An assessment of the DORT method on simple scatterers using boundary element modelling.
An assessment of the DORT method on simple scatterers using boundary element modelling.
复制标题
使用边界元建模对简单散射体的 DORT 方法进行评估。
DOI：
10.1088/0031-9155/60/9/3715
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发表时间：
2015
影响因子：
3.5
通讯作者：
Gélat P
中科院分区：
文献类型：
--
作者：
Gélat P
通过肋骨聚焦的能力克服了用于治疗肝脏肿瘤的高强度聚焦超声（HIFU）系统的一个重要限制。虽然在组织损伤的治疗位置产生足够高的声压很重要，但确保肋骨上的超声剂量保持在规定的阈值以下也是至关重要的，因为肋骨强烈吸收和反射超声。DORT方法能够选择性地聚焦并穿透浸入声介质中的散射体，而无需事先知道它们的位置或几何形状。该方法需要一个多单元传感器，并通过对单元间传递函数的测量矩阵进行奇异值分解来实现。通过散射体进行聚焦的方法的有效性通常通过比较散射体表面和焦点区域的比吸收率（SAR）来评估。SAR可以通过了解声压大小以及介质和散射体的声学特性来获得。众所周知，在坚硬表面或其附近使用经过校准的水听器测量声压存在实验挑战，可能导致测量不确定性增加。因此，DORT方法通常是通过测量散射体从声介质中移除后散射体表面位置的SAR来进行实验评估的。这也可能在声压测量中产生不确定性。因此，通过一个经过验证的理论模型来评估ort方法的有效性是有充分理由的。应用于外部声散射问题的边界元法（BEM）非常适合这种评估。在本研究中，利用边界元理论实现了局部反应球形散射体的DORT方法，并相对于球形聚焦情况、基于几何射线追迹的二值化散射和相位共轭法评估了DORT方法的聚焦能力。
The ability to focus through ribs overcomes an important limitation of a high-intensity focused ultrasound (HIFU) system for the treatment of liver tumours. Whilst it is important to generate high enough acoustic pressures at the treatment location for tissue lesioning, it is also paramount to ensure that the resulting ultrasonic dose on the ribs remains below a specified threshold, since ribs both strongly absorb and reflect ultrasound. The DORT (décomposition de l'opérateur de retournement temporel) method has the ability to focus on and through scatterers immersed in an acoustic medium selectively without requiring prior knowledge of their location or geometry. The method requires a multi-element transducer and is implemented via a singular value decomposition of the measured matrix of inter-element transfer functions. The efficacy of a method of focusing through scatterers is often assessed by comparing the specific absorption rate (SAR) at the surface of the scatterer, and at the focal region. The SAR can be obtained from a knowledge of the acoustic pressure magnitude and the acoustic properties of the medium and scatterer. It is well known that measuring acoustic pressures with a calibrated hydrophone at or near a hard surface presents experimental challenges, potentially resulting in increased measurement uncertainties. Hence, the DORT method is usually assessed experimentally by measuring the SAR at locations on the surface of the scatterer after the latter has been removed from the acoustic medium. This is also likely to generate uncertainties in the acoustic pressure measurement. There is therefore a strong case for assessing the efficacy of the DORT method through a validated theoretical model. The boundary element method (BEM) applied to exterior acoustic scattering problems is well-suited for such an assessment. In this study, BEM was used to implement the DORT method theoretically on locally reacting spherical scatterers, and to assess its focusing capability relative to the spherical focusing case, binarised apodisation based on geometric ray tracing and the phase conjugation method.