Simultaneous <i>T</i>₂ and lipid quantitation using IDEAL‐CPMG

Abstract

Muscle damage, edema, and fat infiltration are hallmarks of a range of neuromuscular diseases. The T(2) of water, T(2,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,w) quantitation as the longer T(2) of fat, T(2,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,w) and T(2,f) quantification. With knowledge of the T(2,w) and T(2,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,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.