In vitro and in vivo comparison of two-, three- and four-point Dixon techniques for clinical intramuscular fat quantification at 3 T.

Abstract

To compare Dixon-based MRI techniques for intramuscular fat quantification at 3 T with MR spectroscopy (MRS) in vitro and in vivo. In vitro, two- three- and four-point mDixon (Philips Medical Systems, Best, Netherlands) sequences with 10°, 20° and 30° flip angles were acquired from seven test phantoms with sunflower oil-water percentages of 0-60% sunflower oil and calculated fat-water ratios compared with MRS. In vivo, two- three- and four-point mDixon sequences with 10° flip angle were acquired and compared with MRS in the vastus medialis of nine healthy volunteers (aged 30.6 ± 5.3 years; body mass index 22.2 ± 2.6). In vitro, all mDixon sequences correlated significantly with MRS (r > 0.97, p < 0.002). The measured phantom percentage fat depended significantly on the flip angle (p ≤ 0.001) and mDixon sequence (p = 0.005). Flip angle was the dominant factor influencing agreement with MRS. Increasing the flip angle significantly increased the overestimation of the mDixon sequences compared with MRS. In vivo, a significant difference was observed between sequences (p < 0.001), with all mDixon sequences overestimating the intramuscular fat content of the vastus medialis muscle compared with MRS. Two-point mDixon agreed best with MRS and had comparable variability with the other mDixon sequences. This study demonstrates that mDixon techniques have good linearity and low variability for use in intramuscular fat quantification. To avoid significant fat overestimation with short repetition time, a low flip angle should be used to reduce T1 effects. This is the first study investigating the optimal mDixon parameters for intramuscular fat quantification compared with MRS in vivo and in vitro.