Model-based scatter correction for computed tomography

1. An apparatus, comprising:

circuitry configured to

obtain projection data representing an intensity of X-ray radiation transmitted through an object and detected at a plurality of detector elements, the projection data being obtained for a plurality of views corresponding to respective projection angles relative to the object,

reconstruct, using the projection data, an image of the object to generate a spatial model of scatter of the X-ray radiation from the object,

simulate, for one or more views of the plurality of views, a scatter flux of the one or more views representing an intensity of scattered X-ray radiation detected at the plurality of detector elements, the intensity of scattered X-ray radiation being determined using a radiative transfer equation (RTE) method based on integrating a radiative transfer equation, and

determine, using the simulated scatter flux of the one or more views together with an accelerated method, which is accelerated relative to the RTE method, primary flux of the plurality of views, the primary flux representing an intensity of X-rays that have not been scattered, which are incident on the plurality of detector elements, wherein

a combination of simulating the scatter flux of the one or more views using the RTE method together with determining of the primary flux using the accelerated method is quicker than a method determining the primary flux using the RTE method to simulate scatter flux for all views of the plurality of views.

2. The apparatus according to claim 1 , wherein the circuitry is further configured to determine the primary flux by

simulating, using the accelerated method, which is based on the scatter flux of the one or more views, a scatter flux of remaining views representing an intensity of scattered X-ray radiation detected at the plurality of detector elements for remaining views of the plurality of views other than the one or more views, and

removing, from the projection data, the scatter flux of the one or more views and the scatter flux of the remaining views to generate the primary flux.

3. The apparatus according to claim 1 , wherein the circuitry is further configured to reconstruct, using the primary flux, another image of the object.

4. The apparatus according to claim 3 , wherein the circuitry is further configured to

generate, using the another image, another spatial model of the scatter of X-ray radiation from the object,

repeat the simulating of scatter flux of the one or more views, but using the another spatial model instead of the spatial model, to generate another scatter flux of the one or more views, and

repeat the determining of the primary flux of the plurality of views, but use the another scatter flux of the one or more views instead of the scatter flux of the one or more views.

5. The apparatus according to claim 1 , wherein the circuitry is further configured to reconstruct the image of the object by

correcting, using a scatter-simulation method, the projection data to remove scatter and generate corrected projection data, and

reconstructing the image using the corrected projection data together with a computed-tomography image-reconstruction method.

6. The apparatus according to claim 1 , wherein the circuitry is further configured to generate the spatial model of scatter of the X-ray radiation from the object by

segmenting the image into a plurality of regions corresponding to material components, and

assigning each region of the plurality of regions an energy-dependent scatter cross-section based of a material component corresponding to the region.

7. The apparatus according to claim 6 , wherein the circuitry is further configured to perform the segmenting of the image using one or more of information of an amplitude of total X-ray attenuation at respective pixels or voxels of the reconstructed image, information of energy dependence of the X-ray attenuation at the respective pixels or voxels of the reconstructed image, and anatomical information.

8. The apparatus according to claim 1 , wherein the circuitry is further configured to generate the spatial model of scatter of the X-ray radiation from the object by extrapolating a model of X-ray scatter from the object outside of an imaging region of the CT scanner.

9. The apparatus according to claim 8 , wherein the circuitry is further configured to perform the step of extrapolating the model of X-ray scatter from the object outside of the imaging region of the CT scanner by using one or more of a low-dose reconstructed image of a part of the object outside of the imaging region, anatomical information, and a reconstructed image from a prior CT scan.

10. The apparatus according to claim 1 , wherein the circuitry is further configured to perform the step of determining of the primary flux using the accelerated method, wherein the accelerated method is one of a multiplicative method, an additive method, and a kernel based method,

the multiplicative method including

interpolating a scatter flux of remaining views based on the scatter flux of the one or more views to generate a scatter flux of all views of the plurality of views, the remaining views being views of the plurality of views other than the one or more views,

determining, using the scatter flux of the all views, a ratio of scatter flux to total flux, and

convolving the projection data with a difference between unity and the ratio of scatter flux to total flux to generate the primary flux of the plurality of views,

the additive method including

interpolating the scatter flux of the remaining views of the plurality of views from the scatter flux of the one or more views to generate the scatter flux of the all views,

determining a scale factor between empirically measured scatter flux and the scatter flux of the one or more views, and

determining the primary flux using a difference between the projection data and a product of the scale factor and the scatter flux of the all views, and

the kernel-based method including

modifying a parameter of a kernel based on the scatter flux of the one or more views, and

determining, using the kernel with the modified parameter, scatter flux of the remaining views to generate the scatter flux of the all views, wherein

the remaining views of the plurality of views include views other than the one or more views.

11. A computed tomography (CT) scanner, comprising:

a gantry having an opening in which an object can be placed;

an X-ray source fixed to a rotatable member of a gantry of the CT scanner and irradiating X-ray radiation;

an X-ray detector comprising a plurality of detector elements, the X-ray detector being fixed to the rotatable member and arranged across the opening of the gantry and diametrically opposed to the X-ray source; and

the circuitry according to claim 1 .

12. An apparatus, comprising:

a memory storing pre-calculated scatter values representing angle-dependent scatter for X-ray radiation from a first part of a computed tomography (CT) scanner, the first part being arranged to have a position and orientation that is constant relative to an X-ray source of the CT scanner, when the CT scanner is rotated according to a plurality of views; and

circuitry configured to

obtain projection data representing an intensity of X-ray radiation transmitted from the X-ray source, through an object, and detected at a plurality of detector elements of the CT scanner, the projection data being obtained for the plurality of views, which correspond to respective projection angles of the X-ray source relative to the object,

reconstruct, using the projection data, an image of the object to generate a spatial model of scatter of X-ray radiation from the object,

simulate, for one or more views of the plurality of views, a scatter flux of the one or more views representing an intensity of scattered X-ray radiation detected at the plurality of detector elements, the scatter flux of the one or more views being simulated using a scatter simulation method that uses the pre-calculated scatter values to simulate a scatter flux from the first part, and

determine, using the simulated scatter flux of the one or more views and a scatter simulation method, primary flux of the plurality of views, the primary flux representing an intensity of X-rays that have not been scattered, which are incident on the plurality of detector elements, wherein

the circuitry is further configured to simulate the scatter flux of the one or more views using the pre-calculated scatter values to simulate the scattering by the first part, wherein the first part is one of a filter and an anti-scatter grid.

13. The apparatus according to claim 12 , wherein the circuitry is further configured to simulate the scatter flux of the one or more views using the RTE method, wherein the RTE method includes

integrating an attenuation from the X-ray source to a detection location or a first scatter location to generate a primary flux,

integrating the primary flux at the scatter location with a predefined scatter cross-section at the first scatter location to generate a first-scatter flux, which includes a plurality of first-scatter spherical-harmonic components, and

iteratively updating a multiple-scatter flux, which is decomposed into a plurality of multiple-scatter spherical-harmonic components, by integrating products of respective spherical-harmonic components of a previous iteration of the multiple-scatter flux at a scatter location of the previous iteration with corresponding spherical-harmonic components of the predefined scatter cross-section at a scatter location of a next iteration to generate the multiple-scatter flux of the next iteration, and the multiple-scatter flux of a first iteration is the first-scatter flux and a scatter location of the first iteration is the first scatter location.

14. The apparatus according to claim 12 , wherein the circuitry is further configured to simulate the scatter flux of the one or more views using another pre-calculated scatter values representing scatter of X-ray radiation from a second part of the CT scanner, wherein the first part is a filter and the second part is an anti-scatter grid.

15. The apparatus according to claim 12 , wherein the circuitry is further configured to determine the pre-calculated scatter values by

determining, based on a geometry of the anti-scatter grid and a trajectory of a ray of X-ray radiation, whether the ray intersects with the anti-scatter grid, and

determining that X-ray radiation having the trajectory of the ray does not reach the plurality of detector elements, when the ray intersects with the anti-scatter grid.

16. The apparatus according to claim 12 , wherein the circuitry is further configured to determine the pre-calculated scatter values by simulating the scatter flux from the first part using one of a Monte Carlo method and an RTE-based method and by using parameters of a geometry of the first part and predefined scatter cross-sections for material components of the first part.

17. The apparatus according to claim 12 , wherein the circuitry is further configured to

simulate the scatter flux of the one or more views using the pre-calculated scatter values together with a radiative transfer equation (RTE) method based on integrating a radiative transfer equation,

simulate, using the pre-calculated scatter values together with an accelerated method that uses the simulated scatter flux of the one or more views, a scatter flux of remaining views, the remaining views being views of the plurality of views other than the one or more views, and the accelerated method simulating the scatter flux of remaining views more quickly than the RTE method, and

remove, from the projection data, the scatter flux of the one or more views and the scatter flux of the remaining views to generate the primary flux.

18. A method, comprising:

obtaining projection data representing an intensity of X-ray radiation transmitted through an object and detected at a plurality of detector elements, the projection data being obtained for a plurality of views corresponding to respective projection angles relative to the object,

reconstructing, using the projection data, an image of the object to generate a spatial model of scatter of the X-ray radiation from the object,

simulating, for one or more views of the plurality of views, a scatter flux of the one or more views representing an intensity of scattered X-ray radiation detected at the plurality of detector elements, the intensity of scattered X-ray radiation being determined using a radiative transfer equation (RTE) method based on integrating a radiative transfer equation, and

determining, using the simulated scatter flux of the one or more views and an accelerated method, which is accelerated relative to the RTE method, primary flux of the plurality of views, the primary flux representing an intensity of X-rays that are incident on the plurality of detector elements without being scattered, wherein

a combination of simulating the scatter flux of the one or more views using the RTE method together with determining of the primary flux using the accelerated method is quicker than a method determining the primary flux using the RTE method to simulate scatter flux for all views of the plurality of views.

19. A non-transitory computer-readable storage medium storing executable instructions, wherein the instructions, when executed by circuitry, cause the circuitry to perform the method according to claim 18 .