Efficient 23Na triple-quantum signal imaging on clinical scanners -CaRtesian Imaging of Single and Triple- Quantum 23Na (CRISTINA)

International audiencePURPOSE To capture the multi-quantum coherence (MQC) sodium signal. Different phase-cycling options and sequences are compared in a unified theoretical layout, and a novel sequence is developed. THEORY and METHODS: An open-source simulation overview is provided (https://github.com/MHoesl/) with graphical explanations to facilitate MQC understanding and access to techniques. Biases such as B0 inhomogeneity and stimulated echo (STE) signal were simulated for four different phase-cycling options previously described. Considerations for efficiency and accuracy lead to the implementation of a 2D Cartesian Single and Triple quantum Imaging of 23Na (CRISTINA) sequence employing two 6-steps cycles in combination with a multi-echo readout. CRISTINA capabilities were assessed on an 8x60ml, 0%–5% agarose phantom with 50mM-154mM 23Na concentration at 7T. CRISTINA was demonstrated subsequently in vivo in the brain.RESULTS Simulation of B0 inhomogeneity showed severe signal drop out, which can lead to erroneous MQC measurement. STE signal was highest at the time of TQC signal maximum. However, STE signal is separated by Fourier Transform as an offset and did not interfere with MQC signals. The multi-echo readout enabled capturing both SQC and TQC signal evolution at once. Signal combination of two phase-cycles with a corresponding B0 map was found to recover the signal optimally. Experimental results confirm and complement the simulations.CONCLUSION CRISTINA captures TQC and SQC signal evolution to provide T2*fast and T2*slow maps by fitting as well as the optimal measurement of TQC signal and extrapolation of SQC signal to TE=0ms. Sodium concentration maps can be estimated