Simultaneous T2 and Lipid Quantitation Using IDEAL-CPMG

Muscle damage, edema, and fat infiltration are hallmarks of a range of neuromuscular diseases. The T-2 of water, T-2,T-w, in muscle lengthens with both myocellular damage and inflammation and is typically measured using multiple spin-echo or Carr-Purcell-Meiboom-Gill acquisitions. However, microscopic fat infiltration in neuromuscular diseases prevents accurate T-2,T-w quantitation as the longer T-2 of fat, T-2,T-f, masks underlying changes in the water component. Fat saturation can be inconsistent across the imaging volume and removes valuable physiological fat information. A new method is presented that combines iterative decomposition of water and fat with echo asymmetry and least squares estimation with a Carr-Purcell-Meiboom-Gill-sequence. The sequence results in water and fat separated images at each echo time for use in T-2,T-w and T-2, f quantification. With knowledge of the T-2,T-w and T-2,T-f, a T-2-corrected fat fraction map can also be calculated. Monte-Carlo simulations and measurements in phantoms, volunteers, and a patient with inclusion body myositis are demonstrated. In healthy volunteers, uniform T-2,T-w and T-2-corrected fat fraction maps are present within all muscle groups. However, muscle-specific patterns of fat infiltration and edema are evident in inclusion body myositis, which demonstrates the power of separating and quantifying the fat and water components. Magn Reson Med 66: 1293-1302, 2011. (C) 2011 Wiley Periodicals, Inc.