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Fabrication and Characterization of Gelatin and Psyllium Husk Ultrasound PhantomsAdrianna N. Battle, Erin Miller, Lauren Wade, Dongyuan Jin
Dr. Abby R. Whittington,Mr. Jerry Contreras
Contact Information
Laboratory Address: 325 Stanger St, Blacksburg, VA 24061
Phone Numbers (in order of appearance): 703-439-7937, 757-705-8759, 303-590-4906, 540-750-9410Emails (in order of appearance): [email protected], [email protected], [email protected], [email protected].
Abstract
Ultrasound imaging is a versatile technique used for a variety of medical procedures. However,
the accuracy and effectiveness of this technology is heavily dependent on proper training of
medical professionals. Ultrasound phantoms are samples used to mimic parts of the body under
ultrasound. Currently phantoms on the market are widely expensive and homemade models,
although cheap, lack characterization and a standard process for fabrication. The aim of this
research was to create an inexpensive ultrasound phantom solution that mimicked the acoustic
and mechanical properties of the current market phantoms. Ultrasound phantoms were fabricated
using psyllium husk and gelatin powder. Tumor and vein mimics were able to be incorporated
into the system. Samples of varying psyllium husk concentrations and gelatin Bloom strengths
were formulated and tested through rheology, thermogravimetric analysis (TGA), and under
ultrasound. It was concluded that bloom strength was directly proportional with the overall
handleability of the sample. It was concluded that the optimal formulation for the gelatin
psyllium husk phantoms was 0.1 wt% psyllium husk, using a 275 Bloom strength gelatin.
Keywords
Ultrasound; Phantom; Gelatin; Psyllium Husk; Vein; Tumor; Rheology
1. Introduction
Ultrasound can be used to help or perform medical procedures by using high frequency sound
waves . The use of ultrasound as a medical tool is increasing, especially in rural and low income
countries (Sippel et al. 2011). The success of ultrasound relies on the ultrasound ability of
medical practitioners and the accuracy of the imaging (Sippel et al. 2011). To improve
ultrasound care, ultrasound phantoms can be used to practice medical procedures and calibrate
ultrasound technology. Phantoms are samples that are designed to replicate a part of the body.
An effective phantom will mimic the acoustic and mechanical properties of the part being
replicated. These phantoms are very important due to the high stakes involved with many of
these ultrasound procedures, and training has been proven to improve the competence of medical
practitioners ( Woo et al. 2009 ; Sippel et al. 2011).
In low income and rural clinics, ultrasound is often the only imaging option, too (Shah et al.
2015). While many clinics in the developing world have the equipment for ultrasound
procedures, they lack medical professionals with competent training (Shah et al. 2015). The lack
of training can be explained in part because of the high cost of commercial phantoms (Earle et al.
2016). This can force medical practitioners to either go without training and calibration or
homemade phantoms must be fabricated.
Homemade phantoms can be made from a variety of materials. Gelatin and psyllium husk
models are commonly used for homemade phantoms because of the low cost of the materials and
the fact that specific models can be fabricated and customized as needed. While many different
materials have been used for homemade phantoms, there are currently no standard options. There
is also little characterization of any homemade models and no guarantee of consistency between
samples. The goal of the project was to create a formulation made of gelatin and psyllium husk
that can be used to create low-cost, ultrasound phantoms that can have vein and tumor mimetics
added.
2. Materials and methods
2.1 Standard phantom
Samples were fabricated using gelatin and psyllium husk powder. Samples were fabricated with
psyllium husk concentrations varying from 0-10 wt% as well as gelatin Bloom strengths of 85,
175, and 275. First, approximately 158 mL of deionized water was heated in a 250 mL beaker to
50 C using a hot plate. Temperature was recorded using a temperature sensor. While being ⁰
heated, the appropriate amounts of gelatin and psyllium husk were weighed out in a balance and
poured into a plastic centrifuge tube. This was then vortexed in order to create a homogenous
mixture of gelatin and psyllium husk powder. A stir bar was added into the heated water and
ramped up to 400 rpm. While stirring, the powder was added piecemeal to the water until fully
dissolved. The dissolved solution was slowly poured into an empty beaker through a common
kitchen strainer in order to remove bubbles and inconsistencies in the solution. Once filtered, this
beaker was placed in an ice bath for approximately 30 minutes in order to partially set the
solution. Next, this solution was placed in the refrigerator for a few hours or until fully set. Once
set, the phantom is taken out of the beaker by running a small metal spatula around the edges of
the beaker and flipping the beaker upside down.
2.2 Vein mimetics
A few of the samples included a vein mimetic feature. The vein mimic itself was fabricated by
using a long thin balloon and filling it with water about three fifths of the way full. Once filled
the balloon is tied off and placed horizontally in a partially set phantom solution so that the
balloon doesn’t sink to the bottom. An alternative fabrication approach includes hanging the
balloon vertically from a string off of a clamp stand.
2.3 Tumor mimetics
When creating tumor mimics, two different solutions of different psyllium husk concentrations
were created. The solution with the lower density was poured into a mold and put in the
refrigerator. The other solution was used to make the phantom. While partially set the “tumor”
was carefully placed in the phantom solution and the entire beaker system was set in the fridge.
Alternatively a humimic gelatin block can also serve as the tumor mimic.
2.4 Rheology
After about 24 hours of the fabrication, samples were taken from top, middle, and bottom from
the phantom. The samples were placed in an isolated plastic box with ice packs around them then
transferred to rheology testing lab. The samples were placed between two parallel plates and
rotated in different angular velocity from 1 to 100 rad/s. The test mode was oscillation and the
temperature was set to be 25°C. After each trial of testing, the storage modulus graph was
recorded. The average value of last three data points was regarded as the storage modulus of the
sample.
2.5 TGA
Like the rheology testing, samples were taken from top, middle and bottom from the phantom
after about 24 hours of the fabrication. The samples were transferred from fridge to TGA lab
through an isolated plastic box with ice bath to make sure they did not degrade during this
process. The initial temperature of the experiment was room temperature and the final
temperature was set to 200-220 °C. The test mode was ramp and the heating rate is 20°C per
minute.
2.6 Ultrasound
Samples were prepared and subsequently imaged approximately 24 hours after fabrication. The
concentration of psyllium husk in each sample was adjusted to give the samples a similar
ultrasound response to the commercial phantom. B-mode ultrasound imaging was used. The
images were either taken with a Philips IU22 ultrasound system or an Aixplorer Multiwave
ultrasound system. The gain was automatically adjusted to match the commercial phantom. The
commercial phantom was imaged and then each sample was imaged at the same gain. If the
sample contained a vein or tumor mimetic, the gain was adjusted to match the sample and the
mimetic was imaged. Certain samples containing vein mimetics were punctured with an eighteen
gauge needle while being filmed under ultrasound.
The ultrasound response of the phantoms was adjusted by changing the concentration of
psyllium husk in the phantoms. The psyllium husk acts as the scattering agent for our phantoms,
therefore decreasing the concentration decreased the brightness of the samples under ultrasound.
Ultrasound Image Analysis
Fig. 1. Ultrasound image of a commercial phantom containing a vein mimetic with ROI coordinates loaded onto it.
Andor Solis was used to analyze the ultrasound images. A set of ROI coordinates was created,
containing 48 ROIs that were each 75 by 75 pixels. The ROI coordinates were uploaded onto the
image [Figure 1] and the data was copied into excel. Any ROI that contained a mimetic, shadow,
or artifact was disregarded. The signal to noise ratios of all relevant ROIs for an image were
averaged. This average was then compared to that of an image of a commercial phantom taken at
the same gain on the same equipment.
3. Results/ Discussion3.1 Rheology
Rheology testing was designed to determine the storage modulus of the phantom since storage
modulus measures the mechanical response of phantom to solid force. The rheology testing was
conducted to phantoms containing 0, 0.5, 1 and 2.5 wt% of psyllium husk as well as phantoms
made of Bloom 85, Bloom 175 and Bloom 275 gelatin.
Phantom Storage Modulus (Pa)(Avg ± Std)
0 wt% psyllium husk Bloom 85
1330.35 ± 205.94
0 wt% psyllium husk Bloom 175
1823.98 ± 212.33
0 wt% psyllium husk Bloom 275
3397.87 ± 680.69
0.5 wt% psyllium husk Bloom 85
1503.85 ± 113.73
0.5 wt% psyllium husk Bloom 175
2819.24 ± 221.31
0.5 wt% psyllium husk Bloom 275
5085.20 ± 131.79
1 wt% psyllium husk Bloom 85
1811.22 ± 96.92
2.5 wt psyllium husk Bloom 85
2489.89 ± 139.37
Table 1 - The storage modulus of phantom with different psyllium husk composition and gelatin types
Two trends were noticed in this table. One is that adding the psyllium husk increased the storage
modulus of phantom and the other is that phantoms made of Bloom 275 gelatin have higher
storage modulus than other phantoms. After obtaining results of the storage modulus, statistical
analysis was conducted to confirm these two trends. The tool of the statistical analysis is one-
way ANOVA and the comparison mode is Tukey.
Graph 1 - Statistical Analysis of storage modulus of different phantoms
According the statistical analysis of the storage modulus of different phantoms, two trends
observed from rheology testing table were confirmed. It can be determined that the storage
modulus of phantoms with high psyllium husk concentration or made of Bloom 275 gelatin are
significantly higher than storage modulus of other phantoms.
3.2 TGA
Thermogravimetric Analysis was conducted after about 24 hours of the fabrication of phantom to
determine the water loss of the phantom overnight. The thermogravimetric analysis was
conducted to phantoms containing 0, 0.5, 1 and 2.5 wt% of psyllium husk made of Bloom 85
gelatin.
Psyllium Husk Composition Theoretical Water Content Experimental Water Content
(Gelatin: Bloom 85) (Avg ± Std)
0 wt% 91.98% 92.87 ± 0.46%
0.5 wt% 91.52% 92.14 ± 0.32%
1 wt% 91.06% 91.74% ± 0.06%
2.5 wt% 89.73% 90.27% ± 0.38%
Table 2 - The Theoretical and Experimental water content for phantoms made of Bloom 85 gelatin with different psyllium husk composition
The theoretical water content were calculated by weight of the materials. This table shows that
the experimental water content matches the theoretical water content for phantoms for all
psyllium husk concentrations, which indicated that the phantoms did not lose much water
overnight.
3.3 Ultrasound
Qualitative Results
Fig. 2. A. Ultrasound image of a commercial phantom containing a vein mimetic. The brightness and speckle pattern is what the homemade phantom should match. B. An initial sample composed of Bloom 175 gelatin and 10 wt% psyllium husk. This sample was too bright under ultrasound and the psyllium husk concentration was decreased.
Fig. 3. A. Ultrasound image a commercial phantom. B. Ultrasound image of a phantom composed of Bloom 275 gelatin and 0.1 wt% psyllium husk. The brightness of this phantom was within the ideal error margins of the commercial phantom.
Initially, visual analysis was used to narrow down the optimal concentration of psyllium husk.
During the first imaging session, samples containing 10, 5, 2.5, and 0 wt% psyllium husk were
tested. All of these samples were determined to be too bright under the ultrasound by visual
analysis. Moving forward, samples containing 1 and 2 wt% psyllium husk were tested. These
samples were also determined to be too bright. Samples containing 0.5, 0.2, and 0.1 wt%
psyllium husk were tested. Image analysis using Andor Solis was then performed on all
concentrations of psyllium husk. This analysis determined that samples made using 0.1wt%
psyllium husk gave the closest ultrasound response to the commercial phantom that was also
tested.
3.4 Image Analysis
Psyllium Husk Concentration Percent Error
0.1 wt% 4.18
0.2 wt% 4.48
0.5 wt% 19.37
1 wt% 34.38
2 wt% 55.01
2.5 wt% 35.81
5 wt% 51.90
10 wt% 22.22
Table 2. The percent error of the signal to noise ratio of phantoms with differing psyllium husk concentrations compared to commercial phantoms.
The average signal to noise ratio of the sample was divided by that of the commercial phantom.
For samples containing 0.1 wt% psyllium husk, this ratio was 0.960 with a 4.18 percent error.
For the initial samples containing 10 wt% psyllium husk, this ratio was 1.286 with a 22.2 percent
error. Samples containing 0.1 wt% psyllium husk visually matched the commercial phantom, as
well containing an average signal to noise ratio within 5 percent of the commercial phantom.
This concentration of psyllium husk was determined to be optimal concentration moving
forward.
3.5 Vein and tumor mimetics
Fig. 4. A. A commercial phantom containing a vein mimetic. B. A phantom composed of Bloom 85 gelatin and 2.5 wt% psyllium husk containing a vein mimetic. Both vein mimetics are visible with clear boundaries.
Fig. 5. A. A commercial phantom containing a tumor mimetic. This phantom also contains numerous needle marks from previous needle work performed on the phantom. B. A phantom composed of Bloom 85 gelatin and 0 wt% psyllium husk containing a tumor mimetic. The tumor is composed of Bloom 85 gelatin and 2.5 wt% psyllium husk. Both tumors are brighter than the surrounding tissue.
Vein and tumor mimetics were successfully added to samples and ultrasound images were taken.
Clear and distinct boundaries were seen in the vein mimetics (figure) as well as the tumor
mimetics (figure). Visually, the vein mimetics had a similar ultrasound response to the
commercial phantoms. The vein walls were brighter than the surrounding tissue, and the inner
vein had no ultrasound response (figure). The tumor mimetics had a similar response as well.
The tumor in the commercial phantom had a more circular shape as opposed to the more
rectangular shape of our phantoms. However, all tumors were brighter than the surrounding
tissue with well defined boundaries. The brightness of the tumors under ultrasound also directly
correlated to their psyllium husk concentration.
4. Conclusions
4.1 Rheology
The storage modulus of phantoms with high psyllium husk concentration or made of Bloom 275
gelatin are significantly higher, which means they have greater strength than other phantoms
therefore Bloom 275 gelatin and high psyllium husk concentration are recommended to make
phantoms with high robustness and handleability.
4.2 TGA
The experimental water content matches the theoretical water content for all of the phantoms,
which means there was no major issue during the fabrication process and the phantom could stay
stable in 24 hours after fabrication. Also, the water content almost stay unchanged in the range of
psyllium husk concentration between 0 to 2.5 wt% therefore we could change the psyllium husk
concentration of the phantom in this range and would not significantly affect its stability.
4.3 Ultrasound
Samples containing 0.1 wt% psyllium husk fell within 5% of the commercial phantom, so this
concentration will be used to make phantoms. Vein and tumor mimetics were successfully added
to phantoms. Both mimetics were visible with clear boundaries under the ultrasound.
Acknowledgments
This research has been funded by the Virginia Polytechnic Institute and State University Materials Science and Engineering Department.
We would like to thank our faculty and graduate advisor, Dr. Abby Whittington and Mr. Jerry Contreras.
We would like to express gratitude to Dr. Martha Larson of the Virginia- Maryland College of Veterinary Medicine for providing ultrasound equipment and supervision.
We would like to thank Dr. Eli Vlaisavljevich and Mr. Connor Edsall of the Biomedical Engineering and Applied Mechanics (BEAM) Department for providing ultrasound equipment and supervision.
Lastly, we would like thank Dr. Thomas Staley and Ms. Christine Burgoyne for assisting with the organization of the research and providing guidance throughout the project.
Appendices
Image analysis results
Psyllium Husk Concentration Signal to Noise Ratio(Avg. ± SD)
Commercial Phantom 3.68 ± 0.13
0.1 wt% 3.54 ± 0.31
Commercial Phantom 2.66 ± 0.26
0.2 wt% 2.78 ± 0.17
Commercial Phantom 3.68 ± 0.13
0.5 wt% 4.57 ± 0.25
Commercial Phantom 5.36 ± 0.03
1.0 wt% 8.17 ± 0.40
Commercial Phantom 5.36 ± 0.03
2.0 wt% 11.92 ± 0.79
Commercial Phantom 5.36 ± 0.03
2.5 wt% 8.35 ± 1.65
Commercial Phantom 3.48 ± 1.53
5.0 wt% 7.24 ± 1.70
Commercial Phantom 3.48 ± 1.53
10.0 wt% 4.48 ± 0.78
Psyllium Husk Concentration S/N of sample/ S/N of commercial phantom
0.1 wt% 0.960
0.2 wt% 1.047
0.5 wt% 1.240
1.0 wt% 1.524
2.0 wt% 2.222
2.5 wt% 1.558
5.0 wt% 2.079
10.0 wt% 1.286
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