運用石墨烯射頻線圈增進7T磁振造影訊雜比之研究

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姓名

林庭瑜(Ting-Yu Lin) 查詢紙本館藏

畢業系所

生物醫學工程研究所

論文名稱

運用石墨烯射頻線圈增進7T磁振造影訊雜比之研究
(Investigation of Signal-to-Noise Ratio Enhancement using Graphene-based Coil at 7T MRI)

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摘要(中)

在臨床的診斷上，磁振造影是非常重要的診斷工具，其具備著非侵入性及非輻射性的特性，並且可量測體內組織的解剖影像及功能性影像，藉由影像的對比度可以清楚知道不同組織的位置及病灶區，為了提高診斷的精確性及影像品質，訊雜比(Signal-to-noise ratio, SNR)是磁振造影硬體設備改進的關鍵因素；然而，磁振造影容易受到外在環境影響，主要來源是射頻線圈(Radiofrequency (RF) coil)本身所產生的熱雜訊。因此，在本研究中，我們採用具有低阻抗性質的石墨烯來設計射頻表面線圈，以達提昇影像訊雜比之目的。在本研究中，設計兩種不同材料的電感式耦合線圈，銅箔材料的表面線圈及銅箔上鍍石墨烯的表面線圈，表面線圈內徑分別設計2、3、4公分，線圈寬度則設計4毫米，將此自製線圈在兩種不同影像序列(FLASH及TurboRARE-T2)下進行假體及大鼠影像的掃描。本研究結果顯示，銅線圈比石墨烯線圈有稍高的Q值，並且在影像訊雜比的部分，所有石墨烯線圈比銅線圈皆有些微高的影像訊雜比，除了使用2公分的石墨烯線圈掃描大鼠影像時訊雜比相對比較差；而影像深度的部分，除了2公分的石墨烯線圈以外，所有的銅線圈比石墨烯線圈皆有些較深的影像。在本研究中，所有石墨烯線圈的影像訊雜比只有些微的提升，主要可能的原因是，石墨烯線圈表面存在著電容的焊點及黏貼材料時產生的皺摺，造成表面線圈上的石墨烯材料脫落，甚至有可能已經破壞掉原有石墨烯的結構，導致影響後續掃描實驗的影像品質，因此本實驗證實，是有需要設計如何讓焊點遠離石墨烯材料，必且還能保有原本石墨烯的低電阻狀態。

摘要(英)

Magnetic resonance imaging (MRI) is an important biomedical imaging technology in clinical diagnosis due to its non-invasiveness and non-radioactivity. To provide high image quality for better precision in diagnosis, the signal-to-noise ratio (SNR) is the key factor in the investigations of MRI hardware improvement. However, the MR images are easily affected by environment noise, majorly originating from the quality of radio-frequency (RF) coil. In this study, our aim is to enhance the imaging sensitivity by designing low-impedance graphene-based RF coils. We designed two types of inductive-coupling coils: (A) surface coils with copper foil and (B) surface coils with copper foil coating the graphene. The inner diameter and wire width of coil were 2, 3, and 4 cm and 4 mm, respectively. We then used the homemade surface coil to map the phantom and SD rats based on the FLASH and TurboRARE-T2 sequence. All Q values of the graphene-based (GB) coil were higher than the copper (Cu) coils. All images of GB coil were with higher SNR than those of the Cu coils, except for the rat images of the 2-cm GB coil. Nevertheless, the observable image depths were slightly longer using Cu coils than using the 2-cm GB coil. In summary, the SNR enhancement using the GB coils was implicit, compared with using Cu coils in our design. The possible reason was that the low-impedance feature of graphene was jeopardized by the solder point and surface wrinkling on the surface coils. Thus, our work confirmed the necessary to design the solder point away from the graphene area in guarantee of the low impedance in the GB coil.

關鍵字(中)

★ 磁振造影
★ 射頻線圈
★ 石墨烯
★ 訊雜比

關鍵字(英)

★ magnetic resonance imaging
★ radio-frequency coil
★ graphene
★ signal-to-noise ratio

論文目次

中文摘要 v
Abstract vi
致謝 vii
Contents viii
List of Tables x
List of Figures xi
Chapter 1 Introduction 1
1.1 Importance of radio frequency (RF) coil in MRI 1
1.2 RF coil development 2
1.2.1 High temperature superconducting RF coils 3
1.2.2 Cryogenic RF coils 4
1.2.3 Carbon nanotube receiver coils 5
1.3 Fundamental problem 7
1.4 Objective of thesis 7
Chapter 2 Materials and methods 8
2.1 Novel material – Graphene 8
2.1.1 Manufacturing graphene 8
2.1.2 Size of RF coils 10
2.1.3 Materials of RF coils 12
2.2 Property measurements 13
2.2.1 Resonance frequency measurement 13
2.2.2 Q-factor measurement 14
2.3 Image acquisition 16
2.3.1 Sample 16
2.3.2 MRI parameters 16
Chapter 3 Result 18
3.1 Coil performances 18
3.1.1 Coils frequency responses 18
3.1.2 Coils Q-factors 21
3.1.3 Prediction SNR gain 22
3.2 SNR of images 23
3.2.1 Phantom experiments 23
3.2.2 Animals experiments 28
3.3 Profile of images 33
3.3.1 Profile of phantom image 33
3.3.2 Profile of animals image 40
3.4 DTI Results 45
Chapter 4 Discussion 46
4.1 Predication and practical SNR gain 46
4.2 Process of manufacturing the surface coils 47
4.3 Measurement 49
4.4 Size of RF coils 52
4.5 Type of graphene-based surface coils 54
4.6 Limitations 55
Chapter 5 Conclusion 56
Reference 57
Appendixes 59
A-1. Graphene property 59
A-2. RF coil design 61
A-2-1 RF coil type 61
A-2-2 Impedance matching circuit 62
A-2-3 Prediction SNR gain 63

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指導教授

吳昌衛(Changwei W Wu)

審核日期

2015-10-6

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