Measurement of Transverse Relaxation Times and Content Ratio of ²³Na in Phantoms Simulating Biological Systems by Use of Multiple-Quantum Filtering

Sodium in most biological systems relaxes biexponentially and generates a multiple-quantum signal. In a multiple-quantum filtering sequence, the sodium contributing to the multiple-quantum signal is in single-quantum coherences during the preparation and acquisition times, while it is in multiple-quantum coherences during the evolution time. In contrast to the biexponential relaxation of single-quantum coherences, double- and triple-quantum coherences relax monoexponentially during the evolution time with fast and slow transverse relaxation rates, respectively. This unique feature of multiple-quantum filtering is exploited to measure the transverse relaxation rates of phantoms simulating intracellular and extracellular sodium by analyzing the double- and triple-quantum signals acquired at various evolution times. As a byproduct, the relative ratio of multiple-quantum signals derived from intracellular and extracellular sodium can also be simultaneously determined. This technique may enable the distinction between intracellular and extracellular sodium content in biological systems without using potentially toxic shift reagents.