X-ray spectral calibration technique for cone-beam CT
A method for X-ray spectral calibration acquires X-ray projections of a calibration phantom formed of known materials. The X-ray spectrum of an X-ray source is calculated according to the acquired X-ray projections. The calculated X-ray spectrum can be stored, transmitted, or displayed.
1. A method for X-ray spectral calibration comprising:
a) acquiring a plurality of X-ray projections of a calibration phantom formed of known materials;
b) calculating the X-ray spectrum of an X-ray source according to the acquired X-ray projections; and
c) storing, transmitting, or displaying the calculated X-ray spectrum
wherein calculating the X-ray spectrum comprises:
reconstructing a digital phantom by processing the acquired X-ray projections, according to the known materials; and
modifying an initial X-ray spectrum for the X-ray source by adjusting the calculated thicknesses of inherent filters according to the digital phantom and the known materials.
2. The method of claim 1 wherein modifying the initial X-ray spectrum further comprises iteratively estimating the acquired projections.
3. The method of claim 1 , wherein acquiring the plurality of X-ray projections comprises acquiring projections from a cone-beam computed tomography (CBCT) apparatus.
4. The method of claim 1 , wherein calculating the spectrum comprises iteratively estimating scatter in the acquired projections.
5. The method of claim 4 further comprising reducing noise content in the estimated scatter.
6. The method of claim 1 , further comprising generating a volume image according to the calculated X-ray spectrum.
7. The method of claim 1 , further comprising providing a user interface control screen that has an instruction for initiating the spectral calibration.
8. The method of claim 1 , further comprising accepting an operator instruction relating to calibration phantom dimensions, shape, or materials from a user interface control screen.
9. A method for X-ray spectral calibration comprising:
reconstructing a volume image of a calibration phantom according to a plurality of acquired X-ray projections of the calibration phantom;
processing the volume image according to prior knowledge of material forming the phantom to generate a digital phantom;
estimating scatter in the acquired X-ray projections according to the digital phantom and according to information about the material forming the phantom and the X-ray spectrum of an X-ray source;
correcting the acquired X-ray projections for scatter according to the estimated scatter to generate scatter corrected projections;
generating a plurality of synthetic projection images according to the digital phantom, information about the material forming the phantom, the X-ray spectrum, and inherent filtration computation for the X-ray source;
comparing the plurality of synthetic projection images with the scatter-corrected projections and updating the inherent filtration computation; and
providing a calibrated X-ray spectrum according to the comparison.
10. A method for X-ray spectral calibration comprising:
reconstructing a volume image of a calibration phantom according to a plurality of acquired X-ray projections of the calibration phantom;
processing the volume image according to prior knowledge of material that forms the calibration phantom to generate a digital phantom free of imaging artifacts;
estimating scatter in the acquired X-ray projections according to the digital phantom and according to information about the material forming the phantom and the X-ray spectrum of an X-ray source;
generating a plurality of synthetic projection images according to the digital phantom, information about the material forming the phantom, the X-ray spectrum, and inherent filtration computation for the X-ray source;
computing the scatter in the generated synthetic projection images according to the X-ray spectrum;
comparing the estimated scatter in the acquired X-ray projections with the computed scatter in the generated synthetic projection images and updating the inherent filtration computation; and
providing a calibrated X-ray spectrum according to the comparison.
11. A method for spectral calibration of an X-ray source comprising:
a) reconstructing a volume image of a calibration phantom according to a plurality of acquired X-ray projections of the phantom;
b) processing the volume image according to prior knowledge of material that forms the calibration phantom to generate a digital phantom free of imaging artifacts;
c) computing actual primary image content and estimated scatter content from the acquired X-ray projections;
d) computing synthetic primary image content and computed scatter content from the digital phantom;
e) comparing the actual primary image content against the computed synthetic primary image content; and
f) estimating the spectral content of the X-ray source and generating and storing the spectral calibration according to the comparison.
12. The method of claim 11 further comprising repeating steps c)-f) until predetermined criteria are satisfied.
13. The method of claim 11 further comprising displaying spectral calibration data.
14. A method for spectral calibration of an X-ray source comprising:
a) reconstructing a volume image of a calibration phantom according to a plurality of acquired X-ray projections of the phantom;
b) processing the volume image according to prior knowledge of material that forms the phantom to generate a digital phantom free of imaging artifacts;
c) computing an estimated primary image and estimated scatter content from the digital phantom;
d) computing the estimated total signal image by combining the estimated primary image and the estimated scatter image;
e) comparing the estimated total signal image against the acquired X-ray projections;
f) estimating a virtual inherent filtration of the X-ray source according to the comparison;
g) repeating procedures c)-f) to generate spectral calibration data until predetermined criteria are satisfied; and
h) storing, transmitting, or displaying the spectral calibration data to image acquisition.
15. The method of claim 14 wherein steps a)-g) execute automatically in response to an operator command.