Medical image processing apparatus, X-ray CT apparatus, and image processing method

1. A medical image processing apparatus, comprising:

storage circuitry configured to store therein pieces of X-ray image data on a subject obtained at a plurality of time phases from a medical image diagnostic apparatus; and

processing circuitry configured to

calculate an index value obtained by comparing a pixel value of X-ray image data of a reference time phase among the pieces of X-ray image data of the time phases and a pixel value of each of the pieces of X-ray image data of the time phases without extracting a lung field region of the subject from the nieces of X-ray image data, and

select at least one of the pieces of X-ray image data of the time phases based on the index value calculated for each of the time phases and associate the one piece of X-ray image data with a breathing time phase in at least one of inspiration and expiration of the subject, wherein

the reference time phase is any one of the time phases, and

the processing circuitry

performs difference processing on each of the pieces of X-ray image data of the time phases and the X-ray image data of the reference time phase to calculate the index value,

selects a time phase at which the index value calculated reaches the maximum value as a time phase of maximum inspiration of the subject, and

selects a time phase at which the index value calculated reaches the minimum value as a time phase of maximum expiration of the subject.

2. The medical image processing apparatus according to claim 1 , wherein the processing circuitry

selects X-ray image data corresponding to a breathing time phase in at least one of the maximum inspiration and the maximum expiration of the subject from among the pieces of X-ray image data of the time phases based on the index value calculated for each of the time phases.

3. The medical image processing apparatus according to claim 1 , wherein

the reference time phase is one of two time phases adjacent to each other among the time phases, and

the processing circuitry

performs difference processing on X-ray image data of the other time phase and X-ray image data of the reference time phase to calculate the index value,

selects a time phase at which the index value calculated decreases to zero or a value near zero as the time phase of maximum inspiration of the subject, and

selects a time phase at which the index value calculated increases to zero or a value near zero as the time phase of maximum expiration of the subject.

4. The medical image processing apparatus according to claim 2 , wherein the processing circuitry performs the difference processing that includes generating a difference X-ray image data obtained by calculating a difference between pixel values of pixels at corresponding positions of the X-ray image data of the reference time phase and each of the pieces of X-ray image data of the time phases, and determining an average of pixel values of the generated difference X-ray image data as the index value.

5. The medical image processing apparatus according to claim 2 , wherein the processing circuitry performs the difference processing that includes generating a difference X-ray image data obtained by calculating a difference between pixel values of pixels at corresponding positions of the X-ray image data of the reference time phase and each of the pieces of X-ray image data of the time phases, and determining a sum of pixel values of the generated difference X-ray image data as the index value.

6. The medical image processing apparatus according to claim 2 , wherein the processing circuitry performs the difference processing that includes calculating a difference between a sum of pixel values of the X-ray image data of the reference time phase and a sum of pixel values of each of the pieces of X-ray image data of the time phases, and determining the calculated difference as the index value.

7. The medical image processing apparatus according to claim 6 , wherein the processing circuitry performs the difference processing on any pixel having a computed tomography (CT) value not larger than a predetermined threshold in each of the pieces of X-ray image data of the time phases.

8. The medical image processing apparatus according to claim 2 , wherein the processing circuitry performs the difference processing on any pixel in a region defined in each of the pieces of X-ray image data of the time phases.

9. The medical image processing apparatus according to claim 1 , wherein the processing circuitry calculates the index value using, as the pieces of X-ray image data, two-dimensional X-ray image data obtained by imaging a chest of the subject, the two-dimensional X-ray image data including a lung field of the subject.

10. The medical image processing apparatus according to claim 9 , wherein the processing circuitry calculates the index value using a plurality of pieces of two-dimensional X-ray image data as the pieces of X-ray image data.

11. The medical image processing apparatus according to claim 9 , wherein the two-dimensional X-ray image data corresponds to at least one of an axial section, a sagittal section, and a coronal section of the subject.

12. The medical image processing apparatus according to claim 1 , wherein the processing circuitry extracts a bronchial region in X-ray image data of a predetermined time phase associated by the processing circuitry.

13. The medical image processing apparatus according to claim 2 , wherein the processing circuitry outputs, through predetermined output circuitry, information indicating that the time phases of the maximum inspiration and the maximum expiration are not selectable, when a plurality of candidates are detected for at least one of the time phases of the maximum inspiration and the maximum expiration.

14. The medical image processing apparatus according to claim 1 , wherein the processing circuitry further generates information including each time phase and the index value at the time phase in association with each other and outputs the information through a predetermined display.

15. The medical image processing apparatus according to claim 1 , wherein the processing circuitry selects X-ray image data corresponding to a breathing time phase in at least one of the maximum inspiration and the maximum expiration of the subject from among the pieces of X-ray image data of the time phases based on the index value calculated for each of the time phases and stores three-dimensional X-ray image data corresponding to a time phase of the selected X-ray image data in predetermined storage circuitry.

16. An X-ray computed tomography (CT) apparatus, comprising:

processing circuitry configured to

acquire pieces of X-ray image data on a subject at a plurality of time phases,

calculate an index value obtained by comparing a pixel value of X-ray image data of a reference time phase among the pieces of X-ray image data of the time phases and a pixel value of each of the pieces of X-ray image data of the time phases without extracting a lung field region of the subject from the pieces of X-ray image data, and

select at least one of the pieces of X-ray image data of the time phases based on the index value calculated for each of the time phases and associate the one piece of X-ray image data with a breathing time phase in at least one of inspiration and expiration of the subject, wherein

the reference time phase is any one of the time phases, and

the processing circuitry

performs difference processing on each of the pieces of X-ray image data of the time phases and the X-ray image data of the reference time phase to calculate the index value,

selects a time phase at which the index value calculated reaches the maximum value as a time phase of maximum inspiration of the subject, and

selects a time phase at which the index value calculated reaches the minimum value as a time phase of maximum expiration of the subject.

17. The X-ray CT apparatus according to claim 16 , wherein

the processing circuitry

acquires pieces of X-ray image data on the subject at a plurality of time phases with an X-ray irradiation condition of preliminary image capturing,

calculates the index value each time X-ray image data of a new time phase is acquired,

determines, each time the index value is calculated, whether the X-ray image data of the new time phase corresponds to a breathing time phase in at least one of the maximum inspiration and the maximum expiration of the subject, and

acquires X-ray image data on the subject with an X-ray irradiation condition of main image capturing when the X-ray image data of the new time phase corresponds to the breathing time phase in at least one of the maximum expiration and the maximum expiration.

18. The X-ray CT apparatus according to claim 16 , wherein the processing circuitry selects X-ray image data corresponding to a breathing time phase in at least one of the maximum inspiration and the maximum expiration of the subject from among the pieces of X-ray image data of the time phases based on the index value calculated for each of the time phases and stores three-dimensional X-ray image data corresponding to a time phase of the selected X-ray image data in predetermined storage circuitry.

19. An image processing method, comprising:

storing, in storage circuitry, pieces of X-ray image data on a subject obtained at a plurality of time phases from a medical image diagnostic apparatus;

calculating an index value obtained by comparing a pixel value of X-ray image data of a reference time phase among the pieces of X-ray image data of the time phases and a pixel value of each of the pieces of X-ray image data of the time phases without extracting a lung field region of the subject from the pieces of X-ray image data;

selecting at least one of the pieces of X-ray image data of the time phases based on the index value calculated for each of the time phases and associating the one piece of X-ray image data with a breathing time phase in at least one of inspiration and expiration of the subject, the reference time phase being any one of the time phases;

performing difference processing on each of the pieces of X-ray image data of the time phases and the X-ray image data of the reference time phase to calculate the index value;

selecting a time phase at which the index value calculated reaches the maximum value as a time phase of maximum inspiration of the subject; and

selecting a time phase at which the index value calculated reaches the minimum value as a time phase of maximum expiration of the subject.