Magnetic resonance imaging (MRI) is one of the most widely used diagnostic tools in the clinic. To improve imaging quality, MRI contrast agents, which can modulate local T₁ and T₂ relaxation times, are often injected prior to or during MRI scans. However, clinically used contrast agents, including Gd³⁺-based chelates and iron oxide nanoparticles (IONPs), afford mediocre contrast abilities. To address this issue, there has been extensive research on developing alternative MRI contrast agents with superior r₁ and r₂ relaxivities. These efforts are facilitated by the fast progress in nanotechnology, which allows for preparation of magnetic nanoparticles (NPs) with varied size, shape, crystallinity, and composition. Studies suggest that surface coatings can also largely affect T₁ and T₂ relaxations and can be tailored in favor of a high r₁ or r₂. However, the surface impact of NPs has been less emphasized. Herein, we review recent progress on developing NP-based T₁ and T₂ contrast agents, with a focus on the surface impact.

中文翻译：

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对基于纳米粒子的磁共振成像造影剂的表面影响

磁共振成像（MRI）是临床上使用最广泛的诊断工具之一。为了提高成像质量，通常在 MRI 扫描之前或期间注射可以调节局部 T ₁和 T _{2弛豫时间的 MRI 造影剂。}然而，临床上使用的造影剂，包括基于 Gd ³⁺的螯合物和氧化铁纳米粒子 (IONP)，只能提供平庸的造影能力。_{为了解决这个问题，人们对开发具有优异 r 1}和 r ₂弛豫度的替代 MRI 造影剂进行了广泛的研究。纳米技术的快速进步促进了这些努力，纳米技术允许制备具有不同尺寸、形状、结晶度和成分的磁性纳米粒子（NP）。研究表明，表面涂层也会在很大程度上影响 T ₁和 T ₂弛豫，并且可以进行定制以支持高 r ₁或 r ₂。然而，纳米粒子的表面影响却很少受到重视。在此，我们回顾了开发基于 NP 的 T ₁和 T ₂造影剂的最新进展，重点关注表面影响。