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Rui Liu ESM Oral Presentation

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Rui Liu ESM Oral Presentation

  1. 1. Title: Evaluation on coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator RUI LIU1, MICHAEL T. LANAGAN2, STEVEN E. PERINI2, THOMAS NEUBERGER3 1ENGINEERING SCIENCE AND MECHANICS, PENN STATE UNIVERSITY;2MATERIALS RESEARCH INSTITUTE, PENN STATE UNIVERSITY; 3HUCK INSTITUTE, PENN STATE UNIVERSITY 14 Tesla system MRI machine
  2. 2. Magnetic Resonance Imagine (MRI) Magnetic resonance imaging (MRI) utilizes strong magnetic fields and radiowaves to form images of the subject. The technology is widely used in medical imaging to investigate anatomy and function of the body for medical diagnosis. An MRI machine contains a large superconducting magnet, a radio frequency (RF) transceiver, and gradient magnets Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  3. 3. Magnetic Resonance Imagine (MRI) (continued) MRI System Block Diagram B1 Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  4. 4. Signal strength “S” & Signal to Noise Ratio (SNR) S = 𝜔0 𝑀0 𝐵1 𝑉𝑠 SNR α 𝑄 RF magnetic field strength, related to coupling of resonator Bandwidth relative to center frequency Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  5. 5. Ceramic Dielectric Resonators Ceramic dielectric resonators are high permittivity, high Q objects that can effectively transmit an electric filed and store energy with a lower rate energy loss. High permittivity High Q-factor (Q factor of >1000 vs. 100 for RF coils) Strong uniform magnetic fields (B1 field) Compact structure/simple geometry Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  6. 6. Mode Designation and Mode Chart Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  7. 7. Methods Anritus 37369D Lightning Network Analyzer Hakki-Coleman method Port 2Port 2 Incident Transmitted Microwave Power (S21 )Reflected Microwave Power (S11 ) Network analyzer Source Receiver AReceiver AReceiver RReceiver R Receiver BReceiver B Port 1Port 1 D.U.T Transmitted Brass Plates Coupler Dielectric Sample Power Out Hakki-Coleman method Power in Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  8. 8. RF Coupling Methods Goals: Maximized power transmission Maintaining High Q-factor Center frequency can be tuned to 600 MHz for 14T MRI machine Resonator: CaTiO3 (relative permittivity of 156) Outer/inner diameter: 46.1 mm/5.32mm; Height: 33.7 mm Five coupling schemes (see next slide) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  9. 9. RF Coupling Methods (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  10. 10. Experimental Results Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  11. 11. Experimental Results (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  12. 12. Experimental Results (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  13. 13. Experimental Results (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  14. 14. Experimental Results (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  15. 15. Experimental Results (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  16. 16. Experimental Results (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator Final design: Wire diameter 0.69 mm Triple loop Shielded in the holder with tuning Center Freq: 600 MHz Loss at REF: -10.6 dB Q: 346 Resonant frequency range: 600 ±5 MHz
  17. 17. CST Microwave Studio Simulation Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator  CST MWS is a specialist tool for the 3D EM simulation of high frequency (HF) components. It enables the fast and accurate analysis of HF devices: antennas, filters, couplers, planar and multi-layer structures.  Using CST Microwave Studio to simulate the electromagnetic field distributions of TE01δ mode around the excited dielectric resonator for 14T MRI machine.  Compare the results to experiment data to try to find the optimized coupling configuration.
  18. 18. Simulation Results: Single Loop Aside Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  19. 19. Simulation Results: Single Loop Aside (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator Center Resonant Frequency: Experimental: 498.5MHz; Simulation: 493.2MHz
  20. 20. Simulation Results: Single Loop Aside (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator E Field (top view)
  21. 21. H Field (top view) Simulation Results: Single Loop Aside (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  22. 22. Simulation Results: Single Loop Around Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  23. 23. Simulation Results: Single Loop Around (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator Center Resonant Frequency: Experimental: 549MHz; Simulation: 538.8MHz
  24. 24. E Field (top view) Simulation Results: Single Loop Around (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  25. 25. H Field (top view) Simulation Results: Single Loop Around (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  26. 26. Simulation Results: Single Loop Around Edge Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  27. 27. Simulation Results: Single Loop Around Edge (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator Center Resonant Frequency: Experimental: 516MHz; Simulation: 510.4MHz
  28. 28. E Field (top view) Simulation Results: Single Loop Around Edge (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  29. 29. H Field (top view) Simulation Results: Single Loop Around Edge (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  30. 30. Simulation Results: Double Loop Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  31. 31. Center Resonant Frequency: Experimental: 555.5MHz; Simulation: 553.2MHz Simulation Results: Double Loop (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  32. 32. Simulation Results: Double Loop (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator E Field (top view)
  33. 33. Simulation Results: Double Loop (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator H Field (top view)
  34. 34. Simulation Results: Triple Loop Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  35. 35. Center Resonant Frequency: Experimental: 595.3MHz; Simulation: 572.4MHz Simulation Results: Triple Loop (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  36. 36. E Field (top view) Simulation Results: Triple Loop (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  37. 37. Simulation Results: Triple Loop (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator E Field (3D view)
  38. 38. H Field (top view) Simulation Results: Triple Loop (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  39. 39. Simulation Results: Triple Loop (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator H Field (3D view)
  40. 40. Simulation Results: Quadruple Loop Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  41. 41. Center Resonant Frequency: Experimental: 627.9MHz; Simulation: 773.6MHz (deviant from experimental) Simulation Results: Quadruple Loop (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  42. 42. Suspect TE01δ Mode H Field (top view) Simulation Results: Quadruple Loop (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  43. 43. Suspect TE01δ Mode H Field (3D view) Simulation Results: Quadruple Loop (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  44. 44. Probe Prototype Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator Probe prototype and design model
  45. 45. Preliminary MRI Imaging Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator Preliminary water/oil mixture phantom imaging
  46. 46. Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator Preliminary MRI Imaging (continued) Water phantom imaging SNR comparison
  47. 47. Conclusions Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  48. 48. Conclusions (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  49. 49. Conclusions (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  50. 50. Conclusions (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator By replacing a single loop coupled on the side of the resonator with coupling loops around the resonator, an increase in the S21 value could be achieved with a sacrifice in Q value, meaning a gain in B1 field strength with a trade-off in SNR. As the number of the turns of the coupling loop increased, the S21 value increased from -16.6 dB to -9.2 dB and reached diminishing return with four turns The Q value also increased from 60.8 to 716.2 and started to decrease beyond three turns. The final designed implemented the triple loop configuration and showed a 157% increase in the effective power transmission compared to previous design.
  51. 51. Conclusions (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator The measured Q values are related to other contributions in the resonant system: 1/𝑄= 1/𝑄 𝑐+ 1/𝑄 𝑑+1/𝑄 𝑟𝑎𝑑+ 1/𝑄 𝑒𝑥 The experimental measurement showed a trade-off between S21 parameters and Qex. The equation also implies the overall quality factor is dominated by the smallest Q-factor among the four. Therefore considering lossy samples being imaged in MRI machine, the small Q-factor of the sample rather than the improved Q on coupling and resonator will dominate the overall Q-factor. Therefore, the improvement on S21 parameter or better power transmission is more significant than improvements on Q-value.
  52. 52. Conclusions (continued) Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator The simulation showed that as the looping scheme became more complicated, the fields were no longer uniformly distributed rendering a decrease in the B1 field component that is perpendicular to B0 field. The more turns presented, the more distortion was rendered on the field distribution. The distortion could render deviant resonance from TE01δ mode resonance. Although experimentally triple loop configuration was the optimum solution for this CDR targeting the 14 T MRI machine, a simpler coupling strategy would be more desirable to yield uniform B1 field distribution.
  53. 53. Experimental: Redesign the probe for simple and reproducible fixtures MRI imaging with more samples such as tobacco seeds Simulation: Add shielding to current structures Add S21 and Q calculations Replace discrete sources with coaxial cables and tuning and matching circuitry Exploring structures of simpler geometry Future Work Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator
  54. 54. Aussenhofer, S., & Webb, A. (2013). High-permittivity solid ceramic resonators for high-field human MRI. NMR in Biomedicine, 26(11), 1555-1561. Aussenhofer, S., & Webb, A. (n.d.). Design and evaluation of a detunable water-based quadrature HEM11 mode dielectric resonator as a new type of volume coil for high field MRI. Magnetic Resonance in Medicine, 68(4), 1325-1331. Aussenhofer, S., & Webb, A. (n.d.). An eight-channel transmit/receive array of TE01 mode high permittivity ceramic resonators for human imaging at 7T. Journal of Magnetic Resonance, 243, 122-129. Haines, K., Neuberger, T., Lanagan, M., Semouchkina, E., & Webb, A. (n.d.). High Q calcium titanate cylindrical dielectric resonators for magnetic resonance microimaging. Journal of Magnetic Resonance, 200(2), 349-353. Neuberger, T., Tyagi, V., Semouchkina, E., Lanagan, M., Baker, A., Haines, K., & Webb, A. (n.d.). Design of a ceramic dielectric resonator for NMR microimaging at 14.1 tesla. Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering, 33B(2), 109-114. Wen, H. (n.d.). The Evaluation of Dielectric Resonators Containing H2O or D2O as RF Coils for High-Field MR Imaging and Spectroscopy. Journal of Magnetic Resonance, Series B, 110(2), 117-123. Pozar, D. (1998). Microwave engineering (2.nd ed.). New York: John Wiley & Sons,. Pyrz, M., Lanagan, M., Perini, S., Neuberger, T., Chen, F., & Semouchkina, E. (2013) Optimization of Electromagnetic Coupling to Ceramic Resonators for Magnetic Resonance Imaging Applications. CICMT, 2013, 000069-000075. References Title: Coupling strategies for ultra-high field MRI probe made of cylindrical dielectric resonator

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