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. T(1) and T(2) 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 T(1) value of 202-1904 ms and a T(2) value of 38-423 ms, when the GdCl(3) concentration is varied from 0-140 micromol/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.

Development of a phantom compatible for MRI and hyperthermia using carrageenan gel—relationship betweenT1andT2values and NaCl concentration

“…The appropriate concentrations of the modifiers and NaCl from the empirical formulae shown in this paper and previous papers 9, 11 can be calculated, when making a certain phantom which has the required relaxation times and electrical conductivity. The materials of the CAGN phantom are not expensive and are easy to obtain and the manufacturing process of the phantom is not difficult.…”

“…A new phantom, CAGN phantom, has now been developed, made by adding NaCl to the CAG phantom, for use in the areas of MRI and hyperthermia. In the previous paper 11 , the dielectric properties of the CAGN phantom are specified.…”

“…Secondly, one was able to change the electrical conductivity of the phantom optionally by adding NaCl at an adequate concentration 11 . This study examined the dependence of the relaxation times of the CAGN phantom on NaCl concentration.…”

“…Formulae were made to calculate the electrical conductivity, (S/m), and relative permittivity, ", of the phantom as a function of NaCl concentration and frequency 11 . Then, the electrical conductivity can be adjusted voluntarily by adding NaCl (0-0.7%) to the phantom.…”

A heterogeneous human tissue mimicking phantom for RF heating and MRI thermal monitoring verification

“…Phantoms that closely mimic the physical properties of human tissues play an important role in testing and evaluating these heating devices and various treatment schemes (Lagendijk and Nilsson 1985, Kato H et al 1986, Marchal et al 1989, Gross EJ et al 1990, Surowiec et al 1992, Wust et al 1998, Madsen et al 1998, Stauffer et al 2003, Kato H et al 2004, Madsen et al 2006). To the best of our knowledge, the phantoms currently being utilized for the purpose of QA are generally simple homogeneous objects that do not accurately mimic the dielectric and thermal properties of human tissue.…”