Magnetic nanoparticles have many advantages in medicine such as their use in non-invasive imaging as a Magnetic Particle Imaging (MPI) tracer or Magnetic Resonance Imaging contrast agent, the ability to be externally shifted or actuated and externally excited to generate heat or release drugs for therapy. Existing nanoparticles have a gentle sigmoidal magnetization response that limits resolution and sensitivity. Here it is shown that superferromagnetic iron oxide nanoparticle chains (SFMIOs) achieve an ideal step-like magnetization response to improve both image resolution & SNR by more than tenfold over conventional MPI. The underlying mechanism relies on dynamic magnetization with square-like hysteresis loops in response to 20 kHz, 15 kAm⁻¹ MPI excitation, with nanoparticles assembling into a chain under an applied magnetic field. Experimental data shows a “1D avalanche” dipole reversal of every nanoparticle in the chain when the applied field overcomes the dynamic coercive threshold of dipole-dipole fields from adjacent nanoparticles in the chain. Intense inductive signal is produced from this event resulting in a sharp signal peak. Novel MPI imaging strategies are demonstrated to harness this behavior towards order-of-magnitude medical image improvements. SFMIOs can provide a breakthrough in noninvasive imaging of cancer, pulmonary embolism, gastrointestinal bleeds, stroke, and inflammation imaging.

中文翻译：

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超铁磁纳米粒子在磁粒子成像中实现数量级的分辨率和灵敏度增益

磁性纳米粒子在医学上有许多优点，例如它们在非侵入性成像中用作磁粒子成像 (MPI) 示踪剂或磁共振成像造影剂，能够从外部移动或驱动，并在外部激发以产生热量或释放药物治疗。现有的纳米粒子具有温和的 S 型磁化响应，限制了分辨率和灵敏度。这里表明，超铁磁性氧化铁纳米粒子链 (SFMIO) 实现了理想的阶梯状磁化响应，从而将图像分辨率和 SNR 提高了传统 MPI 的十倍以上。基本机制依赖于响应于 20 kHz、15 kAm ^{-1的具有方形磁滞回线的动态磁化}MPI 激发，纳米粒子在外加磁场下组装成链。实验数据显示，当施加的场克服来自链中相邻纳米粒子的偶极-偶极场的动态矫顽力阈值时，链中每个纳米粒子的“一维雪崩”偶极反转。该事件会产生强烈的感应信号，从而导致尖锐的信号峰值。新的 MPI 成像策略被证明可以利用这种行为来实现数量级的医学图像改进。SFMIO 可以在癌症、肺栓塞、胃肠道出血、中风和炎症成像的无创成像方面提供突破。