RASER MRI：利用协同非线性相互作用自发形成的磁共振图像
RASER MRI: Magnetic Resonance Images formed Spontaneously exploiting Cooperative Nonlinear Interaction
摘要：
磁共振成像（MRI）的空间分辨率从根本上受到与横向磁化指数衰减率（1/T2*）相关联的洛伦兹点扩散函数（PSF）的宽度的限制。在这里，我们通过在成像介质中建立RASER（受激发射辐射射频放大）来显示MRI中的不同对比机制。当在弱磁场梯度中放置具有充分粒子数反转的自旋时，RASER成像突发从噪声中出现，并且不施加（射频）RF脉冲。初始粒子数反转密度的微小差异产生比常规MRI更强的图像对比度。这种对比是基于所有切片之间的合作非线性相互作用。另一方面，合作的非线性相互作用引起成像伪影，如幅度失真和成像域之外的旁瓣。对比度和伪影都通过实验证明，并根据所提出的理论通过模拟进行预测。RASER MRI的这一理论与协同学和非线性动力学相关的许多其他不同领域密切相关。
英文摘要：
The spatial resolution of magnetic resonance imaging (MRI) is fundamentally limited by the width of Lorentzian point spread functions (PSF) associated with the exponential decay rate of transverse magnetization (1/T2*). Here we show a different contrast mechanism in MRI by establishing RASER (Radio-frequency Amplification by Stimulated Emission of Radiation) in imaged media. RASER imaging bursts emerge out of noise and without applying (Radio Frequency) RF pulses when placing spins with sufficient population inversion in a weak magnetic field gradient. A small difference in initial population inversion density creates a stronger image contrast than conventional MRI. This contrast is based on the cooperative nonlinear interaction between all slices. On the other hand, the cooperative nonlinear interaction gives rise to imaging artifacts, such as amplitude distortions and side lobes outside of the imaging domain. Both the contrast and the artifacts are demonstrated experimentally and predicted by simulations based on a proposed theory. This theory of RASER MRI is strongly connected to many other distinct fields related to synergetics and non-linear dynamics.
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