Matenine Dmitri, Mascolo-Fortin Julia, Goussard Yves, Després Philippe
Département de physique, de génie physique et d'optique, Université Laval, Québec, Québec G1V 0A6, Canada.
Département de génie électrique/Institut de génie biomédical, École Polytechnique de Montréal, C.P. 6079, succ. Centre-ville, Montréal, Québec H3C 3A7, Canada.
Med Phys. 2015 Nov;42(11):6376-86. doi: 10.1118/1.4931604.
The present work evaluates an iterative reconstruction approach, namely, the ordered subsets convex (OSC) algorithm with regularization via total variation (TV) minimization in the field of cone-beam optical computed tomography (optical CT). One of the uses of optical CT is gel-based 3D dosimetry for radiation therapy, where it is employed to map dose distributions in radiosensitive gels. Model-based iterative reconstruction may improve optical CT image quality and contribute to a wider use of optical CT in clinical gel dosimetry.
This algorithm was evaluated using experimental data acquired by a cone-beam optical CT system, as well as complementary numerical simulations. A fast GPU implementation of OSC-TV was used to achieve reconstruction times comparable to those of conventional filtered backprojection. Images obtained via OSC-TV were compared with the corresponding filtered backprojections. Spatial resolution and uniformity phantoms were scanned and respective reconstructions were subject to evaluation of the modulation transfer function, image uniformity, and accuracy. The artifacts due to refraction and total signal loss from opaque objects were also studied.
The cone-beam optical CT data reconstructions showed that OSC-TV outperforms filtered backprojection in terms of image quality, thanks to a model-based simulation of the photon attenuation process. It was shown to significantly improve the image spatial resolution and reduce image noise. The accuracy of the estimation of linear attenuation coefficients remained similar to that obtained via filtered backprojection. Certain image artifacts due to opaque objects were reduced. Nevertheless, the common artifact due to the gel container walls could not be eliminated.
The use of iterative reconstruction improves cone-beam optical CT image quality in many ways. The comparisons between OSC-TV and filtered backprojection presented in this paper demonstrate that OSC-TV can potentially improve the rendering of spatial features and reduce cone-beam optical CT artifacts.
本研究评估一种迭代重建方法，即在锥束光学计算机断层扫描（光学CT）领域中，通过总变差（TV）最小化进行正则化的有序子集凸（OSC）算法。光学CT的用途之一是用于放射治疗的基于凝胶的三维剂量测定，在该领域中，它被用于绘制放射敏感凝胶中的剂量分布。基于模型的迭代重建可以提高光学CT图像质量，并有助于光学CT在临床凝胶剂量测定中的更广泛应用。
使用锥束光学CT系统获取的实验数据以及补充的数值模拟对该算法进行评估。采用OSC-TV的快速GPU实现来获得与传统滤波反投影相当的重建时间。将通过OSC-TV获得的图像与相应的滤波反投影图像进行比较。扫描空间分辨率和均匀性体模，并对各自的重建结果进行调制传递函数、图像均匀性和准确性评估。还研究了由于折射和不透明物体的总信号损失引起的伪影。
锥束光学CT数据重建表明，由于基于模型的光子衰减过程模拟，OSC-TV在图像质量方面优于滤波反投影。结果表明，它能显著提高图像空间分辨率并降低图像噪声。线性衰减系数估计的准确性与通过滤波反投影获得的结果相似。由于不透明物体引起的某些图像伪影减少了。然而，由于凝胶容器壁引起的常见伪影无法消除。
迭代重建的使用在许多方面提高了锥束光学CT图像质量。本文中OSC-TV与滤波反投影的比较表明，OSC-TV有可能改善空间特征的呈现并减少锥束光学CT伪影。
