JP7443153B2 - X-ray computed tomography device and weight distribution sheet - Google Patents

Description

Embodiments disclosed in this specification and the drawings relate to an X-ray computed tomography apparatus and a weight distribution sheet.

Conventionally, for example, according to TG66, which is a guideline required for X-ray computed tomography equipment for treatment planning, it is necessary to measure the accuracy of a bed with a 75 kg weight mounted on the top plate as a human body weight distribution. . For example, if a human-shaped object is placed on a top plate provided with a resistor and the top plate is moved, the amount of deflection of the top plate is determined by the resistance value of the resistor at each position as the top plate is moved. Calculated.

However, it is up to the user to decide how the placement of the weights corresponds to the weight distribution of the human body.

Japanese Patent Application Publication No. 2008-36205

One of the problems to be solved by the embodiments disclosed in this specification and drawings is that when measuring the accuracy of a bed apparatus related to a treatment plan, it is possible to accurately place a weight on the top plate related to the weight distribution of the human body with good reproducibility. , and to realize it easily. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problems. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems.

The X-ray computed tomography apparatus according to this embodiment includes a top plate and a sheet . The subject is placed on the top plate. The sheet displays, on the top plate, the positions of a plurality of weights simulating the weight distribution of a human body in accordance with the guidelines of the treatment plan required for the X-ray computed tomography apparatus , and displays the positions where the weights are placed. It has a sign indicating it . The marks correspond to anatomically divided regions of the human body. The weights are arranged at irregular intervals along the longitudinal direction of the top plate, imitating the parts.

FIG. 1 is a diagram showing a configuration example of an X-ray CT apparatus according to an embodiment. FIG. 2 is a diagram showing, as an example of a display section, a sheet (weight distribution sheet) having markers (marks) indicating positions where a plurality of weights are arranged, according to the embodiment. FIG. 3 is a diagram showing an example of a plurality of weights placed on a plurality of markers on a weight distribution sheet according to the embodiment. FIG. 4 is a perspective view showing an example in which a plurality of weights are arranged in each of a plurality of markers on a weight distribution sheet placed on a top plate according to the embodiment.

Hereinafter, embodiments of a medical image diagnostic apparatus and a weight distribution sheet will be described in detail with reference to the drawings. To make the description more specific, an X-ray computed tomography apparatus (hereinafter referred to as an X-ray CT (Computed Tomography) apparatus) will be taken as an example of the medical image diagnostic apparatus according to the present embodiment. In the following embodiments, parts with the same reference numerals perform similar operations, and redundant explanations will be omitted as appropriate. Note that the medical image diagnostic apparatus according to this embodiment is not limited to an X-ray CT apparatus, and can be implemented as appropriate with any medical image diagnostic apparatus having a gantry, such as a magnetic resonance imaging apparatus or a nuclear medicine diagnostic apparatus. It is.

(Embodiment)
FIG. 1 is a diagram showing an example of the configuration of an X-ray CT apparatus 1 according to the present embodiment. As shown in FIG. 1, the X-ray CT apparatus 1 includes, for example, a gantry device 10, a bed device 30, also called a bed, and a console device 40. The gantry device 10 and the bed device 30 operate based on the user's operation via the console device 40 or the user's operation via the operation unit provided on the gantry device 10 or the bed device 30. The gantry device 10, the bed device 30, and the console device 40 are connected to each other by wire or wirelessly so that they can communicate with each other.

The gantry device 10 is used, for example, for treatment planning for a subject P. The gantry device 10 is a device having an imaging system that irradiates the subject P with X-rays and collects projection data from detection data of the X-rays that have passed through the subject P. The gantry device 10 includes an X-ray tube, an X-ray detector, a rotating frame, an X-ray high voltage device, a control device, a wedge, a collimator, and a DAS (Data Acquisition System).

An X-ray tube is a vacuum tube that generates X-rays by irradiating thermoelectrons from the cathode (filament) to the anode (target) by applying high voltage from an X-ray high voltage device and supplying filament current. . X-rays are generated when thermionic electrons collide with the target. X-rays generated at the tube focal point in the X-ray tube are shaped into a cone beam shape via, for example, a collimator, and are irradiated onto the subject P. For example, there is a rotating anode type X-ray tube that generates X-rays by irradiating a rotating anode with thermoelectrons. Note that in this embodiment, a so-called multi-tube type X-ray CT apparatus in which multiple pairs of X-ray tubes and X-ray detectors are mounted on a rotating frame is used instead of a single-tube type X-ray CT apparatus. It is also applicable to

The X-ray detector detects the X-rays emitted from the X-ray tube and passed through the subject P, and outputs an electrical signal corresponding to the amount of X-rays to the DAS. The X-ray detector has, for example, a plurality of detection element rows in which a plurality of detection elements are arranged in the channel direction along one circular arc centered on the focal point of the X-ray tube. The X-ray detector has, for example, a structure in which a plurality of detection element rows are arranged in a slice direction (column direction, row direction). The X-ray CT device 1 includes a Rotate/Rotate-Type (third generation CT) in which an X-ray tube and an X-ray detector rotate around the subject P as a unit, and a large number of There is a Stationary/Rotate-Type (fourth generation CT) in which the X-ray detection element is fixed and only the X-ray tube rotates around the subject P, and either type is applicable to this embodiment. Hereinafter, in order to make the description more specific, the X-ray CT apparatus 1 of this embodiment will be described using a third generation CT as an example.

Further, the X-ray detector is, for example, an indirect conversion type detector having a grid, a scintillator array, and a photosensor array. The scintillator array includes a plurality of scintillators, and each scintillator includes a scintillator crystal that outputs light in an amount of photons corresponding to the amount of incident X-rays. The grid is disposed on the X-ray incident side of the scintillator array and has an X-ray shielding plate that has a function of absorbing scattered X-rays. Note that the grid is sometimes called a collimator (one-dimensional collimator or two-dimensional collimator). The optical sensor array has a function of converting the amount of light from the scintillator into an electrical signal, and includes optical sensors such as photomultiplier tubes (PMTs). Note that the X-ray detector may be a direct conversion type detector having a semiconductor element that converts incident X-rays into electrical signals. Further, the X-ray detector may be a photon-counting X-ray detector.

The rotating frame has an opening and is fitted with an X-ray tube that generates X-rays. Specifically, the rotating frame is an annular frame that supports an X-ray tube and an X-ray detector so as to face each other, and rotates the X-ray tube and the X-ray detector by a control device described later. The rotating frame receives power from the drive mechanism of the control device and rotates around the rotation axis at a constant angular velocity.

Note that, in addition to the X-ray tube and the X-ray detector, the rotating frame further includes and supports an X-ray high voltage device and a DAS. Such a rotating frame is housed in a substantially cylindrical casing in which an opening forming an imaging space is formed. The central axis of the opening coincides with the rotation axis of the rotating frame. Note that the detection data generated by the DAS is transmitted by optical communication from a transmitter having a light emitting diode (LED) to a receiver having a photodiode provided in a non-rotating part of the gantry device 10, and then sent to the console device 40. will be transferred. Note that the method of transmitting the detection data from the rotating frame to the non-rotating portion of the gantry device 10 is not limited to the above-mentioned optical communication, and any method may be used as long as it is a non-contact data transmission method.

The X-ray high-voltage device is a high-voltage generator that has an electric circuit such as a transformer and a rectifier, and has the function of generating a high voltage to be applied to the X-ray tube and a filament current to be supplied to the X-ray tube. , and an X-ray control device that controls the output voltage according to the X-rays emitted by the X-ray tube. The high voltage generator may be of a transformer type or an inverter type. Note that the X-ray high voltage device may be provided on the rotating frame, or may be provided on the fixed frame side of the gantry device 10.

The control device includes a processing circuit including a CPU (Central Processing Unit), and a drive mechanism such as a motor and an actuator. The processing circuit includes, as hardware resources, a processor such as a CPU or an MPU (Micro Processing Unit), and a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory). In addition, the control device may be an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or another complex programmable logic device (Complex Prog. rammable logic device (CPLD) , may be realized by a Simple Programmable Logic Device (SPLD). The control device controls the X-ray high voltage device, DAS, etc. according to commands from the console device 40. The processor reads and executes a program stored in the memory to achieve the above control.

The control device also has a function of receiving input signals from an input interface attached to the console device 40 or the gantry device 10 and controlling the operations of the gantry device 10 and the bed device 30. For example, the control device receives an input signal and performs control to rotate the rotation frame, control to tilt the gantry device 10, and control to operate the bed device 30 and the top plate 33. Note that the control for tilting the gantry device 10 is achieved by the control device rotating the rotating frame around the horizontal axis based on inclination angle (tilt angle) information input through an input interface attached to the gantry device 10. It's okay. Furthermore, the control device may be provided on the gantry device 10 or may be provided on the console device 40. Note that the control device may be configured to directly incorporate the program into the circuit of the processor instead of storing the program in the memory. In this case, the processor realizes the above control by reading and executing a program installed in the circuit.

The wedge is a filter for adjusting the amount of X-rays emitted from the X-ray tube. Specifically, the wedge is a filter that transmits and attenuates the X-rays emitted from the X-ray tube so that the X-rays emitted from the X-ray tube to the subject P have a predetermined distribution. be. The wedge is, for example, a wedge filter or a bow-tie filter, and is a filter made of aluminum processed to have a predetermined target angle and a predetermined thickness.

The collimator is a lead plate or the like for narrowing down the X-rays transmitted through the wedge into an X-ray irradiation range, and a slit is formed by combining a plurality of lead plates or the like.

DAS has an amplifier that amplifies the electrical signal output from each X-ray detection element of the X-ray detector, and an A/D converter that converts the electrical signal into a digital signal, and converts the detected data. generate. The detection data generated by the DAS is transferred to the console device 40.

The bed device 30 is a device on which a subject P to be scanned is placed and moved, and includes a base 31, a bed driving device 32, a top plate 33, and a top support frame 34. The base 31 is a casing that supports the top support frame 34 movably in the vertical direction. The bed driving device 32 is a motor or an actuator that moves the top plate 33 on which the subject P is placed in the longitudinal axis direction of the top plate 33. The bed driving device 32 moves the top plate 33 under the control of the console device 40 or the control device. The top plate 33 provided on the upper surface of the top plate support frame 34 is a plate on which the subject P is placed. In addition to the top plate 33, the bed driving device 32 may move the top plate support frame 34 in the longitudinal direction of the top plate 33. The top plate 33 can be inserted into the gantry device 10 used for treatment planning for the subject P.

Console device 40 has memory, a display, an input interface, and processing circuitry. Data communication between the memory, display, input interface, and processing circuitry in console device 40 is performed via a bus (BUS).

The memory is a storage device such as an HDD (Hard Disk Drive), an SSD (Solid State Drive), or an integrated circuit storage device that stores various information. The memory stores, for example, projection data and reconstructed image data. In addition to HDDs and SSDs, memory can also be connected to portable storage media such as CDs (Compact Discs), DVDs (Digital Versatile Discs), and flash memories, and semiconductor memory devices such as RAMs (Random Access Memory). It may also be a drive device that reads and writes various information. The memory also stores a control program according to this embodiment. The memory stores volume data generated by pre-scanning.

The display displays various information. For example, the display outputs a medical image (CT image) generated by a processing circuit in the console device 40, a GUI (Graphical User Interface) for accepting various operations from an operator, and the like. For example, the display may be a liquid crystal display (LCD), a CRT (cathode ray tube) display, an organic EL display (OELD), a plasma display, or any other display. Thank you, It is available for use. Further, the display may be provided on the gantry device 10. Further, the display may be of a desktop type, or may be configured of a tablet terminal or the like that can communicate wirelessly with the main body of the console device 40.

The input interface receives various input operations from the operator, converts the received input operations into electrical signals, and outputs the electrical signals to the processing circuit in the console device 40. For example, the input interface receives from the operator information such as acquisition conditions when acquiring projection data, reconstruction conditions when reconstructing a CT image, and image processing conditions when generating a post-processed image from a CT image. As the input interface, for example, a mouse, keyboard, trackball, switch, button, joystick, touch pad, touch panel display, etc. can be used as appropriate.

Note that in this embodiment, the input interface is not limited to one that includes physical operation components such as a mouse, keyboard, trackball, switch, button, joystick, touch pad, and touch panel display. For example, an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the device and outputs this electrical signal to a processing circuit in the console device 40 is also an example of an input interface. included. Further, the input interface may be provided in the gantry device 10. Furthermore, the input interface may be configured with a tablet terminal or the like that can communicate wirelessly with the main body of the console device 40.

The processing circuit in the console device 40 controls the operation of the entire X-ray CT apparatus 1 in accordance with the electrical signal of the input operation output from the input interface. For example, the processing circuit includes, as hardware resources, a processor such as a CPU, MPU, or GPU (Graphics Processing Unit), and a memory such as ROM or RAM. The processing circuit performs a system control function, a preprocessing function, and a reconfiguration processing function by a processor that executes a program loaded in a memory. Each of the system control function, preprocessing function, and reconfiguration processing function is not limited to being realized by a single processing circuit. A processing circuit may be configured by combining a plurality of independent processors, and each processor may execute a program to realize each of the system control function, preprocessing function, and reconfiguration processing function.

The processing circuit in the console device 40 uses a system control function to control each function of the processing circuit based on input operations received from the operator via the input interface. Specifically, the system control function reads a control program stored in a memory, expands it onto the memory in the processing circuit, and controls each part of the X-ray CT apparatus 1 according to the expanded control program.

The processing circuit generates data by performing preprocessing such as logarithmic conversion processing, offset correction processing, inter-channel sensitivity correction processing, and beam hardening correction on the detection data output from the DAS using a preprocessing function. Note that the data before preprocessing is called raw data, and the data after preprocessing is called projection data.

The processing circuit performs a reconstruction process using a filtered back projection method (FBP method), a successive approximation reconstruction method, etc. on the projection data generated by the preprocessing function using a reconstruction processing function. to generate CT image data. The reconstruction processing function stores reconstructed CT image data in memory.

The above is a general description of the X-ray CT apparatus 1 according to the present embodiment. Hereinafter, a display section that displays positions on the top plate 33 where a plurality of weights imitating the weight distribution of a human body related to the guideline are arranged in accordance with the guideline of the treatment plan will be described. FIG. 2 is a diagram showing, as an example of a display section, a sheet 51 (hereinafter referred to as a weight distribution sheet) having markers (marks) indicating positions where a plurality of weights are arranged. As shown in FIG. 2, the weight distribution sheet 51 can be placed on the top plate 33 of the bed device 30 of the medical image diagnostic apparatus. Further, the weight distribution sheet 51 can be attached to and detached from the top plate 33 using various fasteners such as hook-and-loop fasteners. With the fixture, the weight distribution sheet 51 is placed at the same position on the top plate 33 when measuring the accuracy of the bed device 30 in the TG 66. In addition, the weight distribution sheet 51 is fixed at a predetermined position on the top plate 33 when the top plate 33 is moved. The weight distribution sheet 51 is made of, for example, rubber. Note that the material of the weight distribution sheet 51 is not limited to rubber, and any material can be used as long as it is sheet-shaped.

Markers indicating positions where a plurality of weights are placed correspond to anatomically divided regions of the human body. The parts include, for example, the head, chest, thighs, legs, and the like. Note that the region corresponding to the mark, that is, the classification indicating the weight distribution of the human body, is not limited to these regions, and may include other regions such as the buttocks and abdomen, for example. Markers H shown in FIG. 2 indicate positions where two weights corresponding to the head are placed. Marker C shown in FIG. 2 indicates the positions where four weights corresponding to the chest are placed. Marker F shown in FIG. 2 indicates the positions where two weights corresponding to the thighs are placed. Markers L shown in FIG. 2 indicate positions where two weights corresponding to the legs including the upper limbs are placed. The length HL between the mark H and the mark L shown in FIG. 2 is determined according to Subclause 9.8.3.2 of 60601-1 of the International Electrotechnical Commission (IEC), for example, It is set at 1900mm.

Note that additional information such as the number, weight, and name of the corresponding weight may be attached to each of the plurality of markers on the weight distribution sheet 51. Moreover, the shape of each of the plurality of markers may be different depending on the region (rectangle, square, circle, polygon, etc.).

According to TG66 (Task Group 66 in the American Association of Physicists in Medicine (AAPM)), which is a guideline required for the X-ray CT device 1 for treatment planning, in measuring the accuracy of the bed device 30, The total weight of the plurality of weights placed on the top plate 33 is 75 kg. At this time, according to the IEC standard, the weight placed on the mark H corresponding to the head weighs approximately 5.6 kg, which is equivalent to 7.4% of the total weight of 75 kg. In FIG. 2, since there are two markers H, a weight of 2.8 kg is placed in one marker H. Furthermore, according to the IEC standards, the weight placed on mark C corresponding to the chest weighs approximately 41.6 kg, which is equivalent to 55.5% of the total weight of 75 kg. In FIG. 2, since there are four markers C, a weight of about 10.4 kg is placed in one marker C. Note that the ratio of the weight of the plurality of parts to the weight of the human body is not limited to the above, and may be set as appropriate.

Furthermore, according to the IEC standard, the weight placed on the mark F corresponding to the thigh is approximately 16.7 kg, which is equivalent to 22.2% of the total weight of 75 kg. In FIG. 2, since there are two markers F, a weight of about 8.4 kg is placed in one marker F. Further, according to the IEC standard, the weight placed on the mark L corresponding to the leg is approximately 11.1 kg, which is equivalent to 14.8% of the total weight of 75 kg. In FIG. 2, since there are two markers L, a weight of approximately 5.6 kg is placed in one marker L. Note that the number of markers corresponding to one site is not limited to that shown in FIG. 2, and can be set arbitrarily.

FIG. 3 is a diagram showing an example of a plurality of weights WS placed on a plurality of markers on the weight distribution sheet 51. Incidentally, additional information such as a number, name, weight, etc., which is associated with each of the plurality of markers on the weight distribution sheet 51, may be attached to each of the plurality of weights WS. As described above, the plurality of weights WS are prepared according to the plurality of regions on the weight distribution sheet 51 and the number of markers in each region. In an examination room where the X-ray CT apparatus 1 is installed, the weight distribution sheet 51 is mounted on the top plate 33 by a user such as a technician, before measuring the accuracy of the bed apparatus 30. Next, the user places weights at each of the plurality of markers on the weight distribution sheet 51. After that, measurement of the accuracy of the bed device 30 is performed. The accuracy of the bed device 30 is measured by the user, for example, once a month or more.

FIG. 4 is a perspective view showing an example in which a plurality of weights WS are arranged in each of a plurality of markers on the weight distribution sheet 51 placed on the top plate 33. As shown in FIG. 4, the user uses each of the plurality of markers on the weight distribution sheet 51 as a guide regarding the placement of the weights, and arranges the plurality of weights WS on the corresponding plurality of markers.

As a modification of the technical idea of the present embodiment, the display section includes an optical system that projects a mark indicating the position where the weight WS is placed, that is, a weight mounting position, onto the top plate 33 as light or shadow, instead of the weight distribution sheet 51. It may also be realized by a device. The optical device is, for example, a floodlight, a projector, or the like. At this time, the optical equipment is installed, for example, on the ceiling of the examination room where the medical image diagnostic apparatus is installed, on the gantry device 10, or the like. When an optical device is installed on the ceiling of the examination room, the optical device is installed, for example, directly above the center position of the top board 33 before being inserted into the gantry device 10 . Note that the optical device may further project additional information on the top plate 33.

Furthermore, as a modification of the technical idea of this embodiment, the display section may be printed on the top plate 33. At this time, the positions of a plurality of weights simulating the weight distribution of a human body are printed as markers on the surface of the top plate 33 in accordance with the guidelines of the treatment plan.

According to the medical image diagnostic apparatus according to the embodiment described above, the weight distribution of the human body with respect to the guidelines of the treatment plan is determined on the top plate 33 on which the subject P is placed and on the top plate 33. A display unit that displays the positions where the plurality of simulated weights WS is arranged. Further, the weight distribution sheet 51 according to the embodiment can be placed on the top plate 33 of the bed device 30 of the medical image diagnostic apparatus, and is configured to imitate the weight distribution of the human body according to the guidelines of the treatment plan. A mark indicating the position where the plurality of weights WS is arranged is provided. Therefore, a medical image diagnostic apparatus having a display unit realized by a sheet having a mark indicating the position where the weight WS is arranged or an optical device that projects a mark indicating the position where a plurality of weights WS are arranged onto the top plate 33 , and the weight distribution sheet 51 having marks indicating the positions where the weights are arranged, the user places the plurality of weights WS on the top plate 33 using the marks corresponding to the anatomically divided parts of the human body as guides. can be placed in

For these reasons, according to the medical image diagnostic apparatus and the weight distribution sheet 51 according to the present embodiment, when measuring the accuracy of the bed device 30 in the TG66, even if the top plate 33 is made by a different manufacturer, the weight of the human body can be measured. A plurality of weights required for realizing the distribution can be mounted on the top plate 33 simply and with high reproducibility.

(Application example)
The display unit in this application example has two cases: when the head is inserted into the opening in the gantry device 10 before the legs (hereinafter referred to as head first), and when the head is inserted into the opening in the gantry device 10. A plurality of labels have different display modes when inserted before the first part (hereinafter referred to as "foot first"). That is, the plurality of signs have different display modes depending on the cranio-caudal orientation of the human body with respect to the opening of the gantry device 10. The display mode is, for example, hue, line type, etc.

When the display section is realized by the weight distribution sheet 51, the plurality of signs on the weight distribution sheet 51 are a plurality of signs for head first (hereinafter referred to as HF signs) and a plurality of signs for foot first (hereinafter referred to as HF signs). (referred to as FF label) have different display modes. In other words, the display mode of the plurality of labels on the weight distribution sheet 51 is different between the HF label and the FF label. Note that an HF label may be provided on one side of the weight distribution sheet 51, and an FF label may be provided on the other side of the weight distribution sheet 51.

Further, when the display section is realized by an optical device, the HF mark and the FF mark are projected onto the top plate 33 in different display modes. Note that the optical device may include a switch for switching between projection of the HF mark onto the top plate 33 and projection of the FF mark onto the top plate 33.

According to the medical image diagnostic apparatus and the weight distribution sheet 51 according to the application example of the embodiment described above, the plurality of marks indicate the cranio-caudal direction of the human body with respect to the opening of the gantry device 10 (i.e. head first or foot first). It has different display modes depending on the As a result, when measuring the accuracy of the bed device 30 in TG66, multiple weights required to realize the weight distribution of the human body can be easily and highly reproducibly adjusted according to head first or foot first. It can be mounted on the top plate 33.

According to at least the embodiments and modifications described above, when measuring the accuracy of the bed device 30 regarding treatment planning, it is possible to easily and reproducibly place weights related to the weight distribution of the human body on the top plate 33. It can be realized. Thereby, in measuring the accuracy of the bed apparatus 30 regarding the treatment plan, variations in the measured accuracy can be reduced and reliability of the measured accuracy can be improved.

Although several embodiments have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, changes, and combinations of embodiments can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention as well as within the scope of the invention described in the claims and its equivalents.

1 X-ray CT device 10 Mounting device (gantry)
30 Bed device 31 Base 32 Bed drive device 33 Top plate 34 Top plate support frame 40 Console device 51 Weight distribution sheet

Claims (3)

a top plate on which the subject is placed;
On the top plate, displaying positions at which a plurality of weights imitating the weight distribution of a human body with respect to the guideline are to be placed are displayed in accordance with a treatment planning guideline required for an X-ray computed tomography apparatus; a sheet having a sign indicating the location of the
Equipped with
The mark corresponds to an anatomically divided part of the human body,
The weights are arranged at irregular intervals along the longitudinal direction of the top plate, imitating the part.
X-ray computed tomography equipment. The mark has a different display mode depending on the craniocaudal orientation of the human body with respect to the opening of the gantry used for the treatment plan.
The X-ray computed tomography apparatus according to claim 1 . Can be placed on a top plate of a bed of an X-ray computed tomography apparatus,
In accordance with a treatment planning guideline required for the X-ray computed tomography apparatus , a mark indicating a position where a plurality of weights imitating the weight distribution of a human body with respect to the guideline is placed ;
The mark corresponds to an anatomically divided part of the human body,
The weights are arranged at irregular intervals along the longitudinal direction of the top plate, imitating the part.
Weight distribution sheet.

Images