Hoffmann N E, Bischof J C
Department of Biomedical Engineering, University of Minnesota, Minneapolis 55455, USA.
J Biomech Eng. 2001 Aug;123(4):301-9. doi: 10.1115/1.1385838.
Current research in cryosurgery is concerned with finding a thermal history that will definitively destroy tissue. In this study, we measured and predicted the thermal history obtained during freezing and thawing in a cryosurgical model. This thermal history was then compared to the injury observed in the tissue of the same cryosurgical model (reported in companion paper (Hoffmann and Bischof, 2001)). The dorsal skin flap chamber, implanted in the Copenhagen rat, was chosen as the cryosurgical model. Cryosurgery was performed in the chamber on either normal skin or tumor tissue propagatedfrom an AT-1 Dunning rat prostate tumor. The freezing was performed by placing a approximately 1 mm diameter liquid-nitrogen-cooled cryoprobe in the center of the chamber and activating it for approximately 1 minute, followed by a passive thaw. This created a 4.2 mm radius iceball. Thermocouples were placed in the tissue around the probe at three locations (r = 2, 3, and 3.8 mm from the center of the window) in order to monitor the thermal history produced in the tissue. The conduction error introduced by the presence of the thermocouples was investigated using an in vitro simulation of the in vivo case and found to be <10 degrees C for all cases. The corrected temperature measurements were used to investigate the validity of two models of freezing behavior within the iceball. The first model used to approximate the freezing and thawing behavior within the DSFC was a two-dimensional transient axisymmetric numerical solution using an enthalpy method and incorporating heating due to blood flow. The second model was a one-dimensional radial steady state analytical solution without blood flow. The models used constant thermal properties for the unfrozen region, and temperature-dependent thermal properties for the frozen region. The two-dimensional transient model presented here is one of the first attempts to model both the freezing and thawing of cryosurgery. The ability of the model to calculate freezing appeared to be superior to the ability to calculate thawing. After demonstrating that the two-dimensional model sufficiently captured the freezing and thawing parameters recorded by the thermocouples, it was used to estimate the thermal history throughout the iceball. This model was used as a basis to compare thermal history to injury assessment (reported in companion paper (Hoffmann and Bischof, 2001)).
当前冷冻手术的研究致力于寻找一种能够彻底破坏组织的热历程。在本研究中，我们测量并预测了冷冻手术模型在冷冻和解冻过程中获得的热历程。然后将该热历程与在同一冷冻手术模型的组织中观察到的损伤情况进行比较（相关内容发表于配套论文（霍夫曼和比绍夫，2001年））。选用植入哥本哈根大鼠体内的背部皮瓣腔作为冷冻手术模型。在该腔室中，对正常皮肤或源自AT-1邓宁大鼠前列腺肿瘤的肿瘤组织进行冷冻手术。通过将直径约1毫米的液氮冷却冷冻探针置于腔室中央并激活约1分钟，随后被动解冻来进行冷冻。这形成了一个半径为4.2毫米的冰球。在探针周围组织的三个位置（距窗口中心r = 2、3和3.8毫米）放置热电偶，以监测组织中产生的热历程。通过对体内情况进行体外模拟，研究了热电偶的存在所引入的传导误差，发现所有情况下该误差均小于10摄氏度。经校正的温度测量值用于研究冰球内两种冷冻行为模型的有效性。用于近似双相 Stefan 冻结曲线（DSFC）内冷冻和解冻行为的第一个模型是使用焓法并考虑血流加热的二维瞬态轴对称数值解。第二个模型是无血流的一维径向稳态解析解。这些模型对未冻结区域使用恒定热特性，对冻结区域使用与温度相关的热特性。这里提出的二维瞬态模型是对冷冻手术的冷冻和解冻过程进行建模的首批尝试之一。该模型计算冷冻的能力似乎优于计算解冻的能力。在证明二维模型充分捕捉了热电偶记录的冷冻和解冻参数后，它被用于估计整个冰球的热历程。该模型被用作将热历程与损伤评估进行比较的基础（相关内容发表于配套论文（霍夫曼和比绍夫，2001年））。
