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（例如中风或头部创伤）的核心。现有的成像方法需要大型、固定式、高功率仪器，几乎不可能在专业环境之外部署，导致不必要的诊断和治疗延误，从而增加残疾和更高的死亡率。这个项目将创造一种设备，可以简单而快速地应用于任何病人，任何时间，任何地点，利用已经彻底改变了地球物理学成像的进步。我们将使用通过头部传输的超声波对大脑进行成像，并应用先进的计算机建模来消除头骨的扭曲效应，从而实现传统超声波无法实现的高分辨率高对比度大脑成像。石油工业已经投入大量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床。其中最重要的是“全波形反演”（FWI），这是一种计算密集型技术，通过对声波在三维物体中的传播进行精确建模来恢复该物体的详细内部特性。这个项目将对这项技术进行跨学科的调整和转移，以便它可以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。现有用于医学三维成像的主要技术有磁共振成像（MRI）、x射线计算机断层扫描（CT）和脉冲回波超声。MRI具有分辨率高、精度高等优点，但耗时长、价格昂贵、移动不便；如果没有初步的详细调查，以确保在任何新患者体内没有铁磁体，它就不能安全应用。x射线CT更便宜、更快，但它的分辨率通常低于MRI，软组织对比差，而且使用有害的电离辐射。传统的脉冲回波超声便宜、快速、便携，而且普遍安全，但它使用的高频穿透能力有限，而且特别容易被颅骨衰减和扭曲。因此，现有的超声波技术无法在完整的人类颅骨内成功地成像成人大脑。然而，低于通常用于成像的频率的超声波确实具有穿过头部所需的穿透能力。与传统技术相比，全波形反演能够使用低频数据产生精确的高分辨率图像；FWI还能够准确地补偿头骨产生的所有扭曲。因此，低频传输超声与全波形反演的结合能够产生整个人脑的高分辨率精确图像。这种方法的潜力已经在计算机和实验室模拟中得到了证明；该项目现在寻求在实验室中在活体人体上复制这一成功。安全，快速，定量，普遍适用，可连续部署，最重要的是医护人员可携带，我们的设备和方法旨在彻底改变大脑成像，在健康和疾病方面。中风是全球第二大过早死亡原因，也是导致成人残疾的主要原因，且日益严重。该技术与中风以及在资源有限和交通不便的环境中进行脑成像特别相关。

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 pulse-echo ultrasound. MRI is high resolution and high accuracy but is time consuming, expensive and immobile; it cannot be applied safely without a preliminary detailed investigation to ensure the absence of ferromagnetic bodies within any new patient. X-ray CT is cheaper and faster, but it is typically lower resolution than MRI, with poor soft-tissue contrast, and it uses harmful ionising radiation. Conventional pulse-echo ultrasound is cheap, fast, portable and universally safe, but it uses high frequencies that have limited penetration, and that are 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 and laboratory simulations; this project now seeks to replicate that success in the laboratory on a live human subject.Safe, fast, quantitative, 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.