Feasibility of magnetic resonance redox imaging at low magnetic field: comparison at 1 T and 7 T.

The effect of different static magnetic field strengths, 1 T or 7 T, on the quality of nitroxyl radical-based magnetic resonance redox imaging (MRRI) was examined. A stable nitroxyl radical, 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl (MC-PROXYL), was used as a T1 contrast agent. Phantoms and animals were scanned at 1 T and 7 T using a similar gradient echo sequence. The quality of T1-weighted images and susceptibility of T1-weighted signals were compared. The nitroxyl radical-based T1-weighted signal enhancement ratio was higher at 1 T compared with at 7 T when the identical phantom was scanned using a similar gradient echo sequence. The gradient echo scanning at 7 T was sensitive to movement and/or flux of the sample solution, which could result in the distortion of baseline T1-weighted signals. No such wobbling of the signal was observed when the experiment was done at 1 T. The detection at the lower field is less affected by voltex flow in the sample, much stable T1-weighted signal detection is available at the lower field. The visual characteristics of in vivo nitroxyl decay profiles were similar between the 1 T and 7 T experiments, except noises were large at 1 T. The correlation trends of in vivo decay constants among brain regions also similar between 1 T and 7 T experiments. Nitroxyl radical-based MRRI could be an adequate theranostic tool when performed on clinically popular low magnetic field MRI instruments.