游离水分数(FWF)表示每单位体积的脑实质的水量,不与大分子结合。其在多发性硬化症(MS)中的过量与组织损失增加有关。使用mcDESPOT(多分量驱动单脉冲观测T1和T2),一种利用T1和T2对比的3D成像方法,允许FWF在临床上可行的时间内得出。然而,此方法尚未用于量化FWF的变化及其在MS中的潜在临床影响。本研究的目的是探讨MS患者FWF的变化及其与组织损伤和认知功能的关系。假设FWF是临床上有意义的组织损失的代表。为了这个目标,我们测试了FWF之间的关系,MS病变负荷和信息处理速度,通过符号数字模式测试(SDMT)评估。除了标准序列,用于T1和T2加权病变勾画,在3T下采用具有1.7mm各向同性分辨率的mcDESPOT序列和扩散加权成像方案(b=0,1200s/mm2,40个扩散方向)。从扩散数据导出的分数各向异性图用于定义受试者特定白质(WM)图谱。脑实质分割返回灰质(GM)和WM的掩模,和正常的WM(NAWM),除了T1和T2病变面罩(T1L和T2L,分别)。九十九名复发缓解型MS患者(年龄=43.3±9.9岁,疾病持续时间12.3±7.7年)进行了研究,与25名健康对照(HC,年龄=38.8±11.0岁)。MS患者的GM和NAWM中FWF较高,与HC的GM和WM相比(均p<.001)。在MS患者中,FWF在T1L和GM中最高,其次是T2L和NAWM,分别。FWF随T1L和T2L体积显著增加(ρ范围从0.40到0.58,p<.001)。T2L中的FWF与T1L体积和T1L/T2L体积比密切相关(ρ=0.73,p<.001)。MS患者在处理速度测试中的表现比HC差(MS的平均值±SD:54.1±10.3,HC为63.8±10.8)。通用汽车的FWF,T2L,病灶周围组织和NAWM随着SDMT评分的降低而增加(对于T2L,ρ分别=-0.30,-0.29,-0.33,r=-.30,所有p<.005)。区域分析,进行,以确定哪些NAWM区域对解释FWF和认知障碍之间的关系特别重要,显示FWF空间方差与call体和上纵束的SDMT得分呈负相关,已知与认知障碍相关的WM结构,除了左皮质脊髓束,矢状地层,内囊的右前肢。总之,我们在MS患者的脑实质中发现了过量的游离水,不仅涉及MS病变的改变,还有通用汽车和NAWM,影响大脑功能,并与认知处理速度负相关。我们建议FWF度量,源自非侵入性,快速的MRI采集和良好的生物学可解释性,作为MS组织损伤和相关认知障碍的MRI生物标志物可能被证明是有价值的。
Free water fraction (FWF) represents the amount of water per unit volume of brain parenchyma, which is not bound to macromolecules. Its excess in multiple sclerosis (MS) is related to increased tissue loss. The use of mcDESPOT (multicomponent driven single pulse observation of T1 and T2), a 3D imaging method which exploits both the T1 and T2 contrasts, allows FWF to be derived in clinically feasible times. However, this method has not been used to quantify changes of FWF and their potential clinical impact in MS. The aim of this study is to investigate the changes in FWF in MS patients and their relationship with tissue damage and cognition, under the hypothesis that FWF is a proxy of clinically meaningful tissue loss. To this aim, we tested the relationship between FWF, MS lesion burden and information processing speed, evaluated via the Symbol Digit Modalities Test (SDMT). In addition to standard sequences, used for T1- and T2-weighted lesion delineation, the mcDESPOT sequence with 1.7 mm isotropic resolution and a diffusion weighted imaging protocol (b = 0, 1200 s/mm2, 40 diffusion directions) were employed at 3 T. The fractional anisotropy map derived from diffusion data was used to define a subject-specific white matter (WM) atlas. Brain parenchyma segmentation returned masks of gray matter (GM) and WM, and normal-appearing WM (NAWM), in addition to the T1 and T2 lesion masks (T1L and T2L, respectively). Ninety-nine relapsing-remitting MS patients (age = 43.3 ± 9.9 years, disease duration 12.3 ± 7.7 years) were studied, together with twenty-five healthy controls (HC, age = 38.8 ± 11.0 years). FWF was higher in GM and NAWM of MS patients, compared to GM and WM of HC (both p < .001). In MS patients, FWF was the highest in the T1L and GM, followed by T2L and NAWM, respectively. FWF increased significantly with T1L and T2L volume (ρ ranging from 0.40 to 0.58, p < .001). FWF in T2L was strongly related to both T1L volume and the volume ratio T1L/T2L (ρ = 0.73, p < .001). MS patients performed worse than HC in the processing speed test (mean ± SD: 54.1 ± 10.3 for MS, 63.8 ± 10.8 for HC). FWF in GM, T2L, perilesional tissue and NAWM increased with SDMT score reduction (ρ = -0.30, -0.29, -0.33 respectively and r = -.30 for T2L, all with p < .005). A regional analysis, conducted to determine which NAWM regions were of particular importance to explain the relationship between FWF and cognitive impairment, revealed that FWF spatial variance was negatively related to SDMT score in the corpus callosum and the superior longitudinal fasciculus, WM structures known to be associated with cognitive impairment, in addition to the left corticospinal tract, the sagittal stratum, the right anterior limb of internal capsule. In conclusion, we found excess free water in brain parenchyma of MS patients, an alteration that involved not only MS lesions, but also the GM and NAWM, impinging on brain function and negatively associated with cognitive processing speed. We suggest that the FWF metric, derived from noninvasive, rapid MRI acquisitions and bearing good biological interpretability, may prove valuable as an MRI biomarker of tissue damage and associated cognitive impairment in MS.