Nanoparticle-based optical magnetometer for room-temperature magnetoencephalography

项目摘要 本计画旨在研制一种新型的室温脑磁图仪 (MEG)，一种功能性神经成像技术，允许通过以下方式直接对人脑电生理进行成像： 测量活动神经元产生的弱磁场。与功能性磁共振相比 由于其高时间分辨率，MEG在定位和跟踪大脑活动方面更有效。 最先进的MEG采用超导量子干涉器件（SQUID）或微加工 光泵磁力计（µ OPM）作为其传感元件。SQUID提供最高的灵敏度 但需要低温冷却，这严重限制了其便携性。µOPM提供了一种出色的替代方案， 大大降低了形状因子。然而，它仍然需要热绝缘（加热，而不是低温冷却） 并且与SQUID相比，它具有相当有限的带宽和动态范围。 所提出的新型磁力计被设计为大大提高信号强度和带宽， 降低了有源屏蔽的复杂性，并进一步减小了最小信道间隔。感测 该元件由均匀分散的磁铁矿纳米颗粒组成，在室温下工作。热 不再需要绝缘，因此传感元件可以放置在离人体1 mm的地方 头皮，增加信号强度。系统带宽基本上不受限制，而是通过 选择，以便在保持检测所有神经活动的能力的同时可以利用高质量的电子设备 从δ到高伽马频率带。所提出的系统采用芯片级克尔频率梳作为 光源和平衡的同轴Sagnac干涉仪作为光学读出。因此，它可以实现 在强环境下，磁力计灵敏度为20 fT/Hz 1/2，梯度计灵敏度为5 fT/cm Hz 1/2 100 µT的磁场，降低了场屏蔽的复杂性，并使传感器头的密集阵列成为可能。 这项研究有两个关键的创新。首先，磁铁矿纳米颗粒将被合成，稳定 在聚合物基质中并被制造成微光学器件。我们将研究使用不同的掺杂剂 物种和表面钝化，同时实现高费尔德常数，低插入损耗，以及良好的 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源 以同时操作mm尺寸的磁力计传感器头的阵列。我们将利用它的两个优势- 模式压缩特性，用于将噪声降低到量子极限以下，并进一步增强检测 我们的多通道磁梯度仪的灵敏度。在项目结束时，我们将进行基准测试和验证 我们的技术通过在听觉刺激下对两个正常人类受试者进行初步的体内研究。的 建议的磁力仪和梯度仪将大大提高MEG的准确性和便携性 系统，使其更广泛地适用于前线诊断。

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.