臺灣博碩士論文加值系統

血流灌注是生物體內將新鮮含氧血由動脈帶到為血管床，提供細胞組織養份與氧氣後，再將含代謝廢物的去氧血經由靜脈運出的一個過程。充分的組織灌流和氧氣的交換是細胞維持代謝及維持生命所必需的過程。在過去幾年，中風在多數先進國家是主要死亡原因之一，我國在過去幾年中風則高居國人十大死因的第三位。中風有出血性中風和缺血性中風兩大類，缺血性中風是血流供應不足以致養份和氧氣供應不夠。頸動脈狹窄是造成缺血性中風的許多原因之一。

在臨床上，數種的成像技術已經應用於評估腦灌流，如：正子造影，電腦斷層掃描，磁振造影。正子造影和電腦斷層掃描是臨床上診斷頸動脈堵塞後腦灌流的主要定量成像技術。磁振造影灌流則具有非游離輻射及高安全性的特色，但磁振灌流的絕對定量則還未被充分研究。以先進技術對中風病人進行絕對定量的灌流評估，以研究大腦因缺氧級組之受損的情形是當前重要的臨床課題之一。

此研究的主旨在單側頸動脈狹窄之患者比較是評估磁振灌流影像的絕對量化與電腦斷層腦血流灌注影像之絕對定量。在回溯性研究中，在20位患有單側頸動脈堵塞或在內頸動脈或中大腦動脈大於79 % 狹窄而尚未中風之患者，經由磁振灌流影像的後處理，做為一系列的絕對定量的分析研究。磁振腦灌流影像的絕對量化，應用以下技術：(1)腦脊髓液的去除；(2)去除血管； (3)利用校正參數找出縮放因子並將相對腦血流體積和相對腦血流轉化計算成絕對值。去除血管是使用閥值技術，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。計算絕對值是用餘留單純腦實質(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。

磁振腦灌流和電腦斷層腦灌流的相關性依序如下: 平均穿流時間 (相關係數 = 0.83)，峰值時間 (相關係數 = 0.50)，腦血流流量 (相關係數 = 0.52)，腦血流體積 (相關係數 = 0.43)。磁振腦灌流和電腦斷層腦灌流在腦血流體積、腦血流流量、平均穿流時間、峰值時間這些資料之異常側、正常側、異常側和正常側的差異、或異常側與正常側的比值，都沒有顯著性差異 (P > 0.05)。在磁振腦灌流和電腦斷層腦灌流的一致性(平均差 ± 2 標準差)結果如下: 腦血流體積-0.57 ± 1.15 mL/100 g、腦血流流量2.50 ± 17.01 mL/100 g/min、平均穿流時間-0.90 ± 2.76 sec、峰值時間3.83 ± 7.01 sec。

由此研究可知，磁振腦灌流影像的絕對量化是可行的。使用該方法的測量結果和電腦斷層腦灌流的參數比較發現，兩者的定量結果是有線性相關且兩者間之一致性是可接受的。

Perfusion is the process of nutritive delivery of arterial blood to a capillary bed in the biological tissues. Sufficient tissue perfusion and oxygenation are vital for all metabolic processes in cells. Over the past few years, stroke has been the third leading cause of death in Taiwan and the rest of the world. Stroke occurs when the blood flow to the brain is impaired, resulting in an insufficient supply of nutrients and oxygen. Carotid stenosis is one of the many causes of stroke.
Several imaging techniques have been applied to assess cerebral perfusion, such as positron emission tomography (PET), computed tomography (CT), and dynamic susceptibility contrast magnetic resonance imaging (DSC–MRI). Some reports have compared perfusion studies of computed tomography perfusion (CTP) and PET in normal volunteers and in patients with chronic cervical carotid artery occlusion. Quantitative imaging is a key factor for the diagnosis in the clinical examination; however, absolute quantification in DSC–MRI has not been fully investigated.
The aim of the study was to assess absolute quantification of dynamic susceptibility contrast–enhanced magnetic resonance perfusion (MRP) comparing with computed tomography perfusion (CTP) as the standard reference in patients with unilateral stenosis. We retrospectively post-processed MRP in 20 patients with unilateral occlusion or stenosis of > 79% at the internal carotid artery (ICA) or the middle cerebral artery (MCA). Absolute quantification of MRP was performed after applying the following techniques: cerebral spinal fluid (CSF) removal, vessel removal using both relative cerebral blood volume (rCBV) and relative cerebral blood flow (rCBF) masks. A thresholding technique was applied to rCBV and rCBF images to remove the effects of vessel voxels. The thresholds were set at twice of the median values of the rCBV and rCBF histograms. Voxels with rCBV or rCBF values higher than the thresholds were classified as vessel voxels. The vessel voxels were removed from the brain mask. The thresholding technique was also applied to TTP images for finding normal brain parenchyma. The averaged rCBV and rCBF for the voxels segmented as normal brain parenchyma voxels were calculated for finding scaling factors to convert the rCBV and rCBF images into absolute values.
The correlation between MRP and CTP was best for mean transit time (MTT) (r = 0.83), followed by time to peak (TTP) (r = 0.50), cerebral blood flow (CBF) (r = 0.52) and cerebral blood volume (CBV) (r = 0.43). There was no significant difference between MRP and CTP for CBV, CBF, MTT and TTP on the lesion side, the contralateral side, the lesion-contralateral differences, or the lesion-to-contralateral ratios (P > 0.05). The limits of agreement between MRP and CTP were as follows: CBV -0.57 ± 1.15 mL/100 g, CBF 2.50 ± 17.01 mL/100 g/min, MTT -0.90 ± 2.76 sec, and TTP 3.83 ± 7.01 sec.

Absolute quantification of MRP is possible. Using the proposed method, the measured values of MRP and CTP had acceptable linear correlation and acceptable quantitative agreement.

Table of contents
Chinese Abstract i
English Abstract iii
Comprehensive summary of dissertation v
Table of contents xii
List of Figures xiii
List of Tables xiv
List of Acronyms xv

Chapter 1. Introduction 1
1.1 Motivation 1
1.2 Outline 3
1.3 Hemodynamic Perfusion Study in CT vs. MR 5
1.4 Related Research 8
1.5 Original Efforts 11

Chapter 2. Materials and Methods 12
2.1 Experimental Design 12
2.2 Theory of Hemodynamic Estimation from CTP vs. MRP 14
2.3 Data Acquisition 19
2.4 Data Scanning Protocol 21
2.5 Data Analysis 23
2.6 Statistical Analysis 29

Chapter 3. Demonstration for Performance Assessment 30
3.1 Independent Component Analysis technique 30
3.2 Quantitative Assessments after CSF and Vessel Voxel Removal 33

Chapter 4. Result 39
Chapter 5. Discussion 50
Chapter 6. Conclusion 57
References 58

List of Figures
Figure 2-1. Diagram for the perfusion study 13
Figure 2-2. Flowchart for quantitative assessment of perfusion study 24
Figure 3-1. The data outputs from the independent component analysis 31
Figure 3-2. Selection of the AIF after the segmentation results in MRP 32
Figure 3-3. Maximum relative concentration in MRP 34
Figure 3-4 (I). Removal of CSF pixels in MRP 35
Figure 3-4 (II). Removal of vessel voxels in MRP 35
Figure 3-5. Post-processing technique for removing CSF and vessels voxels 36
Figure 3-6. Analysis of ROI manual contours in MCA territory 36
Figure 3-7. All maps of MRP after removal of CSF and vessels 37
Figure 4-1. Scatter plots of absolute data of all parameters in CTP versus MRP 42
Figure 4-2. Bland-Altman analysis of MRP versus CTP for all parameters 43
Figure 4-3. Scatter plots of all parameters ratio in CTP versus MRP 46
Figure 4-4. Bland-Altman analysis of MRP versus CTP for all parameter’s ratio 47
Figure 4-5. Rescaled CBVand CBF, MTT,TTP from MRP vs. CTP imaging 49
Figure 5-1. AIF selection and all maps on a high ventricular plane in CTP 55
Figure 5-2. Bland-Altman plot in CBF difference to mean map 56

List of Tables
Table 2-1. Patient demographics in CTP and MRP 20
Table 4-1. Measured perfusion absolute data obtained using CTP and MRP 41
Table 4-2. Absolute values between normal and impaired hemispheres 44
Table 4-3. Limits of agreement and test of normality 45
Table 4-4. Measured ratio data of CTP and MRP 48

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