Brodin N Patrik, Partanen Ari, Asp Patrik, Branch Craig A, Guha Chandan, Tomé Wolfgang A
Institute for Onco-Physics, Albert Einstein College of Medicine, Bronx, New York 10461 and Department of Radiation Oncology, Montefiore Medical Center, Bronx, New York 10461.
Clinical Science MR Therapy, Philips, Andover, Massachusetts 01810.
Med Phys. 2016 Mar;43(3):1167-74. doi: 10.1118/1.4941361.
Tissue-mimicking thermal therapy phantoms that coagulate at specific temperatures are valuable tools for developing and evaluating treatment strategies related to thermal therapy. Here, the authors propose a simple and efficient method for determining the coagulation threshold temperature of transparent thermal therapy gel phantoms.
The authors used a previously published gel phantom recipe with 2% (w/v) of bovine serum albumin as the temperature-sensitive protein. Using the programmable heating settings of a polymerase chain reaction (PCR) machine, the authors heated 50 μl gel samples to various temperatures for 3 min and then imaged them using the BioRad Gel Doc system to determine the coagulation temperature using an opacity quantification method. The estimated coagulation temperatures were then validated for gel phantoms prepared with different pH levels using high-intensity focused ultrasound (HIFU) heating and magnetic resonance imaging (MRI) thermometry methods on a clinical MR-HIFU system.
The PCR heating method produced consistent and reproducible coagulation of gel samples in precise correlation with the set incubation temperatures. The resulting coagulation threshold temperatures for gel phantoms of varying pH levels were found to be 44.1 ± 0.1, 53.4 ± 0.9, and 60.3 ± 0.9 °C for pH levels of 4.25, 4.50, and 4.75, respectively. This corresponded well with the coagulation threshold temperatures determined by MR-thermometry, with coagulation defined as a 95% decrease in T2 relaxation time, which were estimated at 53.6 ± 1.9 and 62.9 ± 2.4 °C for a pH of 4.50 and 4.75, respectively.
The opacity quantification method provides a fast and reproducible estimate of the coagulation threshold temperature of transparent temperature-sensitive gel phantoms. The temperatures determined using this method were well within the range of temperatures estimated using MR-thermometry. Due to the specific heating capabilities of the PCR machine, and the robust determination of coagulation threshold temperatures based on the statistically significant increase in the opacity of gel samples, coagulation temperatures can be determined more precisely and with less variability compared to MRI-based methods.
在特定温度下发生凝固的组织模拟热疗体模是开发和评估与热疗相关治疗策略的重要工具。在此，作者提出了一种简单有效的方法来确定透明热疗凝胶体模的凝固阈值温度。
作者使用先前发表的凝胶体模配方，其中含有2%（w/v）的牛血清白蛋白作为温度敏感蛋白。利用聚合酶链反应（PCR）仪的可编程加热设置，作者将50μl凝胶样品加热至不同温度3分钟，然后使用BioRad凝胶成像系统对其进行成像，采用不透明度量化方法确定凝固温度。然后，使用临床MR-HIFU系统上的高强度聚焦超声（HIFU）加热和磁共振成像（MRI）测温方法，对不同pH值制备的凝胶体模的估计凝固温度进行验证。
PCR加热方法使凝胶样品产生一致且可重复的凝固，与设定的孵育温度精确相关。发现不同pH值水平的凝胶体模的凝固阈值温度分别为：pH值为4.25时为44.1±0.1℃，pH值为4.50时为53.4±0.9℃，pH值为4.75时为60.3±0.9℃。这与通过MR测温法确定的凝固阈值温度非常吻合，凝固定义为T2弛豫时间降低95%，pH值为4.50和4.75时分别估计为53.6±1.9℃和62.9±2.4℃。
不透明度量化方法可快速且可重复地估计透明温度敏感凝胶体模的凝固阈值温度。使用该方法确定的温度完全在MR测温法估计的温度范围内。由于PCR仪的特定加热能力，以及基于凝胶样品不透明度的统计学显著增加对凝固阈值温度进行可靠测定，与基于MRI的方法相比，凝固温度可以更精确地确定且变异性更小。
