JP2004357724A - X-ray ct apparatus, x-ray generating apparatus, and data collecting method of x-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus which is small in apparatus scale, inexpensive, excellent in maintainability and has high resolution, and to provide an X-ray generating apparatus and a data collecting method of the X-ray CT apparatus. <P>SOLUTION: The X-ray CT apparatus has an X-ray generating unit 1 for generating an X-ray toward a subject in a photographing region, an X-ray detector unit 3 for detecting the X-ray which has been transmitted through the subject, and an image reconstructing unit 12 for re-constructing image data on the basis of an output of the X-ray detector unit. In this X-ray CT apparatus, the X-ray generating unit has a plurality of cathodes 19 arranged in an annular form around the photographing range, an anode 17 having an annular shape opposing the cathodes, a plurality of targets 16 arranged in an annular form on the surface layer of the anode, a plurality of electron-emitting sections 36 formed on the surface of the cathodes, a plurality of gate electrodes 38 arranged in an annular form with a predetermined distance from the cathodes, and an insulating container 21 housing the cathodes, the anode and the gate electrodes. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an X-ray CT apparatus (X-ray computed tomography apparatus) for performing diagnosis by obtaining a tomographic image of a subject (patient) in the field of medical diagnosis, and in particular, to an image based on pulsatile and respiratory motion. The present invention relates to a dynamic (dynamic) CT technique required for a diagnosis that causes blurring of a subject and a diagnosis that captures a dynamic change of a contrast agent in an imaging region.
[0002]
[Prior art]
FIG. 40 is a diagram showing the appearance of a conventional typical X-ray CT apparatus of the Rotate / Rotate type. As is well known, an X-ray CT apparatus uses a tomographic image based on transmitted X-ray intensity data (projection data) repeatedly acquired while an X-ray tube and a detector unit facing the X-ray tube make one rotation around a subject. Reconstruct the data. Therefore, the acquisition time (scan time) of the projection data required for reconstructing one piece of tomographic image data is determined by the rotation speed of the X-ray tube, the detector unit, and the like. However, in order to rotate heavy structures such as the X-ray tube and the detector unit at high speed, a large-scale structure having rigidity capable of withstanding the centrifugal force is required, and the motor and the rotation mechanism are also large-scale. And it is complicated. All of these have the problem that the weight and size of the CT device increase, and the cost increases accordingly.
[0003]
In order to solve this problem, a so-called Stationary / Stationary X-ray CT apparatus having a structure in which an X-ray tube and a detector are fixed has been considered. One type is shown in FIG. This is because the trajectory of an electron beam emitted from one electron gun arranged on the central axis of the gantry is rotated by a deflection electromagnet, and the X-ray beam is focused on an annular target arranged around the gantry circle and incident there. generate. This type of X-ray CT apparatus requires complicated electromagnet control to stably maintain the electron beam trajectory. In addition, when attempting to increase the amount of X-ray generation by increasing the amount of electron beam current, the focused spot diameter of the electron beam increases due to the effect of the space charge effect and the long focusing distance, thereby lowering the resolution. Furthermore, the capacity of the duct that covers the electron beam trajectory is large, it is necessary to maintain the degree of vacuum in this duct, and the shape of the duct is complicated, and there is a problem in maintainability.
[0004]
FIG. 42 and FIG. 43 show other types of configurations for realizing the Stationary / Stationary type. In this type, a plurality of X-ray tubes are installed on the circumference of the gantry. Similarly, by arranging the X-ray detector on the circumference, the rotation mechanism can be eliminated. X-ray CT apparatuses of a similar type are described in JP-A-10-295682, JP-A-2002-320610, JP-A-2002-343291, and U.S. Pat. No. 6,385,292B1. .
[0005]
The biggest problem in this type is due to the size of the X-ray tube. As is well known, an X-ray tube has a structure in which a rotating mechanism for a cathode, a filament, an anode, and an anode is housed in a glass tube, and has a width of several tens of centimeters. Therefore, the resolution of the image decreases as the sampling pitch (view pitch) of the projection data increases. A method has been proposed in which only the hot cathode and the grid portion are separated without using an independent X-ray tube one by one, and a large number of such components are arranged. However, considering the size of the hot cathode type electron gun, it is necessary. Arranging enough numbers to achieve the required view pitch in order to obtain the required resolution requires a large gantry diameter and a considerable increase in the diameter of the circumference on which the X-ray source is placed. However, it is difficult to obtain a required X-ray beam intensity because the use efficiency of X-rays is inversely proportional to the square of the distance from the X-ray tube to the detector.
[0006]
As described in the description of the conventional example described above, in an electron beam deflection type CT apparatus which is one of the stationery / stationary type in order to enable high-speed scanning, the electron beam focusing diameter on the anode target is large. Therefore, it is difficult to increase the resolution, and further, complicated maintenance and high cost are required. Alternatively, in a method in which a large number of X-ray sources are arranged on the circumference of the gantry as an alternative method, the scan angle must be increased due to the restriction due to the size of the X-ray source or the electron gun, and a good CT resolution is obtained. It is expected that the task will be difficult.
[0007]
[Patent Document 1]
JP-A-10-295682
[0008]
[Patent Document 2]
JP-A-2002-320610
[0009]
[Patent Document 3]
JP-A-2002-343291
[0010]
[Patent Document 4]
US Patent No. 6,385,292B1
[0011]
[Problems to be solved by the invention]
An object of the present invention is to provide an X-ray CT apparatus, an X-ray generator, and a data collection method of an X-ray CT apparatus which are small in scale, inexpensive, excellent in maintainability, and have high resolution.
[0012]
[Means for Solving the Problems]
The present invention provides an X-ray generation unit that generates X-rays toward a subject in an imaging region, an X-ray detection unit that detects X-rays that have passed through the subject, and an output based on the output of the X-ray detection unit. An X-ray CT apparatus having an image reconstruction unit for reconstructing image data by means of a plurality of cathodes arranged in an annular shape around the imaging region, and a circle facing the cathodes. An anode having a ring shape, a plurality of targets arranged in an annular shape on the surface layer of the anode, a plurality of electron-emitting portions formed on the surface of each of the cathodes, and an annular shape separated by a predetermined distance from the plurality of cathodes And a hermetically sealed container that houses the cathode, the anode, and the gate electrode.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
First, an outline of an embodiment of the present invention will be briefly described. In the embodiment of the present invention, a plurality of minute electron emitters having an electron emitting portion as a carbon-based structure that emits electrons under a high electric field are provided in a normally cylindrical imaging region in which a subject is accommodated. An R / R type X-ray CT apparatus having a small size, low cost, excellent maintainability, and high resolution is provided by arranging the ring in the periphery and facing the ring-shaped anode to the periphery. Realize the offer.
[0014]
The insulation distance of the electron emitter needs to be a value sufficient to maintain a voltage applied to the gate electrode for controlling the electron emission from the electron emission portion by forming an electric field between the electron emitter and the cathode. If the voltage applied to the gate electrode is 1 kV or less, the insulation distance can be set to 1 mm or less. In the electron emitter, the gate electrode having a plurality of electron emission holes and the cathode should be as close and even as possible to reduce the voltage applied to the gate electrode and to arrange the electron emitters on the cathode with high density. Is important. Therefore, an insulating layer is interposed between the gate electrode and the cathode.
[0015]
Further, in the present embodiment, the focusing property of the electron beam from the electron emitter to the anode surface is improved by providing a focusing electrode and making the surface of the cathode concave, and the area of the electron emitter is increased. As a result, it is possible to achieve an increase in the margin of the electron beam current amount and an improvement in resolution accompanying a reduction in the focal spot size. Similarly, by associating a pair of electron emitters with the same target, arranging the pair of electron emitters in parallel along the imaging region center line (Z-axis), and concentrating the directions on the targets, respectively, The space provided to the electron emitter can be effectively increased, thereby increasing the area of the electron emitter and increasing the upper limit of the electron beam current.
[0016]
In the present embodiment, the electron emitter and the anode may be arranged along the radial direction of the imaging region, or the electron emitter and the anode may be arranged in a direction parallel to the center line of the imaging region. In the former case, the subject is irradiated with a component of the X-rays generated at the target that has passed through the anode. In the latter case, an anode having a larger heat capacity can be provided as compared with the former transmission type anode, which is effective when a larger amount of electron beam current is required. In the latter case, the collimator for shaping the X-ray beam shape is separated from the X-ray generation point. However, in order to obtain a predetermined fan angle, it is necessary to increase the size of the collimator, and the collimator cannot necessarily fit within the space. In order to avoid this, it is necessary to make the collimator close to the X-ray generation point, that is, the electron beam focusing spot (X-ray focal point) on the anode. Therefore, by devising the structure of the anode to have a collimator function, it becomes possible to generate an X-ray beam having a sufficient fan angle in a predetermined space.
[0017]
In the present embodiment, a plurality of electron emitters may be arranged together with the anode in an annular closed container (vacuum container), or a single electron emitter and a single anode may be housed in a small closed container. To form a minute X-ray tube, and a plurality of minute X-ray tubes may be arranged in a ring. In the latter case, the structure of the X-ray tube is very simple, so there is a possibility that the cost can be reduced, and it becomes possible to easily replace, maintain, and repair a tube whose life has expired. As the minute X-ray tube, either a transmission type or a reflection type may be adopted. In the latter case, as described above, the heat capacity of the anode can be increased, and the durability of the anode can be assured even with a heat load due to the incidence of a large electron beam current.
[0018]
In addition, when arranging minute X-ray tubes in a ring shape, the interval between the X-ray focal spots is expanded, though somewhat, compared to arranging a plurality of electron emitters in a ring-shaped closed container, so that the resolution is secured. It will be difficult to do. This can be solved by oscillating the X-ray tube array in a minute angle range. Since the X-ray tube arrangement is swung in a minute angle range, it is not necessary to supply a high voltage using a slip ring, and a high voltage can be supplied with a hard wire.
[0019]
In the case of the transmission type, a thin film of a genus having a high X-ray generation efficiency is coated, impregnated, or impregnated in a metal layer having a high X transmittance and excellent thermal conductivity on a very small surface layer where an electron beam can enter. An anode having a sandwiched structure is provided, and the anode has an X-ray transmission window, a vacuum partition, and a filter function for correcting the spatial intensity distribution of the emitted X-ray beam. In this case, advantages such as easy shaping into a predetermined beam shape, an X-ray beam having a good spatial intensity distribution, and easy removal of heat emitted to the anode can be obtained. it can.
[0020]
The electron emission section emits electrons in an electric field. The electric field for electron emission is generated by a gate electrode arranged from the cathode with the electron emission portion interposed therebetween. Electron emission can be controlled by applying a voltage to the gate electrode. The electrons emitted from the electron emitting portion collide with the anode target by the voltage between the cathode and the anode, and emit X-rays. In this embodiment, in particular, the voltage applied to each part is adjusted so that the electric field between the anode and the electron emitter is lower than the electric field between the cathode and the gate electrode in the electron emitter. If such voltage adjustment is not performed, even if the electron emitter is not operated, if there are field-emission electrons from the surface of the gate electrode, the X-rays generated by the incidence on the anode become noise and the accuracy of data will be reduced. Is likely to decrease. As described above, the driving voltage is applied to the gate electrode by setting the field emission electron current from the gate electrode surface to be negligible and sufficiently lower than the electric field applied between the gate electrode and the cathode. It is possible to suppress the dark current when not adding and to prevent abnormal discharge. The same effect can be obtained by applying a negative bias to the gate electrode of the electron emitter.
[0021]
Further, in this embodiment, the function of detecting the amount of electron current flowing into the gate electrode in the electron emitter and performing feedback control on the magnitude of the voltage pulse applied to the gate electrode so that the amount of the electron current becomes a constant amount is controlled by the gate pulse generation. Hold the unit. In this embodiment, since many electron emitters and targets are arranged, the X-ray intensity tends to be non-uniform due to variations in performance. This causes noise in the CT image. By performing feedback control of the gate voltage based on the amount of electron current flowing into the gate electrode, the output (electron beam current amount) of each electron emitter can be kept constant, and the generation of this noise can be suppressed. Become. This effect corrects projection data derived from X-rays generated by driving the electron emitters based on the electron current value flowing into the gate electrode when each electron emitter is driven, instead of the feedback control of the gate voltage. You can also play by doing.
[0022]
In the present embodiment, a plurality of detection elements are arranged and fixed in an annular shape together with an electron emitter and an annular anode arranged in an annular shape. By driving the electron emitters in sequence, it is possible to collect projection data in multiple directions at high speed. In synchronization with the driving procedure of the electron emitter, the scattering removal collimator rotatably supported on the front surfaces of the plurality of detection elements arranged in a ring is rotated. The scattered X-ray component in the subject (patient) adds noise to the transmission data and becomes a factor of deteriorating the image quality of the CT image. Therefore, it is possible to effectively remove this scattered component by installing a collimator having a slit configuration that can see the X-ray generation point on the front surface of the detector.
[0023]
In the present embodiment, a mechanism is provided for moving the X-ray generation unit including the annularly arranged electron emitters and the annular anode along the center axis of the imaging region substantially coincident with the body axis of the subject. By fixing the top plate on which the subject is placed and moving the X-ray generating unit in the body axis direction instead, the subject on the top plate on which the subject is placed moves back and forth at high speed can be shaken. It is possible to reduce the resulting body motion artifact of the CT image.
[0024]
In the present embodiment, the X-ray generation unit including the electron emitters arranged in a ring shape and the ring-shaped anode may be equipped with one system, or two or more systems. The X-ray generation units of a plurality of systems are arranged side by side along the center axis of the imaging region substantially coincident with the body axis of the subject. As a result, it is possible to complete the scan at a high speed while ensuring a high resolution over a longer region in the axial direction of the subject.
[0025]
As described above, the electron emitter emits electrons in the electric field. The electric field for electron emission is generated by a gate electrode arranged from the cathode with the electron emission portion interposed therebetween. When a voltage pulse is applied to the gate electrode, electrons are emitted and X-rays are generated. When no voltage pulse is applied to the gate electrode, no X-ray is generated. Voltage pulses are sequentially applied to the gate electrodes arranged in a ring according to the arrangement order. By setting the duration τ of the voltage pulse to be shorter than T / N, where N is the number of gate electrodes and T is the scan time, time overlap of voltage pulses between adjacent gate electrodes is avoided. be able to. As a result, even when the closely arranged electron emitters are sequentially driven to generate X-rays, the X-ray beams triggered by the adjacent electron emitters are irradiated with overlapping time. Data interference can be avoided.
[0026]
In addition, a plurality of electron emitters (gate electrodes) arranged in a ring are equally divided into an odd number (M), for example, three segments, and a voltage pulse is sequentially applied to the gate electrodes in each segment according to the arrangement order. More specifically, a voltage pulse is applied to one gate electrode in the first segment, followed by a voltage pulse to a gate electrode in the second segment, and then to a gate electrode in the third segment. By applying a voltage pulse to each segment and moving the application target of the voltage pulse to the adjacent segment each time the voltage pulse is applied in this manner, adjacent electrons can be extended without extending the voltage pulse application cycle. The gap between the voltage pulses between the emitters 18 can be enlarged to improve the reliability of avoiding the overlap.
[0027]
In addition, by simultaneously applying voltage pulses to three gate electrodes that are shifted by a predetermined angle, for example, 120 °, the time required for data collection for 360 °, that is, the scan time, is reduced by a fraction, for example, 1 / 3 can be reduced. Note that simultaneous driving is mutually affected by scattered radiation. However, this effect can be reduced by shifting the irradiation direction.
[0028]
Hereinafter, an X-ray CT apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the entire configuration of the X-ray CT apparatus according to the present embodiment. FIG. 2 is a front view of the gantry of FIG. This X-ray CT apparatus has a gantry 4 for collecting multidirectional projection data on a subject 5 in an imaging region IR having a substantially cylindrical shape. At the time of data collection, the subject 5 is placed on the top 6 of the bed 6a, and the imaging area of the gantry 4 is moved with the movement of the top 6 driven by the top driving mechanism 7 along the body axis direction. Inserted into IR. In or near the gantry 4, a high-voltage power supply 8 for generating a high voltage to be applied to the X-ray generation unit 1 of the gantry 4 and generation of a voltage pulse to be applied to a gate electrode of the X-ray generation unit 1 to be described later. And a cooling unit 10 for cooling the anode in the X-ray generation unit 1 are arranged. The console controls the detector unit 3 in the gantry 4, collects data (raw data) therefrom, and converts the raw data into projection data through preprocessing such as non-uniform sensitivity correction between channels. A data collection unit 11 is provided for performing the operation. The console also has an image reconstruction unit 12 for reconstructing image data based on a set of projection data for 360 ° or (180 + fan angle), a monitor 13 for image display, and an image data storage unit. 14 are equipped.
[0029]
An X-ray generation unit 1 having an annular shape is fixed inside the gantry 4 so as to surround the imaging region. The X-ray generation unit 1 has a plurality of X-ray generation elements 1a divided along a circumferential direction in order to irradiate the subject 5 with X-rays 34 from multiple directions. The X-ray generating element 1a is defined as a structural unit capable of independently controlling generation and stop of X-rays.
[0030]
As shown in FIG. 3, the X-ray generation unit 1 has an anode 17 having an annular shape centered on the center line CL. A plurality of cathodes 19 are arranged in an annular shape concentric with the anode 17 so as to face the anode 17 at a predetermined distance. A plurality of gate electrodes 38 are arranged between the anode 17 and the cathode 19 in an annular shape concentric with the anode 17. A predetermined distance is provided between the cathode 19 and the gate electrode 38. Between the cathode 19 and the gate electrode 38, a plurality of electron emitting portions 36 having a property of emitting electrons in an electric field are arranged in a ring shape concentric with the anode 17. Actually, a plurality of electron emitting portions 36 are discretely formed on the surface of each cathode 19.
[0031]
When a voltage pulse is applied to the gate electrode 38, an electric field is formed between the gate electrode 38 and the cathode 19. Due to this electric field, electrons are emitted from the electron emitting portion 36. The emitted electrons pass through a number of holes formed in the gate electrode 38, fly toward the anode 17, and collide with a target formed on the surface of the anode 17. The collision produces X-rays. An X-ray component transmitted through the target among the generated X-rays is irradiated on the subject.
[0032]
The single X-ray generating element 1a is composed of a single gate electrode 38 and its related components, that is, a single cathode 19, an electron-emitting portion 36 on the cathode 19, a single gate electrode 38, It is defined to consist of one target and a portion of the anode 17 corresponding to a single target. In addition, a single electron emitter 18 is defined to include a single cathode 19, an electron emission portion 36 on the cathode 19, and a single gate electrode 38. A part of the anode 17, a single target, a single gate electrode 38, an electron-emitting portion 36 on the cathode 19, and a single cathode 19 constituting a single X-ray generating element 1a move outward from the center of the ring. Toward each other along the radial direction. In other words, the electron emitters 18 are arranged on the outer periphery of the anode 17.
[0033]
FIG. 4 is a cross-sectional view of a typical X-ray generation unit 1 of the present embodiment, and FIG. 5 is a vertical cross-sectional view thereof. 6 and 7 show the configuration of the electron emitter 18. FIG. In order to secure a predetermined distance between the gate electrode 38 and the cathode 19, an insulating layer 37 having a thickness of several μm is interposed between the gate electrode 38 and the cathode 19. A large number of holes (openings) 39 are formed in the gate electrode 38 for emitting electrons from the electron emitting portion 36. A predetermined number of vertical holes are formed in the insulating layer 37 corresponding to the electron emission holes 39 of the gate electrode 38. An electron emitting portion 36 is provided on the surface of the cathode 19 that forms the bottom of the vertical hole of the insulating layer 37. The electron beam 33 generated by the electron emitting portion 36 passes through the vertical hole of the insulating layer 37, is emitted from the electron emitting hole 39 of the gate electrode 38, and collides with the target 16. As a result, X-rays are generated at the target 16.
[0034]
In practice, the surface of the insulating layer 37 is coated with a metal that will become the gate electrode 38. By adopting this structure, the distance between the cathode 19 on which the electron emission portions 36 are formed and the gate electrode 38 can be kept uniform at a predetermined distance selected from the range of several μm to several tens of μm. . By setting the distance between the cathode 19 and the gate electrode 38 to the above-described short distance, a low voltage of about several tens to 100 V is applied between the cathode 19 and the gate electrode 38, so that the electron emission portion 36 Can be released.
[0035]
The anode 17 includes a pair of annular portions 17-1 and 17-2 having a trapezoidal cross section. The annular portions 17-1 and 17-2 are made of a material having both conductivity and X-ray shielding properties. The annular portions 17-1 and 17-2 are arranged in parallel along the center line (Z axis) of the imaging region at a predetermined distance, so that the annular portions 17-1 and 17-2 have the anode function and the body axis direction (Z axis direction). The function also serves as a collimator 27 for limiting the radiation angle α of the X-ray 34. The target 16 is passed to the ring portions 17-1 and 17-2. An X-ray component transmitted through the target 16 among the X-rays generated by the target 16 due to the electron collision is emitted through the collimator 27. A cooling jacket 15 for circulating a coolant is formed in the annular portions 17-1 and 17-2 of the anode 17.
[0036]
The cathode 19, the electron emission section 36, the gate electrode 38, the target 16 and the anode 17 are accommodated in a single annular insulating container (closed container) 21. The insulating container 21 may be composed of a plurality of container parts. The anode 17 and the target 16 constitute a part of the insulating container 21. The gas inside the insulating container 21 is forcibly exhausted from the exhaust port 32. Thereby, a vacuum chamber 20 is formed inside the insulating container 21. The insulating container 21 is accommodated in a sealed container 26 of an insulating liquid or an insulating gas having a ring shape. A circuit box 24 including a stabilizing resistor 24a and a pulse amplifier circuit 24b is housed in the enclosure 26 together with the insulating container 21.
[0037]
The circuit box 24 is supported inside the enclosure 26 by the insulating support 30. The stabilizing resistor 24 a stabilizes the high voltage supplied by the high-voltage cable 23 and supplies it to the cathode 19. The high-voltage cable 23 is introduced into the enclosure 26 by a high-voltage cable bushing terminal 29. The pulse amplification circuit 24 amplifies a pulse-like gate signal (gate pulse) sent via the optical fiber cable 22 and supplies a voltage pulse to the gate electrode 38. During the period in which the voltage pulse is supplied to the gate electrode 38, an electric field is formed between the cathode 19 and the gate electrode 38, whereby the emission of electrons from the electron emission portion 36 is promoted. These electrons collide with the target 16 of the anode 17 and generate X-rays.
[0038]
The enclosing container 26 is housed in an annular X-ray shielding container 28. The X-ray detector unit 3 is attached to the inner wall surface of the X-ray shielding container 28. The X-ray detector unit 3 has a plurality of channels arranged along a ring. One channel includes an X-ray detection element 3a and an X-ray detection element 3b, which form a pair of connected signal lines. The X-ray detection element 3a and the X-ray detection element 3b are juxtaposed along the imaging region center line (Z-axis) with a gap larger than the path width of the X-ray beam 33 from the collimator 27. The X-ray emitted from the collimator 27 passes through a gap between the X-ray detection element 3a and the X-ray detection element 3b forming a pair, and is irradiated on the subject. X-rays transmitted through the subject are detected by the X-ray detection elements 3a and 3b on the opposite sides. As described above, the X-rays are emitted from the gap between the X-ray detection elements 3a and 3b, so that the X-ray center axis is orthogonal to the Z-axis. Can be realized.
[0039]
In the X-ray generation unit 1 having such a configuration, 10 ^-7 A high voltage of about 100 kV is applied to a cathode installed in a vacuum chamber 210 maintained at a degree of vacuum of Pa or less, and a voltage pulse is applied to a gate electrode 38 of the electron emitter 18, whereby the circulating electron emitter 18 is arranged. The electron beam 33 can be generated only from the specific electron emitter 18 supplied with the voltage pulse. The electron beam 33 collides with the corresponding target 16 on the anode 17 and emits X-rays. Here, most of the energy of the electron beam 33 is converted into heat at the target 16. The heat of the anode 17 is released by the cooling jacket 15. Thereby, melting of the target 16 can be suppressed. X-rays are emitted radially from the spot of the target 16 against which the electron beam 33 collides, but the X-rays are limited to a predetermined fan angle θ by the collimator 27 that is miniaturized by being installed near the target 1. can do.
[0040]
At this time, the required value of the amount of emitted electrons with respect to the electron emitter 18 is determined from the amount of electron current necessary to obtain a predetermined amount of X-ray radiation. ² A very small X-ray generating element 1a can be provided by using a carbon-based structure having a high electron-emitting ability, which is said to be high, as the electron-emitting portion 36.
[0041]
When the electron-emitting portion 36 is formed from a carbon-based material having high electron-emitting performance as described above, an electric field intensity of about 5 kV / mm or less is required to obtain a sufficient electron current density. By bringing the cathode 19 and the gate electrode 38 closer to each other as described above, the voltage applied to the gate electrode 38 can be kept low, whereby the insulating distance between the adjacent electron emitters 18 can be shortened and the arrangement can be made with high density. can do. In addition, since the electron emitting portion 36 is formed of a carbon-based structure having high electron emission performance, a required amount of electron beam current (tube) can be obtained even with a small effective area assigned to each electron emitter 18. Current) can be realized.
[0042]
By adopting the three-terminal structure for controlling electron emission with the gate electrode 38 as described above, the same DC high voltage is continuously applied to the cathodes 19 of all the electron emitters 18, and only from any electron emitter 18. It can emit electrons. As a result, each electron emitter 18 only needs to maintain a withstand voltage of about this gate voltage (generally several tens of volts to 1 kV), and the electron emitters 18 can be arranged close and densely.
[0043]
As an example, consider the case where the electron emitters 18 are arranged in an annular shape with a diameter of 80 cm, the circumferential length is 251 cm, and 2 cm here. ⁹ When (= 512) electron emitters 18 are arranged, the arrangement pitch of the electron emitters 18 in the circumferential direction is about 5 mm. In consideration of insulation between the adjacent electron emitters 18, the width of the cathode 17 and the gate electrode 38 of the electron emitter 18 is limited to about 2 mm. Since the size limit is loose in the body axis direction Z, the cathode 17 of the electron emitter 18 and the gate electrode 38 are designed to have a length of about 10 mm in the body axis direction Z. As a result, the cathode 17 and the gate electrode 38 of each electron emitter 18 are set to 20 mm ² Area. Generally, 50 mA / cm ² When a carbon-based structure having the above-mentioned average electron current density is used as an electron-emitting material, the emission electron current per one electron emitter 18 is 10 mA, and the total electron emitter 18 has 10 mA × 512 = 12 A. The calculation yields an average electron beam current, which sufficiently satisfies the current value (approximately 1 A) required for an electron-driven CT.
[0044]
Increasing the number of electron emitters 18 that can be arranged in one round increases the number of data points (the number of views) per round scan and improves the resolution of a CT image. Therefore, in order to enable a high-density array, it is essential to apply the electron emitter 18 having a high electron emission capability and a gate function of low voltage driving, and satisfy the same specifications by other methods and structures. Cannot be done.
[0045]
Further, when a similar electron-emitting portion is devised so as to obtain a higher electron-emitting ability, or when the electron emitter 18 having a structure devised so that a gate drive voltage can be reduced, a similar average is obtained. It is possible to reduce the area of the electron emitter 18 necessary for obtaining the amount of electron beam current, thereby increasing the number of the X-ray generating elements 1a arranged in a circulating manner, and ensuring a more accurate scan. It becomes.
[0046]
As shown in FIG. 3, by sequentially driving the electron emitters 18 in the X-ray generation unit 1, that is, by sequentially applying a voltage pulse to the gate electrode 36, the X-rays can be generated without using a mechanical rotation mechanism. The X-ray beam can be moved electronically with the generation unit 1 fixed. The electronic movement of the X-ray beam can significantly reduce the scan time as compared with a mechanical rotation mechanism. In other words, the scan time is determined depending on the circulating drive time of the electron emitter 18, and since the restriction of the conventional mechanical drive method is eliminated, the amount of X-ray generation is inversely proportional to the reduction of the scan time. It is decided by increasing. If the X-ray detection unit 3 having the same sensitivity as the conventional mechanical drive type is applied and the above-mentioned electron beam current amount can be secured, the scan time can be reduced to 1/10 or less of the limit value (3 to 5 sec) of the conventional type. Becomes possible. In addition, the detection width in the body axis direction is increased, and the speed of the detector data acquisition unit 11, the speed of the image reconstruction unit 12, and the capacity are increased, so that the three-dimensional CT image can be time-resolved. It is also possible to shoot.
[0047]
8 and 9 show modified examples of the cathode 19. Although the width of the electron emitter 18 is restricted by the density in the circumferential direction, there is no restriction on the length in the body axis direction Z, so that a rectangular shape long in the body axis direction Z can be adopted. On the other hand, it is required that the electrons emitted from the electron emitter 18 be focused on the target 16 of the anode 17 to a smaller spot size. The focal spot size of the X-ray source is determined by the spot size, and from the viewpoint of image quality, it is generally required that a CT apparatus can obtain an X-ray focal spot size of about 1 mmφ.
[0048]
Therefore, as shown in FIG. 8, the electric field can be formed in a direction toward the focusing direction of the electron beam 33 by making the surface of the cathode 19 concavely curved as viewed from the target 16. This makes it possible to reduce the spot size.
[0049]
It is possible to use an electron emitter 18 having an area larger than the spot size of the electron beam 33 required by the target 16 on the anode 17, that is, the X-ray focal spot size. Can be applied to increase the emission electron beam current. A large amount of emitted electron beam current can be obtained while securing a predetermined density of the electron emitter 18, and it is possible to provide an X-ray CT apparatus having a high margin of X-ray beam emission performance.
[0050]
FIG. 10 shows a detailed sectional structure of the X-ray generation unit 1. The insulating container 21 forming the vacuum chamber 20 has an annular overall shape, and has a plurality of access panels (doors) 35 each having a fan-like shape whose side walls can be individually attached and detached. In the sealed integrated structure, it is difficult to replace and repair the electron emitter 18 and the target 16 of the anode 17, and when these elements have reached the end of their life, the entire annular X-ray generation unit 1 needs to be replaced. It is said. However, the employment of the access panel 35 makes it possible to replace or repair only those electron emitters 18 whose life has expired or failed. In such a structure, the side wall of the container 21 of the X-ray generation unit 1 is also provided with a function of a vacuum partition in order to replace and repair the electron emitter 18 and the target 16 of the anode 17 in which the wear related to the life is to be considered. It is assumed that the access panel 35 is used. By adopting this structure, it is possible to open the access panel 35 from the side and remove only the electron emitter 18 and the target 16 of the anode 17 which need to be repaired and replaced, and repair or replace the target. After the repair is completed, the unit 1 can be reused by closing the access panel 35 and driving the vacuum pump to return the vacuum chamber 20 to the original vacuum level.
[0051]
As described with reference to FIGS. 8 and 9, the convergence of the electron beam 33 emitted from the electron emitter 18 contributes to miniaturization of the X-ray focal point and accompanying promotion of image quality improvement. Instead of, or in combination with, making the cathode 19 concave in FIG. 8, as shown in FIG. 11, in the insulating container 21, between the electron emitter 18 and the target 1 of the anode 17, together with the accelerating electrode 40. The focusing electrode 41 may be provided. With this configuration, the electron beam 33 emitted from the electron emitter 18 is accelerated by the acceleration electrode 40, and then decelerated and re-accelerated by the focusing electrode 41, so that focusing can be promoted. This configuration uses a general electron beam focusing mechanism.However, it is possible to effectively and reliably focus the electron beam by controlling the shape of the surface electric field by changing the shape of the cathode. Become. Therefore, it is possible to focus the electron beam on a smaller spot to form a small X-ray focus, thereby realizing higher image quality.
[0052]
The convergence of the electron beam 33 can also be improved by associating a pair of electron emitters 18 with a single target 16 as shown in FIGS. In addition, when electrons are emitted from the electron emitter 18 to near the limit, the life of the electron emitting portion 36 in the electron emitter 18 is shortened. Therefore, it is effective to increase the margin as much as possible to extend the life. It becomes. To extend the life, it is effective to make the pair of electron emitters 18 correspond to the single target 16 to substantially increase the area. Further, in order to prevent a reduction in the circling density of the electron emitters 18, the pair of electron emitters 18 are arranged side by side along the body axis direction Z, and are installed at different angles so as to aim at the same target 16. In other words, the annular arrangement of the electron emitters 18 is divided into two rows in the body axis direction Z.
[0053]
A pair of electron emitters 18 are separately arranged before and after the anode 17 in the body axis direction Z, and the electron beams 33 are simultaneously emitted from the respective electron emitters 18 to the target 16 on the anode 17. As a result, the space that can be provided to the electron emitter 18 can be doubled as compared with the method arranged in the previous example, and it is possible to provide a margin in the electron emission capability.
[0054]
In the above, the electron emitter 18 was arranged so that the electron beam was emitted along the radial direction. However, as shown in FIG. 15, the electron emitter 18 may be arranged so that the electron beam is emitted along the Z-axis direction. In this case, the target 16 is arranged so that its surface is inclined with respect to the center axis of the electron beam, that is, the Z axis. In practice, the anode 17 is arranged so that its surface is inclined with respect to the Z axis, and the target 16 is formed on the inclined surface of the anode 17.
[0055]
Among the X-rays generated on the target 16 by the electron beam emitted from the electron emitter 18, the X-ray component reflected on the target 16 in the direction of the anode surface (reflection direction) is reflected by a collimator 27 provided separately from the anode 17. It is shaped, emitted from the X-ray emission window 42, and irradiated to the subject.
[0056]
Arranging the electron emitters 18 and anodes 17 along the Z-axis direction as shown in FIG. 15 reduces the amount of attenuation of X-rays transmitted through the target 16 as in the case of the transmission type shown in FIG. Freed from constraints. Thereby, the anode 17 having a large thickness can be employed, and the heat capacity of the anode 17 can be increased. This is because when the amount of electron beam current is increased, or when the focused spot of the electron beam is reduced to reduce the X-ray focal point, it is expected that deterioration due to a rise in the temperature of the target surface will become a problem. Is effective in such a case. Further, by designing the inclination angle of the target 16 with respect to the Z axis to be small, it is possible to lengthen the target surface on which the electron beam 33 is incident linearly and to increase the irradiation area. Thereby, the tolerance for the irradiation time is increased, which is advantageous from the viewpoint of the life of the target 16 as compared with the transmission type shown in FIG.
[0057]
The reflection type X-ray generation unit 1 shown in FIG. 15 has an advantage that the heat capacity of the anode 17 is increased. However, due to its configuration, the anode 17 is also used as a collimator for limiting the X-ray fan angle. Can not. Therefore, a collimator for limiting the fan angle is required for each X-ray generating element 1a separately from the anode 17. In the configuration in which the X-ray generating elements 1a are closely arranged, the width of the collimator for limiting the fan angle of the X-ray beam to an assumed angle is restricted. That is, a collimator having a small circumferential width is required. In order to secure a required fan angle with a collimator having a small width, it is necessary to shorten the distance between the X-ray focal point on the target 16 and the collimator for limiting the fan angle.
[0058]
Therefore, as shown in FIG. 16, a collimator 27a for limiting the fan angle is arranged inside the insulating container 21. In practice, a collimator 27a for determining the fan angle of the X-ray beam is directly attached to the tip of the anode 17. Since this collimator 27a is attached to an anode having a large heat load, tungsten and its alloys are considered to have a high melting point and an excellent vapor pressure characteristic in order to suppress the evaporation and have a high X-ray shielding ability. Or a corresponding metal is selected.
[0059]
The fan angle of the X-rays emitted from the surface of the target 16 is limited by a collimator 27 a attached to the anode 17, and furthermore, an annular collimator 27 b installed outside the insulating container 21 has a fan shape in the body axis direction Z. The spread angle is restricted. As described above, in the reflection type X-ray generation element 1a in which the collimator 27a is accommodated in the insulating container 21, a high heat capacity and a high-density arrangement of the X-ray generation elements 1a can be realized.
[0060]
In the above, the structure in which the plurality of X-ray generating elements 1a are arranged in a ring shape in the ring-shaped insulating container (vacuum container) 21 has been described. As shown in FIGS. 17 and 18, a separate vacuum chamber may be provided in the insulating container 21a for each X-ray generating element 1a. About 10 ^-7 The individual anode 17, the target 16, and the electron emitter 18 are accommodated in a small-diameter insulating container 21a secured to a vacuum of Pa to form a small-diameter X-ray tube. The X-ray generation unit 1 is configured by arranging a plurality of micro-diameter X-ray tubes in an X-ray tube support 49 having an annular shape in an annular shape. The insulating container 21a has a circular, elliptical or rectangular cross section. The use of the insulating container 21a having an elliptical or rectangular cross section allows the use of the rectangular electron emitter 18 which is long in the body axis direction Z shown in FIGS.
[0061]
The adoption of such a configuration in which a plurality of micro-diameter X-ray tubes are arranged in an annular shape makes it possible to replace an X-ray tube having a life or failure in units of X-ray tubes. The replacement in units of X-ray tubes can reduce the number of replacement work steps and the return time as compared with replacing the cathode 17, the target 16, and the like individually.
[0062]
As shown in FIGS. 19 and 20, a reflection type may be employed for a plurality of X-ray tubes having a small diameter. As a result, the heat capacity of the anode can be increased, and the durability of the anode can be assured even against a heat load caused by the incidence of a large electron beam current.
[0063]
As shown in FIGS. 17 and 19, when a plurality of micro-diameter X-ray tubes are arranged in a ring shape, the density is lower than in the case where the X-ray generating elements 1a are arranged inside the annular insulating container 21. Lower. In order to collect projection data at a viewpoint having a density higher than the array density of a plurality of micro-diameter X-ray tubes, as shown in FIG. 21 and FIG. The line detector unit 3 is installed on a single support 50 having an annular shape. The support 50 is rotatably supported around the Z-axis, and reciprocates within a small rotation angle range Δθ by using a rotation driving device 51. In other words, the X-ray generation unit 1 and the X-ray detector unit 3 are oscillated at a small amplitude Δθ, and the generation of X-rays and the detection of transmitted X-rays are repeated during that time, thereby collecting projection data at a high density. To achieve. In this case, since it is not continuous rotation, a slip ring is not required, and as shown in FIG. 23, the high-voltage cable 23 to the X-ray tube can be constituted by hard wires. Similarly, the existing optical fiber 22 for supplying the gate pulse of the electron emitter 18, the signal lead-out line 53 from the X-ray detector unit 3, and the cooling hose for circulating the cooling liquid of the X-ray tube should be used as they are. Can be.
[0064]
FIG. 24 shows a cross-sectional structure of the transmission type target 16 described above. The target 16 is one of the most important components that determine the life of the X-ray generation unit 1. When the electron beam 33 emitted from the electron emitter 18 is focused and collides with the target 16, most of the energy (99% or more) is converted into heat. Therefore, it is necessary to determine the material and structure of the transmission type target 16 from the three viewpoints of the amount of X-ray generation, the X-ray transmittance, and the heat removal performance. As the base material 16b of the target 16, low atomic number aluminum, carbon, or the like having a small X-ray attenuation rate and a high thermal conductivity, or an alloy thereof is used. On the surface of the target base material 16b, a target layer 16a of a metal having a high atomic number, such as tungsten or renium, having a high X-ray transmittance and excellent thermal conductivity is formed. Typically, the target layer 16a is formed by coating the metal on the surface of the target base material 16b. The thickness of the target layer 16a is set to about 5 μm in consideration of the penetration depth of incident electrons and the attenuation rate of X-rays.
[0065]
In the transmission type target 16 configured as described above, the collimator 27 can be installed near the anode, and thereby it is possible to shape the X-ray beam having a predetermined divergence angle by the small size collimator 27. Although it has an advantage, the cooling of the anode becomes a problem when a large current electron beam is assumed. In order to solve this problem and improve cooling efficiency, beat pipes are used which are originally arranged on the X-ray path and made of light metal such as aluminum for adjusting the quality of X-rays. Use as The target 16 is placed on the X-ray filter 31 in a contact state. X-ray filter 31 is physically connected to anode 16. That is, the target 16 is supported by the anode 17 via the X-ray filter 31.
[0066]
The heat generated in the target 16 is transmitted to the anode 17 via an X-ray filter 31 as a beat pipe. Thus, the heat of the central portion of the target 16 that is difficult to cool can be supplemented by conduction cooling of the filter 31, and the evaporation and wear of the target 16 can be suppressed.
[0067]
FIG. 25 shows an optimized dimension of the electric field between the cathode 19 and the gate electrode 38 in the electron emitter 18 with respect to the electric field between the anode 17 and the electron emitter 18. Since a direct current (DC) high voltage is applied between the electron emitter 18 and the anode 17, it is expected that the electric field electrons will be emitted from the gate electrode 38 located on the surface of the electron emitter 18 due to this electric field. Is done. Since this electron component is also emitted during a period in which the drive voltage pulse applied to the gate electrode 38 is stopped, X-rays generated when the leaked electrons are incident on the anode 17 become noise and become data noise. There is a concern that the accuracy will be reduced. It is necessary to prevent the generation of leaked electrons.
[0068]
In order to suppress electron leakage from the gate electrode 38, the electric field Ea between the gate electrode 38 and the anode 17 is set to be sufficiently smaller than the electric field Eg due to the voltage applied between the gate electrode 38 and the cathode 17. The distance between the electron emitter 18 and the anode 17 is set sufficiently long. For example, assuming that 100 kV is applied between the cathode and the anode, if the distance between the electron emitter 18 and the anode 17 is 50 mm, the electric field between them becomes 2 kV / mm. Since the electric field necessary for the electron emission from the electron emission portion 36 to reach a sufficient density is typically 5 to 10 kV / mm, the amount of the field emission electrons leaking from the surface of the gate electrode 38 has a sufficient margin. It is possible to suppress with having. That is, a typical upper limit of the tube voltage applied between the cathode and the anode is 200 kV. By designing the distance between the electron emitter 18 and the anode 17 to be 50 mm, even if an upper limit of 200 kV is applied between the cathode and the anode, generation of leakage electrons can be suppressed.
[0069]
As described above, even when a voltage pulse is not applied to the gate electrode 38 of the electron emitter 18, the field electrons are emitted from the surface of the gate electrode 38 by the tube voltage applied between the anode 17 and the electron emitter 18. However, there is a concern that the electric field penetrates into the electron emission holes of the gate electrode 38 and causes the electron emission portions 36 on the surface of the cathode 19 to emit field electrons directly. To solve this problem, as shown in FIGS. 26 and 27, a bias power supply 45 for applying a negative direct current (DC) bias voltage to the gate electrode 38 with respect to the cathode 19 is provided. Thus, when a positive voltage pulse is not applied to the gate electrode 38, it is possible to completely suppress the generation of the leaked electrons from the electron emitting portion 36.
[0070]
As described above, the arrangement of the plurality of X-ray generating elements 1a may cause non-uniform X-ray intensity. It is necessary to make the X-ray intensity uniform among the plurality of X-ray generating elements 1a. Detecting the intensity of X-rays generated from each X-ray generating element 1a with a reference detector as in the related art is preferable because the X-ray generating element 1a is enlarged and the array density of the X-ray generating elements 1a is reduced. Absent.
[0071]
Therefore, as shown in FIG. 28, the amount of electron current flowing into the gate electrode 38 in the electron emitter 18 is detected by the current detector 46. The amount of electron current flowing into the gate electrode 38 corresponds to the intensity of the X-ray generated in the target 16. The feedback control unit 47 controls the pulse amplifier circuit 24a for generating a voltage pulse applied to the gate electrode 38 based on the amount of electron current flowing into the gate electrode 38 detected by the current detector 46. The feedback control unit 47 generates a control signal according to the difference between the amount of electron current flowing into the gate electrode 38 and a predetermined amount. In the pulse amplification circuit 24a, the amplification rate of the gate pulse is changed according to the control signal. When the amount of electron current flowing into the gate electrode 38 is more than a predetermined amount, a feedback control unit 47 generates a control signal for reducing the amplification factor. When the amount of electron current flowing into the gate electrode 38 is smaller than a predetermined amount, a feedback control unit 47 generates a control signal for increasing the amplification factor.
[0072]
By such feedback control, the X-ray intensity can be made uniform among the plurality of X-ray generating elements 1a.
[0073]
The non-uniformity of the X-ray intensity among the plurality of X-ray generating elements 1a eventually appears as an artifact in the reconstructed image. As shown in FIGS. 27 and 28, instead of making the X-ray intensity uniform among the plurality of X-ray generating elements 1a, the electron current value flowing into the gate electrode 38 is detected by the detector 46 as shown in FIG. The same effect can be obtained by detecting and correcting the projection data by the data collection unit 11 based on the detected data.
[0074]
FIGS. 30 and 31 show a collimator 52 for removing scattered radiation generated in the subject. The collimator 52 is composed of a plurality of lead plates arranged in an arc with the X-ray focal point as the center. The direction of each lead plate is adjusted along the radial direction of a circle centered on the X-ray focal point. The collimator 52 is rotatably supported by the support 50 between the subject and the X-ray detector unit 3. The rotation driving device 51 is provided for rotating the collimator 52. The rotary driving device 51 is, for example, a stepping motor, and a driving pulse is supplied from a power source (not shown) in synchronization with the gate pulse. The collimator 52 rotates in synchronization with the movement of the driven gate electrode 38 so as to face the gate electrode 38 driven by the voltage pulse according to the gate pulse. As a result, scattered radiation generated in the subject is removed by the collimator 52 and does not reach the detector 3. A high-definition CT image from which scattered radiation has been removed can be obtained.
[0075]
As shown in FIG. 32, the X-ray CT apparatus of the present embodiment includes a gantry driving mechanism 43 that moves the gantry 4 along the Z axis, and a control device 44 that controls the gantry driving mechanism 43. The gantry 4 is housed in the protective cover 48 together with the gantry driving mechanism 43. By employing the gantry driving mechanism 43, the helical scan or the multi-slice scan can be executed with the top plate 6 on which the subject 5 is placed stopped. The movement of the gantry 4 is such that the weight of the entire gantry 4 including the X-ray detector unit 3 is overwhelming compared to the conventional R / R type since the X-ray generation unit 1 constituting the X-ray CT apparatus does not include a rotation mechanism. It can be adopted because it is lighter in weight. Conventionally, the scan in the body axis direction, which has been performed by moving the table 6 on which the subject 5 is placed back and forth, can be performed by stopping the subject 5 and moving the gantry 4. Since the helical scan or the multi-slice scan can be executed while the subject (patient) is stopped, it is possible to suppress the deterioration of the CT image caused by the movement of the subject 5 due to the movement of the tabletop and the body movement, and to the patient. Problems such as discomfort can be eliminated.
[0076]
As described above, since the X-ray generation unit 1 of the present embodiment is small and lightweight, a plurality of, for example, two systems of X-ray generation units 1-1 and 1-2 are arranged in the body axis direction Z as shown in FIG. They can be arranged side by side at a predetermined distance. Similarly, two X-ray detection units 3-1 and 3-2 are arranged side by side in the body axis direction Z. By providing two systems of the X-ray generation units 1-1 and 1-2 and the X-ray detection units 3-1 and 3-2, the imaging time of the helical scan or the multi-slice scan can be reduced.
[0077]
34 and 35 show a procedure for driving the electron emitter 18 according to the present embodiment. Driving the electron emitter 18 means applying a voltage pulse to the gate electrode 38 of the electron emitter 18. A limited amount of electrons are emitted from the electron emission section 26 only during the period when the voltage pulse is applied to the gate electrode 38. The emitted electrons collide with a spot (X-ray focal point) on the target 16 of the anode 17. X-rays are generated radially around the X-ray focal point. The X-rays restricted to the predetermined fan angle θ by the collimator 27 pass through the subject and are detected by the X-ray detector unit 3. The data collection unit 11 collects only data of a predetermined number of channels (specific channels) corresponding to the position of the X-ray focal point from data of all channels, and does not collect data of other channels. The specific channel for which data is to be collected is a channel arranged within a range of a fan angle θ centered on a position on the X-ray detector unit 3 facing the X-ray focal point. The specific channel for which data is to be collected is switched according to the switching of the electron emitter 18 to be driven. Switching of the specific channel is realized by, for example, switching of an electronic switch provided between the X-ray detector unit 3 and the data acquisition unit 9.
[0078]
Here, it is assumed that the total number of the electron emitters 18 arranged in a ring (= the total number of the gate electrodes 38) is N. In addition, the plurality of electron emitters 18 arranged in a ring shape are numbered from # 1 to #N in accordance with the arrangement order to distinguish them from one another. The time required to collect one round of projection data, that is, the scan time, is denoted by T. The duration of the gate pulse (voltage pulse) is denoted by τ.
[0079]
The gate pulse generation unit 9 drives the plurality of electron emitters 18 arranged in a ring in order according to the arrangement order. That is, the gate pulse generation unit 9 applies a gate pulse (voltage pulse) to the plurality of electron emitters 18 arranged in a ring in order according to the arrangement order. The gate pulse generation unit 9 includes a gate pulse generation unit that repeatedly generates a gate pulse having a predetermined duration at a fixed period, and a gate pulse generation unit that is interposed between the gate pulse generation unit and the pulse amplification circuits 24a of all channels. An electronic switch for selectively connecting the single-channel pulse amplifier circuit 24a, and an electronic switch control unit for controlling the electronic switch. The electronic switch control unit controls the electronic switches to sequentially connect the pulse amplification circuits 24a to the gate pulse generation unit.
[0080]
In order to secure the scan time T, the gate pulse is generated at a period of T / N. Similarly, the connection of the pulse amplifying circuit 24a to the gate pulse generator is switched in order according to the arrangement order at a period of T / N. The duration τ of the gate pulse is set to a time shorter than the cycle T / N of the gate pulse (voltage pulse). That is, the duration τ of the gate pulse (voltage pulse) is selectively set from the range of 0 <τ <T / N. Preferably, τ = T / (2 · N) is set.
[0081]
By setting the duration τ of the gate pulse to a time shorter than the period T / N of the gate pulse, for example, the gate pulse applied to the electron emitter 18 of the number #n and the electron of the number # (n + 1) at the next position There is a time gap between the gate pulse and the gate pulse applied to the emitter 18. That is, after the gate pulse to the electron emitter 18 of the number #n falls, the gate pulse to the electron emitter 18 of the next number # (n +) rises after a predetermined time interval. A period during which X-rays are generated from the X-ray generating element 1a including the electron emitter 18 of the number #n, and a period during which X-rays are generated from the X-ray generating element 1a including the adjacent electron emitter 18 of the number # (n + 1). Are separated in time. Therefore, a situation (data interference) occurs in which data of the specific channel corresponding to the electron emitter 18 of the number # (n + 1) contains information of X-rays from the X-ray focal point corresponding to the electron emitter 18 of the number #n. Absent. Image artifacts due to the data interference can be effectively prevented. For example, if one round scan time is 50 ms and the total number of electron emitters 18 is 514, data interference can be prevented by setting the maximum duration of the gate pulse to less than 97 μs.
[0082]
FIGS. 36 and 37 show a driving procedure that can improve the effect of preventing the above data interference. The plurality of electron emitters 18 arranged in an annular shape are equally divided along the circumference into odd (M) segments. The reason why the segments are set to an odd number is to avoid overlapping of the area of the detector that covers the X-ray beam generated in the segment, and when the number of segments is increased, the coverage area of the X-ray beam is increased. Therefore, it is necessary to narrow the X-ray beam fan angle accordingly. For example, as shown in the example in the figure, when the fan angle is 60 °, the number of divided segments is set to three.
[0083]
The segment to be driven is switched at a cycle of T / N. In each segment, the electron emitters 18 are driven one by one according to the arrangement order. That is, the electron emitters 18 in one segment are driven in order, and the electron emitters 18 in the other two segments are sequentially driven during the period until the driving of the next adjacent electron emitter 18 is started. That is, a voltage pulse is sequentially applied to the gate electrodes 38 in the segment in accordance with the arrangement, and a discrete two-dimensional signal is shifted by a predetermined angle (here, 120 °) during the application of the voltage pulses to the adjacent gate electrodes 38. Voltage pulses are sequentially applied to the gate electrodes 38.
[0084]
Thus, when viewed between the adjacent electron emitters 18, the period of the gate pulse is substantially M × T / N, which is greater than the period T / N in FIGS. 34 and 35. Therefore, interference with an X-ray beam triggered by an adjacent electron emitter 18 can be more reliably avoided.
[0085]
In the examples of FIGS. 36 and 37, two electron emitters 18 that are shifted by 120 ° are sequentially driven during a period from when a certain electron emitter 18 is driven to when the next electron emitter 18 starts to be driven next. It is.
[0086]
As shown in FIGS. 38 and 39, at the same time as driving a certain electron emitter 18, two electron emitters 18 deviated from it by 120 ° may be driven. Thereby, the effect of preventing interference is equivalent to the examples of FIGS. 34 and 35, but the scan time per rotation can be reduced to T / M. For example, when the scanning time per rotation is 50 ms and the three electron emitters 18 shifted by 120 ° are coaxially moved, the scanning time can be reduced to 17 ms.
[0087]
Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements in an implementation stage without departing from the scope of the invention. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments.
[0088]
【The invention's effect】
According to the present invention, it is possible to provide an X-ray CT apparatus, an X-ray generation apparatus, and a data collection method for an X-ray CT apparatus which are small in scale, inexpensive, excellent in maintainability, and have high resolution.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an X-ray CT apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic front view showing the internal structure of the gantry of FIG. 1;
FIG. 3 is a schematic front view showing the internal structure of the X-ray generation unit of FIG.
FIG. 4 is a cross-sectional view showing the internal structure of the X-ray generation unit of FIG.
FIG. 5 is a longitudinal sectional view showing the internal structure of the X-ray generation unit of FIG.
FIG. 6 is a lateral view of the electron emitter 18 of FIG. 4;
FIG. 7 is an external view showing the structure of a cathode, an electron-emitting portion, and a gate electrode in FIG. 6;
8 is a cross-sectional view showing another structure of the electron emitter 18 of FIG.
FIG. 9 is a longitudinal sectional view showing another structure of the electron emitter 18 of FIG. 6;
FIG. 10 is a cross-sectional view showing another internal structure of the X-ray generation unit of FIG. 4;
FIG. 11 is a cross-sectional view showing a focusing electrode of the electron emitter 18 of FIG.
FIG. 12 is a longitudinal sectional view showing another internal structure of the X-ray generation unit of FIG. 4;
FIG. 13 is a transverse sectional view showing the orientation of a pair of electron emitters 18 of FIG.
FIG. 14 is a diagram showing a plane position of a pair of electron emitters 18 of FIG. 12 with respect to a target.
FIG. 15 is a transverse sectional view showing another internal structure of the X-ray generation unit of FIG. 1;
FIG. 16 is a transverse sectional view showing another internal structure of the X-ray generation unit of FIG. 1;
FIG. 17 is a longitudinal sectional view showing another structure of the X-ray generation unit of FIG. 1;
18 is a cross-sectional view of the small-diameter X-ray tube of FIG.
19 is a longitudinal sectional view showing another structure of the X-ray generation unit of FIG.
FIG. 20 is a cross-sectional view of the small-diameter X-ray tube of FIG. 19;
FIG. 21 is a transverse sectional view showing the structure of the swing mechanism of the X-ray generation unit shown in FIG. 17;
FIG. 22 is a view showing a swing operation by the swing mechanism of FIG. 21;
FIG. 23 is a diagram showing a high-voltage cable for the X-ray generation unit in FIG. 21.
FIG. 24 is a longitudinal sectional view showing a target structure of the X-ray generation unit of FIG. 1;
25 is a diagram showing an electric field between a gate electrode and a cathode of the X-ray generation unit of FIG. 1 in comparison with an electric field between an anode and an electron emitter 18;
FIG. 26 is a configuration diagram of the gate pulse generation unit of FIG. 1;
FIG. 27 is a diagram showing a time change of a voltage applied to a gate electrode by the gate pulse generation unit of FIG. 26;
FIG. 28 is a diagram showing another configuration of the gate pulse generation unit of FIG. 26;
FIG. 29 is a diagram showing an intensity uniforming correction function of the detector data collection unit of FIG. 1;
FIG. 30 is a transverse sectional view showing a scatter removing collimator provided in the X-ray detector unit of FIG. 1;
FIG. 31 is a schematic front view showing the rotation operation of the scattering removal collimator of FIG. 30;
FIG. 32 is a view showing a moving mechanism of the gantry of FIG. 1;
FIG. 33 is a view showing another structure of the gantry of FIG. 1 having two X-ray detector units and two X-ray detector units;
FIG. 34 is a diagram showing a driving procedure of the electron emitter 18 by the gate pulse generation unit of FIG. 1;
FIG. 35 is a diagram showing intervals between voltage pulses applied to adjacent electron emitters 18 in the procedure of FIG. 33;
FIG. 36 is a diagram showing another driving procedure of the electron emitter 18 by the gate pulse generation unit of FIG. 1;
FIG. 37 is a diagram showing intervals of voltage pulses applied to adjacent electron emitters 18 in the procedure of FIG. 36.
FIG. 38 is a diagram showing another driving procedure of the electron emitter 18 by the gate pulse generation unit of FIG. 1;
FIG. 39 is a diagram showing intervals of voltage pulses applied to adjacent electron emitters 18 in the procedure of FIG. 38.
FIG. 40 is an external view of a conventional rotation / rotation (R / R) type X-ray CT apparatus.
FIG. 41 is an external view of a conventional Stationary / Stationary X-ray CT apparatus.
FIG. 42 is a configuration diagram of a conventional Stationary / Stationary X-ray CT apparatus.
FIG. 43 is a schematic view showing the internal structure of the gantry of FIG. 42.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... X-ray generation unit, 2 ... Vacuum pump, 3 ... X-ray detector unit, 4 ... Gantry, 5 ... Subject, 6 ... Table, 7 ... Table drive mechanism, 8 ... High voltage power supply, 9 ... Gate pulse generation unit Reference numeral 10: Anode cooling unit, 11: Anode cooling unit, 12: Image reconstruction unit, 13: Monitor, 14: Image data storage unit, 15: Cooling jacket, 16: Cooling jacket, 17: Anode, 18: Electron emitter 18 , 19 ... Cathode, 20 ... Vacuum chamber, 21 ... Insulating container, 22 ... Optical fiber cable for gate pulse signal transmission, 23 ... High voltage cable, 24 ... Circuit box, 24a ... Pulse amplification circuit, 24b ... Stabilizing resistor, 25 ... Insulation Liquid, 26: insulating liquid filling chamber, 27: collimator, 28: X-ray shielding plate, 29: high-voltage cable bushing terminal, 30: insulating support DESCRIPTION OF SYMBOLS 31 ... Filter, 32 ... Exhaust port, 33 ... Electron beam, 34 ... X-ray beam, 35 ... Access panel, 36 ... Electron emission part, 37 ... Insulating layer, 38 ... Gate electrode, 39 ... Electron beam emission hole, 40 ... Acceleration electrode, 41: Focusing electrode, 42: X-ray emission window, 43: Gantry drive mechanism, 44: Gandry drive mechanism controller, 45: Bias power supply, 46: Current detector, 47: Feedback control unit, 48: Protective cover 49, X-ray tube support (with water cooling jacket), 50, support plate, 51, rotary drive, 52, collimator for scattering removal, 53, high-voltage cable (hard wire).

Claims (32)

An X-ray generation unit that generates X-rays toward the subject in the imaging region; an X-ray detection unit that detects X-rays transmitted through the subject; and image data based on the output of the X-ray detection unit. An X-ray CT apparatus having an image reconstruction unit to reconstruct,
The X-ray generator,
A plurality of cathodes arranged in an annular shape around the imaging region,
An anode having an annular shape facing the cathode,
A plurality of targets arranged in a ring on the surface of the anode,
A plurality of electron-emitting portions formed on the surface of each of the cathodes,
A plurality of gate electrodes arranged in an annular shape at a predetermined distance from the plurality of cathodes,
An X-ray CT apparatus comprising: a hermetically sealed container containing the cathode, the anode, and the gate electrode. 2. The X-ray CT apparatus according to claim 1, wherein the gate electrode has a plurality of holes formed at positions corresponding to the electron emission units. The X-ray CT apparatus according to claim 1, wherein the X-ray generation unit has an insulating layer interposed between the cathode and the gate electrode. The X-ray CT apparatus according to claim 1, wherein the cathode has a concave surface. The X-ray CT apparatus according to claim 1, wherein the closed container has an openable / closable access panel. The X-ray CT apparatus according to claim 1, wherein the X-ray generation unit includes an electron beam focusing electrode disposed between the gate electrode and the anode. The X-ray generation unit has another cathode paired with each of the plurality of cathodes, and the paired cathode and the other cathode are arranged side by side along a center line of the imaging region. The X-ray CT apparatus according to claim 1, wherein The anode, the target, the gate electrode, the electron-emitting portion, and the cathode are arranged in order from a center along a radial direction of the ring, and transmit through the target and the anode among X-rays generated by the target. The X-ray CT apparatus according to claim 1, wherein the transmitted component irradiates the subject. The anode, the target, the gate electrode, the electron emitting portion, and the cathode are arranged in order along a center line of the imaging region, and a surface of the anode is arranged in a direction inclined with respect to the center line. 2. The X-ray CT apparatus according to claim 1, wherein a reflection component of the X-rays generated on the target, which is reflected on a surface of the target, irradiates the subject. 2. The X-ray CT apparatus according to claim 1, wherein the X-ray generation unit includes a collimator for limiting a divergence angle of the X-ray disposed in the closed container and near the anode. 3. An X-ray generation unit that generates X-rays toward the subject in the imaging region; an X-ray detection unit that detects X-rays transmitted through the subject; and image data based on the output of the X-ray detection unit. An X-ray CT apparatus having an image reconstruction unit to reconstruct,
The X-ray generation unit has a plurality of X-ray tubes arranged in an annular shape around the imaging region,
Each of the X-ray tubes,
A cathode,
An anode facing the cathode,
A target formed on the surface of the anode,
A plurality of electron-emitting portions formed on the surface of the cathode,
A gate electrode disposed at a predetermined distance from the electron emitting portion;
An X-ray CT apparatus comprising: a hermetically sealed container containing the cathode, the anode, and the gate electrode. The X-ray CT apparatus according to claim 11, wherein the X-ray generating unit has a swing mechanism for swinging the plurality of X-ray tubes around a center line of the imaging region. 13. The X-ray CT apparatus according to claim 12, wherein the X-ray generator has a plurality of hard wires for supplying a high voltage to the plurality of X-ray tubes. The X-ray CT apparatus according to claim 1, wherein the anode forms a part of the closed container and has a filter function for correcting an intensity distribution of the emitted X-ray beam. The X-ray generation unit includes a gate driving unit that applies a voltage to the gate electrode such that an electric field between the cathode and the gate electrode is higher than an electric field between the cathode and the anode. The X-ray CT apparatus according to claim 1. The X-ray CT apparatus according to claim 1, wherein the X-ray generation unit includes a gate driving unit that applies a negative bias voltage to the gate electrode. The X-ray generation unit includes: a gate driving unit that applies a voltage to the gate electrode; a current detector that detects an amount of electron current flowing into the gate electrode; and the gate driving unit based on the detected amount of electron current. The X-ray CT apparatus according to claim 1, further comprising a control unit configured to perform feedback control of the X-ray CT. The X-ray generation unit includes a current detector that detects an amount of an electron current flowing into the gate electrode, and the X-ray CT device outputs an output of the X-ray detection unit based on the detected amount of the electron current. The X-ray CT apparatus according to claim 1, further comprising a correction unit configured to perform correction. The X-ray generation unit includes a gate drive unit that applies a voltage pulse to the plurality of gate electrodes in order according to an arrangement order. The X-ray CT apparatus according to claim 1, wherein when the time is T, the time is shorter than T / N. The X-ray generation unit applies a voltage pulse to the plurality of gate electrodes in order according to an arrangement order, and at least two gate electrodes separated by a predetermined angle while applying a voltage pulse to an adjacent gate electrode. The X-ray CT apparatus according to claim 1, further comprising a gate driving unit that applies a voltage pulse to the X-ray CT apparatus. The X-ray generator according to claim 1, wherein the X-ray generator includes a gate driver configured to simultaneously apply a voltage pulse to an odd number of gate electrodes separated by a predetermined angle among the plurality of gate electrodes. CT device. The X-ray CT apparatus according to claim 1, wherein the X-ray detection unit includes a plurality of X-ray detection elements arranged in a ring around the imaging region. 24. The X-ray CT apparatus according to claim 23, further comprising a scattering removal collimator rotatably provided along the array of the plurality of X-ray detection elements. 12. The X-ray CT apparatus according to claim 1, further comprising a mechanism for moving the X-ray generation unit and the X-ray detector X-ray detection unit with respect to the subject. The apparatus further includes another X-ray generation unit and another X-ray detection unit having substantially the same configuration as the X-ray generation unit and the X-ray detection unit, respectively. The X-ray CT apparatus according to claim 1, wherein the X-ray detection unit is arranged at different positions along the center line of the imaging region with respect to the X-ray generation unit and the X-ray detection unit. . An X-ray generation unit that generates X-rays toward the subject in the imaging region; an X-ray detection unit that detects X-rays transmitted through the subject; and image data based on the output of the X-ray detection unit. An X-ray CT apparatus having an image reconstruction unit to reconstruct,
The X-ray generator,
A plurality of electron emitters arranged in an annular shape around the imaging region,
An anode having an annular shape facing the electron emitter;
A target formed on the surface of the anode,
An X-ray CT apparatus, comprising: a sealed container containing the electron emitter and the anode. A plurality of cathodes arranged,
An anode facing the plurality of cathodes,
A plurality of targets arranged on the surface of the anode,
A plurality of electron-emitting portions formed on the surface of each of the cathodes,
A plurality of gate electrodes arranged at a predetermined distance from the plurality of cathodes,
An X-ray generator comprising: a hermetically sealed container accommodating the cathode, the anode, the electron-emitting portion, and the gate electrode. Comprising a plurality of X-ray tubes arranged,
Each of the X-ray tubes,
A cathode,
An anode facing the cathode,
A target formed on the surface of the anode,
A plurality of electron-emitting portions formed on the surface of the cathode,
A gate electrode disposed at a predetermined distance from the cathode,
An X-ray generator comprising: a hermetically sealed container accommodating the cathode, the anode, the electron-emitting portion, and the gate electrode. A plurality of arrayed electron emitters,
An anode facing the plurality of electron emitters;
A plurality of targets arranged on the surface of the anode,
An X-ray generator comprising: a sealed container that houses the electron emitter and the anode. Assuming that the number of electron emitters is N and the scan time is T, voltage pulses having a duration shorter than T / N are arranged in the arrangement order for a plurality of electron emitters arranged in an annular shape around the imaging region. Apply in order according to
X-ray CT apparatus for detecting X-rays generated by application of the voltage pulse and transmitted through a subject in the imaging region at a position facing an electron emitter to which the voltage pulse is applied. Collection method. A plurality of electron emitters arranged in a ring around the imaging region are driven in order according to the arrangement order, and a voltage is applied to at least two discrete gate electrodes while applying a voltage pulse to an adjacent gate electrode. Apply a pulse,
A data acquisition method for an X-ray CT apparatus, wherein an X-ray generated by driving the electron emitter and transmitted through a subject in the imaging region is detected at a position facing the driven electron emitter. A plurality of electron emitters arranged in a ring around the imaging region are driven in order according to the arrangement order, and a predetermined number of electron emitters are separated by a predetermined angle at the same time as driving each electron emitter,
A data acquisition method for an X-ray CT apparatus, wherein an X-ray generated by driving the electron emitter and transmitted through a subject in the imaging region is detected at a position facing the driven electron emitter.

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