Comparison Of Dixon Sequences For Estimation Of Percent Breast Fibroglandular Tissue

ObjectivesTo evaluate sources of error in the Magnetic Resonance Imaging (MRI) measurement of percent fibroglandular tissue (% FGT) using two-point Dixon sequences for fat-water separation.MethodsTen female volunteers (median age: 31 yrs, range: 23-50 yrs) gave informed consent following Research Ethics Committee approval. Each volunteer was scanned twice following repositioning to enable an estimation of measurement repeatability from high-resolution gradient-echo (GRE) proton-density (PD)-weighted Dixon sequences. Differences in measures of % FGT attributable to resolution, T-1 weighting and sequence type were assessed by comparison of this Dixon sequence with low-resolution GRE PD-weighted Dixon data, and against gradient-echo (GRE) or spin-echo (SE) based T-1-weighted Dixon datasets, respectively.Results% FGT measurement from high-resolution PD-weighted Dixon sequences had a coefficient of repeatability of +/- 4.3%. There was no significant difference in % FGT between high-resolution and low-resolution PD-weighted data. Values of % FGT from GRE and SE T-1-weighted data were strongly correlated with that derived from PD-weighted data (r = 0.995 and 0.96, respectively). However, both sequences exhibited higher mean % FGT by 2.9% (p < 0.0001) and 12.6%(p < 0.0001), respectively, in comparison with PD-weighted data; the increase in % FGT from the SE T-1-weighted sequence was significantly larger at lower breast densities.ConclusionAlthough measurement of % FGT at low resolution is feasible, T-1 weighting and sequence type impact on the accuracy of Dixon-based % FGT measurements; Dixon MRI protocols for % FGT measurement should be carefully considered, particularly for longitudinal or multicentre studies.