Efficient ²³Na triple‐quantum signal imaging on clinical scanners: Cartesian imaging of single and triple‐quantum ²³Na (CRISTINA)

Abstract

Purpose To capture the multiquantum coherence (MQC) 23 Na signal. Different phase‐cycling options and sequences are compared in a unified theoretical layout, and a novel sequence is developed. Methods An open source simulation overview is provided with graphical explanations to facilitate MQC understanding and access to techniques. Biases such as B 0 inhomogeneity and stimulated echo signal were simulated for 4 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 sodium (CRISTINA) sequence employing two 6‐step cycles in combination with a multi‐echo readout. CRISTINA was compared to simultaneous single‐quantum and triple‐quantum‐filtered MRI of sodium (SISTINA) under strong static magnetic gradient. CRISTINA capabilities were assessed on 8 × 60 mL, 0% to 5% agarose phantom with 50 to 154 mM 23 Na concentration at 7 T. CRISTINA was demonstrated subsequently in vivo in the brain. Results Simulation of B 0 inhomogeneity showed severe signal dropout, which can lead to erroneous MQC measurement. Stimulated echo signal was highest at the time of triple‐quantum coherences signal maximum. However, stimulated echo signal is separated by Fourier Transform as an offset and did not interfere with MQC signals. The multi‐echo readout enabled capturing both single‐quantum coherences and triple‐quantum coherences signal evolution at once. Signal combination of 2 phase‐cycles with a corresponding B 0 map was found to recover the signal optimally. Experimental results confirm and complement the simulations. Conclusion Considerations for efficient MQC measurements, most importantly avoiding B 0 signal loss, led to the design of CRISTINA. CRISTINA captures triple‐quantum coherences and single‐quantum coherences signal evolution to provide complete sodium signal characterization including fast, slow, MQC amplitudes, and sodium concentration.

Intracellular Sodium Changes in Cancer Cells Using a Microcavity Array-Based Bioreactor System and Sodium Triple-Quantum MR Signal

“…The major benefit of the proposed technique is that the MR-compatible bioreactor system allows to perform a variety of interventions with a variety of cells and to correlate MR signal changes to cellular processes. Several efforts are already made to image the sodium SQ and TQ signals simultaneously in vivo, as both may represent valuable biomarkers for cell viability [58][59][60].…”

Comprehensive Account of Sodium Imaging and Spectroscopy for Brain Research

“…28,36 Technical advancement in pulse sequences such as Fermat looped, orthogonally encoded trajectories (FLORET), and Cartesian single and triple quantum imaging of 23 Na (CRISTINA) have shown potential in differentiating these compartments and detecting multiple coherences. 36,52 Detection of signals has been accomplished from double-and triple-quantum coherences using appropriate pulses and phase cycling. 53 The methods used to calculate the duration of RF pulse sequence using product operator formalisms are presented by refs 47 and 54.…”

“…It was reported for phantoms with different solutions containing sodium ions. 52 Conventional pulse sequences can detect 40% of the sodium intensity due to sodium's faster relaxation time. The use of different trajectories based on ultrashort echo time (UTE) has enabled the capture of the other 60% of sodium signal but with reduced image quality.…”

The “Spin‐3/2 Bloch Equation”: System matrix formalism of excitation, relaxation, and off‐resonance effects in biological tissue

“…Various formalisms have been derived dependent on the motivation of the study; for simulations concerning sequences with short and strong radiofrequency (RF) pulses, a hard‐pulse approximation is typically made to obtain a closed form expression of the spin dynamics. These approaches model selected experiments such as triple‐quantum filtering (TQF) 6‐8 and steady‐state free precession 9 . For spin‐3/2 dynamics under modulated RF pulses, the spin‐1/2 Bloch Equation (BE) can be used as a first‐order approximation 10,11 .…”