Department of Physics, University of Colorado, Boulder, CO, 80309, USA.
National Institute of Standards and Technology, Boulder, CO, 80305, USA.
Sci Rep. 2023 Jul 17;13(1):11520. doi: 10.1038/s41598-023-38222-6.
We have investigated the efficacy of superparamagnetic iron oxide nanoparticles (SPIONs) as positive T contrast agents for low-field magnetic resonance imaging (MRI) at 64 millitesla (mT). Iron oxide-based agents, such as the FDA-approved ferumoxytol, were measured using a variety of techniques to evaluate T contrast at 64 mT. Additionally, we characterized monodispersed carboxylic acid-coated SPIONs with a range of diameters (4.9-15.7 nm) in order to understand size-dependent properties of T contrast at low-field. MRI contrast properties were measured using 64 mT MRI, magnetometry, and nuclear magnetic resonance dispersion (NMRD). We also measured MRI contrast at 3 T to provide comparison to a standard clinical field strength. SPIONs have the capacity to perform well as T contrast agents at 64 mT, with measured longitudinal relaxivity (r) values of up to 67 L mmol s, more than an order of magnitude higher than corresponding r values at 3 T. The particles exhibit size-dependent longitudinal relaxivities and outperform a commercial Gd-based agent (gadobenate dimeglumine) by more than eight-fold at physiological temperatures. Additionally, we characterize the ratio of transverse to longitudinal relaxivity, r/r and find that it is ~ 1 for the SPION based agents at 64 mT, indicating a favorable balance of relaxivities for T-weighted contrast imaging. We also correlate the magnetic and structural properties of the particles with models of nanoparticle relaxivity to understand generation of T contrast. These experiments show that SPIONs, at low fields being targeted for point-of-care low-field MRI systems, have a unique combination of magnetic and structural properties that produce large T relaxivities.
我们研究了超顺磁氧化铁纳米粒子（SPIONs）作为正 T 对比剂在 64 毫特斯拉（mT）低场磁共振成像（MRI）中的功效。基于氧化铁的试剂，如已获得 FDA 批准的 ferumoxytol，使用各种技术进行了测量，以评估在 64 mT 时的 T 对比。此外，我们对一系列直径（4.9-15.7nm）的单分散羧酸涂层 SPIONs 进行了表征，以了解低场下 T 对比的尺寸依赖性。使用 64 mT MRI、磁强计和核磁共振弥散（NMRD）测量 MRI 对比特性。我们还测量了在 3 T 时的 MRI 对比，以与标准临床场强进行比较。SPIONs 在 64 mT 时具有良好的 T 对比剂性能，测量的纵向弛豫率（r）值高达 67 L mmol s，比 3 T 时的相应 r 值高一个数量级以上。这些粒子表现出尺寸依赖性的纵向弛豫率，并在生理温度下比商业 Gd 基试剂（钆贝葡胺）高出超过八倍。此外，我们对横向与纵向弛豫率的比值 r/r 进行了表征，发现它在 64 mT 时对于基于 SPION 的试剂约为 1，这表明在 T 加权对比成像中弛豫率具有良好的平衡。我们还将粒子的磁性和结构特性与纳米粒子弛豫率模型相关联，以了解 T 对比的产生。这些实验表明，SPIONs 在针对即时护理低场 MRI 系统的低场中，具有产生大 T 弛豫率的独特磁性和结构特性组合。
