Biofunctional Imaging Laboratory, Immunology Frontier Research Center, Annex 1F, Graduate School of Frontier Biosciences, Osaka University, Suita, Japan.
Magn Reson Med Sci. 2011;10(4):219-27. doi: 10.2463/mrms.10.219.
We investigated the spatiotemporal changes in signal in draining lymph nodes of mice to ascertain the size-dependent effects of variously sized particles of iron oxide used to enhance magnetic resonance (MR) lymphography.
We injected iron oxide particles of 50-, 100-, 200-, or 1,000-nm diameter into the footpads of individual mice and obtained sequential MR images of the popliteal and inguinal lymph nodes with 11.7 tesla up to 6 weeks after particle administration.
Up to 30 min after administration of particles smaller than 100 nm, we observed a marked reduction in signal in the popliteal node that spread from the periphery at first observation toward the center of the node in subsequent measurements and persisted up to 6 weeks. In contrast, 1,000-nm particles caused dot-like areas of hypointensity in the popliteal lymph node, primarily in the inner portion, that appeared after 2 days. In the inguinal lymph nodes, signal changes occurred after 2 days for 50- and 100-nm particles and after one week for 1,000-nm particles. For 1,000-nm particles, areas of hypointensity were visible in the inner portion and not the periphery of the inguinal lymph node up to 6 weeks. In this study, we demonstrate the strong dependence of MR imaging contrast in draining lymph nodes on the size of the particle-shaped contrast agents injected subcutaneously. Particle size represented passive and active targeting effects, so micron-sized particles produced delayed enhancement.
Choosing the size of iron oxide particles for MR imaging contrast depends on the objective of observation, such as identifying the morphology or migration of immune cells in the lymph node.
我们研究了小鼠引流淋巴结中信号的时空变化，以确定用于增强磁共振（MR）淋巴造影的不同大小氧化铁颗粒的大小依赖性效应。
我们将直径为 50nm、100nm、200nm 或 1000nm 的氧化铁颗粒分别注入单个小鼠的足底，并在粒子给药后 6 周内使用 11.7T 对腘窝和腹股沟淋巴结进行连续 MR 成像。
在小于 100nm 的粒子给药后 30 分钟内，我们观察到最初观察时从外围开始向淋巴结中心扩散的明显的腘窝淋巴结信号降低，并且持续到 6 周。相比之下，1000nm 的粒子导致腘窝淋巴结出现点状低信号区，主要在内部，在给药后 2 天出现。在腹股沟淋巴结中，50nm 和 100nm 粒子在给药后 2 天出现信号变化，1000nm 粒子在给药后 1 周出现信号变化。对于 1000nm 的粒子，低信号区在腹股沟淋巴结的内部可见，而不是外围，直至 6 周。在这项研究中，我们证明了注射到皮下的颗粒状对比剂的大小对引流淋巴结的 MR 成像对比有很强的依赖性。颗粒大小代表了被动和主动靶向效应，因此微米级的颗粒产生了延迟增强。
选择氧化铁颗粒的大小用于 MR 成像对比取决于观察的目的，例如识别淋巴结中免疫细胞的形态或迁移。
