Total tissue sodium (23Na) content is associated with the viability of cells and can be assessed by 23Na magnetic resonance imaging. However, the resulting total sodium signal (23NaT) represents a volume-weighted average of different sodium compartments assigned to the intra- and extracellular space. In addition to the spin-density weighted contrast of 23NaT imaging, relaxation-weighted (23NaR) sequences were applied. The aim of this study was to evaluate the potential of 23NaR imaging for tissue characterization and putative additional benefits to 23NaT imaging.
Materials and Methods:
For 23NaT and 23NaR imaging, novel magnetic resonance imaging sequences were established and applied in 16 patients suffering from brain tumors (14 WHO grade I–IV and 2 metastases). All 23Na sequences were based on density-adapted three-dimensional radial projection reconstruction to obtain short echo times and high signal-to-noise ratio efficiency.
23NaT imaging revealed increased signal intensities in 15 of 16 brain tumors before therapy. In addition, 23NaR imaging enabled further differentiation of these lesions; all glioblastomas demonstrated higher 23NaR signal intensities as compared with WHO grade I–III tumors. Thus, 23NaR imaging allowed for correct separation between WHO grade I–III and WHO grade IV gliomas. In contrast to the 23NaT signal, the 23NaR signal correlated with the MIB-1 proliferation rate of tumor cells.
These results serve as a proof of concept that 23NaR imaging reveals important physiological tissue characteristics different from 23NaT imaging. Furthermore, they indicate that the combined use of 23NaT and 23NaR imaging might add valuable information for the functional in vivo characterization of brain tissue.