X-ray CT apparatus

1. An X-ray CT apparatus, comprising:

an X-ray source which irradiates X-rays;

an X-ray detector which is arranged opposite to the X-ray source and detects said irradiated X-rays;

a scanner having a rotary disk which rotatably supports the X-ray source and X-ray detector and a power source of the rotary disk;

an image processing device which makes said scanner rotate in a state where an object is inserted in between said X-ray source and said X-ray detector to irradiate said object with X-rays from directions at a plurality of angles, and makes said X-ray detector detect X-rays transmitted through said object in directions at a plurality of angles as projection data, to reconstruct a tomographic image of said object by use of the projection data in the directions at the plurality of angles;

a display device which displays said reconstructed tomographic image;

a setting device which sets an X-ray irradiation condition including a combination of a tube current and a tube voltage supplied to said X-ray source; and

a control device which supplies said X-ray source with said set X-ray irradiation condition, to perform scanning, wherein

said setting device includes

an X-ray irradiation condition information creating section configured to generate X-ray irradiation condition information, by use of a plurality of X-ray irradiation condition candidates and image quality indexes corresponding to the plurality of X-ray irradiation condition candidates, the image quality indexes being based on a transmission thickness of a scanning subject site of said object and an attenuation model of at least two tissues, and

an X-ray irradiation condition information displaying section configured to cause the X-ray irradiation condition information to be displayed on the display device, for selection of an X-ray irradiation condition candidate from among the plurality of X-ray irradiation condition candidates, the X-ray irradiation condition being set to the selected X-ray irradiation condition candidate.

2. The X-ray CT apparatus according to claim 1 , wherein said setting device further includes:

a scanogram analyzing section which analyzes a scanogram of said object to determine the transmission thickness of the scanning subject site of said object; and

an image quality index calculating section configured to calculate an image quality index corresponding to an X-ray irradiation condition candidate from among the plurality of X-ray irradiation condition candidates.

3. The X-ray CT apparatus according to claim 2 , wherein said image quality index calculating section calculates the image quality index based on at least one of a contrast/noise ratio and a signal/noise ratio.

4. The X-ray CT apparatus according to claim 2 , wherein

said image quality index calculating section calculates a contrast/noise ratio, and

said X-ray irradiation condition information creating section calculates an index value obtained by [(the contrast/noise ratio)/the exposed dose], and generates the X-ray irradiation condition information by further correlating said index value with the X-ray irradiation condition candidate.

5. The X-ray CT apparatus according to claim 2 , wherein said image quality index calculating section calculates said image quality index, using the attenuation model obtained by modeling tissue configuration in said scanning subject site.

6. The X-ray CT apparatus according to claim 2 , wherein said image quality index calculating section calculates said image quality index, using the transmission thickness of said scanning subject site based upon a scanogram image obtained by scanogram imaging.

7. The X-ray CT apparatus according to claim 2 , wherein said display section sorts the X-ray irradiation condition information generated by said X-ray irradiation condition information creating section in order of suitability of the image quality indexes or in order of adaptability to a condition designated by the user, and displays the sorted information.

8. The X-ray CT apparatus according to claim 1 , wherein

said setting device further comprises an exposed dose calculating section which calculates an exposed dose of said object expected when scanning is carried out with said X-ray irradiation condition candidate set as the X-ray irradiation condition, the exposed dose being calculated based on the transmission thickness of the scanning subject site of said object and an X-ray absorption coefficient of the scanning subject site, and

said control device displays on said display device said calculated exposed dose correlated with said X-ray irradiation condition candidate.

9. The X-ray CT apparatus according to claim 8 , wherein said exposed dose calculating section calculates said exposed dose, based on the attenuation model obtained by modeling tissue configuration in said scanning subject site.

10. The X-ray CT apparatus according to claim 8 , wherein said exposed dose calculating section calculates said exposed dose by the use of the transmission thickness of said scanning subject site based upon a scanogram image obtained by scanogram imaging.

11. The X-ray CT apparatus according to claim 1 , further comprising:

a protocol storage section which correlates a scanning protocol information including at least one of the scanning subject site, a scanning direction and a scanning kind of said object with an X-ray irradiation condition candidate information by at least one piece of combination of a tube current and a tube voltage which corresponds to the scanning protocol information, and stores the correlated information;

a scanning protocol display section which reads said scanning protocol information from said protocol storage section and displays the read information; and

a protocol selecting section which selects said displayed scanning protocol information, wherein

said control device reads a scanning protocol information selected by said protocol selecting section from said protocol storage section, and calculates an X-ray irradiation condition candidate information from the read scanning protocol information.

12. The X-ray CT apparatus according to claim 11 , wherein

said setting device further comprises an exposed dose calculating section which calculates an exposed dose of said object expected when scanning is carried out with said X-ray irradiation condition candidate set as the X-ray irradiation condition, the exposed dose being calculated based on the transmission thickness of the scanning subject site of said object and an X-ray absorption coefficient of the scanning subject site,

said protocol storage section stores the exposed dose calculated by said exposed dose calculating section, further correlated with said X-ray irradiation condition candidate,

said control device further reads the exposed dose corresponding to an inputted image quality index, and

said X-ray irradiation condition information display section further displays said read exposed dose.

13. The X-ray CT apparatus according to claim 1 , wherein the setting device further includes:

an image quality index calculating section configured to calculate an image quality index for a candidate X-ray irradiation condition, by use of the transmission thickness of the scanning subject site of said object and by applying the candidate X-ray irradiation condition to the attenuation model which models tissue configuration in said scanning subject site and corresponds to a specific scanning protocol.