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Image Quality in Thoracic 4D Cone-Beam CT: A Sensitivity Analysis of Respiratory Signal Source, Binning Method, and Reconstruction Algorithm

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C Shieh

C Shieh1,2*, J Kipritidis1, R O'Brien1, Z Kuncic2, P Keall1, (1) Radiation Physics Lab, Sydney Medical School, The University of Sydney, Sydney, NSW, Australia, (2) Institute of Medical Physics, School of Physics, The University of Sydney, Sydney, NSW, Australia

WE-G-134-6 Wednesday 4:30PM - 6:00PM Room: 134

Purpose: Respiratory signal source, binning method, and reconstruction algorithm are three major factors affecting thoracic 4D cone-beam CT (4D-CBCT) image quality. Various studies have investigated each of them individually, but no sensitivity analysis to these factors has been performed. This study quantitatively compares the impacts of the three factors on thoracic 4D-CBCT image quality.

Methods: A 4D-CBCT patient projection dataset acquired using audio-visual biofeedback with known degree of baseline shift in respiratory motion was reconstructed with the following factors: (i) respiratory signal source (via real-time position management or projection image based method), (ii) binning method (phase, displacement, or equal-projection-density (EPD) displacement binning), and (iii) reconstruction algorithm (Feldkamp-Davis-Kress (FDK), McKinnon-Bates (MKB), or adaptive-steepest-descent projection-onto-convex-sets (ASD-POCS)). The image quality was quantified using signal-to-noise ratio (SNR), contrast ratio (CR), and edge-response width (ERW) to assess noise, contrast, and sharpness, respectively.

Results: Respiratory signal sources had no significant effect on any of the three metrics. Displacement binning was found to produce slightly more inconsistent SNR values owing to unevenly distributed angular views. The binning method otherwise had minimal effects on image quality. For the reconstruction algorithms, MKB resulted in a slightly higher SNR than FDK, while ASD-POCS improved SNR by a factor of three. Conversely, degradation in CR was observed with MKB and ASD-POCS. FDK and MKB produced very similar ERW, while slightly higher values were observed with ASD-POCS, indicating a small degree of blurriness.

Conclusion: Respiratory signal sources and binning methods had a negligible impact on image quality, and did not introduce apparent motion artifacts. The MKB and ASD-POCS reconstruction algorithms reduced the noise and streaking but produced poorer image contrast. Of the reconstruction factors tested, reconstruction algorithms play the most important role in improving 4D-CBCT image quality and therefore represent the highest priority for further development.

Funding Support, Disclosures, and Conflict of Interest: This project is supported by an NHMRC Australia Fellowship, NHMRC project grant 1034060, US NCI P01CA116602, an International Postgraduate Research Scholarships, and an Australian Postgraduate Award.

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