A Phantom for use in a MR Imager

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A Phantom for use in a MR Imager

• BME 301
• February 18, 2005

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• Team Members
• Missy Haehn (Team Leader)
• Can Pi (Communications)
• Laura Sheehan (BWIG)
• Andrea Zelisko (BSAC)
• Advisor
• Mitch Tyler
• Client
• Dr. Victor Haughton, M.D.

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Medical Background

• Spine consists of vertebrae and disks which
• act as shock cushions
• Disks begin to degenerate with age due to
• reduced blood flow and water content
• This causes disk density loss
• and risk for vertebrae shifting
• Patients suffer from back
• pain, pinched nerves, muscle
• spasms, bone spurs

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MRI Background

• MR imaging uses magnets and
• radio waves to image body
• T2 value is relaxation time for protons, relative
  to water
• Can essentially pick a point in the body and ask
  What type of tissue
• are you?
• Phantoms are used to calibrate the scanner as
  well as in tissue simulations

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Motivation

• Dr. Haughton is radiologist at
• UW-Hospital with a specialty in neuroradiology
• Research interest in dynamic spine MR imaging
• Specifically disk degeneration
• Phantom needed for calibration of laboratory
  equipment
• Mimicking intervertebral disks and T2 values

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Problem Statement

• To design a phantom for use in an MR imager to
  assess the accuracy of the scanner using T2
  relaxation values. The phantom will be used to
  determine how certain variables affect the
  scanners accuracy. The phantom will also hold
  artificial intervertebral disks to research the
  relationship between disk composition and
  resulting MR data.

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Client Design Specifications

• Hold artificial lumbar disks
• Contain disks with varying distances to the
  spinal coil
• Include solutions with various relaxation T2
  times
• Sit securely atop of the spinal coil
• Is easy to use

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Current Progress

• Current phantoms water doped solutions with
  corresponding T2 values
• Constructed by companies such as GE, Supertech,
  and CIRS
• Prices range from
• 2000 to 5000
• Not directed towards
• client research needs

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Preliminary Design Construction 1 Fixed

• Sealed container (4 L beaker)
• Stationary disk samples
• Avoids excessive material interfaces that create
  artifacts
• Simple construction
• Limited number of samples and variation due to
  size
• Phantom size may have to be increased to fit
  samples

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Preliminary Design Construction 2 Modular

• Allows for the doped water artificial disk
  samples to be removed (cuvets)
• More samples variation in experiments
• Phantom size can be reduced
• More complex expensive construction
• Must have tight seal between samples phantom to
  avoid artifacts

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Construction Diagrams
Fixed Construction Modular Construction
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Design Options
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Preliminary Design Disk 1 Hydrogels

• Hydrogels cross-linked polymers
• Advantages
• Known procedure and H20 percentage
• Space filling (few artifacts)
• Addition of collagen and GAGs
• Affordable cost
• Disadvantages
• Time consuming
• Transfer of materials

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Preliminary Design Disk 2 Aqueous Mixtures

• Aqueous mixture to mimic actual spinal disks
• Components include H2O, collagen, and
  proteoglycans
• Healthy disks contain between 75-80 H2O
• Degenerative disks contain between 60-65 H2O
• Solution movement and swirling can cause
  artifacts
• Affordable cost

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Design Matrix Disks
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Design Matrix Constructions
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Final Design Choice Fixed with Hydrogels

• Fixed choice will allow more accurate
  measurements due to limited number of material
  interfaces
• Using a cylinder will allow rotation of the
  phantom to obtain various distances
• Hydrogels will provide stable disk samples with
  fewer artifacts

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Potential Problems

• Limited space to work with
• Fixed construction does not allow for as much
  variety in experiments
• Will need to construct holder so that phantom is
  stable on the MR table/coil
• Making hydrogels is a timely procedure

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Future Work

• Determine exact construction procedure
• Research exact T2 values for artificial disks and
  back tissue
• Training in solution preparation techniques and
  equipment use
• Construction and testing of prototype
• Develop and construct modular design alternative,
  time permitting

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References

• Weidenbaum, M., et al. Correlating Magnetic
  Resonance Imaging with the Biochemical Content of
  the Normal Human Intervertebral disk. J. Ortho
  Research. 10(4) 552-61.
• Lumbar Degenerative Disk Disease. DynoMed.
  2/12/05. http//www.dynomed.com/encyclopedia/encyc
  lopedia/spine/Lumbar_Degenerative_Disk_Disease.htm
  l.
• Blechinger, J.C., Madsen, E.L., and Frank, G.R.
  Tissue-mimicking gelatin-agar gels for use in
  magnetic resonance imaging phantoms. Medical
  Physics, Vol. 15, No. 4, Jul/Aug 1988.
• Phantom Applications and Technology Overview.
  2001. Computerized Imaging Reference Systems,
  Inc. httpwww.cirsinc.com/overview.html.
• Rice, J. Robin, et all. Anthropomorphic 1H MRS
  head phantom. Medical Physics, Vol. 25, No. 7,
  July 1998, Part 1.
• http//www.supertechx-ray.com/MRI
• http//www.cirsinc.com/productlist.html

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Thanks to

• Dr. Victor Haughton
• John Perry
• Professor Ernie Madsen
• Professor Wally Block
• Advisor Mitch Tyler

Questions?