OPTIMIZATION OF RCBF MEASUREMENT WITH A 3D PET SCANNER

这个项目的目的是为了确定一种最优的方法 使用三维图像进行脑功能地形图研究 正电子发射断层扫描(PET)和O-15水，一种示踪剂 局部脑血流量(RCBF)。目前的体层摄影术允许三种- 立体成像，大大提高了灵敏度。但是，图像 在rCBF使用团注进行研究时，噪声在高计数率下增加 通常会进行O-15水的注射。虽然这张图片 信噪比(S/N)在低计数率下得到改善 注射的放射性剂量，改善在高计数时会下降 费率。因此，在设计脑图时，有几个因素很重要 实验：每次注射的放射性剂量，注射的数量 注射，以及注射的类型(快速注射与缓慢注射)。 正在进行人体模拟和实验，以找到一种 GE超前层析成像中这些参数的最佳组合 在人体研究中，扫描数据是通过静脉推注获得的 在4名受试者中注射2.5-30mci的0-15水 生成任务。全脑噪声当量计数(NEC)率 在注射剂量12-15 mci时达到峰值；10 mci给出的NEC为92% 峰值。尽管通过扫描检测到一致的局部rCBF变化 60、90和120秒的持续时间，其统计学意义降低 随着扫描时间的增加。因此，我们选择使用10 MCI进行1分钟扫描 用于团注。然后我们进行了模拟以评估效果 论慢速输注示踪剂扫描时间较长的S/N映像上的数据 噪声作为局部放射性的函数通过扫描 大脑幻影。然后，使用模拟来预测组织 用缓慢的示踪剂输注观察到的放射性。 将测量的体模噪声数据与预测的组织数据组合 允许计算S/N。这显示了相当于S/N的60秒 用团注扫描，用缓慢输液扫描一次较长的扫描， 如果注射了等量的放射性物质。在这段时间里 示踪剂摄取对总积分计数的贡献更大 比团注更慢的输液。因此，调查人员不妨 定制不同类型脑图的扫描参数 实验同时维持团注的S/N。

The purpose of this project is to determine an optimal method for performing functional brain mapping studies with three-dimensional positron emission tomography (PET) and O-15 water, a tracer that maps regional cerebral blood flow (rCBF). Current tomographs permit three- dimensional imaging, substantially increasing sensitivity. However, image noise increases at the high count rates at which rCBF studies with bolus injections of O-15 water have typically been performed. Although the image signal-to-noise ratio (S/N) is improved at low count rates with small amounts of injected radioactivity, the improvement falls off at high count rates. Thus, several factors are important in designing brain mapping experiments: the amount of radioactivity per injection, the number of injections, and type of injection (fast bolus vs. slow infusion). Simulations and experiments in humans are being performed to find an optimal combination of these parameters for the GE Advance tomograph. In human studies, scan data were obtained with bolus intravenous injections of 2.5 to 30 mCi of 0-15 water in 4 subjects performing a word generation task. The noise equivalent count (NEC) rate for whole brain peaked at an injected dose of 12-15 mCi; 10 mCi gave an NEC of 92% of the peak value. Although consistent focal rCBF changes were detected with scan durations of 60, 90, and 120 sec, their statistical significance decreased as scan time increased. Therefore, we selected a 1 min scan using 10 mCi for bolus injections. We then performed simulations to evaluate the effect on S/N of longer scan durations with slow tracer infusions. Data on image noise as a function of local radioactivity were obtained by scanning a brain phantom. Then, simulations were used to predict the tissue radioactivity that would be observed with a slow tracer infusion. Combining the measured phantom noise data with the predicted tissue data allowed calculation of the S/N. This showed an equivalent S/N for a 60 sec scan with a bolus injection and a single longer scan with a slow infusion, given the same amount of injected radioactivity. The time over which tracer uptake contributes to the total integrated counts is greater with a slow infusion than a bolus injection. Thus, investigators may wish to customize scanning parameters for different types of brain mapping experiments while maintaining the S/N of bolus injections.