JP5295602B2 - Imaging table, imaging table calibration method, and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain the weight of a subject by a highly practical constitution in an imaging table which is elevated and lowered by a parallel linkage. <P>SOLUTION: A load sensor 354 provided on an actuator part 35 between an oblique side arm 34a and a base 33 forming the parallel linkage has a prescribed relationship between a load W applied to a top plate 31 and a height position H of an upper part frame 32 and detects a compressive load which is independent of a distribution of the load W relative to the top plate 31 and is applied to a piston rod 352. A height position detecting part 37 detects the height position H of the upper part frame 32. A top plate load deriving part 381 derives the load W applied to the top plate 31 from the detected compressive load applied to the piston rod 352 and the detected height position H of the upper part frame 32. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an imaging table (table) for transporting a subject to an imaging space, a calibration method thereof, and an imaging apparatus for imaging the subject using the imaging table.

  In contrast imaging of a subject using an X-ray CT apparatus or the like, generally, the amount of contrast agent to be injected into the subject is determined based on the body weight of the subject. Therefore, it is desirable to be able to immediately identify the weight of the subject in order to improve the efficiency of contrast imaging or respond to an emergency patient.

  In imaging of a subject using an X-ray CT apparatus or the like, generally, the subject is transported to the imaging space by moving the top of the imaging table on which the subject is placed. Therefore, in order to prevent accidents such as finger scissors in the vicinity of the top that may occur during transport, it is desirable that the top can be transported with an appropriate driving force according to the weight of the subject.

  In order to meet such demands, various imaging tables that can measure the weight of the subject placed on the top board on the spot have been proposed.

  For example, Patent Document 1 proposes an imaging table in which a top plate on which a subject is placed or a support base that supports the top plate is provided with a device that measures the weight of the subject with a pressure sensor.

  On the other hand, various photographing tables for raising and lowering the table by a predetermined link mechanism have been proposed so far.

For example, Patent Document 2 proposes a photographing table having a parallel link mechanism.
JP 2006-325615 A JP 2006-231091 A

  By the way, in the imaging table which raises / lowers the table by the link mechanism, a configuration capable of specifying the weight of the subject with a highly practical configuration has not been proposed yet.

  In view of the above circumstances, the present invention provides an imaging table that can determine the body weight of a subject with a highly practical configuration, an imaging method that uses the imaging table, and an imaging that uses the imaging table. An object is to provide an apparatus.

  In a first aspect, the present invention links a top plate on which a subject is placed, a top plate support portion for supporting the top plate, a telescopic actuator (actuator) portion, and a telescopic motion of the actuator portion. And a lifting mechanism having a link mechanism that moves the top plate support part up and down to convert the rotational movement of the top plate support part, the actuator part outputs a signal corresponding to a load applied in a direction in which the actuator part extends and contracts. A top plate load derivation having a sensor for outputting, and deriving a top plate load that is a load applied to the top plate based on an output signal of the sensor and posture specifying information for specifying a posture of the link mechanism A photographing table comprising means is provided.

In a second aspect, the present invention provides that the actuator unit includes a piston rod (piston).
rod), a rod end engaged with the piston rod with a screw, and a lock nut engaged with the screw, and the sensor is connected to the piston rod and the lock nut. An imaging table according to the first aspect of the present invention is provided that is interposed therebetween and is tightened by the lock nut.

  In a third aspect, the present invention provides the imaging table according to the second aspect, wherein the sensor has a center hole, and the center hole is provided so as to pass through the screw.

  In a fourth aspect, the present invention is directed to the above-mentioned top plate load deriving means, wherein the output signal value of the sensor and the value representing the posture specifying information are input parameters, and the sensor is tightened by tightening the lock nut. The imaging table according to the second aspect or the third aspect is provided for deriving the top plate load based on a mathematical expression having a tightening load applied to the sensor and an output gain of the sensor as a coefficient.

  In a fifth aspect, the present invention is obtained in a second period after the first period, wherein the mathematical expression has the tightening load and output gain of the sensor in the first period as the coefficients. A plurality of output signals of the sensor, each based on a plurality of output signals obtained under each condition in which the top plate load is the same and the posture of the link mechanism is a plurality of different postures. An abnormality in which an index value reflecting at least one change amount of the tightening load and output gain of the sensor between the first period and the second period is calculated, and an abnormality is detected by determining a threshold value of the index value A photographing table according to the fourth aspect, further comprising a detecting means, is provided.

  In a sixth aspect, the present invention provides an actuator for controlling the actuator unit so that the posture of the link mechanism takes the plurality of postures in response to a predetermined operation from an operator at the second time. A photographing table according to the fifth aspect, further comprising a control means, is provided.

  In a seventh aspect, the present invention is such that the actuator unit has a cylinder that houses the piston rod, and the piston rod moves according to the amount of fluid accommodated in the cylinder. A pump that is connected to the cylinder by a flow path and sends a fluid to the cylinder; a discharge means for discharging the fluid from the cylinder; and the fluid pressure in the flow path reaches a relief pressure. An imaging table according to any one of the fourth to sixth aspects is further provided, further comprising an actuator drive unit having a relief valve that operates when the actuator is in operation.

  In an eighth aspect of the present invention, the link mechanism includes a base, an upper frame, and an oblique arm attached between the base and the upper frame. A parallel link mechanism having the base and the upper frame as horizontal arms, wherein the top plate support part is supported by the upper frame or integrally formed with the upper frame, and the actuator part is An imaging table according to any one of the first to seventh aspects, which is attached between a base and the oblique arm, is provided.

  In a ninth aspect, the present invention provides the apparatus according to any one of the first to eighth aspects, wherein the posture specifying information is a height position of a predetermined portion that moves up and down depending on the posture of the link mechanism. Provide a shooting table.

  In a tenth aspect, the present invention provides the sensor according to any one of the first to ninth aspects, wherein the sensor is formed of a load cell, a piezo, a piezoelectric ceramic, or a crystal. Providing a shooting table from three viewpoints.

  In an eleventh aspect, the present invention relates to a method for calibrating the top plate load deriving means included in the imaging table according to the seventh aspect, wherein the fluid pressure when the fluid pressure of the cylinder is the relief pressure. And a first posture which is information for specifying the posture when the top plate load is unloaded and the posture of the link mechanism is an arbitrary posture. The specific information and the first output signal that is the output signal of the sensor at this time are acquired, and at least a part of the imaging table is fixed so that the attitude of the link mechanism is maintained, and the relief valve The pump of the actuator driving unit is turned so that the fluid pressure of the cylinder becomes the relief pressure, and a second output signal which is an output signal of the sensor at this time is A relational expression between the step of obtaining, the relief load, the first posture specifying information, the first output signal, the second output signal, and the load applied to the sensor and the value of the output signal of the sensor And determining the tightening load and output gain of the sensor at the time when the first output signal value is obtained, and updating the coefficient of the mathematical formula with the specified tightening load and output gain of the sensor. And a photographing table calibration method comprising the steps of:

  In a twelfth aspect, the present invention captures image information by photographing the imaging table according to any one of the first to tenth aspects and the subject placed on the top plate of the imaging table. An imaging device including an imaging means for generating the image is provided.

  In a thirteenth aspect, the present invention relates to the present invention in which the imaging unit rotates and projects an X-ray imaging system including an X-ray tube and an X-ray detector facing each other with the subject interposed therebetween. An imaging apparatus according to the twelfth aspect including a gantry means for acquiring data is provided.

  In a fourteenth aspect, the present invention provides the imaging apparatus according to the twelfth aspect, wherein the imaging unit includes a gantry unit that detects a spatial nuclear magnetization distribution of the subject by nuclear magnetic resonance.

  According to the present invention, the sensor of the actuator unit outputs a signal corresponding to the top plate load applied to the entire top plate and the compression load of the actuator unit having a predetermined relationship with the attitude of the link mechanism. The top plate load can be specified based on the output signal and the posture specifying information of the link mechanism, and the weight of the subject can be obtained with a highly practical configuration in the imaging table that moves up and down by the link mechanism. .

Embodiments according to the present invention will be described below.
(First embodiment)

  First, the overall configuration of the X-ray CT apparatus 1 according to the first embodiment will be described.

  FIG. 1 is an external view of an X-ray CT apparatus (imaging apparatus) 1. As shown in FIG. 1, the apparatus 1 includes a scanning gantry 2, an imaging table 3, and an operation console 4.

  The imaging table 3 includes an elevating mechanism and a top plate. The lifting mechanism adjusts the height of the top board. In addition, the subject is placed on the top plate, moved by the means (not shown) together with the top plate, and placed at the optimal imaging position.

  The scanning gantry 2 images an object by rotating an X-ray imaging system including an X-ray tube and an X-ray detector facing each other with the object interposed therebetween, and acquires projection data. The operation console 4 controls the scanning gantry 2 and the imaging table 3 based on the input information of the operator, and acquires a tomographic image of the subject.

  FIG. 2 is a block diagram showing the overall configuration of the X-ray CT apparatus 1. The scanning gantry 2 includes an X-ray tube 21, a collimator 22 (collimator), an X-ray detector 23, and the like, and constitutes an X-ray irradiation / detection device. X-rays radiated from the X-ray tube 21 are shaped by the collimator 22 into, for example, a fan-shaped X-ray beam, that is, a fan beam X-ray, and irradiated to the X-ray detector 23.

  The X-ray detector 23 has a plurality of X-ray detection elements arranged in an array in the spreading direction of the fan beam X-rays. The X-ray detector 23 is a multi-channel X-ray detector in which a plurality of X-ray detection elements are arranged in an array.

  A data collection unit 24 is connected to the X-ray detector 23. The data collection unit 24 collects detection data of individual X-ray detection elements constituting the detector array. X-ray irradiation from the X-ray tube 21 is controlled by an X-ray controller 25 in the scanning gantry 2.

  The above-described components from the X-ray tube 21 to the X-ray controller 25 are mounted on the rotating unit 26 of the scanning gantry 2. Here, the subject is placed in a recumbent state on a top plate in a bore positioned at the center of the rotating unit 26. The rotating unit 26 rotates while being controlled by the rotation controller 25, exposes X-rays from the X-ray tube 21, and detects X-rays of the subject in the X-ray detector 23.

  The operation console 4 includes a console control unit 41, a data collection buffer (buffer) 42, an input / output unit 43, a storage unit 44, and the like. A data collection buffer 42 is connected to the console control unit 41, and the data collection buffer 42 is further connected to the data collection unit 24 of the scanning gantry 2. Here, the data collected by the data collection unit 24 is input to the console control unit 41 through the data collection buffer 42.

  The console control unit 41 performs image reconstruction using a transmission X-ray signal collected through the data collection buffer 42, that is, projection data. A storage unit 44 is also connected to the console control unit 41. The storage unit 44 stores projection data collected in the data collection buffer 42, reconstructed tomographic image information, a program for realizing the functions of the apparatus, and the like.

  An input / output unit 43 is connected to the console control unit 41. The input / output unit 43 includes a display device and an operation device, and displays tomographic image information and other information output from the console control unit 41. The input / output unit 43 is operated by an operator and inputs various instructions, information, and the like from the operation device to the control unit 41. An operator operates the apparatus interactively using a display device.

  In addition, the imaging table 3 is connected to the console control unit 41, and elevating control of the elevating mechanism in the imaging table 3 and position control of the top plate are performed. Thereby, the subject on the top is placed at the optimum image acquisition position.

  FIG. 3 is a diagram showing the configuration of the imaging table 3. As shown in FIG. 3, the imaging table 3 includes a top plate 31, an upper frame (top plate support portion) 32, a base 33, oblique side arms 34 a and 34 b, an actuator portion 35, an actuator drive portion 36, and a height position detection portion 37. A table control unit 38, a top plate drive unit 39, a table operation unit 40, and the like. The subject is placed on the top board 31.

  The top plate 31 is supported by the upper frame 32 so as to be slidable. The base 33 is installed on the floor surface. The two hypotenuse arms 34a and 34b having the same length are respectively coupled at one end to the base 33 by coupling portions 341a and 341b and at the other end to the upper frame 32 by coupling portions 342a and 342b. Each coupling portion forms a pivot joint, and the coupling body can freely rotate in the yz plane of FIG. 3 around the coupling portion. That is, the upper frame 32, the base 33, and the oblique side arms 34a and 34b form a parallelogram type parallel link mechanism (link mechanism) 30 having the base 33 and the upper frame 32 as horizontal arms. Thereby, the upper frame 32 and the top plate 31 can be moved up and down while maintaining a parallel state with respect to the base 33, and the imaging table 3 can be moved up and down. The parallel link mechanism is configured such that the load applied to the top plate 31 and the compressive load applied in the expansion / contraction direction of the actuator unit 35 are determined in a one-to-one relationship for each posture of the parallel link mechanism 30.

  The actuator part 35 is extendable and contracted, and one end is rotatably connected to the base 33 by a connecting part 358 and the other end is rotatably connected to the oblique arm 34a by a connecting part 355.

  FIG. 4 is an enlarged cross-sectional view of the actuator unit 35. As shown in FIG. 4, the actuator unit 35 includes a cylinder 351, a piston rod 352, a rod end 353, a load sensor 354, and a lock nut 356. The piston rod 352 is housed in the cylinder 351 and has a screw hole 352a at the end opposite to the cylinder 351 side. The rod end 353 forms a so-called spherical bearing that functions as the coupling portion 358, and has a screw portion 353a. The piston rod 352 and the lock end 353 are fitted by a screw portion 353a. The lock nut 356 engages with the screw portion 353a. The load sensor 354 is a center hole type load sensor having a center hole, and is interposed between the piston rod 352 and the lock nut 356 through the screw 353a in the center hole, and is tightened with a predetermined tightening load by the lock nut 356. Yes.

  The compression load applied to the moving direction of the piston rod 352 (the direction of expansion and contraction of the actuator unit 35) includes the load X caused by the weight of the top plate 31, the upper frame 32, the oblique arm 34a, etc., and the object placed on the top plate 31. Information for specifying the posture of the parallel link mechanism 30 (posture specifying information), for example, the upper frame 32, combined with a load (hereinafter also referred to as a top plate load) W applied in the vertical direction of the top plate 31 depending on the weight. The load α (H) · (X + W) multiplied by a predetermined coefficient α (H) depending on the height position (hereinafter also referred to as frame height position) H and the tightening load β by the lock nut 356 . Note that, due to the configuration of the parallel link mechanism 30, a part of the load applied to the entire top plate 31 appears concentrated on the compressive load applied in the moving direction of the piston rod 352. Therefore, the compressive load applied in the moving direction of the piston rod 352 depends on the magnitude of the top board load W, but does not depend on the load distribution on the top board 31. Therefore, when the subject is placed on the top 31, the subject is placed quietly even if the center of gravity of the subject changes due to a change in the position or posture of the subject relative to the top 31. If the weight does not change, the compressive load applied in the moving direction of the piston rod 352 does not change. The piston rod 352 is slightly deformed by this compressive load, and this compressive load is applied to the load sensor 354. The load sensor 354 outputs a signal representing a signal value (hereinafter also referred to as a sensor output signal value) P obtained by multiplying the compression load applied to the piston rod 352 by the output gain G.

  The actuator portion 35 may be of any form such as a fluid pressure method such as hydraulic pressure or an electric motor method as long as the piston rod 352 can be slidably controlled in the piston direction. Further, the load sensor 354 may be in any form as long as it is provided so as to output a signal representing a signal value corresponding to the compression load applied in the moving direction of the piston rod 352. As the load sensor 354, for example, a load cell, a piezoelectric element, a piezoelectric ceramic, or a quartz crystal can be considered.

  The actuator driving unit 36 is connected to the table control unit 38 and the actuator unit 35, and expands and contracts the actuator unit 352 under the control of the table control unit 38.

  FIG. 5 is a diagram illustrating a configuration of the actuator driving unit 36. As shown in FIG. 5, the actuator driving unit 36 includes a reservoir 361, a pump 362, an electromagnetic valve 363, a constant flow valve 364, and a relief valve 365.

  The cylinder 351 and the electromagnetic valve 363 are connected by a flow path f1. The electromagnetic valve 363 and the pump 362 are connected by a flow path f2. The electromagnetic valve 363 and the constant flow valve 364 are connected by a flow path f3. The constant flow valve 364 and the reservoir 361 are connected by a flow path f4. The relief valve 365 has a fluid inflow side connected to the flow path f2, and a fluid discharge side connected to the reservoir 361 through the flow path f5.

  The electromagnetic valve 363 switches the flow path between a state in which fluid is put into the cylinder 351 and a state in which fluid is drawn from the cylinder 351. The constant flow valve 364 adjusts the flow velocity of the fluid that exits from the cylinder 351. The relief valve 365 is activated when the fluid pressure in the flow path f2 reaches the relief pressure Z, and allows the fluid in the flow path f2 to escape to the flow path f5 and return to the reservoir 361. During operation of the relief valve 365, the fluid pressure in the flow path f2 is kept constant at the relief pressure Z. The pump 362, the electromagnetic valve 363, and the constant flow valve 364 are controlled by the actuator control unit 388.

  When the electromagnetic valve 363 is put into a state where the fluid is put into the cylinder 351 and the pump 362 is turned, the fluid is sent into the cylinder 351 via the flow path f2, the electromagnetic valve 363, and the flow path f1. As a result, the piston rod 352 is pushed out by the fluid pressure, so that the hypotenuse arms 34a and 34b rise and the upper frame 32 rises. On the other hand, when the pump 362 is stopped and the electromagnetic valve 363 is made to draw the fluid from the cylinder 351, the fluid flows from the cylinder 351 through the flow path f1, the electromagnetic valve 363, the flow path f3, the constant flow valve 364, and the flow path f4. Return to reservoir 361. As a result, the piston rod 352 is retracted, so that the hypotenuse arms 34a and 34b fall down and the upper frame 32 descends. In this way, the height position of the upper frame 32 can be adjusted.

  The height position detection unit 37 is connected to the table control unit 38, detects the frame height position H, and sends the information to the table control unit 38. The height position detection unit 37 includes, for example, a potentiometer (not shown) for detecting the inclination of the hypotenuse arm 34a. From the output of the potentiometer and the geometric structure of the parallel link mechanism 30, The frame height position H is obtained.

  The table control unit 38 is connected to the load sensor 354, the actuator driving unit 36, the height position detection unit 37, the table operation unit 40, and the operation console 4. The table control unit 38 controls the actuator drive unit 36 based on input information and commands from the table operation unit 40, the operation console 4, etc., and outputs information derived by a predetermined process to each unit.

  The table control unit 38 includes a top plate load deriving unit 381, a mathematical formula storage unit 382, an analog-digital conversion unit 383, a top plate control unit 384, and an actuator control unit (control means) 388. Are connected via a network 380. The network 380 is connected to the height position detection unit 37, the table operation unit 40, and the operation console 4. The table control unit 383 is configured by, for example, a computer, and functions as the above-described units when the CPU reads and executes a program stored in a storage unit (not shown).

  The actuator control unit 388 drives the actuator driving unit 36 based on information input from the table operation unit 40 or the operation console 4, and controls expansion / contraction of the actuator unit 35.

  The top plate control unit 384 controls the position of the top plate 31 by controlling the top plate drive unit 39.

  The analog / digital conversion unit 383 is connected to the load sensor 354 and converts an analog signal output from the load sensor 354 into a digital signal. The converted digital signal is sent to, for example, the top plate load deriving unit 381.

  The mathematical formula storage unit 382 uses the value of the output signal of the load sensor 354 (hereinafter referred to as sensor output signal value) P and the frame height position H, which is a value representing posture specifying information, as input parameters, and tightens the lock nut 356. Thus, a mathematical expression having the coefficient of the tightening load β applied to the load sensor 354 and the output gain G of the load sensor 354 is stored.

  Here, this mathematical expression will be described. The sensor output signal value P is expressed by the following equation.

    P = G · [α (H) · (X + W) + β] (Formula 1)

  In Equation 1, G is the output gain of the load sensor 354, α (H) is a function of the frame height position H determined by the geometry of the imaging table 3, X is the top plate 31, the upper frame 32, the hypotenuse arm 34a, etc. , W is a top plate load, and β is a tightening load of the lock nut 356, so-called preload.

  FIG. 6 is a diagram showing the relationship between the top board load W and the frame height position H and the sensor output signal value P. FIG. 6A shows the relationship between the top board load W and the sensor output signal value P when the frame height position H is constant. FIG. 6B shows the relationship between the frame height position H and the sensor output signal value P when the top plate load W is constant.

  As shown in FIG. 6A, the sensor output signal value P is linear when G, α (H), X, β is constant when the frame height position H is constant, and the top plate load W increases. Become bigger. In addition, the sensor output signal value P decreases as the frame height position H increases, and α (H) decreases and the sensor output signal value P also decreases.

  Further, as shown in FIG. 6B, the sensor output signal value P is such that G, X, W, and β are constant when the top load W is constant, and the function α (H) of the frame height position H Varies depending on α (H) is a function that changes in a curve so that it gradually decreases as the frame height position H increases.

  Α (H) and X can be obtained from geometry, structural design, and the like. G and β are parameters specific to each imaging table. For example, when the imaging table is shipped or calibrated, the combination of the top board load W and the frame height position H is different under at least two conditions. It can be obtained by measuring the sensor output signal value P and solving a predetermined equation.

  The mathematical formula storage unit 382 stores the mathematical formula 1 including the parameters G and β obtained in advance in this way.

  The top plate load deriving unit 381 is stored in the mathematical formula storage unit 382 based on the frame height position H detected by the height position detection unit 37 and the sensor output signal value P obtained by the load sensor 354. The top plate load W, that is, the weight of the subject is calculated using the following mathematical formula.

  The top board control unit 384 controls the top board driving unit 39 so that the top board 31 is moved with an appropriate driving force according to the weight of the subject based on the calculated top board load W. Further, the console 4 displays the top board load W on the display device as the weight of the subject based on the calculated top board load W, or contrast imaging conditions such as a contrast agent to be injected into the subject. The amount and the injection rate are derived. These derived conditions can also be used for automatic control of an injector for injecting a contrast medium.

  The top plate drive unit 39 is a drive unit for moving the top plate 31 in a predetermined direction. For example, the top plate 31 is moved by rotating a roller that supports the top plate 31 with a motor (not shown).

  The top plate load deriving unit 381 may periodically obtain the sensor output signal value P and the frame height position H, and sequentially calculate and output the top plate load W. Based on the control signal from the console 4, the sensor output signal value P and the frame height position H may be obtained in a single shot to calculate the top load W.

  As described above, according to the present embodiment, the load sensor 354 of the actuator unit 35 is applied to the top plate load W applied to the entire top plate 31 and the compression load of the actuator unit 35 having a predetermined relationship with the attitude of the link mechanism 30. Since the corresponding signal is output, the top board load W can be specified based on the output signal of the single sensor and the posture specifying information of the link mechanism. The weight of the subject can be obtained with a high configuration.

  Further, although the load sensor 354 is deformed by a load applied to the sensor itself, according to the present embodiment, the load sensor 354 does not directly support the top plate 31, so that the top plate 31 deforms the load sensor 354. Accordingly, there is an advantage that the positional deviation of the imaging region of the subject due to the distortion of the top plate 31 is not increased.

  Moreover, according to this embodiment, since the load sensor 354 is provided in the existing actuator part 35, it is not necessary to change the basic structure of a link mechanism, and design is easy. In particular, in this embodiment, the center hole type load sensor 354 is interposed between the piston rod 352 and the lock nut 356 in the center hole through the threaded portion 353a and tightened with the lock nut 356. The structure, processing, and special members are not required, and it can be composed of only commercially available parts, which is very low cost.

  The present invention can be variously modified and added without departing from the spirit of the present invention.

  In the present embodiment, the load sensor 354 is a center hole type load sensor and is provided so as to pass through a screw to which the piston rod 352 and the rod end 353 are fitted. For example, the load sensor 354 is a flat plate type load sensor. Alternatively, the piston rod 352 and the rod end 353 may be directly sandwiched between the piston rod 352 and the rod end 353.

  Further, in this embodiment, the top plate load deriving unit 381 calculates the top plate load W using the mathematical expression representing the correlation stored in the mathematical formula storage unit 382. A correspondence table storage unit for storing the table may be provided, and the top board load deriving unit 381 may determine the top board load W with reference to the correspondence table. The correspondence table corresponds to, for example, each combination of a frame height position and a sensor output signal value for a plurality of representative frame height positions and a plurality of representative sensor output signal values. It can be set as the table | surface with which the top plate load was matched.

In the present embodiment, the screw in the actuator portion 35 is provided on the rod end 353 side, but may be provided on the piston rod 352 side.
(Second Embodiment)

  By the way, it is conceivable that the output gain G of the load sensor 354 and the tightening load β by the lock nut 356 change little by little as time passes. Therefore, in order to always derive the top plate load W with high accuracy, it is indispensable to periodically calibrate the imaging table, that is, update the output gain G and the tightening load β used to derive the top plate load W. Therefore, here, a method for correcting the imaging table will be described.

  First, the first imaging table calibration method will be described.

  FIG. 7 is a flowchart showing the first imaging table calibration method. Note that steps S1 to S4 are preparation stages, and steps S5 to S7 are calibration stages.

  In step S1, in the state where the frame height position H is an arbitrary height position H1, the output signal value obtained by the load sensor 354 when the top board load W is unloaded is acquired as the sensor output signal value P10. In addition, the signal value obtained by the load sensor 354 when the top board load W is the known load W2 is acquired as the sensor output signal value P12. The sensor output signal values P10 and P12 can be expressed by the following equations, respectively.

P10 = G1 [[α (H1). (X + 0) + β1] (Formula 2)
P12 = G1 · [α (H1) · (X + W2) + β1] (Formula 3)

  In Equations 2 and 3, G1 and β1 are output gain and tightening load when the sensor output signal values P10 and P12 are obtained.

  In step S2, the output gain G1 and the tightening load β1 are obtained by substituting known P10, P12, α (H1), X, and W2 into these equations and solving the equations. These G 1 and β 1 are the coefficients of the mathematical formula stored in the mathematical formula storage unit 382.

  In step S3, at least a part of the imaging table is fixed so that the position of the piston rod 352 is maintained. For example, the upper frame 32 and the base 33 are connected by a connecting member. In this state, the electromagnetic valve 363 is switched so that the fluid flows to the cylinder 351, the pump 362 is turned, and the relief valve 365 is operated. Thereby, the fluid pressure in the cylinder 351 is made the same as the relief pressure Z, and a state is created in which the piston rod 352 is pushed with a fluid pressure equal to the relief pressure Z. At this time, the signal value obtained by the load sensor 354 is acquired as the sensor output signal value P1z. The relief pressure Z is a value inherent to the relief valve 365, and can be considered to be always constant with almost no secular change. The sensor output signal value P1z can be expressed as follows.

    P1z = G1 [A + β1] (Formula 4)

  In Formula 4, A is a load (hereinafter referred to as a relief load) applied to the load sensor 354 when the piston rod 362 is pushed by the fluid pressure when the fluid pressure in the cylinder 351 is the relief pressure Z.

  In step S4, the known load P1z, G1, β1 is substituted into this equation to obtain the relief load A. This is the preparation stage, and the subsequent steps are performed during actual calibration. This preparation is performed, for example, at the time of shipment of the imaging table 3.

  In step S5, when the top board load W is no load and the frame height position H is an arbitrary height position, the frame height position H detected by the height position detector 37 is changed to the height position H2 ( (First posture specifying information) and a signal value obtained by the load sensor 354 is obtained as a sensor output signal value (first output signal value) P20. Further, by fixing at least a part of the imaging table 3 so that the posture of the link mechanism, that is, the position of the piston rod 352 is held, and rotating the pump 362, the relief valve 365 is operated and the fluid pressure in the cylinder 351 is relieved. The pressure Z is made the same, and a state is created in which the piston rod 352 is pushed with a fluid pressure equal to the relief pressure Z. At this time, a signal value obtained by the load sensor 354 is acquired as a sensor output signal value (second output signal value) P2z. The sensor output signal values P20 and P2z can be expressed as follows.

P20 = G2, [α (H2), (X + 0) + β2] (Formula 5)
P2z = G2 [A + β2] (Formula 6)

  In Equation 5 and Equation 6, G2 and β2 are the output gain and tightening load when the sensor output signal values P20 and P2z are obtained.

  In step S6, the output gain G2 and the tightening load β2 are obtained by substituting the known P20, P2z, A, α (H2), and X into these equations 5 and 6 and solving the equations.

  In step S7, the coefficients G1 and β1 of the mathematical formula stored in the mathematical formula storage unit 382 are updated to G2 and β2 obtained in step S6.

  In this way, if the relief load A generated by the fluid pressure of the cylinder 351 pushing the piston rod 352 when the relief valve 356 is operated is obtained in advance, and the sensor output signal value is acquired under the same conditions during calibration. By utilizing the fact that the relief pressure Z is little changed over time and the relief load A is always substantially constant, it is possible to create substantially the same state as when the sensor output signal value P is acquired with a known top plate load W. The imaging table can be calibrated without placing a known weight on the top plate 31.

  Next, a second imaging table calibration method will be described.

  Of the parameters G and β, it is considered that only β often changes due to the looseness of the lock nut 356. The second imaging table calibration method is a calibration method particularly effective in such a case.

  FIG. 8 is a flowchart showing the second imaging table calibration method. Step S11 is a preparation stage, and steps S12 to S14 are a calibration stage.

  In step S11, at least a part of the imaging table 3 ′ is fixed so that the position of the piston rod 352 is maintained. For example, the upper frame 32 and the base 33 are connected by a connecting member. In this state, the electromagnetic valve 363 is switched so that the fluid flows to the cylinder 351, the pump 362 is turned, and the relief valve 365 is operated. Thereby, the fluid pressure in the cylinder 351 is made the same as the relief pressure Z, and a state is created in which the piston rod 352 is pushed with a fluid pressure equal to the relief pressure Z. At this time, a signal value obtained by the load sensor 354 is acquired as a sensor output signal value P3z. The sensor output signal value P3z can be expressed as follows.

    P3z = G3 [A + β3] (Formula 7)

  In Equation 7, G3 and β3 are the output gain and tightening load when the sensor output signal value P3z is obtained. This is the preparation stage, and the subsequent steps are performed during actual calibration. This preparation is performed at the time of previous calibration of the imaging table 3, for example.

  In step S12, the signal value obtained by the load sensor 354 when the relief valve 365 is operated as in step S11 is acquired as the sensor output signal value P4z. The sensor output signal value P4z can be expressed as follows.

    P4z = G3 [A + β4] (Equation 8)

  In Expression 8, G4 and β4 are an output gain and a tightening load when the sensor output signal value P4z is obtained.

  In step S13, it is determined whether P3z = P4z. If the result is affirmative, it is considered that the changed β4 can be returned to the original β3, and the calibration process is terminated. Proceeding to S14, the tightening load of the lock nut 356 is adjusted.

  In step S14, when P3z> P4z, the lock nut 356 is finely adjusted in the tightening direction, and when P3z <P4z, the lock nut 356 is finely adjusted in the loosening direction. And it returns to step S12 again.

According to such a second imaging table calibration method, measurement using a weight or the like is unnecessary, and it is only necessary to adjust the tightening load of the lock nut 356, so that calibration can be performed easily.
(Third embodiment)

  By the way, there is a possibility that the output gain G of the load sensor 354 and the tightening load β of the load sensor 354 greatly change due to some cause. For example, it is conceivable that the output gain G changes significantly due to a failure. Further, for example, the tightening load β may change greatly due to a sudden loosening of the lock nut 356. When the output gain G and the tightening load β change drastically, a large error is included in the coefficient of the mathematical formula stored in the mathematical formula storage unit 382, and a large error is also included in the top plate load derived by the top plate load deriving unit 381. Occurs. Under such circumstances, it is very important to detect a large change in the output gain G and the tightening load β so that it can be determined whether or not there is an abnormality in the top plate load deriving system. Therefore, here, an embodiment of the imaging table capable of determining an abnormality in the top plate load deriving system will be described.

  First, an abnormality determination method for the top plate load derivation system will be described.

  It is assumed that the mathematical formula storage unit 382 stores the following formula.

    P = G1 · [α (H) · (X + W) + β1] (Equation 9)

  In Equation 9, G1 and β1 are an output gain and a tightening load obtained by a predetermined method at the first time T1, for example, at the time of shipment of the imaging table or at the previous calibration.

  Further, a sensor output feature amount R defined by the following equation is used as an index for performing abnormality determination of the top board load deriving system.

    R = (P2−G1 · β1) / (P1−G1 · β1) (Equation 10)

  In Equation 10, P1 and P2 are sensor output signal values when the top plate load W is the same and the frame height position H is different, and P1 is the frame height position at the height position H1. Sensor output signal value P2 is a sensor output signal value when the frame height position H is the height position H2. G1 and β1 are coefficients stored in the mathematical formula storage unit 382 as described above, and represent the output gain and the tightening load obtained at the first time T1, respectively.

  Here, a sensor output reference feature amount R1 that is a sensor output feature amount R corresponding to the first time T1, and a sensor output feature amount R corresponding to a second time T2 that is later than the first time T1. Let us consider expressing the sensor output comparison feature R2 by an expression. The first time T1 and the second time T2 can be considered, for example, when the photographing table was previously calibrated and when it is subsequently used.

  First, the sensor output reference feature R1 can be expressed as the following equation.

R1 = (P21−G1 · β1) / (P11−G1 · β1)
= {G1 · [α (H2) · (X + W1) + β1] −G1 · β1}
/ {G1 · [α (H1) · (X + W1) + β1] −G1 · β1}
= {G1 · α (H2) · (X + W1)} / {G1 · α (H1) · (X + W1)}
= Α (H2) / α (H1) (Formula 11)

  In Expression 11, P11 and P21 are sensor output signal values P1 and P2 obtained at the first time T1, the top board load W is the same arbitrary load W1, and the frame height position H is the height position, respectively. It is a sensor output signal value when it is H1 and when it is the height position H2.

  Further, the sensor output comparison feature amount R2 can be expressed as follows.

R2 = (P22−G1 · β1) / (P12−G1 · β1)
= {G 2 · [α (H 2) · (X + W 2) + β 2] −G 1 · β 1}
/ {G 2 · [α (H 1) · (X + W 2) + β 2] −G 1 · β 1} (Formula 12)

  In Expression 12, P12 and P22 are sensor output signal values P1 and P2 obtained at the second time T2, the top plate load W is the same W2, and the frame height position H is the height position H1. It is a sensor output signal value at a certain time and at the height position H2. G2 and β2 are the output gain and tightening load at the first time T2.

  Here, if there is no change in the coefficient between the first time T1 and the second time T2, and G1 = G2 and β1 = β2, the sensor output comparison feature R2 is not related to the value of the top plate load W. It can be seen that it takes the same value as the sensor output reference feature R1. If at least one of the coefficients G2 and β2 at the second time T2 is different from the coefficients G1 and β1 at the first time T1, the sensor output feature value R2 may be different from the sensor output feature value R1. I understand.

  Therefore, by comparing the sensor output comparison feature quantity R2 with the sensor output reference feature quantity R1, it is possible to determine the abnormality of the top board load deriving system.

  In general, the imaging table is lowered to a relatively low predetermined height position when placing the subject, and is raised to a higher predetermined height position during imaging. Therefore, it is desirable to set the height positions H1 and H2 as two different height positions within a range that changes in such a normal lifting operation.

  As described above, according to the above-described abnormality determination method for the top panel load deriving system based on the comparison of the sensor output feature amount R, even if the top panel load W is unknown, the abnormality can be detected without changing the top panel load W. Judgment can be made. In general, the top load W, that is, the weight of the subject is the measurement object itself, and is often unknown during use of the imaging table. Moreover, it is not realistic to change the top plate load W frequently. From this point of view, this method is a desirable method.

  Here, the imaging table 3 ′ according to the third embodiment will be described.

  FIG. 9 is a diagram showing a configuration of the imaging table 3 ′ according to the third embodiment. The imaging table 3 ′ has the same configuration as the imaging table 3 according to the first embodiment except for the table control unit 38 ′. The table control unit 38 ′ in the third embodiment is configured by adding new components to the table control unit 38 in the first embodiment. Specifically, in the table control unit 38 ′, an abnormality detection unit (abnormality detection unit) 389 is additionally connected to the network 380.

  The abnormality detection unit 389 uses the output signal value of the load sensor 354 under the respective conditions in which the top plate load W is the same and the postures of the parallel link mechanism 30 are different from each other, and the temporal change of the output gain G and the tightening load β. And an abnormality is detected based on this change. Specifically, the abnormality detection unit 389 includes a sensor output reference feature amount storage unit 385, a sensor output comparison feature amount acquisition unit 386, and an abnormality determination unit (abnormality determination unit) 387.

  The sensor output reference feature amount storage unit 385 stores, for example, a sensor output reference feature amount R1 that is a sensor output feature amount obtained at the time of previous calibration. The sensor output reference feature value R1 may be obtained by actual measurement or by theoretical calculation.

  The sensor output comparison feature amount acquisition unit 386 determines that the sensor output signal value P12 obtained when the frame height position H is the height position H1 and the frame height position H in a situation where the top load W is constant. The sensor output signal value P22 obtained at the height position H2 is acquired, and the sensor output comparison feature amount R2 is obtained based on these. It should be noted that during the raising / lowering operation of the imaging table, there is no boarding / exiting of the subject, and it can be estimated that the top load W is constant. Therefore, here, the sensor output comparison feature amount acquisition unit 386 monitors the frame height position H during the raising / lowering operation of the imaging table, and sets the sensor output signal value at the frame height position H1 as P12 to set the frame height. The sensor output signal value at the position H2 is acquired as P22.

  When the sensor output comparison feature value R2 is acquired by the sensor output comparison feature value acquisition unit 386, the abnormality determination unit 387 causes the difference ΔR between the sensor output reference feature value R1 and the sensor output comparison feature value R2 to exceed the predetermined value Rth. That is, it is determined that there is an abnormality when the following equation is satisfied.

    ΔR = | R1-R2 |> Rth (Formula 13)

  The determination result that there is an abnormality is sent to the table operation unit 40 or the operation console 4, and the table operation unit 40 or the operation console 4 uses predetermined means using characters, sounds, etc. to notify the operator of the fact. To prompt maintenance and calibration by service personnel.

  The actuator control unit 388 controls the actuator driving unit 36 so that the frame height position H becomes the first height position H1 and the second height position H2 at the second time T2.

  For example, the actuator control unit 388 controls the actuator driving unit 36 so that the frame height position H takes the first height position H1 and the second height position H2 in accordance with an operation from the operator. It may be. As a specific example, the highest frame height position among the height positions when placing the subject on the top 31 is the height position Ha, and the lowest among the height positions when photographing the subject. With the frame height position as the height position Hb, the first height position H1 and the second height position H2 are set to height positions within the range from the height position Ha to the height position Hb. The operator performs an operation of lowering the imaging table using the table operation unit 40 in order to place the subject on the top 31. In response to this, the actuator control unit 388 controls the actuator driving unit 36 to lower the imaging table until the frame height position H becomes equal to or less than the height position Ha. Here, the operator places the subject on the top board 31 and again performs an operation of raising the imaging table using the table operation unit 40. In response to this, the actuator control unit 388 controls the actuator driving unit 36 to raise the imaging table until the frame height position H becomes equal to or higher than the height position Hb. As another specific example, when the operator sets the abnormality determination mode in the table operation unit 40, the actuator control unit 388 automatically controls the actuator driving unit 36 to set the frame height position H to the height position. The predetermined range including H1 and H2 is changed from the start point to the end point.

  The actuator control unit 388 controls the actuator driving unit 36 so that the frame height position H takes the first height position H1 and the second height position H2 when the imaging table 3 ′ is started. May be. As a specific example, when the imaging table 3 ′ is turned on, the actuator control unit 388 automatically controls the actuator driving unit 36 to set the frame height position H within a predetermined range including the height positions H 1 and H 2. Change from the start point to the end point.

  The sensor output comparison feature quantity acquisition unit 386 obtains sensor output signal values P12 and P22 and calculates the sensor output comparison feature quantity R2 in the above-described various imaging table raising / lowering operations, and the abnormality determination unit 387 Abnormality determination is performed based on the output comparison feature amount R2.

  In this way, it becomes easy to periodically perform abnormality determination of the top plate load deriving system.

  In addition, this invention is not limited to each above-mentioned embodiment, A various deformation | transformation is possible unless it deviates from the meaning.

  For example, in the above embodiment, the parallel link mechanism 30 is used as the link mechanism, but a scissors type link mechanism similar to the shape of the scissors may be used.

  Further, for example, in the above-described embodiment, the sensor output reference feature quantity storage unit 385 stores the sensor output reference feature quantity R1 itself. Alternatively, the sensor output signal values P11 and P21 may be stored, and the abnormality determination unit 387 may calculate the sensor output reference feature value R1 based on the sensor output signal values P11 and P21.

  Further, for example, the actuator unit 35 is attached between the base 33 and the oblique arm 34a, but may be attached between the base 33 and the other oblique arm 34b.

  Further, for example, in the above-described embodiment, the imaging table is applied to a general X-ray CT apparatus. The present invention may be applied to other imaging apparatuses using an imaging table, such as an MR apparatus having a gantry means for detecting distribution.

1 is an external view of an X-ray CT apparatus according to a first embodiment. 1 is a diagram illustrating an overall configuration of an X-ray CT apparatus according to a first embodiment. It is a figure which shows the structure of a imaging | photography table. It is an expanded sectional view of an actuator part. It is a figure which shows the structure of an actuator drive part. It is a figure which shows correlation with a top-plate load and a frame height position, and a sensor output signal value. It is a flowchart which shows the 1st imaging table calibration method by 2nd Embodiment. It is a flowchart which shows the 2nd imaging table calibration method by 2nd Embodiment. It is a figure which shows the structure of the imaging | photography table by 3rd Embodiment.

Explanation of symbols

1 X-ray CT system (imaging system)
2 Scanning gantry (gantry means)
3 Shooting table (shooting table)
4 Operation console 21 X-ray tube 22 Collimator 23 X-ray detector 24 Data collection unit 25 X-ray controller 26 Rotation unit 27 Rotation controller 30 Parallel link mechanism (link mechanism)
31 Top plate (top plate)
32 Upper frame (top plate support)
33 Base 34a, 34b Slanted arm 35 Actuator part (actuator part)
36 Actuator drive unit 37 Height position detection unit 38 Table control unit 39 Top panel control unit 40 Table operation unit 41 Console control unit 42 Data collection buffer 43 Input / output unit 44 Storage units 341a, 341b, 42a, 342b Coupling unit 351 Cylinder 352 Piston rod 353 Rod end 353a Screw 354 Load sensor (sensor)
355 Coupling unit 356 Lock nut 358 Coupling unit 380 Network 381 Top plate load deriving unit (top plate load deriving means)
382 Formula storage unit 383 Analog-digital conversion unit 384 Top panel control unit 385 Sensor output reference feature value storage unit 386 Sensor output comparison feature value acquisition unit 387 Abnormality determination unit 388 Actuator control unit 389 Abnormality detection unit

Claims (10)

A top plate on which the subject is placed;
A top plate support for supporting the top plate;
In a photographic table comprising: an extendable and retractable actuator unit; and an elevating unit having a link mechanism that moves the top and bottom plate support unit up and down by converting the expansion and contraction motion of the actuator unit into a rotational motion of a link.

The actuator unit includes a piston rod, a rod end that is fitted to the piston rod with a screw, a lock nut that engages with the screw, and a sensor that outputs a signal corresponding to a load applied in a direction in which the actuator unit expands and contracts. The center hole is provided to pass through the screw so as to be interposed between the piston rod and the lock nut, and the sensor is tightened by the lock nut ,

The shooting table further includes:
The value of the output signal of the sensor and the value indicating the posture specifying information for specifying the posture of the link mechanism are input parameters, and the tightening load applied to the sensor by tightening the lock nut and the output gain of the sensor are coefficients. A top plate load deriving means for deriving a top plate load, which is a load applied to the top plate, based on

A plurality of output signals of the sensor obtained at a second time after the first time when the tightening load and output gain of the sensor as coefficients of the mathematical formula are obtained, each of which is the top plate Based on a plurality of output signals obtained under each condition in which the load is the same and the postures of the link mechanism are a plurality of different postures, the sensor between the first time and the second time An imaging table comprising an abnormality detection means for calculating an index value that reflects at least one change amount of a tightening load and an output gain, and detecting an abnormality by determining a threshold value of the index value.
The actuator control means which controls the actuator part so that the posture of the link mechanism may take the plurality of postures in response to a predetermined operation from an operator at the second time. Shooting table.
The actuator unit includes a cylinder that houses the piston rod, and the piston rod moves according to the amount of fluid accommodated in the cylinder.

A pump that is connected to the cylinder by a flow path and sends a fluid to the cylinder; a discharge means for discharging the fluid from the cylinder; and a relief that operates when the fluid pressure in the flow path reaches a relief pressure The imaging table according to claim 1, further comprising an actuator driving unit having a valve.
The link mechanism is a parallel link mechanism having a base, an upper frame, and a hypotenuse arm attached between the base and the upper frame, wherein the base and the upper frame are horizontal arms,

The top plate support part is supported by the upper frame, or is integrally formed with the upper frame,
The imaging table according to any one of claims 1 to 3, wherein the actuator unit is attached between the base and the oblique arm.
The imaging table according to any one of claims 1 to 4, wherein the posture specifying information is a height position of a predetermined portion that moves up and down depending on a posture of the link mechanism.
The imaging table according to any one of claims 1 to 5, wherein the sensor includes a load cell, a piezo, a piezoelectric ceramic, or a crystal.
A method for calibrating the top plate load deriving means included in the imaging table according to claim 3,
Obtaining a relief load that is a load applied to the sensor by the fluid pressure when the fluid pressure of the cylinder is the relief pressure;

When the top plate load is no load and the link mechanism is in an arbitrary posture, first posture specifying information that is information for specifying the posture and an output signal of the sensor at this time 1 is acquired, and at least a part of the imaging table is fixed so that the posture of the link mechanism is maintained, and the relief valve is operated so that the fluid pressure of the cylinder becomes the relief pressure. Turning the pump of the actuator drive unit to obtain a second output signal which is an output signal of the sensor at this time;

Based on the relief load, the first posture specifying information, the first output signal, the second output signal, and the relational expression between the load applied to the sensor and the value of the output signal of the sensor, Identifying a tightening load and an output gain of the sensor at the time when the first output signal value is acquired;

And a step of updating the coefficient of the mathematical formula with the specified tightening load and output gain of the sensor.
The imaging table according to any one of claims 1 to 6,
An imaging apparatus comprising: imaging means for imaging the subject placed on the top plate of the imaging table and generating image information. The imaging means includes gantry means for acquiring projection data by rotating an X-ray imaging system including an X-ray tube and an X-ray detector facing each other with the subject interposed therebetween. 8. The photographing apparatus according to 8.
The imaging apparatus according to claim 8, wherein the imaging unit includes a gantry unit that detects a spatial nuclear magnetization distribution of the subject by a nuclear magnetic resonance method.

Images