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Using bidirectional chemical exchange for improved hyperpolarized [ 13 C]bicarbonate pH imaging
Author(s) -
Korenchan David E.,
Gordon Jeremy W.,
Subramaniam Sukumar,
Sriram Renuka,
Baligand Celine,
VanCriekinge Mark,
Bok Robert,
Vigneron Daniel B.,
Wilson David M.,
Larson Peder E.Z.,
Kurhanewicz John,
Flavell Robert R.
Publication year - 2019
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.27780
Subject(s) - bicarbonate , chemistry , pulse sequence , pulse (music) , imaging phantom , nuclear magnetic resonance , in vivo , excitation , analytical chemistry (journal) , optics , chromatography , physics , microbiology and biotechnology , organic chemistry , quantum mechanics , detector , biology
Purpose Rapid chemical exchange can affect SNR and pH measurement accuracy for hyperpolarized pH imaging with [ 13 C]bicarbonate. The purpose of this work was to investigate chemical exchange effects on hyperpolarized imaging sequences to identify optimal sequence parameters for high SNR and pH accuracy. Methods Simulations were performed under varying rates of bicarbonate–CO 2 chemical exchange to analyze exchange effects on pH quantification accuracy and SNR under different sampling schemes. Four pulse sequences, including 1 new technique, a multiple‐excitation 2D EPI (multi‐EPI) sequence, were compared in phantoms using hyperpolarized [ 13 C]bicarbonate, varying parameters such as tip angles, repetition time, order of metabolite excitation, and refocusing pulse design. In vivo hyperpolarized bicarbonate–CO 2 exchange measurements were made in transgenic murine prostate tumors to select in vivo imaging parameters. Results Modeling of bicarbonate–CO 2 exchange identified a multiple‐excitation scheme for increasing CO 2 SNR by up to a factor of 2.7. When implemented in phantom imaging experiments, these sampling schemes were confirmed to yield high pH accuracy and SNR gains. Based on measured bicarbonate–CO 2 exchange in vivo, a 47% CO 2 SNR gain is predicted. Conclusion The novel multi‐EPI pulse sequence can boost CO 2 imaging signal in hyperpolarized 13 C bicarbonate imaging while introducing minimal pH bias, helping to surmount a major hurdle in hyperpolarized pH imaging.