G.P.119: Skeletal muscle fatty degenerative changes can be evaluated both qualitatively and quantitatively from whole-body Dixon NMR images with an important gain in acquisition time

Abstract

Fatty infiltration of muscles is a marker of disease progression in many neuromuscular disorders. Muscle MRI is capable of revealing patterns of muscles involvement that are disease specific and facilitates the diagnostic workup of patients. Although routine T1-weighted (T1w) imaging can give an indication of the presence or absence of muscular fat infiltration, it is difficult to extract quantitative data from these images. On the contrary, Dixon methods provide quantitative measure of fat fraction. Usually, whole-body (WB) exams consist in the acquisition of T1w images, followed by Dixon acquisitions on targeted regions to quantitatively assess fat infiltration. With the aim of improving and accelerating the qualitative assessment of neuromuscular disorders, we propose to avoid the T1w acquisition altogether, by allowing to perform the visual diagnosis workup on a WB Dixon imaging. 20 patients underwent WB MRI at 3T. WB T1w images were acquired with a 2D TSE sequence (resolution = 1.1 × 1.1 mm2, slice thickness = 6 mm, Tacq = 5 min 40 s). WB Dixon acquisition consisted in a 3D VIBE sequence with 3 echoes (resolution = 1 × 1 × 5 mm3, Tacq = 14 min 5 s). Quantitative fat fraction maps were derived using a standard 3-points Dixon reconstruction method. A customed lookup table was embedded in the DICOM file to provide a colored lecture of fat fraction maps corresponding to the Mercuri’s scale. Our results show that the acquisition of a high resolution WB Dixon imaging is possible in less than 15 min using an optimized VIBE sequence. This provides quantitative data that are more suitable than T1w images for longitudinal natural history studies, or therapeutic clinical trials. Moreover, the color representation renders the visual grading of the muscles more convenient and less operator dependent as it is based on actual fat fraction measurements. WB Dixon might then overcome the use of WB T1w images for diagnostic of neuromuscular disorders. Fatty infiltration of muscles is a marker of disease progression in many neuromuscular disorders. Muscle MRI is capable of revealing patterns of muscles involvement that are disease specific and facilitates the diagnostic workup of patients. Although routine T1-weighted (T1w) imaging can give an indication of the presence or absence of muscular fat infiltration, it is difficult to extract quantitative data from these images. On the contrary, Dixon methods provide quantitative measure of fat fraction. Usually, whole-body (WB) exams consist in the acquisition of T1w images, followed by Dixon acquisitions on targeted regions to quantitatively assess fat infiltration. With the aim of improving and accelerating the qualitative assessment of neuromuscular disorders, we propose to avoid the T1w acquisition altogether, by allowing to perform the visual diagnosis workup on a WB Dixon imaging. 20 patients underwent WB MRI at 3T. WB T1w images were acquired with a 2D TSE sequence (resolution = 1.1 × 1.1 mm2, slice thickness = 6 mm, Tacq = 5 min 40 s). WB Dixon acquisition consisted in a 3D VIBE sequence with 3 echoes (resolution = 1 × 1 × 5 mm3, Tacq = 14 min 5 s). Quantitative fat fraction maps were derived using a standard 3-points Dixon reconstruction method. A customed lookup table was embedded in the DICOM file to provide a colored lecture of fat fraction maps corresponding to the Mercuri’s scale. Our results show that the acquisition of a high resolution WB Dixon imaging is possible in less than 15 min using an optimized VIBE sequence. This provides quantitative data that are more suitable than T1w images for longitudinal natural history studies, or therapeutic clinical trials. Moreover, the color representation renders the visual grading of the muscles more convenient and less operator dependent as it is based on actual fat fraction measurements. WB Dixon might then overcome the use of WB T1w images for diagnostic of neuromuscular disorders.