Sawada Kazuhiko, Horiuchi-Hirose Miwa, Saito Shigeyoshi, Aoki Ichio
Department of Physical Therapy, Faculty of Medical and Health Sciences, Tsukuba International University, Tsuchiura, Ibaraki 300-0051, Japan.
Neuroimage. 2013 Dec;83:294-306. doi: 10.1016/j.neuroimage.2013.06.024. Epub 2013 Jun 14.
The present study aimed to characterize cerebral morphology in young adult ferrets and its sexual dimorphism using high-field MRI and MRI-based morphometry. Ex vivo short TR/TE (typical T1-weighted parameter setting for conventional MRI) and T2W (long TR/TE) MRI with high spatial resolution at 7-tesla could visualize major subcortical and archicortical structures, i.e., the caudate nucleus, lentiform nucleus, amygdala and hippocampus. In particular, laminar organization of the olfactory bulb was identifiable by short TR/TE-MRI. The primary and secondary sulci observable in the adult ferret were distinguishable on either short TR/TE- or T2W-MRI, and the cortical surface morphology was reproduced well by 3D-rendered images obtained by short TR/TE-MRI. The cerebrum had a significantly lower volume in females than in males, which was attributed to region-specific volume reduction in the cerebral cortex and subcortical white matter in females. A sexual difference was also detected, manifested by an overall reduction in normalized signal ratios of short TR/TE-MRI in all cerebral structures examined in females than in males. On the other hand, an alternating array of higher and lower short TR/TE-MRI intensity transverse zones throughout the cortex, which was reminiscent of the functional cortical areas, was revealed by maximum intensity projection (MIP) in 3D. The normalized signal ratio of short TR/TE-MRI, but not T2W-MRI in the cortex, was negatively correlated with the density of myelin-basic protein immunoreactive fibers (males, r=-0.440; females, r=-0.481). The present results suggest that sexual differences in the adult ferret cerebrum are characterized by reduced volumes of the cerebral cortex and subcortical white matter in females, and by overall reductions in physiochemical characteristics, as obtained by short TR/TE-MRI, in females. It should be noted that short TR/TE-MRI-based MIP delineated functional cortical areas related to myeloarchitecture in 3D. Such an approach makes possible conventional investigation of the functional organization of the cerebral cortex and its abnormalities using high-field MRI.
本研究旨在利用高场磁共振成像（MRI）和基于MRI的形态测量法，对成年幼龄雪貂的脑形态及其性别差异进行表征。在7特斯拉的条件下，具有高空间分辨率的离体短TR/TE（传统MRI的典型T1加权参数设置）和T2W（长TR/TE）MRI能够显示主要的皮质下和原皮质结构，即尾状核、豆状核、杏仁核和海马体。特别地，嗅球的分层组织可通过短TR/TE-MRI识别。成年雪貂中可观察到的初级和次级脑沟在短TR/TE-或T2W-MRI上均可区分，并且通过短TR/TE-MRI获得的三维渲染图像能够很好地再现皮质表面形态。雌性雪貂的大脑体积显著低于雄性，这归因于雌性大脑皮质和皮质下白质中特定区域的体积减小。还检测到了性别差异，表现为在所有检测的脑结构中，雌性短TR/TE-MRI的标准化信号比总体低于雄性。另一方面，通过三维最大强度投影（MIP）显示，整个皮质中短TR/TE-MRI强度的高低交替横带阵列让人联想到功能性皮质区域。皮质中短TR/TE-MRI的标准化信号比与髓磷脂碱性蛋白免疫反应性纤维密度呈负相关，而T2W-MRI则无此相关性（雄性，r = -0.440；雌性，r = -0.481）。目前的研究结果表明，成年雪貂大脑的性别差异表现为雌性大脑皮质和皮质下白质体积减小，以及雌性通过短TR/TE-MRI获得的理化特性总体降低。应当指出的是，基于短TR/TE-MRI的MIP在三维上描绘了与髓鞘结构相关的功能性皮质区域。这种方法使得利用高场MRI对大脑皮质的功能组织及其异常情况进行传统研究成为可能。
