Radio Frequency Current Density Imaging (RF-CDI)
RF-CDI measures external currents applied at a frequency that matches the Larmor frequency of the MRI system (i.e. 63.9MHz for a 1.5 Tesla system). RF-CDI has two major advantages over LF-CDI: it can measure one component of current density with only one orientation of the subject and RF currents do not cause the discomfort and muscle twitching associated with low frequency currents.
Polar Decomposition RF-CDI
In this unconstrained method of RF-CDI, the magnetization rotates around an axis determined by the direction of RF current flow at an angular rate determined by the amplitude of the current. The data acquired in this experiment is difficult to process due to a difficult phase unwrapping problem. Not only does the method require 3D phase unwrapping, but the axes of rotation are unknown [5,6].
Rotary Echo RF-CDI
RF-CDI data processing can be greatly simplified by contraining movement of the magnetization vector to a 2D plane. This can be accomplished by applying an RF rotary echo pulse along with the RF current pulse as described in .