Levi Jacob, Fahmi Rachid, Eck Brendan L, Fares Anas, Wu Hao, Vembar Mani, Dhanantwari Amar, Bezerra Hiram G, Wilson David L
Department of Physics, Case Western Reserve University, Cleveland, OH, 44106, USA.
Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, 44106, USA.
Proc SPIE Int Soc Opt Eng. 2016 Feb-Mar;9784. doi: 10.1117/12.2216623. Epub 2016 Mar 21.
Myocardial perfusion imaging using CT (MPI-CT) and coronary CTA have the potential to make CT an ideal noninvasive gate-keeper for invasive coronary angiography. However, beam hardening artifacts (BHA) prevent accurate blood flow calculation in MPI-CT. BH Correction (BHC) methods require either energy-sensitive CT, not widely available, or typically a calibration-based method. We developed a calibration-free, automatic BHC (ABHC) method suitable for MPI-CT. The algorithm works with any BHC method and iteratively determines model parameters using proposed BHA-specific cost function. In this work, we use the polynomial BHC extended to three materials. The image is segmented into soft tissue, bone, and iodine images, based on mean HU and temporal enhancement. Forward projections of bone and iodine images are obtained, and in each iteration polynomial correction is applied. Corrections are then back projected and combined to obtain the current iteration's BHC image. This process is iterated until cost is minimized. We evaluate the algorithm on simulated and physical phantom images and on preclinical MPI-CT data. The scans were obtained on a prototype spectral detector CT (SDCT) scanner (Philips Healthcare). Mono-energetic reconstructed images were used as the reference. In the simulated phantom, BH streak artifacts were reduced from 12±2HU to 1±1HU and cupping was reduced by 81%. Similarly, in physical phantom, BH streak artifacts were reduced from 48±6HU to 1±5HU and cupping was reduced by 86%. In preclinical MPI-CT images, BHA was reduced from 28±6 HU to less than 4±4HU at peak enhancement. Results suggest that the algorithm can be used to reduce BHA in conventional CT and improve MPI-CT accuracy.
使用CT的心肌灌注成像（MPI-CT）和冠状动脉CT血管造影（CTA）有可能使CT成为侵入性冠状动脉造影理想的无创守门人。然而，束硬化伪影（BHA）妨碍了MPI-CT中血流的准确计算。束硬化校正（BHC）方法要么需要能量敏感型CT（这种设备尚未广泛普及），要么通常采用基于校准的方法。我们开发了一种适用于MPI-CT的无需校准的自动BHC（ABHC）方法。该算法可与任何BHC方法配合使用，并使用提出的特定于BHA的成本函数迭代确定模型参数。在这项工作中，我们使用扩展到三种材料的多项式BHC。基于平均HU值和时间增强，将图像分割为软组织、骨骼和碘图像。获取骨骼和碘图像的前向投影，并在每次迭代中应用多项式校正。然后将校正结果反投影并合并，以获得当前迭代的BHC图像。重复此过程，直到成本最小化。我们在模拟和物理体模图像以及临床前MPI-CT数据上评估了该算法。扫描是在一台原型光谱探测器CT（SDCT）扫描仪（飞利浦医疗保健公司）上进行的。使用单能重建图像作为参考。在模拟体模中，BH条纹伪影从12±2HU减少到1±1HU，杯状伪影减少了81%。同样，在物理体模中，BH条纹伪影从48±6HU减少到1±5HU，杯状伪影减少了86%。在临床前MPI-CT图像中，峰值增强时BHA从28±6HU减少到小于4±4HU。结果表明，该算法可用于减少传统CT中的BHA并提高MPI-CT的准确性。
