Magnetic Detection & Imaging, TechMed Centre, University of Twente, Enschede, Netherlands.
Department of Vascular Surgery, Medisch Spectrum Twente, Enschede, Netherlands.
PLoS One. 2021 Aug 17;16(8):e0256252. doi: 10.1371/journal.pone.0256252. eCollection 2021.
Recently, there has been a renewed interest in low-field MRI. Contrast agents (CA) in MRI have magnetic behavior dependent on magnetic field strength. Therefore, the optimal contrast agent for low-field MRI might be different from what is used at higher fields. Ultra-small superparamagnetic iron-oxides (USPIOs), commonly used as negative CA, might also be used for generating positive contrast in low-field MRI. The purpose of this study was to determine whether an USPIO or a gadolinium based contrast agent is more appropriate at low field strengths. Relaxivity values of ferumoxytol (USPIO) and gadoterate (gadolinium based) were used in this research to simulate normalized signal intensity (SI) curves within a concentration range of 0-15 mM. Simulations were experimentally validated on a 0.25T MRI scanner. Simulations and experiments were performed using spin echo (SE), spoiled gradient echo (SGE), and balanced steady-state free precession (bSSFP) sequences. Maximum achievable SIs were assessed for both CAs in a range of concentrations on all sequences. Simulations at 0.25T showed a peak in SIs at low concentrations ferumoxytol versus a wide top at higher concentrations for gadoterate in SE and SGE. Experiments agreed well with the simulations in SE and SGE, but less in the bSSFP sequence due to overestimated relaxivities in simulations. At low magnetic field strengths, ferumoxytol generates similar signal enhancement at lower concentrations than gadoterate.
最近，人们对低磁场 MRI 重新产生了兴趣。MRI 中的造影剂（CA）的磁性能取决于磁场强度。因此，低磁场 MRI 的最佳造影剂可能与高磁场使用的造影剂不同。超顺磁性氧化铁（USPIO）通常用作阴性 CA，也可用于在低磁场 MRI 中产生正对比。本研究的目的是确定 USPIO 或基于钆的造影剂在低场强度下更合适。本研究使用 ferumoxytol（USPIO）和 gadoterate（基于钆的造影剂）的弛豫率值来模拟浓度范围为 0-15 mM 的归一化信号强度（SI）曲线。在 0.25T MRI 扫描仪上对模拟进行了实验验证。使用自旋回波（SE）、扰相梯度回波（SGE）和平衡稳态自由进动（bSSFP）序列进行了模拟和实验。在所有序列上，评估了两种 CA 在一系列浓度下的最大可实现 SI。在 SE 和 SGE 中，与 gadoterate 相比，在低浓度下，ferumoxytol 的 SI 峰值较高，而在较高浓度下，gadoterate 的 SI 峰值较宽。实验在 SE 和 SGE 中与模拟结果吻合良好，但在 bSSFP 序列中吻合不佳，因为模拟中的弛豫率值过高。在低磁场强度下，ferumoxytol 在较低浓度下产生的信号增强与 gadoterate 相似。
