Method and apparatus for iterative reconstruction
A method is provided for iteratively reconstructing an image of an object. The method includes accessing measurement data associated with the image, and using a simultaneous algorithm to reconstruct the image. Using the simultaneous algorithm to reconstruct the image includes determining a scaling factor that is voxel-dependent, and applying the voxel-dependent scaling factor to a gradient of an objective function to reconstruct the image.
1. A method for iteratively reconstructing an image of an object, the method comprising:
accessing measurement data associated with the image, the measurement data obtained from a detector array; and
using, with a computer operably coupled to the detector array, a simultaneous algorithm to reconstruct the image, wherein using the simultaneous algorithm to reconstruct the image comprises:
determining, with the computer, a scaling factor that is voxel-dependent; and
applying, with the computer, the voxel-dependent scaling factor to a gradient of an objective function to reconstruct the image.
2. The method of claim 1 , wherein determining a scaling factor that is voxel-dependent comprises computing the scaling factor directly based on acquisition geometry.
3. The method of claim 1 , wherein determining a scaling factor that is voxel-dependent comprises computing the scaling factor directly based on acquisition geometry, the measurement data being non-uniformly sampled in a three-dimensional (3D) acquisition geometry.
4. The method of claim 1 , wherein determining a scaling factor that is voxel-dependent comprises generating an coefficient map and using the coefficient map to compute the voxel-dependent scaling factor.
5. The method of claim 4 , wherein generating an coefficient map comprises transforming an update obtained from a difference of one of at least two iterations or at least two sub-iterations.
6. The method of claim 4 , wherein generating an coefficient map comprises generating an coefficient map that is locally smooth and is capable of being low-pass filtered.
7. The method of claim 4 , wherein generating an coefficient map comprises obtaining the coefficient map from an initial image.
8. The method of claim 4 , wherein generating an coefficient map comprises augmenting the coefficient map with at least one of prior information about an initial image, a feature of a current image, or acquisition geometry.
9. The method of claim 1 , wherein applying the voxel-dependent scaling factor to a gradient of an objective function to reconstruct the image comprises scaling the gradient using the voxel-dependent scaling factor.
10. The method of claim 9 , wherein the scaling is at least one of obtained using A T WA or linked to contribution of subsets to every voxel.
11. The method of claim 1 , wherein applying the voxel-dependent scaling factor to a gradient of an objective function to reconstruct the image comprises computing a relaxation factor for each slice of the measurement data, the measurement data being non-uniformly sampled in a three-dimensional (3D) acquisition geometry wherein slices inside a region of interest (ROI) are sampled by a different number of views compared to slices outside the ROI.
12. The method of claim 1 , wherein applying the voxel-dependent scaling factor to a gradient of an objective function to reconstruct the image comprises updating the voxel-dependent scaling factor at a frequency that is reduced to every n-th iteration instead of every iteration.
13. The method of claim 4 , wherein the coefficient map is down-sampled.
14. An imaging system comprising:
a detector array; and
a computer coupled to the detector array, the computer configured to:
access measurement data associated with an image of an object; and
use a simultaneous algorithm to reconstruct the image, wherein the computer is configured to use the simultaneous algorithm to reconstruct the image by determining a scaling factor that is voxel-dependent and applying the voxel-dependent scaling factor to a gradient of an objective function to reconstruct the image.
15. The imaging system of claim 14 , wherein the computer is configured to determine the scaling factor that is voxel-dependent by computing the scaling factor directly based on acquisition geometry.
16. The imaging system of claim 14 , wherein the computer is configured to determine the scaling factor that is voxel-dependent by generating an coefficient map and using the coefficient map to compute the voxel-dependent scaling factor.
17. The imaging system of claim 16 , wherein the computer is configured to generate the coefficient map by transforming an update obtained from a difference of one of at least two iterations or at least two sub-iterations, the transformation being one of discrete or continuous.
18. The imaging system of claim 14 , wherein the computer is configured to apply the voxel-dependent scaling factor to the gradient of the objective function by scaling the gradient using the voxel-dependent scaling factor.
19. The imaging system of claim 14 , wherein the computer is configured to apply the voxel-dependent scaling factor to the gradient of the objective function by computing a relaxation factor for each slice of the measurement data, the measurement data being non-uniformly sampled in a three-dimensional (3D) acquisition geometry wherein slices inside a region of interest (ROI) are sampled by a different number of views compared to slices outside the ROI.