Cone beam local tomography

Abstract

Methods, systems and processes for providing efficient image reconstruction using local cone beam tomography which provide a reduced level of artifacts without suppressing the strength of the useful features; and in a dynamic case provide reconstruction of objects that are undergoing a change during the scan. An embodiment provides a method of reconstructing an image from cone beam data provided by at least one detector. The method includes collecting CB projection data of an object, storing the CB projection data in a memory; and reconstructing the image from the local CB projection data. In the reconstructing step, a combination of derivatives of the CB projection data that will result in suppressing the artifacts are found. The combination of derivatives includes collecting cone beam data that represents a collection of integrals that represent the object.

Description

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an overview of the basic process steps according to the invention.

FIG. 2 is flow diagram for the back-projection substeps corresponding to step 40 of FIG. 1.

FIG. 3 a shows the new LT function g in the case of the clock phantom.

FIG. 3 b shows old LT function g_Λ in the case of the clock phantom.

FIG. 4 a shows the results of reconstructing the three-disk phantom according to the present invention.

FIG. 4 b shows the results of reconstructing the three-disk phantom according to the prior art.

FIG. 5 a shows the results for a phantom consisting of two identical balls having radius 40 centered at (−80,0,0) and (80,0,0), respectively, according to the present invention.

FIG. 5 b shows the results for a phantom consisting of two identical balls having radius 40 centered at (−80,0,0) and (80,0,0), respectively, according to the prior art.

FIG. 6 a shows reconstruction of an ellipsoid in the dynamic case, new LT function g according to the present invention wherein the ellipsoid moves either up or down.

FIG. 6 b shows reconstruction of an ellipsoid in the dynamic case, new LT function g according to the present invention wherein the ellipsoid moves either left or right

FIG. 7 a shows reconstruction of an ellipsoid in the dynamic case, new LT function g according to the present invention wherein the ellipsoid expands and contracts.

FIG. 7 b shows reconstruction of an ellipsoid in the dynamic case, the prior art LT function g wherein the ellipsoid expands and contracts as well as moves left-right.

Claims

1. A method of reconstructing an image from cone beam (CB) data provided by at least one detector, comprising the steps of: collecting CB projection data of an object;storing the CB projection data in a memory; andreconstructing the image from the local CB projection data, wherein artifacts of the reconstructed image are suppressed without suppressing the strength of the useful features.

2. The method of claim 1, wherein the reconstructing step comprises the step of: finding a combination of derivatives of the CB projection data that will result in suppressing the artifacts.

3. The method of claim 2, wherein the finding a combination of derivatives of the CB projection data step comprises the steps of: collecting cone beam data that represents a collection of integrals with or without weight of an unknown function that represents the object being scanned, wherein said integrals are over lines and said lines intersect a curve;finding the combination of derivatives of the CB projection data that is equivalent to differentiating the data along a direction which is tangent to a source trajectory.

4. The method of claim 3, further comprising the step of: computing the combination of derivatives of the CB projection data, which is equivalent to differentiating the data along the direction of the tangent of the source trajectory.

5. The method of claim 4, wherein the differentiation step comprises the step of: computing derivatives

6. The method of claim 5, wherein the reconstruction step further comprises the steps of: multiplying the derivatives by the quantities cos2 α, −2 cos α(w sin α−h/(2π)), and (w sin α−h/(2π))2, respectively;adding the multiplied derivatives to produce a combination of derivatives;multiplying the combination of derivatives by φ(α, w) cos2 α to produce the function Φ(s;α,w) according to

7. The method of claim 4, further comprising the step of: processing the derivative result by multiplying it by a weight.

8. The method of claim 7, further comprising the step of: applying back projection to the processed data to reconstruct an image with suppressed artifacts.

9. The method of claim 1, further comprising the step of: determining a shift between a location of the reconstruction point shown on the reconstructed image and an actual location of the corresponding useful feature to determine a location error of the moving object to correct for the location of the useful features of the actual image.

10. A system for reconstructing an image of an object comprising: a scanner for scanning the object in three-dimensions to produce a cone beam projection data;a processing unit having a memory for storing the cone beam projection data and executing instructions;a first set of instructions for calculating derivatives of the local cone beam projection data;a second set of instruction for reconstructing useful features of the image with suppressed artifacts without suppressing the strength of the useful features; anda display connected with said processing unit for displaying the reconstructed image with suppressed artifacts without suppressing the strength of useful features.

11. The system of claim 10, wherein the first set of instructions comprises: a first subset of instructions for differentiating the cone beam projection data along a direction tangent to the curve that represents the scanner trajectory.

12. The system of claim 10, wherein the first set of instructions comprises: a first subset of instructions for finding a direction of the derivative of the cone beam projection data that will result in suppressed artifacts; anda second subset of instructions for differentiating the cone beam projection data according to the direction.

13. The system of claim 10, wherein the reconstruction set of instructions comprises: a subset of reconstruction instructions for processing the derivative results to reconstruct the useful features of the image with suppressed artifacts.

14. The system of claim 10, further comprising: a third set of instructions for determining a shift between a location of the reconstruction point shown on the reconstructed image and an actual location of the point on the object to correct for the location of the useful features of the actual image.

15. A method for cone beam local tomography comprising the steps of: loading current cone beam projection data into a computer memory, wherein the cone beam projection data corresponds to the focus of beams of radiation located at y(s);calculating derivatives of the cone beam projection data in a direction that results in suppression of the artifacts;processing the derivative results to reconstruct the image with suppressed artifacts without suppressing the strength of the useful features;applying back projection to the processed data; anddisplaying the reconstructed image with suppressed artifacts without suppressing the strength of useful features.

16. The method of claim 15, wherein the differentiation step comprises the steps of: determining a direction of the derivative that results in suppression of the artifacts, wherein the direction is tangent to a cone beam data curve y(s); andcalculating derivatives of the cone beam projection data along the direction tangent to the curve to suppress artifacts.