St Lawrence K S, Lee T Y
Department of Diagnostic Radiology and the Lawson Research Institute, St. Joseph's Health Centre, and the Imaging Research Laboratories, London, Ontario, Canada.
J Cereb Blood Flow Metab. 1998 Dec;18(12):1365-77. doi: 10.1097/00004647-199812000-00011.
Using the adiabatic approximation, which assumes that the tracer concentration in parenchymal tissue changes slowly relative to that in capillaries, we derived a time-domain, closed-form solution of the tissue homogeneity model. This solution, which is called the adiabatic solution, is similar in form to those of two-compartment models. Owing to its simplicity, the adiabatic solution can be used in CBF experiments in which kinetic data with only limited time resolution or signal-to-noise ratio, or both, are obtained. Using computer simulations, we investigated the accuracy and the precision of the parameters in the adiabatic solution for values that reflect 2H-labeled water (D2O) clearance from the brain (see Part II). It was determined that of the three model parameters, (1) the vascular volume (Vi), (2) the product of extraction fraction and blood flow (EF), and (3) the clearance rate constant (kadb), only the last one could be determined accurately, and therefore CBF must be determined from this parameter only. From the error analysis of the adiabatic solution, it was concluded that for the D2O clearance experiments described in Part II, the coefficient of variation of CBF was approximately 7% in gray matter and 22% in white matter.
利用绝热近似，即假设实质组织中的示踪剂浓度相对于毛细血管中的浓度变化缓慢，我们推导出了组织均匀性模型的时域封闭形式解。这个解被称为绝热解，其形式与两室模型的解相似。由于其简单性，绝热解可用于仅获得有限时间分辨率或信噪比或两者兼具的动力学数据的脑血流量（CBF）实验。通过计算机模拟，我们研究了绝热解中反映脑内2H标记水（D2O）清除率的值的参数的准确性和精度（见第二部分）。结果确定，在三个模型参数中，（1）血管容积（Vi），（2）提取分数与血流量的乘积（EF），以及（3）清除率常数（kadb），只有最后一个可以准确确定，因此必须仅根据此参数来确定CBF。从绝热解的误差分析得出结论，对于第二部分中描述的D2O清除实验，灰质中CBF的变异系数约为7%，白质中约为22%。
