A generalized system of tissue-mimicking materials for computed tomography and magnetic resonance imaging

The advent of technologies such as magnetic resonance imaging (MRI)-guided radiation therapy has led to the need for phantom materials that are capable of producing tissue-like contrast on both MRI and computed tomography (CT) imaging modalities. The purpose of this work is to develop a system of easily made and formed materials with adjustable T₁ and T₂ relaxation times, and x-ray attenuation properties, for mimicking soft tissue and bone with both MRI and CT imaging modalities. The effects on T₁/T₂ relaxation times and CT numbers were quantified for a range of gadolinium contrast (0-25 μmol g^-1), agarose (0%-8% w/w), glass microspheres (0%-10% w/w) and CaCO₃ (0%-50% w/w) concentrations in a carrageenan-based gel. 105 gel samples were prepared with the additives, carrageenan and water. Samples were imaged in a 3D-printed holding structure to find the attainable range of T₁/T₂ relaxation time and CT number combinations. T₁ and T₂ relaxation time maps were generated using voxel-wise inversion-recovery and spin-echo techniques, respectively. A multivariate linear regression model was generated to allow the materials system to be generalized to semi-arbitrary T₁/T₂ relaxation times and CT numbers. Nine diverse tissue types were mimicked for fit model validation. The achievable T₁/T₂ relaxation times and CT numbers for the additive concentrations tested in this study spanned from 82 to 2180 ms, 12 to 475 ms, and -117 to +914 Hounsfield units (HU), respectively. The mean absolute error between the fit model predicted and measured T₁/T₂ relaxation times and CT numbers for the nine tested tissue types was 113 ± 64 ms, 16 ± 26 ms and 11 ± 14 HU, respectively. In conclusion, we have created a system of materials capable of producing tissue-like contrast for 3.0 T MRI and CT imaging modalities.