DESCRIPTION
TECHNICAL FIELD
[0001] The present invention relates to a radiation imaging
system for imaging a radiographic image of an object and a control
method thereof, and a radiation image detecting device used in
the radiation imaging system.
BACKGROUND ART
[0002] In a medical field, an X-ray imaging system using X-rays,
for example as a kind of radiation, is known. The X-ray imaging
system is constituted of an X-ray generating apparatus for
applying the X-rays to an object and an X-ray image detecting
device, which receives the X-rays passed through the object and
detects an X-ray image representing image information of the
object. In the X-ray image detecting device, an X-ray film, an
imaging plate (IP), or the like is conventionally used as a
detection panel. However, an X-ray image detecting device using
a flat panel detector (FPD) as the detection panel has become
widespread presently. The FPD has a matrix of pixels each for
accumulating signal charge in accordance with the amount of the
X-rays incident thereon. The FPD converts the accumulated signal
charge into a voltage signal on a pixel-by-pixel basis at its
signal processing circuit, and thereby detects the X-ray image
representing the image information of the object and outputs the
X-ray image as digital image data.
[0003] Some X-ray imaging systems have an automatic exposure
control (AEC) function in which a photo timer disposed in front
of an X-ray imaging apparatus measures a dose of the X-rays passed
through the object and issues a stop signal to the X-ray generating
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apparatus to stop an X-ray emission, as soon as the X-ray dose
has reached a predetermined value. There is also known an X-ray
image detecting device that carries out the AEC using a part of
pixels of the FPD or a dose detection sensor disposed in an image
capturing field of the FPD, instead of the photo timer (for
example, refer to the patent document 1). In performing the AEC
in the X-ray image detecting device having the integral dose
detection sensor, the X-ray image detecting device issues the stop
signal to the X-ray generating apparatus. The photo timer itself
is an X-ray absorber that absorbs the X-rays of the order of
approximately 5. Thus, using the photo timer in the AEC requires
an X-ray dose to be increased by an X-ray absorption amount by
the photo timer, and hence causes increase in radiation exposure
of the object. Using the X-ray sensor of the FPD, contrarily,
does not bring about such a problem.
[0004] In the X-ray imaging system using the X-ray image
detecting device having the FPD, communication of various types
of signals and data is established among the X-ray generating
apparatus, the X-ray image detecting device, and a console. The
console is a device for setting an imaging condition and
displaying the captured X-ray image. The console transmits to
the X-ray image detecting device a life check signal for checking
whether or not the X-ray image detecting device is activated, a
state monitoring signal for making an inquiry about a state such
as a temperature to the X-ray image detecting device, a
calibration command for commanding the X-ray image detecting
device to perform a calibration, and the like. The X-ray image
detecting device transmits to the console a response signal
responding to each of the above signals, an error signal for making
a notification of an error, captured X-ray image data, and the
like. The X-ray generating apparatus and the X-ray image
detecting device transmit and receive therebetween a
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synchronization signal for notifying the X-ray image detecting
device of a start of an X-ray emission from the X-ray generating
apparatus, the stop signal for making the X-ray generating
apparatus stop the X-ray emission, a response signal for making
a notification of the stop of X-ray emission, and the like.
[0005] As described above, the X-ray image detecting device
communicates the various types of signals with the console.
Furthermore, the synchronization signal is communicated before
the start of an X-ray emission between the X-ray image detecting
device and the X-ray generating apparatus, in order to synchronize
X-ray emission timing by the X-ray generating apparatus and image
accumulation timing by the X-ray image detecting device.
Additionally, in performing the AEC, the stop signal is
communicated between the X-ray image detecting device and the
X-ray generating apparatus.
[0006] In the communication among the essential devices of the
X-ray imaging system, e.g. between the X-ray image detecting
device and the console and between the X-ray image detecting
device and the X-ray generating apparatus, communications line
congestion and signal collision cause the occurrence of a
communication delay. The communications line congestion means
a case where a plurality of signals heading for the same direction
are transmitted at almost the same time through a communications
line. The signal collision means a collision of signals
transmitted in both directions of the communications line.
[0007] As measures against the communication delay in the
synchronization signal between the X-ray image detecting device
and the X-ray generating apparatus, according to an X-ray imaging
system of the patent document 2, for example, it is judged that
whether a communications method between the devices adopts
dedicated line communications, wireless communications, or
network communications. In the case of the wireless
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communications or the network communications in which the
communication delay tends to occur, FPD drive timing is changed
in anticipation of the communication delay.
[0008] To be more specific, according to the X-ray imaging system
of the patent document 2, the X-ray image detecting device issues
a preparation completion signal to the X-ray generating
apparatus, when being ready for receiving an X-ray emission. Upon
receiving the preparation completion signal, the X-ray generating
apparatus starts an X-ray emission. An emission time of the
X-rays is set in advance, and the X-ray generating apparatus stops
the X-ray emission after a lapse of the emission time. In the
X-ray image detecting device, the issue of the preparation
completion signal triggers a start of an image accumulation
operation. An image accumulation time is set longer than the
emission time such that the image accumulation operation has been
continued during the set emission time. In a case where the
communications method is the wireless communications or the
network communications excepting the dedicated line
communications, the communication of the preparation completion
signal is delayed more than that in the case of the dedicated line
communications, and thereby the timing of starting the X-ray
emission is delayed. The larger the communication delay, the more
the timing of starting the X-ray emission is delayed. At the
worst, such a situation may occur that the X-ray generating
apparatus keeps emitting the X-rays even after the X-ray image
detecting device completes the image accumulation operation. To
handle such a problem, in the X-ray imaging system of the patent
document 2, the FPD drive timing is varied in the communications
method without using the dedicated line to make the image
accumulation time longer than that of the dedicated line
communications.
[0009] Also, as measures against a communication delay between
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the X-ray image detecting device and the console, according to
an X-ray imaging system of the patent document 3, for example,
bidirectional communications between the X-ray image detecting
device and the console is withdrawn in order to prevent a delay
in communication of imaging order information due to the signal
collision, and using unidirectional communications prevents the
communication delay.
[0010] As described above, the patent document 2 describes the
measures against the communication delay in the synchronization
signal (preparation completion signal) at a time of starting
communication between the X-ray image detecting device and the
X-ray generating apparatus. The patent document 3 describes the
measures against the communication delay between the X-ray image
detecting device and the console.
PRIOR ART DOCUMENTS
Patent Documents
[0011] Patent Document 1: Japanese Patent Application
Publication No. 2004-251892
Patent Document 2 : Japanese Patent Application
Publication No. 2010-035778
Patent Document 3 : Japanese Patent Application
Publication No. 2010-057525
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0012] In carrying out the AEC, as described in the X-ray imaging
system of the patent document 1, it is required that the stop signal
is transmitted without a delay from the X-ray image detecting
device to the X-ray generating apparatus. This is because a delay
occurring in the stop signal prevents the X-ray emission from
stopping at an appropriate time, and therefore brings about
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increase in the radiation exposure of the object. The delay in
stopping the X-ray emission also causes application of the X-rays
beyond a target dose, and hence results in deterioration in the
quality of the X-ray image.
[0013] The methods described in the patent documents 2 and 3 have
no consideration for the AEC, and adopting the methods of the
patent document 2 and 3 does not become measures directed toward
the elimination of the communication delay in the stop signal.
The method of the patent document 2 relates to measures against
a delay in emission start timing due to a delay in synchronization
communication at a time of starting the emission. Elongating the
image accumulation time in anticipation of the communication
delay cannot solve the communication delay in the stop signal,
as a matter of course.
[0014] In the method of the patent document 3, the communication
method between the console and the X-ray image detecting device
is limited to the unidirectional communications from the console
to the X-ray image detecting device, for the purpose of preventing
the communication delay in transmitting the order information
from the console to the X-ray image detecting device. In
performing the AEC, the console sometimes mediates the
transmission of the stop signal from the X-ray image detecting
device to the X-ray generating apparatus. In such a case, the
stop signal has to be transmitted from the X-ray image detecting
device to the console. Furthermore, the bidirectional
communications of the various types of signals is required between
the X-ray image detecting device and the console, which includes
a transmission of the life check signal for checking an actuation
state of the X-ray image detecting device and a response thereof,
a transmission of the state monitoring signal for monitoring the
state such as the temperature of the X-ray image detecting device
and a response thereof, and the like, in addition to a transmission
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and a response of the order information and the stop signal. Thus,
adopting the unidirectional communications, as described in the
patent document 3, is unrealistic.
[0015] The present invention aims at providing a radiation
imaging system and a control method thereof, and a radiation image
detecting device that can prevent a delay in communication of the
stop signal for stopping an X-ray emission.
Means for Solving the Problems
[0016] A radiation imaging system according to the present
invention, having a radiation image detecting device and a console
for controlling the radiation image detecting device, includes
an image detector, a dosimeter, a stop signal issuing unit, a first
communicator, and a first controller. The image detector has an
image capturing field having an array of a plurality of pixels
for accumulating an electric signal in accordance with an incident
amount of radiation, and detects a radiographic image by receiving
the radiation emitted from a radiation generating apparatus. The
dosimeter measures a dose of the radiation emitted from the
radiation generating apparatus and passed through an object
during an accumulation operation of the image detector. The stop
signal issuing unit issues a stop signal to make the radiation
generating apparatus stop an emission of the radiation, upon the
dose of the radiation measured by the dosimeter reaching a target
dose. The first communicator performs communication processing
of the stop signal for transmitting the stop signal to the
radiation generating apparatus during the accumulation
operation, and performs communication processing of a signal
other than the stop signal. The first controller controls the
first communicator. The console includes a second communicator
and a second controller. The second communicator performs
communication processing of a control signal for transmitting the
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control signal to the first communicator. The second controller
controls the second communicator. During the accumulation
operation, communication regulation for regulating
communication of a signal other than the stop signal between the
first communicator and the second communicator is performed by
controlling at least one of the first controller and the second
controller, at least until the first communicator completes
transmission of the stop signal.
[0017] The signal to which the communication regulation is
applied preferably includes the control signal. The control
signal includes at least one of a life check signal for checking
an actuation state of the radiation image detecting device, a
state monitoring signal for checking a state including a
temperature of the radiation image detecting device, and a
calibration command for commanding the radiation image detecting
device to execute a calibration. The stop signal is transmitted
to the radiation generating apparatus through the console.
[0018] The communication regulation preferably includes
processing in which at least one of the first communicator and
the second communicator stops all or a part of communication of
the signals other than the stop signal. For example, the second
controller of the console stops transmitting the control signal
from the second communicator to the first communicator to carry
out the communication regulation. For example, the first
controller of the radiation image detecting device stops
communication of the signal other than the stop signal from the
first communicator to carry out the communication regulation.
[0019] The communication regulation carried out by at least one
of the first controller and the second controller is lifted after
the first communicator completes transmission of the stop signal.
The communication regulation is preferably lifted after receiving
a response signal for indicating a stop of the emission of the
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radiation from the radiation source, after completing the
accumulation operation and furthermore completing a readout
operation for reading out the radiographic image from the image
detector, or after the dosimeter has detected an actual stop of
the emission of the radiation.
[0020] The radiation image detecting device has one the first
communicator, for example, that is shared between communication
of the stop signal and communication of the signal other than the
stop signal. Only one communication port is connected to the
first communicator, and the communication port is shared between
communication of the stop signal and communication of the signal
other than the stop signal. Otherwise, a plurality of
communication ports are connected to the first communicator, and
one of the communication ports is dedicated to transmission of
the stop signal.
[0021] In the radiation image detecting device, a dose detection
sensor is preferably provided in the image capturing field of the
image detector to output a dose detection signal to the dosimeter.
The dose detection sensor preferably uses a part of the pixels.
[0022] The radiation image detecting device is preferably an
electronic cassette having the image detector contained in a
portable housing.
[0023] A control method of a radiation imaging system according
to the present invention has a radiation image detecting device
and a console for controlling the radiation image detecting
device. The control method includes a step of receiving radiation
emitted from a radiation generating apparatus, and accumulating
an electric signal in a plurality of pixels arranged in an image
capturing field in accordance with an incident amount of the
radiation to detect a radiographic image in the radiation image
detecting device; a step of measuring a dose of the radiation
emitted from the radiation generating apparatus and passed
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through an object during the accumulation step in the radiation
image detecting device; a step of issuing a stop signal to be
transmitted to the radiation generating apparatus to make the
radiation generating apparatus stop an emission of the radiation,
upon the measured dose reaching a target dose, in the radiation
image detecting device; and a step of regulating communication
of a signal other than the stop signal between the radiation image
detecting device and the console in the accumulation step, at
least until the radiation image detecting device completes
transmission of the stop signal.
[0024] A radiation image detecting device according to the
present invention includes an image detector, a dosimeter, a stop
signal issuing unit, a communicator, and a controller. The image
detector has an image capturing field having an array of a
plurality of pixels for accumulating an electric signal in
accordance with an incident amount of radiation, and detects a
radiographic image by receiving the radiation emitted from a
radiation generating apparatus. The dosimeter measures a dose
of the radiation emitted from the radiation generating apparatus
and passed through an object during an accumulation operation of
the image detector. The stop signal issuing unit issues a stop
signal to make the radiation generating apparatus stop an emission
of the radiation, upon the dose of the radiation measured by the
dosimeter reaching a target dose. The communicator performs
communication processing of the stop signal for transmitting the
stop signal to the radiation generating apparatus during the
accumulation operation, and performs communication processing of
a signal other than the stop signal. The controller regulates
communication of the signal other than the stop signal by the
communicator during the accumulation operation, at least until
the communicator completes transmission of the stop signal.
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Effect of the Invention
[0025] According to the present invention, the communication of
the signals other than the stop signal is regulated, while the
image detector performs the accumulation operation, at least
until transmission of the stop signal is completed. Thus, it is
possible to provide a radiation imaging system and a control
method thereof, and a radiation image detecting device that can
prevent a delay of the stop signal. Accordingly, it is possible
to stop the emission of the radiation from the radiation source
at appropriate timing, and hence reduce unnecessary radiation
exposure of the object. Furthermore, stopping the emission at
appropriate timing prevents application of an excessive dose
beyond a target dose, and results in preventing degradation in
the quality of the radiographic image.
BRIEF DESCRIPTION OF DRAWINGS
[0026] Fig. 1 is an explanatory view showing the schematic
structure of an X-ray imaging system;
Fig. 2 is an external perspective view showing the structure
of an electronic cassette;
Fig. 3 is a block diagram showing the electrical structure
of a console;
Fig. 4 is an explanatory view showing the electrical
structure of the electronic cassette;
Fig. 5 is an explanatory view showing an X-ray dose and the
details of FPD control based on the X-ray dose;
Fig. 6 is a flowchart of imaging processing of the X-ray
imaging system; and
Fig. 7 is a block diagram showing the electrical structure
of an electronic cassette having a plurality of communication
ports.
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DESCRIPTION OF INVENTION
[0027] In Fig. 1, an X-ray imaging system 10 is constituted of
an X-ray generating apparatus 11, an X-ray imaging apparatus 12,
and a console 13. The X-ray generating apparatus 11 includes an
X-ray source 14, a source control unit 15 for controlling the X-ray
source 14, and an emission switch 16. The X-ray source 14 has
an X-ray tube 14a for radiating X-rays and an irradiation field
limiter (collimator) 14b for limiting an irradiation field of the
X-rays radiating from the X-ray tube 14a.
[0028] The X-ray tube 14a has a cathode composed of a filament
for emitting thermoelectrons, and an anode (target) that radiates
the X-rays by collision of the thermoelectrons emitted from the
cathode. The irradiation field limiter is composed of, for
example, four lead plates for blocking the X-rays. The four lead
plates are disposed in each side of a rectangle so as to form a
rectangular irradiation opening in a middle to pass the X-rays
therethrough. Shifting the position of the lead plates varies
the size of the irradiation opening to limit the irradiation
field.
[0029] The source control unit 15 is provided with a high voltage
generator, a controller, and a cable-type communicator. The high
voltage generator supplies the X-ray source 14 with a high tube
voltage. The controller controls the tube voltage for
determining the radiation quality (energy spectrum) of the X-rays
emitted from the X-ray source 14, a tube current for determining
an emission amount per unit of time, and an emission time of the
X-rays. The cable-type communicator communicates with the
console 13. The high voltage generator generates the high tube
voltage by multiplying an input voltage by a transformer, and
supplies drive power to the X-ray source 14 through a high voltage
cable. An imaging condition including the tube voltage, the tube
current, and the emission time is manually set by an operator such
13
as a radiological technician through an operation panel of the
source control unit 15. Note that, the imaging condition of the
source control unit 15 may be set in the console 13.
[0030] The emission switch 16, which is to be operated by the
radiological technician, is connected to the source control unit
15 through a signal cable. The emission switch 16 is a two-step
press switch. Upon a first-step press of the emission switch 16,
a warm-up start signal is issued to start warming up the X-ray
source 14. Upon a second-step press, an emission start signal
is issued to make the X-ray source 14 start emitting the X-rays.
These signals are inputted to the source control unit 15 through
the signal cable.
[0031] Upon inputting the warm-up start signal from the emission
switch 16, the source control unit 15 starts warming up the X-ray
source 14 and also communicates a synchronization signal to the
X-ray imaging apparatus 12 to synchronize emission start timing
of the X-rays. To be more specific, the source control unit 15
transmits to the X-ray imaging apparatus 12 an emission start
request signal that asks for permission to start an X-ray
emission, and receives an emission permission signal, being a
response signal of the emission start request signal, from the
X-ray imaging apparatus 12.
[0032] Upon receiving the emission permission signal from the
X-ray imaging apparatus 12 and the emission start signal from the
emission switch 16, the source control unit 15 issues a start
command to the X-ray source 14 and starts supplying electric power
to the X-ray source 14. Thus, the X-ray source 14 starts an X-ray
emission. Concurrently with starting the electric power supply
to the X-ray source 14, the source control unit 15 transmits the
synchronization signal indicating the start of the X-ray emission
to the X-ray imaging apparatus 12, and furthermore actuates an
internal timer to start measuring an X-ray emission time.
14
[0033] The X-ray imaging system 10 can carry out AEC in
radiography. In performing the AEC, the X-ray imaging apparatus
12 transmits a stop signal to the source control unit 15. Upon
receiving the stop signal from the X-ray imaging apparatus 12,
the source control unit 15 issues a stop command to the X-ray source
14 and stops the electric power supply to the X-ray source 14.
The X-ray source 14 stops the X-ray emission upon receiving the
stop command.
[0034] The X-ray imaging system 10 can carry out radiography
based on the emission time set in the imaging condition, without
using the AEC. In this case, the emission time is set in the source
control unit 15. The source control unit 15 monitors a lapse of
emission time using the timer, and stops the X-ray emission at
the instant when the set emission time has elapsed. Note that,
even in the case of performing the AEC in radiography, the source
control unit 15 monitors a lapse of emission time using the timer.
The source control unit 15 stops the X-ray emission at the instant
of exceeding a maximum emission time adhering to safety
restrictions, even if no stop signal has been received.
[0035] The X-ray imaging apparatus 12 is constituted of an
electronic cassette 19, which corresponds to a radiation image
detecting device of the present invention, and an imaging stand
20. As shown in Fig. 2, the electronic cassette 19 includes an
FPD 23 and a portable housing 24 for containing the FPD 23. The
electronic cassette 19 receives the X-rays that are emitted from
the X-ray source 14 and passed through an object H, and detects
an X-ray image of the object H. The housing 24 of the electronic
cassette is in an approximately rectangular and flat shape, and
of approximately the same size in plane as the size of a film
cassette and an IP cassette.
[0036] The housing 24 has a multi-terminal 25 at its side surface,
into which a communication terminal (communication port) and a
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power supply terminal are integrated. A multi-connector 26 into
which a communication connector and a power supply connector are
integrated is fitted into the multi-terminal 25. A multi-cable
27 into which a communication cable and a power supply cable are
integrated is connected to the multi-connector 26 at one end. The
other end of the multi-cable 27 is provided with a communication
connector to be connected to a communication port of the console
13 and a power supply connector to be connected to a power supply
for the electronic cassette 19. Thus, the electronic cassette
19 communicates with the console 13 through connection, while
being supplied with power from the outside.
[0037] The imaging stand 20 has a slot into which the electronic
cassette 19 is detachably loaded. The imaging stand 20 holds the
electronic cassette 19 in such a position that an incident surface
on which the X-rays are incident is opposed to the X-ray source
14. Since the housing of the electronic cassette 19 is of
approximately the same size as the size of the film cassette and
the IP cassette, the electronic cassette 19 is loadable in an
imaging stand designed for the film cassette and the IP cassette.
Note that, an upright imaging stand for imaging the object H in
a standing position is illustrated as the imaging stand 20, but
an imaging bed for imaging the object H in a lying position may
be used instead.
[0038] As shown in Fig.3, the console 13 is composed of a display
29 for displaying an imaging order, the X-ray image, and the like,
an input device 30 used for inputting the imaging condition and
the like, a CPU 31 for controlling the entire console 13, a memory
32 used in a processing operation of the CPU 31, a storage device
33 for storing image data of the X-ray image, and a cable-type
communicator 34 communicatably connected to the source control
unit 15 and the electronic cassette 19. These parts are connected
through a data bus 35.
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[0039] The console 13 controls the electronic cassette 19 by
appropriately communicating a control signal through the
communicator 34 with the electronic cassette 19. More
specifically, the console 13 periodically transmits to the
electronic cassette 19 the control signal, which includes a life
check signal for checking whether or not the electronic cassette
19 is activated, a state monitoring signal for making an inquiry
about a state such as a temperature of the electronic cassette
19, and the like. The electronic cassette 19 transmits a response
signal to the console 13 in response to the control signal
transmitted from the console 13. The console 13 executes control
in accordance with the contents of the response signal.
Furthermore, the control signal to be transmitted from the console
13 to the electronic cassette 19 also includes a calibration
command. The console 13 transmits the calibration command to the
electronic cassette 19 in predetermined timing, to make the
electronic cassette 19 perform a calibration.
[0040] Contrarily to the above control signal, an error
notification is another control signal to be transmitted from the
electronic cassette 19 to the console 13. The error notification
is transmitted to the console 13 in case of an error arising in
the electronic cassette 19. Upon receiving the error
notification from the electronic cassette 19, the console 13
executes control depending on the substance of the error. As
described above, out of the control signal to be communicated
between the electronic cassette 19 and the console 13, the control
signal to be transmitted from the console 13 to the electronic
cassette 19 includes the life check signal, the state monitoring
signal, the calibration command, and the like, and the control
signal to be transmitted from the electronic cassette 19 to the
console 13 includes the error notification. The CPU 31
corresponds to a second controller described in claims, and the
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communicator 34 corresponds to a second communicator of the
claims.
[0041] The console 13 transmits the imaging condition to the
electronic cassette 19 to set up a signal processing condition
of the FPD 23. The console 13 also performs synchronization
control to synchronize the start and stop timing of an X-ray
emission by the X-ray generating apparatus 11 and accumulation
and readout operations of the FPD 23, by mediating the
transmission and reception of the synchronization signal upon
starting the X-ray emission and the stop signal for stopping the
X-ray emission between the source control unit 15 and the
electronic cassette 19. Furthermore, the console 13 receives
image data outputted from the electronic cassette 19 and applies
various types of image processing such as gamma correction and
frequency processing to the image data. The X-ray image after
being subjected to the image processing is displayed on the
display 29 of the console 13. The data of the X-ray image is stored
to the storage device 33 of the console 13, or another data storage
device such as an image storage server connected to the console
13 through a network.
[0042] The console 13 receives an input of an examination order
including information about sex and age of a patient, a body part
to be imaged, and an examination purpose, and displays the
examination order on the display 29. The examination order is
inputted from an external system e.g. HIS (hospital information
system) or RIS (radiography information system) that manages
patient data and examination data related to radiography, or
inputted manually by the operator such as the radiological
technician. The operator confirms the contents of the
examination order on the display 29, and inputs the imaging
condition corresponding to the contents through the input device
of the console 13.
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[0043] In Fig. 4, the FPD 23 has a TFT active matrix substrate.
The FPD 23 is provided with a detection panel having an image
capturing field 38 in which a plurality of pixels 37 each for
accumulating signal charge in accordance with an X-ray amount
incident thereon are arranged in the substrate, a gate driver 39
for controlling readout of the signal charge by driving the pixels
37, a signal processing circuit 40 for converting the signal
charge read out from the pixels 37 into digital data and outputting
the digital data, and a controller 41 for controlling the
operation of the FPD 23 by controlling the gate driver 39 and the
signal processing circuit 40. The plurality of pixels 37 are
arranged into a two-dimensional matrix with n rows (x direction)
and m columns (y direction) at a predetermined pitch. “n” and
“m” are integers of two or more. The pixel number of the FPD 23
is, for example, approximately 2000 by 2000.
[0044] A communicator 42 that performs communication processing
with the communicator 34 of the console 13 through a cable, and
a dosimeter 43 that measures an X-ray dose applied to the
electronic cassette 19 through the object H are connected to the
controller 41. To the communicator 42, the multi-terminal 25
described above is connected. The communicator 42, for example,
controls transmission of a signal transmitted or received through
the multi-terminal 25 according to a communication protocol. To
be more specific, the communicator 42 adds transmission control
information (for example, a transmission destination, an IP
address of a sender, and the like) determined in the protocol to
a transmission signal received from the controller 41, and on the
contrary, removes the transmission control information from a
reception signal and passes the signal after the removal to the
controller 41. In addition, in receiving a signal, the
communicator 42 transmits a reception confirmation signal to a
sender. The controller 41 corresponds to a first controller or
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a controller described in the claims, and the communicator 42
corresponds to a first communicator or a communicator of the
claims.
[0045] The FPD 23 is of an indirect conversion type, having a
scintillator (phosphor) for converting the X-rays into visible
light. The pixels 37 perform photoelectric conversion of the
visible light converted by the scintillator. The scintillator
is opposed to the entire image capturing field 38 having an array
of the pixels 37. The scintillator is made of CsI (cesium iodide),
GOS (gadolinium oxysulfide), or the like. Note that, a direct
conversion type FPD, which uses a conversion layer (amorphous
selenium or the like) for directly converting the X-rays into the
electric charge, may be used instead.
[0046] The pixel 37 is composed of a photodiode 45 being a
photoelectric conversion element that produces the electric
charge (electron and hole pairs) upon entry of the visible light,
a capacitor (not shown) for accumulating the electric charge
produced by the photodiode 45, and a thin film transistor (TFT)
46 functioning as a switching element.
[0047] The photodiode 45 has a semiconducting layer (of a PIN
type, for example) of a-Si (amorphous silicon) or the like. An
upper electrode and a lower electrode are disposed on the top and
bottom of the semiconducting layer, respectively. The lower
electrode of the photodiode 45 is connected to the TFT 46. The
upper electrode of the photodiode 45 is connected to a bias line
(not shown).
[0048] Through the bias line, a bias voltage is applied to the
upper electrode of the photodiode 45 of every pixel 37 in the image
capturing field 38. Since the application of the bias voltage
produces an electric field in the semiconducting layer of the
photodiode 45, the electric charge (electron and hole pairs)
produced in the semiconducting layer by the photoelectric
20
conversion is attracted to the upper and lower electrodes, one
of which has a positive polarity and the other of which has a
negative polarity. Thereby, the electric charge is accumulated
in the capacitor.
[0049] A gate electrode of the TFT 46 is connected to a scan line
48. A source electrode of the TFT 46 is connected to a signal
line 49. A drain electrode of the TFT 46 is connected to the
photodiode 45. The scan lines 48 and the signal lines 49 are
routed into a lattice. The number of the scan lines 48 coincides
with the number of the rows (n rows) of the pixels 37 in the image
capturing field 38. Each scan line 48 is common wiring connected
to a plurality of pixels 37 of one row. The number of the signal
lines 49 coincides with the number of the columns (m columns) of
the pixels 37. Each signal line 49 is common wiring connected
to a plurality of pixels 37 of one column. The scan lines 48 are
connected to the gate driver 39, and the signal lines 49 are
connected to the signal processing circuit 40.
[0050] The gate driver 39 drives the TFTs 46 to carry out the
accumulation operation for accumulating the signal charge in the
pixels 37 in accordance with the amount of the X-rays incident
thereon, a readout operation for reading out the signal charge
from the pixels 37, and a reset operation for resetting the
electric charge accumulated in the pixels 37. The controller 41
controls the start timing of each of the above operations carried
out by the gate driver 39.
[0051] In the accumulation operation, the signal charge is
accumulated in the pixels 37 while the TFTs 46 are turned off.
In the readout operation, the gate driver 39 sequentially issues
gate pulses G1 to Gn each of which drives the TFTs 46 of the same
row at a time. Thereby, the scan lines 48 are activated one by
one to turn on the TFTs 46 connected to the activated scan line
48 on a row-by-row basis.
21
[0052] Upon turning on the TFTs 46 of one row, the signal charge
accumulated in each of the pixels 37 of one row is inputted to
the signal processing circuit 40 through each signal line 49. In
the signal processing circuit 40, the signal charge of one row
is converted into voltages and outputted. Thus, the output
voltages corresponding to the signal charge are read out as
voltage signals D1 to Dm. The analog voltage signals D1 to Dm
are converted into digital data, and image data that is composed
of digital pixel values representing density in each of the pixels
of one row is produced. The image data is outputted to a memory
51 contained in the electronic cassette 19.
[0053] A dark current occurs in the semiconducting layer of the
photodiode 45 irrespective of the presence or absence of entry
of the X-rays. Due to the application of the bias voltage, dark
charge according to the dark current is accumulated in the
capacitor. The dark charge becomes noise of the image data, and
therefore the reset operation is carried out to remove the dark
charge. The reset operation is an operation to discharge the dark
charge occurring in the pixels 37 from the pixels 37 through the
signal lines 49.
[0054] The reset operation adopts a sequential reset method, for
example, by which the pixels 37 are reset on a row-by-row basis.
In the sequential reset method, as with the readout operation of
the signal charge, the gate driver 39 sequentially issues the gate
pulses G1 to Gn to the scan lines 48 to turn on the TFTs 46 of
the pixels 37 on a row-by-row basis. While the TFT 46 is turned
on, the dark charge is inputted from the pixel 37 through the signal
line 49 into the signal processing circuit 40.
[0055] In the reset operation, in contrast to the readout
operation, the readout of the output voltage in accordance with
the dark charge is not carried out. In the reset operation, the
controller 41 outputs reset pulses RST to the signal processing
22
circuit 40 in synchronization with the issue of each of the gate
pulses G1 to Gn. In the signal processing circuit 40, an input
of the reset pulse RST turns on reset switches 53a of integration
amplifiers 53 to be described later on, and hence the inputted
dark charge is reset.
[0056] Instead of the sequential reset method, a parallel reset
method or all pixels reset method may be used. In the parallel
reset method, a plurality of rows of pixels are grouped together,
and sequential reset is carried out in each group, so as to
concurrently discharge the dark charge from the rows of the number
of the groups. In the all pixels reset method, the gate pulse
is inputted to every row to discharge the dark charge from every
pixel at a time. The parallel reset method and the all pixels
reset method allow speeding up the reset operation.
[0057] The signal processing circuit 40 includes the integration
amplifiers 53, a MUX 54, an A/D converter 55, and the like. The
integration amplifier 53 is connected to each signal line 49 on
a one-by-one basis. The integration amplifier 53 is composed of
an operational amplifier and a capacitor connected between input
and output terminals of the operational amplifier. The signal
line 49 is connected to one of the input terminals of the
operational amplifier. The other input terminal (not shown) of
the operational amplifier is connected to a ground (GND). The
integration amplifier 53 converts by integration the signal
charge inputted from the signal line 49 into each of the voltage
signals D1 to Dm, and outputs the voltage signals D1 to Dm.
[0058] The output terminal of the integration amplifier 53 of
every column is connected to the MUX 54 through a multiplier (not
shown) for multiplying each of the voltage signals D1 to Dm and
a sample holder (not shown) for holding each of the voltage signals
D1 to Dm. The MUX 54 selects one of the plurality of integration
amplifiers 53 connected in parallel, and inputs the voltage
23
signals D1 to Dm outputted from the selected integration
amplifiers 53 in series to the A/D converter 55.
[0059] The A/D converter 55 converts the inputted analog voltage
signals D1 to Dm of one row into digital pixel values in accordance
with individual signal levels, and outputs the pixel values to
the memory 51. The memory 51 stores the pixel values of one row
as image data that represents one row of the X-ray image, with
being associated with the coordinates of the individual pixels
37 in the image capturing field 38.
[0060] After the voltage signals D1 to Dm of one row are outputted
from the integration amplifiers 53, the controller 41 outputs the
reset pulse RST to the integration amplifiers 53 to turn on the
reset switches 53a of the integration amplifiers 53. Thus, the
signal charge of one row accumulated in the integration amplifiers
53 is reset. Upon resetting the integration amplifiers 53, the
gate driver 39 outputs the gate pulse of the next row to start
reading out the signal charge from the pixels 37 of the next row.
By sequential repetition of this operation, the signal charge is
read out from the pixels 37 of every row.
[0061] After the completion of the readout from every row, the
image data representing the X-ray image of one frame is stored
in the memory 51. The image data stored in the memory 51 is
subjected to image correction processing that includes an offset
correction for removing an offset component, being fixed pattern
noise caused by individual difference or environment of the FPD
23, and a sensitivity correction for correcting variations in
sensitivity of individual photodiodes 45, variations in output
properties of the signal processing circuit 40, and the like. The
image data is read out from the memory 51, and transmitted to the
console 13 through the communicator 42. Thereby, the X-ray image
of the object H is detected.
[0062] The FPD 23 has the function of detecting the amount of
24
the X-rays applied thereto. As shown in a hatch pattern in Fig.
4, the FPD 23 has short pixels 58 in addition to the pixels 37
in the image capturing field 38. The short pixel 58 functions
as a dose detection sensor for detecting the applied amount of
the X-rays. The short pixel 58 always shorts out to the signal
line 49, while the pixel 37 and the signal line 49 are electrically
connected and disconnected by turning on and off the TFT 46.
[0063] The structure of the short pixel 58 is similar to that
of the pixel 37. The short pixel 58 has the photodiode 45 and
the TFT 46, and the photodiode 45 produces the signal charge in
accordance with the amount of the X-rays incident thereon. The
structural difference between the short pixel 58 and the pixel
37 is that the short pixel 38 has the source and the drain of the
TFT 46 that are short out by wiring to lose the switching function
of the TFT 46. Thus, the signal charge produced in the photodiode
45 of the short pixel 58 always flows into the signal line 49,
and is inputted to the integration amplifier 53. Note that,
instead of wiring the source and the drain of the TFT 46 of the
short pixel 58, the photodiode 45 of the short pixel 58 may be
directly connected to the signal line 49 without providing the
TFT 46 itself.
[0064] The controller 41 makes the MUX 54 select the integration
amplifiers 53 to which the signal charge from the short pixels
58 is inputted, to read out voltage signals (dose detection
signals) of the integration amplifiers 53. The dose detection
signals from the integration amplifiers 53 are inputted to the
A/D converter 55 and converted into digital values. The digital
values are outputted to the memory 51. The digital values are
stored to the memory 51 with being associated with the coordinate
information of each short pixel 58 in the image capturing field
38. The FPD 23 repeats a plurality of number of such dose
detecting operations at a predetermine sampling rate during the
25
X-ray emission.
[0065] During the X-ray emission, the dosimeter 43 reads out the
dose detection signals from the memory 51. The dosimeter 43
integrates the read dose detection signals to measure an
accumulative dose of the X-rays that are applied to the FPD 23
through the object H.
[0066] Fig. 5 is a graph that shows an application profile
representing variation with time in the amount of the X-rays
applied to the FPD 23 per unit of time and the progression of an
operational state of the FPD 23 in one imaging operation. In the
application profile, the applied amount of the X-rays takes an
approximately trapezoidal shape in the graph in which a horizontal
axis represents time and a vertical axis represents the applied
amount of the X-rays. When the X-ray source 14 starts an X-ray
emission upon receiving the start command, the applied amount of
the X-rays is gradually increased to a peak value, which is
determined in accordance with the tube current set as the imaging
condition, and is kept in an approximately steady state in the
vicinity of the peak value until receiving the stop command.
Then, when the X-ray source 14 stops the X-ray emission upon
receiving the stop command, the applied amount of the X-rays is
gradually decreases to “0”, and the X-ray emission is completely
stopped. An area of the application profile represents the
accumulative dose.
[0067] The controller 41 sets a target dose to be applied based
on the imaging condition including the sex and age of the patient,
the body part to be imaged, the examination purpose, and the like
inputted from the console 13. For example, in Fig. 5, a hatched
area is set as a target dose TD. In response to an exposure
preparation command inputted from the console 13, the controller
41 shifts the FPD 23 to a standby state. In the standby state,
the controller 41 makes the FPD 23 execute the reset operation.
26
As soon as the synchronization signal is inputted from the source
control unit 15 at the time of starting an X-ray emission, the
controller 41 turns off the TFTs 46 of the pixels 37 and shifts
the FPD 23 from the standby state to the accumulation operation.
Since the TFTs 46 are turned off, the signal charge is accumulated
in the pixels 37 in accordance with the X-ray dose applied thereto.
[0068] The short pixels 58 are always short out to the signal
lines 49 even though the TFTs 46 of the pixels 37 are turned off,
so the dosimeter 43 can measure the accumulative dose of the X-rays
applied to the FPD 23 during the X-ray emission based on output
of the short pixels 58 flowing into the signal lines 49. The
dosimeter 43 integrates the dose detection signal of the short
pixel 58 read from the memory 51 to measure the accumulative dose
of the X-rays, and inputs the measured accumulative dose to the
controller 41. The controller 41 compares the accumulative dose
with the target dose. As soon as the accumulative dose of the
X-rays has reached the target dose TD, the controller 41 issues
the stop signal. The controller 41 inputs the stop signal to the
communicator 42, and the communicator 42 transmits the stop signal
to the source control unit 15. Note that, the controller 41
functions as a stop signal issuing unit in this embodiment, but
the dosimeter 43 may function as the stop signal issuing unit,
instead. In this case, the dosimeter 43 compares the measured
accumulative dose with the target dose TD, and issues the stop
signal as soon as the accumulative dose has reached the target
dose TD.
[0069] Upon receiving the stop signal, the source control unit
15 transmits the stop signal to the X-ray source 14 to stop the
X-ray emission. The controller 41 ends the accumulation
operation of the FPD 23 and starts the readout operation, at the
instant when the response signal indicating the stop of the X-ray
emission is sent back from the source control unit 15. Note that,
27
for the purpose of preventing the occurrence of artifact caused
by the X-ray emission during the readout operation of the FPD 23,
the response signal is transmitted after the stop of the X-ray
emission.
[0070] As described above, the electronic cassette 19 and the
console 13 are connected through one communication line.
Accordingly, if the electronic cassette 19 transmits the stop
signal to the source control unit 15 in the course of communicating
the control signal between the electronic cassette 19 and the
console 13, the transmission of the stop signal may be delayed
due to the congestion or collision of communication.
[0071] Especially, if the reception timing of the control signal
(the life check signal, the state monitoring signal, the
calibration command, or the like) by the electronic cassette 19
from the console 13 overlaps the transmission timing of the stop
signal from the electronic cassette 19 to the console 13, the
congestion or collision of communication tends to occur. Also,
the overlap of transmission and reception processing of a
plurality of signals applies a heavy load of communication
processing on the communicator 42. Furthermore, the electronic
cassette 19 has to transmit the response signal to the console
13 in response to the control signal from the console 13. Thus,
since the transmission timing of the response signal and the stop
signal overlaps, the load of the communication processing on the
communicator 42 is increased. For these reasons, the
transmission of the stop signal is possibly delayed.
[0072] To solve this problem, the controller 41 of the electronic
cassette 19 and the CPU 31 of the console 13 regulate the
communication between the electronic cassette 19 and the console
13 during the accumulation operation of the FPD 23, until the
communicator 42 of the electronic cassette 19 completes the
transmission of the stop signal. More specifically, the
28
controller 41 of the electronic cassette 19 makes the communicator
42 perform only the transmission of the stop signal, and stop the
transmission and reception of any signal other than the stop
signal during the accumulation operation of the FPD 23, until the
transmission of the stop signal is completed. The transmission
of any signal other than the stop signal includes not only the
transmission of the response signal in response to the control
signal from the console 13, but also the transmission of the image
data that is obtained and recorded in the memory 51 in a previous
imaging operation and the like, for example. The communicator
42 stops receiving any signal from the console 13, in addition
to stops transmitting any signal other than the stop signal. In
other words, the controller 41 of the electronic cassette 19
carries out such communication regulation as to stop every
communication, except for the transmission of the stop signal by
the communicator 42, during the accumulation operation of the FPD
23 until the transmission of the stop signal is completed.
[0073] The CPU 31 of the console 13 regulates the communication
with the electronic cassette 19 by controlling the communicator
34. To be more specific, the CPU 31 of the console 13 makes the
communicator 34 perform only the mediation of the stop signal
transmitted from the electronic cassette 19 and stop the
transmission of the control signal (life check signal, the state
monitoring signal, the calibration command, or the like) to the
electronic cassette 19 during the accumulation operation of the
FPD 23.
[0074] More specifically speaking, as for the timing of starting
the communication regulation, the controller 41 of the electronic
cassette 19 and the CPU 31 of the console 13 start the communication
regulation of any signal other than the stop signal, upon
responding to the synchronization signal that is inputted from
the source control unit 15 at the start of an X-ray emission. The
29
communication regulation of any signal other than the stop signal
is continued until the transmission of the stop signal is
completed, at the least.
[0075] Referring to a flowchart of Fig. 6, the operation of the
X-ray imaging system 10 will be described. The positioning of
a body part of an object H and the X-ray source 14 is carried out
with respect to the imaging stand 20 loaded with the electronic
cassette 19. An examination order including the sex and age of
a patient, the body part to be imaged, an examination purpose,
and the like is inputted to the console 13, and an imaging condition
is set based on the examination order (S101). The console 13
transmits the set imaging condition to the electronic cassette
19 through the communicator 34. The controller 41 of the
electronic cassette 19 sets a target dose TD of X-rays based on
the imaging condition received by the communicator 42 (S201). To
the source control unit 15, the imaging condition including a tube
voltage, a tube current, an emission time, and the like is set
from the operation panel (S301).
[0076] The console 13 issues an exposure preparation command,
which makes the electronic cassette 19 prepare for making an
exposure, through the communicator 34 to the electronic cassette
19 (S102). In the electronic cassette 19, the FPD 23 is shifted
to a standby state, upon receiving the exposure preparation
command at the communicator 42 (S202). As soon as an emission
start signal is inputted from the emission switch 16, the source
control unit 15 inputs an emission start command to the X-ray
source 14 (S302). The X-ray source 14 starts applying X-rays to
the object H. At the same time, the source control unit 15
transmits a synchronization signal to the electronic cassette 19
through the console 13 (S302). Upon receiving the
synchronization signal, the controller 41 of the electronic
cassette 19 makes the FPD 23 start an accumulation operation
30
(S203).
[0077] The controller 41 integrates an output voltage Vout during
the accumulation operation of the FPD 23 to measure an
accumulative dose of the X-rays applied to the FPD 23 through the
object H (S203). During the accumulation operation of the FPD
23, the console 13 and the electronic cassette 19 make the
communicators 34 and 42 stop communicating any signal other than
a stop signal, until transmission of the stop signal is completed
at the least (S103, S204). The controller 41 compares the
accumulative dose of the X-rays with the target dose TD. As soon
as the accumulative dose of the X-rays has reached the target dose
TD, the controller 41 makes the communicator 42 transmit a stop
signal through the console 13 to the source control unit 15 (S205).
Upon receiving the stop signal, the source control unit 15 issues
a stop command to the X-ray source 14 to stop the X-ray emission
(S303).
[0078] At the instant when a response signal that indicates the
stop of the X-ray emission is sent back from the source control
unit 15 (S304), the controller 41 ends the accumulation operation
of the FPD (S206), and shifts the FPD 23 to a readout operation
(S207). The CPU 31 of the console 13 and the controller 41 of
the electronic cassette 19 lift the communication regulation, and
make the communicators 34 and 42 restart communicating signals
other than the stop signal (S104, S208). Read X-ray image data
is transmitted from the electronic cassette 19 to the console 13
(S209), and stored to the storage device 33 (S105) after being
subjected to predetermined image processing.
[0079] As described above, since the communication of any signal
other than the stop signal is stopped during the accumulation
operation of the FPD 23, the stop signal is prevented from being
delayed by communication congestion or signal collision. Thus,
it is possible to stop the X-ray emission from the X-ray source
31
14 at appropriate timing, and minimize unnecessary radiation
exposure of the object H. Also, stopping the X-ray emission at
appropriate timing prevents application of an excessive dose
beyond the target dose TD, and allows obtainment of the X-ray image
of preferable image quality.
[0080] As for the communication regulation during the
accumulation operation of the FPD 23, the above embodiment
describes a case in which every communication between the
electronic cassette 19 and the console 13 is stopped except for
the communication of the stop signal, but an error notification
that is transmitted from the electronic cassette 19 to the console
13 may be excluded from the signals under the communication
regulation. This is because the error notification, which
notifies the operator of the occurrence of an error, requires
rapidity in most cases.
[0081] In the above embodiment, both of the controller 41 of the
electronic cassette 19 and the CPU 31 of the console 13 control
the communicators 42 and 34, respectively, to carry out the
communication regulation. However, the communication
regulation between the communicators 42 and 34 may be carried out
under the control of at least one of the controller 41 and the
CPU 31.
[0082] For example, only the CPU 31 of the console 13 may carry
out such control over the communicator 34 as to stop transmission
processing of the control signal (life check signal, the state
monitoring signal, and the like) to the electronic cassette 19.
In other words, the controller 41 of the electronic cassette 19
may carry out no control related to the communication regulation
over the communicator 42.
[0083] This is because main signals to be transmitted from the
electronic cassette 19 to the console 13 are the response signal
responding to the control signal from the console 13, the error
32
notification, and the image data. Out of these signals, in the
case of transmitting the error notification, it is conceivable
that the electronic cassette 19 often fails to function normally
and make an appropriate exposure, irrespective of the presence
or absence of a delay in the stop signal. Also, it is conceivable
that the image data transmitted during the accumulation operation
of the FPD 23 is not the image data of a current exposure (under
accumulation) but the image data of a previous exposure, as
described above. The image data of the previous exposure should
have been completely transmitted before starting the current
accumulation operation in most cases, so transmission processing
is hardly carried out during the accumulation operation of the
FPD 23. Thus, there is not much need for the electronic cassette
19 to actively stop the transmission of the error notification
and the image data.
[0084] On the other hand, the response signal that responds to
the control signal periodically transmitted from the console is
produced more often than the error notification and the image data
do, and hence there is much need to stop the transmission of the
response signal. However, the transmission of the response
signal is triggered by the control signal from the console 13,
so transmission processing of the response signal does not happen
in the electronic cassette 19 unless the control signal is
transmitted to the electronic cassette 19. Accordingly,
stopping the transmission of the control signal in the console
13 results in stopping the transmission processing of the
electronic cassette 19, even if the electronic cassette 19 does
not stop the transmission processing actively.
[0085] For the above reasons, the communication regulation by
the CPU 31 of the console 13 for stopping the transmission
processing of the control signal (life check signal, the state
monitoring signal, and the like) to the electronic cassette 19
33
can bring about the effect of the present invention, that is, the
prevention of a delay in the stop signal.
[0086] It is conceivable as a matter of course that there is a
signal, such as the image data of the previous exposure,
transmitted from the electronic cassette 19 to the console 13
during the accumulation operation of the FPD 23, though it hardly
happens, as described above. Thus, stopping the communication
of any signal other than the stop signal in the electronic cassette
19 ensures the effect of the present invention, that is, the
prevention of a delay in the stop signal.
[0087] Note that, only the electronic cassette 19 may carry out
the communication regulation, instead of the console 13. For
example, the controller 41 of the electronic cassette 19 may carry
out such control as to stop reception processing of the control
signal, by making the communicator 42 abandon the control signal
from the console 13. This can eliminate a load of response
processing to the control signal on the controller 41 and the
communicator 42. However, the console 13 to which no
communication regulation is applied continues transmitting the
control signal, so this case has a little effect on reduction of
the communication congestion or collision in a transmission line.
Also, there can be a case that the console 13 judges it abnormal
to receive no response to the control signal from the electronic
cassette 19. Therefore, the regulation control is preferably
carried out by both of the console 13 and the electronic cassette
19 as described above or by only the console 13.
[0088] In the above embodiments, the life check signal, the state
monitoring signal, the calibration command, the error
notification, and the image data are described as the signals to
be subjected to the communication regulation during the
accumulation operation of the FPD 23, but an arbitrary signal may
be subjected to the communication regulation as long as the signal
34
affects a delay in the stop signal.
[0089] In the above embodiments, the X-ray dose is detected by
the short pixels provided in the image capturing field. The short
pixel has approximately the same structure and X-ray sensitivity
as the normal pixel has, and hence can detect the X-ray dose with
high accuracy. The same structure also allows ease of manufacture
and low cost increase.
[0090] In the above embodiments, the electronic cassette 19 is
provided with only one multi-terminal 25 being the communication
port. However, the present invention is applicable to another
electronic cassette 62, as shown in Fig. 7, in which a plurality
of communication ports 60 and 61 are connected to the communicator
42. One communication port 60 is dedicated to the transmission
of the stop signal and the other port 61 is dedicated to the
transmission of the other signals and data, for example.
Providing the plurality of communication ports reduces
communication congestion and signal collision in each
communication port. However, increase in the number of signals
transmitted and received by the communicator 42 put a heavy load
of processing to be applied to the signals transmitted and
received through each port on the communicator 42, and may cause
a communication delay. An X-ray emission time is several tens
of microseconds in some cases, depending on a body part to be
imaged. In the case of rapidly transmitting the stop signal in
such a short time, a slight increase in a load on the communicator
42 may heavily affect a communication delay. However, according
to the present invention, regulating communication of any signal
other than the stop signal during the accumulation operation of
the FPD 23 can reduce a redundant load on the communicator 42 and
concentrate the processing ability of the communicator 42 at
processing of the stop signal. Therefore, it is possible to
prevent a communication delay in the stop signal.
35
[0091] In addition to providing the plurality of communication
ports, a plurality of communicators 42 that are in charge of
communication processing, e.g. a first communicator dedicated to
the stop signal and a second communicator being in charge of
communication processing of the signals other than the stop
signal, may be provided. According to this method, since the
first communicator performs only the communication processing of
the stop signal, a load on the first communicator is reduced.
Also, the communication ports are isolated from signal to signal,
a communication delay owing to communication congestion and
signal collision is reduced. Therefore, it is possible to prevent
a communication delay in the stop signal.
[0092] Even in the case of providing the plurality of
communicators, however, the present invention is effectively
applied to certainly prevent a communication delay in the stop
signal. This is because providing the plurality of communicators
requires the controller 41 to perform centralized control of the
plurality of communicators, and brings about increase in a load
on the controller 41. In other words, in a case where the
plurality of communicators perform the communication processing
at the same time, the load on the controller 41 is increased because
of increase in the number of devices placed under the centralized
control. If a delay occurs in the centralized control of the
controller 41, the communication processing of each of the
plurality communicators is delayed too. Accordingly, even in the
case of providing the plurality of communicators, the
communication of any signal other than the stop signal is
preferably regulated during the accumulation operation of the
FPD.
[0093] Furthermore, providing the plurality of communicators
has the demerits of increasing costs for providing the ports and
space for disposing the communicators. To eliminate such
36
demerits, one communicator is preferably provided. Also, since
the electronic cassette has the small housing, it is difficult
to obtain space for the communicators therein. Providing one
communicator is especially effective in the electronic cassette.
[0094] In the above embodiments, the communicator 42 independent
of the controller 41 performs the communication processing, but
all or a part of the functions of the communicator 42 may be
integrated into the controller 41.
[0095] Furthermore, the present invention is not limited to the
above embodiments, and can take various configurations within the
confines of claims of the present invention, as a matter of course.
[0096] In the above embodiments, the cable-type communicators
connect among the console 13, the source control unit 15, and the
electronic cassette 19. The present invention, however, is
applicable to an X-ray imaging system having wireless-type
communicators, or an X-ray imaging system having both the
cable-type and wireless-type communicators.
[0097] The X-ray dose may be detected by a method other than the
short pixels. For example, a detection pixel having a TFT for
dose detection, in addition to a TFT for image reading as with
the TFT of the normal pixel, may be provided and used as the dose
detection sensor. In the detection pixel, the TFT for dose
detection is turned on in detecting the dose to output the dose
detection signal, while the TFT for image reading is turned on
in reading the image to output the image signal.
[0098] A part of the pixels are not necessarily used as the dose
detection sensor, such as the short pixel and the detection pixel.
The dose detection sensor may be provided between adjoining
pixels, for example. Otherwise, for example, the photodiode
composing the pixel is applied with the bias voltage, and a bias
current flowing through the bias line varies in accordance with
the amount of the signal charge produced in the photodiode. By
37
detecting the bias current, the X-ray dose may be detected. In
the case of detecting the bias current, the dose detection sensor
is composed of the bias line and a measurement unit for measuring
the bias current. Otherwise, even in a state of turning off the
TFT of the pixel, a slight leak current flows through the signal
line in accordance with the amount of the signal charge produced
in the photodiode. By detecting the leak current, the X-ray dose
may be detected. In the case of detecting the leak current, the
dose detection sensor is composed of the signal line and a
measurement unit for measuring the leak current.
[0099] The TFT type FPD in which the TFT matrix substrate is made
of the glass substrate is described as an example, but the FPD
may have a CMOS image sensor or a CCD image sensor using a
semiconductor substrate. Using the CMOS image sensor has the
following merit. The CMOS image sensor can perform a so-called
nondestructive read by which signal charge accumulated in each
pixel is read out as a voltage signal through an amplifier provided
in the pixel without flowing out to a signal line for readout.
According to this, it is possible to detect the X-ray dose even
in the accumulation operation by selecting an arbitrary pixel in
the image capturing field and reading out the signal charge from
the pixel. Therefore, in the case of using the CMOS image sensor,
it is possible to share any of the normal pixels as the dose
detection sensor, without using a specific dose detection sensor
as with the short pixel described above.
[0100] In the above embodiments, at that point in time when the
response signal is sent back from the source control unit 15 in
response to the transmission of the stop signal, the accumulation
operation is ended, and the communication regulation is lifted
to restart the communication of the signals other than the stop
signal. However, at the instant when the short pixels 58 detect
the actual stop of the X-ray emission after transmitting the stop
38
signal, instead of the response signal, the accumulation
operation may be ended and the communication regulation may be
lifted. As a method for detecting the actual stop of the X-ray
emission, there is a method using the short pixels 58, as an
example. The dose detection operation is continued using the
short pixels 58 even after transmitting the stop signal, and the
dosimeter 43 detects the actual stop of the X-ray emission based
on the dose detection signal. Since the stop of the X-ray emission
makes a signal value of the dose detection signal to substantially
zero, monitoring the signal value of the dose detection signal
makes it possible to detect the actual stop of the X-ray emission.
[0101] In the above embodiments, after the completion of the
accumulation operation, the communication regulation is lifted
and the communication of the signals other than the stop signal
is restarted. However, after the completion of the accumulation
operation and then after the readout operation for reading out
image information has been completed, the communication
regulation may be lifted and the communication of the signals
other than the stop signal may be restarted. This is because an
analog voltage signal outputted from the FPD 23 is susceptible
to noise until being subjected to an A/D conversion, so the restart
of the communication after the completion of the readout operation
is more preferable in terms of preventing degradation in image
quality.
[0102] Note that, in a case where the communication regulation
is lifted after the completion of the readout operation, the
timing of restarting the communication of the signals other than
the stop signal is delayed by time of the readout operation, as
compared with the case of lifting the communication regulation
immediately after the completion of the accumulation operation
as described in the above embodiments, but this affects little
in view of an entire imaging operation. Accordingly, the timing
39
of lifting the communication regulation is preferably set after
the completion of the readout operation, to give a high priority
to preventing the occurrence of noise in the readout operation.
Also, the transmission of the stop signal during the accumulation
operation of the FPD 23 causes deterioration in the image quality
more or less, but stopping at least the transmission of the other
signals can minimize deterioration in the image quality.
[0103] In the above embodiments, the stop signal is transmitted
from the electronic cassette to the X-ray generating apparatus
through the console, but may be transmitted from the electronic
cassette to the X-ray generating apparatus directly without
through the console. Also in this case, stopping the transmission
of the signals from the console to the electronic cassette during
the accumulation operation of the FPD until completing the
transmission of the stop signal allows the electronic cassette
to concentrate the capacity of the communicator on the
transmission of the stop signal, and hence has the effect of
preventing the communication delay of the stop signal. Note that,
in this case, the electronic cassette notifies the console of the
start of the accumulation operation and the transmission of the
stop signal at that point in time when they occur. The
notifications allow the console to grasp a current operational
state of the electronic cassette.
[0104] In the above embodiments, the communication between the
electronic cassette and the console is regulated, as an example.
However, if the electronic cassette communicates with a device
other than the console, the electronic cassette may regulate that
communication.
[0105] In the above embodiments, the electronic cassette 19 into
which an entire control circuit is integrated is described as an
example, but the present invention is applicable to an X-ray image
detecting device that has an electronic cassette with an FPD and
40
an external control unit connected wiredly or wirelessly to the
electronic cassette, for example. In this case, the
communication regulation may be performed between the console and
the control unit and between the control unit and the electronic
cassette. The console may be composed of a main unit having an
image display function and an image processing function and a
control unit having the function of controlling the electronic
cassette. In this case, the communication regulation may be
performed between the control unit and the electronic cassette.
Furthermore, the present invention may be applied to a stationary
X-ray image detecting device, instead of the electronic cassette
being a portable X-ray image detecting device.
[0106] The present invention is applicable to an imaging system
using another type of radiation such as -rays, instead of the
X-rays.
DESCRIPTION OF THE REFERENCE NUMERALS
[0107] 10 X-ray imaging system
11 X-ray generating apparatus
12 X-ray imaging apparatus
13 console
14 X-ray source
15 source control unit
19 electronic cassette
23 FPD
31 CPU
37 pixel
41 controller
34, 42 communicator
58 short pixel
41
42
We Claim:
1. A radiation imaging system having a radiation image
detecting device and a console for controlling said radiation
image detecting device, said radiation imaging system
characterized in that
said radiation image detecting device comprises:
an image detector having an image capturing field having
an arrangement of a plurality of pixels for accumulating an
electric signal in accordance with an incident amount of radiation
from a radiation generating apparatus, for detecting a
radiographic image;
a dosimeter for measuring a dose of said radiation emitted
from said radiation generating apparatus and passed through an
object;
a stop signal issuing unit for issuing a stop signal to make
said radiation generating apparatus stop an emission of said
radiation in accordance with said dose of said radiation measured
by said dosimeter;
a first communicator for performing communication
processing of said stop signal for transmitting said stop signal
to said radiation generating apparatus during an accumulation
operation of said image detector, and performing communication
processing of a signal other than said stop signal; and
a first controller for controlling said first communicator,
and
said console comprises:
a second communicator for performing communication
processing of a control signal for transmitting said control
signal to said first communicator; and
a second controller for controlling said second
communicator, wherein
during said accumulation operation, communication
43
regulation for regulating communication of a signal other than
said stop signal between said first communicator and said second
communicator is performed by controlling at least one of said
first controller and said second controller, at least until the
first communicator completes transmission of said stop signal.
2. The radiation imaging system according to claim 1,
characterized in that said signal to which said communication
regulation is applied includes said control signal.
3. The radiation imaging system according to claim 2,
characterized in that said control signal includes at least one
of a life check signal for checking an actuation state of said
radiation image detecting device, a state monitoring signal for
checking a state including a temperature of said radiation image
detecting device, and a calibration command for commanding said
radiation image detecting device to execute a calibration.
4. The radiation imaging system according to one of claims
1 to 3, characterized in that said stop signal is transmitted to
said radiation generating apparatus through said console.
5. The radiation imaging system according to one of claims
1 to 4, characterized in that said communication regulation
includes processing in which at least one of said first
communicator and said second communicator stops all or a part of
communication of said signals other than said stop signal.
6. The radiation imaging system according to claim 5,
characterized in that said second controller of said console stops
transmitting said control signal from said second communicator
to said first communicator to carry out said communication
44
regulation.
7. The radiation imaging system according to claim 5 or 6,
characterized in that said first controller of said radiation
image detecting device stops communication of said signal other
than said stop signal from said first communicator to carry out
said communication regulation.
8. The radiation imaging system according to one of claims
1 to 7, characterized in that said communication regulation
carried out by at least one of said first controller and said second
controller is lifted after said first communicator completes
transmission of said stop signal.
9. The radiation imaging system according to claim 8,
characterized in that said communication regulation is lifted
after receiving a response signal for indicating a stop of said
emission of said radiation from said radiation source.
10. The radiation imaging system according to claim 8,
characterized in that said communication regulation is lifted
after completing said accumulation operation and furthermore
completing a readout operation for reading out said radiographic
image from said image detector.
11. The radiation imaging system according to claim 8,
characterized in that said communication regulation is lifted
after said dosimeter has detected an actual stop of said emission
of said radiation.
12. The radiation imaging system according to one of claims
1 to 11, characterized in that said radiation image detecting
45
device has one said first communicator that is shared between
communication of said stop signal and communication of said signal
other than said stop signal.
13. The radiation imaging system according to claim 12,
characterized in that only one communication port is connected
to said first communicator, and said communication port is shared
between communication of said stop signal and communication of
said signal other than said stop signal.
14. The radiation imaging system according to claim 12,
characterized in that a plurality of communication ports are
connected to said first communicator, and one of said
communication ports is dedicated to transmission of said stop
signal.
15. The radiation imaging system according to one of claims
1 to 14, characterized in that in said radiation image detecting
device, a dose detection sensor is provided in said image
capturing field of said image detector to output a dose detection
signal to said dosimeter.
16. The radiation imaging system according to claim 15,
characterized in that said dose detection sensor uses a part of
said pixels.
17. The radiation imaging system according to one of claims
1 to 16, characterized in that said radiation image detecting
device is an electronic cassette having said image detector
contained in a portable housing.
18. A control method of a radiation imaging system having
46
a radiation image detecting device and a console for controlling
said radiation image detecting device, said control method
characterized in comprising:
a step of accumulating an electric signal in a plurality
of pixels arranged in an image capturing field in accordance with
an incident amount of radiation from a radiation generating
apparatus to detect a radiographic image in said radiation image
detecting device;
a step of measuring a dose of said radiation emitted from
said radiation generating apparatus and passed through an object
in said radiation image detecting device;
a step of issuing a stop signal to be transmitted to said
radiation generating apparatus to make said radiation generating
apparatus stop an emission of said radiation in accordance with
said measured dose, in said radiation image detecting device; and
a step of regulating communication of a signal other than
said stop signal between said radiation image detecting device
and said console in the accumulation step, at least until said
radiation image detecting device completes transmission of said
stop signal.
19. A radiation image detecting device characterized in
comprising:
an image detector having an image capturing field having
an arrangement of a plurality of pixels for accumulating an
electric signal in accordance with an incident amount of radiation
from a radiation generating apparatus, for detecting a
radiographic image;
a dosimeter for measuring a dose of said radiation emitted
from said radiation generating apparatus and passed through an
object;
a stop signal issuing unit for issuing a stop signal to make
47
said radiation generating apparatus stop an emission of said
radiation in accordance with said dose of said radiation measured
by said dosimeter;
a communicator for performing communication processing of
said stop signal for transmitting said stop signal to said
radiation generating apparatus during an accumulation operation
of said image detector, and performing communication processing
of a signal other than said stop signal; and
a controller for regulating communication of said signal
other than said stop signal by said communicator during said
accumulation operation, at least until said communicator
completes transmission of said stop signal.
20. The radiation image detecting device according to claim
19, characterized in that said communication regulation includes
processing in which said communicator stops all or a part of
communication of said signals other than said stop signal.
21. The radiation image detecting device according to claim
20, characterized in that said controller stops communication of
said signal other than said stop signal by said communicator to
carry out said communication regulation.
22. The radiation image detecting device according to one
of claims 19 to 21, characterized in that said communication
regulation carried out by said controller is lifted after said
communicator completes transmission of said stop signal.
23. The radiation image detecting device according to claim
22, characterized in that said communication regulation is lifted
after receiving a response signal for indicating a stop of said
emission of said radiation from said radiation source.
48
24. The radiation image detecting device according to claim
22, characterized in that said communication regulation is lifted
after completing said accumulation operation and furthermore
completing a readout operation for reading out said radiographic
image from said image detector.
25. The radiation image detecting device according to claim
22, characterized in that said communication regulation is lifted
after said dosimeter has detected an actual stop of said emission
of said radiation.
26. The radiation image detecting device according to one
of claims 19 to 25, characterized in that there is one said
communicator that is shared between communication of said stop
signal and communication of said signal other than said stop
signal.
27. The radiation image detecting device according to claim
26, characterized in that only one communication port is connected
to said communicator, and said communication port is shared
between communication of said stop signal and communication of
said signal other than said stop signal.
28. The radiation image detecting device according to claim
26, characterized in that a plurality of communication ports are
connected to said communicator, and one of said communication
ports is dedicated to transmission of said stop signal.
29. The radiation imaging system according to one of claims
1 to 17, characterized in that said stop signal issuing unit issues
said stop signal, upon said dose of said radiation measured by
said dosimeter reaching a target dose.