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研究生：	吳世偉 Wu, Shih-Wei
論文名稱：	大腦組織磁化率定量在磁場不均勻區域之最佳化 Optimization of Quantitative Magnetic Susceptibility Mapping in Brain Regions with Field Inhomogeneity
指導教授：	吳明龍 Wu, Ming-Long
學位類別：	碩士 Master
系所名稱：	電機資訊學院 - 資訊工程學系 Department of Computer Science and Information Engineering
論文出版年：	2016
畢業學年度：	104
語文別：	英文
論文頁數：	55
中文關鍵詞：	組織磁化率、磁振造影、訊號喪失、echo shift
外文關鍵詞：	tissue susceptibility, MRI, signal loss, echo shift
相關次數：	點閱：111 下載：0
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在核磁共振造影中，有些大腦的區域會因為磁場不均勻而造成訊號喪失，其中尤其在鼻腔附近的區域。因此，很多方法提出去補回訊號喪失來提升影像品質。
在我們的研究中提出一個方法來補回訊號喪失，且我們方法的結果可以有效地補回訊號喪失。首先，我們利用k-space energy spectrum analysis (KESA) 來計算echo shift並且作為我們最佳化演算法的輸入，接著跑完整個最佳化流程的結果會被我們作為加上z-方向梯度磁場(z-shim)的依據。另外，我們還會去探討當訊號喪失時以及補回訊號時對於QSM (Quantitative Susceptibility Map)的影響。因近年來，QSM對於神經疾病的診斷具有極大的潛力。除此之外，我們提出的是一個省時的方法，只需要約莫90秒就可以將整個最佳化流程跑完。總體來說，我們提出的方法不只可以有效的補回訊號喪失提升影像品質，並且因所需執行時間很短，也擁有很大的潛力應用於臨床上。

In MR imaging, some regions of the brain are affected by the field inhomogeneity, especially around the air-filled cavities, e.g. nasal cavity, which can lead to the result of signal loss. Therefore, many methods are proposed to compensate for the artifacts from signal loss and achieve the better quality of MR images.
In this study, a novel method to compensate for the artifact affected by signal loss is proposed and the result of our method effectively corrected signal loss. First, we calculate the echo shifts by the k-space energy spectrum analysis (KESA) for our optimization procedure. Then, the result of the optimization procedure is implemented by applying additional gradients along z-direction (i.e. z-shim). Moreover, we investigate the influence of signal loss and the result of the signal recovery on Quantitative Susceptibility Mapping (QSM), which potentially plays an important role of neuronal disease in recent studies. In addition, the algorithm we proposed is efficient, only takes around 90s to compute the entire processing on line. Therefore, it is concluded that the new method can effectively restore susceptibility signal loss and improve the quality of QSM with short computation time that provides a great potential for clinical applications.

中文摘要	i
Abstract	ii
誌謝 	iii
1	Introduction	1
2	Optimization of k-space coverage in Quantitative Susceptibility Mapping data	3
2.1	K-space Energy Spectrum Analysis and echo-shifting	5
2.2	Optimization of the K-space coverage	12
2.2.1	Estimated echo shift from pre-scan data	12
2.2.2	Conversion of echo shift	13
2.2.3	Thresholding for the coverage of K-space	14
2.2.4	The coverage of lower K-space information 	15
2.3	Quantitative Susceptibility Mapping (QSM)	17
2.3.1	Estimate field distribution	17
2.3.2	Magnetic field calculation by dipole model	18
2.3.3	Background field removal	19
2.3.4	QSM reconstruction	20
3	Experiment design	22
3.1	Numerical simulation	22
3.2	Human subject study	24
3.2.1	Large Kz coverage simulation experiment	24
3.2.2	On-Line Z-shim optimization experiment	25
4	Results	26
4.1	Numerical simulation	26
4.2	Accuracy of estimated echo shift from pre-scan data	29
4.3	Human subject study	31
4.3.1	Large Kz coverage simulation experiment	31
4.3.2	On-Line z-shim optimization experiment	42
5	Discussion	48
5.1	Signal recovery with optimization	48
5.2	Optimal λ determination	49
5.3	Flow-compensation	50
5.4	Thresholding based on echo shift histogram	51
5.5	Human subject experiment	51
5.6	Intra-voxel dephasing and echo-shifting	52
5.7	Field inhomogeneity	52
5.8	Future work	52
References 	54


List of Tables
	Large Kz coverage simulation experiment	
Table 4 - 1.The values of ROI1 (Caudate Nucleus) 	37
Table 4 - 2.The values of ROI2 (Globus Pallidus)	37
Table 4 - 3.The values of ROI3 (Putamen)	38
Table 4 - 4.The values of ROI4 (Red Nucleus) 	38
Table 4 - 5.The values of ROI5 (Substantia Nigra) 	39
Table 4 - 6.The RMSE values of ROI1 (Caudate Nucleus) 	40
Table 4 - 7.The RMSE values of ROI2 (Globus Pallidus) 	40
Table 4 - 8.The RMSE values of ROI3 (Putamen)	40
Table 4 - 9.The RMSE values of ROI4 (Red Nucleus) 	40
Table 4 - 10.The RMSE values of ROI5 (Substantia Nigra) 	41

On-Line Z-shim Optimization Experiment 
Table 4 - 11.The values of ROI1 (Caudate Nucleus) 	46
Table 4 - 12.The values of ROI2 (Globus Pallidus) 	46
Table 4 - 13.The values of ROI3 (Putamen) 	46
Table 4 - 14.The values of ROI4 (Red Nucleus) 	47
Table 4 - 15.The values of ROI5 (Substantia Nigra) 	47



List of Figures
Figure 2 - 1.The flow chart of optimization for the k-space coverage.	3
Figure 2 - 2.The QSM procedure.	3
Figure 2 - 3.3D uni-polar multi-echo gradient echo sequence.	4
Figure 2 - 4.The schematic view for effect of echo-shifting.	5
Figure 2 - 5.The signal loss in magnitude image	6
Figure 2 - 6.The flow chart of KESA implementation	7
Figure 2 - 7.The schematic view of pulse sequence and sampling point in k-space	11
Figure 2 - 8.The schematic diagram of conversion echo shift	13
Figure 2 - 9.The flow chart of thresholding and k-space coverage of lower frequency info		14
Figure 2 - 10.The achievement of adding z-shim gradient 	16
Figure 3 - 1.Numerical phantom simulation	22
Figure 3 - 2.The effect of extracting k-space from high resolution data	24
Figure 3 - 3.The flow chart of implementation for on-line z-shim optimization	25
Figure 4 - 1.The result of numerical phantom simulation (1) 	27
Figure 4 - 2.The result of numerical phantom simulation (2) 	28
Figure 4 - 3.The result of accuracy test of echo shift 	30
Figure 4 - 4.The result of large kz coverage simulation (1) 	34
Figure 4 - 5.The result of high kz coverage simulation (2) 	35
Figure 4 - 6.The result of high kz coverage simulation (3) 	36
Figure 4 - 7.The result of on-line z-shim optimization experiment (1) 	43
Figure 4 - 8.The result of on-line z-shim optimization experiment (2) 	44
Figure 4 - 9.The result of on-line z-shim optimization experiment (3) 	45

                                    

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校內：2019-02-01公開
校外：不公開電子論文尚未授權公開，紙本請查館藏目錄

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