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Using bidirectional chemical exchange for improved hyperpolarized [13 C]bicarbonate pH imaging.

ABSTRACT: 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-CO2 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-CO2 exchange measurements were made in transgenic murine prostate tumors to select in vivo imaging parameters. RESULTS:Modeling of bicarbonate-CO2 exchange identified a multiple-excitation scheme for increasing CO2 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-CO2 exchange in vivo, a 47% CO2 SNR gain is predicted. CONCLUSION:The novel multi-EPI pulse sequence can boost CO2 imaging signal in hyperpolarized 13 C bicarbonate imaging while introducing minimal pH bias, helping to surmount a major hurdle in hyperpolarized pH imaging.

SUBMITTER: Korenchan DE

PROVIDER: S-EPMC6559833 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Using bidirectional chemical exchange for improved hyperpolarized [<sup>13</sup> C]bicarbonate pH imaging.

Korenchan David E DE Gordon Jeremy W JW Subramaniam Sukumar S Sriram Renuka R Baligand Celine C VanCriekinge Mark M Bok Robert R Vigneron Daniel B DB Wilson David M DM Larson Peder E Z PEZ Kurhanewicz John J Flavell Robert R RR

Magnetic resonance in medicine 20190503 3

<h4>Purpose</h4>Rapid chemical exchange can affect SNR and pH measurement accuracy for hyperpolarized pH imaging with [<sup>13</sup> 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.<h4>Methods</h4>Simulations were performed under varying rates of bicarbonate-CO<sub>2</sub> chemical exchange to analyze exchange effects on pH quantification accuracy and SNR ...[more]

PMID: 31050049

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Project description:PurposeA multiecho, field of view (FOV)-oversampled k-t spiral acquisition and direct iterative decomposition of water and fat with echo asymmetry and least-squares estimation reconstruction is demonstrated to improve the stability of hyperpolarized 13 C magnetic resonance spectroscopic imaging (MRSI) in the presence of signal ambiguities attributed to low-SNR (signal-to-noise-ratio) species, local uncertainties in metabolite peaks, and echo-to-echo signal inconsistencies.Theoryk-t spiral acquisitions redistribute readout points to be more densely spaced radially in k-space by acquiring an FOV and matrix that are oversampled by η. These more densely spaced spiral turns constitute effective intraspiral echoes and can supplement conventional interspiral echoes to improve spectral separation and reduce spectral cross-talk to better resolve 13 C-labeled species for spectroscopic imaging.MethodsDigital simulations and imaging phantom experiments were performed for a range of interspiral echo spacings and η using multiecho, k-t spiral acquisitions. Image spectral cross-talk artifacts were evaluated both qualitatively and quantitatively as the percent error in measured metabolite ratios. In vivo murine experiments evaluated the feasibility of multiecho, k-t spiral [1-13 C]pyruvate MRSI to reduce spectral cross-talk for 3 scenarios of different expected reconstruction stability.ResultsDigital simulations and imaging phantom experiments both demonstrated reduced or comparable image spectral cross-talk and percent errors in measured metabolite ratios with increasing η and better choices of echo spacings. In vivo images displayed markedly reduced spectral cross-talk in lactate images acquired with η = 7 versus η = 1.ConclusionThe precision of hyperpolarized 13 C metabolic imaging and quantification in the presence of low-SNR species, local uncertainties in metabolite resonances, and echo-to-echo signal inconsistencies can be improved with the use of FOV-oversampled k-t spiral acquisitions.

Dataset Information

Using bidirectional chemical exchange for improved hyperpolarized [13 C]bicarbonate pH imaging.

Publications

Using bidirectional chemical exchange for improved hyperpolarized [<sup>13</sup> C]bicarbonate pH imaging.

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