Sub-second proton imaging of 13C hyperpolarized contrast agents in water

Indirect proton detection of C-13 hyperpolarized contrast agents potentially enables greater sensitivity. Presented here is a study of sub-second projection imaging of hyperpolarized C-13 contrast agent addressing the obstacle posed by water suppression for indirect detection in vivo. Sodium acetate phantoms were used to develop and test water suppression and sub-second imaging with frequency-selective RF pulses using spectroscopic and imaging indirect proton detection. A 9.8mm aqueous solution of C-13 PHIP hyperpolarized 2-hydroxyethyl-C-13-propionate-d(2,3,3) (HEP), similar to 25% was used for demonstration of indirect proton sub-second imaging detection. Balanced 2D FSSFP (fast steady-state free precession) allowed the recording of proton images with a field of view of 64x64mm(2) and spatial resolution 2x2mm(2) with total acquisition time of less than 0.2s. In thermally polarized sodium 1-C-13-acetate, C-13 to H-1 polarization transfer efficiency of 45.1% of the theoretically predicted values was observed in imaging detection corresponding to an 11-fold overall sensitivity improvement compared with direct C-13 FSSFP imaging. C-13 to H-1 polarization transfer efficiency of 27% was observed in imaging detection, corresponding to a 3.25-fold sensitivity improvement compared with direct C-13 FSSFP imaging with hyperpolarized HEP. The range of potential applications and limitations of this sub-second and ultra-sensitive imaging approach are discussed. Copyright (c) 2014 John Wiley & Sons, Ltd.