Simultaneous imaging of in vivo conductivity and susceptibility.

PURPOSE: Approaches for quantitative mapping of electric conductivity and magnetic susceptibility using MRI have been developed independently. The purpose of this study is to present a method to simultaneously acquire information on conductivity and susceptibility and to produce images based on these properties.
METHODS: A 3D multiecho gradient-echo sequence was used. Phase evolution during the multiecho was used to produce quantitative susceptibility maps, while the phase value at zero echo time was retrieved, and used to generates quantitative conductivity maps. Electromagnetic simulations were performed to evaluate the phase distribution due to conductivity variations. Phantom and in vivo data were also acquired to assess the quality of images produced.
RESULTS: Simulations demonstrated that phase differences across objects increases with size and conductivity. For an accurate conductivity estimate, the maximum echo time was approximately equal to the true T2* value in order to achieve signal-to-noise ratio maximization. The most accurate susceptibility was obtained when separating phase contribution from conductivity. Phantom and in vivo results showed good quality images representing the electromagnetic properties.
CONCLUSION: A simultaneous quantitative electromagnetic property imaging approach is demonstrated here. The approach not only improves the efficiency of mapping electromagnetic properties, but can also improve the accuracy of susceptibility mapping by separating image phases introduced by conductivity and susceptibility.