MR elastography is a fast-evolving field with increasing evidence for its use in the diagnosis of liver fibrosis. Fibrotic livers have, amongst other factors, a higher collagen content which results in a increase in stiffness that can be quantified using magnetic resonance elastography (MRE). Technical difficulties exist however, which may lead to variability in the measured liver stiffness. Standard techniques are phase-based and are therefore sensitive to motion artefact, such as can be seen with breathing.1 MRE in the liver is typically performed at end-expiration, and requires four breath holds.2, 3 Sequential breath holds may result in slightly differing diaphragmatic positions and therefore different position of the liver and other viscera, which may result in misregistration. In addition, some patients may also not be able to accommodate the breath-holds. Respiratory triggering, using navigators, is an alternative method to breath-hold acquisitions but is not supported in the product MRE sequences. The aim of this study is to compare liver stiffness measurements using breath-hold, navigator-gated, and free breathing MREEthical approval was provided for the study. The studies were carried out on six healthy volunteers, 3 male and 3 female, with a mean age of 28 years, with full informed consent. Imaging was peformed using Examinations were performed on a 1.5T whole-body MRI scanner (Discovery MR450, General Electric, Waukesha ha, WI) using an eight-channel receive-only phased-array coil. Examinations were performed on a 1.5T whole-body MRI scanner (Discovery MR450, General Electric, Waukesha ha, WI) using an eight-channel receive-only phased-array coil. Examinations were performed on a 1.5T whole-body MRI scanner (Discovery MR450, General Electric, Waukesha ha, WI) using an eight-channel receive-only phased-array coil. Examinations were performed on a 1.5T whole-body MRI scanner (Discovery MR450, GE Healthcare, Waukesha, WI) using an eight-channel array coil. For the MRE acquisition a passive 18.5-cm-diameter pneumatic driver was placed anteriorly over the right lower ribs superficial to the right lobe of the liver. The passive driver was connected to an active drive unit producing shear waves at 60 Hz. The product gradient-echo based MRE sequence was modified to incorporate a 2D cylindrical excitation navigator. Sequence parameters were TE/TR =22/50ms, matrix 256x64, FOV = 40x36cm, slice thickness=8 mm, gap=5mm, bandwidth = ±31.25kHz, and flip angle =30°. A parallel imaging (ASSET) acceleration factor of 1.5 was used. Four slices were acquired with four phase offsets. In the breath-hold acquisition each offset was acquired in a separate breath-hold. MRE shear modulus-based stiffness and confidence interval maps were subsequently computed. Each subject was imaged twice using the free-breathing, breath-held and navigator-triggered methods. The order in which the sequences were acquired was randomized. The stiffness and the percentage of analyzable liver area were calculated at a per subject level by determining the mean across all 4 slices (Figure 1). The repeatability of each technique was determined by computing the absolute difference in MRE liver stiffness between repeat scans 1 and 2. The Kruskal-Wallis test was performed to assess if there was an overall difference between each the MRI acquisition strategies. Pair-wise comparisons were performed using Wilcoxon’s rank-sum test. The percentage mean area of liver where the stiffness was quantifiable (confidence interval >95%) and mean stiffness values are summarized in Table 1. No statistically significant differences in liver stiffness were noted between acquisition strategies (p=0.199) (Figure 2). We note that liver stiffness during inspiration is elevated relative to expiration as previously noted in the ultrasound literature 4 , however the difference was not significant (p=0.240). The navigator method was not significantly different to the standard expiration (p=0.589) or the inspiration (p=0.180) methods. A comparison of analyzable liver areas (where CI >95%) demonstrates that the overall group difference is significantly different (p=0.002) (Figure 3). The free breathing acquisition is notably lower than the other methods. The group-wise comparison of MRE repeatability (Figure 4) was not statistically significant (p=0.142), however, the free breathing method demonstrates the greatest variability. The navigator method has comparable repeatability to the expiration and inspiration methods (p=0.520 and p=0.521 respectively). The mean acquisition time for the navigator triggered sequence was 4 minutes 55 seconds. The results show that MRE using navigator-triggering gives results similar to the gold-standard end-expiratory breath hold technique in healthy volunteers. The technique may therefore be useful in patients unable to perform extended breath-holds.