Institute of Physical Chemistry, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany.
ACS Nano. 2012 Feb 28;6(2):1619-24. doi: 10.1021/nn204591r. Epub 2012 Jan 31.
Concerning the outer sphere relaxation theory, the sensitivity of a T(2) MRI contrast agent, expressed by the transverse relaxivity r(2), depends on the diffusion length of water molecules relative to the particle size. For T(2)-weighted spin-echo imaging, theoretical concepts reveal three regimes regarding the r(2) relaxivity depending on the nanocrystal size: the motional averaging regime (MAR), the static dephasing regime (SDR), and the echo-limiting regime (ELR). The r(2) maximum corresponds to the SDR, which represents a small size regime. To verify the theoretical concepts and to adjust the SDR, tailor-made T(2) contrast agents were synthesized by controlled self-assembly of superparamagnetic iron oxide nanocrystals (SPIOs) into raspberry-like nanoclusters with diameters of 30-200 nm using a PEG-based ligand. The results highlight an opportunity to optimize the relaxivity of T(2) contrast agents by tuning the cluster size of SPIO nanocrystals.
关于外球弛豫理论，T2 MRI 对比剂的灵敏度，用横向弛豫率 r(2) 表示，取决于水分子的扩散长度相对于颗粒大小。对于 T2 加权自旋回波成像，理论概念揭示了纳米晶大小对 r(2)弛豫率的三种影响：运动平均化（MAR）、静态去相位（SDR）和回波限制（ELR）。r(2)最大值对应于 SDR，代表小尺寸区域。为了验证理论概念并调整 SDR，通过控制超顺磁性氧化铁纳米晶（SPIOs）在基于 PEG 的配体的作用下自组装成直径为 30-200nm 的覆盆子状纳米簇，合成了定制的 T2 对比剂。结果表明，通过调整 SPIOs 纳米晶的簇大小，可以优化 T2 对比剂的弛豫率。
