JP2022001878A - Irradiation time evaluation device, irradiation time evaluation method, and computer program for irradiation time evaluation - Google Patents

Abstract

To improve temporal resolution when evaluating an irradiation time of radiation.SOLUTION: An irradiation time evaluation device evaluating an irradiation time of radiation of constant dose rate includes: a dose calculation part which analyzes frame images composing a moving image and calculates dose of the irradiated radiation; and an irradiation time calculation part which calculates an irradiation time of radiation on the basis of frame dose in a frame corresponding to the frame image. The dose calculation part acquires image property value corresponding to the number of spots in the frame image generated by radiation irradiation and converts the image property value into dose. The irradiation time calculation part calculates an irradiation time of radiation by summing up a start frame irradiation time and a stop frame irradiation time correcting frame intervals respectively on the basis of length during a fixed dose period where the frame dose is a constant reference dose and frame dose and reference dose right before and right after the fixed dose period.SELECTED DRAWING: Figure 16

Description

The present invention relates to a technique for evaluating a radiation dose, and more particularly to a technique for evaluating a radiation irradiation time.

In X-ray tomography equipment, scattered X-rays (scattered rays) affect the image taken by X-ray tomography, so the dose rate of scattered rays at a specific location of the X-ray tomography equipment is measured and X The performance of line tomography equipment is being evaluated. Since the dose rate of scattered rays at such a specific place changes by rotating the gantry in which the X-ray tube and the X-ray detector are housed in the X-ray tomography device, the scattered rays can be measured. Real-time dosimeters capable of measuring time-dependent changes in dose rate with high time resolution (0.1 to 0.5 ms) are used. However, in general, real-time dosimeters are not only expensive, but also susceptible to noise, which makes measurement itself difficult when the dose rate is low.

Therefore, a technique for measuring the dose rate of radiation more easily has been proposed. For example, in Patent Document 2, in order to measure the dose rate of radiation more easily, it is proposed to calculate the dose rate from an image matrix obtained by an image sensor in a mobile phone provided with an image sensor.

Japanese Unexamined Patent Publication No. 2014-173903 Special Table 2015-503086

However, in the method described in Patent Document 2, since the time resolution of the dose rate is determined by the frame rate at which the image matrix is acquired, it is difficult to sufficiently increase the time resolution of the irradiation time of radiation. ..

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a technique for improving the time resolution when evaluating the irradiation time of radiation using moving images.

In order to achieve at least a part of the above object, the present invention can be realized as the following form or application example.

[Application Example 1]
An irradiation time evaluation device that evaluates the time of irradiation to measure the time of irradiation with a constant dose rate, and is an image taken in an environment where the radiation may be irradiated. The moving image reproduction unit that reproduces the moving image recorded in the recording unit, the dose calculation unit that calculates the dose of the irradiated radiation by analyzing the frame image constituting the reproduced moving image, and the frame image. Each of the corresponding frames includes an irradiation time calculation unit that calculates the irradiation time of the radiation based on the frame dose that is the dose of the radiation calculated by the dose calculation unit, and the dose calculation unit includes the radiation. The image characteristic value acquisition unit that acquires the image characteristic value representing the characteristic of the frame image corresponding to the number of spots in the frame image generated by the irradiation, and the image characteristic value is converted into the dose. It has a dose conversion unit, and the irradiation time calculation unit has a length of a constant dose period in which the frame dose is a constant reference dose, and a frame dose in the frame immediately before the reference dose and the constant dose period. The frame interval was corrected based on the start frame irradiation time in which the frame interval, which is the time length of the frame, was corrected based on the above, and the reference dose and the frame dose in the frame immediately after the constant dose period. An irradiation time evaluation device that calculates the irradiation time of the radiation by adding up the stop frame irradiation times.

According to this application example, when radiation with a constant dose rate is irradiated, the irradiation time in the frame immediately before and after the constant dose period is corrected based on the reference dose and the frame dose, so that the frame interval is used. It is possible to evaluate the irradiation time of radiation with high time resolution.

[Application example 2]
The irradiation time evaluation device according to Application Example 1, wherein the image characteristic value acquisition unit has a spot counting unit that counts spots in the frame image as the image characteristic value.

According to this application example, by directly counting the spots in the frame image, the measurement accuracy of the frame dose can be further improved, so that the evaluation accuracy of the irradiation time can be further improved.

[Application example 3]
In the irradiation time evaluation device according to Application Example 1, the moving image recorded in the moving image recording unit is shot in a state where external light can be incident, and the image characteristic value acquiring unit captures the frame image. A smoothed image generation unit that generates a smoothed smoothed image, a difference image generation unit that generates a difference image obtained by subtracting the smoothed image from the frame image, and the characteristics of the difference image as the image characteristic values. An irradiation time evaluation device having a difference image characteristic value acquisition unit for acquiring a representative difference image characteristic value.

According to this application example, the dose of the irradiated radiation is calculated by analyzing the frame image taken in a state where external light can be incident. As a result, the dose at the time corresponding to the frame image can be confirmed together with the frame image of the moving image, so that the situation at the time of evaluation of the irradiation time can be confirmed more easily after the fact.

[Application example 4]
The irradiation time evaluation device according to Application Example 3, wherein the difference image characteristic value acquisition unit has a spot counting unit that counts spots in the difference image as the difference image characteristic value.

According to this application example, by directly counting the spots in the difference image, the measurement accuracy of the frame dose can be further improved, so that the evaluation accuracy of the irradiation time can be further improved.

The present invention can be realized in various aspects. For example, an irradiation time evaluation device and an irradiation time evaluation method, a computer program for realizing those devices or methods, a recording medium on which the computer program is recorded, a data signal embodied in a carrier including the computer program, etc. It can be realized in the embodiment of.

It is explanatory drawing which shows the state of performing the radiation exposure control by applying the 1st Embodiment of this invention. A block diagram showing a functional configuration for realizing a dosimetry function in a smartphone. An explanatory diagram showing how an X-ray dose is measured using a moving image taken with a smartphone. A flowchart showing the flow of the dose calculation process executed in the dose calculation unit. An explanatory diagram showing the effect of the brightness of a frame image on the number of counted spots. A graph showing the relationship between the dose and the number of spots. Explanatory diagram showing the result of comparing the calculated dose rate and the measured dose rate. A graph showing the relationship between X-ray energy and measurement sensitivity. A graph showing the results of performance comparison with a personal dosimeter. The flowchart which shows the flow of the dose calculation process in 2nd Embodiment. Explanatory drawing which shows the state of image processing for dose calculation. A graph showing the relationship between the dose rate and the number of spots. An explanatory diagram showing the results of evaluating whether various parameters representing the characteristics of the difference image can be used for dose calculation. A graph showing the results of measuring the change in dose rate over time. A graph showing the comparison result of the dose rate measurement sensitivity with the real-time dosimeter. An explanatory diagram showing how the time resolution is improved when the irradiation time is measured.

Hereinafter, embodiments for carrying out the present invention will be described in the following order.
A. First Embodiment:
A1. Radiation exposure management:
A2. Measurement of dose with smartphone:
A3. Dose calculation:
A4. Example of the first embodiment:
B. Second embodiment:
B1. Dose calculation:
B2. Example of the second embodiment:
B3. Modification example of the second embodiment:
C. Third embodiment:
C1. Measurement of dose rate time change:
C2. Comparison of measurement sensitivity with real-time dosimeters:
C3. Improved time resolution:
D. Modification example:

A. First Embodiment:
A1. Radiation exposure management:
FIG. 1 is an explanatory diagram showing a state in which radiation exposure control is performed by applying the first embodiment of the present invention. In the example of FIG. 1, the radiologist PRT stands beside the X-ray tomography apparatus CTS in order to prepare for X-ray tomography of the subject PSJ lying on the bed BED. In this way, when the radiologist PRT is at the installation site of the X-ray tomography apparatus CTS, the X-ray tomography apparatus CTS is operated so as not to be irradiated with X-rays. However, due to an operation error of the X-ray tomography device CTS or a malfunction of the X-ray tomography device CTS, the radiologist PRT is at the installation site of the X-ray tomography device CTS, but the X-ray tomography is performed. The possibility that X-rays will be emitted from the device CTS and the radiologist PRT will be exposed is not zero. About radiation doctors (radiologist PRT in the example of Fig. 1) who work in the radiation controlled area such as the installation location of the X-ray tomography device CTS in order to confirm the presence or absence of radiation exposure due to such an unforeseen situation. Is obliged to manage the dose (exposure dose) exposed to each individual within a certain period (exposure management). Conventionally, radiation dose management has been performed by measuring an individual's radiation dose with a film badge, a thermoluminescence dosimeter, a photostimulated luminescence dosimeter, or an electronic dosimeter using a semiconductor detection element. rice field.

In the first embodiment, instead of such a dosimeter, a smartphone SPH is used to measure the exposure dose of the radiologist PRT. As shown in FIG. 1, the radiologist PRT puts a smartphone SPH having an exposure dose measuring function in a chest pocket as a dosimetry device for measuring an exposure dose. The smartphone SPH is held in an exposed state so that the lens LNS of the smartphone SPH can be photographed so that the surrounding situation can be photographed.

A2. Measurement of dose with smartphone:
FIG. 2 is a block diagram showing a functional configuration for realizing a dosimetry function in a smartphone SPH.

As shown in FIG. 2, the smartphone SPH is provided with a lens LNS to which light from the outside (external light) is incident so as to be exposed on the outer surface thereof, and a display panel 102. Further, the housing of the smartphone SPH is provided with two openings APM and APS so that voice can be transmitted inside and outside the smartphone SPH. Inside the smartphone SPH, the image sensor 104 that the external light incident on the lens LNS reaches, the microphone 106 that receives the external sound transmitted through the opening APM, and the sound to the outside through the opening APS. A speaker 108 for transmitting is provided.

This smartphone SPH is configured as a computer having a display panel 102, an image sensor 104, a microphone 106, an interface with a speaker 108, a CPU, a ROM, a RAM, and the like (none of which are shown). The recording processing unit 110, the moving image recording unit 120, and the analysis processing unit 130 as functional units that realize the dosimetry function are realized by the CPU executing a computer program stored in the ROM or RAM.

The recording processing unit 110 includes an image acquisition unit 112, an audio acquisition unit 114, and a moving image data generation unit 116. The image acquisition unit 112 acquires an image formed on the light receiving surface of the image pickup device 104 as an image data FI representing one image (frame image) for each frame. The voice acquisition unit 114 acquires voice data AD representing the voice that has reached the microphone 106. The image data FI and the audio data AD are data representing the image and the audio itself, respectively. Therefore, in the following, the frame image and the image data FI representing the frame image are also referred to as "frame image FI" without distinguishing between the voice and the voice data AD representing the voice, and are also referred to as "voice AD" without distinguishing between the voice and the voice data AD representing the voice. ..

The moving image data generation unit 116 generates the moving image data MV by combining the plurality of frame image FIs acquired by the image acquisition unit 112 and the audio AD acquired by the audio acquisition unit 114. The moving image data MV is generated by compressing the frame image FI and the audio AD and storing the compressed data in a predetermined container format. The moving image data MV generated by the moving image data generation unit 116 is recorded in the moving image recording unit 120. Since the moving image data MV is also data representing the moving image itself, it is also referred to as "moving image MV" in the following without distinguishing between the moving image and the moving image data MV representing the moving image.

The analysis processing unit 130 (FIG. 2) has a moving image data reproduction unit 132, a dose calculation unit 134, and a display processing unit 136. The moving image data reproduction unit 132 reads the moving image data MV recorded in the moving image recording unit 120 and decompresses the compressed data included in the read moving image data MV to reproduce the frame image FI and the audio AD. The frame image FI reproduced by the moving image data reproduction unit 132 is supplied to the dose calculation unit 134 and the display processing unit 136. The dose calculation unit 134 calculates the dose of X-rays irradiated to the smartphone SPH by analyzing the frame image FI supplied from the moving image data reproduction unit 132. The method of calculating the dose from the frame image FI will be described later.

The display processing unit 136 acquires the dose calculated by the dose calculation unit 134, and generates an image (dose display image) that visualizes and represents the dose (or dose rate). As the dose display image, an image showing the time change of the dose and the integrated value of the dose may be generated in place of the dose or in addition to the dose.

The display processing unit 136 also generates a display image DI in which the dose display image is superimposed on the frame image FI supplied from the moving image data reproduction unit 132, and supplies the generated display image DI to the display panel 102. The audio AD reproduced by the moving image data reproduction unit 132 is supplied to the speaker 108. This makes it possible to confirm the dose applied to the smartphone SPH while the audio AD is being reproduced in synchronization with the frame image FI (that is, the moving image representing the moving image MV). Therefore, when radiation exposure occurs, the situation at the time of radiation exposure can be confirmed after the fact by viewing the moving image MV (that is, the frame image FI and the audio AD).

In the first embodiment, the moving image MV used for calculating the dose includes the audio AD, but the moving image not including the audio AD may be used to calculate the dose. Further, when the dose is calculated using the moving image MV including the voice AD, it is possible to omit the reproduction of the voice AD. Even in this way, by viewing the moving image, it is possible to confirm the situation at the time of the exposure after the fact when the exposure occurs. However, it is preferable to calculate the dose using the moving image MV including the voice AD in that the situation at the time of exposure can be grasped more accurately.

A3. Dose calculation:
FIG. 3 is an explanatory diagram showing a state of measuring an X-ray dose using a moving image taken by a smartphone SPH, and in the example of FIG. 1, a frame image in a moving image taken by a smartphone SPH possessed by a radiologist PRT. (Shooted image) is shown.

As shown in FIG. 3A, in a state where X-rays are not emitted from the X-ray tomography apparatus CTS (FIG. 1), the captured image taken by the smartphone SPH is an image sensor in which the light incident from the lens LNS is taken. It becomes an image (background) formed on the light receiving surface of 104 (FIG. 2). At this time, when X-rays are emitted from the X-ray tomography apparatus CTS, as shown in FIG. 3 (b), spot-like noise having high brightness (hereinafter,) in the captured image in a state of being superimposed on the background. , Simply called a "spot") appears.

The spots appearing in this captured image increase or decrease according to the dose of X-rays applied to the smartphone SPH during one frame. Therefore, in the moving image MV stored in the moving image recording unit 120, the dose of X-rays irradiated to the smartphone SPH, that is, the radiologist PRT holding the smartphone SPH, is used as the number of spots in the frame image FI. The dose of the exposed X-ray is recorded every frame. Therefore, as shown in FIG. 3 (c), by counting the number of spots appearing in the frame image FI of the moving image MV (counting the spots), the dose of X-rays irradiated to the smartphone SPH for each frame Can be calculated and the dose of X-rays exposed by the radiologist PRT holding the smartphone SPH can be measured.

As described above, in the first embodiment, the dose is measured for each frame. Therefore, unless otherwise specified, the dose during one frame is simply referred to as the dose. The dose rate can be calculated by dividing the dose during this one frame by the time interval (frame interval) of the frames. Therefore, the dose and the dose rate are substantially equivalent.

The dose irradiated during the desired period was calculated by integrating the dose per frame for a plurality of frame image FIs corresponding to the desired period, or counting by a plurality of frame image FIs corresponding to the desired period. The number of spots can be integrated and calculated from the integrated number of spots (that is, the number of spots included in a plurality of frame image FIs). Further, when calculating the dose rate, it is also possible to calculate the dose irradiated in the preset measurement unit time (for example, 1 second) and divide the calculated dose by the measurement unit time.

FIG. 4 is a flowchart showing the flow of the dose calculation process executed by the dose calculation unit 134 (FIG. 2). Since the dose calculation unit 134 performs processing as shown in the flowchart of FIG. 4, it can be considered that the dose calculation unit 134 has a functional unit corresponding to each step S100 to S108 of the flowchart.

In step S102, the dose calculation unit 134 counts the number of spots in the frame image FI acquired from the moving image data reproduction unit 132. The number of spots is, for example, detected as a point (maximum point) at which the brightness has a two-dimensional maximum value in the frame image FI, and is counted as the number of the detected maximum points.

The dose calculation unit 134 calculates the average luminance of the frame image FI in step S104, and corrects (acquires the number of corrected spots) the number of spots counted in step S102 based on the average luminance in step S106. By correcting the number of spots in this way, it is possible to prevent the number of spots from being counted lower as the average brightness of the frame image FI increases. The order of the step S102 for counting the number of spots and the step S104 for calculating the average luminance can be exchanged.

FIG. 5 is an explanatory diagram showing the influence of the brightness of the frame image FI (that is, the brightness of the background) on the number of counted spots. FIG. 5A shows an image (frame image FI) for one frame when a gray chart is taken by the smartphone SPH and the smartphone SPH is irradiated with X-rays. As shown in FIG. 5A, by irradiating the smartphone SPH with X-rays, spots appear in the frame image FI superimposed on the background gray chart image.

FIG. 5B shows the result of evaluating the relationship between the average luminance (background luminance) Y and the counted number of spots Ns in each region surrounded by a rectangular frame on the image of this gray chart. .. In FIG. 5B, the horizontal axis and the vertical axis represent the background luminance Y and the number of spots Ns, respectively.

As shown in FIG. 5B, the relationship between the background luminance Y and the number of spots Ns is well represented by the regression line. Therefore, the corrected number of spots Ns'can be determined based on the regression line applied to the background luminance Y and the number of spots Ns. Specifically, when the regression line is represented by the following mathematical formula (1), the corrected number of spots Ns'is calculated using the mathematical formula (2). The relationship between the background brightness Y and the number of spots Ns may be experimentally obtained for each smartphone SPH model.

After correcting the number of spots, in step S108 (FIG. 4), the dose calculation unit 134 converts the corrected number of spots into a dose. As described above, since the number of counted spots and the number of corrected spots are both parameters calculated from the frame image FI, they can also be said to be image characteristic values representing the characteristics of the frame image FI. Further, since the number of counted spots and the number of corrected spots are both the number of spots themselves, it is obvious that they are associated with the number of spots.

FIG. 6 is a graph showing the relationship between the dose rate Rd and the corrected number of spots Ns'. In FIG. 6, the horizontal axis and the vertical axis represent the dose rate Rd and the corrected number of spots Ns', respectively. FIG. 6 shows a value measured by a calibration dosimeter placed close to the smartphone SPH as the dose rate Rd. As shown in FIG. 6, the relationship between the dose rate Rd and the number of spots Ns'is also well represented by the regression line. The dose rate Rd is converted from the number of spots Ns'using the regression line experimentally obtained in this way. The number of spots Ns'is zero (that is, the intercept of the regression line is negative) in the region where the dose rate Rd is higher than zero and below a specific value is the lens LNS of the smartphone SPH (FIG. 1). It is probable that X-rays were absorbed by the housing and the housing. In this way, the region where the number of spots Ns'is zero is usually called a dead zone or a dead zone.

A4. Example of the first embodiment:
As an example of the first embodiment, the brightness of the background is changed, the dose rate calculated from the number of spots in the frame image FI (calculated dose rate), and the dose rate measured by a calibration dosimeter (measured dose rate). And compared. Specifically, under specific lighting conditions, a moving image was taken with a smartphone SPH (FIG. 1) while irradiating with X-rays, and the dose rate was calculated from the taken moving image as described above. At the same time as shooting the moving image, a dosimeter for calibration was placed close to the smartphone SPH, and the dose rate at the time of shooting the moving image was measured. The brightness of the background was changed by using the dimming function of the lighting device.

FIG. 7 is an explanatory diagram showing the results of comparing the calculated dose rate and the measured dose rate as an example. The photograph of FIG. 7 shows a frame image used for calculating the dose rate. Below the frame image FI in FIG. 7, the number of counted spots (counting spots), average brightness, corrected number of spots (corrected spots), calculated dose rate, measured dose rate, and the measured dose rate in the frame image. , The error (calculation error) of the calculated dose rate with respect to the measured dose rate is shown. As shown in FIG. 7, it was confirmed that the calculation error was within a sufficiently acceptable ± 8% even though the measured dose rate was relatively low (about 20 μGy / s). ..

Next, the effect of X-ray energy on the measurement sensitivity was evaluated. Specifically, under the state where the energy of the irradiated X-rays was set variously, the relationship between the dose rate of the irradiated X-rays and the number of spots after correction was obtained, and the measurement sensitivity was evaluated. The measurement sensitivity was evaluated by the slope (conversion coefficient) of the regression line (see FIG. 6) applied to the dose rate Rd and the number of spots Ns'. The energy of the irradiated X-ray was adjusted by changing the voltage applied to the X-ray tube (voltage applied to the X-ray tube). FIG. 8 is a graph showing the relationship between the energy of X-rays and the measurement sensitivity, and the horizontal axis and the vertical axis represent the voltage applied to the X-ray tube and the conversion coefficient, respectively. As shown in FIG. 8, even when the voltage applied to the X-ray tube was changed from 80 kVp to 140 kVp, the fluctuation range of the conversion coefficient was within a sufficiently acceptable ± 6%. From this, it was found that according to the first embodiment, the dose can be measured with sufficiently high accuracy even if the energy of the X-ray to be measured changes.

Further, conventionally, measuring the dose of γ-rays using an image pickup element (see, for example, Patent Document 1) and measuring the dose of high-energy proton beams (see, for example, Japanese Patent Application Laid-Open No. 2001-255372). However, for X-rays with relatively low energy, a technique for measuring the dose using an image pickup element has not been established. However, this time, as shown in the above examples, it was confirmed that the dose of X-rays can be measured by using an image sensor according to the present invention.

Next, the measurement sensitivity of the dose measurement technique using the smartphone SPH (FIG. 1) as the first embodiment and the small personal dosimeter (personal dosimeter) was compared. For comparison of measurement sensitivity, a personal dosimeter was placed close to the smartphone SPH, and the corrected number of spots was compared with the reading of the personal dosimeter. FIG. 9 is a graph showing the performance comparison result with the personal dosimeter. In FIG. 9, the horizontal axis and the vertical axis represent the current (X-ray tube current) and the number of spots Ns'that flowed through the X-ray tube when the X-ray tube was driven, respectively. Further, in the graph of FIG. 9, the numbers displayed in close proximity to the black circle markers indicate the readings of the personal dosimeter. Since the dose rate of X-rays emitted by the X-ray tube is proportional to the X-ray tube current, the X-ray tube current corresponds to the dose rate of the irradiated X-rays. As shown in FIG. 9, according to the first embodiment, the number of spots Ns'changed linearly with respect to the X-ray tube current even in a low dose region where it was difficult to measure with a personal dosimeter. From this, it was found that according to the first embodiment, it is possible to measure the dose with higher accuracy than that of a commonly used personal dosimeter.

As described above, in the first embodiment, the moving image MV taken in a state where external light can be incident is recorded in an environment where radiation may be irradiated. Then, by analyzing the frame image FI of the recorded moving image MV, the dose of X-rays applied to the smartphone SPH is calculated. As a result, the dose at the time of recording can be confirmed while the moving image MV is being played, so that when exposure occurs, the situation at the time of exposure can be confirmed after the fact by watching the moving image MV. can.

Further, in the first embodiment, in the calculation of the dose, the number of spots appearing in the frame image FI is counted, and the number of spots counted by the average brightness of the frame image FI is corrected. Then, the dose is calculated by converting the corrected number of spots into the dose. As a result, the influence of the brightness of the background can be reduced, and the dose can be measured with sufficiently high accuracy.

Further, in the first embodiment, the smartphone SPH realizes a dosimetry function. Therefore, the dose can be measured more easily. As a device for realizing the dose measurement function, various portable devices such as a mobile phone, a portable music player, or a portable video recorder are used in addition to the smartphone SPH if it is possible to record and play back a moving image. can do.

In the first embodiment, the number of spots counted by the average brightness of the frame image FI is corrected, but the correction of the number of spots can be omitted. In this case, in order to suppress the influence of the brightness of the background on the count of the number of spots, the aperture may be sufficiently reduced or the shutter speed may be sufficiently increased so that the background can be confirmed. Further, the automatic exposure function may be used so that the average brightness of the background becomes substantially constant. However, in order to increase the accuracy of dose measurement more reliably, it is preferable to correct the number of spots based on the background brightness.

In the first embodiment, the present invention is applied to the measurement of the dose of X-rays, but in the present invention, in addition to the measurement of the dose of X-rays, an image pickup device 104 such as a γ-ray, an electron beam, or a proton beam is used. Any radiation that can reach the above can be applied to measure the dose of various radiations.

B. Second embodiment:
B1. Dose calculation:
FIG. 10 is a flowchart showing the flow of the dose calculation process in the second embodiment. In the second embodiment, the process of calculating the dose from the acquired frame image is different from that in the first embodiment. Other points are the same as those of the first embodiment. Therefore, in the following, the description of the parts common to the first embodiment will be omitted.

FIG. 11 is an explanatory diagram showing a state of image processing executed in the dose calculation processing of the second embodiment. The frame image FI acquired from the moving image data reproduction unit 132 by the dose calculation unit 134 (FIG. 2) is shown. Since the frame image FI shown in FIG. 11A is an image taken in a state of being irradiated with X-rays, spots appear as described above.

In step S202, the dose calculation unit 134 (FIG. 2) generates a smoothed image by performing a smoothing process on the frame image FI acquired from the moving image data reproduction unit 132. The smoothing process can be performed using a well-known median filter. As the filter used for the smoothing process, a moving average filter, a Gaussian filter, or the like can be used in addition to the median filter. However, a median filter is used to suppress the appearance of false images (artifacts) due to edge blur in the frame image FI in the difference image (described later) generated from the frame image FI and the smoothed image. Is preferable.

Generally, the size of the spot appearing in the frame image FI is about the size of one pixel in which X-ray photons are incident. Therefore, by applying the smoothing process to the frame image FI, the spot can be sufficiently made. Will be removed. Therefore, as shown in FIG. 11B, a smoothed image from which spots have been removed can be obtained even when the edge blur in the frame image FI is sufficiently suppressed.

After generating the smoothed image, in step S204, the dose calculation unit 134 subtracts the smoothed image from the frame image FI to generate a difference image. Since the difference image is generated by subtracting the smoothed image from which the spot is removed from the frame image FI in which the spot appears, the difference image has the background removed as shown in FIG. 11 (c). The image contains almost only spots.

In step S206, the dose calculation unit 134 counts the number of spots in the difference image. The counting of the number of spots can be performed in the same manner as the counting of the number of spots (step S102) in the dose calculation process (FIG. 4) of the first embodiment. In step S208, the dose calculation unit 134 converts the number of spots into a dose. The conversion of the number of spots to the dose can also be performed in the same manner as the conversion of the number of spots to the dose (step S108) in the dose calculation process (FIG. 4) of the first embodiment.

As described above, in the second embodiment, the difference image from which the background is removed is used for counting the number of spots. Therefore, the number of spots can be counted with sufficiently high accuracy regardless of the level of the average brightness of the background. Therefore, in the second embodiment, the correction of the number of spots is omitted. Since the counted number of spots is a parameter calculated from the difference image, it can be said to be a difference image characteristic value representing the characteristics of the difference image. Further, since the difference image is an image generated from the frame image FI, the number of spots can be said to be a difference image characteristic value as well as an image characteristic value representing the characteristics of the frame image FI.

B2. Example of the second embodiment:
As an example of the second embodiment, the relationship between the number of spots and the dose rate measured by a dosimeter for calibration was evaluated. Specifically, a moving image was shot by the smartphone SPH (FIG. 1) while irradiating with X-rays, and the number of spots was counted from the shot moving image as described above. At the same time as shooting the moving image, a dosimeter for calibration was placed close to the smartphone SPH, and the dose rate at the time of shooting the moving image was measured.

FIG. 12 is a graph showing the relationship between the dose rate Rd and the number of spots Ns. In FIG. 12, the horizontal axis and the vertical axis represent the actually measured dose rate Rd and the number of spots Ns, respectively. As shown in FIG. 12, also in the second embodiment, the relationship between the dose rate Rd and the number of spots Ns ”is well represented by the regression line. Therefore, it is sufficiently high also in the second embodiment. It was found that it is possible to measure the dose with accuracy.

B3. Modification example of the second embodiment:
As shown in FIG. 10, in the second embodiment, the number of spots appearing in the frame image FI is counted (step S206), and the number of counted spots is converted into a dose, as in the first embodiment. .. However, in the second embodiment, in step S206, the background is removed by subtracting the smoothed image from the frame image FI, and a difference image containing almost only spots is generated. Therefore, as the difference image characteristic value corresponding to the number of spots, it is possible to use various parameters representing the characteristics of the difference image in addition to the number of spots. As such a parameter, for example, the average luminance of the difference image or the luminance variance of the difference image can be used. Here, the luminance variance is a parameter obtained by squared the standard deviation of the luminance.

FIG. 13 is an explanatory diagram showing the results of evaluating whether or not various parameters representing the characteristics of the difference image can be used for calculating the dose. Specifically, for the moving image taken in the embodiment of the second embodiment, the average luminance Y and the luminance variance σ ² (also referred to as “SD ² ”) are calculated as the difference image characteristic values, and the measured dose rate Rd And the relationship between the average luminance Y and the luminance variance σ ² were evaluated.

FIG. 13A is a graph showing the relationship between the dose rate Rd and the average luminance Y. As shown in FIG. 13A, the relationship between the dose rate Rd and the average luminance Y was relatively well represented by the regression line. From this, it was confirmed that it is sufficiently effective to calculate the dose using the average luminance Y of the difference image. However, compared with the relationship between the dose rate Rd and the number of spots Ns ”shown in FIG. 12, the average luminance Y varies widely, and the average luminance Y is particularly high in the region where the dose rate Rd is low (200 μGy / s or less). It deviated greatly from the regression line.

FIG. 13B is a graph showing the relationship between the dose rate Rd and the luminance variance σ ^2. As shown in FIG. 13B, the relationship between the dose rate Rd and the luminance variance σ ² was also relatively well represented by the regression line. From this, it was confirmed that it is sufficiently effective to calculate the dose using the luminance variance σ ^{2 of the difference image.} However, in the region where the dose rate Rd was particularly low (100 μGy / s or less), non-linearity was observed. Further, compared with the relationship between the dose rate Rd and the number of spots Ns ”shown in FIG. 12, the brightness is not as high as when the average brightness Y is used (FIG. 13A), but the brightness is not as high as the dose rate Rd. The variation of the variance σ ^{2 became large.}

From these results, when measuring the dose with higher accuracy, it is more preferable to calculate the dose using the ^{luminance variance σ 2} rather than the average luminance Y, and the number of spots Ns is used rather than ^{the luminance variance σ 2.} On the other hand, the ^{calculation amount required for calculating the luminance variance σ 2} is larger than the calculation amount required for calculating the average luminance Y, and the calculation required for calculating the number of spots Ns ”. Less than the amount. Therefore, in order to calculate the dose more easily, it is more preferable to calculate the dose using the ^{luminance variance σ 2} rather than the number of spots Ns ”, and to calculate the dose using the average luminance Y rather than ^{the luminance variance σ 2.} It is more preferable to calculate.

As described above, in the second embodiment, the difference image including almost only the spots is generated by subtracting the smoothed image from the frame image FI, and the number of spots in the generated difference image is counted. Then, the dose is calculated by converting the counted number of spots into the dose. Therefore, as in the first embodiment, the influence of the brightness of the background can be reduced and the dose can be measured with sufficiently high accuracy.

Further, also in the second embodiment, as in the first embodiment, the dose of X-rays irradiated to the smartphone SPH is analyzed by analyzing the frame image FI of the moving image MV taken in a state where external light can be incident. Is calculated. Therefore, when radiation exposure occurs, the situation at the time of radiation exposure can be confirmed after the fact by watching the moving image MV.

In the first embodiment, since the number of spots is directly counted in the frame image FI, it becomes difficult to distinguish between the spot and the background when the brightness of the background becomes extremely high, and the number of spots is accurate even if correction is performed. May be difficult to obtain. On the other hand, in the second embodiment, since the number of spots is counted in the difference image containing almost only the spots, the number of spots can be counted more accurately even when the brightness of the background is extremely high. .. In this respect, the second embodiment is preferable to the first embodiment.

On the other hand, in the second embodiment, the smoothed image is subtracted from the frame image FI to generate a difference image to be counted by the number of spots. Therefore, when the contrast of the background in the frame image FI is extremely high, a false image due to the blurring of the edges in the frame image FI by the smoothing process appears in the difference image, and it becomes difficult to obtain an accurate number of spots. There is a risk. On the other hand, in the first embodiment, since the number of spots is directly counted in the frame image FI, no false image is generated and the number of spots can be counted more accurately. In this respect, the first embodiment is preferable to the second embodiment.

C. Third embodiment:
C1. Measurement of dose rate time change:
As described above, in the dosimetry technique of the present invention, a moving image is taken by a smartphone SPH (FIG. 2) placed in an environment where X-rays may be irradiated, and the taken moving image is analyzed. The dose of X-rays irradiated to the smartphone SPH is calculated. Since the moving image contains a plurality of frame image FIs taken at frame intervals (usually 1/240 to 1 / 30s), the dose rate is calculated with the time resolution of the frame intervals by calculating the dose for each frame. The time change can be measured. Therefore, as the third embodiment, the dose was calculated for each frame and the time change of the dose rate was measured as in the first embodiment. Since the configuration of the smartphone SPH used for the measurement and the method of calculating the dose are the same as those in the first embodiment, the description thereof will be omitted here.

By the way, in the X-ray tomography apparatus CTS (FIG. 1), scattered X-rays (scattered rays) affect the image taken by the X-ray tomography. Therefore, the dose rate of scattered rays at a specific location of the X-ray tomography apparatus CTS is measured, and the performance of the X-ray tomography apparatus CTS is evaluated. Since the dose rate of scattered rays at a specific location changes by rotating the gantry in which the X-ray tube and the X-ray detector are stored in the X-ray tomography device CTS, it takes a long time to measure the scattered rays. A real-time dosimeter capable of measuring the time change of the dose rate with a resolution (0.1 to 0.5 ms) is used. However, such a real-time dosimeter is not only expensive, but also susceptible to noise, which makes measurement itself difficult when the dose rate is low. Further, depending on the performance evaluation method of the X-ray tomography apparatus CTS, the time resolution does not necessarily have to be high, and a time resolution of about a frame interval (1/240 ≈ 4.17 ms) that can be used in moving images is sufficient. It is considered to be effective for. Therefore, as a third embodiment, whether or not it is useful as a performance evaluation of the X-ray tomography apparatus CTS by measuring the time change of the dose rate by analyzing the moving image taken by the smartphone SPH with the frame interval set to 1/240. Was evaluated.

FIG. 14 is a graph showing the results of measuring the time change of the dose rate. The measured dose rate is the dose rate of scattered rays when the gantry is rotated at one rotation per second and X-rays are irradiated for 1 second. In FIG. 14, the solid line shows the dose rate (calculated dose rate) calculated from the number of spots (the number of spots after correction) in the frame image FI, and the broken line shows the dose rate (measured dose) measured by a real-time dosimeter. Rate) is shown. Further, the horizontal axis and the vertical axis of FIG. 14 represent time and dose rate (arbitrary scale), respectively. In FIG. 14, for convenience of illustration, the calculated dose rate and the measured dose rate are plotted by shifting them in the vertical axis direction. As shown in FIG. 14, the calculated dose rate changed in the same pattern as the measured dose rate. From this, it is possible to evaluate the performance of the X-ray tomography apparatus CTS by calculating the dose rate from the number of spots in the frame image FI when the gantry is rotated at one rotation per second. I understood.

C2. Comparison of measurement sensitivity with real-time dosimeters:
The measurement sensitivity of the dose rate was compared between the dose measurement technique of the third embodiment and the real-time dosimeter. As described above, it is difficult for a real-time dosimeter to measure a dose rate in a region where the dose rate is low (for example, 100 μGy / s or less). Therefore, it was confirmed whether or not the number of spots corresponds to the dose rate measured by the calibration dosimeter in the area including the dose rate that is difficult to measure with the real-time dosimeter.

FIG. 15 is a graph showing the comparison result of the dose rate measurement sensitivity with the real-time dosimeter. In FIG. 15, the horizontal axis and the vertical axis represent the dose rate Rd measured by the calibration dosimeter and the corrected number of spots Ns'calculated from the frame image FI, respectively. The markers indicating the correspondence between the dose rate Rd and the number of spots Ns'are black circles for the measurable range of the real-time dosimeter and white squares for the outside of the measurable range of the real-time dosimeter. As shown in FIG. 15, according to the third embodiment, the number of spots Ns'changed linearly with respect to the dose rate Rd even outside the measurable range of the real-time dosimeter. From this, it was found that according to the third embodiment, it is possible to measure the dose with a higher measurement sensitivity than the real-time dosimeter.

As described above, in the third embodiment, by applying the dosimetry technique of the present invention to the measurement of the time change of the dose rate, the dose rate under specific conditions such as the evaluation of the performance of the X-ray tomography apparatus CTS can be obtained. With regard to the measurement of time change, it is possible to measure with a sufficiently high time resolution. Therefore, according to the third embodiment, it is possible to more easily measure the time change of the dose rate. Further, according to the third embodiment in which the dose measurement technique of the present invention is applied to the measurement of the time change of the dose rate, the dose rate is measured with higher accuracy in the region where the dose rate is low as compared with the real-time dosimeter. be able to.

Further, since the third embodiment applies the dosimetry technique of the present invention, the dose at the time of recording can be confirmed while playing the moving image MV. Therefore, it is easier to understand the relationship between the rotational state of the gantry and the dose of scattered radiation in the X-ray tomography apparatus CTS, or the relationship between the position of the X-ray tube and the dose of scattered radiation in the general X-ray imaging apparatus. be able to.

In the third embodiment, the dosimetry technique of the present invention is applied to the measurement of the time change of the dose rate, but when the time change of the dose rate is measured, the visible light is shielded from the outside of the lens LNS and the radiation is emitted. It is also possible to shoot a moving image in a state where external light is not incident by a method such as attaching a light-shielding member that transmits light. In this case, the number of spots in the uncorrected frame image FI, the luminance dispersion of the frame image FI, or the average luminance of the frame image FI may be converted into the dose rate. In addition, when evaluating only the pattern of time change of the dose rate, the conversion to the dose rate (dose) is omitted, and the number of spots, brightness dispersion, or average brightness is a parameter corresponding to the dose rate. It can also be treated as (dose rate parameter).

C3. Improved time resolution:
When measuring the time change of the dose rate in the third embodiment, as described above, the time resolution is limited to the frame interval. However, when measuring the X-ray irradiation time or the like, it is possible to make the time resolution shorter than the frame interval. FIG. 16 is an explanatory diagram showing how the time resolution is improved when the irradiation time is measured. 16 (a) and 16 (c) show the time change of the dose rate (irradiation dose rate) of the X-rays irradiated to the smartphone SPH (FIG. 1), and the calculated dose per frame (frame), respectively. It is a graph showing the time change of dose). FIG. 16B is a schematic diagram showing each frame constituting the moving image. Further, FIG. 16B is a schematic diagram showing how the irradiation time is corrected and the time resolution is improved. In FIGS. 16 (a) to 16 (d), the horizontal axis represents time. Further, in FIGS. 16A and 16C, the vertical axis represents the irradiation dose rate and the frame dose, respectively.

As shown in FIG. 14, when X-ray irradiation is started or stopped, the dose rate changes sharply at the start time and the stop time. Also, the dose rate of the irradiated X-rays is usually kept constant. Therefore, as shown in FIG. 16A, the graph showing the time change of the irradiation dose rate has a rectangular shape.

In the example of FIG. 16B, the moving image is shot for n frames, and the X-ray irradiation is performed from the middle of the second frame F [2] of the moving image to the n-1st frame F [n−. It is carried out until the middle of 1]. Therefore, as shown in FIG. 16 (c), the frame dose is the third frame F in which irradiation is continued in the second frame F [2] and the n-1st frame F [n-1]. It is lower than the n-2nd frame F [n-2] from [3]. In this way, in the frame where the frame dose is kept constant, the X-ray irradiation is continued, and the X-ray irradiation is started or stopped in the middle of the frame in which the frame dose is low. It can be judged that it was done.

In this way, when the X-ray irradiation is started or stopped in the middle of the frame, the ratio of the frame dose in the frame to the frame dose in the frame in which the irradiation is continued is the ratio of the X-ray irradiation in the frame. Equal to the ratio of time spent to frame spacing.

In the example of FIG. 16, in the second frame F [2], X-rays are irradiated in the half period of the latter half of the frame, and in the n-1st frame F [n-1], the first half of the frame is irradiated. X-rays are irradiated for a period of 1/4. Therefore, the frame doses in the second frame F [2] and the n-1st frame F [n-1] are the frames F [3] to F [n-] in which the X-ray irradiation is continued, respectively. It is 1/2 and 1/4 of the frame dose in 2].

Therefore, as shown in FIG. 16 (d), the frame doses are lower than the frame doses in the frames F [3] to F [n-2] in which the X-ray irradiation is continued. For n-1], the irradiation time is modified according to the ratio of the frame dose, and the frame F [2] immediately before the frames F [3] to F [n-2] where the X-ray irradiation is continued. Then, the X-ray irradiation is started before the end of the frame F [2] by the corrected irradiation time, and the X-ray irradiation is continued in the frames F [3] to F [n-2]. In the frame F [n-1] immediately after, it is assumed that the X-ray irradiation is stopped after the beginning of the frame F [n-1] by the corrected irradiation time. This makes it possible to measure the X-ray irradiation time with a time resolution shorter than the frame interval.

In the example of FIG. 16, by modifying the irradiation time, the X-ray irradiation time in the frame F [2] becomes 1/2 of the frame interval, and the X-ray irradiation time in the frame F [n-1] is the frame interval. It becomes 1/4 of. The X-ray irradiation time is the time length of the period (constant dose period) corresponding to the frames F [3] to F [n-2] at which the frame dose is constant, and the frame F immediately before the constant dose period. It is calculated by adding the corrected irradiation time in [2] and the corrected irradiation time in the frame F [n-1] immediately after the constant dose period.

In this way, the corrected irradiation time in the frames F [2] and F [n-1] immediately before and after the constant dose period added to the time length of the constant dose period when calculating the irradiation time is Based on the ratio of the frame dose in each frame to the frame dose (reference dose) in frames F [3] to F [n-2] during the constant dose period, the frame interval, which is the time resolution in the measurement of irradiation time, is corrected. It will be the time.

In the example of FIG. 16, in the frames F [2] and F [n-1] immediately before and after the constant dose period, the frame interval is corrected based on the ratio of the frame dose to the reference dose. In general, the frame interval may be corrected based on the frame dose and the reference dose in each frame. For example, if the rise of the irradiation dose rate at the start of irradiation and the fall of the irradiation dose rate at the stop of irradiation are not steep enough, the frame interval may be corrected in consideration of the rising and falling characteristics of the irradiation dose rate. It is possible.

In this way, when measuring the time of irradiation with a constant dose rate, the irradiation time is corrected based on the frame dose and the reference dose in the frame immediately before and the frame immediately after the constant dose period, respectively. By adding up the frame interval and the time length of the constant dose period, the radiation irradiation time can be measured with a time resolution higher than that of the frame interval.

D. Modification example:
The present invention is not limited to each of the above embodiments, and can be carried out in various embodiments without departing from the gist thereof. For example, the following modifications can be made.

D1. Modification 1: Modification 1:
In each of the above embodiments, in order to realize the dosimetry function, a smartphone SPH, which is a portable device capable of recording and playing back moving images, is used. However, the dosimetry function does not necessarily have to be realized using a mobile device. For example, it is possible to realize a dosimetry function by using a personal computer or the like capable of recording and playing back a moving image. However, it is preferable to realize the dosimetry function by a portable device such as a smartphone SPH in that the dose can be measured more easily.

D2. Modification 2:
In each of the above embodiments, the integrated smartphone SPH realizes a function of shooting a moving image MV, a function of recording a moving image MV, and a function of calculating a dose using the recorded moving image MV. It is also possible to realize at least a part of each function of the above in a separate device. For example, the present invention uses a surveillance camera having a function of shooting a moving image MV, a recording device having a function of recording a moving image MV, and an analysis computer having a function of calculating a dose using the recorded moving image MV. It is also possible to carry out. Further, the present invention is carried out using a video recorder having a function of shooting a moving image MV and a function of recording a moving image MV, and an analysis computer having a function of calculating a dose using the recorded moving image MV. It may be a thing. However, it is preferable to realize each of these functions in an integrated device in that the dose can be measured more easily. Further, the present invention can also be implemented as a device (dose evaluation device) that realizes only the function of calculating the dose using the recorded moving image MV among each of these functions.

102 ... Display panel 104 ... Image sensor 106 ... Microphone 108 ... Speaker 110 ... Recording processing unit 112 ... Image acquisition unit 114 ... Audio acquisition unit 116 ... Video data generation unit 120 ... Video recording unit 130 ... Analysis processing unit 132 ... Video data playback Part 134 ... Dose rate calculation part 136 ... Display processing part APM, APS ... Opening BED ... Sleeper CTS ... Line tomography device LNS ... Lens PRT ... Radiologist PSJ ... Subject SPH ... Smartphone

Claims (6)

An irradiation time evaluation device that evaluates the time of irradiation in order to measure the time of irradiation with a constant dose rate.
A moving image reproduction unit that reproduces a moving image taken in an environment where the radiation may be applied and recorded in the moving image recording unit, and a moving image reproduction unit.
A dose calculation unit that calculates the dose of the irradiated radiation by analyzing the frame image that constitutes the reproduced moving image, and
An irradiation time calculation unit that calculates the irradiation time of the radiation based on the frame dose, which is the dose of the radiation calculated by the dose calculation unit in each of the frames corresponding to the frame images.
Equipped with
The dose calculation unit
An image characteristic value acquisition unit that acquires an image characteristic value representing the characteristics of the frame image corresponding to the number of spots in the frame image generated by irradiation with the radiation, and an image characteristic value acquisition unit.
A dose conversion unit that converts the image characteristic value into the dose, and
Have and
The irradiation time calculation unit determines the time length of the frame based on the length of the constant dose period in which the frame dose is a constant reference dose, the reference dose, and the frame dose in the frame immediately before the constant dose period. By adding up the start frame irradiation time corrected for the frame interval and the stop frame irradiation time corrected for the frame interval based on the reference dose and the frame dose in the frame immediately after the constant dose period. Calculate the irradiation time of radiation,
Irradiation time evaluation device. The irradiation time evaluation device according to claim 1, wherein the image characteristic value acquisition unit has a spot counting unit that counts spots in the frame image as the image characteristic value. The irradiation time evaluation device according to claim 1.
The moving image recorded in the moving image recording unit is taken in a state where external light can be incident on the moving image.
The image characteristic value acquisition unit is
A smoothed image generator that generates a smoothed image obtained by smoothing the frame image,
A difference image generation unit that generates a difference image obtained by subtracting the smoothed image from the frame image,
As the image characteristic value, a difference image characteristic value acquisition unit that acquires a difference image characteristic value representing the characteristic of the difference image, and a difference image characteristic value acquisition unit.
Have,
Irradiation time evaluation device. The irradiation time evaluation device according to claim 3, wherein the difference image characteristic value acquisition unit has a spot counting unit that counts spots in the difference image as the difference image characteristic value. It is an irradiation time evaluation method for evaluating the time of irradiation in order to measure the time of irradiation with a constant dose rate.
A moving image reproduction process of reproducing a moving image taken in an environment where the radiation may be applied and recorded in the moving image recording unit, and
A dose calculation step for calculating the dose of the irradiated radiation by analyzing the frame image constituting the reproduced moving image, and a dose calculation step.
An irradiation time calculation step of calculating the irradiation time of the radiation based on the frame dose, which is the dose of the radiation calculated by the dose calculation unit in each of the frames corresponding to the frame images.
Equipped with
The dose calculation step is
An image characteristic value acquisition step of acquiring an image characteristic value representing the characteristics of the frame image corresponding to the number of spots in the frame image generated by irradiation with the radiation.
A dose conversion step for converting the image characteristic value into the dose, and
Have and
In the irradiation time calculation step, the time length of the frame is based on the length of the constant dose period in which the frame dose is a constant reference dose, the reference dose and the frame dose in the frame immediately before the constant dose period. By adding up the start frame irradiation time corrected for the frame interval and the stop frame irradiation time corrected for the frame interval based on the reference dose and the frame dose in the frame immediately after the constant dose period. Calculate the irradiation time of radiation,
Irradiation time evaluation method. A computer program for evaluating the time of irradiation to measure the time of irradiation with a constant dose rate.
A moving image reproduction process for reproducing a moving image taken in an environment where the radiation may be applied and recorded in the moving image recording unit, and
A dose calculation process for calculating the dose of the irradiated radiation by analyzing the frame image constituting the reproduced moving image, and a dose calculation process.
Irradiation time calculation processing that calculates the irradiation time of the radiation based on the frame dose, which is the dose of the radiation calculated by the dose calculation unit in each of the frames corresponding to the frame images.
Let the computer run
In the dose calculation process
An image characteristic value acquisition process for acquiring an image characteristic value representing the characteristics of the frame image corresponding to the number of spots in the frame image generated by irradiation with the radiation, and an image characteristic value acquisition process.
The dose conversion process for converting the image characteristic value into the dose, and
Let the computer run
In the irradiation time calculation process, the time length of the frame is based on the length of the constant dose period in which the frame dose is a constant reference dose, the reference dose and the frame dose in the frame immediately before the constant dose period. By adding up the start frame irradiation time corrected for the frame interval and the stop frame irradiation time corrected for the frame interval based on the reference dose and the frame dose in the frame immediately after the constant dose period. Have the computer execute the process of calculating the irradiation time of radiation,
Computer program.

Images