Tilley Steven, Zbijewski Wojciech, Siewerdsen Jeffrey H, Stayman J Webster
Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD.
Proc SPIE Int Soc Opt Eng. 2018 Mar;10573. doi: 10.1117/12.2293776.
Material decomposition in CT has the potential to reduce artifacts and improve quantitative accuracy by utilizing spectral models and multi-energy scans. In this work we present a novel Model-Based Material Decomposition (MBMD) method based on an existing iterative reconstruction algorithm derived from a general non-linear forward model. A digital water phantom with inserts containing different concentrations of calcium was scanned on a kV switching system. We used the presented method to simultaneously reconstruct water and calcium material density images, and compared the results to an image domain and a projection domain decomposition method. When switching voltage every other frame, MBMD resulted in more accurate water and calcium concentration values than the image domain decomposition method, and was just as accurate as the projection domain decomposition method. In a second, slower, kV switching scheme (changing voltage every ten frames) which precluded the use of traditional projection domain based methods, MBMD continued to produce quantitatively accurate reconstructions. Finally, we present a preliminary study applying MBMD to a water phantom containing vials of different concentrations of KHPO which was scanned on a cone-beam CT test bench. Both the fast and slow (emulated) kV switching schemes resulted in similar reconstructions, indicating MBMD's robustness to challenging acquisition schemes. Additionally, the KHPO concentration ratios between the vials were accurately represented in the reconstructed KHPO density image.
CT中的物质分解有潜力通过利用光谱模型和多能量扫描来减少伪影并提高定量准确性。在这项工作中，我们基于从一般非线性正向模型推导而来的现有迭代重建算法，提出了一种新颖的基于模型的物质分解（MBMD）方法。在kV切换系统上对带有包含不同浓度钙的插入物的数字水模体进行了扫描。我们使用所提出的方法同时重建水和钙物质密度图像，并将结果与图像域和投影域分解方法进行比较。当每隔一帧切换电压时，MBMD得到的水和钙浓度值比图像域分解方法更准确，并且与投影域分解方法一样准确。在第二种较慢的kV切换方案（每十帧改变电压）中，由于无法使用基于传统投影域的方法，MBMD继续产生定量准确的重建结果。最后，我们展示了一项将MBMD应用于在锥束CT试验台上扫描的包含不同浓度KHPO小瓶的水模体的初步研究。快速和慢速（模拟）kV切换方案都产生了相似的重建结果，表明MBMD对具有挑战性的采集方案具有鲁棒性。此外，在重建后的KHPO密度图像中准确地呈现了小瓶之间的KHPO浓度比。
