure target value) for high-energy radiation imaging calculated in S102. If the irradiation amount has reached the automatic exposure target value for high-energy imaging, the exposure control unit 106 instructs the radiation generation unit 101 to stop irradiating the radiation 100. On the other hand, if the irradiation amount has not reached the automatic exposure target value, the exposure control unit 106 instructs the radiation generation unit 101 to continue irradiation.

When the irradiation of the radiation 100 is stopped, the radiation distribution information ( _XH ) sampled and held in the radiation detector 12 becomes readable, and the radiography unit 102 transmits the radiation distribution information ( _XH ) acquired based on the high-energy radiation 100 to the measurement quantity calculation unit 103.

In S107, the measurement amount calculation unit 103 calculates the amount of material of the material constituting the subject, using a plurality of radiation images acquired based on radiation from the radiation generation unit 101 controlled by the exposure control unit 106. Specifically, the measurement amount calculation unit 103 calculates the measurement amount related to the bones in the subject, based on the radiation distribution information (X _L ) acquired based on low-energy radiation, the radiation distribution information (X _H ) acquired based on high-energy radiation, and the radiation absorption coefficients (e.g., linear attenuation coefficients or mass attenuation coefficients) of each material. That is, the measurement amount calculation unit 103 solves simultaneous equations using the low-energy radiation distribution information (X _L ) and the high-energy radiation distribution information (X _H ), and the radiation absorption coefficients (e.g., linear attenuation coefficients or mass attenuation coefficients) of each material at high and low energy, to acquire material images (e.g., soft tissue images and bone tissue images) separated into the materials (soft tissue and bone tissue) constituting the subject.

A material image is an image in which a subject is represented by two or more specific materials and separated into two or more images composed of the thickness or density of the materials. When the linear attenuation coefficient is used as the radiation absorption coefficient of each material, an image showing the distribution of the thickness of each material can be obtained as a material image. When the mass attenuation coefficient is used as the radiation absorption coefficient, an image showing the distribution of the density of each material can be obtained as a material image. The measurement quantity calculation unit 103 can obtain bone mineral content (BMC) and bone mineral density (BMD) by image processing based on the material image (bone tissue image).

(Processing flow 2 of the radiation imaging system 10)
Fig. 3 is a flowchart for explaining the flow of processing by the control device 11 to control the operation of the radiation imaging system 10. The same processes as those in Fig. 2 are denoted by the same reference numerals. Each step in Fig. 3 is executed by the CPU of the control device 11 controlling the radiation imaging system 10 based on a computer program.

In S101, the imaging condition acquisition unit 104 acquires, as imaging conditions, multiple tube voltages (tube voltage information: E1, E2) for generating high-energy radiation and low-energy radiation in the radiation generation unit 101, and transmits the acquired multiple tube voltages (tube voltage information) to the exposure control unit 106.

In S201, the exposure control unit 106 calculates an automatic exposure target value for one of the radiography operations to be performed first based on one of the tube voltage information (E1) for generating high-energy radiation and the tube voltage information (E2) for generating low-energy radiation, which are acquired from the imaging condition acquisition unit 104. That is, the exposure control unit 106 calculates an automatic exposure target value for one of the radiography operations to be performed first, either the high-energy imaging or the low-energy imaging, based on one of the multiple pieces of tube voltage information (E1, E2).

In this processing flow, the exposure control unit 106 calculates an automatic exposure target value for radiography based on low-energy radiation, based on tube voltage information (E2) that generates low-energy radiation. Then, in S202 described later, an example is described in which a high-energy automatic exposure target value is calculated based on the low-energy exposure result and high-energy tube voltage information (E1). This process differs from the process (S102) in FIG. 2 in that the low-energy exposure result is reflected in the calculation process of the high-energy automatic exposure target value.

Note that the process flow 2 of the radiation imaging system is not limited to this example, and in S201, it is also possible to set one of the radiation imaging operations to be performed first as high-energy imaging. In this case, in S201, the exposure control unit 106 calculates an automatic exposure target value based on tube voltage information (E1) that generates high-energy radiation. Then, in S202 described later, the exposure control unit 106 can also calculate a low-energy automatic exposure target value based on the high-energy exposure result and low-energy tube voltage information (E2).

In S103, the control device 11 performs low-energy imaging. The exposure control unit 106 of the control device 11 sets tube voltage information (E2) in the radiation generation unit 101 by communication via the communication I/F (interface) unit, and controls the radiation generation unit 101 to generate low-energy radiation. The radiation generation unit 101 generates radiation 100 based on the tube voltage information (E2) for generating low-energy radiation, and irradiates the radiation 100 to the patient, who is the subject.

In low-energy imaging, the exposure detection unit 105 detects the exposure dose of radiation 100 irradiated from the radiation generation unit 101, and the radiation imaging unit 102 acquires radiation distribution information (X _L ) based on the low-energy radiation 100 and samples and holds it in the radiation detector 12.

In S104, the irradiation amount detection unit 105 detects (monitors) the irradiation amount of the radiation 100 irradiated from the radiation generation unit 101 in low-energy imaging, and transmits cumulative information on the detected irradiation amount of the radiation 100 to the exposure control unit 106. The exposure control unit 106 acquires the cumulative information on the irradiation amount of the low-energy radiation 100 transmitted from the irradiation amount detection unit 105, and determines whether the irradiation amount has reached the automatic exposure target value for low-energy radiation imaging (automatic exposure target value for low-energy imaging) calculated in S102. If the irradiation amount has reached the automatic exposure target value for low-energy imaging, the exposure control unit 106 instructs the radiation generation unit 101 to stop irradiating the radiation 100. On the other hand, if the irradiation amount has not reached the automatic exposure target value, the exposure control unit 106 instructs the radiation generation unit 101 to continue irradiation.

When the irradiation of the radiation 100 is stopped, the radiation distribution information (X _L ) sampled and held in the radiation detector 12 becomes readable, and the radiography unit 102 transmits the radiation distribution information (X _L ) acquired based on the low-energy radiation 100 to the measurement quantity calculation unit 103.

In S202, the exposure control unit 106 calculates an exposure target value for the other radiography (high-energy radiography) to be performed later, based on the exposure result (low-energy exposure result) in the previously performed radiography and the other tube voltage information (high-energy tube voltage information (E1). That is, the exposure control unit 106 calculates an automatic exposure target value for high-energy radiography, based on the radiation distribution information (X _L ) (low-energy exposure result) acquired based on the low-energy radiation 100, and the high-energy tube voltage information (E1).

As a method of calculating the automatic exposure target value for high-energy imaging, the exposure control unit 106 can calculate the target value on the high-energy side so that the automatic exposure imaging time for low-energy radiation is the same as the imaging time for high-energy radiation, for example.

The exposure control unit 106 can also calculate the automatic exposure target value by the processes shown in Fig. 8(A) and (B). As a method of calculating the automatic exposure target value for high-energy imaging, first, low-energy imaging is performed as shown in Fig. 8(A). The exposure control unit 106 performs low-energy imaging with automatic exposure so that the detection value (radiation count number) related to low-energy radiation becomes appropriate, and acquires low-energy radiation distribution information (X _L : radiation distribution information based on tube voltage information E2 shown on the left of Fig. 8(A)). Then, the exposure control unit 106 calculates the necessary differential radiation distribution information as the automatic exposure target value so that the high-energy radiation distribution information (X _H ) showing an appropriate detection value is obtained after adding differential radiation distribution information (radiation distribution information of the radiation count number required for the subtraction image) to the low-energy radiation distribution information (X _L ). The exposure control unit 106 stores in advance radiation distribution information regarding the relationship between radiation count number and radiation energy for each of various types of tube voltage information, and for the set tube voltage information, the exposure control unit 106 can calculate the necessary differential radiation distribution information (radiation distribution information of the radiation count number required for the subtraction image) as an automatic exposure target value so as to obtain high-energy radiation distribution information that exhibits an appropriate detection value after energy subtraction ( _XH : radiation distribution information based on tube voltage information E1 shown on the right of FIG. 8(A)). In this case, it is possible to calculate the automatic exposure target value for high-energy imaging based on the exposure result of low-energy imaging and the radiation distribution information based on high-energy tube voltage information (E1).

In the example of process flow 2 (FIG. 8(A)), an example in which low-energy imaging is performed first has been described, but it is also possible to perform high-energy imaging first, in contrast to the example of process flow 2 (FIG. 8(A)), and calculate the automatic exposure target value for low-energy imaging based on the exposure result of the high-energy imaging and radiation distribution information based on the low-energy tube voltage information (E2).

In this case, as a method of calculating an automatic exposure target value for low-energy imaging, first, high-energy imaging is performed as shown in Fig. 8(B). The exposure control unit 106 performs high-energy imaging with automatic exposure so that the detection value (radiation count number) for high-energy radiation becomes appropriate, and acquires high-energy radiation distribution information ( _XH : radiation distribution information based on tube voltage information E1 shown on the left of Fig. 8(B)). Then, the exposure control unit 106 calculates the necessary differential radiation distribution information as the automatic exposure target value so that the low-energy radiation distribution information ( _XL ) exhibits an appropriate detection value after subtracting differential radiation distribution information (radiation distribution information of the radiation count number required for the subtraction image) from the high-energy radiation distribution information ( _XH ). The exposure control unit 106 stores in advance radiation distribution information regarding the relationship between radiation count number and radiation energy for each of various types of tube voltage information, and for the set tube voltage information, the exposure control unit 106 is also able to calculate the required differential radiation distribution information (radiation distribution information of the radiation count number required for the subtraction image) as an automatic exposure target value so as to obtain low-energy radiation distribution information that exhibits an appropriate detection value after energy subtraction (X _L : radiation distribution information based on tube voltage information E2 shown on the right of FIG. 8(B)).

When low-energy imaging is performed first, the problem of a decrease in the detection value of low-energy radiation in cases where the subject is thicker than in cases where the subject is of normal build can be eliminated, and the dose on the high-energy side can be reduced. On the other hand, when high-energy imaging is performed first, it is possible to prevent an increase in radiation exposure due to excessive dose and blackout due to excessive dose.

Then, in S105, the control device 11 performs high-energy imaging. The control device 11 sets tube voltage information (E1) in the radiation generation unit 101 by communication via the communication I/F (interface) unit, and controls the radiation generation unit 101 to generate high-energy radiation. The radiation generation unit 101 generates radiation 100 based on the tube voltage information (E1) for generating high-energy radiation, and irradiates the radiation 100 to a patient, who is the subject.

The dose detection unit 105 detects the dose of radiation 100 irradiated from the radiation generation unit 101 , and the radiography unit 102 acquires radiation distribution information (X _H ) based on the high-energy radiation 100 and samples and holds it in the radiation detector 12 .

In S106, the irradiation amount detection unit 105 detects (monitors) the irradiation amount of the radiation 100 irradiated from the radiation generation unit 101 in high-energy imaging, and transmits cumulative information on the detected irradiation amount of the radiation 100 to the exposure control unit 106. The exposure control unit 106 acquires the cumulative information on the irradiation amount of the high-energy radiation 100 transmitted from the irradiation amount detection unit 105, and determines whether the irradiation amount has reached the automatic exposure target value (high-energy automatic exposure target value) for high-energy radiation imaging calculated in S102. If the irradiation amount has reached the automatic exposure target value for high-energy imaging, the exposure control unit 106 instructs the radiation generation unit 101 to stop irradiating the radiation 100. On the other hand, if the irradiation amount has not reached the automatic exposure target value, the exposure control unit 106 instructs the radiation generation unit 101 to continue irradiation.

When the irradiation of the radiation 100 is stopped, the radiation distribution information ( _XH ) sampled and held in the radiation detector 12 becomes readable, and the radiography unit 102 transmits the radiation distribution information ( _XH ) generated based on the high-energy radiation 100 to the measurement quantity calculation unit 103.

In S107, the measurement quantity calculation unit 103 calculates measurement quantities related to the bones in the subject based on the radiation distribution information (X _L ) acquired based on the low-energy radiation and the radiation distribution information (X _H ) acquired based on the high-energy radiation, and the radiation absorption coefficients (e.g., linear attenuation coefficients or mass attenuation coefficients) of each material.

[Second embodiment]
Next, a schematic configuration of a radiation imaging system 10 according to a second embodiment of the present invention will be described. FIG. 4 is a diagram showing a schematic configuration of the radiation imaging system 10 according to the second embodiment. In FIG. 4, the same components as those in the radiation imaging system 10 described in FIG. 1 are given the same reference numerals. In FIG. 4, the control device 11 is different from the radiation imaging system 10 in FIG. 1 in that it has an irradiation stop information acquisition unit 201. The irradiation stop information acquisition unit 201 is realized by the CPU of the control device 11 expanding a computer program in the RAM and executing it, as with other functional configurations. In addition, the functional configuration of the control device 11 (measurement amount calculation unit 103, imaging condition acquisition unit 104, exposure control unit 106, and irradiation stop information acquisition unit 201) may be provided inside the radiation detector 12.

(Processing flow 3 of the radiation imaging system 10)
Fig. 5 is a flow chart for explaining the flow of processing in which the control device 11 controls the operation of the radiation imaging system 10. The same processes as those in Fig. 2 (process flow 1) and Fig. 3 (process flow 2) are denoted by the same reference numerals. Each step in Fig. 5 is executed by the CPU of the control device 11 controlling the radiation imaging system 10 based on a computer program. The processing from S101 to S103 is the same as that in process flow 2 in Fig. 3.

In S101, the imaging condition acquisition unit 104 acquires, as imaging conditions, multiple tube voltages (tube voltage information: E1, E2) for generating high-energy radiation and low-energy radiation in the radiation generation unit 101.

In S201, the exposure control unit 106 calculates an automatic exposure target value for one of the high-energy and low-energy radiography to be performed first, based on one of the multiple pieces of tube voltage information (E1, E2) acquired from the imaging condition acquisition unit 104. In this processing flow, the exposure control unit 106 calculates an automatic exposure target value for radiography based on low-energy radiation, based on tube voltage information (E2) that generates low-energy radiation.

In S103, the control device 11 performs low-energy imaging. The exposure control unit 106 of the control device 11 sets tube voltage information (E2) in the radiation generation unit 101 by communication via the communication I/F (interface) unit, and controls the radiation generation unit 101 to generate low-energy radiation. When low-energy imaging is started, the CPU of the control device 11 uses an internal timer to measure the imaging time using low-energy radiation.

In S301, the exposure control unit 106 monitors whether the amount of radiation irradiated by low-energy imaging has reached the automatic exposure target value for low energy or whether the irradiation switch has been released before the automatic exposure target value has been reached, and determines whether radiation irradiation has stopped at either point. If it is determined in S301 that the amount of radiation irradiated by low-energy imaging has reached the automatic exposure target value for low energy (S301-automatic exposure), processing proceeds to S202. The processing in S202 is the same as in process flow 2 in Fig. 3, and the exposure control unit 106 calculates the automatic exposure target value for high energy based on radiation distribution information (X _L ) (exposure result for low energy) acquired based on the low-energy radiation 100 and tube voltage information for high energy (E1).

On the other hand, if the irradiation of radiation is stopped by releasing the irradiation switch based on the user's operation (S301-irradiation switch) before the dose of radiation irradiated in the previously performed radiography (low-energy radiography) reaches the automatic exposure target value, the process proceeds to S302. When the user releases the irradiation switch, the CPU of the control device 11 ends the measurement of the imaging time using the internal timer.

In S302, the exposure control unit 106 calculates the automatic exposure target value for high-energy shooting using the results of the low-energy shooting that was stopped by releasing the exposure switch.

In this step, the irradiation stop information acquisition unit 201 acquires the imaging time measured by the timer inside the CPU as irradiation stop information, and transmits the acquired irradiation stop information to the exposure control unit 106. Here, the irradiation stop information is information indicating the imaging time from the start of the previously performed radiation imaging (low energy imaging) to the end of the radiation irradiation by releasing the irradiation switch (imaging time T1 using low energy radiation).

Then, the exposure control unit 106 calculates the automatic exposure target value (imaging time) for the other radiation imaging (high-energy imaging) to be performed later based on the irradiation stop information (imaging time T1 using low-energy radiation) and the other tube voltage information (high-energy tube voltage information (E1)).

As a method of calculating the automatic exposure target value in high-energy imaging, the exposure control unit 106 can calculate the automatic exposure target value (imaging time) in the other radiography (high-energy imaging) to be performed later so that the imaging time is the same as the imaging time (T1) in the previously performed radiography (low-energy imaging). For example, the exposure control unit 106 can set an imaging time that is shorter than the imaging time Tref during automatic exposure set as an imaging condition based on the imaging time (T1) in low-energy imaging.

The exposure control unit 106 can also correct the tube voltage information (E1) to reduce the radiation energy by the amount of the shortened imaging time (Tref-T1). The exposure control unit 106 can also perform a combined correction of the imaging time and the tube voltage information.

Then, in S105, the control device 11 performs high-energy imaging. The control device 11 sets tube voltage information (E1) in the radiation generation unit 101 by communication via the communication I/F (interface) unit, and controls the radiation generation unit 101 to generate high-energy radiation. The radiation generation unit 101 generates radiation 100 based on the tube voltage information (E1) for generating high-energy radiation, and irradiates the radiation 100 to a patient, who is the subject.

In S106, the irradiation amount detection unit 105 detects (monitors) the irradiation amount of the radiation 100 irradiated from the radiation generation unit 101 in high-energy imaging, and transmits cumulative information on the detected irradiation amount of the radiation 100 to the exposure control unit 106. The exposure control unit 106 acquires the information on the irradiation amount of the high-energy radiation 100 transmitted from the irradiation amount detection unit 105, and determines whether the irradiation amount has reached the automatic exposure target value (high-energy automatic exposure target value) for high-energy radiation imaging calculated in S102. If the irradiation amount has reached the automatic exposure target value for high-energy imaging, the exposure control unit 106 instructs the radiation generation unit 101 to stop irradiating the radiation 100. On the other hand, if the irradiation amount has not reached the automatic exposure target value, the exposure control unit 106 instructs the radiation generation unit 101 to continue irradiation.

When the irradiation of the radiation 100 is stopped, the radiation distribution information ( _XH ) sampled and held in the radiation detector 12 becomes readable, and the radiography unit 102 transmits the radiation distribution information ( _XH ) generated based on the high-energy radiation 100 to the measurement quantity calculation unit 103.

In S107, the measurement quantity calculation unit 103 calculates measurement quantities related to the bones in the subject based on the radiation distribution information (X _L ) acquired based on the low-energy radiation and the radiation distribution information (X _H ) acquired based on the high-energy radiation, and the radiation absorption coefficients (e.g., linear attenuation coefficients or mass attenuation coefficients) of each material.

In the process flow of FIG. 5, an example has been described in which the exposure control unit 106 calculates an automatic exposure target value for radiography based on low-energy radiation based on tube voltage information (E2) that generates low-energy radiation, and performs low-energy radiography first, but the process flow of the radiography system is not limited to this example. For example, in S201, it is also possible to calculate an automatic exposure target value for radiography based on high-energy radiation based on tube voltage information (E1) that generates high-energy radiation, and perform high-energy radiography first.

[Third embodiment]
Next, a schematic configuration of a radiation imaging system 10 according to a third embodiment of the present invention will be described. FIG. 6 is a diagram showing a schematic configuration of the radiation imaging system 10 according to the third embodiment. In FIG. 6, the same components as those in the radiation imaging system 10 described in FIG. 1 and FIG. 4 are given the same reference numerals. In FIG. 6, the control device 11 is different from the radiation imaging system 10 in FIG. 4 in that it has a characteristic information acquisition unit 301. The characteristic information acquisition unit 301 is realized by the CPU of the control device 11 expanding a computer program in the RAM and executing it, as with other functional configurations. In addition, the functional configuration of the control device 11 (measurement amount calculation unit 103, imaging condition acquisition unit 104, exposure control unit 106, irradiation stop information acquisition unit 201, characteristic information acquisition unit 301) may be provided inside the radiation detector 12.

The characteristic information acquisition unit 301 acquires characteristic information indicating the distribution characteristics of radiation energy that can be generated by the multiple energy generation methods of the radiation generation unit 101 through communication with the radiation generation unit 101 or communication with an external device, and transmits the acquired characteristic information to the exposure control unit 106. The exposure control unit 106 calculates a target exposure value for radiation based on the imaging conditions such as tube voltage and the characteristic information. In addition, the exposure control unit 106 can control the radiation generation unit 101 to generate radiation of different energies using an energy generation method selected based on the characteristic information.

Figure 7 is a diagram explaining the radiation energy generation method. Radiation spectra 701 and 703 exemplify the distribution of radiation spectra based on a tube voltage (tube voltage information: E2) that generates low-energy radiation, and radiation spectra 702 and 704 exemplify the distribution of radiation spectra based on a tube voltage (tube voltage information: E1) that generates high-energy radiation.

The radiation energy generation method includes, for example, a method of switching the tube voltage of the radiation generating unit 101 (first generation method), and a method of placing a filter in front of the radiation tube of the radiation generating unit 101 to switch between high-energy radiation and low-energy radiation (second generation method).

The tube voltage switching method (first generation method) uses beam hardening to bichromatize the radiation spectrum, and obtains radiation spectra with two types of energy by switching the tube voltage of the radiation tube.

In the method of switching the tube voltage (first generation method), the attenuation information for each energy is separated in time, so that, for example, energy crosstalk in which low-energy radiation spectrum 701 and high-energy radiation spectrum 702 overlap, as shown in Figure 7 (A), does not occur.

On the other hand, the method of placing a filter in front of the radiation tube and switching the radiation energy (second generation method) is a method of filtering white radiation using, for example, an absorbing substance with a K-shell absorption edge, and artificially bicoloring the radiation spectrum. With the second generation method, for example, the low-energy radiation spectrum 703 and the high-energy radiation spectrum 704 as shown in Figure 7 (B) overlap, and complete bicoloring is not possible, so it is necessary to consider the effects of beam hardening, energy crosstalk, etc.

In general, the greater the difference in tube voltage between the tube voltage (E2) that generates low-energy radiation and the tube voltage (E1) that generates high-energy radiation, the better the signal-to-noise ratio of the image obtained by signal processing. On the other hand, if the tube voltage for low-energy radiation is lowered too much, the amount of exposure required to achieve the same signal-to-noise ratio tends to increase.

Therefore, in order to emphasize the contrast of a substance of interest as a substance to be measured, the exposure control unit 106 can set the lower limit low-energy tube voltage (E2) to match the average energy 705, 706 of the radiation spectrum, or set a high-energy tube voltage (E1) that has a predetermined tube voltage difference with respect to the tube voltage (E2).

In other words, the exposure control unit 106 can set at least one of the tube voltages (E1) that generates high-energy radiation and the tube voltage (E2) that generates low-energy radiation in accordance with the distribution of the radiation spectrum in the radiation energy generation method selected based on the characteristic information.

This makes it possible to enhance the contrast of the substance of interest (e.g., bone tissue) as the measurement target in the material separation image obtained by energy subtraction.

According to each embodiment of the present invention, a radiography technique can be provided that can obtain the amount of a substance that constitutes a subject by using a plurality of radiographic images acquired based on exposure-controlled radiation in a radiography system for general radiography. In addition, even when obtaining the amount of a substance that constitutes a subject by using a plurality of radiographic images acquired in a radiography system for general radiography (e.g., when performing bone density measurement), it is possible to suppress radiography due to insufficient or excessive dose.

[Other embodiments]
The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

The invention is not limited to the above-described embodiment, and various modifications and variations are possible without departing from the spirit and scope of the invention. Therefore, the following claims are appended to disclose the scope of the invention.

10: Radiography system, 11: Control device, 12: Radiation detector,
101: radiation generating unit, 102: radiation imaging unit, 103: measurement amount calculation unit,
104: photography condition acquisition unit, 105: irradiation amount detection unit, 106: exposure control unit,
201: Irradiation stop information acquisition unit, 301: Characteristic information acquisition unit

Claims (19)

a radiation generating means for generating radiation having different energies in response to different tube voltages set as imaging conditions;
a radiation detection means for detecting radiation of different energies ;
an exposure control means for controlling generation of the radiation by the radiation generating means based on a comparison between an irradiation amount of the radiation and a target exposure value of the radiation calculated according to the imaging conditions;
A radiation imaging system comprising:
If the radiation exposure is stopped by releasing the exposure switch before the radiation exposure amount from the previous radiography reaches the exposure target value,
the exposure control means sets a target exposure value for another radiography to be performed later, the target exposure value being different from the target exposure value for the previously performed radiography, based on the radiography time from the start of the previously performed radiography to the stop of radiation irradiation by the release of the irradiation switch, and on the other tube voltage information . The radiography system according to claim 1, further comprising a calculation means for calculating the amount of material of a material constituting a subject, using a plurality of radiation images corresponding to the different energies acquired based on the radiation from the radiation generating means controlled by the exposure control means. The radiography system according to claim 2, wherein the calculation means obtains the amounts of the substances for the multiple substances constituting the subject by image processing using different radiation absorption coefficients and the multiple radiation images. The radiography system according to claim 2 or 3, wherein the calculation means obtains bone density as the substance amount of the bone tissue by image processing using the radiation absorption coefficients of the soft tissue and the bone tissue constituting the subject and the multiple radiation images. the radiation generating means generates low-energy radiation and high-energy radiation having a higher energy level than the low-energy radiation in response to different tube voltages set as the imaging conditions;
5. The radiation imaging system according to claim 1, wherein the radiation detection means obtains a plurality of radiation images based on the low-energy radiation and the high-energy radiation. an acquisition unit that acquires, as the imaging condition, a plurality of pieces of tube voltage information for generating the high-energy radiation and the low-energy radiation by the radiation generating unit;
The radiation imaging system according to claim 5 , wherein the exposure control means sets the plurality of pieces of tube voltage information acquired by the acquisition means in the radiation generation means. 7. The radiation imaging system according to claim 6, wherein the exposure control means calculates an exposure target value for the first radiation imaging operation based on either one of tube voltage information for generating high-energy radiation and tube voltage information for generating low-energy radiation, both of which are acquired from the acquisition means. 8. The radiation imaging system according to claim 7, wherein the exposure control means calculates an exposure target value for the other radiation imaging to be performed later , based on an exposure result for the previously performed radiation imaging and the other tube voltage information. 9. The radiation imaging system according to claim 7, further comprising an irradiation stop information acquisition means for acquiring, as irradiation stop information, the imaging time from the start of the previously performed radiation imaging to the stop of the radiation irradiation by the release of the irradiation switch. When the irradiation of radiation is stopped by releasing the irradiation switch before the amount of irradiation of radiation irradiated in the previously performed radiography reaches the exposure target value,
10. The radiation imaging system according to claim 9, wherein the exposure control means calculates a target exposure value for the other radiation imaging to be performed later so that the imaging time of the other radiation imaging to be performed later is the same as the imaging time of the previously performed radiation imaging. further comprising an irradiation amount detection means for detecting an irradiation amount of the radiation,
11. The radiation imaging system according to claim 5, wherein the irradiation amount detection means detects the irradiation amount in the same detection area for the irradiation of the high-energy radiation and the irradiation of the low-energy radiation. the radiation generating means generates cone beam radiation,
The radiation imaging system according to claim 1 , wherein the radiation detection means detects the cone beam type radiation. a characteristic information acquiring unit that acquires characteristic information indicating a distribution characteristic of radiation energy that can be generated by a plurality of energy generation methods of the radiation generating unit,
The radiation imaging system according to claim 1 , wherein the exposure control means calculates a target exposure value of the radiation based on the imaging conditions and the characteristic information. The radiation imaging system according to claim 13 , wherein the exposure control means controls the radiation generating means to generate the radiation with the different energies by an energy generation method selected based on the characteristic information. The plurality of energy generation methods include:
a first generation method for switching a tube voltage of the radiation generating means;
15. The radiation imaging system according to claim 13 or 14, further comprising a second generation method for switching between high energy radiation and low energy radiation lower than the high energy radiation by arranging a filter in front of a radiation tube of the radiation generating means. The radiation imaging system according to any one of claims 13 to 15, wherein the exposure control means sets at least one of a tube voltage that generates high-energy radiation and a tube voltage that generates low-energy radiation lower than the high-energy radiation, in accordance with a distribution of the radiation spectrum in a radiation energy generation method selected based on the characteristic information . a control device including an exposure control means for controlling generation of radiation by a radiation generating means for generating radiation of different energies according to an imaging condition, based on a comparison between an exposure amount of radiation obtained using a radiation detection means for detecting radiation of different energies generated according to different tube voltages set as an imaging condition and an exposure target value of the radiation obtained according to the imaging condition,
If the radiation exposure is stopped by releasing the exposure switch before the radiation exposure amount from the previous radiography reaches the exposure target value,
The exposure control means is a control device that sets an exposure target value for the other radiation imaging to be performed later, which is different from the exposure target value for the previously performed radiation imaging, based on the imaging time from the start of the previously performed radiation imaging to the stop of radiation irradiation by releasing the irradiation switch, and the other tube voltage information . 1. A control method comprising: an exposure control step of controlling generation of radiation by a radiation generating means for generating radiation of different energies according to an imaging condition, based on a comparison between an exposure amount of radiation obtained using a radiation detecting means for detecting radiation of different energies generated according to different tube voltages set as an imaging condition and an exposure target value of the radiation obtained according to the imaging condition, the control step comprising:
If the radiation exposure is stopped by releasing the exposure switch before the radiation exposure amount from the previous radiography reaches the exposure target value,
In the exposure control step, a target exposure value for the other radiography to be performed later, which is different from the target exposure value for the previously performed radiography, is set based on the radiography time from the start of the previously performed radiography to the stop of radiation irradiation by releasing the irradiation switch, and on the other tube voltage information . A program for causing a computer to execute the control method according to claim 18 .

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