Department of Earth Science and Engineering, Imperial College London, London, UK; Department of Bioengineering, Imperial College London, London, UK.
Department of Bioengineering, Imperial College London, London, UK.
Ultrasound Med Biol. 2022 Oct;48(10):1995-2008. doi: 10.1016/j.ultrasmedbio.2022.05.023. Epub 2022 Jul 25.
The main techniques used to image the brain and obtain structural data are magnetic resonance imaging and X-ray computed tomography. These techniques produce images with high spatial resolution, but with the disadvantage of requiring very large equipment with special installation needs. In addition, X-ray tomography uses ionizing radiation, which limits their use. Ultrasound imaging is a safe technology that is delivered using compact and mobile devices. However, conventional ultrasound reconstruction techniques have failed to obtain images of the brain because of, fundamentally, the presence of the skull and the distortion that it produces on ultrasound. Recent studies have indicated that full-waveform inversion, a computational technique originally from Earth science, has the potential to generate accurate 3-D images of the brain. This technology can overcome the limitations of conventional ultrasound imaging, but a prototype for transcranial applications does not yet exist. Here, we investigate different designs of an annular array of ultrasound transducers to optimize the number of elements and rotations needed to conduct transcranial imaging with full-waveform inversion. This device uses small-diameter, low-frequency transducers that readily propagate ultrasound through the skull with good signal-to-noise ratios. It also incorporates the use of rotations to produce a high-density coverage of the target and acquire redundant traces that are beneficial for full-waveform inversion. We have built a ring of 40 transducers to illustrate that this design is capable of reconstructing images of the brain, retrieving its anatomy and acoustic properties with millimeter resolution. Laboratory results reveal the ability of this device to successfully image a 2.5-D brain- and skull-mimicking phantom using full-waveform inversion. To our knowledge, this is the first prototype ever used for transcranial-like imaging. The importance of these findings and their implications for the design of a 3-D reconstruction system with possible clinical applications are discussed.
用于对大脑进行成像并获取结构数据的主要技术是磁共振成像和 X 射线计算机断层扫描。这些技术产生具有高空间分辨率的图像，但缺点是需要具有特殊安装需求的非常大的设备。此外，X 射线断层扫描使用电离辐射，这限制了它们的使用。超声成像是一种安全的技术，使用紧凑且移动的设备来提供。然而，由于颅骨的存在及其在超声中产生的失真，传统的超声重建技术未能获得大脑图像。最近的研究表明，全波反演，一种最初来自地球科学的计算技术，具有生成大脑准确 3D 图像的潜力。该技术可以克服传统超声成像的局限性，但尚未存在用于颅穿透应用的原型。在这里，我们研究了超声换能器的环形阵列的不同设计，以优化进行全波反演颅穿透成像所需的元素数量和旋转次数。该设备使用小直径、低频换能器，可通过颅骨很好地传播具有良好信噪比的超声波。它还结合了旋转的使用，以产生目标的高密度覆盖并获取对全波反演有益的冗余迹线。我们已经构建了一个 40 个换能器的环，以说明这种设计能够重建大脑图像，以毫米分辨率检索其解剖结构和声学特性。实验室结果表明，该设备能够使用全波反演成功地对大脑和颅骨模拟体的 2.5D 图像进行成像。据我们所知，这是首次用于颅穿透样成像的原型。讨论了这些发现的重要性及其对具有可能临床应用的 3D 重建系统设计的意义。
