12, a product (tube current-time product) mAs of a tube current and an irradiation time, a pulse width msec, a pulse rate, a type and a thickness of the beam filter, an X-ray irradiation field size, a focus size, a radiation dose, etc. In other words, a set of X-ray conditions includes various parameters relating to setting of a dose of X-rays with which irradiation is to be performed.

In ABC control, a set of X-ray conditions is changed in such a manner that a mean value (statistical value) of a plurality of values of pixels included in an ROI, for example, becomes identical to or substantially identical to a target value (threshold value) of the ROI. In other words, in ABC control, the X-ray diagnostic apparatus 1 determines a set of X-ray conditions in such a manner that a statistical value of an ROI satisfies a threshold value.

On the other hand, in CNR control, an image quality index (statistical value) estimated based on a plurality of values of pixels included in an ROI, for example, is calculated. Specifically, the X-ray diagnostic apparatus 1 acquires in advance correspondence information in which an imaging geometry of the imaging device (e.g., an X-ray irradiation field size, a Source-to-Image Distance (SID)), a plurality of values of pixels included in an ROI, and a set of X-ray conditions relating to collection of the values of pixels are associated with the estimated image quality index. The X-ray diagnostic apparatus 1 acquires an image quality index by referring to the correspondence information based on an imaging geometry in X-ray irradiation, an SID, and a plurality of values of pixels of an ROI obtained by the X-ray irradiation. The image quality index is, for example, a contrast-to-noise ratio. That is, in CNR control, the X-ray conditions are changed in such a manner that a contrast-to-noise ratio (statistical value) estimated based on a plurality of values of pixels corresponding to an ROI becomes identical to or substantially identical to a target value (threshold value) of the ROI. In other words, in CNR control, the X-ray diagnostic apparatus 1 determines a set of X-ray conditions in such a manner that a statistical value of an ROI satisfies a threshold value.

Alternatively, in CNR control, the statistical value to be calculated may be directly calculated from the X-ray image. For example, in CNR control, a value (contrast value) obtained by subtracting a mean value of a plurality of values of pixels included in an ROI from a mean value of a plurality of values of pixels included in a peripheral region of the ROI is calculated. By dividing the calculated contrast value by a standard deviation of the values of pixels included in the peripheral region, a contrast-to-noise ratio is calculated. That is, in CNR control, the X-ray conditions may be changed in such a manner that a contrast-to-noise ratio (statistical value) relating to an ROI becomes identical to or substantially identical to a target value (threshold value) of the ROI. In other words, in CNR control, the X-ray diagnostic apparatus 1 may determine a set of X-ray conditions in such a manner that a statistical value of an ROI satisfies a threshold value.

A set of image quality conditions includes a spatial resolution of the FPD included in the X-ray detector 13, a binning number, the element size and the number of elements, and the pixel size and the number of pixels (resolution) of the X-ray image. In other words, a set of image quality conditions includes various parameters relating to generation of an X-ray image.

The processing circuitry 44 controls, with the X-ray condition control function 442, a set of X-ray conditions relating to capturing of an X-ray image. Specifically, the processing circuitry 44 controls, based on a set of X-ray conditions set by the imaging condition setting function 441, a tube voltage kV, a tube current-time product mAs, a pulse width msec, a pulse rate, a type and a thickness of the beam filter, etc. in the imaging unit 10 in real time. Thereby, X-rays are generated in accordance with a desired set of X-ray conditions, and used for irradiation. Also, projection data relating to a subject P is obtained.

The processing circuitry 44 performs, with the driving control function 443, control to drive the C-Arm driver 15 of the imaging unit 10 and to drive the bed driving unit 32 of the bed unit 30. Specifically, the processing circuitry 44 generates a drive signal based on information relating to driving of the C-Arm driver 15 and the bed driving unit 32 input from the input interface 43, and generates a drive signal. The processing circuitry 44 outputs the generated drive signal to the C-Arm driver 15 and the bed driving unit 32, and controls the motions of the C-Arm 14 and the top 33 in real time. Thereby, projection data relating to the subject P is obtained.

The processing circuitry 44 generates an X-ray image with the image generation function 444. Specifically, the processing circuitry 44 generates an X-ray image using projection data output from the X-ray detector 13 of the imaging unit 10 based on a set of image quality conditions set by the imaging condition setting function 441. Thereby, an X-ray image is generated in accordance with a desired set of image quality conditions. The generated X-ray image is stored in the memory 41.

The processing circuitry 44 performs, with the image processing function 445, various types of image processing on the X-ray image. For example, the processing circuitry 44 adjusts the brightness of an X-ray image generated by the image generation function 444 based on a magnification of the automatic gain control (hereinafter referred to as “AGC”) input from the input interface 43. That is, the processing circuitry 44 performs a gain correction process on the generated X-ray image. The processing circuitry 44 may perform various types of synthesis and subtraction processing on the X-ray image. The image-processed X-ray image is stored in the memory 41.

The AGC control is a digital gain process applied to the entire X-ray image if the dose of X-rays incident on the X-ray detector 13 cannot be sufficiently secured due to the limitation of exposure to the subject P and the restriction in the tube output. The magnification of AGC is defined by a ratio of a brightness of an X-ray image after AGC application to a brightness of an X-ray image before AGC application. In the present embodiment, if a halation region is present in the generated X-ray image, the processing circuitry 44 performs a gain correction process on the X-ray image to darken the halation region.

The processing circuitry 44 causes, with the display control function 446, the X-ray image to be displayed on the display 42. For example, the processing circuitry 44 acquires, based on information input from the input interface 43 and relating to an X-ray image which the operator desires to browse, an X-ray image corresponding to the information from the memory 41, and causes the display 42 to display the acquired X-ray image. The processing circuitry 44 may cause the display 42 to sequentially display X-ray images (frame images) subjected to image processing.

The processing circuitry 44 sets, with the setting function 447A, a plurality of ROIs in the X-ray image. Specifically, the processing circuitry 44 sets a plurality of ROIs in an X-ray image (first X-ray image) displayed on the display 42.

First, the processing circuitry 44 may set one of a plurality of ROIs over an entire region or a substantially entire region of the X-ray image, and set at least one of the ROIs excluding said one of the ROIs at at least one image region including at least one target photographed in the X-ray image. If, for example, a single target is photographed in the X-ray image, the processing circuitry 44 may set an ROI over an entire region or a substantially entire region of the X-ray image, and may set another ROI at a position of the single target. If two targets are photographed in an X-ray image, the processing circuitry 44 may set an ROI over an entire region or a substantially entire region of the X-ray image, and respectively set ROIs at the positions of the two targets. A plurality of ROIs may overlap one another at least partially.

Second, based on position information of a dose-reducing filter (punched filter) with an opening formed at its central part, the processing circuitry 44 may set, in an X-ray image, an image region corresponding to the opening as one of a plurality of ROIs, and set a peripheral region of the ROI as another ROI. In other words, an ROI is set at a region on an X-ray image corresponding to the opening portion of the punched filter, and another ROI may be set at a region on an X-ray image corresponding to the metal-plate portion of the punched filter.

At least one target photographed in the X-ray image is, for example, a medical device, a marker on a medical device, or an anatomical structure. Examples of the medical device include a catheter, a balloon catheter, a stent, a guide wire, a pacemaker, a transesophageal echo probe, and a prosthetic joint. Examples of the anatomical structure include bones, teeth, muscles, organs, blood vessels, and nerves. As a matter of course, at least one of the targets includes a combination of various types of such objects.

The processing circuitry 44 calculates, with the calculation function 447B, a statistical value of each of a plurality of ROIs based on a plurality of values of pixels included in each of the ROIs, thereby obtaining a plurality of statistical values. First, the processing circuitry 44 may calculate a mean value of a plurality of values of pixels included in each of the ROIs as a statistical value. Second, the processing circuitry 44 may calculate a contrast-to-noise ratio estimated based on a plurality of values of pixels included in each of the ROIs as a statistical value. For example, the processing circuitry 44 may use a mean value in ABC control, and may use a contrast-to-noise ratio estimated based on the mean value in CNR control. The statistical value may be any value calculated based on values of pixels. Specifically, the statistical value is not limited to a mean value or a contrast-to-noise ratio, and values directly calculated from values of pixels, such as a weighted mean value, an extracted value, a mode value, a median value, a maximum value, or any other values relating to the image quality such as an evaluation index may be suitably used.

“Values of pixels” means numerical values given to the respective pixels of an X-ray image. The values of pixels may be respectively given to a plurality of semiconductor detection elements (pixels) configuring an FPD included in the X-ray detector 13 of the imaging unit 10. That is, the values of pixels are values proportional to doses of X-rays that have been transmitted through the subject P. The values of pixels are represented on the display 42 in accordance with 256-level brightness values (e.g., 0-255) with, for example, a known gradation process (window process).

The processing circuitry 44 acquires, with the threshold value acquisition function 447C, a plurality of threshold values respectively relating to a plurality of statistical values. Specifically, the processing circuitry 44 acquires a plurality of threshold values from the input interface 43. The processing circuitry 44 may acquire a plurality of threshold values stored in the memory 41. Different threshold values may be given to a plurality of ROIs, or an identical threshold value may be given to at least two of the ROIs. The threshold value, which is a factor relating to determination of a dose of X-rays with which irradiation is to be performed, may also be called an “X-ray dose target value”. The threshold value may be a numerical value such as “400” or “500”.

The processing circuitry 44 determines, with the X-ray condition determination function 447D, a set of X-ray conditions relating to capturing of an X-ray image (second X-ray image) subsequent to an X-ray image (first X-ray image) subjected to processing, based on a statistical value and a threshold value relating to each of the ROIs. First, the processing circuitry 44 may calculate, for each of the ROIs, a set of X-ray conditions under which a statistical value satisfies a threshold value, thereby obtaining a plurality of sets of X-ray conditions, and determine, as a set of X-ray conditions relating to capturing of the second X-ray image, a set of X-ray conditions under which irradiation is performed with a highest dose of X-rays, of the plurality of sets of X-ray conditions. Second, the processing circuitry 44 may determine a set of X-ray conditions relating to capturing of the second X-ray image in such a manner that, if the number of the plurality of ROIs is two, statistical values of both of the two ROIs satisfy corresponding threshold values. Third, the processing circuitry 44 may determine a set of X-ray conditions relating to capturing of a second X-ray image in such a manner that, if the number of the plurality of ROIs is three or more, statistical values of at least two of the three or more ROIs satisfy corresponding threshold values.

In the present embodiment, the processing circuitry 44 feeds back information relating to the determined set of X-ray conditions to capturing of the next X-ray image. The processing circuitry 44 updates, with the imaging condition setting function 441, a set of X-ray conditions relating to capturing of a previous X-ray image, using the information. Hereinafter, the processing circuitry 44 sequentially executes, based on the updated set of X-ray conditions, the X-ray condition control function 442, the driving control function 443, the image generation function 444, the image processing function 445, and the display control function 446. As a result of the series of processing, a new X-ray image based on the updated set of X-ray conditions is displayed. The processing circuitry 44 sequentially executes, on the new X-ray image as a processing target, the setting function 447A, the calculation function 447B, the threshold value acquisition function 447C, and the X-ray condition determination function 447D. The above-described series of processing may be repeatedly executed over a given number of times.

FIG. 2 shows an operation example of an X-ray diagnostic apparatus 1 according to the first embodiment. The present operation example may be started in response to a start command input by the operator via the input interface 43 of the X-ray diagnostic apparatus 1. On the other hand, the present operation example may end at a given timing in response to an end command input by the operator via the input interface 43 of the X-ray diagnostic apparatus 1.

(Step S101) The X-ray diagnostic apparatus 1 sets, with the imaging condition setting function 441, imaging conditions relating to a subject P. As described above, a set of imaging conditions includes a set of X-ray conditions and a set of image quality conditions.

(Step S102) Thereafter, the X-ray diagnostic apparatus 1 irradiates, with the X-ray condition control function 442 and the driving control function 443, the subject P with X-rays based on the set of X-ray conditions set at step S101. Thereby, projection data relating to the subject P is obtained.

(Step S103) Subsequently, the X-ray diagnostic apparatus 1 generates, with the image generation function 444, an X-ray image based on a set of image quality conditions set at step S101 and projection data obtained at step S102.

(Step S104) Subsequently, the X-ray diagnostic apparatus 1 performs, with the image processing function 445, image processing on the X-ray image generated at step S103. As described above, the image processing includes a gain correction process.

(Step S105) Subsequently, the X-ray diagnostic apparatus 1 causes, with the display control function 446, the display 42 to display an X-ray image subjected to image processing at step S104. Through the above-described series of processing, an X-ray image of a subject P based on predetermined imaging conditions is captured and displayed.

(Step S106) Here, the X-ray diagnostic apparatus 1 decides, with the setting function 447A, whether or not to set ROIs in the X-ray image displayed at step S105. If the X-ray diagnostic apparatus 1 decides to set ROIs (YES at step S106), the processing advances to step S107. The X-ray diagnostic apparatus 1 may determine, for example, to set ROIs upon receiving an input operation relating to setting of ROIs from the operator. On the other hand, if the X-ray diagnostic apparatus 1 does not decide to set ROIs (NO at step S106), the processing returns to step S101. In this case, the processing from step S101 to S105 may be executed based on imaging conditions differing from the above-described predetermined imaging conditions. As a result, a new X-ray image relating to the subject P is captured and displayed.

(Step S107) Thereafter, the X-ray diagnostic apparatus 1 sets, with the setting function 447A, a plurality of ROIs in the X-ray image displayed at step S105. For example, the X-ray diagnostic apparatus 1 may automatically set a plurality of ROIs using a trained model (e.g., a neural network) that realizes an image recognition process of detecting a target. As a matter of course, the X-ray diagnostic apparatus 1 may, based on an input operation made by the operator via the input interface 43, set ROIs corresponding to the input operation. Also, the X-ray diagnostic apparatus 1 may set a plurality of ROIs using a material separation process of separating materials contained in a subject, such as spectral imaging, dual-energy technology, etc.

(Step S108) Subsequently, the X-ray diagnostic apparatus 1 calculates, with the calculation function 447B, statistical values relating to the respective ROIs based on a plurality of values of pixels included in each of the ROIs set at step S107, thereby obtaining a plurality of statistical values. As described above, in ABC control, the X-ray diagnostic apparatus 1 calculates, as a statistical value, a mean value of values of pixels of each ROI. On the other hand, in CNR control, the X-ray diagnostic apparatus 1 calculates, as a statistical value, a contrast-to-noise ratio corresponding to values of pixels of each ROI.

(Step S109) Subsequently, the X-ray diagnostic apparatus 1 acquires, with the threshold value acquisition function 447C, a threshold value relating to each of the statistical values calculated at step S108.

(Step S110) After that, the X-ray diagnostic apparatus 1 determines, with the X-ray condition determination function 447D, a set of X-ray conditions relating to an X-ray image (second X-ray image) subsequent to the X-ray image (first X-ray image) displayed at step S105, based on the statistical value and the threshold value relating to each of the ROIs calculated at steps S108 and S109. After execution of this step, the processing returns to step S101. The set of X-ray conditions determined at step S110 is fed back to the setting of the imaging conditions at step S101.

FIG. 3 shows a first example relating to setting of a plurality of ROIs and calculation of a plurality of sets of X-ray conditions by the X-ray diagnostic apparatus 1 according to the first embodiment. In an X-ray image 200A displayed by the display 42 of the X-ray diagnostic apparatus 1, two ROIs 250A and 250B are set. Moreover, the sets of X-ray conditions calculated based on the ROIs 250A and 250B are shown on the X-ray condition table 260A. The present processing may be executed inside the memory 41 or the processing circuitry 44 of the X-ray diagnostic apparatus 1.

A plurality of targets (a spine 210, a catheter 220, and a heart 230) relating to the subject P are displayed on the X-ray image 200A. Of the targets, the spine 210 and the heart 230 correspond to anatomical structures of the subject P. On the other hand, the catheter 220 corresponds to a medical device inserted into the subject P. Furthermore, dot-like radiopaque markers 220A and 220B are put on the catheter 220.

The solid lines in the X-ray image 200A show contours of targets that are displayed distinctly. On the other hand, the dashed lines in the X-ray image 200A show contours of targets that are displayed indistinctly. Also, the hatched portion in the X-ray image 200A shows an image region (i.e., a portion with a large subject thickness) that is darker than an image region on the periphery thereof. In the X-ray image 200A, the markers 220A and 220B on the catheter 220 are positioned on the outside (e.g., at a portion with a small subject thickness) of the hatched portion. Specifically, the markers 220A and 220B are positioned at the heart 230.

The X-ray diagnostic apparatus 1 sets a rectangular ROI 250A over a substantially entire region of the X-ray image 200A. Specifically, the X-ray diagnostic apparatus 1 arranges an ROI 250A in such a manner that the center of the ROI 250A matches the center of the X-ray image 200A. From a quantitative standpoint, the ROI 250A occupies approximately 80% of all the pixels configuring the X-ray image 200A. The ROI 250A includes part of the spine 210, part of the catheter 220, and part of the heart 230. The ROI 250A may also be called a general ROI.

On the other hand, the X-ray diagnostic apparatus 1 sets a circular ROI 250B so as to include markers 220A and 220B in the X-ray image 200A. Specifically, the X-ray diagnostic apparatus 1 arranges an ROI 250B inside the ROI 250A. From a quantitative standpoint, the ROI 250B occupies approximately 10% of all the pixels configuring the X-ray image 200A. The ROI 250B includes part of the catheter 220 and part of the heart 230. The ROI 250B may also be called a local ROI.

After the two ROIs 250A and 250B are set, the X-ray diagnostic apparatus 1 executes ABC or CNR control based on each of the ROIs. A given known approach may be applied to the ABC control or the CNR control. As described above, the X-ray diagnostic apparatus 1 calculates a statistical value for each ROI, and then calculates a set of X-ray conditions for each ROI based on the calculated statistical value and a threshold value corresponding to the statistical value. Thereby, a set of X-ray conditions based on each of the ROIs 250A and 250B is calculated.

According to the X-ray condition table 260A, the set of X-ray conditions calculated based on the ROI 250A is “tube voltage: A1 kV; tube current: B1 mA; pulse width: C1 msec; and beam filter: 1”. On the other hand, the set of X-ray conditions calculated based on the ROI 250B are “tube voltage: A2 kV; tube current: B2 mA; pulse width: C2 msec; and beam filter: 1”. Here, it is assumed that A1>A2. The X-ray diagnostic apparatus 1 compares the two sets of X-ray conditions based on the ROIs, and decides that both the value of the tube voltage kV and the irradiation dose are higher in the former set of X-ray conditions than those in the latter set of X-ray conditions. Accordingly, the X-ray diagnostic apparatus 1 determines the set of X-ray conditions based on the ROI 250A as a set of X-ray conditions relating to capturing of an X-ray image subsequent to the X-ray image 200A.

FIG. 4 shows a display example of an X-ray image based on the first example of FIG. 3. Herein, a new X-ray image 300A based on the ROI 250A and a new X-ray image 300B based on the ROI 250B are shown. Of the two images, the X-ray image 300A is displayed on the display 42. On the other hand, the X-ray image 300B may be either displayed together with the X-ray image 300A, or not displayed.

On the X-ray images 300A and 300B, a plurality of targets relating to the subject P are displayed, similarly to the X-ray image 200A. Also, the ROI 250A used for determining the set of X-ray conditions relating to capturing of the X-ray image 300A is displayed on the X-ray image 300A. On the other hand, the ROI 250B used for determining the set of X-ray conditions relating to capturing of the X-ray image 300B is displayed on the X-ray image 300B.

When the two X-ray images are compared, it can be appreciated that the X-ray image 300A offers both a brightness of the entire image and an image visibility higher than those of the X-ray image 300B. Also, the X-ray image 300A offers a high visibility of the markers 220A and 220B on the catheter 220 compared to the X-ray image 300B. On the other hand, due to an insufficient dose, the X-ray image 300B is relatively dark in its entirety, leading to a low visibility of the markers 220A and 220B. That is, for the markers 220A and 220B in the X-ray image 200A, a set of X-ray conditions should be determined by setting a general ROI 250A, rather than by setting a local ROI 250B, to achieve a higher visibility of the markers 220A and 220B in the next X-ray image to be obtained by the determined set of X-ray conditions.

FIG. 5 shows a second example relating to setting of a plurality of ROIs and calculation of a plurality of sets of X-ray conditions by the X-ray diagnostic apparatus 1 according to the first embodiment. In an X-ray image 200B displayed by the X-ray diagnostic apparatus 1, two ROIs 250A and 250C are set. Moreover, the sets of X-ray conditions calculated based on each of the ROIs 250A and 250C are shown on the X-ray condition table 260B. A plurality of targets displayed on the X-ray image 200B are identical to the plurality of targets displayed on the X-ray image 200A. Also, the hatched portion in the X-ray image 200B shows an image region (i.e., a portion with a large subject thickness) that is darker than an image region on the periphery thereof. It is to be noted that the brightness of the entire X-ray image 200B is roughly identical to the brightness of the entire X-ray image 200A.

However, the position of the catheter 220 in the X-ray image 200B differs from the position of the catheter 220 in the X-ray image 200A. In particular, the markers 220A and 220B on the catheter 220 are positioned at the spine 210 or in the vicinity of the spine 210. The ROI 250A set in the X-ray image 200B is identical to the ROI 250A set in the X-ray image 200A.

The X-ray diagnostic apparatus 1 sets a rectangular ROI 250C so as to include markers 220A and 220B in the X-ray image 200B. Specifically, the X-ray diagnostic apparatus 1 arranges an ROI 250C inside the ROI 250A. From a quantitative standpoint, the ROI 250C occupies approximately 10% of all the pixels configuring the X-ray image 200B. The ROI 250C includes part of the spine 210 and part of the catheter 220. The ROI 250C may also be called a local ROI. The markers 220A and 220B on the catheter 220 are positioned inside the hatched portion on the X-ray image 200B (i.e., at a portion with a large subject thickness).

After the two ROIs 250A and 250C are set, the X-ray diagnostic apparatus 1 executes ABC or CNR control based on each of the ROIs. Thereby, the set of X-ray conditions based on each of the ROIs 250A and 250C is calculated.

According to the X-ray condition table 260B, the set of X-ray conditions calculated based on the ROI 250A is “tube voltage: A1 kV; tube current: B1 mA; pulse width: C1 msec; and beam filter: 1”. On the other hand, the set of X-ray conditions calculated based on the ROI 250C are “tube voltage: A3 kV; tube current: B3 mA; pulse width: C3 msec; and beam filter: 1”. Here, it is assumed that A1<A3. The X-ray diagnostic apparatus 1 compares the two sets of X-ray conditions based on the ROIs, and decides that both the value of the tube voltage kV and the irradiation dose are higher in the latter set of X-ray conditions than those in the former set of X-ray conditions. Accordingly, the X-ray diagnostic apparatus 1 determines the set of X-ray conditions based on the ROI 250C as a set of X-ray conditions relating to capturing of an X-ray image subsequent to the X-ray image 200B.

FIG. 6 shows a display example of an X-ray image based on the second example of FIG. 5. Herein, a new X-ray image 400A based on the ROI 250A and a new X-ray image 400B based on the ROI 250C are shown. Of the two images, the X-ray image 400B is displayed on the display 42. On the other hand, the X-ray image 400A may be either displayed together with the X-ray image 400B, or not displayed.

On the X-ray images 400A and 400B, a plurality of targets relating to the subject P are displayed, similarly to the X-ray image 200B. Also, the ROI 250A used for determining the set of X-ray conditions relating to capturing of the X-ray image 400A is displayed on the X-ray image 400A. On the other hand, an ROI 250C used for determining a set of X-ray conditions relating to capturing of the X-ray image 400B is displayed on the X-ray image 400B.

When the two X-ray images are compared, it can be appreciated that the X-ray image 400B offers both a brightness of the entire image and an image visibility higher than those of the X-ray image 400A. Also, the X-ray image 400B offers a high visibility of the markers 220A and 220B on the catheter 220 compared to the X-ray image 400A. On the other hand, due to an insufficient dose, the X-ray image 400A is relatively dark in its entirety, leading to a low visibility of the markers 220A and 220B. That is, a set of X-ray conditions should be determined by setting a local ROI 250C for the markers 220A and 220B in the X-ray image 200B, rather than by setting a general ROI 250A, to achieve a higher visibility of the markers 220A and 220B in the next X-ray image obtained by the determined set of X-ray conditions.

FIG. 7 shows an example of gain correction of an X-ray image upon occurrence of a halation. In the X-ray images 300A and 400B generated under a set of X-ray conditions under which the irradiation dose is high, a phenomenon in which the values of pixels are saturated (halation) may occur in part of the image region. Thus, if a halation region exists in part of the X-ray image, the X-ray diagnostic apparatus 1 performs a gain correction process to decrease the values of pixels of the halation region by a single level. With such a configuration of the X-ray diagnostic apparatus 1, it is possible to provide an X-ray image capable of easily identifying a target present in a halation region.

It is assumed, for example, that a halation region (white circle) has occurred at positions of the markers 220A and 220B in the X-ray image 300A (left). At this time, the X-ray diagnostic apparatus 1 applies a gain correction process to the X-ray image 300A. Thereby, the markers 220A and 220B are displayed on the display 42 in a recognizable manner in the gain-corrected X-ray image 300A (right).

The X-ray diagnostic apparatus 1 according to the first embodiment has been described above. The X-ray diagnostic apparatus 1 sets a plurality of ROIs in an X-ray image, and determines, based on a statistical value and a threshold value relating to each of the ROIs, a set of X-ray conditions relating to capturing of an X-ray image subsequent to the X-ray image. With such a configuration of the X-ray diagnostic apparatus 1, it is possible to determine a more appropriate set of X-ray conditions as compared to the method of determining a set of X-ray conditions based on a single ROI. Accordingly, with the X-ray diagnostic apparatus 1, it is possible to avoid a situation in which a dose to the entire X-ray image becomes insufficient, causing a decrease in visibility of the X-ray image, as shown in the X-ray images 300B and 400A. Rather, with the X-ray diagnostic apparatus 1, it is possible to provide an X-ray image with high visibility by securing a sufficient dose for the entire X-ray image, as shown in the X-ray images 300A and 400B. Also, with the X-ray diagnostic apparatus 1, it is possible to provide an optimum X-ray image, taking into consideration both visibility (image quality) relating to a local ROI on the X-ray image and visibility (image quality) relating to the general ROI on the X-ray image.

Moreover, the X-ray diagnostic apparatus 1 according to the first embodiment may set one of a plurality of ROIs over an entire region or a substantially entire region of an X-ray image, and set at least one ROI excluding said one of the ROIs at an image region including a target photographed in the X-ray image. With such a configuration of the X-ray diagnostic apparatus 1, it is possible to maintain or improve visibility relating to both the entire region or the substantially entire region of the X-ray image and the image region including the target in the X-ray image.

Furthermore, the X-ray diagnostic apparatus 1 according to the first embodiment may estimate, based on a plurality of values of pixels included in each of a plurality of ROIs, an image quality index (e.g., a contrast-to-noise ratio) of each of the ROIs, and calculate the estimated image quality index as a statistical value. For example, the X-ray diagnostic apparatus 1 may calculate, using a plurality of values of pixels included in a single ROI, a mean value of the values of pixels, and converts the calculated mean value into a water-equivalent thickness. Subsequently, the X-ray diagnostic apparatus 1 may convert the water-equivalent thickness into a contrast-to-noise ratio via a lookup table, etc. The X-ray diagnostic apparatus 1 may use the mean value, the contrast-to-noise ratio, or the like calculated by the above-described series of processing as a statistical value relating to the ROI. In this case, with the X-ray diagnostic apparatus 1, it is possible to maintain or improve visibility relating to each of the ROIs represented by the statistical value. That is, the statistical value may be a scale or index of the visibility of each ROI.

Moreover, the X-ray diagnostic apparatus 1 according to the first embodiment may obtain a plurality of sets of X-ray conditions by calculating, for each of a plurality of ROIs, a set of X-ray conditions under which a statistical value satisfies a threshold value, and set, as a set of X-ray conditions relating to capturing of a next X-ray image, a set of X-ray conditions under which irradiation is performed with a highest dose of X-rays, of the plurality of sets of X-ray conditions. With such a configuration of the X-ray diagnostic apparatus 1, it is possible to capture and display an X-ray image with a higher brightness.

Furthermore, the X-ray diagnostic apparatus 1 according to the first embodiment may determine a set of X-ray conditions relating to capturing of a next X-ray image in such a manner that, if the number of a plurality of ROIs is two, statistical values of both of the two ROIs satisfy corresponding threshold values. With such a configuration of the X-ray diagnostic apparatus 1, it is possible to maintain or improve visibility relating to both of the two ROIs.

Moreover, the X-ray diagnostic apparatus 1 according to the first embodiment may determine a set of X-ray conditions relating to capturing of a next X-ray image in such a manner that, if the number of a plurality of ROIs is three or more, statistical values of at least two of the three or more ROIs satisfy corresponding threshold values. With such a configuration of the X-ray diagnostic apparatus 1, it is possible to maintain or improve visibility relating to the at least two ROIs.

Furthermore, the X-ray diagnostic apparatus 1 according to the first embodiment may perform, if a halation region is present in an X-ray image generated based on a determined set of X-ray conditions, a gain correction process on the X-ray image to darken the halation region. With such a configuration of the X-ray diagnostic apparatus 1, it is possible to decrease a brightness of the halation region that has occurred by X-ray irradiation under a set of X-ray conditions under which a dose of X-ray irradiation is relatively high, thereby maintaining or improving visibility relating to the halation region.

Moreover, the X-ray diagnostic apparatus 1 according to the first embodiment may, based on position information of a dose-reducing filter (punched filter) with an opening formed at its central part, set an image region in an X-ray image corresponding to the opening as one of the ROIs, and set a peripheral region of the ROI as another ROI. With such a configuration of the X-ray diagnostic apparatus 1, it is possible to maintain or improve visibility relating to both the image region corresponding to the opening portion of the beam filter and an image region corresponding to a metal-plate portion of the beam filter. As a result, with the X-ray diagnostic apparatus 1, it is possible to avoid a situation in which visibility of a medical device, etc. substantially decreases due to an insufficient dose to an image region overlapping the dose-reducing filter.

Furthermore, the X-ray diagnostic apparatus 1 according to the first embodiment is configured to set an ROI at an image region including a target photographed in an X-ray image. With such a configuration of the X-ray diagnostic apparatus 1, it is possible to maintain or improve visibility relating to the ROI including the target.

Second Embodiment

Hereinafter, an X-ray diagnostic apparatus 1 according to the second embodiment will be described. The X-ray diagnostic apparatus 1 according to the second embodiment sets priorities for a plurality of ROIs. The X-ray diagnostic apparatus 1 secures a required dose for an ROI for which a highest priority is set, while securing a minimum dose for ROIs for which second highest and subsequent priorities are set. To realize such processing, the processing circuitry 44 according to the second embodiment performs the processing shown below. The other configuration is similar to that of the first embodiment.

The processing circuitry 44 sets, with the setting function 447A, a priority for each of the ROIs. The processing circuitry 44 calculates, with the calculation function 447B, a statistical value relating to each of the ROIs based on a plurality of values of pixels included in each of the ROIs for which priorities are set, thereby obtaining a plurality of statistical values. The processing circuitry 44 acquires, with the threshold value acquisition function 447C, a maximum value and a minimum value relating to corresponding threshold values of the statistical values.

The processing circuitry 44 determines, with the X-ray condition determination function 447D, a set of X-ray conditions relating to capturing of a next X-ray image in such a manner that a statistical value of an ROI with a highest priority of a plurality of ROIs falls in a range between a threshold value and a maximum value, and a statistical value of at least one of the ROIs excluding the ROI with the highest priority falls in a range between the threshold value and a minimum value.

FIG. 8 shows an operation example of the X-ray diagnostic apparatus 1 according to the second embodiment. Similarly to the first embodiment, the present operation example may be started in response to a start command, and may end in response to an end command.

(Steps S201-S205) First, the X-ray diagnostic apparatus 1 performs processing similar to steps S101 to S105 of the first embodiment. Thereby, an X-ray image relating to a subject P based on predetermined imaging conditions is captured and displayed.

(Step S206) Here, the X-ray diagnostic apparatus 1 decides, with the setting function 447A, whether or not to set ROIs in the X-ray image displayed at step S205. Step S206 is similar to step S106.

(Step S207) Thereafter, the X-ray diagnostic apparatus 1 sets, with the setting function 447A, a plurality of ROIs in an X-ray image displayed at step S205. Step S207 is similar to step S107.

(Step S208) Subsequently, the X-ray diagnostic apparatus 1 sets, with the setting function 447A, priorities for the respective ROIs set at step S207. For example, the X-ray diagnostic apparatus 1 sets, as an ROI with a highest priority, one of the ROIs including at least one target photographed in the X-ray image. Specifically, the X-ray diagnostic apparatus 1 may set a highest priority (priority 1) for a local ROI including a medical device, to which the operator is highly likely to be currently paying attention. Also, the X-ray diagnostic apparatus 1 may set a second highest priority (priority 2) for an ROI set over an entire region or a substantially entire region of the X-ray image. Alternatively, the X-ray diagnostic apparatus 1 may set a second highest priority (priority 2) for a local ROI including a medical device, to which the operator is less likely to be currently paying attention. Different priorities may be set for a plurality of ROIs, or an identical priority may be set for at least two of the ROIs.

(Step S209) Subsequently, the X-ray diagnostic apparatus 1 calculates, with the calculation function 447B, a statistical value relating to each of the ROIs based on a plurality of values of pixels included in each of the ROIs set at step S207, thereby obtaining a plurality of statistical values. Step S209 is similar to step S108.

(Step S210) Subsequently, the X-ray diagnostic apparatus 1 acquires, with the threshold value acquisition function 447C, a maximum value and a minimum value relating to a threshold value of each of the statistical values calculated at step S209. The X-ray diagnostic apparatus 1 may acquire the maximum value and the minimum value of each threshold value from the input interface 43, or acquire the maximum value and the minimum value of each threshold value stored in the memory 41. The maximum value of the threshold value defines, for example, the maximum value of the irradiation dose of X-rays. On the other hand, the minimum value of the threshold value defines, for example, the minimum value of the irradiation dose of X-rays.

(Step S211) After that, the X-ray diagnostic apparatus 1 determines, with the X-ray condition determination function 447D, a set of X-ray conditions relating to an X-ray image (second X-ray image) subsequent to the X-ray image (first X-ray image) displayed at step S205, based on the priority, the statistical value, the threshold value, the maximum value, and the minimum value relating to each of the ROIs calculated at steps S208 to S210. For example, the X-ray diagnostic apparatus 1 determines a set of X-ray conditions relating to capturing of the second X-ray image in such a manner that a statistical value of an ROI with a highest priority falls in a range between a threshold value and a maximum value, and a statistical value of at least one of the ROIs excluding the ROI with the highest priority falls in a range between the threshold value and a minimum value. After execution of this step, the processing returns to step S201. The set of X-ray conditions determined at step S211 is fed back to the setting of the imaging conditions at step S201.

The X-ray diagnostic apparatus 1 according to the second embodiment has been described above. With the X-ray diagnostic apparatus 1 according to the second embodiment, it is possible to obtain advantageous effects similar to those of the first embodiment. With the X-ray diagnostic apparatus 1 according to the second embodiment, it is possible to secure a sufficient dose for obtaining a statistical value between the threshold value and the maximum value for the ROI with the highest priority, and to secure a required minimum dose for obtaining a statistical value between the threshold value and the minimum value for the ROI with a second highest priority. With the X-ray diagnostic apparatus, it is possible to secure a minimum dose for each of the ROIs with the third highest and subsequent priorities. It is thus possible, with the X-ray diagnostic apparatus