Simultaneous quantification of SPIO and gadolinium contrast agents using MR fingerprinting

Purpose: Develop a magnetic resonance fingerprinting (MRF) methodology with R-2* quantification, intended for use with simultaneous contrast agent concentration mapping, particularly gadolinium (Gd) and iron labelled CD8+ T cells. Methods: Variable-density spiral SSFP MRF was used, modified to allow variable TE, and with an exp.(-TE.R-2*) dictionary modulation. In vitro phantoms containing SPIO labelled cells and/or gadolinium were used to validate parameter maps, probe undersampling capacity, and verify dual quantification capabilities. A C57BL/6 mouse was imaged using MRF to demonstrate acceptable in vivo resolution and signal at 8 x undersampling necessary for a 25-min scan. Results: Strong agreement was found between conventional and MRF-derived values for R1, R2, and R-2*. Expanded MRF allowed quantification of iron-loaded CD8+ T cells. Results were robust to 8x undersampling and enabled recreation of relaxation profiles for both a Gd agent and iron labelled cells simultaneously. In vivo data demonstrated sufficient SNR in undersampled data for parameter mapping to visualise key features. Conclusion: MRF can be expanded to include R1, R2, and R-2* mapping required for simultaneous quantification of gadolinium and SPIO in vitro, allowing for potential implementation of a variety of future in vivo studies using dual MR contrast agents, including molecular imaging of labelled cells.