本研究為利用雙極多迴訊序列收取多迴訊影像，並搭配T2* IDEAL方法，分解水與脂肪訊號以及磁場和T2*值。多迴訊脈衝序列依照收取資料時的編碼可以分為單極多迴訊序列與雙極多迴訊序列。一般而言雙極多迴訊序列的迴訊間隔比單極多迴訊序列小，因此可縮短掃描時間，而此特性在需要閉氣的腹部磁場量化參數造影時可減少受檢者因閉氣所帶來的負擔。
但是因為雙極多迴訊序列會因為渦電流以及梯度延遲造成相位差現象，所以本文提出一個修正相位差的校正方法，使其既可以縮短掃描時間，也可以配合T2* IDEAL方法，以利縮短人體所需的閉氣時間以及獲得正確的水與脂肪的分解和磁場與T2*值。本研究先於水和油水仿體上進行校正方法的可行性評估與T2* IDEAL方法的測試，接著再於人體腹部外圍放上水溶液試管作為校正基準，利用此水溶液試管來求出隨空間分布的相位差，再加以校正原始資料。由實驗結果可發現，本研究提出的方法能夠有效使用雙極多迴訊取得的資料進行水與脂肪分解並同時估算T2*弛緩常數與磁場。研究中亦同時發現到作為校正基準的水溶液試管需要在頻率編碼的方向佔據較大的範圍，才能獲得較正確的相位修正基礎，獲得較精準的T2* IDEAL方法的分解結果。

This research aims at developing a method using data from a bipolar Multi-echo Gradient Echo sequence and T2* IDEAL to decompose the signal of water and fat with evaluation of field map and the value of T2*. Data acquisition for Multi-echo Gradient Echo sequence can be divided into two schemes, acquisition at the same gradient polarity (Unipolar multi-echo sequence) and acquisition with alternating gradient polarity (Bipolar multi-echo sequence). In general, the echo spacing of bipolar multi-echo sequence is smaller than the one of unipolar multi-echo sequence leading to shorter scan duration. And based on this fact, the burden of breath-hold duration will be eased when a subject undergoes to a MR protocol including a quantitative abdominal T2* evaluations.
While bipolar multi-echo sequence has potential to shorten scan time, the phase difference caused by eddy current and gradient delay due to the alternating readout gradients becomes another critical problem. In this article, we propose a calibration method to amend the phase difference so as to prevent from registering the decomposed signal in T2* IDEAL erroneously. In addition, the corrected phase information should help to provide estimation in the water and fat composition as well as the T2* and field susceptibility with accuracy. Feasibility study of the proposed calibration method was firstly engaged in the phantom experiments with a water phantom and a composite oil-water phantom. And then, in human studies we included the water solution tube placed around the abdomen of a scanned subject as a calibration reference to estimate the spatially varied phase differences for correction. The results suggested that with the proposed calibration method, components including water and fat composition, the T2* value and the field strength can be evaluated properly from the acquired data using bipolar multi-echo sequence. In addition, we also discovered that the water solution tube as a calibration reference must be spatially distributed to cover a larger extent along the frequency encoding direction, so that the calibration method can extract adequate basis phase correction to have the decomposing result of T2* IDEAL method more precisely.

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