JP2008108440A - X-ray high voltage device and x-ray diagnostic apparatus including x-ray high voltage device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that, the smaller a tube current and an imaging time are, the larger deviation from an actual measurement value is, because a quantity of radiation is calculated using a calculating formula assuming that the quantity of radiation is proportional to the tube current and imaging time in an X-ray high voltage device having capability to calculate the quantity of radiation on the basis of an imaging condition. <P>SOLUTION: As a calculating formula, a dosage characteristic constant DT (V) of a term corresponding to the quantity of radiation of an X-ray irradiated as a wave tail X-ray is added to an existing term in proportion to a tube current and an imaging time, and the DT (V) and the dosage characteristic coefficient Dt (V) of the term in proportion to the tube current and the imaging time is beforehand stored in a DT (V) memory 14 and a Dt (V) memory 15, respectively. Then, a computational part 16 calculates the quantity of radiation from the calculating formula using the imaging condition obtained from an X-ray controller 3 at the setup time of the imaging condition and memory values stored in both the memories. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an X-ray high voltage apparatus used for X-ray fluoroscopy and radiography and an X-ray diagnostic apparatus including the X-ray high voltage apparatus.

  An example of an X-ray high voltage apparatus having a function of calculating an irradiation dose from imaging conditions will be described with reference to FIG. The X-ray high voltage apparatus 1 supplies a high voltage to the X-ray tube 6 via a high voltage cable 5 in order to irradiate X-rays from the X-ray tube 6, and is a high voltage mainly composed of a high voltage transformer. The voltage generator 2 is composed of, for example, a microcomputer and its memory, and is composed of an X-ray controller 3 that controls the high voltage generator 2 in accordance with an operation of an operator (not shown). In X-ray imaging, it is extremely important for the health of the subject to know the exposure dose of the subject (not shown) for each radiographing and manage the dose so as not to exceed an allowable value. For this purpose, a dosimeter 8 constituted by, for example, an ionization chamber or the like shown by a broken line in FIG. 4 may be attached to the front part of the collimator 7 attached to the X-ray tube 6 to measure the dose of X-rays to be irradiated. However, even in such a case, it is impossible to predict whether or not the allowable value is exceeded by predicting the X-ray dose before irradiation. Therefore, for example, a dose calculator 4 composed of a microcomputer and a memory is built in, and X-ray irradiation is performed based on imaging conditions set in the high voltage generator 2 by the X-ray controller 3, that is, tube voltage, tube current, and imaging time. There is an X-ray high voltage apparatus 1 having a function of calculating an irradiation dose before and displaying it on a panel (not shown) of the X-ray controller 3 or the like. (For example, see Patent Document 1)

Calculation of the X-ray irradiation dose by the dose calculator 4 as described above is usually performed using (Equation 1).
Dose = D (V) × A × B (Formula 1)
Here, Dose: irradiation dose, A: tube current value, B: imaging time, D (V): dose characteristic coefficient depending on tube voltage value V. The dose characteristic coefficient D (V) is acquired in advance by the following method. That is, as shown by a broken line in FIG. 4, a dosimeter 8 is attached to the front portion of the collimator 7, and the tube current value A and the imaging time B set from the X-ray controller 3 to the high voltage generator 2 are set to appropriate values. The X-ray is irradiated for each tube voltage value V, and the irradiation dose Dose at each tube voltage value V is measured. The calculation unit 12 receives the imaging conditions from the X-ray controller 3 every time X-rays are irradiated and the irradiation dose Dose from the dosimeter 8, and calculates the dose characteristic coefficient for each tube voltage value V by calculating back (Equation 1). D (V) is calculated and stored in the D (V) storage unit 13.

When the imaging conditions, that is, the tube voltage value V, the tube current value A, and the imaging time B are set before imaging is performed thereafter, the arithmetic unit 12 captures the imaging conditions received from the X-ray controller 3 and the tubes in the imaging conditions. The irradiation dose Dose is calculated from the dose characteristic coefficient D (V) read from the D (V) storage unit 13 with respect to the voltage value V by (Equation 1). Since this value is displayed on the panel of the X-ray controller 3 or the like, the operator (not shown) can determine whether or not the subject does not exceed the permissible exposure value by performing the image capturing to be performed. Further, when the high voltage generator 2 has a function of actually measuring imaging conditions during X-ray irradiation, the calculation of (Equation 1) is performed after imaging using the actually measured imaging conditions to calculate an irradiation dose Dose that is closer to the actually measured value. It can also be displayed on the panel of the X-ray controller 3 or the like.
JP 2003-203797 A

  The method of calculating the irradiation dose from the imaging conditions in the X-ray high-voltage apparatus is as described above. However, (Equation 1) assumes that the irradiation dose is proportional to the tube current value and the imaging time. However, when the irradiation dose is actually measured, the proportionality shifts as the tube current value decreases and the imaging time decreases. This is because the electric capacity exists in the high voltage cable connecting the high voltage generator and the X-ray tube, and even if the application of the tube voltage by the high voltage generator is completed, the period X-ray shown as the wave tail period in FIG. The tube continues to be applied with a high voltage due to the charge charged in the cable capacity during tube voltage application. The tube voltage decreases according to a time constant determined by the cable capacity and the tube current value, as electric charges are discharged as a tube current during the wave tail period. Therefore, X-ray irradiation does not stop with the end of the application of the tube voltage by the high voltage generator, but continues while gradually decreasing during the wave tail period. The irradiation dose during this wave tail period is It is not assumed. Since the cable capacity is constant as long as the cable does not change, the discharge time constant depends only on the tube current value, and increases as the tube current value decreases. Therefore, the irradiation dose according to (Equation 1) deviates from the proportional relationship as the tube current value decreases. In addition, the shorter the imaging time, the larger the ratio of the wave tail portion in the irradiation dose, and the larger the deviation from the proportional relationship.

  In order to improve this problem, a method using a dose characteristic coefficient depending on the tube current and the imaging time in addition to the tube voltage instead of the dose characteristic coefficient depending on the tube voltage has been proposed. In addition to the tube current value and the imaging time, it is necessary to actually measure the irradiation dose with respect to many values and collect the dose characteristic coefficient, which requires a lot of labor and time. An object of the present invention is to reduce a deviation from a measured value of a calculation value of an irradiation dose caused by a wave tail portion of a tube voltage waveform existing after the tube voltage is cut off by a simpler method.

  In order to achieve the above object, the invention described in claim 1 is an X-ray high voltage apparatus having dose calculation means for calculating an irradiation dose from a set or measured tube voltage, tube current, and imaging time. In order for the means to calculate and display the irradiation dose in advance by a calculation formula that adds a dose characteristic constant depending on the tube voltage to the product of the tube current and the dose characteristic coefficient depending on the imaging time and the tube voltage, It is obtained by solving a plurality of formulas obtained by substituting the plurality of irradiation doses actually measured by the dose measuring means for each tube voltage and the tube current and the imaging time for each irradiation dose into the calculation formula. An X-ray high voltage apparatus having dose characteristic coefficient storage means for storing a dose characteristic coefficient depending on the tube voltage and dose characteristic constant storage means for storing a dose characteristic constant depending on the tube voltage Subjected to.

  According to a second aspect of the present invention, in order to achieve the above object, in an X-ray diagnostic apparatus including an X-ray high voltage apparatus, the tube voltage, tube current, and imaging time set or measured by the X-ray high voltage apparatus are adjusted. In order to receive the information and calculate and display the irradiation dose with a calculation formula that adds a dose characteristic constant depending on the tube voltage to a product of the tube current and the dose characteristic coefficient depending on the imaging time and the tube voltage, Solving a plurality of formulas obtained by substituting a plurality of irradiation doses measured in advance by the dose measuring means for each tube voltage in advance and the tube current and the imaging time for each irradiation dose into the calculation formula Dose characteristic coefficient storage means for storing the obtained dose characteristic coefficient depending on the tube voltage and dose calculation means having dose characteristic constant storage means for storing the dose characteristic constant depending on the tube voltage are provided. To provide a line diagnostic equipment.

  Instead of a calculation formula based on the premise that the irradiation dose conventionally used according to the present invention is proportional to the tube current and the imaging time, a calculation formula in which a term corresponding to the wave tail portion of the tube voltage waveform is added to the formula. It is possible to greatly reduce the deviation of the calculated value of the irradiation dose from the actual measurement value by a simple method of using.

  An embodiment of the present invention will be described with reference to FIGS. The X-ray high voltage device 21 supplies a high voltage to the X-ray tube 6 via the high voltage cable 5 in order to irradiate the X-ray from the X-ray tube 6, and is a high voltage mainly composed of a high voltage transformer. The voltage generator 2 is composed of, for example, a microcomputer and its memory, etc., and is composed of an X-ray controller 3 for controlling the high voltage generator 2 in accordance with an operation of an operator (not shown), and, for example, a microcomputer and memory. The X-ray controller 3 is configured by a dose calculator 24 that calculates the X-ray dose irradiated from the imaging conditions set in the high voltage generator 2, that is, the tube voltage, the tube current, and the imaging time. Since the irradiation dose calculated by the dose calculator 24 is displayed on a panel (not shown) of the X-ray controller 3, the operator does not exceed the permissible exposure value by the imaging performed by the subject (not shown). Can be determined. In addition, when the high voltage generator 2 has a function of actually measuring the imaging conditions during the X-ray irradiation, the calculation of (Equation 1) is performed using the imaging conditions actually measured after the imaging to calculate an irradiation dose closer to the actual measurement value. Can be displayed on the panel of the X-ray controller 3.

In the present invention, the dose calculator 24 calculates the irradiation dose using (Equation 2) instead of (Equation 1).
Doset = Dt (V) × A × B + DT (V) (Formula 2)
Where Doset: irradiation dose, A: tube current value, B: imaging time, Dt (V): dose characteristic coefficient depending on tube voltage value V, DT (V): dose characteristic constant depending on tube voltage value V is there.

  Whereas (Equation 1) described in the background art presupposes an ideal state in which the X-ray irradiation stops simultaneously with the high voltage application stop, (Equation 2) indicates that the high voltage cable 5 The electric charge charged in the cable capacity is emitted as so-called wave tail X-rays while discharging according to the time constant determined by the cable capacity and the tube current value after the high voltage application is completed, that is, during the period shown as the wave tail period in FIG. The X-ray irradiation dose is incorporated as a dose characteristic constant DT (V) in the constant term of (Equation 2) with the tube current value A and the imaging time B as variables. Since the irradiation dose by the wave tail X-ray mainly depends on the tube voltage value V, the dose characteristic constant DT (V) is a constant determined for each tube voltage value V.

The values of the dose characteristic coefficient Dt (V) and the dose characteristic constant DT (V) are acquired in advance by the following method. That is, as shown by a broken line in FIG. 1, a dosimeter 8 is attached to the front portion of the collimator 7, and an appropriate tube current value A1 and imaging time B1 are set from the X-ray controller 3 to the high voltage generator 2, and further arbitrarily After the tube voltage value V is set, X-rays are irradiated, and the radiation dose value Doset1 is actually measured by the dosimeter 8. Thereafter, the tube voltage value remains V, the tube current value is changed to A2, the imaging time is changed to B2, and X-rays are irradiated to measure the irradiation dose value Doset2. The calculation unit 16 of the dose calculator 24 substitutes the irradiation dose values and the respective imaging conditions obtained by these two imaging operations into (Equation 2) to obtain the following (Equation 3) and (Equation 4).
Doset1 = Dt (V) × A1 × B1 + DT (V) (Formula 3)
Doset2 = Dt (V) × A2 × B2 + DT (V) (Formula 4)
The calculation unit 16 solves these two equations as simultaneous equations having the dose characteristic coefficient Dt (V) and the dose characteristic constant DT (V) as unknowns, thereby obtaining values of the dose characteristic coefficient Dt (V) and the dose characteristic constant DT (V). Get.

  Each tube voltage obtained by repeatedly performing the above X-ray irradiation, measurement of irradiation dose, and calculation of the dose characteristic coefficient Dt (V) and dose characteristic constant DT (V) for all tube voltage values V that can be set The dose characteristic coefficient Dt (V) and the dose characteristic constant DT (V) for the value V are stored in the Dt (V) storage unit 15 and the DT (V) storage unit 14 by the calculation unit 12, respectively. The above operation must be performed every time one of the X-ray tube 6 and the high voltage cable 5 is replaced.

  When the imaging conditions, that is, the tube voltage value, the tube current value, and the imaging time are set before imaging is performed thereafter, the calculation unit 16 sets the imaging conditions received from the X-ray controller 3 and the set tube voltage value. On the other hand, the irradiation dose Doset is calculated by (Equation 2) from the dose characteristic coefficient Dt (V) and the dose characteristic constant DT (V) read from the Dt (V) storage unit 15 and the DT (V) storage unit 14, respectively. . Since this value is displayed on the panel of the X-ray controller 3, etc., the operator can determine whether or not the subject does not exceed the permissible exposure value by performing the imaging to be performed. Further, when the high voltage generator 2 has a function of actually measuring imaging conditions during X-ray irradiation, the calculation of (Equation 2) is performed after imaging using the actually measured imaging conditions, and the calculated irradiation dose Doset is controlled by X-ray control. It can also be displayed on the panel of the device 3 or the like.

  Hereinafter, the irradiation dose value calculated by (Equation 1) and (Equation 2) is compared with the actual measurement value to confirm the high accuracy of (Equation 2). FIG. 2 (a) shows that for each of the seven tube voltages from 50 kV to 110 kV, the imaging time is fixed at 8 msec, the tube current is switched to three values of 100 mA, 200 mA, and 500 mA, and at any current value. The integrated value of irradiation dose when X-ray irradiation is repeatedly performed 150 times is actually measured and tabulated. FIG. 2 (b) shows the D (V) for each tube voltage value obtained by back-calculating (Equation 1) using the actual measured radiation dose when the tube current is 100 mA and the imaging time is 8 msec in FIG. 2 (a). FIG. 2 (c) shows the irradiation dose actual measurement value when the tube current is 100 mA and the imaging time is 8 msec, and the irradiation dose actual measurement value when the tube current is 200 mA and the imaging time is 8 msec. The dose characteristic coefficient Dt (V) and dose characteristic constant DT (V) with respect to each tube voltage value obtained by solving simultaneous equations obtained by substituting into (Formula 2) are tabulated.

  Using these tables, for example, when the integrated values of the irradiation dose when X-ray irradiation is repeated 150 times at 80 kV, 500 mA, and 8 msec are calculated by (Equation 1) and (Equation 2), respectively, (0.082 μGy × 500 mA × 8 msec) × 150/1000 = 49.2 mGy is obtained, whereas in the case of (Expression 2) {(0.069 μGy × 500 mA × 8 msec) +10.107 μGy} × 150/1000 = 42.9 mGy is obtained. When these results are compared with the measured integrated value 42.80 mGy of the irradiation dose when X-ray irradiation is repeated 150 times at 80 kV, 500 mA, and 8 msec in the table of FIG. It can be seen that is substantially closer to the actually measured value than calculated by (Equation 1).

  The irradiation dose Doset calculated in the above embodiment corresponds to the dose at the position of the dosimeter 8, but the dose is inversely proportional to the square of the distance from the focal point of the X-ray tube 6. The dose at any position can be obtained.

  In the above embodiment, when the values of the dose characteristic coefficient Dt (V) and the dose characteristic constant DT (V) are acquired in advance, the dosimeter 8 is attached to the front part of the collimator 7. It may be attached at any measurable position. The dosimeter 8 may be always attached.

  In the above embodiment, the dose calculator 24 is built in the X-ray high voltage apparatus 21. However, the dose calculator 24 can be connected to the X-ray controller 3, the high voltage generator 2, and the dosimeter 8 so that the X-ray high voltage can be connected. A configuration independent of the device 21 may be adopted.

  The present invention relates to an X-ray high voltage apparatus used for X-ray fluoroscopy and radiography and an X-ray diagnostic apparatus including the X-ray high voltage apparatus.

It is a figure for demonstrating the Example of this invention. FIG. 5 is a diagram showing a relationship between imaging conditions and actually measured irradiation doses and an example of a table of dose characteristic coefficient D (V), dose characteristic coefficient Dt (V) and dose characteristic constant DT (V) obtained by Expression 1 or 2. is there. It is a figure for demonstrating a wave tail X-ray. It is a figure for demonstrating the prior art example with respect to this invention.

Explanation of symbols

1: X-ray high voltage device 2: High voltage generator 3: X-ray controller 4: Dose calculator 5: High voltage cable 6: X-ray tube 7: Collimator 8: Dosimeter 12: Calculation unit 13: D (V) Storage unit 14: DT (V) storage unit 15: Dt (V) storage unit 16: Calculation unit 21: X-ray high voltage device 24: Dose calculator

Claims (2)

In an X-ray high voltage apparatus having a dose calculation means for calculating an irradiation dose from a set or measured tube voltage, tube current, and imaging time, the dose calculation means depends on the tube current, the imaging time, and the tube voltage. In order to calculate and display the irradiation dose by a calculation formula in which a dose characteristic constant depending on the tube voltage is added to the product of the dose characteristic coefficient, a plurality of pieces measured in advance by the dose measuring means for each tube voltage are displayed. Dose characteristic coefficient storage for storing a dose characteristic coefficient depending on the tube voltage obtained by solving a plurality of sets of expressions obtained by substituting the tube current and the imaging time for each irradiation dose into the calculation formula An X-ray high voltage apparatus comprising: means and dose characteristic constant storage means for storing a dose characteristic constant depending on the tube voltage. In an X-ray diagnostic apparatus including an X-ray high voltage apparatus, information on tube voltage, tube current, and imaging time set or measured by the X-ray high voltage apparatus is received, and the tube current, imaging time, and tube voltage are received. In order to calculate and display the irradiation dose with a calculation formula that adds a dose characteristic constant that depends on the tube voltage to the product of the dose characteristic coefficient that depends on, a plurality of values measured in advance by the dose measuring means for each tube voltage Dose characteristics for storing dose characteristic coefficients depending on the tube voltage obtained by solving a plurality of formulas obtained by substituting individual irradiation doses and the tube current and the imaging time for each irradiation dose into the calculation formula An X-ray diagnostic apparatus, comprising: a dose storage means having a coefficient storage means and a dose characteristic constant storage means for storing a dose characteristic constant depending on the tube voltage.

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