Chaplin Vandiver, Caskey Charles F
Vanderbilt University Institute of Imaging Science, 1161 21st Avenue South, Nashville, TN 37232 USA.
Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, 1161 21st Avenue South, Nashville, TN 37232 USA.
J Ther Ultrasound. 2017 Apr 13;5:12. doi: 10.1186/s40349-017-0089-8. eCollection 2017.
Mild-hyperthermia therapy (40-45 °C) with high-intensity focused ultrasound (HIFU) is a technique being considered in a number of different treatments such as thermally activated drug delivery, immune-stimulation, and as a chemotherapy adjuvant. Mechanical damage and loss of cell viability associated with HIFU-induced acoustic cavitation may pose a risk during these treatments or may hinder their success. Here we present a method that achieves mild heating and reduces cavitation by using a multi-focused HIFU beam. We quantify cavitation level and temperature rise in multi-focal sonications and compare it to single-focus sonications at the transducer geometric focus.
Continuous wave sonications were performed with the Sonalleve V2 transducer in gel phantoms and pork at 5, 10, 20, 40, 60, 80 acoustic watts for 30 s. Cavitation activity was measured with two ultrasound (US) imaging probes, both by computing the raw channel variance and using passive acoustic mapping (PAM). Temperature rise was measured with MR thermometry at 3 T. Cavitation and heating were compared for single- and multi-focal sonication geometries. Multi-focal sonications used four points equally spaced on a ring of either 4 mm or 8 mm diameter. Single-focus sonications were not steered.
Multi-focal sonication generated distinct foci that were visible in MRI thermal maps in both phantoms and pork, and visible in PAM images in phantoms only. Cavitation activity (measured by channel variance) and mean PAM image value were highly correlated (r > 0.9). In phantoms, cavitation exponentially decreased over the 30-second sonication, consistent with depletion of cavitation nuclei. In pork, sporadic spikes signaling cavitation were observed with single focusing only. In both materials, the widest beam reduced average and peak cavitation level by a factor of two or more at each power tested when compared to a single focus. The widest beam reduced peak temperature by at least 10 °C at powers above 5 W, and created heating that was more spatially diffuse than single focus, resulting in more voxels in the mild heating (3-8 °C) range.
Multi-focal HIFU can be used to achieve mild temperature elevation and reduce cavitation activity.
高强度聚焦超声（HIFU）进行的温和热疗（40 - 45°C）是一种在多种不同治疗中被考虑应用的技术，如热激活药物递送、免疫刺激以及作为化疗辅助手段。与HIFU诱导的声空化相关的机械损伤和细胞活力丧失可能在这些治疗过程中带来风险，或者可能阻碍其成功实施。在此，我们提出一种通过使用多焦点HIFU束来实现温和加热并减少空化的方法。我们对多焦点超声处理中的空化水平和温度升高进行量化，并将其与换能器几何焦点处的单焦点超声处理进行比较。
使用Sonalleve V2换能器在凝胶体模和猪肉中以5、10、20、40、60、80声瓦的功率进行30秒的连续波超声处理。使用两个超声（US）成像探头测量空化活动，既通过计算原始通道方差，也使用被动声映射（PAM）。在3T场强下用磁共振温度测量法测量温度升高。比较单焦点和多焦点超声处理几何形状下的空化和加热情况。多焦点超声处理使用在直径为4毫米或8毫米的环上均匀间隔的四个点。单焦点超声处理不进行声束转向。
多焦点超声处理产生了在体模和猪肉的MRI热图中都可见的明显焦点，并且仅在体模的PAM图像中可见。空化活动（通过通道方差测量）与平均PAM图像值高度相关（r > 0.9）。在体模中，空化在30秒的超声处理过程中呈指数下降，这与空化核的耗尽一致。在猪肉中，仅在单焦点处理时观察到表明空化的零星尖峰。在两种材料中，与单焦点相比，在每个测试功率下，最宽的声束将平均和峰值空化水平降低了两倍或更多。在功率高于5瓦时，最宽的声束将峰值温度降低了至少10°C，并产生了比单焦点更空间扩散的加热，导致在温和加热（3 - 8°C）范围内有更多体素。
多焦点HIFU可用于实现温和的温度升高并降低空化活动。
