MR imaging of a novel NOE-mediated magnetization transfer with water in rat brain at 9.4 T

Purpose To detect, map, and quantify a novel nuclear Overhauser enhancement (NOE)-mediated magnetization transfer (MT) with water at approximately −1.6 ppm [NOE(−1.6)] in rat brain using MRI. Methods Continuous wave MT sequences with a variety of radiofrequency irradiation powers were optimized to achieve the maximum contrast of this NOE(−1.6) effect at 9.4 T. The distribution of effect magnitudes, resonance frequency offsets, and line widths in healthy rat brains and the differences of the effect between tumors and contralateral normal brains were imaged and quantified using a multi-Lorentzian fitting method. MR measurements on reconstituted model phospholipids as well as two cell lines (HEK293 and 9L) were also performed to investigate the possible molecular origin of this NOE. Results Our results suggest that the NOE(−1.6) effect can be detected reliably in rat brain. Pixel-wise fittings demonstrated the regional variations of the effect. Measurements in a rodent tumor model showed that the amplitude of NOE(−1.6) in brain tumor was significantly diminished compared with that in normal brain tissue. Measurements of reconstituted phospholipids suggest that this effect may originate from choline phospholipids. Conclusion NOE(−1.6) could be used as a new biomarker for the detection of brain tumor. Magn Reson Med 78:588–597, 2017. © 2016 International Society for Magnetic Resonance in Medicine