- 學位論文
磁化率定量功能性磁振影像於鼠腦視覺刺激之研究
Quantitative Susceptibility Functional MRI (QS-fMRI) of Rat Brain during Visual Stimulation
摘要
血氧濃度相依功能性磁振影像已被廣泛應用於量測大腦活化反應之工具，它可以定性地觀察大腦在刺激下活化反應區的血氧濃度變化。近年來，磁化率定量影像技術被提出用來計算活體中的磁化率特性，更能進一步估算出靜脈血氧飽和濃度。本研究應用磁化率定量技術於大鼠視覺閃光刺激之大腦功能性研究模型，建立磁化率定量功能性磁振影像之實驗流程，以提供大腦功能性研究定量的生理資訊。 本研究採用5赫茲之閃光刺激進行功能性磁振掃描，並將掃描所得之相位影像計算成磁化率影像，接著將磁化率定量影像與強度影像分別進行相關性之群組分析來觀察其大腦活化區。此外，我們也改變了氧氣濃度來探討不同狀態下之磁化率變化，將其計算成靜脈血氧飽和濃度，並校正部分體積效應所產生的定量誤差。 結果顯示，在視覺刺激下，外側膝狀核和四疊體上丘皆有強烈的大腦活化反應。比較兩種影像，由於局部帶氧血紅素增加使得磁化率下降，強度影像訊號上升，故可觀察到磁化率與血氧濃度相依訊號有著相反的趨勢。在呼吸30%氧氣的狀態下，其磁化率與靜脈血氧飽和濃度在刺激開啟與關閉之平均值分別為148.00±3.90 ppb、153.00±4.80 ppb與83.62±0.44%、82.99±0.53%。在呼吸100%氧氣下，其磁化率與靜脈血氧飽和濃度在刺激開啟與關閉之平均之值別為109.50±6.00 ppb、115.20±6.30 ppb與87.93±0.67%、87.30±0.70%。同樣地，在兩種不同氧氣濃度狀態下，磁化率改變量均大幅提升為血氧濃度相依功能性磁振影像之訊號改變量的4倍。 本研究成功地驗證磁化率定量功能性磁振影像技術應用於視覺刺激之動物功能性磁振影像之可行性，並藉以定量地觀察鼠大腦血氧濃度於視覺刺激下之變化。其中，磁化率之血流動力學反應有血氧代謝之反應趨勢，以及類似於大腦血流之反應趨勢，此結果還需未來更進一步的驗證。如此一來，藉由其可定量化之優勢，且可同步提供磁化率以及一般血氧濃度相依功能性磁振訊號，此技術將有潛力成為定量研究大腦功能性影像之有利輔助工具。
並列摘要
BOLD-fMRI has been used to measure brain activity by detecting associated changes in oxygenation fluctuation. Recently, quantitative susceptibility mapping (QSM) has been proposed to measure susceptibility property and further calculate to venous oxygen saturation (SvO2) using phase information. The purpose of this study is to apply the QSM technique to BOLD-fMRI during visual stimulation to provide quantitative and physiological information while the brain processing. In this study, we used 5 Hz flashing stimulus during fMRI acquisition. Phase information was extracted to calculate QSM, and the activation map of both magnitude (conventional BOLD) and QSM time-series were calculated in group analysis. Furthermore, we changed inhaled oxygenation levels (30% and 100%) to observe rat brain venous susceptibility changes to quantify SvO2; and intended to calibrate the underestimated susceptibility caused by partial volume effect. The flashing light stimulation evoked strong responses on lateral geniculate nucleus (LGN) and superior colliculus (SC) on both BOLD-fMRI and QS-fMRI results. Comparing to conventional BOLD-fMRI time course, QS-fMRI signal was introduced from the compensation of oxygenated hemoglobin after neural activity and causes a reduced signal change due to susceptibility in local cerebral regions, where BOLD response would show accordingly enhanced signal of EPI magnitude images. During 30 % oxygen inhalation, the calibrated susceptibility was 148.00 ± 3.90 ppb while the task is on, and susceptibility was 153.00 ± 4.80 ppb while the task is off. The calibrated SvO2 was 83.62 ± 0.44 % while the task is on, and SvO2 was 82.99 ± 0.53 % while the task is off. During 100% oxygen inhalation, the calibrated susceptibility was 109.50 ± 6.00 ppb while the task is on, and susceptibility was 115.20 ± 6.30 ppb while the task is off. The calibrated SvO2 was 87.93±0.67% while the task is on, and SvO2 was 87.30±0.70% while the task is off. Interestingly, susceptibility change of QS-fMRI is 4 times larger than BOLD signal change in both inhalation oxygenation conditions; indicated the high sensitivity of QS-fMRI. To summarize, we here demonstrated the feasibility of animal QS-fMRI technique to calculate SvO2 during functional task. According to previous studies, we suggested susceptibility hemodynamic response of was similar/dominated to both the responses of cerebral metabolism of oxygenation and cerebral blood flow. With further validation, the quantitative QS-fMRI technique could be a powerful tool for functional studies.