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Metal Artifact reduction for Cone-Beam Computed Tomography (CBCT)
To ensure patient positioning and re-positioning in radiotherapy a common method is to use a cone-beam CT (CBCT) mounted on the treatment devise. The CBCT gives a volumetric image of the patient which is used to define the position of the patient.
However, the CBCT is sensitive to materials of high atomic number causing metal artifacts in the image,. The artifacts arise from high attenuation of the x-rays in the metal leading to gaps in projections This causes bright and dark strikes around the metal in the reconstructed images. Examples are dental fillings and screws in vertebras. The artifacts are often less severe in CBCT than CT, but in CBCT the soft tissue contrast is lower and the impact of metal artifacts are therefore of greater magnitude.. Metal artifacts can in some cases make the positioning of the patient less accurate and it is therefore need to find and reduce the artifacts.
There have been several algorithms proposed in the scientific literature that alleviates the problem. The solution is often to inpaint the projection images where the metal is projected. The problem is how to effectively locate the metal parts and then find out what to replace this part with.
Implement a metal artifact detection and reduction method in a MATLAB prototype. The choice of method shall be based on an evaluation of the methods described in the scientific literature. If time admits several methods shall be prototyped and evaluated. Existing projection data of phantoms with and without metal implants are used as input to make quantitatively assessments of discrepancies between reconstructed images with the metal artifact reduction algorithm and the reconstructed images of the phantom without images.
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