A Phantom for use in an MR Imager

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A Phantom for use in an MR Imager

• BME 402
• February 24, 2006

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• Team Members
• Missy Haehn (Communications)
• Can Pi (BWIG)
• Ben Sprague (Team Leader)
• Andrea Zelisko (BSAC)
• Advisor
• Professor Kristyn Masters
• Client
• Dr. Victor Haughton, M.D.

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Outline

• Background
• Design Components
• Phantom
• Disks
• The Ultimate Goal
• Summary

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Problem Statement

• To create an MR phantom for use in assessing the
  relationship between T2 values and disk health.
• Develop gelatin samples with T2 values between 50
  and 150 ms
• Assess the precision and accuracy of MR
  measurements using the phantom
• Using cadaver disks, assess relative disk health
  using the T2 measurements
• Ultimate goal find preliminary data to support
  disk health based on T2 measurement

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Intervertebral Disks

• Spine consists of vertebrae and disks which act
  as shock cushions
• Disks are made up of varying percentages of
  water, collagen, and glycoaminoglycans (GAG)
• Variations correspond to differing degrees of
  health
• Disks begin to degenerate with age due to reduced
  blood flow and water content

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Imaging Modality MRI

• MR imaging uses magnets and
• radio freq. waves to image body
• T2 value is relaxation time rate of decay for
  protons
• Can essentially pick a point in the body and ask
  What type of tissue are you?
• Phantoms facilitates scanner calibration as well
  as research in MR scanners

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Project Motivation

• Dr. Haughton is Neuroradiologist at
  UW-Hospital
• Research interest in dynamic spine MR imaging
• One focus in disk degeneration
• Design Project
• Phantom needed for calibration of laboratory
  equipment and research
• Gels needed to predict health of disks

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Necessary Components for the Design

• Gelatin hydrogels to hold water and GAGs
  suspended in solution
• Known amounts of water and GAGs
• T2 values 50 to 150 ms
• Gadolinium doped water solutions to assess
  precision/accuracy in scanner
• T2 values 50 to 150 ms
• Phantom container to hold Gd water and gelatin
  samples

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Current Research

• Research by Nightingale, et al. determined a
  positive correlation between water content and
  GAG content
• Performed on NMR
• Research by Masi, et al. found similar results
  with Gd concentration and T2 values
• Commercial phantoms are
  typically filled with doped water
  from GE, Supertech, CIRS

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Phantom Last Semesters Design
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Phantom Progress

• Started with a larger, more cumbersome design
• Attempted to use materials to eliminate water
• Standard Imaging ( tissue mimicking, blue water,
  virtual water)
• Materials didnt work showed up on MR scan
• Decided to use acrylic
• Commonly used in commercial and research phantoms
• New design
• Disk samples held close
• Has spigot for easy fill and empty
• Less cumbersome

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Phantom Current Work

• Final adjustments
• Cross-like pattern for vials
• 9 total slots
• Made from acrylic
• Construction Todd Kyle
• Constructed by UW ME instrument shop

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Phantom Potential Problems

• Construction is slow
• Dependant on machine shop
• Possible problems with construction due to
  difficulty
• Friction fit holes may wear down
• Artifacts possible at material interfaces

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Phantom Future Work

• Testing on the phantom
• With and without samples
• Utilizing phantom for data collection
• More accurate placement
• Easier identification
• Utilizing phantom for tests that depend on
  spacing
• Can vary distance and position from coil

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Disk Mimicking Samples Last Semester

• Original Samples
• Did not maintain homogeneity
• Evaluated different hydrogels
• gelatin, agarose, acrylamide, alginates
• Tests/results

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Disk Mimicking Samples Progress

• Addition of components
• GAGs
• Tests/results

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Disk Mimicking Samples Current Work

• Varying components
• Water
• GAGs
• Correlate water-T2
• and GAG-T2
• Test results

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Analysis
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Disk Mimicking Samples Potential Problems

• Gels
• Not mimicking disks correctly
• Components in gels not the same as in body
• Can rule out collagen effect on T2 based on study
  performed by Nightingale, et al.
• Multiple water/GAG conc. for various T2 values
  pose problems for analysis

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Disk Mimicking Samples Future Work

• From the relationships we determine from our gels
  and T2 values, we can test cadaver intervertebral
  disks
• Quantifying components of disks
• Two methods
• Scan disk and then fully digest to find out
  composition
• Scan disk and digest in successions to find out
  correlation between T2 and composition of disk

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The Ultimate Goal

• To assess the health of a disk based on T2 values
• No definite values, only a range
• Healthy
• Unhealthy
• Inconclusive

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Summary

• Why we are doing this?
• To find a relationship between T2 and water
  content
• This will lead to a determination of disk health
  after more human testing in completed
• Our progress
• Currently gathering initial relationship data
• Cadaver disks for proof of concept
• What we hope to finish by May
• Preliminary research into relationship for T2 and
  disk health

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References

• Nightingale, T., et al. A Model of Unloaded Human
  Intervertebral Disk Based on NMR Relaxation.
  Magnetic Resonance in Medicine. 2000. 43 34-44.
• Elliott, Dawn M. A Linear Material Model for
  Fiber-Induced Anisotropy of the Anulus
• Fibrosus. J. Biomechanical Engineering,
  Vol. 122 p. 127. April 2000.
• Masi, J., et al. Optimization of Gadodiamide
  Concentration for MR Arthrography at a 3T.
  American Journal of Radiology. 2005. 184
  1754-1760.
• 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 too

• Dr. Victor Haughton
• John Perry
• Dan Schmidt, Standard Imaging
• Professor Bill Murphy
• Professor Wally Block
• Advisor Kristyn Masters
• Ernie Madsen and Maritza Hobson, Medical Physics

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• Questions?