Physical Sciences Platform, Sunnybrook Research Institute, Toronto, Ontario M4N 3M5, Canada and Department of Medical Biophysics, University of Toronto, Toronto, Ontario M4N3M5, Canada.
Med Phys. 2013 Dec;40(12):122901. doi: 10.1118/1.4829510.
Transcranial focused ultrasound is an emerging therapeutic modality that can be used to perform noninvasive neurosurgical procedures. The current clinical transcranial phased array operates at 650 kHz, however the development of a higher frequency array would enable more precision, while reducing the risk of standing waves. However, the smaller wavelength and the skull's increased distortion at this frequency are problematic. It would require an order of magnitude more elements to create such an array. Random sparse arrays enable steering of a therapeutic array with fewer elements. However, the tradeoffs inherent in the use of sparsity in a transcranial phased array have not been systematically investigated and so the objective of this simulation study is to investigate the effect of sparsity on transcranial arrays at a frequency of 1.5 MHz that provides small focal spots for precise exposure control.
Transcranial sonication simulations were conducted using a multilayer Rayleigh-Sommerfeld propagation model. Element size and element population were varied and the phased array's ability to steer was assessed.
The focal pressures decreased proportionally as elements were removed. However, off-focus hotspots were generated if a high degree of steering was attempted with very sparse arrays. A phased array consisting of 1588 elements 3 mm in size, a 10% population, was appropriate for steering up to 4 cm in all directions. However, a higher element population would be required if near-skull sonication is desired.
This study demonstrated that the development of a sparse, hemispherical array at 1.5 MHz could enable more precision in therapies that utilize lower intensity sonications.
经颅聚焦超声是一种新兴的治疗方式，可用于进行非侵入性的神经外科手术。目前的临床经颅相控阵工作在 650 kHz，但开发更高频率的相控阵将能够提高精度，同时降低驻波的风险。然而，较小的波长和颅骨在该频率下的增加的失真都是问题。这将需要数量级更多的元件来创建这样的阵列。随机稀疏阵列能够用较少的元件来控制治疗阵列的转向。然而，在经颅相控阵中使用稀疏性的固有权衡尚未得到系统研究，因此本模拟研究的目的是研究在 1.5 MHz 频率下稀疏性对经颅阵列的影响，该频率提供小的焦点光斑以实现精确的暴露控制。
使用多层瑞利-索末菲传播模型进行经颅超声模拟。改变元件尺寸和元件数量，并评估相控阵的转向能力。
随着元件的去除，焦点压力成比例下降。然而，如果使用非常稀疏的阵列尝试高度转向，会产生离焦热点。由 1588 个 3 毫米大小的元件组成，元件数量为 10%的相控阵，适合在所有方向上转向 4 厘米。然而，如果需要近颅骨超声，需要更高的元件数量。
本研究表明，在 1.5 MHz 开发稀疏的半球形阵列可以提高利用低强度超声的治疗的精度。
