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

肝脏硬度和肝脏脂肪含量的测量有助于肝脏疾病的治疗。通过磁共振弹性成像(MRE)测量剪切波在组织中的传播速度，可以在不进行活检的情况下评估肝脏硬度。磁共振弹性成像是一种对组织施加稳定振动并测量整个组织体积的剪切波模式的技术。脂肪含量也可以用磁共振成像来测量。需要的是以超声波提供的成本和可及性进行MRI质量测量。在最近与我们的合作伙伴的工作中，我们展示了电子扫描的3D超声换能器可以用来精确测量模拟组织模体和健康志愿者中由多频稳态振动引起的稳态波动。开发的技术称为S波，目前不能就图像采集质量向操作员提供实时反馈，也不能实时提供刚度图。此外，患者的成像与为健康志愿者成像不同，因为他们的肝脏要僵硬得多，脂肪含量也高得多，而且涉及的患者往往很大，这使得扫描他们变得困难，无论是通过MRI还是超声波。与我们在这个项目中的合作伙伴将：(1)开发在S波数据采集过程中实时显示2D横波图像和计算的刚度图的方法，我们将评估该系统在健康志愿者中的可用性和重复性；(2)通过新的图像配准技术，比较用S波和MRE获取的剪切和损失模量，还将建立弹性和粘度及其随频率的依赖关系的成像方法；(3)以磁共振成像为金标准，建立基于超声衰减和剪切波衰减的脂肪含量模型。为了执行(2)和(3)中所要求的建模，我们将使用(1)中开发的系统获取健康志愿者和患者的数据。我们的技术的优势是能够通过比MRI简单得多的检查来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.