Development of a Tissue-Equivalent MRI Phantom Using Carrageenan Gel

A new tissue-equivalent MRI phantom based on carrageenan gel was developed. Carrageenan gel is an ideal solidifying agent for making large, strong phantoms in a wide variety of shapes. GdCl₃ was added as a T ₁ modifier and agarose as a T₂ modifier. The relaxation times of a very large number of samples were estimated using 1.5-T clinical MRI equipment. The developed phantom was found to have a T₁, value of 202-1904 ms and a T₂ value of 38-423 ms when the GdCl₃ concentration was varied from 0-140 μmol/kg and the agarose concentration was varied from 0-1.6% in a carrageenan concentration that was fixed at 3%. The range of measured relaxation times covered those of all types of human tissue. Empirical formulas linking the relaxation time with the concentration of the modifier were established to enable the accurate and easy calculation of the modifier concentration needed to achieve the required relaxation times. This enables the creation of a phantom having an arbitrary combination of T ₁ and T₂ values and which is capable of retaining its shape.