Quantification of near-field heating during volumetric MR-HIFU ablation
Quantification of near-field heating during volumetric MR-HIFU ablation
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DOI：
10.1118/1.3518083
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发表时间：
2011-01-01
期刊：
影响因子：
3.8
通讯作者：
Moonen, C.
中科院分区：
文献类型：
--
作者：
Mougenot, C.;Kohler, M. O.;Moonen, C.
目的：在过去的十年中，磁共振成像引导的高强度聚焦超声作为肿瘤组织热消融的临床替代方案得到了广泛的评价。然而，最大消融体积受到与平均肿瘤尺寸相比小的焦点尺寸导致的长时间治疗的限制。体积超声处理已被证明有效地扩大每次超声处理的消融体积，但仍然受到皮肤和脂肪层中诱导的温度升高的限制。在这项研究中，多平面磁共振测温提出了监测近场温度上升，以防止相关的意外热damage.Methods：该方法进行了评估，通过执行超声在11只猪的大腿肌肉维持全身麻醉。通过沿沿着由多个向外移动的同心圆组成的轨迹操纵焦点来进行容积消融。近场致热的特征在于MR温度图和热剂量图。MR测量的结果进行了比较simulation.Results：在这项研究中，测得的最大温升被发现线性相关的表面能量密度的近场内的光束路径的斜率为4.2 K mm（2）/J。这个简单的线性模型似乎是几乎独立的轨迹模式和超声深度。避免猪大腿皮下组织致命损伤的安全极限被确定为绝对温度为50 ℃，对应于1.2 MHz时的表面能量密度为2.5 J/mm（2）。可以建立线性关系以基于消融之前所选择的功率来估计温度增加，从而使用已知的表面能量密度阈值提供对可能的过度近场加热的先验安全检查。如果在造成脂肪层损伤或皮肤烧伤之前看到过度的近场温度升高，则该方法还将使临床医生有可能中止超声处理。(C)2011年美国医学物理学家协会。[DOI：10.1118/1.3518083]
Purpose: High-intensity focused ultrasound guided by magnetic resonance imaging has been extensively evaluated during the past decade as a clinical alternative for thermal ablation of tumor tissue. However, the maximal ablation volume is limited by the extensive treatment duration resulting from the small size of the focal point as compared to the average tumor size. Volumetric sonication has been shown to efficiently enlarge the ablated volume per sonication, but remains limited by the temperature increase induced in the skin and fat layers. In this study, multiplane MR thermometry is proposed for monitoring the near-field temperature rise in order to prevent related unintended thermal damage.Methods: The method was evaluated by performing sonications in the thigh muscle of 11 pigs maintained under general anesthesia. Volumetric ablations were performed by steering the focal point along trajectories consisting of multiple outward-moving concentric circles. Near-field heating was characterized with MR temperature maps and thermal dose maps. The results from the MR measurements were compared to simulations.Results: In this study, the measured maximum temperature rise was found to correlate linearly with the surface energy density within the near field of the beam path with a slope of 4.2 K mm(2)/J. This simple linear model appears to be almost independent of the trajectory pattern and the sonication depth. The safety limit to avoid lethal damage of the subcutaneous tissues of the porcine thigh was identified to be an absolute temperature of 50 C, corresponding to a surface energy density of 2.5 J/mm(2) at 1.2 MHz.Conclusions: A linear relationship can be established to estimate the temperature increase based on the chosen power prior to ablation, thereby providing an a priori safety check for possible excessive near-field heating using a known surface energy density threshold. This method would also give the clinician the possibility to abort the sonication should excessive near-field temperature rise be seen before fat layer damage or skin burns are inflicted. (C) 2011 American Association of Physicists in Medicine. [DOI: 10.1118/1.3518083]