Nano Lett. 2020 Oct 14;20(10):7207-7212. doi: 10.1021/acs.nanolett.0c02549. Epub 2020 Sep 14.
Paramagnetic relaxation enhancement (PRE) is the current strategy of choice for enhancing magnetic resonance imaging (MRI) contrast and for accelerating MRI acquisition schemes. Yet, debates regarding lanthanides' biocompatibility and PRE-effect on MRI signal quantification have raised the need for alternative strategies for relaxation enhancement. Herein, we show an approach for shortening the spin-lattice relaxation time (T) of fluoride-based nanocrystals (NCs) that are used for in vivo F-MRI, by inducing crystal defects in their solid-crystal core. By utilizing a phosphate-based rather than a carboxylate-based capping ligand for the synthesis of CaF NCs, we were able to induce grain boundary defects in the NC lattice. The obtained defects led to a 10-fold shorter T of the NCs' fluorides. Such paramagnetic-free relaxation enhancement of CaF NCs, gained without affecting either their size or their colloidal characteristics, improved 4-fold the obtained F-MRI signal-to-noise ratio, allowing their use, in vivo, with enhanced hotspot MRI sensitivity.
顺磁弛豫增强（PRE）是目前增强磁共振成像（MRI）对比度和加速 MRI 采集方案的首选策略。然而，关于镧系元素的生物相容性和 PRE 对 MRI 信号定量的影响的争论，引发了对替代弛豫增强策略的需求。在此，我们展示了一种通过在其固晶核中诱导晶体缺陷来缩短用于体内 F-MRI 的基于氟化物的纳米晶体（NCs）的自旋晶格弛豫时间（T）的方法。通过利用基于磷酸盐而不是基于羧酸盐的封端配体来合成 CaF NCs，我们能够在 NC 晶格中诱导晶界缺陷。所获得的缺陷导致 NC 氟化物的 T 缩短了 10 倍。这种无顺磁性的 CaF NCs 弛豫增强是在不影响其尺寸或胶体特性的情况下获得的，将获得的 F-MRI 信噪比提高了 4 倍，从而允许其在体内使用，以增强热点 MRI 的灵敏度。
