Possible 31P magnetization transfer pathways in skeletal muscle. (a) A simplified 2-site exchange model for evaluation of the ATP synthesis reaction Pi → γ-ATP using EBIT sequence with co-inversion of PCr and ATP spins. Through chemical exchange or NOE, all inverted spins contribute to the apparent exchange between Pi and γ-ATP. (b) A 7T 31P MR spectrum acquired from human calf muscle using the EBIT sequence for band inversion of PCr and ATP signals showing the pathways of magnetization transfer between inverted and non-inverted 31P signals. Abbreviation: Pi, Inorganic phosphate; PCr, phosphocreatine; ATP, adenosine triphosphate; Ad, adenosine. Chemical exchange, marked as solid arrows; dipolar cross-relaxation (NOE), marked as dashed arrows.