Next generation neuroimaging using optically pumped magnetometers

我们对人脑的了解在很大程度上来自功能神经成像--一系列极其强大的非侵入性技术，可以实时测量大脑活动，如功能磁共振成像(FMRI)或脑磁图(MEG)。然而，这些技术的最大局限性可能是它们严重依赖于在巨大而笨重的扫描仪中静止躺着的对象。例如，脑磁图测量大脑中的电流在头部外产生的磁场。在目前的设备中，对低温冷却磁场传感器的要求意味着这些传感器被固定在适当的位置，扫描过程中磁头的任何移动都会降低数据质量。对受试者留下来的要求仍然限制了可以扫描的受试者队列(例如，很难扫描儿童)和可以获得的实验范式的类型(例如，在自然任务期间，例如学习演奏乐器，或者当受试者沉浸在虚拟现实中时，测量大脑活动是具有挑战性的)。然而，随着量子技术被引入到功能成像中，这些限制正在解除。诺丁汉和其他地方正在开发新的量子可穿戴式脑磁图系统。这些系统围绕光泵式磁力计--可以直接安装在磁头上的小而轻的现场传感器--而构建。传感器放置的灵活性意味着系统可以适应任何头部形状或大小。此外，如果背景场被适当地清零，则受试者可以在数据收集期间自由移动。尽管这些新的可穿戴式扫描仪仍是一项新兴技术，但在实现新一代神经科学实验方面取得了重大进展。然而，人们对它们的基本能力知之甚少。在这个博士学位中，我们将致力于诺丁汉可穿戴MEG设备的开发、特性和应用，以期将其转化为商业设备。在基本层面上，我们将研究如何在头皮周围的优化阵列中部署OPM传感器，以最大化覆盖范围和空间分辨率。使用包括盲源分离在内的技术，我们将表征空间分辨率及其与传感器分离、传感器串扰(我们将对其进行数学建模)和信噪比(后者通过参考阵列测量来改善)的相关性。我们将致力于描述基于OPM的扫描仪的带宽：带宽对于临床研究尤为重要；在这里，我们将着眼于非常高频的测量，试图测量传统上被认为是OPM带宽高端之外的信号。最后，我们将开发新的实验范式。具体地说，我们将在诺丁汉新安装的磁屏蔽房间内建立一个虚拟现实洞穴，使用设置好的三个投影仪和偏振光。然后，我们将利用这一点来评估人脑在压力环境下对做出决定的反应。

Much of what we understand about the human brain comes from functional neuroimaging - a collection of extremely powerful non-invasive techniques which can measure brain activity in real time, such as functional magnetic resonance imaging (fMRI) or magnetoencephalography (MEG). However, perhaps the biggest limitation of these techniques is that they are heavily reliant on subjects lying very still within large and cumbersome scanners. For example, MEG measures magnetic fields outside the head generated by current flow in the brain. In current devices, the requirement for cryogenically cooled magnetic field sensors means that those sensors are fixed in position, and any head movement during scanning degrades the quality of the data. The requirement that subjects remain still limits both the subject cohorts that can be scanned (e.g. it is hard to scan children) and the types of experimental paradigm that can be accessed (e.g. it is challenging to measure brain activity during natural tasks such as learning to play a musical instrument, or whilst a subject is immersed in virtual reality). These limitations are however being lifted by the introduction of quantum technology to functional imaging. New quantum enabled 'wearable' MEG systems are now under development in Nottingham and elsewhere. These systems are built around optically pumped magnetometers - small and lightweight field sensors that can be mounted directly on the head. Flexibility in sensor placement means that systems can be adapted to any head shape or size. Further, if background fields are appropriately nulled, subjects can move freely during data collection. Though still a nascent technology, these new wearable scanners are making significant headway in enabling a new generation of neuroscientific experimentation. However, little is yet known about their fundamental capabilities. In this Ph.D., we will work on the development, characterisation, and application of Nottingham's wearable MEG device, with a view to turning it into a commercial device. At a fundamental level we will work on how to deploy OPM sensors in an optimised array around the scalp to maximise both coverage and spatial resolution. Using techniques including blind source separation we will characterise spatial resolution and its dependence on sensor separation, sensor cross talk (which we will mathematically model), and signal to noise ratio (the latter being improved by reference array measurements). We will work on characterising the bandwidth of the OPM based scanner: Bandwidth is particularly important for clinical studies; here we will look to very high frequency measurements, attempting to measure signals outside what is conventionally thought to be the higher end of the bandwidth of an OPM. Finally, we will develop new experimental paradigms. Specifically, using a three-projector set up and polarised light, we will build a virtual reality CAVE inside Nottingham's newly installed magnetically shielded room. We will then use this to assess how the human brain responds to making decisions in stressful situations.