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Dickmann, Jannis; Sarosiek, Christina; Rykalin, Victor; Pankuch, Mark; Coutrakon, George; Johnson, Robert P.; Bashkirov, Vladimir; Schulte, Reinhard W.; Parodi, Katia; Landry, Guillaume und Dedes, George (2021): Proof of concept image artifact reduction by energy-modulated proton computed tomography (EMpCT). In: Physica Medica-European Journal of Medical Physics, Bd. 81: S. 237-244

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Abstract

Purpose: To reduce imaging artifacts and improve image quality of a specific proton computed tomography (pCT) prototype scanner by combining pCT data acquired at two different incident proton energies to avoid protons stopping in sub-optimal detector sections. Methods: Image artifacts of a prototype pCT scanner are linked to protons stopping close to internal structures of the scanner's multi-stage energy detector. We aimed at avoiding such protons by acquiring pCT data at two different incident energies and combining the data in post-processing from which artifact-reduced images of the relative stopping power (RSP) were calculated. Energy-modulated pCT (EMpCT) images were assessed visually and quantitatively and compared to the original mono-energetic images in terms of RSP accuracy and noise. Data were acquired for a homogeneous water phantom. Results: RSP images reconstructed from the mono-energetic datasets displayed local image artifacts which were ring-shaped due to the homogeneity of the phantom. The merged EMpCT dataset achieved a superior visual image quality with reduced artifacts and only minor remaining rings. The inter-quartile range (25/75) of RSP values was reduced from 0.7% with the current standard acquisition to 0.2% with EMpCT due to the reduction of ring artifacts. In this study, dose was doubled compared to a standard scan, but we discuss strategies to reduce excess dose. Conclusions: EMpCT allows to effectively avoid regions of the energy detector that cause image artifacts. Thereby, image quality is improved.

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