Technical Field
[0001] The present invention relates to an X-ray imaging apparatus including an X-ray source
that gives high voltage between a cathode and a target, as well as keeps a tube current
value at a set value by performing feedback control of grid voltage given to a grid
disposed between the cathode and the target, and to a consumption level estimation
method for the X-ray source.
Background Art
[0002] When imaging an image using an X-ray imaging apparatus, an X-ray source is given
tube voltage and tube current adapted to imaging of an object. In such an X-ray source,
feedback control is performed which, in a state where a predetermined tube voltage
is applied between a cathode and a target, adjusts grid voltage to be applied to a
grid electrode arranged in the vicinity of the cathode between the cathode and the
target so that a tube current value becomes constant, and thereby matches the tube
current value with a set value.
[0003] It is known that in such an X-ray source, the consumption level of the cathode can
be determined from the value of the grid voltage at the time of controlling the tube
current value to the set value (see Patent Literature 1). That is, it can be determined
that even when the potential difference between the grid and the cathode is large,
when the tube current is detectable, the consumption level is low, whereas when unless
the potential difference between the grid and the cathode is decreased, the tube current
is undetectable, the consumption of the cathode progresses.
Citation List
Patent Literatures
[0004] Patent Literature 1: International Publication No.
WO2003/092336
Summary of Invention
Technical Problem
[0005] In order to measure the consumption level of a cathode by the above-described conventional
method, grid voltage has to be measured. However, a grid electrode is arranged in
an X-ray tube, and therefore it is difficult to measure the voltage value of the grid
voltage from outside the X-ray tube. For this reason, the grid voltage has to be preliminarily
designed to be taken out via a control circuit or the like of an X-ray source. Accordingly,
an X-ray source incapable of measuring grid voltage from the outside has the problem
of being unable to measure the consumption level of a cathode.
[0006] The present invention has been made in order to solve the above-described problem,
and intends to provide an X-ray imaging apparatus and a consumption level estimation
method for an X-ray source, which are capable of estimating the consumption level
of an X-ray source without measuring grid voltage.
Solution to Problem
[0007] A first aspect of the present invention includes: an X-ray source that gives high
voltage between a cathode and a target, as well as keeps a tube current value at a
set value by performing feedback control of grid voltage given to a grid disposed
between the cathode and the target; a tube current value setting part that sets the
tube current value; and a time measurement part that measures the time when the tube
current value is set and the time when the tube current value reaches the set value.
[0008] A second aspect of the present invention includes a consumption level estimation
part that estimates the consumption level of the X-ray source on the basis of the
time until the tube current value reaches the set value after the tube current value
has been set.
[0009] A third aspect of the present invention includes an alarm display part that displays
an alarm when the time until the tube current value reaches the set value after the
tube current value has been set exceeds a preset set time.
[0010] A fourth aspect of the present invention includes a control unit that, when performing
aging on the X-ray source, performs measurement of the time until the tube current
value reaches the set value after the tube current value has been set.
[0011] A fifth aspect of the present invention is a consumption level estimation method
for an X-ray source that gives high voltage between a cathode and a target, as well
as keeps a tube current value at a set value by performing feedback control of grid
voltage given to a grid disposed between the cathode and the target, and the consumption
level estimation method estimates the consumption level of the X-ray source on the
basis of the time until the tube current value reaches the set value after the tube
current values has been set.
Advantageous Effects of Invention
[0012] According to the first and fifth aspects of the present invention, the consumption
level of the X-ray source can be estimated by using the time when the tube current
value is set and the time when the tube current value reaches the set value. For this
reason, the consumption level of the X-ray source can be estimated without measuring
the grid voltage.
[0013] According to the second aspect of the present invention, since the consumption level
of the X-ray source is estimated on the basis of the time until the tube current value
reaches the set value after the tube current value has been set, the consumption level
of the X-ray source can be estimated without measuring grid voltage.
[0014] According to the third aspect of the present invention, since the alarm display part
that displays the alarm when the time until the tube current value reaches the set
value after the tube current value has been set exceeds the preset set time is included,
the alarm can be given on the basis of the consumption level of the X-ray source without
measuring the grid voltage.
[0015] According to the fourth aspect of the present invention, since when performing the
aging, the measurement of the time until the tube current value reaches the set value
after the tube current value has been set is performed, the time until the tube current
value reaches the set value can be measured under the same conditions, thus making
it possible to more accurately estimate the consumption level of the X-ray source.
Brief Description of Drawings
[0016]
FIG. 1 is a schematic diagram illustrating the X-ray imaging apparatus according to
the present invention together with the main control system of the apparatus;
FIG. 2 is a schematic diagram of an X-ray source 41;
FIG. 3 is a functional block diagram of an X-ray control part 33 in a control unit
30;
FIG. 4 is a flowchart illustrating one embodiment of a consumption level estimating
operation for estimating the consumption level of a cathode 12 in the X-ray source
41;
FIG. 5 is a graph illustrating the time until a tube current value reaches a set value;
and
FIG. 6 is a graph illustrating the time until the tube current value reaches the set
value.
Description of Embodiments
[0017] In the following, an embodiment of the present invention will be described on the
basis of the drawings. FIG. 1 is a schematic diagram illustrating the X-ray imaging
apparatus according to the present invention together with the main control system
of the apparatus.
[0018] The X-ray imaging apparatus according to the present invention includes: an X-ray
source 41 that irradiates a work W as a test object with X-rays; an X-ray detector
42 that detects X-rays transmitting through the work W after the irradiation from
the X-ray source 41, such as a flat panel detector or an image intensifier (I. I.);
and a stage 43 that is disposed between the X-ray source 41 and the X-ray detector
42 and for placing the work W. The stage 43 is adapted to be horizontally movable
in two mutually orthogonal directions by action of a stage moving mechanism 44 provided
with an unillustrated motor. The X-ray source 41, the X-ray detector 42, the stage
43, and the stage moving mechanism 44 are disposed inside a casing 40 formed of an
X-ray shielding member. The stage moving mechanism 44 may be configured to be vertically
movable.
[0019] The X-ray imaging apparatus according to the present invention is provided with a
control unit 30 that includes: a CPU that performs logical operations as a processor;
a ROM in which an operation program necessary to control the apparatus is stored;
a RAM in which data and the like are temporarily stored at the time of control; and
the like, and controls the whole of the apparatus. The control unit 30 includes a
computer installed with software. Functions of respective parts included in the control
unit 30 are implemented by executing the software installed in the computer. The control
unit 30 is connected to: a display part 45 that displays an X-ray image detected by
the X-ray detector 42, or the like, such as a liquid crystal display panel; and an
operation part 46 including a mouse, a keyboard, and the like for performing various
types of operations.
[0020] Also, the control unit 30 includes: an image processing part 31 for image-processing
an X-ray image detected by the X-ray detector 42 to display the processed image on
the display part 45; a movement control part 32 for controlling the stage moving mechanism
44; an X-ray control part 33 for controlling the X-ray source 41; and an alarm display
part 34 for performing the below-described alarm display.
[0021] FIG. 2 is a schematic diagram of the X-ray source 41.
[0022] The X-ray source 41 is one provided with an indirectly-heated electron beam generating
part, and includes: a cathode 12; a cathode heater 11 for heating the cathode 12;
a grid electrode 13, and a target 14. An electron beam 101 generated from the cathode
12 heated by the cathode heater 11 is emitted from the cathode 12 toward the target
14 by the tube voltage between the cathode 12 and the target 14, collides with the
target 14 after passing through the gird electrode 13, and thereby generates X-rays
102. At this time, target current A generated by electrons reaching the target 14
flows toward the target 14, and cathode current (emission current) B generated by
electrons emitted from the cathode 12 flows from the cathode 12.
[0023] The cathode current B is detected by a cathode current detector 15 as tube current
flowing through the X-ray source 41. Note that the target current A and the cathode
current B usually match each other, and these currents correspond to the tube current.
For this reason, instead of detecting the cathode current B as the tube current by
the cathode current detector 15, a detector for the target current A may be disposed
to measure a tube current value.
[0024] FIG. 3 is a functional block diagram of the X-ray control part 33 in the control
unit 30.
[0025] The X-ray control part 33 includes: a tube current value setting part 51 for setting
the value of the tube current to be supplied to the X-ray source 41; a tube current
value measurement part 52 that measures a cathode current value as the tube current
value by the cathode current detector 15 illustrated in FIG. 2; a time measurement
part 53 that measures the time when the tube current value is set by the tube current
value setting part 51 and the time when the tube current value measured by the tube
current value measurement part 52 reaches a set value; and a consumption level estimation
part 54 that estimates the consumption level of the cathode 12 in the X-ray source
41 on the basis of the time until the tube current value reaches the set value after
the tube current value has been set.
[0026] A consumption level estimating operation for estimating the consumption level of
the cathode 12 in the X-ray source 14 of the X-ray imaging apparatus having the above-described
configuration will be described. FIG. 4 is a flowchart illustrating one embodiment
of the consumption level estimating operation for estimating the consumption level
of the cathode 12 in the X-ray source 41.
[0027] Note that in the following embodiment, at the time of aging (seasoning, warming up)
of the X-ray source 41, the consumption level of the cathode 12 in the X-ray source
41 is estimated. The aging of the X-ray source 41 is one that, for example, must be
performed at the start of a workday, and X-ray conditions at the time are constant,
such as the tube voltage and the tube current. For this reason, the consumption level
can be estimated under the same conditions, and the consumption level of the X-ray
source 41 can be more accurately estimated. Note that the consumption level of the
cathode 12 in the X-ray source 41 may be estimated at timing other than the aging
time.
[0028] When estimating the consumption level of the cathode 12 in the X-ray source 41, it
is determined whether or not to perform the aging (Step S1). Then, when performing
the aging, the tube current value is set (Step S2). The setting of the tube current
value is performed by the tube current value setting part 51 in the X-ray control
part 33. In addition, the setting of the tube current value may be performed manually
by an operator or performed by reading a preset value. Also, the time T1 when the
tube current value is actually set is stored (Step S3).
[0029] In this state, the tube current value measurement part 52 in the X-ray control part
33 measures the tube current value using the cathode current detector 15. Then, it
is waited until the actual tube current value reaches the set tube current value (Step
S4). When the measured tube current value reaches the set value, the corresponding
reaching time T2 is stored (Step S5).
[0030] After that, the time measurement part 53 in the X-ray control part 33 measures the
time (T2 - T1) until the actual tube current value reaches the set value after the
tube current value has been set. Then, the consumption level estimation part 54 in
the X-ray control part 33 estimates the consumption level of the cathode 12 in the
X-ray source 41 on the basis of whether or not the time (T2 - T1) is larger than a
preset set time T3.
[0031] FIGS. 5 and 6 are graphs illustrating the time until the tube current value reaches
the set value. In addition, in these graphs, the horizontal axis represents time (second).
Also, the vertical axis represents the tube current value with a target tube current
value normalized to 1.
[0032] When the consumption level of the cathode 12 in the X-ray source 41 is low, as illustrated
in FIG. 5, the time from the time when the tube current value was set, which corresponds
to 0 on the horizontal axis in FIG. 5, to the time when the tube current value reached
the set value is approximately 0.2 seconds. On the other hand, when the consumption
level of the cathode 12 in the X-ray source 41 is high, as illustrated in FIG. 6,
the time from the time when the tube current value was set, which corresponds to 0
on the horizontal axis in FIG. 6, to the time when the tube current value reached
the set value is approximately 4.5 seconds.
[0033] When the cathode 12 in the X-ray source 41 is consumed, feedback control performed
so that the tube current value matches the set value requires time until the tube
current value reaches the set value. For this reason, by measuring the time from the
time when the tube current value is set to the time when the tube current value reaches
the set value, the consumption level of the cathode 12 can be estimated.
[0034] Referring to FIG. 4 again, when the time (T2 - T1) until the actual tube current
value reaches the set value after the tube current value has been set exceeds the
preset set time T13 (Step S6), the consumption level estimation part 54 in the X-ray
control part 33 transmits an alarm signal to the control unit 30. Then, upon receipt
the alarm signal, the control unit 30 displays the alarm display on the display part
45 by action of the alarm display part illustrated in FIG. 1 (Step S7). Also, as necessary,
alarm display using sound or the like is also performed. In doing so, the consumption
of the cathode 12 can be preliminarily recognized.
[0035] In addition, in the above-described embodiment, as the X-ray source 41, the indirectly-heated
type provided with the cathode heater 11 for heating the cathode 12 is used. However,
the present invention may be applied to an X-ray source having a filament type cathode.
[0036] Also, the above-described embodiment employs a configuration in which, when the time
until the tube current value reaches the set value exceed the preset set time T3,
an alarm is displayed, but may employ a configuration in which the time when the tube
current value is set and the time when the tube current value reaches the set value
are displayed on the display part 45 or the like, and an operator checks them.
[0037] Further, the present invention may be adapted to preliminarily store the relationship
between the time (T2 - T1) until the actual tube current value reaches the set value
after the tube current value has been set and the consumption level (e.g., %) of the
cathode 12, and acquire and display a consumption level (%) corresponding to a measured
time (T2 - T1).
[0038] Further, in the above-described embodiment, the present invention is applied to the
X-ray imaging apparatus. However, the X-ray source 41 itself may be disposed with
the tube current value setting part that sets the tube current value and the time
measurement part that measures the time when the tube current value is set and the
time when the tube current value reaches the set value.
Reference Signs List
[0039]
11: Cathode heater
12: Cathode
13: Grid electrode
14: Target
15: Cathode current detector
30: Control unit
31: Image processing part
32: Movement control part
33: X-ray control part
34: Alarm display part
40: Casing
41: X-ray source
42: X-ray detector
43: Stage
44: Stage moving mechanism
45: Display part
46: Operation part
101: Electron beam
102: X-rays
A: Target current
B: Cathode current
W: Work
1. An X-ray imaging apparatus comprising:
an X-ray source that gives high voltage between a cathode and a target, as well as
keeps a tube current value at a set value by performing feedback control of grid voltage
given to a grid disposed between the cathode and the target;
a tube current value setting part that sets the tube current value; and
a time measurement part that measures a time when the tube current value is set and
a time when the tube current value reaches the set value.
2. The X-ray imaging apparatus according to claim 1, comprising
a consumption level estimation part that estimates a consumption level of the X-ray
source on a basis of a time until the tube current value reaches the set value after
the tube current value has been set.
3. The X-ray imaging apparatus according to claim 1, comprising
an alarm display part that displays an alarm when a time until the tube current value
reaches the set value after the tube current value has been set exceeds a preset set
time.
4. The X-ray imaging apparatus according to any of claims 1 to 3, comprising
a control unit that, when performing aging on the X-ray source, performs measurement
of the time until the tube current value reaches the set value after the tube current
value has been set.
5. A consumption level estimation method for an X-ray source that gives high voltage
between a cathode and a target, as well as keeps a tube current value at a set value
by performing feedback control of grid voltage given to a grid disposed between the
cathode and the target,
the consumption level estimation method estimating a consumption level of the X-ray
source on a basis of a time until the tube current value reaches the set value after
the tube current value has been set.