JP4862767B2 - X-ray diagnostic equipment - Google Patents

Description

  The present invention is detected by an X-ray irradiation means such as an X-ray tube for irradiating a subject with X-rays, an X-ray detector for receiving X-rays irradiated from the X-ray irradiation means, and the X-ray detector. An image processing unit that acquires and processes detection signals as image data, an imaging condition setting unit that sets X-ray imaging conditions irradiated from the X-ray irradiation unit, and light that irradiates a backlight for removing afterimages to the X-ray detector The present invention relates to an X-ray diagnostic apparatus including an irradiation unit.

  In this type of X-ray diagnostic apparatus, in the X-ray detector, charges accumulated between the divided electrodes constituting the X-ray detector are swept out after X-ray irradiation, or charges are accumulated in the divided electrode region and the potential near the divided electrodes is There has been a problem that the phenomenon of rising occurs, resulting in an afterimage.

In order to remove such an afterimage, the backlight is irradiated. Conventionally, the following is known.
A. First Conventional Example During the detection of radiation (X-rays), light having a wavelength shorter than the transmittance half wavelength of the semiconductor to be used and longer than the wavelength corresponding to the band gap energy is irradiated ( Patent Document 1).

B. Second Conventional Example A plurality of radiation sensitive sensors are arranged on a substrate layer, a photoconductive layer is formed around the sensor, an upper dielectric layer is provided on the photoconductive layer, and an upper dielectric layer is provided on the upper dielectric layer. A top dielectric layer is provided.
A first light emitting panel for irradiating the photoconductive layer with a first substantially uniform pattern of light is provided on the top dielectric layer. A second light-emitting panel that supplies a low-energy light beam having a second pattern to the photoconductive layer is provided below the substrate layer (see Patent Document 2).
JP 2004-146769 A JP-A-9-9153

  However, in both cases of the first and second conventional examples, the light irradiation, that is, the backlight energy is not set to an appropriate value, and there is still room for improvement.

  The present invention has been made in view of the circumstances as described above, and an object thereof is to improve the afterimage removal rate by paying attention to the correlation between the voltage value of the backlight and the photographing conditions. To do.

The invention according to claim 1 has the following configuration in order to achieve the above-described object.
That is, X-ray irradiation means for irradiating a subject with X-rays, an X-ray detector for receiving X-rays emitted from the X-ray irradiation means, and detection signals detected by the X-ray detector as image data An image processing unit that performs acquisition processing, an imaging condition setting unit that sets X-ray imaging conditions irradiated from the X-ray irradiation unit, and a light irradiation unit that irradiates a backlight for removing afterimages to the X-ray detector. In the X-ray diagnostic apparatus provided,
Voltage value setting means for setting the voltage value of the backlight irradiated from the light irradiation unit, and the backlight voltage value optimum for the afterimage removal determined in accordance with each of the shooting conditions set in advance by the shooting condition setting means And the voltage value setting means by extracting the optimum backlight voltage value corresponding to the imaging condition set by the imaging condition setting means from the imaging condition-voltage value correlation table. And a voltage value control means for substituting the backlight voltage value with an optimum backlight voltage value.

As a result of considering the correlation between the imaging conditions and the backlight voltage value, it is impossible to find a proportional or inversely proportional relationship between the X-ray dose and the backlight voltage value. It came to find out that it was necessary to set to a backlight voltage value.
According to the configuration of the X-ray diagnostic apparatus of the first aspect of the present invention, based on the above knowledge, an optimal backlight voltage value is obtained for each imaging condition by trial and error, and the imaging condition and the optimal backlight voltage value are determined. Create a correlation table and extract the optimal backlight voltage value from the imaging condition-voltage value correlation table each time the imaging condition changes, replace it with the backlight voltage value in the voltage value setting means, and replace the backlight. Irradiate.
Therefore, the backlight can be irradiated with the optimum backlight voltage value even if the photographing conditions are changed, and the afterimage removal rate can be improved.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an overall configuration diagram showing an X-ray diagnostic apparatus according to an embodiment of the present invention. X-ray irradiation means for irradiating a subject H with X-rays above an imaging table 1 on which the subject H is placed. An X-ray tube 2 is provided via an X-ray tube holding device 3. A flat panel X-ray detector 4 as an X-ray detector that receives X-rays irradiated from the X-ray tube 2 and transmitted through the subject H is provided on the lower surface of the imaging table 1.

  An X-ray generator 5 for generating X-rays is connected to the X-ray tube 2, and the X-ray generator 5 is connected to an X-ray tube 2 such as a tube voltage and a tube current for adjusting the X-ray intensity. An X-ray condition setting means 6 for setting the condition of X-rays to be irradiated is connected.

  The flat panel X-ray detector 4 is connected to an image processing unit 7 that acquires and processes the detection signal received and detected as image data, and the image processing unit 7 displays an image that displays the processed image. A display unit 8 is connected.

  As shown in the cross-sectional view of the schematic configuration of the flat panel X-ray detector of FIG. 2 and the plan view of the schematic configuration of the flat panel X-ray detector of FIG. In this order, an application electrode 9 for applying a bias voltage, a semiconductor layer 10 for converting X-rays into electric charges, and an active matrix substrate 12 having divided electrodes 11, switching elements s, and the like are stacked in this order from the X-ray incident side. Configured. The divided electrode 11 collects charges converted by the semiconductor layer 10 as detection signals. The switching element s shifts the collected detection signals to an on state and reads them. Examples of the semiconductor layer 10 include amorphous and selenium.

  On the back surface of the active matrix substrate 12 (the surface opposite to the surface on which the semiconductor layer 10 is provided), a backlight for removing afterimages is directed toward the side on which the divided electrodes 11 of the semiconductor layer 10 are provided. The light irradiation part 13 to irradiate is provided. In FIG. 2, light is schematically shown by a one-dot chain line. Furthermore, the gate driver 14 that drives each switching element s, the drive control circuit 15 that controls the reading of the detection signal by operating the gate driver 14, and the detection signal that is read out in cooperation with the drive control circuit 15 Are provided with two amplifier array circuits 16 a and 16 b for processing the light and a light control unit 17 for controlling the light irradiation unit 13 in cooperation with the drive control circuit 15.

  The active matrix substrate 12 is configured by forming a polarizable electrode 11, a capacitor Ca, a switching element s, a scanning line 19, a signal line 20 and the like on a transparent glass substrate 18 having electrical insulation. There are a large number of divided electrodes 11, which are arranged in a state of being separated from each other along rows and columns that are biaxially intersecting on the lower surface side of the semiconductor layer 10. Each divided electrode 11 is connected to a capacitor Ca for storing the collected detection signals. A switching element s is connected to each pair of the divided electrode 11 and the capacitor Ca. An example of the switching element s is a thin film transistor (TFT).

  The pair of divided electrodes 11, the capacitor Ca, and the switching element s constitute one detection element d together with the semiconductor layer 10 and the application electrode 9 in a region corresponding thereto. Therefore, when the detection surface of the flat panel X-ray detector 4 is viewed in plan, it can be seen that a large number of detection elements d are arranged in a matrix as shown in FIG.

  Further, the scanning line 19 is formed for each row of the detection elements d, and is connected in common to the gates of the switching elements s in each row. Two signal lines 20 are formed for each column, and extend from the approximate center to both sides. Then, approximately half of the switching elements s in each column are connected to the signal line 20 in common. Note that rows and columns are merely used for convenience in order to distinguish directions, and it may be considered that a scanning line 19 is provided for each column and a signal line 20 is provided for each row.

The gate driver 15 is connected to one end side of each scanning line 19. A gate pulse for driving on / off the switching elements s in each row is output via each scanning line 19. The amplifier array circuits 16a and 16b are separately provided on both sides of the detection element d group, and the signal lines 20 drawn from the detection element d group are connected thereto.
As a result, all the switching elements s are divided into two element groups G1 and G2 corresponding to the amplifier array circuits 16a and 16b, and each of the amplifier array circuits 16a and 16b has a corresponding element group G1 and G2 respectively. The detection signal read out from the switching element s included in is processed. The drive control circuit 15 comprehensively controls the gate driver 14 and the amplifier array circuits 16a and 16b described above based on the vertical synchronization signal and the horizontal synchronization signal.

  The light irradiation unit 13 includes a planar light guide unit 21 and a light emitting unit 22. The planar light guide unit 21 is a plate-like object that is formed of a light-transmitting plate-like object such as acrylic or glass and has an active matrix substrate 12 side as a light emitting surface. The light emitting unit 22 emits light to the end surface of the planar light guide unit 21. As this light emission part 22, a light emitting diode, a cold cathode tube, etc. are illustrated.

  The light control unit 17 controls switching on / off of the light irradiation unit 13 in cooperation with the drive control circuit 15 described above. Specifically, it is realized by a current limiting circuit, a switching circuit, a booster circuit using an inverter, or the like according to the type of the light emitting unit 22.

Connected to the drive control circuit 15 is a voltage value setting means 23 for setting the voltage value of the backlight irradiated from the light irradiation unit 13.
As shown in the block diagram of FIG. 4, voltage value control means 24 is connected to the voltage value setting means 23. The voltage value control means 24 includes an imaging condition setting means 6 and an imaging condition-voltage value correlation table 25. It is connected.

The voltage value control means 24 extracts the optimum backlight voltage value corresponding to the photographing condition from the photographing condition-voltage value correlation table 25 based on the photographing condition set by the photographing condition setting means 6 and then sets the voltage value setting means. The backlight voltage value at 23 is replaced with an optimal backlight voltage value.
In the imaging condition-voltage value correlation table 25, backlight voltage values optimum for afterimage removal, which are obtained in advance corresponding to each imaging condition set by the imaging condition setting means 6, are stored.

Next, the optimum backlight voltage value stored in the imaging condition-voltage value correlation table 25 will be described.
The afterimage rate was measured under the following photographing conditions (1) and (2).
The afterimage rate was calculated as follows.
Irradiate a certain dose, divide the remaining dose after a certain period of time by the irradiation dose, and calculate the ratio of the remaining dose to the irradiated dose. Actually, the pixel value A after the first irradiation is calculated, and a certain amount of time has elapsed. The subsequent pixel value B is calculated and calculated as A / B × 100 (%).
The pixel value A is a read value at the time of X-ray irradiation, and the pixel value B is a value read again after a predetermined time has elapsed.

Shooting conditions (1)
X-ray tube voltage 80 kV, tube current 160 mA, X-ray irradiation time 71 msec (no additional filter)
Predetermined set voltage such that the luminance and the backlight voltage V _BL of the normal, the backlight voltage V _BL, normal backlight voltage V _BL constant voltage lower voltage than (V _BL - [Delta] V) The backlight voltage value was set for each of the voltages (V _BL + ΔV) that was a certain voltage larger than the normal backlight voltage V _BL , and the backlight was irradiated.

Shooting conditions (2)
X-ray tube voltage 80 kV, tube current 250 mA, X-ray irradiation time 200 msec (no additional filter)
Predetermined set voltage such that the luminance and the backlight voltage V _BL of the normal, the backlight voltage V _BL, normal backlight voltage V _BL constant voltage lower voltage than (V _BL - [Delta] V) The backlight voltage value was set for each of the voltages (V _BL + ΔV) that was a certain voltage larger than the normal backlight voltage V _BL , and the backlight was irradiated.

As a result of measuring the afterimage rate under the above conditions, the following results were obtained.
Shooting conditions Backlight voltage value Afterimage ratio (%)
Condition (1): V _BL -ΔV: 0.0076
: V _BL: 0.0056
: V _BL + ΔV : 0.0084
Condition (2): V _BL -ΔV: 0.0094
: V _BL: 0.0126
: V _BL + ΔV : 0.0169

From the above results, if imaging conditions of (1), when irradiated with backlight backlight voltage V _BL of the normal has been found to be reduced afterimage can be increased the most afterimage removal rate. On the other hand, if the imaging conditions of (2) is, when irradiated with the backlight at normal voltage is lowered than the backlight voltage V _BL during has been found to be reduced afterimage can be increased the most afterimage removal rate.
Even in other shooting conditions, the optimal backlight voltage value for each shooting condition shows a unique value, and the optimal backlight voltage value is determined by trial and error according to each shooting condition and replaced with that voltage value. It has been found that it is preferable to irradiate a backlight. The preferred backlight voltage value obtained in this way is stored in the photographing condition-voltage value correlation table 25 in association with the photographing condition.
As a result of obtaining a suitable voltage value by trial and error as described above, the backlight voltage value in the case of the shooting condition (1) is 8.9 V, while the backlight voltage in the case of the shooting condition (2) is The voltage value was 8.0V.

Next, an operation example of the flat panel X-ray detector 4 will be described with reference to the timing chart of FIG.
FIG. 5 schematically shows an X-ray detection operation, a vertical synchronization signal, a horizontal synchronization signal, a switching element, and backlight irradiation. As for the backlight voltage value, the voltage value corresponding to the photographing condition is extracted from the photographing condition-voltage value correlation table 25 by the voltage control means 24 in accordance with the setting of the photographing condition, and the optimum value corresponding to the photographing condition is obtained. The voltage value is set by the voltage value setting means 23.

  In the detection period (time t1 to time t6) in which the detection operation is performed, the semiconductor layer 10 is applied with a bias voltage by the application electrode 9, and converts incident X-rays into electric charges. The converted electric charge is collected by one of the divided electrodes 11. During this detection period, under the control of the drive control circuit 15, a read operation for reading the collected charges (time t2 to time t3, time t4 to time t5), and an accumulation operation for storing charges (time t1 to time t2) , Time t3 to time t4 and time t5 to time t6) are alternately performed.

<Read operation>
The drive control circuit 15 operates the gate driver 14 based on the vertical synchronization signal and the horizontal synchronization signal. Thus, the gate driver 14 sequentially outputs a gate pulse to each scanning line 19 in synchronization with the horizontal synchronization signal, and drives the switching element s (time t2 to time t3 and time t4 to time t5). Therefore, the period from time t2 to time t3 and the period from time t4 to time t5 correspond to a “reading period” in which the detection signal is read from any switching element s. In the timing chart of the switching element s in FIG. 5, a period during which any switching element s is driven to shift to the ON state is indicated as “ON”. The period of the vertical synchronization signal is 33.3 msec, for example.

  In addition, the light control unit 17 turns on the light irradiation unit 13 during the readout period in cooperation with the drive control circuit 15. The light irradiation unit 13 irradiates the backlight through the active matrix substrate 12 toward the side where the divided electrodes 11 of the semiconductor layer 10 are formed. Thereby, the electric charge according to the irradiated light is stored in the space between the divided electrodes 11 without being swept out.

  The switching elements s are sequentially turned on in units of one row connected to the scanning line 19, and the detection signals are sequentially read out via the switching elements s in the on state. The detection signal read from the switching element s in the element group G1 is sent to the amplifier array circuit 16a, and the detection signal read from the switching element s in the element group G2 is sent to the amplifier array circuit 16b. The amplifier array circuits 16a and 16b perform processing such as amplifying the detection signal in cooperation with the drive control circuit 15, respectively. Then, an image is generated for each detection signal obtained in each readout period.

<Accumulation operation>
The gate driver 14 does not drive any switching element s by the operation by the drive control circuit 15. Therefore, the period from time t1 to time t2, the period from time t3 to time t4, and the period from time t5 to time t6 correspond to an “accumulation period” in which no detection signal is read from any switching element s. To do. In FIG. 5, a period in which any switching element s is in an off state is displayed as “OFF”. The light control unit 17 turns off the light irradiation unit 13 during the accumulation period in cooperation with the drive control circuit 15.

  In this way, in the readout period, the light irradiation unit 13 is turned on with the optimal backlight voltage value according to the shooting conditions, and the backlight is illuminated. Therefore, when the detection signal is read from each switching element s, the residual output is output. It is possible to prevent the occurrence of an afterimage in an image obtained based on the read detection signal.

1 is an overall configuration diagram showing an X-ray diagnostic apparatus according to an embodiment of the present invention. It is a cross-sectional view showing a schematic configuration of a flat panel X-ray detector. It is a top view which shows schematic structure of a flat panel type X-ray detector. FIG. 6 is a block diagram illustrating a control system according to a second embodiment. It is a timing chart with which it uses for description of the operation example of a flat panel type X-ray detector.

Explanation of symbols

2 ... X-ray tube (X-ray irradiation means)
4. Flat panel X-ray detector (X-ray detector)
6 ... Imaging condition setting means 7 ... Image processing section 13 ... Light irradiation section 23 ... Voltage value setting means 24 ... Voltage value control means 25 ... Imaging condition-voltage value correlation table H ... Subject

Claims (1)

X-ray irradiation means for irradiating a subject with X-rays, an X-ray detector for receiving X-rays emitted from the X-ray irradiation means, and a detection signal detected by the X-ray detector as image data acquisition processing An image processing unit, an imaging condition setting unit that sets an X-ray imaging condition irradiated from the X-ray irradiation unit, and a light irradiation unit that irradiates the X-ray detector with a backlight for removing afterimages. In X-ray diagnostic equipment,
Voltage value setting means for setting the voltage value of the backlight irradiated from the light irradiation unit, and the backlight voltage value optimum for the afterimage removal determined in accordance with each of the shooting conditions set in advance by the shooting condition setting means And the voltage value setting means by extracting the optimum backlight voltage value corresponding to the imaging condition set by the imaging condition setting means from the imaging condition-voltage value correlation table. An X-ray diagnostic apparatus comprising: voltage value control means for replacing the backlight voltage value in FIG. 1 with an optimal backlight voltage value.

Images