Pulsed Focused Ultrasound (pFUS) exposures and devices for tissue permeabilization without contrast agents

摘要 超声联合全身给予超声造影剂（UCA）诱导的空化 在过去的十年里，已经得到了广泛的研究，并成功地应用于交付一些 不同的药物来治疗实体瘤。这种方法的局限性在于UCA局限于血管， 血管周围空间，这限制了他们进入肿瘤血管化不良的区域。间质性增加 压力、高肿瘤细胞密度和基质屏障进一步抑制药物递送。诱导从头空化 因此，使用脉冲聚焦超声（pFUS）穿透肿瘤组织将非常有益于克服 这些药物渗透的屏障。然而，根据该领域目前的共识， 成核和维持惯性空化所需的能量显著高于UCA增强超声 并且只能用具有大覆盖区的高功率、高度聚焦的换能器来实现。这限制了 这种方法的实用性。我们的初步数据表明，惯性空化活动，导致组织 如果在震源处形成冲击波阵面，则在较低的峰值负压下可以实现透化 波形，由于非线性传播效应。此外，我们已经证明， 冲击幅度和峰值负压主要由FUS换能器的F数确定， 而较少聚焦的换能器在最低峰值负压值处产生冲击。我们还展示 可以使用诊断超声探头在相对低的机械指数下获得冲击波形 (MI~ 4-6）在衰减组织中的相关深度。本提案的总体目标是开发反馈 用于向实体瘤递送药物的受控pFUS治疗方案， 足迹，（潜在的诊断）超声探头。这样的透化过程可以仅在 在对任何可以用超声成像的肿瘤进行化疗之前。实现我们 目标，我们建议确定局灶波形指标和相关的空化活动的依赖性 通过数值模拟和一系列实验， 透明的组织模拟凝胶体模和离体组织（相应的特定目的1和2）。直接 在透明凝胶中使用高速摄影观察气泡动力学将与活性相关。 以及用于随后的组织实验的被动空化检测观察。优化的pFUS 然后将治疗方案应用于健康的猪组织（肝、肾和胰腺）， 皮下施用Dunning大鼠前列腺腺癌，然后全身施用 不同分子量的荧光标记葡聚糖（具体目标3）。透化效果将是 根据组织中葡聚糖的绝对浓度和分布进行急性评价。的耐久性 在大鼠短期存活研究中，通过改变时间间隔，评价pFUS诱导的透化作用 pFUS应用和染料施用。

ABSTRACT Cavitation induced by ultrasound combined with systemically administered ultrasound contrast agents (UCAs) has been extensively studied over the past decade, and successfully applied to the delivery of a number of different drugs to solid tumours. A limitation of this approach is that the UCAs are confined to blood vessels and the perivascular space, which limits their access to poorly vascularized regions of a tumor. Increased interstitial pressure, high tumor cell density, and stromal barriers further inhibit drug delivery. Inducing de novo cavitation throughout tumor tissue using pulsed focused ultrasound (pFUS) would thus be very beneficial for overcoming these barriers to drug penetration. However, according to current consensus in the field, the focal pressure levels required to nucleate and sustain inertial cavitation are substantially higher than for UCA-enhanced ultrasound and can only be achieved with high-power, highly focused transducers with a large footprints. This limits the practicality of this approach. Our preliminary data indicate that the inertial cavitation activity that results in tissue permeabilization can be achieved at lower peak negative pressures if a shock front develops in the focal waveform, due to nonlinear propagation effects. Further, we have demonstrated that the relationship between the shock amplitude and peak negative pressure is primarily determined by the F-number of a FUS transducer, with less focused transducers producing shocks at the lowest peak negative pressure values. We also showed that shocked waveforms can be achieved using diagnostic ultrasound probes at relatively low mechanical index (MI ~ 4-6) at relevant depth in attenuative tissue. The overall goal of this proposal is to develop feedback controlled pFUS treatment protocols for drug delivery to solid tumours that can be implemented using small footprint, (potentially diagnostic) ultrasound probes. Such permeabilization procedures could be performed just prior to the administration of chemotherapy on any tumor that can be imaged with ultrasound. To achieve our goal, we propose to determine the dependence of the focal waveform metrics and associated cavitation activity on the shape and frequency of the transducer through numerical modelling and a series of experiments in transparent tissue-mimicking gel phantoms and ex vivo tissues (Specific Aims 1 and 2 correspondingly). Direct observation of bubble dynamics using high-speed photography in transparent gels will be correlated with active and passive cavitation detection observations for use in subsequent experiments in tissue. The optimized pFUS treatment protocols will then be applied to healthy porcine tissues (liver, kidney and pancreas), and to subcutaneous Dunning rat prostatic adenocarcinoma, and will be followed by systemic administration of fluorescent labelled dextrans of different molecular weights (Specific Aim 3). The permeabilization effect will be evaluated acutely from the absolute concentration and distribution of the dextrans in tissue. The durability of pFUS-induced permeabilization will be evaluated in a short survival study in rats, by varying the time interval pFUS application and dye administration.