RAPID REPEAT RCBF MEASUREMENT WITH POSITRON EMISSION TOMOGRAPHY AND O15 WATER

室内施用的O-15水被广泛用于测量区域 PET脑血流（rCBF），特别是重复rCBF 在同一扫描会话中的测量，例如，用于脑成像研究 测量之间的时间间隔通常为12分钟，以允许 放射性背景衰减（O-15的半衰期为2分钟）。 我们 正在开发一种更快速地执行顺序测量的方法， 包括对示踪剂动力学中残余背景的校正 用于计算rCBF的公式。 预计这一方法将 增加重复rCBF测量的频率将提供更大的 PET实验的灵活性，如脑映射和急性 药物作用。 它还将减少执行此类任务所需的时间。 问题研究 在基线rCBF扫描后，在时间点建立新的生理状态。 T. 然后收集扫描数据以记录残留的大脑 放射性 注射第二团O-15水，并进一步扫描 收集数据。 通过应用凯蒂的一室模型，可以 建立一个公式，将大脑中放射性的时间过程联系起来， 在时间T后，rCBF，时间T时的背景脑放射性值 T和动脉时间-活动曲线。 一种快速的最小二乘法， 用于根据测量的扫描和血液数据拟合rCBF的方程 在时间T之后收集。 模拟研究表明，只有 由于使用此方法，rCBF估计中的噪声增加2-3% 法 该方法的可行性已被初步验证 在4例受试者中获得的研究，在静息和视觉期间进行扫描 刺激. 对于快速重复扫描，扫描间隔为6 分钟下的 在白色物质中，% rCBF校正的平均值为17%， 岛叶皮层和视皮层各占6%。 的绝对幅度 校正是更大的rCBF值，虽然%校正 更少。 该项目的进一步计划包括（1）比较血流 标准的12分钟扫描间隔获得的测量值 （2）进一步进行模拟研究， 方法的实验误差;（3）扩展方法， 可用于估计相对rCBF，而无需 动脉时间-活动曲线

Intravenously administered O-15 water is widely used to measure regional cerebral blood flow (rCBF) with PET, especially to perform repeat rCBF measurements in the same scan session, e.g., for brain mapping studies. The time interval between measurements is typically 12 mins., to allow for decay of the radioactivity background (half-life of O-15 is 2 mins.). We are developing a method to perform sequential measurements more rapidly, by including a correction for residual background in the tracer kinetic equation used to calculate rCBF. It is anticipated that this approach to increase the frequency of repeat rCBF measurements will provide greater flexibility in PET experiments such as brain mapping and studies of acute drug effects. It will also decrease the time required to perform such studies. After a baseline rCBF scan, a new physiologic state is established at time T. Scan data are then collected to record the residual brain radioactivity. A second bolus of O-15 water is injected, and further scan data are collected. By applying the one-compartment model of Kety, one can develop an equation which relates the time course of radioactivity in brain after time T to the rCBF, the background brain radioactivity value at time T, and the arterial time-activity curve. A rapid, lease-squares method is used to fit this equation for rCBF from the measured scan and blood data collected after time T. Simulation studies demonstrated that there is only a 2-3% increase in the noise in estimates of rCBF due to use of this method. The feasibility of the approach has been demonstrated in preliminary studies obtained in 4 subjects scanned at rest and during visual stimulation. For the rapidly repeated scans, the interscan interval was 6 mins. Mean values for % rCBF correction were 17% in white matter, 8% in insular cortex, and 6% in visual cortex. The absolute magnitude of the correction was greater with higher rCBF values, although the % correction was less. Further plans for this project include (1) comparing blood flow measurements obtained with the standard 12 min. interscan interval to those obtained with the new method; (2) performing further simulation studies of the experimental errors of the method; (3) extending the method so that it can be used to estimate relative rCBF without the requirement for an arterial time-activity curve.