小腦型多重系統萎縮症(MSA-C)是一種中樞神經系統萎縮的疾病。本研究應用兩種方法，一為“立體碎形維度(3D-FD)”，另一為“立體腦廻指數（3D-GI）”以達量化MSA-C病人小腦（包括腦幹）萎縮程度及比較與正常人有無明顯差異的目的。我們嘗試評估此兩種方法是否能排除性別差異及抑制因隨年齡增加而造成小腦縮小的現象，並且是否能精確地量化小腦和腦幹的萎縮程度。總計有16位正常人和16 位MSA-C患者參加此研究。我們根據腦部T1核磁共振影像(MR image)重建小腦白質及小腦灰質的三維立體影像，進而探討MSA-C病人小腦各部區域的萎縮情形。正常人與MSA-C病人的小腦灰質與白質的立體碎形維度、立體腦廻指數及體積分別被仔細計算並加以比較。結果顯示正常人的小腦灰質及白質立體碎形維度與立體腦廻指數的數值均在穩定的範圍區間且具微小變異量，沒有明顯的性別差異，也沒有會隨年齡增加而下降的情形。MSA-C病人小腦白質的三種量測數據，皆比正常人明顯的偏低，且在發病初期就十分明顯，顯示MSA-C病人的小腦白質的萎縮為小腦萎縮的最初發病區域。在初期的發病階段，病人中的小腦灰、白質的腦廻指數皆比正常人明顯的偏低。本研究所應用的立體碎形維度及立體腦廻指數分析法皆能準確的呈現小腦萎縮情形及精確的量化小腦形態複雜度的變化。另一方面，使用立體腦廻指數為二維基底的K-means分類法，我們可以很容易且精確的將正常人與MSA-C病人分群及歸類。Multiple System Atrophy of the Cerebellar Type (MSA-C) is a degenerative neurological disease of the central nervous system. This study aimed to employ two methods named, “three-dimensional fractal dimension (3D-FD)” and “surface-based three-dimensional gyrification index (3D-GI)” to quantify morphological changes in normal cerebellum (including brainstem) and atrophic cerebellum in MSA-C patients. We assessed whether the 3D-FD and 3D-GI can alleviate the effects of gender and age in volumetric measure, so that cerebellum and brainstem atrophy can be quantified more accurately. Sixteen healthy subjects and 16 MSA-C patients participated in this study. We compared the images of 3D reconstructed cerebellum gray matter (3D-CBGM) and cerebellum white matter (3D-CBWM) to detect the atrophic region of cerebellum in MSA-C patients. Furthermore, we compared 3D-FD, 3D-GI and volumes of CBGM and CBWM between normal and MSA-C patient groups based on T1-weighted MR images. Both the 3D-FD and 3D-GI values of normal group were in a stable range with small variances, exhibited no gender effect and no age-related shrinkage. All the CBWM measures of MSA-C group revealed significantly lower values compared to the control group, even in the early stage of MSA-C. This result indicated that CBWM is supposed to be the onset region of cerebellar atrophy in MSA-C patients. Both the 3D-FD and 3D-GI methods are superior to conventional volumetric methods in quantifying the structural changes of CBGM and CBWM because they exhibit smaller variances, no gender effect and less age-related shrinkage. Among the three measures, both the CBGM 3D-GI and CBWM 3D-GI revealed significantly lower values in the MSA-C patients compared with healthy subjects, especially in the early phases of the disease. The 3D-FD and 3D-GI methods can precisely indicate the degeneration of the cerebellar folding structure and exactly reflect the morphological changes in cerebellum. Using the two-dimensional K-means classifier of CBWM and CBGM 3D-GI values, we can effectively discriminate the MSA-C patients from healthy subjects.