Shear-mode Transcranial Ultrasound Imaging

描述(由申请人提供)： 超声脑成像有可能提供一种低成本、便携的方法来成像血流、检测出血和诊断某些脑部疾病。然而，颅骨的变形和低信噪比严重限制了经颅多普勒超声(TCD)和经颅彩色编码超声(TCCS)等现有临床设备的使用。信号退化是由颅骨的反射、折射、衰减和散射引起的。然而，我们最近的工作表明，在某些条件下，通过使用大入射角度，可以以更小的失真和更高的信号幅度通过颅骨传播超声波。数值和实验研究都表明，这是由于颅骨中诱导的剪切模式的行为。当超声入射角超过斯内尔的纵向压力波的临界角时，在骨骼中的传播纯粹是由于剪切波。然后，这一波在大脑中转换回纵向声波。这种从纵波(皮肤)到横波(头骨)再到纵波(大脑)的转换不一定会产生高度扭曲或小幅度的波。初步数据显示，通过头骨获得的高角度信号可能比纵向信号的失真要小。这项建议调查了这样一种想法，即通过横波而不是纵向声学模式在颅骨中传播可以实现经颅超声成像的实质性改进。同时，本工作设计的多周期编码激励序列将显著提高整体信号强度。由此产生的图像预计将经历更少的失真和更高的SNR，从而获得更清晰、更准确的大脑图像。这项研究将测试经颅剪切模式在一些成像问题上的应用，包括血管检测、肿瘤检测、组织形态和脑出血。这项研究将提供有关人类头骨物理特性的新数据，并将包括对超声波检测大脑功能的能力的有价值的评估。这项高风险的提案可能会为大脑的临床诊断提供相当大的好处。它可能提供一种可以在临床上操作的非电离成像方法，同时将一种新技术引入医学和生物成像。

DESCRIPTION (provided by applicant): Ultrasound brain imaging holds the potential to provide a low cost, and portable method for imaging blood flow, detecting hemorrhaging, and diagnosing certain brain disorders. However, distortion and low signal to noise ratios (SNR) caused by the skull have severely limited the use of existing clinical devices such as trancranial Doppler sonography (TCD) and transcranial color coded sonography (TCCS). Signal degradation is caused by reflection, refraction, attenuation, and scattering by the skull. Our recent work, however, indicates that under certain conditions it is possible to propagate ultrasound through the skull with reduced distortion and higher signal amplitudes by using high incident angles. Both numeric and experimental investigation suggest this is due to the behavior of shear modes induced in the skull bone. When the ultrasound angle of entry is beyond Snell's critical angle for the longitudinal pressure wave, propagation in the bone is purely due to a shear wave. This wave then converts back to a longitudinal acoustic wave in the brain. This conversion from a longitudinal wave (skin) to a shear wave (skull) and again to a longitudinal wave (brain) does not necessarily produce a highly distorted or small-amplitude wave. Preliminary data shows that a signal obtained through the skull at high angles may be less distorted than a longitudinal one. This proposal investigates the idea that substantial improvement of transcranial ultrasound imaging can be achieved by propagating through the skull as a shear wave as opposed to a longitudinal acoustic mode. Simultaneously, a multi-cycle coded excitation sequence, devised in the present work, will significantly increase overall signal strength. The resulting images are expected to experience reduced distortion and increased an SNR, allowing clearer and more accurate brain images. The investigation will test the application of the transcranial shear mode to a number of imaging problems including the vessel detection, tumor detection, tissue morphology, and hemorrhaging in the brain. This study will provide new data on physical properties of human skulls, and will include a valuable assessment of the ability of ultrasound to detect features in the brain. The high-risk proposal could provide considerable benefits to clinical diagnostics of the brain. It could potentially offer a non-ionizing imaging method that could in operate clinically, while introducing a new technique into medical and biological imaging.