功能性磁振照影之區域再測性研究: 血氧濃度、腦血灌流、與腦血容積之比較

On the Localization and Reproducibility of Brain Activation Mapping: Comparison of BOLD, FAIR, and VASO fMRI Techniques

李家瑋(Chia-Wei Li)

指導教授 ： 陳志宏

國立臺灣大學/電機資訊學院/電機工程學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.01861

摘要

磁振照影在解剖影像上提供了優越的軟組織對比與高解析度，一直是臨床醫療上的利器。而藉由偵測血液動力學上的改變，所衍生出來的功能性磁振照影是一項研究神經系統功能的重要工具，提供了較其他照影技術更好的區域定位，被廣泛的運用在探討心理活動與特定大腦區域之間的關連性。而傳統使用的血氧濃度依賴(BOLD)技術，參雜有腦血灌流、腦血容積、與腦血氧等因素的影響，只能得到不同心理活動狀態下訊號變化的相對值，無法將特定生理參數的變化情形加以定量化，也無法在不同實驗或是不同受試者間做比較，於是後來學界便開始研發各種以定量單一生理因素為目標的技術。

腦血灌流(CBF)與腦血容積(CBV)功能性磁振照影技術，是利用藥物或是射頻電磁波對於血液做標記，利用血液的運輸，佐以影像相減或是不同的時間參數選擇，以求得腦血灌流與腦血容積的改變影像，可依此推論大腦組織受到特定作業的活化。本論文旨在開發非侵入式的腦血灌流與腦血容積之功能性磁振照影技術，並和傳統血氧濃度依賴技術加以比較。根據理論的推導結果，可以藉由偵測影像上每一個位置的T1參數值，定量腦血灌流隨時間的變化曲線，提供一個更客觀且量化的腦神經細胞活化依據。

腦血灌流與腦血容積功能性磁振照影這兩項技術所得到的活化反應區域有較大的比例位於大腦灰質區，表示它們偵測的訊號變化更接近實際神經細胞產生活動之處。而我們讓受試者反覆接受相同的視覺刺激實驗，即使三個月之後仍能得到穩定的效果，證明了重複實驗的結果再現性足以進行長期縱向研究(longitudinal study)。我們進一步比較這三種照影技術在兩項心理實驗作業的異同。在一項較複雜的認知作業中，腦血灌流和傳統方法都得到相似的大腦活動區域。而在另一項作業中三種照影結果的差異，可以讓我們推論某項抑制現象的確是來自神經活動的減少，而不是單純由於血容積的降低所造成。

本論文證明這兩項先進技術的實用價值，未來我們將以現有的腦血容積技術為基礎，繼續開發定量腦血容積的技術，並朝向更高解析度，且更大的造影範圍的提供，未來可望成為研究大腦功能的有利工具。

關鍵字

功能性磁振造影 ； 血氧濃度依賴 ； 腦血灌流 ； 腦血容積 ； 縱向研究

並列摘要

Magnetic Resonance Imaging (MRI) provides superior images with high contrast of soft tissues and spatial resolution and wildly used in clinical practices. In the past decade, Functional MRI (fMRI) is used widely to explore the brain function by detecting the hemodynamic change induced by specified cognitive or sensorimotor tasks.
However, traditional Blood Oxygenation Level Dependent (BOLD) fMRI technique contains complicated influences from cerebral blood flow (CBF), cerebral blood volume (CBV), and cerebral metabolic rate of oxygenation (CMRO2). It is difficult to achieve the quantification of parameters and the intra-subject comparison. Therefore, other non-invasive fMRI techniques based on CBF-weighted and CBV-weighted contrasts were developed recently. For example, FAIR and VASO fMRI techniques utilize the adiabatic inversion recovery radiofrequency pulse to label the blood outside the imaging region. Image subtraction or special parameter selection were used to acquire CBF or CBV contrast which reflects neural activation. The major objective of this dissertation is to develop and optimize FAIR and VASO techniques, and also compare with traditional BOLD fMRI. With detecting of T1 value in each voxel, we can obtain the quantified value of regional CBF and its time-course variation.
Inversion recovery EPI T1-mapping sequences are designed to investigate the localization of activation voxels according to the T1 value in each voxel. The results revealed that the activation of FAIR and VASO technique show better localization at gray matters than traditional BOLD fMRI, implicating that their activation are closer to the regions of active neurons. The activated regions measured by three techniques were stable even after 3 months in the reproducibility fMRI studies. The evidence suggests these techniques are sufficient for longitudinal study. Furthermore, we compared these techniques in two cognitive tasks. In a mental arithmetic task, all these techniques achieve similar brain activation. In another visual fMRI experiment, the difference among these techniques implicated an inhibitory phenomenon is resulted from decreased neural activity. The result of VASO indicated that this inhibition in BOLD and FAIR cannot be attributed simply by blood volume changes.
In summary, FAIR and VASO fMRI techniques provide better spatial localization and their results are quantifiable and reproducible. In the future, we will develop the quantified VASO technique and providing better spatial resolution and more coverage of FAIR and VASO techniques. Combining all these information together, they will turn out to be more useful and powerful techniques for brain functional studies.

並列關鍵字

fMRI ； BOLD ； CBF ； CBV ； longitudinal study

參考文獻

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