제주대학교 Repository

Ray Based Skull Compensation for Transcranial Focused Ultrasound

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Abstract
The numerical compensation of skull bone induced phase aberration significantly recover the focal quality in the transcranial focused ultrasound (TcFUS). In spite of the high accuracy of a full wave simulation approach, it is not feasible for this technology to be adopted in a clinical environment because of long computation time. However, the over-simplified method that was implemented in the current clinical system is incapable of elevating the focal temperature on some of patients with thicker skull because of the lack of acoustic model in the clinical system. This thesis investigates to develop a phase compensation algorithm operating in real-time with reasonable accuracy. A visualization platform utilizing the Open Graphics Library was constructed and the ray method was implemented based on Snell's Law. Three homogeneous layers containing water-skull-brain media were adopted. The registration between the developed software and the clinical system was achieved by localizing the fiducial points embedded in the skull fixed frame. The phase compensation considering refraction was derived by implementing ray method on scanned skull CT volume of two human cadaver skulls. The focal quality was measured by a hydrophone scanning on the focal plane to confirm the results from the developed software with ray method. Finally, the proposed phase correction was verified by the improvement of focal pressure and focal spot location compared to the case without phase correction or with phase correction without refraction accounted. These results will be useful for patient screening, treatment planning, and for during treatment, and analysis even after treatment in a clinical environment as well as transducer design.
Author(s)
김창수
Issued Date
2017
Awarded Date
2017. 8
Type
Dissertation
URI
http://dcoll.jejunu.ac.kr/jsp/common/DcLoOrgPer.jsp?sItemId=000000008259
Alternative Author(s)
Jin, Changzhu
Affiliation
제주대학교 일반대학원
Department
대학원 해양시스템공학과
Advisor
팽동국
Table Of Contents
LIST OF FIGURES I
CHAPTER 1 INTRODUCTION 1
1.1. Brain tumor 2
1.2. Skull bone and mathematical models 3
1.2.1. Wavelength and skull thickness 3
1.2.2. Mathematical model 6
1.3. Transcranial Focused ultrasound (TcFUS) 9
1.3.1. Treatable neurological disease using TcFUS 9
1.3.2. Focal spot aberration by skull 11
1.3.3. Skull compensation studies 11
1.4. The treatment protocol 13
CHAPTER 2 MATERIALS AND EXPERIMENT SETUP 17
2.1. Experiment preparation-hardware setup and system wiring 17
2.2. Skull-frame setup on the FUS transducer 19
2.3. Supporting pad removal on the CT image 19
2.4. Fiducial point coordinate in CT image 22
2.5. Fiducial point coordinate in transducer system 25
2.6. Skull-frame CT and FUS transducer registration 28
2.7. Further coordinate configuration 29
CHAPTER 3 RAY TRACING SOFTWARE 31
3.1. The infrastructure of the software 31
3.2. Ray-skull collision detection 33
3.3. Surface normal estimation 34
CHAPTER 4 RAY BASED FOCAL QUALITY ESTIMATION 37
4.1. Introduction of ray method 37
4.2. Focal pressure estimation (Empirical approach) 42
4.2.1. The traveling plane wave model 42
4.2.2. Near field boundary (NFB) 46
4.3. Measurement based calibration 52
4.4. Single element pressure field measurement 58
4.4.1. Single element pressure field measurement with skull 59
4.4.2. Simplified transducer beam spread(Approximation) 61
4.4.3. Beam divergence measured from single element 62
4.5. Focal Pressure estimation simulation 64
CHAPTER 5 RAY BASED PHASE COMPENSATION 67
5.1. Phase compensation 67
5.1.1. Baseline phase 67
5.1.2. Refraction accounted phase compensation 70
5.2. The focal pressure improvement 73
CHAPTER 6 LIMITATIONS 82
CHAPTER 7 DISCUSSION AND CONCLUSION 83
7.1. Discussion 83
7.2. Conclusion 88
CHAPTER 8 THE FUTURE WORKS 90
8.1. Skull density ratio computation for patient screening 90
8.2. Patient screening and treatment planning tool 93
8.3. Ellipsoidal shape FUS transducer design 95
BIBLIOGRAPHY 101
ACKNOWLEGEMENTS 107
Degree
Doctor
Publisher
제주대학교 일반대학원
Citation
김창수. (2017). Ray Based Skull Compensation for Transcranial Focused Ultrasound
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Faculty of Earth and Marine Convergence > Ocean System
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