P.96 - Effects of water compartmentation and distribution on skeletal muscle T1 values assessed by quantitative NMR imaging

Abstract

NMR imaging, and particularly T1-weighted acquisitions, can be used for the diagnostic of NMDs taking advantage of the high contrast between healthy and fatty infiltrated muscles. However, very little is known about the effects of tissue water compartmentation and distribution on muscle T1 values. With the development of fast T1 mapping sequences, it is now possible to monitor this parameter within scan times compatible with clinical research. The goal of this study was to investigate the variations of skeletal muscle T1 values under various physiopathological conditions using a fast T1 mapping sequence. NMR imaging of the lower limbs was performed at 3T on 10 healthy volunteers at rest and after a 10' plantar flexion bout and at rest on 43 patients suffering from different neuromuscular pathologies: Becker muscular dystrophy (BMD: N = 30) and inclusion body myositis (IBM: N = 13). The T1 mapping sequence consisted in the acquisition of a 1000 radial spokes FLASH echo train after magnetization inversion (TE/TR = 2.75/5.08 ms, resolution = 1.8x1.8 mm2, 5 slices, Tacq = 50s). Water T2 and fat fractions were also quantitatively assessed with the “tri-exponential fitting” and “Dixon” reference methods. After exercise, a significant 7.2% increase of T1 was measured on the 10 volunteers in the gastrocnemius lateralis and medialis, corresponding to the muscle groups recruited by plantar flexion of the foot. T1 and water T2 values measured at the different time-points before and after this paradigm were correlated (R = 0.75, p < 0.05). Combining FF and T1 mapping, we measured higher T1s in the muscle of the IBM group compared to the BMD group, and global T1 was systematically increased when water T2 was increased. The sensitivity of the T1 and T2 approaches were equivalent to discriminate between the different muscle conditions. The next step will be to develop a bi-compartment fitting approach in order to simultaneously estimate water T1 and fat fractions from this T1 mapping sequence.