Distance measuring device, radiographic system, operation method of distance measuring device, and operation program

Abstract

To provide a distance measuring device, a radiographic system, an operation method of the distance measuring device, and an operation program that make it possible to perform measurement quickly with high accuracy.SOLUTION: The distance measuring device comprises: a distance measuring camera of ToF type that measures the distance to a measurement object and the distance to a reference object whose distance is known; and a processor. The processor calculates a correction coefficient on the basis of a first measurement value representing a measured value of distance from the distance measuring camera to the reference object by the distance measuring camera and the known distance from the distance measuring camera to the reference object, and corrects a second measurement value representing a measured value of distance from the distance measuring camera to the measurement object by the distance measuring camera, or a calculation value calculated using the second measurement value.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The technology disclosed herein relates to a distance measurement device, a radiation imaging system, an operation method for the distance measurement device, and an operation program. [Background technology]

[0002] In radiography, it is desirable to set radiography conditions appropriately according to the body thickness of a subject such as a patient. The radiography conditions include the tube voltage and tube current time product of a radiation source. It is desirable to set the radiography conditions so that radiography is performed with an appropriate radiation dose according to the body thickness of the subject.

[0003] Since the body thickness varies depending on the subject to be radiographed, it is necessary to measure the body thickness with high accuracy in order to set the radiographing conditions appropriately. Patent Document 1 describes that the body thickness is obtained using the measurement value obtained by a ToF (Time of Flight) distance measuring camera. The ToF distance measuring camera is also used in fields other than the medical field. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2021-191389 A Summary of the Invention [Problem to be solved by the invention]

[0005] While ToF distance measuring cameras have the advantage of being able to perform highly accurate measurements, they have a problem of so-called temperature drift, in which the measured value changes due to the rise in temperature inside the device after power is turned on. It is possible to measure the temperature inside the device and perform temperature correction, but the sensor used in ToF distance measuring cameras is small, making it difficult to measure the temperature of the sensor itself. It is also possible to measure the temperature around the sensor rather than the temperature of the sensor itself and perform temperature correction, but it is difficult to perform highly accurate measurements because the temperature around the sensor is different from the temperature of the sensor itself. Furthermore, it is possible to perform measurements after the temperature inside the device has stabilized, but it takes a certain amount of time for the temperature to stabilize, so measurements cannot be performed quickly.

[0006] An object of the technology disclosed herein is to provide a distance measurement device, a radiation imaging system, an operating method for a distance measurement device, and an operating program that enable measurements to be performed quickly and with high accuracy. [Means for solving the problem]

[0007] In order to achieve the above-mentioned objective, the distance measuring device disclosed herein includes a ToF type distance measuring camera that measures the distance to a measurement object and the distance to a reference object whose distance is known, and a processor, and the processor calculates a correction coefficient based on a first measurement value, which is a measurement value of the distance from the distance measuring camera to the reference object by the distance measuring camera, and the known distance from the distance measuring camera to the reference object, and corrects a second measurement value, which is a measurement value of the distance from the distance measuring camera to the measurement object by the distance measuring camera, or a calculated value calculated using the second measurement value.

[0008] It is preferable that a plurality of reference objects are provided, and the processor calculates a correction coefficient based on an average value of a plurality of first measurement values, which are measurements of distances from the distance measuring camera to the plurality of reference objects by the distance measuring camera, and known distances from the distance measuring camera to the plurality of reference objects.

[0009] The first measurement value is preferably an average value of a plurality of measurement values ​​obtained by measuring the distance from the distance measuring camera to the reference object a plurality of times with the distance measuring camera.

[0010] The calculated value is preferably a difference value between the first measured value and the second measured value.

[0011] The processor preferably corrects the second measured or calculated value by dividing the first measured value by the known distance to obtain a correction coefficient, and multiplying the second measured or calculated value by the correction coefficient.

[0012] It is preferable that the processor updates the correction coefficient by obtaining the first measurement value at regular time intervals and calculating the correction coefficient.

[0013] It is preferable that the processor updates the correction coefficient by obtaining the first measurement value and calculating the correction coefficient at shorter intervals as the time that has elapsed since the power of the distance measuring camera is turned on is shorter.

[0014] It is preferable that a detection sensor is provided for detecting the position of the distance measuring camera relative to the reference object, and the processor determines the known distance using a detection value detected by the detection sensor.

[0015] It is preferable that the reference object is an imaging table, the measurement target is a subject placed relative to the imaging table, the calculated value is a difference value between the first measurement value and the second measurement value, and the processor calculates the body thickness of the subject by multiplying the calculated value by a correction coefficient.

[0016] A radiography system according to the present disclosure includes the above-described distance measurement device, a radiation source that emits radiation toward an imaging table, and a radiographic image detector that is provided on the imaging table and detects the radiation to generate a radiographic image.

[0017] The range finding camera is preferably attached to the radiation source.

[0018] The operating method of a distance measuring device disclosed herein is a method of operating a distance measuring device equipped with a ToF type distance measuring camera that measures the distance to a measurement object and the distance to a reference object whose distance is known, in which a processor performs processing including calculating a correction coefficient based on a first measurement value, which is a measurement value of the distance from the distance measuring camera to the reference object by the distance measuring camera, and the known distance from the distance measuring camera to the reference object, and correcting a second measurement value, which is a measurement value of the distance from the distance measuring camera to the measurement object by the distance measuring camera, or a calculated value calculated using the second measurement value.

[0019] The operating program of the present disclosure is an operating program for operating a distance measuring device equipped with a ToF type distance measuring camera that measures the distance to a measurement object and the distance to a reference object whose distance is known, and causes a processor to execute processes including calculating a correction coefficient based on a first measurement value, which is a measurement value of the distance from the distance measuring camera to the reference object by the distance measuring camera, and the known distance from the distance measuring camera to the reference object, and correcting a second measurement value, which is a measurement value of the distance from the distance measuring camera to the measurement object by the distance measuring camera, or a calculated value calculated using the second measurement value. Effect of the Invention

[0020] According to the technique of the present disclosure, it is possible to provide a distance measurement device, a radiation imaging system, an operating method of a distance measurement device, and an operating program that enable measurements to be performed quickly and with high accuracy. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of a radiation imaging system. [Diagram 2] FIG. 2 is a block diagram showing a configuration example of a console. [Diagram 3] FIG. 2 is a block diagram showing an example of a function relating to determination of a shooting condition. [Figure 4]FIG. 2 is a diagram showing the positional relationship between a radiation source, a distance measuring camera, and a standing imaging stand. [Diagram 5] 11 is a flowchart showing an example of the flow of a shooting condition determination process. [Figure 6] FIG. 4 is a diagram showing an example of icons representing a plurality of shooting conditions. [Figure 7] 11 is a diagram showing an example of the relationship between the internal temperature of the distance measuring camera and the elapsed time since the power was turned on; FIG. [Figure 8] FIG. 11 is a diagram illustrating an example of update timing of a correction coefficient. [Figure 9] FIG. 11 is a diagram illustrating another example of the update timing of the correction coefficient. [Figure 10] FIG. 11 is a perspective view showing an automobile equipped with a distance measurement device according to a second embodiment. [Figure 11] FIG. 2 is a diagram illustrating an example of the positional relationship between a distance measuring camera and a plurality of reference objects. [Figure 12] FIG. 11 is a block diagram showing an example of the configuration of a distance measurement device according to a second embodiment. [Figure 13] FIG. 2 is a block diagram showing an example of a function relating to distance measurement. [Figure 14] 11 is a diagram illustrating a method for acquiring a first measurement value. FIG. [Figure 15] FIG. [Figure 16] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] An example of an embodiment of the technology of the present disclosure will be described with reference to the accompanying drawings.

[0023] [First embodiment] 1 shows a schematic example of the configuration of a radiation imaging system 2. The radiation imaging system 2 is a system that performs radiation imaging of a subject H using radiation (e.g., X-rays) R, and is made up of a radiation imaging device 10 and a radiation generating device 11. The radiation imaging device 10 includes an upright imaging table 12, an electronic cassette 13, and a console 14. The radiation generating device 11 includes a radiation source suspension device 15, a radiation source 16, a radiation source control device 17, a tube voltage generator 18, and an exposure switch 19. A ToF distance measuring camera 20 is attached to the radiation source 16.

[0024] The upright imaging table 12 is an imaging table for performing radiography on the subject H in an upright position. The upright imaging table 12 has a base 35 placed on the floor of a radiography room, a support 36 extending in the height direction from the base 35, and a holder 37 that holds the electronic cassette 13 therein. The holder 37 is connected to the support 36 via a connection part 38. The holder 37 is raised and lowered along the support 36 by a motor or the like in accordance with the body part to be imaged. The upright imaging table 12 is an example of an "imaging table" according to the technology of the present disclosure.

[0025] The electronic cassette 13 is a portable radiation image detector that detects radiation R that has passed through the subject H to generate a radiation image. The electronic cassette 13 is communicably connected to the console 14 by wire or wirelessly. The electronic cassette 13 is housed in a holder 37 of the upright imaging stand 12 when in use.

[0026] The electronic cassette 13 has a detection panel in which a plurality of pixels are arranged in a two-dimensional matrix and accumulate electric charges according to the radiation R. The detection panel is also called an FPD (Flat Panel Detector).

[0027] The console 14 is, for example, a personal computer. The console 14 includes a display 40 that displays various screens, and an input device 41 that receives operation instructions from an operator. The input device 41 includes a keyboard, a mouse, and the like. The console 14 transmits various signals to the electronic cassette 13. The console 14 also receives a radiological image 66 from the electronic cassette 13. The console 14 displays the radiological image 66 on the display 40.

[0028] The radiation source suspension device 15 includes an arm 45 and a cart 46. The radiation source 16 is attached to the tip of the arm 45. The base end of the arm 45 is attached to the cart 46. The arm 45 is extendable and contractable in the vertical direction by a motor or the like. By extending and contracting the arm 45 in the vertical direction, the height position of the radiation source 16 can be changed in accordance with the region to be imaged. In addition, the radiation source 16 is rotated by a motor or the like about an axis perpendicular to the plane of the drawing relative to the arm 45 in order to adjust the angle of incidence of radiation R on the subject H.

[0029] The dolly 46 is connected to a rail 48 laid on the ceiling 47 of the radiography room 25. The rail 48 is parallel to a normal to a detection surface of the radiation R of the electronic cassette 13 housed in the holder 37. The dolly 46, and therefore the radiation source 16, can move parallel along the rail 48 by a motor or the like. When the radiation source 16 moves along the rail 48, a source-to-image receptor distance (SID) that is a distance from a focus F of the radiation R to the detection surface of the radiation R of the electronic cassette 13 is changed. The position of the dolly 46 with respect to the rail 48 is detected by a detection sensor 42 such as a potentiometer or a linear encoder. A position detection value by the detection sensor 42 corresponds to the SID and is output to the console 14.

[0030] The radiation source 16 has a radiation tube 49 and an irradiation field limiter 50. The radiation tube 49 is provided with a filament, a target, a grid electrode, etc. (all not shown). A voltage is applied between the filament, which is the cathode, and the target, which is the anode. This voltage applied between the filament and the target is called the tube voltage. The filament emits thermoelectrons toward the target according to the applied tube voltage. The target emits radiation R due to collision of the thermoelectrons from the filament. The grid electrode is disposed between the filament and the target. The grid electrode changes the flow rate of thermoelectrons from the filament toward the target according to the applied voltage. This flow rate of thermoelectrons from the filament toward the target is called the tube current.

[0031] The irradiation field limiter 50 is also called a collimator, and limits the irradiation field of the radiation R emitted from the radiation tube 49. The irradiation field limiter 50 is configured, for example, such that four shielding plates made of lead or the like that block the radiation R are arranged on each side of a rectangle, and a rectangular opening that transmits the radiation R is formed in the center. The irradiation field limiter 50 changes the irradiation field of the radiation R by changing the position of each shielding plate to change the size of the opening.

[0032] A tube voltage generator 18 and an exposure switch 19 are connected to the radiation source controller 17. The radiation source controller 17 controls the operation of the radiation source 16 in response to an instruction signal from the exposure switch 19. The exposure switch 19 is operated when an operator instructs the radiation source 16 to start irradiating radiation R.

[0033] For example, the exposure switch 19 is a two-step motion switch. When the operator presses the exposure switch 19 to the first step, the anode starts to rotate and enters a standby state. Then, when the operator presses the exposure switch 19 to the second step, a tube voltage is applied between the anode and the cathode from the tube voltage generator 18, and radiation R is generated.

[0034] The imaging conditions are set in the radiation source control device 17. The imaging conditions are conditions defined by the tube voltage, tube current, and tube current time product (product of tube current and irradiation time) applied to the radiation tube 49. When an instruction to start irradiating radiation R is given by operating the irradiation switch 19, the radiation source control device 17 operates the tube voltage generator 18 based on the set imaging conditions, and irradiates radiation R from the radiation tube 49. The tube voltage generator 18 generates a tube voltage by boosting an input voltage using a transformer. The tube voltage generated by the tube voltage generator 18 is supplied to the radiation tube 49.

[0035] The distance measuring camera 20 has a light transmitting section and a light receiving section (not shown), and is configured to be able to measure the distance from the distance measuring camera 20 to the surface of the holder 37 and the surface of the subject H by measuring the time from when the measuring light B is emitted from the light transmitting section toward the subject H until when the light receiving section receives the measuring light B reflected by the surface of the subject H and returned. For example, the measuring light B is an infrared laser light. The measuring light B may be a pulsed light or an intensity-modulated continuous light. When continuous light is used as the measuring light B, the above-mentioned time can be measured by obtaining the phase difference between the measuring light B emitted from the light transmitting section and the measuring light B received by the light receiving section. For example, the distance measuring camera 20 of this embodiment measures the distance to one point of the measurement object. The measurement value by the distance measuring camera 20 is output to the console 14. The distance measuring camera 20 may be built into the irradiation field limiter 50.

[0036] 2 shows an example of the configuration of the console 14. In addition to the above-mentioned display 40 and input device 41, the console 14 includes a memory 56, a CPU (Central Processing Unit) 57, and a communication I / F (Interface) 58. The display 40, the input device 41, the memory 56, the CPU 57, and the communication I / F 58 are interconnected.

[0037] The memory 56 is a storage device such as a flash memory built into or connected to the CPU 57. The memory 56 stores an operating program 56A, various data, etc. The CPU 57 executes processing based on the operating program 56A stored in the memory 56. In this way, the CPU 57 comprehensively controls each part of the computer. The CPU 57 is an example of a "processor" according to the technology of the present disclosure. The communication I / F 58 controls the transmission of various information between the electronic cassette 13 and an external device.

[0038] The CPU 57 displays a plurality of types of imaging menus on the display 40 in a selectable form. The imaging menu specifies an imaging technique that is a set of an imaging region of the subject H, an imaging posture of the subject H, and an imaging direction of the subject H, such as "chest, upright position, front". The operator operates the input device 41 to register one of the plurality of types of imaging menus. In this embodiment, a case where the upright position is selected as the imaging posture will be described.

[0039] Before starting radiography, the CPU 57 acquires the measurement values ​​output from the distance measuring camera 20 and the detection values ​​output from the detection sensor 42 via the communication I / F 58, and calculates the body thickness TB of the subject H based on information including the acquired measurement values ​​and detection values. The CPU 57 also determines the radiography conditions based on the radiography menu and the calculated body thickness TB, and transmits the determined radiography conditions to the radiation source control device 17 via the communication I / F 58.

[0040] When an instruction to start irradiation of radiation R is given to the radiation source control device 17 via the irradiation switch 19, the CPU 57 receives from the radiation source control device 17 an irradiation start signal indicating that irradiation of radiation R will start. When the irradiation start signal is received, the CPU 57 transmits a synchronization signal indicating that irradiation of radiation R will start to the electronic cassette 13. Furthermore, the CPU 57 receives from the radiation source control device 17 an irradiation end signal indicating that irradiation of radiation R has ended. When the irradiation end signal is received, the CPU 57 transmits a synchronization signal indicating that irradiation of radiation R has ended to the electronic cassette 13.

[0041] When receiving a synchronization signal from the console 14 indicating that irradiation of radiation R has started, the electronic cassette 13 causes the detection panel to start a storage operation. Also, when receiving a synchronization signal from the console 14 indicating that irradiation of radiation R has ended, the electronic cassette 13 causes the detection panel to start a readout operation.

[0042] The CPU 57 receives the radiation image from the electronic cassette 13 via the communication I / F 58. The CPU 57 performs various image processing on the radiation image, and then displays the radiation image on the display 40 for viewing by the operator.

[0043] 3 shows an example of functions related to the determination of the imaging conditions configured in the CPU 57. The CPU 57 executes processing based on the operating program 56A, thereby functioning as an acquisition unit 60, a correction coefficient calculation unit 61, a body thickness calculation unit 62, a correction unit 63, and an imaging condition determination unit 64. In this embodiment, the CPU 57, the memory 56, the distance measurement camera 20, and the detection sensor 42 configure a "distance measurement device" according to the technology of the present disclosure.

[0044] The acquisition unit 60 acquires a detection value P output from the detection sensor 42 by controlling the detection sensor 42. The detection value P is a value corresponding to the SID (see FIG. 4). The relationship between the detection value P and the SID may be stored in the memory 56 in advance.

[0045] Moreover, the acquiring unit 60 acquires a first measurement value L1 and a second measurement value L2 output from the distance measuring camera 20 by controlling the distance measuring camera 20. The first measurement value L1 is a measurement value in a state where the subject H is not placed, and represents the distance from the distance measuring camera 20 to the surface of the holder 37 (see FIG. 4). The second measurement value L2 is a measurement value in a state where the subject H is placed, and represents the distance from the distance measuring camera 20 to the surface of the subject H (see FIG. 4).

[0046] The correction coefficient calculation unit 61 calculates a correction coefficient K using the SID corresponding to the detection value P, the first measurement value L1, and the known information D stored in the memory 56. Specifically, the correction coefficient calculation unit 61 calculates the correction coefficient K based on the following equations (1A) and (1B). The correction coefficient calculation unit 61 stores the calculated correction coefficient K in the memory 56. K = LP / L1 (1A) LP=SID-Δ1-Δ2 (1B)

[0047] Here, Δ1 is the distance between the distance measuring camera 20 and the focus F of the radiation R (see FIG. 4). Δ2 is the distance from the surface of the holder 37 to the detection surface of the electronic cassette 13 (see FIG. 4). The distances Δ1 and Δ2 are known and are included in the known information D. In other words, LP is a known distance obtained from the device information and represents the distance from the distance measuring camera 20 to the surface of the holder 37. Note that the holder 37 is an example of a "reference object whose distance is known" according to the technology of the present disclosure.

[0048] If the measurement accuracy of the distance measuring camera 20 is high, K should be 1. However, since the measurement value by the distance measuring camera 20 changes over time due to temperature drift, K will not be 1, particularly if the time that has elapsed since the power of the distance measuring camera 20 was turned on is short. The correction coefficient α is a correction coefficient for correcting the temperature drift of the measurement value by the distance measuring camera 20.

[0049] The body thickness calculation unit 62 uses the first measurement value L1 and the second measurement value L2 to calculate the body thickness BT0 of the subject H. Specifically, the body thickness calculation unit 62 calculates the body thickness BT0 by subtracting the second measurement value L2 from the first measurement value L1 based on the following formula (2). BT0 = L1 - L2 (2)

[0050] The body thickness BT0 is a value before correction that includes the influence of temperature drift, and is therefore referred to as the primary body thickness BT0 below. The primary body thickness BT0, which is the difference between the first measurement value L1 and the second measurement value L2, is an example of the "calculated value calculated using the second measurement value" according to this embodiment.

[0051] The correction unit 63 calculates the body thickness BT of the subject H using the primary body thickness BT0 and a correction coefficient K read out from the memory 56. Specifically, the correction unit 63 calculates the body thickness BT with the temperature drift corrected by multiplying the primary body thickness BT0 by the correction coefficient K based on the following formula (3). BT = BT0 × K (3)

[0052] The imaging condition determination unit 64 determines imaging conditions based on an imaging menu registered by an operator operating the input device 41 and the body thickness TB corrected by the correction unit 63. Specifically, the larger the body thickness TB is, the larger the tube current and the tube current time product are made. The imaging condition determination unit 64 stores the determined imaging conditions in the memory 56.

[0053] 5 shows an example of the flow of a photographing condition determination process by the CPU 57. First, the CPU 57 determines whether or not a photographing menu has been registered by the operator operating the input device 41 (step S10). If a photographing menu has not been registered (step S10: NO), the CPU 57 repeats step S10.

[0054] When the imaging menu is registered (step S10: YES), the CPU 57 acquires the detection value P from the detection sensor 42 by the acquisition unit 60 (step S11). Next, the CPU 57 acquires the first measurement value L1 from the distance measuring camera 20 by the acquisition unit 60 (step S12). At this time, the subject H is not placed on the upright imaging platform 12. The detection value P may be acquired in advance before the imaging menu is registered.

[0055] Next, the CPU 57 causes the correction coefficient calculation unit 61 to calculate the correction coefficient K as described above using the detection value P, the first measurement value L1, and the known information D (step S13).

[0056] Next, the CPU 57 judges whether or not the subject H has been placed on the upright imaging platform 12 (step S14). For example, the CPU 57 judges whether or not the subject H has been placed based on whether or not the operator has operated the input device 41 to input that the subject H has been placed. If the subject H has not been placed (step S14: NO), the CPU 57 repeats step S14. If the subject H has been placed (step S14: YES), the CPU 57 acquires the second measurement value L2 from the distance measuring camera 20 by the acquisition unit 60 (step S15).

[0057] Next, the CPU 57 calculates the primary body thickness BT0 as described above using the first measurement value L1 and the second measurement value L2 by the body thickness calculation unit 62 (step S16). Next, the CPU 57 calculates the body thickness BT with the temperature drift corrected as described above by correcting the primary body thickness BT0 by the correction unit 63 using the correction coefficient K (step S17).

[0058] Then, the CPU 57 determines the imaging conditions as described above using the imaging menu and the body thickness BT by the imaging condition determination unit 64 (step S18). This ends the imaging condition determination process.

[0059] The imaging conditions determined in the imaging condition determination process are transmitted to the radiation source control device 17. Thereafter, when the exposure switch 19 is operated, radiation imaging is performed based on the imaging conditions transmitted to the radiation source control device 17.

[0060] For example, when SID=1200mm, Δ1=100mm, and Δ2=20mm, LP=1080mm. When L1=1050mm, K=1.029. When L2=850mm, BT0=200mm, but by correcting this with the correction coefficient K, BT=205.7mm.

[0061] As described above, in this embodiment, the correction coefficient K is calculated by dividing a known distance by a measurement value measured by the distance measuring camera 20, and the measurement value measured by the distance measuring camera 20 is corrected using the correction coefficient K, so that measurement can be performed before the temperature drift stabilizes. In other words, according to the technology disclosed herein, measurement can be performed quickly and with high accuracy.

[0062] In the above embodiment, the body thickness BT of the subject H placed in an upright position on the upright imaging platform 12 is measured, but it is also possible to measure the body thickness BT of the subject H placed in a lying position on a lying position imaging platform (not shown). In this case, the value of SID may be found based on the detection value of the vertical position detected by a detection sensor such as a potentiometer or a linear encoder built into the radiation source suspension device 15.

[0063] In the above embodiment, the CPU 57 determines the imaging conditions corresponding to the body thickness BT obtained by the measurement using the distance measuring camera 20, but the imaging conditions corresponding to the obtained body thickness BT may be proposed to the operator, and the operator may finally determine the imaging conditions to be used for radiography. For example, as shown in FIG. 6, the CPU 57 displays icons 70 representing a plurality of imaging conditions 71 to 73 including the imaging conditions corresponding to the obtained body thickness BT on the display 40, and allows the operator to select one of the imaging conditions 71 to 73 included in the displayed icon 70 using the input device 41. The imaging condition 71 is an imaging condition corresponding to a thin person. The imaging condition 72 is an imaging condition corresponding to a person of normal build. The imaging condition 73 is an imaging condition corresponding to an obese person.

[0064] In the example shown in FIG. 6, the CPU 57 displays a bar 74 on the imaging condition 72 corresponding to the body thickness BT obtained by measurement using the distance measuring camera 20, thereby indicating that the imaging condition is the optimum imaging condition proposed to the operator. The operator can also select an imaging condition other than the proposed imaging condition 72 using the input device 41. In the example shown in FIG. 6, the operator selects the imaging condition 73. The CPU 57 transmits the selected imaging condition to the radiation source control device 17.

[0065] In the above embodiment, the CPU 57 acquires the first measurement value L1 and calculates the correction coefficient K when the shooting menu is registered. However, after the power supply of the distance measurement camera 20 is turned on, the CPU 57 may periodically acquire the first measurement value L1 and calculate the correction coefficient K. This is because, as shown in FIG. 7, the internal temperature of the distance measurement camera 20 changes according to the elapsed time from the time of power supply. Due to the change in the internal temperature, a temperature drift occurs in the first measurement value L1 as shown in FIG. 8, and the correction coefficient K changes. T0 to T7 shown in FIG. 8 represent update timings for acquiring the first measurement value L1 and calculating the correction coefficient K. The interval of these update timings is, for example, 30 minutes. The correction coefficient K calculated at each update timing is overwritten in the memory 56. That is, the correction coefficient K is updated at regular intervals. In this case, the CPU 57 acquires the second measurement value L2 and calculates the primary body thickness BT0, and then calculates the body thickness BT by correcting the primary body thickness BT0 using the correction coefficient K updated at the immediately preceding update timing.

[0066] Furthermore, the interval between update timings does not have to be constant. Since the shorter the time that has elapsed since power-on is, the greater the temperature change, as shown in FIG. 9, the shorter the time that has elapsed since power-on is, the shorter the interval between update timings may be. In other words, the more times the correction coefficient K is updated, the less frequently it is possible to update it. Furthermore, once the rate of change in temperature (i.e., the temperature gradient) becomes equal to or less than a certain value, the correction coefficient K does not have to be updated.

[0067] In addition, in the above embodiment, the CPU 57 acquires the second measurement value L2 from the distance measuring camera 20 when the subject H is placed, but the CPU 57 may also acquire the second measurement value L2 from the distance measuring camera 20 when it detects that the operator has pressed the irradiation switch 19 to the first position.

[0068] In the above embodiment, the CPU 57 calculates the primary body thickness BT0, and then calculates the body thickness BT by correcting the primary body thickness BT0 using the correction coefficient K. Alternatively, the CPU 57 may calculate the body thickness BT by correcting the first measurement value L1 and the second measurement value L2 using the correction coefficient K, and then subtracting the corrected second measurement value L2 from the corrected first measurement value L1.

[0069] In the above embodiment, the measurement value obtained by measuring the distance from the distance measuring camera 20 to the reference object (the holder 37 in the above embodiment) once by the distance measuring camera 20 is set as the first measurement value L1. Alternatively, the first measurement value L1 may be set as an average value of multiple measurement values ​​obtained by measuring the distance from the distance measuring camera 20 to the reference object multiple times by the distance measuring camera 20. This improves the accuracy of the first measurement value L1, and therefore the accuracy of the correction coefficient K.

[0070] The above embodiment is an example of applying a distance measurement device to a radiography system, but the distance measurement device according to the technology disclosed herein is not limited to the medical field such as radiography, and can also be applied to other fields.

[0071] [Second embodiment] Fig. 10 shows an automobile equipped with a distance measurement device according to the second embodiment. As shown in Fig. 10, the distance measurement device according to this embodiment includes a ToF distance measurement camera 80 and a rotation device 81. The rotation device 81 is attached to the upper part of a vehicle body 83, and rotates the distance measurement camera 80 360° around a rotation axis A. The distance measurement camera 80 and the rotation device 81 constitute a so-called LiDAR (Light Detection And Ranging) device, and measure the distance to a measurement target existing around the vehicle body 83.

[0072] The distance measuring camera 80 has a configuration similar to that of the distance measuring camera 20 according to the first embodiment, and measures the distance to a measurement target by measuring the time from when measurement light B is emitted from a light transmitting section until when the light receiving section receives the measurement light B that is reflected by the surface of the specimen H and returned. The distance measuring camera 80 may have a two-dimensional sensor and obtain distance information within the angle of view θ for each pixel for each distance measurement.

[0073] A plurality of reference objects 84A to 84D are provided on the vehicle body 83. The reference objects 84A to 84D are, for example, poles fixed to corners of the vehicle body 83.

[0074] Fig. 11 shows an example of the positional relationship between the distance measuring camera 80 and the reference objects 84A to 84D. Fig. 11 shows a schematic diagram of a car body 83 seen from above. The distances S between the distance measuring camera 80 and each of the reference objects 84A to 84D are equal and known. For example, the distance S is 1000 mm.

[0075] 12 shows an example of the configuration of a distance measurement device according to the second embodiment. The distance measurement device according to this embodiment includes a distance measurement camera 80, a rotation device 81, a memory 85, and a CPU 86. The memory 85 and the CPU 86 have the same configuration as the memory 56 and the CPU 57 according to the first embodiment. The memory 85 stores an operating program 85A, various data, etc. The CPU 86 is an example of a "processor" according to the technology of the present disclosure.

[0076] 13 shows an example of functions related to distance measurement configured in the CPU 86. The CPU 86 functions as an acquisition unit 90, a correction coefficient calculation unit 91, and a correction unit 92 by executing processes based on an operating program 85A.

[0077] The acquiring unit 90 acquires a first measurement value L1 and a second measurement value L2 output from the distance measuring camera 80 by controlling the distance measuring camera 80 while controlling the rotation device 81 to rotate the distance measuring camera 80. In this embodiment, the first measurement value L1 is a measurement value of the distance from the distance measuring camera 80 to each of the reference objects 84A to 84D. The second measurement value L2 is a measurement value of the distance from the distance measuring camera 80 to the measurement target.

[0078] Specifically, as shown in FIG. 14, the acquisition unit 90 acquires a first measurement value L1a of the distance from the distance measuring camera 80 to the reference object 84A, a first measurement value L1b of the distance from the distance measuring camera 80 to the reference object 84B, a first measurement value L1c of the distance from the distance measuring camera 80 to the reference object 84C, and a first measurement value L1d of the distance from the distance measuring camera 80 to the reference object 84D.

[0079] The correction coefficient calculation unit 91 calculates a correction coefficient K using the first measurement values ​​L1a to L1d and known information D stored in the memory 85. In this embodiment, the known information D is the above-mentioned distance S. Specifically, the correction coefficient calculation unit 91 calculates the correction coefficient K based on the following equations (4A) and (4B). The correction coefficient calculation unit 91 stores the calculated correction coefficient K in the memory 85. K = S / L1av (4A) L1av=(L1a+L1b+L1c+L1d) / 4 ···(4B)

[0080] Here, L1av is the average value of the first measurement values ​​L1a to L1d. If the measurement accuracy of the distance measurement camera 80 is high, K should be 1. However, since the measurement values ​​by the distance measurement camera 80 change over time due to temperature drift, K will not be 1, particularly if the time that has elapsed since the distance measurement camera 80 was turned on is short.

[0081] The correction unit 92 calculates the distance L to the measurement object using the second measurement value L2 and the correction coefficient K read out from the memory 85. Specifically, the correction unit 92 calculates the distance L to the measurement object by multiplying the second measurement value L2 by the correction coefficient K based on the following formula (5). L = L2 × K (5)

[0082] As described above, in this embodiment, the correction coefficient K is calculated using the average value of the measurement values ​​of the distances to the multiple reference objects 84A to 84D, so that the correction accuracy is improved and it is possible to perform measurement with higher accuracy. Note that the number of reference objects is not limited to four and can be changed as appropriate. In addition, the type, arrangement, etc. of the reference objects can also be changed as appropriate.

[0083] Furthermore, in this embodiment, the distance measuring camera 80 is rotated by the rotation device 81, so that it is possible to prevent a reference object that is not intended to be photographed from being captured in the image.

[0084] It is assumed that the range of distances measured by the distance measuring device according to this embodiment is about 0.5 m to 2 m, and the required measurement accuracy is about ±30 mm. In this case, the distance measuring device according to this embodiment can be used in cases such as measuring the distance to an obstacle that is within 2 m of the vehicle body when parking the vehicle. For example, if the error in the measurement value of the distance to the obstacle exceeds ±30 mm, there is a high risk that the vehicle body will come into contact with the obstacle. The distance measuring device according to this embodiment can reduce the risk of coming into contact with an obstacle when parking.

[0085] The distance measurement device according to this embodiment is not limited to being mounted on an automobile, but can also be mounted on other moving bodies.

[0086] [Third embodiment] 15 and 16 show a shutter device 100 to which a distance measurement device according to the third embodiment is attached. Fig. 15 is a front view of the shutter device 100. Fig. 16 is a side view of the shutter device 100.

[0087] The shutter device 100 is provided at an opening that is the entrance and exit of a structure such as a building, and for example, moves a shutter curtain 102, which is an opening and closing body, to open and close along a pair of guide rails 101. On the upper part of the guide rails 101, there are provided a winding shaft that winds up the shutter curtain 102, a motor that rotates and drives the winding shaft, and a shutter case 103 that incorporates a control device that controls the motor, etc.

[0088] A ToF distance measurement camera 110 capable of measuring the distance to an obstacle present below is attached to the front of the shutter case 103. The distance measurement device according to this embodiment includes the distance measurement camera 110, and a memory and a CPU (not shown). The distance measurement device according to this embodiment has the same configuration as the distance measurement device according to the second embodiment, except that the distance measurement camera 110 is not configured to be rotatable.

[0089] A reference object 111 is provided near the ground on one of the pair of guide rails 101. The reference object 111 is preferably provided at a position that does not hinder the opening and closing of the shutter curtain 102 and does not hinder the opening when the shutter curtain 102 is open. The reference object 111 may be formed integrally with the guide rail 101.

[0090] It is possible to use the ground below the distance measuring camera 110 as the reference object, but since the ground is easily deformed due to the influence of temperature, etc., it is difficult to distinguish whether the change in distance is due to the presence of an obstacle. For this reason, it is preferable to use a structure other than the ground as the reference object 111.

[0091] As shown in Fig. 15, a distance S from a distance measuring camera 110 to a reference object 111 is known. Moreover, as shown in Fig. 16, it is preferable that the reference object 111 is formed in a slope shape with an apex at the top. This makes it possible to prevent an obstacle 112, such as a person, from climbing onto the reference object 111.

[0092] The function of the distance measurement device according to this embodiment is basically the same as the function of the distance measurement device according to the second embodiment. In this embodiment, the first measurement value L1 is a measurement value of the distance from the distance measurement camera 110 to the reference object 111. The second measurement value L2 is a measurement value of the distance from the distance measurement camera 110 to an obstacle 112 as a measurement target. The distance measurement process according to this embodiment is similar to the distance measurement process according to the second embodiment shown in FIG. 13 except that one first measurement value L1 is used. This makes it possible to accurately measure the distance from the distance measurement camera 110 to the obstacle 112.

[0093] By using the distance measurement device of this embodiment, it is possible to constantly measure the distance from the distance measurement camera 110 to the obstacle 112, and when the obstacle 112 passes through the opening when the shutter curtain 102 is opened or closed, the opening and closing operation can be stopped accurately and safely.

[0094] The range of distance measurement by the distance measurement device according to this embodiment is about 0.5 m to 2 m, and the required measurement accuracy is assumed to be about ±30 mm. Since the shutter device is often used outdoors, a measurement error of about ±30 mm caused by factors such as diurnal and seasonal temperature fluctuations may cause malfunction. By applying the distance measurement device according to this embodiment, such malfunctions can be prevented.

[0095] The hardware configuration of the processor in each of the above embodiments can be modified in the following various ways.

[0096] Processors include CPUs, PLDs (Programmable Logic Devices), dedicated electrical circuits, and combinations of these. As is well known, a CPU is a general-purpose processor that executes software (i.e., programs) and functions as various processing units. A PLD is a processor whose circuit configuration can be changed after manufacture, such as an FPGA (Field Programmable Gate Array). A dedicated electrical circuit is a processor having a circuit configuration designed specifically to execute specific processing, such as an ASIC (Application Specific Integrated Circuit). Furthermore, the hardware structure of these various processors is, more specifically, an electrical circuit (circuitry) that combines circuit elements such as semiconductor elements.

[0097] Two or more of the above-described embodiments and modifications may be combined with each other as long as no contradiction occurs.

[0098] The technology of the present disclosure is not limited to the above-described embodiments and modifications, and various configurations may be adopted without departing from the spirit of the present disclosure. Furthermore, the technology of the present disclosure extends to a computer-readable storage medium that non-temporarily stores a program, in addition to a program.

[0099] The above explanation makes it possible to understand the following techniques. [Additional note 1] A ToF distance measurement camera that measures the distance to a measurement target object and the distance to a reference object whose distance is known; A processor; Equipped with The processor, calculating a correction coefficient based on a first measurement value, which is a measurement value of a distance from the distance measuring camera to the reference object by the distance measuring camera, and a known distance from the distance measuring camera to the reference object; correcting a second measurement value, which is a measurement value of a distance from the distance measuring camera to the measurement object by the distance measuring camera, or a calculated value calculated using the second measurement value; Distance measuring device. [Additional note 2] A plurality of the reference objects are provided, The processor, calculating the correction coefficient based on an average value of the first measurement values, which are measurement values ​​of distances from the distance measuring camera to the plurality of reference objects by the distance measuring camera, and known distances from the distance measuring camera to the plurality of reference objects; Item 1. A distance measuring device according to claim 1. [Additional note 3] the first measurement value is an average value of a plurality of measurement values ​​obtained by measuring a distance from the distance measuring camera to the reference object a plurality of times by the distance measuring camera; 3. The distance measuring device according to claim 1 or 2. [Additional note 4] The calculated value is a difference value between the first measurement value and the second measurement value. A distance measuring device according to any one of claims 1 to 3. [Additional note 5] The processor, The correction coefficient is a value obtained by dividing the first measurement value by the known distance; correcting the second measured value or the calculated value by multiplying the second measured value or the calculated value by the correction coefficient; A distance measuring device according to any one of claims 1 to 4. [Additional note 6] The processor, updating the correction coefficient by acquiring the first measurement value at regular time intervals and calculating the correction coefficient; A distance measuring device according to any one of claims 1 to 5. [Additional note 7] The processor, the shorter the time that has elapsed since the power-on of the distance measuring camera is, the shorter the interval at which the first measurement value is obtained and the correction coefficient is calculated, thereby updating the correction coefficient. A distance measuring device according to any one of claims 1 to 5. [Additional note 8] a detection sensor for detecting a position of the distance measuring camera relative to the reference object, The processor determines the known distance using a detection value detected by the detection sensor. A distance measuring device according to any one of claims 1 to 7. [Additional note 9] the reference object is a photography stand; the measurement object is a subject placed on the imaging table, the calculated value is a difference value between the first measurement value and the second measurement value, The processor, calculating a body thickness of the subject by multiplying the calculated value by the correction coefficient; A distance measuring device according to any one of claims 1 to 8. [Additional Note 10] A distance measuring device according to claim 9; A radiation source that emits radiation toward the imaging table; a radiation image detector that is provided on the imaging table and detects the radiation to generate a radiation image; A radiation imaging system comprising: [Additional Note 11] A distance measuring camera is attached to the radiation source. Item 11. A radiation imaging system according to item 10. [Explanation of symbols]

[0100] 2 Radiography system 10 Radiography equipment 11 Radiation Generator 12 Standing photography stand 13 Electronic Cassette 14 Console 15 Source suspension system 16 Radiation source 17 Radiation source control device 18 Tube voltage generator 19 Irradiation switch 20 Distance measuring camera 25 Radiography Room 35 Pedestal 36 Posts 37 Holder 38 Connection 40 Display 41 Input Devices 42 Detection sensor 45 Arm 46 Trolley 47 Ceiling 48 Rail 49 Radiation Tube 50 Irradiation field limiter 56 Memory 56A Operation Program 57 CPU 58 Communication I / F 60 Acquisition Department 61 Correction coefficient calculation unit 62 Body Thickness Calculation Section 63 Correction section 64 Shooting condition determination unit 66 Radiological Images 70 Icons 71~73 Shooting conditions 74 Bar 80 Distance Measuring Camera 81 Rotating Device 83 Body 84A~84D Reference Objects 85 Memory 85A Operation Program 86 CPU 90 Acquisition Department 91 Correction coefficient calculation section 92 Correction section 100 Shutter device 101 Guide rail 102 Shutter Curtain 103 Shutter Case 110 Distance Measuring Camera 111 Reference Objects 112 Obstacles A Rotation Axis B measurement light D. Known Information F focus H Subject K correction factor L1, L1a~L1d First measurement value L2 Second measurement value L distance P detection value R Radiation

Claims

1. A ToF distance measurement camera that measures a distance to a measurement target object and a distance to a reference object whose distance is known; A processor; Equipped with The processor, calculating a correction coefficient based on a first measurement value, which is a measurement value of a distance from the distance measuring camera to the reference object by the distance measuring camera, and a known distance from the distance measuring camera to the reference object; correcting a second measurement value, which is a measurement value of a distance from the distance measuring camera to the measurement object by the distance measuring camera, or a calculated value calculated using the second measurement value; Distance measuring device.

2. A plurality of the reference objects are provided, The processor, calculating the correction coefficient based on an average value of the first measurement values, which are measurement values ​​of distances from the distance measuring camera to the plurality of reference objects by the distance measuring camera, and known distances from the distance measuring camera to the plurality of reference objects; The distance measurement device according to claim 1 .

3. the first measurement value is an average value of a plurality of measurement values ​​obtained by measuring a distance from the distance measuring camera to the reference object a plurality of times by the distance measuring camera; The distance measurement device according to claim 1 .

4. The calculated value is a difference value between the first measurement value and the second measurement value. The distance measurement device according to claim 1 .

5. The processor, The correction coefficient is a value obtained by dividing the first measurement value by the known distance; correcting the second measured value or the calculated value by multiplying the second measured value or the calculated value by the correction coefficient; The distance measurement device according to claim 1 .

6. The processor, updating the correction coefficient by acquiring the first measurement value at regular time intervals and calculating the correction coefficient; The distance measurement device according to claim 1 .

7. The processor, the shorter the time that has elapsed since the power-on of the distance measuring camera, the shorter the interval at which the first measurement value is obtained and the correction coefficient is calculated, thereby updating the correction coefficient. The distance measurement device according to claim 1 .

8. a detection sensor for detecting a position of the distance measuring camera relative to the reference object, The processor determines the known distance using a detection value detected by the detection sensor. The distance measurement device according to claim 1 .

9. the reference object is a photography stand; the measurement object is a subject placed on the imaging table, the calculated value is a difference value between the first measurement value and the second measurement value, The processor, calculating a body thickness of the subject by multiplying the calculated value by the correction coefficient; The distance measurement device according to claim 1 .

10. A distance measurement device according to claim 9 ; A radiation source that emits radiation toward the imaging table; a radiation image detector that is provided on the imaging table and detects the radiation to generate a radiation image; A radiation imaging system comprising:

11. a distance measuring camera attached to the radiation source; The radiation imaging system according to claim 10.

12. A method for operating a distance measurement device equipped with a ToF distance measurement camera that measures a distance to a measurement target object and a distance to a reference object whose distance is known, comprising the steps of: The processor: calculating a correction coefficient based on a first measurement value, which is a measurement value of a distance from the distance measuring camera to the reference object by the distance measuring camera, and a known distance from the distance measuring camera to the reference object; correcting a second measurement value, which is a measurement value of a distance from the distance measuring camera to the measurement object by the distance measuring camera, or a calculated value calculated using the second measurement value; A method for operating a distance measuring device that performs a process including the steps of:

13. An operating program for operating a distance measurement device equipped with a ToF distance measurement camera that measures a distance to a measurement target object and a distance to a reference object whose distance is known, comprising: calculating a correction coefficient based on a first measurement value, which is a measurement value of a distance from the distance measuring camera to the reference object by the distance measuring camera, and a known distance from the distance measuring camera to the reference object; correcting a second measurement value, which is a measurement value of a distance from the distance measuring camera to the measurement object by the distance measuring camera, or a calculated value calculated using the second measurement value; An operating program that causes a processor to execute a process including the steps of:

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