High resolution hyperpolarized ¹³C MRSI using SPICE at 9.4T

Purpose: To test the feasibility of using the SPICE (SPectroscopic Imaging by exploiting spatiospectral CorrElation) technique, which uses the partial separability of spectroscopic data, for high resolution hyperpolarized (HP) ¹³C spectroscopic imaging. Methods: Numerical simulations were performed to investigate the impact of transient HP signals on SPICE reconstruction. Furthermore, spectroscopic imaging exams from SPICE and conventional EPSI (echo-planar spectroscopic imaging) were simulated for comparison. For in vivo experiments, HP ¹³C SPICE was performed in a mouse kidney by means of the injection of HP [1-¹³C] pyruvate at 9.4T. Results: The variation of lactate/pyruvate from the simulated SPICE was less than 4% under various factors that affect the transient HP signal, suggesting that the impact is negligible. We found that while HP ¹³C EPSI was limited to the low signal-to-noise ratio (SNR) of lactate, these limitations were mitigated through HP ¹³C SPICE, facilitating the improved SNR of lactate and the distinction of tissues. Acquisition of a high resolution HP ¹³C spectroscopic image was possible for the in vivo experiments. With the fine structural information, the acquired image showed higher signal of pyruvate and lactate in the renal cortices than in the medullas, which is known to be attributed to higher activity of lactate dehydrogenase. Conclusion: The feasibility of HP ¹³C SPICE was investigated. Simulation studies were conducted and in vivo experiments were performed in the mouse kidney at 9.4T. Results confirmed that a high resolution HP ¹³C spectroscopic image with adequate spectral resolution can be obtained. Magn Reson Med 80:703–710, 2018.