Methods and apparatus for scatter correction for CBCT system and cone-beam image reconstruction
Embodiments of methods and/or apparatus for 3-D volume image reconstruction of a subject, executed at least in part on a computer for use with a digital radiographic apparatus, can obtain image data for 2-D projection images over a range of scan angles. For each of the plurality of projection images, an enhanced projection image can be generated. In one embodiment, a first scatter intensity distribution through the plurality of projection images can be modulated based on a first scaling function and a SPR to generate a second scatter intensity distribution through the plurality of projection images, which can be combined with the original plurality of projection images.
1. A method for digital radiographic 3D volume image processing of a subject, executed at least in part on a computer, comprising:
obtaining image data for a plurality of 2D projection images over a range of scan angles;
generating, for each of the plurality of 2D projection images, a first scatter intensity distribution by:
estimating a first scatter distribution in an air region from at least one 2D current projection image,
segmenting the at least one 2D current projection image to determine an object shadow portion, and
determining a coarse scatter intensity within the object shadow portion based on an interpolation of the first scatter distribution;
generating, for said each of the plurality of 2D projection images, a second scatter intensity distribution for the 2D projection image by:
modulating the first scatter intensity distribution for the plurality of 2D projection images by a rescaled processed object intensity in log space, where the modulating comprises,
determining a first scaling factor for at least one point in the range of scan angles that occurs within the object shadow portion using a scatter-to-primary ratio,
dividing all the projections by the first scaling factor to get scaled projections,
inverting the scaled projections to determine a moderating function, and
applying the moderating function to the plurality of first scatter intensity distributions for the plurality of 2D projection images to generate the plurality of second scatter intensity distribution for the plurality of 2D projection images for the range of scan angles, and
combining the plurality of second scatter intensity distribution for the plurality of 2D projection images to the plurality of 2D projection images to determine a plurality of scatter corrected 2D projection images; and
storing the scatter corrected plurality of 2D projection images in a computer-accessible memory.
2. The method of claim 1 where the coarse scatter intensity within the object shadow portion is determined by using a linear interpolation or a non-linear interpolation of the segmented scatter image in the air region, where the estimating the first scatter distribution in an air region comprises subtracting calibrated primary radiation in the air region.
3. The method of claim 1 , where the determining a first scaling factor includes searching all the viewing projection images to get the highest intensity in log space for a current CBCT system scan.
4. The method of claim 1 , where the inverting the scaled projections to determine the moderating function further comprises apodizing the inverted scaled projections by a scatter intensity over-correction compensation function to dampen the scatter intensity over correction at a boundary part of the object shadow portion to adjust the moderating function within the object shadow.
5. The method of claim 4 , where the scatter intensity over-correction compensation function comprises:
parameterizing a first distance from a peak to a first side of the object shadow; and
parameterizing a second distance from the peak to a second side of the object shadow.
6. The method of claim 5 , where the first distance and the second distance are parameterized using a Gaussian equation, where the peak is a 1-dimensional maximum or minimum.
7. The method of claim 1 , where the plurality of scatter corrected 2D projection images are determined without using an anti-scatter grid.
8. The method of claim 1 , where the scatter correction is used for radiographic imaging conditions that prevent the use of an anti-scatter grid including low dose radiographic imaging.
9. The method of claim 8 , wherein processing the plurality of scatter corrected projection images comprises:
performing one or more of geometric correction, scatter correction, beam-hardening correction, and gain and offset correction on the plurality of 2D projection images;
performing a logarithmic operation on the scatter corrected plurality of 2D projection images to obtain line integral data; and
performing a row-wise ramp linear filtering to the line integral data.
10. The method of claim 1 further comprising processing the plurality of scatter corrected projection images to reconstruct the 3D volume image reconstruction of the subject.
11. The method of claim 1 wherein obtaining image data for a plurality of 2D projection images comprises obtaining image data from a cone-beam computerized tomography apparatus.
12. The method of claim 1 further comprising:
processing the plurality of scatter corrected projection images to reconstruct a 3D volume image reconstruction of the subject;
displaying the 3D volume image reconstruction; and
storing the 3D volume image reconstruction in the computer-accessible memory, wherein the 3D volume image reconstruction is a orthopedic medical image, a dental medical image, a pediatric medical image or generated by image data from a flat panel detector.
13. The method of claim 1 wherein the subject is a limb, an extremity, a weight bearing extremity or a portion of a dental arch.
14. The method of claim 1 wherein the scatter corrected is based on an examination type and x-ray radiation source exposure setting.
15. The method of claim 1 wherein the scatter corrected is 2D and angularly dependent.
16. A method for digital radiographic 3D volume image reconstruction of a subject, executed at least in part on a computer, comprising:
obtaining cone-beam computed tomography image data for a plurality of 2D projection images over a range of scan angles;
generating, for each of the plurality of 2D projection images, a first scatter corrected projection image by:
estimating a first scatter distribution in an air region from at least one 2D current projection image;
segmenting the at least one 2D current projection image to determine an object shadow portion;
determining a coarse scatter intensity within the object shadow portion based on an interpolation of the first scatter distribution;
generating, for each of the plurality of first scatter corrected 2D projection images, a second scatter corrected projection image by:
modulating the coarse scatter intensity distribution within the object shadow by a rescaled processed object intensity in log space, where the modulating comprises,
determining a first scaling factor for at least one point in an exposure sequence that occurs within the object shadow portion using a scatter-to-primary ratio,
applying a function of the first scaling factor to the projections to determine a moderating function, and
applying the moderating function to the plurality of first scatter corrected 2D projection images to generate a scatter estimate for the range of scan angles, and
combining the second scatter intensity estimate for the range of scan angles to determine a plurality of scatter corrected 2D projection image; and
displaying at least one of the scatter corrected plurality of 2D projection images.