Department of Medical Physics, Princess Margaret Cancer Center, University Health Network, Toronto, Ontario, Canada. Department of Surgery, University of Toronto, Toronto, Ontario, Canada.
Phys Med Biol. 2018 Mar 27;63(7):075010. doi: 10.1088/1361-6560/aab33e.
The design, construction and application of a multimodality, 3D magnetic resonance/computed tomography (MR/CT) image distortion phantom and analysis system for stereotactic radiosurgery (SRS) is presented. The phantom is characterized by (1) a 1 × 1 × 1 (cm) MRI/CT-visible 3D-Cartesian grid; (2) 2002 grid vertices that are 3D-intersections of MR-/CT-visible 'lines' in all three orthogonal planes; (3) a 3D-grid that is MR-signal positive/CT-signal negative; (4) a vertex distribution sufficiently 'dense' to characterize geometrical parameters properly, and (5) a grid/vertex resolution consistent with SRS localization accuracy. When positioned correctly, successive 3D-vertex planes along any orthogonal axis of the phantom appear as 1 × 1 (cm)-2D grids, whereas between vertex planes, images are defined by 1 × 1 (cm)-2D arrays of signal points. Image distortion is evaluated using a centroid algorithm that automatically identifies the center of each 3D-intersection and then calculates the deviations dx, dy, dz and dr for each vertex point; the results are presented as a color-coded 2D or 3D distribution of deviations. The phantom components and 3D-grid are machined to sub-millimeter accuracy, making the device uniquely suited to SRS applications; as such, we present it here in a form adapted for use with a Leksell stereotactic frame. Imaging reproducibility was assessed via repeated phantom imaging across ten back-to-back scans; 80%-90% of the differences in vertex deviations dx, dy, dz and dr between successive 3 T MRI scans were found to be ⩽0.05 mm for both axial and coronal acquisitions, and over >95% of the differences were observed to be ⩽0.05 mm for repeated CT scans, clearly demonstrating excellent reproducibility. Applications of the 3D-phantom/analysis system are presented, using a 32-month time-course assessment of image distortion/gradient stability and statistical control chart for 1.5 T and 3 T GE TwinSpeed MRI systems.
本文介绍了一种用于立体定向放射外科（SRS）的多模态、3D 磁共振/计算机断层扫描（MR/CT）图像失真体模及分析系统的设计、构建和应用。该体模具有以下特点：（1）1×1×1（cm）的 MRI/CT 可见 3D 笛卡尔网格；（2）2002 个网格顶点，是所有三个正交平面中 MR-/CT-可见“线”的 3D 交点；（3）MR 信号为正/CT 信号为负的 3D 网格；（4）顶点分布足够“密集”，能够正确描述几何参数；（5）网格/顶点分辨率与 SRS 定位精度一致。当正确定位时，体模任何正交轴上的连续 3D 顶点平面会呈现为 1×1（cm）-2D 网格，而在顶点平面之间，图像由 1×1（cm）-2D 信号点阵列定义。使用质心算法评估图像失真，该算法自动识别每个 3D 交点的中心，然后计算每个顶点点的偏差 dx、dy、dz 和 dr；结果以偏差的彩色编码 2D 或 3D 分布呈现。体模组件和 3D 网格加工精度达到亚毫米级，使该设备非常适合 SRS 应用；因此，我们以适应 Leksell 立体定向框架的形式呈现。通过在 10 次连续扫描中对体模进行重复成像，评估成像可重复性；在 3T MRI 轴向和冠状采集中，80%-90%的连续扫描中顶点偏差 dx、dy、dz 和 dr 的差异小于 0.05mm，超过 95%的差异小于 0.05mm在重复 CT 扫描中，这清楚地表明了出色的可重复性。本文还介绍了 3D 体模/分析系统的应用，包括使用 32 个月的时间评估 1.5T 和 3T GE TwinSpeed MRI 系统的图像失真/梯度稳定性和统计控制图。
