MRI-guided gas bubble enhanced ultrasound heating in in vivo rabbit thigh
MRI-guided gas bubble enhanced ultrasound heating in in vivo rabbit thigh
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DOI：
10.1088/0031-9155/48/2/306
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发表时间：
2003-01-21
影响因子：
3.5
通讯作者：
Hynynen, K
中科院分区：
文献类型：
--
作者：
Sokka, SD;King, R;Hynynen, K
在本研究中，我们提出了一种聚焦超声手术方案，该方案在焦点处诱导并使用气泡来增强超声吸收，最终在体内产生更大的病变。研究了该加热方法的MRI和超声可视化监测方法。通过仔细监测单次超声暴露产生的较大病变可以极大地提高聚焦超声的肿瘤凝固速度。所有实验均在MRI（临床，1.5 T）引导下进行，使用两个八扇形球形弯曲压电换能器之一。换能器采用1.1或1.7 MHz阵列，由多通道射频驱动系统驱动。换能器安装在mri兼容的手动定位系统中，兔子位于系统的顶部。超声检测环与治疗传感器固定在一起，以监测治疗过程中的气泡活动。聚焦超声手术暴露于7只新西兰大白兔的大腿。实验中，气泡增强的加热暴露包括高振幅300声瓦，半秒脉冲，然后是7 W， 14 W或21 W连续波暴露19.5 s。对照分别为14 W、21 W和28 W的20 s暴露。在暴露过程中，通过质子共振频移的温度依赖性获得了磁共振测温。使用MR t2增强成像评估所产生的病变。使用特定指标来评估气泡增强暴露与其各自控制超声之间的差异：与时间和空间相关的温度，病变大小和形状，以及它们与热剂量预测的一致性。与未形成气泡的超声相比，气泡增强的超声在前4 s内温度上升更快，总体温度更高。MRI测温得到的空间温度图和热剂量图与t2加权成像检查的病变密切相关。与控制暴露相比，气泡增强加热暴露产生的病变体积大2-3倍，形状更一致，更接近换能器。然后将捕获的信号传输到采集工作站并计算其频谱。对超声过程中不同时间点的亚谐波声发射频谱进行了检测，这是气泡振荡的特征（Lele 1977, Hynynen 1991）。频谱在次谐波处的尖峰被归类为稳定空化，而在次谐波附近的宽带发射被标记为气泡崩溃。
In this study, we propose a focused ultrasound surgery protocol that induces and then uses gas bubbles at the focus to enhance the ultrasound absorption and ultimately create larger lesions in vivo. MRI and ultrasound visualization and monitoring methods for this heating method are also investigated. Larger lesions created with a carefully monitored single ultrasound exposure could greatly improve the speed of tumour coagulation with focused ultrasound. All experiments were performed under MRI (clinical, 1.5 T) guidance with one of two eight-sector, spherically curved piezoelectric transducers. The transducer, either a 1.1 or 1.7 MHz array, was driven by a multi-channel RF driving system. The transducer was mounted in an MRI-compatible manual positioning system and the rabbit was situated on top of the system. An ultrasound detector ring was fixed with the therapy transducer to monitor gas bubble activity during treatment. Focused ultrasound surgery exposures were delivered to the thighs of seven New Zealand white rabbits. The experimental, gas-bubble-enhanced heating exposures consisted of a high amplitude 300 acoustic watt, half second pulse followed by a 7 W, 14 W or 21 W continuous wave exposure for 19.5 s. The respective control sonications were 20 s exposures of 14 W, 21 W and 28 W. During the exposures, MR thermometry was obtained from the temperature dependency of the proton resonance frequency shift. MR T2-enhanced imaging was used to evaluate the resulting lesions. Specific metrics were used to evaluate the differences between the gas-bubble-enhanced exposures and their respective control sonications: temperatures with respect to time and space, lesion size and shape, and their agreement with thermal dose predictions. The bubble-enhanced exposures showed a faster temperature rise within the first 4 s and higher overall temperatures than the sonications without bubble formation. The spatial temperature maps and the thermal dose maps derived from the MRI thermometry closely correlated with the resulting lesion as examined by T2-weighted imaging. The lesions created with the gas-bubble-enhanced heating exposures were 2-3 times larger by volume, consistently more spherical in shape and closer to the transducer than the control exposures. The study The captured signals were then transferred to the acquisition workstation and their spectrums were computed. The spectrums at the different time points during sonication were inspected for subharmonic acoustic emission, which is characteristic of bubble oscillation (Lele 1977, Hynynen 1991). Sharp peaks in the spectrum at the subharmonic were categorized as stable cavitation, and broadband emissions around the subharmonic were noted as bubble collapse.