High-resolution ultrasound imaging of micro-bubble cavitation using separate emission / reception transducers

使用单独的发射/接收换能器对微泡空化进行高分辨率超声成像

• 批准号: 571518-2021
• 负责人: Quaegebeur, Nicolas
• 金额: $ 3.28万
• 依托单位: Université de Sherbrooke
• 依托单位国家: 加拿大
• 项目类别: Alliance Grants
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=729177
• 关键词: resolution; ultrasound; imaging; micro; bubble

The use of microbubbles or cavitation agents has enabled a wide and rapidly expanding field of research, with their benefits being repeatedly demonstrated, both in localized drug delivery applications and ultrasound image enhancement. In both cases, the oscillations of microbubbles are exploited but their effects may vary depending on the ultrasound frequency and intensity. At low ultrasound intensities, the microbubbles oscillate in a stable motion, also known as stable cavitation, inducing linear reflection and harmonic response to an incident ultrasound field. In contrast, at higher ultrasound intensities, inertial cavitation characterized by rapid growth and collapse of the microbubbles occur, and is thus characterized by an extended bandwidth. Since high intensity ultrasound can cause irreversible thermal damage to tissue, inertial cavitation should be prevented, and the local intensity thus controlled. For this purpose, a dual system capable of focusing and monitoring the local intensity is required at the targeted area.Existing dual systems are based on the use of classical beamforming algorithms and dedicated ultrasound probe used for both cavitation and imaging with a central frequency selected to induce stable cavitation. However, due to the limited bandwidth of existing ultrasound probes, the harmonic imaging is often limited to the second harmonic. Other technologies based on the separation of therapeutic and imaging transducers have been proposed in the literature for low- and high-intensity focused ultrasound. Those assemblies allow separation of emission and reception but are cumbersome and limited in resolution, and thus not adapted to drug delivery or imaging within complex loci where the access window is limited to 1 cm2 at best (spinal cord or temporal bone window for instance). Moreover, in the case of constrained areas, surroundings organs (bones, interfaces) induce reflections, refraction and diffusion of ultrasound waves that may influence the focusing and imaging performance. Based on these observations, two challenges should be addressed in order to better exploit contrast agents in the case of complex loci for both focalization and imaging: 1) the design and manufacturing of dedicated compact transducers and 2) the adaptation of imaging algorithms for cavitation regime tracking with a limited data bandwidth. This research project is thus organized following three distinct thrusts, conducted in parallel by 2 PhD and 1 MASc students, that aim 1) to propose novel compact transducer design based on separate emission / reception and spatial compounding, 2) to adapt existing micro-machining techniques for compact theranostic transducer assemblies and 3) to develop high-resolution correlation-based imaging techniques for contrast agent imaging in complex media. Different applications will be considered using numerical simulations and in-vitro phantoms such as: spinal cord for which multiple reflections at the vertebra impair the imaging and focusing, and contrast agent-based transcranial applications for which the phase and amplitude aberrations induced by the transmission through the skull will be considered. Real-time implementation for clinical and pre-clinical researchers on a commercial ultrasound prototyping platform (Verasonics Vantage) will be achieved for use in a further project.

微泡或空化器的使用使研究领域得到了广泛和迅速的扩展，其好处在局部药物输送应用和超声图像增强方面都得到了反复证明。在这两种情况下，都利用了微泡的振荡，但它们的效果可能会因超声波频率和强度而异。在较低的超声强度下，微泡以稳定的运动方式振荡，也称为稳定空化，对入射超声场产生线性反射和谐响应。相反，在较高的超声强度下，以微泡的快速生长和崩溃为特征的惯性空化发生，因此以扩展的带宽为特征。由于高强度超声可对组织造成不可逆转的热损伤，应防止惯性空化，从而控制局部强度。为此，需要一个能够聚焦和监测目标区域局部强度的双重系统。现有的双重系统是基于使用经典的波束形成算法和用于空化和成像的专用超声探头，并选择中心频率来诱导稳定的空化。然而，由于现有超声探头的带宽有限，谐波成像往往局限于二次谐波。在低强度和高强度聚焦超声的文献中已经提出了基于治疗和成像换能器分离的其他技术。这些组件允许分离发射和接收，但繁琐且分辨率有限，因此不适合在访问窗口最多限制为1cm2的复杂部位内进行药物输送或成像(例如脊髓或颞骨窗口)。此外，在受限区域的情况下，周围器官(骨骼、界面)会引起超声波的反射、折射和扩散，这可能会影响聚焦和成像性能。基于这些观察，为了更好地利用造影剂在复杂位置进行聚焦和成像，应该解决两个挑战：1)专用紧凑型换能器的设计和制造；2)在有限数据带宽下对空化状态跟踪的成像算法的适应。因此，本研究项目由2名博士生和1名MASC学生并行进行，旨在1)提出基于独立发射/接收和空间复合的新型紧凑型换能器设计，2)将现有的微加工技术应用于紧凑型热声换能器组件，3)开发用于复杂介质中造影剂成像的高分辨率基于相关性的成像技术。将使用数值模拟和体外模型来考虑不同的应用，例如：脊髓，脊椎的多次反射损害成像和聚焦，以及基于造影剂的经颅应用，其中将考虑通过颅骨传输引起的相位和幅度像差。临床和临床前研究人员在商业超声原型平台(Verasonics Vantage)上的实时实施将用于进一步的项目。