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MRI phantoms - are there alternatives to agar?

Hellerbach A, Schuster V, Jansen A, Sommer J - PLoS ONE (2013)

Bottom Line: With such characteristics, it was even possible to embed sensitive objects and retrieve them after testing.This was demonstrated with a fiber phantom for Diffusion Weighted MRI applications.Since Carbomer-980 and Carbopol-974P are non-hazardous, they are also suitable for multimodal setups (e.g., MRI as well as ultrasonic imaging).

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry and Psychotherapy, Philipps-University Marburg, Marburg, Germany. hellerba@med.uni-marburg.de

ABSTRACT
The suitability of different gelling agents as MRI phantoms was evaluated in terms of homogeneity, gel stability and reproducibility. Time and effort for preparation were also taken into account. The relaxation times of various gel compositions were estimated. Carbomer-980 and Carbopol-974P were determined to be promising novel phantom materials. These gelling agents are readily available, inexpensive and easy to handle given that thermal treatment is not required. Furthermore, the viscoelasticity of their polymer network is pH-dependent. With such characteristics, it was even possible to embed sensitive objects and retrieve them after testing. This was demonstrated with a fiber phantom for Diffusion Weighted MRI applications. Since Carbomer-980 and Carbopol-974P are non-hazardous, they are also suitable for multimodal setups (e.g., MRI as well as ultrasonic imaging).

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T1- and T2-weighted images.A+B PNC-400 gel, C+D sodium alginate gel, E+F PAC-300 gel, G+H xanthan gel, I+J Carbopol-974P gel, K+L Carbomer-980 gel.
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pone-0070343-g002: T1- and T2-weighted images.A+B PNC-400 gel, C+D sodium alginate gel, E+F PAC-300 gel, G+H xanthan gel, I+J Carbopol-974P gel, K+L Carbomer-980 gel.

Mentions: The prepared test gels are shown in Fig. 1. Measurements of T1- and T2-weighted images of test gels are shown in Fig. 2. Sodium alginate and xanthan both formed a creamier liquid gel as oppose to a solid gel. Moreover, xanthan was highly susceptible to fungal growth, which was visible after 5 days. Fig. 1D shows mold formation after 2 weeks. Fungal growth was not observed to develop on any other test gels (three-month observation period). PAC-300, PNC-400, Carbopol-974P and Carbomer-980 formed solid transparent gels. Handling of PAC-300 gel seemed to lead to deterioration of gel strength. Carbopol-974P and Carbomer-980 polymers had to be neutralized to achieve maximum gel viscosity because gelation process of polyacrylic acids (e.g. Carbomer-980 and Carbopol-974P) is pH-dependent. Gelation of Carbomer-980 and Carbopol-974P gels has started at a pH of about 4.0. Non-neutralized polymer solution of Carbomer-980 and Carbopol-974P had an approximate pH of 2.0–3.0 depending on polymer concentration. Sodium hydroxide was used as neutralizer for gel preparation of Carbomer-980 and Carbopol-974P gels. Without adding a neutralizer, both Carbopol-974P and Carbomer-980 gels were essentially liquid. Once sodium hydroxide was added, thickening gradually occurred. High viscosities were observed when pH ranged from 5.0–8.0. Gel viscosity began to decrease at pH 8.0 and higher. This can be explained by dampening of electrostatic repulsion caused by the excess of electrolytes at high pH values. Desired gel viscosity can be obtained by adjusting pH, and gelation could be easily reversed for Carbomer-980 and Carbopol-974P gels. Another type of polyacrylic acid is PNC-400. Non-neutralized polymer mixture of PNC-400 had an approximate pH of 6.0–8.0, so gelation process has started instantly. Formation of an abundance of air bubbles, especially using PNC-400, was noted in all test gels. Gel preparation with warm (30°C-40°C) or degassed water will reduce air bubble formation (Fig. 1F–H).


MRI phantoms - are there alternatives to agar?

Hellerbach A, Schuster V, Jansen A, Sommer J - PLoS ONE (2013)

T1- and T2-weighted images.A+B PNC-400 gel, C+D sodium alginate gel, E+F PAC-300 gel, G+H xanthan gel, I+J Carbopol-974P gel, K+L Carbomer-980 gel.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3734012&req=5

pone-0070343-g002: T1- and T2-weighted images.A+B PNC-400 gel, C+D sodium alginate gel, E+F PAC-300 gel, G+H xanthan gel, I+J Carbopol-974P gel, K+L Carbomer-980 gel.
Mentions: The prepared test gels are shown in Fig. 1. Measurements of T1- and T2-weighted images of test gels are shown in Fig. 2. Sodium alginate and xanthan both formed a creamier liquid gel as oppose to a solid gel. Moreover, xanthan was highly susceptible to fungal growth, which was visible after 5 days. Fig. 1D shows mold formation after 2 weeks. Fungal growth was not observed to develop on any other test gels (three-month observation period). PAC-300, PNC-400, Carbopol-974P and Carbomer-980 formed solid transparent gels. Handling of PAC-300 gel seemed to lead to deterioration of gel strength. Carbopol-974P and Carbomer-980 polymers had to be neutralized to achieve maximum gel viscosity because gelation process of polyacrylic acids (e.g. Carbomer-980 and Carbopol-974P) is pH-dependent. Gelation of Carbomer-980 and Carbopol-974P gels has started at a pH of about 4.0. Non-neutralized polymer solution of Carbomer-980 and Carbopol-974P had an approximate pH of 2.0–3.0 depending on polymer concentration. Sodium hydroxide was used as neutralizer for gel preparation of Carbomer-980 and Carbopol-974P gels. Without adding a neutralizer, both Carbopol-974P and Carbomer-980 gels were essentially liquid. Once sodium hydroxide was added, thickening gradually occurred. High viscosities were observed when pH ranged from 5.0–8.0. Gel viscosity began to decrease at pH 8.0 and higher. This can be explained by dampening of electrostatic repulsion caused by the excess of electrolytes at high pH values. Desired gel viscosity can be obtained by adjusting pH, and gelation could be easily reversed for Carbomer-980 and Carbopol-974P gels. Another type of polyacrylic acid is PNC-400. Non-neutralized polymer mixture of PNC-400 had an approximate pH of 6.0–8.0, so gelation process has started instantly. Formation of an abundance of air bubbles, especially using PNC-400, was noted in all test gels. Gel preparation with warm (30°C-40°C) or degassed water will reduce air bubble formation (Fig. 1F–H).

Bottom Line: With such characteristics, it was even possible to embed sensitive objects and retrieve them after testing.This was demonstrated with a fiber phantom for Diffusion Weighted MRI applications.Since Carbomer-980 and Carbopol-974P are non-hazardous, they are also suitable for multimodal setups (e.g., MRI as well as ultrasonic imaging).

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry and Psychotherapy, Philipps-University Marburg, Marburg, Germany. hellerba@med.uni-marburg.de

ABSTRACT
The suitability of different gelling agents as MRI phantoms was evaluated in terms of homogeneity, gel stability and reproducibility. Time and effort for preparation were also taken into account. The relaxation times of various gel compositions were estimated. Carbomer-980 and Carbopol-974P were determined to be promising novel phantom materials. These gelling agents are readily available, inexpensive and easy to handle given that thermal treatment is not required. Furthermore, the viscoelasticity of their polymer network is pH-dependent. With such characteristics, it was even possible to embed sensitive objects and retrieve them after testing. This was demonstrated with a fiber phantom for Diffusion Weighted MRI applications. Since Carbomer-980 and Carbopol-974P are non-hazardous, they are also suitable for multimodal setups (e.g., MRI as well as ultrasonic imaging).

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