Exhibit Hall | Forum 8
Purpose: We aim at developing a model-based algorithm that compensates for the effect of both pulse pileup (PP) and charge sharing (CS), and evaluate the performance using computer simulations.
Methods: The proposed PCP algorithm for PP and CS compensation utilizes cascaded models for CS and PP we previously developed, maximizes Poisson log-likelihood, and performs an efficient 3-step exhaustive search. For comparison, we also developed LCP algorithm that combines models for a loss of counts (LC) and CS. Two types of simulation, slab-based and CT-based, were performed to assess the performance of both PCP and LCP. A slab-based assessment used a pair of adipose and iodine with different thicknesses, attenuated x-rays, assessed the bias and noise; a CT-based assessment simulated a chest/cardiac scan and a head-and-neck scan using 3-D phantom and noisy cone-beam projections.
Results: With the slab simulation, the PCP had little or no biases when the expected counts was sufficiently large, even though a probability of count loss (PCL) due to deadtime loss or pulse pileup was as high as 0.8. In contrast, the LCP had significant biases (>±2 cm of adipose) when the PCL was higher than 0.15. The noise of PCP was within 8% from Cramér–Rao lower bounds for most cases, when no significant bias was present. The two CT studies essentially agreed with the slab simulation study. PCP had little or no biases in the estimated basis line integrals, reconstructed basis density maps, and synthesized monoenergetic CT images. But the LCP had significant biases in basis line integrals when PCL were above 0.15. As a consequence, basis density maps and monoenergetic CT images obtained by LCP had biases throughout the imaged space.
Conclusion: The proposed PCP algorithm with the cascaded attenuation–CS–PP model can address the spectral distortion in PCD.
Funding Support, Disclosures, and Conflict of Interest: NIH, Siemens Healthineers, Canon Healthcare