3Tesla gradient-echo 3-point Dixon imaging for robust water-only imaging of the extra-ocular muscles

Introduction The extra-ocular (EO) muscles control movement of the eyes and are pathologically involved in conditions including thyroid eye disease [1] and progressive external ophthalmoplegia (PEO) arising from mitochondrial diseases [2]. Pathologies such as inflammation and atrophy of these muscles are routinely investigated on clinical MRI using techniques that suppress potentially confounding background signal due to the surrounding fatty adipose substrate. Spectral fat-saturation (fatsat) and short tau inversion recovery (STIR) [3] are both sequences frequently used for this purpose although both have potential shortcomings in the homogeneity and efficiency of fat-suppression. The so called ‘multi-point Dixon’ [4] and IDEAL methods [5] are commonly used to separate and quantify fat and water signals in organs including the liver and skeletal muscle. Despite an encouraging initial report using spin-echobased 3-point Dixon imaging to increase contrast to noise ratio (CNR) between background fat and extra-ocular muscle, as compared to STIR imaging in pediatric patients at 1.5T, [6] there appears to have been limited investigation in this area since. In the present work we evaluated gradient-echo 3-point Dixon in comparison to STIR and fatsat imaging of the extra-ocular muscles in adult subjects at 3T, with a view to application in fat-suppressed imaging studies of extra-orbital myopathy.