University of Alberta Excitation of Ultrasonic Guided Waves In Bone Plates Using A Phased Array System by Kim-Cuong Thi Nguyen A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science Medical Sciences - Radiology and Diagnostic Imaging c Kim-Cuong Thi Nguyen Fall 2013 Edmonton, Alberta Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author’s prior written permission. Abstract Ultrasonic guided waves have been exploited to study long bones using the axial transmission technique.
The application of phased array (PA) technol- ogy to bone study is uncommon and the conventional technique involves the employment of a pair of angled beam transducers, which is laborious. In this thesis, we investigated the use of a commercial non-medical ultrasonic PA system to study Lamb waves in Plexiglas and bovine bone plates using a single array probe and two array probes. Data acquired by the single probe was deteriorated by the presence of crosstalk. We developed a Radon-based adaptive crosstalk cancellation algorithm to remove the crosstalk and recover the signals.
Using the two array probes, we studied beam steering to preferen- tially excite guided modes for bone assessment. The results have demonstrated the advantages of the PA system over the conventional single-emitter-single- receiver system in terms of accuracy, speed, and patient comfort, if used in clinical settings. Acknowledgements First and foremost, I would like to thank my parents, brother, and beloved people for their support and encouragement throughout my studies. I missed them very much for the past two years when I was away from home.
I would like to express my deepest gratitude to my supervisors for giving me the freedom to develop my own ideas. I gratefully appreciate Dr. Lawrence Le for his enthusiasm in research, his creative ideas, and his critical and useful comments on my thesis project, presentations, and writings. I also thank my co-supervisor, Dr.
Edmond Lou for giving me an opportunity to participate in the clinical scoliosis ultrasound project and guiding me throughout my studies. I would like to thank Drs. Mauricio Sacchi and Jeffrey Gu, from whom I learnt enthusiastically about signal processing and wave propagation. Also, I sincerely thank Dr.
Larry Filipow for his critical comments on my thesis. I thank all my colleagues: Dr. Rui Zheng, Wei Chen, Tho Tran, Quang Vo, and Duc Nguyen. They all together created an enjoyable and stimulating working environment.
I really appreciate Ms. Joanne Houtstra and Ms. Lynda Loiseau for their kind assistance in administration matters. Last but not the least, I want to thank the Vietnam Ministry of Education and Training, Faculty of Medicine and Dentistry, Department of Radiology and Diagnostic Imaging, and Women’s and Children’s Health Research Institute for financially supporting my graduate research.
Table of Contents 1 Introduction 1 1.1 Background of Osteoporosis .2 Current Techniques to Evaluate Osteoporosis .1 Ionizing Radiation Based Methods .2 Non-radiation Based Methods .3 Quantitative Ultrasound Techniques .1 Pulse-Echo Technique .2 Transverse Transmission Technique .3 Axial Transmission Technique .4 Recent Application of Linear Array Transducer System to Study Bone Tissues .4 Guided Waves and Their Application in the Study of Bone Tissues 17 1.5 Objectives of the Thesis .6 Organization of the Thesis. 21 2 Excitation of Ultrasonic Waves Using A Phased Array System with A Single Array Probe 23 2.1 Phased Array System .1 TomoScan FOCUS LT TM Ultrasound Scanner .1 Near Field Length .2 The Linear τ − p Transform .3 Adaptive Crosstalk Cancellator .1 Adaptive Crosstalk Cancellator .2 Validation of Adaptive Crosstalk Cancellator .1 24-mm Thick Plexiglas plate .2 9-mm Thick Plexiglas plate .3 6-mm Thick Bovine Bone Plate. 47 3 Excitation of Guided Waves by Beam Steering Using Two Ar- ray Probes∗ 50 3.1 Materials and Methods .1 Preparation of Samples .2 Source Influence Theory: Excitation Function .3 Results and Discussion .2 Bovine Bone Plate. 68 4 Conclusions and future directions 70 Bibliography 74 Appendix A Effective Aperture Angle 83 List of Tables 3.1 Parameters used to simulate dispersion curves for the brass plate and bone plate.
The compressional wave velocity (vp ) and shear wave velocity (vs ) of the brass plate were taken from Table A-2 of Olympus NDT (2010) while the density (ρ) was measured. The vp , vs , and ρ of the bone plate were taken from Dodd et al. (2006) while the attenuation coefficients, αp and αp were from Le et al. We also measured the vp of the brass and bone plates and the measurements were 4.09 km/s respectively, which are very close to the the reported values in the literature (Olympus NDT, 2010; Dodd et al.2 Parameters for the -9 dB phase velocity bandwidth for five steer- ing angles.
The c− − p1 and cp2 refer to the phase velocities (< co ) of the peaks of the first and second sidelobes. 68 List of Figures 1.1 Bone classifications based on shape (TCHS Sports Medicine ROP, 2013).2 Bone structure with two main forms: cortical bone and trabec- ular bone (The Altanta Equine Clinic, 2013) .3 Normal bone versus osteoporotic bone (INNOVATE R&D, 2013) 3 1.4 A schematic diagram of a pulse-echo measurement showing an echo backscattered by the internal cancellous bone structure.5 A schematic diagram of the transverse transmission measure- ment technique.6 Process flow sheet .7 The deformation of particle planes and the retrograde elliptical motion at the plate surface of the A0 and S0 modes (Wenzel, 1992).1 Possible crosstalk in an array probe.2 The ultrasound phased array system: (a) The TomoScan FO- CUS LTTM phased array acquisition system (1), the Windows XP-based computer with the TomoViewTM software to control the acquisition process (2), and the probe unit (3). (b) the 64-element phased array probe.3 (a) The dimensional parameters of an array transducer: p−the pitch, e−the elevation, and A−the aperture.4 The phantom experiment with the 64-element array probe on a 9-mm thick Plexiglas plate.5 The in vitro experiment with the 64-element array probe on a 6-mm thick bovine bone plate.6 A schematic diagram of axial resolution of the beam (modified from Olympus NDT (2007)).7 A schematic diagram of lateral resolution of the beam (modified from Olympus NDT (2007)).8 The schematic diagram for forward and inverse linear τ -p trans- form. The records are summed along straight lines with dif- ferent slopes, p and time intercepts, τ.
Stacking along p1 goes through strong peaks of the records and thus yields a strong am- plitude focus in the τ -p panel (dark gray ellipse) while stacking along p2 encounters amplitudes of opposite polarities and thus leads to less Radon energy. Stacking along p3 leads to triv- ial Radon energy due to very small amplitudes of the signals (modified from Gu and Sacchi (2009)).9 Principle of adaptive crosstalk cancellator(Widrow et al.10 A noiseless example shows the simulated and ACC-filtered crosstalk and signals with their corresponding τ − p panels. (a) The sim- ulated reference crosstalk; (b) The simulated data consisting of signals (A and B) and crosstalk (C and D) where the amplitudes of the latter are only half of those of the reference crosstalk; (c) The predicted crosstalk; (d) The ACC-filtered signals.11 Comparison between the ACC-filtered (red) and simulated (black) data at 17.12 The MSE between the signal and filtered signal for different values of step-size β and filter length L.13 A noisy example shows the simulated and ACC-filtered crosstalk and signals with their corresponding τ − p panels. The SNR is 10 dB.
(a) The simulated reference crosstalk; (b) The simulated data consisting of signals (A and B) and crosstalk (C and D) where the amplitudes of the latter are only half of those of the reference crosstalk; (c) The predicted crosstalk; (d) The ACC- filtered signals.14 Comparison between the ACC-filtered (red) and noisy (black) data at 17.15 The reference crosstalk plotted in three different domains: (a) (t − x), (b) (τ − p), and (c) (f − c). The letters A, B, and C de- note the three different arrivals existing in the transducer array, which correspond to the direct wave, guided waves propagating in the matching layer, and reflection arrivals (refer to Fig.16 for further details).16 Crosstalk inside an array transducer.17 The crosstalk-corrupted data for the 24-mm thick Plexiglas plot- ted in three different domains: (a) (t − x) ; (b) (τ − p) and (c) (f − c).18 The crosstalk-filtered signals for the 24-mm thick Plexiglas us- ing three approaches: (a) the conventional ACC in (t − x), (b) normal subtraction in (τ − p), and (c) ACC in (τ − p). The results are represented in three different panels ((t − x), (τ − p), and (f − c)) for verification.19 Crosstalk removal in a 9-mm thick Plexiglas: (a) the original data, (b) the data after multiple reflections are muted in the τ − p domain, and (c) the ACC-filtered signal.20 Crosstalk removal for the 6-mm bovine bone plate: (a) the orig- inal data, (b) the data after multiple reflections are muted in the τ − p domain, and (c) the ACC-filtered signal.5-mm thick bovine bone plate.2 The ultrasound phased array system: (a) The TomoScan FO- CUS LTTM phased array acquisition system (1), the Windows XP-based computer with the TomoViewTM software to control the acquisition process (2), and the probe unit (3). (b) The housing with the 16-element and 64-element probes.
The P16 was the transmitter array while the P64 was the receiver array.3 A cross-section of the experiment setup. The housing hosted two ultrasound probes in place: a 16-element (P16) probe as the transmitter and a 64-element probe as the receiver. The probes rested on the ultrasound gel pads, which acted as coupling me- dia. The pads then overlaid the plate.
Only one group (five elements) in P16 was used as source generator and 60 groups in P64 as receivers. The receivers were steered at the same inclination as the transmitting beam to enhance the receiving sensitivities to propagating guided waves with phase velocity, co related to the inclination, θi by Snell’s law, sin θi = vw /co where vw was the velocity of the coupling medium.4 The normalized excitation spectra for six different steering an- gles. The velocity value shown above each figure is the phase velocity determined by Snell’s law (Eq.1) in the text). The phase velocity determined by Snell’s law is denoted by co ; The phase velocities, c− + o and co , are defined at the values of |F | equal to -9 dB of the maximum; The c− − p1 and cp2 refer to the phase velocities (< co ) of the peaks of the first and second sidelobes.5 The time-offset data for the brass plate at six different incident angles: (a) 0◦ , (b) 20◦ , (c) 30◦ , (d) 40◦ , (e) 50◦ , and (f) 60◦ .6 The dispersion panels of the brass plate data for the six different steering angles: (a) 0◦ , (b) 20◦ , (c) 30◦ , (d) 40◦ , (e) 50◦ , and (f) 60◦.
Superimposed are the theoretical dispersion curves. The − − co , c− + o , co , cp1 , and cp2 are referred to Fig.4 for their definitions.7 The time-offset data for the bone plate at six different incident angles: (a) 0◦ , (b) 20◦ , (c) 30◦ , (d) 40◦ , (e) 50◦ , and (f) 60◦ .