Material analysis for a new kind of hybrid phantoms utilized in multimodal imaging

Abstract

The use of phantoms for medical imaging is of increasing importance, especially concerning hybrid imaging technologies. The purpose of this study was to find new materials suitable for hybrid phantoms which can be used in magnet resonance imaging, CT and nuclear medicine. Suitable phantom materials have to meet the requirements: tissue-equivalent relaxation and absorption/scattering coefficients, material stability/strength to reproduce tissue structures, no bacterial infestation of the material, cost-effective use. The material samples in this study were based on the basic components: carrageenan (3%, m/m), agarose (0.8–1.0%, m/m), GdCl3 (30–100 µmol/kg), NaNO3 (antiseptic agent, <0.1%, m/m) and H2O. Additional modifiers were added: Ba(NO3)2, SiO2, CuSO4, MgCl2. These modifiers influence the relaxation times and abortion characteristics. For tissue-equivalency, T1/T2-times and Hounsfield Units (HU) of material samples were compared to various human tissues after performing the following experiments: MR-relaxometry was measured using a 1.5T MRI scanner. HU were acquired at 80 kV/110 kV/130 kV using a CT scanner; for nuclear medicine, material samples (10 MBq, TC-99 m) were examined in a water-phantom utilizing a SPECT-system. Tissue structures, like soft-tissue, brain (gray/white matter), kidney and liver can be simulated with high accuracy in their relaxation times and HU-values using (Ba(NO3)2 as an additional modifier. This modifier meets all requirements and covers T1/T2-times of 700–1400 ms/50–80 ms and HU-values of 12–740 HU. Functional relationships were investigated by describing the T1/T2-times in dependency of the T1/T2-modifiers. Other modifiers did not meet all tissue-equivalent characteristics. Our gel-based approach can also be used in nuclear medicine to generate active tissue structures, e.g. hot nodules with TC-99 m.