Evaluation of six-point modified dixon and magnetic resonance spectroscopy for fat quantification: a fat–water–iron phantom study

This study aimed to evaluate (1) the agreement between the true fat fraction (FF) and proton density FF (PDFF) measured using a six-echo modified Dixon (6mDixon) and magnetic resonance spectroscopy (MRS) and (2) the influence of fat on T2* values. The study was performed using phantoms of varying fat and iron content. Point-resolved spectroscopy (PRESS) and stimulated echo acquisition mode (STEAM) with single-echo (S) and multiecho (M) (PRESS-S, PRESS-M, STEAM-S, and STEAM-M) were used for MRS. In phantoms without iron, the agreement between the true FF and measured PDFF was tested using Bland–Altman analysis. The influence of iron on PDFF was evaluated in phantoms with iron. The relationship between the true FF and T2* value was assessed in phantoms without iron, wherein the mean differences (limits of agreement) for each method were as follows: 6mDixon 2.9% (−2.4 to 8.1%); STEAM-S 3.2% (−9.5 to 16.0%); STEAM-M −0.7% (−6.9 to 5.5%); PRESS-S 8.9% (−14.5 to 32.4%); and PRESS-M −5.8% (−18.3 to 6.7%). In the 20% fat phantoms with iron, as iron increased, PDFFs with STEAM-S, PRESS-S, and PRESS-M were considerably overestimated, while, PDFF with STEAM-M was stable at 0.04–0.2 mM iron concentrations (17.2 and 21.4%, respectively), and PDFF with 6mDixon was reliable at even 0.4 mM iron concentration (24.8%). The T2* value showed a negative correlation with the true FF (r = −0.942, P = 0.005). STEAM-M and 6mDixon were reliable methods of fat quantification in the absence of iron, and the T2* value was shortened by fat.