Multiband spectral-spatial RF excitation for hyperpolarized [2-¹³C]dihydroxyacetone ¹³C-MR metabolism studies

Purpose: To develop a specialized multislice, single-acquisition approach to detect the metabolites of hyperpolarized (HP) [2-¹³C]dihydroxyacetone (DHAc) to probe gluconeogenesis in vivo, which have a broad 144 ppm spectral range (∼4.6 kHz at 3T). A novel multiband radio-frequency (RF) excitation pulse was designed for independent flip angle control over five to six spectral-spatial (SPSP) excitation bands, each corrected for chemical shift misregistration effects. Methods: Specialized multiband SPSP RF pulses were designed, tested, and applied to investigate HP [2-¹³C]DHAc metabolism in kidney and liver of fasted rats with dynamic ¹³C-MR spectroscopy and an optimal flip angle scheme. For comparison, experiments were also performed with narrow-band slice-selective RF pulses and a sequential change of the frequency offset to cover the five frequency bands of interest. Results: The SPSP pulses provided a controllable spectral profile free of baseline distortion with improved signal to noise of the metabolite peaks, allowing for quantification of the metabolic products. We observed organ-specific differences in DHAc metabolism. There was two to five times more [2-¹³C]phosphoenolpyruvate and about 19 times more [2-¹³C]glycerol 3-phosphate in the liver than in the kidney. Conclusion: A multiband SPSP RF pulse covering a spectral range over 144 ppm enabled in vivo characterization of HP [2-¹³C]DHAc metabolism in rat liver and kidney. Magn Reson Med 77:1419–1428, 2017.