Chung Y C, Duerk J L, Lewin J S
Department of Radiology, Case Western Reserve University, Cleveland, Ohio, USA.
Invest Radiol. 1997 Aug;32(8):466-74. doi: 10.1097/00004424-199708000-00006.
Recently, there has been increased interest in interventional magnetic resonance (MR) imaging and minimally invasive cancer therapy via radio frequency (RF) thermal ablation. In this work, we examined RF thermal lesion generation in phantoms and ex vivo bovine liver and correlated them with MR images under a variety of conditions, which begins our assessment of the role of MR imaging in this new method for cancer treatment.
Radio frequency lesions were created in gel phantoms and ex vivo bovine liver, using stationary (bovine liver) and variable speed (gel) moving electrodes to create lesions with shapes mimicking tumors. Ex vivo bovine liver lesions were made with the tissue held at room temperature (n = 4) and in a 37 degrees C saline bath (n = 3) using a 16-gauge electrode (tip temperature: 70 degrees C, 80 degrees C, and 90 degrees C; ablation time: 1-13 minutes). Electrical impedance and RF power were plotted during ablation. After ablation, RF-induced lesions were imaged with a 0.2-tesla (T) MR system using a variety of pulse sequences.
Complex shaped lesions were created successfully in phantoms. Averaged maximum ex vivo lesion volume made at 90 degrees C ablation experiments holding the tissue temperature at 37 degrees C and at room temperature were 1.58 +/- 0.35 cm3 and 1.0 +/- 0.26 cm3 respectively (confidence interval: 90%). The aspect ratios and RF power of the lesions decreased as ablations proceeded. Impedance dropped during the first 2 minutes of the ablation. Ex vivo lesions appeared as regions of low-signal amplitude in T2-weighted MR images.
Phantom ablation experience may be useful and applicable in thermotherapy planning. Lesions made in ex vivo bovine liver held at 37 degrees C via a saline bath are larger than those created at room temperature. Lesions shapes are ablation time dependent until thermal equilibrium is reached. Impedance reduction and lesion formation are related; 0.2-T MR systems can image RF energy-induced thermal lesions.
近来，人们对介入磁共振（MR）成像以及通过射频（RF）热消融进行的微创癌症治疗兴趣日增。在本研究中，我们检测了在体模和离体牛肝中产生的射频热损伤，并将其与在各种条件下的MR图像相关联，以此开启我们对MR成像在这种新癌症治疗方法中作用的评估。
在凝胶体模和离体牛肝中制造射频损伤，使用固定电极（牛肝）和变速电极（凝胶）制造形状模拟肿瘤的损伤。使用16号电极（尖端温度：70℃、80℃和90℃；消融时间：1 - 13分钟）在室温（n = 4）和37℃生理盐水浴（n = 3）中对离体牛肝进行损伤制造。在消融过程中绘制电阻抗和射频功率曲线。消融后，使用多种脉冲序列通过0.2特斯拉（T）MR系统对射频诱导的损伤进行成像。
在体模中成功制造出复杂形状的损伤。在组织温度保持在37℃和室温下进行的90℃消融实验中，平均最大离体损伤体积分别为1.58±0.35 cm³和1.0±0.26 cm³（置信区间：90%）。随着消融进行，损伤的纵横比和射频功率降低。在消融的前2分钟电阻抗下降。在T2加权MR图像中，离体损伤表现为低信号幅度区域。
体模消融经验可能对热疗规划有用且适用。通过生理盐水浴在37℃下对离体牛肝制造的损伤比在室温下制造的损伤更大。在达到热平衡之前，损伤形状与消融时间有关。电阻抗降低与损伤形成相关；0.2 - T MR系统能够对射频能量诱导的热损伤进行成像。
