Shear wave absolute vibro-elastography of the liver: method optimization and characterization

肝脏僵硬度和肝脏脂肪含量的测量可使肝病管理受益。肝脏硬度可以通过使用磁共振弹性成像（MRE）测量组织中剪切波的传播速度来评估，而无需活检。磁共振弹性成像（MRE）是一种将稳定振动应用于组织并测量整个组织体积的剪切波模式的技术。脂肪含量也可以通过磁共振成像来测量。我们需要的是磁共振成像质量测量的成本和超声提供的可及性。在最近与我们的合作伙伴的工作中，我们已经证明了电子扫描的3D超声换能器可以用于精确测量由组织模拟幽灵和健康志愿者的多频稳态振动引起的稳态波运动。该技术被称为S-WAVE，目前不能向操作员提供图像采集质量的实时反馈，也不能提供实时的刚度图。此外，对患者进行成像与对健康志愿者进行成像不同，因为他们的肝脏要硬得多，脂肪含量也高得多，而且涉及的患者通常体型较大，这使得无论是用核磁共振成像还是超声波扫描他们都很困难。与我们的合作伙伴在这个项目中，我们将：(1)开发在S-WAVE数据采集过程中实时显示二维剪切波图像和计算刚度图的方法，我们将评估系统在健康志愿者中的可用性和可重复性；(2)通过使用新的图像配准技术，比较S-WAVE和MRE获得的剪切模量和损失模量，并开发弹性和粘度成像方法及其对频率的依赖关系；(3)以MRI为金标准，建立超声衰减和横波衰减的脂肪含量模型。为了进行(2)和(3)所要求的建模，我们将使用(1)中开发的系统获取健康的志愿者和患者数据。我们的技术的优点是能够通过比核磁共振成像简单得多的检查，对肝脏体积进行深度成像。它的成功实施有可能产生重大影响。

Liver disease management can benefit from the measurement of liver stiffness and liver fat content. Liver stiffness can be assessed without biopsy by measuring the propagation speed of shear waves in tissue using magnetic resonance elastography (MRE), a technique in which a steady vibration is applied to tissue and the shear wave pattern throughout the tissue volume is measured. Fat content can also be measured with MR imaging. What is needed is MRI quality measurements at the cost and accessibility offered by ultrasound. In recent work with our partner, we have demonstrated that an electronically scanned 3D ultrasound transducer can be used to accurately measure steady-state wave motion induced by multi-frequency steady-state vibrations in tissue-mimicking phantoms and in healthy volunteers. The technique developed, called S-WAVE, currently does not provide real-time feedback to the operator on the quality of the image acquisition and does not provide the stiffness map in real time. Furthermore, imaging of patients is different than imaging healthy volunteers because their livers are much stiffer and have much higher fat content, and the patients involved are often large which makes scanning them difficult, whether by MRI or ultrasound. With our partner in this project, we will: (1) develop methods for real-time display of 2D shear-wave images during S-WAVE data acquisition and of the computed stiffness maps, and we will evaluate the usability and repeatability of the system in healthy volunteers; (2) compare shear and loss moduli acquired with S-WAVE and MRE, by using new image registration techniques, and also develop methods for imaging both elasticity and viscosity and their dependence on frequency; and (3) develop a model of fat content from ultrasound attenuation and shear wave attenuation, with MRI as the gold standard. To carry out the modeling required under (2) and (3), we will acquire healthy volunteer and patient data with the system developed in (1). Our technique has the advantage of being able to image the liver volume at depth, through a much simpler examination than by MRI. Its successful implementation has the potential to make a significant impact.