Data adaptive regularization with reference tissue constraints for liver quantitative susceptibility mapping

Abstract

Purpose: To improve repeatability and reproducibility across acquisition parameters and reduce bias in quantitative susceptibility mapping (QSM) of the liver, through development of an optimized regularized reconstruction algorithm for abdominal QSM.

Methods: An optimized approach to estimation of magnetic susceptibility distribution is formulated as a constrained reconstruction problem that incorporates estimates of the input data reliability and anatomical priors available from chemical shift-encoded imaging. The proposed data-adaptive method was evaluated with respect to bias, repeatability, and reproducibility in a patient population with a wide range of liver iron concentration (LIC). The proposed method was compared to the previously proposed and validated approach in liver QSM for two multi-echo spoiled gradient-recalled echo protocols with different acquisition parameters at 3T. Linear regression was used for evaluation of QSM methods against a reference FDA-approved $R_2$ -based LIC measure and $R_2^{\ast }$ measurements; repeatability/reproducibility were assessed by Bland-Altman analysis.

Results: The data-adaptive method produced susceptibility maps with higher subjective quality due to reduced shading artifacts. For both acquisition protocols, higher linear correlation with both $R_2$ - and $R_2^{\ast }$ -based measurements were observed for the data-adaptive method ( $r^2=0.74/0.69$ for $R_2$ , $0.97/0.95$ for $R_2^{\ast }$ ) than the standard method ( $r^2=0.60/0.66$ and $0.79/0.88$ ). For both protocols, the data-adaptive method enabled better test-retest repeatability (repeatability coefficients 0.19/0.30 ppm for the data-adaptive method, 0.38/0.47 ppm for the standard method) and reproducibility across protocols (reproducibility coefficient 0.28 vs. 0.53ppm) than the standard method.

Conclusions: The proposed data-adaptive QSM algorithm may enable quantification of LIC with improved repeatability/reproducibility across different acquisition parameters as 3T.

Keywords: QSM; iron; liver; susceptibility.