臺灣博碩士論文加值系統

目的：
本實驗使用閥值技術，辨識出磁振影像上血管或鄰近血管而受影響的區域，將之移除，另外，也使用篩選標準找出正常腦組織遮罩，對照文獻上絕對值，以校正參數將相對腦血流體積與相對腦血流流量轉換成絕對值。藉此改善部份體積效應的影響，增進腦血流體積與腦血流流量定量準確性。
材料與方法：
將腦灌流磁振影像進行獨立成份分析法，得到動脈成份為主的遮罩，找出動脈之平均濃度時間曲線，作為動脈輸入函數，計算腦血流體積與腦血流流量相對值。先將腦脊髓液與背景移除，再依據血管或受血管磁化率影響的區域有較高的腦血流體積與腦血流流量數值的特性，使用閥值技術，辨識相對腦血流體積與相對腦血流流量影像上血管或鄰近血管而受影響的區域。畫出相對腦血流體積與相對腦血流流量之直方圖，計算兩直方圖的中位數，以兩倍中位數為閥值，將相對腦血流體積與相對腦血流流量過高的體素，視為血管並移除。將血管、腦脊髓液與背景移除後，餘留單純腦實質(灰質與白質)之腦組織影像，應用閥值技術於此腦組織峰值時間影像，找出正常腦組織遮罩，將遮罩內的相對腦血流體積與相對腦血流流量數值，利用校正參數換為絕對值，校正部份體積效應的影響。
結果：
此方法可以改善磁振造影礙於解析力，難以絕對定量之缺陷，並提供不受血管影響，單純腦白質或灰質組織腦血流體積與腦血流量參數，防止血管磁化率效應帶來高估或錯估之情形。
結論：
本研究提出移除血管的後處理技術，減少血管磁化率效應影響，並提供一個不必使用靜脈輸入函數，便可作部份體積效應校正的方法，增進臨床上腦血流動力參數之定量評估。

關鍵字：腦血流灌注磁振影像、動脈輸入函數、血管移除、腦血流體積、腦血流流量

Purpose：A thresholding technique was applied to the relative cerebral blood volume (CBV) and relative cerebral blood flow (CBF) images for removing voxels either containing vessels or near vessels. Scaling factors were calculated for converting relative CBV and relative CBF values to absolute values. Quantitative measurements of CBV and CBF on brain parenchyma were improved.
Material and methods：The independent component analysis technique was utilized to segment the arterial region on brain perfusion MRI for normal subjects and patients with stenosis, and found the arterial input function (AIF) for following calculation. Because voxels containing or near vessels had much higher relative CBV and relative CBF values than voxels containing only brain parenchyma, a thresholding technique can be applied to relative CBV and relative CBF images for segmenting vessel voxels. The relative CBV and relative CBF histograms were plotted for voxels included in the brain mask with CSF voxels removed. The median values of the two histograms were calculated. The thresholds were set at twice of the median values of the relative CBV and relative CBF histograms. Voxels with relative CBV or relative CBF values higher than the thresholds were classified as vessel voxels. These vessel voxels were removed from the brain mask. The thresholding technique was also applied to TTP images for finding normal brain parenchyma. The averaged relative CBV and relative CBF for the voxels segmented as normal brain parenchyma voxels were calculated for finding scaling factors to convert the relative CBV and relative CBF images into absolute CBV and CBF image, and correct the partial volume effect.
Results：This method can solve the defects of absolute quantification caused by its poor resolving power in magnetic resonance imaging; moreover, CBV and CBF of white matter or gray matter were measured without magnetic susceptibility effect of the blood vessels.
Conclusion：A post-processing technique was proposed for removing voxels either containing vessels or affected by vessels. And the proposed partial volume estimation technique provides a possible alternative for achieving quantitative measurements without using venous output function correction.

Key words：brain perfusion MRI；arterial input function；vessel removal；cerebral blood volume；cerebral blood flow.

中文摘要 i
Abstract ii
目錄 iii
圖表目錄 v
第一章 緒論 1
1.1 研究背景 1
1.2 論文架構 4
第二章 對比劑灌注造影 5
2.1 磁振造影量測腦血流動力參數 7
2.2 動態磁化率對比造影 9
2.2.1 訊號變化轉換成對比劑濃度變化 10
2.2.2 動脈輸入函數 12
2.2.3 曲線特性參數 13
2.2.4 部份體積效應修正 15
2.2.5 腦血流體積 17
2.2.6 腦血流流量 18
2.2.7 穿流時間 20
第三章 實驗方法及流程 21
3.1 影像擷取 22
3.2 影像後處理 23
3.2.1 獨立成分分析法 23
3.2.2 去除空氣及頭皮組織 26
3.2.3 動脈輸入函數選擇 28
3.2.4 腦脊髓液遮罩 30
3.2.5 腦血管遮罩 31
3.2.6 部份體積效應的校正 32
3.2.7 數據分析 34
第四章 實驗結果 35
4.1 獨立成分分析結果 35
4.2 動脈輸入函數結果 37
4.3 腦脊髓液與血管移除前後之結果 38
4.4 部份體積校正結果 42
4.5 腦血流動力參數分析 50
第五章 討論與結論 56
5.1 討論 56
5.1.1 動脈輸入函數 56
5.1.2部份體積效應的校正 57
5.1.3 血管遮罩 61
5.1.4 腦血流動力參數 64
5.2 結論 66
參考文獻 67

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