MEASUREMENT OF RCBF WITH PET UNDER NON-STEADY STATE CONDITIONS--ERROR ANALYSIS

用PET测量rCBF的方法是基于一室法 假设流量在扫描期间是恒定的模型。这 然而，假设在几种实验情况下可能不成立，例如 如在药物干预后，在癫痫发作期间和之后，如果 在激活研究期间存在习惯性，或者如果动脉血二氧化碳分压 视情况而定。我们使用模拟来确定流量值， 在实践中得到的模型是在这种非稳态下使用的 条件。模拟的条件包括流量的阶跃变化和 线性或指数漂移。进行了两次计算 广泛使用的流动法、放射自显影法和快速最小二乘法 方块技术。模拟表明，当流量发生变化时， 计算的rCBF反映扫描开始时的流量，而不是 扫描期间的平均流量。例如，使用一个步骤 扫描20秒时正/负50%的rCBF变化，估计rCBF 在两种流量方法中都在基线流量的正负4-6%范围内。之前 为了准备稿件，正在进行进一步的模拟 半定量0-15次水扫描，当仅使用组织计数时 映射rCBF的变化。 这些发现将有助于解释rCBF数据，并将 协助设计激活实验，因为 早期扫描周期决定观察到的rCBF的演示 改变。

Methods for measuring rCBF with PET are based upon a one-compartment model which assumes that flow is constant during the scan period. This assumption may not hold in several experimental situations, however, such as after a pharmacologic intervention, during and after a seizure, if there is habituation during activation studies, or if arterial pC02 varies. We used simulations to determine the flow values that would be obtained in practice when the model is used under such non-steady state conditions. Conditions simulated included a step change in flow and linear or exponential drifts. Calculations were performed for two widely-used flow methods, the autoradiographic method and a rapid least squares technique. Simulations showed that when flow changes, the calculated rCBF reflects the flow at the start of the scan, rather than the mean flow during the scanning period. For example, with a step change in rCBF of plus/minus50% at 20 sec into the scan, estimated rCBF is within plus/minus4-6% of baseline flow for both flow methods. Prior to manuscript preparation, further simulations are being performed for semiquantitative 0-15 water scans, when tissue counts alone are used to map rCBF changes. These findings will help in the interpretation of rCBF data, and will assist in the design of activation experiments, because of the demonstration that the early scan period determines the observed rCBF changes.