Missy Haehn, Can Pi, Ben Sprague, Andrea Zelisko

1
PHANTOM FOR USE IN MR IMAGER
Missy Haehn, Can Pi, Ben Sprague, Andrea
Zelisko Advisor Professor Kristyn
Masters Client Dr. Victor Haughton
Abstract
In order to meet a clients needs for research
and calibration of an MR scanner, a phantom was
constructed by students of BME 400. To how the
samples distance from the coil affects the MR
measurement, the phantom was to hold
intervertebral disk samples whose distance to the
MR coil varies. In order to study how accurate
the MR scanner measurements are, solutions with
known T2 values were also included in the
phantom. The phantom held approximately 2 Liters
of water to produce enough loading for quality
measurements. Periodic scans were taken in the
MR while developing the hydrogel samples which
mimicked the intervertebral disks. The phantom
as a whole has not yet been tested in the MR
scanner, but its creators anticipate doing so
within one month.
Disk Samples
-needed a homogeneous mixture for disks
-improvement from last semester -four samples
researched acrylamide, gelatin, agarose,
alginate -only two proved feasible for
phantom -acrylamide and gelatin samples
-different concentrations -prepared,
tested -analyzed scans with Matlab
program -gelatin sample within better range of
T2 -next step to add proteoglycans
Design Components
Phantom Purpose The phantom is mainly a
container or frame for gadolinium solutions or
disk samples. The phantom will be scanned along
with the disk samples in an MR imager to obtain
T2 values. Gadolinium Solutions Purpose
Gadolinium (Gd) doped water samples will be
tested in a relaxometer to obtain a correlation
between the concentration of gadolinium and T2
values. This relationship can be used to
determine the theoretical T2 values of Gd samples
tested on the MR scanner. Disk
Samples Purpose Artificial disk samples are
used to compositionally mimic the actual human
lumbar disks at various degrees of health. The
goal is to obtain relationships between the T2
value and the concentrations of the components.
Motivation
Figure 3 First prototype of phantom.
Our client, Dr. Victor Haughton, is a
neuroradiologist at the UW-Hospital with research
interests in dynamic spine MR imaging. Two
primary goals of project 1) Test and establish
relationship between T2 value and disk
composition -T2 time to be used in
assessment of patients intervertebral disk
health without invasive procedures 2)
Assess the accuracy of the MR scanner in
calibration -done by placing solutions
of known T2 time in the scanner and
comparing this to the T2 measurement from MR
-see how certain variables in scanning
affect measurements obtained -know the
validity of tests performed and measurements made
Figure 7 (above right) MR image from testing of
gelatin and acrylamide hydrogels. Table 1
(right) T2 values for hydrogel samples in MR
testing
Conclusions
We created a design for a phantom and integrated
the three components from the criteria our client
gave us. We created Gadolinium samples and
confirmed that our samples matched the desired T2
values. Further, we gathered MR data to help us
determine the best hydrogel for our design.
Finally, we constructed a prototype phantom and
are in the process of getting our design
fabricated by an outside source.
Figure 4 Hydrogel samples and Gd solutions.
Background
Magnetic Resonance Imaging Magnetic resonance
imaging, or MR imaging, is an imaging modality
which utilizes the spin of hydrogen atoms to
image the human body. MR uses extremely powerful
magnets to align the hydrogen atoms in a main
magnetic field. Figures 1 and 2 depict the
alignment and spin, respectively, of the hydrogen
atoms. A radio frequency (RF) is then applied in
pulses to alter the main magnetic field 90
degrees out of phase. After the RF pulse is
turned off, the hydrogen atoms realign with the
magnetic field. The time it takes to realign is
the T1 value. The exponential decay of the MR
signal during the sequence of RF pulses is the T2
value. Spinal Anatomy and
Imaging -Disks act as cushions between
vertebrae -Disks degenerate with age due to
decreased water and blood flow -Health problems
include back pain, pinched nerves, muscle
spasms -MRs high proton sensitivity proves
superior image quality to X-ray
Component Development
Future Work
Phantom

• Size and Dimensions
• - compact for ease of storage and use
• sufficient number of sample tubes water volume
  for loading
• tubes extend through container to limit number
  of seals
• Sample Orientation and Arrangement
• - aligned with bore of MR
• arranged close together
• - symmetric arrangement
• Material
• - translucent for viewing of samples and water
• - can be molded to design shape
• - two options acrylic, translucent ABSi
• Construction
• - rapid prototyping not possible
• - molded with removable scaffolding and gluing of
  sixth side
• currently pursuing MetroRP, 3D Moldless
  Technology Inc. and the UW Mechanical
  Engineering student design lab

-More testing of samples -Reducing artifact on
scans -Fabrication of phantom -Testing of our
phantom with and without samples -Testing human
intervertebral disks -Naming our phantom
(Ballots)  -Patent publication for our design
Figures 1 (left) and 2 (right) show the alignment
and spin, respectively, of hydrogen atoms in a
magnetic field.
Potential Problems
Figure 5 Computer modeling of phantom design.
-Conducting additional and more accurate scans of
samples -Finding a way to make a more
concentrated GAG solutions -Phantom construction
References
Acknowledgements
Wed like to thank Professor Kristyn Masters,
Advisor Dr. Haughton, Client John Perry,
Medical Physics Graduate Student Ernie Madsen,
Professor Emeritus Maritza Hobson, Medical
Physics Graduate Student Dan Schmidt, Standard
Imaging Professor Tim Oswald, Mechanical
Engineering.
1. How Stuff Works online http//electronics.h
owstuffworks.com/mri.htm. 2/1/05.2. Lumbar
Degenerative Disk Disease. online
http//www.dynomed.com/encyclopedia/encyclopedia/
spine/Lumbar_Degenerative_Disk_Disease.html.
2/12/05. 3. Weidenbaum, M., et al. Correlating
Magnetic Resonance Imaging with the Biochemical
Content of the Normal Human Intervertebral disk.
J. Ortho Research. 10(4) 552-61.4. Standard
Imaging. online http//www.standardimaging.com/i
ndex.html. 4/20/05.
Gd Samples
Design Specifications
-Gadolinium obtained from client and diluted to
known T2 values from last semesters data -Tested
in relaxometer (Ernie Madsen's lab) -T2 values
obtained from new samples fit very close to curve
from last semester's data and to projected T2
values -Produced accurate samples for final design
To design and develop an MR phantom that
can -Hold artificial intervertebral disk
samples -Contain samples of known T2 time -Place
samples at varying distances from MR coil -Sit
securely atop the MR coil and table
Figure 6 Relationship between T2 and Gd
concentration.