Imaging the brain with ultrasound full-waveform inversion

快速脑成像是诊断和治疗急性神经系统疾病的核心，例如中风或头部创伤。现有的成像方法需要大型的、固定的、高功率的仪器，而这些仪器几乎不可能部署在专门的环境之外，导致不必要的诊断和治疗延迟，从而增加残疾和更高的死亡率。该项目将创造一种可以在任何时间、任何地点简单、快速地应用于任何患者的设备，利用已经彻底改变了地球物理学成像技术的进步。我们将使用穿过头部的超声波对大脑进行成像，应用先进的计算机建模来消除头骨的扭曲效应，从而实现常规超声波无法实现的高分辨率、高对比度的大脑成像。石油行业花了大笔资金开发先进的地球物理算法，以三维成像石油和天然气矿藏。其中最重要的是“全波形反转”(FWI)，这是一种计算密集的技术，在这种技术中，通过对声波在三维物体中传播的准确建模来恢复该物体的详细内部特性。该项目将对这项技术进行跨学科的调整和转移，以便将其直接应用于大脑的医学成像，从而实现更便宜、更快、更准确的临床诊断和治疗。目前用于三维医学成像的主要技术是磁共振成像(MRI)、X射线计算机断层扫描(CT)和反射超声。MRI具有高分辨率和高准确度，但耗时、昂贵和固定，如果没有初步的详细调查以确保任何新患者体内没有磁体，它就不能安全应用。X光CT更便宜也更快，但它的分辨率通常较低，软组织对比度较差，而且它使用有害的电离辐射。传统的反射式超声波便宜、快速、便携，而且普遍安全，但它使用的高频超声波穿透力有限，而且尤其受到头骨的衰减和扭曲。因此，现有的超声波技术无法在完整的人体头骨内成功地对成人大脑进行成像。然而，频率低于正常成像频率的超声波确实具有穿过头部所需的穿透力。全波形反演能够使用比传统技术更低的频率数据产生准确的高分辨率图像；FWI还能够准确地补偿头骨产生的所有扭曲。因此，将低频透射式超声波与全波形反转相结合，能够产生分辨率良好的整个人脑的准确图像。这种方法的潜力已经在计算机模拟中得到了证明；这个项目现在试图在实验室复制这种成功。安全、快速、普遍适用、可持续部署，最重要的是护理人员可以携带，我们的设备和方法旨在为健康和疾病领域的大脑成像带来革命性的变化。这项技术与中风尤其相关--中风是全球第二常见的过早死亡原因，也是导致成人残疾的主要、日益严重的原因--以及资源有限和无法进入的环境中的大脑成像。

Rapid brain imaging is central to the diagnosis and treatment of acute neurological conditions - for example stroke or head trauma. Existing imaging methods require large, immobile, high-power instruments that are near-impossible to deploy outside specialized environments, leading to unnecessarily delayed diagnosis and treatment, and consequent increased disability and higher fatality rates. This project will create a device that can be simply and rapidly applied to any patient, any time, any place, exploiting advances that have already revolutionised imaging in geophysics. We will image the brain using ultrasound waves, transmitted across the head, applying advanced computer modelling to remove the distorting effects of the skull, thereby enabling high-resolution high-contrast imaging of the brain unachievable by conventional ultrasound. The petroleum industry has spent large sums developing advanced geophysical algorithms to image oil and gas deposits in three dimensions. Foremost among these is "full-waveform inversion" (FWI), a computationally intensive technique in which accurate modelling of soundwave propagation through a three-dimensional object is used to recover the detailed internal properties of that object. This project will adapt and transfer that technology across disciplines so that it can be applied directly for medical imaging of the brain leading to cheaper, faster, more-accurate clinical diagnosis and treatment.The main existing technologies used in three-dimensional medical imaging are magnetic resonance imaging (MRI), x-ray computed tomography (CT), and reflection ultrasound. MRI is high resolution and high accuracy but is time consuming, expensive and immobile, and it cannot be applied safely without a preliminary detailed investigation to ensure the absence of magnetic bodies within any new patient. X-ray CT is cheaper and faster, but it is typically lower resolution, with poor soft-tissue contrast, and it uses harmful ionising radiation. Conventional reflection ultrasound is cheap, fast, portable and universally safe, but it uses high-frequency ultrasound that has limited penetration, and that is especially attenuated and distorted by the bones of the skull. Consequently, existing ultrasound technology is unable to image the adult brain successfully within an intact human skull.Ultrasound at frequencies below those normally used for imaging does however have the penetration required to travel right across the head. Full-waveform inversion is able to produce accurate high-resolution images using lower-frequency data than is possible using conventional techniques; FWI is also able to compensate accurately for all the distortions generated by the skull. Consequently, the combination of low-frequency transmitted ultrasound with full-waveform inversion is able to produce well-resolved accurate images of the entire human brain. The potential of this approach has already been demonstrated in computer simulations; this project now seeks to replicate that success in the laboratory. Safe, fast, universally applicable, deployable continuously, and above all portable by paramedics, our device and our approach aim to revolutionise brain imaging, in health and disease. The technology has particular relevance to stroke - globally the second-commonest cause of premature death and a major, growing cause of adult disability - and to brain imaging in resource-limited and inaccessible environments.