Histotripsy beyond the intrinsic cavitation threshold using very short ultrasound pulses: microtripsy.
Histotripsy beyond the intrinsic cavitation threshold using very short ultrasound pulses: microtripsy.
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DOI：
10.1109/tuffc.2014.6722611
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发表时间：
2014-02
期刊：
影响因子：
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通讯作者：
Cain CA
中科院分区：
文献类型：
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作者：
Lin KW;Kim Y;Maxwell AD;Wang TY;Hall TL;Xu Z;Fowlkes JB;Cain CA
组织解剖学通过短高压超声波脉冲产生的密集高能气泡云产生组织分离。传统的组织解剖治疗使用 3 至 10 个周期的较长脉冲，其中产生病变的气泡云的生成取决于来自先前启动的、稀疏分布的气泡的非常高峰值正激波前沿的压力释放散射（“激波散射”机制）。在我们最近的工作中，测量了通过单个负半周期直接生成致密气泡云的峰值负压（P−），即“固有阈值”。在本文中，研究了这些超本征阈值脉冲产生的密集气泡云和由此产生的病变（在红细胞模型和犬组织中）。使用 32 元件 PZT-8、500 kHz 治疗传感器以 1 Hz 的脉冲重复频率 (PRF) 和 24.5 至 80.7 MPa 的 P− 产生非常短（< 2 个周期）的组织解剖脉冲。结果表明，随着施加的 P− 增加，组织解剖引起的损伤的空间范围增加，并且这些损伤的大小与内在空化阈值以上的焦点区域的估计值很好地对应，至少在较低压力状态下 (P− = 26-35 MPa) 是这样。最小可再现病灶的平均尺寸约为 0.9 × 1.7 mm（横向 × 轴向），明显小于换能器的 -6dB 波束宽度 (1.8 × 4.0 mm)。这些结果表明，使用内在阈值机制，可以精确地生成限制良好的微观损伤，并且可以根据超过内在空化阈值的焦点区域的分数来估计它们的空间范围。由于负半周期的阈上部分可以精确控制，因此很容易产生远小于波长的损伤，因此称为“显微解剖”。
Histotripsy produces tissue fractionation through dense energetic bubble clouds generated by short, high-pressure, ultrasound pulses. Conventional histotripsy treatments have used longer pulses from 3 to 10 cycles wherein the lesion-producing bubble cloud generation depends on the pressure-release scattering of very high peak positive shock fronts from previously initiated, sparsely distributed bubbles (the “shock-scattering” mechanism). In our recent work, the peak negative pressure (P−) for generation of dense bubble clouds directly by a single negative half cycle, the “intrinsic threshold,” was measured. In this paper, the dense bubble clouds and resulting lesions (in RBC phantoms and canine tissues) generated by these supra-intrinsic threshold pulses were studied. A 32-element, PZT-8, 500 kHz therapy transducer was used to generate very short (< 2 cycles) histotripsy pulses at a pulse repetition frequency (PRF) of 1 Hz and P− from 24.5 to 80.7 MPa. The results showed that the spatial extent of the histotripsy-induced lesions increased as the applied P− increased, and the sizes of these lesions corresponded well to the estimates of the focal regions above the intrinsic cavitation threshold, at least in the lower pressure regime (P− = 26–35 MPa). The average sizes for the smallest reproducible lesions were approximately 0.9 × 1.7 mm (lateral × axial), significantly smaller than the −6dB beamwidth of the transducer (1.8 × 4.0 mm). These results suggest that, using the intrinsic threshold mechanism, well-confined and microscopic lesions can be precisely generated and their spatial extent can be estimated based on the fraction of the focal region exceeding the intrinsic cavitation threshold. Since the supra-threshold portion of the negative half cycle can be precisely controlled, lesions considerably less than a wavelength are easily produced, hence the term “microtripsy.”