Selective spectroscopic imaging of hyperpolarized pyruvate and its metabolites using a single-echo variable phase advance method in balanced SSFP.

Magnetic Resonance in Medicine

PubMedID: 26507361

Varma G, Wang X, Vinogradov E, Bhatt RS, Sukhatme VP, Seth P, Lenkinski RE, Alsop DC, Grant AK. Selective spectroscopic imaging of hyperpolarized pyruvate and its metabolites using a single-echo variable phase advance method in balanced SSFP. Magn Reson Med. 2016;76(4):1102-15.
PURPOSE
In balanced steady state free precession (bSSFP), the signal intensity has a well-known dependence on the off-resonance frequency, or, equivalently, the phase advance between successive radiofrequency (RF) pulses. The signal profile can be used to resolve the contributions from the spectrally separated metabolites. This work describes a method based on use of a variable RF phase advance to acquire spatial and spectral data in a time-efficient manner for hyperpolarized 13C MRI.

THEORY AND METHODS
The technique relies on the frequency response from a bSSFP acquisition to acquire relatively rapid, high-resolution images that may be reconstructed to separate contributions from different metabolites. The ability to produce images from spectrally separated metabolites was demonstrated in vitro, as well as in vivo following administration of hyperpolarized 1-13C pyruvate in mice with xenograft tumors.

RESULTS
In vivo images of pyruvate, alanine, pyruvate hydrate, and lactate were reconstructed from four images acquired in 2 s with an in-plane resolution of 1.25 × 1.25 mm(2) and 5 mm slice thickness.

CONCLUSION
The phase advance method allowed acquisition of spectroscopically selective images with high spatial and temporal resolution. This method provides an alternative approach to hyperpolarized 13C spectroscopic MRI that can be combined with other techniques such as multiecho or fluctuating equilibrium bSSFP. Magn Reson Med 76:1102-1115, 2016. © 2015 Wiley Periodicals, Inc.