Extension of the field of view of a computed tomography system in the presence of interfering objects

1. A method of generating a field of view extension of a CT scan and minimizing the effect of interfering objects, comprising:

generating a full sinogram based upon CT scan data of a scanned object and any interfering objects within the scanning field;

determining the location of any interfering objects within the CT data based on physical and geometrical properties of the interfering objects;

generating an ideal sinogram of any interfering objects based on their location and physical properties;

subtracting the ideal sinogram from the full sinogram;

extending a sinogram free of any interfering objects; and

adding the ideal sinogram of interfering objects to the extended sinogram of the scanned object.

2. A method according to claim 1 , further including exposing the scanned object to therapeutic radiation.

3. A method of generating a field of view extension of a CT scan as a function of the input values, comprising:

computing a second order coefficient of the field of view extension on a density grid of input values as a function of scanner geometry and forming a look-up table based thereon;

storing the look-up table in a file;

loading the file before a scan;

using the look-up table during reconstruction so as to pre-tune the second-order coefficient of the extension.

4. A method of claim 3 , wherein using the look-up table provides a faster generation of the field of view extension than iterative tuning of the second order coefficient of the extension.

5. A method according to claim 3 , comprising:

extending the truncated view in accordance with an elliptical function.

6. A method according to claim 5 , wherein the elliptical function is in the form of f(X)=(AX^2+BX+C)^{½},

wherein X is the local coordinate in the extension, with X=0 at the truncation point,

B and C are parameters chosen to preserve the value and slope of a CT projection at the truncation point, and

A is a parameter tuned to ensure that the area under the extension curve is substantially equal to the missing area.

7. A method according to claim 5 , further including generating a sinogram of an object and any interfering objects within a truncated field of view of a CT scanner, wherein extending the truncated view in accordance with an elliptical function includes generating an interference-free sinogram in which data representing the interfering objects have been removed, and extending the interference-free sinogram.

8. A method according to claim 7 , wherein data representing any interfering object in the extended view including the data that was removed is added back to make a full extended sinogram of both the scanned object and any interfering objects, so as to insure that any interfering objects are present in the final reconstructed image.

9. A method according to claim 5 , wherein the elliptical function is in the form of f(X)=(AX^2+BX+C)^{½},

wherein B and C of the extension function f(X) are parameters defined by a CT projection; and

A is a parameter that needs to be tuned.

10. A method according to claim 9 , wherein the value of A is retrieved from a table of A(iE,iB,iC) using bilinear interpolation so as to shorten the time to perform the step of extending the truncated view, wherein the look-up table is pre-computed on a rectangular grid of discreet values of area, iE, slope, iB, and projection value, iC.

11. A method according to claim 10 , wherein the table is stored on the reconstruction computer and loaded into reconstruction engine prior to taking a scan.

12. A method according to claim 5 , further including extending the CT truncated view by distributing missing area between left and right extensions in doubly truncated views, the step of extending includes dividing the missing area E between the left and the right extension based on the projection values at truncation points, Y L and Y R according to the following:

E L =EY L ^3/( Y L ^3 +Y R ^3), for the left extension, and

E R =EY R ^3/( Y L ^3 +Y R ^3) for the right extension.

13. A method according to claim 3 , further including exposing the scanned object to therapeutic radiation.

14. A system including CT scanner comprising a system for extending a truncated reconstructed field-of-view (FOV) of the CT scanner to an extended reconstructed FOV while accounting for the presence of any interfering objects, wherein the CT scanner has a measured FOV and interfering objects are objects which reside fully or partially outside of the measured FOV but within an extended FOV corresponding to the extended reconstructed FOV and whose properties and positions are known, the CT scanner comprising:

a processor for acquiring data from the scanner of a scanned object of interest and any interfering objects disposed within the measured FOV, and processing the data from the scanner including predicting a sinogram of any part of interfering objects within the extended measured FOV, subtracting the sinogram from the original sinogram of the scanned object of interest and any interfering objects within the measured FOV, extending the remaining sinogram in order to provide an extended sinogram of the patient for the extended FOV, and adding a sinogram of any interfering objects back into the extended sinogram.

15. The system of claim 14 , wherein the processor is configured and arranged so as to extend the sinogram of any interfering objects extracted from the original sinogram of the scanned object and any interfering objects within the measured field of view using information known a-priori about the interfering objects so as to create an extended sinogram of any interfering object for the extended FOV prior to adding the extended sinogram of any interfering object back into the extended sinogram of the scanned object.

16. The system of claim 14 , further including a source of therapeutic radiation.

17. The system of claim 16 , wherein the CT scanner and source of therapeutic radiation are positioned with respect to one another so that the CT scanner maps the region of therapeutic treatment, and the source of therapeutic radiation provides therapeutic radiation to the mapped region.