Li H H, Votaw J R
Emory University Center for PET, Atlanta, GA 30322, USA.
IEEE Trans Med Imaging. 1998 Aug;17(4):596-605. doi: 10.1109/42.730404.
This work investigates the noise properties of O-15 water PET images in an attempt to increase the sensitivity of activation studies. A method for computing the amount of noise within a region of interest (ROI) from the uncertainty in the raw data was implemented for three-dimensional (3-D) positron emission tomography (PET). The method was used to study the signal-to-noise ratio (SNR) of regions-of-interest (ROI's) inside a 3-D Hoffman brain phantom. Saturation occurs at an activity concentration of 2.2 mCi/l which corresponds to a 75-mCi O-15 water injection into a normal person of average weight. This establishes the upper limit for injections for human brain studies using 3-D PET on the Siemens ECAT 921 EXACT scanner. Data from human brain activation studies on four normal volunteers using two-dimensional (2-D) PET were analyzed. The biological variation was found to be 5% in 1-ml ROI's. The variance for a complete activation study was calculated, for a variety of protocols, by combining the Poisson noise propagated from the raw data in the phantom experiments with the biological variation. A protocol that is predicted to maximize the SNR in dual-condition activation experiments while remaining below the radiation safety limit is: ten scans with 45 mCi per injection. The data should not be corrected for random or scatter events since they do not help in the identification of activation sites while they do add noise to the image. Due to the lower noise level of 3-D PET, the threshold for detecting a true change in activity concentration is 10%-20% lower than 2-D PET. Because of this, a 3-D activation experiment using the Siemens 921 scanner requires fewer subjects for equal statistical power.
这项工作研究了O-15水PET图像的噪声特性，旨在提高激活研究的灵敏度。针对三维（3-D）正电子发射断层扫描（PET），实施了一种根据原始数据的不确定性来计算感兴趣区域（ROI）内噪声量的方法。该方法用于研究三维霍夫曼脑模型内感兴趣区域（ROI）的信噪比（SNR）。当活度浓度为2.2 mCi/l时会出现饱和，这相当于向平均体重的正常人注射75 mCi的O-15水。这确定了在西门子ECAT 921 EXACT扫描仪上使用三维PET进行人脑研究时注射剂量的上限。分析了来自四名正常志愿者使用二维（2-D）PET进行的人脑激活研究的数据。发现在1 ml的ROI中生物变异为5%。通过将体模实验中原始数据传播的泊松噪声与生物变异相结合，针对各种方案计算了完整激活研究的方差。预计在双条件激活实验中能使信噪比最大化同时又保持在辐射安全限值以下的方案是：每次注射45 mCi进行十次扫描。数据不应针对随机或散射事件进行校正，因为它们无助于识别激活位点，反而会给图像增加噪声。由于三维PET的噪声水平较低，检测活度浓度真实变化的阈值比二维PET低10% - 20%。因此，使用西门子921扫描仪进行的三维激活实验在同等统计功效下所需的受试者更少。
