Purpose: To identify an inexpensive, low-dielectric liquid for large magnetic resonance imaging (MRI) phantoms that can be used at multiple magnetic field strengths. Methods: The T1 and T2 of four candidate phantom liquids (pure mineral oil, food-grade white mineral oil, silicone oil, and glycerol) with low dielectric constants were measured at three field strengths (0.35, 1.5, and 3 T) and extrapolated for 7 T. The complex permittivities of the liquids were measured for frequencies from 13 to 600 MHz. Proton densities were calculated based on molecular weight, proton number, and density. The results were compared to the American College of Radiology (ACR) large MRI phantom electrolyte liquid (10 mM NiCl2 and 75 mM NaCl in water) and deionized water. The liquids were evaluated based on the NEMA standards (T1 < 1200 ms, T2 > 50 ms, proton density within 20% of water, and produces minimal dielectric artifacts). The radiofrequency (RF) wavelengths were computed for each liquid at the four field strengths to determine the risk of dielectric artifacts. Results: The mineral oils were the only liquids to satisfy all of the NEMA guidelines. Excluding deionized water, silicone oil had the longest T1 and T2, and was the most expensive liquid ($200/L). Glycerol had the shortest T1 and T2, and the highest dielectric (excluding the ACR phantom electrolyte and deionized water). All of the liquids except silicone oil met the NEMA proton density guidelines. Conclusions: Food-grade white mineral oil is a good candidate for use in a phantom due to its relaxation times, low dielectric, high proton density, and low cost. Glycerol and deionized water are poor choices for phantom liquids due to their relaxation times and high dielectric constants.
- complex permittivity