Clement G T, White J, Hynynen K
Brigham & Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
Phys Med Biol. 2000 Apr;45(4):1071-83. doi: 10.1088/0031-9155/45/4/319.
Non-invasive treatment of brain disorders using ultrasound would require a transducer array that can propagate ultrasound through the skull and still produce sufficient acoustic pressure at a specific location within the brain. Additionally, the array must not cause excessive heating near the skull or in other regions of the brain. A hemisphere-shaped transducer is proposed which disperses the ultrasound over a large region of the skull. The large surface area covered allows maximum ultrasound gain while minimizing undesired heating. To test the feasibility of the transducer two virtual arrays are simulated by superposition of multiple measurements from an 11-element and a 40-element spherically concave test array. Each array is focused through an ex vivo human skull at four separate locations around the skull surface. The resultant ultrasound field is calculated by combining measurements taken with a polyvinylidene difluoride needle hydrophone providing the fields from a 44-element and a 160-element virtual array covering 88% and 33% of a hemisphere respectively. Measurements are repeated after the phase of each array element is adjusted to maximize the constructive interference at the transducer's geometric focus. An investigation of mechanical and electronic beam steering through the skull is also performed with the 160-element virtual array, phasing it such that the focus of the transducer is located 14 mm from the geometric centre. Results indicate the feasibility of focusing and beam steering through the skull using an array spread over a large surface area. Further, it is demonstrated that beam steering through the skull is plausible.
使用超声对脑部疾病进行无创治疗需要一个能使超声穿过颅骨并在脑内特定位置仍产生足够声压的换能器阵列。此外，该阵列不得在颅骨附近或脑内其他区域引起过度发热。提出了一种半球形换能器，它能将超声分散在颅骨的大片区域上。所覆盖的大表面积可实现最大超声增益，同时将不期望的发热降至最低。为测试该换能器的可行性，通过叠加来自一个11元球形凹面测试阵列和一个40元球形凹面测试阵列的多次测量结果来模拟两个虚拟阵列。每个阵列通过离体人类颅骨聚焦于颅骨表面周围的四个不同位置。通过结合使用聚偏二氟乙烯针式水听器进行的测量来计算合成超声场，该水听器提供了分别覆盖半球88%和33%的44元虚拟阵列和160元虚拟阵列的场。在调整每个阵列元件的相位以最大化换能器几何焦点处的相长干涉后重复测量。还使用160元虚拟阵列对通过颅骨的机械和电子束转向进行了研究，对其进行相位调整，使换能器焦点位于距几何中心14毫米处。结果表明，使用分布在大表面积上的阵列实现通过颅骨聚焦和束转向是可行的。此外，还证明了通过颅骨进行束转向是可行的。
