Iterative CT image reconstruction of a ROI with objects outside the scan FoV

1. An apparatus for computed tomography image reconstruction of an object, comprising:

an image processor, including:

an input port configured to receive a plurality of projection images of an object acquired by an imager, each of the projection images being along a different projection angle with respect to a field of view, FoV, wherein the object resides in a bore of said imager with at least a part of said object inside the FoV;

a reconstructor configured to reconstruct the plurality of projection images to generate an image with a first reconstruction algorithm or with a second reconstruction algorithm;

an out-of-FoV-determiner configured to measure an amount of the object in a region between the bore and the FoV and instruct the reconstructor to employ the first reconstruction algorithm to reconstruct the image in response to the amount failing to exceed a predetermined threshold and employ the second reconstruction algorithm to reconstruct the image in response to the amount exceeding the predetermined threshold;

an output port configured to output the reconstructed image.

2. The apparatus for image reconstruction of claim 1 , wherein the first reconstruction algorithm includes a reconstruction of the full field of view.

3. The apparatus for image reconstruction of claim 1 , wherein the reconstruction according to the first or the second reconstruction algorithm is a region of interest, ROI, only reconstruction.

4. The apparatus for image reconstruction of claim 1 , wherein the reconstruction according to the first reconstruction algorithm is at a first resolution and the reconstruction according to the second reconstruction algorithm is at a second resolution, and the first resolution is less than the second resolution.

5. The apparatus for image reconstruction of claim 1 , wherein the first reconstruction algorithm delivers a first signal to noise ratio and the second reconstruction algorithm delivers a second signal to noise ratio, and the first signal to noise ratio is higher than the second signal to noise ratio.

6. The apparatus for image reconstruction of claim 1 , wherein the first or second reconstruction algorithm includes filtered back projection, FBP, reconstruction algorithm.

7. The apparatus for image reconstruction of claim 1 , wherein the first or second reconstruction algorithm includes an iterative reconstruction algorithm.

8. The apparatus for image reconstruction of claim 7 , wherein the iterative reconstruction algorithm is a statistical iterative reconstruction, SIR, algorithm.

9. The apparatus for image reconstruction of claim 1 , wherein the second reconstruction algorithm further includes an algebraic reconstruction algorithm, ART.

10. The apparatus for image reconstruction according to claim 1 , wherein the amount of the object outside of FoV is measured by an optical camera.

11. The apparatus for image reconstruction according to claim 1 , wherein the measurement operation of the out-of-FoV-determiner includes instructing the reconstructor to reconstruct an exploratory image of the full field of view by using a third reconstruction algorithm or by executing at least a part of the first reconstruction algorithm, wherein the out-of-FoV measurement is at discrete locations in the region as per the exploratory image or wherein the out-of-FoV measurement is over a whole of the region as per the exploratory image.

12. An image processing method, comprising:

receiving a plurality of projection images of an object acquired by an computed tomography imager, each of the projection images being along a different projection angles within a field of view, FoV, wherein said object resides in a bore of said imager with at least a part of said object inside the FoV;

measuring an amount of the object in an annular region outside the FoV and inside of the bore;

selecting a first reconstruction algorithm if the measured amount fails to exceed a threshold;

switching from the first reconstruction algorithm to a second reconstruction algorithm, if the measured amount exceeds the threshold;

reconstructing the plurality of projection images to generate an image according to the first or second reconstruction algorithm; and

outputting the image.

13. A non-transitory computer readable medium having stored thereon a program with computer executable instructions which when executed by a computer causes the computer to:

receive a plurality of projection images of an object acquired by an computed tomography imager, each of the projection images being along a different projection angle within a field of view, FoV, wherein said object resides in a bore of said imager with at least a part of said object inside the FoV;

measure an amount of the object in an annular region outside the FoV and inside of the bore;

select a first reconstruction algorithm if the measured amount fails to exceed a threshold;

switch from the first reconstruction algorithm to a second reconstruction algorithm, if the measured amount exceeds the threshold;

reconstruct the plurality of projection images to generate an image according to the first or second reconstruction algorithm; and

output the image.

14. The image processing method of claim 12 , wherein the first reconstruction algorithm includes a reconstruction of the full field of view.

15. The image processing method of claim 12 , wherein the reconstruction according to the first or the second reconstruction algorithm is a region of interest, ROI, only reconstruction.

16. The image processing method of claim 12 , wherein the reconstruction according to the first reconstruction algorithm is at a first resolution and the reconstruction according to the second reconstruction algorithm is at a second resolution, and the first resolution is less than the second resolution.

17. The image processing method of claim 12 , wherein the first reconstruction algorithm delivers a first signal to noise ratio and the second reconstruction algorithm delivers a second signal to noise ratio, and the first signal to noise ratio is higher than the second signal to noise ratio.

18. The image processing method of claim 12 , wherein the first or second reconstruction algorithm includes filtered back projection reconstruction algorithm.

19. The image processing method of claim 12 , wherein the first or second reconstruction algorithm includes one of an iterative reconstruction algorithm or an algebraic reconstruction algorithm.

20. The image processing method of claim 12 , further comprising:

measuring the amount of the object outside of FoV with an optical camera.