Method and apparatus for modulating x-ray tube current in computed tomography

1. A computed tomography (CT) system, comprising:

a rotatable gantry having an opening to receive an object to be scanned;

a high-voltage generator;

an x-ray tube positioned on the gantry to generate x-rays through the opening;

a pixelated detector positioned on the gantry to receive the x-rays; and

a computer programmed to:

obtain a scout image of the object;

calculate an equivalent diameter of a water cylinder based on the scout image over a length of the scout image;

calculate a major axis and a minor axis for an equivalent ellipse over the length;

calculate, based on a noise index and based on the equivalent diameter as the function of the length, an mA modulation as a function of the length; and

obtain image data of the object by modulating an mA applied to the x-ray tube based on the calculated mA modulation.

2. The CT system of claim 1 , wherein the computer is further programmed to:

calculate a modulation magnitude as a function of gantry angle, based on the calculated major axis and minor axis; and

obtain the image data by applying the modulation magnitude as the function of gantry angle.

3. The CT system of claim 1 , wherein the computer is further programmed to calculate the major axis and the minor axis based on at least a total number of pixels considered around a centerline of the scout image.

4. The CT system of claim 1 , wherein the computer is further programmed to apply a smooth filter of the equivalent diameter and the equivalent ellipse.

5. The CT system of claim 1 , wherein the computer is further programmed to calculate the noise index based on a maximum equivalent phantom diameter of the equivalent diameter calculated over a length of the scout image.

6. The CT system of claim 1 , wherein the computer is further programmed to establish a relationship between mA and noise via an empirically determination.

7. The CT system of claim 1 , wherein the computer is further programmed to calculate the noise index based on the calculated equivalent diameter and based on a known relationship between mA and noise for the CT system.

8. A method of obtaining image data for a computed tomography (CT) system, comprising:

obtaining a scout image of an object;

calculating an equivalent diameter of a water cylinder based on the scout image over a length of the scout image;

calculating a major axis and a minor axis for an equivalent ellipse over the length;

calculating, based on a noise index and based on the equivalent diameter as the function of the length, an mA modulation as a function of the length; and

obtaining image data of the object by modulating an mA applied to the x-ray tube based on the calculated mA modulation.

9. The method of claim 8 , further comprising:

calculating a modulation magnitude as a function of gantry angle, based on the calculated major axis and minor axis; and

obtaining the image data by applying the modulation magnitude as the function of gantry angle.

10. The method of claim 8 , further comprising calculating the major axis and the minor axis based on at least a total number of pixels considered around a centerline of the scout image.

11. The method claim 8 , further comprising applying a smooth filter of the equivalent diameter and the equivalent ellipse.

12. The method claim 8 , further comprising calculating the noise index based on a maximum equivalent phantom diameter of the equivalent diameter calculated over a length of the scout image.

13. The method of claim 8 , further comprising establishing a relationship between mA and noise via an empirically determination.

14. The method of claim 8 , further comprising calculating the noise index based on the calculated equivalent diameter and based on a known relationship between mA and noise for the CT system.

15. A computer readable storage medium having stored thereon a computer comprising instructions, which, when executed by a computer, cause the computer to:

obtain a scout image of the object;

calculate an equivalent diameter of a water cylinder based on the scout image over a length of the scout image;

calculate a major axis and a minor axis for an equivalent ellipse over the length;

calculate, based on a noise index and based on the equivalent diameter as the function of the length, an mA modulation as a function of the length; and

obtain image data of the object by modulating an mA applied to the x-ray tube based on the calculated mA modulation.

16. The computer readable storage medium of claim 15 , wherein the computer is further programmed to:

calculate a modulation magnitude as a function of gantry angle, based on the calculated major axis and minor axis; and

obtain the image data by applying the modulation magnitude as the function of gantry angle.

17. The computer readable storage medium of claim 15 , wherein the computer is further programmed to:

calculate the major axis and the minor axis based on at least a total number of pixels considered around a centerline of the scout image; and

apply a smooth filter of the equivalent diameter and the equivalent ellipse.

18. The computer readable storage medium of claim 15 , wherein the computer is further programmed to calculate the noise index based on a maximum equivalent phantom diameter of the of the equivalent diameter calculated over a length of the scout image.

19. The computer readable storage medium of claim 15 , wherein the computer is further programmed to establish a relationship between mA and noise via an empirically determination.

20. The computer readable storage medium of claim 15 , wherein the computer is further programmed to calculate the noise index based on the calculated equivalent diameter and based on a known relationship between mA and noise for the CT system.