Mandl René C W, Pasternak Ofer, Cahn Wiepke, Kubicki Marek, Kahn René S, Shenton Martha E, Hulshoff Pol Hilleke E
Brain Center Rudolf Magnus, Department of Psychiatry, University Medical Center Utrecht, The Netherlands.
Harvard Medical School, Brigham and Women's Hospital, Departments of Psychiatry and Radiology, Boston, USA.
Schizophr Res. 2015 Jan;161(1):126-32. doi: 10.1016/j.schres.2014.09.046. Epub 2014 Oct 22.
Diffusion weighted imaging (DWI) has been extensively used to study the microarchitecture of white matter in schizophrenia. However, popular DWI-derived measures such as fractional anisotropy (FA) may be sensitive to many types of pathologies, and thus the interpretation of reported differences in these measures remains difficult. Combining DWI with magnetization transfer ratio (MTR) - a putative measure of white matter myelination - can help us reveal the underlying mechanisms. Previous findings hypothesized that MTR differences in schizophrenia are associated with free water concentrations, which also affect the DWIs. In this study we use a recently proposed DWI-derived method called free-water imaging to assess this hypothesis. We have reanalyzed data from a previous study by using a fiber-based analysis of free-water imaging, providing a free-water fraction, as well as mean diffusivity and FA corrected for free-water, in addition to MTR along twelve major white matter fiber bundles in 40 schizophrenia patients and 40 healthy controls. We tested for group differences in each fiber bundle and for each measure separately and computed correlations between the MTR and the DWI-derived measures separately for both groups. Significant higher average MTR values in patients were found for the right uncinate fasciculus, the right arcuate fasciculus and the right inferior-frontal occipital fasciculus. No significant results were found for the other measures. No significant differences in correlations were found between MTR and the DWI-derived measures. The results suggest that MTR and free-water imaging measures can be considered complementary, promoting the acquisition of MTR in addition to DWI to identify group differences, as well as to better understand the underlying mechanisms in schizophrenia.
扩散加权成像（DWI）已被广泛用于研究精神分裂症患者白质的微观结构。然而，诸如分数各向异性（FA）等常用的DWI衍生指标可能对多种类型的病变敏感，因此对这些指标报告差异的解释仍然困难。将DWI与磁化传递率（MTR）（一种推测的白质髓鞘形成指标）相结合，有助于我们揭示潜在机制。先前的研究结果假设，精神分裂症患者的MTR差异与自由水浓度有关，而自由水浓度也会影响DWI。在本研究中，我们使用一种最近提出的DWI衍生方法——自由水成像来评估这一假设。我们通过对自由水成像进行基于纤维的分析，重新分析了先前一项研究的数据，除了沿40例精神分裂症患者和40例健康对照者的12条主要白质纤维束测量MTR外，还提供了自由水分数以及校正自由水后的平均扩散率和FA。我们分别测试了每组纤维束和每个指标的组间差异，并分别计算了两组中MTR与DWI衍生指标之间的相关性。结果发现，患者右侧钩束、右侧弓状束和右侧额枕下束的平均MTR值显著更高。其他指标未发现显著结果。MTR与DWI衍生指标之间的相关性未发现显著差异。结果表明，MTR和自由水成像指标可被视为互补指标，除DWI外，增加MTR测量有助于识别组间差异，并更好地理解精神分裂症的潜在机制。
