Division of Neuroscience and Mental Health, MRC Clinical Sciences Centre, Imperial College London, London, UK.
Neuroimage. 2010 May 1;50(4):1427-37. doi: 10.1016/j.neuroimage.2010.01.064. Epub 2010 Jan 28.
As population-based studies may obtain images from scanners with different field strengths, a method to normalize regional brain volumes according to intracranial volume (ICV) independent of field strength is needed. We found systematic differences in ICV estimation, tested in a cohort of healthy subjects (n=5) that had been imaged using 1.5T and 3T scanners, and confirmed in two independent cohorts. This was related to systematic differences in the intensity of cerebrospinal fluid (CSF), with higher intensities for CSF located in the ventricles compared with CSF in the cisterns, at 3T versus 1.5T, which could not be removed with three different applied bias correction algorithms. We developed a method based on tissue probability maps in MNI (Montreal Neurological Institute) space and reverse normalization (reverse brain mask, RBM) and validated it against manual ICV measurements. We also compared it with alternative automated ICV estimation methods based on Statistical Parametric Mapping (SPM5) and Brain Extraction Tool (FSL). The proposed RBM method was equivalent to manual ICV normalization with a high intraclass correlation coefficient (ICC=0.99) and reliable across different field strengths. RBM achieved the best combination of precision and reliability in a group of healthy subjects, a group of patients with Alzheimer's disease (AD) and mild cognitive impairment (MCI) and can be used as a common normalization framework.
由于基于人群的研究可能会从具有不同磁场强度的扫描仪中获取图像，因此需要一种方法来根据颅内体积（ICV）对区域脑体积进行标准化，而无需考虑磁场强度。我们发现，在使用 1.5T 和 3T 扫描仪对一组健康受试者（n=5）进行成像的测试中，ICV 估计存在系统差异，并在两个独立的队列中得到了证实。这与脑脊液（CSF）强度的系统差异有关，与 1.5T 相比，3T 下脑室中的 CSF 强度高于脑池中的 CSF，这是三种不同应用的偏置校正算法无法消除的。我们开发了一种基于 MNI（蒙特利尔神经学研究所）空间和反向归一化（反向脑掩模，RBM）的组织概率图的方法，并通过手动 ICV 测量对其进行了验证。我们还将其与基于统计参数映射（SPM5）和脑提取工具（FSL）的替代自动 ICV 估计方法进行了比较。所提出的 RBM 方法与手动 ICV 归一化等效，具有较高的组内相关系数（ICC=0.99），并且在不同磁场强度下可靠。RBM 在一组健康受试者、一组阿尔茨海默病（AD）和轻度认知障碍（MCI）患者中实现了最佳的精度和可靠性组合，可以用作通用的归一化框架。
