On the fat saturation effect in quantitative ultrashort TE MR imaging

Abstract

Purpose: To investigate the effect of fat saturation (FatSat) on quantitative UTE imaging of variable knee tissues on a 3T scanner.

Methods: Three quantitative UTE imaging techniques, including the UTE multi-echo sequence for $T_2^{\ast }$ measurement, the adiabatic T_1ρ prepared UTE sequence for T_1ρ measurement, and the magnetization transfer (MT)-prepared UTE sequence for MT ratio (MTR) and macromolecular proton fraction (MMF) measurements were used in this study. Twelve samples of cartilage and twelve samples of meniscus, as well as six whole knee cadaveric specimens, were imaged with the three above-mentioned UTE sequences with and without FatSat. The difference, correlation, and agreement between the UTE measurements with and without FatSat were calculated to investigate the effects of FatSat on quantification.

Results: Fat was well-suppressed using all three UTE sequences when FatSat was deployed. For the small sample study, the quantification difference ratio (QDR) values of all the measured biomarkers ranged from 0.7% to 12.6%, whereas for the whole knee joint specimen study, the QDR values ranged from 0.2% to 12.0%. Except for T_1ρ in muscle and MMF in meniscus (p > 0.05), most of the measurements showed statistical differences for T_1ρ , MTR, and MMF (p < 0.05) between FatSat and non-FatSat scans. Most of the measurements for $T_2^{\ast }$ showed no significant differences (p > 0.05). Strong correlations were found for all the biomarkers between measurements with and without FatSat.

Conclusion: The UTE biomarkers showed good correlation and agreement with some slight differences between the scans with and without FatSat.

Keywords: fat saturation; knee; quantitative UTE imaging.