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MRI Gradient Coils

MRI Gradient Coils. Peter Kleinschmidt, Luisa Meyer, Anne Loevinger, Neal Haas Client: Orhan Unal , Ph.D. Dept. of Medical Physics, Krishna Kurpad , Ph.D. Dept. of Medical Physics Advisor: Prof. Walter Block BME 200/300 October 17, 2008. Presentation Overview. Background on MRI

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MRI Gradient Coils

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  1. MRI Gradient Coils Peter Kleinschmidt, Luisa Meyer, Anne Loevinger, Neal Haas Client: OrhanUnal, Ph.D. Dept. of Medical Physics, Krishna Kurpad, Ph.D. Dept. of Medical Physics Advisor: Prof. Walter Block BME 200/300 October 17, 2008

  2. Presentation Overview • Background on MRI • Need for compact system • Product Design Specifications • Simulation and Validation • Future Work

  3. Magnetic Resonance Imaging • Composed of: • Main magnetic field • Gradient coils in X- Y- and Z- axis • RF stimulator • Data acquisition • Gradients http://www.spiralock.com

  4. Nuclear Magnetic Resonance • Subatomic particles have “spin” • Non-zero spin gives a magnetic moment. • 1H (proton), spin = +1/2 • H2O everywhere in your body http://www.umkcradres.org/

  5. Magnetic Resonance Imaging • All H atoms align. • RF signal causes change • Changing B-field creates E-field. • Signal density in k-space gives contrast • An image is formed http://en.wikipedia.org/wiki/Magnetic_resonance_imaging

  6. Big Picture • Use MR technology to address specific problems • Validation of MRI probe designs • Eliminate testing inconveniences • Client’s ultimate goal: desktop test unit

  7. Our Part • Client is currently developing RF Stimulator • Focus on z-gradient coils • Design simulation and testing environment Permanent Magnet S N Z Gradient

  8. Product Design Specification • MRI Testing System • Low cost: system < $10,000 • Clinical Magnetic Field Strength = 1.5 T • Pulse Duration = 0.008 – 11 msec • Quantity = 1 system (for now)

  9. Product Design Specification • Gradient Coils • Small size: • Magnet (outer cylinder), coils (inner cylinder) • Inner radius of coils = 12 in. • Materials: Cu wire (gauge TBD) • Highly linear magnetic field

  10. Design Alternatives • Common Coil Designs • Helmholtz • Pair of circular coils with common axis • Apply current and calculate magnetic field www.oersted.com/helmholtz_coils_1.shtml http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/helmholtz.html

  11. Design Alternatives • Common coil designs • Maxwell pair coil • Similar to Helmholz • Two opposing currents http://physics-nmr.la.asu.edu/probes/hightemp/Images/maxwellpair.jpg

  12. Design Alternatives • Common Coil Designs • Golay coil (saddle coils) • Our modifications www.dotynmr.com/mri/mri_fcgcpg.htm

  13. Simulation • To simulate, compute Biot-Savart Law • Symbolically works about a symmetric axis. • Need numerical computation capabilities

  14. Simulation • Option 1: ANSYS • Versatile Simulation Environment • Pros • Wide range of capabilities, powerful • Cons • Complicated, steep learning curve, lots of parameters

  15. Simulation • Option 2: MATLAB • Write simulation script to calculate numerically • Pros • Flexible, does what we want • Cons • Time investment of programming and manipulation

  16. Validation • Need to validate theoretical results with actual observed results • Will use a Hall Probe and Gauss Meter • Custom built stand to mount Hall Probe

  17. Future Work • Complete Test Environment • Simulate more coil designs • Validate Simulations • Build Coils and Test

  18. Acknowledgements • Dr. Orhan Unal • Dr. Krishna Kurpad • Dr. Susan Hagness • Dr. Walter Block

  19. Questions?

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