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PurposeThe balanced steady-state free precession sequence has been previously explored to improve the efficient use of nonrecoverable hyperpolarized 13C magnetization, but suffers from poor spectral selectivity and long acquisition time. The purpose of this study was to develop a novel metabolite-specific 3D bSSFP ("MS-3DSSFP") sequence with stack-of-spiral readouts for improved lactate imaging in hyperpolarized [1-13 C]pyruvate studies on a clinical 3T scanner.MethodsSimulations were performed to evaluate the spectral response of the MS-3DSSFP sequence. Thermal 13C phantom experiments were performed to validate the MS-3DSSFP sequence. In vivo hyperpolarized [1-13 C], pyruvate studies were performed to compare the MS-3DSSFP sequence with metabolite-specific gradient echo ("MS-GRE") sequences for lactate imaging.ResultsSimulations, phantom, and in vivo studies demonstrate that the MS-3DSSFP sequence achieved spectrally selective excitation on lactate while minimally perturbing other metabolites. Compared with MS-GRE sequences, the MS-3DSSFP sequence showed approximately a 2.5-fold SNR improvement for lactate imaging in rat kidneys, prostate tumors in a mouse model, and human kidneys.ConclusionsImproved lactate imaging using the MS-3DSSFP sequence in hyperpolarized [1-13 C]pyruvate studies was demonstrated in animals and humans. The MS-3DSSFP sequence could be applied for other clinical applications such as in the brain or adapted for imaging other metabolites such as pyruvate and bicarbonate.

PurposeThe balanced steady-state free precession sequence has been previously explored to improve the efficient use of nonrecoverable hyperpolarized 13C magnetization, but suffers from poor spectral selectivity and long acquisition time. The purpose of this study was to develop a novel metabolite-specific 3D bSSFP ("MS-3DSSFP") sequence with stack-of-spiral readouts for improved lactate imaging in hyperpolarized [1-13 C]pyruvate studies on a clinical 3T scanner.MethodsSimulations were performed to evaluate the spectral response of the MS-3DSSFP sequence. Thermal 13C phantom experiments were performed to validate the MS-3DSSFP sequence. In vivo hyperpolarized [1-13 C], pyruvate studies were performed to compare the MS-3DSSFP sequence with metabolite-specific gradient echo ("MS-GRE") sequences for lactate imaging.ResultsSimulations, phantom, and in vivo studies demonstrate that the MS-3DSSFP sequence achieved spectrally selective excitation on lactate while minimally perturbing other metabolites. Compared with MS-GRE sequences, the MS-3DSSFP sequence showed approximately a 2.5-fold SNR improvement for lactate imaging in rat kidneys, prostate tumors in a mouse model, and human kidneys.ConclusionsImproved lactate imaging using the MS-3DSSFP sequence in hyperpolarized [1-13 C]pyruvate studies was demonstrated in animals and humans. The MS-3DSSFP sequence could be applied for other clinical applications such as in the brain or adapted for imaging other metabolites such as pyruvate and bicarbonate.

Purpose: Metabolite‐specific balanced SSFP (MS‐bSSFP) sequences are increasingly used in hyperpolarized [1‐13C]Pyruvate (HP 13C) MRI studies as they improve SNR by refocusing the magnetization each TR. Currently, pharmacokinetic models used to fit conversion rate constants, kPL and kPB, and rate constant maps do not account for differences in the signal evolution of MS‐bSSFP acquisitions. Methods: In this work, a flexible MS‐bSSFP model was built that can be used to fit conversion rate constants for these experiments. The model was validated in vivo using paired animal (healthy rat kidneys n = 8, transgenic adenocarcinoma of the mouse prostate n = 3) and human renal cell carcinoma (n = 3) datasets. Gradient echo (GRE) acquisitions were used with a previous GRE model to compare to the results of the proposed GRE‐bSSFP model. Results: Within simulations, the proposed GRE‐bSSFP model fits the simulated data well, whereas a GRE model shows bias because of model mismatch. For the in vivo datasets, the estimated conversion rate constants using the proposed GRE‐bSSFP model are consistent with a previous GRE model. Jointly fitting the lactate T2 with kPL resulted in less precise kPL estimates. Conclusion: The proposed GRE‐bSSFP model provides a method to estimate conversion rate constants, kPL and kPB, for MS‐bSSFP HP 13C experiments. This model may also be modified and used for other applications, for example, estimating rate constants with other hyperpolarized reagents or multi‐echo bSSFP. [ABSTRACT FROM AUTHOR]

Purpose: The balanced steady‐state free precession sequence has been previously explored to improve the efficient use of nonrecoverable hyperpolarized 13C magnetization, but suffers from poor spectral selectivity and long acquisition time. The purpose of this study was to develop a novel metabolite‐specific 3D bSSFP ("MS‐3DSSFP") sequence with stack‐of‐spiral readouts for improved lactate imaging in hyperpolarized [1-13C]pyruvate studies on a clinical 3T scanner. Methods: Simulations were performed to evaluate the spectral response of the MS‐3DSSFP sequence. Thermal 13C phantom experiments were performed to validate the MS‐3DSSFP sequence. In vivo hyperpolarized [1-13C], pyruvate studies were performed to compare the MS‐3DSSFP sequence with metabolite‐specific gradient echo ("MS‐GRE") sequences for lactate imaging. Results: Simulations, phantom, and in vivo studies demonstrate that the MS‐3DSSFP sequence achieved spectrally selective excitation on lactate while minimally perturbing other metabolites. Compared with MS‐GRE sequences, the MS‐3DSSFP sequence showed approximately a 2.5‐fold SNR improvement for lactate imaging in rat kidneys, prostate tumors in a mouse model, and human kidneys. Conclusions: Improved lactate imaging using the MS‐3DSSFP sequence in hyperpolarized [1-13C]pyruvate studies was demonstrated in animals and humans. The MS‐3DSSFP sequence could be applied for other clinical applications such as in the brain or adapted for imaging other metabolites such as pyruvate and bicarbonate. [ABSTRACT FROM AUTHOR]

Purpose: Metabolite-specific balanced SSFP (MS-bSSFP) sequences are increasingly used in hyperpolarized [1- 13 C]Pyruvate (HP 13 C) MRI studies as they improve SNR by refocusing the magnetization each TR. Currently, pharmacokinetic models used to fit conversion rate constants, k PL and k PB , and rate constant maps do not account for differences in the signal evolution of MS-bSSFP acquisitions., Methods: In this work, a flexible MS-bSSFP model was built that can be used to fit conversion rate constants for these experiments. The model was validated in vivo using paired animal (healthy rat kidneys n = 8, transgenic adenocarcinoma of the mouse prostate n = 3) and human renal cell carcinoma (n = 3) datasets. Gradient echo (GRE) acquisitions were used with a previous GRE model to compare to the results of the proposed GRE-bSSFP model., Results: Within simulations, the proposed GRE-bSSFP model fits the simulated data well, whereas a GRE model shows bias because of model mismatch. For the in vivo datasets, the estimated conversion rate constants using the proposed GRE-bSSFP model are consistent with a previous GRE model. Jointly fitting the lactate T 2 with k PL resulted in less precise k PL estimates., Conclusion: The proposed GRE-bSSFP model provides a method to estimate conversion rate constants, k PL and k PB , for MS-bSSFP HP 13 C experiments. This model may also be modified and used for other applications, for example, estimating rate constants with other hyperpolarized reagents or multi-echo bSSFP., (© 2024 International Society for Magnetic Resonance in Medicine.)