JP6494160B2 - Imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to an imaging apparatus that captures a subject and a control method thereof.

  In recent years, in the field of radiological image diagnosis, an X-ray imaging apparatus (FPD: Flat Panel Detector) that converts X-ray information into electric charges using an X-ray detector in which fine solid-state image sensors are arranged as pixels in a two-dimensional grid. Is starting to be used. In the FPD, the amount of light is converted into a charge by a photodiode for each pixel during one imaging, and the charge is transferred to a capacitor to be converted into a voltage proportional to the X-ray dose rate. And X-ray information is obtained by reading the voltage between the electrodes of this capacitor. In general, the FPD amplifies the voltage between the capacitor electrodes with an amplifier, converts the amplified signal into a digital value with an AD converter, and transfers the converted signal to an external processing device (for example, a personal computer (PC)). To do. The signal output from the FPD is subjected to image processing by a PC or the like and displayed on a display or the like.

  The transfer frame rate from the FPD to the PC is limited by the limitation of the data transfer rate from the FPD to the PC. For this reason, when high gain and low gain images are transferred as they are from the FPD to the PC, the frame rate that can be transferred is limited to half and the maximum frame rate that can be shot is halved compared to shooting with only high gain or low gain. In order to solve such a problem, Patent Document 1 captures a plurality of images by changing the exposure amount, selects data having the highest signal-to-noise ratio for each pixel, and synthesizes one image. It discloses that a synthesized image is transferred to a PC.

JP 2005-286819 A

  However, in the method described in Patent Document 1, it is necessary to configure a circuit that selects data having the highest signal-to-noise ratio for each pixel in the FPD, which increases the manufacturing cost of the FPD that is the imaging unit.

  The present invention has been made in view of the above problems, and an object thereof is to provide an imaging apparatus capable of transferring an image with a high dynamic range at a high frame rate and a control method thereof.

In order to achieve the above object, an imaging apparatus according to an aspect of the present invention has the following arrangement. That is,
An image pickup means having a plurality of image pickup devices and outputting an image pickup signal obtained at least with a high gain gain and a low gain gain ;
Conversion means for converting an imaging signal output from the imaging means into a quantized value represented by a bit string of a predetermined length;
A selection means for selecting a bit to be combined used for combining imaging signals with respect to a bit string representing a quantization value acquired at the high gain amplification factor and the low gain amplification factor ;
It said selection means, you select the bits corresponding to the amplification factor of the low gain and the corresponding bit in the amplification factor of the high-gain differently.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to implement | achieve the apparatus which images the image of a high dynamic range with a high frame rate.

The block diagram which shows the structural example of an X-ray detection part. The block diagram which shows the structural example of an X-ray imaging apparatus. 6 is a flowchart showing imaging processing by the X-ray imaging apparatus. The flowchart which shows the bit selection process of 1st Embodiment. The figure which shows an example of the bit selection by a bit selector. The figure which shows the weighting addition coefficient of a high gain signal and a low gain signal. The figure which shows the relationship between a signal, a signal noise ratio, and a dose. The flowchart which shows the decision processing of the selection bit mode of 2nd Embodiment. The flowchart which shows the bit selection process of 2nd Embodiment. The figure which shows the relationship between a signal, a signal noise ratio, and a dose. The figure which shows the relationship between a signal, a signal noise ratio, and a dose. The flowchart which shows the determination process of the selection bit mode of 3rd Embodiment. The flowchart which shows the decision processing of the selection bit mode of 4th Embodiment. The flowchart which shows the bit selection process of 4th Embodiment. The figure which shows the weighting addition coefficient of a high gain signal and a low gain signal. The figure which shows the relationship between a signal, a signal noise ratio, and a dose.

  Hereinafter, some preferred embodiments to which the present invention is applied will be described in detail with reference to the accompanying drawings. In the following description of each embodiment, a case where the present invention is applied to an X-ray imaging apparatus that captures X-ray image data of a subject using X-rays that are a kind of radiation will be described as an example. Note that the present invention is not limited to the X-ray imaging apparatus, and is applied to, for example, a radiation imaging apparatus that captures a radiographic image of a subject using other radiation (for example, α rays, β rays, γ rays, etc.). Is also possible. The present invention can also be applied to imaging apparatuses other than radiation imaging apparatuses such as digital single-lens reflex cameras and television cameras.

<First Embodiment>
FIG. 2 is a diagram illustrating an overall configuration of the X-ray imaging apparatus 200 according to the first embodiment. The X-ray imaging apparatus 200 is used particularly for medical purposes. In FIG. 2, the X-ray irradiation unit 201 irradiates the subject P with X-rays under the control of the imaging control unit 204. The X-ray irradiation unit 201 includes an X-ray generation unit 2011 (tube) that generates X-rays and a collimator 2012 that defines a beam divergence angle of the X-rays generated by the X-ray generation unit 2011. The X-ray detection unit 202 has an FPD, detects X-rays transmitted through the subject P, and generates X-ray image data. The X-ray detection unit 202 transmits the generated X-ray image data to the image processing unit 205. Details of the configuration of the X-ray detection unit 202 will be described later with reference to FIG.

  The imaging condition setting unit 203 has an input interface for an operator to input imaging conditions such as an imaging region, an X-ray dose irradiated to a subject, a frame rate, and binning. The shooting condition setting unit 203 transmits information indicating the shooting conditions input by the operator via the input interface to the shooting control unit 204. The imaging control unit 204 controls the X-ray irradiation unit 201, the X-ray detection unit 202, and the image processing unit 205 based on information from the imaging condition setting unit 203. The image processing unit 205 performs processing such as synthesis processing, gradation processing, and noise reduction processing for combining a plurality of images into one image on the X-ray image data transmitted from the X-ray detection unit 202, The processed X-ray image data is transmitted to the image display unit 206. The image display unit 206 outputs the image information transmitted from the image processing unit 205 to a monitor or the like.

  In the above configuration, the frame rate of the image output from the X-ray detection unit 202 to the image processing unit 205 is limited by the limitation on the data transfer rate of communication from the X-ray detection unit 202 to the image processing unit 205. In the present embodiment, the image processing unit 205 is included as a configuration of the X-ray imaging apparatus 200, but is not limited thereto. For example, the image processing unit 205 may be configured as an apparatus (for example, a personal computer) external to the X-ray imaging apparatus 200. In this case, the X-ray detection unit 202 and the image processing unit 205 are connected by a predetermined communication interface that is wired or wireless.

  FIG. 1 is a diagram illustrating a configuration example of the X-ray detection unit 202 in the X-ray imaging apparatus 200. In FIG. 1, an image sensor 101 includes a photodiode that converts X-ray information transmitted through a subject into a charge amount, and a plurality of image sensors 101 are two-dimensionally arranged to form an FPD. The gain setting unit 102 is a capacitor that converts the amount of charge converted by each image sensor 101 into a voltage. The gain setting unit 102 has a plurality of capacitors, and the gain (gain) at the time of changing the charge amount to the voltage can be changed by switching the combination thereof. Such a configuration is well known and will not be described in detail here. The image sensor 101 and the gain setting unit 102 described above have a plurality of image sensors and constitute an image capturing unit that outputs image signals obtained with a plurality of gains.

  The AD converter 103 constitutes a conversion unit that converts the imaging signal output from the imaging unit described above into a quantized value represented by a bit string of a predetermined length. More specifically, the AD converter 103 converts the voltage (imaging signal) converted by the gain setting unit 102 into a 16-bit unsigned integer (quantized value represented by a bit string of a predetermined length). It is a converter circuit. The bit selector 104 selects bits to be used for combining image signals obtained with a plurality of gains from a bit string representing quantized values acquired at each of the plurality of gains set by the gain setting unit 102. select. More specifically, the bit selector 104 selects the bit to be synthesized from the 16-bit unsigned integer digital value obtained from the AD converter 103 at each gain set by the gain setter 102 and is selected. The bit is supplied to the transmitter 105 as a transmission target.

  The transmitter 105 outputs the bit selected by the bit selector 104 to the image processing unit 205. In the present embodiment, the bit received by the transmitter 105 from the bit selector 104 is transmitted to the image processing unit 205 at the data transfer rate of the communication interface between the transmitter 105 and the image processing unit 205. In the present embodiment, the bit selector 104 selects a selected bit (in this example, the lower 5 bits and the lower 5 bits) from the bit string representing the quantized value of the selected gain among the plurality of gains provided by the gain setting unit 102. The bit string length is shortened by discarding the upper 2 bits. By shortening the bit string length transmitted in this way, it is possible to realize shooting at a higher frame rate within a restricted data transfer rate.

  Hereinafter, the processing from the start to the end of imaging of the X-ray imaging apparatus 200 according to the first embodiment will be described with reference to FIG. In the first embodiment, an example will be described in which the gain setting unit 102 can set two types of gains, high gain and low gain, and the ratio of these voltage gains is 32 times. In this case, the ratio of the system noise included in the low gain subject signal obtained from the gain setting unit 102 is 32 times higher than that of the high gain subject signal. In the first embodiment, a processing example for realizing a high frame rate in cine imaging will be described. In cine imaging, an image after passing through the subject includes a region from a low dose after passing through the subject, such as the mediastinum, to a region with a high dose, such as the lung field. Therefore, it is required that the output signal of the X-ray detection unit 202 does not saturate in the high dose region, and the system noise is low in the low dose region to ensure a good signal to noise ratio. Note that since the appropriate bit and the number of bits to be transmitted differ depending on the photographing application, it is desirable to switch the processing of the bit selector 104 according to the selected photographing application in a configuration in which the photographing application can be selected. A configuration in which the bit selector 104 switches the selection of bits according to a shooting application selected from a plurality of shooting applications including cine shooting and a frame rate will be described in a second embodiment.

  In step S <b> 101, an imaging condition at the time of subject imaging, such as an imaging mode, an irradiation dose, and a frame rate, input by an operator via an input interface provided in the imaging condition setting unit 203 is received. The input shooting conditions are transmitted to the shooting control unit 204. The imaging control unit 204 determines an X-ray irradiation condition, a bit selection method, an image composition method, and an image processing method based on the received imaging condition. In step S102, the imaging control unit 204 transmits an X-ray irradiation signal including the determined X-ray irradiation condition to the X-ray irradiation unit 201. The X-ray irradiation unit 201 starts generation of X-rays under designated X-ray irradiation conditions based on the received X-ray irradiation signal.

  In steps S <b> 103 to S <b> 106, the imaging control unit 204 transmits an imaging control signal to the X-ray detection unit 202 to alternately specify a high gain and a low gain to the gain setting unit 102. As a result, high gain and low gain imaging signals are alternately obtained from the gain setting unit 102. The bit selector 104 selects a bit to be used for the composition processing of the image processing unit 205 from the high gain and low gain imaging signals, and generates a bit string to be transmitted.

  First, the imaging control unit 204 designates a high gain in the gain setting unit 102 and transmits a high gain bit selection signal to the bit selector 104 to generate a high gain transmission bit string (steps S103 and S104). More specifically, in step S103, the gain setting unit 102 that has received the designation of high gain sets the amplification factor to high gain. Thereby, the charge amount for each pixel generated in the image sensor 101 by the X-ray irradiation is converted into a voltage for each pixel with high gain. The AD converter 103 converts the voltage (imaging signal) for each pixel of the high gain imaging signal into a quantized value represented by a 16-bit unsigned integer.

  In step S104, the bit selector 104 receiving the high gain bit selection signal selects some bits from the bit string of a predetermined length representing the 16-bit unsigned integer for each pixel converted in step S103, and transmits the selected bit. 105. In the present embodiment, the bit selector 104 that has received the high gain bit selection signal truncates the lower 5 bits and the upper 2 bits from the 16-bit bit string representing the integer value obtained in step S103, thereby generating a 9-bit transmission target bit string. Select. The bit selected by the bit selector 104 is transmitted to the image processing unit 205 by the transmitter 105. Here, when at least one of the truncated upper 2 bits is “1”, a maximum value of 9 bits to be transmitted (that is, all 9 bits are 1) is transmitted.

  The details of the bit selection processing in step S104 will be described below with reference to FIGS. First, in step S201, the bit selector 104 truncates a lower-order predetermined number of bits (5 bits in the present embodiment) for each pixel of the 16-bit unsigned integer for each pixel. As described above, the magnification of the high gain amplification factor to the low gain amplification factor is 32. The truncation of the lower 5 bits corresponds to dividing the high gain quantized value by 32, and this process matches the high gain value with the low gain value. In the examples of FIGS. 5A, 5B, and 5C, the lower 5 bits of 39045LSB, 26194LSB, and 1449LSB, which are 16-bit unsigned integer values, are truncated and converted to 1220LSB, 818LSB, and 45LSB, respectively. . Next, in step S202, the bit selector 104 determines whether or not the most significant bit is 1 for the signal for each pixel after being processed in step S201. If the most significant bit is 1, the process proceeds to step S204, and otherwise, the process proceeds to step S203. In step S203, it is determined whether the second bit from the most significant bit is 1. If the second bit from the most significant bit is 1, the process proceeds to step S204. Otherwise, the process proceeds to step S205.

  In step S204, the signal of all bits is converted to 1. In the example of FIG. 5A, the most significant bit is 1, and the process proceeds from step S202 to step S205, where 1220LSB is converted to 2047LSB. In the example of FIG. 5B, the second bit from the most significant bit is 1, and the process proceeds from step S203 to step S204, where 818LSB is converted to 2047LSB. In step S205, the bit selector 104 truncates the upper predetermined number of bits (2 bits in this embodiment). As will be described later with reference to FIG. 6, when the high gain signal is 511 or more, the weighting coefficient k is 0, and the high gain signal does not contribute to the synthesis. That is, a numerical expression of 512 or more (a state in which any of the upper 2 bits is 1) is not necessary in a high gain signal. In this embodiment, such unnecessary bits are rounded down in advance to reduce the number of bits to be transmitted. It is decreasing. In the examples of FIGS. 5A and 5B, both 2047LSB are converted to 511LSB. In the case of the example in FIG. 5C, the process proceeds from step S203 to step S205, and the upper 2 bits are discarded. However, the value does not change before and after step S205, and remains 45LSB. Next, in step S206, the transmitter 105 built in the X-ray detection unit 202 transmits the signal for each pixel converted in step S205 to the image processing unit 205.

  Returning to FIG. 3, when transmission of the high-gain bit string in steps S <b> 103 and S <b> 104 is finished, the imaging control unit 204 transmits a signal for setting the gain to low gain to the gain setting unit 102 and selects the low gain bit to the bit selector 104. Send a signal. Thereby, a transmission bit string in low gain is generated (steps S105 and S106).

  First, in step S105, the gain setting unit 102 that has received the signal to set to low gain sets the gain to low gain. Then, a 16-bit unsigned integer, which is a low gain quantized value, is obtained from the AD converter 103 by the same processing as in step S103. Next, in step S106, a bit to be transmitted is selected by the bit selector 104 that has received the low gain bit selection signal. In this example, the low gain bit selection signal is a signal instructing to select all the bits of a 16-bit unsigned integer of low gain. Therefore, the bit selector 104 transmits the signal (16-bit bit string) received from the AD converter 103 to the transmitter 105 as it is. The transmitter 105 receives the transmitted signal, and transmits the received signal to the image processing unit 205.

  In step S107, the image processing unit 205 synthesizes the high gain and low gain subject signals received in steps S104 and S106 into one signal for each pixel, based on the image synthesis control signal received from the imaging control unit 204. To do. Details of the processing will be described with reference to FIGS. In step S107, the image processing unit 205 adds the high gain signal H and the low gain signal L at a ratio of k × H + (1−k) × L using the weighting coefficient k for each pixel. As shown in FIG. 6, the weighting coefficient k changes from 1 to 0 as the high gain signal changes from 255 to 511. In the present embodiment, the high gain signal is a bit string consisting of 9 bits at the center, with the lower 5 bits and the upper 2 bits truncated by the bit selector 104, and therefore the mixing ratio (weight) of the high gain signal of 511 or higher is 0. It is said. From another aspect, in a region where the high gain signal is 511 or more, a sufficient S / N ratio can be obtained even if a composite image is generated using only the low gain signal. Therefore, by truncating the upper 2 bits of the high gain signal in the bit selector 104, the bit string to be transmitted can be further shortened while avoiding the influence on the image quality.

  FIG. 7 shows the relationship between the high gain and low gain signals after the AD conversion in steps S103 and S105, the signal noise ratio, and the signal noise ratio after the signals are combined in step S107. As shown in FIG. 7, by performing weighted addition, a high gain signal and a low gain signal can be synthesized without generating a dose at which the signal-to-noise ratio becomes discontinuous with respect to the dose.

  Next, in step S108, the image processing unit 205 that has received the image processing signal from the imaging control unit 204 performs gradation processing and recursive processing on the subject signal for each pixel synthesized in step S107. The image processing unit 205 transmits the processed signal to the image display unit 206. In step S109, the image display unit 206 converts the received information into a two-dimensional image and displays it on the display. The operator confirms the image data displayed on the image display unit 206 and determines whether or not to continue shooting. When the operator inputs shooting continuation information from the input interface of the shooting condition setting unit 203, the process returns from step S110 to step S102, and the processes of steps S102 to S109 described above are repeated. If the end of imaging is instructed from the input interface, X-ray image imaging is terminated.

  As described above, the imaging apparatus according to the first embodiment includes a plurality of imaging devices, and outputs an imaging signal obtained with a plurality of gains (for example, the imaging device 101 and the gain setting unit 102). A conversion unit (for example, AD converter 103) that converts an imaging signal output from the imaging unit into a quantized value represented by a bit string of a predetermined length, and a bit string that represents a quantized value acquired with a plurality of gains By providing a selection unit (for example, bit selector 104) that selects bits to be used for combining image signals, it is possible to realize a device that captures a high dynamic range image at a high frame rate. It becomes.

More specifically, the bit selector 104 generates a bit signal (in the above example, the lower 5 bits) that is not essential for cine radiography because the X-ray quantum noise of the high gain signal is larger than the subject signal. It is automatically deleted. In addition, among the high gain signals, the bit signals (the upper 2 bits in the above example) that can satisfy the signal-to-noise ratio required for cine imaging even when the low gain signals are used are automatically deleted. Then, the bit string composed of the bits selected as described above in the high gain signal and all the bit strings of the low gain signal are transmitted to the image processing unit 205. for that reason,
By reducing the number of bits per frame composed of high gain and low gain signals from 16 + 16 bits to 9 + 16 bits, a high frame rate imaging device can be realized,
-Signal saturation is suppressed even in high-dose rate X-ray irradiation, and a composite image with low system noise can be generated.

  Furthermore, according to the configuration of the present embodiment, since it can be realized simply by providing the bit selector 104 in a general FPD, the imaging device has a high dynamic range and a high frame rate at a lower cost than the imaging device of Patent Document 1. Can be realized.

Second Embodiment
In the first embodiment described above, the bit selector 104 selects the bit to be transmitted for the high gain and low gain signals so as to generate a bit string suitable for cine imaging. On the other hand, in the second embodiment, a configuration will be described in which the bit selection by the bit selector 104 can be switched in accordance with the shooting application selected by the operator and the shooting frame rate. In the radiological image diagnosis, the X-ray dose irradiated to the subject differs depending on the imaging application such as cine imaging or fluoroscopic imaging, and the X-ray dose range of the region of interest after the subject transmission differs accordingly. Therefore, it is preferable that the X-ray detection unit 202 does not saturate in the region of interest and can appropriately select an appropriate gain and bit selection method for lowering system noise according to the imaging application.

  Even when the same shooting application is used, the shooting frame rate desired by the operator may be different. If the imaging frame rate desired by the operator is low, all bits of the acquired imaging signal can be transmitted to the image processing unit 205, and a high dynamic image with high saturation dose and low system noise can be provided to the operator. . However, when the operator requests a high frame rate, the frame rate is limited by the data transfer rate from the X-ray detection unit 202 to the image processing unit 205. Therefore, it is necessary to appropriately select the bit of the subject signal so that an image suitable for radiological image diagnosis can be provided to the operator at a high frame rate within the limitation of the data transfer rate. That is, it is necessary to appropriately select the bit of the imaging signal transmitted from the X-ray detection unit 202 to the image processing unit 205 according to the imaging application selected by the operator and the imaging frame rate. In the second embodiment, appropriate bit selection is realized by adding a condition determination function for switching the bit of a subject signal to be transmitted according to a shooting application and a shooting frame rate to the shooting control unit 204.

  The configurations of the X-ray imaging apparatus 200 and the X-ray detection unit 202 of the second embodiment are the same as those of the first embodiment (FIGS. 1 and 2). In the second embodiment, a case will be described in which the X-ray imaging apparatus 200 has two imaging applications, a cine imaging application and a fluoroscopic application. In the following, the operation of the second embodiment will be described mainly with respect to differences from the processing of the first embodiment, using the flowchart of FIG.

  In step S101, the shooting control unit 204 accepts setting of shooting conditions at the time of shooting a subject including a shooting application and a shooting frame rate performed by the operator via the input interface. Based on the input imaging conditions, the imaging control unit 204 determines the selection bit mode of the subject signal transmitted from the X-ray detection unit 202 to the image processing unit 205 by the selection bit mode determination process shown in FIG. The selected bit mode determination process shown in FIG. 8 will be described below.

  In step S301, the imaging control unit 204 determines whether the imaging application selected by the operator in step S101 is cine imaging. If the selected shooting application is cine shooting, the process proceeds to step S302; otherwise, the process proceeds to step S303. In step S302, the imaging control unit 204 determines whether the imaging frame rate received in step S101 is 5 fps or less. If the shooting frame rate is 5 fps or less, the process proceeds to step S304; otherwise, the process proceeds to step S305. In step S303, it is determined whether the shooting frame rate received in step S101 is 10 fps or less. If the shooting frame rate is 10 fps or less, the process proceeds to step S306; otherwise, the process proceeds to step S307. In step S304, the imaging control unit 204 records “low speed cine mode” in the internal memory as the selection bit mode of the subject signal. Similarly, in steps S305, S306, and S307, “high-speed cine mode”, “low-speed fluoroscopy mode”, and “high-speed fluoroscopy mode” are stored in the internal memory as the subject signal selection bit modes, respectively.

  Steps S103 and S105 are the same as those in the first embodiment. In steps S104 and S106, the process is switched according to the selected bit mode specified by the selected bit mode determination process described above. Prior to the bit selection process in steps S <b> 104 and S <b> 106, the imaging control unit 204 transmits information on the selected bit mode recorded in the internal memory in step S <b> 101 to the bit selector 104.

  When the low-speed cine mode is selected as the selection bit mode, in steps S104 and S106, processing similar to that in step S106 of the first embodiment is performed. That is, the bit selector 104 selects all bits of the high-gain and low-gain imaging signals as transmission target bits, and the transmitter 105 transmits the selected bits (all bits) to the image processing unit 205. On the other hand, when the high-speed cine mode is selected as the selected bit mode, processes similar to those in steps S104 and S106 of the first embodiment are performed in steps S104 and S106, respectively. That is, the bit selector 104 selects some bits of the high gain subject signal and all bits of the low gain subject signal, and the transmitter 105 transmits the selected bits to the image processing unit 205.

  When the low-speed fluoroscopy mode is selected as the selection bit mode, in step S104, processing for selecting all bits is performed in the same manner as in step S106 in the first embodiment, and all bits of the high gain subject signal are selected as transmission targets. Is done. In step S106, the bit selector 104 performs a process of truncating the upper 3 bits of the low gain signal. A flowchart of this process is shown in FIG. The bit selector 104 sets all the lower bits to 1 if at least one of the upper 3 bits of the low gain includes 1 (steps S401, S402, S403, and S404). Then, the bit selector 104 discards the upper 3 bits of the low gain signal and sets a 13-bit bit string as a transmission target (step S405), and the transmitter 105 transmits the bit string to the image processing unit 205 (step S406). That is, the X-ray detection unit 202 transmits all bits of the high gain subject signal and some bits of the low gain subject signal to the image processing unit 205.

  When the high-speed fluoroscopy mode is selected as the selection bit mode, in step S104, processing similar to that in step S104 of the first embodiment is performed on the high gain subject signal. In step S106, processing similar to that in the low-speed fluoroscopic mode is performed on the low gain subject signal. In other words, the bit selector 104 images a part of bits of the high gain subject signal (a bit string excluding the lower 5 bits and the upper 2 bits) and a part of bits of the low gain object signal (a bit string excluding the upper 3 bits). Select to send to processing unit 205.

  The image composition process in step S107 in the second embodiment differs depending on the selected bit mode. When the low-speed cine mode is selected as the selected bit mode, the image processing unit 205 divides the high gain signal received in step S104 by 32. Then, the high gain signal and the low gain signal are combined into one signal by the method described in step S107 of the first embodiment. However, unlike the first embodiment, the upper 2 bits of the high gain signal are present and an 11-bit signal is handled, so the range in which the synthesis using the weighting coefficient is performed is different from that in FIG. On the other hand, when the high-speed cine mode is selected as the selected bit mode, a bit string similar to that in the first embodiment is transmitted to the image processing unit 205, and thus the same processing as that described in step S107 in the first embodiment. Is synthesized.

  When the low speed fluoroscopy mode is selected as the selection bit mode, the composition processing in step S107 is the same as when the low speed cine mode is selected. When the high-speed fluoroscopy mode is selected as the selected bit mode, the bit string of the high gain signal has the same configuration as that of the first embodiment, and the synthesis process in step S107 is the same as the synthesis process of the first embodiment. .

  10 and 11 show the relationship between each selected bit mode, the high gain and low gain signals after AD conversion in steps S103 and S105, the signal noise ratio, and the signal noise ratio after the signals are combined in step S107. Shown in When the low-speed cine mode is selected as the selection bit mode, the relationship shown in FIG. 10 is obtained. As described above, in cine imaging, an image after passing through the subject includes a region from a low dose after passing through the subject such as the mediastinum to a region where the dose is high such as lung field. As shown in FIG. 10, in the low-speed cine mode, after synthesizing the high-gain and low-gain signals, a good signal-to-noise ratio is maintained even in a low dose range, and it does not saturate even at a high dose, and has a high dynamic range required for cine imaging. doing. Further, when the high-speed cine mode is selected, the same characteristics as in the first embodiment (FIG. 7) are obtained. The high-speed cine mode has a higher dose that can be imaged in the low-dose region than the low-speed cine mode, and the dynamic range is lower than that in the low-speed cine mode, but can be imaged at a higher frame rate than the low-speed cine mode.

  When the low-speed fluoroscopy mode is selected as the selected bit mode, a good signal-to-noise ratio is maintained in the low-dose region after combining the high-gain and low-gain signals as shown in FIG. Also meets the maximum dose required for fluoroscopy. In addition, when the high-speed fluoroscopy mode is selected as the selection bit mode, as shown in FIG. 11B, the storable dose in the low-dose region is higher than in the low-speed fluoroscopy mode, which is higher than that in the low-speed fluoroscopy mode. The dynamic range decreases. However, in the high-speed fluoroscopy mode, the number of bits to be transmitted is further reduced, and shooting at a higher frame rate is possible than in the low-speed fluoroscopy mode.

  The processing from step S108 to S110 in the second embodiment is the same as the processing from step S108 to S110 in the first embodiment. Through the above processing, in the second embodiment, it is possible to automatically and appropriately switch the bit of the subject signal to be transmitted according to the shooting application and the shooting frame rate. Accordingly, it is possible to appropriately select the bit of the subject signal transmitted from the X-ray detection unit 202 to the image processing unit 205 according to the imaging application and the imaging frame rate selected by the operator. The operator can obtain an image with the maximum dynamic range within the requested frame rate, and can obtain an image that does not saturate even with the maximum dose required for each imaging method.

<Third Embodiment>
In the third embodiment, in the X-ray imaging apparatus 200 having the image quality priority mode and the imaging frame rate priority mode as operation modes, the transmission target of the pixel signals acquired according to the operation mode selected by the bit selector 104 is selected. A configuration for switching bits will be described. In radiological image diagnosis, an operator may desire a high-quality image or a high-frame-rate image depending on the procedure, and the operability is improved by enabling such switching. . In the third embodiment, a condition determination function for switching the bit of a subject signal to be transmitted according to the selection result of the shooting application and the image quality priority mode and the frame rate priority mode is added to the shooting control unit 204.

  The configurations of the X-ray imaging apparatus 200 and the X-ray detection unit 202 of the third embodiment are the same as those of the first embodiment (FIGS. 1 and 2). The operation of the third embodiment is obtained by replacing the bit selection mode determination process (FIG. 8) described in the second embodiment with the bit selection mode determination process shown in the flowchart of FIG. It is the same as the form.

  The operator can select the image quality priority mode or the frame rate priority mode via the input interface of the shooting condition setting unit 203. In step S101 of FIG. 3, when the imaging control unit 204 receives selection of the image quality priority mode or the frame rate priority mode by the operator, the shooting control unit 204 determines the selection bit mode by the process shown in FIG. When cine shooting is selected as the shooting application (YES in S501), the bit selection mode is determined as the low-speed cine or the high-speed cine according to the selection of the image quality priority mode or the frame rate priority mode by the operator (S502, S503). , S504). When the shooting application is other than cine shooting (NO in S501), the bit selection mode is determined to be low-speed fluoroscopy or high-speed fluoroscopy according to the selection of the image quality priority mode or the frame rate priority mode by the operator (S502, S503). , S504). The generation of the bit string to be transmitted in the determined bit selection mode and the synthesis of the high gain and low gain subject signals are the same as in the second embodiment.

  According to the third embodiment described above, the operator can select which of the image quality and the frame rate should be prioritized, and the bit selector 104 appropriately transmits to the image processing unit 205 according to the selection. Select a bit. At this time, even in the same shooting application, the total number of bits of the synthesis target bit string selected in the shooting frame rate priority mode is smaller than the total number of bits of the synthesis target bit string selected in the image quality priority mode. Therefore, it is possible to improve the image quality in the image quality priority mode, and to realize a higher frame rate in the shooting frame rate priority mode. As a result, the operator can obtain a desired image both when a high-quality image is desired and when a high frame rate image is desired.

<Fourth embodiment>
In the fourth embodiment, the image processing unit 205 has a plurality of high-gain and low-gain signal combining methods, and depending on the combining method executed by the image processing unit 205, bits to be transmitted in the acquired pixel signal. Switch. By adding such a function, it becomes possible to transmit a bit string with a reduced number of bits according to the synthesis method from the X-ray detection unit 202 to the image processing unit 205, and to capture an image at a higher frame rate. It becomes possible.

  The configurations of the X-ray imaging apparatus 200 and the X-ray detection unit 202 of the fourth embodiment are the same as those of the first embodiment (FIGS. 1 and 2). In the fourth embodiment, as the bit selection mode, among the low-speed cine, high-speed cine, low-speed fluoroscopy, and high-speed fluoroscopy modes shown in the second embodiment, the high-speed fluoroscopy mode is further changed according to the frame rate. 5 types of bit selection modes are used. Therefore, in the fourth embodiment, the process shown by the flowchart of FIG. 13 is executed instead of the bit selection mode determination process (FIG. 8) of the second embodiment. Accordingly, in the bit selection process in steps S104 and S106 in the flowchart shown in FIG. 3, a process different from that of the second embodiment is executed. Other processes are the same as those in the second embodiment, and differences from the second embodiment will be mainly described below.

  In FIG. 13, the same step number is assigned to the same process as in FIG. 8. In the fourth embodiment, in a case other than the cine shooting mode, when the set shooting frame rate is greater than 10 fps, the shooting control unit 204 determines whether the set shooting frame rate is 15 fps or less (step S601). ). When the shooting frame rate is 15 fps or less, the shooting control unit 204 sets the selected bit mode to high-speed fluoroscopy A (step S602), and otherwise sets high-speed fluoroscopy B (step S603).

  Subsequent processing when classified as high-speed fluoroscopy A is the same as the high-speed fluoroscopy processing of the second embodiment. On the other hand, in the case of high-speed fluoroscopy B, the weighting shown in FIG. 15 is used in the composition processing in the image processing unit 205. That is, in this embodiment, the synthesis process is changed according to the requested frame rate, and the bit selection process (steps S104 and S106) in the bit selector 104 is also changed accordingly. In the combining process using the weighting shown in FIG. 15, when the high gain signal is 255, the signal is switched to the low gain signal. Therefore, a signal representing a high gain of 255 or higher is not required, and as a result, in this embodiment, the upper 3 bits of the high gain signal are discarded. Details of this processing are shown in the flowchart of FIG.

  If it is classified as high-speed fluoroscopy B, in step S104, the bit selector 104 performs processing of truncating the lower 5 bits and the upper 3 bits of the high gain signal as shown in FIG. That is, the bit selector 104 first truncates the lower 5 bits of the high gain signal (step S701). If 1 is included in at least one of the upper 3 bits of the high gain signal, all the lower bits are set to 1 (steps S702, S703, S704, and S705). Then, the bit selector 104 truncates the upper 3 bits of the high gain signal and sets a 13-bit bit string as a transmission target (step S706), and the transmitter 105 transmits the bit string to the image processing unit 205 (step S707).

  Note that the bit selection processing (step S106) of the bit selector 104 for the low gain signal is the same as in the high-speed fluoroscopic mode of the second embodiment (FIG. 9), and the upper 3 bits of the low gain signal are discarded.

  Then, in the image composition processing in step S107, as shown in FIG. 15, the weighting coefficient is stepped with the threshold value 255LSB to synthesize the high gain and low gain signals. The signal-to-noise ratio after the above processing changes in a stepwise manner between the high gain signal usage dose range and the low gain signal usage dose range as shown in FIG. However, in the high-speed fluoroscopy B, since the total number of bits transmitted from the X-ray detection unit 202 to the image processing unit 205 is smaller than that in the high-speed fluoroscopy A, it is possible to perform imaging at a higher frame rate.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (18)

An image pickup means having a plurality of image pickup devices and outputting an image pickup signal obtained at least with a high gain gain and a low gain gain;
Conversion means for converting an imaging signal output from the imaging means into a quantized value represented by a bit string of a predetermined length;
A selection means for selecting a bit to be combined used for combining imaging signals with respect to a bit string representing a quantization value acquired at the high gain amplification factor and the low gain amplification factor;
The image pickup apparatus, wherein the selection unit selects a bit corresponding to the high gain amplification factor and a bit corresponding to the low gain amplification factor differently.   The selection unit discards a bit string that shortens a bit string length and discards a bit string that represents a quantized value acquired with the high gain amplification factor and the low gain amplification factor according to a shooting application selected from a plurality of shooting applications. The imaging apparatus according to claim 1, wherein a bit to be selected is selected.   The selection means discards a bit string that shortens a bit string length among bit strings representing quantized values acquired at the high gain amplification factor and the low gain amplification factor according to a frame rate selected from a plurality of frame rates. The imaging device according to claim 1, wherein a bit to be selected is selected.   The selection unit is configured to select an image quality priority mode that prioritizes image quality over the shooting frame rate and an operation mode selected from a plurality of operation modes including a shooting frame rate priority mode that prioritizes the shooting frame rate over image quality. 4. The bit string for shortening the bit string length and the bits to be discarded are selected from the bit string representing the quantized value acquired at the high gain amplification factor and the low gain amplification factor. The imaging device described in 1.   In the selection of the bits to be combined by the selection unit, the total number of bits to be combined selected in the shooting frame rate priority mode is smaller than the total number of bits to be combined selected in the image quality priority mode. The imaging device according to claim 4.   The selection means is configured to select the high gain gain based on a combining method selected from a plurality of combining methods for combining a plurality of frames obtained with the high gain amplification factor and the low gain amplification factor. 6. The imaging apparatus according to claim 1, wherein a gain for shortening a bit string length and a bit to be discarded are selected from a bit string representing a quantized value acquired with the amplification factor of the low gain. .   The imaging device according to claim 1, wherein the selection unit selects a part of bits from a bit string representing a quantization value acquired with the gain of the high gain.   The imaging apparatus according to claim 1, wherein the selection unit selects an entire bit string representing a quantization value acquired with the amplification factor of the low gain.   The imaging apparatus according to claim 1, wherein the selection unit truncates a first predetermined number of bits from the lower order of a bit string representing a quantized value acquired with the gain of the high gain.   The imaging apparatus according to claim 9, wherein the selection unit further truncates a second predetermined number of bits from the upper part of a bit string representing a quantized value acquired with the gain of the high gain.   11. The imaging apparatus according to claim 9, wherein the first predetermined number is a bit number corresponding to a magnification of the high gain amplification factor with respect to the low gain amplification factor.   The second predetermined number of bits is a numerical value when a signal obtained with the high gain amplification factor does not contribute to the synthesis when a plurality of frames obtained with the high gain amplification factor and the low gain amplification factor are synthesized. The imaging apparatus according to claim 10, wherein the higher-order bits that constitute the upper-order bit.   The said selection means truncates a 3rd predetermined number of bits from the high-order of the bit sequence showing the quantization value obtained with the amplification factor of the said low gain, The one of Claim 9 thru | or 12 characterized by the above-mentioned. Imaging device.   The imaging apparatus according to claim 1, further comprising an output unit that outputs a bit selected by the selection unit. An imaging means having a plurality of imaging elements and outputting an imaging signal obtained with a plurality of gains;
Conversion means for converting an imaging signal output from the imaging means into a quantized value represented by a bit string of a predetermined length;
A selection unit that selects a bit to be combined used for combining imaging signals with respect to a bit string representing a quantization value acquired by the plurality of gains;
The selecting means discards a gain and a bit string length that are shortened from the plurality of gains based on a combining method selected from a plurality of combining methods for combining a plurality of frames obtained with the plurality of gains. An imaging device, wherein a bit to be selected is selected. A control method for an imaging apparatus having a plurality of imaging elements and having imaging means for outputting an imaging signal obtained at least with a high gain amplification factor and a low gain amplification factor ,
A conversion step of converting the imaging signal output from the imaging means into a quantized value represented by a bit string of a predetermined length;
The bit string representing the quantized value acquisition gain and an amplification factor of the low gain of the high gain, possess a selection step of selecting bits to be combined for use in the synthesis of the image signal, and
In the selecting step, the bit corresponding to the gain of the high gain and the bit corresponding to the gain of the low gain are selected to be different from each other . A control method for an image pickup apparatus having an image pickup unit having a plurality of image pickup elements and outputting an image pickup signal obtained with a plurality of gains,
A conversion step of converting the imaging signal output from the imaging means into a quantized value represented by a bit string of a predetermined length;
A selection step of selecting a bit to be combined used for combining image pickup signals for a bit string representing quantized values acquired at the plurality of gains, and
In the selecting step, gain and discarding that shortens a bit string length from the plurality of gains based on a combining method selected from a plurality of combining methods for combining a plurality of frames obtained by the plurality of gains. A method for controlling an imaging apparatus, wherein a bit to be selected is selected.   The program for making a computer perform each process of the control method described in Claim 16 or 17.

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