磁共振影像(Magnetic Resonance Imaging, MRI)是一項非常有用且不使用游離輻射又能提供三維空間資訊的非侵入式檢測方法，在材料科學、生物醫學與醫療診斷、食品科學等領域中取得了豐富的成果。然而，在許多情況下，例如疾病的檢測會因為影像對比度不足難以判斷病變組織或器官的正確位置。透過MRI造影劑中高順磁性的金屬離子可以有效且有選擇性地加速水分子上1H的核鬆弛速率，從而改善影像對比度，提高診斷精準度。
現今的MRI造影劑理論假定造影劑處於一小分子組成的稀釋溶液中以便獲得一個較簡單、容易處理的近似環境。但生物細胞內是一個非常擁擠且複雜的環境。細胞內充斥著水、賀爾蒙、維生素等小分子以及離子外，還含有核酸、核醣體、蛋白質和碳水化合物等生物巨分子。因此MRI造影劑的行為與功能可能會被細胞環境內的離子與生物巨分子所影響。了解造影劑如何與細胞中其他分子或離子作用是非常重要也非常複雜的問題。
本工作聚焦於常見小離子對MRI造影劑在擁擠環境下的影響。我們選取的MRI造影劑是醫院常用的釓多酸水溶液(Dotarem)；使用生物體中常見的鹽類(LiCl, NaCl, KCl, MgCl2, CaCl2, NaI)當作離子來源；使用人工合成不具有確定結構的惰性分子polyethylene glycol 6000 (PEG6k)作為擁擠劑，模擬細胞內擁擠環境。透過高場（500 MHz）核磁共振儀上的脈衝場梯度（Pulse Filed Gradient, PFG）NMR方法以及NMR鬆弛方法測量添加Dotarem溶液中水分子的平移與轉動擴散，探討溶液中水分子、鹽離子、高分子擁擠劑與造影劑間的交互作用。我們可以從NMR實驗中看到水分子上1H的轉動與平移擴散會被離子與擁擠效應顯著地影響。我們發現，隨著離子濃度變化，水的鬆弛速率及擴散速率呈現一些規則，與離子價數，離子大小以及擁擠劑的濃度和造影劑濃度有關。我們也利用變場式核磁共振儀測量NMR鬆弛分散(NMR Dispersion)，了解水分子在各種磁場(0 – 40 MHz)下的動態資訊來佐證高場NMR鬆弛及PFG擴散結果。藉由與鬆弛與擴散機制研究鹽離子與擁擠環境下造影劑分子的動態，可以增加對MRI影像對比度生成的微觀機制之確認，避免核磁共振成像解讀上的誤判。

Magnetic resonance imaging (MRI) has become the most important non-invasive method for providing three dimensional detailed images without using damaging radiation and is a powerful tool in materials science, biomedicine, medical diagnosis, food science and many other fields. In many situations such as in disease detection, however, the image contrast is not sufficient. Therefore, through the MRI contrast agent, its high paramagnetic ion can effectively and selectively accelerate water 1H nuclear relaxation rates. Therefore, water molecules in different microenvironments obtain a different relaxation acceleration so that a better contrast is achieved for the diseased regions.
However, current theory for MRI contrast agent was developed by assuming that the paramagnetic ions are located in a dilute aqueous solution. This is a good approximation in many situations such as water in a relatively free microenvironments, but cellular environment is highly crowded with various kinds of biomacromolecules (proteins, hydrocarbonates, genetic materials etc), small molecules (hormones, vitamins etc) and ions (H+, Na+, K+, Cl- etc). The performance of MRI contrast agent may be significantly altered by crowders and ions. Understanding how the contrast agent interacts with other molecules in cell is a very important and challenging problem.
In this work, we focus on the influence of common ions in organisms and macromolecular crowding effect on the performance of MRI contrast agent. The MRI contrast agent we chose is Dotarem which is the mostly used in medical diagnosis.. Then we follow the standard practice of selecting a macromolecular crowder (polyethylene glycol, M.W. 6000, PEG6k, an artificial inert macromolecule, with no specific structure in aqueous solutions) to mimic cellular environment. The ions used here are those mostly commonly found in humans (LiCl, NaCl, KCl, MgCl2, CaCl2, NaI). 1H NMR relaxation rates and translational diffusion rate of water and PEG6k are measured on a 500 MHz NMR spectrometer equipped with a Pulse Filed Gradient (PFG) unit. It is found that the longitudinal relaxation rates and translational diffusion coefficient are sensitive measures for quantifying the effects of ions and macromolecular crowders on the performance of MRI contrast agent. Within the concentration range typically present in an organism, these dynamic parameters are found to clearly depend on the concentration, type and valence number of the ions besides the concentration of MRI contrast agent and macromolecular crowding effect. These results are further supplemented by fast field cycling relaxometry (NMR relaxation dispersion) over a range between 0.01 – 40 MHz. The physical chemistry mechanism of these effects is elucidated by analyzing the experimental results. The significance of these effects to practical MRI is discussed. Based on the experimental and theoretical results as well as the analysis, we conclude that both the ionic and macromolecular effects must be taken into account for more precise MRI diagnosis or functional MRI studies.

摘要 i
Abstract iii
目錄 v
圖目錄 vii
表目錄 x
第一章 緒論 1
1.1 前言 1
1.2 研究動機 3
第二章 核磁共振原理與磁共振造影劑介紹 4
2.1 核磁共振簡介 4
2.2 核磁共振鬆弛 (Relaxation) 7
2.3 NMRD鬆弛速率隨磁場變化 9
2.4 脈衝場梯度擴散 11
2.5 MRI基礎原理 15
2.6 造影劑 18
2.6.1 順磁分子鬆弛理論 20
2.6.2 內層質子鬆弛機制 21
2.6.3 外層質子鬆弛機制 23
2.6.4 內外層水分子間的交換機制 24
第三章 擁擠和侷限效應 26
3.1擁擠和侷限效應 26
3.2熱力學觀點解釋擁擠和侷限 28
3.3 擁擠效應文獻回顧 32
第四章 溶液離子效應 35
4.1 鹽離子水溶液 35
4.2 水合離子半徑、水合交換速率 36
4.3 構築離子與解構離子 38
4.4 霍夫梅斯特序列 (Hofmeister Series) 41
4.5 高分子與離子間交互作用力 43
4.6 水溶液鹽離子效應與蛋白質 45
第五章 實驗部分 47
5.1 實驗藥品 47
5.1.1 Polyethylene glycol (PEG) 47
5.1.2 Dotarem (Gd-DOTA) 48
5.1.3 鹽離子 48
5.1.4 4,4-dimethyl-4-silapentane-1-sulfonic acid (DSS) 48
5.2 樣品製備 49
5.2.1 擁擠劑水溶液製備 49
5.2.2 Dotarem水溶液製備 49
5.2.3 鹽離子水溶液製備 50
5.2.4 溶劑製備 51
5.3儀器實驗配製 51
5.3.1 平移與轉動擴散實驗 51
5.3.2 NMRD實驗 51
5.4儀器設備 52
5.5實驗參數 52
第六章 結果與討論 54
6.1 在無造影劑，不同鹽離子、擁擠劑濃度溶液中水的平移擴散速率 54
6.2 在有造影劑，不同鹽離子、擁擠劑濃度溶液中水與PEG6k的平移擴散速率 58
6.3 不同擁擠劑濃度氘代溶液中PEG6k的變溫1H，R1，R2，T1rho 65
6.4 不同鹽離子、擁擠劑與Dotaram造影劑濃度溶液中PEG6k的縱向鬆弛速率 68
6.5 1H NMRD實驗 71
6.6 與分子動力學模擬結果比較 75
第七章 結論 77
參考文獻 79

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