(Top row) The phantom consists of two tubes, one is 1 M NaCl in solution and the other is 1 M NaCl in 4% agarose (Panel A). They simulate extracellular and intracellular sodium, respectively without use of inversion recovery pulse. It can be seen that an inversion time of TI = 20 ms completely suppressed intracellular sodium (Panel B) and TI = 30 ms completely suppressed the extracellular sodium signal from the tube containing NaCl in solution (Panel C). At TI = 40 ms partial suppression of extracellular sodium is highlighted (Panel D). (Middle row) Two 1 M NaCl phantom image intensities (with 4% agarose, open circles; and, without 4% agarose, closed circle) were plotted during single quantum acquisition and for 9 different inversion recovery times (TI) showed two distinct null points shown at right.