Development of a phantom compatible for MRI and hyperthermia using carrageenan gel—relationship between dielectric properties and NaCl concentration

Abstract

A phantom has previously been developed containing carrageenan, agarose and gadolinium chloride (called CAG phantom) for MRI with 1.5 T. T₁ and T₂ relaxation times of this phantom are independently changeable by varying concentrations of relaxation-time modifiers to simulate relaxation times of the various types of human tissues. The CAG phantom has a T₁ value of 202–1904 ms and a T₂ value of 38–423 ms, when the GdCl₃ concentration is varied from 0–140 µmol/kg and the agarose concentration is varied from 0–1.6%. A new phantom has now been developed (called CAGN phantom), made by adding an electric conductive agent, NaCl, to the CAG phantom for use in the areas of MRI and hyperthermia research. Dielectric properties of the CAGN phantom were measured and the results of experiments were expressed by the Cole–Cole equation in the frequency range of 5–130 MHz. The relationship between the conductivity of the CAGN phantom and the concentration of NaCl was expressed by a linear function in the frequency range of 1–130 MHz. The linear function involves a parameter of frequency and, when the frequency is 10 MHz, the conductivity of the CAGN phantom can be changed from 0.27–1.26 Sm⁻¹ by increasing the NaCl concentration from 0–0.7%. The CAGN phantom developed can be employed in basic experiments for non-invasive temperature measurement using MRI and as a loading phantom for MRI with up to 3 T.

• Phantom
• hyperthermia
• MRI
• tissue-equivalent
• dielectric property