Sechopoulos I
Emory University, Atlanta, GA.
Med Phys. 2012 Jun;39(6Part24):3914. doi: 10.1118/1.4735974.
To reduce the impact of x-ray scatter in dedicated breast computed tomography (BCT) images.
The inclusion of x-ray scatter in BCT projections results in cupping artifacts, loss of contrast, and quantitative inaccuracies. To correct for this, an additional set of BCT projections is acquired with a tungsten plate placed between the x-ray source and the patient breast. The tungsten plate includes a two-dimensional grid of perforations to generate an array of pencil beams. Due to the limited area illuminated by the x-ray pencil beams, an array of signals of primary x-rays only is obtained. At the pencil beam locations, the difference between the plate projections and the standard projections is an estimate of the scatter present in the latter. These estimates are interpolated to obtain scatter-only estimates of the whole images, which are subtracted from the standard projections, resulting in BCT projections with primary signal only, which are then reconstructed. To reduce the impact of the quantum noise of the scatter signal, the resulting reconstructions are noise filtered. Monte Carlo simulations were performed to estimate the amount of scatter included in the pencil beams and the dose from these additional projections. The algorithm was tested using breast phantoms on a BCT clinical prototype system.
The maximum scatter signal in the pencil beams is 2.2% (mean of 0.7%) of the total signal, so the pencil beams are an excellent estimate of the primary-only signal. The additional projections Result in only 0.4% of the glandular dose of the standard projections. The homogeneity of the resulting phantom images, the signal difference between adipose and glandular tissue, reconstruction accuracy, and contrast-to-noise ratios were improved with this algorithm.
The proposed algorithm has the potential to substantially improve BCT image quality with practically no additional dose to the patient breast.
降低专用乳腺计算机断层扫描（BCT）图像中X射线散射的影响。
BCT投影中包含的X射线散射会导致杯状伪影、对比度损失和定量不准确。为了校正此问题，在X射线源和患者乳房之间放置一块钨板，获取一组额外的BCT投影。钨板包含一个二维穿孔网格，以生成一系列笔形束。由于X射线笔形束照射的区域有限，因此仅获得初级X射线的信号阵列。在笔形束位置，平板投影与标准投影之间的差异是对后者中存在的散射的估计。对这些估计进行插值，以获得整个图像的仅散射估计，然后从标准投影中减去该估计，从而得到仅具有初级信号的BCT投影，然后对其进行重建。为了降低散射信号量子噪声的影响，对所得重建图像进行噪声滤波。进行了蒙特卡罗模拟，以估计笔形束中包含的散射量以及这些额外投影的剂量。该算法在BCT临床原型系统上使用乳腺体模进行了测试。
笔形束中的最大散射信号为总信号的2.2%（平均为0.7%），因此笔形束是对仅初级信号的出色估计。额外的投影仅导致标准投影腺体剂量的0.4%。该算法提高了所得体模图像的均匀性、脂肪组织与腺体组织之间的信号差异、重建精度以及对比度噪声比。
所提出的算法有可能在几乎不增加患者乳房额外剂量的情况下，大幅提高BCT图像质量。
