Anthropomorphic Liver Phantom for CT and Ultrasound

1
Anthropomorphic Liver Phantom for CT and
Ultrasound  Katelyn Herbert Advisor Dr.
Robert Galloway (BME) Department of Biomedical
Engineering, Vanderbilt University, Nashville,
Tennessee
ABSTRACT
THE MODEL and METHODS
DISCUSSION
The purpose of this project is to create an
anthropomorphic liver phantom in which liver
tumors can be imaged using both CT (Computed
Tomography) and Ultrasound to investigate whether
imaging liver tumors with CT and Ultrasound is
comparable. We tested the different imaging
modalities by locating the tumors in the images,
and then finding the actual physical space of the
tumor using proximity detectors embedded in the
tumors in the liver. We found that the tumors
were observable in CT and Ultrasound images, and
the proximity detectors worked in a range of 32
mm or less.

• Anthropomorphic phantom of the liver
• Liver Tissue- 11 ratio of Ecoflex Silicone
  mixture.
• Liver Tumors-11 ratio of Ecoflex Silicone
  mixture.
• -Small amount of barium powder added-
  makes visible in CT
• -introduced air bubbles in to the
  mixture-makes visible to US
• Proximity Detectors
• 4.7 mm reed switch (GR200) from Standex
  Electronics is embedded inside the tumor, tumor
  embedded in liver
• -activated by the presence of a
  magnetic field
• Small magnet from KJ Magnetics (D11SH)
  placed in tip of ablation tool.
• As magnet nears the tumor, the reed switch
  closes the circuit and turns on an LED.
• Imaging
• Imaged the phantom using CT (120kV,79mAs,slice
  thickness-2mm)
• Imaged the phantom using Ultrasound

• Tested the distance the magnet needed to be away
  from the reed switch in order to make it close
  while approaching it from several different
  angles
• Found that depending on the angle, the magnet
  needed to be about 32mm-10mm away from the
  reed switch in order to make it close.
• Locating the Tumor Using Images
• The phantom was imaged using CT and Ultrasound.
• Able to locate the tumor using both modalities.
• Imaging method was able to guide us to the actual
  physical space in which the tumor was located.
• Proximity detectors were effective in guiding us
  to the location of the tumor.

.
INTRODUCTION

• 20,000 people are diagnosed with liver cancer
  every year. A very invasive and difficult type of
  liver tumor to treat is the Hepatocellular
  Carcinomas (HCCs), but the removal of these
  tumors is very difficult.
• Surgical resection only available for 20 of
  patients
• RF ablation is the alternative method for tumor
  removal

CONCLUSION
RESULTS

• RF Ablation
• Needle-like ablation tool is placed inside the
  tumor
• High frequency RF signal heats the surrounding
  tissue, killing it.
• Surgery is tomographically guided using CT or
  ultrasound imaging.
• Success is dependent on being accurately

We were able to create a phantom that had tumors
that were visible using both CT imaging and
Ultrasound imaging, and were able to accurately
locate them in the physical space of the phantom.
We embedded proximity detectors in the tumors to
give a range of distances the ablation tool
(magnet) was away from the tumor by using the
reed switches that close the circuit when a
magnetic field is present. However, this is a
binary result (the reed switch closes when the
magnet is at least 32 mm away). Therefore we are
not able to get the exact distance of the
ablation tool to the tumor and further work would
need to be done to achieve that result.
FUTURE DIRECTION
Figure 1. CT image of the liver phantom and
tumor. The Liver tissue appears grey in the
image, and the tumor appears white in the image.

• Attempt to use a different method in which the
  actual distance of the ablation tool to the tumor
  could be found
• May be implemented with an antenna and signal
  source

• guided imaging modality to correctly place the
  ablation tool in the center of a tumor.
• 44 percent of all liver tumors are
  indistinguishable from healthy tissue using CT
  and Ultrasound
• Finding the center of the three-dimensional
  object (the tumor) in a two-dimensional view of
  CT or US images is difficult.
• Objective
• The purpose of this project is to create an
  anthropomorphic liver phantom that will allow the
  investigation of whether CT and Ultrasound
  imaging guidance are comparable for finding liver
  tumors.
• Be able to determine whether the methods
  currently used to locate tumors are the accurate
  enough for actual surgeries.

Figure 2. US Image of phantom. Red
circlelocation of tumor
REFERENCES
Angle of Approach (degrees) Distance From Reed Switch (mm)
90 from front 10
90 from back 10
45 from left 30.1
45 from right 30.1
90 from top 32.2
1. Schöber et al, Guidance and monitoring of
radiofrequency liver tumor ablation with
contrast-enhanced ultrasound., European Journal
of Radiology 0720-048Xyr. 2004 vol. 51 pg.
19 2. Meloni et al, Hepatocellular Carcinoma
Treated with Radiofrequency Ablation. American
Journal of Roentgenology 2001 vol. 177 pg. 375 3.
Gazelle et al. Tumor Ablation with
Radiofrequency Energy. Radiology 2000 vol. 217
633-646 4. http//www.hopkins-gi.org
Table 1. Tested at what the distance the magnet
was when it caused the reed switch to close
(caused LED to turn on). Approached the reed
switch from several different angles.