Characterization of the RF ablation-induced 'oven effect': The importance of background tissue thermal conductivity on tissue heating
Characterization of the RF ablation-induced 'oven effect': The importance of background tissue thermal conductivity on tissue heating
复制标题
DOI：
10.1080/02656730600609122
复制
发表时间：
2006-06-01
影响因子：
3.1
通讯作者：
Goldberg, S. Nahum
中科院分区：
文献类型：
--
作者：
Liu, Zhengjun;Ahmed, Muneeb;Goldberg, S. Nahum
目的：采用体外琼脂模型和计算机模拟的方法，研究背景组织热导率对射频消融加热的影响。方法：建立两室柱状琼脂模型(5%琼脂、5%氯化钠、3%蔗糖)。其中包括一个代表肿瘤的标准化内室(直径2厘米，长4厘米，0.25%琼脂)，由代表背景组织的外室包围。通过在琼脂中加入脂肪饱和的油基溶质(10-90%)，外层隔室的热导率从0.48Wm(-1)℃(正常肝脏)到0.23Wm(-1)℃(脂肪)变化。射频消融电流为2000 mA，消融时间为2min。每隔1厘米记录一次距离电极尖端4厘米的温度。随后，使用二维有限元计算机模型对直径2-4 cm的肿瘤进行2-24min的射频消融，肿瘤周围被不同热导率的组织包围，有或没有灌注(0-5kgm(-3)S(-1))(n=44)。结果：在琼脂模型中，背景组织中的脂肪含量与热导率呈负指数函数相关(r(2)=0.98)。随着外室脂肪含量的增加，内室边缘(距电极尖端1 cm)的温度显著升高(p<；0.01)。因此，在导热系数为0.46Wm(-1)摄氏度(10%脂肪)和0.23Wm(-1)摄氏度(90%脂肪)的情况下，在2分钟测得的温度分别为31.5+/-2.2摄氏度和45.1+/-3.1摄氏度。另一方面，较高的脂肪水平导致背景隔间的温度上升较低(90%脂肪为0.2+/-0.3摄氏度，10%脂肪为1.1+/-0.05摄氏度，p<；0.05)。体模加热模式与计算机模型的相关性非常好(r(2)=0.93)，表明低热导率的背景组织增加了中心肿瘤内的加热，特别是在较长时间的射频消融和较小的肿瘤中。此外，计算机模拟显示，在存在灌注的情况下，低导热系数的背景组织的肿瘤边缘温度持续升高，对于一个3 cm的肿瘤，灌注2kgm(-3)S(-1)治疗12分钟，临床上脂肪和软组织的背景导热系数相差4.5℃。结论：较低的背景组织导热系数显著增加了特定消融目标内的温度。这些发现有助于深入了解“烤箱效应”(即对被肝硬变或脂肪包围的肿瘤提高加热效率)，并强调在考虑射频消融疗效时，肿瘤及其周围组织特征的重要性。
Purpose: To determine the effect of background tissue thermal conductivity on RF ablation heating using ex vivo agar phantoms and computer modelling.Method: Two-compartment cylindrical agar phantom models (5% agar, 5% NaCl, 3% sucrose) were constructed. These included a standardized inner compartment (2cm diameter, 4 cm length, 0.25% agar) representing a tumour, surrounded by an outer compartment representing background tissue. The thermal conductivity of the outer compartment was varied from 0.48Wm(-1)degrees C(normal liver) to 0.23Wm(-1)degrees C ( fat) by adding a fat-saturated oil-based solute (10-90%) to the agar. RF ablation was applied at 2000mA current for 2min. Temperatures were recorded up to 4 cm from the electrode tip at 1 cm intervals. Subsequently, a 2-D finite element computer model was used to simulate RF ablation of 2-24min duration for tumours measuring 2-4cm in diameter surrounded by tissues of different thermal conductivity with the presence or absence of perfusion (0-5 kgm(-3) s(-1)) (n = 44). A comparison of results was performed.Results: In agar phantoms, the amount of fat in the background tissue correlated with thermal conductivity as a negative exponential function (r(2) = 0.98). Significantly increased temperatures were observed at the edge of the inner compartment (1cm from the electrode tip) as the fat content of the outer compartment increased (p < 0.01). Thus, temperatures at 2 min measured 31.5 +/- 2.2 degrees C vs 45.1 +/- 3.1 degrees C for thermal conductivities of 0.46Wm(-1)degrees C (10% fat) and 0.23Wm(-1)degrees C (90% fat), respectively. On the other hand, higher levels of fat led to lower temperature increases in the background compartment (0.2 +/- 0.3 degrees C for 90% fat vs. 1.1 +/- 0.05 degrees C for 10% fat, p < 0.05). Phantom thermal heating patterns correlated extremely well with computer modelling (r(2) = 0.93), demonstrating that background tissues with low thermal conductivity increase heating within the central tumour, particularly for longer durations of RF ablation and in smaller tumours. Furthermore, computer modelling demonstrated that increases in temperature at the tumour margin for background tissues of lower thermal conductivity persisted in the presence of perfusion, with a clinically relevant 4.5 degrees C difference between background thermal conductivities of fat and soft tissue for a 3 cm tumour with perfusion of 2 kgm(-3)s(-1), treated for 12 min.Conclusion: Lower thermal conductivity of background tissues significantly increases temperatures within a defined ablation target. These findings provide insight into the 'oven effect' (i.e. increased heating efficacy for tumours surrounded by cirrhotic liver or fat) and highlight the importance of both the tumour and the surrounding tissue characteristics when contemplating RF ablation efficacy.