Method and apparatus for controlling fluence in computed X-ray imaging
The present invention pertains to a system and method for X-ray imaging wherein a targeted fluence at the detector for projection images can be achieved at a plurality of projection angles around the imaging subject by control of exposure times implemented during image acquisition. Exposure time for a second projection image may be determined by the fluence in a first projection image, and in a third projection image by the fluence in a second projection image, where projection images are acquired within two degrees of one another. An acquisition parameter calculation can be configured to calculate acquisition parameters, such as said exposure times, to achieve the targeted fluence in projection images and can be coupled to a rotation controller that implements the acquisition parameters by controlling a relative angle between the imaging subject and X-ray image acquisition device.
1. A method of acquiring an X-ray image of an object comprising:
positioning said object in field of view of an X-ray image acquisition device;
selecting a set of a plurality of unique projection angles between said X-ray image acquisition device and an axis through said object, wherein said set spans at least 45 degrees around said object;
selecting a targeted X-ray fluence at a detector region for each of said projection angles;
determining a targeted total exposure time for each of said projection angles corresponding to said targeted X-ray fluence;
implementing said plurality of targeted total exposure times in said X-ray image acquisition device over said set of projection angles to acquire an image data set; and
reconstructing an X-ray image from said image data set.
2. The method of claim 1 further comprising:
increasing said targeted exposure time with at least one of said projection angles based on increase of attenuation at said projection angle.
3. The method of claim 1 further comprising:
reducing saturation of said detector by reducing said targeted exposure time with at least one of said projection angles.
4. The method of claim 1 further comprising:
adjusting said targeted exposure time based on attenuation characteristics information.
5. The method of claim 1 further comprising:
determining attenuation characteristics at each of said projection angles.
6. The method of claim 1 further comprising:
controlling total exposure times by modulating individual exposure time of each exposure.
7. The method of claim 1 further comprising:
predicting attenuation characteristics at each of said projection angles.
8. The method of claim 1 wherein said region is a user-selected region of interest.
9. The method of claim 1 wherein said region is a predetermined region of interest.
10. The method of claim 1 further comprising:
excluding edges of a projection image that are over-saturated.
11. The method of claim 1 further comprising:
adjusting said targeted total exposure times at said projection angles depending on fluence in a previously acquired projection.
12. The method of claim 1 wherein said region is a full detector area.