Production of a human-tissue-equivalent MRI phantom: Optimization of material heating

Purpose: We conceived a 2-stage heating method to dissolve the ingredients of magnetic resonance (MR) imaging phantoms to overcome issues of uneven quality in conventional MR imaging phantoms, and we evaluated uniformity and the reproducibility of our method. Methods: We used a 3-liter capacity, column-shaped, enamel-coated porcelain container to produce a muscle-equivalent phantom (diameter, 160 mm; height, 100 mm; volume, 2 liters). The phantom contained: 1) carrageenan as a gelling agent; 2) agarose as a T₂ modifier; 3) GdCl₃ as a T₁ modifier; 4) NaN₃ as an antiseptic; and 5) distilled water. We applied both direct heating and 2-stage heating of pre-soaked materials. We placed powdered materials directly into hot water for direct heating but soaked them in water one day before use (post-swelling) in 2-stage heating. The materials in the container were melted in a silicone oil bath of 120 or 140°C under various conditions, then allowed to gel by natural cooling. We observed the resulting gel phantoms macroscopically using a CCD camera and evaluated their uniformity by microscopy and MR imaging. Results: We found it necessary to raise the temperature inside the phantom to 100.0°C, to produce a uniform gel with stable homogeneity and few bubbles. Use of an enamel-coated porcelain container required setting the temperature of the oil bath at 140°C. Conclusion: A uniform and reproducible human tissue-equivalent phantom with few bubbles can be manufactured using our 2-stage heating method, which employs pre-soaking in a silicone oil bath at 140°C for 30 min. We then added the swollen carrageenan to the agarose solution, which heating the temperature to 140°C for 30 min while continuously stirring at 120 rpm, following with natural cooling.