Susceptibility-weighted imaging for metabolic pathway mapping of low-dosage nanoparticles in organisms

Accurate and noninvasive monitoring of nanoparticles' (NPs) distribution and metabolism in organism is important, especially for NPs at low-dosage, but remains challenging due to the insufficient sensitivity and resolution of the existing imaging techniques. Herein, Fe₃O₄ NPs with different sizes were synthesized for low-dosage NPs' metabolism study with susceptibility weighted imaging (SWI) technique. SWI, as a functional MRI technique with phase postprocessing, can sensitively detect the differences of magnetic susceptibilities between tissues, so can measure the Fe₃O₄ contents even at low dosage in tissues. After in vivo intravenous injection, Fe₃O₄ NPs could be visually distinguished in major organs (kidney, liver, spleen) by SWI, and the corresponding content changes over time were also sensitively detected, but cannot be achieved via the conventional T₂-weighted imaging (T₂WI). With the SWI technique, the metabolic pathways of Fe₃O₄ NPs in body were mapped, revealing the critical dependence on the sizes of NPs. This is significant for the assessment of NPs' metabolic time, toxicity risk, and application potentiality. Undoubtedly, SWI is a powerful tool for real-time metabolism low-dose NPs with designed characteristics (shapes, sizes, surface properties, etc.), and noninvasive detection of targets with magnetic nano-sensors in vivo.