# A flexible MRF approach to improve kinetic rate estimation with bSSFP‐based hyperpolarized [1‐ 13C]pyruvate MRI

## TL;DR

This paper introduces a new MRF-based method for improving the accuracy of metabolic rate estimation using hyperpolarized MRI in rat kidneys.

## Contribution

A novel MRF-Sigmoid approach is proposed to enhance kinetic rate estimation with bSSFP-based hyperpolarized [1-13C]pyruvate MRI.

## Key findings

- MRF-Sigmoid showed <0.1% bias in kPL estimation across 86% of tested conditions.
- MRF-Sigmoid improved pyruvate SNR by 3.5-fold over prior methods while maintaining lactate SNR.
- In vivo kPL estimates showed positive linear correlations across all experimental methods.

## Abstract

In this work, we adopt the MR fingerprinting (MRF) framework and leverage its flexibility in quantitative pulse sequence design to propose improved balanced steady‐state free precession (bSSFP)–based hyperpolarized Carbon‐13 (13C) acquisitions for robust metabolic conversion rate quantification.

Spectrally selective bSSFP‐based acquisitions with variable RF excitation were implemented for [1‐13C]pyruvate and used in conjunction with prior implementation of [1‐13C]lactate selective bSSFP imaging. MRF framework parameter estimation was performed using dictionary‐based template matching. Influences of bSSFP‐based acquisitions and sigmoid RF excitation scheme were assessed with simulation experiments and Monte Carlo evaluation. Methods were then compared using experimental data from rat kidney acquired on a clinical 3 T scanner.

Simulations indicated that combining bSSFP‐based acquisitions and variable RF excitation (MRF‐Sigmoid) exhibited bias <0.1% across the majority (86%) of combinations of pyruvate‐to‐lactate conversion rate (kPL) and noise level investigated when estimating kPL with the MRF framework. bSSFP‐based experiments, with and without sigmoid excitation scheme, showed lower variance in fits at all levels of kPL and noise investigated compared to the method used in prior work by this group (hybrid gradient echo). Positive, linear correlations were found for in vivo voxel‐wise estimates of kPL in healthy rat kidneys when comparing all experiment methods. MRF‐Sigmoid experiment design increased pyruvate cumulative SNR by 3.5‐fold over hybrid gradient echo while maintaining similar lactate cumulative SNR.

The use of the MRF framework for kPL estimation demonstrates the feasibility of dictionary‐based template matching and can be used to accurately estimate physiologically relevant kPL and improve cumulative SNR.