Proton NMR microscopy of multicellular tumor spheroid morphology

We report proton NMR images obtained at microscopic (less than 30 microns) resolution of EMT6/Ro and HT1080 multicellular tumor spheroids 1.2-1.7 mm in diameter. T1-weighted images showed little contrast across a slice through the spheroid. There was also no difference between the inner and outer spheroid regions when signal intensity was measured as a function of the repetition time (TR), showing that T1 was the same across the spheroid. Conversely, T2-weighted and multi-echo images clearly revealed the central necrosis that occurs as the spheroids develop. Measurements of the thickness of the viable cell zone made on NMR images agreed with those made on standard histology sections for two different cell lines. The basis for the NMR discrimination of the necrotic region from the viable rim cells was found to be a shortened apparent T2 in the necrotic region (132 +/- 17 ms) with respect to that in the viable cells (173 +/- 9 ms). These results illustrate the applicability of NMR microscopy to assaying conditions inside intact tumor spheroids and suggest that this technology will allow the use of spheroids to investigate several important questions in tumor biology and pathophysiology.