Assländer Jakob, Novikov Dmitry S, Lattanzi Riccardo, Sodickson Daniel K, Cloos Martijn A
Department of Radiology, Center for Biomedical Imaging, New York University School of Medicine, New York, NY, USA.
Center for Advanced Imaging Innovation and Research, New York University School of Medicine, New York, NY, USA.
Commun Phys. 2019;2. doi: 10.1038/s42005-019-0174-0. Epub 2019 Jun 25.
The dynamics of large spin-1/2 ensembles are commonly described by the Bloch equation, which is characterized by the magnetization's non-linear response to the driving magnetic field. Consequently, most magnetic field variations result in non-intuitive spin dynamics, which are sensitive to small calibration errors. Although simplistic field variations result in robust spin dynamics, they do not explore the richness of the system's phase space. Here, we identify adiabaticity conditions that span a large experiment design space with tractable dynamics. All dynamics are trapped in a one-dimensional subspace, namely in the magnetization's absolute value, which is in a transient state, while its direction adiabatically follows the steady state. In this hybrid state, the polar angle is the effective drive of the spin dynamics. As an example, we optimize this drive for robust and efficient quantification of spin relaxation times and utilize it for magnetic resonance imaging of the human brain.
大自旋1/2系综的动力学通常由布洛赫方程描述，其特征是磁化强度对驱动磁场的非线性响应。因此，大多数磁场变化会导致非直观的自旋动力学，这种动力学对小的校准误差很敏感。虽然简单的磁场变化会导致稳健的自旋动力学，但它们并未探索系统相空间的丰富性。在这里，我们确定了跨越具有可处理动力学的大实验设计空间的绝热条件。所有动力学都被困在一个一维子空间中，即磁化强度的绝对值处于瞬态，而其方向绝热地跟随稳态。在这种混合状态下，极角是自旋动力学的有效驱动力。例如，我们优化这种驱动力以实现对自旋弛豫时间的稳健且高效的量化，并将其用于人类大脑的磁共振成像。
