Department of Biomedical Engineering, Sungkyunkwan University, Suwon, South Korea.
IBS Center for Neuroscience Imaging Research, Suwon, South Korea.
PLoS One. 2019 Aug 5;14(8):e0220639. doi: 10.1371/journal.pone.0220639. eCollection 2019.
Fabrication of a spherical multi-compartment MRI phantom is demonstrated that can be used to validate magnetic resonance (MR)-based susceptibility imaging reconstruction. The phantom consists of a 10 cm diameter gelatin sphere that encloses multiple smaller gelatin spheres doped with different concentrations of paramagnetic contrast agents. Compared to previous multi-compartment phantoms with cylindrical geometry, the phantom provides the following benefits: (1) no compartmental barrier materials are used that can introduce signal voids and spurious phase; (2) compartmental geometry is reproducible; (3) spherical susceptibility boundaries possess a ground-truth analytical phase solution for easy experimental validation; (4) spherical geometry of the overall phantom eliminates background phase due to air-phantom boundary in any scan orientation. The susceptibility of individual compartments can be controlled independently by doping. During fabrication, formalin cross-linking and water-proof surface coating effectively blocked water diffusion between the compartments to preserve the phantom's integrity. The spherical shapes were realized by molding the inner gel compartments in acrylic spherical shells, 3 cm in diameter, and constructing the whole phantom inside a larger acrylic shell. From gradient echo images obtained at 3T, we verified that the phantom produced phase images in agreement with the theoretical prediction. Factors that limit the agreement include: air bubbles trapped at the gel interfaces, imperfect magnet shimming, and the susceptibility of external materials such as the phantom support hardware. The phantom images were used to validate publicly available codes for quantitative susceptibility mapping. We believe that the proposed phantom can provide a useful testbed for validation of MR phase imaging and MR-based magnetic susceptibility reconstruction.
制作了一个球形多腔磁共振（MR）体模，可用于验证基于磁共振的磁化率成像重建。该体模由一个 10 厘米直径的明胶球组成，其中包含多个掺杂有不同浓度顺磁对比剂的较小明胶球。与具有圆柱几何形状的先前多腔体模相比，该体模具有以下优点：（1）不使用会引入信号空洞和虚假相位的分腔阻挡材料；（2）分腔几何形状可重现；（3）球形磁化率边界具有真实的解析相位解，便于实验验证；（4）整个体模的球形几何形状消除了任何扫描方向上空气-体模边界的背景相位。通过掺杂可以独立控制各个分腔的磁化率。在制造过程中，甲醛交联和防水表面涂层有效地阻止了分腔之间的水分扩散，从而保持了体模的完整性。球形形状是通过在直径为 3 厘米的丙烯酸球形壳内成型内部凝胶分腔，并在更大的丙烯酸壳内构建整个体模来实现的。从 3T 获得的梯度回波图像中，我们验证了该体模产生的相位图像与理论预测一致。限制一致性的因素包括：凝胶界面处的气泡、不完善的磁场匀场、以及像体模支撑硬件这样的外部材料的磁化率。该体模图像用于验证公开的定量磁化率映射代码。我们相信，所提出的体模可以为 MR 相位成像和基于 MR 的磁化率重建的验证提供一个有用的测试平台。
