使用前向投影模型进行专用锥形束乳腺 CT 的 X 射线散射校正。
X-ray scatter correction for dedicated cone beam breast CT using a forward-projection model.
机构信息
Nuclear and Radiological Engineering and Medical Physics Programs, The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA.
Department of Radiology, University of Massachusetts Medical School, Worcester, MA, 01655, USA.
出版信息
Med Phys. 2017 Jun;44(6):2312-2320. doi: 10.1002/mp.12213. Epub 2017 Apr 25.
PURPOSE
The quality of dedicated cone-beam breast CT (CBBCT) imaging is fundamentally limited by x-ray scatter contamination due to the large irradiation volume. In this paper, we propose a scatter correction method for CBBCT using a novel forward-projection model with high correction efficacy and reliability.
METHOD
We first coarsely segment the uncorrected, first-pass, reconstructed CBBCT images into binary-object maps and assign the segmented fibroglandular and adipose tissue with the correct attenuation coefficients based on the mean x-ray energy. The modified CBBCT are treated as the prior images toward scatter correction. Primary signals are first estimated via forward projection on the modified CBBCT. To avoid errors caused by inaccurate segmentation, only sparse samples of estimated primary are selected for scatter estimation. A Fourier-Transform based algorithm, herein referred to as local filtration hereafter, is developed to efficiently estimate the global scatter distribution on the detector. The scatter-corrected images are obtained by removing the estimated scatter distribution from measured projection data.
RESULTS
We evaluate the method performance on six patients with different breast sizes and shapes representing the general population. The results show that the proposed method effectively reduces the image spatial non-uniformity from 8.27 to 1.91% for coronal views and from 6.50 to 3.00% for sagittal views. The contrast-to-deviation ratio is improved by an average factor of 1.41. Comparisons on the image details reveal that the proposed scatter correction successfully preserves fine structures of fibroglandular tissues that are lost in the segmentation process.
CONCLUSION
We propose a highly practical and efficient scatter correction algorithm for CBBCT via a forward-projection model. The method is attractive in clinical CBBCT imaging as it is readily implementable on a clinical system without modifications in current imaging protocols or system hardware.
目的
由于照射体积大，专用锥形束乳腺 CT（CBBCT）成像的质量受到 X 射线散射污染的根本限制。本文提出了一种使用具有高校正功效和可靠性的新型正向投影模型对 CBBCT 进行散射校正的方法。
方法
首先，我们将未校正的、首次重建的 CBBCT 图像粗略地分割为二进制对象图，并根据平均 X 射线能量为分割的纤维腺体和脂肪组织分配正确的衰减系数。修改后的 CBBCT 作为散射校正的先验图像。首先通过在修改后的 CBBCT 上进行正向投影来估计原始信号。为了避免由于不准确的分割而导致的错误，仅选择估计的原始信号的稀疏样本进行散射估计。在此，开发了一种基于傅里叶变换的算法，称为局部滤波，以有效地估计探测器上的全局散射分布。通过从测量的投影数据中减去估计的散射分布来获得散射校正的图像。
结果
我们在六个具有不同乳房大小和形状的患者上评估了该方法的性能，这些患者代表了一般人群。结果表明，该方法有效地将冠状视图的图像空间不均匀性从 8.27%降低到 1.91%，将矢状视图的图像空间不均匀性从 6.50%降低到 3.00%。对比度偏差比提高了平均 1.41 倍。图像细节的比较表明，该散射校正方法成功地保留了在分割过程中丢失的纤维腺体组织的精细结构。
结论
我们提出了一种通过正向投影模型对 CBBCT 进行高度实用和高效散射校正的算法。该方法在临床 CBBCT 成像中很有吸引力，因为它可以在不修改当前成像协议或系统硬件的情况下在临床系统上轻松实现。
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