Radiology Department, Academic Medical Centre, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
Med Phys. 2012 Apr;39(4):1793-810. doi: 10.1118/1.3685579.
Typically spatial modulation of the magnetization (SPAMM) tagged magnetic resonance imaging (MRI) requires many repeated motion cycles limiting the applicability to highly repeatable tissue motions only. This paper describes the validation of a novel SPAMM tagged MRI and post-processing framework for the measurement of complex and dynamic 3D soft tissue deformation following just three motion cycles. Techniques are applied to indentation induced deformation measurement of the upper arm and a silicone gel phantom.
A SPAMM tagged MRI methodology is presented allowing continuous (3.3-3.6 Hz) sampling of 3D dynamic soft tissue deformation using non segmented 3D acquisitions. The 3D deformation is reconstructed by the combination of three mutually orthogonal tagging directions, thus requiring only three repeated motion cycles. In addition a fully automatic post-processing framework is presented employing Gabor scale-space and filter-bank analysis for tag extrema segmentation and triangulated surface fitting aided by Gabor filter bank derived surface normals. Deformation is derived following tracking of tag surface triplet triangle intersections. The dynamic deformation measurements were validated using indentation tests (∼20 mm deep at 12 mm/s) on a silicone gel soft tissue phantom containing contrasting markers which provide a reference measure of deformation. In addition, the techniques were evaluated in vivo for dynamic skeletal muscle tissue deformation measurement during indentation of the biceps region of the upper arm in a volunteer.
For the phantom and volunteer tag point location precision were 44 and 92 μm, respectively resulting in individual displacements precisions of 61 and 91 μm, respectively. For both the phantom and volunteer data cumulative displacement measurement accuracy could be evaluated and the difference between initial and final locations showed a mean and standard deviation of 0.44 and 0.59 mm for the phantom and 0.40 and 0.73 mm for the human data. Finally accuracy of (cumulative) displacement was evaluated using marker tracking in the silicone gel phantom. Differences between true and predicted marker locations showed a mean of 0.35 mm and a standard deviation of 0.63 mm.
A novel SPAMM tagged MRI and fully automatic post-processing framework for the measurement of complex 3D dynamic soft tissue deformation following just three repeated motion cycles was presented. The techniques demonstrate dynamic measurement of complex 3D soft tissue deformation at subvoxel accuracy and precision and were validated for 3.3-3.6 Hz sampling of deformation speeds up to 12 mm/s.
通常情况下，磁共振成像（MRI）的磁化空间调制（SPAMM）需要多次重复运动周期，这限制了它仅适用于高度可重复的组织运动。本文介绍了一种新型的 SPAMM 标记 MRI 及其后处理框架的验证，该框架可用于仅经过三个运动周期即可测量复杂和动态的 3D 软组织变形。该技术应用于上臂和硅凝胶体模的压痕诱导变形测量。
本文提出了一种 SPAMM 标记 MRI 方法，允许使用非分段的 3D 采集连续（3.3-3.6Hz）采样 3D 动态软组织变形。通过三个相互正交的标记方向的组合来重建 3D 变形，因此仅需要三个重复的运动周期。此外，还提出了一种全自动后处理框架，该框架采用 Gabor 尺度空间和滤波器组分析进行标签极值分割，并通过 Gabor 滤波器组得到的表面法向量辅助三角化表面拟合。变形是通过跟踪标记表面三重三角形交点来获得的。通过在含有对比标记的硅凝胶软组织体模上进行的深度约为 20mm（以 12mm/s 的速度）的压痕测试，对动态变形测量进行了验证，该标记提供了变形的参考测量值。此外，还在志愿者的上臂肱二头肌区域进行压痕时，对动态骨骼肌组织变形测量进行了体内评估。
对于体模和志愿者，标记点位置精度分别为 44μm 和 92μm，导致个体位移精度分别为 61μm 和 91μm。对于体模和志愿者数据，都可以评估累积位移测量精度，并且初始位置和最终位置之间的差异分别显示出体模的平均值和标准差为 0.44mm 和 0.59mm，而人体数据的平均值和标准差为 0.40mm 和 0.73mm。最后，使用硅凝胶体模中的标记跟踪评估了（累积）位移的准确性。真实位置和预测位置之间的差异平均值为 0.35mm，标准差为 0.63mm。
本文提出了一种新型的 SPAMM 标记 MRI 和全自动后处理框架，用于仅经过三个重复运动周期即可测量复杂的 3D 动态软组织变形。该技术证明了亚像素精度和精度的复杂 3D 软组织变形的动态测量，并且已经验证了高达 12mm/s 的变形速度的 3.3-3.6Hz 采样。
