X-ray CT apparatus and tomography method

1. An X-ray CT apparatus comprising:

an imaging unit configured to irradiate a subject, switching scanning conditions, with X-rays continuously or intermittently, and to reconstruct an image by detecting X-rays passed through the subject;

an index-value detecting unit configured to detect an index value that indicates a contrast medium density in the image reconstructed by the imaging unit during a scan;

a switch-timing detecting unit configured to detect switch timing of the scanning conditions based on the index value detected by the index-value detecting unit; and

an imaging control unit configured to control the imaging unit so as to perform a prep scan and a main scan, the main scan including a first scan with a first scanning condition and a second scan with a second scanning condition; wherein

the imaging control unit controls, during the prep scan, the imaging unit so as to start the main scan with a timing when the index value exceeds a threshold value, and controls, during the main scan, the imaging unit so as to skip a rest of the first scan in execution and to start the second scan upon detecting the switch timing by the switch-timing detecting unit.

2. The apparatus according to claim 1 , wherein the imaging unit performs as the main scan a dynamic scan through which as the image a dynamic image of a scan subject portion of the subject is reconstructed by repeatedly irradiating a region including the scan subject portion with X-rays.

3. The apparatus according to claim 2 , wherein the imaging unit detects X-rays with a Flat Panel Detector of multiple arrays that simultaneously detects X-rays passed through the region including the scan subject portion.

4. The apparatus according to claim 1 , wherein the switch-timing detecting unit creates a curve that indicates temporal variations in the contrast medium density based on the index value, and detects the switch timing based on a gradient of the created curve.

5. The apparatus according to claim 4 , wherein

the index-value detecting unit detects as the index value an index value that indicates the contrast medium density in a region of interest set on the image reconstructed by the imaging unit, and

the switch-timing detecting unit creates as the curve a curve that indicates the temporal variations in the contrast medium density in the region of interest.

6. The apparatus according to claim 4 , wherein the switch-timing detecting unit detects the switch timing by detecting an inflection point that appears on the curve based on a gradient of the curve.

7. The apparatus according to claim 1 , wherein the imaging control unit controls the imaging unit so as to skip the rest of the main scan currently in execution and to terminate scanning, when the index value detected by the index-value detecting unit becomes below a termination threshold value.

8. The apparatus according to claim 1 , wherein the imaging control unit controls the imaging unit so as to skip the rest of the main scan currently in execution and to terminate scanning, when a total scan time from a start of the main scan reaches a predetermined maximum scan time.

9. The apparatus according to claim 1 , further comprising a display control unit configured to display during the main scan a curve that indicates temporal variations in the contrast medium density based on the index value detected by the index-value detecting unit.

10. An X-ray CT apparatus comprising:

an imaging unit configured to irradiate a subject, switching scanning conditions, with X-rays continuously or intermittently, and to reconstruct an image by detecting X-rays passed through the subject;

an index-value detecting unit configured to detect an index value that indicates a contrast medium density in the image reconstructed by the imaging unit during a scan;

an imaging control unit configured to control the imaging unit so as to perform a prep scan and a main scan, and control, during the prep scan, the imaging unit so as to start the main scan with a timing when the index value exceeds a threshold value; and

a display control unit configured to display during the main scan a curve that indicates temporal variations in the contrast medium density based on the index value detected by the index-value detecting unit.

11. The apparatus according to claim 10 , further comprising:

an instruction receiving unit configured to receive from an operator an instruction to skip a rest of a first scan with a first scanning condition in execution and to start a second scan with a second scanning condition, the first scan and the second scan being included in the main scan; and

an imaging control unit configured to control the imaging unit so as to skip the rest of the first scan with the first scanning condition and to start the second scan with the second scanning condition upon receiving the instruction by the instruction receiving unit.

12. The apparatus according to claim 10 , wherein

the index-value detecting unit detects as the index value an index value that indicates the contrast medium density in a region of interest set on the image reconstructed by the imaging unit, and

the display control unit displays during the main scan as the curve a curve that indicates the temporal variations in the contrast medium density in the region of interest.

13. The apparatus according to claim 12 , wherein the display control unit displays as the curve a plurality of curves that indicates temporal variations in contrast medium densities in respective of a plurality of regions of interest, when as the region of interest the plurality of regions of interest are set on the image reconstructed by the imaging unit.

14. The apparatus according to claim 10 , wherein the display control unit further displays information about executed scans during the main scan.

15. A tomography method comprising:

irradiating a subject, switching scanning conditions, with X-rays continuously or intermittently, and reconstructing an image by detecting X-rays passed through the subject, by an imaging unit;

detecting by an index-value detecting unit an index value that indicates a contrast medium density in the image reconstructed by the imaging unit during a scan;

detecting by a switch-timing detecting unit switch timing of the scanning conditions based on the index value detected by the index-value detecting unit; and

controlling the imaging unit by an imaging control unit so as to perform a prep scan and a main scan, the main scan including a first scan with a first scanning condition and a second scan with a second scanning condition; wherein

the imaging control unit controls, during the prep scan, the imaging unit so as to start the main scan with a timing when the index value exceeds a threshold value, and controls, during the main scan, the imaging unit so as to skip a rest of the first scan in execution and to start the second scan upon detecting the switch timing by the switch-timing detecting unit.

16. The method according to claim 15 , wherein the imaging unit performs as the main scan a dynamic scan through which as the image a dynamic image of a scan subject portion of the subject is reconstructed by repeatedly irradiating a region including the scan subject portion with X-rays.

17. The method according to claim 16 , wherein the imaging unit detects X-rays with a Flat Panel detector of multiple arrays that simultaneously detects X-rays passed through the region including the scan subject portion.

18. The method according to claim 15 , wherein the switch-timing detecting unit creates a curve that indicates temporal variations in the contrast medium density based on the index value, and detects the switch timing based on a gradient of the created curve.

19. The method according to claim 18 , wherein

the index-value detecting unit detects as the index value an index value that indicates the contrast medium density in a region of interest set on the image reconstructed by the imaging unit, and

the switch-timing detecting unit creates as the curve a curve that indicates the temporal variations in the contrast medium density in the region of interest.

20. The method according to claim 18 , wherein the switch-timing detecting unit detects the switch timing by detecting an inflection point that appears on the curve based on a gradient of the curve.

21. The method according to claim 15 , wherein the imaging control unit controls the imaging unit so as to skip the rest of the main scan currently in execution and to terminate scanning, when the index value detected by the index-value detecting unit becomes below a termination threshold value.

22. The method according to claim 15 , wherein the imaging control unit controls the imaging unit so as to skip the rest of the main scan currently in execution and to terminate scanning, when a total scan time from a start of the main scan reaches a predetermined maximum scan time.

23. The method according to claim 15 , further comprising displaying by a display control unit during the main scan a curve that indicates temporal variations in the contrast medium density based on the index value detected by the index-value detecting unit.

24. A tomography method comprising:

irradiating a subject, switching scanning conditions, with X-rays continuously or intermittently, and reconstructing an image by detecting X-rays passed through the subject, by an imaging unit;

detecting by an index-value detecting unit an index value that indicates a contrast medium density in the image reconstructed by the imaging unit during a scan;

controlling the imaging unit by an imaging control unit so as to perform a prep scan and a main scan, and controlling, during the prep scan, the imaging unit by the imaging control unit so as to start the main scan with a timing when the index value exceeds a threshold value, and

displaying by a display control unit during the main scan a curve that indicates temporal variations in the contrast medium density based on the index value detected by the index-value detecting unit.

25. The method according to claim 24 , further comprising:

receiving by an instruction receiving unit from an operator an instruction to skip a rest of a first scan with a first scanning condition in execution and to start a second scan with a second scanning condition, the first scan and the second scan being included in the main scan; and

controlling the imaging unit by an imaging control unit so as to skip the rest of the first scan with the first scanning condition and to start the second scan with the second scanning condition upon receiving the instruction by the instruction receiving unit.

26. The method according to claim 25 , wherein

the index-value detecting unit detects as the index value an index value that indicates a contrast medium density in a region of interest set on the image reconstructed by the imaging unit, and

the display control unit displays during the main scan as the curve a curve that indicates the temporal variations in the contrast medium density in the region of interest.

27. The method according to claim 24 , wherein the display control unit displays as the curve a plurality of curves that indicates temporal variations in contrast medium densities in of a plurality of respective regions of interest, when as the region of interest the plurality of regions of interest are set on the image reconstructed by the imaging unit.

28. The method according to claim 24 , wherein the display control unit further displays information about executed scans during the main scan.