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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

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

presentation overview
Presentation Overview
  • Background on MRI
  • Need for compact system
  • Product Design Specifications
  • Simulation and Validation
  • Future Work
magnetic resonance imaging
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

nuclear magnetic resonance
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/

magnetic resonance imaging5
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

slide6

Big Picture

  • Use MR technology to address specific problems
  • Validation of MRI probe designs
  • Eliminate testing inconveniences
  • Client’s ultimate goal: desktop test unit
slide7

Our Part

  • Client is currently developing RF Stimulator
  • Focus on z-gradient coils
  • Design simulation and testing environment

Permanent Magnet

S

N

Z Gradient

product design specification
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)
product design specification9
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
design alternatives
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

design alternatives11
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

design alternatives12
Design Alternatives
  • Common Coil Designs
    • Golay coil (saddle coils)
      • Our modifications

www.dotynmr.com/mri/mri_fcgcpg.htm

simulation
Simulation
  • To simulate, compute Biot-Savart Law
    • Symbolically works about a symmetric axis.
    • Need numerical computation capabilities
simulation14
Simulation
  • Option 1: ANSYS
    • Versatile Simulation Environment
  • Pros
    • Wide range of capabilities, powerful
  • Cons
    • Complicated, steep learning curve, lots of parameters
simulation15
Simulation
  • Option 2: MATLAB
    • Write simulation script to calculate numerically
  • Pros
    • Flexible, does what we want
  • Cons
    • Time investment of programming and manipulation
validation
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
future work
Future Work
  • Complete Test Environment
  • Simulate more coil designs
  • Validate Simulations
  • Build Coils and Test
acknowledgements
Acknowledgements
  • Dr. Orhan Unal
  • Dr. Krishna Kurpad
  • Dr. Susan Hagness
  • Dr. Walter Block