Background

Conventional motion algorithms utilized during High Intensity Focused Ultrasound (HIFU) procedures usually sonicate successive tissue cells, thereby inducing excess deposition of thermal dose in the pre-focal region. Long delays (~60 s) are used to reduce the heating around the focal region. In the present study the experimental evaluation of six motion algorithms so as to examine the required delay and algorithm for which the pre-focal (near-field) and post-focal (far-field) heating can be reduced using thermal dose estimations is presented.

Materials and Methods

A single element spherically focused transducer operating at 1.1 MHz and focusing beam at 9 cm, was utilized for sonication on a 400 mm² area of an agar-based phantom. Movement of the transducer was performed with each algorithm, using 0–60 s (10 s step) delays between sonications. Temperatures were recorded at both near and far-field regions and thermal dose calculations were implemented.

Results

With the algorithms used in the present study, a delay of 50–60 s was required to reduce heating in the near-field region. A 30 s delay induced a safe thermal dose in the far-field region using all algorithms except sequential which still required 60 s delay.

Conclusions

The study verified the conservative need for 60 s delay for the sequential plan treatment. Nevertheless, present findings suggest that prolonged treatment times can be significantly reduced in homogeneous tissues by selection of the optimized nonlinear algorithm and delay.

中文翻译：

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使用热剂量概念对聚焦超声的近场和远场加热进行实验评估

 背景

高强度聚焦超声 (HIFU) 过程中使用的传统运动算法通常会对连续的组织细胞进行超声处理，从而导致热剂量在聚焦前区域过量沉积。使用长延迟（约 60 秒）来减少焦点区域周围的加热。在本研究中，对六种运动算法进行了实验评估，以检查所需的延迟和可以使用热剂量估计来减少焦前（近场）和后焦（远场）加热的算法。

 材料和方法

使用工作频率为 1.1 MHz 且聚焦光束为 9 cm 的单元件球形聚焦换能器对基于琼脂的模型的 400 mm ²区域进行超声处理。使用每种算法执行换能器的移动，在超声处理之间使用 0-60 秒（10 秒步长）延迟。记录近场和远场区域的温度并进行热剂量计算。

 结果

使用本研究中使用的算法，需要 50-60 秒的延迟来减少近场区域的加热。使用除仍需要 60 秒延迟的顺序算法之外的所有算法，30 秒的延迟在远场区域引起安全热剂量。

 结论

该研究证实序贯计划治疗保守需要延迟 60 秒。然而，目前的研究结果表明，通过选择优化的非线性算法和延迟，可以显着减少同质组织中延长的治疗时间。