Robust assessment of macromolecular fraction in muscle with differing fat fraction using ultrashort echo time magnetization transfer modeling

Magnetization transfer (MT) MR imaging can indirectly characterize the spatial distribution of the relative contents of the macromolecular and water proton pools (MMF) of skeletal muscles. Fat presence in muscle has always been a source of concern in MMF calculation where some studies have reported significant underestimation of MMF for muscles with a considerable fat fraction (FF). We investigated the impact of FF on MMF in muscle/fat phantoms using an ultrashort echo time (UTE) MT model after T1 compensation. MMF demonstrated a relatively robust value with under 5% and 20% changes for FF increases up to 30 and 45%, respectively.