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.
Highlights
Nonalcoholic fatty liver disease (NAFLD) has recently seen a rise in prevalence both in Western countries and worldwide[1] as the manifestation of metabolic syndrome in the liver. It can be asymptomatic for prolonged periods of time and might not even progress to more severe stages, its natural progression includes the stages of accumulation of fat, fatty inflammation of the liver and later the additional development of fibrosis
This study investigated the dependence of liver shortened modified Look-Locker inversion recovery (shMOLLI) T1 on body hydration status and on liver glycogen concentration
Our in vivo results are in agreement with what has been previously reported in the literature in glycogen phantoms: a decrease in glycogen concentration led to a longer liver shMOLLI T1; in addition, we have found that a decrease in inferior vena cava (IVC)/Ao ratio led to a shorter liver shMOLLI T1
Summary
Nonalcoholic fatty liver disease (NAFLD) has recently seen a rise in prevalence both in Western countries and worldwide[1] as the manifestation of metabolic syndrome in the liver. Two to 6 days later there was another standardized, high-calorie (1300 kcal), high-carbohydrate meal consumed for dinner, a 12-h long overnight fast with the final 3 h water fasting, followed at 8 a.m. by a fourth scan, to measure T1 at moderately low amounts of glycogen and lowerthan-normal hydration levels (participants were in a underhydrated state – state 4). Single-shot images were reconstructed into a T1 map on the scanner console using the shMOLLI conditional fitting algorithm.[17] Proton density fat fraction (PDFF), B0 and T2* values were quantified using a multiple-echo spoiled GRE sequence with parameters: FOV = 330 Â 248 mm[2], matrix size 128 Â 96, TR/TE = 17/0.94, 2.28, 3.60, 4.92, 6.24, 7.56, 8.88, 10.20, 11.52, 12.84, 14.16 and 15.48 ms, FA = 3, phase-encoding direction anterior–posterior, BW = 1560 Hz/px, monopolar gradient readout scheme, and slice thickness 10 mm.
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