OBTAINING LOCAL SAR AND BLOOD PERFUSION DATA FROM TEMPERATURE-MEASUREMENTS - STEADY-STATE AND TRANSIENT TECHNIQUES COMPARED
OBTAINING LOCAL SAR AND BLOOD PERFUSION DATA FROM TEMPERATURE-MEASUREMENTS - STEADY-STATE AND TRANSIENT TECHNIQUES COMPARED
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DOI：
10.1016/0360-3016(85)90343-8
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发表时间：
1985-01-01
影响因子：
7
通讯作者：
CETAS, TC
中科院分区：
文献类型：
--
作者：
ROEMER, RB;FLETCHER, AM;CETAS, TC
进行了一系列的分析和实验，以确定从稳态温度值和随着施加功率的阶跃变化而从瞬时温度测量中提取比吸收率和血液灌注率信息的程度。在2450 MHz微波加热的犬大腿上进行了多次局部温度测量，以评估两个参数：组织中的局部吸收功率和局部“有效血液灌注量”。提出这些计算的理论基础是为了确定它们的基本假设，并为比较以前调查人员使用的各种计算方法提供一个统一的基础。从能量平衡的考虑可以看出，局部吸收功率可以由功率阶跃增加后的温度上升速率或功率阶跃下降后的温度下降速率获得。通过比较狗大腿固定位置的按递增和递减功率阶跃计算的SAR结果，这些理论观察得到了实验验证。对于减少功率步长，如果包括热传导，则所产生的温度下降曲线也可用于计算有效血液灌注率。或者，可以根据稳态数据计算出相同的有效血液灌注率。(这两种方法已经被以前的研究人员用来确定“血液灌注值”。添加“有效”修饰符是为了在这种灌流计算中特别表示热传导效应的存在。)从实验结果和理论计算来看，两种计算方法的预测结果之间的差异似乎是由于热间隙法在冷却期间改变热传导值而引起的。稳态计算方法比Washout方法更容易应用，但它需要对局部SAR值进行额外了解。重要的是要认识到，在热传导性很重要的情况下，使用热学技术计算的有效血液灌注值容易产生很大的误差，除非这种传导性明确包含在计算中。这样的有效血液灌注值不应与不受热传导影响的非热技术计算的值进行定量比较。除非已知这种传导效应可以忽略不计，否则有效灌注值只是血液灌注量变化的定性指标。
A series of analyses and experiments was performed to determine the extent that SAR [specific absorption rate] and blood perfusion information can be extracted from steady state temperature values and from transient temperature measurements following a step change in applied power. Multiple local temperature measurements were made in canine thighs heated by 2450 MHZ microwaves to evaluate 2 parameters: the local absorbed power in the tissue and the local "effective blood perfusion." The theoretical bases for these calculations are presented in order to identify their underlying assumptions and to obtain a unified basis for comparison of the various calculation methods used by previous investigators. From energy balance considerations it can be shown that the local absorbed power can be obtained from either the rate of increase of temperature immediately following a step increase in power, or from the rate of decrease in temperature immediately following a step decrease in power. These theoretical observations are verified experimentally by comparing the SAR results at fixed positions in canine thighs as calculated from both increasing and decreasing power steps. For decreasing power steps, the resulting decreasing temperature curves can also be used to calculate an effective blood perfusion rate if thermal conduction is included. Alternatively, this same effective blood perfusion rate can be calculated from steady state data. (These 2 approaches have been used by previous investigators to determine "blood perfusion" values. The modifier "effective" was added to specifically denote the presence of thermal conduction effects in such perfusion calculations.) From experimental results and theoretical calculations, it appears that differences between the predictions of the 2 calculation methods arises from changing thermal conduction values during the cooling period of the thermal clearance method. The steady state calculation approach is easier to apply than the washout method, but it requires the additional knowledge of the local SAR value. It is important to realize that effective blood perfusion values calculated using thermal techniques are subject to large errors under conditions where thermal conduction is important, unless this conduction is explicitly included in the calculation. Such effective blood perfusion values should not be quantitatively compared to values calculated from nonthermal techniques that are not affected by thermal conduction. Unless such conduction effects are known to be negligible, effective perfusion values are only qualitative indicators of the presence of changes in blood perfusion.