Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO 63110, USA.
Med Phys. 2012 Feb;39(2):922-32. doi: 10.1118/1.3679015.
Phase-binning algorithms are commonly utilized in 4DCT image reconstruction for characterization of tumor or organ shape and respiration motion, but breathing irregularities occurring during 4DCT acquisition can cause considerable image distortions. Recently, amplitude-binning algorithms have been evaluated as a potential improvement to phase-binning algorithms for 4DCT image reconstruction. The purpose of this study was to evaluate the performance of the first commercially available on-line retrospective amplitude-binning algorithm for comparison to the traditional phase-binning algorithm.
Both phantom and clinical data were used for evaluation. A phantom of known geometry was mounted on a 4D motion platform programmed with seven respiratory waves (two computer generated and five patient trajectories) and scanned with a Philips Brilliance Big bore 16-slice CT simulator. 4DCT images were reconstructed using commercial amplitude- and phase-binning algorithms. Image quality of the amplitude- and phase-binned image sets was compared by evaluation of shape and volume distortions in reconstructed images. Clinical evaluations were performed on 64 4DCT patient image sets in a blinded review process. The amplitude- and phase-binned 4DCT maximum intensity projection (MIP) images were further evaluated for 28 stereotactic body radiation therapy (SBRT) cases of total 64 cases. A preliminary investigation of the effects of respiratory amplitude and pattern irregularities on motion artifact severity was conducted.
The phantom experiments illustrated that, as expected, maximum inhalation occurred at the 0% amplitude and maximum exhalation occurred at the 50% amplitude of the amplitude-binned 4DCT image sets. The phantom shape distortions were more severe in the images reconstructed from the phase-binning algorithm. In the clinical study, compared to the phase-binning algorithm, the amplitude-binning algorithm yielded fewer or less severe motion artifacts in 37.5% of the cases (24∕64), comparable artifacts in 54.7% of the cases (35∕64), and slightly greater artifacts in 7.8% of the cases (5∕64). Evaluation of SBRT cases demonstrated that the reconstructed tumor sizes and locations were comparable in 96% (1∕28) of the MIP image pairs generated from both amplitude- and phase-binning algorithms. In this case the amplitude-binned image set rendered a smaller tumor size, which was likely due to very shallow respiratory amplitudes occurring over several breathing cycles.
Overall, the amplitude-binning algorithm for 4DCT reconstruction reduced the severity of tumor distortion and image artifacts compared to the phase-binning algorithm. However, the full range of motion may not be characterized using amplitude-binning algorithms. Despite superior performance, amplitude binning can still be susceptible to motion artifacts caused by large variations in amplitude of respiratory waves.
在 4DCT 图像重建中，相位-bin 算法常用于描述肿瘤或器官的形状和呼吸运动，但 4DCT 采集过程中出现的呼吸不规则会导致相当大的图像变形。最近，振幅-bin 算法已被评估为 4DCT 图像重建中相位-bin 算法的潜在改进方法。本研究的目的是评估第一个商业上可用的在线回顾性振幅-bin 算法的性能，并与传统的相位-bin 算法进行比较。
使用体模和临床数据进行评估。一个已知几何形状的体模安装在一个 4D 运动平台上，该平台由七个呼吸波（两个计算机生成和五个患者轨迹）编程，并使用飞利浦 Brilliance Big bore 16 层 CT 模拟器进行扫描。使用商业振幅和相位-bin 算法重建 4DCT 图像。通过评估重建图像中的形状和体积变形，比较振幅和相位-bin 图像集的图像质量。在盲法审查过程中，对 64 例 4DCT 患者图像集进行了临床评估。进一步评估了 28 例立体定向体部放疗（SBRT）病例的 64 例总病例的振幅和相位-bin 4DCT 最大密度投影（MIP）图像。初步研究了呼吸幅度和模式不规则对运动伪影严重程度的影响。
体模实验表明，正如预期的那样，在振幅-bin 4DCT 图像集中，最大吸气发生在 0%的振幅，最大呼气发生在 50%的振幅。在相位-bin 算法重建的图像中，体模的形状变形更为严重。在临床研究中，与相位-bin 算法相比，在 37.5%的病例（24/64）中，振幅-bin 算法产生的运动伪影较少或较轻，在 54.7%的病例（35/64）中，运动伪影相当，在 7.8%的病例（5/64）中，运动伪影略大。SBRT 病例的评估表明，在 96%（28/29）的 MIP 图像对中，使用振幅和相位-bin 算法重建的肿瘤大小和位置相似。在这种情况下，由于几个呼吸周期中呼吸幅度非常浅，重建的肿瘤大小较小，这可能是由于振幅-bin 图像集造成的。
总体而言，与相位-bin 算法相比，4DCT 重建的振幅-bin 算法降低了肿瘤变形和图像伪影的严重程度。然而，可能无法使用振幅-bin 算法来描述整个运动范围。尽管性能优越，但振幅 binning 仍然容易受到呼吸波振幅变化较大引起的运动伪影的影响。
