Takagi S, Kenny P J, Gilson A J
J Cereb Blood Flow Metab. 1984 Dec;4(4):564-73. doi: 10.1038/jcbfm.1984.81.
A mathematical method has been developed by which the cerebral vascular extraction fraction of flow- and diffusion-limited tracers injected intravenously can be measured quantitatively. Successive injections of three tracers are required: a test tracer such as 15O-labeled water; a completely diffusible tracer as a reference tracer and also as a flow tracer; and a tracer for cerebral blood volume (CBV). The arterial tracer concentration curves and total integrated head counts of the test and reference tracers, as well as CBF and CBV values, are required to calculate the extraction fraction. No calibration is required between the head counts and arterial curves. No decay correction of the head and arterial activity is required, because isotopic decay is explicitly included in the equation. The effect of nonextracted test tracer can be corrected. Simulation studies have shown that the calculated extraction fraction values are not sensitive to measurement error in CBF, CBV, partition coefficient, change in measurement time, or time shift effect between the arterial and head data. If there is mixing of two different tissues in the brain, the calculated extraction fraction values are close to the weighted mean values of extraction fraction by relative weight of the tissues. It is concluded that it is possible to apply this method to human studies with a positron emission tomograph scanner and to animal studies with external coincidence detectors.
已开发出一种数学方法，通过该方法可定量测量静脉注射的流量限制型和扩散限制型示踪剂的脑血管提取分数。需要连续注射三种示踪剂：一种测试示踪剂，如15O标记的水；一种完全可扩散的示踪剂，用作参考示踪剂以及流量示踪剂；以及一种用于测量脑血容量（CBV）的示踪剂。计算提取分数需要测试示踪剂和参考示踪剂的动脉示踪剂浓度曲线、头部总积分计数以及CBF和CBV值。头部计数和动脉曲线之间无需校准。头部和动脉活性无需进行衰变校正，因为方程中明确包含了同位素衰变。未提取的测试示踪剂的影响可以校正。模拟研究表明，计算得到的提取分数值对CBF、CBV、分配系数的测量误差、测量时间的变化或动脉与头部数据之间的时间偏移效应不敏感。如果大脑中有两种不同组织混合，计算得到的提取分数值接近按组织相对权重计算的提取分数加权平均值。得出的结论是，可以将该方法应用于使用正电子发射断层扫描仪的人体研究以及使用外部符合探测器的动物研究。
