Temperature maps and accuracy in Magnetic Resonance Imaging thermometry using temperature sensitive superparamagnetic particles*

We present data for the estimation of the accuracy of temperature determination in MRI thermometry using a homogenous phantom with embedded superparamagnetic particles exposed to a temperature gradient. We designed the MRI compatible setup in which a near-infrared 808 nm/5 W continuous wave laser produced an in-plane temperature gradient across the phantom through a glass fiber terminated with a light diffuser. The setup is based on heating the core, made of agar gel with polydopamine (PDA) nanoparticles with a laser. PDA possesses unique properties, making photothermal conversion more efficient. The heated core is surrounded by a tubular shell consisting of agar gel with homogenously embedded nanoparticles. Laser light temporarily produces a strong thermal gradient of 22 ^oC of 14 mm over agar gel with embedded Mn_0.48Zn_0.46Fe_2.06O₄ nanoparticles (concentration of 0.5 mM). Axial T₂ weighted MR images of the phantom before and after heating were acquired. Using these images, we calculated thermal and spatial resolution. Temperature maps of phantoms with isothermal lines are shown. We estimate that we can determine a temperature difference of about 3 ^oC within a spatial extent of 3 mm.