A hydrophobic gel phantom for study of thermochemical ablation: initial results using a weak acid and weak base.
OBJECTIVE
To develop a model for study of exothermic chemical reactions potentially useful for tissue ablation.


METHODS
Seven gelatins ranging from 0.5% to 30% wt/vol with and without 15% or 30% caps and several commercial gels were evaluated. Baseline temperature measurements were taken. Acetic acid and ammonium hydroxide were sequentially injected over periods of 10-15 seconds in 1-mL aliquots, forming a discrete aqueous reaction chamber. Congo red pH indicator was included to assess the reaction. A thermocouple allowed data collection at completion of injection and every 15 seconds for 5 minutes. Injections were performed in triplicate, and average temperatures for each time point were reported.


RESULTS
Gelatins fractured or refluxed even at the lowest concentrations tested. Most commercial gels proved too viscous and likewise led to reflux along the needle tract. A mineral oil-based gel was selected because of its ability to form a chamber without reflux or fracture and its clear colorless character, hydrophobic nature, chemical stability, viscosity, specific gravity, and cost. Temperatures during the first 60 seconds of the neutralization reaction showed an immediate increase that correlated well with concentration.


CONCLUSIONS
The oil gel phantom is a safe, useful, readily available, inexpensive model to study mixing behaviors and maximum heating potentials for reactions that may prove useful in thermochemical tissue ablation for oncologic interventions. Measurable temperature changes occurred even at the lowest concentrations, and higher concentrations produced a greater release of heat energy.
Misselt
Andrew J
AJ
Department of Radiology, University of Minnesota Medical Center, Minneapolis, MN 55455, USA.
Edelman
Theresa L
TL
Choi
Jeung H
JH
Bischof
John C
JC
Cressman
Erik N K
EN
D055011:Ablation Techniques / Q000379:methods*; D005782:Gels / Q000737:chemistry* / Q000627:therapeutic use; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D006979:Hyperthermia, Induced / Q000379:methods*; D008422:Materials Testing
D005782:Gels