abstract: Electromagnetic fields (EMFs) generated by biologically active neural tissue are critical in the diagnosis and treatment of neurological diseases. Biological EMFs are characterized by electromagnetic properties such as electrical conductivity, permittivity and magnetic susceptibility. The electrical conductivity of active tissue has been shown to serve as a biomarker for the direct detection of neural activity, and the diagnosis, staging and prognosis of disease states such as cancer. Magnetic resonance electrical impedance tomography (MREIT) was developed to map the cross-sectional conductivity distribution of electrically conductive objects using externally applied electrical currents. Simulation and in vitro studies of invertebrate neural tissue complexes demonstrated the correlation of membrane conductivity variations with neural activation levels using the MREIT technique, therefore laying the foundation for functional MREIT (fMREIT) to detect neural activity, and future in vivo fMREIT studies. The development of fMREIT for the direct detection of neural activity using conductivity contrast in in vivo settings has been the focus of the research work presented here. An in vivo animal model was developed to detect neural activity initiated changes in neuronal membrane conductivities under external electrical current stimulation. Neural activity was induced in somatosensory areas I (SAI) and II (SAII) by applying electrical currents between the second and fourth digits of the rodent forepaw. The in vivo animal model involved the use of forepaw stimulation to evoke somatosensory neural activations along with hippocampal fMREIT imaging currents contemporaneously applied under magnetic field strengths of 7 Tesla. Three distinct types of fMREIT current waveforms were applied as imaging currents under two inhalants – air and carbogen. Active regions in the somatosensory cortex showed significant apparent conductivity changes as variations in fMREIT phase (φ_d and ∇^2 φ_d) signals represented by fMREIT activation maps (F-tests, p <0.05). Consistent changes in the standard deviation of φ_d and ∇^2 φ_d in cortical voxels contralateral to forepaw stimulation were observed across imaging sessions. These preliminary findings show that fMREIT may have the potential to detect conductivity changes correlated with neural activity. / Dissertation/Thesis / Doctoral Dissertation Biomedical Engineering 2020

從1906到1999年間，台灣地區男性出生時平均餘命增加了43.55歲，女性增加了47.63歲，雖然台灣地區平均餘命不斷地在增加，地區間死亡風險的差異情形則未有所改善。本研究以生命表方式計算台灣地區縣市級、鄉鎮級平均餘命，尤以鄉鎮級為研究重心，配合統計地圖的使用以瞭解小地區間死亡風險的差異情形。 在縣市層級方面，男性與女性出生時平均餘命皆以七大都市較高，西部其他地區次之，東部地區的花蓮縣、台東縣最低。各縣市出生時平均餘命的差異，正指出各縣市之間的死亡風險差異甚大，特別是東部地區明顯地比西部地區更處於不利的狀態。 在鄉鎮層級方面，男性與女性各生命階段平均餘命皆呈現出西部地區高、東部地區低的明顯差異，而且平均餘命數值越低的地區其兩性平均餘命的差距也越大，此種現象尤以男性平均餘命越低的地區越為明顯。在空間模式上，男、女平均餘命最高的地區皆以大都市為中心向外擴散至其鄰近地區，平均餘命最低的地區則廣散在山地鄉之間。總的來說，中央山脈兩側的鄉鎮不僅死亡風險較其他地區高、兩性的死亡風險差異大，山地鄉之間的死亡風險結構更是呈現高度的異質性。 關鍵字：鄉鎮市區、死亡風險、平均餘命、性別差異、統計地圖、空間模式。 / Over the twentieth century (1906-1999), the life expectancy at birth in Taiwan has increased 43.55 and 47.63 years for males and females respectively. Undoubtedly, such a dramatic increase in life expectancy is resulted from the improvement of living quality in Taiwan over the past century. Nevertheless, after detailed examination of historical data, it shows that the areal variation in life expectancy over the life cycle is significant and has never diminished. This study, by applying the life table methods and statistical maps, attempts to analyze the areal variation in risks of death at small areas in Taiwan. The data sources for achieving this purpose come from the vital statistics and death-registration- profiles. The research findings show that life expectancies for both males and females are highest in the most-developed urban counties. On the contrary, the life expectancies are lower in rural counties. The gaps in life expectancies at birth between Taipei City and Taitung county reach 11 years and 7 years for males and females respectively. The spatial pattern of variation in life expectancy at the township-level is consistent with the research findings at the county-level. In general, the life expectancies for townships within the central metropolitan area are highest, and then gradually decrease for townships distant from the metropolis center. The life expectancies for both males and females are lowest in the rural-mountain townships. The gap in life expectancies between males and females is also larger in these rural-mountain areas. Finally, the life expectancies for the aboriginal townships are lowest in Taiwan. However, the age profiles for risks of death are heterogeneous in these aboriginal townships. Keywords: life expectancy, life table, statistical maps, spatial pattern