Department of Electrical, Electronic, and Information Engineering "Guglielmo Marconi", University of Bologna, Bologna, Italy.
"Mario Serio" Department of Experimental and Clinical Biomedical Sciences, University of Florence, Florence, Italy.
J Neuroimaging. 2018 Nov;28(6):688-693. doi: 10.1111/jon.12534. Epub 2018 Jul 5.
Fractal dimension (FD) is an index of structural complexity of cortical gray matter (GM) and white matter (WM). Application of FD to pontocerebellar degeneration has revealed cerebellar changes. However, so far, possible concurrent cerebral changes and progression of changes in brain complexity have not been investigated.
We computed FD of cerebellar and cerebral cortex and WM derived from longitudinal brain MRI of patients with spinocerebellar ataxia type 2 (SCA2), which is an inherited cause of pontocerebellar degeneration. Nine SCA2 patients and 16 age-matched healthy controls were examined twice (3.6 ± .7 and 3.3 ± 1.0 years apart, respectively) on the same 1.5T MR scanner with T1-weighted imaging. Cortical GM and WM of the cerebrum and cerebellum were segmented using FreeSurfer and FD of these segmentations were computed.
At baseline, FD values of cerebellar GM and WM were significantly (P < .001) lower in SCA2 patients (2.48 ± .04 for GM and 1.74 ± .09 for WM) than in controls (2.56 ± .02 for GM and 2.22 ± .19 for WM). Also, FD values of cerebral GM were significantly (P < .05) lower in SCA2 patients (2.39 ± .03) than in controls (2.43 ± .02). No significant differences were observed for FD of the cerebral WM. The rate of change of FD values was not significantly different between SCA2 patients and controls.
The structural complexity of the cerebellum and cerebral cortex is reduced in SCA2 patients. Fractal analysis seems not to be able to demonstrate progression of changes associated with degeneration in SCA2.
分形维数（FD）是皮质灰质（GM）和白质（WM）结构复杂性的指标。将 FD 应用于桥脑小脑变性，揭示了小脑的变化。然而，到目前为止，还没有研究可能同时存在的大脑变化和脑复杂性变化的进展。
我们计算了脊髓小脑性共济失调 2 型（SCA2）患者的纵向脑 MRI 中的小脑和大脑皮层以及 WM 的 FD，SCA2 是桥脑小脑变性的遗传性原因。9 例 SCA2 患者和 16 名年龄匹配的健康对照者在同一 1.5T 磁共振扫描仪上进行了两次检查（分别相隔 3.6 ±.7 和 3.3 ± 1.0 年），使用 FreeSurfer 对大脑和小脑的 GM 和 WM 进行分割，并计算这些分割的 FD。
在基线时，SCA2 患者的小脑 GM 和 WM 的 FD 值显著降低（P <.001）（GM 为 2.48 ±.04，WM 为 1.74 ±.09），明显低于对照组（GM 为 2.56 ±.02，WM 为 2.22 ±.19）。此外，SCA2 患者的大脑 GM 的 FD 值也显著降低（P <.05）（2.39 ±.03），明显低于对照组（2.43 ±.02）。大脑 WM 的 FD 值没有显著差异。SCA2 患者和对照组之间 FD 值的变化率没有显著差异。
SCA2 患者的小脑和大脑皮层的结构复杂性降低。分形分析似乎不能证明与 SCA2 变性相关的变化进展。
