Utah Center for Advanced Imaging Research, Salt Lake City, UT, USA.
Med Phys. 2011 Sep;38(9):4971-81. doi: 10.1118/1.3618729.
This study presents the results obtained from both simulation and experimental techniques that show the effect of mechanically or electronically steering a phased array transducer on proximal tissue heating.
The thermal response of a nine-position raster and a 16-mm diameter circle scanning trajectory executed through both electronic and mechanical scanning was evaluated in computer simulations and experimentally in a homogeneous tissue-mimicking phantom. Simulations were performed using power deposition maps obtained from the hybrid angular spectrum (HAS) method and applying a finite-difference approximation of the Pennes' bioheat transfer equation for the experimentally used transducer and also for a fully sampled transducer to demonstrate the effect of acoustic window, ultrasound beam overlap and grating lobe clutter on near-field heating.
Both simulation and experimental results show that electronically steering the ultrasound beam for the two trajectories using the 256-element phased array significantly increases the thermal dose deposited in the near-field tissues when compared with the same treatment executed through mechanical steering only. In addition, the individual contributions of both beam overlap and grating lobe clutter to the near-field thermal effects were determined through comparing the simulated ultrasound beam patterns and resulting temperature fields from mechanically and electronically steered trajectories using the 256-randomized element phased array transducer to an electronically steered trajectory using a fully sampled transducer with 40 401 phase-adjusted sample points.
Three distinctly different three distinctly different transducers were simulated to analyze the tradeoffs of selected transducer design parameters on near-field heating. Careful consideration of design tradeoffs and accurate patient treatment planning combined with thorough monitoring of the near-field tissue temperature will help to ensure patient safety during an MRgHIFU treatment.
本研究通过模拟和实验技术展示了机械或电子控制相控阵换能器对近场组织加热的影响，呈现了研究结果。
在计算机模拟和同质组织模拟体模中进行实验，评估了九位置光栅和 16mm 直径圆形扫描轨迹通过电子和机械扫描执行时的热响应。模拟使用混合角谱（HAS）方法获得的功率沉积图，并应用有限差分逼近 Pennes 生物传热方程，对实验中使用的换能器和完全采样换能器进行计算，以证明声窗、超声束重叠和栅瓣杂波对近场加热的影响。
模拟和实验结果均表明，与仅通过机械引导相比，使用 256 阵元相控阵电子引导两种轨迹的超声束可显著增加近场组织中沉积的热剂量。此外，通过比较使用 256 随机元相控阵换能器机械和电子引导轨迹的模拟超声束模式和由此产生的温度场，以及使用具有 40401 个相位调整采样点的完全采样换能器电子引导轨迹，确定了波束重叠和栅瓣杂波对近场热效应的个别贡献。
模拟了三种明显不同的换能器，以分析所选换能器设计参数对近场加热的权衡。仔细考虑设计权衡和准确的患者治疗计划，并结合对近场组织温度的彻底监测，将有助于确保在磁共振引导高强度聚焦超声治疗期间患者的安全。
