Low-field MRI can be more sensitive than high-field MRI
Low-field MRI can be more sensitive than high-field MRI
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DOI：
10.1016/j.jmr.2013.10.013
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发表时间：
2013-12-01
影响因子：
2.2
通讯作者：
Chekmenev, Eduard Y.
中科院分区：
文献类型：
--
作者：
Coffey, Aaron M.;Truong, Milton L.;Chekmenev, Eduard Y.
磁共振成像的信噪比是影响图像质量的关键因素。常规地，SNR与核自旋极化成比例，核自旋极化与磁场强度成线性比例。然而，越来越强的磁铁存在许多技术和财务限制。低场MRI可以从非平衡“超极化”方案中以等效SNR减轻这些约束，该方案独立于磁场而增加极化的数量级。这里，理论和实验验证表明，场独立极化（例如超极化）与频率优化的MRI检测线圈（即，使用最大允许导体长度的多匝线圈）的组合导致低场MRI灵敏度接近并且甚至与高场MRI的灵敏度相媲美。使用具有相同数量的H-1和C-13自旋的样品测试四个读出频率。0.0475 T下的实验SNR与4.7 T下获得的SNR的40%相似。保守地说，在0.0475 T下的理论SNR可能比在4.7 T下的SNR高1.13倍，尽管检测频率低100倍，这表明在没有技术上具有挑战性的昂贵高场磁体的情况下，高灵敏度MRI是可行的。在4.7 T和0.0475 T下的数据是从具有不同RF探针的不同光谱仪获得的。两种场强之间的SNR比较说明了参数的许多差异，例如系统噪声系数和探头检测线圈的变化，包括Q因子和线圈直径。(C)2013 Elsevier Inc. All rights reserved.
MRI signal-to-noise ratio (SNR) is the key factor for image quality. Conventionally, SNR is proportional to nuclear spin polarization, which scales linearly with magnetic field strength. Yet ever-stronger magnets present numerous technical and financial limitations. Low-field MRI can mitigate these constraints with equivalent SNR from non-equilibrium 'hyperpolarization' schemes, which increase polarization by orders of magnitude independently of the magnetic field. Here, theory and experimental validation demonstrate that combination of field independent polarization (e.g. hyperpolarization) with frequency optimized MRI detection coils (i.e. multi-turn coils using the maximum allowed conductor length) results in low-field MRI sensitivity approaching and even rivaling that of high-field MRI. Four read-out frequencies were tested using samples with identical numbers of H-1 and C-13 spins. Experimental SNRs at 0.0475 T were,similar to 40% of those obtained at 4.7 T. Conservatively, theoretical SNRs at 0.0475T 1.13-fold higher than those at 4.7 T were possible despite an similar to 100-fold lower detection frequency, indicating feasibility of high-sensitivity MRI without technically challenging, expensive high-field magnets. The data at 4.7 T and 0.0475 T was obtained from different spectrometers with different RF probes. The SNR comparison between the two field strengths accounted for many differences in parameters such as system noise figures and variations in the probe detection coils including Q factors and coil diameters. (C) 2013 Elsevier Inc. All rights reserved.