多迴訊非平衡穩定態掃描序列及其參數圖譜應用

Abstract

由於其優越之信噪比特性，平衡穩定態磁振造影序列逐漸成為一種廣為使用之掃描序列。非平衡穩定態造影序列亦逐漸受到重視，尤其在於此種掃描序列在臨床上的應用。舉例而言，雙重迴訊穩定態造影序列能同時接收到兩種截然不同特性之信號，並可藉由分析這兩種不同來源之信號而擷取出組織特性。 此份論文旨在利用雙重迴訊穩定態造影序列，藉以研究、分析其所收集之信號特性。我們提出了一種雙重迴訊穩定態之變體造影序列，並應用於腦部磁振造影。利用我們的方法，可以從該序列所收取到之兩種特性迥異的信號中，同時解析出兩種橫向磁緩速率以及組織內部磁場擾動。而解析出之組織特性在腦部鐵質含量定量上有相當大的助益。 此外，為了能獲得最佳的掃瞄參數，我們運用了數值分析模擬了解該此兩種信號的演進，以及掃描序列之特性。在此篇論文的最末一章，我們針對可能影響組織參數特性解析之因素加以討論；同時，我們也提出了兩種可能適用此改良序列的應用。我們期待此篇論文能貢獻于非平衡穩定態掃描序列的發展；同時，也希望我們的改良序列亦能在其他應用上發揮貢獻。

As balanced steady-state sequence becomes a popular MR imaging modality for its terrific efficiency in terms of SNR per TR, unbalanced steady-state sequences draw more and more attention for their clinical applicability. In particular, dual-echo in the steady-state (DESS) sequence acquires diverse signals of two different signal pathways, so that tissue properties may be revealed. In this thesis, we aim to exploit the sampling ability of unbalanced steady-state sequence to investigate signal evolutions of different pathways. A variant of DESS sequence is designed and applied to brain imaging. To be specific, transverse relaxation rates and the internal field perturbation are simultaneously extracted from signals acquired by our proposed compact method, and the extracted information could be valuable in estimating brain iron concentration. To obtain a proper set of scanning parameters, numerical simulations are employed to evaluate sequence performance. In addition, potential image artifacts are discussed, and two possible applications are proposed in a later chapter in this thesis. We expect this work may advance the current development of unbalanced steady-state sequences, and the proposed sequence would be a handy imaging sequence for other applications as well.