Novel Transducer Technology for Transcranial Ultrasound

项目摘要 脑转移瘤是最常见的恶性颅内肿瘤，发生在高达40%的癌症患者中。 如果不治疗，预后很差，预期寿命只有1个月。手术和放疗通常 联合治疗脑转移瘤;然而，随着原发性癌症治疗的改善， 患有脑转移的患者群体已经增加，因此正在寻求最小化或 避免侵入性手术的风险和辐射对大脑的毒性作用。虽然立体定向放射 越来越多地用于限制全脑放射的副作用，肿瘤控制可能不如 立体定向手术一种可能的替代方案，磁共振引导的聚焦超声，正在被 研究作为一种非侵入性手段消融脑肿瘤和增加癌症治疗的交付 穿过血脑屏障 将超声波发射到大脑中的常规技术传统上是通过以下方式实现的： 由大量单元件换能器组成的大孔径球形换能器的方法 通过头骨发射超声波束这些换能器的几何聚焦限制了治疗 然而，大多数癌症，尤其是转移瘤，发生在沿着 大脑的外围。此外，颅骨显著衰减超声波。为了补偿 衰减的能量，并在焦点处实现足够的可输送功率， 换能器（即，输入功率）必须保持足够高。即使在中等输入功率下也能实现高吸收 导致颅骨内过热，需要主动冷却以防止烧伤骨骼或皮肤。 为了解决上述困难，我们提出了一种新的楔形换能器阵列 将聚焦超声波引入大脑的技术。阵列将超声波耦合到大脑中 通过双模转换：从楔中的纵波到颅骨中的高阶兰姆波， 然后从颅骨中的高阶兰姆波到大脑中的纵波。我们方法的好处 是提高效率，减少头骨发热，解决大脑中 靠近头骨，并且可以在更宽的频率范围内自由操作。治疗和神经调节 使用这种类型的耦合技术的应用仍将依赖于诸如MR的成像模态来确定 焦点的位置和质量，以及对各种楔块的反馈控制将用于控制大小 和大脑中焦点的位置，类似于今天用传统方法进行的跨- 头颅超声波具体工作目标如下：（1）开发三维计算机模拟技术 模型的经颅超声用于设计和优化的楔形换能器。(2)发展 允许控制换能器参数以校正射束畸变的电子反馈控制系统 和散焦。(3)在真实的人类颅骨上构建、表征和基准测试MR兼容楔形探头。

Project Summary Brain metastases, the most common malignant intracranial tumors, occur in up to 40% of patients with cancer. Left untreated, prognosis is abysmal, with a life expectancy of 1 month. Surgery and radiation are typically combined to treat brain metastases; however, with improved treatment of primary cancers, survival for some groups of patients with brain metastases has increased such that alternatives are being sought that minimize or avoid the risks of invasive surgery and the toxic effects of radiation to the brain. Although stereotactic radiation is increasingly used to limit the side effects of whole brain radiation, tumor control may not be as effective with stereotactic surgery alone. One possible alternative, magnetic resonance guided focused ultrasound, is being researched as a noninvasive means of ablating brain tumors and of increasing delivery of cancer therapeutics through the blood-brain barrier. Conventional techniques to transmit ultrasound into the brain have traditionally been implemented by means of a large-aperture spherical transducer consisting of a very large number of single element transducers transmitting ultrasound beams through the skull. The geometric focus of these transducers limits the treatment envelope to the center of the brain, whereas the majority of cancers, especially metastases, occur along the periphery of the brain. In addition, the skull significantly attenuates ultrasound. In order to compensate for the attenuated energy in the skull and achieve a sufficient deliverable power at the focus, the surface pressure of the transducer (i.e., input power) must be kept sufficiently high. High absorption at even moderate input powers leads to excess heating inside the skull, requiring active cooling to prevent burning of the bone or skin. To address the difficulties outlined above, we propose to develop a novel wedge transducer array technology for introducing focused ultrasound waves into the brain. The array couples ultrasound into the brain through double mode conversion: from longitudinal wave in the wedge to a high order Lamb wave in the skull, then from the high order Lamb wave in the skull to a longitudinal wave in the brain. The benefits of our approach are in improved efficiency, reduction in heating of the skull, the ability to address regions in the brain that are close to the skull, and freedom in operating at a wider range of frequencies. Therapy and neuro-modulation applications using this type of coupling technology will still rely on an imaging modality such as MR to ascertain the location and quality of the focus, and feedback control on the various wedges will be used to control the size and location of the focal spot in the brain, similar to what is done today with conventional approaches to trans- cranial ultrasound. The specific aims of the proposed work are as follows: (1) Develop three-dimensional in-silico models of transcranial ultrasound to be utilized in the design and optimization of wedge transducers. (2) Develop electronics feedback control system allowing control of transducer parameters to correct for beam aberration and defocusing. (3) Build, characterize, and benchmark MR-compatible wedge transducers on real human skull.