神經纖維束白質微結構之年齡相關變化的正常模式: 校正腦脊髓液部分體積效應的重要性

Abstract

擴散張量磁振造影(diffusion tensor imaging, DTI)是一種可以評估大腦白質神經纖維微結構的技術,但是因其固有的造影技術限制,幾乎無法避免腦脊髓液部分體積效應(cerebrospinal fluid partial volume effect, PVECSF)的產生。因此,在先前與年齡相關變化的研究中,因為大腦白質神經纖維微結構與 PVECSF皆會隨著年齡而變化,使得兩者常常被混淆。 在本研究中,我們使用結合了高階對位策略的腦神經纖維自動化分析(tract-based automatic analysis, TBAA)技術來測量擴散參數指標,並提出一種藉由估計擴散參數指標和CSF機率之間的線性關係來排除PVECSF的新創校正方法。為了確保此方法的可行性,我們設計了多種情況來進行模擬驗證、以及確認不同PVECSF程度的大腦白質神經纖維在校正後的兩側對稱性,並且更進一步視覺化以比較未校正和校正結果在各方面的差異性。 在排除PVECSF的影響後,我們透過一群橫跨生命週期且年齡均勻分布之正常受試者,建構出大腦白質神經纖維微結構隨著年齡變化的軌跡,並清楚地揭示了各個主要的神經纖維束組別的特性,包括終其一生的特異性質、於各個年齡的成熟與衰退速率、以及發育和退化的時間點。而統計檢定的結果表示PVECSF對於年齡相關變化的研究確實會造成顯著的影響,因此使用此新創校正方法是必要的,而且將有助於產生更精闢的研究。 本研究提出了一種快速、簡單、可行的新創校正方法,並證明了校正PVECSF對於相關研究的重要性,也藉此清楚地揭示基於大腦白質神經纖維微結構於年齡相關變化的“真實”正常模式。

Diffusion tensor imaging (DTI) is a technique that can investigate white matter microstructure, while its inherent limitations are cerebrospinal fluid partial volume effect (PVECSF). Furthermore, white matter microstructure is often confused with the changes of PVECSF in age-related studies previously. Here, tract-based automatic analysis (TBAA) was used to measure the diffusion indices and a novel correction method which regressed out PVECSF by estimating the linear relationship between diffusion indices and CSF probability was proposed. Moreover, demonstration was conducted to ensure the feasibility, and comparisons of the differences between uncorrected and corrected results were performed. Through eliminating PVECSF, the characteristics of the trajectories on large healthy participants whose age distribute uniformly across lifespan clearly revealed the specific properties, rates of maturation and decline, and timing of development and degeneration for each tract group. In addition, statistical results suggested our novel correction method could be recommended for incisive studies. The present study demonstrates the importance of correcting PVECSF and the ‘true’ normal patterns of age-related changes in tract-based white matter microstructure.