Combining scatter reduction and correction to improve image quality in cone-beam computed tomography (CBCT)
Combining scatter reduction and correction to improve image quality in cone-beam computed tomography (CBCT)
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DOI：
10.1118/1.3497272
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发表时间：
2010-11-01
期刊：
影响因子：
3.8
通讯作者：
Chetty, Indrin J.
中科院分区：
文献类型：
--
作者：
Jin, Jian-Yue;Ren, Lei;Chetty, Indrin J.
目的：作者提出了一种结合散射减少和校正的方法，以提高锥形束计算机断层扫描（CBCT）的图像质量。虽然使用类似于先前技术的束块方法来测量散射，但是该方法的不同之处在于，作者利用在CBCT图像重建的散射测量期间获得的部分阻挡的投影数据。本研究旨在评估该方法的可行性。方法：在辐射源和成像目标之间放置一个由铅隔组成的一维网格，进行散射测量。图像数据从网格间隙区域收集，而散射分布在网格下的阻挡区域中测量。通过从成像数据中减去测量的散射来执行散射校正。在网格的半影区域中的图像信息被导出。开发了三种成像模式，以从部分投影数据重建完整的CBCT图像。单旋转半扇模式使用插值来填充缺失的数据。双旋转半扇模式使用两次旋转，网格偏移半个网格周期，以获取两组互补的投影，然后合并以形成完整的投影用于重建。单旋转全扇形模式设计用于对小物体或感兴趣区域进行成像。在360扫描角度上采集全扇形投影图像，扫描期间网格移动一定距离。使用放大的Catphan体模来评价所提出的技术对图像质量的潜在改善。使用拟人骨盆体模来验证使用三种成像模式从部分遮挡投影重建一组完整CBCT图像的可行性。将单旋转半扇模式的CBCT图像与模拟CT图像进行刚体图像配准，并将配准结果与双旋转模式的CBCT图像和常规CBCT图像进行比较。结果：与常规CBCT相比，该方法将条纹伪影指数从58%降低到1%。它还将CT数线性度从0.880提高到0.998，对比度噪声比（CNR）从4.29提高到6.42。所有三种图像模式均获得了图像质量整体改善的完整CBCT图像集。单旋转半风扇模式的纵向分辨率略有下降。在纵向方向上的双旋转半风扇和单旋转全风扇模式保持了高分辨率。从单旋转半扇模式的CBCT图像的配准误差为0.8 +/- 0.3 mm的纵向方向和可忽略不计的其他verses.Conclusions：所提出的方法提供了组合的散射校正和直接散射减少。散射校正可以消除散射伪影，而直接散射减少可以改善CNR以补偿由于散射校正引起的CNR劣化。在所有三种成像模式下重建完整的CBCT图像集。尽管纵向分辨率降低，但单次旋转模式可用于刚体患者对准。双旋转模式可用于改善CBCT图像质量，以用于自适应放射治疗中的软组织描绘。(C)2010年美国医学物理学家协会。[DOI 10.1118/1.3497272]
Purpose: The authors propose a combined scatter reduction and correction method to improve image quality in cone-beam computed tomography (CBCT). Although using a beam-block approach similar to previous techniques to measure the scatter, this method differs in that the authors utilize partially blocked projection data obtained during scatter measurement for CBCT image reconstruction. This study aims to evaluate the feasibility of the proposed approach.Methods: A 1D grid, composed of lead septa, was placed between the radiation source and the imaging object for scatter measurement. Image data were collected from the grid interspace regions while the scatter distribution was measured in the blocked regions under the grid. Scatter correction was performed by subtracting the measured scatter from the imaging data. Image information in the penumbral regions of the grid was derived. Three imaging modes were developed to reconstruct full CBCT images from partial projection data. The single-rotation half-fan mode uses interpolation to fill the missing data. The dual-rotation half-fan mode uses two rotations, with the grid offset by half a grid cycle, to acquire two complementary sets of projections, which are then merged to form complete projections for reconstruction. The single-rotation full-fan mode was designed for imaging a small object or a region of interest. Full-fan projection images were acquired over a 360 scan angle with the grid shifting a distance during the scan. An enlarged Catphan phantom was used to evaluate potential improvement in image quality with the proposed technique. An anthropomorphic pelvis phantom was used to validate the feasibility of reconstructing a complete set of CBCT images from the partially blocked projections using three imaging modes. Rigid-body image registration was performed between the CBCT images from the single-rotation half-fan mode and the simulation CT and the results were compared to that for the CBCT images from dual-rotation mode and conventional CBCT images.Results: The proposed technique reduced the streak artifact index from 58% to 1% in comparison with the conventional CBCT. It also improved CT number linearity from 0.880 to 0.998 and the contrast-to-noise ratio (CNR) from 4.29 to 6.42. Complete sets of CBCT images with overall improved image quality were achieved for all three image modes. The longitudinal resolution was slightly compromised for the single-rotation half-fan mode. High resolution was retained for the dual-rotation half-fan and single-rotation full-fan modes in the longitudinal direction. The registration error for the CBCT images from the single-rotation half-fan mode was 0.8 +/- 0.3 mm in the longitudinal direction and negligible in the other directions.Conclusions: The proposed method provides combined scatter correction and direct scatter reduction. Scatter correction may eliminate scatter artifacts, while direct scatter reduction may improve the CNR to compensate the CNR degradation due to scatter correction. Complete sets of CBCT images are reconstructed in all three imaging modes. The single-rotation mode can be used for rigid-body patient alignment despite degradation in longitudinal resolution. The dual-rotation mode may be used to improve CBCT image quality for soft tissue delineation in adaptive radiation therapy. (C) 2010 American Association of Physicists in Medicine. [DOI: 10.1118/1.3497272]