Hydration and glycogen affect T1 relaxation times of liver tissue

Abstract

T₁ mapping is a useful tool for the assessment of patients with nonalcoholic fatty liver disease but still suffers from a large unexplained variance in healthy subjects. This study aims to characterize the potential effects of liver glycogen concentration and body hydration status on liver shortened modified Look-Locker inversion recovery (shMOLLI) T₁ measurements. Eleven glycogen phantoms and 12 healthy volunteers (mean age: 31 years, three females) were scanned at 3 T using inversion recovery spin echo, multiple contrast spin echo (in phantoms), shMOLLI T₁ mapping, multiple-echo spoiled gradient recalled echo and ¹³ C spectroscopy (in healthy volunteers). Phantom r₁ and r₂ relaxivities were determined from measured T₁ and T₂ values. Participants underwent a series of five metabolic experiments to vary their glycogen concentration and hydration levels: feeding, food fasting, exercising, underhydration, and rehydration. Descriptive statistics were calculated for shMOLLI T₁ , inferior vena cava to aorta cross-sectional area ratio (IVC/Ao) as a marker of body hydration status, glycogen concentration, T₂ * and proton density fat fraction values. A linear mixed model for shMOLLI R₁ was constructed to determine the effects of glycogen concentration and IVC/Ao ratio. The mean shMOLLI T₁ after fasting was 737 ± 67 ms. The mean within-subject change was 80 ± 45 ms. The linear mixed model revealed a glycogen r₁ relaxivity in volunteers (0.18 M^-1 s^-1 , p = 0.03) close to that determined in phantoms (0.28 M^-1 s^-1 ). A unit change in IVC/Ao ratio was associated with a drop of -0.113 s^-1 in R₁ (p < 0.001). This study demonstrated a dependence of liver shMOLLI T₁ values on liver glycogen concentration and overall body hydration status. Interparticipant variation of hydration status should be minimized in future liver MRI studies. Additionally, caution is advised when interpreting liver T1 measurements in participants with excess liver glycogen.

Keywords: glycogen; hydration; liver; shMOLLI T1.