Nanoparticle-based optical magnetometer for room-temperature magnetoencephalography

项目总结 本项目旨在研制一种用于室温脑磁图的新型磁强计。 (MEG)，这是一种功能性神经成像技术，可以通过以下方式直接成像人类大脑电生理 测量活动神经元产生的弱磁场。与功能磁共振相比 由于其高时间分辨率，脑磁图在定位和跟踪大脑活动方面更有效。 最先进的MEG使用超导量子干涉装置(SQUID)或微制造 光泵磁力计(µOPM)作为其传感元件。鱿鱼提供最高的敏感度 但需要低温冷却，这严重限制了它的便携性。µOPM提供了一个出色的替代方案， 大大降低了外形尺寸。然而，它仍然需要隔热(加热而不是低温冷却) 与SQUID相比，它的带宽和动态范围相当有限。 提出的新型磁强计旨在极大地提高信号强度和带宽， 降低主动屏蔽的复杂性，进一步降低最小通道间隔。感官 元素由均匀分散的磁铁纳米颗粒组成，在室温下运行。热能 不再需要绝缘，因此传感元件可以放置在距离人体1 mm的地方 头皮，增加信号强度。系统带宽从根本上不受限制，而是设置为1 khz 选择，这样就可以利用高质量的电子设备，同时保持检测所有神经活动的能力 从三角洲频段到高频伽马频段。所提出的系统采用芯片级克尔频率梳作为 光源和平衡式直列式Sagnac干涉仪作为光学读出装置。因此，它可以实现 在强环境下，磁力计灵敏度为20ft/Hz1/2，梯度计灵敏度为5ft/cm∙Hz1/2 100µT的场强，降低了场屏蔽的复杂性，并使密集的传感器磁头阵列成为可能。 这项拟议的研究有两个关键创新。首先，将合成磁铁矿纳米颗粒，使其稳定 在聚合物基质中，并制造成微型光学器件。我们将调查不同掺杂剂的使用情况 物种和表面钝化同时实现高Verdet常数、低插入损耗和良好的 适用于MEG应用的长期稳定性。其次，我们将采用一种新的芯片级频率梳状源 以同时操作毫米大小的磁力计传感器磁头阵列。我们将利用它的两个优势- 模压缩特性使噪声降到量子极限以下，进一步提高探测能力 我们的多通道磁梯度仪的灵敏度。在计划结束时，我们将进行基准测试和验证 我们的技术通过对两名正常人在听觉刺激下的体内初步研究。这个 提出的磁强计和梯度计将显著提高磁强计的精度和便携性。 系统，使其更广泛地适用于一线诊断。

PROJECT SUMMARY This project is aimed at developing a novel magnetometer for room-temperature magnetoencephalography (MEG), a functional neuroimaging technique that allows direct imaging of human brain electrophysiology by measurement of weak magnetic fields generated by active neurons. Compared to functional magnetic resonance imaging, MEG is more effective in localizing and tracking brain activities thanks to its high temporal resolution. State-of-the-art MEG employs either superconducting quantum interference device (SQUID) or microfabricated optically pumped magnetometers (µOPMs) as their sensing elements. SQUID provides the highest sensitivity but requires cryogenic cooling, which severely limits its portability. µOPM offers an excellent alternative with much reduced form factor. However, it still requires thermal insulation (heating as opposed to cryogenic cooling) and it has a rather limited bandwidth and dynamic range compared to SQUID. The proposed new type of magnetometer is designed to greatly improve the signal strength and bandwidth, reduce the complexity of active shielding and further decrease the minimum channel spacing. The sensing element consists of uniformly dispersed magnetite nanoparticles that operate at room temperature. Thermal insulation is no longer needed, and thus the sensing element can be placed as close as 1 mm to the human scalp, increasing the signal strength. The system bandwidth is not fundamentally limited but set to be 1 kHz by choice so that high-quality electronics can be utilized while maintaining the capability to detect all neural activities from delta to high gamma frequency bands. The proposed system employs chip-scale Kerr frequency comb as the light source and balanced in-line Sagnac interferometer as the optical readout. It can thus achieve a magnetometer sensitivity of 20 fT/Hz1/2 and a gradiometer sensitivity of 5 fT/cm∙Hz1/2 under a strong ambient field of 100 µT, reducing the complexity in field-shielding and making possible a dense array of sensor heads. The proposed research has two key innovations. First, magnetite nanoparticles will be synthesized, stabilized in polymer matrices and fabricated into micro-optical devices. We will investigate the use of different dopant species and surface passivation to simultaneously achieve high Verdet constant, low insertion loss, and good long-term stability for MEG applications. Second, we will incorporate a novel chip-scale frequency comb source to simultaneously operate an array of mm-size magnetometer sensor heads. We will take advantage of its two- mode squeezing property for noise reduction to below the quantum limit and further enhance the detection sensitivity of our multichannel magnetic gradiometer. At the end of the program, we will benchmark and validate our technology by a preliminary in vivo study of two normal human subjects under auditory stimulation. The proposed magnetometer and gradiometer would significantly improve the accuracy and portability of MEG system, making it much more widely applicable to frontline diagnostics.