Abstract
The purpose of the research was to develop an automated program incorporating a predictive artifact correction technique (PACT) to correct for the signal deviations from metal beam hardening artifacts in Computed Tomography (CT) detector raw data. Thin-slice sequential CT scans were performed on a dosimetry head phantom using a Somatom Sensation 16 scanner to establish a ground truth image. Metal pins were then affixed to either side of the phantom at the three and nine o’clock positions to cause streak artifact in detector raw data and a subsequent streak image. The program automatically detected the extent of the overlap peaks in the detector raw data causing the artifact. It profiled a correction using adjacent projections so that the peak error could be corrected rather than simply being removed or smoothed by interpolation. The PACT algorithm modified raw data was then reconstructed on a SYNGO CT reconstruction workstation. This image was then compared against ground truth and that produced by commercially available metal artifact reduction projection completion and also a research based iterative technique. Qualitative results illustrate superior suppression of streak artifact in images using PACT when compared directly to tested projection completion methods but inferior to iterative reconstruction. Recovery of voxel data underlying the streak is also demonstrated to be quantitatively superior with PACT when referenced to the original ground truth image. Limitations were however detected with the threshold technique for initial localisation of the streak sources. The work still demonstrates the feasibility of this predictive artifact correction technique in correcting beam hardening affected voxel data without recourse to expensive additional options such as iterative reconstruction or dual energy that are not so commonly available in the clinical setting.
Highlights
In order to accurately test the efficacy of the correction algorithm, were images required demonstrating beam hardening artifact and equivalent images without artifact to determine the effects of the correction compared to a ground truth
While linear interpolation clearly suppresses the impact of the primary streak artifact on the image, it causes the addition of streak effects in other peripheral areas of the image, the frontal sinus area of the skull phantom, for both the linear interpolation Metal Artifact Reduction (LI-metal artifact reduction (MAR)) 10(b) and LI-MAF 1o(c) images
Linear interpolation affected the data from the primary structures treated and from other structures that aligned with these structures throughout the complete rotation which caused this additional image degradation
Summary
CT since its inception has become one of the anthropomorphic phantom These image defects can often be a result of more than one cause as this artifact can have both a beam-hardening component due to the aforementioned polychromaticity related signal error but can contain a partial volume artifact due to the fan nature of the x-ray beam in the z direction [7]. They can be further complicated by the use of outer slices in multi-slice detectors that causes smearing due to the nutating or wobbling slice acquisition [8]. There have been many other approaches at implementing beam-hardening and metallic artifact suppression including Iterative [14,15,16,17] and Dual Energy (DE) reconstruction [18,19,20,21] techniques
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