High intensity focussed ultrasound (HIFU) treatment planning with geometrical optics acoustics

结合几何光学声学的高强度聚焦超声 (HIFU) 治疗计划

• 批准号: 2425111
• 金额: --
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2425111
• 关键词: intensity; focussed; ultrasound; HIFU; treatment

Focussed ultrasound is increasingly being exploited in therapeutic applications, for example for thermal ablation of tumours and lithotriptic destruction of urological stones. Accurate planning of the treatment requires acoustic modelling to predict where the ultrasound waves will focus. In the high acoustic pressure regimes required for these treatments, the acoustic waves propagate nonlinearly - in other words they steepen and push energy into higher harmonics, sometimes as much as an order of magnitude higher than the fundamental frequency. This can significantly alter the rate of heat deposition, or the shape of the acoustic wave, and thereby have an effect on the treatment. It is therefore necessary to model the nonlinearity accurately. The leading numerical models of acoustic propagation are grid or mesh-based, and require nodes spaced closer than half-the-highest-wavelength (in practice quite a bit closer) and so the generation of harmonics leads to a requirement for very large grids, and the computations become impractically large. HIFU simulations (forward problem) therefore call for a different approach. As for most of these applications, the propagation is linear until close to the focus, and so the focal position does not change from the linear regime, just the amplitude of the field. Based on this observation we propose to devise a method that calculates the ray trajectories using fast linear geometric optics, and then computes the acoustic pressure amplitude along these rays by solving nonlinear acoustic equations, eg. Burgers equation or Westervelt equation, or a derivative from them, along the rays. This method can then be used as a forward solver in the optimisation of the treatment plan (inverse problem).

聚焦超声越来越多地被用于治疗应用，例如肿瘤的热消融和泌尿系统结石的碎石破坏。准确的治疗计划需要声学模型来预测超声波将集中在哪里。在这些处理所需的高声压条件下，声波非线性传播——换句话说，它们变陡并将能量推入更高的谐波，有时比基频高一个数量级。这可以显著改变热沉积的速率，或声波的形状，从而对治疗产生影响。因此，有必要对非线性进行精确建模。声学传播的主要数值模型是网格或基于网格的，并且要求节点的间隔接近于最高波长的一半（在实践中相当接近），因此谐波的产生导致对非常大的网格的需求，并且计算量变得不切实际。因此，HIFU模拟（正向问题）需要一种不同的方法。对于大多数这些应用，传播是线性的，直到接近焦点，因此焦点位置不会从线性状态改变，只是场的振幅。在此基础上，我们提出了一种利用快速线性几何光学计算射线轨迹的方法，然后通过求解非线性声学方程来计算沿这些射线的声压振幅。汉堡方程或韦斯特维尔方程，或它们的导数，沿着射线。该方法可用作优化处理方案（逆问题）的正向求解器。