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 multi-echo gradient-echo sequence was used. Phase evolution during the multi-echo was used to produce quantitative susceptibility maps, while the phase value at zero echo time (TE) was retrieved, which were used to generate quantitative conductivity maps. Electromagnetic (EM) 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 increase
with size and conductivity. For an accurate conductivity estimate, the maximum TE 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 EM properties.
Conclusion
A simultaneous quantitative EM property imaging approach is demonstrated here. The approach not only improves the efficiency of mapping EM properties, but can also improve the accuracy of susceptibility mapping by separating image phases introduced by conductivity and susceptibility.