Respiratory Motion Tracking in Magnetic Resonance Imaging with Pilot Tone Technology Thesis Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Mary Lenk Graduate Program in Electrical and Computer Engineering The Ohio State University 2018 Thesis Committee Dr. Lee Potter, Advisor Dr. Rizwan Ahmad 1 Copyrighted by Mary Lenk 2018 2 Abstract This thesis explores the hypothesis that Pilot Tone (PT) technology can encode respiratory induced motion of the heart to improve cardiac magnetic resonance (MR) imaging. Pilot tone technology is advantageous due to its high sampling rate to provide high temporal resolution in tracking and predicting respiration. Also, the PT signal has the potential to provide motion information without interrupting the pulse sequence to perform motion compensated scans. A prediction model is hypothesized to account for in-plane and through-plane motions due to respiration. A proof-of-concept experiment was designed to explore the ability of the PT signal to encode respiratory-induced motion. The PT signal was processed retrospectively offline and compared to a reference for respiratory motion. The two signals had a high correlation and show preliminary success for the PT to detect respiration. A linear filter was then designed to predict motion from a training phase using the same reference signal. The linear filter was successful with peak/trough locations between the prediction and the reference signal having a correlation coefficient of 0.9999 for end-expiration and end-inspiration prediction. Furthermore, a PT transmitter was designed and constructed for implementation of additional experiments. The transmitter was designed to be programmable, battery- ii powered, MR-safe, and portable for placement at various locations in the bore during scans. iii Dedication To my family and friends for their love and support. iv Acknowledgments In working on this thesis I have had the pleasure of working with many brilliant individuals. I would first like to thank my advisor Dr. Lee Potter for encouraging me to pursue this research and sharing his knowledge of signal processing throughout my undergraduate and graduate studies. This thesis came about as an extension to the work done by Michael Bush, and I’d like to thank him for providing me with the appropriate background knowledge and goals to drive the project. I would also like to thank Dr. Rizwan Ahmad and the CMR research group at The Ohio State University (OSU) for providing their expertise in cardiac MR and guidance on the project. Also, Yingmin Liu was very helpful in conducting scans for the experiments. In designing the transmitter, the antenna design was created by Xiozhen Yang and Dr. Villoroel in the Electrical and Computer Engineering department at OSU. The transmitter was developed with the help of Siddarth Baskar who further designed the electronics layout for the printed circuit board. Finally, I’d like to thank my family and friends for their unconditional support. This work was supported by the National Science Foundation under grant IIP-1539961. v Vita 2016 ............................................................. B.S. Electrical and Computer Engineering, The Ohio State University 2017 to 2018 ................................................ Graduate Research Associate, The Ohio State University Fields of Study Major Field: Electrical and Computer Engineering vi Table of Contents Abstract .......................................................................................................................... ii Dedication ...................................................................................................................... iv Acknowledgments ........................................................................................................... v Vita ................................................................................................................................ vi Table of Contents .......................................................................................................... vii List of Tables ............................................................................................................... viii List of Figures ................................................................................................................ ix Chapter 1. Introduction ................................................................................................... 1 Chapter 2. Signal Model .................................................................................................. 7 Chapter 3. Signal Processing ......................................................................................... 10 3.1 Preprocessing ...................................................................................................... 11 3.2 Linear Predictive Coding ..................................................................................... 13 Chapter 4. Transmitter Design ....................................................................................... 16 Chapter 5. Experimentation ........................................................................................... 20 5.1 Experiment 1, Proof-of-Concept .......................................................................... 20 5.2 Experiment 2, Transmitter Performance............................................................... 29 Chapter 6. Discussion .................................................................................................... 34 Chapter 7. Future Work and Conclusion ........................................................................ 35 References .................................................................................................................... 37 Appendix A. Transmitter Antenna ................................................................................. 40 Appendix B. Transmitter Electronics ............................................................................. 44 Appendix C. Matlab Code ............................................................................................. 47 Appendix D. Programming Transmitter ......................................................................... 60 vii List of Tables Table 1: Antenna Dimensions ....................................................................................... 40 Table 2: Transmitter bill of materials. ........................................................................... 46 viii List of Figures Figure 1: Description of PROCO (10). ........................................................................... 3 Figure 2: High-level description of PROMPT (10). ........................................................ 5 Figure 3: Data acquisition for the training phase (10). .................................................... 5 Figure 4: Example of PT in image domain (10). ............................................................. 8 Figure 5: Block diagram of PT path for respiratory training. ......................................... 10 Figure 6: Block diagram of system H. .......................................................................... 12 Figure 7: Derived Weiner-Hopf filter coefficients for a sinusoid with AWGN. ............. 15 Figure 8: Block diagram of pilot tone transmitter.......................................................... 18 Figure 9: Pilot tone transmitter with monopole antenna. ............................................... 18 Figure 10: Reverse side of pilot tone transmitter with lithium-ion battery. .................... 19 Figure 11: Experimental setup for proof-of-concept experiment (10). ........................... 21 Figure 12: FFT of raw image data in read-out direction ................................................ 22 Figure 13: Absolute value of raw pilot tone data for 9 receive channels. ....................... 22 Figure 14: Low pass filter of pilot tone with cutoff at 0.75 Hz. ..................................... 23 Figure 15: MOCO region of interest highlighted at ribcage........................................... 24 Figure 16: SVD of filtered pilot tone compared to MOCO signal.................................. 25 Figure 17: Comparing peak and trough location for pilot tone and MOCO signal. ........ 26 Figure 18: Stem plot of L = 100 trained filter coefficients for each ICA vector. ............ 27 Figure 19: Prediction results from applying filter coefficients to previous 100 samples. 28 Figure 20: Peak and trough locations for predictions results. ........................................ 29 Figure 21: Programming of pilot tone transmitter using Eval Kit. ................................. 30 Figure 22: Imaging of phantom with pilot tone. ............................................................ 31 Figure 23: Primary singular vector of demodulated PT signal. ...................................... 33 Figure 24: Meander line antenna design. ...................................................................... 40 Figure 25: Antenna simulation circuit model. ............................................................... 41 Figure 26: Antenna simulation S11 results. ................................................................... 42 Figure 27: Simulation gain pattern. ............................................................................... 42 Figure 28: Simulation realized gain. ............................................................................