D'Arceuil Helen, de Crespigny Alex
Athinoula Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, MGH-NMR Center, Rm 2301, Bldg 149, 13th St., Charlestown, MA 02129, USA.
Neuroimage. 2007 May 15;36(1):64-8. doi: 10.1016/j.neuroimage.2007.02.039. Epub 2007 Mar 6.
There have been numerous high resolution diffusion tensor imaging studies in fixed animal brains, but relatively few studies in human brains. While animal tissues are generally fixed pre-mortem or directly postmortem, this is not possible for human tissue, therefore there is always some delay between death and tissue fixation. The elapsed time between death and tissue fixation, the postmortem interval (PMI), will most likely adversely affect the tissue's diffusion properties. We studied the effects of PMI on the diffusion properties of rodent brain. Eight mice were euthanized and the brains (kept in the skull) were placed in formalin at PMIs of 0, 1, 4 and 14 days. Post fixation they were placed in a solution of GdDTPA and phosphate buffered saline. Brains were scanned with a 3D EPI DTI sequence at 4.7T. DTI data were processed to generate apparent diffusion coefficient (ADC) and fractional anisotropy (FA) maps. DTI tractography was also performed. The temporal changes in regional ADC and FA values were analyzed statistically using a one-way ANOVA, followed by individual Student's T-tests. Regional FA and ADC of gray and white matter decreased significantly with time (p<0.05). DTI tractography showed a decrease in the number and coherence of reconstructed fiber pathways between PMIs 0 and 14. Elapsed time between death and tissue fixation has a major effect upon the brain's diffusion properties and should be born in mind when interpreting fixed brain DTI.
在固定的动物大脑中已经进行了大量高分辨率扩散张量成像研究，但在人类大脑中的研究相对较少。虽然动物组织通常在死前或死后立即固定，但人类组织无法做到这一点，因此从死亡到组织固定之间总会有一些延迟。死亡与组织固定之间的时间间隔，即死后间隔（PMI），很可能会对组织的扩散特性产生不利影响。我们研究了PMI对啮齿动物大脑扩散特性的影响。将八只小鼠安乐死，其大脑（保留在颅骨内）分别在PMI为0、1、4和14天时置于福尔马林中。固定后，将其置于钆喷酸葡胺和磷酸盐缓冲盐水溶液中。在4.7T下用3D EPI DTI序列对大脑进行扫描。对DTI数据进行处理以生成表观扩散系数（ADC）和分数各向异性（FA）图。还进行了DTI纤维束成像。使用单因素方差分析对区域ADC和FA值的时间变化进行统计分析，随后进行个体学生t检验。灰质和白质的区域FA和ADC随时间显著降低（p<0.05）。DTI纤维束成像显示，在PMI为0和14之间，重建纤维束的数量和连贯性减少。死亡与组织固定之间的时间间隔对大脑的扩散特性有重大影响，在解释固定大脑DTI时应牢记这一点。
