近期發現的膠淋巴系統是一個在腦內沿著血管旁路徑、類似淋巴循環的系統，科學家推測它可以用來清除中樞神經系統的代謝廢物，其功能可能與神經退行性疾病相關，例如阿茲海默症、失智症。在先前的大鼠重水微灌流實驗顯示，透過注射2% 體重的重水在雙隔室平行模型的分析觀察到腦內慢速灌流的液體，我們可能量測到了重水經由膠淋巴系統流入腦脊髓液的流速，因此這個技術有潛力在活體評估膠淋巴系統的功能。在本論文中，我們選擇自發性高血壓大鼠進行後續研究，自發性高血壓大鼠其高血壓的特性常被用來作為血管性痴呆症及阿茲海默症的動物模型，本實驗除了重水微灌流實驗，我們額外注射了等量的食鹽水至其他自發性高血壓大鼠，並在前後分別收取多自旋迴訊時序影像及擴散影像，藉由正規化非負數最小平方法分析腦液分布。結果顯示大量的液體注射能夠使大腦組織產生變化，其T2縮短的組織在影像中的空間分布與重水慢速流影像吻合，而在腦液分布上展示了細胞內外液的比例增加，因此造成T2縮短的現象；此外，我們從磁振擴散影像得知這些T2縮短區域的擴散係數也有降低的現象，而其餘區域的擴散係數則普遍的增加。我們推測同樣是組織中過多的液體進入細胞間隙所致。我們也額外比較正常大鼠，自發性高血壓大鼠在變化的表現上更為明顯，尤其在腦室與負責記憶功能的海馬迴。我們以重水灌流、T2量測、與擴散影像方法進行實驗，皆觀察到了膠淋巴系統運作的相關現象，換句話說，這些實驗方法應可用來獲取膠淋巴系統調控液體的功能性資訊，而自發性高血壓大鼠的實驗結果與對照組的確有顯著不同。未來應持續探討及應用此技術，以進一步了解神經退化性疾病與腦內膠淋巴系統的液體調節功能的關係。

The recently discovered glymphatic system which is a lymphatic-like circulation system along paravascular pathway in brain tissue. Scientists speculated that it would be contributed to the waste clearance in central nervous system (CNS), and the function could be associated with neurodegenerative disorders, such as Alzheimer’s disease (AD) and dementia. In our previous D2O perfusion experiment on rats, we used 2% of body weight of D2O with two compartment parallel model (2CPM) analysis to observe the fluid of the slow perfusion, and we might measure the flow rate of D2O entering the cerebrospinal fluid (CSF) through glymphatic system. Hence, the technique has a potential for evaluating the function of glymphatic system in vivo. In this study, we proceeded to the research on spontaneously hypertensive rat (SHR). Due to the hypertension characteristic, SHR is used as an animal model of vascular dementia (VaD) or AD. Except for the D2O experiment, we further performed 2% body weight of saline to extra group of SHR and conducted the multiple spin echo sequence and diffusion image before and after fluid injection. Brain fluid distributions were analyzed by regularized nonnegative least square (rNNLS). The results showed the massive fluid would induce brain tissue alternation, and the T2-shortened regions were spatially matched with slow flow maps, and the intra/extracellular water fraction showed an increase in these regions. Moreover, by MR diffusion image, the apparent diffusion coefficient (ADC) decreased in T2-shortened regions, and increased generally in other regions. Therefore, we anticipated that the excessive fluid were entering the intra/extracellular space in tissue. We further compared with normal tensive rat WKY, and SHR demonstrated much more clearly in tissue alternation, especially in ventricles and hippocampus which is in charge of the function of memory. According to the experiment of D2O perfusion, T2 measurement, and diffusion image, we all observed the phenomenon related to glymphatic system, in other words, these experiments can be utilized to acquire the functional information of fluid modulation in glymphatic system. The experimental results of SHR differ significantly from those in control group. Further investigations and application of these techniques should be conducted, to validate the relation between neurodegenerative disorder and fluid regulation of glymphatic system.

1. Iliff JJ, Wang M, Liao Y, Plogg BA, Peng W, Gundersen GA, Benveniste H, Vates GE, Deane R, Goldman SA, Nagelhus EA, Nedergaard M. A paravascular pathway facilitates CSF flow through the brain parenchyma and the clearance of interstitial solutes, including amyloid beta. Science translational medicine 2012;4(147):147ra111.
2. Kress BT, Iliff JJ, Xia M, Wang M, Wei HS, Zeppenfeld D, Xie L, Kang H, Xu Q, Liew JA, Plog BA, Ding F, Deane R, Nedergaard M. Impairment of paravascular clearance pathways in the aging brain. Annals of neurology 2014;76(6):845-861
3. SabbatiniM, CatalaniA, ConsoliC, MarlettaN, TomassoniD, AvolaR. The hippocampus in spontaneously hypertensive rats: An animal model of vascular dementia? Mech Ageing Dev. 2002;123(5):547-559. doi:10.1016/S0047-6374(01)00362-1.
4. BedussiB, NaessensDMP, deVosJ, et al. Enhanced interstitial fluid drainage in the hippocampus of spontaneously hypertensive rats. Sci Rep. 2017;7(1):744. doi:10.1038/s41598-017-00861-x.
5. TayebatiSK, TomassoniD, AmentaF. Spontaneously hypertensive rat as a model of vascular brain disorder: Microanatomy, neurochemistry and behavior. J Neurol Sci. 2012;322(1-2):241-249. doi:10.1016/j.jns.2012.05.047.
6. TajimaA, HansFJ, LivingstoneD, et al. Smaller local brain volumes and cerebral atrophy in spontaneously hypertensive rats. Hypertension. 1993;21(1):105-111. doi:10.1161/01.HYP.21.1.105
7. RitterS, DinhTT. Progressive postnatal dilation of brain ventricles in spontaneously hypertensive rats. Brain Res. 1986;370(2):327-332. doi:10.1016/0006-8993(86)90488-9.
8. Al-SarrafH, PhilipL. Effect of hypertension on the integrity of blood brain and blood CSF barriers, cerebral blood flow and CSF secretion in the rat. Brain Res. 2003;975(1-2):179-188. doi:10.1016/S0006-8993(03)02632-5.
9. TomassoniD, BramantiV, AmentaF. Expression of aquaporins 1 and 4 in the brain of spontaneously hypertensive rats. Brain Res. 2010;1325:155-163. doi:10.1016/j.brainres.2010.02.023.
10. Li CH., Simultaneously trace blood perfusion and glymphatic passage by analyzing deuterium oxide profusion imaging with a two-compartmental parallel model. [master’s thesis] National Tsing Hua University; 2016
11. Wang FN, PengSL, Lu CT, Peng HH, Yeh TC. Water signal attenuation by D2O infusion as a novel contrast mechanism for 1H perfusion MRI. NMR in biomedicine 2013;26(6):692-698.
12. WhittallKP, MacKayAL. Quantitative interpretation of NMR relaxation data. J Magn Reson. 1989;84(1):134-152. doi:10.1016/0022-2364(89)90011-5.
13. MackayA, WhittallK, AdlerJ, LiD, PatyD, GraebD. In vivo visualization of myelin water in brain by magnetic resonance. Magn Reson Med. 1994;31(6):673-677. doi:10.1002/mrm.1910310614.
14. MilfordD, RosbachN, BendszusM, HeilandS. Mono-exponential fitting in T2-relaxometry: Relevance of offset and first echo. PLoS One. 2015; 10(12):1-13.
15. KimD, JensenJH, WuEX, ShethSS, BrittenhamGM. NIH Public Access. 2009; 62(2):300-306.
16. LauleC, KozlowskiP, LeungE, LiDKB, MacKayAL, MooreGRW. Myelin water imaging of multiple sclerosis at 7 T: Correlations with histopathology. Neuroimage. 2008; 40(4):1575-1580.
17. GrahamSJ, StanchevPL, BronskillMJ. Criteria for analysis of multicomponent tissue T2 relaxation data. Magn Reson Med. 1996; 35(3):370-378.
18. MacKayA, LauleC, VavasourI, BjarnasonT, KolindS, MädlerB. Insights into brain microstructure from the T2 distribution. Magn Reson Imaging. 2006;24(4):515-525.
19. Lawson CL, Hanson RJ. Solving Least Squares Problems. Prentice-Hall, Englewood Cliffs, NJ, 1974.
20. Kim SG, Ackerman JJ. Multicompartment analysis of blood flow and tissue perfusion employing D2O as a freely diffusible tracer: a novel deuterium NMR technique demonstrated via application with murine RIF-1 tumors. Magnetic resonance in medicine 1988;8(4):410-426.
21. Gambhir SS, Huang SC, Hawkins RA, Phelps ME. A study of the single compartment tracer kinetic model for the measurement of local cerebral blood flow using 15O-water and positron emission tomography. Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 1987;7(1):13-20.
22. KaiserD, WeiseG, MöllerK, et al. Spontaneous white matter damage, cognitive decline and neuroinflammation in middle-aged hypertensive rats: an animal model of early-stage cerebral small vessel disease. Acta Neuropathol Commun. 2014;2(1):169. doi:10.1186/s40478-014-0169-8.
23. DuningT, KloskaS, SteinsträterO, KugelH, HeindelW, KnechtS. Dehydration confounds the assessment of brain atrophy. Neurology. 2005; 64, 548–550.
24. StreitbürgerDP, MöllerHE, TittgemeyerM, Hund-GeorgiadisM, SchroeterML, MuellerK. Investigating Structural Brain Changes of Dehydration Using Voxel-Based Morphometry. PLoS One. 2012;7(8). doi:10.1371/journal.pone.0044195.
25. NakamuraK, BrownRA, AraujoD, NarayananS, ArnoldDL. Correlation between brain volume change and T2 relaxation time induced by dehydration and rehydration: Implications for monitoring atrophy in clinical studies. NeuroImage Clin. 2014;6:166-170. doi:10.1016/j.nicl.2014.08.014.
26. ZahrNM, MayerD, RohlfingT, et al. A Mechanism of Rapidly Reversible Cerebral Ventricular Enlargement Independent of Tissue Atrophy. Neuropsychopharmacology. 2013;38(6):1121-1129. doi:10.1038/npp.2013.11.
27. LiachenkoS, RamuJ. Quantification and reproducibility assessment of the regional brain T2relaxation in naïve rats at 7T. J Magn Reson Imaging. 2017;45(3):700-709. doi:10.1002/jmri.25378.
28. KozlerP, RiljakV, PokornýJ. Both water intoxication and osmotic BBB disruption increase brain water content in rats. Physiol Res. 2013;62(SUPPL 1).
29. BiancardiVC, SonSJ, AhmadiS, FilosaJA, SternJE. Circulating angiotensin II gains access to the hypothalamus and brain stem during hypertension via breakdown of the blood-brain barrier. Hypertension. 2014;63(3):572-579. doi:10.1161/HYPERTENSIONAHA.113.01743.
30. Kim T, Richard Jennings J, Kim SG. Regional cerebral blood flow and arterial blood volume and their reactivity to hypercapnia in hypertensive and normotensive rats. Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 2014;34(3):408-414.51.
31. Lee JT, Liu HL, Yang JT, Yang ST, Lin JR, Lee TH. Longitudinal MR imaging study in the prediction of ischemic susceptibility after cerebral hypoperfusion in rats: Influence of aging and hypertension. Neuroscience 2014;257:31-40.
32. Calcinaghi N, Wyss MT, Jolivet R, Singh A, Keller AL, Winnik S, Fritschy JM, Buck A, Matter CM, Weber B. Multimodal imaging in rats reveals impaired neurovascular 52 coupling in sustained hypertension. Stroke; a journal of cerebral circulation 2013;44(7):1957-1964.
33. Al-Sarraf H, Philip L. Increased brain uptake and CSF clearance of 14C-glutamate in spontaneously hypertensive rats. Brain research 2003;994(2):181-187.
34. Neuro and Dr Usman Bashir et al, Diffusion weighted imaging, Radiopaedia
35. XieL, KangH, XuQ, et al. Sleep Drives Metabolite Clearance from the Adult Brain. NIH Public Access. 2014;342(6156):1-11. doi:10.1126/science.1241224.Sleep.