Purpose or Case Report: MR elastography (MRE) is increasingly being used to non-invasively assess diffuse liver disease in children. However, there are limited normal liver stiffness data for MRE in children. The purpose of this study was to determine normal liver stiffness measured by MRE for children and assess for associations with demographic factors, MRI field strength and MRI vendor.
Methods & Materials: This was a prospective multi-institutional study conducted under IRB approval with written informed consent. 98 children with no known history of liver disease and with body mass index (BMI) ≤85^th percentile were recruited to undergo MRE, evenly distributed across GE, Philips and Siemens scanners at 1.5T and 3T. Participants were evenly recruited into 2 age groups (7-11.9y or 12-17.9y). Participants completed a questionnaire confirming absence of liver disease, had liver function tests drawn, and were weighed and measured (height, girth). MRE was performed using the manufacturer’s product sequence, and chemical shift-encoded MRI was performed to determine liver proton density fat fraction (PDFF) and T2*. Stiffness data were excluded for participants with any abnormal laboratory value, PDFF >5%, or T2* <20 ms at 1.5T.

Descriptive statistics were used to summarize population characteristics. Students t-test, Pearson correlation, and the Kruskal Wallis test were used for comparison of groups.
Results: 76 (77.6%) participants with a mean age of 12.5±2.9 years met all inclusion criteria. 42 (55.3%) were female. Mean BMI was 18.7±2.4 (range: 14.6-24.3), and mean BMI percentile was 50.9±22.5% (range: 13.6-85%). 40 (52.6%) participants were scanned at 1.5T and 36 (47.4%) at 3T. 25 (32.9%) participants were scanned on GE magnets, 27 (35.5%) on Siemens, and 24 (31.6%) on Philips.

Mean liver stiffness for the population was 2.2±0.4 kPa (range: 1.3-3.4 kPa). Mean PDFF was 2.2±0.9%, and mean T2* was 34.5±8.3 ms. There were no statistically significant differences in liver stiffness based on sex (p=0.74), MRI field strength (p=0.15), or MRI manufacturer (p=0.12), and there were no statistically significant correlations between liver stiffness and age (r=0.58, p=0.62) or BMI (r=-0.071, p=0.54).
Conclusions: Normal liver stiffness by MRE for children 7-17.9y is approximately 2.2kPa (±2 SD: 1.4-3 kPa) and is not dependent on demographic or technical factors.