Mapping tissue water T1 in the liver using the MOLLI T1 method in the presence of fat, iron and B0 inhomogeneity

Abstract

Modified Look-Locker inversion recovery (MOLLI) T₁ mapping sequences can be useful in cardiac and liver tissue characterization, but determining underlying water T₁ is confounded by iron, fat and frequency offsets. This article proposes an algorithm that provides an independent water MOLLI T₁ (referred to as on-resonance water T₁ ) that would have been measured if a subject had no fat and normal iron, and imaging had been done on resonance. Fifteen NiCl₂ -doped agar phantoms with different peanut oil concentrations and 30 adults with various liver diseases, nineteen (63.3%) with liver steatosis, were scanned at 3 T using the shortened MOLLI (shMOLLI) T₁ mapping, multiple-echo spoiled gradient-recalled echo and ¹ H MR spectroscopy sequences. An algorithm based on Bloch equations was built in MATLAB, and water shMOLLI T₁ values of both phantoms and human participants were determined. The quality of the algorithm's result was assessed by Pearson's correlation coefficient between shMOLLI T₁ values and spectroscopically determined T₁ values of the water, and by linear regression analysis. Correlation between shMOLLI and spectroscopy-based T₁ values increased, from r = 0.910 (P < 0.001) to r = 0.998 (P < 0.001) in phantoms and from r = 0.493 (for iron-only correction; P = 0.005) to r = 0.771 (for iron, fat and off-resonance correction; P < 0.001) in patients. Linear regression analysis revealed that the determined water shMOLLI T₁ values in patients were independent of fat and iron. It can be concluded that determination of on-resonance water (sh)MOLLI T₁ independent of fat, iron and macroscopic field inhomogeneities was possible in phantoms and human subjects.

Keywords: MOLLI; NAFLD; fat; iron; off-resonance; shMOLLI.