发表机构
Utrecht University Medical Center（乌得勒支大学医学中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文针对经典布洛赫方程难以描述生物组织等异质材料磁共振动力学的问题，提出有效介质策略，构建保留拉莫尔力矩的非线性弛豫模型，为磁共振现象的有效介质描述提供了原则性基础。
AI 中文摘要
经典布洛赫方程是磁共振理论的基础，但可能不足以捕捉生物组织等异质材料中观测到的复杂有效动力学。本文提出一种有效介质策略，用于描述毫米立方级宏观尺度观测的磁共振动力学。该框架保留经典拉莫尔力矩，同时将弛豫项替换为通用非线性场（即有效介质项）。该场需满足旋转对称性、热平衡全局稳定性和耗散性等关键物理性质。这些要求实现了可容许弛豫场的完整表征，并为生成非线性弛豫模型提供了建设性框架。所得理论在特殊情况下可还原经典布洛赫动力学，为磁共振现象的有效介质描述提供了原则性基础。
英文摘要
The classical Bloch equation forms the foundation of magnetic resonance theory but may be insufficient to capture the complex effective dynamics observed in heterogeneous materials such as biological tissue. Here an effective-medium strategy is proposed to describe magnetic resonance dynamics from observations at macro-scale (order 1 mm$^3$). In this framework, the classical Larmor torque is retained while the relaxation term is replaced by a general nonlinear field (i.e. the effective medium term). This field is required to preserve key physical properties, including rotational symmetry, global stability of thermal equilibrium, and dissipativity. These requirements lead to a complete characterization of admissible relaxation fields and provide a constructive framework for generating nonlinear relaxation models. The resulting theory recovers classical Bloch dynamics as a special case and provides a principled foundation for effective-medium descriptions of magnetic resonance phenomena.
