X-ray diagnostic apparatus

1. An X-ray diagnostic apparatus comprising:

processing circuitry configured to

successively generate a plurality of X-ray images based on X-rays emitted from an X-ray tube and transmitted through a subject,

detect a position of a target in each of the plurality of X-ray images,

identify a first region that is stationary among the plurality of X-ray images and that includes all the positions of the detected target in each of the plurality of X-ray images, the first region being a region in which the target is visible throughout the plurality of X-ray images,

perform control to reduce an X-ray irradiation dose to a second region that excludes the first region,

acquire an X-ray image which the X-ray irradiation dose to the second region is reduced,

extract a first period having an amount of change in the position of the target that is smaller than a threshold and is periodically repeated in a period for successively generating the plurality of X-ray images, and

alternately switch between a first frame rate in the first period and a second frame rate in a second period that excludes the first period by controlling the first frame rate to be lower than the second frame rate.

2. The X-ray diagnostic apparatus according to claim 1 , wherein the processing circuitry is configured to

perform the identifying of the first region by identifying third regions that are non-stationary regions that respectively include the detected target in each corresponding X-ray image of the plurality of X-ray images, and

determining the first region to be a stationary region among the plurality of X-ray images that covers each of the third regions.

3. The X-ray diagnostic apparatus according to claim 1 , wherein the processing circuitry is further configured to

control image processing on the first region, and

perform the control to reduce the X-ray irradiation dose to the first region, based on the image processing on the first region.

4. The X-ray diagnostic apparatus according to claim 1 , wherein, the processing circuitry is configured to alternately change the number of X-ray images to be generated per unit time for the period for successively generating the plurality of X-ray images based on the first frame rate and the second frame rate.

5. The X-ray diagnostic apparatus according to claim 1 , wherein, based on heartbeats of the subject, the processing circuitry is configured to extract the first period.

6. The X-ray diagnostic apparatus according to claim 1 , wherein the processing circuitry is configured to reduce the X-ray irradiation dose to the second region by inserting an X-ray collimator or an X-ray absorption filter into the second region.

7. The X-ray diagnostic apparatus according to claim 1 , wherein the processing circuitry is further configured to successively generate corrected images obtained by subjecting newly generated X-ray images to correction processing to cause a position of the target detected in the newly generated X-ray images to coincide with a reference position that is a position of the target detected in a reference image.

8. The X-ray diagnostic apparatus according to claim 1 , wherein the processing circuitry is configured to

perform the identifying of the first region by

detecting positions of a plurality of targets in each of the plurality of X-ray images,

identifying in each of the plurality of X-ray images a respective third region including a corresponding detected target of the plurality of detected targets, the respective third regions being non-stationary among the plurality of X-ray images,

determining the first region to be a stationary region among the plurality of X-ray images that covers each of the respective third regions.

9. The X-ray diagnostic apparatus according to claim 1 , wherein the target is a stent marker.

10. The X-ray diagnostic apparatus according to claim 1 , wherein the processing circuitry is configured to execute high-frequency noise reduction filtering on the X-ray image based on X-rays with the reduced irradiation dose, by using an image filter.

11. The X-ray diagnostic apparatus according to claim 1 , wherein, when a enlarging operation is executed on an X-ray image displayed at a present time, the processing circuitry is configured to control an imaging system so that all the positions of the detected target in each of the plurality of X-ray images are included in an enlarged region.

12. The X-ray diagnostic apparatus according to claim 2 , wherein the processing circuitry is further configured to

control image processing on the third regions, and

perform the control to reduce the X-ray irradiation dose to the first region, based on the image processing on the third regions.

13. The X-ray diagnostic apparatus according to claim 4 , wherein, based on heartbeats of the subject, the processing circuitry is configured to extract the first period.